“Stealth” Protein-Polymer Conjugates

Many peptide and protein drugs have a short plasma half-life. PEGylation—conjugation of polyethylene glycol (PEG) to biologics—is commonly used to increase the half-life. Unlike previously thought, PEG has proven to be antigenic. This has recently led to early termination of a Phase III clinical trial of a new PEGylated drug candidate, and several PEGylated drugs have been withdrawn from the market because of severe allergic reactions in patients. The problems have been traced to circulating anti-PEG antibodies that are found in patients even in individuals who have never been on a PEGylated drug before. To overcome these limitations, we recently designed a new PEG-like “stealth” polymer, poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA). POEGMA has a significantly different architecture —it is an amphiphilic hyperbranched polymer that breaks up the long antigenic ethylene glycol sequence in PEG and presents them as much shorter Oligomeric-Ethylene Glycol (OEG) side-chains along a hydrophobic backbone. Importantly, POEGMA conjugates show prolonged circulation and do not bind to pre-existing anti-PEG antibodies because of its short OEG that lacks the epitope. POEGMA conjugation hence provides a new and innovative approach to combat the growing problem of PEG antigenicity without abandoning the well-tested PEGylation. Current work is focused on applying this technology to pharmacologically relevant biomolecules and further improving pharmacokinetics of POEGMA conjugates.

We have also developed two new and general routes to grow POEGMA from N-terminus or C-terminus of a protein by in situ atom-transfer radical polymerization (ATRP) under aqueous conditions to yield site-specific (N- or C-terminal) and stoichiometric conjugates (1:1) with low polydispersity and high yield. Current work is focused on applying this technology at the amino acid level by utilizing unnatural amino acid incorporation technology.



I Ozer and A Chilkoti, Site-specific and stoichiometric stealth polymer conjugates of therapeutic peptides and proteins, Bioconjugate Chemistry, 28: 713-723 (2017).

Y Qi, A Simakova, S Averick, D Konkolewicz, X Li, K Matyjaszewski, and A Chilkoti, C-terminal PEG brush polymer conjugate of exendin-4 reduces blood glucose for five days with a single injection, Nature Biomedical Engineering, 1: 0002 (2016).

Y Qi, M Amiram, W Gao, DG McCafferty, and A Chilkoti, Sortase-catalyzed initiator attachment enables high yield in situ growth of a polyethylene glycol comb polymer from the C-terminus of green fluorescent protein by atom transfer radical polymerization, Macromolecular Rapid Communications, 34: 1256-1260 (2013).

W Gao, W Liu, T Christensen, MR Zalutsky, and A Chilkoti, In situ growth of a PEG-like polymer from the C-terminus of an intein fusion protein improves pharmacokinetics and tumor accumulation, Proceedings of the National Academy of Sciences, USA, 107: 16432-16437 (2010). PMCID: PMC2944699

W Gao, W Liu, JA Mackay, M Zalutsky, E Toone, and A Chilkoti, In situ growth of a stoichiometric PEG-like conjugate at a protein’s N-terminus with significantly improved pharmacokinetics, Proceedings of the National Academy of Sciences USA, 106: 15231-15236 (2009). PMCID: PMC: 2731796