Abstract
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.
Footnotes
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↵1 Current affiliation: Laboratory of Drug Design and Medicinal Chemistry, Showa Pharmaceutical University, Higashi-tamagawagakuen, Machida, Tokyo, Japan.
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This work was partly supported by Health Science Research Grants from the Ministry of Health Labour and Welfare of Japan and a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
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doi:10.1124/dmd.107.015602.
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ABBREVIATIONS: 1α,25(OH)2D3,1α,25-dihydroxyvitamin D3; 25(OH)D3, 25-hydroxyvitamin D3; 25(OH)-19-nor-D3, 25-hydroxy-19-nor-vitamin D3;1α,25(OH)2-19-nor-D3,1α,25-dihydroxy-19-nor-vitamin D3;1α,25(OH)2-19-nor-D2,1α,25-dihydroxyvitamin 19-nor-D2; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate; ADX, adrenodoxin; ADR, NADPH-adrenodoxin reductase; HPLC, high-performance liquid chromatography; ODS, octadecylsilane; AM, acetoxymethyl ester; LC/MS, liquid chromatography/mass spectometry; VDR, vitamin D receptor.
- Received March 5, 2007.
- Accepted June 5, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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