Abstract: Objective To explore the mechanism of metformin in inhibiting breast cancer cell line MCF-7. Methods MCF-7 cells were cultured for 48 h in the presence or absence of 16.56 g/L metformin，total protein was extracted from cells and expression of nu-clear factor-kappa B（NF-κB） p65 and Lin28B were detected by Western blot. Furthermore， transcription levels of HMGA2 and H-Ras， which are regulated by microRNA let-7，were determined by RT-PCR. Results NF-κB p65 and Lin28B expression declined signifi-cantly after 48-h drug treatment（t=23.44，t=14.24；P<0.05）.Transcription levels of HMGA2 and H-Ras，which are related to self-renewal and multipotent differentiation of tumor cells，decreased 85%（P＜0.05） and 96%（P＜0.05），respectively，based on 2-△△Ct measurements. Conclusions Metformin at 16.56 g/L can effectively reduce NF-κB and Lin28B expression and inhibit HMGA2 and H-Ras transcrip-tion in MCF-7 cells.These findings suggest that metformin inhibits breast cancer at the cellular level.

Key words:  Breast neoplasms, Metformin, NF-κB p65, Lin28B, HMGA2, H-Ras