Abstract 4612: Inhibition of BCL2 and XPO1 demonstrates synergistic effects in triple-negative breast cancer cell lines
Authors: Jackson Marilyn Marie , Smoots Stephen G. , Dominguez Adrian T. , Dus Evan , Bagby Stacey , Binns Cameron , Pitts Todd M. , Diamond Jennifer R. 
Published: March 2024

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer, accounting for about 15-20% of all breast cancers. Characterized by a lack of estrogen and progesterone receptors and non-amplified HER2, treatment options are limited compared to other breast cancer subtypes. The aim of this study was to evaluate eltanexor (Elta), an XPO1 inhibitor, in combination with venetoclax (Ven), a Bcl-2 inhibitor to promote apoptosis in TNBC models.

Methods: CellTiter-Glo Cell Viability Assay was utilized to determine cell viability in 6 TNBC cell lines after 72-hour exposure to no drug, Elta, Ven or the combination. Synergy scores were determined using the Bliss model in SynergyFinder+, scores 10 or above indicating synergy. Apoptosis (by Annexin V) was assessed after 24- and 48-hour exposure to drug via flow cytometry. Immunoblots were used to assess the mechanism of action in cell lines treated for 24 hours.

Results: CellTiter Glo displayed greater anti-proliferative activity in combination versus single agent exposure. Synergy was observed in CAL-120, BT-20, and MDA-MB-468 cell lines, with synergy score values ranging from -13.22 - 25.07. Additive effects were observed in other cell lines. An increase in apoptosis was observed in CAL-51 and MDA-MB-231 cells after 24- and 48-hour treatment that was greater with the combination. CAL-51 cells exposed to single agent Ven or Elta [0.5 µM] for 24 hours had significantly less apoptosis than those exposed to the combo (p = &lt;0.0001). After a 48-hour exposure, CAL-51 cells exposed to single agent Ven had less apoptosis than in combination with Elta [0.1 µM] (p = 0.0431) or Elta [0.5 µM] (p = 0.0036 µM]. Additionally, single agent Elta [0.5 µM] resulted in less apoptosis than the combination (p = 0.0067). Similar results were observed in MDA-MB-231 cells. We observed an increase in apoptotic markers with the combination in all cell lines treated. In all cell lines, DNA-damage marker pH2Ax increased with Ven and the combination. In the CAL-51 cells, p53 increased following Elta or combination exposure. In the MDA-MB-231 cells, a decrease in the anti-apoptotic protein MCL1 was observed with Elta or combination.

Conclusion: The combination of Elta and Ven resulted in increased apoptosis and antiproliferative activity in TNBC cell lines. Combined, the two drugs synergistically functioned to increase DNA damage and promote apoptotic cell death. This work supports the continued evaluation of Elta and Ven in TNBC.

Citation Format: Marilyn Marie Jackson, Stephen G. Smoots, Adrian T. Dominguez, Evan Dus, Stacey Bagby, Cameron Binns, Todd M. Pitts, Jennifer R. Diamond. Inhibition of BCL2 and XPO1 demonstrates synergistic effects in triple-negative breast cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4612.