(686a) A Novel Reactive Oxygen Species Sensitive Delivery Vehicle for the Oral Delivery of siRNA

Inflammatory diseases of the gastrointestinal tract, such as inflammatory bowel disease (IBD) and cancer, causes millions of deaths each year and new strategies for treating these diseases are greatly needed. In this presentation, we demonstrate that nanoparticles formulated from an ROS sensitive polymer, termed a polythioketal (PTK), can deliver siRNA against TNF-α orally and rescue mice from inflammatory bowel disease. Polythioketals are a new class of polymers that are stable to the extreme pHs of the GI tract, resistant to proteolysis, and degrade in the presence of reactive oxygen species (ROS). These unique properties allow polythioketal nanoparticles (TKNPs) to transport TNF-α siRNA through the acidic environment of the stomach, release siRNA in inflamed mucosal tissues and inhibit TNF-α gene expression in the gastrointestinal tract after oral delivery. Homo and copolymer PTKs were synthesized using the acetal exchange reaction between a variety of dimercaptans and 2,2-dimethoxypropane. PTKs have been shown to degrade in hours in the presence of superoxide, but are stable to pHs from 1.0- 14.0 over the same time period. ROS sensitive microparticles loaded with both hydrophobic small molecules and hydrophilic biomolecules such as proteins and siRNA have been formulated from PTKs. Cell culture experiments demonstrate that dye-loaded TKNPs degrade more rapidly in cells that overproduce superoxide. This conclusion is based off of results that show increased dye release into cells treated with dye-loaded TKNPs and subsequently with the endotoxin lipopolysaccharide (LPS), which is known to activate macrophages and cause the overproduction of superoxide, when compared to cells receiving only dye-loaded TKNPs and no LPS. These results demonstrate the ability of TKNPs to target therapeutics to cells or regions of the body where there is an excess of ROS such as in and around inflamed tissue. We investigated the ability of TKNPs to orally deliver siRNA in mice with dextran sodium sulfate induced IBD. Mice suffering from experimental IBD were treated daily via gavage with either PBS, free siRNA against TNF- α, PLGA nanoparticles loaded with siRNA against TNF-α, TKNPs loaded with a scrambled siRNA sequence, or TKNPs loaded with siRNA against TNF-α. IBD-mice receiving a daily oral dose of TKNPs loaded with TNF-α siRNA showed a lower level of disease development and a decreased level of TNF-á mRNA and extracellular TNF-α levels compared to IBD-mice receiving any of the other treatments. Given the tremendous therapeutics benefits of targeting therapeutics to inflamed mucosal tissues and the increased patient compliance of oral delivery, we anticipate numerous applications of TKNPs for the oral delivery of biotherapeutics.