Abstract A48: Antiapoptotic gene expression and sensitivity to BH3-mimetics in chemoresistant, high-grade serous ovarian cancer cell lines

Introduction: The development of chemotherapy resistance is common in relapsed high-grade serous ovarian cancer (HGSOC). An understanding of mechanisms that are associated with the development of chemotherapy resistance in the clinical setting is needed to improve treatment outcomes. In this study, cell lines newly derived from patients with relapsed HGSOC were characterized at a molecular level to determine associations with response to commonly used chemotherapy drugs. RNA sequencing combined with high-throughput drug library screening was used to determine potential resistance mechanisms and identify drugs and combinations that may be effective in chemoresistant HGSOC. Methods: Six ovarian cancer cell lines derived from ascites of relapsed HGSOC patients who had developed chemoresistant disease were characterized using multigene panel mutation testing, whole-genome DNA copy number analysis, and RNA sequencing. Drug responses to carboplatin and paclitaxel were determined using the CellTitre 96® AQueous One Solution Cell Proliferation Assay (Promega). For two of the resistant cell lines, high-throughput drug screens using three drug libraries—NCI-Approved Oncology Drug set (101 compounds), Kinase Inhibitor Library (210 compounds), and Targeted Agent Library (73 compounds)—were carried out to identify agents with activity in these resistant models. Apoptosis activation was measured using CellPlayer Caspase 3/7 assay (Essen Bioscience). Sensitivity to BH3-mimetics, ABT-737 and navitoclax (ABT-263), was tested in three of the cell lines and in one line, the effects of combining these agents with paclitaxel were assessed using CompuSyn. Results: TP53 mutations were identified in all cell lines, consistent with high-grade serous histology, and all lines were relatively resistant to carboplatin. AOCS5 and AOCS15 were the most resistant to carboplatin and AOCS5 was also highly resistant to paclitaxel. Drug library screens carried out on both AOCS5 and AOCS15 showed differential sensitivity to a number of drug classes. While AOCS5 was found to be generally resistant to most drugs, it was sensitive to ABT-737. RNA-seq identified relative overexpression of antiapoptotic genes in AOCS5, in particular BCL2L1, BCL2, and BCL2L2, in comparison to the other five cell lines. AOCS5 was more sensitive to navitoclax and ABT-737 compared with cell lines that did not overexpress antiapoptotic genes. Combining BH3-mimetics and paclitaxel showed synergism in the highly paclitaxel-resistant cell line AOCS5. Conclusion: Inhibition of apoptosis was identified as a potential mechanism of paclitaxel resistance, and overexpression of antiapoptotic genes may constitute a biomarker profile to predict sensitivity to BH3-mimetics in relapsed HGSOC. Citation Format: Cristina Mapagu, Sivatharsny Srirangan, George Au-Yeung, Australian Ovarian Cancer Study, Paul R. Harnett, David D. Bowtell, Anna deFazio. Antiapoptotic gene expression and sensitivity to BH3-mimetics in chemoresistant, high-grade serous ovarian cancer cell lines [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A48.