HUMAN PROSTATE CELLS SYNTHESIZE 1,25-DIHYDROXYVITAMIN D-3 FROM 25-HYDROXYVITAMIN D-3(1)

Epidemiological and laboratory data support a role for vitamin D in th e growth and differentiation of human prostatic cells. These findings prompted us to ask whether prostatic cells could convert 25-hydroxyvit amin D-3 (25-OH-D-3), the major circulating metabolite of vitamin D-3, to 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3], the hormonally active metabolite, in a manner similar to cultured human keratinocytes. There fore, we investigated three well-characterized human prostate cancer c ell lines, LNCaP, DU 145, and PC-3; two primary cultures of cells deri ved from noncancerous human prostates (one normal and one benign prost atic hyperplasia); and primary cultures of normal human keratinocytes for their ability to synthesize 1,25(OH)(2)D-3. Assays were performed in the presence of 25-OH-D-3 as the enzyme substrate and 1,2-dianilino ethane, 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)(2 )D-3/mg protein/h, respectively. No measurable 1,25(OH)(2)D-3 was dete cted in LNCaP cells. The normal and benign prostatic hyperplasia prima ry cultures and keratinocyte cultures produced 3.08 +/- 1.56, 1.05 +/- 0.31, and 2.1 +/- 0.1 pmol of 1,25(OH)(2)D-3/mg protein/h, respective ly, using a calf thymus receptor binding assay to measure 1,25(OH)(2)D -3 in the presence of I,2-dianilinoethane. The identity of the analyte as 1,25(OH)(2)D-3 was supported by high performance liquid chromatogr aphy using [H-3]25-OH-D-3 as the enzyme substrate and a solvent system that is specific for 1,25(OH)(2)D-3. The production of 1,25(OH)(2)D-3 in the prostate cancer cell lines and in the primary cultures was com pletely inhibited in the presence of clotrimazole. This report demonst rates that two of three human prostate cancer cell lines, as well as p rimary cultures of noncancerous prostatic cells, possess 1 alpha-hydro xylase activity and can synthesize 1,25(OH)(2)D-3 from 25-OH-D-3. Toge ther with recent data indicating that 1,25(OH)(2)D-3 inhibits the inva siveness of human prostate cancer cells (G. G. Schwartz et al., Cancer Epidemiol. Biomark. Prev., 6: 727-732, 1997), these data suggest a po tential role for 25-OH-D-3 in the chemoprevention of invasive prostate cancer.