Estrogen-dependent disruption of intracellular iron metabolism augments the cytotoxic effects of doxorubicin in select breast and ovarian cancer cells

Introduction: Increased iron content in cancer cells is associated with resistance to chemotherapy. Recent studies have demonstrated that estrogen (E-2) suppresses hepcidin synthesis and enhances intracellular iron efflux. Herein, we investigated whether E-2-driven intracellular iron efflux renders cancer cells more susceptible to doxorubicin (Dox)-induced cytotoxicity. Methods: Breast, ovarian, and liver cancer cell lines treated with E-2, Dox, or a combination of both were assessed for intracellular iron status, mitochondrial function, cell cycle, and apoptosis. Results: E-2+Dox treatment in MCF7, SKOV3 and MDA-MB231 cells resulted in enhanced apoptosis compared with Dox-treated cells. Expression of gamma H2AX was significantly higher and that of survivin significantly lower in E-2+Dox-treated cells than Dox-treated cells. At 48 hours, E-2+Dox had induced a significant increase in the percentage of sub-G(1) apoptotic cells, increased CHK1 expression, and decreased cyclin D1, CDK4, and CDK6 expression. Ferroportin and ferritin expression was significantly higher and that of TfR1 significantly lower in E-2+Dox-treated cells than Dox-treated cells. Intracellular iron content was significantly reduced in E-2+Dox-treated cells at 48 hours posttreatment. Lastly, E-2+Dox-treated cells showed higher levels of mitochondrial membrane hyperpolarization than Dox-treated cells. Conclusion: These findings suggest that E-2 disrupts intracellular iron metabolism in such a way that increases cell susceptibility to Dox-induced cytotoxicity.