Property-Driven Design and Development of Lipids for Efficient Delivery of siRNA

Ionizable cationic lipids are critical components involved in nanoparticle formulations, which are utilized in delivery platforms for RNA therapeutics. While general criteria regarding lipophilicity and measured pK_a in formulation are understood to have impacts on utility in vivo, greater granularity with respect to the impacts of the structure on calculated and measured physicochemical parameters and the subsequent performance of those ionizable cationic lipids in in vivo studies would be beneficial. Herein, we describe structural alterations made within a lipid class exemplified by 4, which allow us to tune calculated and measured physicochemical parameters for improved performance, resulting in substantial improvements versus the state of the art at the outset of these studies, resulting in good in vivo activity within a range of measured basicity (pK_a = 6.0-6.6) and lipophilicity (cLogD = 10-14).