Abstract 3710: Synergistic cell death induction in ovarian cancer by cisplatin and ABT-199 is mediated by expression of NOXA

Abstract Ovarian cancer is among the top ten leading causes of cancer death in women worldwide with a mortality rate of roughly 5% among all cancer deaths. So far, there are no recommended screening tests for the early detection of ovarian cancer. Therefore, patients are frequently diagnosed at late stages of ovarian cancer, which is associated with unfavorable 5-year survival. Patients suffering from ovarian cancer often show a good response to initial therapy with platinum-based compounds and/or taxanes subsequent to resection of the affected tissue. Unfortunately, ovarian cancer shows a high frequency of relapse and after chemotherapy persistent tumor cells re-expand and successively evolve into therapy-resistant tumors. We recently reported that cisplatin (cisPt) treatment of ovarian cancer cells enhances mitochondrial content and mitochondrial reactive oxygen species (Kleih et al. 2019). We therefore speculated that the enhanced mitochondrial content primes cisPt-treated cells for apoptosis induced by BH3 mimetic drugs, such as Venetoclax (ABT-199), that act on anti-apoptotic Bcl-2 proteins at the outer mitochondrial membrane. To explore this hypothesis, we investigated whether the combined administration of cisPt and ABT-199 leads to a synergistic cell death induction in ovarian cancer cells with different cisPt resistance and mitochondrial content. Detection of cell death by flow cytometric measurements of the mitochondrial membrane potential and exposure of phosphatidylserine demonstrated a synergistic cell death induction by cisPt and ABT-199 in OVCAR4 and OVCAR8 cells, irrespective of the cisPt resistance. Interestingly, Western blot analysis revealed that ABT-199 induced the accumulation of the BH3-only protein NOXA in both cancer cell lines. Accumulation of NOXA was dependent on ABT-199-mediated activation of the stress-responsive transcription factor ATF4. Knock-down experiments showed that apoptosis of cisPt-resistant OVCAR8 cells by the combined treatment with ABT-199 and cisPt was entirely dependent on NOXA. Moreover, also cisPt-sensitive OVCAR4 cells revealed an initially reduced apoptosis induction by the NOXA knock-down. Our data therefore elucidate the molecular mechanism of the synergistic efficacy of cisPt/ABT-199 combination therapies, which should be promising especially for the treatment of recurrent tumors developing reduced sensitivity to cisPt-based treatments. Citation Format: Benjamin Schaefer, Sandra Weller, Tobias B. Beigl, Klaus Schulze-Osthoff, Hans-Georg Kopp, Walter E. Aulitzky, Frank Essmann. Synergistic cell death induction in ovarian cancer by cisplatin and ABT-199 is mediated by expression of NOXA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3710.