Poly(2-oxazoline) decorated lipid nanoparticles for robust mRNA delivery in the presence of pre-existing anti-PEG antibodies

Messenger RNA-lipid nanoparticle (mRNA-LNP) vaccines have demonstrated extraordinary efficacy against severe acute respiratory syndrome coronavirus 2, establishing LNPs as the premier platform for mRNA therapeutics. However, the pervasive presence of anti-polyethylene glycol (PEG) antibodies undermines PEGylated LNP performance by diminishing therapeutic efficacy. To address this challenge, we synthesized a panel of lipid-poly(2-oxazoline) (lipid-POx) conjugates as alternatives to lipid-PEG and systematically evaluated how their polymer backbone, degree of polymerization, and lipid tail structure influence LNP physicochemical properties and mRNA delivery performance. Among POx-LNPs formulated with heptadecan-9-yl 8-((2-hydroxyethyl)(6-oxo-6-(undecyloxy)hexyl)amino)octanoate (SM-102) as the base lipid, those constructed with single-tailed C18-POx exhibited smaller particle sizes and superior freeze-thaw stability. These C18-POx-LNPs maintained comparable in vivo transfection efficiency to PEG-LNPs even when fully replacing 1,2-dimyristoyl-sn-glycero-3 (DMG)-PEG. Notably, in mice bearing pre‑existing anti‑PEG antibodies, C18-POx-LNPs demonstrated over 200-fold higher transfection efficiency than PEG-LNPs. Additionally, repeated administration of POx-LNPs induced dose-dependent anti-POx immunoglobulin M (IgM) and IgG responses, with antibody titers inversely correlated with POx hydrophilicity. This study underscores the effectiveness of substituting PEG with POx in LNP construction to address the transfection efficiency in populations with pre-existing anti-PEG antibodies, and would inspire the development of more hydrophilic polymers for LNP formulation.