PROJECT SUMMARY/ABSTRACT High-grade serous ovarian cancer (HGSOC) is often diagnosed at an advanced stage and has a poor prognosis. Although many patients initially respond to platinum and paclitaxel chemotherapy, most patients develop recurrent disease that is resistant to chemotherapy. Chemotherapy resistance is an unmet therapeutic need in HGSOC. To address this challenge, Dr. Stover performed systematic functional genomic screens to identify mediators of platinum and paclitaxel resistance. Anti-apoptotic proteins that protect cells from apoptotic cell death were strongly associated with chemotherapy resistance. Conversely, targeted drugs that inhibit anti-apoptotic proteins BCL-XL and MCL1 sensitized HGSOC cells to chemotherapy. In this proposal, Dr. Stover will test the hypothesis that BCL-XL and MCL1 are key mediators of HGSOC survival following chemotherapy-induced DNA damage. Aim 1 will determine whether BCL-XL and MCL1 inhibitors increase apoptosis when combined with DNA-damaging chemotherapy in HGSOC cell lines and patient cells, and explore effects of DNA-damaging agents on BCL-XL and MCL1 interactions with pro-apoptotic proteins. Aim 2 will assess whether the DNA damage repair capacity of HGSOC cells affects their dependency upon BCL-XL and MCL1 for survival. A chemical screen will aim to identify DNA-damaging agents and other drugs that synergize with BCL-XL and MCL1 inhibitors to kill HGSOC cells. Aim 3 will evaluate the role of BCL-XL and MCL1 in the survival of chemotherapy-resistant HGSOC. Combinations of BCL-XL and MCL1 inhibitors and chemotherapy will be tested in HGSOC cell lines with empiric platinum resistance in vitro, and HGSOC cell-line xenografts and patient-derived xenografts in vivo. Finally, we will use genomic and proteomic approaches to analyze patient samples of untreated and chemotherapy-resistant HGSOC for changes in BCL-XL and MCL1 and related anti-apoptotic proteins, as well as other chemotherapy resistance pathways. In summary, this study will assess the requirement for BCL-XL and MCL1 in HGSOC chemotherapy resistance, and begin to elucidate the crosstalk between apoptosis and DNA damage repair pathways in resistance. Combinations of BCL-XL or MCL1 inhibitors with DNA-damaging agents may be effective therapies for HGSOC. Dr. Stover's long-term goal is to contribute to new treatment options for patients with ovarian cancer through independent research focusing on ovarian cancer biology, genomics, and therapeutics. The pursuit of this goal will be facilitated by the outstanding institutional environment of the Dana-Farber Cancer Institute and accomplished mentors, including Drs. Matthew Meyerson, MD PhD and Anthony Letai, MD PhD. Collaborations with the Broad Institute will contribute exceptional resources for clinical genomics and chemical screening, and an expert advisory committee will provide guidance on experimental design and career advancement. A research training program, including courses and mentoring in key biological topics and professional development, will support Dr. Stover's goal of an independent research career pursuing laboratory research with a clinical focus to improve outcomes in ovarian cancer.