Induction of differentiation by 1α-hydroxyvitamin D5 in T47D human breast cancer cells and its interaction with vitamin D receptors

The role of the active metabolite of vitamin D. 125 dihydroxyvitamin D-3 (1,25(OH)(2)D-3), in cell differentiation is well established. However. its use as a differentiating agent in a clinical setting is precluded due to its hypercalcaemic activity. Recently, we synthesised a relatively non-calcaemic analogue of vitamin D-5, 1 alpha-hydroxyvitamin D-5 (1 alpha(OH)D-5), which inhibited the development of carcinogen-induced mammary lesions in culture and suppressed the incidence of chemically induced mammary carcinogmas in rats. In the present study, we determined the differentiating effects of 1 alpha-(OH)D-5 in T47D human breast cancer cells and compared its effects with 1.25(OH)(2)D-3. Cells incubated with either 10 or 100 nM of the analogues inhibited cell proliferation in a dose-dependent manner. as measured by the dimethylthiazolyl-2,5-diphenyltetrazolium bromide (MTT) assay. Similar growth-inhibitory effects were also observed for MCF10(neo) cells. Both vitamin D analogues induced cell differentiation, as determined by induction of casein expression and lipid production. However, MCF10(neo) cells failed to respond to either vitamin D analogue and did not undergo cell differentiation. Since the cell differentiating effect of vitamin D is considered to be mediated via the vitamin D receptor (VDR), we examined the induction of VDR using reverse transcriptase-polymerase chain reaction (RT-PCR) in both cells. The results showed that, in T47D cells, both 1,25(OH)(2)D-3 and 1 alpha(OH)D-5 induced VDR in a dose-dependent manner. Moreover, both analogues of vitamin D upregulated the expression of vitamin D response element-chloramphenicol acetyl transferase (VDRE-CAT). These results collectively indicate that 1 alpha-(OH)D-5 may mediate its. cell-differentiating action via VDR in a manner similar to that of 1,25(OH)(2)D-3. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.