Project Summary/Abstract Joint trauma is a significant risk factor for development of osteoarthritis, a leading cause of disability worldwide. Current treatments following traumatic joint injuries include anti-inflammatory drugs, low impact exercise, and lifestyle changes; however, many patients still develop post-traumatic osteoarthritis (PTOA) and there are no proven preventive therapies for PTOA currently available. In advanced disease, joint replacement is the only effective intervention and implant wear can necessitate revision procedures, the lifetime risk of which is highest for younger patients. Consequently, there is a major unmet medical need for a drug that can help reduce the risk of developing PTOA in vulnerable populations. To directly address this need, we propose nonclinical evaluation and development of our product candidate, AB002 (E-WE thrombin), for the PTOA indication. E-WE thrombin, a recombinant human thrombin analog, does not clot blood but selectively induces long-acting surface-associated endogenous activated protein C (APC), the body’s essential cytoprotective, anti- inflammatory, and antithrombotic protease. Because cell death and inflammation are the earliest pathological events following traumatic joint injuries, immediate targeting of inflammation and apoptosis may be a promising approach to prevent subsequent PTOA. APC, and our protein C activator E-WE thrombin, have been shown to mitigate experimental inflammatory diseases in various animal models. Most notably, in independent studies it was discovered that repeat systemic administration of an E-WE thrombin prototype or APC reduced signs of joint damage in mouse models of inflammatory arthritis. We have also found that repeat systemic administration of APC was chondroprotective in a mouse model of PTOA. While systemic APC administration can cause potentially dangerous bleeding, E-WE thrombin lacks any measurable bleeding side effects due to its unique mechanism of action, making it potentially much safer for repeat administration. These observations lend strong support to the hypothesis that administration of E-WE thrombin in the acute phase following traumatic joint injury could be a safe and effective preventive therapy for PTOA. Our objective for this SBIR Phase I feasibility project is to determine if early E-WE thrombin treatment following joint injury can beneficially alter the development of experimental PTOA in mice. Reaching our Phase I feasibility milestone of improved outcomes in this model will justify progression into Phase II towards evaluation of E-WE thrombin in additional PTOA models and toxicity/safety evaluation of repeat dose E-WE thrombin administration. The ultimate goal is to obtain FDA approval of E-WE thrombin as a safe and effective preventative therapy against PTOA development in patients with traumatic joint injuries.