Search

Pigs are sometimes used in preclinical drug metabolism studies, with growing interest, and thus their drug-metabolizing enzymes, including the cytochromes P450 (P450 or CYP; EC 1.14.14.1), need to be examined. In the present study, novel CYP4A cDNAs were isolated and characterized, namely, pig CYP4A23 and CYP4A90; cat CYP4A37 and CYP4A106; and tree shrew CYP4A11a, CYP4A11d, CYP4A11e, CYP4A11f, and CYP4A11g. For comparison, the following known CYP4A cDNAs were also analyzed: pig CYP4A21 and dog CYP4A37, CYP4A38, and CYP4A39. These CYP4A cDNAs all contained open reading frames of 504-513 amino acids and had high amino acid sequence identity (74%-80%) with human CYP4As. Phylogenetic analysis of amino acid sequences revealed that these CYP4As were clustered in each species. All CYP4A genes contained 12 coding exons and formed a gene cluster in the corresponding genomic regions. A range of tissue types were analyzed, and these CYP4A mRNAs were preferentially expressed in liver and/or kidney, except for pig CYP4A90, which showed preferential expression in lung and duodenum. CYP4A enzymes, heterologously expressed in Escherichia coli , preferentially catalyzed lauric acid 12-hydroxylation and arachidonic acid 20-hydroxylation, just as human CYP4A11 does, with the same regioselectivity (i.e., at the ω -position of fatty acids). These results imply that dog, cat, pig, and tree shrew CYP4As have functional characteristics similar to those of human CYP4A11, with minor differences in lauric acid 12-hydroxylation. SIGNIFICANCE STATEMENT: Cytochrome P450 (P450, CYP) 4As are important P450s in human biological processes because of their fatty acid-metabolizing ability. Pig CYP4A21, CYP4A23, and CYP4A90; cat CYP4A37 and CYP4A106; tree shrew CYP4A11a, CYP4A11d, CYP4A11e, CYP4A11f, and CYP4A11g; and dog CYP4A37, CYP4A38, and CYP4A39 cDNAs were isolated and analyzed. These CYP4A cDNAs shared relatively high sequence identities with human CYP4A11 and CYP4A22. Pig, cat, tree shrew, and dog CYP4As in the liver and kidneys are likely to catalyze the ω -hydroxylation of fatty acids., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Flavin-containing monooxygenases (FMOs) are a family of enzymes that are involved in the oxygenation of heteroatom-containing molecules. In humans, FMO3 is the major hepatic form, whereas FMO1 is predominant in the kidneys. FMO1 and FMO3 have also been identified in monkeys, dogs, and pigs. The predicted contribution of human FMO3 to drug candidate N- oxygenation could be estimated using the classic base dissociation constants of the N -containing moiety. A basic quinuclidine moiety was found in natural quinine and medicinal products. Consequently, N -oxygenation of quinuclidine was evaluated using liver and kidney microsomes from humans, monkeys, dogs, and pigs as well as recombinant FMO1, FMO3, and FMO5 enzymes. Experiments using simple reversed-phase liquid chromatography with fluorescence monitoring revealed that recombinant FMO1 mediated quinuclidine N -oxygenation with a high capacity in humans. Moreover, recombinant FMO1, FMO3, and/or FMO5 in monkeys, dogs, and pigs exhibited relatively broad substrate specificity toward quinuclidine N -oxygenation. Kinetic analysis showed that human FMO1 efficiently, and pig FMO1 moderately, mediated quinuclidine N -oxygenation with high capacity, which is consistent with the reported findings for larger substrates readily accepted by pig FMO1 but excluded by human FMO1. In contrast, human FMO3-mediated quinuclidine N -oxygenation was slower than that of the typical FMO3 substrate trimethylamine. These results suggest that some species differences exist in terms of FMO-mediated quinuclidine N- oxygenation in humans and some animal models (monkeys, dogs, and minipigs); however, the potential for quinuclidine, which has a simple chemical structure, to be inhibited clinically by co-administered drugs should be relatively low, especially in human livers. SIGNIFICANCE STATEMENT: The high capacity of human flavin-containing monooxygenase (FMO) 1 to mediate quinuclidine N -oxygenation, a basic moiety in natural products and medicines, was demonstrated by simple reversed-phase liquid chromatography using fluorescence monitoring. The substrate specificity of FMO1 and FMO3 toward quinuclidine N -oxygenation in monkeys, dogs, and pigs was suggested to be relatively broad. Human FMO3-mediated quinuclidine N -oxygenation was slower than trimethylamine N -oxygenation. The likelihood of quinuclidine, with its simple chemical structure, being clinically inhibited by co-administered drugs is relatively low., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Tree shrews are a nonprimate species used in a range of biomedical studies. Recent genome analysis of tree shrews found that the sequence identities and the numbers of genes of cytochrome P450 (CYP or P450), an important family of drug-metabolizing enzymes, are similar to those of humans. However, tree shrew P450s have not yet been sufficiently identified and analyzed. In this study, novel CYP2D8a and CYP2D8b cDNAs were isolated from tree shrew liver and were characterized, along with human CYP2D6, dog CYP2D15, and pig CYP2D25. The amino acid sequences of these tree shrew CYP2Ds were 75%-78% identical to human CYP2D6, and phylogenetic analysis showed that they were more closely related to human CYP2D6 than rat CYP2Ds, similar to dog and pig CYP2Ds. For tree shrew CYP2D8b, two additional transcripts were isolated that contained different patterns of deletion. The gene and genome structures of CYP2Ds are generally similar in dogs, humans, pigs, and tree shrews. Tree shrew CYP2D8a mRNA was most abundantly expressed in liver, among the tissue types analyzed, similar to dog CYP2D15 and pig CYP2D25 mRNAs. Tree shrew CYP2D8b mRNA was also expressed in liver, but at a level 7.3-fold lower than CYP2D8a mRNA. Liver microsomes and recombinant protein of both tree shrew CYP2Ds metabolized bufuralol and dextromethorphan, selective substrates of human CYP2D6, but the activity level of CYP2D8a greatly exceeded that of CYP2D8b. These results suggest that tree shrew CYP2D8a and CYP2D8b are functional drug-metabolizing enzymes, of which CYP2D8a is the major CYP2D in liver. SIGNIFICANCE STATEMENT: Novel tree shrew CYP2D8a and CYP2D8b cDNAs were isolated from liver. Their amino acid sequences were 75%-78% identical to human CYP2D6. For CYP2D8b, two additional transcripts contained different patterns of deletion. Tree shrew CYP2D8a mRNA was abundantly expressed in liver, similar to dog CYP2D15 and pig CYP2D25 mRNAs. Recombinant tree shrew CYP2Ds catalyzed the oxidation of bufuralol and dextromethorphan. Tree shrew CYP2D8a and CYP2D8b are functional drug-metabolizing enzymes, of which CYP2D8a is the major CYP2D in liver., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Cynomolgus and rhesus macaques are used in drug metabolism studies due to their evolutionary and phylogenetic closeness to humans. Cytochromes P450 (P450s or CYPs), including the CYP2C family enzyme, are important endogenous and exogenous substrate-metabolizing enzymes and play major roles in drug metabolism. In cynomolgus and rhesus macaques, six CYP2Cs have been identified and characterized, namely, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2C76, and CYP2C93. In this study, CYP2C119, a new CYP2C, was identified and characterized in cynomolgus and rhesus macaques. Cynomolgus and rhesus CYP2C119 contained open reading frames of 489 amino acids with high sequence identities to human CYP2C8 and to cynomolgus and rhesus CYP2C8. Phylogenetic analysis showed that cynomolgus and rhesus CYP2C119 were closely related to cynomolgus and rhesus CYP2C8. In cynomolgus and rhesus genomes, CYP2C genes, including CYP2C119 , form a cluster. Among the tissues analyzed, cynomolgus CYP2C119 mRNA was predominantly expressed in liver. Hepatic expressions of CYP2C119 mRNA in four cynomolgus and two rhesus macaques varied, with no expression in one rhesus macaque. Among the CYP2C mRNAs, CYP2C119 mRNA was expressed less abundantly than CYP2C8, CYP2C9, CYP2C19, and CYP2C76 mRNAs but more abundantly than CYP2C18 mRNA. Recombinant cynomolgus and rhesus CYP2C119 catalyzed progesterone 16α-, 17α-, and 21-hydroxylation and diclofenac and omeprazole oxidations, indicating that CYP2C119 is a functional enzyme. Therefore, the novel CYP2C119 gene, expressed in macaque liver, encodes a functional enzyme that metabolizes human CYP2C substrates and is likely responsible for drug clearances. SIGNIFICANCE STATEMENT: Cytochrome P450 2C119 was found in cynomolgus and rhesus macaques, in addition to the known P450 2C8, 2C9, 2C18, 2C19, 2C76, and 2C93. Cynomolgus and rhesus CYP2C119 contain open reading frames of 489 amino acids with high sequence identity to human CYP2C8. Cynomolgus CYP2C119 mRNA is predominantly expressed in the liver. Recombinant CYP2C119 catalyzed progesterone hydroxylation and diclofenac and omeprazole oxidations. Therefore, the novel CYP2C119 gene expressed in the macaque liver encodes a functional enzyme that metabolizes human CYP2C substrates., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Cytochromes P450 (P450s or CYPs) are important drug-metabolizing enzymes. Because dogs are frequently used in drug metabolism studies, knowledge of dog CYP2C enzymes is essential because in humans these enzymes are abundant and play major roles in liver and intestine. The present study identified and characterized novel dog CYP2C94 along with previously identified dog CYP2C21 and CYP2C41. Dog CYP2C21, CYP2C41, and CYP2C94 cDNAs, respectively, contained open reading frames of 490, 489, and 496 amino acids and shared high-sequence identities (70%, 75%, and 58%) with human CYP2Cs. Dog CYP2C94 mRNA was preferentially expressed in liver, just as dog CYP2C21 and CYP2C41 mRNAs were. In dog liver, CYP2C21 mRNA was the most abundant, followed by CYP2C94 and CYP2C41 mRNAs. Moreover, the hepatic expressions of all three dog CYP2C mRNAs varied in four individual dogs, two of which did not express CYP2C41 mRNA. The three dog CYP2C genes had similar gene structures, and CYP2C94 , although located on the same chromosome, was in a genomic region far from the gene cluster containing CYP2C21 and CYP2C41 Metabolic assays with recombinant proteins showed that dog CYP2C94, along with CYP2C21 and CYP2C41, efficiently catalyzed oxidations of diclofenac, warfarin, and/or omeprazole, indicating that dog CYP2C94 is a functional enzyme. Novel dog CYP2C94 is expressed abundantly in liver and encodes a functional enzyme that metabolizes human CYP2C substrates; it is, therefore, likely responsible for drug clearances in dogs. SIGNIFICANCE STATEMENT: Novel dog cytochrome P450 2C94 (CYP2C94) was identified and characterized along with dog CYP2C21 and CYP2C41. Dog CYP2C94, isolated from liver, had 58% sequence identity and a close phylogenetic relationship with its human homologs and was expressed in liver at the mRNA level. Dog CYP2C94 (and CYP2C21 and CYP2C41) catalyzed oxidations of diclofenac and omeprazole, human CYP2C9 and CYP2C19 substrates, respectively, but CYP2C41 also hydroxylated warfarin. CYP2C94 is therefore a functional drug-metabolizing enzyme likely responsible for drug clearances in dogs., (Copyright © 2023 by The American Society for Pharmacology and Experimental Therapeutics.)

The tree shrew, a non-rodent primate-like species, is used in various fields of biomedical research, including hepatitis virus infection, myopia, depression, and toxicology. Recent genome analysis found that the numbers of cytochrome P450 (P450 or CYP ) genes are similar in tree shrews and humans and their sequence identities are high. Although the P450s are a family of important drug-metabolizing enzymes, they have not yet been fully investigated in tree shrews. In the current study, tree shrew CYP2A13 cDNA was isolated from liver, and its characteristics were compared with those of pig, dog, and human CYP2As. Tree shrew CYP2A13 amino acid sequences were highly identical (87-92%) to the human CYP2As and contained sequence motifs characteristic of P450s. Phylogenetic analysis revealed that tree shrew CYP2A13 was more closely related to human CYP2As than to rat CYP2As, similar to dog and pig CYP2As. Among the tissue types analyzed, tree shrew CYP2A13 mRNA was preferentially expressed in liver and lung, similar to dog CYP2A13 mRNA, whereas dog CYP2A25 and pig CYP2A19 mRNAs were predominantly expressed in liver. Tree shrew liver microsomes and tree shrew CYP2A13 proteins heterologously expressed in Escherichia coli catalyzed coumarin 7-hydroxylation and phenacetin O -deethylation, just as human, dog, and pig CYP2A proteins and liver microsomes do. These results demonstrate that tree shrew CYP2A13 is expressed in liver and lung and encodes a functional drug-metabolizing enzyme. SIGNIFICANCE STATEMENT: Novel tree shrew cytochrome P450 2A13 (CYP2A13) was identified and characterized in comparison with human, dog, and pig CYP2As. Tree shrew CYP2A13 isolated from liver had high sequence identities and close phylogenetic relationships to its human homologs and was abundantly expressed in liver and lung at the mRNA level. Tree shrew CYP2A13 metabolized coumarin and phenacetin, human selective CYP2A6 and CYP2A13 substrates, respectively, similar to dog and pig CYP2As, and is a functional drug-metabolizing enzyme likely responsible for drug clearances., (Copyright © 2023 by The American Society for Pharmacology and Experimental Therapeutics.)

Dogs are frequently used in drug metabolism studies, and their important drug-metabolizing enzymes, including cytochromes P450 (P450), have been analyzed. In humans, CYP3A4 is an especially important P450 due to its abundance and major roles in liver and intestine. In the present study, dog CYP3A98 and CYP3A99 were identified and characterized, along with previously identified CYP3A12 and CYP3A26. The dog CYP3A cDNAs contained open reading frames of 503 amino acids and shared high sequence identity (78%-80%) with human CYP3As. Among the dog CYP3A mRNAs, CYP3A98 mRNA was expressed most abundantly in small intestine. In contrast, dog CYP3A12 and CYP3A26 mRNAs were expressed in liver, where CYP3A12 mRNA was the most abundant. The four CYP3A genes had similar gene structures and formed a gene cluster in the dog and human genomes. Metabolic assays of dog CYP3A proteins heterologously expressed in Escherichia coli indicated that the dog CYP3As tested were functional enzymes with respect to typical human CYP3A4 substrates. Dog CYP3A98 efficiently catalyzed oxidations of nifedipine, alprazolam, and midazolam, indicating major roles of CYP3A98 in the small intestine. Dog CYP3A12 and CYP3A26 metabolizing nifedipine and/or midazolam would play roles in these reactions in the liver. In contrast, dog CYP3A99 showed minimal mRNA expression and minimal metabolic activity, and its contribution to overall drug metabolism is, therefore, negligible. These results indicated that newly identified dog CYP3A98, a testosterone 6 β - and estradiol 16 α -hydroxylase, was abundantly expressed in the small intestine and is likely the major CYP3A in the small intestine in combination with liver-specific CYP3A12. SIGNIFICANCE STATEMENT: Novel dog cytochromes P450 3A98 (CYP3A98) and CYP3A99 were identified and characterized to be functional and highly identical to human CYP3A4. Known CYP3A12 and new CYP3A98 efficiently catalyzed estradiol 16α-hydroxylation and midazolam 1'-hydroxylation. CYP3A98 mRNA was expressed in small intestine, whereas CYP3A12 mRNA was predominant in liver. Dog hepatic CYP3A12 and intestinal CYP3A98 are the enzymes likely responsible for the metabolic clearances of orally administered drugs, unlike human CYP3A4/5, which are in both the liver and intestine., (Copyright © 2022 by The American Society for Pharmacology and Experimental Therapeutics.)

Cytochrome P450s (P450s) have been identified and analyzed in dogs and pigs, species that are often used in preclinical drug studies. Moreover, P450s are clinically important for drug therapy not only in humans, but also in species under veterinary care, including dogs and cats. In the present study, seven P450s homologous to human CYP2J2, namely, dog CYP2J2; cat CYP2J2; and pig CYP2J33, CYP2J35, CYP2J91, and CYP2J93, were newly identified and characterized, along with pig CYP2J34 previously identified. The cDNAs of these CYP2Js contain open reading frames of 502 amino acids, except for CYP2J35 (498 amino acids), and share high sequence identity (77%-80%) with human CYP2J2. Phylogenetic analysis revealed that dog and cat CYP2J2 were closely related, whereas pig CYP2Js formed a cluster. All seven CYP2J genes contain nine coding exons and are located in corresponding genomic regions, with the pig CYP2J genes forming a gene cluster. These CYP2J2 mRNAs were predominantly expressed in the small intestine with additional expression in the kidney and brain for dog CYP2J2 and pig CYP2J91 mRNAs, respectively. All seven CYP2Js metabolized human CYP2J2 substrates terfenadine, ebastine, and astemizole, indicating that they are functional enzymes. Dog CYP2J2 and pig CYP2J34 and CYP2J35 efficiently catalyzed ebastine primary hydroxylation and secondary carebastine formation at low substrate concentrations, just as human CYP2J2 does. Velocity - versus-substate plots exhibited sigmoidal relationships for dog CYP2J2, cat CYP2J2, and pig CYP2J33, indicating allosteric interactions. These results suggest that dog, cat, and pig CYP2Js have similar functional characteristics to human CYP2J2, with slight differences in ebastine and astemizole oxidations. SIGNIFICANCE STATEMENT: Dog CYP2J2; cat CYP2J2; and pig CYP2J33, CYP2J34, CYP2J35, CYP2J91, and CYP2J93, homologous to human CYP2J2, were identified and characterized by sequence, phylogenetic, and genomic structure analyses. Intestinal expression patterns of CYP2J mRNAs were characteristic in dogs, cats, and pigs. Dog, cat, and pig CYP2Js likely play roles as drug-metabolizing enzymes in the small intestine, similar to human CYP2J2., (Copyright © 2022 by The American Society for Pharmacology and Experimental Therapeutics.)

Arylamine N -acetyltransferases (NATs) are drug-metabolizing enzymes that are essential for the metabolism of endogenous substrates and xenobiotics. The molecular characteristics of NATs have been extensively investigated in humans but remain to be investigated in common marmosets and pigs, animal species that are often used in drug metabolism studies. In this study, marmoset NAT1 and pig NAT1 cDNAs were isolated from liver samples and were characterized by molecular analyses and drug-metabolism assays. These NAT genes were intronless and formed gene clusters with one other NAT gene in the genome, just as human NAT genes do. Marmoset NAT1 and pig NAT1 amino acid sequences showed high sequence identities (94% and 85%, respectively) to human NAT1. Phylogenetic analysis indicated that marmoset NAT1 and pig NAT1 were more closely clustered with human NATs than with rat or mouse NATs. Marmoset NAT1 and pig NAT1 mRNAs were expressed in all the tissue types analyzed, with the expression levels being highest in the small intestine. Metabolic assays using recombinant proteins found that marmoset NAT1 and pig NAT1 metabolized human NAT substrates p -aminobenzoic acid, 2-aminofluorene, sulfamethazine, and isoniazid. Marmoset NAT1 and pig NAT1 substantially acetylated p -aminobenzoic acid and 2-aminofluorene relevant human NAT1, but their activities were lower toward sulfamethazine and isoniazid than those of the relevant human NAT2. Therefore, marmoset and pig NATs are functional enzymes with molecular similarities to human NAT1, but their substrate specificities, while similar to human NAT1, differ somewhat from human NAT2. SIGNIFICANCE STATEMENT: Marmoset N -acetyltransferase NAT1 and pig NAT1 were identified and showed high sequence identities to human NAT1. These NAT mRNAs were expressed in various tissues. Marmoset and pig NAT1s acetylated typical human NAT substrates, although their substrate specificities differed somewhat from human NAT2. Marmoset NAT1 and pig NAT1 have similarities with human NAT1 in terms of molecular and enzymatic characteristics., (Copyright © 2022 by The American Society for Pharmacology and Experimental Therapeutics.)

For drug development, species differences in drug-metabolism reactions present obstacles for predicting pharmacokinetics in humans. We characterized the species differences in hydrolases among humans and mice, rats, dogs, and cynomolgus monkeys. In this study, to expand the series of such studies, we attempted to characterize marmoset hydrolases. We measured hydrolase activities for 24 compounds using marmoset liver and intestinal microsomes, as well as recombinant marmoset carboxylesterase (CES) 1, CES2, and arylacetamide deacetylase (AADAC). The contributions of CES1, CES2, and AADAC to hydrolysis in marmoset liver microsomes were estimated by correcting the activities by using the ratios of hydrolase protein levels in the liver microsomes and those in recombinant systems. For six out of eight human CES1 substrates, the activities in marmoset liver microsomes were lower than those in human liver microsomes. For two human CES2 substrates and three out of seven human AADAC substrates, the activities in marmoset liver microsomes were higher than those in human liver microsomes. Notably, among the three rifamycins, only rifabutin was hydrolyzed by marmoset tissue microsomes and recombinant AADAC. The activities for all substrates in marmoset intestinal microsomes tended to be lower than those in liver microsomes, which suggests that the first-pass effects of the CES and AADAC substrates are due to hepatic hydrolysis. In most cases, the sums of the values of the contributions of CES1, CES2, and AADAC were below 100%, which indicated the involvement of other hydrolases in marmosets. In conclusion, we clarified the substrate preferences of hydrolases in marmosets. SIGNIFICANCE STATEMENT: This study confirmed that there are large differences in hydrolase activities between humans and marmosets by characterizing marmoset hydrolase activities for compounds that are substrates of human CES1, CES2, or arylacetamide deacetylase. The data obtained in this study may be useful for considering whether marmosets are appropriate for examining the pharmacokinetics and efficacies of new chemical entities in preclinical studies., (Copyright © 2021 by The American Society for Pharmacology and Experimental Therapeutics.)

In contrast to a single human carboxylesterase 2 (CES2) isozyme (hCE2), three CES2 genes have been identified in cynomolgus monkeys: mfCES2A , mfCES2B , and mfCES2C . Although mfCES2A protein is expressed in several organs, mfCES2B is a pseudogene and the phenotype of the mfCES2C gene has not yet been clarified in tissues. In previous studies, we detected an unidentified esterase in the region of CES2 mobility upon nondenaturing PAGE analysis of monkey intestinal microsomes, which showed immunoreactivity for anti-mfCES2A antibody. The aim of the present study was to identify this unidentified esterase from monkey small intestine. The esterase was separated on nondenaturing PAGE gel and digested in-gel with trypsin. The amino acid sequences of fragmented peptides were analyzed by tandem mass spectrometry. The unidentified esterase was shown to be identical to mfCES2C (XP_015298642.1, predicted from the genome sequence data). mfCES2C consists of 559 amino acid residues and shows approximately 90% homology with mfCES2A (561 amino acid residues). In contrast to the ubiquitous expression of mfCES2A, mfCES2C is only expressed in the small intestine, kidney, and skin. The hydrolytic properties of recombinant mfCES2C, expressed in HEK293 cells, with respect to p -nitrophenyl derivatives, 4-methylumbelliferyl acetate, and irinotecan were similar to those of recombinant mfCES2A. However, mfCES2C showed a hydrolase activity for O - n -valeryl propranolol higher than mfCES2A. It is concluded that the previously unidentified monkey intestinal CES2 is mfCES2C, which shows different hydrolytic properties to mfCES2A, depending on the substrate. SIGNIFICANCE STATEMENT: In the present research, we determined that mfCES2C, a novel monkey CES2 isozyme, is expressed in the small intestine and kidney of the cynomolgus monkey. Interestingly, mfCES2C showed a relatively wide substrate specificity for ester-containing compounds. These findings may, in early stages of drug development, support the use of in vitro -to- in vivo extrapolation for the intestinal hydrolysis of ester drugs in the cynomolgus monkey., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

A β -blocker, metoprolol, is one of the in vivo probes for human cytochrome P450 (P450) 2D6. Investigation of nonhuman primate P450 enzymes helps to improve the accuracy of the extrapolation of pharmacokinetic data from animals into humans. Common marmosets ( Callithrix jacchus ) are a potential primate model for preclinical research, but the detailed roles of marmoset P450 enzymes in metoprolol oxidation remain unknown. In this study, regio- and stereo-selectivity of metoprolol oxidations by a variety of P450 enzymes in marmoset and human livers were investigated in vitro. Although liver microsomes from cynomolgus monkeys and rats preferentially mediated S -metoprolol O -demethylation and R -metoprolol α -hydroxylation, respectively, those from humans, marmosets, minipigs, and dogs preferentially mediated R -metoprolol O -demethylation, in contrast to the slow rates of R - and S -metoprolol oxidation in mouse liver microsomes. R - and S -metoprolol O -demethylation activities in marmoset livers were strongly inhibited by quinidine and ketoconazole, and were significantly correlated with bufuralol 1'-hydroxylation and midazolam 1'-hydroxylation activities and also with P450 2D and 3A4 contents, which is different from the case in human livers that did not have any correlations with P450 3A-mediated midazolam 1'-hydroxylation. Recombinant human P450 2D6 enzyme and marmoset P450 2D6/3A4 enzymes effectively catalyzed R -metoprolol O -demethylation, comparable to the activities of human and marmoset liver microsomes, respectively. These results indicated that the major roles of P450 2D enzymes for the regio- and stereo-selectivity of metoprolol oxidation were similar between human and marmoset livers, but the minor roles of P450 3A enzymes were unique to marmosets., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

Common marmosets ( Callithrix jacchus ), New World monkeys, are a promising primate model for preclinical drug metabolism studies because of the similarities of cytochrome P450 (P450) enzyme function to those of humans. Despite an increasing number of drug candidates catalyzed by non-P450 enzymes, drug metabolizing enzymes other than P450s have been hardly identified or characterized in marmosets. In this study, we identified aldehyde oxidase ( AOX ) 1 gene by marmoset genome analysis. AOX1 cDNA was cloned from marmoset livers by reverse transcription-polymerase chain reaction. Deduced amino acid sequences of AOX1 cDNA showed high sequence identities (92-93%) with primate AOX1s. Phylogenetic analysis showed that marmoset AOX1 was closely clustered with primate AOX1s, unlike nonprimate animal model AOX1s of pig, rabbit, rat, and mouse used in drug metabolism. The tissue expression analyses by real-time reverse-transcription polymerase chain reaction and immunoblotting showed that marmoset AOX1 mRNA and protein were abundantly expressed in livers, similar to cynomolgus monkeys and humans. Marmoset AOX1 heterologously expressed in Escherichia coli catalyzed the oxidation of carbazeran and phthalazine, typical AOX1 substrates, similar to cynomolgus monkey and human AOX1s. Human and marmoset AOX1 effectively catalyzed phthalazine oxidation when assessed with Michaelis-Menten kinetics, but cynomolgus monkey AOX1 catalyzed this reaction with cooperative kinetics with high capacity. These results indicated that tissue distribution and enzymatic function of AOX1 enzyme is similar between marmosets and humans, suggesting that marmosets are a suitable primate model for AOX-dependent drug metabolism in preclinical studies., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

Common marmosets ( Callithrix jacchus ) are potentially primate models for preclinical drug metabolism studies because there are similarities in the molecular characteristics of cytochrome P450 enzymes between this species and humans. However, characterization of non-cytochrome P450 enzymes has not been clarified in marmosets. Here, we report characterization of flavin-containing monooxygenases FMO1-FMO5 identified in marmoset tissues. Marmoset FMO forms shared high amino acid sequence identities (93%-95%) and phylogenetic closeness with human homologous FMO forms. FMO1 and FMO3 mRNA were abundantly expressed in the liver and kidneys among five marmoset tissues examined, where FMO3 protein was detected by immunoblotting. FMO inhibition assays using preheated tissue microsomes indicated that benzydamine N -oxygenation and sulindac sulfide S -oxygenation in the marmoset liver was mainly catalyzed by FMO3, the major hepatic FMO. Marmoset FMO3 protein heterologously expressed in Escherichia coli effectively catalyzed benzydamine N -oxygenation and sulindac sulfide S -oxygenation comparable to marmoset liver microsomes. These results indicate that the FMO3 enzyme expressed in marmoset livers mainly metabolizes benzydamine and sulindac sulfide (typical human FMO substrates), suggesting its importance for FMO-dependent drug metabolism in marmosets., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

Common marmosets ( Callithrix jacchus ), small New World primates, are increasingly attracting attention as potentially useful animal models for drug development. However, characterization of cytochrome P450 (P450) 3A enzymes involved in the metabolism of a wide variety of drugs has not investigated in marmosets. In this study, sequence homology, tissue distribution, and enzymatic properties of marmoset P450 3A4 ortholog, 3A5 ortholog, and 3A90 were investigated. Marmoset P450 3A forms exhibited high amino acid sequence identities (88-90%) to the human and cynomolgus monkey P450 3A orthologs and evolutionary closeness to human and cynomolgus monkey P450 3A orthologs compared with other P450 3A enzymes. Among the five marmoset tissues examined, P450 3A4 ortholog mRNA was abundant in livers and small intestines where P450 3A4 ortholog proteins were immunologically detected. Three marmoset P450 3A proteins heterologously expressed in Escherichia coli membranes catalyzed midazolam 1'- and 4-hydroxylation, alprazolam 4-hydroxylation, nifedipine oxidation, and testosterone 6 β -hydroxylation, similar to cynomolgus monkey and human P450 3A enzymes. Among the marmoset P450 3A enzymes, P450 3A4 ortholog effectively catalyzed midazolam 1'-hydroxylation, comparable to microsomes from marmoset livers and small intestines. Correlation analyses with 23 individual marmoset liver microsomes suggested contributions of P450 3A enzymes to 1'-hydroxylation of both midazolam (human P450 3A probe) and bufuralol (human P450 2D6 probe), similar to cynomolgus monkey P450 3A enzymes. These results indicated that marmoset P450 3A forms had functional characteristics roughly similar to cynomolgus monkeys and humans in terms of tissue expression patterns and catalytic activities, suggesting marmosets as suitable animal models for P450 3A-dependent drug metabolism., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

Marmoset cytochrome P450 2C19, highly homologous to human P450 2C9 and 2C19, has been identified in common marmosets (Callithrix jacchus), a nonhuman primate species used in drug metabolism studies. Although genetic variants in human and macaque P450 2C genes account for the interindividual variability in drug metabolism, genetic variants have not been investigated in the marmoset P450 2C19 In this study, sequencing of P450 2C19 in 24 marmosets identified three variants p.[(Phe7Leu; Ser254Leu; Ile469Thr)], which showed substantially reduced metabolic capacity of S-warfarin compared with the wild-type group in vivo and in vitro. Although mean plasma concentrations of R-warfarin in marmosets determined after chiral separation were similar between the homozygous mutant and wild-type groups up to 24 hours after the intravenous and oral administrations of racemic warfarin, S-warfarin depletion from plasma was significantly faster in the three wild-type marmosets compared with the three homozygous mutant marmosets. These variants, cosegregating in the marmosets analyzed, influenced metabolic activities in 18 marmoset liver microsomes because the homozygotes and heterozygotes showed significantly reduced catalytic activities in liver microsomes toward S-warfarin 7-hydroxylation compared with the wild-type group. Kinetic analysis for S-warfarin 7-hydroxylation indicated that the recombinant P450 2C19 Ser254Leu variant would change the metabolic capacity. These results indicated that the interindividual variability of P450 2C-dependent drug metabolism such as S-warfarin clearance is at least partly accounted for by P450 2C19 variants in marmosets, suggesting that polymorphic P450 2C-dependent catalytic functions are relatively similar between marmosets and humans., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

Common marmosets (Callithrix jacchus) are attracting attention as animal models in preclinical studies for drug development. However, cytochrome P450s (P450s), major drug-metabolizing enzymes, have not been fully identified and characterized in marmosets. In this study, based on the four novel P450 4F genes found on the marmoset genome, we successfully isolated P450 4F2, 4F3B, 4F11, and 4F12 cDNAs in marmoset livers. Deduced amino acid sequences of the four marmoset P450 4F forms exhibited high sequence identities (87%-93%) to the human and cynomolgus monkey P450 4F homologs. Marmoset P450 4F3B and 4F11 mRNAs were predominantly expressed in livers, whereas marmoset P450 4F2 and 4F12 mRNAs were highly expressed in small intestines and livers. Four marmoset P450 4F proteins heterologously expressed in Escherichia coli catalyzed the ω-hydroxylation of leukotriene B4 In addition, marmoset P450 4F12 effectively catalyzed the hydroxylation of antiallergy drug ebastine, a human P450 2J/4F probe substrate. Ebastine hydroxylation activities by small intestine and liver microsomes from marmosets and cynomolgus monkeys showed greatly higher values than those of humans. Ebastine hydroxylation activities by marmoset and cynomolgus monkey small intestine microsomes were inhibited (approximately 60%) by anti-P450 4F antibodies, unlike human small intestine microsomes, suggesting that contribution of P450 4F enzymes for ebastine hydroxylation in the small intestine might be different between marmosets/cynomolgus monkeys and humans. These results indicated that marmoset P450 4F2, 4F3B, 4F11, and 4F12 were expressed in livers and/or small intestines and were functional in the metabolism of endogenous and exogenous compounds, similar to those of cynomolgus monkeys and humans., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

The common marmoset (Callithrix jacchus), a New World monkey, has potential to be an animal model for drug metabolism studies. In this study, we identified and characterized cytochrome P450 (P450) 1A1 and 1B1 in addition to the known P450 1A2 in marmosets. Marmoset P450 1A1 and 1B1 cDNA contained open reading frames encoding 512 and 543 amino acids, respectively, with high sequence identities (90%-93%) to other primate P450 1A1s and 1B1s. A phylogenetic tree based on amino acid sequences showed close evolutionary relationships among marmoset, macaque, and human P450 1A and 1B enzymes. By mRNA quantification and immunoblot analyses in five marmoset tissues, P450 1A1 was mainly expressed in lungs and small intestines, and P450 1A2 was expressed predominantly in livers. In contrast, P450 1B1 was expressed in all tissues tested. Marmoset P450 1A1, 1A2, and 1B1 heterologously expressed in Escherichia coli catalyzed 7-ethoxyresorufin O-deethylation, 7-ethoxycoumarin O-deethylation, and phenacetin O-deethylation, similar to those of humans and cynomolgus monkeys. Notably, marmoset P450 1A1 and 1A2 more efficiently catalyzed 7-ethoxyresorufin O-deethylation than those of the human homologs, but were comparable to those of the cynomolgus monkey homologs. Additionally, marmoset P450 1B1 preferentially catalyzed estradiol 4-hydroxylation; however, rat P450 1B1 more favorably catalyzed estradiol 2-hydroxylation, indicating that the estradiol hydroxylation specificity of marmoset P450 1B1 was similar to those of human and cynomolgus monkey P450 1B1. These results indicated that marmoset P450 1A and 1B enzymes had functional characteristics similar to those of humans and cynomolgus monkeys, suggesting that P450 1A and 1B-dependent metabolism was similar among marmosets, cynomolgus monkeys, and humans., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

The common marmoset (Callithrix jacchus), a small New World monkey, has the potential for use in human drug development due to its evolutionary closeness to humans. Four novel cDNAs, encoding cytochrome P450 (P450) 2C18, 2C19, 2C58, and 2C76, were cloned from marmoset livers to characterize P450 2C molecular properties, including previously reported P450 2C8. The deduced amino acid sequence showed high sequence identities (>86%) with those of human P450 2Cs, except for marmoset P450 2C76, which has a low sequence identity (∼70%) with any human P450 2Cs. Phylogenetic analysis showed that marmoset P450 2Cs were more closely clustered with those of humans and macaques than other species investigated. Quantitative polymerase chain reaction analysis showed that all of the marmoset P450 2C mRNAs were predominantly expressed in liver as opposed to the other tissues tested. Marmoset P450 2C proteins were detected in liver by immunoblotting using antibodies against human P450 2Cs. Among marmoset P450 2Cs heterologously expressed in Escherichia coli, marmoset P450 2C19 efficiently catalyzed human P450 2C substrates, S-warfarin, diclofenac, tolbutamide, flurbiprofen, and omeprazole. Marmoset P450 2C19 had high Vmax and low Km values for S-warfarin 7-hydroxylation that were comparable to those in human liver microsomes, indicating warfarin stereoselectivity similar to findings in humans. Faster in vivo S-warfarin clearance than R-warfarin after intravenous administration of racemic warfarin (0.2 mg/kg) to marmosets was consistent with the in vitro kinetic parameters. These results indicated that marmoset P450 2C enzymes had functional characteristics similar to those of humans, and that P450 2C-dependent metabolic properties are likewise similar between marmosets and humans., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

The common marmoset (Callithrix jacchus), a New World primate species, is potentially a useful animal model for preclinical studies in drug development. However, cytochrome P450 (P450) enzymes have not been fully identified and characterized in marmosets. In this study, we identified P450 2A6 cDNA with the sequence highly identical (91-94%) to human P450 2A6, 2A7, and 2A13 cDNA and cynomolgus monkey P450 2A23, 2A24, and 2A26 cDNA. Among the tissue types examined, marmoset P450 2A6 mRNA was most abundantly expressed in livers where P450 2A6 protein was also detected by immunoblotting. Phylogenetic analysis showed that marmoset P450 2A6 was more closely clustered with human and cynomolgus monkey P450 2As than P450 2As of dog, rat, and mouse (the species also used in drug metabolism). Marmoset P450 2A6 heterologously expressed in Escherichia coli membranes efficiently catalyzed 7-ethoxycoumarin O-deethylation, similar to human P450 2A6 and 2A13 and cynomolgus monkey P450 2A23, 2A24, and 2A26, but much less effectively coumarin 7-hydroxylation, showing some difference as well. Interestingly, marmoset P450 2A6 and cynomolgus monkey P450 2A23 catalyzed phenacetin O-deethylation, which is catalyzed by human P450 1A2 and 2A13, but not by P450 2A6. Marmoset P450 2A6 also exhibited catalytic activity toward testosterone by the multiple sites, but not rat P450 2A-specific testosterone 7α-hydroxylation activity. These results indicated that marmoset P450 2A6 had functional characteristics different from those of human and cynomolgus monkey P450 2As in terms of partially different substrate specificities and catalytic activities, indicating its importance of further studies for P450 2A-dependent drug metabolism in marmosets., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

Cynomolgus monkeys are widely used as primate models in preclinical studies, because of their evolutionary closeness to humans. In humans, the cytochrome P450 (P450) 2C enzymes are important drug-metabolizing enzymes and highly expressed in livers. The CYP2C enzymes, including CYP2C9, are also expressed abundantly in cynomolgus monkey liver and metabolize some endogenous and exogenous substances like testosterone, S-mephenytoin, and diclofenac. However, comprehensive evaluation regarding substrate specificity of monkey CYP2C9 has not been conducted. In the present study, 89 commercially available drugs were examined to find potential monkey CYP2C9 substrates. Among the compounds screened, 20 drugs were metabolized by monkey CYP2C9 at a relatively high rates. Seventeen of these compounds were substrates or inhibitors of human CYP2C9 or CYP2C19, whereas three drugs were not, indicating that substrate specificity of monkey CYP2C9 resembled those of human CYP2C9 or CYP2C19, with some differences in substrate specificities. Although efavirenz is known as a marker substrate for human CYP2B6, efavirenz was not oxidized by CYP2B6 but by CYP2C9 in monkeys. Liquid chromatography-mass spectrometry analysis revealed that monkey CYP2C9 and human CYP2B6 formed the same mono- and di-oxidized metabolites of efavirenz at 8 and 14 positions. These results suggest that the efavirenz 8-oxidation could be one of the selective markers for cynomolgus monkey CYP2C9 among the major three CYP2C enzymes tested. Therefore, monkey CYP2C9 has the possibility of contributing to limited specific differences in drug oxidative metabolism between cynomolgus monkeys and humans., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

The potential proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces Parkinson-like syndromes in common marmosets, other primates, and humans. MPTP is metabolically activated to 1-methyl-4-phenyl-2,3-dihydropyridinium and 1-methyl-4-phenylpyridinium ions (MPDP(+) and MPP(+), respectively) by desaturation reactions. MPTP is deactivated to 4-phenyl-1,2,3,6-tetrahydropyridine (PTP) by N-demethylation and is also deactivated to MPTP N-oxide. The roles of cytochrome P450 (P450) enzymes and flavin-containing monooxygenases (FMOs) in the oxidative metabolism of MPTP-treated marmosets are not yet fully clarified. This study aimed to elucidate P450- and FMO-dependent MPTP metabolism in marmoset liver and brain. Rates of MPTP N-oxygenation in liver microsomes were similar to those in brain microsomes from 11 individual marmosets (substrate concentration, 50 μM) and were correlated with rates of benzydamine N-oxygenation (r = 0.75, P < 0.05); the reactions were inhibited by methimazole (10 μM). MPTP N-oxygenation was efficiently mediated by recombinantly expressed marmoset FMO3. Rates of PTP formation by MPTP N-demethylation in marmoset liver microsomes were correlated with bufuralol 1'-hydroxylation rates (r = 0.77, P < 0.01) and were suppressed by quinidine (1 μM), thereby indicating the importance of marmoset CYP2D6 in PTP formation. MPTP transformations to MPDP(+) and MPP(+) were efficiently catalyzed by recombinant marmoset CYP2D6 and human CYP1A2. These results indicated the contributions of multiple drug-metabolizing enzymes to MPTP oxidation, especially marmoset FMO3 in deactivation (N-oxygenation) and marmoset CYP2D6 for both MPTP deactivation and MPTP activation to MPDP(+) and MPP(+). These findings provide a foundation for understanding MPTP metabolism and for the successful production of preclinical marmoset models., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

Cynomolgus monkeys are widely used in preclinical studies during drug development because of their evolutionary closeness to humans, including their cytochrome P450s (P450s). Most cynomolgus monkey P450s are almost identical (≥90%) to human P450s; however, CYP2C76 has low sequence identity (approximately 80%) to any human CYP2Cs. Although CYP2C76 has no ortholog in humans and is partly responsible for species differences in drug metabolism between cynomolgus monkeys and humans, a broad evaluation of potential substrates for CYP2C76 has not yet been conducted. In this study, a screening of 89 marketed compounds, including human CYP2C and non-CYP2C substrates or inhibitors, was conducted to find potential CYP2C76 substrates. Among the compounds screened, 19 chemicals were identified as substrates for CYP2C76, including substrates for human CYP1A2 (7-ethoxyresorufin), CYP2B6 (bupropion), CYP2D6 (dextromethorphan), and CYP3A4/5 (dextromethorphan and nifedipine), and inhibitors for CYP2B6 (sertraline, clopidogrel, and ticlopidine), CYP2C8 (quercetin), CYP2C19 (ticlopidine and nootkatone), and CYP3A4/5 (troleandomycin). CYP2C76 metabolized a wide variety of the compounds with diverse structures. Among them, bupropion and nifedipine showed high selectivity to CYP2C76. As for nifedipine, CYP2C76 formed methylhydroxylated nifedipine, which was not produced by monkey CYP2C9, CYP2C19, or CYP3A4, as identified by mass spectrometry and estimated by a molecular docking simulation. This unique oxidative metabolite formation of nifedipine could be one of the selective marker reactions of CYP2C76 among the major CYP2Cs and CYP3As tested. These results suggest that monkey CYP2C76 contributes to bupropion hydroxylation and formation of different nifedipine oxidative metabolites as a result of its relatively large substrate cavity., (Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.)

Carboxylesterase (CES) is important for detoxification of a wide range of drugs and xenobiotics and catalyzes cholesterol and fatty acid metabolism. Cynomolgus macaques are widely used in drug metabolism studies; however, cynomolgus CES has not been fully investigated at molecular levels, partly due to the lack of gene information. In this study, we isolated and characterized cDNAs for CES homologous to human CES1, CES2, and CES5A in cynomolgus macaques. By genome analysis, in the cynomolgus macaque genome, three gene sequences were found for CES1(v1-3) and CES2(v1-3), whereas one gene sequence was found for CES5A. Cynomolgus CES1, CES2, and CES5A genes were located in the genomic regions corresponding to the human genes. We successfully identified CES1v1, CES1v2, CES2v1, CES2v3, and CES5A cDNAs from cynomolgus liver. Sequence analysis showed that amino acid sequences of each CES were highly homologous to that of the human homolog. All five CESs had sequences characteristic for CES enzymes, including the catalytic triad and oxyanion hole loop. By quantitative polymerase chain reaction, the most abundant expression of CES mRNAs among the 10 tissue types analyzed was observed in liver (CES1v1 and CES2v3 mRNAs), jejunum (CES2v1 mRNAs), and kidney (CES1v2 and CES5A mRNA), the organs important for drug metabolism and excretion. The results indicated that cynomolgus macaques express at least five CES genes, which potentially encode intact CES proteins., (Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.)

Cynomolgus macaques and rhesus macaques are nonhuman primate species widely used in drug metabolism studies. Cynomolgus CYP2D17, highly homologous to human CYP2D6, metabolizes human CYP2D6 substrates such as bufuralol and dextromethorphan, and the gene is expressed predominantly in liver. Although human CYP2D6 variants account for the variability of the enzyme properties among individuals and populations, genetic variants have not been investigated in CYP2D17. In the present study, CYP2D17 from 87 cynomolgus and 40 rhesus macaques was resequenced. The analysis found a total of 36 nonsynonymous variants, among which 5 were located in substrate recognition sites, the region important for protein function. Twenty-two variants were unique to cynomolgus macaques, of which 11 and 9 were found only in Indochinese and Indonesian cynomolgus macaques, respectively. Eight variants were unique to rhesus macaques. The functional characterization showed that two variant proteins (S188Y and V227I) heterologously expressed in Escherichia coli did not show substantial differences in the rate of bufuralol 1'-hydroxylation as compared with wild-type. However, measuring catalytic activities of the genotyped liver microsomes revealed that I297M and N337D were together significantly associated with higher rates, approximately 2.3- and 11.5-fold, of bufuralol 1'-hydroxylation and dextromethorphan O-demethylation, respectively, in the homozygotes than wild-type animals. The present study provided the first evidence that variability of a CYP2D-dependent metabolism in macaque liver is partly accounted for by CYP2D genotypes., (Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.)

Due to the importance of in vitro cytochrome P450 (P450) induction assay to assess the possible drug-drug interaction events, the recent US Food and Drug Administration draft guidance and European Medicines Agency guideline recommend to assess P450 induction using fresh or cryopreserved hepatocytes at mRNA level and/or enzyme activity level. Although cryopreserved hepatocytes are commercially available for P450 induction assays, feasibility and practicability of these hepatocytes have not been fully investigated. In this study, a total of 23 lots of human cryopreserved hepatocytes were treated with three typical inducers (omeprazole, phenobarbital, and rifampicin), and induction of CYP1A2, CYP2B6, and CYP3A4 enzyme activity was measured. In 8 of these 23 hepatocyte lots, induction of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP3A4 mRNA was also analyzed. The results revealed that CYP1A2, CYP2B6, and CYP3A4 were induced (>2.0-fold) by omeprazole, phenobarbital, and rifampicin, respectively, in all the hepatocyte lots tested at enzyme activity level (23 lots) and mRNA level (8 lots). In contrast, of the 8 hepatocyte lots treated with rifampicin, CYP2C8 and CYP2C9 mRNA were not induced in 5 and 2 hepatocyte lots, respectively, and CYP2C19 mRNA was not induced in any of the 8 hepatocyte lots tested. These results suggest that induction of CYP1A2, CYP2B6, and CYP3A4 can be readily assessed, but evaluation for CYP2C mRNA induction might not be feasible, using commercially available human cryopreserved hepatocytes.

Drug-drug interactions (DDIs) caused by the inhibition of hepatic uptake transporters such as organic anion transporting polypeptide (OATP) can affect therapeutic efficacy and cause adverse reactions. We investigated the potential utility of pitavastatin as an in vivo probe substrate for preclinically studying OATP-mediated DDIs using cynomolgus monkeys. Cyclosporine A (CsA) and rifampicin (RIF), typical OATP inhibitors, inhibited active uptake of pitavastatin into monkey hepatocytes with half-maximal inhibitory concentration values comparable with those in human hepatocytes. CsA and RIF increased the area under the plasma concentration-time curve (AUC) of intravenously administered pitavastatin in cynomolgus monkeys by 3.2- and 3.6-fold, respectively. In addition, there was no apparent prolongation of the elimination half-life of pitavastatin due to the decrease in both hepatic clearance and volume of distribution. These findings suggest that DDIs were caused by the inhibition of hepatic uptake of pitavastatin. CsA and RIF increased the AUC of orally administered pitavastatin by 10.6- and 14.8-fold, respectively, which was additionally caused by the effect of the CsA and RIF in the gastrointestinal tract. Hepatic contribution to the overall DDI for oral pitavastatin with CsA was calculated from the changes in hepatic availability and clearance, and it was shown that the magnitude of hepatic DDI was comparable between the present study and the clinical study. In conclusion, pharmacokinetic studies using pitavastatin as a probe in combination with drug candidates in cynomolgus monkeys are useful to support the assessment of potential clinical DDIs involving hepatic uptake transporters.

The glutathione S-transferase (GST) family comprises cytosolic, mitochondrial, and microsomal GSTs, all essential enzymes that metabolize a wide range of endogenous and exogenous substrates. Among the microsomal GSTs (MGSTs) in humans, MGST1, MGST2, and MGST3 are involved in detoxification; however, MGSTs have not been fully investigated in cynomolgus macaque, an important primate species widely used in drug metabolism and toxicity studies. In the present study, cynomolgus MGST2 and MGST3 cDNAs were isolated from liver tissue and characterized along with previously isolated cynomolgus MGST1. For comparison with the cynomolgus cDNAs, MGST2 and MGST3 cDNAs were also isolated from rhesus macaque (closely related to cynomolgus macaque) liver. Cynomolgus MGST2 and MGST3, respectively, were highly identical (99 and 98%) to human MGST2 and MGST3 and nearly identical to the amino acid sequences of the rhesus orthologs, and they were closely clustered with human MGST2 and MGST3 by phylogenetic analysis. The analysis of genome data indicated that MGST1, MGST2, and MGST3, respectively, had similar gene structures and genomic organization in macaque and human. Therefore, cynomolgus MGSTs have molecular similarities to the corresponding human MGSTs. Cynomolgus MGST2 and MGST3 were expressed in liver, jejunum, and kidney, but at lower levels than MGST1. GST activities were measured with 1-chloro-2,4-dinitrobenzene and 1,2-epoxy-3-(p-nitrophenoxy)propane as substrates, using proteins heterologously expressed in Escherichia coli. Cynomolgus MGST1, MGST2, and MGST3 conjugated 1-chloro-2,4-dinitrobenzene and 1,2-epoxy-3-(p-nitrophenoxy)propane, indicating that cynomolgus MGST1, MGST2, and MGST3 are functional enzymes. These results suggest that these functional cynomolgus MGST enzymes and the corresponding human MGSTs are molecularly similar.

Estrogen regulation of gene expression is essential for physiological function of estrogen-responsive tissues, such as mammary glands, ovaries, and the uterus. In the liver, estrogen is responsible for sex-dependent gene expression of drug-metabolizing enzymes in rodents. However, the influence of estrogen on hepatic gene expression has not been fully investigated in primates, including human. Macaque, including cynomolgus macaque, is an important species for comparative studies aimed at understanding human physiology due to its evolutionary closeness to human. To identify estrogen-responsive genes in primate liver, therefore, hepatic gene expression was compared, by microarray analysis, in ovariectomized cynomolgus macaques treated with estradiol or solvent (control). The analysis identified 98 estradiol-responsive genes; 47 and 51 were up- and down-regulated by estradiol, respectively (≥2.0-fold, P < 0.05). Expression of drug-metabolizing enzyme genes was also influenced by estradiol treatment; estradiol enhanced expression of GSTM5 (3.8-fold, P < 0.05) and CYP3A8(4) (2.7-fold, P < 0.01), but lowered expression of CYP4F12 (2.2-fold, P < 0.01), as verified by quantitative polymerase chain reaction. In particular, CYP3A8(4), orthologous to human CYP3A4, is an essential drug-metabolizing enzyme in cynomolgus macaque liver. These results suggest that expression of hepatic genes, including drug-metabolizing enzyme genes, is at least partly regulated by estradiol in cynomolgus macaque.

CYP2G2P is pseudogenized in humans because of two nonsense mutations (c.76C>T in exon 1 and c.382C>T in exon 3) in the putative coding region of the gene sequence, whereas mouse, rat, and rabbit CYP2Gs are expressed and functional in nasal mucosa. In this study, we assessed the intactness of CYP2G in a cynomolgus monkey, a macaque species important for drug metabolism studies because of its evolutionary closeness to human. On the basis of a gene sequence (highly identical to human CYP2G2P) found in the macaque genome, CYP2G2 cDNA was successfully isolated from cynomolgus monkey nasal mucosa. CYP2G2 cDNA, containing an open reading frame of 494 amino acids, was shown to share high sequence identity (nearly 95%) with the putative coding region of human CYP2G2P. Cynomolgus monkey CYP2G2 shared the highest sequence identity (59-61%) with CYP2A23, CYP2A24, and CYP2A26 among cynomolgus monkey cytochromes P450. Cynomolgus monkey CYP2G2 mRNA was predominantly expressed in the nasal mucosa, where CYP2G2 protein expression was also detected. Metabolic assays indicated that cynomolgus monkey CYP2G2 metabolized coumarin, similar to cynomolgus monkey CYP2A23, CYP2A24, and CYP2A26. Moreover, among 39 cynomolgus monkeys and 11 rhesus monkeys examined in this study, only 2 cynomolgus monkeys and 1 rhesus monkey were heterozygous for c.76C>T. No animals carried c.382C>T. These results suggest that cynomolgus monkey CYP2G2 is a functional drug-metabolizing enzyme in nasal mucosa.

Induction of the cytochrome P450 (P450) enzyme is a major concern in the drug discovery processes. To predict the clinical significance of enzyme induction, it is helpful to investigate pharmacokinetic alterations of a coadministered drug in a suitable animal model. In this study, we focus on the induction of CYP3A, which is involved in the metabolism of approximately 50% of marketed drugs and is inducible in both the liver and intestine. As a marker substrate for CYP3A activity, alprazolam (APZ) was selected and characterized using recombinant CYP3A enzymes expressed in Escherichia coli. Both human CYP3A4 and its cynomolgus P450 ortholog predominantly catalyzed APZ 4-hydroxylation with sigmoidal kinetics. When administered intravenously and orally to cynomolgus monkeys, APZ had moderate clearance; its first-pass extraction ratio after oral dosing was estimated to be 0.09 in the liver and 0.45 in the intestine. Pretreatment with multiple doses of rifampicin (20 mg/kg p.o. for 5 days), a known CYP3A inducer, significantly decreased plasma concentrations of APZ after intravenous and oral administrations (0.5 mg/kg), and first-pass extraction ratios were increased to 0.39 in the liver and 0.63 in the intestine. The results were comparable to those obtained in clinical drug-drug interaction (DDI) reports related to CYP3A induction, although the rate of recovery of CYP3A activity seemed to be slower than rates estimated in clinical studies. In conclusion, pharmacokinetic studies using APZ as a probe in monkeys may provide useful information regarding the prediction of clinical DDIs due to CYP3A induction.

The cynomolgus monkey is used in drug metabolism studies, because of its evolutionary closeness to human, including cytochrome P450. Cynomolgus monkey CYP2D17, highly homologous to human CYP2D6, has been identified and characterized. Here, we report characterization of another CYP2D, CYP2D44, identified in cynomolgus monkey liver. The CYP2D44 cDNA contained an open reading frame of 497 amino acids sharing high sequence identity (87-93%) with other primate CYP2Ds. CYP2D44 mRNA was predominantly expressed in liver, similar to CYP2D17 mRNA. CYP2D17 and CYP2D44 form a gene cluster in the genome, similar to human CYP2Ds. Metabolic assays of the CYP2D17 and CYP2D44 proteins heterologously expressed in Escherichia coli indicated that CYP2D44 metabolized human CYP2D6 substrates, bufuralol and dextromethorphan (bufuralol 1'-hydroxylation and dextromethorphan O-demethylation) but to a lesser extent than CYP2D17. Kinetic analysis of dextromethorphan metabolism indicated that the apparent K(m) and V(max) of CYP2D17 and CYP2D44 catalyzed O-demethylation were similar, and, the V(max) values of CYP2D17 and CYP2D44 catalyzed N-demethylation (which human CYP2D6 catalyzes much less effectively) were similar, but the apparent K(m) of the CYP2D44 reaction was higher. Western blot analysis showed that CYP2D proteins were expressed in cynomolgus and rhesus monkey liver as well as in human and marmoset liver. Similar to CYP2D6, CYP2D44 copy number varied among the eight cynomolgus monkeys and four rhesus monkeys used in this study. These results indicated that CYP2D44, together with CYP2D17, had functional characteristics similar to those of human CYP2D6 but measurably differed in dextromethorphan N-demethylation, suggesting its importance for CYP2D-dependent drug metabolism in macaque.

Cynomolgus and rhesus macaques are frequently used in preclinical trials due to their close evolutionary relationships to humans. We conducted an initial screening for genetic variants in cynomolgus and rhesus macaque genes orthologous to human CYP3A4 and CYP3A5. Genetic screening of 78 Indochinese and Indonesian cynomolgus macaques and 34 Chinese rhesus macaques revealed a combined total of 42 CYP3A4 genetic variants, including 12 nonsynonymous variants, and 34 CYP3A5 genetic variants, including nine nonsynonymous variants. Four of these nonsynonymous variants were located at substrate recognition sites or the heme-binding region, domains essential for protein function, including c.886G>A (V296M) and c.1310G>A (S437N) in CYP3A4 and c.1437C>G (N479K) and c.1310G>C (T437S) in CYP3A5. The mutant proteins of these genetic variants were expressed in Escherichia coli and purified. Metabolic activity of these proteins measured using midazolam and nifedipine as substrates showed that none of these protein variants substantially influences the drug-metabolizing capacity of CYP3A4 or CYP3A5 protein. In Indonesian cynomolgus macaques, we also found IVS3+1delG in CYP3A4 and c.625A>T in CYP3A5, with which an intact protein cannot be produced due to a frameshift generated. Screening additional genomes revealed that two of 239 animals and three of 258 animals were heterozygous for IVS3+1delG of CYP3A4 and c.625A>T of CYP3A5, respectively. Some genetic variants were unevenly distributed between Indochinese and Indonesian cynomolgus macaques and between cynomolgus and rhesus macaques. Information on genetic diversity of macaque CYP3A4 and CYP3A5 presented here could be useful for successful drug metabolism studies conducted in macaques.

Glutathione S-transferase (GST) is one of the most important phase II drug-metabolizing enzymes, catalyzing the conjugation of electrophilic substrates to glutathione. Unlike in humans, a surprisingly limited number of GST genes have been identified in monkeys. The identification of additional GST genes in this model system would prove to be advantageous, because monkeys remain an important predictor of drug effects and toxicities in humans during preclinical studies. In this study, we report the identification and characterization of the following six cDNAs in cynomolgus monkeys: mfGSTA1, mfGSTA2, mfGSTM5, mfMGST1, mfGSTO1, and mfGSTZ1. These cDNAs encode GSTs highly homologous (approximately 95%) to human GST cDNAs. Among these, the mfGSTA1, mfGSTM5, mfMGST1, mfGSTO1, and mfGSTZ1 cDNAs correspond to a single human GST counterpart, whereas the mfGSTA2 cDNA is highly similar to human GSTA1 and GSTA2 cDNAs. An analysis of tissue samples indicates that these GST genes are predominantly expressed in the liver along with some extrahepatic expression as determined by real-time reverse transcriptase-polymerase chain reaction. It is interesting to note that mfGSTA2 is significantly differentially expressed between males and females in the jejunum, where a striking 8-fold higher expression level is observed in males. These results suggest that a potential sex difference in the metabolism of drugs may be mediated by mfGSTA2. This also provides a basis for the investigation of sex-dependent drug metabolism in monkeys.

The monkey CYP2C76 gene does not correspond to any of the human CYP2C genes, and its enzyme is at least partly responsible for the species difference occasionally seen in drug metabolism between monkeys and humans. To establish a line and/or lines of monkeys that are expected to show metabolic patterns highly similar to humans, we set out to find monkeys that lacked CYP2C76 activity. By genetic screening of 73 monkeys and a database search of expressed sequence tags, we found a total of 10 nonsynonymous genetic variants in the coding region of CYP2C76, including a null genotype (c.449TG>A). Some of the variants were differently distributed between two animal groups originating from different geographical regions (Indochina and Indonesia). After screening 170 additional genomic samples, we identified a total of eight animals (six males and two females) that were heterozygous for c.449TG>A, which could be used for establishing a homozygous line. If the homozygotes show drug-metabolizing properties more similar to humans than wild-type monkeys, the homozygotes may serve as a better animal model for drug metabolism. The data presented in this article provide the essential genetic information to perform a successful study by using cynomolgus monkeys and present a possible tool to generate a better animal model for drug metabolism.