Abstract P3-03-09: Dual targeting of BCL2 and MDM2 as a novel therapeutic strategy in ER+ breast cancer model
Authors: De Pradip , Aske Jennifer Carlson , Pocha Poulin , Sulaiman Michael , Thompson Ethan , Dey Nandini 
Published: March 2020

Abstract
Background: Apoptosis is the therapeutic goal following the administration of anti-cancer drugs. BCL2 and p53 are two critical nodes in the apoptosis signaling pathway. BCL2 is overexpressed in approximately 80% of primary ER+ breast cancer (BC) patients (Merino D et al. Oncogene 2016). Venetoclax is a BCL2 selective inhibitor found to be active in clinical trials for solid tumors, including ER+ BC breast cancer (Lok SW et al. Cancer Discovery 2019). MDM2/MDM4 is a proliferating protein involved in tumorigenesis via degradation of p53. In our ER+ BC breast cancer cohort (Avera Cancer Institute, Sioux Falls, South Dakota), we observed TP53 and MDM2/4 alterations in 25% and 14% of patients respectively. Aim: Here, we hypothesize that concomitant p53 activation (by an MDM2 inhibitor, e.g., AMG232) and BCL2 inhibition (by venetoclax) induce maximum apoptosis and markedly reduce tumor cell proliferation in ER+/TP53 WT BC cells. Methods: We analyzed the expression pattern of 129 ER+ BC breast cancer patients whose tumors were subjected to comprehensive genomic profiling [FoundationOne]. We tested the anti-proliferative and apoptotic activity of venetoclax alone, AMG 232 alone, and a combination of venetoclax plus AMG 232 along with fulvestrant in ER+ BC breast cancer cells (MCF7, Zr-75-1, & MDA-MB415). Results: 1) AMG 232 binds the MDM2 protein, blocks MDM2-p53 interaction, and induces p53 expression and activity, 2) p53 effector molecule p21 is robustly induced following the treatment of AMG 232, 3) the anti-proliferative activity of venetoclax or AMG232 was observed by 3D-ON-TOP clonogenic assay and real-time monitoring in an IncuCyte Zoom, 4) ER+ /TP53 wild-type (WT) cell lines exhibited an increase in annexin V positivity (initiation of apoptotic activity) following venetoclax or AMG 232 treatment, 5) importantly, a combination of venetoclax plus AMG232 robustly induced the apoptotic markers e.g. cleaved-CASPASE3/7 and cleaved PARP1 protein expression in all ER+ BC cell lines, 6) high mitochondrial depolarization was also observed following the combination of treatment, and 7) similar to protein expression data, mRNA data also showed that pro-apoptotic/cell cycle inhibitor transcripts such as p21 and PUMA mRNA expression were significantly increased and pro-survival transcripts such as survivin and stathmin mRNA expression were significantly decreased following the combination treatment. Conclusion: Our data reveal the potential of simultaneously targeting these two apoptosis regulators and provides a rational basis for clinical testing of this therapeutic approach for ER+ BC breast cancer patients that retain WT-TP53.
Citation Format: Pradip De, Jennifer Carlson Aske, Poulin Pocha, Michael Sulaiman, Ethan Thompson, Nandini Dey. Dual targeting of BCL2 and MDM2 as a novel therapeutic strategy in ER+ breast cancer model [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-03-09.