[Effect and regulation of metformin on endometrial carcinoma subline of progestin-resistance].

OBJECTIVE To investigate the effect and mechanism of metformin on endometrial carcinoma subline of progestin-resistance and find whether metformin could regulate progestin-resistance in endometrial carcinoma. METHODS Ishikawa endometrial carcinoma cells were cultured for a long period in the presence of the synthetic medroxyprogesterone 17-acetate (MPA) to generate a subline refractory to the growth-suppressive effects of MPA, named Ishikawa/MPA cells. The effect of MPA (1, 5, 10, 20, 40 and 60 μmol/L) or metformin (1, 10, 20, 40, 60, 70 and 80 mmol/L) on proliferation of the Ishikawa/MPA and parental Ishikawa cells was detected by cell counting kit-8 (CCK-8) method. Western blot was used to detect the effect of metformin and (or) MPA on the expression of PR-B in the Ishikawa/MPA and Ishikawa cells. RESULTS The Ishikawa/MPA showed that growth stimulation rather than inhibition in the Ishikawa cells after low MPA concentration treatment. The doubling time of Ishikawa/MPA cell lines were (43±4) hours and that of Ishikawa cell line were (47 ± 3) hours. No changes in doubling time were observed (t=0.349, P= 0.572). Low concentration (1 and 5 μmol/L) of MPA could promote the growth of Ishikawa/MPA cells (by 3% and 13%). High concentration (10, 20, 40 and 60 μmol/L) of MPA could inhibited the growth of Ishikawa/MPA cells (by 4%, 3%, 9% and 40%) and the growth of Ishikawa cells (by 41%, 55%, 65% and 66% ). At the same concentration, the difference of inhibition rates between the two cell lines were statistically significant (P<0.01). Metformin (1, 10, 20, 40, 60, 70 and 80 mmol/L) could inhibite the growth of Ishikawa/MPA (by -10%, 20%, 56%, 89%, 97%, 98% and 99%) greater than those in parental Ishikawa cells (by -6%, 19%, 37%, 54%, 70%, 72% and 83%), and the inhibitory effect was dose-dependent manner. Western blot assay showed that for Ishikawa cells, the protein expression levels of PR-B in metformin group and MPA+metformin group were respectively (53.5±4.0)% and (37.7±5.2)%, which were higher than that in the control group [(23.4 ± 3.0)%], and there were significant the differences (P<0.01). For Ishikawa/MPA cells, the protein expression levels of PR-B in metformin group and MPA+metformin group were respectively (38.6±1.7)%, (36.3±2.5)%, which were higher than those in the control group [(6.4±1.6)%], and there were also significant differences (P<0.01). CONCLUSION Metformin may regulate the progestin-resistance in endometrial carcinoma by increasing the expression of PR-B.