US20190112357A1 - Prevention of protein disulfide bond reduction - Google Patents

Prevention of protein disulfide bond reduction Download PDF

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US20190112357A1
US20190112357A1 US16/300,315 US201716300315A US2019112357A1 US 20190112357 A1 US20190112357 A1 US 20190112357A1 US 201716300315 A US201716300315 A US 201716300315A US 2019112357 A1 US2019112357 A1 US 2019112357A1
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interest
disulfide bond
protein
reduction
cell culture
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Sanjeev AHUJA
Wai Keen CHUNG
Deborah Sweet GOLDBERG
Michael HANDLOGTEN
Someet NARANG
Brian Russell
Min Zhu
Suzanne HUDAK
Kenneth Hwang
Jihong Wang
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MedImmune LLC
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MedImmune LLC
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Priority to US16/300,315 priority Critical patent/US20190112357A1/en
Assigned to MEDIMMUNE LLC reassignment MEDIMMUNE LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AHUJA, Sanjeev, WANG, JIHONG, RUSSELL, BRIAN, NARANG, Someet, GOLDBERG, DEBORAH SWEET, HWANG, KENNETH, HUDAK, Suzanne, ZHU, MIN, CHUNG, WAI KEEN, HANDLOGTEN, Michael
Publication of US20190112357A1 publication Critical patent/US20190112357A1/en
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K16/00—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K39/00—Medicinal preparations containing antigens or antibodies
    • A61K39/395—Antibodies; Immunoglobulins; Immune serum, e.g. antilymphocytic serum
    • A61K39/39591—Stabilisation, fragmentation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/10—Immunoglobulins specific features characterized by their source of isolation or production
    • C07K2317/14—Specific host cells or culture conditions, e.g. components, pH or temperature
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/40—Immunoglobulins specific features characterized by post-translational modification

Definitions

  • the present disclosure relates to reduction of monoclonal antibodies and resulting product variants. It discloses methods for increasing the yield of an intact disulfide bond-containing protein, methods for mitigating reduction of disulfide-bond containing proteins, and methods for mitigating reduction potential of disulfide-bond containing proteins.
  • Monoclonal antibodies are capable of binding to a wide range of targets with high affinity and exceptional specificity. Accordingly, mAbs have been successfully designed to treat a wide variety of diseases and conditions including cancers, infectious diseases, autoimmunity and inflammation, cardiovascular disease, and ophthalmological diseases. The high success rate of mAbs in the clinic has made them a rapidly growing and increasingly important class of therapeutics. To keep up with the increasing demand for these lifesaving molecules, significant effort has been invested in the development of manufacturing processes for mAbs designed to increase antibody titer while maintaining consistent product quality. Rapid increases in antibody titers have been achieved over the past decade, with current manufacturing processes generating greater than 10 g/L mAb.
  • Protein molecules only function with the formation of stable inter- and intra-molecular disulfide bonds to properly fold and maintain function.
  • these protein molecules are immunoglobulins and cell surface receptors containing immunoglobulin domains, ribonucleases, lactalbumin, insulin, keratin, hemagglutinin, viral membrane proteins, neuroendocrine protein 7B2, epidermal growth factor, androgenic gland hormone, AP-1-like transcription factor YAP1, acetylcholine receptor, dendrotoxins, bone morphogenic protein 2-A, chorionic gonadotropin, histones H3, thrombospondin 1, disintegrin schistatin, snaclec botrocetin, acetylcholinesterase collagenic tail peptide, conglutin delta-2, oxidoreductases, sulfide dehydrogenase, and lysozyme.
  • Standard antibody molecules include four peptide chains, two heavy chains and two light chains. These four peptide chains properly fold together in a functional antibody molecule by forming disulfide bonds between the four chains. The number of disulfide bonds formed within the peptide chains of an antibody molecule varies depending on antibody subtype.
  • fragments and aggregates have to be removed to adequate levels due to their associated risks with increased immunogenicity and unknown effects on drug efficacy. Further, the presence of these impurities can also affect the stability of the product during storage leading to reduced shelf life.
  • Fragmentation of proteins or polypeptides can arise from either product instability (Cordoba A. et al., 2005, J. Chrom. B., 818(2):115-21) or proteolytic activity through the host cell proteins (HCP) present in the cells (Gao et al., 2011, Biotechnol. Bioeng. 108(4):977-982), while aggregation can occur at various steps during and after the manufacturing process such as during cell culture, harvest, purification, freeze thaw, vialing and storage.
  • Strategies are often implemented during process development to improve both of these product quality attributes. These include: optimizing bioreactor conditions to prevent fragmentation or aggregate formation during cell culture; optimizing harvest conditions to minimize cell lysis (Hutchinson N.
  • This disclosure relates to methods for preventing reduction of disulfide bonds in disulfide bond-containing proteins to increase stability of the intact protein throughout its shelf life.
  • the methods improve stability of purified disulfide bond-containing proteins by mitigating reduction of the disulfide bond-containing protein or by mitigating reduction potential of the disulfide bond-containing protein during the manufacturing process.
  • the disclosure relates to a method for increasing the yield of an intact disulfide bond-containing protein of interest in a cell culture or solution, comprising manufacturing the disulfide bond-containing protein of interest in the presence of a glutathione reductase inhibitor, a thioredoxin reductase inhibitor, or both a glutathione reductase inhibitor and a thioredoxin reductase inhibitor, whereby the amount of intact disulfide bond-containing protein is higher in the cell culture or solution manufactured in the presence of a glutathione reductase inhibitor, a thioredoxin reductase inhibitor, or a glutathione reductase inhibitor and a thioredoxin reductase inhibitor.
  • the disclosure relates to a method for increasing the yield of an intact disulfide bond-containing protein of interest in a manufacturing process, comprising: detecting the presence of glutathione reductase and/or thioredoxin reductase in the culture and or solution containing the disulfide bond-containing protein of interest, and adding a glutathione reductase and/or thioredoxin reductase inhibitor to mitigate reduction of the disulfide bond-containing protein of interest.
  • the disclosure relates to a method further comprising determining the activity of the glutathione reductase and/or thioredoxin reductase detected.
  • determining the activity of the glutathione reductase and/or thioredoxin reductase comprises adding 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) to a sample obtained during the manufacturing process; adding at least one of thioredoxin reductase inhibitor and glutathione reductase inhibitor to a portion of the sample containing DTNB; and monitoring reduction of DTNB at a wavelength of 412 nm in the sample; wherein a higher reduction of DTNB in the samples without at least one of thioredoxin reductase inhibitor and glutathione reductase inhibitor, indicates activity of thioredoxin reductase and/or glutathione reductase.
  • NADPH, oxidized glutathione, and buffer are added to the sample prior to monitoring reduction.
  • this disclosure relates to a method for increasing the yield of an intact disulfide bond-containing protein of interest or diminishing the reduction potential of the disulfide containing protein of interest in a cell culture or fermentation process by maintaining the extracellular cystine levels above 0 during the process.
  • the intact protein of interest is released into the cell culture fluid (CCF).
  • the process comprises maintaining the cells in CCF for at least 2 days, at least 8 days, at least 10 days, at least 12 days, at least 14 days, or at least 16 days.
  • the cell culture process is a mammalian or insect cell culture process
  • the fermentation process is a bacterial, yeast, or fungi fermentation process.
  • the cystine levels are maintained in the cell culture or fermentation process above 0 to prevent disulfide bond reduction.
  • the potential for disulfide bond reduction is decreased relative to a process in which an effective amount of cystine is not maintained above 0 in the CCF.
  • the disclosure relates to a method for improving the stability of a purified disulfide bond-containing protein of interest, comprising using a manufacturing process that maintains the disulfide bond-containing protein of interest in a form with minimal free thiols, thereby mitigating reduction or reduction potential of the disulfide bond-containing protein of interest during the manufacturing process.
  • the manufacturing process comprises a cell culture phase, a harvest phase, at least one hold phase, a purification phase, or any combination thereof.
  • the hold phase comprises storing the material in any of the phases during the manufacturing process.
  • the hold phase comprises storing harvested cell culture fluid (HCCF) for a period of up to one hour, up to one day, at least four days, at least one week, at least 10 days, at least two weeks, at least one month, or at least three months following the harvest phase and prior to the purification phase.
  • minimizing free thiols in the disulfide bond-containing protein of interest comprises mitigating disulfide bond reduction throughout the manufacturing process.
  • the HCCF is stored at 2-8° C. in airtight bags during the hold phase.
  • FIG. 1 Schematic representing the enzymes and chemical intermediates of the thioredoxin system and the glutathione system.
  • Trx is thioredoxin
  • GSH is reduced glutathione
  • GSSG is oxidized glutathione
  • L is immunoglobulin light chain
  • H is immunoglobulin heavy chain
  • NADPH is reduced nicotinamide adenine dinucleotide phosphate.
  • FIG. 2A and FIG. 2B Reduction in Cell Culture.
  • FIG. 2A Depicts a time course of the percent intact (non-reduced) antibody in supernatant samples from small scale production reactors of mAb A (diamonds), mAb B (squares), and mAb C (triangles), which were evaluated using capillary electrophoresis.
  • FIG. 2B Depicts a time course of the total reductase activity measured in samples from the same small scale reactors, determined using a colorimetric assay based on the reduction of 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB). Data represents the mean ⁇ SD of triplicate experiments.
  • DTNB 5,5′-dithio-bis(2-nitrobenzoic acid)
  • FIG. 3A and FIG. 3B Effect of Specific Reductase Inhibitors on reductase activity as determined using a colorimetric assay based on the reduction of DTNB.
  • FIG. 3A Addition of aurothioglucose (ATG), a thioredoxin reductase inhibitor, to solutions of recombinant TrxR1/Trx1 (black bars), GR/GSSG (gray bars), or TrxR1/Trx1 with GR/GSSG (hashed bars)
  • FIG. 3A Addition of aurothioglucose (ATG), a thioredoxin reductase inhibitor, to solutions of recombinant TrxR1/Trx1 (black bars), GR/GSSG (gray bars), or TrxR1/Trx1 with GR/GSSG (hashed bars)
  • FIG. 3A Addition of aurothioglucose (ATG), a thioredoxin reducta
  • FIG. 4A and FIG. 4B Impact of Specific Reductase Inhibitors on Antibody Reduction.
  • FIG. 4A Percent of intact (non-reduced) antibody obtained after adding increasing concentrations of ATG to solutions of purified mAb B with TrxR1/Trx1 (black bars) or GR/GSSG (gray bars) and incubating overnight at room temperature.
  • FIG. 4B Percent of intact (non-reduced) antibody after adding increased concentrations of Cu 2+ to solutions of purified mAb B with TrxR1/Trx1 (black bars) or GR/GSSG (gray bars) and incubating overnight at room temperature. Data represents the mean ⁇ SD of duplicate experiments.
  • FIG. 5A and FIG. 5B Sensitivity of CHO Reductases to Identified Inhibitors.
  • FIG. 5A TrxR1 and GR reductase activity of collected fractions evaluated using no inhibitor (black bars); 0.5 ⁇ M ATG (gray bars); 100 ⁇ M 2-AAPA (hashed bars); and both 0.5 ⁇ M ATG and 100 ⁇ M 2-AAPA (white bars).
  • FIG. 5B Percent of total intact mAb B after an overnight incubation with different combinations of pooled fractions of active TrxR1 and GR, 0.4 mM NADPH, 1 mM GSSG, 3 ⁇ M Cu 2+ , Trx1, and 100 ⁇ M ATG. Data represents the mean ⁇ SD of duplicate experiments.
  • FIG. 6A and FIG. 6B Cell Culture Activity of the Thioredoxin and Glutathione Systems.
  • FIG. 6A Reductase activity of day 14 samples from small scale production reactors of mAb A (black bars), mAb B (gray bars), mAb C (hashed bars), and mAb D (white bars) in the presence of 0.5 ⁇ M ATG, 100 ⁇ M 2-AAPA, and both 0.5 ⁇ M ATG and 100 ⁇ M 2-AAPA.
  • FIG. 6A Reductase activity of day 14 samples from small scale production reactors of mAb A (black bars), mAb B (gray bars), mAb C (hashed bars), and mAb D (white bars) in the presence of 0.5 ⁇ M ATG, 100 ⁇ M 2-AAPA, and both 0.5 ⁇ M ATG and 100 ⁇ M 2-AAPA.
  • FIG. 7 Percent of intact (non-reduced) antibody remaining in day 14 cell culture samples from small scale bioreactors of mAb A (black bars), mAb B (gray bars), mAb C (hashed bars), and mAb D (light gray bars) spiked with 0.1 mM ATG, 3 ⁇ M Cu 2+ , or both 0.1 mM ATG and 3 ⁇ M Cu 2+ . Data represents the mean ⁇ SD of duplicate experiments.
  • FIG. 8 Time course of cysteine/cystine concentration in the production bioreactor runs BR-A, BR-B, BR-C, and BR-D, measured using ultra-performance liquid chromatography (UPLC) amino acid analysis.
  • UPLC ultra-performance liquid chromatography
  • FIG. 9 The amount of intact mAb B (LHHL) ( FIG. 9A ) and intact mAb A (LHHL) ( FIG. 9B ) was measured via capillary electrophoresis from unpurified cell culture samples. Note, the amount of intact antibody is never 100% as these were measured in unpurified cell culture samples. Above a threshold cell culture redox potential, indicated with a dashed black line there is minimal reduction of the interchain disulfide bonds. The conditions in FIG.
  • FIG. 10 Time course of Bioreactor cystine concentrations measured by UPLC-amino acid analysis for conditions with (BR-J2) and without increased nutrient feed BR-J1).
  • FIG. 11 Time course cystine concentrations measured by UPLC-amino acid analysis of BR-K bioreactor for conditions with (BR-K-2) and without increased nutrient feed (BR-K-1).
  • FIG. 12A to FIG. 12C Non-Reduced GX (NR-GX) electropherograms of harvested cell culture fluid (HCCF) ( FIG. 12A ); Capture product ( FIG. 12B ); and Final polishing product ( FIG. 11C ).
  • Grey trace Reference standard; Black Trace: sample.
  • FIG. 13 Percent of free thiol obtained from mass spectrometry quantification of HCCF held for 2 weeks in the absence of cystine, or the presence of 2 mM cystine, and 4 mM cystine in the locations of the molecule where reduction occurred.
  • FIG. 14A and FIG. 14B Changes in free thiol and aggregation ratio with changing pH.
  • FIG. 14A Change of the ratio of free thiol to IgG concentration with time when the HCCF is incubated at pH 3.2, pH 3.4, and pH 3.6.
  • FIG. 14B Change in aggregate with time when HCCF is incubated at pH 3.2, pH 3.4, and pH 3.6.
  • FIG. 15 Percent of inter-chain free thiol levels obtained by spectrometry quantification of HCCF across a 2 week hold in the presence of no cystine (0 mM) and 4 mM cystine.
  • FIG. 16 Free thiol levels obtained by DNTB quantification of purification process intermediates generated from HCCF purified immediately, or held for two weeks in the presence of no cystine (0 mM) and 4 mM cystine.
  • FIG. 17A to FIG. 17C Change in percent aggregate levels over time for formulated bulk product generated from HCCF.
  • FIG. 17A Formulated bulk product generated from HCCF that was held at 2-8° C. for 2 weeks in the absence of cystine (0 mM) or in the presence of 4 mM cystine.
  • FIG. 17B Formulated bulk product generated from HCCF that was held at 25° C. for 2 weeks in the absence of cystine (0 mM) or in the presence of 4 mM cystine.
  • FIG. 17C Formulated bulk product generated from HCCF that was held at 40° C. for 2 weeks in the absence of cystine (0 mM) or in the presence of 4 mM cystine.
  • FIG. 18A to FIG. 18C Non-Reduced GX (NR-GX) electropherograms of Protein A capture products purified from BRX-L-1 ( FIG. 18A ), BRX-L-2 ( FIG. 18B ) BRX-L-3 ( FIG. 18C )
  • FIG. 19 Time course of percent aggregate at 2-8° C. of mAb A drug substance generated from 14 day fed-batch process.
  • FIG. 20 Time course of percent aggregate at 2-8° C. of mAb A drug substance generated from 14 day or 8 day fed batch process.
  • FIG. 21A to FIG. 21C Electropherograms from non-reduced (NR) GXII analysis of end of run cell culture sample exposed to reduction potential analysis.
  • FIG. 21A Cell culture sample from 14 day fed-batch process.
  • FIG. 21B Cell culture sample from 8 day fed-batch process.
  • FIG. 22 Time course of percent aggregate at 2-8° C. of mAb A drug substance from culture with and without additional copper and cystine in feeds.
  • a or “an” entity refers to one or more of that entity; for example, “a binding molecule,” is understood to represent one or more binding molecules.
  • the terms “a” (or “an”), “one or more,” and “at least one” can be used interchangeably herein.
  • polypeptide and protein are intended to encompass a singular “polypeptide” or “protein,” as well as plural “polypeptides,” or “proteins” and refers to a molecule composed of monomers (amino acids) linearly linked by amide bonds (also known as peptide bonds).
  • polypeptide and protein refer to any chain or chains of two or more amino acids, and does not refer to a specific length of the product and are used interchangeably herein.
  • polypeptides dipeptides, tripeptides, oligopeptides, “amino acid chain,” or any other term used to refer to a chain or chains of two or more amino acids are included within the definition of “polypeptide,” or “protein” and the terms can be used instead of, or interchangeably with any of these terms.
  • polypeptide and protein are also intended to refer to the products of post-expression modifications of the polypeptide or protein, including without limitation glycosylation, acetylation, phosphorylation, amidation, and derivatization by known protecting/blocking groups, proteolytic cleavage, or modification by non-naturally occurring amino acids.
  • a polypeptide or protein can be derived from a biological source or produced by recombinant technology, but is not necessarily translated from a designated nucleic acid sequence.
  • protein of interest and “disulfide bond-containing protein of interest” are used interchangeably and refer to a protein that contains at least one disulfide bond.
  • protein of interest refers to the active form of the protein, e.g., the properly folded, properly assembled form of the protein that can achieve the commercial and/or therapeutic purpose.
  • a “protein of interest” can be manufactured according to the methods provided herein.
  • a protein of interest can be, e.g., a therapeutic protein such as an antibody or antigen-binding fragment thereof or a decoy receptor protein.
  • “Increasing the yield” of a protein of interest means increasing the amount of the intact and properly folded protein that can achieve the commercial and/or therapeutic purpose, e.g., by maintaining a higher proportion of the protein in its intact and properly folded, properly assembled form.
  • polynucleotide is intended to encompass a singular nucleic acid as well as plural nucleic acids, and refers to an isolated nucleic acid molecule or construct, e.g., messenger RNA (mRNA), cDNA, or plasmid DNA (pDNA).
  • a polynucleotide can comprise a conventional phosphodiester bond or a non-conventional bond (e.g., an amide bond, such as found in peptide nucleic acids (PNA)).
  • PNA peptide nucleic acids
  • nucleic acid refers to any one or more nucleic acid segments, e.g., DNA or RNA fragments, present in a polynucleotide.
  • a “nucleic acid sequence” is the sequence of nucleotides found in the cited nucleic acid.
  • an “isolated” nucleic acid or polynucleotide is intended any form of the nucleic acid or polynucleotide that is separated from its native environment.
  • gel-purified polynucleotide, or a recombinant polynucleotide encoding a polypeptide or protein contained in a vector would be considered to be “isolated.”
  • a polynucleotide segment e.g., a PCR product, which has been engineered to have restriction sites for cloning is considered to be “isolated.”
  • Further examples of an isolated polynucleotide include recombinant polynucleotides maintained in heterologous host cells or purified (partially or substantially) polynucleotides in a non-native solution such as a buffer or saline.
  • Isolated RNA molecules include in vivo or in vitro RNA transcripts of polynucleotides, where the transcript is not one that would be found in nature. Isolated polynucleotides or nucleic acids further include such molecules produced synthetically.
  • polynucleotide or a nucleic acid can be or can include a regulatory element such as a promoter, ribosome binding site, or a transcription terminator.
  • a non-naturally occurring polynucleotide or any grammatical variants thereof, is a conditional definition that explicitly excludes, but only excludes, those forms of the nucleic acid or polynucleotide that are, or might be, determined or interpreted by a judge, or an administrative or judicial body, to be “naturally-occurring.”
  • antibody and “immunoglobulin” can be used interchangeably herein.
  • An antibody (or a fragment, variant, or derivative thereof as disclosed herein) includes at least the variable domain of a heavy chain (for camelid species) or at least the variable domains of a heavy chain and a light chain.
  • Basic immunoglobulin structures in vertebrate systems are relatively well understood.
  • the term “antibody” encompasses anything ranging from a small antigen-binding fragment of an antibody to a full sized antibody, bispecific antibodies, fusion proteins, and antibody drug conjugates.
  • a full-sized antibody may be an IgG antibody that includes two complete heavy (H) chains and two complete light (L) chains, an IgA antibody that includes four complete heavy chains and four complete light chains and optionally includes a J chain and/or a secretory component, or an IgM antibody that includes ten or twelve complete heavy chains and ten or twelve complete light chains and optionally includes a J chain.
  • fragment as disclosed herein includes any antibody reduced species.
  • An intact antibody has two heavy chains and two light chains (LHHL); an antibody fragment may have two heavy chains and one light chain (LHH); or two heavy chains (HH); or one light chain and one heavy chain (LH); or one heavy chain (H); or one light chain (L).
  • LHH light chain
  • HH heavy chains
  • LH heavy chain
  • H heavy chain
  • L light chain
  • immunoglobulin comprises various broad classes of polypeptides or proteins that can be distinguished biochemically.
  • immunoglobulin heavy chains are classified as gamma, mu, alpha, delta, or epsilon, ( ⁇ , ⁇ , ⁇ , ⁇ , ⁇ ) with some subclasses among them (e.g., ⁇ 1- ⁇ 4 or ⁇ 1- ⁇ 2)). It is the nature of this chain that determines the “isotype” of the antibody as IgG, IgM, IgA IgG, or IgE, respectively.
  • immunoglobulin subclasses e.g., IgG 1 , IgG 2 , IgG 3 , IgG 4 , IgA 1 , IgA 2 , etc. are well characterized and are known to confer functional specialization. Modified versions of each of these immunoglobulins are readily discernible to the skilled artisan in view of the instant disclosure and, accordingly, are within the scope of this disclosure.
  • Immunoglobulin light chains are classified as either kappa or lambda (K, or X). Each immunoglobulin heavy chain class can be bound with either a kappa or lambda light chain by covalent disulfide linkages.
  • the light and heavy chains are covalently bonded to each other by disulfide linkages, and the “tail” portions of the two heavy chains are bonded to each other by covalent disulfide linkages or non-covalent linkages when the immunoglobulins are expressed, e.g., by hybridomas, B cells, or genetically engineered host cells.
  • the amino acid sequences run from an N-terminus at the forked ends of the Y configuration to the C-terminus at the bottom of each chain.
  • the basic structure of certain antibodies includes two heavy chain subunits and two light chain subunits covalently connected via disulfide bonds to form a “Y” structure, also referred to herein as an “H2L2” or “LHHL” structure, or a “binding unit.”
  • valency refers to the number of binding domains in given binding molecule or binding unit.
  • bivalent tetravalent
  • hexavalent in reference to a given binding molecule, e.g., an IgM antibody or fragment thereof, denote the presence of two binding domains, four binding domains, and six binding domains, respectively.
  • a bivalent or multivalent binding molecule can be monospecific, i.e., all of the binding domains are the same, or can be bispecific or multispecific, e.g., where two or more binding domains are different, e.g., bind to different epitopes on the same antigen, or bind to entirely different antigens.
  • epitope includes any molecular determinant capable of specific binding to an antibody.
  • an epitope can include chemically active surface groupings of molecules such as amino acids, sugar side chains, phosphoryl, or sulfonyl, and, in certain aspects, can have a three dimensional structural characteristics, and or specific charge characteristics.
  • An epitope is a region of a target that is bound by an antibody.
  • variable domains of both the variable light (VL) and variable heavy (VH) chain portions determine antigen recognition and specificity.
  • the constant domains of the light chain (CL) and the heavy chain e.g., CH1, CH2 or CH3 confer biological properties such as secretion, transplacental mobility, Fc receptor binding, complement binding, and the like.
  • CL light chain
  • CH1, CH2 or CH3 constant domains of the light chain
  • CH1 variable region domain
  • CL constant domains of the heavy chain
  • CH1, CH2 or CH3 confer biological properties such as secretion, transplacental mobility, Fc receptor binding, complement binding, and the like.
  • the N-terminal portion is a variable region and at the C-terminal portion is a constant region; the CH3 (or CH4 in the case of IgM) and CL domains actually comprise the carboxy-terminus of the heavy and light chain, respectively.
  • Antibodies or antigen-binding fragments, variants, or derivatives thereof include, but are not limited to, polyclonal, monoclonal, human, humanized, or chimeric antibodies, single chain antibodies, epitope-binding fragments, e.g., Fab, Fab′ and F(ab′) 2 , Fd, Fvs, single-chain Fvs (scFv), single-chain antibodies, disulfide-linked Fvs (sdFv), fragments comprising either a VL or VH domain, fragments produced by an Fab expression library.
  • polyclonal, monoclonal, human, humanized, or chimeric antibodies single chain antibodies, epitope-binding fragments, e.g., Fab, Fab′ and F(ab′) 2 , Fd, Fvs, single-chain Fvs (scFv), single-chain antibodies, disulfide-linked Fvs (sdFv), fragments comprising either a VL or VH
  • an antibody or antigen-binding fragment thereof binds to an epitope via its antigen binding domain, and that the binding entails some complementarity between the antigen binding domain and the epitope.
  • an antibody or antigen-binding fragment thereof is said to “specifically bind” to an epitope when it binds to that epitope, via its antigen binding domain more readily than it would bind to a random, unrelated epitope.
  • the term “specificity” is used herein to qualify the relative affinity by which a certain binding molecule binds to a certain epitope.
  • binding molecule “A” can be deemed to have a higher specificity for a given epitope than binding molecule “B,” or binding molecule “A” can be said to bind to epitope “C” with a higher specificity than it has for related epitope “D.”
  • Antibody fragments including single-chain antibodies or other binding domains can exist alone or in combination with one or more of the following: hinge region, CH1, CH2, CH3, or CH4 domains, J chain, or secretory component. Also included are antigen-binding fragments that can include any combination of variable region(s) with one or more of a hinge region, CH1, CH2, CH3, or CH4 domains, a J chain, or a secretory component.
  • Binding molecules, e.g., antibodies, or antigen-binding fragments thereof can be from any animal origin including birds and mammals.
  • the antibodies can be human, murine, donkey, rabbit, goat, guinea pig, camel, llama, horse, or chicken antibodies.
  • variable region can be cartilaginous in origin (e.g., from sharks).
  • “human” antibodies include antibodies having the amino acid sequence of a human immunoglobulin and include antibodies isolated from human immunoglobulin libraries or from animals transgenic for one or more human immunoglobulins and can in some instances express endogenous immunoglobulins and some not.
  • the term “heavy chain subunit” includes amino acid sequences derived from an immunoglobulin heavy chain, e.g., an antibody comprising a heavy chain subunit can include at least one of: a VH domain, a CH1 domain, a hinge (e.g., upper, middle, and/or lower hinge region) domain, a CH2 domain, a CH3 domain, a CH4 domain, or a variant or fragment thereof.
  • a binding molecule e.g., an antibody or fragment, variant, or derivative thereof can include without limitation, in addition to a VH domain, a CH1 domain; a CH1 domain, a hinge, and a CH2 domain; a CH1 domain and a CH3 domain; a CH1 domain, a hinge, and a CH3 domain; or a CH1 domain, a hinge domain, a CH2 domain, and a CH3 domain.
  • a binding molecule, e.g., an antibody or fragment, variant, or derivative thereof can include, in addition to a VH domain, a CH3 domain and a CH4 domain; or a CH3 domain, a CH4 domain, and a J chain.
  • a binding molecule for use in the disclosure can lack certain constant region portions, e.g., all or part of a CH2 domain. It will be understood by one of ordinary skill in the art that these domains (e.g., the heavy chain subunit) can be modified such that they vary in amino acid sequence from the original immunoglobulin molecule.
  • the term “light chain subunit” includes amino acid sequences derived from an immunoglobulin light chain.
  • the light chain subunit includes at least a VL, and can further include a CL (e.g., C ⁇ or C ⁇ ) domain.
  • VH domain includes the amino terminal variable domain of an immunoglobulin heavy chain and the term “CH1 domain” includes the first (most amino terminal) constant region domain of an immunoglobulin heavy chain.
  • CH1 domain is adjacent to the VH domain and is amino terminal to the hinge region of a typical IgG heavy chain molecule.
  • the term “manufacturing process” includes techniques used to grow cells, e.g., recombinant cells, in culture and to obtain a protein of interest produced by the cultured cells in an appropriate form for use.
  • the manufacturing process can include various steps, including, but not limited to one or more of the following: inserting of a gene of interest into a host cell to create an engineered host cell, culturing the host cell to expand the number of cells, inducing expression of the protein of interest by the host cell, screening for host cells expressing the protein of interest, harvesting the protein of interest, e.g., by separating the protein of interest from the cultured cells and cell culture medium, and/or purifying the protein of interest.
  • the protein of interest can be an endogenous protein expressed by the native cell, or a recombinant heterologous protein encoded in an expression vector inserted into the cell (either transiently or stably).
  • engineered includes manipulation of nucleic acid or polypeptide molecules by synthetic means (e.g. by recombinant techniques, in vitro peptide synthesis, by enzymatic or chemical coupling of peptides or some combination of these techniques).
  • expression refers to a process by which a gene produces a biochemical, for example, a polypeptide or protein.
  • the process includes any manifestation of the functional presence of the gene within the cell including, without limitation, gene knockdown as well as both transient expression and stable expression. It includes without limitation transcription of the gene into RNA, e.g., messenger RNA (mRNA), and the translation of such mRNA into polypeptide(s) or protein(s). If the final product is a biochemical, expression includes the creation of that biochemical and any precursors.
  • RNA messenger RNA
  • a gene product can be either a nucleic acid, e.g., a messenger RNA produced by transcription of a gene, or a polypeptide or protein that is translated from a transcript.
  • Gene products described herein further include nucleic acids with post transcriptional modifications, e.g., polyadenylation, or polypeptides and proteins with post translational modifications, e.g., methylation, glycosylation, the addition of lipids, association with other protein subunits, proteolytic cleavage, and the like.
  • disulfide bond or “disulfide bridge” or “S-S bond” includes the covalent bond formed between two sulfur atoms.
  • the amino acid cysteine comprises a thiol group that can form a disulfide bond or bridge with a second thiol group.
  • the second thiol group can be found in the side chain of a residue on the same polypeptide or protein (intra-disulfide bond), or on a different polypeptide or protein (inter-disulfide bond).
  • Such bonds are created during protein biosynthesis and/or by oxidation of sulfhydryl groups, a process referred to as oxidative protein folding.
  • disulfide bond-containing protein and “disulfide bond-containing protein” are used interchangeably herein and refer to a protein that in its properly folded state contains one or more disulfide bridges.
  • the disulfide bond-containing protein can have a disulfide bond that is inter- or intra-molecular. Such inter- or intra-molecular disulfide bonds are present in a properly folded disulfide bond-containing protein.
  • the activity of the disulfide bond-containing protein can be dependent on the presence and reduction state of the disulfide bonds.
  • Many molecules function best with the formation of stable inter- and intra-molecular disulfide bonds that contribute to proper folding, such as immunoglobulins and cell surface receptors containing immunoglobulin domains, ribonucleases, lactalbumin, insulin, keratin, hemagglutinin, viral membrane proteins, neuroendocrine protein 7B2, epidermal growth factor (EGF), androgenic gland hormone, sulfide dehydrogenase, and lysozyme.
  • Many therapeutic proteins such as antibodies, EGF, and insulin, contain disulfide bonds. Manufacturing a therapeutic protein of interest under conditions that increase disulfide bond reduction can result in low yield of the intact protein of interest.
  • yield refers to the amount of protein of interest obtained that is intact, active, properly folded, and with the correct pairing of disulfide bonds.
  • a process may produce a high overall amount of protein of interest, but if significant reduction of the disulfide bonds occurs in the protein of interest, the yield of intact protein may be low.
  • reduced protein means a protein that is exposed to reducing conditions sufficient to reduce a reducible residue in the protein structure, such as a cysteine. If the reduced protein contains a thiol group, or sulfur-containing residue, then the thiol group in the reduced protein exists in a state in which it is reduced. For instance, a reduced protein that contains a cysteine residue will exist in a state in which the sulfur atom of the cysteine residue is in the reduced state, often indicated as “-SH.” A reduced protein can be a disulfide bond-containing protein.
  • a disulfide bond-containing protein can become a reduced protein by exposure to reducing conditions that cause one or more disulfide bonds (disulfide bridges) in the disulfide bond-containing protein to break, which can contribute to destabilization of the disulfide bond-containing protein and potential loss of activity or function of the disulfide bond-containing protein.
  • oxidized protein means a protein that is exposed to oxidizing conditions sufficient to oxidize an oxidizable moiety in the protein structure. If the oxidized protein contains a thiol group, or sulfur-containing side chain, then the thiol group in the oxidized protein exists in a state in which it is oxidized.
  • An oxidized protein can be a disulfide bond-containing protein.
  • a disulfide bond-containing protein can become an oxidized protein by exposure to oxidizing conditions that cause one or more disulfide bonds (disulfide bridges) in the disulfide bond-containing protein to form.
  • Oxidizing conditions during protein manufacture can contribute to stabilization of a disulfide bond-containing protein of interest, can contribute to proper folding, can contribute to retention of activity or function of the disulfide bond-containing protein, and can thereby increase the yield of the protein of interest during a manufacturing process.
  • polypeptide a protein or polypeptide
  • intact protein mean the native conformation, or native state, of a protein or polypeptide, which has a tertiary structure that provides the protein or polypeptide with its intended optimal wild type activity.
  • a protein biochemical or polypeptide folds into its proper tertiary structure during or after biosynthesis. Mis-folding of proteins results in dysfunctional or non-functional proteins or polypeptides.
  • Proper tertiary structure leading to proper folding is governed by many factors including the formation of inter-molecular and intra-molecular disulfide bonds that help to stabilize the tertiary structure of the protein or polypeptide.
  • a properly folded protein is one that possesses the disulfide bonds normally found in the native form of the protein or polypeptide.
  • reduction potential refers to the propensity of a properly-folded disulfide bond-containing protein of interest to undergo reduction at any point during a manufacturing process or during the storage time or “shelf life” of the protein following expression, purification, formulation and/or packaging.
  • the reduction potential at any point in time can be measured by subjecting a protein sample obtained at a desired time point to storage under vacuum for a given period of time (e.g., for a portion of an hour, for one hour, for a portion of a day (such as 8 hours, 10 hours, or 12 hours), one day, two days, 36 hours, or more) to induce reduction of the disulfide containing protein of interest in the absence oxygen.
  • the sample is then analyzed for fragmentation using, e.g., a bioanalyzer to separate protein fragments under non-reducing conditions.
  • LabChip GX assay and “GX assay” are used interchangeably herein. These terms relate to the assays used to visualize antibodies and antibody fragments using LabChip GX II instrument and software.
  • thioredoxin system means the enzymes thioredoxin reductase-1 (TrxR1), and thioredoxin-1 (Trx-1), and the cofactor NADPH. These three components make up the thioredoxin system which supports several processes needed for eukaryotic cell function including cell proliferation, antioxidant defense, and redox signaling (Lu et al., 2014 , Free Radic. Biol. Med., 66:75-87).
  • glutathione system means the components glutathione, glutathione reductase (GR), glutaredoxin (Grx), and the cofactor NADPH (Lillig et al., 2008 , Biochim. Biophys. Acta—Gen. Subj., 1780:1304-1317).
  • the glutathione system and the thioredoxin system are collectively and alternatively referred to herein as “reductase system” or “reductase systems.” That is, the term “reductase systems” encompasses both the glutathione system and/or the thioredoxin system.
  • a specific inhibitor is an agent that decreases or eliminates entirely the activity of a target enzyme to the exclusion of other, unrelated, enzymes, such as reductase enzymes.
  • a specific inhibitor of glutathione reductase is an inhibitor that predominantly or exclusively inhibits glutathione reductase enzymes.
  • a specific inhibitor of thioredoxin reductase is an inhibitor that predominantly or exclusively inhibits thioredoxin reductase enzymes.
  • a thioredoxin reductase-specific inhibitor is ineffective in inhibiting glutathione reductase enzymes.
  • a glutathione reductase-specific inhibitor is ineffective in inhibiting thioredoxin reductase enzymes.
  • a non-specific inhibitor is an agent that decreases or eliminates the activity of multiple enzymes. That is, a non-specific inhibitor is indiscriminate and can decrease or eliminate the activity of multiple different enzymes, such as both glutathione reductase and thioredoxin reductase.
  • Indirect inhibitors are inhibitors that decrease or eliminate the activity of a target enzyme by acting on a component other than the target enzyme itself.
  • an indirect inhibitor can act on an upstream substrate of the target enzyme, an upstream enzyme that produces a substrate of the target enzyme, or bind and sequester or remove from access a cofactor of the target enzyme, thereby decreasing or eliminating the activity of the target enzyme.
  • a cell culture manufacturing process for producing a disulfide bond-containing protein of interest can lead to reduction of protein disulfide bonds, and thereby reduce the yield of the intact protein of interest. Reduction of protein disulfide bonds or disulfide bridges can lead to misfolding of the protein of interest and loss of activity.
  • Eukaryotic cells contain reductase enzyme systems that control reduction and oxidation within the cell. For instance, reduced thioredoxin 1 (Trx1) is thought to be the enzyme responsible for antibody disulfide bond reduction (Hutterer et al., 2013, mAbs, 5:608-613; Kao et al., 2010 , Biotechnol.
  • FIG. 1 depicts a schematic representation of the enzymes and chemical intermediates of the thioredoxin system and the glutathione system.
  • the glutathione system is composed of glutathione, glutathione reductase (GR), glutaredoxin (Grx), and NADPH, which share a number of similarities and roles with the thioredoxin system (Lillig et al., 2008 , Biochim. Biophys. Acta—Gen. Subj., 1780:1304-1317).
  • Grx can be reduced non-enzymatically in the glutathione system by the oxidation of reduced glutathione (GSH) while oxidized glutathione (GSSG) can be reduced enzymatically by GR using NADPH as a cofactor.
  • thioredoxin Trx1 is reduced by thioredoxin reductase-1 (TrxR1) using NADPH as an electron donor. These three molecules, TrxR1, Trx1, and NADPH, make up the thioredoxin system.
  • the thioredoxin system and the glutathione system protect eukaryotic cells from oxidative stress and maintain the intracellular redox environment.
  • An imbalance in the intracellular redox state leads to increased oxidative stress, degradation of proteins, DNA damage, and eventually cell death.
  • the thioredoxin system and the glutathione system found in nearly all living cells, control the cellular redox environment.
  • This disclosure provides a method for increasing the yield of an intact disulfide bond-containing protein of interest in a manufacturing process, where the method includes preventing reduction-based degradation of the protein of interest by manufacturing the protein of interest, e.g., culturing a host cell, inducing expression of the protein of interest in the host cell, harvesting the protein of interest from the host cell and/or cell culture supernatant, and/or purifying the protein of interest, in the presence of a thioredoxin reductase inhibitor, a glutathione reductase inhibitor, or both a thioredoxin reductase inhibitor and a glutathione reductase inhibitor.
  • inhibitors of thioredoxin reductase and glutathione reductase can be included at one or more steps of a manufacturing process for the disulfide bond-containing protein of interest to diminish the activity of thioredoxin reductase or glutathione reductase on the protein of interest, thereby increasing the yield of the protein of interest.
  • Both, thioredoxin reductase and glutathione reductase can be active at varying levels in host cell lines commonly used for protein manufacturing. Moreover, the relative amount and activity of each of these reductases can vary between different host cell lines, or within the same host cell line depending on the cell culture conditions. In addition, the extent to which each of the reductases is “associated with” the protein of interest, i.e., is available to interact with and use the protein of interest as a substrate, can vary with the host cell, the properties of the protein of interest, and/or the time point in the manufacturing process.
  • the method for increasing the yield of a disulfide bond-containing protein of interest in a manufacturing process as discussed above further includes detecting whether the protein of interest is associated with specific reductases at any point during the manufacturing process, e.g., the growth phase, the production phase, the pre-harvest phase, the harvest phase, the purification phase, or any combination phases. Similarly mitigation of specific reductases can occur at any point during the manufacturing process.
  • a method of increasing the yield of an intact disulfide bond-containing protein of interest in a cell culture or solution comprising manufacturing the disulfide bond-containing protein of interest, e.g., culturing a host cell, inducing expression of the protein of interest in the host cell, harvesting the protein of interest from the host cell and/or cell culture supernatant, and/or purifying the protein of interest, in the presence of one or more reductase inhibitors, such as inhibitors of thioredoxin reductase and/or inhibitors of glutathione reductase.
  • one or more reductase inhibitors such as inhibitors of thioredoxin reductase and/or inhibitors of glutathione reductase.
  • the presence of active thioredoxin reductase and/or active glutathione reductase can be determined for the cell line expressing the protein of interest.
  • the amounts and identities of the inhibitors of thioredoxin reductase and/or inhibitors of glutathione reductase can be optimized depending on which reductase activities are present in the cell line.
  • thioredoxin system is active in the cell line expressing the protein
  • one or more inhibitors of thioredoxin reductase can be added during the manufacturing process to increase the yield of the intact disulfide bond-containing protein of interest.
  • glutathione system is active in the cell line expressing the protein
  • one or more inhibitors of glutathione reductase can be added during the manufacturing process to increase the yield of the intact disulfide bond-containing protein of interest.
  • both, the thioredoxin system and the glutathione system are active in the cell line, then one or more inhibitors for both reductases can be added during the manufacturing process.
  • Example 1, below provides exemplary assays useful for detecting the components of the thioredoxin system and the glutathione system, such as, but not limited to, Western blot techniques and other immunochemical techniques.
  • the activity of the thioredoxin system and/or glutathione system associated with the disulfide bond-containing protein of interest can be quantitated, and at certain points of the manufacturing process one or more inhibitors can be included in proportion to the levels of reductase activities detected in the vicinity of the protein of interest. For example, if it is determined that the quantity and/or activity of the thioredoxin system associated with the protein of interest is high at one or more points in a given manufacturing process, then a proportionally higher amount of one or more thioredoxin reductase inhibitors can be added during the manufacturing process to increase the yield of the disulfide bond-containing protein of interest expressed in the manufacturing process.
  • a proportionally higher amount of one or more glutathione reductase inhibitors can be added during the manufacturing process to increase the yield of the disulfide bond-containing protein of interest expressed in the manufacturing process.
  • a proportionally higher amount of one or more thioredoxin reductase inhibitors and one or more glutathione reductase inhibitors can be added during the manufacturing process to increase the yield of the disulfide bond-containing protein of interest expressed in the manufacturing process.
  • the amount of reductase inhibitor(s) added during the manufacturing process can be proportional to the quantity of each reductase system associated with the protein of interest at any point during the manufacturing process.
  • quantitating the activity of thioredoxin reductase and/or glutathione reductase associated with a disulfide bond-containing protein of interest during a manufacturing process includes adding 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) to a sample obtained during the manufacturing process, e.g., lysed cells, in cell culture medium, cell culture medium cleared of cells, or a solution containing the protein of interest in a downstream purification step; monitoring the reduction of DTNB in the sample at a wavelength of 412 nm; and repeating these steps in the presence of a thioredoxin reductase inhibitor, or a glutathione reductase inhibitor.
  • DTNB 5,5′-dithio-bis(2-nitrobenzoic acid)
  • components such as NADPH, oxidized glutathione, and buffer can be added to the sample prior to monitoring the wavelength.
  • the difference between the reduction of DTNB in the sample with the added inhibitor and the reduction of DTNB in the sample without the added inhibitor indicates the activity of thioredoxin reductase and/or glutathione reductase, respectively. That is, both the thioredoxin system and the glutathione system can reduce DTNB under the appropriate assay conditions.
  • the increase in absorbance at 412 nm is an indication of the reductase activity of a given sample.
  • the total reductase activity of a sample is first determined in the absence of any reductase inhibitor.
  • a thioredoxin system-specific inhibitor such as ATG
  • ATG a thioredoxin system-specific inhibitor
  • the difference in reductase activity between the sample with the thioredoxin system-specific inhibitor and the sample assayed without any thioredoxin system-specific inhibitor represents the reductase activity in the sample attributable to the thioredoxin system.
  • the sample can be analyzed in the presence of a glutathione system-specific inhibitor, such as 2-AAPA, and in the presence of no reductase inhibitor.
  • the difference in activity between the sample assayed with the glutathione system-specific inhibitor and the sample without any glutathione system-specific inhibitor represents the reductase activity attributable to the glutathione system.
  • Other exemplary methods for detecting reductase system components and increasing the yield of intact disulfide bond-containing protein in cell cultures are disclosed in Examples 2 to 8, below.
  • thioredoxin reductase examples include, but are not limited to, aurothioglucose (ATG), aurothiomalate (ATM), Auranofin, and 2-[(1-methylpropyl)dithio]-1H-imidzole (PX 12).
  • ATG aurothioglucose
  • ATM aurothiomalate
  • Auranofin 2-[(1-methylpropyl)dithio]-1H-imidzole
  • PX 12 2-[(1-methylpropyl)dithio]-1H-imidzole
  • a combination of thioredoxin inhibitors can be included in the manufacturing process.
  • the thioredoxin inhibitor added during protein manufacturing can be ATG.
  • glutathione reductase examples include, but are not limited to, carmustine, 2-Acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthiocarbonylamino)-phenylthiocarbamoylsulfanyl]propionic acid (2-AAPA), Ni 2+ salts, Ca 2+ salts, and Cu 2+ salts (at concentrations of about 50 ⁇ M or lower).
  • a combination of glutathione inhibitors can be added during the manufacturing process.
  • the glutathione inhibitor added during protein manufacturing can be 2-AAPA, a Cu 2+ salt, or both 2-AAPA and a Cu 2+ salt.
  • Non-specific inhibitors of both the glutathione system and thioredoxin system include, but are not limited to, cystine, and various metal ions, such as Cu 2+ (at concentrations higher than about 50 ⁇ M), Hg 2+ , Zn 2+ , Co 2+ , Fe 2+ , Cd 2+ , Pb 2+ , and Mn 2+ .
  • Indirect inhibitors of both the glutathione system and the thioredoxin system include, but are not limited to, metal chelators such as ethylenediamine tetraacetic acid (EDTA) or ethylene glycol tetraacetic acid (EGTA) to inhibit hexokinase, sorbose-1-phosphate, polyphosphates, 6-deoxy-6-fluoroglucose, 2-C-hydroxy-methylglucose, xylose, and lyxose.
  • metal chelators such as ethylenediamine tetraacetic acid (EDTA) or ethylene glycol tetraacetic acid (EGTA) to inhibit hexokinase, sorbose-1-phosphate, polyphosphates, 6-deoxy-6-fluoroglucose, 2-C-hydroxy-methylglucose, xylose, and lyxose.
  • EDTA ethylenediamine tetraacetic acid
  • Such indirect methods of decreasing reduction of a disulfide-bond containing protein of interest during a manufacturing process can be combined with the inclusion of specific inhibitors during the manufacturing process, as discussed above.
  • specific thioredoxin system- and/or glutathione system-specific inhibitors can be combined with inhibitors of enzymes that are responsible for biosynthesis of NADPH in the cell.
  • NADPH biosynthetic enzyme inhibitors indirect inhibitors can be employed during and/or after harvest (e.g., during a hold phase between harvest and purification) to prevent toxicity caused by the inhibitors during the growth of the cells.
  • the amount of reductase inhibitor included during a manufacturing process can be any amount effective for inhibiting the detected thioredoxin system and/or glutathione system activity, and in certain aspects is the minimum amount effective for inhibiting the detected thioredoxin system and/or glutathione system activity.
  • the effective amount of reductase inhibitor(s) can be empirically determined using the assays provided herein, such as in Examples 10-13.
  • one or more reductase-specific inhibitors can be added during the manufacturing process in the amounts provided below.
  • the amount of 2-AAPA included in a manufacturing process with detected glutathione system activity can be from about 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, 0.05 mM, 0.06 mM, 0.07 mM, 0.08 mM, 0.09 mM, 0.1 mM, 0.11 mM, 0.12 mM, 0.13 mM, 0.14 mM, 0.15 mM, 0.16 mM, 0.17 mM, 0.18 mM, or 0.19 mM to about 0.2 mM, 0.21 mM, 0.22 mM, 0.23 mM, 0.24 mM, 0.25 mM, 0.26 mM, 0.27 mM, 0.28 mM, 0.29 mM, 0.3 mM, 0.4 mM, or 0.5 mM final concentration.
  • the amount of 2-AAPA included in a manufacturing process with detected glutathione system activity can be from about 0.05 mM to about 0.3 mM final concentration, from about 0.1 mM to about 0.25 mM final concentration, or from about 0.15 mM to about 0.22 mM final concentration.
  • the amount of 2-AAPA included in a manufacturing process with detected glutathione system activity can be about 0.2 mM final concentration.
  • Cu 2+ salt can specifically inhibit the glutathione system or both, the glutathione system and thioredoxin system, in a concentration-dependent manner.
  • Copper ion can be added by any means known in the art, such as by addition of copper chloride (CuCl 2 ), cupric sulfate (CuSO 4 , pentahydrate or anhydrous), copper acetate, and combinations thereof.
  • the final concentration of Cu 2+ salt (copper ion) included in a manufacturing process with detected glutathione system activity can be about 0.1 ⁇ M, 0.2 ⁇ M, 0.3 ⁇ M, 0.4 ⁇ M, 0.5 ⁇ M, 0.6 ⁇ M, 0.7 ⁇ M, 0.8 ⁇ M, 0.9 ⁇ M, 1.0 ⁇ M, 1.5 ⁇ M, 2.0 ⁇ M, 2.5 ⁇ M, 3.0 ⁇ M, 3.5 ⁇ M, 4.0 ⁇ M, 4.5 ⁇ M, 5.0 ⁇ M, 5.5 ⁇ M, 6.0 ⁇ M, 6.5 ⁇ M, 7.0 ⁇ M, or 7.5 ⁇ M to about 8 ⁇ M, 9 ⁇ M, 10 ⁇ M, 11 ⁇ M, 12 ⁇ M, 13 ⁇ M, 14 ⁇ M, 15 ⁇ M, 16 ⁇ M, 18 ⁇ M, 20 ⁇ M, 25 ⁇ M, 30 ⁇ M, 35 ⁇ M, 40 ⁇ M, 45
  • both, the thioredoxin system and the glutathione system can be inhibited by addition of copper ion during the manufacturing process.
  • the final concentration of Cu 2+ salt included in a manufacturing process can be from about 5 ⁇ M, 10 ⁇ M, 20 ⁇ M, 30 ⁇ M, 40 ⁇ M, 50 ⁇ M, or 75 ⁇ M to about 100 ⁇ M, 110 ⁇ M, 120 ⁇ M, 130 ⁇ M, 140 ⁇ M, 150 ⁇ M, 175 ⁇ M, or 200 ⁇ M.
  • the final concentration of copper ion included in a manufacturing process can be from about 5 ⁇ M to about 200 ⁇ M, from about 5 ⁇ M to about 200 ⁇ M, from about 10 ⁇ M to about 175 ⁇ M, from about 20 ⁇ M to about 150 ⁇ M, from about 40 ⁇ M to about 150 ⁇ M, or from about 5 ⁇ M to about 200 ⁇ M. In certain aspects, the final concentration of copper ion included in a manufacturing process can be about 50 ⁇ M.
  • the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be from about 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, 0.05 mM, 0.06 mM, 0.07 mM, 0.08 mM, 0.09 mM, 0.1 mM, 0.11 mM, 0.12 mM, 0.13 mM, 0.14 mM, 0.15 mM, 0.16 mM, 0.17 mM, 0.18 mM, or 0.19 mM to about 0.2 mM, 0.21 mM, 0.22 mM, 0.23 mM, 0.24 mM, 0.25 mM, 0.26 mM, 0.27 mM, 0.28 mM, 0.29 mM, 0.3 mM, 0.4 mM, 0.5 mM, 0.6 mM, 0.7 mM, 0.8 mM, 0.9 mM, 1.0 mM, 1.5
  • the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be from about 0.05 mM to about 5 mM final concentration. In certain aspects, the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be from about 0.10 mM to about 1 mM final concentration. In certain aspects, the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be from about 0.1 mM to about 0.5 mM final concentration. In certain aspects, the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be from about 0.10 mM to about 0.20 mM final concentration. In certain aspects, the amount of ATG included in a manufacturing process with detected thioredoxin system activity can be about 0.1 mM final concentration.
  • Any cell culture technique known in the art can be used to grow host cells that express a disulfide bond-containing protein of interest using any cell lines known in the art. Standard techniques for culturing cell lines are available.
  • Manufacture of a disulfide bond-containing protein of interest can include culturing a host cell that is amenable to culturing and biosynthesizes the disulfide bond-containing protein of interest.
  • Cell culture conditions vary depending on the type of cell.
  • Cell culture media can include, without limitation, buffers, salts, carbohydrates, amino acids, vitamins, and trace essential elements.
  • the term “serum-free” medium applies to a cell culture medium that does not contain animal sera, such as fetal bovine serum.
  • tissue culture media, including defined culture media are commercially available and can be used in the manufacture of the disulfide bond-containing protein of interest.
  • Eukaryotic cells can be either adherent or suspended in culture, and such cells can be grown in containers such as test tubes, flasks, roller bottles, plates, bags, fluidized bed reactors, hollow fiber bed reactors, or stirred tank bioreactors (single-use and standard stainless steel and glass vessel bioreactors).
  • Cell culture can be performed on a small or a large scale, where cells are incubated for growth in containers of varying sizes from a few milliliters to thousands of liters or more.
  • Cell culture systems are commercially available that allow for incubation under optimal conditions of temperature, pH, O 2 and CO 2 .
  • Basic equipment useful in culturing cells includes a laminar-flow hood, incubator, centrifuge, refrigerator and freezer, cell counter, microscope, autoclave (sterilizer), vacuum or pump, pH meter, and flow cytometer.
  • Cells can be grown in a batch culture, where nutrients and media are not replaced during cell growth; fed-batch culture, where nutrients are added during the cell growth; or perfusion culture, where fresh nutrients and media are continuously added to the cell culture and spent media is continuously removed.
  • Cell cultures can be grown using commercially available automated systems designed to maximize cell growth under specific conditions.
  • the manufacturing process of a disulfide bond-containing protein of interest can include multiple phases. For example, in a multiple stage process, cells are cultured in two or more distinct phases. In a multi-phase production process, cells are cultured first in one or more growth phases, under environmental conditions that maximize cell proliferation and viability, then transferred to a production phase, under conditions that maximize protein production. In a commercial process for production of a protein of interest by mammalian cells, there are commonly multiple, for example, at least about 2, 3, 4, 5, 6, 7, 8, 9, or 10 growth phases that occur in different culture vessels preceding a final production culture. The growth and production phases can be preceded by, or separated by, one or more transition phases.
  • a production phase can be conducted at large scale.
  • a large scale process can be conducted in a volume of at least about 50, 100, 500, 1000, 2000, 3000, 5000, 7000, 8000, 10,000, 15,000, 20,000, 25,000 liters.
  • production is conducted in a 500 L, 1000 L, 2000 L, 12000 L and/or 20000 L bioreactor.
  • Cells can be cultured in a stirred tank bioreactor system and a fed batch culture procedure can be employed.
  • mammalian host cells and culture medium can be supplied to a culturing vessel initially and additional culture nutrients can be fed, continuously or in discrete increments, to the culture during culturing, with or without periodic cell and/or product harvest before termination of culture.
  • a fed batch culture can include, for example, a semi-continuous fed batch culture, wherein the partial or entire culture (including cells and medium) is removed and replaced by fresh medium.
  • Fed batch culture can be distinguished from simple batch culture in which all components for cell culturing (including the cells and all culture nutrients) are supplied to the culturing vessel at the start of the culturing process.
  • Fed batch culture can be further distinguished from perfusion culturing, where the supernatant is not removed from the culturing vessel during the process (in perfusion culturing, the cells are restrained in the culture by, e.g., filtration, encapsulation, anchoring to microcarriers, etc. and the culture medium is continuously or intermittently introduced and removed from the culturing vessel).
  • fed batch or continuous cell culture conditions can be used to enhance growth of the mammalian cells in the growth phase of the cell culture.
  • cells are grown under conditions and for a period of time that is maximized for growth.
  • Culture conditions such as temperature, pH, dissolved oxygen (dO 2 ) and the like, are those used with the particular host and will be apparent to the ordinarily skilled artisan.
  • the pH is adjusted to a desired level using either an acid (e.g., CO 2 ) or a base (e.g., Na 2 CO 3 or NaOH).
  • a suitable temperature range for culturing mammalian cells such as CHO cells is between about 30° C. and 38° C.; a suitable pH is between about 6.5 and 7.5; and a suitable dO 2 is between 5 and 90% of air saturation.
  • the cells may be used to inoculate a production phase or step of the cell culture.
  • the production phase or step may be continuous with the inoculation or growth phase or step.
  • the cell culture environment during the production phase of the cell culture is typically controlled.
  • factors affecting cell specific productivity of the mammalian host cell may be manipulated such that the desired sialic acid content is achieved in the resulting glycoprotein.
  • the production phase of the cell culture process is preceded by a transition phase of the cell culture in which parameters for the production phase of the cell culture are engaged.
  • Suitable host cells include, but are not limited to, bacteria, plant cells, mammalian cells, yeast cells, and insect cells. Eukaryotic cells from many different animals are amenable to cell culturing and commercially available, including, but not limited to, fibroblast cell lines such as BALB/3T3, and BHK-21; epithelial cell lines such as the Human Embryonic Kidney cell line HEK293 (293), the HeLa cell line, Madin-Darby canine kidney (MDCK) cells, A549, HepG2, VERO, Caco-2, Chinese Hamster Ovary (CHO), COS-1; lymphoblasts such as Daudi, Jurkat, and H9; myeloblasts cells such as NSO, KG-1; endothelial cell lines such as HUVEC; retinal cells such as the PER.C6 cell line; insect cell lines such as Sf9, BTI-TN-5B1-4, and D.Mel-2; and yeast cell lines, such as Pichia pastoris strains SMD116
  • the nucleic acid encoding the disulfide bond-containing protein of interest is inserted into the host cell either transiently or stably, for expression.
  • the expression of the protein from the nucleic acid can be triggered, for instance by culturing the host cells under conditions that facilitate expression of the gene.
  • a manufacturing process can include pre-harvest steps such as, e.g., addition of reagents to facilitate purification and protein stability.
  • the disulfide bond-containing protein of interest After the disulfide bond-containing protein of interest is expressed, it can be harvested, e.g., separated from other components of the cell culture, and purified in a protein purification process.
  • Harvesting of the protein of interest can be accomplished by many different means that achieve separation of the protein of interest from other cell culture components.
  • secretion of a recombinant protein into the culture medium is achieved by engineering a protein of interest to be secreted outside the cell into the culture medium.
  • One such engineering technique includes designing an expression vector to include a signal peptide that causes the recombinant protein to be secreted outside of the host cell upon expression.
  • Vectors comprising protein secretion signal sequences are commercially available.
  • the protein of interest When the protein of interest is expressed by the cell line and secreted into the cell culture medium, the protein of interest can be isolated from the culture medium. Separation of the secreted protein of interest from the cells and cell culture medium can be accomplished by known techniques such as centrifugation, ultrafiltration/diafiltration, and/or chromatography. If the protein of interest is not secreted by the host cell, host cells can be separated from the cell culture medium, e.g., by centrifugation or filtration, and then lysed by various known means and the protein can be separated from other cell components in the cell lysate by various methodologies, such as centrifugation, column chromatography, and/or precipitation and dialysis techniques.
  • Further purification techniques can include various chromatography methodologies such as ion exchange, size exclusion, hydroxylapatite, and affinity chromatography. These can be performed in small scale on HPLC, FPLC, and capillary systems, or on a large scale using large batch chromatography techniques known in the art.
  • the protein of interest can be applied to the column and in some instances bound to the column. In some instances the protein of interest will pass through the column, while other cell line components remain behind, bound to the column.
  • Bound protein can be eluted from the column by application of an elution agent that interferes with binding of the protein of interest to the column media.
  • purification of antibodies can be achieved by binding secreted proteins, such as antibodies, in the culture medium to a protein-A affinity column.
  • the disulfide bond-containing protein of interest can be an endogenous disulfide bond-containing protein.
  • the disulfide bond-containing protein of interest can be a recombinant heterologous disulfide bond-containing protein encoded on an expression vector and transiently transfected into the host cell, or stably transfected into the host cell.
  • the disulfide bond-containing protein of interest can be an antibody or antigen-binding fragment thereof.
  • the disulfide bond-containing protein of interest can be a human, chimeric, or humanized antibody or fragment thereof.
  • the antibody can be an IgG antibody or fragment thereof.
  • the disulfide bond-containing protein of interest can be a human, humanized, or chimeric antibody of IgG subtype IgG 1 , IgG 2 , IgG 3 , or IgG 4 .
  • the immunoglobulin or fragment thereof can be monovalent or bivalent.
  • the antibody can be an IgA, IgM, IgD, or IgE.
  • the antibody or fragment thereof can be an Fab, Fab′, F(ab′)2, or disulfide-linked Fvs (sdFv).
  • the antibody or fragment thereof can be a monoclonal antibody or part of a polyclonal mixture of antibodies.
  • the protein of interest can be immediately purified or alternatively, the harvested cell culture fluid (HCCF) containing the protein of interest can be held or stored for a period time, e.g., for at least one hour, at least one day, at least four days, at least one week, at least 10 days, or at least two weeks following the harvest phase and prior to the purification phase.
  • HCCF harvested cell culture fluid
  • the harvest steps of the manufacturing process occurs when the cells are separated from the supernatant containing the protein of interest.
  • the process of separating the cells from the supernatant can cause cell lysis, which releases reductase pathway components into the supernatant where they can associate with the protein and catalyze protein disulfide bond reduction of the disulfide bond-containing protein of interest.
  • the harvest step is typically at about day 14 of the manufacturing process, but can vary depending, e.g., on the identity of the cell line employed, the cell culture conditions, and/or the characteristics of the protein of interest.
  • Reductase inhibitors can be added before the harvest step, during the harvest step, during a hold period following harvest and prior to purification, and/or during the purification process.
  • a solution is provided containing cell culture media, one or more components of one or more reductase pathways, the disulfide bond-containing protein of interest, and one or more reductase inhibitors.
  • Manufacturing processes for disulfide bond-containing proteins of interest can likewise exhibit disulfide bond reduction in the bioreactor towards the end of the cell culture but prior to harvest, e.g., day 8-14 for a two week culture.
  • the reductase inhibitors can be added earlier than at harvest, e.g., at day 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 of a typical cell culture process, or can be present throughout the cell culture process.
  • the precise day on which inhibitors are added to the culture can vary depending, e.g., on the identity of the cell line used and the characteristics of the disulfide bond-containing protein of interest being manufactured. In either case, the reductase inhibitors can be added before reduction occurs.
  • a solution can be provided comprising one or more reductase inhibitors.
  • Reductase-specific inhibitors can be screened and their optimal concentrations determined in assays employing purified recombinant mammalian reductases as shown below.
  • the reductase screening assays disclosed below can be helpful in detecting both the activity and amount of reduction of the disulfide bond-containing protein of interest individually caused by the thioredoxin system and the glutathione system.
  • reductase inhibitors that are specific for either the glutathione system or the thioredoxin system, it can be possible to determine the individual contributions of the thioredoxin system and the glutathione system to reduction of the disulfide bond-containing protein of interest at various points during the manufacturing process.
  • the quantity, or amount, of an intact disulfide bond-containing protein of interest reduced by the glutathione system and/or the thioredoxin system can be determined with these assays.
  • the methods described herein utilize the correlation between reductase enzyme activity and protein reduction activity in cell cultures.
  • the amounts of the thioredoxin system and glutathione system components associated with a disulfide bond-containing protein of interest during a manufacturing process can vary for reasons described elsewhere herein. For instance, in the Examples below, it was found that a manufacturing process employing CHO cell line A (CHO CAT-S) to express mAb A exhibited glutathione reductase activity during the manufacturing process, and the reduction of mAb A in this process was thus sensitive to specific inhibition of the glutathione system.
  • methods are provided in which either glutathione system-specific inhibitors are added, or thioredoxin system-specific inhibitors are added, or both, glutathione system-specific inhibitors and thioredoxin system-specific inhibitors are added depending on the determination of whether enzymes in these systems are associated with the protein of interest at any point during the manufacturing process, and the amount of activity of each system present.
  • the cocktail of inhibitors added during the manufacturing process can be tailored to the specific reductase systems associated with the protein of interest during the manufacturing process.
  • the percent of increase in yield of the intact disulfide bond-containing protein of interest can be from 20% to 100% depending on the type of reductase inhibitor, or combination of reductase inhibitors, employed during the manufacturing process and the amount of thioredoxin system and/or glutathione system activity associated with the disulfide bond-containing protein of interest during the manufacturing process.
  • the percent increase in yield of the, disulfide bond-containing protein of interest when adding the inhibitor ATG, can be from about 30% to about 90%, from about 40% to about 80%, from about 50% to about 70%, or higher than 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%. In certain aspects, when adding the inhibitor Cu 2+ to the manufacturing process, the percent increase in yield of the disulfide bond-containing protein of interest can be from about 20% to about 100%, from about 30% to about 90%, from about 40% to about 80%, or higher than 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%.
  • glutathione system inhibitor(s) to the manufacturing process in addition to thioredoxin system inhibitor(s) can provide a higher yield of properly folded, disulfide bond-containing protein of interest as compared to the same manufacturing process performed in the presence of only a thioredoxin system inhibitor.
  • a copper ion to inhibit glutathione reductase in addition to the inclusion of a thioredoxin system-specific inhibitor, such as ATG, provided an increase in yield of properly folded, disulfide bond-containing protein of interest of over 20%, 30%, 40%, 50%, or even 60%.
  • inclusion of a glutathione system-specific inhibitor in a manufacturing process for a disulfide bond-containing protein of interest can result in a marked increase in yield of that protein of interest as compared to an identical manufacturing process performed in the presence of only a thioredoxin system-specific inhibitor.
  • the inhibition of the glutathione system during a manufacturing process can substantially, or completely, prevent reduction of disulfide bonds of a disulfide-bond containing protein of interest, thereby increasing the yield of that protein.
  • enzyme assays can be employed to determine the relative amount of each reduction system, and their imputed impact, on protein disulfide bond reduction. This information can be used to select the best disulfide-bond containing protein manufacturing process reduction mitigation strategy for the protein of interest.
  • the methods described herein balance the risks and benefits of thioredoxin system and glutathione system inhibitors to maximize the production yield of a disulfide bond-containing protein of interest.
  • Reduction mitigation strategies often have unique drawbacks. For example, excessive addition of copper ion can decrease cell growth, reduce titer, lower the activity of a disulfide bond-containing protein of interest, trigger increased environmental disposal concerns, or increase the burden of monitoring the clearance of metal ions during the downstream processing (protein purification) of the protein of interest. Consequently, in certain aspects, the presence and quantity of the thioredoxin system and the glutathione system associated with a protein of interest during a manufacturing process can be detected, and then mitigation strategies can be designed based on that information.
  • a reduction mitigation strategy does not increase the yield of a disulfide bond-containing protein of interest
  • the mitigation strategy as well as the drawbacks of that strategy, can be avoided, reducing protein manufacturing costs and reducing production time while maintaining and/or increasing the overall yield of the disulfide bond-containing protein of interest.
  • detrimental side-effects of too much of any glutathione system and thioredoxin system inhibitor(s) can be avoided by limiting the concentration of the inhibitors employed during the manufacturing process to the minimum required to increase the yield of the disulfide bond-containing protein of interest.
  • This disclosure provides a method for increasing the yield of an intact disulfide bond-containing protein of interest, and/or decreasing or mitigating the reduction potential of the disulfide bond-containing protein in a manufacturing process.
  • the method provides improvements to a manufacturing process that mitigates, e.g., prevents or reduces, the potential for disulfide bond reduction at one or more time points during the process.
  • the manufacturing process can include expressing the protein of interest in a cultured eukaryotic host cell grown and maintained in cell culture fluid (CCF).
  • CCF cell culture fluid
  • a manufacturing process according to the method provided herein can include a growth phase, a production phase, a pre-harvest phase, a harvest phase, a hold phase, a purification phase, or any combination thereof.
  • the production phase can include maintaining the cells in CCF for any period of time, at least one day, at least 8 days, at least 10 days, at least 12 days, at least 14 days, or at least 16 days.
  • the manufacturing process includes maintaining an effective amount of cystine in the CCF during the production bioreactor or any portion thereof, e.g., late in the production phase, thereby mitigating the potential for disulfide bond reduction.
  • mitigating the potential for disulfide bond reduction is meant that the potential for reduction is decreased relative to a control manufacturing process in which an effective amount of cystine is not maintained in the CCF at any given point in the production phase. In certain aspects reduction of the disulfide bond-containing protein of interest is prevented entirely.
  • the amount of disulfide bond reduction is less than observed in the control CCF, e.g., about 5% less, about 10% less, about 20% less, about 30% less, about 40% less, about 50% less, about 60% less, about 70% less, about 80% less, about 90% less, or about 99% less than that observed in the control CCF.
  • Reduction potential can be measured by the vacuum/bioanalyzer assay described elsewhere herein.
  • reduction potential can be measured by a method comprising: storing a sample of the CCF obtained at a selected time point during the manufacturing process in a vacuum chamber, and measuring the level of fragmentation of the protein of interest relative to control sample.
  • samples recovered from the CCF at various time points during the production phase can be centrifuged to remove cells, and the supernatants can be immediately frozen, e.g., at ⁇ 80° C. Once all the samples are collected they can be thawed and subjected to vacuum treatment at the same time. In certain aspects the level of fragmentation is measured on a bioanalyzer under non-reducing conditions.
  • the method provided herein can increase the yield of the intact disulfide containing protein of interest, and/or can decrease the reduction potential of the disulfide bond-containing protein during storage. Yield can be increased, e.g., about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 99% more than relative to the yield of a control manufacturing process.
  • an effective amount of cystine to be maintained during a production phase or portion thereof can be easily determined by a person of ordinary skill in the art using the methods provided herein, e.g., measuring the cystine concentration in CCF at any point, or one or more points, during the manufacturing process, determining the reduction potential of the disulfide bond-containing protein of interest at the same point or points, and determining the concentration of cystine required to decrease or eliminate the propensity of the protein of interest to undergo reduction at that time point.
  • the effective amount of cystine can be from about 0.5 mM to about 1 mM; from about 0.9 mM to about 3 mM; from about 2.5 mM to about 4.5 mM.
  • the effective amount of cystine can be at least about 0.5 mM; at least about 1 mM; at least about 2.0 mM, at least about 2.5 mM, at least about 3.0 mM, at least about 3.5 mM, at least about 4.0 mM, at least about 4.5 mM, at least about 5.0 mM, or at least about 5.5 mM.
  • the concentration of cystine in the CCF can be determined, e.g., by amino acid analysis using UPLC at any one or more time points during the manufacturing process, or at regular intervals during the manufacturing process, e.g., at regular intervals during the production phase.
  • a method for mitigating the potential for disulfide bond reduction includes changing the redox potential of the solution during any step of the manufacturing process (including bioreactor) by adding redox modifiers including metal ions (including Zn 2+ , Mn 2+ , Fe 3+ Cu 2+ , Se 2+ ), cystine, dissolved oxygen, beta mercaptoethanol, glutathione, or a combination thereof.
  • redox modifiers including metal ions (including Zn 2+ , Mn 2+ , Fe 3+ Cu 2+ , Se 2+ ), cystine, dissolved oxygen, beta mercaptoethanol, glutathione, or a combination thereof.
  • a method for mitigating the potential for disulfide bond reduction is controlled via an online cell culture redox potential.
  • the control system based on the cell culture redox potential, is used to increase the concentration of Zn 2+ , Mn 2+ , Fe 3+ , Cu 2+ , Se 2+ , cystine, dissolved oxygen, beta mercaptoethanol, or glutathione in response to a decrease in the cell cutlure redox potential.
  • Use of a control system based on the cell culture redox potential prevents the unnecessary over-addition of the chemical mitigator (or increase in DO set point). This is advantageous as the chemical required to prevent reduction must be cleared by the downstream purification process and elevated DO can reduce the final process titer.
  • a production phase according to the methods provided herein can be a “fed batch” process, in which a nutrient feed solution that includes cystine is added to the CCF during the production phase.
  • the nutrient feed solution containing cystine can include one or more additional nutrients to facilitate expression of the protein of interest in functional form.
  • the nutrient feed solution may contain, for example, at least one amino acid.
  • the nutrient feed solution includes L-cystine by itself or with one or more additional components.
  • the nutrient feed solution that includes cystine is added to the CCF at regular intervals during the production phase, e.g., about every day, about every two days, about every three days, about every four days, or about every five days during the production phase.
  • an additional nutrient feed solution can include at least one additional nutrient to facilitate expression of the protein of interest in functional form, for example, amino acids, glucose, vitamins, protein hydrolysate, or any combination thereof.
  • One or more nutrient feed solutions can be added according to the same schedule that the nutrient feed solution comprising cystine is added. This second nutrient feed solution can be added using a different schedule than the one used for the first nutrient feed solution.
  • the nutrient feed solution containing cystine is added to the CCF about every two days, and five or six additions of the nutrient feed solution occur during the production phase.
  • an effective amount of cystine can be maintained in the CCF throughout the production phase, and/or during other phases of the manufacturing process. In certain aspects, however, the effective amount of cystine need only be maintained in the CCF during the later portions of the production phase, e.g., the part of the production phase occurring just before the pre-harvest and/or harvest phases.
  • the effective amount of cystine can be maintained in the CCF for the last 14 days of the production phase, the last 12 days of the production phase, the last 10 days of the production phase, the last 8 days of the production phase, the last 6 days of the production phase, the last 4 days of the production phase, the last 2 days of the production phase, or the last day of the production phase.
  • additional cystine can be included in the last and/or the next to last additions of a nutrient feed solution (NF), e.g., the fifth NF addition where the process includes five batch feedings, or the fifth and/or sixth NF additions.
  • NF nutrient feed solution
  • the amount of cystine in the later feedings can be at least about 10% more, at least about 20% more, at least about 30% more, at least about 40% more, at least about 50% more, at least about 60% more, at least about 70% more, at least about 80% more, at least about 90% more, or at least about 100% more.
  • concentration of cystine in the control CCF at a certain time point in the production phase can be about 2.0 mM where at the same time point, the concentration of cystine in the CCF according to the method provided herein can be 3.5 mM, 4.0 mM, or 4.5 mM.
  • the same nutrient feed solution as is used in the earlier feedings is used, but an increased volume is added in the later feedings to increase the amount of cystine added to the CCF.
  • a modified nutrient feed solution can be used in the later feedings, where the remaining ingredients in the solution are kept at the same concentration but the concentration of cystine is increased. According to this aspect, the volume of NF solution added can remain constant.
  • a method for increasing the yield of an intact disulfide bond-containing protein of interest in a cell culture or solution comprising manufacturing the disulfide bond-containing protein of interest in the presence of a glutathione reductase inhibitor, a thioredoxin reductase inhibitor, or both a glutathione reductase inhibitor and a thioredoxin reductase inhibitor, whereby the amount of intact disulfide bond-containing protein is higher in the cell culture or solution manufactured in the presence of a glutathione reductase inhibitor, a thioredoxin reductase inhibitor, or a glutathione reductase inhibitor and a thioredoxin reductase inhibitor as compared to the amount of intact disulfide bond-containing protein in a cell culture or solution not manufactured in the presence of a glutathione reductase inhibitor, a thioredoxin reductase inhibitor, or a glutathione reductase
  • a method for increasing the yield of an intact disulfide bond-containing protein of interest in a culture or solution in a manufacturing process comprising: detecting the presence of glutathione reductase and/or thioredoxin reductase in the culture or solution containing the protein of interest, and adding a glutathione reductase and/or thioredoxin reductase inhibitor to the manufacturing process to mitigate reduction of the disulfide bond-containing protein of interest.
  • invention 2A further comprising determining the activity of the glutathione reductase and/or thioredoxin reductase in the culture or solution.
  • determining the activity of the glutathione reductase and/or thioredoxin reductase comprises: adding 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) to a sample obtained during the manufacturing process; adding at least one of thioredoxin reductase inhibitor and glutathione reductase inhibitor to a portion of the sample containing DTNB; and monitoring reduction of DTNB at a wavelength of 412 nm in the sample; wherein a higher reduction of DTNB in the samples without at least one of thioredoxin reductase inhibitor and glutathione reductase inhibitor, indicates activity of thioredoxin reductase and/or glutathione reductase.
  • DTNB 5,5′-dithio-bis(2-nitrobenzoic acid)
  • any one of embodiments 1A to 6A wherein the disulfide bond-containing protein of interest is manufactured in the presence of a glutathione reductase inhibitor and a thioredoxin reductase inhibitor, and wherein the presence of the glutathione reductase inhibitor and the thioredoxin reductase inhibitor increases yield of intact disulfide bond-containing protein by at least 5 percent, at least 10 percent, at least 20 percent, at least 30 percent, or at least 40 percent as compared to manufacturing the disulfide bond-containing protein in the absence of the glutathione reductase inhibitor and the thioredoxin reductase inhibitor.
  • any one of embodiments 1A to 6A wherein the disulfide bond-containing protein of interest is manufactured in the presence of a thioredoxin reductase inhibitor and not in the presence of a glutathione reductase inhibitor, and wherein the presence of the thioredoxin reductase inhibitor increases yield of intact disulfide bond-containing protein by at least 5 percent, at least 10 percent, at least 20 percent, at least 30 percent, or at least 40 percent as compared to manufacturing the disulfide bond-containing protein in the absence of the thioredoxin reductase inhibitor.
  • any one of embodiments 1A to 6A wherein the disulfide bond-containing protein of interest is manufactured in the presence of a glutathione reductase inhibitor and not in the presence of a thioredoxin reductase inhibitor, and wherein the presence of the glutathione reductase inhibitor increases yield of intact disulfide bond-containing protein by at least 5 percent, at least 10 percent, at least 20 percent, at least 30 percent, or at least 40 percent as compared to manufacturing the disulfide bond-containing protein in the absence of the glutathione reductase inhibitor.
  • thioredoxin reductase inhibitor is at least one of aurothioglucose (ATG), aurothiomalate (ATM), Auranofin, 2-[(1-methylpropyl)dithio]-1H-imidzole (PX 12), or any combinations thereof.
  • thioredoxin reductase inhibitor comprises ATG, ATM, or a combination of ATG and ATM.
  • the thioredoxin reductase inhibitor comprises ATG and ATG and wherein the final concentration of ATG in the cell culture is about 0.1 to about 0.5 mM and the final concentration of ATM is about 0.1 to about 0.5 mM; or the final concentration of ATM is about 0.1 to about 0.5 mM and the concentration of ATG is about 0.1 to about 0.5 mM.
  • the glutathione reductase inhibitor is at least one of carmustine, 2-Acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthio-carbonylamino)phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), a Cu 2+ salt, a Ni 2+ salt, a Ca 2+ salt, or any combinations thereof.
  • the glutathione reductase inhibitor comprises 2-AAPA, a Cu 2+ salt, or a combination of 2-AAPA and a Cu 2+ salt.
  • the glutathione reductase inhibitor comprises 2-AAPA and a Cu 2+ salt
  • the final concentration of 2-AAPA is about 0.1 mM to about 0.25 mM
  • the final concentration of Cu 2+ salt is about 0.5 ⁇ M to less than about 50 ⁇ M
  • the final concentration of 2-AAPA is about 0.1 mM to about 0.25 mM
  • the final concentration of Cu 2+ salt is about 1 ⁇ M to less than about 50 ⁇ M.
  • any one of embodiments 1A to 15A further comprising manufacturing the disulfide bond-containing protein of interest in the presence of cystine, Hg 2+ , Zn 2+ , Co 2+ , Fe 2+ , Cd 2+ , Pb 2+ , Mn 2+ , more than about 50 ⁇ M Cu 2+ , or any combination thereof.
  • EDTA ethylenediamine tetraacetic acid
  • EGTA ethylene glycol tetraacetic acid
  • sorbose-1-phosphate polyphosphates, 6-deoxy-6-fluoroglucose, 2-C-hydroxy-methylglucose, xylose, lyxose, or any combination thereof.
  • disulfide bond-containing protein of interest is a recombinant protein manufactured in a host cell.
  • the glutathione reductase inhibitor is a Cu 2+ salt
  • the Cu 2+ salt is added during the harvesting step, and wherein the yield of the intact disulfide bond-containing protein of interest is increased by about 20% to about at least 100%, as compared to the yield of intact disulfide bond-containing protein manufactured by the same manufacturing process in the absence of the Cu 2+ salt.
  • disulfide bond-containing protein of interest is an antibody or antigen-binding fragment thereof.
  • the antibody or fragment thereof is a monoclonal antibody, a bispecific antibody, a fusion protein, or an antibody drug conjugate, or fragment thereof.
  • the method of embodiment 2B, wherein the production phase comprises maintaining the cells in CCF for at least 2 days, at least 8 days, at least 10 days, at least 12 days, at least 14 days, or at least 16 days.
  • cystine levels are maintained at about 0.2 mM, at least 2.0 mM, at least about 2.5 mM, at least about 3.0 mM, at least about 3.5 mM, or at least about 4.0 mM.
  • the production phase comprises adding a nutrient feed solution to the CCF, wherein the nutrient feed solution comprises cystine.
  • composition of the nutrient feed solution is uniform throughout the production phases, and wherein an additional volume of nutrient feed solution is added throughout the additions, resulting in an increased amount of cystine in the culture or fermentation process.
  • composition of the nutrient feed solution is uniform throughout the production phases, and wherein an additional volume of nutrient feed solution is added in the fifth addition, the sixth addition, or the fifth and sixth additions, resulting in an increased amount of cystine in the culture or fermentation process.
  • the nutrient feed solution added in at least one of the fifth or sixth additions comprises at least about 10% more, at least about 20% more, at least about 30% more, at least about 40% more, at least about 50% more, at least about 60% more, at least about 70% more, at least about 80% more, at least about 90% more, or at least about 100% more cystine than the nutrient feed solution added in the first to fourth or first to fifth additions.
  • the at least one additional nutrient comprises amino acids, glucose, vitamins, protein hydrolysate, or any combination thereof.
  • the production phase further comprises adding an additional nutrient feed solution to the CCF, wherein the additional nutrient feed solution comprises at least one additional nutrient.
  • the at least one additional nutrient comprises amino acids, glucose, vitamins, protein hydrolysate, or any combination thereof.
  • bioanalyzer comprises a GX LabChip.
  • disulfide bond-containing protein of interest is an antibody or antigen-binding fragment thereof.
  • the IgG is an IgG1, an IgG 2 , an IgG 3 , or an IgG 4 .
  • any of embodiments 1B to 39B wherein the culture process is a batch process, a fed batch process, a repeated fed batch process, a perfusion process, a continuous process, or a combination thereof.
  • cystine levels are maintained in the culture or fermentation by directly adding at least one of a cystine solution, a nutrient feed, a nutrient solution, a solution containing monomeric cysteine, or a solution containing cystine.
  • a method for improving stability of a purified disulfide bond-containing protein of interest comprising using a manufacturing process that maintains the disulfide bond-containing protein of interest in a form with minimal free thiols, thereby mitigating reduction or reduction potential of the disulfide bond-containing protein of interest during the manufacturing process.
  • the hold phase comprises storing harvested cell culture fluid (HCCF) for a period of up to one day, at least four days, at least one week, at least 10 days, at least two weeks, at least one month, or at least three months following the harvest phase and prior to the purification phase.
  • HCCF harvested cell culture fluid
  • disulfide bond-containing protein of interest is an antibody or antigen-binding fragment thereof.
  • mitigating disulfide bond reduction comprises maintaining an effective amount of cystine, Cu ++ , or cystine and Cu ++ in the HCCF during the hold phase or any portion thereof.
  • minimizing free thiols in the disulfide bond-containing protein of interest further comprises mitigating disulfide bond reduction in the harvest cell culture fluid (HCCF) during the production phase or any portion thereof, during the pre-harvesting phase or any portion thereof, during harvesting phase or any portion thereof, or any combination thereof.
  • HCCF harvest cell culture fluid
  • any one of embodiment 15C or 16C, wherein the effective amount of cystine comprises at least about 2.0 mM, at least about 2.5 mM, at least about 3.0 mM, at least about 3.5 mM, or at least about 4.0 mM.
  • any one of embodiments 15C to 18C, wherein the effective amount of Cu ++ comprises at least about 2.0 ppm, at least about 3.0 ppm, at least about 4.0 ppm, at least about 4.5 ppm, at least about 5.0 ppm, or at least about 5.5 ppm.
  • the method any one of embodiments 15C to 19C, wherein the effective amount of cystine, Cu ++, or cystine and Cu ++ is maintained in the CCF during the last 14 days, the last 12 days, the last 10 days, the last 8 days, the last 6 days, the last 4 days, the last 2 days, or the last day of the manufacturing process.
  • any one of embodiments 1C to 22C wherein the manufacturing process comprises maintaining the cells in CCF for at least 8 days, at least 10 days, at least 12 days, at least 14 days, or at least 16 days.
  • the supplement addition comprises adding a nutrient feed solution, wherein the nutrient feed solution comprises a sufficient amount of cystine, Cu ++, or cystine and Cu ++ to maintain the effective amount of cystine, Cu ++, or cystine and Cu ++ in the CCF.
  • the at least one additional nutrient comprises amino acids, glucose, vitamins, protein hydrolysate, or any combination thereof.
  • disulfide bond-containing protein of interest is an antibody or antigen-binding fragment thereof.
  • the antibody or fragment thereof is an IgG antibody, an IgG 2 antibody, an IgG 3 antibody, an IgG 4 antibody, or a fragment thereof.
  • disulfide bond-containing protein of interest comprises at least two disulfide bonds when properly folded.
  • Rat recombinant Thioredoxin reductase 1 (TrxR1) is commercially available (e.g., Cayman Chemical, Ann Arbor, Mich.).
  • Affinity resin 2′5′ adenine dinucleotide phosphate (ADP) Sepharose 4B can be obtained from GE Healthcare, Pittsburgh, Pa.
  • Anti-thioredoxin antibody, anti-glutathione reductase antibody, anti-glutaredoxin antibody, human recombinant thioredoxin (Trx1) and human recombinant glutathione reductase (GR) are available from Abcam, Cambridge, Mass.
  • Anti-thioredoxin reductase antibody is available from Santa Cruz Biotechnology, Dallas, Tex. Reagents are used as received and without further purification.
  • the 3 L autoclaveable bioreactor vessels (Applikon Biotechnology; Delft, The Netherlands) were connected with all peripheral equipment including probes, feed bottles, and other equipment with all ports sealed to form a closed, but vented system.
  • the vessels were autoclaved for greater than 30 minutes at greater than 121° C.
  • SCADA Supervisory Control and Data Acquisition
  • the dissolved oxygen probes were calibrated to 94% air saturation and the pH was adjusted to the offline measurement using a blood gas analyzer (BGA).
  • BGA blood gas analyzer
  • Applikon or Braun 50 L (steam-in-place) bioreactors were used for the larger scale runs.
  • the 50 L bioreactors used a programmable logic controller (PLC) and human machine interface (HMI) from Allen Bradley for process control.
  • PLC programmable logic controller
  • HMI human machine interface
  • a 1 mL vial of the Development Working Cell Bank (DWCB) of investigational IgG 2 monoclonal antibody-A (mAb-A) was thawed from liquid nitrogen storage into 30 mL of the inoculum expansion medium in a 250 mL Nalgene vented-cap shake flask.
  • the shake flasks were placed in a 37° C., 6% CO 2 incubator on a shaker platform at an agitation rate of 120 RPM.
  • VCD viable cell density
  • the culture volume was expanded using successively larger shake flasks including 500 mL and 1 L Nalgene vented-cap shake flasks and Nalgene 2 L baffled vented-cap shake flasks to produce inoculum for the bioreactors.
  • the temperature of the cultibags was controlled at 37° C., the rocker angle was 8°, and the rock rate was 25 RPM.
  • the medium in the bioreactor was the same growth medium used for the inoculum expansion.
  • the initial working volume was 1.5 L (45 L in the 50 L bioreactors).
  • the split ratio of cells into the production bioreactor was 1:5 by volume (1 part cells and 4 parts medium) so at the time of inoculation 300 mL cells and an additional 200 mL of growth medium was charged into the 3 L vessels where temperature, pH, and DO were controlled.
  • the culture was analyzed for growth using periodic viable cell counts using a ViCell XR cell counter.
  • Offline measurements were collected periodically using a BGA Rapidpoint 400 to measure pH and pCO 2 ; using a Nova Bioprofile 400 Bioanalyzer to measure Glucose, Lactate, and Ammonia; using an Advanced Instruments Model 2020 freezing point osmometer to measure osmolality; using an Agilent 1100 HPLC with a Protein-A column to measure titer; and using an Waters Ultra Performance Liquid Chromatography (UPLC) Amino Acid Analysis System with the AccQ tag assay to measure amino acids.
  • the culture was grown in the batch phase until the viable cell density reached 2.5 ⁇ 6/mL, the criteria to begin the supplemental nutrient feed scheme.
  • the fed-batch process duration was about 14 days.
  • the first nutrient feed (NF) was administered on the first day that the production bioreactor met the VCD criteria of 2.5 ⁇ 6 viable cells/mL. After the initial nutrient feed addition, subsequent nutrient feed additions were performed every other day. A total of 5 or 6 nutrient feed additions were administered to the bioreactor, each consisting of Part A and Part B.
  • Nutrient feed Part A consisted of the majority of nutrient feed components including amino acids, vitamins, and other cell culture nutrients.
  • Nutrient Feed Part B contained a basic solution of L-cystine and an additional component. Each nutrient feed addition consisted of different amounts of nutrient feed parts A and B, as noted in Table 1, below.
  • Bioreactor samples (1 mL) were obtained daily and centrifuged at 3000-4000 RPM and the supernatant was frozen immediately at ⁇ 80° C. On the day prior to the assay, the samples were removed from ⁇ 80° C. storage, thawed, and placed in a vacuum chamber at room temperature overnight to induce reduction of the monoclonal antibody without the interference of oxygen. After the vacuum hold, the samples were analyzed for protein fragmentation under non-reducing conditions using a BioAnalyzer system (Agilent Technologies) or a LABCHIP® GXII system (PerkinElmer) to detect antibody fragments resulting from the breakage of the antibody's interchain disulfide bonds. The LabChip GX II assay reports a purity value which indicates the percent of the intact antibody (two heavy chains and two light chains) present in the sample.
  • Samples were stored frozen until analyzed. Once thawed, 400-600 ⁇ L of each sample was transferred to culture tubes and mixed in non-reducing sample buffer containing N-Ethylmaleimide (NEM). After being denatured and the free thiols being capped by NEM, the samples were analyzed using a Perkin Elmer Labchip® GXII (Perkin Elmer, Waltham, Mass.) to perform size fractionation and quantification. Using the Labchip® GXII, the protein and fragments were detected by laser-induced fluorescence and translated into gel-like images (bands) and electropherograms (peaks).
  • NEM N-Ethylmaleimide
  • the percent of antibody aggregates was determined using standard size exclusion chromatography (HP-SEC) methods.
  • HP-SEC standard size exclusion chromatography
  • An Agilent 1200 series system was used with a Tosoh Bioscience TSKgel G3000SW XL column (Tosoh Bioscience LLC, King of Prussia, Pa.) (7.8 mm ⁇ 300 mm) at 1 mL/min flow rate using a mobile phase buffer of 0.1 M sodium phosphate, 0.1 M sodium sulfate, pH 6.8.
  • the absorbance chromatography at 280 nm was used to quantify the results.
  • the amount of free thiol in harvested cell culture fluid was determined by matching predicted masses of disulfide-linked peptides to observed masses from non-reducing Lys-C peptide mapping. Briefly, the sample was denatured and diluted prior to digestion with a serine protease. Following protease digestion, half of each reaction mixture was reduced by the addition of DTT. The digests were separated by RP-HPLC using a C18 column and analyzed using a UV-detector and an on-line mass spectrometer. Disulfide-bond linked peptides are only present in non-reducing runs and will disappear under reducing conditions.
  • the free thiol assay evaluates the integrity of the disulfide connections in a protein by measuring the levels of free thiol groups on unpaired cysteine residues. Samples are incubated under native and denatured conditions with a compound (5, 5′-dithiobis-(2-nitrobenzoic acid) or DTNB) that binds to free thiol and releases a colored thiolate ion. The colored thiolate ion is detected with a UV-visible spectrophotometer. The concentration of free thiol is interpolated from a standard curve and the free thiol-to-antibody molar ratio is reported.
  • a compound (5, 5′-dithiobis-(2-nitrobenzoic acid) or DTNB) that binds to free thiol and releases a colored thiolate ion.
  • the colored thiolate ion is detected with a UV-visible spectrophotometer.
  • the concentration of free thiol is
  • Chinese Hamster Ovary (CHO) cells were cultured in 3 L glass stirred tank bioreactors under conditions representative of large scale manufacturing processes with initial volumes of 1.5 L each. Culture conditions (temperature, pH, DO, and agitation) were controlled and monitored on-line. Off-line measurements of pH, dissolved gases (pO 2 , pCO 2 ), sodium and metabolite concentrations (glucose, lactate, ammonia) were obtained with a BIOPROFILE® Analyzer (NOVA Biomedical, Waltham, Mass.) and RAPIDPOINT® 500 BGA system (Siemens, Malvern, Pa.). Cell growth was monitored with a VI-CELL® (Beckman Coulter, Indianapolis, Ind.) and titer was measured using protein-A affinity chromatography.
  • VI-CELL® Beckman Coulter, Indianapolis, Ind.
  • the CHO cell lines used in the examples were stably transfected with polycucleotides encoding immunoglobulins.
  • the culture samples were thawed on ice; followed by centrifugation of the samples to remove cell pellets (i.e., for 3 minutes at 12,000 rpm), filtered through 0.2 am filters, and the supernatant samples were stored on ice.
  • the samples were transferred to culture tubes and the tubes were vortexed to ensure the sample and inhibitor were well mixed.
  • Cell culture tubes were placed in a vacuum chamber to purge oxygen from the samples by connecting the vacuum chamber to N 2 gas and vacuum lines, vacuum was pulled from the chamber, followed by a one minute wait.
  • the vacuum line was closed and the N 2 line opened briefly, and then the vacuum step and addition of N 2 were repeated twice.
  • the vacuum chamber was then stored at room temperature overnight.
  • the vacuum chamber was then stored at room temperature overnight. Samples were analyzed using the 2100 Bioanalyzer using the standard non-reduced procedure.
  • Antibody reduction in cell culture supernatant samples was measured by detecting the presence of reduced species via capillary electrophoresis using standard procedures on a 2100 Bioanalyzer system (Agilent Technologies, Santa Clara, Calif.). Samples were diluted 1-6 fold depending on titer and analyzed under non-reducing conditions following 2100 Bioanalyzer standard protocols. Supernatant samples from 3 L bioreactors were stored frozen until all samples had been acquired and were ready for analysis. Samples were thawed on ice and analyzed immediately to evaluate the amount of reduced antibody in the reactor on each day of the run.
  • This assay allows determination of the total reductase activity in a culture sample, as well as determination of the individual contribution made by thioredoxin reductase and glutathione reductase to the total reductase activity of the sample.
  • culture samples (cells+media) from 3 L bioreactors were stored frozen until the end of the run, after which the samples were centrifuged to remove the cell pellet then the resulting supernatant was diluted 20-fold into 100 mM tris buffer, pH 7.4, containing 0.4 mM NADPH, 0.15 mM oxidized glutathione, and 3 mM DTNB with the indicated concentration of specific reductase inhibitor.
  • the total reductase activity was determined in the absence of any inhibitor.
  • the thioredoxin reductase inhibitor, ATG completely inhibits the reductase activity of the thioredoxin system.
  • the difference in activity between a sample with ATG, and a sample without any inhibitor indicates the amount of reductase activity contributed the thioredoxin system.
  • the glutathione reductase inhibitor, 2-AAPA completely inhibits the reductase activity of the glutathione system.
  • the difference in reductase activity between a sample with 2-AAPA, and a sample without any inhibitor indicates the amount of reductase activity contributed by the glutathione system.
  • ATG and 2-AAPA are provided as exemplary specific inhibitors, other specific inhibitors discussed above can be employed in this assay instead of ATG and 2-AAPA.
  • culture samples were thawed on ice.
  • Thawed samples were centrifuged to remove cell pellets (for instance, 3 minutes at 12,000 rpm), and the supernatant samples were stored on ice.
  • To the wells of a 96-well, clear bottom plate the following reagents were added: 100 mM Tris Buffer, pH 7.4 (160 ⁇ L-X-Y-Z), where X is the volume of sample, which was either 10 ⁇ L, or 0 ⁇ L for the background wells, Y is the volume of ATG, which was either 4.1 ⁇ L, or 0 ⁇ L.
  • the 4.1 ⁇ L addition yielded a final concentration of 0.5 ⁇ M ATG, Z is the volume of 2-AAPA, which was either 5.2 ⁇ L, or 0 ⁇ L.
  • the 5.2 ⁇ L addition yielded a final concentration of 100 ⁇ M 2-AAPA, 10 ⁇ L NADPH, at a final concentration of 0.2 mM, ATG and/or 2-AAPA (at the indicated concentrations, or any reductase-specific inhibitor), and 10 ⁇ L of the cell culture supernatant from step.
  • the samples were then allowed to incubate 5 minutes.
  • Activity of the reductases was calculated as follows. The change in absorbance per minute ( ⁇ 412 ) for each well was determined. Typically, the first 1-3 minutes and last 5-10 minutes were excluded due to lag time at the onset of the experiment and saturation of the detector/exhaustion of the reagents in the well towards the end of the assay. Next, the background was subtracted from each cell culture sample well ( ⁇ 412, sample ⁇ 412, background ) to obtain the corrected value of ⁇ 412, corrected . The activity was then calculated by the following equation:
  • Western blots were performed in various Examples noted below to detect reductase enzymes.
  • cell pellets from 3 L bioreactors were stored frozen until the end of the run after which standard methods were used to conduct the western blot as previously described (Handlogten, et al., Chem. Biol., 21:1445-1451, 2014).
  • the primary antibodies were used at the indicated concentrations: anti-TrxR1 at 1/333, anti-Trx1 at 1/1000, anti-Grx at 1/333, and anti-GR at 1/2000.
  • Reductases were purified from cell samples to verify the specificity of reductase inhibitors.
  • a day 14 culture of mAb B IgG antibody produced by CHO cell line B CHO-K1SV was pelleted by centrifugation, washed once with PBS and re-suspended in 50 mM tris buffer, pH 7.5. The solution was homogenized and filtered at 0.2 ⁇ m prior to loading onto a column of 2′5′-ADP Sepharose 4B resin.
  • the reductases were eluted using a linearly increasing gradient of 0 to 0.3 mM NADP + in the same tris buffer (Yadav, et al., Parasitol. Int., 62:193-198, 2013).
  • the reductase activity of the collected fractions was determined using the assay described in Example 3. Additionally, western blot analysis was used to detect TrxR1 and GR in the collected fractions.
  • Protein A resin MobSelectSuRe, GE Healthcare
  • HCCF harvested cell culture fluid
  • Intermediate and final polishing chromatography steps include anion exchange (Super Q 650-M, Tosoh Bioscience) and cation exchange (POROS 50HS resin, Thermo Fisher Scientific) chromatography, respectively.
  • the product was subsequently formulated into drug substance using ultrafiltration/diafiltration.
  • mAb A is an IgG1 molecule
  • mAb B is an IgG2 molecule
  • mAb C is an IgG4, molecule. All three processes have similar cell growth, cell viability, and titer production. Additionally, all three expression systems produced reductase activity during the manufacturing processes.
  • the amount of reduced antibody in each cell culture supernatant was determined starting on day 6 of the culture.
  • the degree of reduction of mAb molecules was determined by capillary electrophoresis following the procedure described above. As shown in FIG. 2A , in all three expression systems, the percent of intact antibody decreased with time starting at day 8, with cell line B yielding the highest degree of antibody reduction, and cell line C yielding the highest amount of intact antibody at day 14.
  • TrxR1, Trx1, G R, and Grx Western blot analysis was conducted on cell pellets from days 6 and 10 of the individual cell cultures to detect the expression of the enzymes of the glutathione and thioredoxin systems. All three cell lines express TrxR1, Trx1, G R, and Grx, the molecules needed for active thioredoxin and glutathione systems. Previous work demonstrated that glutathione was present in CHO cells at concentrations exceeding 10 mM (Lin, et al., 1992 , Ann. N. Y. Acad. Sci., 665:117-126).
  • the glutathione system was evaluated by spiking mAb B into five solutions containing: 1) no enzyme, 2) 1 mM GSSG (oxidized glutathione), 3) 0.2 ⁇ M GR (glutathione reductase), 4) 0.2 ⁇ M GR with 1 mM GSSG, and 5) 0.02 ⁇ M GR with 1 mM GSSG.
  • all samples were prepared in tris buffer, pH 7.4, containing 0.4 mM NADPH, and were stored at room temperature overnight. The results indicated a minimal mAb B reduction in the solutions containing GSSG alone. This is the result of an impurity in the GSSG.
  • the mAb A was reduced in the solutions containing both GR and GSSG. These results are consistent with a mechanism involving reduction of GSSG by GR to produce GSH (reduced glutathione), which subsequently reduces the disulfide bonds of mAb B.
  • TrxR1 is the primary enzyme that reduces Trx1 and is therefore the central component of the thioredoxin system and a target for inhibition.
  • GR is the analogous central component of the glutathione system. Consequently inhibition of the activity of TrxR1 causes inhibition of the entire thioredoxin system, and inhibition of the activity of GR causes inhibition of the entire glutathione system.
  • TrxR1 and GR There are several commercially-available inhibitors of TrxR1 and GR, and the specificities of these inhibitors can be empirically ascertained to allow for the quantification of the reductase activity from each enzymatic system.
  • Several inhibitors were screened, and ATG was selected as the inhibitor of TrxR1, and 2-AAPA was initially selected as the inhibitor of GR.
  • ATG and 2-AAPA were evaluated using purified recombinant reductases from human and rat. Solutions of the purified recombinant enzymes were prepared such that the reductase activity of the solutions was similar to the activity observed in the culture samples shown in FIG. 2B . Solutions containing recombinant TrxR1/Trx1, GR/GSSG, or both enzymatic systems were prepared with increasing concentrations of ATG ranging from 0.05 ⁇ M to 5 ⁇ M. All samples were prepared in Tris buffer, pH 7.4 containing 0.4 mM NADPH. Reductase activity was determined by monitoring the reduction of DTNB as explained above. As seen in FIG.
  • the reductase activity of the solutions containing TrxR1/Trx1 decreased with increasing concentrations of ATG.
  • the TrxR1/Trx1 reductase activity was negligible.
  • the reductase activity of the solutions containing GR/GSSG were unaffected by ATG concentrations lower than 5 ⁇ M.
  • the reductase activity of solutions containing both the thioredoxin and glutathione systems was approximately equal to the combined activity of the samples containing TrxR1/Trx1 and the samples containing GR/GSSG at all concentrations of ATG. This result supports the conclusion that one enzymatic system can be selectively inhibited without affecting the activity of the other enzymatic system.
  • 2-AAPA had a minimal effect on the reductase activity of TrxR1/Trx1 solutions while completely inhibiting GR/GSSG activity at 100 ⁇ M and higher concentrations. Similar to the previous results, the activity of the solutions containing both enzymatic systems was approximately equal to the addition of the activity from the TrxR1/Trx1 and GR/GSSG solutions, providing further evidence that one enzymatic system can be selectively inhibited without affecting the reductase activity of the other reductase system.
  • 2-AAPA was a specific inhibitor of the glutathione system activity at concentrations from 50 to 200 M and ATG was a specific inhibitor of thioredoxin system activity at concentrations from 0.5 to 1 ⁇ M. Furthermore, the difference in the reductase activity without an inhibitor and with either ATG or 2-AAPA was the activity from the thioredoxin and glutathione systems, respectively.
  • a second method was developed to determine the impact of each reductase system on antibody reduction.
  • the principle of the reduction assay is similar to the reductase activity assay described above.
  • the percent of protein reduction without an inhibitor was compared to the percent of protein reduction in the presence of specific inhibitors for GR or TrxR1.
  • purified mAb B was spiked into solutions containing recombinant mammalian TrxR1/Trx1 or recombinant mammalian GR/GSSG and stored in an oxygen-free environment overnight.
  • the percent of reduced mAb B antibody was evaluated using capillary electrophoresis, as set forth above.
  • the TrxR1 inhibitor, ATG was evaluated at concentrations ranging from 0 to 1 mM. As seen in FIG. 4A , at 0.1 mM, ATG specifically inhibited reduction from the thioredoxin system as indicated by the complete inhibition of antibody reduction in the sample containing TrxR1/Trx1 (black bars) and the complete reduction of the antibody in the sample containing GR/GSSG (gray bars). At higher concentrations, ATG was no longer specific for the thioredoxin system, as indicated by the increasing amount of intact antibody in the GR/GSSG samples treated with 0.5 mM and 1 mM ATG. Consequently, to evaluate the amount of reduced antibody caused by the thioredoxin system, ATG was included in the cell culture samples at 0.1 mM, a concentration in which it specifically prevents reduction caused by TrxR1/Trx1.
  • the GR inhibitor, 2-AAPA functions by forming a covalent bond to the cysteine residues in the active site of GR.
  • 2-AAPA was initially evaluated using the same method described for ATG, above, but 2-AAPA directly caused antibody reduction making it unsuitable for this assay. Consequently, the GR inhibitor copper (II) sulfate (CuSO 4 ), was used instead (Rafter, G. W., 1982 , Biochem. Med., 27:381-391).
  • a concentration of Cu 2+ ranging from 0 to 100 ⁇ M was investigated. The results shown in FIG. 4B indicate that Cu 2+ concentrations from 3-100 ⁇ M prevented antibody reduction in the samples containing GR/GSSG (gray bars).
  • the reductase-specific inhibitors were evaluated above using purified recombinant mammalian enzymes from rat and human. To ensure that the reductase enzymes produced by cell cultures are similarly affected by the same inhibitor concentrations, GR and TrxR1 enzymes were purified from a day 14 culture of cell line B using a 2′5′-ADP affinity column. This column retains enzymes that use NADPH as a cofactor. The reductases were eluted with a linearly increasing gradient of NADP + . Western blot analysis revealed that GR and TrxR1 co-eluted in column fractions B1-C2. As shown in FIG.
  • Purified mAb B was spiked into several solutions containing different combinations of the pooled fractions (PF), recombinant Trx1, GSSG, NADPH, ATG, and Cu 2+ . The solutions were incubated at room temperature overnight and the amount of intact antibody remaining was determined by capillary electrophoresis according to the protocol described above. In the first set of samples, purified mAb B was spiked into the pooled fractions with, and without, NADPH. As seen in FIG. 5B , neither of these samples exhibited antibody reduction activity, demonstrating that GR and TrxR1 alone cannot reduce antibodies, even in the presence of NADPH.
  • purified mAb B was spiked into solutions containing the pooled enzymes, NADPH, GSSG, and either no inhibitor, 3 ⁇ M Cu 2+ , or 100 ⁇ M ATG.
  • the solution containing the pooled enzymes, NADPH, and GSSG exhibited measurable antibody reduction.
  • This solution contained GR, GSSG, and NADPH, which are needed for the glutathione system.
  • Cu 2+ completely inhibited all antibody reduction, while ATG did not inhibit antibody reduction, indicating that 3 ⁇ M Cu 2+ is sufficient to completely prevent antibody reduction by the glutathione system, while 100 ⁇ M ATG has no effect on antibody reduction by GR isolated from CHO cell culture.
  • the third set of solutions contained the pooled enzymes, NADPH, Trx1, and either no inhibitor, 3 ⁇ M Cu 2+ , or 100 ⁇ M ATG.
  • the solution containing the pooled enzymes, NADPH, and Trx1 exhibited complete antibody reduction, while Cu 2+ marginally prevented antibody reduction, and ATG completely prevented reduction. This result again confirms the specificity of ATG for TrxR1.
  • mAb B was spiked into a solution containing NADPH, Trx1, and GSSG.
  • FIG. 5B in this sample, no antibody reduction was detected, demonstrating that the GR or TrxR1 purified from CHO cell cultures were needed for antibody reduction.
  • the reductase activities of the thioredoxin and glutathione systems were evaluated in day 14 culture samples of the same CHO cell lines A, B, C, and D, using the previously evaluated specific inhibitors 2-AAPA and ATG at 100 ⁇ M and 0.5 ⁇ M respectively. Data in FIG. 6A were normalized to viable cell density. Cell lines A, B, and C were described in Example 6, above. Cell line D is the cell line CHO CAT-S, and is stably transfected to produce an IgG1 mAb (mAb D).
  • the reductase activity with either ATG or 2-AAPA was compared to the activity without an inhibitor to determine the amount of activity from the thioredoxin and glutathione systems and the data is shown in FIG. 6B .
  • the TrxR1-specific inhibitor, ATG it was determined that 35%, 60%, 87%, and 60%, respectively, of the total reductase activity in cell lines A, B, C, and D, was from the thioredoxin system.
  • the results with the GR-specific inhibitor, 2-AAPA demonstrated that 70%, 45%, 5%, and 45%, of the total reductase activity was caused by the glutathione system in cell lines A, B, C, and D, respectively.
  • the data show that the contribution of reductase activity from each reductase system varied from cell line to cell line.
  • the effect of the thioredoxin and glutathione systems on antibody reduction was determined using day 14 culture samples (cells+media) from cell lines A, B, C, and D as described in Example 2. Samples were prepared with and without inhibitors and were incubated overnight in an oxygen free environment and the percent of reduced antibody was determined using capillary electrophoresis and the results shown in FIG. 7 . In the absence of a reductase inhibitor all four mAbs from the four cell lines were reduced. In the presence of 100 ⁇ M ATG, mAb A was completely reduced, while about 67.5%, about 87%, and about 35% of mAb B, mAb C, and mAb D remained intact, respectively.
  • TrxR1 inhibitor failed to prevent mAb A reduction yet the GR inhibitor prevented mAb A reduction. Similarly, the combination of both inhibitors prevented reduction. These results indicate that mAb A reduction was primarily caused by the glutathione system, with very little involvement of the thioredoxin system. The TrxR1 and GR inhibitors each partially prevented mAb B reduction, while the combination of both inhibitors completely prevented reduction. These results demonstrated the involvement of both enzyme systems in mAb B reduction.
  • mAb D experienced substantial reduction (about 35% intact), and in the presence of the GR inhibitor mAb D also experienced substantial reduction (about 20% intact). However, when both inhibitors were included the percent of intact mAb D raised to about 80% demonstrating the involvement of both enzyme systems in mAb D reduction.
  • mAb C In the presence of the TrxR1 inhibitor, mAb C experienced minor reduction (about 87% intact), and in the presence of the GR inhibitor mAb C experienced significant reduction (about 46% intact). As determined above, Cu 2+ partially inhibited the thioredoxin system. Combined these results demonstrated mAb C is primarily reduced by the thioredoxin system.
  • the concentrations of all amino acids were determined by UPLC amino acid analysis according to manufacturer's specifications in bioreactor samples taken throughout runs BR-A through BR-D. These results showed that the reduced concentration of cysteine/cystine correlated with increased reduction potential.
  • a comparison of the results in FIG. 8 with the fragmentation results shown in Table 2 indicates that the reduction potential correlated with the level of cystine in the cell culture medium. As the cystine was depleted or nearly depleted by days 11 to 13, an increase in reduction potential was observed. On Day 14, the cystine levels were elevated due to nutrient feed (NF) additions that occurred on Day 13, and a diminished reduction potential was observed.
  • NF nutrient feed
  • the cell culture redox potential was used to monitor the likelihood of antibody interchain disulfide bond reduction occurring in a bioreactor.
  • the cell culture redox potential was measured online via a redox probe (Metler Toledo). An increase in the cell culture redox potential indicates a more oxidizing environment while a lower cell culture redox potential indicates a more reducing environment. Processes where the culture redox potential was maintained above ⁇ 55 mV or above ⁇ 70 mV had minimal amounts of reduced antibody for mAb A and mAb B, respectively. Processes where the cell culture redox potential was below ⁇ 55 mV or below ⁇ 70 mV had variable and high levels of reduced mAb A and mAb B respectively ( FIG. 9A and FIG. 9B ).
  • This analysis included data from >20 different process at the 3 L scale where reduction was either not controlled or controlled through the addition of different concentrations of Zn2+, Mn2+, Fe3+, Cu2+, Se2+, cystine, dissolved oxygen, beta mercaptoethanol, and glutathione.
  • the results demonstrated that, irrespective of the reduction mitigation strategy used, as long as the cell culture redox potential was maintained above a threshold value of ⁇ 55 mV for mAb A or ⁇ 70 mV for mAb B, the amount of reduced antibody was minimized.
  • the threshold value required to prevent reduction can be further calibrated if needed based on the characteristics of the therapeutic protein, cell line, basal medium, or redox probe calibration.
  • the methods disclosed can be used to evaluate the effectiveness of the reduction mitigation strategy via the online redox measurement. With maintenance of the redox potential above the identified threshold value, a reduction mitigation strategy is achieved. Additionally, the redox probe can be combined with a control system that automatically adjusts the reduction mitigation strategy to maintain the cell culture redox potential above the threshold where reduction is unlikely to occur.
  • the control system can be used to increase the concentration of Zn2+, Mn2+, Fe3+, Cu2+, Se2+, cystine, dissolved oxygen, beta mercaptoethanol, or glutathione in response to a decrease in the cell cutlure redox potential.
  • Using a control system based on the cell culture redox potential prevents the unnecessary over-addition of the chemical mitigator (or increase in DO set point). This is advantageous as the chemical required to prevent reduction must be cleared by the downstream purification process and elevated DO can reduce the final process titer.
  • the vacuum assay results are summarized in Table 4, below.
  • the purity of the intact MAb decreased significantly in the bioreactors receiving the control amount of NF Part B.
  • conditions with increased amounts of NF Part B showed no antibody reduction or decrease in the purity of the intact antibody in samples from Day 12 or Day 14 after vacuum treatment, as measured by the non-reduced GX assay.
  • NF Part B 3 L (BR-G and BR-H) and 50 L (BR-I) bioreactors with mAb-B were operated using a fed-batch (2-part feed) process.
  • the bioreactors were operated under similar conditions as the control process but with an overall increase in NF Part B, as shown in Table 5, below.
  • the amount of each nutrient feed addition of NF Part B was increased to 150% of the control, except NF5 which was increased to 225% of the control amount.
  • the amount of NF Part A at NF5 was also increased to 150% of the control process amount. While the number of nutrient feed additions was reduced from 6 to 5, the total amount of NF Part B in the process was increased by 38%. This amounted to about a 2 mM increase in L-cystine.
  • mAb-A 3 L scale bioreactors
  • the manufacturing process for mAb-A differed from that of mAb-B in terms of basal medium formulation, criteria for inoculation and feeds, feed amounts, and bioreactor set points such as temperature and pH.
  • This process comprises six nutrient feeds relative to the five nutrient feeds used in the mAb-B process.
  • the process also started with a lower initial working volume (1.2 L) relative to the mAb-B process (1.5 L).
  • the process comprised a fed-batch animal-protein-free cell culture of approximately 14 days. Similar to mAb-B expression, mAb-A was secreted into the cell culture medium.
  • the nutrient feed protocol for the mAb-A cell culture process was modified relative to the mAb-B process described in the feeding scheme, in that it included increasing the amounts of NF Part B in each of the six nutrient feeds (NF1-6) to 200% of the control volume as indicated on Table 7, an increase of 0.60 mM per NF addition over the control.
  • Cell culture samples were retained and frozen on days 5, 8, 10, 12, and 14 of the bioreactor process.
  • mAb-C monoclonal antibody-C
  • basal medium formulation which contained different amounts of cell culture medium components and feeds, feed amounts, and bioreactor set points such as temperature and pH.
  • This process comprises six nutrient feeds relative to the five nutrient feeds used in the mAb-B process. Similar to the mAb-A process described in Example 1, the process comprised a fed-batch animal-protein-free cell culture of approximately 14 days.
  • mAb-C was secreted into the cell culture medium.
  • the mAb-C process comprised modifications to the nutrient feed protocol which included adding additional NF Part B with each of the nutrient feeds (NF1-6). As indicated in Table 8, below, the additional NF Part B increased the levels of cystine compared to the control bioreactor. Cell culture samples were retained and frozen on days 1, 4, 5, 6, 8, 10, 12, and 14 of the bioreactor process.
  • the samples were later thawed and analyzed for reduction potential using the Vacuum/BioA assay.
  • Cells were lysed using a freeze-thaw cycle by freezing 1 ml of culture in an Eppendorf tube in a ⁇ 80° C. freezer, and after at least 12 hours the culture sample was thawed in a 37° C. water bath.
  • an ⁇ KTA purifier was used to control the flow rate of the culture sample at 22.2 mL/min through a 0.007′′ ID ⁇ 10 cm stainless steel capillary tube connected to the system outlet.
  • the lysed cell samples were centrifuged at between 2100 and 10000 ⁇ g for 5-10 minutes to remove the cells and cell debris, and the supernatant was analyzed for reduction potential.
  • This assay used a BioA analyzer (Agilent Technologies) instead of the GX analyzer used in the earlier Examples. Images of intact antibodies and antibody fragments of BR-K BioA/vacuum reduction assay for mAb-C bioreactor samples with and without additional nutrient feed including cystine were obtained. These images showed that the purity of samples which were lysed showed a lower fraction of completely reduced Mab for the condition with increased NF Part B compared to the control condition.
  • Samples were stored frozen until analyzed. Once thawed, 400-600 ⁇ L of each sample was transferred to culture tubes and mixed in non-reducing sample buffer containing N-Ethylmaleimide (NEM). After being denatured and the free thiols being capped by NEM, the samples were analyzed using a Perkin Elmer Labchip® GXII (Perkin Elmer, Waltham, Mass.) to perform size fractionation and quantification. Using the Labchip® GXII, the protein and fragments were detected by laser-induced fluorescence and translated into gel-like images (bands) and electropherograms (peaks).
  • NEM N-Ethylmaleimide
  • the percent of antibody aggregates was determined using standard size exclusion chromatography (HP-SEC) methods.
  • HP-SEC standard size exclusion chromatography
  • An Agilent 1200 series system was used with a Tosoh Bioscience TSKgel G3000SW XL column (Tosoh Bioscience LLC, King of Prussia, Pa.) (7.8 mm ⁇ 300 mm) at 1 mL/min flow rate using a mobile phase buffer of 0.1 M sodium phosphate, 0.1 M sodium sulfate, pH 6.8.
  • the absorbance chromatography at 280 nm was used to quantify the results.
  • the amount of free thiol in harvested cell culture fluid was determined by matching predicted masses of disulfide-linked peptides to observed masses from non-reducing Lys-C peptide mapping. Briefly, the sample was denatured and diluted prior to digestion with a serine protease. Following protease digestion, half of each reaction mixture was reduced by the addition of DTT. The digests were separated by RP-HPLC using a C18 column and analyzed using a UV-detector and an on-line mass spectrometer. Disulfide-bond linked peptides are only present in non-reducing runs and will disappear under reducing conditions.
  • the free thiol assay evaluates the integrity of the disulfide connections in a protein by measuring the levels of free thiol groups on unpaired cysteine residues. Samples are incubated under native and denatured conditions with a compound (5, 5′-dithiobis-(2-nitrobenzoic acid) or DTNB) that binds to free thiol and releases a colored thiolate ion. The colored thiolate ion is detected with a UV-visible spectrophotometer. The concentration of free thiol is interpolated from a standard curve and the free thiol-to-antibody molar ratio is reported.
  • a compound (5, 5′-dithiobis-(2-nitrobenzoic acid) or DTNB) that binds to free thiol and releases a colored thiolate ion.
  • the colored thiolate ion is detected with a UV-visible spectrophotometer.
  • the concentration of free thiol is
  • a small-scale (3 L) bioreactor fed-batch study was conducted with mAb E (IgG 1 monoclonal antibody) and the conditioned medium was collected on day 14.
  • mAb E IgG 1 monoclonal antibody
  • a portion of the harvested material was subjected to shear stress using a capillary tube described in Example 15, to mimic the effects of a large scale harvest using continuous centrifuge. After dividing up the sheared material into 40 ml aliquots, the aliquots were spiked with either EDTA, CuSO4-5H20, Cystine, a combination of CuSO4-5H20 and Cystine, or left unspiked.
  • the un-sheared material and the sheared aliquots were centrifuged in 50 ml centrifuge tubes and the supernatant was decanted from each condition.
  • the supernatant from each of these conditions was then either frozen immediately at ⁇ 80C or stored at 2-8° C. for 8 days followed by freezing at ⁇ 80° C.
  • the frozen samples were later tested for reduction potential by holding the samples under vacuum for 12 hours and tested in a non-reduced GXII assay to measure reduced species of light and heavy chain fragments.
  • the samples were also tested for the level of aggregation of the mAb using high performance size exclusion chromatography (HPSEC).
  • L-cystine has been reported to be a potential competitive inhibitor of a reducing enzyme or act as a surrogate substrate for the enzyme in place of the mAb product (Trexler-Schmidt, M., et al., cited above).
  • the level of L-cystine in the harvested HCCF was adjusted to 0 mM, 2 mM, and 4 mM through the spiking of L-cystine and cell lysate into the HCCF immediately after harvest.
  • aliquots of the HCCF were sealed in drug substance storage bags without headspace and held for 2 weeks at 2° C.-8° C. before being analyzed.
  • the HCCF containing 2 mM cystine was purified after a four day hold at 2° C.-8° C. in a vessel with headspace.
  • Table 10 shows that during the purification of the HCCF containing 2 mM cystine, increased aggregate levels were observed after the low pH viral inactivation step, which were ultimately cleared during the final polishing step.
  • FIG. 14A The ratio of free thiol to IgG concentration with time when the HCCF is incubated at pH 3.2, pH 3.4, and pH 3.6 is shown in FIG. 14A .
  • FIG. 14B The change in aggregate with time when HCCF is incubated at pH 3.2, pH 3.4, and pH 3.6 is shown in FIG. 14B .
  • HCCF cell culture harvest
  • the formulated bulk from the four products purified above were held at 5° C., 25° C., and 40° C. for up to one month and aggregate levels were measured weekly using HP-SEC.
  • FIG. 17A to FIG. 17C the material generated from HCCF that had been held for two weeks in the presence of 4 mM cystine showed similar starting and final purity levels as bulk material generated from HCCF that had been purified immediately.
  • the bulk material generated from the HCCF that had been held for two weeks in the absence of cystine had higher starting and final aggregate levels despite going through the same purification and formulation process.
  • the rate of aggregate formation was also significantly higher when compared to the other samples.
  • IgG2 molecules have been reported to be more susceptible to aggregate formation with increased free thiol levels as compared to other monoclonal antibody formats, it is not enough to merely provide an oxidative environment to allow the reduced species to be re-oxidized, rather, reduction has to be prevented from happening in the first place to prevent an increase in free thiol levels which is the pre-cursor to increased aggregate formation.
  • mAb F was purified by protein A chromatography after cell culture (Table 11, BRX-L-1) and harvest and subsequently subjected to a low pH hold at pH 3.6 before being neutralized to pH7.4. After low pH treatment, aggregate levels increased by 0.1% (from 4.8% to 4.9%). When purification was performed after a second cell culture run (BRX-L-2), aggregate levels increased by 8.7% (2.4% to 11.1%) after low pH treatment.
  • NR-GX analysis of Protein A product generated from both runs showed lower levels of intact mAb for Brx-L-2 (38.5%) as compared to BRX-L-1 (98.4%).
  • the electropherograms FIG. 18A & FIG.
  • Example 20 Aggregation and Reduction Potential of IgG1 mAb
  • the cell culture entailed growing and expanding GS-CHO based CAT-S suspension cells in animal protein free medium at 37° C. with regular passaging every 3 or 4 days.
  • the production was carried out in fed-batch mode in bioreactors with controlled temperature, pH and dissolved oxygen levels.
  • nutrient and glucose supplementation feeds were added to cell culture.
  • Viable cell counts and cell viability were measured by the trypan blue exclusion method using ViCell XR cell counter (Beckman Coulter, Calif.).
  • a blood-gas analyzer (RAPIDPOINT 400; Siemens Medical Solutions Diagnostics; Tarrytown, N.Y.) was used to measure pH and dissolved oxygen and to calibrate the bioreactor probes as needed.
  • a biochemical analyzer was used to measure glucose levels in cell culture samples (BioProfile 400; Nova Biomedical; Waltham, Mass.). The productivity in cell culture was measured using analytical Protein A HPLC. At the end of fed-batch process, cell culture was harvested using depth filtration. The cell free harvest material was then purified and formulated to produce the final drug substance.
  • Reduction potential i.e. the potential of the molecule to be reduced under anaerobic condition
  • Reduction potential was measured by subjecting samples to vacuum analysis as described above followed addition of non-reducing sample buffer. This mixture was then analyzed using a Perkin Elmer Labchip® GXII (Perkin Elmer, Waltham, Mass.) to perform size fractionation and quantification.
  • GXII Perkin Elmer Labchip® GXII
  • protein and fragments were detected by laser-induced fluorescence and translated into gel-like images (bands) and electropherograms (peaks).
  • a formulated drug substance of an IgG1 monoclonal antibody was produced using a typical 14 day mammalian fed-batch cell culture that was harvested, purified and formulated. Aggregate levels in the formulated drug substance was measured weekly by HP-SEC for the first month and then again at 3 months and 9 months. Optimized liquid formulations, such as the one used here, should typically show no change in aggregate levels after 1 month of storage at 2-8° C. However, as seen in FIG. 19 , the formulated drug substance in this case showed a very high aggregate increase in the first month (0.35% by HP-SEC) at the intended storage temperatures (2-8° C.). Although the rate of aggregation slowed down after the first month, this degree of aggregation is unacceptable for a liquid drug product and would increase substantially for higher protein concentration (100-150 mg/ml) which is often required.
  • Electropherograms from non-reduced (NR) GXII analysis of end of fed-batch cell culture samples exposed to reduction potential analysis are shown in FIG. 21 . Electropherograms from the end of run cell culture samples are from standard 14 day fed-batch process and are shown in FIG. 21A ; those from a shorter 8 day fed-batch process are shown in FIG.
  • FIG. 21B and those from a standard duration fed-batch process with feeds enhanced with copper and cystine are shown in FIG. 21C .
  • FIG. 21C These figures show that only about 5% intact product (IgG) remains in drug substance from standard 14 day fed-batch process. This number significantly increases (>70%) if the end of run cell culture sample is from an earlier (day 8) harvest. The same effect was also achieved when the feeds during the fed-batch process were enriched in copper and cysteine while keeping the original length (14 days) of fed-batch process.
  • IgG intact product

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