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

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.

Diabetic concentrations of metformin inhibit platelet-mediated ovarian cancer cell progression

“…However, in our in vitro model we observed no change in proliferation or cell cycle in the presence of platelets. Furthermore, we previously reported that micromolar metformin did not alter the proliferation of SKOV3 or A2780 ovarian cancer cells, which was reaffirmed by Zhang and colleagues [21, 57]. Herein, we confirm that micromolar concentrations of metformin have no effect in SKOV3 cell proliferation and report that this is also true for UCI101 cells.…”

Association of metformin use with ovarian cancer incidence and prognosis: a systematic review and meta-analysis

“…Metformin had been shown to act as an inhibitor of proliferation by activating AMPK and consequently inactivating the mammalian target of rapamycin (mTOR)-related signaling pathway, which was considered one of the potential key mechanisms mediating the anti-tumor activity of metformin 31. Furthermore, metformin had been found to reduce ovarian cancer stem cells population,32 induce cell cycle arrest,33 and increase protein acetylation to alter patterns of gene expression34 by some in vitro and in vivo analyses. Recently, metformin was reported to have the potential to improve antitumor T cell immunity by dampening CD39/CD73-dependent myeloid-derived suppressor cells suppressive activity in ovarian cancer patients 20…”

Overexpression of the cancer stem cell marker CD117 predicts poor prognosis in epithelial ovarian cancer patients: evidence from meta-analysis

“…This speculation can be partly supported by a previous study that demonstrated that CD117 enhanced the tumorigenicity of EOC cells by conferring a CSC phenotype 29. Additionally, other mechanistic investigations have revealed that CD117 might contribute to EOC development by inducing epithelial–mesenchymal transition, a well-established molecular event that is involved in cell invasion and metastasis 30,31. Chene et al recently even have detected high expression of CD117 in the premalignant lesions of EOC, suggesting its potential role as a diagnostic marker for early ovarian tumorigenesis 32.…”