Esculentoside A suppresses breast cancer stem cell growth through stemness attenuation and apoptosis induction by blocking IL-6/STAT3 signaling pathway.

Breast cancer stem cells (CSCs) survive in inflammatory microenvironment, their survival are regulated by inflammatory cytokines and signaling pathways. Esculentoside A (EsA), a triterpene saponin derived from the root of Phytolacca esculenta, possesses antiinflammation effects; but whether it has anticancer activity is unknown. The purpose of this study is to test the inhibitory effect of EsA on the growth of breast CSCs and to elucidate its probable mechanisms of action. The proliferation inhibitory effect of EsA on breast CSCs in vitro were determined by cytotoxicity, mammosphere formation inhibition, apoptotic cell detection assays, and in vivo tumor growth inhibition experiment. The possible molecular mechanisms elucidating the inhibitory effect of EsA on breast CSC growth were examined with western blotting. EsA caused proliferation and mammosphere formation inhibition of breast CSCs; induced breast CSCs apoptotic death; suppressed the growth of tumors generated from breast CSCs significantly; the expressions of stemness proteins including ALDH1A1, Sox2, and Oct4 were downregulated; proapoptotic proteins, Bax and cleaved caspase-3 were upregulated, whereas the antiapoptotic protein Bcl-2 was reduced; IL-6/STAT3 pathway proteins including IL-6, phosphorylated STAT3 (Tyr705), and STAT3 (Ser727) were downregulated significantly in EsA-treated breast CSCs and tumor tissues. EsA inhibited breast CSC growth in vitro and in vivo through stemness attenuation and apoptosis induction by blocking IL-6/STAT3 signaling pathway; it might serve as a novel candidate agent for human breast cancer treatment and/or prevention.