Kinetic studies of 25-hydroxy-19-nor-vitamin D3 and 1α,25-dihydroxy-19-nor-vitamin D3 hydroxylation by CYP27B1 and CYP24A1

Naoko Urushino, Sachie Nakabayashi, Midori A. Arai, Atsushi Kittaka, Tai C. Chen, Keiko Yamamoto, Keiko Hayashi, Shigeaki Kato, Miho Ohta, Masaki Kamakura, Shinichi Ikushiro, Toshiyuki Sakaki

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Abstract

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.

Original languageEnglish
Pages (from-to)1482-1488
Number of pages7
JournalDrug Metabolism and Disposition
Volume35
Issue number9
DOIs
Publication statusPublished - 2007 Sep 1
Externally publishedYes

ASJC Scopus subject areas

  • Pharmacology
  • Pharmaceutical Science

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    Urushino, N., Nakabayashi, S., Arai, M. A., Kittaka, A., Chen, T. C., Yamamoto, K., Hayashi, K., Kato, S., Ohta, M., Kamakura, M., Ikushiro, S., & Sakaki, T. (2007). Kinetic studies of 25-hydroxy-19-nor-vitamin D3 and 1α,25-dihydroxy-19-nor-vitamin D3 hydroxylation by CYP27B1 and CYP24A1. Drug Metabolism and Disposition, 35(9), 1482-1488. https://doi.org/10.1124/dmd.107.015602