Combined effects of 1,25-dihydroxyvitamin D3 and platinum drugs on the growth of MCF-7 cells.

The effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and platinum treatments (both singly and combined) on the growth inhibition of MCF-7 cells, an epithelial cell line shown to possess specific receptors for 1,25(OH)2D3, were evaluated. The inhibitory effects of 1,25(OH)2D3 and platinum on MCF-7 cell proliferation in vitro were time and dose related. The data showed that 10 nM and 100 nM 1,25(OH)2D3 inhibited MCF-7 cell growth by 10.8 +/- 2.4% and 34.9 +/- 0.5% (mean +/- SE), respectively. The degrees of growth inhibition induced by 0.2 to 200 micrograms/ml of cis-diammine-1,1-cyclobutane dicarboxylatoplatinum(II) (carboplatin) were slightly less than those induced by 0.02 to 20 micrograms/ml of cis-diamminedichloroplatinum(II) (cisplatin). The combined administration of 10 nM and 100 nM 1,25(OH)2D3 with either carboplatin (200 to 0.2 micrograms/ml) or cisplatin (20 to 0.02 micrograms/ml) was evaluated. Addition of 1,25(OH)2D3 to the platinum resulted in marginal to marked enhancement of growth inhibition over that observed with either platinum alone. The strength of these interactions varied inversely with the dose of the platinum drugs. Evaluation of drug interactions with isobolograms showed that at near-serum levels, carboplatin or cisplatin interacted synergistically with 1,25(OH)2D3 to inhibit MCF-7 cell growth. Our findings suggest potential usefulness in combining 1,25(OH)2D3, a biological modifier, with cytotoxic agents for the treatment of malignant disease.