Isomerization of poly(ethylene glycol) : a strategy for the evasion of anti-PEG antibody recognition

Abstract

PEGylation, the conjugation of poly(ethylene glycol) (PEG) to nanocarriers or protein-based active pharmaceutical ingredients (APIs), is a key strategy in nanomedicine to extend the circulation time of therapeutics in the bloodstream based on the stealth effect of PEG. However, the growing prevalence of anti-PEG antibodies in the population can lead to pronounced immune responses upon drug administration and accelerated blood clearance of PEGylated drugs, resulting in the loss of the stealth effect. We introduce the randomized PEG (rPEG) technology designed to strongly reduce the antigenicity of PEG while preserving its core benefits. This conceptually novel approach is based on an introduction of hydrophilic side chains along the PEG backbone. The synthesis is performed via anionic ring-opening copolymerization of ethylene oxide (EO) and glycidyl methyl ether (GME), resulting in constitutional isomers of PEG. By optimization of the reaction conditions, an ideally random distribution of the side chains in the polymer backbone could be achieved. Since previous studies show a relation between polymer chain regularity and immune system response, our approach specifically aims at introducing an irregular comonomer sequence via copolymerization, while translating the hydrophilicity and low toxicity of PEG to rPEG. Biocompatibility was evaluated using peripheral blood mononuclear cells (PBMC). Increasing the GME content in the copolymers did not decrease cell viability. Furthermore, all rPEG samples did not show complement activation in vitro at all tested concentrations. Enzyme-linked immunosorbent assays (ELISA) utilizing backbone- and end group-selective anti-PEG antibodies showed drastically reduced recognition and antibody binding for the constitutional isomers of PEG.