Abstract NT-118: SEQUENTIAL THERAPEUTIC TARGETING OF OVARIAN CANCER HARBORING DYSFUNCTIONAL BRCA1

Abstract

Abstract BACKGROUND: Ovarian cancer is the most lethal gynecologic cancer. High grade serous ovarian cancer (HGSC) is the most common and deadly histological subtype. The current standard treatment protocol involves primary debulking surgery followed by platinum-based combination chemotherapy. PARP inhibitors(PARPi) are the first approved personalized treatments used in BRCA1-mutated recurrent ovarian cancer patients and have shown promising clinical results. Previously published data in collaboration with Dr. Witcher's lab, we described a significant reduction in PARP1 protein levels in patients after giving standard carboplatinum-paclitaxel chemotherapy that is effecting the clinical efficacy of PARP inhibitors in clinical trials. PARP inhibitors are currently administered after standard chemotherapy, when PARP levels are the lowest which was clearly shown in the previous published paper. Applying novel strategy and following the sequence of administration, giving PARP inhibitors first followed by standard chemotherapy might improve response rates. This study aims to evaluate this strategy (in vitro) in the pre-clinical models. METHODS: BRCA1 mutated (UWB1.287, SNU-251), epigenetically silenced (OVCAR8), and wild-type BRCA1 (OVCAR3, SKOV3, A2780P & A2780R) cell lines were exposed to clinically relevant doses of PARPi, either followed by standard chemotherapy, or the inverse sequence. Therapeutic efficacy was assessed using colony formation assay. Apoptotic index was evaluated by cell cycle analysis and apoptotic assays using flow cytometry. Western Blotting was used to detect the levels of relevant apoptotic and cell cycle proteins. RESULTS: Exposure to PARPi prior to standard chemotherapy sensitized BRCA1 mutated or epigenetically silenced BRCA1 cell lines to lower doses of Cisplatin (CP) or Paclitaxel (PT). Similarly, pre-treatment with PARPi prior to chemotherapy induced apoptosis more effectively in the same cell lines. Similar results were observed in BRCA1 wild-type cell lines and cell lines in which BRCA1 functionality was restored. CONCLUSION: Pre-treatment of cell lines with PARPi followed by standard chemotherapy is more efficient (in vitro) in inhibiting growth and inducing apoptosis than the present sequence of chemotherapy followed by PARPi. Citation Format: Tahira Baloch, Roy Kessous, David Octeau , Liron Kogan, Ido Laskov, Michael Witcher, Walter H. Gotlieb and Amber Yasmeen. SEQUENTIAL THERAPEUTIC TARGETING OF OVARIAN CANCER HARBORING DYSFUNCTIONAL BRCA1 [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-118.