Project Summary / Abstract Osteoarthritis (OA) is a chronic degenerative disease that affects joints and their surrounding tissues. OA can occur spontaneously with aging or be secondary to injury in the case of post-traumatic osteoarthritis (PTOA). OA/PTOA causes significant morbidity and loss of quality of life, resulting in an estimated financial burden in the U.S. of over $44 billion annually. Non-steroidal anti-inflammatory drugs are typically the first line of treatment to deal with pain but do not slow cartilage deterioration and can cause gastrointestinal problems. The Osteoarthritis Research Society International recommends corticosteroids for temporary pain relief, but steroids also do not target the underlying cause of disease and may even worsen cartilage thinning. These shortcomings leave an unmet need for disease-modifying OA/PTOA drugs (DMOADs) that block or reduce disease progression. In OA/PTOA, synoviocytes and chondrocytes produce inflammatory cytokines and matrix metalloproteinases (MMPs) that drive the joint degenerative process. Small molecule MMP inhibitors have been tested clinically for cancer but failed largely due to systemic toxicities caused by the lack of MMP selectivity. RNA interference is a promising strategy for creation of target selective therapeutics against difficult to drug molecular targets. This project is focused on development and PTOA therapeutic testing of siRNA therapeutics that can selectively inhibit specific collagenases, either alone or in combination. The proposed approach builds from our recent work developing siRNA molecules end-modified through a PEG linker with a diacyl lipid (siRNA-L2), which spontaneously forms a molecular complex with albumin (alb/ siRNA-L2) in situ following intravenous injection. This albumin “hitchhiking” siRNA-L2 enhances siRNA PK, is very safe, and increases level and homogeneity of delivery, particularly to tissues characterized by inflammation and vascular leakiness. The overall goal of this proposal is to implement siRNA-L2 to systemically treat and block progression of PTOA. This project will assess siRNA-L2 therapeutic index in a PTOA mouse model and then test the disease efficacy of targeting single versus multiple proteases in a guinea pig PTOA model.