Disulfide-Based Poly(amido amine)s for siRNA Delivery: Effects of Structure on siRNA Complexation, Cellular Uptake, Gene Silencing and Toxicity

ABSTRACT Purpose RNA interference (RNAi) is a process by which small interfering RNAs (siRNA) induce sequence-specific gene silencing. Therefore, siRNA is an emerging promise as a novel therapeutic. In order to realize the high expectations for therapeutic applications, efficient delivery systems for siRNA are necessary. Methods In this study, a new series of biodegradable poly(amido amine)s with disulfide linkages in the backbone was synthesized out of N,N′-cystaminebisacrylamide (CBA), 4-amino-1-butanol (ABOL) and ethylene diamine (EDA). Effects of different percentages of butanolic side chains and protonatable fragments in the main chain on siRNA complexation, cellular uptake, gene silencing and toxicity were investigated. Results Incorporation of EDA in the polymer resulted in increased siRNA condensation. Efficient siRNA condensation was shown to be necessary for cellular uptake; however, excess of polymer decreased siRNA uptake for polymers with high amounts of EDA. Silencing efficiency did not correlate with uptake, since silencing increased with increasing w/w ratio for all polymers. More than 80% knockdown was found for polyplexes formed with polymers containing 25% or 50% EDA, which was combined with low cytotoxicity. Conclusions Poly(amido amine)s with minor fractions of protonatable fragments in the main chain are promising carriers for delivery of siRNA.