Journal
JOURNAL OF MEDICINAL CHEMISTRY
Volume 63, Issue 12, Pages 6513-6522Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jmedchem.9b01849
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Funding
- National Institutes of Health [R01 GM118122]
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Orteronel (TAK-700) is a substituted imidazole that was developed for the treatment of castration-resistant prostate cancer but was dropped in phase III clinical trials. Both enantiomers of this inhibitor of cytochrome P450 (P450) 17A1 show some selectivity in differentially blocking the 17 alpha-hydroxylation and lyase activities of the enzyme. Although both enantiomers of this compound have sub-micromolar IC50 values and bind to the enzyme with a type II spectral change (indicative of nitrogen-iron bonding) and reported K-d values of 56 and 40 nM (R and S, respectively), the rates of binding to P450 17A1 were relatively slow. We considered the possibility that the drug is a slow, tight-binding inhibitor. Analysis of the kinetics of binding revealed rapid formation of an initial complex, presumably in the substrate binding site, followed by a slower change to the spectrum of a final iron complex. Similar kinetics were observed in the interaction of another inhibitor, the triazole (S)-seviteronel (VT-464), with P450 17A1. Kinetic tests and modeling indicate that the further change to the iron-complexed form of the orteronel- or seviteronel-P450 complex is not a prerequisite for enzyme inhibition. Accordingly, the inclusion of heme-binding heterocyclic nitrogen moieties in P450 17A1 inhibitors may not be necessary to achieve inhibition but may nevertheless augment the process.
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