(340u) Polycationic Hydrogel Nanocarriers for siRNA Delivery in Inflammatory Bowel Diseases

Introduction: Inflammatory Bowel Diseases (IBDs) are a group of chronic, relapsing conditions characterized by the inflammation of the gastrointestinal tract. As the disease is idiopathic in nature, the development of treatments with long-term efficacy has been challenging. Current therapies are reportedly only effective in a fraction of the ailing population, in addition to reports of undesirable side effects. RNA interference (RNAi) therapy has emerged as a new approach to mitigate the aberrant cytokine signaling observed in the pathogenesis of IBDs. By using synthetically derived RNA molecules called small-interfering RNAs (siRNAs), undesirable genes are silenced. These siRNAs, however, are susceptible to enzymatic degradation and rapid clearance by the excretory system in vivo; hence there is a need for the development of adequate carriers to ensure the delivery of these agents to the desired site of action.

Materials and Methods: The nanoparticle hydrogels (nanogels) were synthesized via an ARGET ATRP emulsion polymerization reaction, a facile synthesis approach that enables high throughput screening of formulations. Post-synthesis, the nanogels were purified and dialyzed with deionized water. The nanogels were characterized with dynamic light scattering, zeta potential measurement, FTIR spectroscopy and NMR spectroscopy to determine the overall size, charge, composition, and pH-response to surrounding biological solutions.

Results and Discussion: Nanoparticles synthesized with these methods exhibited hydrodynamic diameters between 100-180 nm and overall positive surface charge (14-24 mV) under acidic pH conditions. The nanogels exhibited pH-dependent swelling behavior, with shift of the pK_a towards lower pH values by incorporating more hydrophobic co-monomers. The cationic charges within the nanoparticles facilitated excellent siRNA loading efficiencies (≥ 80%) as nanoparticles with greater zeta potential values (≥ 10 mV) showed a better capacity to condense the negatively charged siRNA molecules. However, these cationic properties also caused increased cellular toxicities. The nanogel formulations with higher amounts of cationic polymer elicited a 60% decrease in cell viability in L929 cells at a concentration of 0.25 mg/mL. Improved cell viabilities were observed in the nanogel formulations that contained less cationic polymer with only a 30% decrease in cell viability at a 2 mg/mL nanoparticle concentration.

Conclusion: These hydrogel nanoparticles are optimal in size and charge for cellular internalization, deeming them promising candidates for intracellular RNA interference. These nanoparticles also show excellent siRNA loading properties. Further work will be conducted to investigate approaches to mitigate the cellular toxicities associated with the use of cationic materials as drug delivery vectors.

(Research Interests: biotechnology, drug delivery and drug development)