Polyethylene Glycol-Like Brush Polymer Conjugate of a Protein Drug Does Not Induce an Antipolymer Immune Response and Has Enhanced Pharmacokinetics than Its Polyethylene Glycol Counterpart

Protein therapeutics, except for antibodies, have a short plasma half-life and poor stability in circulation. Covalent coupling of polyethylene glycol (PEG) to protein drugs addresses this limitation. However, unlike previously thought, PEG is immunogenic. In addition to induced PEG antibodies, ≈70% of the US population has pre-existing anti-PEG antibodies. Both induced and preexisting anti-PEG antibodies result in accelerated drug clearance, reduced clinical efficacy, and severe hypersensitivity reactions that have limited the clinical utility of uricase, an enzyme drug for treatment for refractory gout that is decorated with a PEG corona. Here, the authors synthesize a poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) conjugate of uricase that decorates the protein with multiple polymer chains to create a corona to solve these problems. The resulting uricase-POEGMA is well-defined, has high bioactivity, and outperforms its PEG counterparts in its pharmacokinetics (PK). Furthermore, the conjugate does not induce anti-POEGMA antibodies and is not recognized by anti-PEG antibodies. These findings suggest that POEGMA conjugation may provide a solution to the immunogenicity and antigenicity limitations of PEG while improving upon its PK benefits. These results transcend uricase and can be applied to other PEGylated therapeutics and the broader class of biologics with suboptimal PK.

[The Pharmacokinetics and Pharmacodynamics of Intravenous Uricase Multivesicular Liposomes]

OBJECTIVE

To determine and compare the pharmacokinetics and pharmacodynamics of uricase-multivesicular liposomes (UOMVLs) with free uricase (UOX) in rats.

METHODS

UOMVLs were prepared by the double emulsion method and confirmed with its entrapment efficiency, size and Zeta potential. Twelve healthy rats were randomly divided into two groups: one with i. v. injection of UOMVLs, and the other with i. v. injection of UOX. Their serum activity of uricase was assayed. The pharmacokinetic parameters were calculated using software DAS 2. 1. 1. Another 24 male SD rats were enrolled, the rat model of hyperuricemia was established with hypoxanthine and potassium oxonate, while normal group (n=6) was set as control. Injection of UOMVLs (1 mL, 0. 47 U/mL), UOX (1 mL, 0. 47 U/mL) and nothiy were given 1 h later in UOMVLs group (n=6), UOX group (n=6) and model group (n=6), and their serum uric acid levels were determined 1, 2, 3, 5, 7, 9, 12, 24, 36, 48 h after the establishment of hyperuricemia model.

RESULTS

The entrapment efficiency of UOMVLs was (63. 75 ± 3. 65) %, with an average particle size of (22. 56 ± 1. 70) µm and Zeta potential of (-41. 81±6. 59) mV. The pharmacokinetic parameters of UOMVLs and UOX were as follows, respectively: area under time-concentration curve from 0 to infinity time (AUC0-∞) (498. 83 ± 58. 85) U/L . h and (28. 49 ± 9. 95) U/L . h; time to peak concentration (Tmax) (1. 00±0. 00) h and (0. 00±0. 00) h; peak concentration (Cmax) (73. 04±6. 35) U/L and (31. 00±6. 03) U/L; elimination half-life (t1/2) (3. 49±0. 80) h and (1. 17±0. 33) h. The relative bioavailability of UOMVLs was (1 750. 90±206. 56) %. UOMVLs decreased serum uric to normal in 9 h; whereas it took 48 h for the UOX group and the model group to return to normal.

CONCLUSION

UOMVLs can prolong tmax and t1/2 and improve the relative bioavailability. UOMVLs decrease serum uric acid levels in rats with hyperuricemia more effectively than UOX.

Site-specific albumination of a therapeutic protein with multi-subunit to prolong activity in vivo

Albumin fusion/conjugation (albumination) has been an effective method to prolong in vivo half-life of therapeutic proteins. However, its broader application to proteins with complex folding pathway or multi-subunit is restricted by incorrect folding, poor expression, heterogeneity, and loss of native activity of the proteins linked to albumin. We hypothesized that the site-specific conjugation of albumin to a permissive site of a target protein will expand the utilities of albumin as a therapeutic activity extender to proteins with a complex structure. We show here the genetic incorporation of a non-natural amino acid (NNAA) followed by chemoselective albumin conjugation to prolong therapeutic activity in vivo. Urate oxidase (Uox), a therapeutic enzyme for treatment of hyperuricemia, is a homotetramer with multiple surface lysines, limiting conventional approaches for albumination. Incorporation of p-azido-l-phenylalanine into two predetermined positions of Uox allowed site-specific linkage of dibenzocyclooctyne-derivatized human serum albumin (HSA) through strain-promoted azide-alkyne cycloaddition (SPAAC). The bio-orthogonality of SPAAC resulted in the production of a chemically well-defined conjugate, Uox-HSA, with a retained enzymatic activity. Uox-HSA had a half-life of 8.8 h in mice, while wild-type Uox had a half-life of 1.3 h. The AUC increased 5.5-fold (1657 vs. 303 mU/mL x h). These results clearly demonstrated that site-specific albumination led to the prolonged enzymatic activity of Uox in vivo. Site-specific albumination enabled by NNAA incorporation and orthogonal chemistry demonstrates its promise for the development of long-acting protein therapeutics with high potency and safety.

Pegloticase, a polyethylene glycol conjugate of uricase for the potential intravenous treatment of gout

Savient Pharmaceuticals Inc (formerly Bio-Technology General Corp), under license from Duke University, is developing pegloticase, PEG conjugates of uricase (urate oxidase), for the potential treatment of gout. The in-life portion of the phase III trials have been completed.

Rasburicase represents a new tool for hyperuricemia in tumor lysis syndrome and in gout

Hyperuricemia is a feature of several pathologies and requires an appropriate and often early treatment, owing to the severe consequences that it may cause. A rapid and massive raise of uric acid, during tumor lysis syndrome (TLS), and also a lower and chronic hyperuricemia, as in gout, mainly damage the kidney. To prevent or treat these consequences, a new therapeutic option is represented by rasburicase, a recombinant form of an enzyme, urate oxidase. This enzyme converts hypoxanthine and xanthine into allantoin, a more soluble molecule, easily cleared by kidney. The several types of urate oxidase have followed each other, with progressive reduction of adverse reactions. The most important among them are allergenicity and the development of antibodies which compromise their effectiveness. Nevertheless, a limit of rasburicase's use remains its cost, which obliges to a judicious choice to prevent TLS in high risk patients with cancer and in case of allergy or impossibility to take allopurinol orally both in TLS and in gout. A large body of evidence confirms the efficacy and safety of rasburicase, even in comparison to the standard drugs used in the aforementioned pathologies.

Control of hyperuricemia in subjects with refractory gout, and induction of antibody against poly(ethylene glycol) (PEG), in a phase I trial of subcutaneous PEGylated urate oxidase

PEG-modified recombinant mammalian urate oxidase (PEG-uricase) is being developed as a treatment for patients with chronic gout who are intolerant of, or refractory to, available therapy for controlling hyperuricemia. In an open-label phase I trial, single subcutaneous injections of PEG-uricase (4 to 24 mg) were administered to 13 such subjects (11 had tophaceous gout), whose plasma uric acid concentration (pUAc) was 11.3 +/- 2.1 mg/dl (mean +/- SD). By day seven after injection of PEG-uricase, pUAc had declined by an average of 7.9 mg/dl and had normalized in 11 subjects, whose mean pUAc decreased to 2.8 +/- 2.2 mg/dl. At doses of 8, 12, and 24 mg, the mean pUAc at 21 days after injection remained no more than 6 mg/dl. In eight subjects, plasma uricase activity was still measurable at 21 days after injection (half-life 10.5 to 19.9 days). In the other five subjects, plasma uricase activity could not be detected beyond ten days after injection; this was associated with the appearance of relatively low-titer IgM and IgG antibodies against PEG-uricase. Unexpectedly, these antibodies were directed against PEG itself rather than the uricase protein. Three PEG antibody-positive subjects had injection-site reactions at 8 to 9 days after injection. Gout flares in six subjects were the only other significant adverse reactions, and PEG-uricase was otherwise well tolerated. A prolonged circulating life and the ability to normalize plasma uric acid in markedly hyperuricemic subjects suggest that PEG-uricase could be effective in depleting expanded tissue stores of uric acid in subjects with chronic or tophaceous gout. The development of anti-PEG antibodies, which may limit efficacy in some patients, is contrary to the general assumption that PEG is non-immunogenic. PEG immunogenicity deserves further investigation, because it has potential implications for other PEGylated therapeutic agents in clinical use.

Pharmacokinetics and pharmacodynamics of intravenous PEGylated recombinant mammalian urate oxidase in patients with refractory gout

OBJECTIVE

To evaluate the efficacy, immunogenicity, and tolerability of intravenous (IV) PEGylated recombinant mammalian urate oxidase (PEG-uricase) for the treatment of severe gout.

METHODS

Single infusions of PEG-uricase (at doses ranging from 0.5 mg to 12 mg) were administered to 24 patients (6 cohorts of 4 patients each) in a phase I clinical trial. Plasma uricase activity (pUox), the plasma urate concentration (pUAc), and the uric acid-to-creatinine ratio (UAc:Cr) in urine were monitored for 21 days after dosing. Adverse events and the IgG antibody response to PEG-uricase were followed up for 35 days.

RESULTS

All patients completed the trial. Maximum pUox was linearly related to the IV dose of PEG-uricase, the area under the curve (AUC) value increased linearly (up to a dose of 8 mg), and the pUox half-life was 6.4-13.8 days. After doses of 4-12 mg, the pUAc fell within 24-72 hours, from a mean +/- SD value of 11.1 +/- 0.6 mg/dl to 1.0 +/- 0.5 mg/dl; the AUC value for the pUAc was equivalent to maintaining the pUAc at 1.2-4.7 mg/dl for 21 days postinfusion. The UAc:Cr ratio in urine fell in parallel with the pUAc. IgG antibodies to PEG-uricase, mostly IgG2 and specific for PEG, developed in 9 patients, who had more rapid enzyme clearance but no allergic reactions. All adverse events were mild to moderate, with gout flares being most common.

CONCLUSION

The bioavailability, efficacy, and tolerability of IV PEG-uricase were greater than the bioavailability, efficacy, and tolerability observed in a previous phase I trial of subcutaneous PEG-uricase. Infusing 4-12 mg of PEG-uricase every 2-4 weeks should maintain the pUAc well below the therapeutic target of 6 mg/dl and greatly reduce renal uric acid excretion. This treatment could be effective in depleting expanded tissue urate stores in patients with chronic or tophaceous gout.

Pharmacology of drugs for hyperuricemia. Mechanisms, kinetics and interactions

The pharmacological profile of drugs for hyperuricemia is reviewed. These agents may reduce the amount of uric acid in blood by means of two different ways: (1) by reducing uric acid production through the inhibition of the enzyme xanthine oxidase (as allopurinol); (2) by increasing uric acid clearance through an inhibition of its renal tubular reabsorption (as probenecid), or through its metabolic conversion to a more soluble compound (as urate oxidase). Allopurinol is rapidly converted in the body to the active metabolite oxypurinol whose total body exposure may be 20-fold greater than that of the parent compound due to a much longer elimination half-life. Allopurinol undergoes several pharmacokinetic interactions with concomitant administered drugs, some of which may be potentially hazardous (especially with mercaptopurine and azathioprine). Probenecid is an uricosuric agent which undergoes extensive hepatic metabolism and whose elimination after high doses may become dose dependent. It may inhibit renal tubular secretion of several coadministered agents, including methotrexate and sulphonylureas. Rasburicase is a recombinant form of the enzyme urate oxidase which catalyzes the conversion of uric acid to the more soluble compound allantoin. Unlike allopurinol, it does not promote accumulation of hypoxanthine and xanthine in plasma, thus preventing the risk of xanthine nephropathy. Rasburicase showed no significant accumulation in children after administration of either 0.15 or 0.20 mg/kg/daily for 5 days. Rasburicase probably undergoes peptide hydrolysis and in in vitro studies was shown neither to inhibit or induce cytochrome P450 isoenzymes nor to interact with several drugs, so that no relevant interaction is expected during cotreatment in patients.

Rasburicase for the treatment and prevention of hyperuricemia

OBJECTIVE

To review the information currently available on rasburicase for treatment and prevention of hyperuricemia.

DATA SOURCES

MEDLINE (1966-August 2002) was searched for primary and review articles.

STUDY SELECTION/DATA EXTRACTION

Studies evaluating rasburicase, including abstracts and proceedings, were considered for inclusion. English-language literature was evaluated for the pharmacology, pharmacodynamics, pharmacokinetics, therapeutic use, and adverse effects of rasburicase.

DATA SYNTHESIS

Rasburicase, a recombinant urate oxidase, has been shown to be effective in lowering uric acid and preventing uric acid accumulation in patients with hematologic malignancies who had hyperuricemia or who were at high risk for developing hyperuricemia. It has been approved for pediatric use in the US.

CONCLUSIONS

In addition to allopurinol, hydration, and urinary alkalinization, rasburicase is a new alternative for the treatment and prevention of hyperuricemia in patients with hematologic malignancies. Its rapid onset of action and the ability to lower preexisting elevated uric acid levels are the advantages of rasburicase compared with allopurinol. It may allow the patient to receive chemotherapy treatment without delay.

Rasburicase

Rasburicase (recombinant urate oxidase) is a uricolytic agent which has been developed for the prevention and treatment of chemotherapy-induced hyperuricaemia at a dosage of 0.15 or 0.2 mg/kg/day in patients with haematological malignancies. Significant reductions from baseline in plasma uric acid levels were seen in 3 noncomparative and 1 randomised comparative trial of rasburicase in patients with, or at high risk of, hyperuricaemia. A multicentre, nonblind, randomised trial found that patients who received intravenous rasburicase 0.2 mg/kg/day experienced an average 2.6-fold less exposure to uric acid than those who received oral allopurinol 10 mg/kg/day. There was no evidence of renal insufficiency in 3 noncomparative trials which monitored creatinine levels to assess renal function during chemotherapy and rasburicase treatment. Rasburicase was generally well tolerated in clinical trials, with skin rashes reported in approximately equals 2% of patients. Bronchospasm, nausea and vomiting, and haemolysis occurred less frequently. In all cases the patients had also received chemotherapy prior to the adverse event.

Urate oxidase in the prophylaxis or treatment of hyperuricemia: the United States experience

Nonrecombinant urate oxidase (Uricozyme, Sanofi-Synthélabo, Inc, Paris, France) is a highly effective uricolytic agent, but its use is associated with hypersensitivity reaction manifested mainly by bronchospasm in approximately 5% of patients. Recently, several multi-institutional studies have evaluated the efficacy and safety of a recombinant urate oxidase (rasburicase). In a phase I/II study, all 131 patients with newly diagnosed acute lymphoblastic leukemia (ALL) or stage III/IV non-Hodgkin's lymphoma (NHL) experienced rapidly decreased plasma uric acid concentrations after receiving recombinant urate oxidase. Serum creatinine levels also decreased significantly. Toxicity was negligible, and none of the patients required dialysis. In a phase III trial, children with newly diagnosed ALL or stage III/IV NHL were stratified and randomized to receive recombinant urate oxidase or allopurinol. Results showed that the 27 patients who received recombinant urate oxidase had a significantly lower plasma uric acid concentration and a more rapid decline in serum creatinine level than did the 25 who took allopurinol. One patient in the recombinant urate oxidase group had hemolysis of unknown cause, and one in the allopurinol group required hemofiltration for hyperphosphatemia. To further assess the safety profile of recombinant urate oxidase, the data on 245 patients (173 children and 72 adults) who received this agent in a compassionate-use program were reviewed retrospectively. The drug produced dramatic decreases in uric acid concentrations in all patients. Nine patients (four children and five adults) had mild adverse reactions that were drug-related or of unknown etiology. These data suggest that recombinant urate oxidase is safe and effective in the prophylaxis and treatment of hyperuricemia associated with malignancy or chemotherapy.

Therapeutic proteins: a comparison of chemical and biological properties of uricase conjugated to linear or branched poly(ethylene glycol) and poly(N-acryloylmorpholine)

Uricase from Bacillus fastidiosus (UC) was covalently linked to linear PEG (PEG-1) (Mw 5 kDa), branched PEG (PEG-2) (Mw 10 kDa) and to poly(N-acryloylmorpholine) (PAcM) (Mw 6 kDa). The conjugation of UC with linear PEG and PAcM was accompanied by complete loss of enzymatic activity but, if uric acid as site protecting agent was included in the reaction mixture, the conjugate protein retained enzymatic activity. On the other hand, the modification with PEG-2 gave a conjugate that also maintained enzymatic activity in the absence of any active site protection. This behaviour must be related to hindrance of the branched polymer in reaching the enzyme active site. The UC conjugates exhibited increased resistance to proteolytic digestion while minor variations in the inhibitory constant, optimal pH, heat stability, affinity for substrate, were observed. Pharmacokinetic investigations in mice demonstrated increased residence time in blood for all the conjugates as compared with native uricase. Uricase conjugated with linear PEG was longer lasting in blood UC derivative, followed by branched PEG and the PAcM conjugates. Unconjugated uricase was rapidly removed from circulation. All these data are in favour of the use of the less known amphiphilic polymer PAcM as an alternative to PEGs in modification of enzymes devised for therapeutic applications.

Biopharmaceutical properties of uricase conjugated to neutral and amphiphilic polymers

A comparative pharmacokinetic and biodistribution investigation of polymer-protein conjugates prepared with various amphiphilic polymers was carried out using uricase as a model. Four polymer-uricase derivatives have been obtained by covalent binding of a similar number of polymer chains of (a) linear poly(ethylene glycol) (Mw 5000 Da); (b) branched poly(ethylene glycol) (Mw 10 000 Da); (c) poly(N-vinylpyrrolidone) (Mw 6000 Da); (d) poly(N-acryloilmorpholine) (Mw 6000 Da). By intravenous administration to Balb/c mice, the conjugates displayed different pharmacokinetic and organ distribution behaviors. (1) The unmodified enzyme and the poly(N-vinylpyrrolidone) conjugate were the enzyme forms with the shortest and the longest permanence in blood respectively (mean residence time 45 and 4378 min). (2) Native uricase was found to localize soon after administration significantly in heart, lungs, and liver from where it was also rapidly cleared. (3) The poly(N-acryloilmorpholine) derivative showed the highest concentration levels in liver (up to 25.5% of the dose) and considerable accumulation took also place in the other considered organs. (4) Poly(N-vinylpyrrolidone)-uricase displayed a relevant tropism for liver but low uptake indexes were found for the other organs. (5) The branched poly(ethylene glycol) derivative accumulated preferentially in liver and spleen. (6) The linear poly(ethylene glycol) conjugate was, among the various uricase forms, the species with the lowest distribution levels in all the examined organs. (7) Finally, all the enzyme forms slowly disposed in kidneys with higher levels for the poly(N-acryloilmorpholine) derivative (15% after 2880 min) and unmodified uricase (14% after 1440 min).

Development of a two-site immunoassay of recombinant urate oxidase (SR 29142) and its use for determination of pharmacokinetic parameters in rats and baboons

Two monoclonal antibodies (Mabs), 12C7 and 11G11, both directed against recombinant urate oxidase (SR 29142), were selected for their epitope specificity to develop a two-site immunoassay of urate oxidase in plasma. A quantitative recovery of urate oxidase in plasma was obtained at all the concentrations tested, and the limit of quantification was found to be 0.5 ng/mL. Intra-and interassay coefficients of variation ranged from 1.2 to 6.7% and from 3.5 to 10.8%, respectively. The specificity of the two antibodies was studied in Western-blot experiments. This assay was used successfully to determine urate oxidase pharmacokinetic parameters after intravenous injection in rats and baboons. In these two species, urate oxidase pharmacokinetics was characterized by a low clearance and a low volume of distribution without gender difference.

Tissue distribution of 111In-labeled uricase conjugated with charged dextrans and polyethylene glycol

Uricase (UC) was conjugated with dextran, cationic diethylaminoethyl-dextran (DEAED), and anionic carboxymethyl-dextran (CMD) giving a molecular weight of 10000 by the periodate oxidation method. Their disposition characteristics were studied after intravenous injection (i.v.) in mice. Disposition of the conjugate with activated polyethylene glycol (PEG2) with a similar molecular weight was also studied for comparison. Tissue distribution of the 111In-labeled UC in these conjugates was evaluated by a tissue uptake clearance index calculated in terms of clearance. After i.v. injection, 111In-UC was slowly eliminated from the circulation and gradually accumulated in the liver, spleen, and kidney. Conjugation with neutral dextran slightly enhanced the uptake of 111In-UC by the liver and spleen, while PEG2 conjugation decreased the tissue uptake and resulted in extremely long plasma retention. On the other hand, DEAED and CMD conjugation resulted in significant enhancement and reduction of hepatic uptake, respectively. These results demonstrated that the pharmacokinetic behaviour of UC can be widely controlled by chemical modification with macromolecules having adequate physiochemical properties.

Biochemical and biopharmaceutical properties of macromolecular conjugates of uricase with dextran and polyethylene glycol

Uricase (UC) was conjugated with dextran and polyethylene glycol and their biochemical and biopharmaceutical properties were studied. UC-dextran conjugates (UC-D) synthesized by four methods, periodate oxidation, cyanogen bromide, carbodiimide and cyanuric chloride largely retained the UC enzymatic activity depending on the extent to which they modified amino groups. The periodate oxidation method seemed best because it gave a conjugate with high yield and satisfactory activity retention. The conjugate of UC with activated polyethylene glycol (UC-PEG2) was also obtained with high yield but the remaining activity was somewhat lower than those of dextran conjugates at the same modification extent. UC-D and UC-PEG2 showed sustained enzymatic activity in plasma after intravenous injection to rats. The advantage of chemical modification of proteins, especially with dextran, by the periodate oxidation method for preparation of a protein-delivery system was thus suggested.