HK1144701B - Aggregate-free urate oxidase for preparation of non-immunogenic polymer conjugates - Google Patents

Description

Aggregate-free urate oxidase for preparing non-immunogenic polymer conjugates

The present application is a divisional application of the patent application entitled "aggregate-free urate oxidase for producing non-immunogenic polymer conjugates" filed on 7/2/2001, application No. 01807750.1.

Statement of government interest of the invention

Part of the research introduced by the invention is carried out under the support of the foundation for the development of industrial research and development in the United states-Israel. Accordingly, the U.S. government has certain rights in the invention.

Background

Technical Field

The present invention relates to the purification and chemical modification of proteins to prolong their circulation time and reduce their immunogenicity. More specifically, the invention relates to the removal of aggregates above the urate oxidase (uricase) octamer, which are then conjugated with poly (ethylene glycol) or poly (ethylene oxide). This substantially eliminates uricase immunogenicity without affecting its uricolytic activity.

Introduction to related Art

The statements contained in this background section do not constitute an admission of prior art, but, on the contrary, reflect the subjective opinion and interpretation of the state of the art at the time the inventors performed the invention. These interpretations may include insights not heretofore disclosed by the inventors, which insights themselves are not part of the prior art.

Urate oxidase (uricase; e.c.1.7.3.3.) is an enzyme that catalyzes the oxidation of uric acid to the more soluble product allantoin, a purine metabolite that is more easily excreted. Humans cannot produce uricase with enzymatic activity because higher primates have acquired several mutations in the uricase gene during evolution. Wu, X et al (1992) J Mol Evol 34: 78-84. As a result, in susceptible individuals, excessive concentrations of uric acid in blood (hyperuricemia) and urine (hyperuricuria) can cause painful arthritis (gout), impaired urate deposition (tophus), and renal failure. In some patients, effective drugs such as allopurinol, an inhibitor of uric acid synthesis, produce therapeutically limiting side effects or do not adequately alleviate the above conditions. Hande, KR et al (1984) Am J Med 76: 47-56; fam, AG, (1990) Bailire's Clin Rheumatoid 4: 177-192. Injection of uricase may at least transiently alleviate hyperuricemia and hyperuricemia. Since uricase is a human exogenous protein, even the first injection of unmodified uricase protein from Aspergillus flavus results in several percent of treated patients developing anaphylactic reactions (Pui, C-H et al (1997) Leukemia 11: 1813-1816), and immune responses limit their long-term or intermittent therapeutic applications. Donadio, D et al (1981) Nouv pressure M ed 10: 711-712; leaustic, M et al (1983) Rev Rhum Mal Osteoaric 50: 553-554.

U.S. patent application Ser. No. 09/370,084 and published International application No. PCT/US99/17514 disclose poly (ethylene glycol) -urate oxidase (PEG-uricase) that retains at least about 75% of the uricolytic activity of unconjugated uricase and greatly reduces its immunogenicity. In one such purified uricase, an average of 2 to 10 PEGs are covalently attached to each subunit, wherein each PEG molecule may have a molecular weight of about 5kDa to about 100 kDa.

Protein aggregation is known to increase its immunogenicity. This recognition has led to the development of methods aimed at aggregating proteins by treatments such as heat denaturation and glutaraldehyde cross-linking before they are used in the preparation of vaccines or to immunize animals to produce antisera.

Furthermore, it is known that during the clinical application of therapeutic proteins, such as human gamma globulin (Henney et al (1968) N. Engl. J. Med.278: 2244-.

In contrast to the known effects of protein aggregation on immunogenicity, there have been no reports of aggregation having an effect on the immunogenicity of proteins conjugated to poly (alkylene glycols), such as PEG. There is a need for poly (alkylene glycol) -uricase conjugates that substantially eliminate uricase immunogenicity without affecting their uricolytic activity. The present invention provides such a composition.

Summary of The Invention

Conjugation of proteins to poly (alkylene glycols), particularly PEG, results in conjugates with reduced immunogenicity and increased maintenance time in the blood. In an attempt to prepare uricase conjugates that are substantially non-immunogenic and retain substantially all of the uricolytic activity of the unmodified uricase preparation, it was found that upon repeated injections of PEG conjugates prepared from uricase comprising large uricase aggregates, the small amounts of large uricase aggregates in the starting material have surprising effects in both stimulating antibody formation and accelerating clearance from the blood, both of which are detrimental. Surprisingly, the inventors have found that the increased immunogenicity and accelerated clearance are not due to the presence of well-defined medium-sized aggregates of uricase subunits, e.g., aggregates containing eight subunits (octamers), which are larger than the native tetramer. An octamer form of uricase is present in sufficiently high concentrations in most uricase preparations that it can be detected by ultraviolet light absorbance (e.g., 214nm or 276nm) or by refractive index or other protein concentration measurements. However, the octamer itself was found to have very little effect on immunogenicity and on accelerating clearance of the PEG-uricase conjugate, compared to much less and much larger aggregates which could not be detected by UV absorbance under the detection conditions, but were readily detected by static (Raleigh) or dynamic light scattering. It was therefore found that removal of said traces of very large aggregates prior to conjugation with PEG reduced the immunogenicity and rapid clearance of the PEG-uricase conjugates obtained to a surprising extent.

One embodiment of the invention is a purified urate oxidase (uricase) that is substantially free of aggregates larger than octamers. Preferably, the uricase is mammalian uricase. More preferably, the uricase is porcine liver uricase, bovine liver uricase or ovine liver uricase. In one aspect of this preferred embodiment, the uricase is recombinant uricase. In another aspect of this preferred embodiment, the uricase has substantially the sequence of porcine, bovine, ovine, or baboon liver uricase. The uricase is preferably a chimera. Preferably, the uricase is PKC uricase. In another aspect of this preferred embodiment, the uricase has substantially the sequence of baboon liver uricase, wherein tyrosine 97 is replaced with histidine. The preferred uricase comprises one amino terminus and one carboxy terminus, wherein the uricase is truncated at one or both termini. Advantageously, the uricase is fungal uricase or microbial uricase. Preferably the fungal uricase or the microbial uricase is isolated from Aspergillus flavus (Aspergillus flavus))Arthrobacter globiformis, Bacillus sp, or Candida utilis, or a recombinant uricase having substantially one of the uricase sequences. Or the uricase is invertebrate uricase. Preferably, said invertebrate uricase is isolated from Drosophila melanogaster or Drosophila pseudoscura, or is a recombinant uricase having essentially one of said uricase sequences. In another aspect of this preferred embodiment, the uricase is a plant uricase. Preferably, the plant uricase is isolated from root nodules of soybean (Glycine max) or is a recombinant uricase having substantially the sequence of said uricase.

In one aspect of this preferred embodiment, the uricase described above is conjugated to poly (ethylene glycol) or poly (ethylene oxide) under conditions such that the conjugate uricase is substantially free of aggregates that are larger than an octamer. Preferably, the uricase is conjugated to the poly (ethylene glycol) or poly (ethylene oxide) through a urethane (urethane) linkage, a secondary amine linkage, or an amide linkage. In one aspect of this preferred embodiment, the poly (ethylene glycol) is monomethoxypoly (ethylene glycol). In another aspect of this preferred embodiment, the poly (ethylene glycol) or poly (ethylene oxide) has a molecular weight of about 5kDa to about 30 kDa. Preferably, the poly (ethylene glycol) or poly (ethylene oxide) has a molecular weight of about 10kDa to about 20 kDa. Advantageously, the average number of chains of poly (ethylene glycol) or poly (ethylene oxide) is from about 2 to about 12 per uricase subunit. More advantageously, the average number of chains of poly (ethylene glycol) or poly (ethylene oxide) is about 6-10 chains per uricase subunit. Most advantageously, the average number of poly (ethylene glycol) or poly (ethylene oxide) chains is about 7-9 per uricase subunit. Preferably the poly (ethylene glycol) or poly (ethylene oxide) is linear. Or the poly (ethylene glycol) or poly (ethylene oxide) is branched.

The invention also provides a pharmaceutical composition for reducing uric acid levels in body fluids or tissues, comprising the uricase conjugate and a pharmaceutically acceptable carrier. The composition is preferably stabilised by freeze-drying, and upon reconstitution dissolves to give a solution suitable for parenteral administration.

Another embodiment of the invention is a method for purifying uricase having reduced immunogenicity comprising the steps of isolating uricase aggregates that are larger than octamers in a uricase fraction, and removing the aggregates from the purified uricase. Preferably, said separating step comprises the steps of detecting aggregates larger than octamers in at least a portion of said uricase fraction, and removing a fraction comprising said aggregates. Preferably, the detecting step comprises a light scattering detection step.

The invention also provides the isolated uricase prepared by the method.

Brief Description of Drawings

FIG. 1 illustrates the uricase activity, total protein concentration and salt concentration of Pharmacia Biotech Mono Q (1X 10cm) anion exchange column fractions. Uricase activity was measured by monitoring the decrease in absorbance at 292nm of a 200mM sodium borate solution of 100. mu.M uric acid, pH9.2, at room temperature. Total protein was determined from the area under the uricase absorption peak curve in a size exclusion HPLC analysis.

FIG. 2 illustrates size exclusion HPLC analysis of a load sample (load) containing the mutations R291K and T301S (PKS uricase) and selected fractions from a preparative Mono Q chromatograph on pig uricase on a Pharmacia Superdex200 column (1X 30cm) showing data obtained from detection of 90 ℃ incident light on a light scattering detector (upper curve) and 276nm absorbance (lower curve). The difference in signal intensity for tetramer, octamer, and higher aggregated forms of uricase in unfractionated samples (loaded samples) and various fractions is evident. The loaded sample was diluted 5-fold with Mono Q column buffer, fraction 5 was diluted 3-fold, and fraction 6 was diluted 9-fold. Fraction 5 and fraction 6 were mixed to form a "low salt pool".

FIG. 3 illustrates a size exclusion analysis of the Mono Q column fraction of FIG. 1, the same as in FIG. 2, showing data from a light scattering detector detecting 90 incident light and from an absorbance measurement at 276 nm. The fractions shown in this figure were used to form "high salt pools" from which PEG conjugates were prepared and injected into BALB/c mice. The serum activity and immune response of the resulting BALB/c mice are shown in FIGS. 5 and 6.

FIG. 4 illustrates the octamer content in a selected fraction of a preparative MonoQ column chromatography without fractionation of PKC uricase and PKS uricase (FIG. 1), obtained by absorbance at 276nm and light scattering measurements at 90 ℃ and calculated from the data in FIG. 2 and FIG. 3.

FIG. 5 illustrates UV assay of uricase activity after incubation of serum at 37 ℃ for 4 hours 24 hours after each injection (once weekly, 6 total) of 6X 10-kDaPEG conjugate of PKS uricase or Mono Q column fraction pool (same as FIG. 1).

FIG. 6 illustrates an ELISA analysis of IgG antibody formation of PKS uricase PEG conjugates and of PEG conjugates in the Mono Q column fraction pool shown in FIG. 1, which was performed on BALB/c female mice by serum withdrawal 24 hours after each injection (once weekly, 6 times total) of 0.2mg uricase protein/20 g body weight. For each mouse, data obtained from a 24 hour blood draw analysis after the first to sixth injection are shown from left to right. The detection conditions are described in example 6. Data for 8 mice in each group are arranged from left to right in increasing order of immunoreactivity.

Detailed description of the preferred embodiments

Previous studies have shown that conjugation to PEG (pegylation) achieves significant reductions in uricase immunogenicity and/or antigenicity, all the while accompanied by a substantial loss of uricolytic activity. It is observed in the present invention that trace amounts of urate oxidase aggregates larger than octamers are directly related to immunogenicity and induction of rapid clearance of PEG-uricase conjugates. This finding is most likely applicable to proteins other than uricase, including interferons and growth factors.

The safety, convenience, and cost effectiveness of biopharmaceuticals are adversely affected by reduced potency of the drug, with the result that increased dosages need to be administered. There is therefore a need for safe and effective alternative methods of reducing hyperuricemia levels in body fluids, including blood and urine. The present invention provides methods for producing uricase for synthesizing PEG-uricase with the removal of uricase aggregates larger than octamers. The PEG-uricase retains all or substantially all of the uricolytic activity of the unmodified uricase. The invention also provides purified uricase that is substantially free of aggregates that are larger than octamers. The term "substantially free" refers to a purified uricase comprising no more than about 2%, preferably no more than about 1%, aggregates larger than octamers.

The present invention provides a method for purifying uricase, thereby removing uricase larger than an octamer from a purified uricase preparation. Because these larger aggregates are highly immunogenic, the purified uricase preparation cannot contain the aggregates. The method involves monitoring the fractions separated by the column by light scattering rather than by 280nm uv absorbance or by both light scattering and 280nm uv absorbance, as the aggregates may be too small to be detected with uv absorbance. The purified uricase is then conjugated to a water soluble polymer, preferably poly (ethylene glycol) or poly (ethylene oxide), as described in co-pending U.S. patent application Ser. No. 09/370,084.

Removal of aggregated uricase from a preparation consisting essentially of tetrameric uricase may be accomplished by any method known to those skilled in the art, including size exclusion chromatography, ion exchange chromatography, ultrafiltration through microporous membranes, and centrifugation, including ultracentrifugation. The separation process may include separation and analysis of the fractions and removal of the fraction containing excess large aggregates. The resulting uricase preparation is more suitable for synthesizing uricase conjugates that are substantially non-immunogenic than uricase that is not fractionated. For long-term administration, it is important that PEG conjugates of proteins such as PEG-uricase have low immunogenicity and do not cause progressive, faster clearance of the drug from the blood upon repeated administration.

The invention also provides pharmaceutical compositions of the polymer-uricase conjugates. The conjugates are substantially non-immunogenic and retain at least 75%, preferably 85%, more preferably 95% or more than 95% of the uricolytic activity of unmodified uricase. Uricases suitable for conjugation to water-soluble polymers include native uricase isolated from bacteria, fungi, plant tissues, and animal tissues, including vertebrates and invertebrates, as well as recombinant forms of uricase, including variant uricases, hybrid uricases, and/or enzymatically truncated active uricase variants. Water-soluble polymers suitable for use in the present invention include linear and branched poly (ethylene glycol) or poly (ethylene oxide), both commonly referred to as PEG. Examples of branched PEGs are those of U.S. Pat. No. 5,643,575. A preferred example of linear PEG is monomethoxyPEG, of general structure CH₃O-(CH₂CH₂O)_nH, where n is about 100-2,300.

One embodiment of the invention is a urate oxidase (uricase) conjugate that retains at least about 75% of the uricolytic activity of unconjugated uricase and significantly reduces immunogenicity. The uricase of this aspect of the invention may be recombinant uricase. The uricase may be of mammalian origin, whether recombinant or non-recombinant. In one aspect of this embodiment, the uricase may be porcine, bovine, or ovine liver uricase. In another aspect of this embodiment. The uricase may be a chimera. The chimeric uricase may comprise a component of porcine liver and/or baboon liver uricase. For example, the chimeric uricase may be porcine uricase (PKS uricase) comprising the mutations R291K and T301S. In another aspect, the uricase may be baboon liver uricase, wherein the tyrosine at position 97 is replaced with histidine, such that the specific activity of the uricase may be increased by at least about 60%. Whatever the source, the uricase of the invention may also be truncated, either at the amino terminus, or at the carboxy terminus, or both. Also the uricase may be fungal uricase or microbial uricase. In one embodiment of the invention, the fungal uricase or the microbial uricase may be derived from Aspergillus flavus (Aspergillus flavus))Natural or recombinant uricases of Arthrobacter globiformis, Bacillus sp, or Candida utilis. Alternatively, the uricase may be an invertebrate uricase, such as a native or recombinant uricase derived from Drosophila melanogaster (Drosophila melanogaster) or Drosophila pseudoscura. The uricase of the invention may also be a plant uricase, such as a natural or recombinant uricase derived from root nodules of soybean (Glycine max). The PEG average molecular weight may be about 5kDa to 100 kDa; preferably the PEG has an average molecular weight of about 8kDa to about 60 kDa; more preferably, the PEG has an average molecular weight of about 10kDa to about 40kDa, e.g., about 10kDa to about 20 kDa. The average number of covalently linked PEG chains may be 2-12 per uric acidAn enzyme subunit; preferably the average number of covalently linked chains may be 6-10 per subunit; more preferably, the average number of PEG chains can be 7-9 per subunit. In one aspect of this embodiment, the uricase may be a tetramer. The PEG chain may be covalently linked to uricase via a urethane (carbamate) linkage, a secondary amine linkage, and/or an amide linkage. When the uricase is in a recombinant form any one of the uricases described herein, the recombinant form of the uricase may have substantially the sequence of the uricase in its native form.

A preferred mammalian uricase is a recombinant porcine-baboon chimera uricase, consisting of a porcine liver uricase partial sequence and a baboon liver uricase partial sequence, both portions first determined by Wu et al (1989). An example of such a chimeric uricase comprises the first 288 amino acids of the pig uricase sequence (SEQ ID NO: 1) and the last 16 amino acids of the baboon uricase sequence (SEQ ID NO: 2). Hershfield et al, International publication WO00/08196, urate oxidase, 2000, 2.17.D. Since the latter sequence differs from the pig uricase sequence in only two positions, lysine (K) replaces the arginine residue 291, and serine (S) replaces the threonine residue 301, this mutein is referred to as pig-K-S uricase or PKS uricase (SEQ ID NO: 3). PKS uricase also has one lysine residue and thus one potential pegylation site more than the pig or baboon uricase sequence.

cDNA for various mammalian uricases, including PKS uricase, were subcloned and the optimal conditions for expression in E.coli were determined using standard methods. See Erlich, HA, (Ed.) (1989) PCR technology principles and Applications for dnaamplification new York: stockton Press; sambrook et al (1989) Molecular cloning, laboratory Manual, second edition, Cold Spring Harbor, NY: cold Spring Harbor Laboratory Press. The recombinant uricase was extracted and purified, and its stability and activity were determined using modified standard assays. See Fridovich, I, (1965) J Biol Chem 240: 2491-2494; nishimura et al (1979) and examples 1 and 5.

In one embodiment of the invention, uricase may be conjugated to a smaller number of PEG chains through biologically stable, non-toxic covalent bonds. The covalent bonds may include urethane (carbamate) bonds, secondary amine bonds, and amide bonds. Various activated PEGs suitable for such conjugation are available from Shearwater Polymers, Hunsville, AL..

For example, incubation of uricase in the presence of a Succinimidyl Carbonate (SC) derivative of PEG or a p-nitrophenyl carbonate (NPC) derivative can form a urethane linkage that links to uricase. SC-PEG can be synthesized by the method described in U.S. Pat. No. 5,612,460. NPC-PEG can be prepared according to Veronese, FM et al (1985) Appl Biochem Biotechnol 11: 141-152 and the method described in U.S. Pat. No. 5,286,637 were synthesized by reacting PEG with p-nitrophenyl chloroformate. The method described in us patent 5,286,637 can be adapted to high molecular weight PEG by adjusting the concentration of the reactants to maintain similar stoichiometry. An alternative method for the synthesis of NPC-PEG is described by B ü ttner, W et al, east German patent specification DD279486A 1.

Amide bonds to uricase may be obtained using N-hydroxysuccinimide esters of PEG carboxylic acid derivatives (Shearwater Polymers). Secondary amine linkages can be formed by reductive alkylation using 2, 2, 2-trifluoroethanesulfonyl PEG (tresyl PEG; Shearwater Polymer) or PEG aldehyde (Shearwater Polymers) and sodium cyanoborohydride.

In conjugates with PEG having a molecular weight of 10kDa, the maximum number of mammalian uricases (e.g., PKC uricase, a mutein of porcine uricase; see assay conditions in example 5) per subunit attached PEG chains is about 12, while retaining at least 75% of the uricolytic activity of unmodified uricase. The latter degree of pegylation corresponds to about 40% of the total amino groups. In one embodiment of the invention, the average number of strands of PEG attached per uricase subunit is about 2 to about 12. In a preferred embodiment, the average number of strands of PEG attached per uricase subunit is about 6 to about 10. In a more preferred embodiment, the average number of covalently attached PEG chains per uricase subunit is about 7 to about 9. In another embodiment, the PEG used in the ligation reaction has a molecular weight of about 5kDa to about 30kDa, preferably about 10kDa to about 20 kDa.

Several factors may influence the optimal molecular weight and optimal number of strands of PEG for attachment to a given type of uricase. Generally, reducing or eliminating immunogenicity without significant loss of uricolytic activity may require the attachment of uricase to a greater number of low molecular weight PEG chains, as compared to a lesser number of high molecular weight PEG chains. Likewise, each different form of uricase may have a different optimal choice in terms of the size and number of PEG chains. The optimal number of PEG chains and the optimal PEG molecular weight can be readily determined using the methods described herein.

When PEG conjugates of mammalian uricase are prepared with purified uricase tetramers and octamers (containing four or eight subunits of about 35 kDa), their immunogenicity in mice is significantly reduced, in contrast, PEG conjugates of uricase preparations containing large aggregates (see FIG. 6) have moderate immunogenicity while the immunogenicity of unmodified uricase is very high.

Natural and recombinant uricase purification preparations typically contain a very large aggregate mixture of uricase in addition to uricase in tetrameric (140-kDa) and octameric (280kDa) forms. The percentage of uricase preparations in tetrameric or octameric forms is typically in the range of about 20% to 95% (see FIGS. 2-4). Although there is evidence that unpegylated aggregates of several other proteins are highly immunogenic (see, e.g., Moore, WV et al (1980) J Clin Endocrinol Metab 51: 691-697), previous PEG-uricase studies did not introduce any compensation for limiting aggregate content, suggesting that the potential immunogenicity of PEG-modified aggregates is not considered. Based on the observations of the present invention, it appears that the aggregates are present in the enzyme preparation previously used for the synthesis of PEG-uricase. Their presence may make the preparation of non-immunogenic conjugates more difficult. It can also be seen that the large loss of uricolytic activity of the pegylated uricase previously observed is associated with the high number of low molecular weight PEG chains attached. On the other hand, at least for certain uricases, such as PKS uricase (a mutein of porcine uricase) and uricase derived from Bacillus thermophilus, the uricase purification and PEGylation methods described herein allow each uricase subunit to be covalently linked to up to 12 PEG chains while retaining uricolytic activity above 75%.

In another preferred embodiment of the invention, substantially all large aggregates of the uricase may be removed by ion exchange chromatography (FIGS. 1-3) or size exclusion chromatography at a pH of about 9-10.5, preferably 10.2, prior to conjugation of the resulting substantially aggregate-free uricase preparation to PEG. The molecular weight of the uricase in each fraction of the preparative column may be monitored by any size-dependent analytical technique including, for example, HPLC, conventional size-exclusion chromatography, centrifugation, light scattering, capillary electrophoresis in non-denaturing buffer, or gel electrophoresis. For uricase without aggregates separated using size-exclusion chromatography, fractions containing only the 140-kD and 280-kDa forms of uricase may be pooled for polymerization with PEG. For tetrameric and octameric uricases separated using ion exchange chromatography, each fraction of the ion exchange column may be analyzed in size to determine fractions containing large amounts of tetrameric or octameric forms without large aggregates detected by light scattering. Thus, in the purified product, the undesired aggregates may constitute only about 1% or less of the total uricase.

The results described herein indicate that, even with sufficient pegylation, PKS uricase forms larger than the octamer can stimulate mice to rapidly clear the uricase (fig. 5) and to some extent immunogenicity (fig. 6). In contrast, conjugates prepared from uricase substantially free of large aggregates (detectable by light scattering) can be injected at least 6 times repeatedly over a1 week period with slower clearance rates (FIG. 5) and no detectable antibody formation by sensitive enzyme-linked immunoassays (FIG. 6). The use of highly purified tetrameric or octameric uricase further distinguishes the improved PEG conjugates of the present invention from the PEG-uricase preparations introduced previously. In contrast, the large number of large aggregates contained in uricase preparations used by some previous researchers may link uricase to a large number of PEG chains to inhibit its immunogenicity. The enzymatic activity of the resulting conjugate is thus greatly reduced.

The PEG-uricase conjugates of the present invention are useful for lowering uric acid levels in body fluids and tissues of mammals, preferably humans, and thus are useful for treating elevated uric acid levels associated with conditions including gout, gout nodules, renal insufficiency, organ transplantation, and malignancies. PEG-uricase conjugates may be administered to mammals having elevated levels of uric acid by injection by any of a number of routes of administration, including intravenous, subcutaneous, intradermal, intramuscular, and intraperitoneal routes. Alternatively, the PEG-uricase conjugate may be inhaled by nebulization. See pattern, JS, (1996) Adv Drug Delivery Rev 19: 3-36 and us patent 5,458,135. The effective dose of the PEG-uricase of the invention depends on the uric acid level and the size of the individual patient. In one embodiment of this aspect of the invention, PEG-uricase is administered in a dose of about 10 μ g to about 1g with a pharmaceutically acceptable excipient or diluent. In a preferred embodiment, a dosage of about 100 μ g to 500mg is administered. More preferably, the conjugated uricase is administered at a dose of about 1mg to 100mg, such as 5mg, 20mg, or 50 mg. The mass of the administered dose of the embodiment refers to the mass of protein in the conjugate.

Pharmaceutical formulations comprising PEG-uricase may be prepared by conventional techniques, see, for example, Gennaro, AR (Ed.) (1990) Remington's Pharmaceutical Science, 18 th edition, Easton, PA: mack Publishing co. Suitable excipients for the preparation of injectable solutions include, for example, phosphate buffered saline, lactated Ringer's solution, water, polyols and glycerol. Pharmaceutical compositions for parenteral injection include pharmaceutically acceptable sterile aqueous or non-aqueous solutions, dispersions, suspensions or emulsions as well as sterile powders for reconstitution into sterile injectable solutions or dispersions before use. The formulation may contain additional components such as preservatives, solubilizers, stabilizers, wetting agents, emulsifiers, buffers, antioxidants and diluents.

PEG-uricase may also be implanted into a patient as a controlled release composition for sustained control of elevated levels of uric acid in the body fluid. Such as polylactic acid, polyglycolic acid, regenerated collagen, poly-L-lysine, sodium alginate, gelling gums, chitosan, agarose, multilamellar liposomes, and many other conventional depot formulations including bioerodible or biodegradable substances that can be formulated with bioactive compositions. The substance, when implanted or injected into the body, gradually disintegrates, releasing the active substance into the surrounding tissue. For example, one method for encapsulating PEG-uricase includes the method disclosed in U.S. Pat. No. 5,653,974. The present invention specifically contemplates the use of bioerodible, biodegradable, and other depot formulations. The use of infusion pumps and matrix-embedded systems for delivery of PEG-uricase is also within the scope of the present invention. PEG-uricase may also be advantageously encapsulated in micelles or liposomes. Liposome encapsulation techniques are well known in the art. See, e.g., Lasic, D et al (Eds.) (1995) stem lipids. CRC Press.

The PEG-uricase pharmaceutical composition of the invention reduces the need for hemodialysis in patients at high risk for urate-induced renal failure, such as organ transplant recipients (see Venkataseshan, VS et al (1990) Nephron 56: 317-321 and patients with certain malignancies).

The following examples illustrate various aspects of the above disclosure and are in no way to be construed as limiting the invention. These examples illustrate PEG-uricase prepared by the attachment of activated PEG (e.g., a p-nitrophenyl carbonate derivative) to a pig uricase mutein. The following examples direct one skilled in the art to produce uricase conjugates that retain at least about 75% uricolytic activity of unmodified uricase and are well suited for long-term administration, substantially non-immunogenic.

Example 1

Preparative ion exchange chromatography of uricase

Preparative ion exchange chromatography was performed on a Fast Protein Liquid Chromatography (FPLC) instrument (Amersham Pharmacia, Piscataway, NJ). A Mono Q column (1X 10cm, Amersham Pharmacia) was eluted at a flow rate of 0.5 ml/min with gradient of 50mM sodium carbonate pH10.3, 0.1M sodium chloride (buffer A) to 50mM sodium carbonate pH10.3, 0.6M sodium chloride (buffer B), except that the sample was loaded at a lower flow rate. This technique was used to fractionate 25mL of PKS uricase solution (pH 10.3). PKS uricase was obtained from Bio-Technology General Limited (Rehovot, Israel). The latter is recombinant pig uricase in which one lysine residue (K) and one serine residue (S) replace, respectively, one arginine residue and one threonine residue in the original pig uricase sequence (Lee et al (1988) Science 239: 1288-1291; Wu et al (1989) Proc. Natl. Acad. Sci. U.S.A.86: 9412-9416). After loading, the column was washed with 100mL of buffer A. The uricase peak began to elute at the end of 31mL 0-26% linear gradient buffer B. Most uricase was eluted isocratically through 7mL of buffer containing 26% buffer B. The remaining portion of uricase was recovered by elution with 89mL of 26% -100% linear gradient buffer B. Fractions of 4ml or 6ml were collected. Aliquots #4-11 were assayed for uricase and total protein (FIG. 1) and analyzed by size exclusion High Performance Liquid Chromatography (HPLC) as described in example 2 (FIGS. 2 and 3). The remainder of the #5-10 fraction was attached to PEG as described in example 3. Based on the analysis results of example 2, as shown in FIG. 1, the PEG conjugates of #5-6 fractions were pooled into a "low salt pool", and the PEG conjugates of #7-10 fractions were pooled into a "high salt pool".

Example 2

Resistive chromatography for monitoring uricase size through light scattering and ultraviolet absorbance

The unfractionated PKS uricase and selected fractions from the preparative Mono Q chromatographic analysis of PKS uricase from example 1 were subjected to size exclusion HPLC at room temperature using a Superdex200 column (1X 30cm, Amersham Pharmacia Biotech). The eluate from the absorption monitor (UV2000) of Thermo separations HPLC (Sunnyvale, CA) was analyzed by scattering of the incident light at 90 degrees using the MiniDawn detector of Wyatt Technologies (Santa Barbara, CA).

The results shown in FIGS. 2-4 demonstrate resolution of tetramers, octamers, and larger aggregates of uricase subunits, as well as the detection of different signal ratios of the forms of uricase in different samples. Unlike the absorption signal, which is proportional to concentration, the light scattering signal is proportional to the product of concentration and the size of the light scattering unit. The resulting sensitivity of the light scattering detector to very small amounts of highly aggregated uricase indicates the presence of the largest aggregates that elute at or near void volume (about 7 ml).

Example 3

Synthesis of PEG uricase conjugates

Unfractionated PKC uricase (Bio-Technology General Limited) and example 1Mono Q column fraction uricase were linked to 10-kDa PEG using p-nitrophenyl carbonate derivatives of PEG (NPC-PEG) from Shearwater Polymer (Huntsville, AL). The preparation of NPC-PEG from PEG using phenyl chloroformate has been described in several reports (e.g., Veronese, FM et al, (1985) applied Biochem Biotechnol 11: 141-152; Kito, M et al (1996) J Clin Biochem Nutr 21: 101-111), and previous researchers, including the present inventors, have used NPC-PEG for the synthesis of PEG-protein conjugates (e.g., Veronese et al, supra; Sherman, MR et al, by Eds. Harris et al (ethylene glycol) Chemistry and Biological Application), Symposium Series680 (155-176) Washingg, DC: American Chemical Society). According to Kunitani, M et al (1991) J Chromatogr 588: 125-137), and determining the number of 10-kDaPEG chains attached to each uricase subunit to be 6.

Example 4

In vivo serum duration and immunogenicity of uricase, PEG-uricase

Recombinant mammalian uricase PEG conjugates prepared according to the method of example 3 were adjusted to 1mg protein/mL in Phosphate Buffered Saline (PBS) at pH7.4 for injection. The samples were frozen and stored for analysis or injection. Samples were warmed to 37 ℃ for 1 hour, then given by injection to BALB/c female mice (8/group). The average body weight of each group of mice at the beginning of the study was 18-22 g.

Body weights of all mice were monitored and side effects or other unhealthy manifestations of experimental injections were recorded. 24 hours after each injection (once weekly, 6 injections), mice were anesthetized with ketamine, 100-. Serum was prepared from blood coagulated at 2-8 ℃ for 4-32 hours. The sera were stored at-20 ℃. Uricolytic activity was measured by assaying serum as described in example 5, and anti-uricase antibodies in serum were assayed as described in example 6.

Example 5

Assay of uricolytic Activity of PEG-uricase in serum of mice injected with PEG-uricase

The activity assay based on UV absorbance (UV assay) was carried out in the I.Fridovich method (J Biol Chem. (1965) 240: 2491-. The data is analyzed by observing the maximum absorbance ramp (milliabsorbance units per minute) of absorbance measured during the time that 10% to 40% of the substrate is oxidized. The results obtained for this assay are shown in FIGS. 1 and 5.

Based on serum data obtained at 24 and 72 hours post-injection, the mean half-life of serum uricase in mice injected for the first time with PKS uricase linked to 6 strips of 10-kDa PEG/subunit (6X 10kDa PEG PKS) was 29. + -. 4 hours.

Independent experiments found that detectable uricolytic activity was decreased in serum from mice injected with PEG-uricase during storage at-20 ℃ and maximal recovery of uricase activity was obtained by incubating the serum for 4 hours at 37 ℃ prior to analysis. FIG. 5 shows that the maximal uricolytic activity is recovered after weekly repetitive injections of 6X 10-kDa PEG PKS uricase, before PEGylation according to the method of example 3, when PEG PKS uricase is purified by Mono Q column chromatography as in the examples. The highest degree of uricolytic activity recovery was obtained after injection of the conjugate prepared from the high salt chaotropic pool of example 1 (see FIG. 1) containing the least amount of very large aggregates (see light scattering curves for fractions 7-10 in FIG. 3). Moderate recovery was obtained with the conjugate prepared from the low salt eluent pool of the Mono Q column of example 1, and the worst recovery of uricase activity was obtained with the conjugate prepared from unfractionated PKS uricase, which contains the largest amount of very large aggregates (see FIG. 2). The same relative activity recovery sequence of serum was observed after repeated injections, whether using the UV assay described above or the modified colorimetric method of P.Fossati et al (J.Clin Chem (1980) 26: 227-.

Example 6

Enzyme-linked immunosorbent assay (ELISA) of PEG-uricase injected mouse serum

Non-competitive ELISA assays were performed with pig uricase bound to 96-well Immulon2 plates (Dynex Technologies, VWR Scientific, San Francisco, Calif.). The first antiserum was obtained from mice injected with uricase or with a 6X 10-kDa PEG conjugate prepared according to the method of example 3. The secondary antibody was goat anti-mouse IgG conjugated to horseradish peroxidase (Calbiochem-Novabiochem #401253, La Jolla, CA) and the substrate was o-phenylenediamine dihydrochloride (Sigma P-9187, St. Louis, Mo.) as described in B.Porstmann et al (J Clin. chem. Clin. biochem. (1981) 19: 435-440).

FIG. 6 illustrates the results of a non-competitive ELISA assay. This result demonstrates that 6X 10-kDa PEGPKS uricase synthesized according to example 3 using the high salt eluate of the Mono Q column of example 1 (see FIG. 1) did not produce any detectable immune response in 8 mice that received weekly injections for 6 consecutive weeks. Several mice injected with conjugates prepared from unfractionated PKS uricase following the method of example 3 exhibited low but detectable immune responses. The highest incidence of immune responses was mice injected with conjugates prepared according to the method of example 3 from the low salt eluate pool of the Mono Q column of example 1.

Without the advantage of the light scattering detector for size exclusion HPLC analysis as described in example 2, the presence of uricase in its largest aggregate form, rather than in its octamer form, was associated with a progressive decrease in the recovery of BALB/c mouse PEG-uricase conjugate after repeated injections (see example 5 observation (fig. 5)), while the immunogenicity was improved (see example 6 observation (fig. 6)), such a result being not evident. The results are of great significance for uricase specifications to be used as a starting material for the production of PEG-uricase for clinical use.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that: certain changes and modifications may be made to the invention without departing from the spirit and scope of the invention as described and claimed herein.

Sequence listing

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Claims (16)

1. A method of purifying urate oxidase that retains uricolytic activity by reducing the amount of aggregates that are larger than octamers, the method comprising:

(a) fractionating said urate oxidase;

(b) detecting aggregates larger than octamers in the urate oxidase-containing fraction; and is

(c) Removing the fraction containing said aggregates larger than octamers.

2. The method of claim 1, wherein said fractionating is accomplished using a method selected from the group consisting of ion exchange chromatography, size exclusion chromatography, and ultrafiltration.

3. The method of claim 1, wherein said detecting comprises measuring light scattering.

4. Purified urate oxidase prepared by the method of claim 1, wherein said purified urate oxidase comprises tetrameric and octameric urate oxidase.

5. A method of making a urate oxidase conjugate, the method comprising:

conjugating urate oxidase purified by the method of any of claims 1-3 to polyethylene glycol.

6. The method of claim 1, wherein (a) comprises applying the urate oxidase to the preparative column at a pH of 10.2.

7. The method of claim 6, wherein the preparative column is selected from the group consisting of an ion exchange column and a size exclusion column.

8. The method of claim 1, further comprising analyzing the fraction to determine at least one characteristic selected from the group consisting of: the presence of said tetrameric and octameric urate oxidases, and the absence of urate oxidase aggregates larger than octamers.

9. The method of claim 8, wherein said analysis comprises at least one analysis selected from the group consisting of: chromatography, centrifugation, light scattering and electrophoresis.

10. The method of claim 9, wherein the chromatography is high performance liquid chromatography.

11. An isolated urate oxidase conjugate prepared by the method of claim 5.

12. Use of purified urate oxidase conjugated to polyethylene glycol and a pharmaceutically acceptable carrier in the manufacture of a medicament for reducing uric acid levels in a bodily fluid or tissue of a mammal, wherein the purified urate oxidase comprises urate oxidase in tetrameric and octameric forms, and wherein the purified urate oxidase comprises no more than 2% aggregates larger than octamer.

13. The use of claim 12, wherein the mammal is a human.

14. The use of claim 12, wherein the elevated uric acid level is associated with a condition selected from the group consisting of gout, gout nodules, renal insufficiency, organ transplantation, and malignancy.

15. A pharmaceutical composition for reducing uric acid levels in body fluids or tissues comprising purified urate oxidase conjugated to polyethylene glycol and a pharmaceutically acceptable carrier, wherein the purified urate oxidase comprises urate oxidase in tetrameric and octameric forms, wherein the purified urate oxidase comprises no more than 2% aggregates larger than octamer, and wherein the composition is stabilized by freeze-drying.

16. A pharmaceutical composition comprising purified urate oxidase conjugated to polyethylene glycol, wherein each subunit of said urate oxidase is covalently attached to an average of 2 to 12 polyethylene glycol chains, wherein the average molecular weight of said polyethylene glycol is about 10kDa-30kDa, wherein said purified urate oxidase comprises urate oxidase in tetramer and octamer forms, and wherein said purified urate oxidase comprises no more than 2% aggregates larger than octamer.