25Hydroxyvitamin D3, the prohormone of 1,25-dihydroxyvitamin D3, inhibits the proliferation of primary prostatic epithelial cells

The hormonal metabolite of vitamin D, 1a,25-dihydroxyvitamin D3 [1,25(OH)2D3] is known to inhibit the proliferation of prostatic epithelial cells. This has stimulated interest in vitamin D compounds as therapeutic agents for prostate cancer. However, the therapeutic use of 1,25(OH)2D3 is limited because elevations in serum 1,25(OH)2D3 can cause dangerous elevations in serum calcium levels. We wondered whether the prohormone of 1,25(OH)2D3, 25-hydroxyvitamin D3 (25-OH-D3), which is much less calcemic, could also achieve antiproliferative effects in prostatic cells. 25-OH-D3 is converted to 1,25(OH)2D3 by the mitochondrial enzyme 1-a-hydroxylase. We have recently shown that human prostatic cells also possess significant 1-a