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  • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
  • C12N9/96—Stabilising an enzyme by forming an adduct or a composition; Forming enzyme conjugates
• • A—HUMAN NECESSITIES
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  • A61K38/00—Medicinal preparations containing peptides
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  • A61K38/50—Hydrolases (3) acting on carbon-nitrogen bonds, other than peptide bonds (3.5), e.g. asparaginase
• • A—HUMAN NECESSITIES
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  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
  • A61K47/50—Medicinal 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
  • A61K47/51—Medicinal 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
  • A61K47/56—Medicinal 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 organic macromolecular compound, e.g. an oligomeric, polymeric or dendrimeric molecule
  • A61K47/59—Medicinal 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 organic macromolecular compound, e.g. an oligomeric, polymeric or dendrimeric molecule obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polyureas or polyurethanes
  • A61K47/60—Medicinal 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 organic macromolecular compound, e.g. an oligomeric, polymeric or dendrimeric molecule obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polyureas or polyurethanes the organic macromolecular compound being a polyoxyalkylene oligomer, polymer or dendrimer, e.g. PEG, PPG, PEO or polyglycerol
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  • C12Y305/03—Hydrolases acting on carbon-nitrogen bonds, other than peptide bonds (3.5) in linear amidines (3.5.3)
  • C12Y305/03006—Arginine deiminase (3.5.3.6)
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

Definitions

• the present invention is directed to arginine deiminase modified with polyethylene glycol, to methods for treating cancer, and to methods for treating and/or inhibiting metastasis.
• Malignant melanoma (stage 3) and hepatoma are fatal diseases which kill most patients within one year of diagnosis. In the United States, approximately 16,000 people die from these diseases annually. The incidence of melanoma is rapidly increasing in the United States and is even higher in other countries, such as Australia. The incidence of hepatoma, in parts of the world where hepatitis is endemic, is even greater. For example, hepatoma is one of the leading forms of cancer in Japan and Taiwan. Effective treatments for these diseases are urgently needed.
• a problem associated with the therapeutic use of such a heterologous protein is its antigenicity.
• the chemical modification of arginine deiminase from Mycoplasma arginini, via a cyanuric chloride linking group, with polyethylene glycol was described by Takaku et al., Jpn. J. Cancer Res., 84: ⁇ 195-1200 (1993).
• the modified protein was toxic when metabolized due to the release of cyanide from the cyanuric chloride linking group.
• the present invention is directed to arginine deiminase modified with polyethylene glycol.
• the arginine deiminase is modified with polyethylene glycol, having a total weight average molecular weight of about 1,000 to about 50,000, directly or through a biocompatible linking group.
• Another embodiment of the invention is directed to methods of treating cancer, including, for example, sarcomas, hepatomas and melanomas.
• the invention is also directed to methods of treating and/or inhibiting the metastasis of tumor cells.
• Figure 1 depicts the amino acid sequences of arginine deiminase cloned from Mycoplasma arginini (the top amino acid sequence identified as ADIPROT), Mycoplasma arthritides (the middle amino acid sequence identified as ARTADIPRO), and Mycoplasma hominus (the bottom amino acid sequence identified as HOMADIPRO).
• Figures 2A and 2B are graphs showing the effect of a single dose of native arginine deiminase and arginine deiminase modified with polyethylene glycol ⁇ e.g., molecular weight 5,000) on serum arginine levels and serum citrulline levels in mice.
• Figure 3 is a graph showing the effects on serum arginine levels when
• PEG 10,000 is covalently bonded to ADI via various linking groups.
• Figure 4 is a graph showing the effect that the linking group and the molecular weight of the polyethylene glycol have on citrulline production in mice injected with a single dose of PEG- ADI.
• Figures 5A and 5B are graphs showing the dose response that ADI-SS-
• Figures 5C and 5D are graphs showing the dose response that ADI-SS-PEG20,000 had on serum arginine and citrulline levels.
• Figure 6 is a graph showing the antigenicity of native ADI, ADI-SS- PEG5,000, and ADI-SS-PEG20,000.
• Figure 7 is a graph showing the effect that treatments with ADI-SS- PEG5,000, ADI-SS-PEG12,000 or ADI-SS-PEG20,000 had on tumor size in mice which were injected with SK-mel 2 human melanoma cells.
• Figure 8 is a graph showing the effect that treatments with ADI- PEG20,000 had on tumor size in mice which were injected with SK-mel 28, SK-mel 2 or M24-met human melanoma cells.
• Figure 9 is a graph showing the effect that treatments with ADI-PEG5,000, ADI-PEG12,000 or ADI-PEG20,000 had on the survival of mice which were injected with human hepatoma SK-Hepl cells.
• arginine deiminase catalyzes the conversion of arginine to citrulline, and may be used to eliminate arginine.
• arginine deiminase may be utilized as a treatment for melanomas, hepatomas and some sarcomas.
• Native arginine deiminase may be found in microorganisms and is antigenic and rapidly cleared from circulation in a patient. These problems may be overcome by covalently modifying arginine deiminase with polyethylene glycol (PEG).
• PEG polyethylene glycol
• Arginine deiminase covalently modified with polyethylene glycol (with or without a linking group) may be hereinafter referred to as "ADI-PEG.”
• ADI-PEG When compared to native arginine deiminase, ADI-PEG retains most of its enzymatic activity, is far less antigenic, has a greatly extended circulating half-life, and is much more efficacious in the treatment of tumors.
• Polyethylene glycol or “PEG” refers to mixtures of condensation polymers of ethylene oxide and water, in a branched or straight chain, represented by the general formula H(OCH 2 CH 2 ) n OH, wherein n is at least 4.
• Polyethylene glycol or “PEG” is used in combination with a numeric suffix to indicate the approximate weight average molecular weight thereof.
• PEG5,000 refers to polyethylene glycol having a total weight average molecular weight of about 5,000
• PEG 12,000 refers to polyethylene glycol having a total weight average molecular weight of about 12,000
• PEG20,000 refers to polyethylene glycol having a total weight average molecular weight of about 20,000.
• Melanoma may be a malignant or benign tumor arising from the melanocytic system of the skin and other organs, including the oral cavity, esophagus, anal canal, vagina, leptomeninges, and/or the conjunctivae or eye.
• melanoma includes, for example, acral-lentiginous melanoma, amelanotic melanoma, benign juvenile melanoma, lentigo maligna melanoma, malignant melanoma, nodular melanoma, subungual melanoma and superficial spreading melanoma.
• Hepatoma may be a malignant or benign tumor of the liver, including, for example, hepatocellular carcinoma.
• Patient refers to an animal, preferably a mammal, more preferably a human.
• Biocompatible refers to materials or compounds which are generally not injurious to biological functions and which will not result in any degree of unacceptable toxicity, including allergenic and disease states.
• PEG polyethylene glycol
• ADI arginine deiminase
• SS succinimidyl succinate
• SSA succinimidyl succinamide
• SPA succinimidyl propionate
• NHS N-hydroxy- succinimide
• the present invention is based on the unexpected discovery that ADI modified with polyethylene glycol provides excellent results in treating certain types of cancer and inhibiting the metastasis of cancer.
• ADI may be covalently bonded to polyethylene glycol with or without a linking group, although a preferred embodiment utilizes a linking group.
• the arginine deiminase gene may be derived, cloned or produced from any source, including, for example, microorganisms, recombinant biotechnology or any combination thereof.
• arginine deiminase is cloned from microorganisms of the genus Mycoplasma. More preferably, the arginine deiminase is cloned from Mycoplasma arginini, Mycoplasma hominus, Mycoplasma arthritides, or any combination thereof.
• the arginine deiminase used in the present invention may have one or more of the amino acid sequences depicted in Figure 1.
• the polyethylene glycol (PEG) has a total weight average molecular weight of about 1,000 to about 50,000; more preferably from about 3,000 to about 40,000, more preferably from about 5,000 to about 30,000; more preferably from about 8,000 to about 30,000; more preferably from about 11 ,000 to about 30,000; even more preferably from about 12,000 to about 28,000; still more preferably from about 16,000 to about 24,000; even more preferably from about 18,000 to about 22,000; even more preferably from about 19,000 to about 21,000, and most preferably about 20,000.
• polyethylene glycol with a molecular weight of 30,000 or more is difficult to dissolve, and yields of the formulated product are greatly reduced.
• the polyethylene glycol may be a branched or straight chain, preferably a straight chain. Generally, increasing the molecular weight of the polyethylene glycol decreases the immunogenicity of the ADI.
• the polyethylene glycol having a molecular weight described in this embodiment may be used in conjunction with ADI, and, optionally, a biocompatible linking group, to treat cancer, including, for example, melanomas, hepatomas and sarcomas, preferably melanomas.
• the polyethylene glycol has a total weight average molecular weight of about 1 ,000 to about 50,000; preferably about 3,000 to about 30,000; more preferably from about 3,000 to about 20,000; more preferably from about 4,000 to about 12,000; still more preferably from about 4,000 to about 10,000; even more preferably from about 4,000 to about 8,000; still more preferably from about 4,000 to about 6,000; with about 5,000 being most preferred.
• the polyethylene glycol may be a branched or straight chain, preferably a straight chain.
• the polyethylene glycol having a molecular weight described in this embodiment may be used in conjunction with ADI, and optionally, a biocompatible linking group, to treat cancer, including, for example, melanomas, hepatomas and sarcomas, preferably hepatomas.
• the linking group used to covalently attach ADI to PEG may be any biocompatible linking group. As discussed above, "biocompatible" indicates that the compound or group is non-toxic and may be utilized in vitro or in vivo without causing injury, sickness, disease or death.
• PEG can be bonded to the linking group, for example, via an ether bond, an ester bond, a thiol bond or an amide bond.
• Suitable biocompatible linking groups include, for example, an ester group, an amide group, an imide group, a carbamate group, a carboxyl group, a hydroxyl group, a carbohydrate, a maleimide group (including, for example, succinimidyl succinate (SS), succinimidyl propionate (SPA), succinimidyl carboxymethylate (SCM), succinimidyl succinamide (SSA) orN-hydroxy succinimide (NHS)), an epoxide group, an oxycarbonylimidazole group (including, for example, carbonyldimidazole (CDI)), a nitro phenyl group (including, for example, nitrophenyl carbonate (NPC) or trichlorophenyl carbonate (TPC)), a trysylate group, an aldehyde group, an isocyanate group, a vinylsulfone group, a tyrosine group, a cysteine group, a his
• the biocompatible linking group is an ester group and/or a maleimide group. More preferably, the linking group is SS, SPA, SCM, SSA or NHS; with SS, SPA or NHS being more preferred, and with SS or SPA being most preferred.
• ADI may be coupled directly to PEG (i.e., without a linking group) through an amino group, a sulfhydral group, a hydroxyl group or a carboxyl group.
• ADI may be covalently bonded to PEG, via a biocompatible linking group, using methods known in the art, as described, for example, by Park et al., Anticancer Res., 7:373-376 (1981); and Zaplipsky and Lee, Polyethylene Glycol Chemistry: Biotechnical and Biomedical Applications, J.M. Harris, ed., Plenum Press, NY, Chapter 21 (1992), the disclosures of which are hereby incorporated by reference herein in their entirety.
• PEG polyethylene glycol
• Selection of the attachment site of polyethylene glycol on the arginine deiminase is determined by the role of each of the sites within the active domain of the protein, as would be known to the skilled artisan.
• PEG may be attached to the primary amines of arginine deiminase without substantial loss of enzymatic activity. For example, ADI cloned from Mycoplasma arginini, Mycoplasma arthritides and Mycoplasma hominus has about 17 lysines that may be modified by this procedure.
• the 17 lysines are all possible points at which ADI can be attached to PEG via a biocompatible linking group, such as SS, SPA, SCM, SSA and/or NHS.
• PEG may also be attached to other sites on ADI, as would be apparent to one skilled in the art in view of the present disclosure.
• PEG molecules may be covalently bonded to ADI.
• ADI is modified with about 7 to about 15 PEG molecules, more preferably from about 9 to about 12 PEG molecules.
• about 30% to about 70% of the primary amino groups in arginine deiminase are modified with PEG, preferably about 40%) to about 60%), more preferably about 45%> to about 55%, and most preferably about 50% of the primary amino groups in arginine deiminase are modified with PEG.
• PEG is covalently bonded to the end terminus of ADI, preferably only 1 PEG molecule is utilized.
• Increasing the number of PEG units on ADI increases the circulating half life of the enzyme. However, increasing the number of PEG units on ADI decreases the specific activity of the enzyme. Thus, a balance needs to be achieved between the two, as would be apparent to one skilled in the art in view of the present disclosure.
• a common feature of the most preferred biocompatible linking groups is that they attach to a primary amine of arginine deiminase via a maleimide group.
• SS-PEG Once coupled with arginine deiminase, SS-PEG has an ester linkage next to the PEG, which may render this site sensitive to serum esterase, which may release PEG from ADI in the body.
• SPA-PEG and PEG2-NHS do not have an ester linkage, so they are not sensitive to serum esterase.
• the particular linking groups do not appear to influence the circulating half-life of PEG- ADI or its specific enzyme activity.
• PEG which is attached to the protein may be either a single chain, as with SS-PEG, SPA-PEG and SC- PEG, or a branched chain of PEG may be used, as with PEG2-NHS.
• the structural formulas of the preferred linking groups in the present invention are set forth below.
• a therapeutically effective amount of one of the compounds of the present invention is an amount that is effective to inhibit tumor growth.
• treatment is initiated with small dosages which can be increased by small increments until the optimum effect under the circumstances is achieved.
• a therapeutic dosage of compounds of the present invention may be from about 1 to about 200 mg/kg twice a week to about once every two weeks.
• the dosage may be about 1 mg/kg once a week as a 2 ml intravenous injection to about 20 mg/kg once every 3 days.
• the optimum dosage with ADI-SS-PEG5,000 may be about twice a week, while the optimum dosage with ADI-SS- PEG20,000 may be from about once a week to about once every two weeks.
• PEG-ADI may be mixed with a phosphate buffered saline solution, or any other appropriate solution known to those skilled in the art, prior to injection.
• the PEG- ADI formulation may be administered as a solid (lyophalate) or as a liquid formulation, as desired.
• the methods of the present invention can involve either in vitro or in vivo applications.
• in vitro applications including cell culture applications
• the compounds described herein can be added to the cells in cultures and then incubated.
• the compounds of the present invention may also be used to facilitate the production of monoclonal and/or polyclonal antibodies, using antibody production techniques well known in the art.
• the monoclonal and/or polyclonal antibodies can then be used in a wide variety of diagnostic applications, as would be apparent to one skilled in the art.
• the in vivo means of administration of the compounds of the present invention will vary depending upon the intended application.
• administration of the PEG- ADI composition of the present invention can be carried out, for example, orally, intranasally, intraperitoneally, parenterally, intravenously, intralymphatically, intratumorly, intramuscularly, interstitially, intra- arterially, subcutaneously, intraocularly, intrasynovial, transepithelial, and transdermally.
• Mycoplasma arginini ATCC 23243
• Mycoplasma hominus ATCC 23114
• Mycoplasma arthritides ATCC 23192
• Arginine deiminase was cloned from Mycoplasma arginini, Mycoplasma hominus and Mycoplasma arthritides and expressed in E. coli as previously described by S. Misawa et al, J. Biotechnology, 36:145-155 (1994), the disclosure of which is hereby incorporated herein by reference in its entirety.
• the amino acid sequences of arginine deiminase from each of the above species is set forth in Figure 1.
• the top amino acid sequence, identified as ADIPROT is from Mycoplasma arginini
• the middle amino acid sequence, identified as ARTADIPRO is from Mycoplasma arthritides
• the bottom amino acid sequence, identified as HOMADIPRO is from Mycoplasma hominus.
• Each of the amino acid sequences are more than 96%> conserved. Characterization, by methods known to those skilled in the art, of each of the proteins with respect to specific enzyme activity, K,,,, V max and pH optima revealed that they were biochemically indistinguishable from each other.
• the pH optima was determined using a citrate buffer (pH 5-6.5), a phosphate buffer (pH 6.5-7.5) and a borate buffer (pH 7.5-8.5).
• the K m and V max were determined by incubating the enzyme with various concentrations of arginine and quantifying citrulline production.
• the K m for the various enzymes was about 0.02 to 0.06 ⁇ M and the V max was about 15-20 ⁇ mol/min/mg, the values of which are within standard error of each other.
• arginine deiminase genes were amplified by polymerase chain reaction using the following primer pair derived from the published sequence of M. arginini, as described, for example, by T. Ohno et al, Infect. Immun., 58:3788-3795 (1990), the disclosure of which is hereby inco ⁇ orated by reference herein in its entirety:
• Recombinant ADI was expressed in inclusion bodies at levels of 10% > of total cell protein.
• the proteins from each of the above three species of Mycoplasma have approximately 95%> homology and are readily purified by column chromatography. Approximately 1.2 g of pure protein may be isolated from 1 liter of fermentation broth.
• Recombinant ADI is stable for about 2 weeks at 37 °C and for at least 8 months when stored at 4°C. As determined by methods known to those skilled in the art, the proteins had a high affinity for arginine (0.04 ⁇ M), and a physiological pH optima of about 7.2 to about 7.4.
• Example 2 Renaturation and Purification of Recombinant ADI
• ADI protein was renatured, with minor modifications, as described by Misawa et al, J. Biotechnology, 36:145-155 (1994), the disclosure of which is hereby incorporated herein by reference in its entirety.
• 100 g of cell paste was resuspended in 800 ml of 10 mM K 2 PO 4 pH 7.0, 1 mM EDTA (buffer 1) and the cells were disrupted by two passes in a Micro fluidizer (Micro fluidics Corporation, Newton, MA). Triton X-100 was added to achieve a final concentration of 4% (v/v). The homogenate was stirred for 30 min at 4°C, then centrifuged for 30 min at 13,000 g.
• the pellet was collected and resuspended in one liter of buffer 1 containing 0.5% Triton X-100.
• the solution was diafiltered against 5 volumes of denaturation buffer (50 mM Tris HC1, pH 8.5, 10 mM DTT) using hollow-fiber cartridges with 100 kD retention rating (Microgon Inc., Madison Hills, CA). Guanidine HC1 was added to achieve a final concentration of 6 M and the solution was stirred for 15 min at 4°C.
• the solution was diluted 100-fold into refolding buffer 1, 10 mm K 2 PO 4 , pH 7.0 and stirred for 48 hours at 15°C, particulates were removed by centrifugation at 15,000 x g.
• the resulting supernatant was concentrated on a Q Sepharose Past Flow (Pharmacia Inc., Piscataway, NJ) column preequilabrated in refolding buffer.
• ADI was eluted using refolding buffer containing 0.2 M NaCl.
• the purification procedure yielded ADI protein, which was >95%> pure as estimated by SDS-PAGE analysis. 8 g of pure renatured ADI protein was produced from 1 kg of cell paste which corresponds to 200 mg purified ADI per liter of fermentation.
• ADI activity was determined by micro-modification of the method described by Oginsky et al, Meth. Enzymol, (1957) 3:639-642. 10 ⁇ l samples in 0.1 m Na 2 PO 4 , pH 7.0 (BUN assay buffer) were placed in a 96 well microliter plate, 40 ⁇ l of 0.5 mM arginine in BUN assay buffer was added, and the plate was covered and incubated at 37°C for 15 minutes. 20 ⁇ l of complete BUN reagent (Sigma Diagnostics) was added and the plate was incubated for 10 minutes at 100°C. The plate was then cooled to 22 °C and analyzed at 490 nm by a microliter plate reader (Molecular Devices, Inc).
• 1.0 IU is the amount of enzyme which converts 1 ⁇ mole of L-arginine to L-citrulline per minute. Protein concentrations were determined using Pierce Coomassie Blue Protein Assay Reagent (Pierce Co., Rockford, IL) with bovine serum albumin as a standard.
• PEG was covalently bonded to ADI in a 100 mM phosphate buffer, pH 7.4. Briefly, ADI in phosphate buffer was mixed with a 100 molar excess of PEG. The reaction was stirred at room temperature for 1 hour, then the mixture was extensively dialisized to remove unincorporated PEG.
• PEG 10,000 and ADI were covalently bonded via four different linking groups: an ester group or maleimide group, including SS, SSA, SPA and SSPA, where the PEG had a total weight average molecular weight of 5,000, 10,000, 12,000, 20,000, 30,000 and 40,000; an epoxy group, PEG-epoxy, where the PEG had a total weight average molecular weight of 5,000; and a branched PEG group, PEG2-NHS, where the PEG had a total weight average molecular weight of 10,000, 20,000 and 40,000.
• an ester group or maleimide group including SS, SSA, SPA and SSPA
• PEG had a total weight average molecular weight of 5,000, 10,000, 12,000, 20,000, 30,000 and 40,000
• an epoxy group, PEG-epoxy where the PEG had a total weight average molecular weight of 5,000
• PEG2-NHS a branched PEG group
• mice 5.0 IU of the resulting compositions were injected into mice (5 mice in each group).
• the mice were bled from the retro orbital plexus (100 ul).
• an equal volume of 50%> (w/v) of trichloroacetic acid was added.
• the precipitate was removed by centrifugation (13,000 x g for 30 minutes) and the supernatant removed and stored frozen at -70°C.
• the samples were then analyzed using an automated amino acid analyzer and reagents from Beckman Instruments using protocols supplied by the manufacturer. The limits of sensitivity for citrulline by this method was approximately 2-6 uM and the reproducibility of measurements within about 8%>.
• the amount of serum arginine was determined by amino acid analysis.
• the linking group covalently bonding the PEG and ADI did not have an appreciable effect on the ability of ADI to reduce serum arginine in vivo.
• the linking group may not be critical to the results of the experiment, except that a non-toxic linking group must be used for in vivo applications.
• the limits of sensitivity for citrulline by this method was approximately 2-6 uM and the reproducibility of measurements within about 8%.
• the amount of citrulline was determined, and the area under the curve approximated and expressed as ⁇ mol days.
• the open circles indicate the amount of citrulline produced by native ADI
• the filled circles are ADI-SC-PEG
• the open squares are ADI-SS-PEG
• the open triangles are ADI-SPA-PEG
• the filled triangles are branched chain PEG-NHS- PEG 2 .
• the results in Figure 4 demonstrate that the molecular weight of the PEG determines the effectiveness of the PEG-ADI composition.
• the effectiveness of the PEG- ADI compositions is not necessarily based on the method or means of attachment of the PEG to ADI, except that a biocompatible linking group must be used for in vivo applications.
• mice (5 in each group) were given a single injection of 0.05 IU, 0.5 IU or 5.0 IU of either ADI-SS-PEG5,000 or ADI-SS-PEG20,000.
• serum was collected, as described above, and an amino acid analysis was performed to quantify serum arginine ( Figures 5A and 5C) and serum citrulline ( Figures 5B and 5D). Both formulations induced a dose dependent decrease in serum arginine and an increase in serum citrulline.
• the effects induced by ADI-SS-PEG20,000 were more pronounced and of longer duration than the effects induced by ADI-SS-PEG5,000.
• Example 4 Selectivity of ADI Mediated Cytotoxicity
• arginine deiminase mediated cytotoxicity was demonstrated using a number of human tumors. Specifically, human tumors were tested in vitro for sensitivity to ADI-SS-PEG5,000 (50 ng/ml). Viability of cultures was determined after 7 days. For a culture to be defined as "inhibited,” greater than 95% of the cells must take up Trypan blue dye. A host of normal cells were also tested, including endothelial cells, smooth muscle cells, epithelial cells and fibroblasts, and none were inhibited by ADI-SS-PEG5,000.
• ADI-SS-PEG5,000 greatly inhibited all human melanomas and hepatomas that were commercially available from the ATCC, MSKCC and Europe.
• mRNA was isolated from the tumors.
• Northern blot analyses using the human arginosuccinate synthase cDNA probe, indicated complete concordance between the sensitivity to arginine deiminase treatment and an inability to express arginosuccinate synthase. This data suggests that ADI toxicity results from an inability to induce arginosuccinate synthase. Therefore, these cells cannot synthesize arginine from citrulline, and are unable to synthesize the proteins necessary for growth.
• mice (5 in each group) were injected intravenously with a single 5.0 IU does of either native arginine deiminase or various formulations of arginine deiminase modified with polyethylene glycol, as indicated in Figures 3A and 3B.
• the mice were bled from the retro orbital plexus (100 ul).
• an equal volume of 50%> (w/v) of trichloro- acetic acid was added.
• the precipitate was removed by centrifugation (13,000 x g for 30 minutes) and the supernatant removed and stored frozen at -70°C.
• the samples were then analyzed using an automated amino acid analyzer and reagents from Beckman Instruments using protocols supplied by the manufacturer.
• the limits of sensitivity for arginine by this method was approximately 6 pM and the reproducibility of measurements within about 8%.
• Example 6 Antigenicity of PEG modified ADI To determine the antigenicity of native ADI, ADI-SS-PEG5,000, and ADI-
• SS-PEG20,000 the procedures described in, for example, Park, Anticancer Res., supra, and Kamisaki, J. Pharmacol. Exp. Ther., supra, were followed.. Briefly, Balb C mice (5 in each group) were intravenously injected weekly for 12 weeks with approximately 0.5 IU (100 ug of protein) of native ADI, ADI-SS-PEG5,000 or ADI-SS-PEG20,000. The animals were bled (0.05 ml) from the retro orbital plexus at the beginning of the experiment and at weeks 4, 8 and 12. The serum was isolated and stored at -70°C. The titers of anti-ADI IgG were determined by ELISA.
• the titer was defined as the highest dilution of the serum which resulted in a two-fold increase from background absorbance (approximately 0.50 OD).
• the results are shown in Figure 6.
• the open circles represent the data obtained from animals injected with native ADI, which was very antigenic.
• the filled circles represent the data obtained from the animals injected with ADI-SS-PEG5,000, while the open triangles represent the data obtained from the animals injected with ADI- SS-PEG20,000.
• PEG20,000 are significantly less antigenic than native ADI. For example, as few as 4 injections of native ADI resulted in a titer of about 10 6 , while 4 injections of any of the PEG-ADI formulations failed to produce any measurable antibody. However, after 8 injections, the ADI-PEG5,000 had a titer of about 10 2 , while ADI-PEG20,000 did not induce this much of an immune response until after 12 injections. The results demonstrate that attaching PEG to ADI blunts the immune response to the protein.
• Example 7 Tumor Inhibition of Human Melanomas
• mice The effect of PEG-ADI on the growth of human melanoma (SK-Mel 28) in nude mice was determined.
• Nude mice (5 in each group) were injected with 10 6 SK-mel 2 human melanoma cells which were allowed to grow until the tumors reached a diameter of about 3-5 mm.
• the mice were left untreated (open circles) or were treated once a week for 12 weeks with 5.0 IU of ADI-SS-PEG5,000 (filled triangles), ADI-SS-PEG 12,000 (open triangles) or ADI-SS-PEG20,000 (filled circles).
• the tumor size was measured weekly, and the mean diameter of the tumors is presented in Figure 7.
• Figure 8 shows the effectiveness of ADI-SS-PEG20,000 on three human melanomas (SK-mel 2, SK-mel 28, M24-met) grown in vivo in nude mice.
• Nude mice (5 in each group) were injected with 10 6 SK-mel 2, SK-mel 28 or M24-met human melanoma cells. The tumors were allowed to grow until they were approximately 3-5 mm in diameter. Thereafter, the animals were injected once a week with 5.0 IU of ADI-SS- PEG20,000.
• the results are shown in Figure 8, and show that PEG-ADI inhibited tumor growth and that eventually the tumors began to regress and disappear. Because the tumors did not have argininosuccinate synthatase, they were unable to synthesize proteins (because ADI eliminated arginine and the tumors could not make it) so that the cells "starved to death.”
• M24-met human melanoma is highly metastatic
• the animals injected with M24-met human melanoma cells were sacrificed after 4 weeks of treatment and the number of metastases in the lungs of the animals was determined.
• the control animals had an average of 32 metastases, while the animals treated with ADI-SS-PEG20,000 did not have any metastases.
• the results appear to indicate that ADI-SS-PEG20,000 not only inhibited the growth of the primary melanoma tumor, but also inhibited the formation of metastases.
• Example 8 Tumor Inhibition of Human Hepatomas The ability of PEG5,000-ADI to inhibit the growth of a human hepatoma in vivo was tested. Nude mice (5 in each group) were injected with 10 6 human hepatoma SK- Hepl cells. The tumors were allowed to grow for two weeks and then the animals were treated once a week with 5.0 IU of SS-PEG5.000-ADI (solid circles), SS-PEG12,000-ADI (solid triangles) or SS-PEG20,000-ADI (open triangles). The results are set forth in Figure 9.
• PEG5,000-ADI is most effective in inhibiting hepatoma growth in vivo.
• the exact mechanism by which this occurs is unknown. Without being bound to any theory of the invention works, it appears that proteins formulated with SS- PEG5,000-ADI become sequestered in the liver. Larger molecular weights of PEG do not, which may be due to the uniqueness of the hepatic endothelium and the spaces (fenestrae) being of such a size that larger molecular weights of PEG-ADI conjugates are excluded.
• Example 9 Application to Humans
• PEG5,000-ADI and PEG20,000-ADI were incubated ex vivo with normal human serum and the effects on arginine concentration was determined by amino acid analysis, where the enzyme was found to be fully active and capable of degrading all the detectable arginine with the same kinetics as in the experiments involving mice.
• the reaction was conducted at a volume of 0.1 ml in a time of 1 hour at 37 °C. Additionally, the levels of arginine and citrulline in human serum are identical with that found in mice. PEG-proteins circulate longer in humans than they do in mice.
• the circulating half life of PEG conjugated adenosine deiminase, asparaginase, glucocerbrocidase, uricase, hemoglobulin and superoxide dismutase all have a circulating half life that is 5 to 10 times longer than the same formulations in mice.
• the human dose is most often 1/5 to 1/10 of that used in mice. Accordingly, PEG-ADI should circulate even longer in humans than it does in mice.

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