From PEG to randomized PEG: a macromolecular strategy tackling PEG immunogenicity.

PEGylation is a crucial strategy in modern nanomedicine, offering effective and safer therapeutics. However, the growing prevalence of anti-PEG antibodies (APAs) in patients has raised critical concerns, with multiple studies demonstrating reduced clinical efficacy and safety risks associated with APA formation. This has generated broad consensus on the need for next-generation nanomedicine solutions, leading to the development of several promising alternatives to PEG. However, antibodies against some alternatives have already been reported. Furthermore, full understanding of PEG immunogenicity and clinical impact is highly relevant before switching to another polymeric structure. Therefore, a detailed consideration of immunogenicity and molecular recognition patterns is recommended to guide the next generation of nanomedicine. To address these challenges, the randomized PEG (rPEG) technology has recently been introduced, capitalizing on APA structure knowledge. The random incorporation of "synthetic point mutations", i.e., glycidyl methyl ether, disrupts the regularity of PEG, while preserving the polyether key properties. Reduced antigenicity of rPEG was confirmed via ELISA, MST, and FCS analysis. Further in vitro studies demonstrated that rPEG is noncytotoxic, does not interact with blood, and is unlikely to activate complement. In nanoparticle applications, rPEG-based polymeric micelles and lipid nanoparticles exhibited reduced antigenicity and comparable mRNA transfection efficiency to their PEGylated counterparts, respectively. Recent in vivo studies demonstrated that rPEG-liposomes, across a series of PEG alternatives, were the only formulations that did not exhibit accelerated blood clearance, even following cross-immunization with PEGylated liposomes. Although stealth performance requires further optimization, rPEG represents a highly promising PEG alternative.