Cytochrome P450s (CYP) comprise a superfamily of enzymes that catalyzes the oxidation of a wide variety of xenobiotic chemicals, including drugs and carcinogens. [3][4][5] Multiple-drug therapy is a common therapeutic practice, particularly in patients with several diseases or conditions, and many drug-drug interactions involving metabolic inhibition are reported. 6,7) Antifungal drugs, including fluconazole, itraconazole, micafungin, miconazole, and voriconazole ( Fig. 1), are widely used in the treatment of systemic candidal infections and mycoses. The mechanism of action of these antifungal drugs is the inhibition of fungal CYP (14a-sterol demethylase), an enzyme responsible for the conversion of lanosterol to 14a-demethyllanosterol in the ergosterol biosynthetic pathway, 8,9) except that micafungin inhibits 1,3-b-D-glucan synthase, leading to disruption of the growing fungal cell wall and death of the fungal cell.10,11) Because antibiotics, including antifungal drugs, are coadministered in most cases, the possibility of interactions between them and other drugs exists. Recently, we have investigated the effects of antifungal drugs excluding voriconazole on CYP3A4 activity and multidrug resistance protein 1 (MDR1), and found that itraconazole and miconazole, as well as ketoconazole, had greater inhibitory effects on both CYP3A4 metabolic and MDR1 transport activities than fluconazole and micafungin.12) In addition, it has been demonstrated that the K i values of fluconazole and micafungin against nifedipine oxidation activity, a marker enzyme activity of CYP3A4, are 10.7 mM and 17.3 mM, respectively.13) Zhang et al. 14) reported that miconazole competitively inhibits several CYPs, including CYP2C9, CYP2C19, and CYP3A4, with K i values ranging from 0.01 to 7.3 mM. Furthermore, it is likely that fluconazole and voriconazole inhibit CYP2C9, CYP2C19, and CYP3A4. Post-marketing Development Research Center, Fujisawa Pharmaceutical Co., Ltd.; 3-4-7 Doshomachi, Chuo-ku, Osaka 541-8514, Japan: and b Biopharmaceutical and Pharmacokinetic Research Laboratories, Fujisawa Pharmaceutical Co., Ltd.; 2-1-6 Kashima, Yodogawa-ku, Osaka 532-8514, Japan. Received March 22, 2005; accepted May 31, 2005 The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4-hydroxylation, and CYP3A4-mediated nifedipine oxidation activities in human liver microsomes were compared. In addition, the effects of preincubation were estimated to investigate the mechanism-based inhibition. The IC 50 value against tolbutamide hydroxylation was the lowest for miconazole (2.0 m mM), followed by voriconazole (8.4 m mM) and fluconazole (30.3 m mM). Similarly, the IC 50 value against S-mephenytoin 4-hydroxylation was the lowest for miconazole (0.33 m mM), followed by voriconazole (8.7 m mM) and fluconazole (12.3 m mM). On the other hand, micafungin at a concentration of 10 or 25 m mM neither inhibited nor ...

1. The effects of substrate concentration and enzyme source (human liver microsomes and recombinant cytochrome P450s, CYP) on the activation of 7-benzyloxyresorufin O-debenzylation and nifedipine oxidation were investigated. 2. 7-Benzyloxyresorufin O-debenzylase activity in human liver microsomes was inhibited by a monoclonal antibody against CYP2B6 and a polyclonal antibody against CYP3A2 by 53-69 and 19-44%, respectively, suggesting that CYP2B6 and CYP3A4 mainly catalyse 7-benzyloxyresorufin O-debenzylation in human liver microsomes. 3. 7-Benzyloxyresorufin O-debenzylase activity at 0.2-5 micro M substrate concentrations in human liver microsomes was increased by the addition of alpha-naphthoflavone, quinidine, testosterone and progesterone, and the V(max) of 7-benzyloxyresorufin O-debenzylation increased with increasing alpha-naphthoflavone concentrations, whereas the K(m) remained constant. Additionally, 7-benzyloxyresorufin O-debenzylation by recombinant CYP3A4 was increased by the addition of alpha-naphthoflavone, testosterone and progesterone but not by quinidine, whereas no chemicals tested could activate the O-debenzylation of 7-benzyloxyresorufin by CYP2B6. 4. The K(m) for nifedipine oxidation activity by CYP3A4 decreased by the addition of progesterone, whereas the V(max) remained constant. Quinidine and testosterone increased 7-benzyloxyresorufin O-debenzylase and nifedipine oxidase activities, respectively, in human liver microsomes, whereas activation was not observed in CYP3A4. 5. The results suggest that in vitro activation patterns are substrate dependent and that selection of the enzyme source can influence the activation phenomenon.

The eŠects of cyclosporine and tacrolimus on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresoruˆn O-deethylation, CYP2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4′ -hydroxylation, CYP2D6-mediated debrisoquine 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, CYP3A4-mediated nifedipine oxidation, and CYP3A4-mediated testosterone 6b-hydroxylation activities in human liver microsomes were compared. Cyclosporine and tacrolimus, at concentrations of 0.2 or 2 mM, neither inhibited nor stimulated any of the metabolic activities except for those of CYP3A4. On the other hand, cyclosporine and tacrolimus competitively inhibited CYP3A4-mediated nifedipine oxidation activity, with inhibition constants (K i ) of 1.42 and 0.36 mM, respectively. In addition, 20 mM cyclosporine inhibited CYP2C19 and CYP2D6 activities by 29％ and 30％, respectively. These results suggest that tacrolimus would not cause clinically signiˆcant interactions with other drugs, which are metabolized by CYPs, via the inhibition of hepatic metabolism and that the reason why cyclosporine, but not tacrolimus, has a pharmacokinetic inhibitory eŠect might be that the dosage and/or the unbound concentrations around its metabolic enzymes are higher than those of tacrolimus, rather than the diŠerences in the inhibition potential. Obvious substrate-dependent eŠects on CYP3A4-inhibition potential were not observed.

Triple-stage quadrupole (TSQ) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and ion trap ESI-MS/MScan be used to cleave protonated molecules to produce carbocations and neutral molecules in the positive ion mode. Dissociation products which correspond to protonated forms of neutral fragment molecules can also be trapped and detected. These protonated molecules in turn can cleave via carbocation cleavage, ipso cleavage, onium cleavage or McLafferty or related rearrangements. One can elucidate the structures of metabolites from the differences in m/z ratios of the fragments arising from the original drug compound and its metabolite. This strategy for structural elucidation is further facilitated by estimates of the reactivity of drugs with oxygen diradicals involved in cytochrome P-450 cycles.

Antifungal drugs, including fluconazole, itraconazole, micafungin, miconazole, and voriconazole, are widely used in the treatment of systemic candidal infections and mycoses. The mechanism of action of these antifungal drugs except for micafungin is the inhibition of fungal cytochrome P450 (CYP, 14a-sterol demethylase), an enzyme responsible for the conversion of lanosterol to 14a-demethyllanosterol in the ergosterol biosynthetic pathway, 1,2) whereas micafungin inhibits 1,3-b-D-glucan synthase, leading to disruption of growing fungal cell wall and death of the fungal cell. 3,4)Multiple drug therapy is a common therapeutic practice, particularly in patients with several diseases or conditions, and many drug-drug interactions involving metabolic inhibition are being reported. 5,6) Recently, we have demonstrated that itraconazole and miconazole, as well as ketoconazole, had higher inhibitory effects on CYP3A4 metabolic activities than fluconazole and micafungin.7) In addition, the K i values of fluconazole and micafungin against nifedipine oxidation activity, a marker enzyme activity of CYP3A4, have been reported to be 10.7 mM and 17.3 mM, respectively. 8) Zhang et al. 9) reported that miconazole inhibits several CYPs, including CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, with K i values ranging from 0.01 to 7.3 mM. Furthermore, it is likely that fluconazole and voriconazole inhibit CYP2C9, CYP2C19, and CYP3A4.2,10-13) On the other hand, fluconazole and itraconazole are reported to exhibit no inhibition of CYP2E1, whereas the K i value of miconazole against CYP2E1 activity is 4 mM. 14) However, there are few studies comparing the effect of antifungal drugs on the drugmetabolizing activity by human hepatic CYPs, such as CYP1A2, CYP2D6, and CYP2E1, under the same experimental conditions.Many inhibitors are known to be activated metabolically to a reactive intermediate(s) that, in turn, is irreversibly or quasi-irreversibly bound to the enzyme(s).15) For example, some acetylenes, including those synthetic steroids such as gestodene and ethinyl estradiol, cause mechanism-based inactivation of CYP3A4.16) Sorivudine is converted by gut flora to (E)-5-(2-bromovinyl)uracil (BVU), which is metabolized to dihydro-BVU by dihydropyrimidine dehydrogenase (DPD), and the dihydro-BVU binds to DPD itself.17) Numerous laboratories have indicated that these mechanism-based inactivators exhibit preincubation time-dependence of inhibition. [16][17][18][19][20][21][22][23][24][25][26][27] In the present study, we compared the effects of five antifungal drugs on specific activities by CYP1A2, CYP2D6, and CYP2E1 in human liver microsomes under the same experimental conditions. In addition, the effect of preincubation was estimated in order to investigate whether these antifungal drugs are the mechanism-based inhibitors. ) and itraconazole from Janssen-Kyowa (Tokyo, Japan). 7-Ethoxyresorufin, resorufin, debrisoquine sulfate, and chlorzoxazone were obtained from Sigma Chemical Co. (St. Louis, MO, U.S.A.). 4-Hydroxydebrisoquine ...

The metabolic activities of six psychotropic drugs, diazepam, clotiazepam, tofisopam, etizolam, tandospirone, and imipramine, were determined for 14 isoforms of recombinant human hepatic cytochrome P450s (CYPs) and human liver microsomes by measuring the disappearance rate of parent compounds. In vitro kinetic studies revealed that V max /K m values in human liver microsomes were the highest for tofisopam, followed by tandospironeϾclotiazepamϾimipramine, diazepam, and etizolam. Among the recombinant CYPs, CYP3A4 exhibited the highest metabolic activities of all compounds except for clotiazepam and imipramine. The metabolism of clotiazepam was catalyzed by CYP2B6, CYP3A4, CYP2C18, and CYP2C19, and imipramine was metabolized by CYP2D6 most efficiently. In addition, the metabolic activities of diazepam, clotiazepam, and etizolam in human liver microsomes were inhibited by 2.5 m mM ketoconazole, a CYP3A4 inhibitor, by 97.5%, 65.1%, and 83.5%, respectively, and the imipramine metabolism was not detected after the addition of 1 or 10 m mM quinidine, a CYP2D6 inhibitor. These results suggest that the psychotropic drugs investigated are metabolized predominantly by CYP3A4, except that CYP2D6 catalyzes the metabolism of imipramine. In addition, this approach based on the disappearance rate appears to be useful for the identification of the responsible CYP isoform(s) of older drugs, for which metabolic profiles have not been reported.

FK228 (also known as FR901228 and depsipeptide, Fig. 1) is a unique bicyclic peptide containing a noncysteine disulfide bond, isolated from Chromobacterium violaceum strain WB968.1-3) FK228 is a potent histone deacetylase inhibitor currently in phase II clinical trials for the treatment of patients with peripheral or cutaneous T-cell lymphoma. 4-7)Histone deacetylases (HDACs) catalyze the hydrolysis of acetylated lysine residues. Modification of histone acetylation is important for basic cellular functions such as DNA replication, transcription, differentiation, and apoptosis. The antitumor efficacy of FK228 depends on the effect on expression of angiogenesis factors, such as vascular endothelial growth factor and basic fibroblast growth factor.8) A recent study demonstrated that reduction of an intramolecular disulfide bond of FK228 to sulfhydryl groups greatly enhanced its inhibitory activity, and that the disulfide bond was rapidly reduced in cells by glutathione (GSH). 9) One of the sulfhydryl groups of reduced FK228 is coordinated to the zinc metal ion present in the HDAC binding pocket.9) In addition, FK228 has been found to undergo conjugation with GSH during incubation with rat or human plasma in the presence of GSH.10) These results suggest that GSH plays an important role in the metabolism and antitumor activity of FK228.After intravenous administration of 14 C-FK228 to bile duct-cannulated male rats at a dose of 0.3 mg/kg, excretion of radioactivity in the bile was 66% of the dose up to 48 h after dosing. Biliary excretion of unchanged FK228 accounted for 3% of the dose and more than 30 types of metabolites were detected in the bile (unpublished data). These results indicate that FK228 is extensively metabolized in vivo. To date, there are no published reports that describe comprehensive metabolic pathways of FK228 in humans. Identification of the enzymes involved in the biotransformation of FK228 may help explain and/or predict individual differences in the metabolic clearance of FK228 and pharmacokinetic drug-drug interactions between FK228 and other drugs in humans.In the present study, a combination of five different in vitro strategies was used to identify the cytochrome P450 (P450) enzymes responsible for FK228 metabolism in human liver microsomes: 1) kinetic analysis in human liver microsomes; 2) correlation analysis using a panel of human liver microsomal preparations; 3) metabolism by recombinant human P450s; 4) chemical inhibition; and 5) immunoinhibition. MATERIALS AND METHODS Materials 14C-FK228 was synthesized at Amersham Biosciences (Cardiff, U.K.). The chemical structures of FK228 and its reduced metabolite M1 are shown in Fig. 1 Identification of Cytochrome P450 Enzymes Involved in the Metabolism of FK228, a Potent Histone Deacetylase Inhibitor, in Human Liver MicrosomesToshifumi SHIRAGA,* Zenzaburo TOZUKA, Rika ISHIMURA, Akio KAWAMURA, and Akira KAGAYAMA Biopharmaceutical and Pharmacokinetic Research Laboratories, Fujisawa Pharmaceutical Co., Ltd.; 2-1-6 Kashima, Yodogawa-ku, Osaka...

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