Abstract 2931: Calmodulin-DR5 binding in breast cancer: Independent of TRA-8 sensitivity

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Breast cancer is estimated to be the leading cause of new cancer cases and second in cancer related deaths among American women (Cancer: 63, 1153-1154, 2013). Classification of breast cancers into receptor-based subtypes, including estrogen receptor (ER) positive or triple negative breast cancers, establish targets that guide individualized treatment for patients (J Clin Oncol: 27,1153-1154, 2009). Drug resistant ER positive breast cancers and triple-negative breast cancers are prolific breast cancers with poor clinical outcome. TRA-8 is a death receptor-5 (DR5) specific agonistic antibody with tumoricidal activity in vitro and in vivo without inducing normal hepatocyte apoptosis (Nature Med: 7, 954-960, 2001). ER positive and triple negative breast cancer cell lines have a range of in vitro sensitivity to TRA-8 mediated cytotoxicity (Clin Cancer Res: 9, 3731-3741, 2003, Breast Cancer Res Treat: 133, 417-426, 2012). Calmodulin (CaM) is overexpressed in breast cancer (J Clin Oncol: 4, 994-1012, 1986, Cancer Res: 42, 2571-2574, 1982). Our lab has shown CaM binds to DR5 and plays a role in DR5 mediated DISC formation in ER positive MCF-7 and triple negative MDA-MB231 breast cancer cell lines (Proc. AACR; 2014, Abstract nr 2282). The goal of this study is to characterize an interaction between CaM and DR5 in a panel of ER positive and triple negative breast cancer cell lines representing a range of sensitivity to TRA-8 mediated cytotoxicity. CaM-DR5 interaction was characterized in a panel of triple negative breast cancer cell lines: MDA-MB-231, MDA-MB-468, HCC1937, and HCC1143 and ER positive breast cancer cell lines: ZR-75-1, T47D, and MCF-7 representing the range of sensitivity to TRA-8 (Clin Cancer Res: 9, 3731-3741, 2003, Breast Cancer Res Treat: 133, 417-426 2012). DR5 was immunoprecipitated, using TRA-8 conjugated beads, from the panel of breast cancer cell lines lysates. CaM co-immunoprecipitated with DR5 from all breast cancer cell lines lysates, showing endogenous CaM and DR5 form a complex. CaM pull-down of DR5 from the breast cancer lysates in the presence of 1 mM Ca2+ or 2 mM EGTA showed CaM/DR5 interaction is calcium dependent. We present evidence for a Ca2+ dependent interaction between CaM and DR5 in a panel of ER positive and triple negative breast cancer cell lines independent of TRA-8 sensitivity. Results from this study provide the basis to further characterization of CaM-DR5 interactions and to investigate the role of CaM/DR5 binding in DR5-mediated DISC formation, which could lead to novel strategies to overcome drug resistance in breast cancers. Results suggest that direct interaction between CaM and DR5 could represent a potential site for breast cancer chemotherapeutics. Citation Format: Romone M. Fancy, Donald J. Buchsbaum, Tong Zhou, Yuhua Song. Calmodulin-DR5 binding in breast cancer: Independent of TRA-8 sensitivity. [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 2931. doi:10.1158/1538-7445.AM2015-2931