Selective Inhibition of Human Cytochrome P4502c8 by Montelukast

Abstract

ABSTRACT:The leukotriene receptor antagonist montelukast was examined for its inhibition of the human drug-metabolizing enzyme cytochrome P4502C8 (CYP2C8). Montelukast was demonstrated to be a potent inhibitor of CYP2C8-catalyzed amodiaquine N-deethylase, rosiglitazone N-demethylase, and paclitaxel 6␣-hydroxylase in human liver microsomes. Inhibition was also observed when the reaction was catalyzed by recombinant heterologously expressed CYP2C8. The mechanism of inhibition was competitive, with K i values ranging from 0.0092 to 0.15 M. Inhibition potency was highly dependent on the microsomal protein concentration. Increasing the microsomal protein concentration by 80-fold yielded a 100-fold decrease in inhibition potency. Preincubation of montelukast with human liver microsomes and NADPH did not alter the inhibition potency, suggesting that montelukast is not a mechanism-based inactivator. Montelukast was a selective inhibitor for human CYP2C8; inhibition of other human cytochrome P450 enzymes was substantially less. These in vitro data support the use of montelukast as a selective CYP2C8 inhibitor that could be used to determine the contribution of this enzyme to drug metabolism reactions. These data also raise the possibility that montelukast could have an effect on the metabolic clearance of drugs possessing CYP2C8-catalyzed metabolism as a major clearance pathway, thereby eliciting pharmacokinetic drug-drug interactions.Cytochrome P450 (P450) enzymes represent a family of proteins that contribute predominantly in the metabolism of drugs and other xenobiotics. Alteration in the activity of these enzymes in vivo represents the major underlying mechanism behind pharmacokinetic drug-drug interactions (Clarke and Jones, 2002). In humans, some P450 enzymes have been designated as more predominant in the metabolism of drugs than others. These include CYP1A2, 2C9, 2C19, 2D6, and 3A. These five enzymes have been studied extensively with regard to their role in drug metabolic clearance as well as drug-drug interactions. However, recent investigations have uncovered roles for other cytochrome P450 enzymes, such as CYP2C8, in the metabolism of some drugs. Thus, CYP2C8 can also be the target of drug-drug interactions for those drugs in which it plays a predominant role in the clearance. Drugs for which CYP2C8 appears to play a major role in metabolic clearance include repaglinide, rosiglitazone, and cerivastatin. Drug interactions that arise by inhibition of CYP2C8 have been described recently, including interactions between cerivastatin and gemfibrozil (Backman et al., 2002), repaglinide, and gemfibrozil (Niemi et al., 2003b), and repaglinide and trimethoprim (Niemi et al., 2004).In previous work, a vast number of drugs have been tested for their potential to inhibit CYP2C8 (Bun et al., 2003, Ong et al., 2000Walsky et al., 2005). In a study conducted in our laboratories, we found that montelukast (Fig. 1), a leukotriene receptor antagonist used in the treatment of asthma, potently inhibited CYP2C8-catalyzed amodiaquin...

Selective, competitive and mechanism-based inhibitors of human cytochrome P450 2J2

“…As far as vascular CYPs are concerned, Table 5 summarizes data obtained on 4 (this work, Table 1) and on ticlopidine [71,72], montelukast [73], sulfaphenazole [74] and ketoconazole [74] as selective inhibitors of CYP2B6, 2C8, 2C9 and 3A4, respectively. These data show that each compound is a selective inhibitor of a given P450 -i.e.…”

“…Montelukast 11 [73] 0.02 [73] 1.2 [73] 1.2-7.9 [73] > 100 Sulfaphenazole > 100 [74] 120 [74] 0.6 [74] > 200 [74] > 150 Ketoconazole 6.3 [74] 5.5 [74] 16 [74] 0.02 [74] …”

Comparative Metabolism of Cinobufagin in Liver Microsomes from Mouse, Rat, Dog, Minipig, Monkey, and Human

“…In brief, CB (20 M, relevant to the K m values) was incubated in HLM (0.125 mg of protein/ml) with an NADPH-generating system in the absence (control) or presence of known P450 isoform-specific inhibitors/substrates. The selective inhibitors and their concentrations were as follows (Bjornsson et al, 2003): montelukast (2 M) for CYP2C8 (Walsky et al, 2005), sulfaphenazole (10 M) for CYP2C9, omeprazole (20 M) for CYP2C19, quinidine (10 M) for CYP2D6, clomethiazole (50 M) for CYP2E1, and ketoconazole (1 M) for CYP3A4. Inhibition by furafylline (10 M) for CYP1A2, 8-methoxypsoralen (2.5 M) for CYP2A6, triethylenethiophosphoramide (50 M) for CYP2B6 (Rae et al, 2002), and ABT (500 M) for broad P450s (Emoto et al, 2003) was examined by adding CB after preincubation with an NADPH-generating system at 37°C for 20 min.…”

Deoxyschizandrin, a Naturally Occurring Lignan, Is a Specific Probe Substrate of Human Cytochrome P450 3A

“…The selection of a 2 mM concentration was based on the K m value. The selective inhibitors and their concentrations were as follows (Bjornsson et al, 2003): montelukast (5 mM) for CYP2C8 (Walsky et al, 2005), sulfaphenazole (10 mM) for CYP2C9, omeprazole (20 mM) for CYP2C19, quinidine (10 mM) for CYP2D6, clomethiazole (50 mM) for CYP2E1, and ketoconazole (1 mM) for CYP3A4. Inhibition by furafylline (10 mM) for CYP1A2, 8-methoxypsoralen (2.5 mM) for CYP2A6, triethylenethiophosphoramide (50 mM) for CYP2B6 (Rae et al, 2002) and ABT (500 mM) for broad P450s (Emoto et al, 2003) were examined by adding DS after preincubation with NADPH-generating system at 37°C for 10 minutes.…”