Buthionine sulfoximine and 1,25-dihydroxyvitamin D induce apoptosis in breast cancer cells via induction of reactive oxygen species.

Calcitriol or 1,25(OH)(2)D(3) is a negative growth regulator of breast cancer cells. The aim of this study was to determine whether L-buthionine-S,R-sulfoximine, a glutathione-depleting drug, modifies the antiproliferative effects of 1,25(OH)(2)D(3) on MCF-7 cells. For comparison, we included studies in MCF-7 cells selected for vitamin D resistance and in human mammary epithelial cells transformed with SV40 and ras. Our data indicate that L-buthionine-S,R-sulfoximine enhances the growth inhibition of 1,25(OH)(2)D(3) in all transformed breast cell lines. This effect is mediated by ROS leading to apoptosis. In conclusion, BSO alters redox state and sensitizes breast cancer cells to 1,25(OH)(2)D(3)-mediated apoptosis.