RESUMO
High doses of metformin induces oxidative stress (OS) and transforming growth factor ß1 (TGF-ß1) in breast cancer cells, which was associated with increased cancer stem cell population, local invasion, liver metastasis and treatment resistance. Considering the impact of TGF- ß1 and OS in breast cancer and the interrelation between these two pathways, the objective of this work was to investigate the effects of consecutive metformin treatments, at a non-cytotoxic dosage, in TGF- ß1 targets in MCF-7 and MDA-MB-231 cells. Cells were exposed to 6 µM of metformin for seven consecutive passages. Samples were collected to immunocytochemistry (evaluation of p53, Nf-кB, NRF2 and TGF-ß1), biochemical (determination of lipoperoxidation, total thiols and nitric oxide/peroxynitrite levels) and molecular biology analyzes (microarray and Real-time quantitative array PCR). Microarray analysis confirmed alterations in genes related to OS and TGF-ß1. Treatment interfered in several TGF-ß1 target-genes. Metformin upregulated genes involved in OS generation and apoptosis, and downregulated genes associated with metastasis and epithelial mesenchymal transition in MCF-7 cells. In MDA-MB-231 cells, metformin downregulated genes involved with cell invasion, viability and proliferation. The results shows that even a non-cytotoxic dosage of metformin can promote a less aggressive profile of gene expression in breast cancer cells.