Pancreatic cancer remains the 4th leading cause of cancer death in the United States. These tumors appear to be relatively resistant to standard available therapies. An agent capable of sensitizing pancreatic cancer cells to oncology therapies may improve the outcomes of these patients. A central hypothesis of this project is that elevated levels of homologous recombinational (HR) DNA repair can cause human pancreatic tumors to be resistant to some chemotherapies and radiotherapy, and that specific inhibition of HR may help overcome this resistance to therapy. The proposed research plan will develop a multi-step screen for identifying small molecule inhibitors of human RAD51, which is the central protein involved in initiating HR. The initial submission of this project included an aim proposing to develop a high-throughput (HT) assay and to screen a na[unreadable]ve library of small molecules in search of compounds that can inhibit the formation of RAD51 filaments on single-stranded DNA. A portion of initial work has been completed and is now summarized in the Preliminary Studies / Progress Report section. The screen of a 10k library identified 72 compounds that inhibit RAD51 filament formation by = 50%. This work successfully validated the filament formation assay as an HT screen, and it provided important information including refinement of assay techniques and data analysis. Using this information, the screen will be now be repeated using a larger starting library (130k compounds) and robotic liquid handling, which will likely yield compounds with even greater activities and specificities (Aim 1). To determine which have specific activities, the compounds resulting from both screens will be tested further in secondary and tertiary assays. Aim 2 will employ a set of in-vitro secondary assays aimed at identifying those compounds that can specifically block particular functions of purified RAD51 protein. In the third aim, compounds will be further characterized with tertiary cell-based assays, to identify the subset capable of sensitizing pancreatic cancer cells to the lethal effects of DNA damaging therapies via HR-specific mechanisms. The ultimate goal is to identify at least one optimal compound suitable for further development in clinical trials as an oncology drug. Pancreatic cancer remains the 4th leading cause of cancer death in the United States. These tumors appear to be relatively resistant to presently available therapies. A drug capable of overcoming the cellular resistance to radiotherapy and/or chemotherapeutic drugs may improve on the outcomes of these patients. The goal of this proposal is to develop an agent capable of sensitizing pancreatic cancer cells to these common oncology therapies. [unreadable] [unreadable] [unreadable]