Abstract 1235: EPHA2-targeted therapy enhances the cytotoxicity of eicosapentaenoic acid against triple-negative inflammatory breast cancer

Abstract

Abstract Background: Inflammatory breast cancer (IBC) is the most aggressive form of breast cancer. We have previously reported that mediators of inflammation, such as COX-2, promote the growth of Triple-Negative receptor (TN) IBC xenografts; therefore, inflammation in TN-IBC has a unique opportunity as a therapeutic strategy. Eicosapentaenoic acid (EPA), a non-toxic omega-3 fatty acid with anti-inflammatory properties, has partially reduced tumor growth in pre-clinical models of TN-IBC. Therefore, our goal is to develop a novel non-toxic approach that enhances EPA efficacy against TN-IBC in combination with targeted therapy. Methods and Results: Using a high-throughput, siRNA screen (939 genes) in the TN-IBC cell line SUM149PT, we identified Ephrin type-A receptor 2 (EPHA2), an oncogenic cell-surface receptor tyrosine kinase, as a target that modulates the sensitivity of TN-IBC cells to EPA treatment. To determine the clinical relevance of EPHA2, we interrogated a meta-analysis of breast cancer mRNA expression data sets, and found that high EPHA2 tumor expression was significantly correlated with poor overall survival in TN-IBC patients, compared to low EPHA2 expressing tumors (P = 0.01). We observed no significant correlations to other breast cancer subtypes. Similar findings were observed in vitro were EPHA2 expression predominantly occurred in the TN-IBC subtypes (19 of 30) among 49 breast cancer cell lines. Gain/loss-of-expression studies were performed to functionally validate EPHA2 as a synergistic combinational target with EPA in two EPHA2-expressing TN-IBC models, SUM149PT and BCX010, using proliferation and apoptosis assays in vitro and established tumor xenografts in vivo. EPHA2 gene silencing significantly reduced cell growth and induced apoptosis in combination with EPA when compared with untreated control and monotherapy in vitro (P < 0.05) and in vivo (P < 0.001), while vector-induced EPHA2 expression reversed cell growth reduction and apoptosis induction following combination treatment with EPA in vitro (P < 0.05). To translate our findings to the clinic, we validated that dasatinib, a small molecule inhibitor of EPHA2, in combination with EPA significantly enhanced cell death of SUM149PT and BCX010 cells in vitro when compared to non-treated and monotherapy (P < 0.05). Finally, using membrane fluidity assessment and reverse-phase protein array (300 antibodies), we determined that combination treatment efficacy depended on EPA/EPHA2 inhibition-mediated increase in cell membrane rigidity (P < 0.001, compared to monotherapy), which subsequently inhibited receptor tyrosine kinase signaling activity, potentially resulting in induction of apoptosis. Conclusions: Our preclinical findings provide a rationale for the development of a phase 1 clinical trial investigating combination EPA and EPHA2-inhibitors in patients with EPHA2-positive TN-IBC. Citation Format: Angie M. Torres-Adorno, Heidi Vitrac, Yuan Qi, Yiwen Yang, Peiying Yang, Bedrich L. Eckhardt, Naoto T. Ueno. EPHA2-targeted therapy enhances the cytotoxicity of eicosapentaenoic acid against triple-negative inflammatory breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1235. doi:10.1158/1538-7445.AM2017-1235