Inhibitory effects of metformin at low concentration on epithelial–mesenchymal transition of CD44+CD117+ ovarian cancer stem cells

Rongrong Zhang,Wentao Li,Ping Zhang,Hong Wang,Guishan Xiao,Chenwei Li,Dongming Hou

doi:10.1186/s13287-015-0249-0

Abstract

BackgroundAlthough metformin, a first-line drug for treating diabetes, may play an important role in inhibition of epithelial ovarian cancer cell growth and cancer stem cells (CSCs), metformin at low dose showed less effect on the proliferation of ovarian cancer cells. In this study, we evaluated the effect of metformin at low dose on ovarian CSCs in order to understand the molecular mechanisms underlying.MethodsThe inhibitory effects of metformin at los dose on proliferation and population of ovarian cancer cells including SKOV3 and A2780 were assessed by cell proliferation assay and flow cytometry. Quantitative real-time PCR assay on expression of Bcl-2, Survivin and Bax was performed to determine the effect of metformin at low dose on epithelial-mesenchymal transition (EMT) of cancer cells and CSCs. Tumor sphere formation assay was also performed to evaluate the effect of metformin on spheres forming ability of CSCs. The therapeutic efficacy and the anti-CSC effects of metformin at low dose were investigated by using both SKOV3 cells and primary tumor xenografts. In addition, the CSC frequency and EMT in tumor xenograft models were also assessed by flow cytometry and quantitative real-time PCR.ResultsMetformin at low dose did not affect the proliferation of ovarian cancer cells. However, it inhibited population of CD44+CD117+ selectively, neither CD133+ nor ALDH+ cells. It suppressed expression of snail2, twist and vimentin significantly in cancer cells and CD44+CD117+ CSCs in vitro. Low dose of metformin reduced survivin expression in CSCs. Low concentrations of metformin inhibited the secondary and the tertiary tumor sphere formation, decreased SKOV3 and primary ovarian tumor xenograft growth, enhanced the anticancer effect of cisplatin, and lowered the proportion of CD44+CD117+ CSCs in the xenograft tissue. Metformin was also associated with a reduction of snail2, twist, and vimentin in CD44+CD117+ ovarian CSCs in vivo.ConclusionsOur results implicate that metformin at low dose inhibits selectively CD44+CD117+ ovarian CSCs through inhibition of EMT and potentiates the effect of cisplatin.

Highlights

Metformin, a first-line drug for treating diabetes, may play an important role in inhibition of epithelial ovarian cancer cell growth and cancer stem cells (CSCs), metformin at low dose showed less effect on the proliferation of ovarian cancer cells
Flow cytometry assay was performed by analysis of the percentage of aldehyde dehydrogenase (ALDH)+, CD133+, and CD44+CD117+ cells in SKOV3 and A2780 cells treated with metformin at a dose range of 0.03–0.3 mM for 72 hours
Metformin at low dose resulted in a 2.5-fold decrease in the CD44+CD117+ CSC population at a metformin dose of 0.1 mM and in a 2.8-fold decrease at a dose of 0.3 mM in SKOV3 cells (Fig. 2a)

Summary

Introduction

A first-line drug for treating diabetes, may play an important role in inhibition of epithelial ovarian cancer cell growth and cancer stem cells (CSCs), metformin at low dose showed less effect on the proliferation of ovarian cancer cells. We evaluated the effect of metformin at low dose on ovarian CSCs in order to understand the molecular mechanisms underlying. To understand the exact biological features of ovarian carcinoma, series of new studies are being focused on cancer stem cells (CSCs). Study of CSCs suggests that these are a rare population of cancer cells with inherent chemoresistance, capable of regeneration of the various cell types within tumors, which leads to relapse of therapy [3, 4]. Well-studied cell surface biomarkers including CD44/ CD117, CD133, and aldehyde dehydrogenase (ALDH) are used extensively to identify ovarian CSCs [5,6,7,8,9,10,11]

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