Thioester-Containing Ionizable Lipids with Enhanced Endosomal Escape and Biodegradability for mRNA and tRNA Delivery

Background/Objectives: Lipid nanoparticles (LNPs) containing ionizable lipids represent the most advanced non-viral delivery vehicles and have become state-of-the-art carriers for RNA therapeutics. However, further improvements in endosomal escape efficiency and biodegradability are still needed, especially for nucleic acids with transient activity such as messenger RNA (mRNA) and transfer RNA (tRNA). Methods: In this study, a novel library of highly biodegradable ionizable lipids featuring thioester groups within the linker region was designed and synthesized, thereby expanding the chemical linker toolbox for future ionizable lipid development. Results: Comprehensive in vivo structure–activity relationship studies led to the identification of CP-LC-1272 as a lead candidate that markedly enhances endosomal escape and exhibits superior in vivo biodegradability, attributed to the high acid-lability of thioester bonds. LNPs containing CP-LC-1272 maintained in vivo activity after six months of storage in lyophilized form and demonstrated superior in vivo efficiency compared to SM-102 in mRNA expression studies, as well as similar protein restoration in a tRNA delivery model targeting premature stop-codon mutations. Conclusions: The rapid biodegradability of these thioester-activated ionizable lipids (TAILs) suggests a reduced risk of accumulation, with the potential to enable safe repeated dosing or high-dosage RNA therapies, positioning TAILs as a versatile and safe platform for next-generation RNA therapeutics.