Project Summary Diabetic retinopathy (DR) is a leading cause of vision loss in working adults. A major breakthrough in DR therapy is the advent and approval of vascular endothelial growth factor (VEGF) inhibitors. However, anti-VEGF therapy has limited efficacy. The critical barrier is how to improve treatment efficacy in patients resistant to VEGF inhibitors. One of the strategies is to simultaneously inhibit two different angiogenic factors for additive or synergistic combination therapy of anti-VEGF-resistant DR. We have discovered a novel disease-selective angiogenic factor that contributes to DR pathogenesis through a VEGF-independent receptor pathway and, therefore, is a potential target for combination therapy. We further developed neutralizing monoclonal antibodies and demonstrated their high efficacy to alleviate DR in animal models with minimal side effects. The goal of this project is to develop a new pharmacological agent that enables concurrent inhibition of VEGF and this novel angiogenic factor for combination therapy of DR. In Aim 1, we will engineer such dual pharmacological inhibitors to simultaneously targets VEGF and our novel angiogenic factor and characterize their ligand-binding affinity and neutralizing activity. In Aim 2, we will characterize therapeutic efficacy of these dual inhibitors and analyze their safety profiles. The efficacy and safety profiles of these dual inhibitors will be compared to monotherapies. One of the optimal dual inhibitors with maximal improved efficacy and minimal side effects will be selected for further development toward clinical trials in the next phase. Therefore, this project has a potential to develop a new drug entity for combination anti-angiogenic therapy of DR with improved efficacy.