Delivery Of Small Interfering RNA With Nanoparticular Systems For Cancer Therapy

Since the discovery of RNA interference, siRNA has generated great interests as a revolutional therapeutic agent for numerous diseases because of its ability to efficiently silence specific genes. However, the in vivo delivery of siRNA to target tissue and cells remains the biggest challenge for its clinical applications. In this dissertation, a few of delivery systems have been developed for systemic delivery of siRNA and cancer therapy. These delivery systems can efficiently carry siRNA into tumor cells, and with the delivery of siPlk1 targeting polo-like kinase 1 （Plk1）, the gene experession can be significantly down-regulated in tumor tissue and tumor cells, which further induces significant inhibition to tumor growth in murine xerograft models following intravenous injections.In the first part of this dissertation, we describe a cationic lipid assisted polymeric nanoparticle system with stealthy property for efficient siRNA encapsulation and delivery, which was fabricated with poly（ethylene glycol）-poly（d,l-lactide）, siRNA and a cationic lipid, using a double emulsion-solvent evaporation technique. By incorporation of the cationic lipid, the encapsulation efficiency of siRNA into the nanoparticles could be above 90% and the siRNA loading weight ratio was up to 4.47%, while the diameter of the nanoparticles was around 170 to 200 nm. The siRNA retained its integrity within the nanoparticles, which were effectively internalized by cancer cells and escaped from the endosome, resulting in significant gene knockdown. Furthermore, the nanoparticles carrying siRNA targeting the Plk1 gene were found to induce remarkable apoptosis in both HepG2 and MDA-MB-435s cancer cells. Systemic delivery of specific siRNA by nanoparticles significantly inhibited luciferase expression in an orthotopic murine liver cancer model and suppressed tumor growth in a MDA-MB-435s murine xenograft model, suggesting its therapeutic promise in disease treatment.In the second part, we have developed cationic lipid-polymer hybrid nanoparticles for systemic delivery of siRNA by a single-step assembly process. The hybrid nanoparticles can efficiently adsorb siRNA, and exhibit excellent stability in the presence of serum. The effect of the composition of nanoparticles on the cellular uptake has been investigated, and the efficiency of siRNA delivery into tumor cells has also been studied. The hybrid nanoparticles can efficiently deliver siPlk1 into tumor cells and significantly down-regulate polo-like kinase 1 expression in BT474 cells. Furthermore, the nanoparticles efficiently carry siPlk1 to tumor via tail-vein injection and significantly suppress the tumor growth in a murine xenograft model.In the third part, we report a sheddable nanoparticular system for tumor acidity-targeted siRNA delivery by introducing a tumor acidity-responsive PEGylated anionic polymer layer to the surface of positively charged nanoparticles of disulfide cross-linked polyethylenimines (ssPEI₈₀₀) and siRNA through electrostatic interaction. The ssPEI₈₀₀/siRNA nanoparticles are shielded by such a PEGylated polymer, which markedly minimizes non-specific interactions with serum components during circulation and significantly improves their accumulation in the tumor site. However, the sheddable nanoparticles unsheild the PEGylated polymer layer after accumulating in the tumor site, and re-expose the highly and positively charged ssPEI₈₀₀/siRNA nanoparticles. Accordingly, this promotes its uptake by the tumor cell and further enhances the RNA-interfering and tumor-growth-suppression efficiencies.