Mechanistic investigation of poly(ethylene imine)-based siRNA delivery: Disulfide bonds boost intracellular release of the cargo

Abstract Poly(ethylene imine) (PEI) has gained increasing attention in the delivery of small interfering RNAs (siRNAs) into cells. In order to further optimize PEI for this application, the first goal of this study was to examine particular steps of siRNA delivery with various PEI derivatives as carriers. Furthermore, the hypothesis that disulfide cleavable carrier systems are favorable for the release of siRNA into the cell cytoplasm was investigated. Flow cytometry and confocal microscopy were used to assess the cellular uptake and intracellular distribution of siRNA, which were then related to gene silencing efficacy. We observed a strong correlation between cellular uptake and RNAi activity. The cellular uptake of siRNA was more efficient with increasing branching of the polymer, i.e. linear PEI (lPEI) 5 kDa