17-β estradiol promotes autophagy and induces cellular senescence in breast cancer cells.

e12523 Background: The fact that estrogen (17-β estradiol or E2) is a known carcinogen notwithstanding, mounting evidence suggest that E2 has the potential to exert anti-cancer effects against various forms of cancer. Using in vitro models we, and others, have previously demonstrated that E2 disrupts intracellular iron metabolism in such a way that arrests cell cycling in breast and ovarian cancer cells. However, the cellular and molecular correlates underlying this cytostatic effect of E2 in cancer cells remain elusive. Methods: In this study, metastatic (MDA-MB-231) and non-metastatic (MCF-7) breast cancer cells treated with 20 nM E2 were assessed for mitochondrial function, cell proliferation, apoptosis and senescence at different time points post treatment. Results: E2 treatment resulted in a significant mitochondrial membrane depolarization; an outcome that associated with a significant loss of mitochondrial function and the accumulation of auto-phagosomes. It also significantly upregulated the expression of the cell cycle regulating cyclin-dependent kinase inhibitor, p21 protein and enhanced the activation (de-phosphorylation) of the tumour suppressor retinoblastoma (Rb) protein. Although, as previously shown, E2 did not induced classis apoptosis; it resulted in a significant elevation in senescence-associated β- galactosidase levels. Conclusions: In summary, these findings suggest that E2 treatment mediates its anti-cancer potential by disrupting mitochondrial function and precipitating autophagy and cell senescence.