TY - JOUR
T1 - Kinetic studies of 25-hydroxy-19-nor-vitamin D3 and 1α,25-dihydroxy-19-nor-vitamin D3 hydroxylation by CYP27B1 and CYP24A1
AU - Urushino, Naoko
AU - Nakabayashi, Sachie
AU - Arai, Midori A.
AU - Kittaka, Atsushi
AU - Chen, Tai C.
AU - Yamamoto, Keiko
AU - Hayashi, Keiko
AU - Kato, Shigeaki
AU - Ohta, Miho
AU - Kamakura, Masaki
AU - Ikushiro, Shinichi
AU - Sakaki, Toshiyuki
PY - 2007/9/1
Y1 - 2007/9/1
N2 - Our previous study demonstrated that 25-hydroxy-19-nor-vitamin D 3 [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)2D 3], 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-D 3 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/K m 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.
AB - Our previous study demonstrated that 25-hydroxy-19-nor-vitamin D 3 [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)2D 3], 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-D 3 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/K m 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.
UR - http://www.scopus.com/inward/record.url?scp=34548077902&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34548077902&partnerID=8YFLogxK
U2 - 10.1124/dmd.107.015602
DO - 10.1124/dmd.107.015602
M3 - Article
C2 - 17553915
AN - SCOPUS:34548077902
VL - 35
SP - 1482
EP - 1488
JO - Drug Metabolism and Disposition
JF - Drug Metabolism and Disposition
SN - 0090-9556
IS - 9
ER -