Selective Inhibition of Cyp2b6-Catalyzed Bupropion Hydroxylation in Human Liver Microsomes in Vitro

Abstract

ABSTRACT:Some inhibitory agents against CYP2B6 have been reported, but none of these has been extensively characterized or compared with others, as to the potency and selectivity of inhibition toward CYP2B6. The goal of this work was to find a selective and potent chemical in vitro inhibitor toward CYP2B6 using bupropion hydroxylation as a model reaction. At the initial screening of more than 30 substances, ticlopidine, triethylenethiophosphoramide (thioTEPA), metyrapone, xanthate C8, and benzylisothiocyanate displayed IC 50 values of <10 M and were selected for a more detailed analysis. Metyrapone, xanthate C8, and benzylisothiocyanate inhibited several other cytochrome P450 activities rather effectively, some of them even more potently than CYP2B6, and consequently are unsuitable as CYP2B6-selective probes. Ticlopidine and thioTEPA were the most potent inhibitors of bupropion hydroxylation with K i values of 0.2 and 2.8 M, respectively. The inhibition type of ticlopidine was found to be mixed type, with a component of mechanism-based inhibition, whereas thioTEPA inhibited CYP2B6 in a competitive manner. In addition to CYP2B6, ticlopidine also inhibited both mephenytoin 4-hydroxylation (CYP2C19) (IC 50 , 2.7 M) and dextromethorphan O-demethylation (CYP2D6) (IC 50 , 4.4 M). For thioTEPA the next sensitive P450 activity after CYP2B6 was coumarin 7-hydroxylation (IC 50 , 256 M). Thus, although both compounds proved to be relatively potent inhibitors of CYP2B6, thioTEPA was about 2 orders of magnitude more selective than ticlopidine. Thus, thioTEPA is a drug of choice when high CYP2B6 selectivity among major P450 enzymes is required. Ticlopidine is a useful alternative under a controlled experimental setup and when higher potency is needed.

Gene Variants in CYP2C19 Are Associated with Altered In Vivo Bupropion Pharmacokinetics but Not Bupropion-Assisted Smoking Cessation Outcomes

“…The CYP2B6-mediated terminal hydroxylation of bupropion to OH-BUP was hypothesized to be a major bupropion metabolic clearance pathway (Hesse et al, 2000;Kirchheiner et al, 2003). However, a number of studies have reported that variation in CYP2B6 activity significantly altered OH-BUP pharmacokinetics, but not bupropion pharmacokinetics (Kirchheiner et al, 2003;Turpeinen et al, 2004Turpeinen et al, , 2005Zhu et al, 2012;Benowitz et al, 2013). Our study suggested that CYP2C19-mediated hydroxylation of bupropion is a quantitatively important bupropion metabolic clearance pathway since reduced CYP2C19 activity resulted in a significant increase in bupropion exposure (Chen et al, 2010).…”

“…However, no associations between CYP2B6 genotype and the levels of the parent drug bupropion were observed (Kirchheiner et al, 2003;Zhu et al, 2012;Benowitz et al, 2013). Furthermore, when the potent CYP2B6 inhibitors clopidogrel and ticlopidine were given to healthy volunteers, their OH-BUP formation decreased dramatically (.80%), but there was little alteration in bupropion levels (Turpeinen et al, 2004(Turpeinen et al, , 2005. Together, these data have suggested that alternative bupropion clearance pathways exist, which may be able to compensate for the reduction in CYP2B6-mediated bupropion metabolism.…”

Quantitative structure-activity relationships (QSARs) for inhibitors and substrates of CYP2B enzymes: importance of compound lipophilicity in explanation of potency differences

“…The inhibition data was collated from the literature for several series of structurally related compounds, including: primary aliphatic amines [15] and 2-alkyl-benzimidazoles [16], together with a range of diverse compounds [17]. In addition, CYP2B-related activities for a series of 7-alkoxycoumarins [18] and of barbiturates [19] were retrieved from previously reported studies.…”

Mechanism-Based Inhibition of Human Cytochrome P450 2B6 by Ticlopidine, Clopidogrel, and the Thiolactone Metabolite of Prasugrel

“…Because of the P450 dependency of the metabolic pathways, ticlopidine, clopidogrel, and the thiolactone metabolites of ticlopidine, clopidogrel, and prasugrel could have the potential to cause a drug-drug interaction through the inhibition of P450s. Indeed, several in vitro studies indicated that ticlopidine, clopidogrel, and their thiolactone metabolites are competitive inhibitors of several P450s (Ko et al, 2000;Turpeinen et al, 2004;Hagihara et al, 2008). R-95913 was shown not to be an inhibitor of CYP1A2, CYP3A, CYP2C9, CYP2C19, and CYP2D6 at clinical doses (K i values ranged from 7.2 to 82 M) (Rehmel et al, 2006).…”