Abstract 2535: KX-01, a novel Src kinase inhibitor directed towards the peptide substrate site, induces robust apoptosis and synergizes with tamoxifen and chemotherapy in breast cancer

Abstract

Abstract New therapeutic regimens are needed to increase efficacy and reduce resistance of endocrine therapy and chemotherapy in breast cancer. c-Src is an oncogenic non-receptor tyrosine kinase that is up-regulated in approximately half of all breast cancer. However the efficacy of existing multi-kinase src inhibitors in breast cancer has been limited. KX-01 (Kinex Pharmaceuticals) is a novel class of clinical non-ATP src inhibitor that targets the peptide binding site. In a panel of breast cancer cell lines, KX-01 resulted in dose dependent inhibition of growth and induction of apoptosis that was independent of p53 status, and was preceded by rapid inhibition of src activity. KX-01 induced apoptosis in MDA-MB-468 cells and BT-549 cell lines reported to be resistant to multi-kinase src inhibitors. KX-01 (50 nM, 6 hours) resulted in significant accumulation of MDA-MB-231 cells (ERα−/PR−/HER2/neu−) and MCF-7 cells (ERα+) in G2/M phase. Immunofluorescent staining for mitotic phase marker phospho-histone 3 indicated that cells had arrested in mitotic phase and many of the mitotic arrested cells were undergoing apoptosis (TUNEL), a novel cell death for a small molecule tyrosine kinase inhibitor. KX-01 induced nuclear accumulation of cyclin B1 and activation of CDK1, MPM2 and Cdc25C that is required for progression past the G2/M checkpoint. KX-01 resulted in cytochrome C release and activation of caspases 6, 7, 8 and 9. Combinations of KX-01 (5-75 nM) with tamoxifen (TAM), paclitaxel (PAC) or doxorubicin (DOX) resulted in synergistic growth inhibition of MCF-7 cells (KX-01 + TAM) and MDA-MB-231 cells (KX-01 + DOX or PAC). In addition, synergistic induction of apoptosis was achieved with combination of KX-01 with DOX, PAC or TAM. c-Src induces phosphorylation of ERα at serines 118 and 167, sites required for full ERα activity. KX-01 combined with TAM resulted in decreased serine 167 phosphorylation and reduced ERα transcriptional activity. In tumor xenografts, KX-01 resulted in a dose dependent inhibition of MDA-MB-231 and MCF-7 tumor growth (1, 2.5 or 5 mg/kg body weight, twice daily by oral gavage). KX-01 exhibited synergistic growth inhibition of MCF-7 tumor xenografts when combined with tamoxifen and caused regression of MDA-MB-231 tumor xenografts when combined with paclitaxel or doxorubicin. Immunohistochemical (IHC) analysis in MCF-7 xenografts revealed that KX-01 + TAM induced robust apoptosis and inhibited neovascularization. KX-01 reduced metastasis to bone (femur) and lung as measured by PCR for detection of human chromosome 17. Interestingly, KX-01 resulted in reexpression of ERα and E-cadherin in MDA-MB-231 xenografts. These data define KX-01 as a potent and unique src kinase inhibitor that synergizes with endocrine therapy and chemotherapy to induce robust cell death, tumor growth inhibition/regression and inhibit metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2535.