Epidemiological and laboratory data support a role for
vitamin D in the growth and differentiation of human prostatic cells. These findings prompted us to ask whether prostatic cells could convert
25-hydroxyvitamin D3 (25-OH-D3), the major circulating metabolite of
vitamin D3, to
1,25-dihydroxyvitamin D3 [
1,25(OH)2D3], the hormonally active metabolite, in a manner similar to cultured human keratinocytes. Therefore, we investigated three well-characterized human
prostate cancer cell lines, LNCaP, DU 145, and PC-3; two primary cultures of cells derived from noncancerous human prostates (one normal and one
benign prostatic hyperplasia); and primary cultures of normal human keratinocytes for their ability to synthesize
1,25(OH)2D3. Assays were performed in the presence of 25-OH-D3 as the
enzyme substrate and
1,2-dianilinoethane, an
antioxidant and
free radical scavenger, and in the presence and absence of
clotrimazole, a
cytochrome P450 inhibitor. DU 145 and PC-3 cells produced 0.31 +/- 0.06 and 0.07 +/- 0.01 pmol of
1,25(OH)2D3/mg
protein/h, respectively. No measurable
1,25(OH)2D3 was detected in LNCaP cells. The normal and
benign prostatic hyperplasia primary cultures and keratinocyte cultures produced 3.08 +/- 1.56, 1.05 +/- 0.31, and 2.1 +/- 0.1 pmol of
1,25(OH)2D3/mg
protein/h, respectively, using a calf thymus receptor binding assay to measure
1,25(OH)2D3 in the presence of
1,2-dianilinoethane. The identity of the analyte as
1,25(OH)2D3 was supported by high performance liquid chromatography using [3H]25-
OH-D3 as the
enzyme substrate and a
solvent system that is specific for
1,25(OH)2D3. The production of
1,25(OH)2D3 in the
prostate cancer cell lines and in the primary cultures was completely inhibited in the presence of
clotrimazole. This report demonstrates that two of three human
prostate cancer cell lines, as well as primary cultures of noncancerous prostatic cells, possess 1alpha-hydroxylase activity and can synthesize
1,25(OH)2D3 from 25-OH-D3. Together with recent data indicating that
1,25(OH)2D3 inhibits the invasiveness of human
prostate cancer cells (G. G. Schwartz et al.,
Cancer Epidemiol. Biomark. Prev., 6: 727-732, 1997), these data suggest a potential role for 25-OH-D3 in the
chemoprevention of invasive
prostate cancer.