Abstract 1725: HDAC inhibition induces Bim expression and apoptosis in breast cancer cells undergoing paclitaxel or antiestrogen treatment.

Abstract Paclitaxel functions by preventing microtubule degradation, leading to mitotic arrest and apoptotic death. Of particular interest, paclitaxel-induced death in breast cancer cells is dependent, in part, on the levels of BimEL, a pro-apoptotic member of the Bcl-2 family of proteins. In addition, our recent studies demonstrated that BimEL is required for 4-hydroxytamoxifen-induced apoptosis of estrogen receptor positive (ER+) MCF-7 breast cancer cells [Breast Cancer Res. 2012 Mar 19;14(2):R52]. In contrast, we demonstrated low-level BimEL expression in ER+ T47D breast cancer cells that do not undergo antiestrogen-induced apoptosis. Thus, low-level BimEL expression in ER+ breast cancer may predict a poor apoptotic threshold which ultimately would facilitate the development of acqured resistance to paclitaxel, as well as antiestrogen therapy. Based on the ability of HDAC inhibitors to increase the transcription of pro-apoptotic genes, we hypothesized that the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) would increase BimEL expression in T47D breast cancer cells and induce a robust apoptotic response to paclitaxel chemotherapy and antiestrogen treatment. In this study, we now demonstrate that SAHA does significantly up-regulate BimEL expression in T47D cells, as well as in MCF-7 cells. Concomitant with BimEL upregulation, SAHA sensitizes T47D and MCF-7 cells to paclitaxel-induced apoptosis. Similarly, SAHA sensitizes T-47D cells to antiestrogen-induced apoptosis, while augmenting the level of antiestrogen-induced apoptosis in MCF-7 cells. These studies indicate that the pro-apoptotic protein BimEL is required for SAHA-induced sensitization of breast cancer cells to paclitaxel and/or antiestrogen-induced apoptosis. Currently, siRNA studies are being conducted to determine if BimEL is a key death effector in response to SAHA treatment and if the increased death from SAHA and paclitaxel or SAHA and antiestrogens is synergistic or additive. Our results provide strong support for the use of HDAC inhibitors when designing novel combination therapies to reduce the emergence of acquired resistance in breast cancer cells undergoing chemo- or antihormonal therapy. Acknowledgement: this work was supported by teh MCG foundation and NIHRO1 CA121438 to P.V.S. Citation Format: Aric Berning, Alexander Eason, Nathan Gilley, Suchreet Takhar, Sally ElShafey, Muthusamy Thangaraju, Patricia V. Schoenlein. HDAC inhibition induces Bim expression and apoptosis in breast cancer cells undergoing paclitaxel or antiestrogen treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1725. doi:10.1158/1538-7445.AM2013-1725