Delivery Of Small Interfering RNA With Nanoparticles For Overcoming Barriers Of Systemic Administration

With special physical and chemical properties, nanocarriers can achieve drug loading, protecting and controlled releasing. By the nanoscale effect, targeted modification or microenvironment response ability, nanocarriers can enhance the drug accumulation in the lesions and reduce the side effects. RNA interference has shown great potential in the treatment of diseases due to its efficient and specific gene silencing ability. However, as siRNA is a negative charged macromolecule, which is easily degradable, hard to be taken up by cells and bears no targeting ability, it remains the biggest obstacle for development of siRNA to be a real clinic therapeutic modality. Hence, it is necessary to develop efficient, safe and targeted nanocarriers for siRNA delivery. It has been clear that multi-barriers should be overcome in systemic siRNA delivery with nanoparticles, mainly including prolonged circulation, enhanced tumor accumulation, facilitated cellular internalization, and sufficiently intracellular siRNA release. In this dissertation, we have developed two delivery systems for siRNA systemic administration, and evaluated their performances in vitro and in vivo on overcoming barriers of systemic administration, gene silence and tumor inhibition effect.In the first part, we have designed a mixed micellar nanoparticles assembled from two amphiphilic biodegradable diblock copolymers for siRNA delivery. The properties of nanoparticles, including particle size, zeta potential and the density of poly(ethylene glycol) could be easily regulated by changing the molar ratio of two polymers. The nanoparticles were modified by N-acetylgalactosamine and developed to a liver targeting siRNA delivery systems Gal-MNP. The hepatocyte-targeting effect of Gal-MNP was demonstrated by significant enriching of fluorescent siRNA in primary hepatocytes in vitro and in vivo and successful down-regulation of liver-specific apolipoprotein B (apoB) expression was achieved in mouse liver. The results of this study suggested therapeutic potential for the Gal-MNP/siRNA system in liver disease.In the second part, we have designed a tumoral microenvironment sensitive shedable micelleplex system for siRNA delivery. By the in vitro and in vivo experiments, we evaluated its performance on overcoming barriers of systemic administration:First, the micelles carrying siRNA could circulate enough time in blood, enrich accumulation at tumor sites, shed the PEG layer when triggered by tumor overexpressing matrix metalloproteinase2, and then the exposing cell penetrating peptide r9enhanced cellular uptake of siRNA. Accordingly, this design strategy enhanced the inhibition of breast tumor growth following systemic injection of this micelles carrying siRNA against Polo-like kinase1, which demonstrated this micelleplex could be a potential system for systemic siRNA delivery in cancer therapy.