Rational design of a potent, long-lasting form of interferon: a 40 kDa branched polyethylene glycol-conjugated interferon alpha-2a for the treatment of hepatitis C

Pharmacokinetic consequences of pegylation

Pegylation, generally described as the molecular attachment of polyethylene glycols (PEGs) with different molecular weights to active drug molecules or surface treatment of drug-bearing particles with PEGs, is one of the most promising and extensively studied strategies with the goal of improving the pharmacokinetic behavior of the therapeutic drugs. A variety of PEGs, both linear and branched, with different molecular weights have been exploited successfully for use in this procedure in the form of reactive PEG species. Both reversible and irreversible PEG-drug conjugates have been prepared with relative advantages/disadvantages. The main pharmacokinetic outcomes of pegylation are summarized as changes occurring in overall circulation life-span, tissue distribution pattern, and elimination pathway of the parent drug/particle. Based on these favorable pharmacokinetic consequences leading to desired pharmacodynamic outcomes, a variety of proteins/peptides as well as small molecule drugs have been pegylated and evaluated successfully. Also a number of corresponding products have been approved by the U.S. FDA for specific clinical indications and some others are underway. In this article, the chemistry, rationale, strategies, pharmacokinetic outcomes, and therapeutic possibilities of pegylated drugs are reviewed with pharmacokinetic aspects presented with more details.

Pegylated protein encapsulated multivesicular liposomes: a novel approach for sustained release of interferon alpha

Hepatitis C viral chemotherapy suffers from a relatively short half-life of the interferon alpha-2a (IFN alpha). To address this issue, we investigated the effects of polyethylene glycol modification and their subsequent encapsulation in multivesicular liposomes (MVLs), on the release properties of IFN alpha. In the present study, interferon-alpha was conjugated with methoxy-polyethylene glycol (mPEG, MW 5000). Prepared IFN alpha-mPEG5000 conjugate (IFN alpha-mPEG5000) was purified with size exclusion chromatography. The relative in vitro anti-viral activity of pegylated interferon alpha-2a was found to 87.9% of the unmodified IFN alpha. Pegylated IFN alpha encapsulated multivesicular liposomes were prepared by double emulsification technique followed by evaporation of organic solvents from chloroform ether spherules suspended in water. Prepared MVLs were then characterized for shape, size, vesicle count, encapsulation efficiency, and in vitro release rate. In process stability studies of pegylated IFN alpha protein exhibited better stability when exposed to chloroform: diethyl ether (1:1 ratio) mixture as well as variable vortexing time as compared to native IFN alpha. Relatively high percentage of encapsulation of protein ( approximately 75%) was achieved. In vitro release profile of pegylated IFN alpha-mPEG5000 containing MVLs in the PBS showed lower initial burst release with sustained and incomplete release over a period of 1 week. In contrast, native IFN alpha entrapped MVLs were observed as higher initial burst release, i.e., nearly 35% followed by almost complete release. The results confirmed the possibility of multivesicular liposomes as a long-acting or sustained-release delivery system using a combination of pegylation and encapsulation technique for controlled delivery of interferon alpha.

High-yield production of biologically active mono-PEGylated salmon calcitonin by site-specific PEGylation

The purpose of this study was to develop and optimize a unique one-pot, two-step site-specific PEGylation method suitable for the high-yield production of mono-PEGylated (Lys(18)) salmon calcitonin (Lys(18)-PEG-sCT), which was previously demonstrated to have superior pharmaceutical properties to other conjugates. For the site-specific PEGylation, this study used the sCT derivative (FMOC(1,11)-sCT), which was FMOC protected at Cys(1)- and Lys(11)-amines among three PEGylation sites including Lys(18)-amine. This PEGylation process was achieved by the consecutive one-pot, two-step reaction: (i) the PEG conjugation to FMOC(1,11)-sCT; and (ii) the subsequent deprotection of FMOC group from the PEGylated FMOC(1,11)-sCT. The optimized reaction resulted in the high production yield of Lys(18)-PEG-sCT (about 86%), compared with that from conventional non-specific PEGylation (about 18%). The prepared Lys(18)-PEG-sCT conjugate showed improved biological stability without the loss in the in vitro and in vivo biological activity by PEGylation. Consequently, this site-specific PEGylation using an FMOC protection/deprotection strategy showed great usefulness in the production of the most promising Lys(18)-PEG-sCT conjugate with a high yield.

Engineering of a VPAC2 Receptor Peptide Agonist To Impart Dipeptidyl Peptidase IV Stability and Enhance in Vivo Glucose Disposal

VPAC2P-PEG is a VPAC2 receptor agonist peptide that acts as a glucose-dependent insulin secretagogue. Proteolysis by DPPIV may contribute to the in vivo clearance of VPAC2P-PEG. Here, the N-terminus of VPAC2P-PEG is modified by N-terminal acetylation to impart DPPIV resistance. The acetylated peptide, Ac-VPAC2P-PEG, is a selective and potent VPAC2 agonist, resistant to DPPIV proteolysis, and exhibits substantially improved half-life and glucose disposal in rodents. Ac-VPAC2P-PEG has therapeutic potential for diabetes management.

Safety, efficacy and pharmacokinetics of peginterferon alpha2a (40 kd) in children with chronic hepatitis C

Chronic hepatitis C virus (HCV) infection in children is a problem affecting thousands of children worldwide. Although standard interferon (INF) has better efficacy in pediatric patients than in adults, results in children with genotype 1 are poor; response rates to combination treatment with standard INF and ribavirin are better but the treatment requires thrice-weekly injections. The improved antiviral efficacy of weekly pegylated interferons relative to standard interferons in adults with chronic HCV infection suggests that pegylated interferons may also improve antiviral efficacy in children. We therefore investigated the pharmacokinetics, efficacy and safety of peginterferon alpha2a (pegINF-alpha2a) (40 kd) in 14 children ages 2 to 8 years with chronic hepatitis C (13 genotype 1, 1 non-1 genotype). Drug dose was calculated from each patient's body surface area (BSA) according to the formula BSA (m2)/(1.73 m2) x 180 microg, and patients were administered once-weekly subcutaneous injections for 48 weeks. Viral load and pharmacokinetic parameters were determined from blood drawn throughout the study and during follow-up. At week 24, the mean trough concentration was about 20% below values obtained from adults treated with pegINF-alpha2a, and the area under the curve from 0 to 168 hours was about 20% above adult values, suggesting that drug doses calculated from BSA achieved therapeutically adequate concentrations. Six of 14 patients (43%), all infected with genotype 1, achieved a sustained virological response. Adverse events were those commonly associated with INF-based treatment, and none was deemed serious. In conclusion, our findings provide a basis for larger studies evaluating the efficacy and safety of pegINF-alpha2a as monotherapy as well as in combination with ribavirin in pediatric patients with chronic hepatitis C.

Mapping the antigenic determinants and reducing the immunogenicity of trichosanthin by site-directed mutagenesis

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) possessing multiple pharmacological properties. One of its interesting properties is to inhibit human immunodeficiency virus (HIV) replication but its strong immunogenicity has limited the repeated clinical administration. To map the antigenic determinants and reduce the immunogenicity of TCS, two potential antigenic sites (YFF81-83 and KR173-174) were identified by computer modeling, and then three TCS mutants namely TCS(YFF81-83ACS), TCS(KR173-174CG), and TCS(YFF-KR) were constructed by site-directed mutagenesis. The RI activity and DNase-like activity of the three constructed TCS mutants were similar to natural TCS but with much lower immunogenicity. Results suggested that the two selected sites are all located at or near the antigenic determinants of TCS. In toxicity studies, the LD(50) of the three TCS mutants was not different from natural TCS. These findings would be useful in designing a better therapeutic agent for AIDS.

PEGylation and multimerization of the anti-p185HER-2 single chain Fv fragment 4D5: effects on tumor targeting

A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity, affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating, disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.

Viral kinetics in the treatment of chronic hepatitis C

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and hepatic fibrosis, and chronic infection can frequently progress to cirrhosis, end-stage liver disease and hepatocellular carcinoma. Treatment with pegylated interferons (INFs) plus ribavirin has been shown to be more effective than pegylated INFs alone or standard INFs with or without ribavirin. The early response of HCV to treatment with peg-INF has been used to predict treatment outcomes in infected patients, emphasizing the importance of viral kinetics and genotyping in their treatment. Mathematic modelling of viral dynamics has shown the importance of optimal doses of drug, with early virologic response at week 12 predictive of sustained virologic response. Maintaining INF concentration above a therapeutically effective level is necessary to prevent viral rebound and subsequent treatment failure. Once-weekly dosing with peg-INF-alpha2a, which has a longer half-life than other forms of INF, plus daily dosing with ribavirin, has been shown to be effective in reducing viral load.

A randomised trial to compare the pharmacokinetic, pharmacodynamic, and antiviral effects of peginterferon alfa-2b and peginterferon alfa-2a in patients with chronic hepatitis C (COMPARE)

BACKGROUND/AIMS

To compare the pharmacokinetics, pharmacodynamics, and antiviral activity of peginterferon alfa-2b and peginterferon alfa-2a in patients with chronic hepatitis C virus genotype 1.

METHODS

Thirty-six patients were randomised to peginterferon alfa-2b (1.5 microg/kg/week) or peginterferon alfa-2a (180 microg/week) for 4 weeks, then in combination with ribavirin (13 mg/kg/day) for a further 4 weeks. The pharmacokinetic profile of both peginterferons, mRNA expression of a selected group of interferon-induced gene transcripts, and serum HCV-RNA levels were assessed.

RESULTS

Patients receiving peginterferon alfa-2b had significantly greater up-regulation of interferon-alfa response genes compared with those receiving peginterferon alfa-2a. Correspondingly, patients treated with peginterferon alfa-2b also had a significantly greater log10 maximum and log10 time-weighted average decrease in serum HCV-RNA. A greater proportion of peginterferon alfa-2b patients achieved a > or = 2.0 log10 reduction in serum HCV-RNA levels by week 8 (72% vs 44% of peginterferon alfa-2a patients, P = 0.09). There was an approximately 16-fold greater exposure to peginterferon in the serum of patients treated with peginterferon alfa-2a.

CONCLUSIONS

These findings suggest that the biological activity, measured by early interferon-induced gene transcripts and early antiviral responsiveness, may have been greater in patients treated with peginterferon alfa-2b despite their lower exposure to the drug compared with patients treated with peginterferon alfa-2a.

Strategies towards a longer acting factor VIII

The reduced mortality, improved joint outcomes and enhanced quality of life, which have been witnessed in the developed world for patients with haemophilia, have been an outstanding achievement. Advancements in biotechnology contributed significantly through the development of improved pathogen screening, viral inactivation techniques and the development of recombinant clotting factors. These were partnered with enhanced delivery of care through comprehensive haemophilia centres, adoption of home therapy and most recently effective prophylaxis. This came at great costs to governments, medical insurers and patients' families. In addition, barriers persist limiting the adoption and adherence of effective prophylactic therapy. Biotechnology has been successful at overcoming similar barriers in other disease states. Long-acting biological therapeutics are an incremental advance towards overcoming some of these barriers. Strategies that have been successful for other therapeutic proteins are now being applied to factor VIII (FVIII) and include modifications such as the addition of polyethylene glycol (PEG) polymers and polysialic acids and alternative formulation with PEG-modified liposomes. In addition, insight into FVIII structure and function has allowed targeted modifications of the protein to increase the duration of its cofactor activity and reduce its clearance in vivo. The potential advantages and disadvantages of these approaches will be discussed.

Site-specific PEGylation of native disulfide bonds in therapeutic proteins

Native disulfide bonds in therapeutic proteins are crucial for tertiary structure and biological activity and are therefore considered unsuitable for chemical modification. We show that native disulfides in human interferon alpha-2b and in a fragment of an antibody to CD4(+) can be modified by site-specific bisalkylation of the two cysteine sulfur atoms to form a three-carbon PEGylated bridge. The yield of PEGylated protein is high, and tertiary structure and biological activity are retained.

Design of homogeneous, monopegylated erythropoietin analogs with preserved in vitro bioactivity

OBJECTIVE

Erythropoietin (Epo) bioactivity is significantly reduced by modification of lysine residues with amine-reactive reagents, which are the most commonly used reagents for attaching polyethylene glycols (PEGs) to proteins to improve protein half-life in vivo. The aims of this study were to determine whether Epo bioactivity can be preserved by targeting attachment of maleimide-PEGs to engineered cysteine analogs of Epo, and to determine whether the pegylated Epo cysteine analogs have improved pharmacokinetic properties in vivo.

MATERIALS AND METHODS

Thirty-four Epo cysteine analogs were constructed by site-directed mutagenesis and expressed as secreted proteins in baculovirus-infected insect cells. Following purification, monopegylated derivatives of 12 cysteine analogs were prepared using 20-kDa maleimide-PEGs. In vitro biological activities of the proteins were measured in an Epo-dependent cell proliferation assay. Plasma levels of insect cell-expressed wild-type Epo (BV Epo) and a pegylated Epo cysteine analog were quantitated by ELISA following intravenous administration to rats.

RESULTS

Biological activities of 17 purified Epo cysteine analogs and 10 purified pegylated Epo cysteine analogs were comparable to that of BV Epo in the in vitro bioassay. The only pegylated cysteine analogs that displayed consistently reduced in vitro bioactivities were substitutions for lysine residues, PEG-K45C and PEG-K154C. The pegylated Epo cysteine analog had a slower initial distribution phase and a longer terminal half-life than BV Epo in rats, but the majority of both proteins were cleared rapidly from the circulation.

CONCLUSIONS

Targeted attachment of maleimide-PEGs to engineered Epo cysteine analogs permits rational design of monopegylated Epo analogs with minimal loss of in vitro biological activity. Insect cell-expressed Epo proteins are cleared rapidly from the circulation in rats, possibly due to improper glycosylation. Site-specific pegylation appears to improve the pharmacokinetic properties of Epo.

Impact of obesity on treatment of chronic hepatitis C

Obesity and the metabolic syndrome have hepatic manifestations, including steatosis and progression of fibrosis. In individuals with chronic hepatitis C, obesity is associated with inflammation, insulin resistance, steatosis, progression of fibrosis, and nonresponse to treatment with interferon or peginterferon alpha and ribavirin. Patients with both hepatitis C and obesity-related nonalcoholic fatty liver disease are at greater risk for more advanced liver disease. We review the mechanisms by which obesity may be associated with decreased efficacy of interferon-based therapies in individuals with chronic hepatitis C and the therapeutic strategies that may increase the effectiveness of these therapies in obese individuals.

Extension Arm Facilitated PEGylation of Hemoglobin: Correlation of the Properties with the Extent of PEGylation

Human hemoglobin (Hb) conjugated with six copies of PEG-5K is nonhypertensive. The hexaPEGylated Hb exhibits molecular size homogeneity in spite of the chemical heterogeneity with respect to the sites of conjugation (Manjula et al., 2005). In the present study, Hb conjugated with an average of 4, 6, 8 and 10 copies of PEG-5K chains have been generated using the extension arm facilitated PEGylation protocol. Except for the tetraPEGylated Hb, all the other products exhibit molecular size homogeneity. The molecular, colligative and functional properties of PEG-Hb conjugates have been correlated with the extent of PEGylation. The results imply that six copies of PEG-5K chains are accommodated on Hb without significant crowding on the molecular surface. As more copies of PEG-5K chains are conjugated to form octa and deca PEGylated Hb, the PEG-chains conjugated appear to undergo transition from a mushroom (compact) to a brush-like conformation (extended conformation) with a concomitant decrease in the propensity of the molecule to transition from oxy to deoxy conformation in the presence of allosteric effectors. The viscosity and the colloidal osmotic pressure of Hb increase with the number of the PEG-chains conjugated in an exponential fashion. The composition of the PEGylated Hb generated appears to be controlled by (i) high reactivity of thiol groups of the extension arms on Hb with maleimide-PEG, (ii) increase in the viscosity of the reaction mixture as the level of PEGylation increases and (iii) increased resistance induced by the PEG-shell of PEGylated Hb to accommodate more PEG-chains as the level of PEGylation increases. Potential implications of extent of PEGylation on the oxygen delivery by PEG-Hb conjugate in vivo have been discussed.

Future Therapies for Hepatitis C

Although pegylated interferon-α plus ribavirin has become the standard for treating chronic hepatitis C virus infection, a substantial number of patients do not tolerate therapy and require dose reduction or discontinuation, or do not respond to this combination therapy. Thus, new therapeutic options are needed. An increased knowledge of the hepatitis C virus and an understanding of its replication cycle, as well as advances in biotechnology, have stimulated the development of numerous new antiviral treatments for patients with hepatitis C virus infection. This review focuses on four classes of new agents: new interferons, ribavirin-like molecules, specific small-molecule hepatitis C virus inhibitors and new immune therapies, with particular emphasis on medications in the later stages of development.

Peginterferon α-2b in the treatment of hepatitis C

Hepatitis C virus (HCV) is a leading public health problem affecting as many as 4 million Americans. Chronic HCV infection can progress to hepatocellular carcinoma, cirrhosis and death. Interferon-α-based therapies, initially as monotherapy and later in combination with ribavirin, have proven effective in the treatment of HCV infection, but standard interferon is hampered pharmacokinetically by a short half life. With the advent of the pegylated-interferons, administered in combination with oral ribavirin, the chances for HCV eradication have improved further. Peginterferon α-2b, the formuation discussed in this review, provides greater antiviral pressure while maintaining a tolerable side-effect profile with more convenient once-weekly dosing. Clinical trials have focused on treatment-naïve patients as well as on many different HCV subpopulations, including difficult-to-treat patients such as previous interferon therapy failures and patients with HCV cirrhosis.

48 weeks pegylated interferon alpha-2a is superior to 24 weeks of pegylated interferon alpha-2b in achieving hepatitis B e antigen seroconversion in chronic hepatitis B infection

BACKGROUND/AIM

Although 48-week therapy with pegylated-interferons has been shown to be effective for the treatment of chronic hepatitis B virus infection, the efficacy of a shorter duration of therapy with pegylated interferons is unknown.

METHOD

We reviewed 53 hepatitis B e antigen positive Chinese patients treated with 48 weeks of pegylated interferon alpha-2a or 24 weeks of pegylated interferon alpha-2b. Sustained virological response was defined as hepatitis B e antigen seroconversion and hepatitis B virus DNA <10(5) copies/mL at week 72.

RESULTS

Twenty-nine patients were treated with 48 weeks of pegylated-interferon-alpha-2a and 24 patients with 24 weeks of pegylated-interferon-alpha-2b. At the end-of-therapy, hepatitis B e antigen seroconversion and hepatitis B virus DNA <10(5) copies/mL were similar between the two groups of patients [9/29 (31.0%) vs. 2/24 (8.3%), respectively, P = 0.09]. At week 72, 10 of the 29 patients (34.5%) treated with 48 weeks of pegylated-interferon-alpha-2a compared with two of the 24 patients (8.3%) treated with 24 weeks of pegylated-interferon-alpha-2b had sustained virological response (P = 0.04). By logistic analysis, 48 weeks of pegylated-interferon-alpha-2a was independently associated with sustained virological response (P = 0.04 adjusted hazards-ratio 9.37).

CONCLUSION

Further studies are required to determine the optimal duration of therapy with pegylated interferons in chronic hepatitis B.

Enhancement of the therapeutic index: from nonmyeloablative and myeloablative toward pretargeted radioimmunotherapy for metastatic prostate cancer

PURPOSE

New strategies that target selected molecular characteristics and result in an effective therapeutic index are needed for metastatic, hormone-refractory prostate cancer.

EXPERIMENTAL DESIGN

A series of preclinical and clinical studies were designed to increase the therapeutic index of targeted radiation therapy for prostate cancer. (111)In/90Y-monoclonal antibody (mAb), m170, which targets aberrant sugars on abnormal MUC1, was evaluated in androgen-independent prostate cancer patients to determine the maximum tolerated dose and efficacy of nonmyeloablative radioimmunotherapy and myeloablative combined modality radioimmunotherapy with paclitaxel. To enhance the tumor to liver therapeutic index, a cathepsin degradable mAb linkage ((111)In/90Y-peptide-m170) was used in the myeloablative combined modality radioimmunotherapy protocol. For tumor to marrow therapeutic index improvement in future studies, anti-MUC1 scFvs modules were developed for pretargeted radioimmunotherapy. Anti-MUC1 and anti-DOTA scFvs were conjugated to polyethylene glycol scaffolds tested on DU145 prostate cancer cells and prostate tissue arrays, along with mAbs against MUC1 epitopes.

RESULTS

The nonmyeloablative maximum tolerated dose of 90Y-m170 was 0.74 GBq/m2 for patients with not more than 10% axial skeleton involvement. Metastatic prostate cancer was targeted in all 17 patients; mean radiation dose was 10.5 Gy/GBq and pain response occurred in 7 of 13 patients reporting pain. Myeloablative combined modality radioimmunotherapy with 0.4 GBq/m2 of 90Y-peptide-m170 and paclitaxel showed therapeutic effects in 4 of 6 patients and 30% less radiation to the liver per unit of activity. Neutropenia was dose limiting without marrow support and patient eligibility was a major limitation to dose escalation. Hypoglycosylated MUC1 epitopes were shown to be abundant in prostate cancer and to increase with disease grade. Anti-MUC1 scFvs binding to prostate cancer tissue and live cells were developed into di-scFv binding modules.

CONCLUSIONS

The therapeutic index enhancement for prostate radioimmunotherapy was achieved in clinical studies by the addition of cathepsin cleavable linkers to 90Y-conjugated mAbs and the use of paclitaxel. However, the need for marrow support in myeloablative combined modality radioimmunotherapy restricted eligible patients. Therefore, modular pretargeted radioimmunotherapy, aiming at improving the tumor to marrow therapeutic index, is being developed.

Long-acting interferon-alpha 2a modified with a trimer-structured polyethylene glycol: preparation, in vitro bioactivity, in vivo stability and pharmacokinetics

The proper selection of size and shape for polyethylene glycol (PEG) is one of the most important points in PEGylation technology. Therefore, PEGs of various sizes and shapes have been widely developed to endow specific properties. In this study, a unique, trimer-structured, 43 kDa PEG was conjugated to interferon-alpha 2a (IFN) by forming an amide bond to improve the pharmacokinetic properties and minimize the loss of IFN bioactivity. Mono-PEGylated IFN (PEG(3)-IFN) prepared by utilizing this unique PEG was purified and characterized by cation-exchange chromatography and MALDI-TOF mass spectrometry. The in vitro bioactivity, in vivo stability, and pharmacokinetics of PEG(3)-IFN were examined and compared to those of native IFN. PEG(3)-IFN exhibited comparable in vitro bioactivities to native IFN and an excellent stability of the conjugation linkage in rat serum and various organs following subcutaneous injection. Furthermore, it showed slow absorption and markedly reduced clearance in rats, thereby increasing the biological half-life by about 40-fold compared to that of native IFN. This is the first report on the application of unique, trimer-structured PEG to bioactive proteins. The results suggest that unique, trimer-structured 43 kDa PEG can provide some advantages to improve the pharmacokinetic properties and to maintain the bioactivity of therapeutic proteins in clinical use.

Patient education and treatment strategies implemented at a pharmacist-managed hepatitis C virus clinic

Hepatitis C virus (HCV) infection is a major public health concern. Approximately 4 million people in the United States have been infected with the virus, and up to 85% of them will develop chronic infection. Chronic HCV infection has often been associated with progression of hepatic fibrosis and, in some cases, cirrhosis and end-stage liver disease. The standard of care is combination therapy with pegylated interferon (peginterferon) alfa plus ribavirin. More than 50% of patients with HCV treated with combination therapy achieve a sustained viral response, defined as undetectable hepatitis C viral RNA 6 months after the end of therapy. Effective patient education and drug therapy management are critical in enabling patients to adhere to the treatment regimen, which is either 24 or 48 weeks long, depending on the virus strain. The drug regimen is associated with several possible adverse events as well as weekly subcutaneous administration (of peginterferon alfa). Frequent monitoring of patients and, often, adjustments in the dosage of one or both components of the therapy are necessary during the treatment course. Strategies used by clinical pharmacists at an HCV clinic are discussed that can facilitate a successful treatment outcome for patients with HCV treated with combination therapy, while enabling them to maintain a reasonable quality of life.

Influence of the chemistry of conjugation of poly(ethylene glycol) to Hb on the oxygen-binding and solution properties of the PEG-Hb conjugate

Our recent studies on PEG-Hb [poly(ethylene glycol)-Hb] conjugates generated by thiolation-mediated maleimide-chemistry based PEGylation demonstrated that the vasoactivity of the PEG-Hb conjugates is a function of the configuration of the PEG chains on the surface of the protein and is independent of the PEG/protein-mass ratio [Manjula, A. G. Tsai, Intaglietta, H.-C. Tsai, Ho, Smith, Perumalsamy, Kanika, Friedman and Acharya (2005) Protein J. 24, 133-146]. A Hb conjugated with six PEG5k chains (SP-PEG5k)6-Hb, was vasoinactive. In an attempt to understand whether the chemistry of conjugation of PEG to Hb has any influence on the modulation of its functional and solution properties, we have now generated a new hexaPEGylated-Hb, (propyl-PEG5k)6-Hb, by reductive alkylation chemistry. CD (circular dichroism) spectral measurements indicated that the overall secondary structure of Hb is not adversely influenced upon PEGylation. (Propyl-PEG5k)6-Hb exhibited an increased O2 affinity with decreased co-operativity and decreased modulation by allosteric effectors comparable with that of (SP-PEG5k)6-Hb, although its Cys-93(b) is not derivatized as in the latter. On a molecular mass basis, PEG linked to Hb by reductive alkylation increased its COP (colloidal osmotic pressure) more efficiently than when linked by thiolation-mediated maleimide-chemistry. These results demonstrate that the functional properties of PEG-Hb conjugates may be a direct consequence of surface decoration of Hb with PEG, but are independent of the site (pattern) and/or the chemistry of PEGylation. However the solution properties of PEGylated Hb are influenced by the site (pattern) and/or the chemistry of PEGylation and the presence or absence of an 'extension arm' between the conjugating site of Hb and the PEG chain.

PEG conjugation moderately protects adeno-associated viral vectors against antibody neutralization

AAV gene therapy vectors have significant clinical promise, but serum neutralization poses a challenge that must be overcome. We have examined the potential of conjugating the AAV surface with activated polyethylene glycol chains to protect the vector from neutralizing antibodies. Two key parameters were investigated: the polymer chain size and the PEG:lysine conjugation ratio. Transduction data revealed that the vector is fully infectious until a critical PEG conjugation reaction ratio was exceeded, and this critical level was found to vary with polymer chain size. At this key conjugation ratio, however, particles were moderately protected from serum neutralization, 2.3-fold over unmodified vector, demonstrating that there is a small window of PEGylation for which particles are still fully infective and benefit from antibody protection. TEM results and structural analysis indicate that the drop of infectivity as the PEG concentration is increased beyond the critical conjugation ratio may be due to a combination of steric interference with viral regions necessary for infection as well as reaction at important lysine residues. However, this first study analyzing the potential of PEG to protect AAV from serum neutralization shows that the approach has promise, which can be further enhanced if the locations of PEG attachment can be more finely controlled.

Site-specific polymer modification of therapeutic proteins

Recent advances in chemoselective ligation technology have made possible the modification of proteins with polymers in a site-specific and controlled manner. These approaches rely on the incorporation of chemoselective anchors into the protein backbone by either chemical or recombinant means, and subsequent modification with a polymer carrying a complementary linker. As a result, the assembly process and the covalent structure of the resulting protein-polymer conjugate are completely controlled, enabling the rational optimization of drug properties, in particular efficacy and pharmacokinetic properties. Application of chemoselective ligation technologies to cytokines and chemokines has led to the generation of new lead proteins for use as erythropoietic agents and HIV fusion inhibitors.

Contribution of site-specific PEGylation to the dipeptidyl peptidase IV stability of glucose-dependent insulinotropic polypeptide

The effects of PEGylation of glucose-dependent insulinotropic polypeptide (GIP) on potency and dipeptidyl peptidase IV (DPPIV) stability are reported. N-terminal modification of GIP(1-30) with 40 kDa polyethylene glycol (PEG) abrogates functional activity. In contrast, C-terminal PEGylation of GIP(1-30) maintains full agonism and reasonable potency at the GIP receptor and confers a high level of DPPIV resistance. Moreover, the dual modification of N-terminal palmitoylation and C-terminal PEGylation results in a full agonist of comparable potency to native GIP that is stable to DPPIV cleavage. The results provide the basis for the development of long acting, PEGylated GIP, GIP variants, or GIP-based hybrid peptide therapeutics.

Protein PEGylation decreases observed target association rates via a dual blocking mechanism

PEGylation is an attractive strategy to enhance the therapeutic efficacy of proteins with a short serum half-life. It can be used to extend the serum persistence and to reduce the immunogenicity of proteins. However, PEGylation can also lead to a decrease in the functional activity of the molecule to which it is applied. We constructed site-specifically PEGylated variants of anti-p185(HER-2) antibody fragments in the format of a monovalent single-chain variable fragment and a divalent miniantibody and characterized the antigen binding properties in detail. Mass-transport limited BIAcore measurements and binding assays on HER-2-overexpressing cells demonstrated that the immunoreactivity of the antibody fragments is fully maintained after PEGylation. Nevertheless, we found that the attachment of a 20-kDa polyethylene glycol (PEG) moiety led to a reduction in apparent affinity of approximately 5-fold, although in both formats, the attachment site was most distal to the antigen binding regions. This decrease in affinity was observed in kinetic BIAcore measurements as well as in equilibrium binding assays on whole cells. By analysis of the binding kinetics, we could pinpoint this reduction exclusively to slower apparent on rates. Through both experimental and computational analyses, we demonstrate that these reduced on-rates do not arise from diffusion limitations. We show that a mathematical model accounting for both intramolecular and intermolecular blocking mechanisms of the PEG moiety can robustly explain the observed binding kinetics. The results suggest that PEGylation can significantly alter the binding-competent fraction of both ligands and receptors and may help to explain some of the beneficial effects of PEGylation in vivo.

PEGylation, successful approach to drug delivery

PEGylation defines the modification of a protein, peptide or non-peptide molecule by the linking of one or more polyethylene glycol (PEG) chains. This polymer is non-toxic, non-immunogenic, non-antigenic, highly soluble in water and FDA approved. The PEG-drug conjugates have several advantages: a prolonged residence in body, a decreased degradation by metabolic enzymes and a reduction or elimination of protein immunogenicity. Thanks to these favorable properties, PEGylation now plays an important role in drug delivery, enhancing the potentials of peptides and proteins as therapeutic agents.

Phase I Evaluation of a 40-kDa Branched-Chain Long-Acting Pegylated IFN-α-2a With and Without Cytarabine in Patients with Chronic Myelogenous Leukemia

PURPOSE

Pegasys (PEG-IFN) is a modified form of recombinant human IFN-alpha-2a in which IFN-alpha is attached to a branched methoxypolyethylene glycol (PEG) moiety of large molecular weight (40 kDa). Such molecular modification results in sustained absorption after s.c. drug administration and a prolonged half-life. A phase I study of PEG-IFN was conducted in patients with chronic myelogenous leukemia (CML) who were previously treated with IFN-alpha to evaluate the effect of sustained exposure to IFN on patients with CML.

EXPERIMENTAL DESIGN

Twenty-seven patients with long-term or IFN-refractory CML were enrolled in cohorts of three or six patients. PEG-IFN was given once weekly by s.c. injections starting at a dose of 270 microg/wk to a maximum dose of 630 microg/wk. Sixteen additional patients were treated with escalating doses of PEG-IFN ranging from 450 to 540 microg/wk in combination with two different schedules of low-dose cytarabine (1-beta-D-arabinofuranosylcytosine, ara-C). Serial venous blood samples were collected to evaluate the pharmacokinetic and pharmacodynamic characteristics of PEG-IFN in these patients.

RESULTS

The dose-limiting toxicity (DLT) as defined by the protocol was not achieved at the highest dose tested of 630 mug/wk. With the addition of ara-C, the DLT was reached at 540 microg/wk. The safety profile was similar to that of unmodified IFNs. Of 27 patients treated with PEG-IFN, 14 (52%) achieved or maintained a complete hematologic response and three (11%) achieved a complete cytogenetic response. Among 16 patients treated with the combination of PEG-IFN and ara-C, 11 (69%) achieved or maintained complete hematologic remission and two (13%) achieved complete cytogenetic remission. The mean serum peak concentration (C(max)) of PEG-IFN increased from 9.4 to 28 ng/mL as the dose increased from 270 to 450 microg/wk, with no further increases in C(max) at higher dose levels. Serum concentration reached peak value starting about 48 hours after drug administration and was maintained at close to peak value throughout the dosing interval. The mean +/- SD area under the serum concentration-time curve (AUC) calculated after the first dose also increased from 1,022 +/- 694 to 3,343 +/- 2,728 ng hour/mL as dose was increased from 270 to 450 microg/wk, showing a dose-related increase in systemic exposure of PEG-IFN. As with C(max), the AUC did not increase at higher dose levels. The maximum induction (E(max)) of neopterin, the surrogate marker of the pharmacodynamic activity of PEG-IFN, increased from 120% to 361% over baseline values as the dose was increased from 270 to 540 microg/wk. On the once-weekly multiple dosing schedule, both the PEG-IFN and neopterin concentration seemed to reach steady state by week 5 and the steady-state values were maintained with chronic dosing over 6 months.

CONCLUSION

Pegasys provided a significant advantage over standard IFN-alpha by enabling once-weekly dosing while maintaining acceptable safety, tolerability, and activity profiles. This branched 40-kDa PEG-IFN was well tolerated both as a monotherapy as well as in combination with ara-C. Demonstration of its sustained exposure, pharmacodynamic activity, hematologic response, and evidence of cytogenetic response in several patients in this limited study with either IFN-refractory or INF-intolerant patients provides a promise for further investigation in combination with new agents like imatinib.

Site-specific PEGylation of engineered cysteine analogues of recombinant human granulocyte-macrophage colony-stimulating factor

Granulocyte macrophage colony-stimulating factor (GM-CSF) stimulates proliferation of hematopoietic cells of the macrophage and granulocyte lineages and is used clinically to treat neutropenia and other myeloid disorders. Because of its short circulating half-life, GM-CSF is administered to patients by daily injection. We describe here the engineering of highly potent, long-acting human GM-CSF proteins through site-specific modification of GM-CSF cysteine analogues with a cysteine-reactive poly(ethylene glycol) (PEG) reagent. Thirteen cysteine analogues of GM-CSF were constructed, primarily in nonhelical regions of the protein believed to lie away from the major receptor binding sites. The GM-CSF cysteine analogues were properly processed but insoluble following secretion into the Escherichia coli periplasm. The proteins were refolded and purified by column chromatography. Ten of the cysteine analogues could be modified with a 5-kDa maleimide PEG, and seven of the mono-PEGylated proteins were purified by ion-exchange column chromatography. Biological activities of the 13 cysteine analogues and 7 PEGylated cysteine analogues were comparable to that of wild-type GM-CSF in an in vitro cell proliferation assay using human TF-1 cells. One cysteine analogue was modified with larger 10-, 20-, and 40-kDa PEGs, with only minimal loss of in vitro bioactivity. Pharmacokinetic experiments in rats demonstrated that the PEGylated proteins had up to 47-fold longer circulating half-lives than wild-type GM-CSF. These data demonstrate the utility of site-specific PEGylation for creating highly potent, long-acting GM-CSF analogues and provide further evidence that the nonhelical regions of human GM-CSF examined are largely nonessential for biological activity of the protein.

PEGylated interferon-alpha2b: a branched 40K polyethylene glycol derivative

PURPOSE

The conjugation of interferon-alpha2b (IFN-alpha2b) to a branched-chain (40,000) polyethylene glycol (PEG2,40K) was studied.

METHODS

We studied the conjugation of IFN-alpha2b at different pH values (6.5, 7, and 8), using the PEG2,40K reagent in either solution or solid state. MonoPEGylated interferon was isolated by ion-exchange chromatography and characterized using (1) sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (2) cation exchange high-performance liquid chromatography, (3) bicinchoninic acid protein assay, (4) enzyme-linked immunosorbent assay, (5) cell-based bioassays, (6) thermal stability (at 60 degrees C), (7) tryptic digestion, and (8) pharmacokinetics in rats.

RESULTS

PEGylation reaction gave 30-55% PEG2,40K-IFN-alpha2b, 1-10% polyPEGylated interferon, and 35-70% unmodified IFN-alpha2b. Compared to the polyPEGylated IFN-alpha2b species, the pure (96%) monoPEGylated conjugate retained a significantly higher bioactivity (IU/mg): 1.7x10(4)+/-8.5x10(3) vs. 2.8x10(6)+/-1.4x10(6) for antiviral and 1.9x10(4)+/-9.5x10(3) vs. 3.1x10(6)+/-1.6x10(6) for antiproliferative activity. Immunorecognition against IFN was reduced by the PEG2,40K moiety in the conjugate. This monoPEGylated IFN-alpha2b, which migrated as a single band in gel electrophoresis, was found to be a heterogeneous, complex mixture of different positional isomers. PEGylation markedly enhanced both the resistance to tryptic degradation and the thermal stability of IFN-alpha2b. The serum half-life of 40K PEG-IFN was 330-fold longer, while plasma residence time was increased 708 times compared to native IFN.

CONCLUSION

The PEG2,40K conjugate of IFN-alpha2b has increased in vitroand in vivo stability as compared to the native cytokine.

Improving the therapeutic efficacy of peptides and proteins: A role for polysialic acids

Peptide and protein drugs are a growing class of therapeutics. However, their effective application in the clinic is compromised by problems, for instance proteolysis in the circulating blood, premature clearance through the kidneys, and immunogenicity. A number of approaches have been used to circumvent such shortcomings including changes in the primary peptide structure, entrapment into nanoparticles (e.g. liposomes) and conjugation to polymers. Polysialylation, namely, conjugation of peptides and proteins to the naturally occurring, biodegradable alpha-(2-->8) linked polysialic acid is a recent development, which promises to be at least as effective as PEGylation but without its potential toxicity. Polysialylation of a range of peptide and protein therapeutics has led to markedly reduced proteolysis, retention of their activity in vivo, prolongation of their half-life in the circulation and reduction in immunogenicity and antigenicity. It is anticipated that polysialylation will lead to a new generation of peptide and protein constructs with significantly improved pharmacological profiles.

Carbohydrate-specifically polyethylene glycol-modified ricin A-chain with improved therapeutic potential

Ricin A-chain, which exhibits excellent cytotoxicity to tumor cells, has been widely used as an immunotoxin source. However, it has the fatal shortcoming of poor pharmacokinetics due to the tremendous liver uptake via carbohydrate-mediated recognition. Modification of proteins with polyethylene glycol, PEGylation, has the advantages of shielding the specific sites and prolonging the biological half-life. In this study, the carbohydrate-specific PEGylation of ricin A-chain was considered to be a novel approach to overcome this limitation. The carbohydrate group of ricin A-chain was oxidized by sodium m-periodate and further specifically conjugated with hydrazide-derivatized PEG. For a comparative study, the PEGylated ricin A-chain at amino groups was prepared using the hydroxysuccinimide ester-derivatized PEG. The carbohydrate-specifically PEGylated ricin A-chain showed a markedly lower liver uptake and systemic clearance compared with the amine-directly PEGylated ricin A-chain as well as the unmodified ricin A-chain. Furthermore, carbohydrate-specifically PEGylated ricin A-chain showed a significantly higher in vitro ribosome-inactivating activity than the amine-directly PEGylated ricin A-chain. These findings clearly demonstrate that the carbohydrate-specificity as well as PEGylation plays an important role in improving the in vivo pharmacokinetic properties and in vitro bioactivity. Therefore, these results suggest that the therapeutic use of immunotoxins constructed using this carbohydrate-specifically PEGylated ricin A-chain has potential as a cancer therapy.

Peginterferon Alfa-2a, lamivudine, and the combination for HBeAg-positive chronic hepatitis B

BACKGROUND

Current treatments for chronic hepatitis B are suboptimal. In the search for improved therapies, we compared the efficacy and safety of pegylated interferon alfa plus lamivudine, pegylated interferon alfa without lamivudine, and lamivudine alone for the treatment of hepatitis B e antigen (HBeAg)-positive chronic hepatitis B.

METHODS

A total of 814 patients with HBeAg-positive chronic hepatitis B received either peginterferon alfa-2a (180 microg once weekly) plus oral placebo, peginterferon alfa-2a plus lamivudine (100 mg daily), or lamivudine alone. The majority of patients in the study were Asian (87 percent). Most patients were infected with hepatitis B virus (HBV) genotype B or C. Patients were treated for 48 weeks and followed for an additional 24 weeks.

RESULTS

After 24 weeks of follow-up, significantly more patients who received peginterferon alfa-2a monotherapy or peginterferon alfa-2a plus lamivudine than those who received lamivudine monotherapy had HBeAg seroconversion (32 percent vs. 19 percent [P<0.001] and 27 percent vs. 19 percent [P=0.02], respectively) or HBV DNA levels below 100,000 copies per milliliter (32 percent vs. 22 percent [P=0.01] and 34 percent vs. 22 percent [P=0.003], respectively). Sixteen patients receiving peginterferon alfa-2a (alone or in combination) had hepatitis B surface antigen (HBsAg) seroconversion, as compared with 0 in the group receiving lamivudine alone (P=0.001). The most common adverse events were those known to occur with therapies based on interferon alfa. Serious adverse events occurred in 4 percent, 6 percent, and 2 percent of patients receiving peginterferon alfa-2a monotherapy, combination therapy, and lamivudine monotherapy, respectively. Two patients receiving lamivudine monotherapy had irreversible liver failure after the cessation of treatment--one underwent liver transplantation, and the other died.

CONCLUSIONS

In patients with HBeAg-positive chronic hepatitis B, peginterferon alfa-2a offers superior efficacy over lamivudine, on the basis of HBeAg seroconversion, HBV DNA suppression, and HBsAg seroconversion.

Pegylated IFNs for chronic hepatitis C: an update

For over a decade, IFN-alpha(2) has been the standard treatment for chronic hepatitis C. However, the drug's rapid clearance and short half-life have led to low rates of sustained virological response. Pegylation is a well-established method of modifying the pharmacological properties of IFNs, causing significant improvements in pharmacokinetics, which in turn lead to improved efficacy. Two pegylated forms of IFN-alpha(2) have been developed: PEG-IFN-alpha(2b) and PEG-IFN-alpha(2a), and their efficacy has been established in randomised, controlled trials. However, the two differ significantly in structure, in vitro activity and pharmacological properties, and this may translate into -differences in clinical efficacy. Comparative trials have been initiated that will provide insight into relative importance of pharmacokinetics, bioactivity and dosing regimen.

Pegylating IFNs at his-34 improves the in vitro antiviral activity through the JAK/STAT pathway

Pegylated interferon alpha-2, alone or in combination with ribavirin, has become the standard therapy for patients with chronic hepatitis C infection. Pegylation of interferon alpha-2 results in a substantially extended half-life that permits once-weekly dosing, because of reduced clearance and more sustained absorption. The size of PEG moiety appears to influence the relative antiviral activities of peginterferon alpha-2. Increasing the size of the polyethylene glycol (PEG) moiety results in a reduction of the specific antiviral activity of the pegylated protein. For example, peginterferon alpha-2b (12 kDa) has an in vitro antiviral specific activity 25-35-fold higher than peginterferon alpha-2a (40 kDa). The antiviral activity of pegylated interferon alpha-2 is also governed by the site of pegylation of the interferon alpha core proteins. Interferon alpha-2a is monopegylated at four major positional lysine (Lys) residues. The major site of interferon alpha-2b monopegylation is histidine (His34), with additional pegylation sites at lysine and cysteine residues. The 12 kDa pegylated His34 positional isomer of peginterferon alpha-2b has the highest antiviral and antiproliferative in vitro specific activity compared with both the 12 kDa Lys positional isomers and the 40 kDa Lys positional isomers. The correlative effects of size and site of pegylation on the JAK/STAT signalling pathway, as evidenced by differences in the formation of the Stat1 homodimer complex, are suggestive of a receptor-mediated mechanism that governs the antiviral activity of pegylated interferons. The elucidation of the in vitro effects of pegylation is important and this will ultimately have a positive impact on the in vivo efficacy of treatment for patients with hepatitis C.

Methoxypoly(ethylene glycol)-conjugated carboxypeptidase A for solid tumor targeting

We have evaluated effects of mPEG modification on pharmacokinetic properties of carboxypeptidase A (CPA) in normal rats. Attachment of two or three mPEG chains to CPA resulted in the generation of mPEG2-CPA and mPEG3-CPA analogs with significantly enhanced plasma half-lives, especially during the distribution phase. Moreover, the assessment of real-time whole-body kinetics in CT26 tumor-bearing mice showed both mPEG2-CPA and mPEG3-CPA exhibited increased body retention at 48 h post-injection. In addition, tumor localization of mPEG3-CPA at 72 h was visualized and confirmed by fusion of the gamma-scintigraphy and microCT data sets. Results from the imaging studies support our hypothesis of a correlation between tumor uptake and enhanced circulatory half-life. Tissue distribution data indicated the combination of increased tumor extravasation and effective renal elimination observed with mPEG2-CPA at 48 h following administration led to the highest observed tumor-to-blood ratio of 4.8:1. Although the total concentration of mPEG3-CPA accumulated in tumor was higher than that of mPEG2-CPA and CPA at predetermined time intervals, a higher tumor-to-blood ratio was not obtained owing to a higher level of blood activity. Clearly, the attachment of an appropriate number of mPEG chains can facilitate tumor localization as effectively as can the use of a tumor-specific antibody.

Conjugation of Multiple Copies of Polyethylene Glycol to Hemoglobin Facilitated Through Thiolation: Influence on Hemoglobin Structure and Function

PEGylation induced changes in molecular volume and solution properties of HbA have been implicated as potential modulators of its vasoconstrictive activity. However, our recent studies with PEGylated Hbs carrying two PEG chains/Hb, have demonstrated that the modulation of the vasoconstrictive activity of Hb is not a direct correlate of the molecular volume and solution properties of the PEGylated Hb and implicated a role for the surface charge and/or the pattern of surface decoration of Hb with PEG. HbA has now been modified by thiolation mediated maleimide chemistry based PEGylation that does not alter its surface charge and conjugates multiple copies of PEG5K chains. This protocol has been optimized to generate a PEGylated Hb, (SP-PEG5K)(6)-Hb, that carries approximately six PEG5K chains/Hb - HexaPEGylated Hb. PEGylation increased the O(2) affinity of Hb and desensitized the molecule for the influence of ionic strength, pH, and allosteric effectors, presumably a consequence of the hydrated PEG-shell generated around the protein. The total PEG mass in (SP-PEG5K)(6)-Hb, its molecular volume, O(2) affinity and solution properties are similar to that of another PEGylated Hb, (SP-PEG20K)(2)-Hb, that carries two PEG20K chains/Hb. However, (SP-PEG5K)(6)-Hb exhibited significantly reduced vasoconstriction mediated response than (SP-PEG20K)(2)-Hb. These results demonstrate that the enhanced molecular size and solution properties achieved through the conjugation of multiple copies of small PEG chains to Hb is more effective in decreasing its vasoconstrictive activity than that achieved through the conjugation of a comparable PEG mass using a small number of large PEG chains.

Characterizing biological products and assessing comparability following manufacturing changes

Changes in production methods of a biological product may necessitate an assessment of comparability to ensure that these manufacturing changes have not affected the safety, identity, purity, or efficacy of the product. Depending on the nature of the protein or the change, this assessment consists of a hierarchy of sequential tests in analytical testing, preclinical animal studies and clinical studies. Differences in analytical test results between pre- and post-change products may require functional testing to establish the biological or clinical significance of the observed difference. An underlying principle of comparability is that under certain conditions, protein products may be considered comparable on the basis of analytical testing results alone. However, the ability to compare biological materials is solely dependent on the tests used, since no single analytical method is able to compare every aspect of protein structure or function. The advantages and disadvantages of any given method depends on the protein property being characterized.

Synthetic Erythropoietic Proteins: Tuning Biological Performance by Site-Specific Polymer Attachment

Chemical synthesis in combination with precision polymer modification allows the systematic exploration of the effect of protein properties, such as charge and hydrodynamic radius, on potency using defined, homogeneous conjugates. A series of polymer-modified synthetic erythropoiesis proteins were constructed that had a polypeptide chain similar to the amino acid sequence of human erythropoietin but differed significantly in the number and type of attached polymers. The analogs differed in charge from +5 to -26 at neutral pH and varied in molecular weight from 30 to 54 kDa. All were active in an in vitro cell proliferation assay. However, in vivo potency was found to be strongly dependent on overall charge and size. The trends observed in this study may serve as starting points for the construction of more potent synthetic EPO analogs in the future.

Chronic hepatitis C treatment patterns in African American patients: an update

There are large racial disparities in the incidence of chronic hepatitis C virus (HCV) infection in the United States. The prevalence of HCV, and the prevalence of infection with HCV genotype 1, is higher among African Americans than among other ethnic groups. African Americans also have a higher incidence of complications of HCV infection, including a higher incidence of antibodies to HCV RNA and higher incidences of occurrence of and mortality from hepatocellular carcinoma. Combination therapy with pegylated interferons and ribavirin has increased the sustained virologic response (SVR) rates, and decreased the rates and severity of adverse events, over those observed with standard interferons, with or without ribavirin, although SVR rates with peginterferons plus ribavirin are lower in African Americans than in other ethnic groups. A recent clinical trial of peginterferon alpha-2a plus ribavirin in African American patients resulted in a higher SVR rate, 26%, than observed previously, and 90% of patients showed stabilization or improvement in fibrosis. No host or viral genetic differences have yet been identified to explain the racial disparities in incidence of HCV or response to treatment, but clinical trials are currently ongoing to identify these factors. Because treatment with pegylated interferons plus ribavirin yields improved SVR rates with good tolerability, while the basis for lower response rates in African Americans is not yet known, it is recommended that all patients with chronic HCV infection, regardless of ethnic or racial background, receive combination therapy.

The development of a modified human IFN-alpha2b linked to the Fc portion of human IgG1 as a novel potential therapeutic for the treatment of hepatitis C virus infection

Interferon-alpha (IFN-alpha), in conjunction with ribavirin, is the current standard for the treatment of chronic hepatitis C virus (HCV) infection. This treatment requires frequent dosing, with a significant risk of the development of anti-IFN-alpha neutralizing antibodies that correlates with lack of efficacy or relapse. We have developed an IFN-alpha linked to the Fc region of human IgG1 for improved half-life and less frequent dosing. We have also identified, using a human T cell proliferation assay, three regions of IFN-alpha2b that are potentially immunogenic, and a variant containing a total of six mutations within these regions was made. This variant was made as a fusion to Fc either with or without a flexible linker between the fusion partners. Both configurations of the variant were less active than native IFN-alpha alone, although the variant containing the flexible linker had in vitro antiviral activity within the range of other modified IFN-alphas currently in clinical use. Peptides spanning the modified regions were tested in T cell proliferation assays and found to be less immunogenic than native controls when using peripheral blood mononuclear cells (PBMCs) from both healthy individuals and HCV-infected patients who had been treated previously with IFN-alpha2b.

Site of Pegylation and Polyethylene Glycol Molecule Size Attenuate Interferon-α Antiviral and Antiproliferative Activities through the JAK/STAT Signaling Pathway

Therapeutic pegylated interferon-alphas (IFN-alpha) are mixtures of positional isomers that have been monopegylated at specific sites on the core IFN-alpha molecule. The pegylation results in lower in vitro specific activity associated with the core IFN-alpha molecule that is related to the site of pegylation and size of polyethylene glycol (PEG) attached. We prepared purified, homogeneous, positional pegylation isomers of IFN-alpha2b that were monopegylated using 5-30-kDa linear PEG molecules attached at 7 primary reactive amino acid residues: Cys(1), His(34), Lys(31), Lys(83), Lys(121), Lys(131), and Lys(134). The isomers were evaluated for STAT translocation and antiviral and antiproliferative activity. The site of pegylation strongly influenced activity relative to an IFN-alpha2b control. The highest residual activity was observed with the His(34) positional isomers, and the lowest was observed with the Cys(1) positional isomers. The Lys positional isomers demonstrated intermediate activity, with a general order of Lys(134) > Lys(83) approximately Lys(131) approximately Lys(121) > Lys(31). The progressive relationship between decreased activity and increased PEG size suggests that pegylation may interfere with interaction and binding of IFN-alpha to the IFNAR1-IFNAR2 heterodimeric receptor. The higher specific activity associated with the His(34) positional isomer suggests that this site may be favorable for pegylating IFN-alpha2b molecules.

Novel polyethylene glycol derivative suitable for the preparation of mono-PEGylated protein

A novel methoxypolyethylene glycol (mPEG) derivative, containing a reactive group of 1-methyl pyridinium toluene-4-sulfonate, was synthesized and characterized. The mPEG derivative was successfully conjugated with two proteins: recombinant human granulocyte-colony stimulating factor (rhG-CSF) and consensus interferon (C-IFN). Homogeneous mono-PEGylated proteins were obtained which were identified by high performance size-exclusion chromatography and MALDI-TOF mass spectrometry. The biological activities of the mono-PEGylated rhG-CSF and the mono-PEGylated C-IFN were maintained at 90% and 88%, respectively.