Triethylenethiophosphoramide is a specific inhibitor of cytochrome P450 2B6

Implications for cyclophosphamide metabolism

James M. Rae, Nadia V. Soukhova, David A. Flockhart, Zeruesenay Desta

Research output: Contribution to journalArticle

104 Citations (Scopus)

Abstract

Cytochrome P450 2B6 is a genetically polymorphic enzyme that is important in the metabolism of a number of clinically used drugs. This enzyme is not as well studied as other cytochrome P450 (P450) isoforms because of the lack of specific antibodies, probe drugs, and inhibitors. Although recent progress has been made toward specific antibodies and probe drugs, a specific enzyme inhibitor is still lacking. Studies suggest that CYP2B6 plays an important role in the 4-hydroxylation of cyclophosphamide and that this reaction can be inhibited by triethylenethiophosphoramide (thioTEPA). We therefore wished to test the hypothesis that thioTEPA is an inhibitor of CYP2B6. Using human liver microsomes (HLMs) and recombinant P450 enzymes, we demonstrated that thioTEPA is a potent and specific inhibitor of CYP2B6. Enzyme activity was reduced 78.1 ± 0.2% by 50 μM thioTEPA when CYP2B6 activity was measured by following the metabolism of 200 μM S-mephenytoin to nirvanol. thioTEPA did not significantly inhibit (<20% at 100 μM) the other isoforms tested (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4). thioTEPA seems to be a potent noncompetitive inhibitor of CYP2B6, with Ki values of 4.8 ± 0.3 and 6.2 ± 0.7 μM for HLMs and recombinant CYP2B6, respectively, values that are within the plasma concentration range of thioTEPA at therapeutic doses (1.1-18.6 μM). We conclude that thioTEPA is a potent and specific inhibitor of CYP2B6 and that this is the likely mechanism by which thioTEPA inhibits the activation of cyclophosphamide. Furthermore, thioTEPA may prove to be a valuable new tool for the study of this important drug-metabolizing enzyme.

Original languageEnglish
Pages (from-to)525-530
Number of pages6
JournalDrug Metabolism and Disposition
Volume30
Issue number5
DOIs
StatePublished - 2002
Externally publishedYes

Fingerprint

Thiotepa
Metabolism
Cyclophosphamide
Liver Microsomes
Enzymes
Pharmaceutical Preparations
Liver
Cytochrome P-450 Enzyme System
Protein Isoforms
Cytochrome P-450 CYP2B6
Mephenytoin
Cytochrome P-450 CYP3A
Cytochrome P-450 CYP2E1
Cytochrome P-450 CYP1A2
Cytochrome P-450 CYP2D6
Hydroxylation
Antibodies
Enzyme activity
Enzyme Inhibitors

ASJC Scopus subject areas

  • Pharmacology
  • Toxicology

Cite this

Triethylenethiophosphoramide is a specific inhibitor of cytochrome P450 2B6 : Implications for cyclophosphamide metabolism. / Rae, James M.; Soukhova, Nadia V.; Flockhart, David A.; Desta, Zeruesenay.

In: Drug Metabolism and Disposition, Vol. 30, No. 5, 2002, p. 525-530.

Research output: Contribution to journalArticle

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