Polysarcosine as an Alternative to PEG for Therapeutic Protein Conjugation

The performance of many therapeutic proteins, including human interferon-α2b (IFN), is often impeded by their intrinsic instability to protease, poor pharmacokinetics, and strong immunity. Although PEGylation has been an effective approach to improve the pharmacokinetics of many proteins, a few noticeable limitations have aroused vast research efforts in seeking alternatives to PEG for bioconjugation. Herein, we report our investigation on the use of polysarcosine (PSar), a nonionic and hydrophilic polypeptoid, for IFN modification. The site-specific conjugate PSar-IFN, generated by native chemical ligation in high yield, is systematically compared with a similarly produced PEG-interferon conjugate (PEG-IFN) to evaluate the in vitro and in vivo behaviors. PSar is found to show comparable ability in stabilizing IFN from protease digestion in vitro and prolonging the circulation half-life in vivo. Interestingly, PSar-IFN retains more activity in vitro and accumulates more in the tumor sites upon systemic administration than PEG-IFN. Most importantly, PSar-IFN is significantly more potent in inhibiting tumor growth and elicits considerably less anti-IFN antibodies in mouse than PEG-IFN. Together, our results demonstrate for the first time that PSar is an outstanding candidate for therapeutic protein conjugation. Considering the low toxicity, biodegradability, and excellent stealth effect of PSar, this study suggests that such polypeptoids hold enormous potential for many biomedical applications including protein delivery, colloidal stabilization, and nanomedicine.