Inhibition of Human Cancer Cell Growth by 1,25-Dihydroxyvitamin D3 Metabolites1

Specific high-affinity 1,25-dihydroxyvitamin D3 [1,25-{OH)2D3] receptors, which can undergo hormone-dependent activation and nuclear localization, have been demonstrated in a wide variety of established human cancer cell lines and surgically obtained human cancer tissues. 1,25-(OH)2D3 has been reported by some workers to stimulate cancer cell replication at low "physiological" concentrations and by ourselves and others to inhibit at higher concentrations. We report here that 1,25-(OH)2D3 had a biphasic effect on the replication of two distinct human cancer cell lines, i.e., the breast cancer T-47D and the malignant melanoma MM96, an effect analogous to that of estrogens on the breast cancer cell line MCF-7. These inhibitory effects were accompanied by marked morphological changes. Furthermore, two known metabolites of 1,25-(OH)2D3, i.e., 1,24,25-trihydroxyvitamin D3 and 1,25,26-trihydroxyvitamin D3, which compete for binding to the 1,25-(OH)2D3 receptor, did not stimulate but were almost equipotent with 1,25-(OH)2D3 in inhibiting the replication of both cell lines. The stimulatory but not the inhibitory effect of 1,25-(OH)2D3 was abolished by cortisone. These 1,25-dihydroxy vitamin D3 metabolites show promise for the inhibition of cancer growth, analogous to the effect of estrogens and antiestrogens in breast cancer but with potential application in a much wider range of human cancers.