KX-01, a novel Src kinase inhibitor directed toward the peptide substrate site, synergizes with tamoxifen in estrogen receptor α positive breast cancer

Abstract

KX-01 is the first clinical Src inhibitor of the novel peptidomimetic class that targets the peptide substrate site of Src providing more specificity toward Src kinase. The present study was designed to evaluate the effects of KX-01 as a single agent and in combination with tamoxifen (TAM) on cell growth and apoptosis of ERα positive breast cancer in vitro and in vivo. Flow cytometry demonstrated that KX-01 induced cell cycle arrest in G2/M phase. Immunofluorescent staining for mitotic phase markers and TUNEL staining indicated that cells had arrested in the mitotic phase and mitotic arrested cells were undergoing apoptosis. 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. Apoptosis resulted from activation of caspases 6, 7, 8, and 9. Combinational index analysis revealed that combinations of KX-01 with TAM resulted in synergistic growth inhibition of breast cancer cell lines. KX-01 combined with TAM resulted in decreased ERα phosphorylation at Src-regulated phosphorylation sites serines 118 and 167 that were associated with reduced ERα transcriptional activity. Orally administered KX-01 resulted in a dose dependent growth inhibition of MCF-7 tumor xenografts, and in combination with TAM exhibited synergistic growth inhibition. Immunohistochemical analysis revealed that combinational treatment reduced angiogenesis, and ERα signaling in tumors compared to either drug alone that may underlie the synergistic tumor growth inhibition. Combinations of KX-01 with endocrine therapy present a promising new strategy for clinical management of ERα positive breast cancer.

Melatonin: an inhibitor of breast cancer

“…Other signaling pathways elevated or activated in response to dLEN-induced circadian/melatonin disruption include c-SRC, FAK, cAMP, PKA, CREB, STAT3, NF-kB, and protein kinase C alpha and delta (PKCα and δ) (Lazennec et al 2001; Gonzalez-Angulo et al 2007; Díaz-Bessone et al 2011; Zhang et al 2011; Anbalagan et al 2012). In tissue-isolated tumors grown in a lighting schedule of 12h light/12 h dark (LD 12:12) with nocturnal circadian melatonin elevated during dark night, or in 12:12dLEN schedule but supplemented with melatonin in the nighttime drinking water, melatonin (endogenous or exogenous) was able to block or dramatically suppress the expression and/or phospho-activation of each of these signaling pathways to dramatically suppress tumor cell proliferation and resistance to endocrine and chemotherapies (Dauchy et.…”

The regulatory roles of phosphatases in cancer

“…PTPN13 can also inhibit tumour aggressiveness via the direct dephopshporylation of Src at Y419 (224), which is upregulated in tamoxifen resistance ERpositive breast cancer patients (228). New therapeutic routes using tamoxifen and SRC inhibitors are currently being examined (229,230).…”

Circadian Gating of Epithelial-to-Mesenchymal Transition in Breast Cancer Cells Via Melatonin-Regulation of GSK3β

“…The effect of MLT administration on E-cadherin and vimentin expression was examined in MCF-7/caSrc cells that were stably transfected with the caSrc kinase and exhibit low E-cadherin and elevated vimentin expression (28). Protein expression levels of E-cadherin were significantly increased, and vimentin expression was almost completely abolished (Fig.…”