Lipidoid Tail Structure Strongly Influences siRNA Delivery Activity
RNA interference therapeutics have been limited, in large part, by the lack of efficient, non-toxic, non-immunogenic delivery systems. Among previously established methods, lipidoid nanoparticles (LNPs) show particular promise in delivering siRNA to diverse cell and organ targets in vitro and in vivo. However, a better understanding of structure–function relationships is needed to facilitate broad translation to clinical applications. Here, we demonstrate the critical role of tail chemistry in conferring delivery efficacy to lipidoid molecules with three or four aliphatic tails. Tail length and structure significantly affected siRNA transfection in HeLa cells, with methacrylate (vs. acrylate) tails and tails containing ethers causing reductions in efficacy. Notably, we report a novel tail precursor, isodecyl acrylate, that conveyed marked siRNA delivery ability in vitro and in vivo. LNPs with isodecyl acrylate lipidoids uniformly induced greater than 90% gene silencing, both in vitro and in mice (hepatocytes), at 40 nM and 0.1 mg/kg, respectively. Furthermore, we found that tail chemistry significantly influenced the surface pKa values of formulated LNPs, with tails that conferred higher pKa facilitating higher levels of gene knockdown. Together, these data underscore the importance of lipidoid tail structure and provide guidance for the development of next generation lipid nanoparticle siRNA delivery systems.