Fluorination Enhances Serum Stability of Bioreducible Poly(amido amine) Polyplexes and Enables Efficient Intravenous siRNA Delivery

The use of small interfering RNA (siRNA) in cancer treatment has been limited by the lack of effective systemic delivery methods. Although synthetic polycations have been widely explored in siRNA delivery, polycation/siRNA polyplexes often suffer from insufficient stability in vivo. Here, rationally designed siRNA delivery systems that meet the requirements for systemic siRNA delivery to distant tumors are reported. The hypothesis that modular design of delivery systems based on poly(amido amine)s that combine fluorination for systemic stability with bioreducibility for easy intracellular siRNA release, and PEGylation for improved safety and colloidal stability will overcome problems with contradicting siRNA delivery demands is tested. PEGylated, fluorinated, and bioreducible copolymers (PEG-PCD-F) with different degree of fluorination are thus synthesized. The fluorinated copolymers readily formed polyplexes with siRNA and achieved greatly improved gene silencing efficacy in multiple cell lines in vitro when compared with nonfluorinated controls. The results show fluorination-induced enhancement of stability, cellular uptake, and endosomal escape of the polyplexes, while exhibiting efficient siRNA release in reducing intracellular environment. PEG-PCD-F polyplexes with siRNA against Bcl2 inhibit breast tumor growth following systemic intravenous administration. The results provide strong evidence of successful combination of bioreducibility with fluorination and PEGylation to achieve systemic siRNA polyplex delivery.