RT Journal Article
SR Electronic
T1 Kinetic Studies of 25-Hydroxy-19-nor-vitamin D<sub>3</sub> and 1α,25-Dihydroxy-19-nor-vitamin D<sub>3</sub> Hydroxylation by CYP27B1 and CYP24A1
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1482
OP 1488
DO 10.1124/dmd.107.015602
VO 35
IS 9
A1 Naoko Urushino
A1 Sachie Nakabayashi
A1 Midori A. Arai
A1 Atsushi Kittaka
A1 Tai C. Chen
A1 Keiko Yamamoto
A1 Keiko Hayashi
A1 Shigeaki Kato
A1 Miho Ohta
A1 Masaki Kamakura
A1 Shinichi Ikushiro
A1 Toshiyuki Sakaki
YR 2007
UL http://dmd.aspetjournals.org/content/35/9/1482.abstract
AB Our previous study demonstrated that 25-hydroxy-19-nor-vitamin D3 [25(OH)-19-nor-D3] inhibited the proliferation of immortalized noncancerous PZ-HPV-7 prostate cells similar to 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], suggesting that 25(OH)-19-nor-D3 might be converted to 1α,25-dihydroxy-19-nor-vitamin D3 [1α,25(OH)2-19-nor-D3] by CYP27B1 before exerting its antiproliferative activity. Using an in vitro cell-free model to study the kinetics of CYP27B1-dependent 1α-hydroxylation of 25(OH)-19-nor-D3 and 25-hydroxyvitamin D3 [25(OH)D3] and CYP24A1-dependent hydroxylation of 1α,25(OH)-19-nor-D3 and 1α,25(OH)2D3, we found that kcat/Km for 1α-hydroxylation of 25(OH)-19-nor-D3 was less than 0.1% of that for 25(OH)D3, and the kcat/Km value for 24-hydroxylation was not significantly different between 1α,25(OH)2-19-nor-D3 and 1α,25(OH)2D3. The data suggest a much slower formation and a similar rate of degradation of 1α,25(OH)2-19-nor-D3 compared with 1α,25(OH)2D3. We then analyzed the metabolites of 25(OH)D3 and 25(OH)-19-nor-D3 in PZ-HPV-7 cells by high-performance liquid chromatography. We found that a peak that comigrated with 1α,25(OH)2D3 was detected in cells incubated with 25(OH)D3, whereas no 1α,25(OH)2-19-nor-D3 was detected in cells incubated with 25(OH)-19-nor-D3. Thus, the present results do not support our previous hypothesis that 25(OH)-19-nor-D3 is converted to 1α,25(OH)2-19-nor-D3 by CYP27B1 in prostate cells to inhibit cell proliferation. We hypothesize that 25(OH)-19-nor-D3 by itself may have a novel mechanism to activate vitamin D receptor or it is metabolized in prostate cells to an unknown metabolite with antiproliferative activity without 1α-hydroxylation. Thus, the results suggest that 25(OH)-19-nor-D3 has potential as an attractive agent for prostate cancer therapy. The American Society for Pharmacology and Experimental Therapeutics