Melatonin and vitamin D3 increase TGF-beta1 release and induce growth inhibition in breast cancer cell cultures.

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 [3H]thymidine uptake. The presence of TGF-beta(1) in serum-free conditioned medium was determined by inhibition antibody binding assay.
RESULTS: In 17-betaE cultured RM4 cells both MEL and 1,25-(OH)(2)D(3) alone and in combination significantly reduced [3H]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 [3H]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-beta(1) secretion from RM4 cells and vitamin D(3) increased the TGF-beta(1) secretion in a dose-dependent manner, from 2- to 7-fold. Moreover, a further enhancement of the TGF-beta(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-beta(1) antibody to the medium of RM4 cells exposed to vitamin D(3) alone or in combination with MEL increased the [3H]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-beta(1) secretion.