ReviewChimeric mice with humanized liver
Introduction
There is large interindividual variability in the efficacy and toxicity of drugs, which may be mainly caused by differences in the drug pharmacokinetics. The pharmacokinetics can be determined by ADME (absorption, distribution, metabolism, and excretion), especially drug metabolism. Drug metabolism consists of the phase I reactions (oxidation, reduction, and hydrolysis) and phase II reaction (conjugation), which occur predominantly in the liver. Therefore, the liver is the essential organ to determine the drug pharmacokinetics. One of the phase I enzymes, cytochrome P450 (P450, CYP), plays a central role in drug metabolism. P450 can metabolize various compounds including xenobiotic and endogenous compounds (Nelson et al., 1996). In addition, bioactivation leading to toxicity can sometimes be initiated by some P450s. Recently, the phase II reaction has been well studied since a parent drug and/or phase I metabolites are frequently excreted after conjugation. Furthermore, several drug-metabolizing enzymes have been shown to be polymorphic (Ingelman-Sundberg, 2002, Miners et al., 2002) indicating that genetic polymorphism can affect differences in the drug pharmacokinetics.
The mechanism of drug interactions can be often explained by the induction and inhibition of drug metabolizing enzymes. Serious drug interactions involving P450 have been reported (Dresser et al., 2000, Niemi et al., 2003). The QT prolongation caused by the inhibition of CYP3A4 by a coadministered drug resulted in the withdrawal of terfenadine and cisapride from the market. The prediction of adverse drug reactions is essential in drug development.
There are many reports regarding drug interactions and toxicity of various drugs, although the drugs were approved only after their safety was thought to have been confirmed in preclinical and clinical studies. In the preclinical stage, the pharmacokinetics of a drug candidate are investigated using human-derived sources or experimental animals. The results from experimental animals and in vitro studies sometimes wrongly predict the human pharmacokinetics and toxicity. Many researchers have made much effort to overcome such difficulties including those caused by species differences. Nowadays, human liver microsomes and human hepatocytes in primary culture are recognized as better tools and are frequently used during drug development. Human liver microsomes can be stored for a few years without the loss of enzyme activities but cannot be used to evaluate the induction potencies. Human hepatocytes express all the drug metabolizing enzymes, but a novel technique for culture is needed to avoid decreasing the enzyme activities. Such in vitro models have various advantages and limitations, as have been described previously (Gomez-Lechon et al., 2003, Rodrigues and Rushmore, 2002).
To develop an artificial human liver is one of the best approaches for predicting human pharmacokinetics and safety. An urokinase-type plasminogen activator (uPA)+/+/severe combined immunodeficient transgenic mouse line, in which the liver could be replaced by 80–90% with human hepatocytes, was established in Japan (Tateno et al., 2004). In this review, basic researches concerning drug metabolism and drug interactions are summarized for the application of chimeric mice in drug development and toxicology.
Section snippets
Generation of chimeric mice with humanized liver
In 2001, chimeric mice with partially humanized liver were described by Dandri et al. (2001) and Mercer et al. (2001). In the former report, the livers in uPA/recombinant activation gene-2 mice could be repopulated with approximately 15% human hepatocytes (Dandri et al., 2001). In the latter, a portion the liver in uPA+/+/SCID mice was replaced with human hepatocytes (Mercer et al., 2001). Since they were investigating on hepatitis virus, their chimeric mice with low replacement might be
Cytochrome P450
The most important drug metabolizing enzyme involving phase I reactions is P450. One of the major isoforms, CYP3A4, has been reported to be responsible for the metabolism of more than 50% of clinical drugs (Pelkonen et al., 1998). In chimeric mice, human CYP3A4 mRNA and human CYP3A4 protein could be detected in an hAlb concentration-dependent manner by real-time reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting, respectively, which detected human CYP3A4 but not
Induction of P450 in chimeric mice with humanized liver
Enzyme induction of a drug-metabolizing enzyme is a long-term consequence of chemical exposure and leads to an elevation of the enzyme activity (Lin and Lu, 2001). Drug interactions caused by the induction of P450, especially CYP3A4, are sometimes a serious problem because the induction may result in changes in the efficacy and toxicity of a drug (Pascussi et al., 2003, Niemi et al., 2003). Many CYP3A4 inducers are used as drugs in clinical practice and they can induce CYP3A4 at clinically used
Inhibition of P450 in chimeric mice with humanized liver
Enzyme inhibition is an acute decrease of metabolism by a co-administered drug or a time-dependent decrease in the amount of an enzyme by several factors (Pelkonen et al., 1998). Drug interactions are often caused by the inhibition of P450 activities (Dresser et al., 2000). The prediction of human pharmacokinetic parameters from in vitro technologies has progressed (Houston and Galetin, 2003) but quantitative extrapolations from in vitro to human in vivo and from experimental animals to humans
In vivo excretion in chimeric mice with humanized liver
A drug is mostly eliminated by biliary and urinary excretion. To elucidate the excretion of a drug as well as the metabolism is essential for understanding the pharmacokinetics and toxicity. Species differences in the excretory pathway may make the extrapolation from experimental animals to humans difficult. In the case of an antibiotic agent, cefmetazole was mainly excreted in urine in humans (Ko et al., 1989) but in feces in rats and mice in an unchanged form (Murakawa et al., 1980, Okumura
Conclusions
The chimeric mice have been shown to exhibit a humanized profile of drug metabolism, induction and inhibition of drug metabolizing enzymes, and excretion in in vivo studies. This chimeric mouse line should be a promising model for evaluating the in vivo pharmacokinetics in humans. In recent drug development, adverse pharmacokinetic and bioavailability have reduced as a cause of attrition although toxicology has increased (Kola and Landis, 2004). Drug-induced hepatotoxicity is one of the major
Acknowledgments
This work was supported by a Research on Advanced Medical Technology, Health, and Labor Sciences Research Grant from the Ministry of Health, Labor, and Welfare of Japan. We thank Mr. Brent Bell for reviewing the manuscript.
References (55)
- et al.
Lethal toxicity of uracil/tegafur in the treatment of sigmoid carcinoma
Ann. Oncol.
(2007) - et al.
Repopulation of mouse liver with human hepatocytes and in vivo infection with hepatitis B virus
Hepatology
(2001) Polymorphism of cytochrome P450 and xenobiotic toxicity
Toxicology
(2002)- et al.
Kinetic analyses for species differences in P-glycoprotein-mediated drug transport
J. Pharm. Sci.
(2006) - et al.
In vivo drug metabolism model for human cytochrome P450 enzyme using chimeric mice with humanized liver
J. Pharm. Sci.
(2007) - et al.
Primary human hepatocytes as a tool for the evaluation of structure-activity relationship in cytochrome P450 induction potential of xenobiotics: evaluation of rifampin, rifapentine and rifabutin
Chem. Biol. Interact.
(1997) - et al.
Genetic polymorphisms of UDP-glucuronosyltransferases and their functional significance
Toxicology
(2002) - et al.
Interindividual variability in nicotine metabolism: C-oxidation and glucuronidation
Drug Metab. Pharmacokinet.
(2005) - et al.
Evaluation of approach to predict the contribution of multiple cytochrome P450s in drug metabolism using relative activity factor: effects of the differences in expression levels of NADPH-cytochrome P450 reductase and cytochrome b5 in the expression system and the differences in the marker activities
J. Pharm. Sci.
(2002) - et al.
Induction of human CYP1A2 and CYP3A4 in primary culture of hepatocytes from chimeric mice with humanized liver
Drug Metab. Pharmacokinet.
(2005)
Species differences of inhibitory effects on P-glycoprotein-mediated drug transport
J. Pharm. Sci.
Near completely humanized liver in mice shows human-type metabolic responses to drugs
Am. J. Pathol.
Dexamethasone metabolism in vitro: species differences
J. Steroid. Biochem. Mol. Biol.
Evaluation of human CYP1A2 and CYP3A4 mRNA expression in hepatocytes from chimeric mice with humanized liver
Drug Metab. Pharmacokinet.
The conduct of in vitro and in vivo drug-drug interaction studies: a Pharmaceutical Research and Manufacturers of America (PhRMA) perspective
Drug Metab. Dispos.
Clinical implications of the competitive inhibition of the debrisoquin-metabolizing isozyme by quinidine
Arch. Intern. Med.
Influence of CYP2D6 polymorphism on 3,4-methylenedioxymethamphetamine (’Ecstasy’) cytotoxicity
Pharmacogenet. Genomics
Arylamine-N-acetyltransferase (NAT2) mutations and their allelic linkage in unrelated Caucasian individuals: correlation with phenotypic activity
Am. J. Hum. Genet.
Pharmacokinetic–pharmacodynamic consequences and clinical relevance of cytochrome P450 3A4 inhibition
Clin. Pharmacokinet.
Pharmacogenomics and individualized drug therapy
Annu. Rev. Med.
The role of hepatic and extrahepatic UDP-glucuronosyltransferases in human drug metabolism
Drug Metab. Rev.
Human hepatocytes as a tool for studying toxicity and drug metabolism
Curr. Drug Metab.
Selective serotonin reuptake inhibitors and cytochrome P-450 mediated drug-drug interactions: an update
Curr. Drug Metab.
St John's wort (Hypericum perforatum): drug interactions and clinical outcomes
Br. J. Clin. Pharmacol.
Progress towards prediction of human pharmacokinetic parameters from in vitro technologies
Drug Metab. Rev.
Metabolism of isoniazid in man as related to the occurrence of peripheral neuritis
Am. Rev. Tuberc.
Genetic polymorphisms of cytochrome P450 2D6 (CYP2D6): clinical consequences, evolutionary aspects and functional diversity
Pharmacogenomics J.
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