Enhanced endosomal escape of siRNA-incorporating hybrid nanoparticles from calcium phosphate and PEG-block charge-conversional polymer for efficient gene knockdown with negligible cytotoxicity

Development of safe and efficient short interfering RNA (siRNA) delivery system for RNA interference (RNAi)-based therapeutics is a current critical challenge in drug delivery field. The major barriers in siRNA delivery into the target cytoplasm are the fragility of siRNA in the body, the inefficient cellular uptake, and the acidic endosomal entrapment. To overcome these barriers, this study is presenting a hybrid nanocarrier system composed of calcium phosphate comprising the block copolymer of poly(ethylene glycol) (PEG) and charge-conversional polymer (CCP) as a siRNA vehicle. In these nanoparticles, the calcium phosphate forms a stable core to incorporate polyanions, siRNA and PEG-CCP. The synthesized PEG-CCP is a non-toxic endosomal escaping unit, which induces endosomal membrane destabilization by the produced polycation through degradation of the flanking cis-aconitylamide of CCP in acidic endosomes. The nanoparticles prepared by mixing of each component was confirmed to possess excellent siRNA-loading efficiency (∼80% of dose), and to present relatively homogenous spherical shape with small size. With negligible cytotoxicity, the nanoparticles efficiently induced vascular endothelial growth factor (VEGF) mRNA knockdown (∼80%) in pancreatic cancer cells (PanC-1). Confocal laser scanning microscopic observation revealed rapid endosomal escape of siRNA with the nanoparticles for the excellent mRNA knockdown. The results obtained demonstrate our hybrid nanoparticle as a promising candidate to develop siRNA therapy.