Conjugation of Palmitic Acid Improves Potency and Longevity of siRNA Delivered via Endosomolytic Polymer Nanoparticles

Abstract

Clinical translation of siRNA therapeutics has been limited by the inability to effectively overcome the rigorous delivery barriers associated with intracellular-acting biologics. Here, in order to address both potency and longevity of siRNA gene silencing, siRNA conjugated to palmitic acid (siRNA-PA) was paired with pH-responsive micellar nanoparticle (NP) carriers in order to improve siRNA stability and endosomal escape, respectively. Conjugation to hydrophobic PA improved NP loading efficiency relative to unmodified siRNA, enabling complete packaging of siRNA-PA at a lower polymer:siRNA ratio. PA conjugation also increased intracellular uptake of the nucleic acid cargo by 35-fold and produced a 3.1-fold increase in intracellular half-life. The higher uptake and improved retention of siRNA-PA NPs correlated to a 2- to 3-fold decrease in gene silencing IC50 in comparison to siRNA NPs in both mouse fibroblasts and mesenchymal stem cells for both the model gene luciferase and the therapeutically relevant gene PHD2. PA conjugation also increased longevity of silencing activity, as indicated by an increase in silencing half-life from 24 hours to 186 hours. Thus, conjugation of PA to siRNA paired with endosomolytic NPs is a promising approach to enhance the functional efficacy of siRNA in tissue regenerative and other applications.