Metformin inhibits proliferation and promotes apoptosis of HER2 positive breast cancer cells by downregulating HSP90

Purpose: To investigate the effects and the possible molecular mechanisms of metformin on HER2 positive breast cancer cells. Methods: SK-BR-3 HER2 positive breast cancer cells were treated with different concentrations of metformin. The growth inhibitory rate of the cells was calculated by MTT assay, apoptosis was detected by flow cytometry, and the expression level of heat shock protein 90 (HSP90) was performed by Western blot analysis. A control group consisted of cells treated with PBS. Results: With increased concentrations of metformin, cell growth inhibitory rates increased. The growth inhibitory rates with 0.5 mM, 2mM or 8mM metformin were significantly higher compared with the control group (p<0.05). Apoptosis in the metformin treated cells was also significantly higher compared with the control group (p=0.003). The expression level of HSP90 in the metformin group was significantly lower than that in the control group. Conclusion: Metformin can inhibit the proliferation and promote apoptosis of HER2 positive breast cancer cells,which is maybe related to inhibition of HSP90.