Effects of metformin on radiosensitivity of breast carcinoma cells with different estrogen receptors stasus and its mechanism / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the effects of metformin on the radiosensitivity of breast carcinoma cells with different estrogen receptors stasus (MCF-7 and MDA-MB-231) and to explore the underlying mechanisms.Methods Two cell lines,MCF-7 and MDA-MB-231 in logarithmic phase were divided into four groupscontrol group,drug group (mefformin),irradiation group and experimental group (irradiation plus metformin).MTT assay and the clonogenic assay were performed to evaluate the effects of metformin on the proliferation and survival of breast carcinoma cell lines,respectively.The change of cell cycle distribution and apoptosis rates were measured by propidium iodide (PI) and Hoechst 33342 staining analysis repectively.Western blot was used to detect the expression of p-AMPK and p-mTOR.Resutls Metformin could obviously inhibit the proliferation of the two breast carcinoma cell lines in a dose dependent manner.The cloning formation capacity was decreased in the group of metformin plus irradiation,which displayed the values of Dq,D0 and SF2 significantly lower than those of irradiation alone group (MCF-7t =9.305,14.528,13.708,P ＜0.05;MDA-MB-231t =19.560,16.893,36.048,P ＜0.05),and the sensitizing enhance rate (SER) of D0 were 1.29 and 1.21 for MCF-7 and MDA-MB-231 cell lines,respectively.Compared with irradiation alone,metformin plus irradiation obviously increased the proportion of cells in the G2/M phase in both cell lines (t =6.103,38.431,P ＜ 0.05).Metformin plus irradiation also enhanced radiation-induced apoptosis in both cell lines so that the apoptosis rates were higher than that in the metformin group or irradiation alone group (t =9.143,14.561,P ＜ 0.05).In MCF-7 cell lines,the expression of p-AMPK in the metformin combined with irradiation group was significantly higher than other treatment groups (t =35.194,8.647,10.316,P ＜ 0.05),but no significant changes of p-AMPK expression in MDA-MB-231 cell lines was observed (P ＞ 0.05).While inhibition of p-mTOR by metformin was observed in both cell lines (MCF-7t =80.133,31.820,11.308,P＜0.05;MDA-MB-231t=12.436,15.757,8.402,P＜0.05).Conclusions This study suggests that metformin possessed a strong radiosensitizing potential in both breast carcinoma cell lines of MCF-7 (ER positive) and MDA-MB-231 (ER negative).This radiosensitizing effect may result from the activation of AMPK or AMPK-independent pathway,inhibition of mTOR signaling pathway,and the enhancement of radiation-induced G2/M phase arrest and cell apoptosis after metformin treatment.