Structural Exploration of Polycationic Nanoparticles for siRNA Delivery

RNA interference (RNAi) is a promising approach tothe treatment of genetic diseases by the specific knockdown of targetgenes. Functional polymers are potential vehicles for the effectivedelivery of vulnerable small interfering RNA (siRNA), which isrequired for the broad application of RNAi-based therapeutics. Thedevelopment of methods for the facile modulation of chemicalstructures of polymeric carriers and an elucidation of detaileddelivery mechanisms remain important areas of research. In thispaper, we synthesized a series of methacrylate-based polymers withcontrollable structures and narrow distributions by atom transferradical polymerization using various combinations of cationicmonomers (2-dimethylaminoethyl methacrylate, 2-diethylaminoeth-yl methacrylate, and 2-dibutylaminoethyl methacrylate) and hydro-phobic monomers (2-butyl methacrylate (BMA), cyclohexyl methacrylate, and 2-ethylhexyl methacrylate). These polymers exhibitedvarying hydrophobicities, charge densities, and pKavalues, enabling the discovery of effective carriers for siRNA byin vitrodeliveryassays. For the polymers with BMA segments, 50% of cationic segments were beneficial to the formation of siRNA nanoparticles(NPs) and thein vitrodelivery of siRNA. The optimal ratio varied for different combinations of cationic and hydrophobic segments.In particular, 20k PMB 0.5, PME 0.5, and PEB 1.0 showed >75% luciferase knockdown. Efficacious delivery was dependent on highsiRNA binding, the small size of NPs, and balanced hydrophobicity and charge density. Cellular uptake and endosomal escapeexperiments indicated that carboxybetaine modification of 20k PMB 0.5 did not remarkably affect the internalization ofcorresponding NPs after incubation for 6 h but significantly reduced the endosomal escape of NPs, which leads to the notabledecrease in delivery efficacy of polymers. These results provide insights into the mechanism of polymer-based siRNA delivery andmay inspire the development of novel polymeric carriers