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Journal of pineal research

Melatonin sensitizes human breast cancer cells to ionizing radiation by downregulating proteins involved in double-strand DNA break repair.


PMID 25623566

Abstract

Radiation and adjuvant endocrine therapy are nowadays considered a standard treatment option after surgery in breast cancer. Melatonin exerts oncostatic actions on human breast cancer cells. In the current study, we investigated the effects of a combination of radiotherapy and melatonin on human breast cancer cells. Melatonin (1xa0mm, 10xa0μm and 1xa0nm) significantly inhibited the proliferation of MCF-7 cells. Radiation alone inhibited the MCF-7 cell proliferation in a dose-dependent manner. Pretreatment of breast cancer cells with melatonin 1xa0wk before radiation led to a significantly greater decrease of MCF-7 cell proliferation compared with radiation alone. Melatonin pretreatment before radiation also decreased G2 -M phase arrest compared with irradiation alone, with a higher percentage of cells in the G0 -G1 phase and a lower percentage of cells in S phase. Radiation alone diminished RAD51 and DNA-protein kinase (PKcs) mRNA expression, two main proteins involved in double-strand DNA break repair. Treatment with melatonin for 7xa0days before radiation led to a significantly greater decrease in RAD51 and DNA-PKcs mRNA expression compared with radiation alone. Our findings suggest that melatonin pretreatment before radiation sensitizes breast cancer cells to the ionizing effects of radiation by decreasing cell proliferation, inducing cell cycle arrest and downregulating proteins involved in double-strand DNA break repair. These findings may have implications for designing clinical trials using melatonin and radiotherapy.