Synergistic anticancer activity of 1,25-dihydroxyvitamin D3 and immune cytokines : the involvement of reactive oxygen species

Abstract It was previously shown that 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) enhances the cytotoxic activity of tumor necrosis factor α (TNFα), doxorubicin and menadione. A feature shared by these anticancer agents is the involvement of reactive oxygen species (ROS) in their action. In this work we found that 1,25(OH) 2 D 3 acted synergistically with interleukin 1 β (IL-1β) or interleukin 6 (IL-6) to inhibit the proliferation of MCF-7 breast cancer cells. The extent of the synergism was maximal at 1 nM, a concentration at which 1,25(OH) 2 D 3 , acting singly, only marginally reduced the cell number. The thiol antioxidant, N -acetylcysteine (NAC) abolished the synergism between IL-1β or IL-6 and 1,25(OH) 2 D 3 , but had only a small protective effect when the cytokines acted alone. NAC and reduced glutathione (GSH) protected MCF-7 cells from cytotoxicity induced both by TNFα alone and by TNFα and 1,25(OH) 2 D 3 . A two-day exposure to TNFα caused a 27.7±3.1% (mean ± SEM) reduction in GSH content. This effect increased to 46.4±5.5% by co-treatment with 1,25(OH) 2 D 3 which did not affect GSH levels on it own. We conclude that 1,25(OH) 2 D 3 can act synergistically with anticancer cytokines present in the tumor milieu and that ROS plays a mediatory role in this interaction.