Poly(2-methacryloyloxyethyl phosphorylcholine) for Protein Conjugation

The water-soluble, biocompatible polymer poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was evaluated for protein conjugation. PMPC is a zwitterionic polymer that is able to form a more compact conformation in aqueous solution than poly(ethylene glycol) (PEG). While a terminally functionalized N-hydroxysuccinimide derivative of PMPC was not efficient for conjugation to an amine moiety on interferon-alpha 2a (IFN), we found that a bis-thiol specific derivative of PMPC could be conjugated after reduction of the disulfide bonds in IFN. Utilizing PMPC that displayed a similar hydrodynamic volume to 20 kDa PEG, we evaluated the in vitro antiviral and antiproliferative activity and pharmacokinetics of a PMPC-IFN conjugate. As a hygroscopic zwitterionic polymer, PMPC is able to form a compact conformation in aqueous solution, which was found to be more compact than PEG. This suggests that PMPC protein conjugates may display different plasma elimination characteristics than PEG protein conjugates. PMPC-IFN displayed marked resistance to antibody binding in Western blot analysis with a polyclonal anti-IFN antibody while displaying comparable in vitro antiviral and antiproliferative activity to PEG-IFN. During an in vivo pharmacokinetic study, the absorption t(1/2) for PMPC-IFN was considerably extended compared to the native IFN and 20 kDa PEG analogue. This is also consistent with the SDS-PAGE result where an apparent reduction in mobility through a hydrated medium was observed. The elimination t(1/2) was also vastly extended over the native IFN and twice the value of 20 kDa PEG-IFN. This suggests that tissue migration of PMPC-IFN occurs more slowly than the 20 kDa PEG-IFN despite their similarity in hydrodynamic volume, leading to an an improved depot effect, which could explain the longer elimination t(1/2). In this study, we demonstrate a potential use of PMPCylation as a novel tool for enhancing the pharmacokinetic profile of therapeutic proteins in ways that complement PEGylation.