Design, synthesis, and biological properties of novel metabolizable pH-responsive lipids for use in lipid nanoparticles for siRNA delivery and mRNA vaccination.

We developed pH-responsive lipids, LIPIDs-1 and LIPIDs-2, which feature an N,N-dimethylaminopropyl head and 2 hydrophobic tails connected by carbonate esters. These lipids are metabolizable owing to acetyl ester structures that can be cleaved by esterases, reducing their affinity for biological membranes after hydrolysis of the esters. We evaluated both lipids in vivo using siRNA-loaded lipid nanoparticles (LNPs) targeting Factor VII, which resulted in significant knockdown activity for up to 6 days. Toxicological studies of LNPs using LIPIDs-1 and LIPIDs-2 in rats indicated minimal liver toxicity and rapid metabolism of the lipids, confirming their safety. Moreover, we tested LNPs using LIPIDs-1 as an mRNA vaccine carrier, which resulted in strong immune responses against both ovalbumin and SARS-CoV-2 antigens with a notable Th1-biased profile. These findings suggest that LNPs made using LIPIDs-1 and LIPIDs-2 are promising candidates for drug delivery and vaccine applications.