Abstract 2289: Potential role for Src kinase inhibitors in PKCα-overexpressing breast cancer

Abstract

Abstract The purpose of this study was to evaluate the role of Src kinase in estrogen induced growth inhibition in the T47D/PKCα breast cancer cell line. Our lab has previously shown that constitutive overexpression of protein kinase Cα (PKCα) imparts a tamoxifen-resistant, hormone-independent phenotype in the T47D:A18 breast cancer cell line (Chisamore, et al. Clin Cancer Res 2001; 7(10):3156-65). Furthermore 17β-estradiol (E2) inhibits tumor growth in vivo as well as inhibits colony formation when cells are grown in 3D Matrigel (Zhang, et al. Mol Cancer Res 2009; 7(4):498-510). Here we show that the Src kinase inhibitor PP2 (5 μM) significantly inhibited T47D/PKCα colony formation in 3D Matrigel, but was unable to inhibit proliferation in vitro. The combination of PP2 and E2 treatment in 3D Matrigel did not further decrease colony number when compared to either alone. This suggests that these compounds may be acting on the same pathway and that E2 may be inhibiting Src kinase activity. To examine the effect of E2 on Src in T47D/PKCα xenograft tumors we probed the phosphorylation state of Src on Tyr416, known to be necessary for its full kinase activity. Src is basally phosphorylated on Tyr416 in T47D/PKCα cells. Interestingly, E2 treatment in vivo resulted in a decrease in phospho-Src. Erk 1/2, a downstream target of Src, is basally phosphorylated in T47D/PKCα cells. E2 treatment also resulted in a decrease in phospho-Erk1/2, in accordance with decreased Src phosphorylation. A reduction in phosphorylated Src and Erk1/2 was not seen in vitro indicating that the extracellular matrix is necessary for E2 to elicit an inhibitory effect on these proteins. In this study, we report that E2 treatment in vivo inhibited Src phosphorylation in tamoxifen resisitant T47D/PKCα tumors. Additionally pharmacological inhibition of Src inhibited T47D/PKCα colony formation in 3D Matrigel. Taken together, our results suggest that a Src inhibitor may be a potential therapeutic option for patients with PKCα-overexpressing breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2289. doi:10.1158/1538-7445.AM2011-2289