Deregulation of the CD44-NANOG-MDR1 associated chemoresistance pathways of breast cancer stem cells potentiates the anti-cancer effect of Kaempferol in synergism with Verapamil

Abstract

Chemoresistance is an imminent therapeutic challenge for breast cancer. Previous evidence suggests that breast cancer stem cells (BCSC) develop resistance through upregulation of stemness and chemo-evasion markers viz. SOX2, OCT4, NANOG, MDR1 and CD44, following anticancer chemotherapeutic treatments. Early studies suggest an inhibitory role of Kaempferol in BCSC propagation through downregulation of epithelial to mesenchymal transition. We hypothesized that the pathway involved in chemoresistance could be effectively addressed through Kaempferol (K), alone or in combination with Verapamil (V), which is an inhibitor of MDR1. We used K in combination with V, in multiple assays to determine if there was an inhibitory effect on BCSC. Both K and KV attenuated pH-dependent mammosphere formation in primary BCSC and MDA-MB-231 cells. RNA and protein (immunocytochemistry, western blot) expression of candidate markers viz. SOX2, OCT4, NANOG, MDR1 and CD44 were carried out in the presence or absence of candidate drugs in ex-vivo grown primary BCSC and MDA-MB-231 cell line. Immunoprecipitation assay, cell cycle analysis was carried out in MDA-MB-231. Our candidate drugs were not only anti-proliferative, but also downregulated candidate genes expression at RNA and protein level in both settings, with more robust efficacy in KV treatment than K; induced G2/M dependent cell cycle arrest, and interrupted physical association of CD44 with NANOG as well as MDR1 in MDA-MB-231. In primary tumor explant but not in adjacent normal tissue, our candidate drugs K and KV induced robust γH2AX expression. Thus, our candidate drugs are effective in attenuating BCSC survival.