Antiproliferative activity of vitamin D compounds in combination with cytostatics.

Calcitriol is a potent antiproliferative agent against various tumour cells in vitro. Here, the results of a study on vitamin D compounds (calcitriol's analogues PRI-1906 and PRI-2191) as potential agents in combined antitumour therapy in vitro are presented. Applying antiproliferative SRB and MTT assays, the growth inhibitory effects of the vitamin D compounds, applied alone or in combination with either cisplatin or doxorubicin, were measured. The following cancer cell lines were employed: A549 (human non-small cell lung carcinoma), B16 (murine melanoma), CCRF, HL-60 (human leukaemia), SW707 (human colon cancer), MCF-7, T47D (human breast cancer), WEHI-3 (mouse leukaemia) and normal cells: BALB 3T3 (normal murine fibroblast cell line). It was shown that the treatment of tumour cells, which are sensitive to vitamin D compounds, with the combination of vitamin D compounds and cytostatics decreased the inhibitory concentration 50% (IC50) values compared with the effects of the cytostatics applied alone.