Lipid 20b is a thiophene-based ionizable lipid synthesized via the Gewald reaction. It features dual unsaturated linoleic tails (C18:2) attached to the same side of the thiophene core and a tertiary amine headgroup. Formulated into LNPs (~100 nm, PDI ~0.2) with DSPC/cholesterol/DMG-PEG, it exhibits high mRNA encapsulation (>90%). Unlike traditional lipids, 20b lacks a pH-dependent ionization profile, likely due to electron delocalization in the thiophene ring. Intravenously, 20b LNPs transfect the liver and spleen in mice. Notably, subretinal delivery in mice and non-human primates (NHPs) achieved robust mRNA expression in photoreceptors (35% rods, 45% cones at high dose) and retinal pigment epithelium (RPE) with minimal acute toxicity. Immunosuppression enhanced rod transfection efficiency. High-dose administration in NHPs caused subretinal debris, but low doses (2.5 µg mRNA) maintained retinal health. This lipid demonstrates potential for liver and retinal gene therapy.
