700. Formulation of Chemically Modified Short Interfering RNA (siRNA) for Local Delivery to the Respiratory Tract

RNA interference using synthetic siRNAs to inhibit gene expression in a sequence-specific manner offers a novel opportunity for treating pulmonary diseases including asthma, airway inflammation, and respiratory viral infections. Developing siRNAs as therapeutics will however require chemical modifications to avoid degradation by nucleases, and delivery formulations to improve lung exposure. In the studies summarized here, we compared the time course of exposure in lung tissue of unmodified siRNA and greater than 95% stabilized siRNA. As part of a program to evaluate siRNAs that target inflammatory cytokines and their receptors, IL-4Ra siRNA, 20 |[mu]|g total administered dose (1.0 mg/kg), was given intratracheally in anesthetized mice. siRNA in lung tissues was assessed at multiple time points after dosing using a hybridization assay. In addition, the time course of exposure in lung tissue of siRNA in proprietary lipid nanoparticle formulations were also evaluated. Chemical modification increased the half life of lung exposure of unstabilized siRNA from less than 2.0 min to 2.7h. Formulation of chemically modified siRNA increased the half life of lung exposure to 22h. Direct intratracheal adminstration of non- formulated Cy3-labeled siRNAs resulted in diffuse, dose|[ndash]|dependent uptake by respiratory epithelia and macrophages. Chemically modified, formulated siRNAs against specific targets will provide the tools for exploring the pathophysiology of lung diseases and have the potential to provide novel therapies.