(514b) Synthesis and in-Vitro Characterization of pH-Responsive Nanogels for Oral Delivery of siRNA

The landmark discovery of RNA mediated interference (RNAi) in 1998 has sparked a massive research effort in all fields of biological science and redefined our understanding of gene regulation mechanisms. Theoretically, RNAi mediated by small interfering RNA (siRNA) could be used as a powerful and versatile treatment modality to treat nearly any disease resulting from aberrant gene expression. Furthermore, recent advances in genomics, bioinformatics, and increased understanding of the molecular and genetic nature of disease enable siRNA technology to be rapidly adapted for disease treatment. Owing to its remarkable potency and low therapeutic dosage, siRNA holds extraordinary promise as a new biological therapeutic. However, efficient delivery has been implicated as the major hurdle to its widespread clinical application. Although much effort has been directed toward synthetic polymer carriers for siRNA, there remains a paucity of data on the development of oral delivery systems. The goal of our work is to develop a novel hydrogel platform for siRNA delivery, a synthetic polymer carrier capable of providing siRNA to disease targets, specifically those along the gastrointestinal tract.

We recently described a novel photoemulsion polymerization to synthesize polycationic nanoscale hydrogels composed of a crosslinked core of poly[2-(diethylaminoethyl) methacrylate] surface grafted with poly(ethylene glycol) (M_n ~ 2080). A panel of polymers with varying cross-linking density and core hydrophobicity have been synthesized and display reversible, pH-dependant swelling near physiological pH. Particles were demonstrated to have a dry diameter of 40 - 60 nm as determined by SEM and TEM and a collapsed hydrodynamic diameter of 70 - 100 nm as determined by dynamic light scattering. Physicochemical properties of the polymer network, including particle size, volume swelling ratio, critical swelling pH, and zeta potential were investigated using electron microscopy and dynamic and electrophoretic light scattering. As expected, the degree of volume swelling is inversely related to cross-linking density. Hemolysis experiments suggest these nanogels have utility in intracellular delivery applications as polymers mediate erythrocyte membrane disruption in a concentration- and pH-dependant manner. Ongoing experiments aim to optimize molecular architecture for siRNA binding, hemolytic ability, cellular compatibility, and silencing efficiency.