In vitro metabolism of exemestane by hepatic cytochrome P450s: impact of nonsynonymous polymorphisms on formation of the active metabolite 17beta-dihydroexemestane.
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Peterson A, Xia Z, Chen G, Lazarus P
In vitro metabolism of exemestane by hepatic cytochrome P450s: impact of nonsynonymous polymorphisms on formation of the active metabolite 17beta-dihydroexemestane.
Pharmacol Res Perspect. 2017 Apr 27;5(3):e00314. doi: 10.1002/prp2.314. eCollection 2017 Jun.
- PubMed ID
- 28603633 [ View in PubMed]
- Abstract
Exemestane (EXE) is an endocrine therapy commonly used by postmenopausal women with hormone-responsive breast cancer due to its potency in inhibiting aromatase-catalyzed estrogen synthesis. Preliminary in vitro studies sought to identify phase I EXE metabolites and hepatic cytochrome P450s (CYP450s) that participate in EXE biotransformation. Phase I metabolites were identified by incubating EXE with HEK293-overexpressed CYP450s. CYP450s 1A2, 2C8, 2C9, 2C19, 2D6, 3A4, and 3A5 produce 17beta-dihydroexemestane (17beta-DHE), an active major metabolite, as well as two inactive metabolites. 17beta-DHE formation in pooled human liver microsomes subjected to isoform-specific CYP450 inhibition was also monitored using tandem mass spectrometry. 17beta-DHE production in human liver microsomes was unaffected by isoform-specific inhibition of CYP450s 2A6, 2B6, and 2E1 but decreased 12-39% following inhibition of drug-metabolizing enzymes from CYP450 subfamilies 1A, 2C, 2D, and 3A. These results suggest that redundancy exists in the EXE metabolic pathway with multiple hepatic CYP450s catalyzing 17beta-DHE formation in vitro. To further expand the knowledge of phase I EXE metabolism, the impact of CYP450 genetic variation on 17beta-DHE formation was assessed via enzyme kinetic parameters. Affinity for EXE substrate and enzyme catalytic velocity were calculated for hepatic wild-type CYP450s and their common nonsynonymous variants by monitoring the reduction of EXE to 17beta-DHE. Several functional polymorphisms in xenobiotic-metabolizing CYP450s 1A2, 2C8, 2C9, and 2D6 resulted in deviant enzymatic activity relative to wild-type enzyme. Thus, it is possible that functional polymorphisms in EXE-metabolizing CYP450s contribute to inter-individual variability in patient outcomes by mediating overall exposure to the drug and its active metabolite, 17beta-DHE.
DrugBank Data that Cites this Article
- Drug Enzymes
Drug Enzyme Kind Organism Pharmacological Action Actions Exemestane Cytochrome P450 3A4 Protein Humans UnknownSubstrateDetails - Drug Interactions
Drugs Interaction Integrate drug-drug
interactions in your softwareExemestanePhenytoin The metabolism of Exemestane can be increased when combined with Phenytoin. ExemestanePentobarbital The metabolism of Exemestane can be increased when combined with Pentobarbital. ExemestaneCarbamazepine The metabolism of Exemestane can be increased when combined with Carbamazepine. ExemestaneMitotane The metabolism of Exemestane can be increased when combined with Mitotane. ExemestanePrimidone The metabolism of Exemestane can be increased when combined with Primidone.