A phospholipid-like charge-reversible lipid for PEG-free, stable, and low-inflammatory mRNA lipid nanoparticles

The development of lipid nanoparticles (LNPs) facilitated optimal usage of mRNA drugs to achieve clinical success during the COVID-19 pandemic. Conventional LNPs rely on ionizable lipids for mRNA encapsulation and endosomal escape. However, the high hydrophobicity of ionizable lipids leads to aggregation of these LNPs under physiological conditions, requiring polyethylene glycol (PEG) modification for stabilization. Ionizable lipids and PEG induce inflammation and hypersensitivity reactions, respectively, after intramuscular administration. Therefore, developing low-inflammatory LNPs is essential for safer application of mRNA therapeutics. In this study, we synthesized 2-{[2-(dimethylamino)ethyl]methylamino}ethyl 1,2-dioleoyl-1,2-dioleoyl-sn‑glycero‑3-phosphate (DOP-TMDEDA), a novel charge-reversible lipid structurally similar to natural glycerophospholipids. In contrast with LNPs prepared using commercially available ionizable lipids, which exhibit poor dispersibility without PEG modification in phosphate-buffered saline, DOP-TMDEDA-based LNPs (TM LNPs) formed uniformly without PEG modification and showed high dispersibility. PEG-free TM LNPs [TM LNPs PEG (-)] induced markedly lower inflammatory cytokine production in vivo than LNPs prepared with commercially available lipids. Furthermore, TM LNPs PEG (-) showed a slightly higher level of protein expression in vivo than PEGylated TM LNPs. Collectively, these results indicate that TM LNPs PEG (-) provide a promising and biocompatible mRNA delivery platform for mRNA therapeutics.