SG11201809830WA - Selective reduction of cysteine-engineered antibodies - Google Patents

Selective reduction of cysteine-engineered antibodies

Info

Publication number
SG11201809830WA
SG11201809830WA SG11201809830WA SG11201809830WA SG11201809830WA SG 11201809830W A SG11201809830W A SG 11201809830WA SG 11201809830W A SG11201809830W A SG 11201809830WA SG 11201809830W A SG11201809830W A SG 11201809830WA SG 11201809830W A SG11201809830W A SG 11201809830WA
Authority
SG
Singapore
Prior art keywords
international
cysteine
microweg
nijmegen
pct
Prior art date
Application number
SG11201809830WA
Inventor
Rudy Gerardus Elisabeth Coumans
Henri Johannes Spijker
Original Assignee
Synthon Biopharmaceuticals Bv
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Synthon Biopharmaceuticals Bv filed Critical Synthon Biopharmaceuticals Bv
Publication of SG11201809830WA publication Critical patent/SG11201809830WA/en

Links

Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6851Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell
    • A61K47/6869Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell the tumour determinant being from a cell of the reproductive system: ovaria, uterus, testes, prostate
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6801Drug-antibody or immunoglobulin conjugates defined by the pharmacologically or therapeutically active agent
    • A61K47/6803Drugs conjugated to an antibody or immunoglobulin, e.g. cisplatin-antibody conjugates
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6801Drug-antibody or immunoglobulin conjugates defined by the pharmacologically or therapeutically active agent
    • A61K47/6803Drugs conjugated to an antibody or immunoglobulin, e.g. cisplatin-antibody conjugates
    • A61K47/6807Drugs conjugated to an antibody or immunoglobulin, e.g. cisplatin-antibody conjugates the drug or compound being a sugar, nucleoside, nucleotide, nucleic acid, e.g. RNA antisense
    • A61K47/6809Antibiotics, e.g. antitumor antibiotics anthracyclins, adriamycin, doxorubicin or daunomycin
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6851Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6851Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell
    • A61K47/6855Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell the tumour determinant being from breast cancer cell
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K16/00Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/28Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants
    • C07K16/30Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants from tumour cells
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K45/00Medicinal preparations containing active ingredients not provided for in groups A61K31/00 - A61K41/00
    • A61K45/06Mixtures of active ingredients without chemical characterisation, e.g. antiphlogistics and cardiaca
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/30Immunoglobulins specific features characterized by aspects of specificity or valency
    • C07K2317/31Immunoglobulins specific features characterized by aspects of specificity or valency multispecific
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/70Immunoglobulins specific features characterized by effect upon binding to a cell or to an antigen
    • C07K2317/77Internalization into the cell

Abstract

OMeVii), P SO H (II) (I) (V) S031 - 1 (vi) W O 20 17 / 137 6 28 Al (12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (10) International Publication Number (43) International Publication Date WO 2017/137628 Al 17 August 2017 (17.08.2017) WIPO I PCT (51) International Patent Classification: A61K 47/50 (2017.01) (21) International Application Number: PCT/EP2017/053157 (22) International Filing Date: 13 February 2017 (13.02.2017) (25) Filing Language: English (26) Publication Language: English (30) Priority Data: 16155481.1 12 February 2016 (12.02.2016) EP 16206761.5 23 December 2016 (23.12.2016) EP (71) Applicant: SYNTHON BIOPHARMACEUTICALS B.V. [NL/NL]; Microweg 22, 6545CM Nijmegen (NL). (72) Inventors: COUMANS, Rudy Gerardus Elisabeth; Syn- thon Biopharmaceuticals B.V., Microweg 22, 6545 CM Nijmegen (NL). SPIJKER, Henri Johannes; Synthon Biopharmaceuticals B.V., Microweg 22, 6545 CM Nijme- gen (NL). (74) Agent: VISSCHER, Inge; P.O. BOX 7071, 6503 GN Nijmegen (NL). (81) Designated States (unless otherwise indicated, for every kind of national protection available): AE, AG, AL, AM, AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY, BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DJ, DK, DM, DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IR, IS, JP, KE, KG, KH, KN, KP, KR, KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. (84) Designated States (unless otherwise indicated, for every kind of regional protection available): ARIPO (BW, GH, GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, KM, ML, MR, NE, SN, TD, TG). Declarations under Rule 4.17: as to applicant's entitlement to apply for and be granted a patent (Rule 4.17(ii)) as to the applicant's entitlement to claim the priority of the earlier application (Rule 4.17(iii)) Published: — with international search report (Art. 21(3)) (54) Title: SELECTIVE REDUCTION OF CYSTEINE-ENGINEERED ANTIBODIES (57) : The present invention relates to a process for the selective reduction of cysteine- engineered antibodies comprising reacting an antibody comprising one or more engineered cysteines at positions selected from HC40, HC41,HC42, HC89, HC152, HC153, HC155, HC171, LC40, LC41, LC165, and LC168 with a compound according to formula (I), (II), (III), (IV), (V), (VI) or (VII): (I) (II) (III) (IV) (V) (VI) (VII), and to a process for the preparation of antibody conjugates, including antibody-drug conjug - ates (ADCs). 1111111111111101110111111111110101111101110111011111111111110111110111111111110111111
SG11201809830WA 2016-02-12 2017-02-13 Selective reduction of cysteine-engineered antibodies SG11201809830WA (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP16155481 2016-02-12
EP16206761 2016-12-23
PCT/EP2017/053157 WO2017137628A1 (en) 2016-02-12 2017-02-13 Selective reduction of cysteine-engineered antibodies

Publications (1)

Publication Number Publication Date
SG11201809830WA true SG11201809830WA (en) 2018-12-28

Family

ID=58044063

Family Applications (1)

Application Number Title Priority Date Filing Date
SG11201809830WA SG11201809830WA (en) 2016-02-12 2017-02-13 Selective reduction of cysteine-engineered antibodies

Country Status (14)

Country Link
US (1) US10814009B2 (en)
EP (1) EP3458100B1 (en)
AU (1) AU2017218615B2 (en)
CA (1) CA3026139C (en)
CY (1) CY1124630T1 (en)
DK (1) DK3458100T3 (en)
ES (1) ES2818575T3 (en)
HR (1) HRP20201183T1 (en)
HU (1) HUE050726T2 (en)
LT (1) LT3458100T (en)
PL (1) PL3458100T3 (en)
PT (1) PT3458100T (en)
SG (1) SG11201809830WA (en)
WO (1) WO2017137628A1 (en)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20200010491A (en) * 2017-05-23 2020-01-30 신톤 바이오파머슈티칼즈 비.브이. Double Conjugation Method for Preparing Antibody-Drug Conjugates
US20210346513A1 (en) * 2017-08-04 2021-11-11 Amgen Inc. Method of conjugation of cys-mabs
KR20200091431A (en) 2017-11-24 2020-07-30 비온디스 비.브이. Improved method for the synthesis of linker-drug vc-seco-DUBA
WO2019191630A1 (en) * 2018-03-29 2019-10-03 Abbvie Inc. Selective reduction of antibodies
KR20210125034A (en) 2019-02-15 2021-10-15 우시 바이올로직스 아일랜드 리미티드 Method for preparing antibody-drug conjugates with improved homogeneity
MX2022009696A (en) 2020-02-06 2022-09-07 Byondis Bv Combination containing a duocarmycin derivative-comprising antibody-drug conjugate and thiosulfate.
IL299184A (en) 2020-07-06 2023-02-01 Byondis Bv Antifolate linker-drugs and antibody-drug conjugates
EP4320152A1 (en) 2021-04-08 2024-02-14 Byondis B.V. Anti-c-met antibodies and antibody-drug conjugates
CN117794581A (en) 2021-06-28 2024-03-29 拜奥迪斯私人有限公司 Conjugates comprising phosphoantigen and their use in therapy
WO2023126297A1 (en) 2021-12-30 2023-07-06 Byondis B.V. Antifolate linker-drugs and antibody-drug conjugates
WO2023222580A1 (en) 2022-05-16 2023-11-23 Byondis B.V. Novel masked antibodies

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DK1791565T3 (en) 2004-09-23 2016-08-01 Genentech Inc Cysteingensplejsede antibodies and conjugates
ES2434032T3 (en) * 2005-06-17 2013-12-13 Novo Nordisk Health Care Ag Dimeric and multimeric FVIIA compounds
WO2011133039A2 (en) 2010-04-21 2011-10-27 Syntarga B.V. Novel conjugates of cc-1065 analogs and bifunctional linkers
CA2938450C (en) 2014-02-11 2023-10-17 Seattle Genetics, Inc. Selective reduction of proteins
PL3151865T3 (en) * 2014-05-22 2022-01-03 Byondis B.V. Site-specific conjugation of linker drugs to antibodies and resulting adcs

Also Published As

Publication number Publication date
HUE050726T2 (en) 2021-01-28
ES2818575T3 (en) 2021-04-13
CY1124630T1 (en) 2022-03-24
LT3458100T (en) 2020-08-25
EP3458100B1 (en) 2020-07-01
PT3458100T (en) 2020-08-05
CA3026139C (en) 2023-09-12
EP3458100A1 (en) 2019-03-27
PL3458100T3 (en) 2020-11-30
US10814009B2 (en) 2020-10-27
AU2017218615B2 (en) 2022-02-10
CA3026139A1 (en) 2017-08-17
WO2017137628A1 (en) 2017-08-17
AU2017218615A1 (en) 2018-12-13
US20190388552A1 (en) 2019-12-26
HRP20201183T1 (en) 2021-02-05
DK3458100T3 (en) 2020-08-03

Similar Documents

Publication Publication Date Title
SG11201809830WA (en) Selective reduction of cysteine-engineered antibodies
SG11201908813QA (en) Anti-sirp alpha antibodies
SG11201903857UA (en) Antibodies to pd-1 and uses thereof
SG11201811431VA (en) Multispecific antibodies against cd40 and cd137
SG11201807252QA (en) Anti-lag-3 antibodies
SG11201808108XA (en) Synthesis of indazoles
SG11201909011PA (en) Niraparib compositions
SG11201807827VA (en) Process for the preparation of pegylated drug-linkers and intermediates thereof
SG11201811706RA (en) Process for the preparation of microcapsules
SG11201808686VA (en) Synthesis of indazoles
SG11201805001UA (en) Method of treating influenza a
SG11202000333UA (en) Bicyclic ketone compounds and methods of use thereof
SG11201807949WA (en) Engineered immunoglobulins with altered fcrn binding
SG11201908325PA (en) Process for the preparation of glucuronide drug-linkers and intermediates thereof
SG11201803918VA (en) Production of steviol glycosides in recombinant hosts
SG11201909680UA (en) Phenyl-2-hydroxy-acetylamino-2-methyl-phenyl compounds
SG11201806393QA (en) Use of gabaa receptor modulators for treatment of itch
SG11201805149XA (en) Compositions comprising 15-hepe and methods of using the same
SG11201903076QA (en) Carbamoyl phenylalaninol compounds and uses therof
SG11201901986SA (en) Process for the manufacture of a solid pharmaceutical adminstration form
SG11201901188VA (en) Metal powder feedstocks for additive manufacturing, and system and methods for producing the same
SG11201908091QA (en) Aqueous anti-pd-l1 antibody formulation
SG11201811708QA (en) Process for the preparation of microcapsules
SG11202000494UA (en) Drug delivery composition
SG11201803692PA (en) Anti-5t4 antibodies and antibody-drug conjugates