Melatonin and vitamin D3 increase TGF-β1 release and induce growth inhibition in breast cancer cell cultures

Abstract Background. Evidence has accumulated that 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2 D 3 ] is involved in the regulation of the proliferation of breast tumor cells. For complete tumor suppression high hypercalcemic doses of 1,25-(OH) 2 D 3 are needed. The aim of this study was to assess the effect of combined treatment of 1,25-(OH) 2 D 3 at low doses and melatonin (MEL) on the proliferation of estrogen-responsive rat breast cancer cell line RM4. Materials and methods. RM4 cell proliferation was assessed by [ 3 H]thymidine uptake. The presence of TGF-β 1 in serum-free conditioned medium was determined by inhibition antibody binding assay. Results. In 17-βE cultured RM4 cells both MEL and 1,25-(OH) 2 D 3 alone and in combination significantly reduced [ 3 H]thymidine incorporation in a dose-related fashion. MEL by itself was ineffective in inhibiting the FCS-cultured RM4 cells, while 1,25-(OH) 2 D 3 strongly inhibited [ 3 H]thymidine incorporation. Meanwhile, MEL increased the sensitivity of the FCS-cultured RM4 cells to 1,25-(OH) 2 D 3 in the combined regimen, from 20- to 100-fold. MEL significantly enhanced the TGF-β 1 secretion from RM4 cells and vitamin D 3 increased the TGF-β 1 secretion in a dose-dependent manner, from 2- to 7-fold. Moreover, a further enhancement of the TGF-β 1 release was obtained with the combined treatment, but only for low 1,25-(OH) 2 D 3 concentrations. The addition of monoclonal anti-TGF-β 1 antibody to the medium of RM4 cells exposed to vitamin D 3 alone or in combination with MEL increased the [ 3 H]thymidine uptake compared to the correspondent cells cultured without antibody. Conclusions. Our data point to a potential benefit of combination therapy with 1,25-(OH) 2 D 3 and MEL in the treatment of breast cancer and suggest that the growth inhibition could be related, at least in part, to the enhanced TGF-β 1 secretion.