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Anti-Tumor Activity of Metformin in Human Epidermal Growth Factor Receptor 2 Positive Breast Cancer Cells

Breast Cancer (BC) is the leading cause of cancer death in women. One BC subtype is very aggressive with amplification of human epidermal growth factor receptor 2 (HER2) protein. Although specific HER2+ targeting agents are available, most of HER2+ BC patients develop resistant to these agents. Recent studies show that metformin, is able to become anti-tumor in various cancer cells. This research aims to evaluate anti-tumor activities of metformin to HER2+ BC cells in both sensitive and resistant to trastuzumab. A series of assays were performed to evaluate metformin anti-tumor activities in HCC-1954 and SKBR-3 HER2+ BC cells. MTT assay was performed to evaluate cell death, and inhibitory concentration (IC50), while scratch assay was performed to assess inhibition of cell migration and clonogenic assay to assess cell proliferation. p<0.05 was considered to be significant. Metformin could suppress the number of HER2+ BC cells. Viability assay showed suppression of viable cells after metformin incubation of 60 and 600 µM compared to control, 30 and 90%, respectively. Surprisingly, IC50 of metformin was smaller in HER2+ BC HCC-1954 cells that resistant to trastuzumab compare to the sensitive one (SKBR-3). Both were below 1 µM, with R2 more than 0.95. Additionally, clonogenic assay showed less colony number and colony area with at least p < 0.05 in colony number and p < 0.01 in the area. In addition, metformin inhibited cell migration of HER2+ BC cells. Metformin shows a potency as anti-tumor by inducing cell death, inhibiting cell proliferation and cell migration of HER2+ BC cells.