Catalytic activity of three variants (Ile, Leu, and Thr) at amino acid residue 359 in human CYP2C9 gene and simultaneous detection using single-strand conformation polymorphism analysis

One Rare Warfarin Resistance Case and Possible Mechanism Exploration

One 59-year-old female patient with deep venous thrombosis (DVT) and pulmonary embolism (PE) was treated with 6 mg warfarin once daily as an anticoagulant. Before taking warfarin, her international normalized ratio (INR) was 0.98. Two days after warfarin treatment, her INR did not change from baseline. Due to the high severity of the PE, the patient needed to reach her target range (INR goal = 2.5, range = 2~3) rapidly, so the dose of warfarin was increased from 6 mg daily to 27 mg daily. However, the patient's INR did not improve with the dose escalation, still maintaining an INR of 0.97-0.98. We drew a blood sample half an hour before administering 27 mg warfarin and detected single nucleotide polymorphism for the following genes, which were identified to be relevant with warfarin resistance: CYP2C9 rs1799853, rs1057910, VKORC1 rs9923231, rs61742245, rs7200749, rs55894764, CYP4F2 rs2108622, and GGCX rs2592551. The trough plasma concentration of warfarin was 196.2 ng/mL after 2 days of warfarin administration with 27 mg QD, which was much lower than the therapeutic drug concentration ranges of warfarin (500-3,000 ng/mL). The genotype results demonstrate that the CYP4F2gene has rs2108622 mutation which can explain some aspect of warfarin resistance. Further investigations are necessary to fully characterize other pharmacogenomics or pharmacodynamics determinants of warfarin dose-response in Chinese.

Effects of polymorphic variation on the thermostability of heterogenous populations of CYP3A4 and CYP2C9 enzymes in solution

The effect of non-synonymous single nucleotide polymorphisms (SNPs) on cytochrome P450 (CYP450) drug metabolism is currently poorly understood due to the large number of polymorphisms, the diversity of potential substrates and the complexity of CYP450 function. Previously we carried out in silico studies to explore the effect of SNPs on CYP450 function, using in silico calculations to predict the effect of mutations on protein stability. Here we have determined the effect of eight CYP3A4 and seven CYP2C9 SNPs on the thermostability of proteins in solution to test these predictions. Thermostability assays revealed distinct CYP450 sub-populations with only 65–70% of wild-type CYP3A4 and CYP2C9 susceptible to rapid heat-induced P450 to P420 conversion. CYP3A4 mutations G56D, P218R, S222P, I223R, L373F and M445T and CYP2C9 mutations V76M, I359L and I359T were destabilising, increasing the proportion of protein sensitive to the rapid heat-induced P450 to P420 conversion and/or reducing the half-life of this conversion. CYP2C9 Q214L was the only stabilising mutation. These results corresponded well with the in silico protein stability calculations, confirming the value of these predictions and together suggest that the changes in thermostability result from destabilisation/stabilisation of the protein fold, changes in the haem-binding environment or effects on oligomer formation/conformation.

Pharmacogenetics and cardiovascular disease--implications for personalized medicine

The past decade has seen tremendous advances in our understanding of the genetic factors influencing response to a variety of drugs, including those targeted at treatment of cardiovascular diseases. In the case of clopidogrel, warfarin, and statins, the literature has become sufficiently strong that guidelines are now available describing the use of genetic information to guide treatment with these therapies, and some health centers are using this information in the care of their patients. There are many challenges in moving from research data to translation to practice; we discuss some of these barriers and the approaches some health systems are taking to overcome them. The body of literature that has led to the clinical implementation of CYP2C19 genotyping for clopidogrel, VKORC1, CYP2C9; and CYP4F2 for warfarin; and SLCO1B1 for statins is comprehensively described. We also provide clarity for other genes that have been extensively studied relative to these drugs, but for which the data are conflicting. Finally, we comment briefly on pharmacogenetics of other cardiovascular drugs and highlight β-blockers as the drug class with strong data that has not yet seen clinical implementation. It is anticipated that genetic information will increasingly be available on patients, and it is important to identify those examples where the evidence is sufficiently robust and predictive to use genetic information to guide clinical decisions. The review herein provides several examples of the accumulation of evidence and eventual clinical translation in cardiovascular pharmacogenetics.

Genetic Polymorphisms of Cytochrome P450 Enzymes and the Effect on Interindividual, Pharmacokinetic Variability in Extensive Metabolizers

Genetic polymorphisms of cytochrome P450 (CYP) enzymes are one of the factors that contribute to the pharmacokinetic (PK) variability of drugs. PK variability is observed in the bimodal distribution between extensive metabolizers (EMs) and poor metabolizers (PMs). PK variability may also exist between individuals genotyped as homozygous EMs and heterozygous EMs. This may carry implications for drug dosing and drug response (e.g., risk of therapeutic failure or drug toxicity). Studies have reported significant PK differences between homozygous and heterozygous EMs. Some literature suggests that this distinction may be of clinical relevance. Due to study design limitations and data that are either sparse or conflicting, generalizations regarding the potential impact of the CYP genotype, within EMs, are difficult. Optimally designed clinical trials are needed. This review evaluates the potential impact of CYP genetic polymorphisms on interindividual PK variability of drugs within an EM population.

Role of pharmacogenomics in the management of traditional and novel oral anticoagulants

Warfarin is the most commonly prescribed oral anticoagulant. However, it remains a difficult drug to manage mostly because of its narrow therapeutic index and wide interpatient variability in anticoagulant effects. Over the past decade, there has been substantial progress in our understanding of genetic contributions to variable warfarin response, particularly with regard to warfarin dose requirements. The genes encoding for cytochrome P450 (CYP) 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) are the major genetic determinants of warfarin pharmacokinetics and pharmacodynamics, respectively. Numerous studies have demonstrated significant contributions of these genes to warfarin dose requirements. The CYP2C9 gene has also been associated with bleeding risk with warfarin. The CYP4F2 gene influences vitamin K availability and makes minor contributions to warfarin dose requirements. Less is known about genes influencing warfarin response in African-American patients compared with other racial groups, but this is the focus of ongoing research. Several warfarin pharmacogenetic dosing algorithms and United States Food and Drug Administration-cleared genotyping tests are available for clinical use. Clinical trials are ongoing to determine the clinical utility and cost-effectiveness of genotypeguided warfarin dosing. Results from these trials will likely influence clinical uptake and third party payer reimbursement for genotype-guided warfarin therapy. There is still a lack of pharmacogenetic data for the newly approved oral anticoagulants, dabigatran and rivaroxaban, and with other oral anticoagulants in the research and development pipeline. These data, once known, could be of great importance as routine monitoring parameters for these agents are not available.

In vitro assessment of the allelic variants of cytochrome P450

The cytochrome P450 (CYP) superfamily is one of the most important groups of enzymes involved in drug metabolism. It is responsible for the metabolism of a large number of drugs. Many CYP isoforms are expressed polymorphically, and catalytic alterations of allelic variant proteins can affect the metabolic activities of many drugs. The CYP2D6, CYP2C9, CYP2C19, and CYP2B6 genes are particularly polymorphic, whereas CYP1A1, CYP1A2, CYP2E1, and CYP3A4 are relatively well conserved without common functional polymorphisms. In vitro studies using cDNA expression systems are useful tools for evaluating functional alterations of the allelic variants of CYP, particularly for low-frequency alleles. Recombinant CYPs have been successfully expressed in bacteria, yeast, baculoviruses, and several mammalian cells. Determination of CYP variant-mediated kinetic parameters (Km and Vmax) in vitro can be useful for predicting drug dosing and clearance in humans. This review focuses on the advantages and disadvantages of the various cDNA-expression systems used to determine the kinetic parameters for CYP allelic variants, the methods for determining the kinetic parameters, and the findings of in vitro studies on highly polymorphic CYPs, including CYP2D6, CYP2C9, CYP2C19, and CYP2B6.

Impact of CYP2C8 and 2C9 polymorphisms on coronary artery disease and myocardial infarction in the LURIC cohort

Aims: As data on the cardiovascular risk associated with CYP2C8 and CYP2C9 polymorphisms is controversial, we performed a cross-sectional analysis of subjects enrolled in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study. Materials & methods: CYP2C8 and CYP2C9 genetic polymorphisms were determined with real-time PCR in 2827 patients. Based on angiography, 1052 of these patients had coronary artery disease (CAD) and 615 did not; 1160 patients had signs or a history of myocardial infarction (MI) in addition to CAD. The association of genotypes with CAD and MI was determined by logistic regression analysis, adjusted for age, sex, dyslipidemia, hypertension, diabetes mellitus and smoking status. Results: Frequencies of CYP2C8 and 2C9 variants were neither significantly different between CAD and control patients, nor between MI and control patients. Men carrying the CYP2C9*3 allele had an increased risk of MI (odds ratio [OR]: 1.67; 95% CI: 1.06–2.63; p = 0.03) and women carrying the CYP2C9*3 allele had a decreased risk of CAD (OR: 0.65; 95%CI: 0.42–0.9; p = 0.05). Conclusion: Overall, LURIC data confirmed that there is no major cardiovascular risk associated with CYP2C8 and CYP2C9 variants in a cardiovascular risk population of patients having undergone coronary angiography.

The rules of variation: amino acid exchange according to the rotating circular genetic code

General guidelines for the molecular basis of functional variation are presented while focused on the rotating circular genetic code and allowable exchanges that make it resistant to genetic diseases under normal conditions. The rules of variation, bioinformatics aids for preventative medicine, are: (1) same position in the four quadrants for hydrophobic codons, (2) same or contiguous position in two quadrants for synonymous or related codons, and (3) same quadrant for equivalent codons. To preserve protein function, amino acid exchange according to the first rule takes into account the positional homology of essential hydrophobic amino acids with every codon with a central uracil in the four quadrants, the second rule includes codons for identical, acidic, or their amidic amino acids present in two quadrants, and the third rule, the smaller, aromatic, stop codons, and basic amino acids, each in proximity within a 90 degree angle. I also define codifying genes and palindromati, CTCGTGCCGAATTCGGCACGAG.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

Catalytic activities of human cytochrome P450 2C9*1, 2C9*3 and 2C9*13

Cytochrome P450 2C9 (CYP2C9) is a geneticly polymorphic enzyme responsible for the metabolism of some clinically important drugs. CYP2C9*13 is an allele identified in a Chinese poor metabolizer of lornoxicam which has a Leu90Pro amino acid substitution. This paper reports on a study aimed at comparing the catalytic properties of CYP2C9*13 with those of the wild-type CYP2C9*1 and mutant CYP2C9*3 (Ile359Leu) in the COS-7 expression system using various substrates. CYP2C9*3 and *13 produced far lower luminescence than CYP2C9*1 in luciferin H metabolism. CYP2C9*13 exhibited an 11-fold increase in Km but no change in Vmax with tolbutamide as the substrate, a five-fold increase in Km and an 88.8% reduction in Vmax with diclofenac. These data indicate that CYP2C9*13 exhibits reduced metabolic activity toward all studied CYP2C9 substrates. The magnitude of the CYP2C9*13-associated decrease in intrinsic clearance (Vmax/Km) is greater than that associated with CYP2C9*3.

Interindividual variability of methadone response: impact of genetic polymorphism

Methadone, an opioid analgesic, is used clinically in pain therapy as well as for substitution therapy in opioid addiction. It has a large interindividual variability in response and a narrow therapeutic index. Genetic polymorphisms in genes coding for methadone-metabolizing enzymes, transporter proteins (p-glycoprotein; P-gp), and mu-opioid receptors may explain part of the observed interindividual variation in the pharmacokinetics and pharmacodynamics of methadone. Cytochrome P450 (CYP) 3A4 and 2B6 have been identified as the main CYP isoforms involved in methadone metabolism. Methadone is a P-gp substrate, and, although there are inconsistent reports, ABCB1 genetic polymorphisms also contribute slightly to the interindividual variability of methadone kinetics and influence dose requirements. Genetic polymorphism is the cause of high interindividual variability of methadone blood concentrations for a given dose; for example, in order to obtain methadone plasma concentrations of 250 ng/mL, doses of racemic methadone as low as 55 mg/day or as high as 921 mg/day can be required in a 70-kg patient without any co-medication. The clinician must be aware of the pharmacokinetic properties and pharmacological interactions of methadone in order to personalize methadone administration. In the future, pharmacogenetics, at a limited level, can also be expected to facilitate individualized methadone therapy.

Combination of phenotype assessments and CYP2C9-VKORC1 polymorphisms in the determination of warfarin dose requirements in heavily medicated patients

The relative contribution of phenotypic measures and CYP2C9-vitamin K epoxide reductase complex subunit 1 (VKORC1) polymorphisms to warfarin dose requirements at day 14 was determined in 132 hospitalized, heavily medicated patients. Phenotypic measures were (1) the urinary losartan metabolic ratio before the first dose of warfarin, (2) the S:R-warfarin ratio at day 1, and (3) a dose-adjusted international normalized ratio (INR) at day 4. CYP2C9 and VKORC1 genotypes were determined by gene chip analysis. In multivariate analyses, the dose-adjusted INR at day 4 explained 31% of variability observed in warfarin doses at day 14, whereas genotypic measures (CYP2C9-VKORC1) contributed 6.5%. When S:R-warfarin ratio was used, genotypes contributed more significantly (23.5%). Finally, urinary losartan metabolic ratio was of low predictive value. The best models obtained explained 51% of intersubject variability in warfarin dose requirements. Thus, combination of a phenotypic measure to CYP2C9-VKORC1 genotypes represents a useful strategy to predict warfarin doses in patients receiving multiple drugs (11+/-4 drugs/day).

Warfarin dose and the pharmacogenomics of CYP2C9 and VKORC1 - rationale and perspectives

Warfarin is the most widely prescribed oral anticoagulant, but there is greater than 10-fold interindividual variability in the dose required to attain a therapeutic response. Information from pharmacogenomics, the study of the interaction of an individual's genotype and drug response, can help optimize drug efficacy while minimizing adverse drug reactions. Pharmacogenetic analysis of two genes, the warfarin metabolic enzyme CYP2C9 and warfarin target enzyme, vitamin K epoxide reductase complex 1 VKORC1, confirmed their influence on warfarin maintenance dose. Possession of CYP2C9*2 or CYP2C9*3 variant alleles, which result in decreased enzyme activity, is associated with a significant decrease in the mean warfarin dose. Several single nucleotide polymorphisms (SNPs) in VKORC1 are associated with warfarin dose across the normal dose range. Haplotypes based on these SNPs explain a large fraction of the interindividual variation in warfarin dose, and VKORC1 has an approximately three-fold greater effect than CYP2C9. Algorithms incorporating genetic (CYP2C9 and VKORC1), demographic, and clinical factors to estimate the warfarin dosage, could potentially minimize the risk of over dose during warfarin induction.

Breast cancer treatment and ovarian failure: risk factors and emerging genetic determinants

Most premenopausal women diagnosed with primary breast cancer receive adjuvant chemotherapy, and many experience chemotherapy-induced ovarian failure (CIOF). CIOF is associated with menopausal symptoms, fertility concerns and long-term implications including bone loss. Ironically, CIOF might confer a disease-specific benefit to women whose breast cancers express hormone receptors. Risk factors of CIOF include the woman's age at the time of therapy, and the type, dose and schedule of chemotherapy. Because inherited genetic factors have an important role in determining who will experience CIOF, genetic testing has the potential to provide optimal counselling about risks and possible interventions.

Effect of genetic polymorphisms in cytochrome p450 (CYP) 2C9 and CYP2C8 on the pharmacokinetics of oral antidiabetic drugs: clinical relevance

Type 2 diabetes mellitus affects up to 8% of the adult population in Western countries. Treatment of this disease with oral antidiabetic drugs is characterised by considerable interindividual variability in pharmacokinetics, clinical efficacy and adverse effects. Genetic factors are known to contribute to individual differences in bioavailability, drug transport, metabolism and drug action. Only scarce data exist on the clinical implications of this genetic variability on adverse drug effects or clinical outcomes in patients taking oral antidiabetics. The polymorphic enzyme cytochrome P450 (CYP) 2C9 is the main enzyme catalysing the biotransformation of sulphonylureas. Total oral clearance of all studied sulphonylureas (tolbutamide, glibenclamide [glyburide], glimepiride, glipizide) was only about 20% in persons with the CYP2C9*3/*3 genotype compared with carriers of the wild-type genotype CYP2C9*1/*1, and clearance in the heterozygous carriers was between 50% and 80% of that of the wild-type genotypes. For reasons not completely known, the resulting differences in drug effects were much less pronounced. Nevertheless, CYP2C9 genotype-based dose adjustments may reduce the incidence of adverse effects. The magnitude of how doses might be adjusted can be derived from pharmacokinetic studies. The meglitinide-class drug nateglinide is metabolised by CYP2C9. According to the pharmacokinetic data, moderate dose adjustments based on CYP2C9 genotypes may help in reducing interindividual variability in the antihyperglycaemic effects of nateglinide. Repaglinide is metabolised by CYP2C8 and, according to clinical studies, CYP2C8*3 carriers had higher clearance than carriers of the wild-type genotypes; however, this was not consistent with in vitro data and therefore further studies are needed. CYP2C8*3 is closely linked with CYP2C9*2. CYP2C8 and CYP3A4 are the main enzymes catalysing biotransformation of the thiazolidinediones troglitazone and pioglitazone, whereas rosiglitazone is metabolised by CYP2C9 and CYP2C8. The biguanide metformin is not significantly metabolised but polymorphisms in the organic cation transporter (OCT) 1 and OCT2 may determine its pharmacokinetic variability. In conclusion, pharmacogenetic variability plays an important role in the pharmacokinetics of oral antidiabetic drugs; however, to date, the impact of this variability on clinical outcomes in patients is mostly unknown and prospective studies on the medical benefit of CYP genotyping are required.

The pharmacogenetics of coumarin therapy

Vitamin K antagonists (coumarins) are widely-used oral anticoagulants for the prevention of venous thromboembolism and strokes. Wide inter-individual variation in dose response and frequent bleeds characterize the initiation of coumarin therapy. Over the past 10 years both genetic and nongenetic determinants of coumarin dose response have been identified. A comprehensive pharmacogenetics approach to warfarin therapy has the potential to improve the safety and efficiency of warfarin initiation.

Pharmacogenetics of oral anticoagulants

The use of oral anticoagulants (OA) is problematic due to its association with hemorrhagic complications. OA metabolism relies on the CYP2C9 complex. Genetic variations compromising metabolic competence of this complex may explain the risk of excessive and hazardous anticoagulation. A pharmacogenetics-based approach to this issue could be beneficial for choosing adequate dose and duration of treatment, in addition to having a better understanding of pharmacological interactions to which OA are susceptible. However, evidence from several basic and clinical studies indicates that both a complicated system of regulation of expression of multiple genes and the influence of a wide variety of epigenetic factors could be responsible for adverse drug reactions associated with the use of OA. Emphasis on understanding the gene-environment interactions could attain new paths to facilitate the use of these important drugs in the quotidian clinical practice.

Variable therapeutic response in asthma: a genetic perspective

Asthma is a complex clinical syndrome with multiple genetic and environmental factors contributing to its phenotypic expression. This etiological heterogeneity adds to the complexity when addressing variation in the response to antiasthma treatment. There is regular progress in the field of asthma pharmacogenetics in determining the efficacy and potential for adverse effects of the asthma medication from a patient's genetic background. This reveals that a clinically relevant variability in response to the asthma medications may be due to genetic determinants, and refers to the polymorphisms in the genes encoding either the drug targets, or the molecular component of the downstream signal transduction pathways responsible for drug actions. The major classes of asthma therapy, β-agonists, leukotriene antagonists and inhaled corticosteroids, demonstrate wide interindividual variability. The statistical issues, such as population stratification, sample size and statistical power, are crucial factors for the identification of significant biological marker(s) for patient's response. The aim of this review is to discuss the scientific rationale and outline the genetic impact on the variability in response to different asthma medications. In conclusion, despite of new developments and recent studies in asthma pharmacogenetics, significant gaps in knowledge still remain, and several replicate studies are needed in different populations to derive firm conclusions that may help to bring pharmacotyping into clinical practice.

Contribution of CYP2C9 to variability in vitamin K antagonist metabolism

CYP2C9 is the third most important cytochrome P450 (CYP) in terms of number of drugs metabolised. A considerable amount of information on this isoform is now available with respect to its structural biology, the mechanisms by which it can be induced and the existence of a range of variant alleles, which are often functionally significant. CYP2C9 makes a very important contribution to metabolism of vitamin K antagonist anticoagulants, and is the main oxidising enzyme for S-warfarin and S-acenocoumarol as well as contributing to phenprocoumon metabolism. A large number of studies have now shown that CYP2C9 genotype predicts dose requirement for both warfarin and acenocoumarol, with a possible contribution for phenprocoumon. Patients with variant alleles are likely to require a lower dose and may be at risk of overcoagulation and resultant bleeding, especially during the induction phase of therapy. Although CYP2C9 genotype is clearly a predictor of vitamin K antagonist dose requirement, especially in Caucasian populations in whom variant alleles are common, a number of recent studies have shown that age, genotype for the gene encoding the target gene vitamin K epoxide reductase and concomitant drugs are equally important factors in determining dose. There is a need for prospective studies to assess the value of predicting dose requirement on the basis of all these factors, including the CYP2C9 genotype.

Effect of the CYP2C9*3 allele on lornoxicam metabolism

BACKGROUND

We investigated whether the CYP2C9 genotypes would affect lornoxicam metabolism in healthy volunteers.

METHODS

Twelve healthy volunteers who had been genotyped for CYP2C9 gene were selected to participate in our study. After 8 mg lornoxicam was taken, blood samples were drawn from 0 to 36 h. The plasma concentrations of lornoxicam and 5'-hydroxylornoxicam were determined by HPLC method. 5'-hydroxylornoxicam was purified from rabbits'urine by semi-preparative HPLC.

RESULTS

Lornoxicam and 5'-hydroxylornoxicam both exhibit CYP2C9 genotype-dependent pharmacokinetic profiles. The area under the plasma concentration-time curve (AUC) of lornoxicam increased by 60 +/- 9.78% (P <0.05) and the AUC of 5'-hydroxylornoxicam decreased by 65 +/- 11.75% (p <0.001) in heterozygous CYP2C9*1/*3 subjects (n=6) compared with CYP2C9*1/*1 group (n=6). t1/2 value of lornoxicam and 5'-hydroxylornoxicam prolonged by 39 +/- 8.35% and curtailed by 59 +/- 6.83% respectively in CYP2C9*1/*3 subjects. But no significant differences in Tmax of lornoxicam and 5'-hydroxylornoxicam were observed between these 2 genotypes. In addition, for the first time we exploit the purification method for 5'-hydroxylornoxicam from rabbits' urine.

CONCLUSION

The CYP2C9*3 allele significantly affected the metabolism of lornoxicam. The pharmacokinetic parameters of both lornoxicam and 5'-hydroxylornoxicam were significantly different between these 2 genotypes.

CYP2C9, CYP2C19, ABCB1 (MDR1) genetic polymorphisms and phenytoin metabolism in a Black Beninese population

The genetically polymorphic cytochrome P450 2C9 (CYP2C9) metabolizes many important drugs. Among them, phenytoin has been used as a probe to determine CYP2C9 phenotype by measuring the urinary excretion of its major metabolite, S-enantiomer of 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH). Phenytoin pharmacokinetic is also dependent on the activity of CYP2C19 and p-glycoprotein (ABCB1). To determine the influence of CYP2C9, CYP2C19 and ABCB1 genetic polymorphisms on phenytoin metabolism in a Black population, 109 healthy Beninese subjects received a single 300 mg oral dose of phenytoin. Blood was drawn 4 h after drug intake and urine was collected during the first 8 h. Plasma phenytoin and urine S- and R-enantiomers of p-HPPH were determined by high-performance liquid chromatography. Urinary excretion of (S)-p-HPPH [defined as urinary volumex(S)-p-HPPH urinary concentration] and PMR (defined as the ratio of p-HPPH in urine to 4 h phenytoin plasma concentration), both markers of CYP2C9 activity, were used to determine the functional relevance of new variants of CYP2C9 (*5, *6, *8, *9 and *11) in this population. Plasma phenytoin concentration was significantly associated with ABCB1 haplotype/genotype (P=0.05, Kruskal-Wallis test) and levels increased significantly in the genotype order: wild-type, T3421A and Block-2 genotypes (P=0.015, Jonckheere-Terpstra test). Urinary excretion of (S)-p-HPPH and PMR were significantly associated with the CYP2C9 genotype (P=0.001, analysis of variance (ANOVA) and P<0.0001, Kruskal-Wallis test, respectively) and decreased in the order: CYP2C9*1/*1, CYP2C9*1/*9, CYP2C9*9/*9, CYP2C9*1/*8, CYP2C9*8/*9, CYP2C9*9/*11, CYP2C9*1/*5, CYP2C9*6/*9, CYP2C9*1/*6, CYP2C9*8/*11, CYP2C9*5/*8 and CYP2C9*5/*6 (P<0.001, Jonckheere-Terpstra test). A combined analysis of CYP2C9, 2C19 and ABCB1 revealed that only ABCB1 predicted phenytoin concentration at 4 h and explained 8% of the variability (r=0.08, P=0.04). On the other hand, only CYP2C9 was predictive for the urinary excretion of (S)-p-HPPH and PMR (r=0.21, P=0.001 and r=0.25, P<0.001, respectively). Furthermore, significant relation was found between urinary excretion of (R)-p-HPPH and CYP2C9 genotype (P=0.035) and levels significantly increased in the genotype order: CYP2C9*1/*9, CYP2C9*1/*1, CYP2C9*9/*11, CYP2C9*1/*8 and CYP2C9*1/*5 (P<0.001, Jonckheere-Terpstra test). In summary, the present study demonstrates that, in a Black population, CYP2C9*5, *6, *8 and *11 variants, but not CYP2C9*9, are associated with a decreased phenytoin metabolism. The data also confirm the limited contribution of MDR1 gene to inter-individual phenytoin pharmacokinetic variation.

Cancer treatment and pharmacogenetics of cytochrome P450 enzymes

For the treatment of cancer, the window between drug toxicity and suboptimal therapy is often narrow. Interindividual variation in drug metabolism therefore complicates therapy. Genetic polymorphisms in phase I and phase II enzymes may explain part of the observed interindividual variation in pharmacokinetics and pharmacodynamics of anticancer drugs. The cytochrome P450 superfamily is involved in many drug metabolizing reactions. Information on variant alleles for the different isoenzymes of this family, encoding proteins with decreased enzymatic activity, is rapidly growing. The ultimate goal of ongoing research on these enzymes would be to enable pharmacogenetic screening prior to anticancer therapy. At this moment, potential clinically relevant application of CYP450 pharmacogenetics for anticancer therapy may be found for CYP1A2 and flutamide, CYP2A6 and tegafur, CYP2B6 and cyclophosphamide, CYP2C8 and paclitaxel, CYP2D6 and tamoxifen, and CYP3A5. For this latter enzyme, the drugs of interest still need to be identified.

Functional Characterization of Novel Allelic Variants of CYP2C9 Recently Discovered in Southeast Asians

CYP2C9 was recently resequenced in 150 Asian subjects from Singapore. Several new coding variants were reported, and these variants are now named CYP2C9*14 (R125H), CYP2C9*15 (S162X), CYP2C9*16 (T299A), CYP2C9*17 (P382S), CYP2C9*18 (D397A), and CYP2C9*19 (Q454H). The CYP2C9*18 variant also contained an I359L change previously associated with the CYP2C9*3 allele. In this study, we assessed the functional consequences of the new coding changes. cDNAs containing each of the new coding changes were constructed by site-directed mutagenesis and expressed in a bacterial cDNA expression system, the allelic proteins were partially purified, and their ability to hydroxylate a prototype CYP2C9 substrate was assayed. Expression of cDNAs in Escherichia coli containing either the D397A change or the S162X (premature stop codon) could not be detected either spectrally or at the apoprotein level. CYP2C9.14 and CYP2C9.16 exhibited 80 to 90% lower catalytic activity toward tolbutamide at two substrate concentrations compared with wild-type CYP2C9.1. Kinetic analysis confirmed that CYP2C9.14 and CYP2C9.16 have a higher Km and a >90% lower intrinsic clearance of tolbutamide compared with wild-type CYP2C9.1. Both CYP2C9.17 and CYP2C9.19 proteins exhibited modest 30 to 40% decreases in catalytic activity toward tolbutamide. Thus, CYP2C9*15 and CYP2C9*18 may represent null alleles, whereas CYP2C9*14 and CYP2C9*16 allelic variants produce proteins that are clearly catalytically defective in vitro, indicating the existence of new defective putative alleles of CYP2C9 in Asians.

Clinical and toxicological relevance of CYP2C9: drug-drug interactions and pharmacogenetics

CYP2C9 is a major cytochrome P450 enzyme that is involved in the metabolic clearance of a wide variety of therapeutic agents, including nonsteroidal antiinflammatories, oral anticoagulants, and oral hypoglycemics. Disruption of CYP2C9 activity by metabolic inhibition or pharmacogenetic variability underlies many of the adverse drug reactions that are associated with the enzyme. CYP2C9 is also the first human P450 to be crystallized, and the structural basis for its substrate and inhibitor selectivity is becoming increasingly clear. New, ultrapotent inhibitors of CYP2C9 have been synthesised that aid in the development of quantitative structure-activity relationship (QSAR) models to facilitate drug redesign, and extensive resequencing of the gene and studies of its regulation will undoubtedly help us understand interindividual variability in drug response and toxicity controlled by this enzyme.

Potential genetic influences on the response to asthma treatment

Genetic factors play a key role in determining the widely heterogeneous response to pharmacological treatment detectable among asthmatics. In particular, polymorphisms of the genes encoding relevant anti-asthma drug targets contribute significantly to such a variability. Therefore, it is very important to characterize asthmatic patient's genotypes and the related phenotypic patterns, in order to predict the individual therapeutic outcome. This pharmacogenetic approach will eventually help clinicians to optimize and personalize anti-asthma treatment, and will also provide useful information with regard to pre- and post-marketing evaluation of both effectiveness and side effects of newly introduced drugs.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.

The CYP2C9 polymorphism: from enzyme kinetics to clinical dose recommendations

CYP2C9 is the major human enzyme of the cytochrome P450 2C subfamily and metabolizes approximately 10% of all therapeutically relevant drugs. Two inherited SNPs termed CYP2C9*2 (Arg144Cys) and *3 (Ile359Leu) are known to affect catalytic function. Numerous rare or functionally silent polymorphisms have been identified. About 35% of the Caucasian population carries at least one *2 or *3 allele. CYP2C9 metabolizes several oral hypoglycemics, oral anticoagulants, non-steroidal anti-inflammatory drugs and other drugs, including phenytoin, losartan, fluvastatin, and torsemide. In vitro studies with several drugs indicate that the Cys144 (.2) and Leu359 (.3) variants confer only about 70 and 10% of the intrinsic clearance of the wild-type protein (.1), respectively. The clinical pharmacokinetic implications of these polymorphisms vary depending on the enzymes contribution to total oral clearance. Several studies demonstrated that the CYP2C9 polymorphisms are medically important for non-steroidal anti-inflammatory drugs, for oral hypoglycemics, vitamin K antagonistic oral anticoagulants, and phenytoin. In particular, CYP2C9 polymorphisms should be routinely considered in therapy with oral anticoagulants where severe adverse events at initiation of therapy might be reduced by genotyping. CYP2C9 polymorphisms were also clinically associated with side effects of phenytoin, with gastric bleeding during therapy with non-steroidals and with hypoglycemia under oral hypoglycemic drugs. Data appear mature enough for the routine consideration of CYP2C9 genotypes in therapy with acenocoumarol, phenytoin, warfarin, and some other drugs. Nevertheless, it is advisable before the routine clinical use of these genotype data to rigorously test the benefits of genotype-based therapeutic recommendations by randomized controlled clinical trials.

Predicting drug clearance from recombinantly expressed CYPs: intersystem extrapolation factors

1. Recombinantly expressed human cytochromes P450 (rhCYPs) have been underused for the prediction of human drug clearance (CL). 2. Differences in intrinsic activity (per unit CYP) between rhCYP and human liver enzymes complicate the issue and these discrepancies have not been investigated systematically. We define intersystem extrapolation factors (ISEFs) that allow the use of rhCYP data for the in vitro-in vivo extrapolation of human drug CL and the variance that is associated with interindividual variation of CYP abundance due to genetic and environmental effects. 3. A large database (n = 451) of metabolic stability data has been compiled and used to derive ISEFs for the most commonly used expression systems and CYP enzymes. 4. Statistical models were constructed for the ISEFs to determine major covariates in order to optimize experimental design to increase prediction accuracy. 5. Suggestions have been made for the conduct of future studies using rhCYP to predict human drug clearance.

Discovery of new potentially defective alleles of human CYP2C9

CYP2C9 is a clinically important enzyme, responsible for the metabolism of numerous clinically important therapeutic drugs. In the present study, we discovered 38 single nucleotide polymorphisms in CYP2C9 by resequencing of genomic DNA from 92 individuals from three different racial groups. Haplotype analysis predicted that there are at least 21 alleles of CYP2C9 in this group of individuals. Six new alleles were identified that contained coding changes: L19I (CYP2C9*7), R150H (CYP2C9*8), H251R (CYP2C9*9), E272G (CYP2C9*10), R335W(CYP2C9*11) and P489S (CYP2C9*12). When expressed in a bacterial cDNA expression system, several alleles exhibited altered catalytic activity. CYP2C9*11 appeared to be a putative poor metabolizer allele, exhibiting a three-fold increase in the Km and more than a two-fold decrease in the intrinsic clearance for tolbutamide. Examination of the crystal structure of human CYP2C9 reveals that R335 is located in the turn between the J and J' helices and forms a hydrogen-bonding ion pair with D341 from the J' helix. Abolishing this interaction in CYP2C9*11 individuals could destabilize the secondary structure and alter the substrate affinity. This new putative poor metabolizer (PM) allele was found in Africans. A second potentially PM allele CYP2C9*12 found in a racially unidentified sample also exhibited a modest decrease in the Vmax and the intrinsic clearance for tolbutamide in a recombinant system. Further clinical studies are needed to determine the effect of these new polymorphisms on the metabolism of CYP2C9 substrates.

Haplotype-Oriented Genetic Analysis and Functional Assessment of Promoter Variants in theMDR1(ABCB1) Gene

Recently, a number of nucleotide variants have been described in the multidrug resistance 1 (MDR1/ABCB1) gene; however, most studies have focused on the coding region. In the present study, we identified promoter variants of the MDR1 gene and evaluated their phenotypic consequences using a reporter gene assay and the real-time polymerase chain reaction method. Ten allelic variants were detected in the promoter region (approximately 2 kilobases), seven of which were newly identified. Certain mutations occurred simultaneously, and a total of 10 haplotypes were observed. These promoter polymorphisms were found more frequently in Japanese than Caucasians. Some haplotypes were associated with changes in luciferase activity and placental and hepatic mRNA levels. We also determined DNA methylation status in the proximal promoter region of the MDR1 gene. The promoter region around potential binding sites for transcription factors was found to be hypomethylated and thus likely to be independent of the gene expression. Nucleotide and/or haplotype variants not only in the coding region but also in the promoter region of the MDR1 gene may be important for interindividual differences of P-glycoprotein expression.

A simple method for the detection of CYP2C9 polymorphisms: nested allele-specific multiplex polymerase chain reaction

BACKGROUND

Cytochrome P4502C9 (CYP2C9), a principle drug-metabolizing enzyme is polymorphic in humans and is responsible for important pharmacokinetic and pharmacodynamic variations of CYP2C9 substrates. We developed an allele-specific multiplex polymerase chain reaction (PCR) method for the detection of common CYP2C9 alleles.

METHOD

Genomic DNA was extracted from blood obtained from 40 unrelated healthy Malaysian Indian volunteers. The DNA was subjected to a first PCR that was used to amplify both exons 3 and 7 simultaneously in one reaction tube and a second PCR that was used to detect the polymorphic sites of CYP2C9 alleles using allele-specific primers. Sequencing was performed to validate the test results.

RESULTS

We were successful in amplifying the fragments of interest from the DNA samples. The method was also reproducible and specific. The amplified sequences showed 100% homology to CYP2C9 sequence.

CONCLUSION

This is the first nested allele-specific multiplex PCR method reported to allow for the simultaneously detection of five CYP2C9 alleles.

Differential activation of CYP2C9 variants by dapsone

Studies have shown that CYP2C9.1 mediated metabolism of flurbiprofen or naproxen is activated by co-incubation with dapsone. However, dapsone activation has not been examined in the known variant forms of CYP2C9. Six concentrations of flurbiprofen (2-300microM) or naproxen (10-1800 microM) were co-incubated with six concentrations of dapsone (0-100 microM) and with reconstituted, purified CYP2C9.1, CYP2C9.2 (R144C), CYP2C9.3 (I359L), or CYP2C9.5 (D360E), in order to assess degrees of activation. Dapsone increased the efficiency (V(m)/K(m)) of flurbiprofen 4'-hydroxylation by CYP2C9.1, CYP2C9.2, CYP2C9.3, and CYP2C9.5 by 8-, 31-, 47-, and 22-fold, respectively. In similar experiments using the substrate naproxen, dapsone increased the efficiency of naproxen demethylation 7-, 15-, 13-, and 22-fold, in CYP2C9.1, CYP2C9.2, CYP2C9.3, and CYP2C9.5, respectively. Also, dapsone normalized naproxen's kinetic profile from biphasic (CYP2C9.1 and CYP2C9.2) or linear (CYP2C9.3 and CYP2C9.5) to hyperbolic for all variant forms. Thus, amino acid substitutions of CYP2C9 variants affect the degree of dapsone activation in a genotype-dependent fashion. Furthermore, the degree of effect noted across variants appeared to be dependent on the substrate studied.

Influence of CYP2C9 and CYP2D6 Polymorphisms on the Pharmacokinetics of Nateglinide in Genotyped Healthy Volunteers

BACKGROUND

The oral hypoglycaemic drug nateglinide is eliminated from the human body via hepatic biotransformation and renal tubular secretion. According to in vitro data, about 70% of nateglinide intrinsic clearance may be mediated by cytochrome P450 (CYP) 2C9 and a smaller fraction by CYP3A4 and CYP2D6.

OBJECTIVE

To assess the impact of CYP2C9 polymorphisms and of the CYP2D6 poor metaboliser genotype on the pharmacokinetics of nateglinide and its effects on insulin, glucose and glucagon in plasma.

DESIGN AND PARTICIPANTS

A prospective clinical study in 26 healthy volunteers chosen for their CYP2C9 and CYP2D6 genotype was conducted with individuals carrying wild-type genotype as reference group.

METHODS

Serial plasma nateglinide, glucose, insulin and glucagon concentrations were measured over 34 hours after a 180 mg dose of nateglinide under challenge with 75 g of oral glucose at 0, 4 and 8 hours after nateglinide intake. Kinetics were evaluated by nonparametric methods and by population pharmacokinetic-pharmacodynamic modelling.

RESULTS

Significantly reduced oral nateglinide clearance was found in carriers of CYP2C9*3 alleles, (p < 0.01), whereas carriers of CYP2C9*2 alleles had kinetic parameters similar to those of carriers of the wild-type allele (p = nonsignificant). Median total clearances were 7.9, 8.4, 6.5, 6.9, 5.8 and 4.1 L/h in carriers of the CYP2C9 genotypes *1/*1, *1/*2, *2/*2, *1/*3, *2/*3 and *3/*3. Median clearance in three carriers of two deficient CYP2D6 alleles was 9.4 L/h. These differences in nateglinide kinetics due to CYP2C9 genotypes did not result in statistically significant differences in plasma glucose, insulin and glucagon. Pharmacokinetic-pharmacodynamic modelling revealed a minor effect of CYP2C9 genotype on insulin and glucose, and extrapolations indicated that carriers of the CYP2C9*3/*3 genotype may be at a slightly higher risk of hypoglycaemia compared with carriers of CYP2C9*1, particularly when taking nateglinide doses above 120 mg.

CONCLUSION

The effect of CYP2C9 polymorphisms on nateglinide kinetics may cause a slightly increased risk for hypoglycaemia, which may become relevant in diabetic patients.

Effects of CYP2C9 polymorphisms on the pharmacokinetics of R- and S-phenprocoumon in healthy volunteers

CYP2C9 catalyses the biotransformation of the oral anticoagulants S-warfarin and R- and S-acenocoumarol. According to data obtained in vitro, phenprocoumon is also metabolized by CYP2C9 but the impact of the CYP2C9 polymorphism on phenprocoumon pharmacokinetics has not been studied. Twenty-six healthy heterozygous and homozygous carriers of the CYP2C9 alleles *1 (wild-type), *2 (Arg144Cys), and *3 (Ile359Leu) received a single oral dose of 12 mg of racemic phenprocoumon. Plasma and 12 h urine concentrations of both enantiomers and their monohydroxylated metabolites were measured by high-performance liquid chromatography with mass spectrometry detection. No significant effect of the CYP2C9 variants *2 and *3 on R-phenprocoumon pharmacokinetic parameters was detected, but S-phenprocoumon clearance tended to decrease with increasing number of CYP2C9*2 and *3 alleles. The ratios of S- to R-phenprocoumon plasma clearances were higher with a median of 0.95 in carriers of *1/*1 versus 0.65 in *3/*3 (P < 0.001 for trend). Plasma and urine concentrations of 4'-, 6- and 7-hydroxyphenprocoumon were significantly lower in homozygous carriers of the CYP2C9*2 and *3 variants compared to CYP2C9*1/*1. Carriers of CYP2C9*3/*3 had a median AUC of (R,S) 7-OH-phenprocoumon of only approximately 25% compared to the wild-type genotype. The AUC of (R,S) 6-OH-phenprocoumon was only approximately 50% in CYP2C9*3/*3 compared to the homozygous wild-type genotype. In conclusion, carriers of CYP2C9*2 and *3 alleles had a lower metabolic capacity regarding phenprocoumon hydroxylation than those with CYP2C9*1/*1. However, regarding phenprocoumon hydroxylation CYP2C9 genotypes had only marginal effects on S- and R-phenprocoumon total clearance in healthy volunteers.

Clinical relevance of genetic polymorphisms in the human CYP2C9 gene

Cytochrome p450 (CYP) 2C9 hydroxylates about 16% of drugs in current clinical use. Of special interest are those with a narrow therapeutic index, such as S-warfarin, tolbutamide and phenytoin, where impairment in CYP2C9 metabolic activity might cause difficulties in dose adjustment as well as toxicity. Single-nucleotide polymorphisms (SNP) in the CYP2C9 gene have increasingly been recognized as determinants of the metabolic phenotype that underlies interindividual and ethnic differences. Apart from the wild-type protein CYP2C9*1 at least five allelic variants produce allozymes with reduced or deficient metabolic activity. Among white populations only CYP2C9*2 and CYP2C9*3 variants are of significance, with allelic frequencies of 0.08-0.14 and 0.04-0.16, respectively. In contrast, in Africans (African-Americans and Ethiopians) and Asians both variants are much less frequent (0.005-0.04), and CYP2C9*2 has not yet been detected in Asians. CYP2C9*4 has been exclusively identified in Japanese patients, and CYP2C9*5 and *6 were only found among African-Americans with a low allelic frequency of 0.017 and 0.006, respectively. Furthermore in Japanese a CYP2C9 promotor variant of four linked SNPs was correlated with reduced intrinsic clearance of phenytoin in vitro. Subjects who are carriers of one or more variant alleles may be at risk for adverse drug reactions/toxicities when prescribed drugs extensively metabolized by CYP2C9.

Sequence variability and candidate gene analysis in two cancer patients with complex clinical outcomes during morphine therapy

In this case report, we present genetic differences in two morphine-related gene sequences, UDP-glucuronosyltransferase 2B7 (UGT2B7) and mu opioid receptors (MOR1), in two cancer patients whose clinical responses to morphine were very different [i.e., sensitive (patient 1) and low responder (patient 2)]. In addition, allelic variants in the UGT2B7 gene were analyzed in 46 Japanese individuals. Amplified DNA fragments for the two genes of interest were screened using single strand conformation polymorphism and then sequenced. In the UGT2B7 gene, 12 single nucleotide polymorphisms (SNPs) were newly identified with an allelic frequency ranging from 0.022 to 0.978. Six SNPs in the promoter region (A-1302G, T-1295C, T-1111C, G-899A, A-327G, and T-125C) and two coding SNPs (UGT2B7*2 in exon 2 and C1059G in exon 4) appeared to be consistently linked. Remarkable differences in the nucleotide sequence of UGT2B7 were observed between the two patients; in contrast to patient 1 who had "reference" alleles at almost SNP positions, but a rare ATTGAT*2(AT)C haplotype as homozygosity, patient 2 was a homozygous carrier for the predominant GCCAGC*1(TC)G sequence. Serum morphine and two glucuronide concentrations in patient 2 suggest that the predominant GCCAGC*1G sequence was not associated with a "poor metabolizer" phenotype. In the MOR1 gene, patient 1 had no SNPs, whereas patient 2 was a heterozygous carrier for both the G-1784A and A118G alleles. The present study describes substantial differences in genotype patterns of two genes of interest between the two patients. The results necessitate larger trials to confirm these observations in larger case control studies.

Personalised prescribing for asthma--is pharmacogenetics the answer?

An individual's response to anti-asthma medication is likely to arise from a complex interaction between social, environmental and inherited factors. Studies indicate that genetic factors may account for 60-80% of the heterogeneity in treatment responsiveness in asthmatics. Identifying the genetic variants responsible may potentially lead to the development of novel treatments, improved effectiveness in the use of existing treatments and better prediction of efficacy in phase II and III trials. This article will briefly outline the current methods of identifying relevant treatment-responsive genes and their genetic variants. The pharmacogenetics of the main asthma treatment groups will then be reviewed in detail. Finally, the impact of pharmacogenetics on the pharmaceutical industry, and clinical practice in the future will be discussed.

CYP2C9 allelic variants: ethnic distribution and functional significance

Cytochrome P-450 (CYP) 2C9 CYP2C9 is a polymorphically expressed enzyme responsible for the metabolism of several clinically important drugs, some with a low therapeutic index. This review summarizes the structure-function relationship of the CYP2C9 promoter and coding regions, known polymorphisms, the functional significance of various CYP2C9 alleles in vitro and in vivo, and their population frequencies. In addition, possible molecular mechanisms underlying ethnic variability in the metabolism of CYP2C9 substrate drugs are discussed.

Cloning of cytochrome P-450 2C9 cDNA from human liver and its expression in CHL cells

AIM

Using bacterial, yeast, or mammalian cell expressing a human drug metabolism enzyme would seem good way to study drug metabolism-related problems. Human cytochrome P-450 2C9(CYP2C9) is a polymorphic enzyme responsible for the metabolism of a large number of clinically important drugs. It ranks among the most important drug metabolizing enzymes in humans. In order to provide a sufficient amount of the enzyme for drug metabolic research, the CYP2C9 cDNA was cloned and expressed stably in CHL cells.

METHODS

After extraction of total RNA from human liver tissue, the human CYP2C9 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR), and cloned into cloning vector pGEM-T. The cDNA fragment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant vector of pREP9-CYP2C9 into CHL cells. The enzyme activity of CYP2C9 catalyzing oxidation of tolbutamide to hydroxy tolbutamide in S9 fraction of the cell was determined by high performance liquid chromatography(HPLC).

RESULTS

The amino acid sequence predicted from the cDNA segment was identical to that of CYP2C9*1, the wild type CYP2C9. However, there were two base differences, i.e. 21T>C, 1146C>T, but the encoding amino acid sequence was the same, L7, P382. The S9 fraction of the established cell line metabolizes tolbutamide to hydroxy tolbutamide; tolbutamide hydroxylase activity was found to be 0.465 +/- 0.109 micromol.min(-1).g(-1) S9 protein or 8.62 +/- 2.02mol.min(-1).mol(-1) CYP, but was undetectable in parental CHL cell.

CONCLUSION

The cDNA of human CYP2C9 was successfully cloned and a cell line of CHL- CYP2C9, efficiently expressing the protein of CYP2C9, was established.