Abstract 1946: Synergistic cell death induction in breast cancer cell lines by combining ABT-199 and cisplatin irrespective of estrogen receptor and p53 expression
Authors: Schaefer Benjamin , Weller Sandra , Beigl Tobias , Boepple Kathrin , Hoppe Reiner , Schulze-Osthoff Klaus , Kopp Hans-Georg , Aulitzky Walter E. , Essmann Frank 
Published: July 2021

Abstract
50 Years after the generation of the most studied human breast cancer cell line, MCF-7, many research results fundamentally changed patient outcomes for the better. The mortality of breast cancer in women has decreased significantly, especially in the last 30 years. But the total number of deaths is rising again in the last ten years. Considering that breast cancer is the most common cancer in women and the second most common cancer overall, with incidences of 24,2% and 11,6%, respectively, total numbers of new cases are in the millions every year.
First line drugs for the treatment of breast cancer often target microtubules (e.g. Vinblastine and Paclitaxel) or induce DNA damage (e.g. Carboplatin and Cisplatin (CisPt)). In addition to these classic therapeutic drugs new compounds that specifically target cancer-driving molecular alterations have been developed. Among these is the group of BH3-mimetics. The efficacy of several BH3-mimetics is investigated in numerous clinical trials while the BCL-2 specific inhibitor ABT-199 (Venetoclax) is already approved for clinical application in chronic lymphatic leukemia (CLL), acute myeloid leukemia (AML) and small lymphocytic lymphoma (SLL). BH3-mimetics target the apoptosis machinery by interacting with anti-apoptotic Bcl-2 proteins, mimicking the function of pro-apoptotic BH3-only proteins. In turn, the pro-apoptotic potential of pore-forming BCL-2 effectors BAX, BAK and BOK is released inducing mitochondrial outer membrane permeabilization and cell death.
Recently we reported synergistic cell death induction by ABT-199 in combination with the proteasome inhibitor Bortezomib (BOZ) in soft tissue sarcoma (STS) cells. ABT-199 and BOZ induce accumulation of BOK and the BH3-only protein NOXA (Muenchow et al. 2020). Here, we combined ABT-199, CisPt and Nutlin-3 in breast cancer cell lines that differ in expression of the estrogen receptor (ER) and p53 activity. Similar to the results in STS cells synergistic induction of apoptotic cell death was observed by FACS analysis of the mitochondrial membrane potential (TMRM) and exposure of phosphatidyl serine (Annexin-V). Western blot analysis revealed that ABT-199 induced accumulation of NOXA and MCL-1, irrespective of the ER status or p53 mutation. Simultaneous treatment with ABT-199 and CisPt or Nutlin-3 further increased expression of NOXA and MCL-1. Interestingly, qRT-PCR revealed enhanced expression of NOXA and MCL-1 mRNA in ABT-199 treated cells indicating transcriptional regulation. However, transcriptional induction of NOXA was also detected independent of p53 activity. Thus, combined therapeutic approaches using CisPt and ABT-199 should be effective irrespective of ER and p53 expression. Nevertheless, in p53 proficient tumors Nutlins might increase therapeutic efficacy.
Citation Format: Benjamin Schaefer, Sandra Weller, Tobias Beigl, Kathrin Boepple, Reiner Hoppe, Klaus Schulze-Osthoff, Hans-Georg Kopp, Walter E. Aulitzky, Frank Essmann. Synergistic cell death induction in breast cancer cell lines by combining ABT-199 and cisplatin irrespective of estrogen receptor and p53 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1946.