Antiproliferative action of menadione and 1,25(OH)2D3 on breast cancer cells

Calcitriol or 1,25(OH)2D3 is a negative growth regulator of MCF-7 breast cancer cells. The growth arrest is due to apoptosis activation, which involves mitochondrial disruption. This effect is blunted in vitamin D resistant cells (MCF-7DRes cells). Menadione (MEN), a glutathione (GSH)-depleting compound, may potentiate antitumoral effects of anticancer drugs. The aim of this study was to investigate whether MEN enhances cellular responsiveness of MCF-7 cells to 1,25(OH)2D3. Cells were cultured and treated with different concentrations of 1,25(OH)2D3 ± MEN or vehicle for 96 h. GSH levels and the activity of antioxidant enzymes were determined by spectrophotometry and ROS production by flow cytometry. Both drugs decreased growth and enhanced ROS in MCF-7 cells, obtaining the maximal effects when 1,25(OH)2D3 was combined with MEN (P < 0.01 vs. Control and vs. each compound alone). MCF-7DRes cells were not responsive to 1,25(OH)2D3, but the cell proliferation was slightly inhibited by the combined treatment. Calcitriol and MEN separately enhanced antioxidant enzyme activities, but when they were used in combination, the effect was more pronounced (P < 0.05 vs. Control and vs. each compound alone). MEN, calcitriol and the combined treatment decreased GSH levels (P < 0.05 vs. Control). The data indicate that MEN potentiates the effect of 1,25(OH)2D3 on growth arrest in MCF-7 cells by oxidative stress and increases the activities of antioxidant enzymes, probably as a compensatory mechanism.