Compound C rescues the anti-proliferative effects induced by metformin following E2 stimulation. 5′-bromo-2′-deoxyuridine assay results in Ishikawa and HEC-1-A cells following treatment with E2, E2 and metformin or E2, metformin and pre-treatment with compound C for 24 h. Cells were incubated with metformin and/or E2 for 24 h with or without pre-treatment with compound C for 24 h. Results represent the mean ± standard error of the mean of triplicate samples and are representative of three independent experiments. *P<0.05, E2 group compared with control. ΔP<0.05, E2 + Met group compared with the E2 group. #P<0.05, E2 + Met + Com group compared with the E2 + Met group. Con, control; E2, 10−6 M 17β-estradiol; E2 + Met, 10−6 M 17β-estradiol combined with 5 mM metformin; E2+ Met + Com, 10−6 M 17β-estradiol combined with 5 mM metformin and pre-treatment with 5 µM compound C.