Abstract 1005: Dual targeting of MEK/MAPK1/2 and pro-survival autophagy to optimize antiestrogen treatment toward the eradication of antiestrogen resistant breast cancer

Abstract

Abstract In past studies, we showed that pro-survival autophagy mediates resistance to antiestrogen-induced apoptosis and facilitates the emergence of antiestrogen resistant breast cancer cells (Sammadar et al., Molecular Cancer Ther. 9, 2008). We also identified the pro-apoptotic BimEL protein as a key death effector of antiestrogen treatment and determined that BimEL pro-apoptotic activity is abrogated by a MEK1/MAPK1/2-dependent phosphorylation (Periyasamy-Thandavan et al., Breast Cancer Res. 14, 2012). In this study, we tested the hypothesis that the MEK1/MAPK1/2/BimEL signaling node simultaneously regulates antiestrogen- induced pro-survival autophagy and apoptosis in ER+ breast cancer cells. In our approach, we utilized T47-D and MCF-7 breast cancer cells and modulated the activity of MEK1/MAPK1/2/ BimEL expression with U0126, a small molecule inhibitor of MEK1, BimEL cDNA over-expression, or siRNA targeting under a variety of endocrine treatments. We also conducted studies in the presence or absence of the pan-caspase inhibitor ZVAD-fmk so that autophagy levels/function could be analyzed independent of effects mediated by BimEL-dependent caspase activation. Autophagic flux was measured by comparing the levels of lipidated LC3II in cell populations undergoing the different treatments in the presence or absence of chloroquine (CQ), a lysosomotropic agent that prevents autolysosomal turnover. These studies determined that: 1) dephosphorylated BimEL significantly attenuates autophagic flux, but primarily as a consequence of BimEL-induced caspase-activation; (2) BimEL-dependent apoptotic death induced in antiestrogen-treated ER+ breast cancer cells by MEK1 inhibition is not dependent on autophagy; and (3) agents that selectively target autophagy (i.e. CQ and spautin) enhance apoptosis induced by MEK1 blockade in breast cancer cells undergoing endocrine treatment. Based on these pre-clinical in vitro studies, we postulate that the eradication of antiestrogen resistant breast cancer will require the targeting of MEK1/MAPK1/2 to activate BimEL and pro-survival autophagy to eradicate cells surviving BimEL-dependent apoptosis. Citation Format: Mathew Manning, Suchreet Takhar, Sudharsan Periyasamy-Thandavan, Michael Cheng, Thomas Barrett, William Hill, Darren Browning, Muthusamy Thangaraju, Meghan McGee-Lawrence, Patricia V. Schoenlein. Dual targeting of MEK/MAPK1/2 and pro-survival autophagy to optimize antiestrogen treatment toward the eradication of antiestrogen resistant breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1005. doi:10.1158/1538-7445.AM2015-1005