Lung cancer risk in relation to the CYP2C9 genetic polymorphism among Caucasians in Los Angeles County

Metabolism pathways of arachidonic acids: mechanisms and potential therapeutic targets

The arachidonic acid (AA) pathway plays a key role in cardiovascular biology, carcinogenesis, and many inflammatory diseases, such as asthma, arthritis, etc. Esterified AA on the inner surface of the cell membrane is hydrolyzed to its free form by phospholipase A2 (PLA2), which is in turn further metabolized by cyclooxygenases (COXs) and lipoxygenases (LOXs) and cytochrome P450 (CYP) enzymes to a spectrum of bioactive mediators that includes prostanoids, leukotrienes (LTs), epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid (diHETEs), eicosatetraenoic acids (ETEs), and lipoxins (LXs). Many of the latter mediators are considered to be novel preventive and therapeutic targets for cardiovascular diseases (CVD), cancers, and inflammatory diseases. This review sets out to summarize the physiological and pathophysiological importance of the AA metabolizing pathways and outline the molecular mechanisms underlying the actions of AA related to its three main metabolic pathways in CVD and cancer progression will provide valuable insight for developing new therapeutic drugs for CVD and anti-cancer agents such as inhibitors of EETs or 2J2. Thus, we herein present a synopsis of AA metabolism in human health, cardiovascular and cancer biology, and the signaling pathways involved in these processes. To explore the role of the AA metabolism and potential therapies, we also introduce the current newly clinical studies targeting AA metabolisms in the different disease conditions.

A novel four-gene of iron metabolism-related and methylated for prognosis prediction of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a liver disease with a complex underlying mechanism, and patients with HCC have low survival rates. Iron metabolism plays a crucial role in the pathogenesis of HCC; however, the prognostic value of iron metabolism-related and methylated genes for HCC needs to be further explored. In the present study, we identified differentially expressed genes (DEGs) that play a role in iron metabolism and DNA methylation in HCC from The Cancer Genome Atlas. Four of these DEGs, whose expression levels are correlated with HCC prognosis, namely, RRM2, FTCD, CYP2C9, and ATP6V1C1, were further used to construct a prognostic model for HCC, wherein the risk score was calculated using the gene expression of the four DEGs. This could be used to predict the overall survival of HCC patients for 1, 3, and 5 years. Results of a multivariate Cox regression analysis further indicated that the risk score was an independent variable correlated with the prognosis of HCC patients. The identified gene signature was further validated using an independent cohort of HCC patients from the International Cancer Genome Consortium. Weighted gene co-expression network analysis and gene set enrichment analysis were performed to identify potential regulatory mechanisms of the gene signature in HCC. Taken together, we identified key prognostic factors of iron metabolism-related and methylated genes for HCC, providing a potential treatment strategy for HCC.

FREQUENCIES OF POLYMORPHISMS IN THE CYTOCHROME’S P450 GENES OF WARFARIN TRANSFORMATION IN A EUROPEAN POPULATION OF EASTERN SIBERIA

Background. Genotypes of the cytochrome p450 isoform (CYP2C9 and CYP4F2) determine warfarin dose requirements. Frequencies of risk alleles and genotypes of CYP2C9 and CYP4F2 gene vary in different races and ethnic groups.

Aim. This study analyzed the frequencies of *2, *3 alleles of CYP2C9 gene and the 1347 C>T allele of CYP4F2 gene in the Caucasians of Eastern Siberia, and compare with other populations.

Materials and methods. Participants were 147 patients (Caucasians): 67 (45.58 %) man and 80 (54.42 %) women), taking warfarin for the prevention of thrombosis with a mean age of 64.74 ± 14.29 years. There were patients with atrial fibrillation – 77 (52.38 %) persons, coronary artery disease – 10 (6.80 %), pulmonary embolism – 5 (3.40 %), 15 (10.20 %) patients after implantation of an mechanical heart valve, etc. The subjects were genotyped for CYP2C9 (*1,*2,*3), and CYP4F2 (1347 C>T) by real-time polymerase chain reaction (RT-PCR) using “Pharmacogenetics Warfarin” reagent kits (DNA technology, Russia).

Results. 69.4 % of Caucasians of Eastern Siberia (Russians), have two functional alleles (*1/*1) of CYP2C9 (they’re extensive/normal metabolizers), the number of intermediate metabolizers (*1/*2, *1/*3) was 29.8 % and 0.68 % of slow metabolizers (*3/*3). Homozygous carriers of two non-functional alleles *2 and *3 (*2/*2, *2/*3) were absent. Carriers of one coumarin-resistant Т-allele of CYP4F2 were 57 (38.7 %) respondents, two coumarin-resistant alleles – 10 (6.8 %) respondents.

Conclusions. Frequencies of polymorphisms in the Cytochrome’s p450 genes of warfarin transformation in a European population of Eastern Siberia have no differences with other European populations of the world

Suppression of CYP2C9 by microRNA hsa-miR-128-3p in human liver cells and association with hepatocellular carcinoma

Published studies have identified genetic variants, somatic mutations, and changes in gene expression profiles that are associated with hepatocellular carcinoma (HCC), particularly involving genes that encode drug metabolizing enzymes (DMEs). CYP2C9, one of the most abundant and important DMEs, is involved in the metabolism of many carcinogens and drugs and is down-regulated in HCC. To investigate the molecular mechanisms that control CYP2C9 expression, we applied integrative approaches including in silico, in vitro, and in vivo analyses to elucidate the role of microRNA hsa-miR-128-3p in the regulation of CYP2C9 expression and translation. RNA electrophoresis mobility shift assays demonstrated a direct interaction between hsa-miR-128-3p and its cognate target, the CYP2C9 transcript. Furthermore, the expression of a luciferase reporter gene containing the 3′-UTR of CYP2C9 and the endogenous expression of CYP2C9 were suppressed by transfection of hsa-miR-128-3p. Importantly, chemically-induced up- or down-regulation of hsa-miR-128-3p correlated inversely with the expression of CYP2C9. Finally, an association analysis revealed that the expression of hsa-miR-128-3p is inversely correlated with the expression of CYP2C9 in HCC tumor tissues. Altogether, the study helped to elucidate the mechanism of CYP2C9 regulation by hsa-miR-128-3p, and the inverse association in HCC.

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Esophageal cancer proliferation is mediated by cytochrome P450 2C9 (CYP2C9)

Cytochrome P450 epoxygenases (CYP450) have been recently shown to promote malignant progression. Here we investigated the mRNA and protein expression and potential clinical relevance of CYP2C9 in esophageal cancer. Highest expression was detected in esophageal adenocarcinoma (EAC; n=78) and adjacent esophageal mucosa (NEM; n=79). Levels of CYP2C9 in EAC and NEM were significantly higher compared to esophageal squamous cell carcinoma (ESCC; n=105). Early tumor stages and well-differentiated tumors showed a significantly higher CYP2C9 expression compared to progressed tumors. Moreover, CYP2C9 expression was correlated to high Ki-67 labeling indices in EAC and Ki-67 positive tumor cells in EAC and ESCC. Selective inhibition of CYP2C9 decreased tumor cell proliferation (KYSE30, PT1590 and OE19) in vitro, which was abolished by 11,12-epoxyeicosatrienoic acid (11,12-EET). Cell-cycle analysis using FACS revealed that inhibition of CYP2C9 leads to a G0/G1 phase cell-cycle arrest. CYP2C9 seems to be relevant for early esophageal cancer development by promoting tumor cell proliferation. Pharmacological inhibition of CYP2C9 might contribute to a more efficient therapy in CYP2C9 highly expressing esophageal cancers.

Genetic variations in xenobiotic metabolic pathway genes, personal hair dye use, and risk of non-Hodgkin lymphoma

From 1996 to 2000, the authors conducted a population-based case-control study among Connecticut women to test the hypothesis that genetic variation in xenobiotic metabolic pathway genes modifies the relation between hair dye use and risk of non-Hodgkin lymphoma. No effect modifications were found for women who started using hair dyes in 1980 or afterward. For women who started using hair dye before 1980 as compared with never users, a statistically significantly increased risk of non-Hodgkin lymphoma was found for carriers of CYP2C9 Ex3-52C>T TT/CT genotypes (odds ratio (OR) = 2.9, 95% confidence interval (CI): 1.4, 6.1), CYP2E1 -332T>A AT/AA genotypes (OR = 2.0, 95% CI: 1.2, 3.4), a homozygous or heterozygous 3-base-pair deletion in intron 6 of GSTM3 (OR = 2.3, 95% CI: 1.3, 4.1), GSTP1 Ex5-24A>G AA genotypes (OR = 1.8, 95% CI: 1.1, 2.9), or NAT2 genotypes conferring intermediate/rapid acetylator status (OR = 1.6, 95% CI: 1.0, 2.7). The observed associations were mainly seen for follicular lymphoma. In contrast, no significantly increased risk was observed for starting hair dye use before 1980 (relative to never use) among women who were homozygous wild-type for the CYP2C9, CYP2E1, or GSTM3 polymorphisms, women carrying 1 or 2 copies of the variant GSTP1 allele, or women who were slow NAT2 acetylators. A possible role of genetic variation in xenobiotic metabolism in the carcinogenicity of hair dye use needs to be confirmed in larger studies.

Roles of Eicosanoids in Prostate Cancer

Eicosanoids, the metabolites of arachidonic acid, have diverse functions in the regulation of cancer including prostate cancer. This review will provide an overview of the roles of eicosanoids and endocannabinoids and their potential as therapeutic targets for prostate cancer treatment.

The association of CYP2C9 gene polymorphisms with colorectal carcinoma in Han Chinese

BACKGROUND

Cytochrome P450 (CYP) 2C9 is an important enzyme involved in xenobiotics metabolism. This study investigated the association of CYP2C9 gene coding region polymorphisms with colorectal cancer (CRC) in Chinese Han population.

METHODS

Four hundred and eighty-three healthy controls and 286 sporadic CRC patients participated in this study. Direct sequencing was used to identify the sequence polymorphisms.

RESULTS

We detected the significant association of 2 coding region SNPs, rs1057910 and rs1057911, of CYP2C9 with the risk of developing sporadic CRC for Han Chinese. These 2 SNPs showed a strong linkage disequilibrium (LD) (r(2)=0.97, D'=0.985). Significantly different minor allele frequencies were found for SNPs rs1057910 and rs1057911 between the cases (7% and 7.2%, respectively) and controls (3% and 2.9%, respectively) with adjusted P=0.0004 and 0.0002, respectively. Individuals heterozygous for rs1057910A/C or rs1057911A/T showed 2.589-fold (95% CI: 1.549-4.330) or 2.770-fold (95% CI 1.653-4.643) increased risk of developing sporadic CRC. We did not detect any homozygote minor allele carrier for either rs1057910 or rs1057911 in our study population. The CRC association appeared to be more evident for individuals over age 50 y, for men, and for rectum cancer site.

CONCLUSION

There is an association of CYP2C9 coding region polymorphisms with the risk of developing CRC in Han Chinese after genotyping cases and controls recruited from different locations in China.

Distribution of soluble epoxide hydrolase, cytochrome P450 2C8, 2C9 and 2J2 in human malignant neoplasms

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with a C-terminal epoxide hydrolase activity and an N-terminal phosphatase activity. Arachidonic acid epoxides, previously suggested to be involved in apoptosis, oncogenesis and cell proliferation, are generated by cytochrome P450 epoxygenases and are good substrates of the sEH C-terminal domain. In addition, the N-terminal phosphatase domain hydrolyzes isoprenoid mono- and pyrophosphates, which are involved in cell signaling and apoptosis. Here we provide a comprehensive analysis of the distribution of sEH, CYP2C8, 2C9 and 2J2 in human neoplastic tissues using tissue micro-arrays. The human neoplastic tissue micro-arrays provide a well-controlled side by side analysis of a wide array of neoplastic tissues and their surrounding normal tissue controls. Many of the neoplastic tissues showed altered expression of these enzymes as compared to normal tissues. Altered expression was not limited to the neoplastic tissues but also found in the surrounding non-neoplastic tissues. For example, sEH expression in renal and hepatic malignant neoplasms and surrounding non-neoplastic tissues was found to be significantly decreased, whereas expression was found to be increased in seminoma as compared to normal tissues. Our study warrants further investigation of the role of altered expression of these enzymes in neoplastic tissues.

Genetic polymorphism of CYP2C9 in a Vietnamese Kinh population

Cytochrome P450 2C9 (CYP2C9) shows genetic polymorphism with high interethnic variation, but no report has addressed the genetic polymorphism in the Vietnamese population. In the present study, the distribution of 2 common allelic variations of CYP2C9 was investigated in Vietnamese Kinh population, a major ethnic group in Vietnam. Genomic DNA from 157 Vietnamese subjects was amplified by polymerase chain reaction, and the presence of CYP2C9*2 and CYP2C9*3 allelic variants was determined by pyrosequencing. Among 157 Vietnamese subjects, no subject with the CYP2C9*2 allele was detected, but 7 subjects were heterozygous for the CYP2C9*3 allele. The allele frequency of CYP2C9*3 was 2.2% in the Vietnamese Kinh population. This genotype distribution was well correlated with previous reports suggesting no occurrence of CYP2C9*2 in Asians. These results suggest that CYP2C9*2 may be absent in Vietnamese Kinh population and that CYP2C9*3 is major allelic variant that causes interindividual variation of drug responses to CYP2C9 substrate drugs in the Vietnamese Kinh population.

Pharmacokinetics of meloxicam in patients with juvenile rheumatoid arthritis

The pharmacokinetics of a meloxicam suspension were studied in 18 children with juvenile rheumatoid arthritis. Children received a single 0.25-mg/kg dose up to a maximum of 15 mg. Pharmacokinetic parameters after the first dose were calculated by noncompartmental methods. Geometric mean (percent coefficient of variation for geometric mean [gCV]) C(max), AUC(0- infinity ), apparent clearance, apparent volume of distribution, and elimination half-life values were 1.24 microg/mL (47% gCV), 25.6 microg x h/mL (81% gCV), 0.17 mL/min/kg (83% gCV), 0.19 L/kg (63% gCV), and 13.4 hours (54% gCV) in the younger group and 1.89 microg/mL (25% gCV), 35.8 microg x h/mL (21% gCV), 0.12 mL/min/kg (23% gCV), 0.13 L/kg (22% gCV), and 12.7 hours (21% gCV) for the older group, respectively. Area under the curve, volume of distribution, and clearance tended to be higher in the younger group, whereas elimination half-lives were similar. A post hoc comparison to pharmacokinetic data in adults revealed no relevant differences. Thus, a common body weight-normalized dose is considered appropriate for children older than 2 years.

A prospective study of genetic polymorphisms in the cytochrome P-450 2C9 enzyme and the risk for distal colorectal adenoma

BACKGROUND & AIMS

Regular aspirin use is associated with a reduced risk for colorectal adenoma, whereas smoking increases risk. The cytochrome P-450 (CYP) 2C9 (CYP2C9) enzyme is involved in the metabolism of several drugs, including possibly aspirin, and such carcinogens as smoking-related polycyclic aromatic hydrocarbons. Genetic variation in this enzyme may modulate the influence of aspirin and smoking on adenoma risk.

METHODS

We examined the risk for incident distal colorectal adenoma according to CYP2C9 genotype, aspirin use, and smoking in a prospective nested case-control study of women.

RESULTS

Among 394 cases and 396 controls, women with at least 1 variant CYP2C9 allele had a significantly greater risk for adenoma (multivariate odds ratio [OR], 1.56; 95% confidence interval [CI], 1.13-2.15; P = 0.007). Although women who used aspirin regularly (>/=2 standard tablets/wk) experienced a lower risk for adenoma compared with non-regular users, the effect was similar irrespective of genotype. Women who smoked >20 pack-years had an OR of adenoma of 1.50 (95% CI, 1.07-2.12; P = 0.02) compared with those who smoked </=20 pack-years. Among women with at least 1 variant allele who smoked >20 pack-years, the OR of adenoma was 2.50 (95% CI, 1.44-4.38; P = 0.001) compared with women with no variant alleles who smoked </=20 pack-years.

CONCLUSIONS

Polymorphisms in the CYP2C9 enzyme are associated with elevated risk for colorectal adenoma. This observation does not appear to be related to modification of the effect of aspirin on adenoma risk, but may be associated with differential metabolism of environmental carcinogens.

The role of cyclooxygenase-2 inhibition for the prevention and treatment of prostate carcinoma

Experimental and epidemiologic studies have demonstrated that nonsteroidal antiinflammatory drugs (NSAIDs) are effective in the prevention of human cancers. Nonsteroidal antiinflammatory drugs inhibit the cyclooxygenase (COX) enzyme that functions to convert arachidonic acid to prostaglandins (PGs). Cyclooxygenase-2, a key COX isoenzyme, is rapidly induced in response to inflammatory stimuli, growth factors, cytokines, and promoters of neoplastic growth. Cyclooxygenase-2-catalyzed reactions may be involved in carcinogenesis via 2 distinct mechanisms: (1). DNA damage and (2). PG-mediated effects. Reactions mediated by COX-2 form reactive oxygen species that can directly induce the oxidation of DNA or instigate the bioactivation of carcinogens. Prostaglandin E2, a byproduct of COX-2-mediated arachidonic acid metabolism, exhibits several biologic actions that have been shown to promote tumorigenesis and tumor progression. These actions include increased cell proliferation, promotion of angiogenesis, and the elevated expression of the antiapoptotic protein Bcl-2. In addition, PGE2 decreases natural killer cell activity and alters immune surveillance. In vitro experimental studies find that COX-2 inhibitors decrease cellular proliferation, increase apoptosis, and modulate genes involved in cell cycle regulation. Evidence from animal studies supports a role for NSAIDs in prostate cancer (CaP) prevention. Population-based studies have observed a reduced incidence of CaP among men using NSAIDs. Because CaP evolves slowly and rarely strikes men before the sixth or seventh decade of life, any strategy to delay or lengthen the time to development of clinically evident CaP, such as chemoprevention strategies, would greatly impact the natural history of this disease. Recent progress and critical analyses in the roles of COX-2 inhibition on prostate carcinogenesis and CaP prevention will be presented.

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.

Influence of cytochrome P450 CYP2C9 genotypes in lung cancer risk

Cytochrome P-450 CYP2C9 enzyme is involved in the metabolism of xenobiotics and carcinogens. Variant alleles CYP2C9*2 and CYP2C9*3 encode enzymes with altered properties, and CYP2C9*2 has been related to lung cancer risk. The frequency of CYP2C9 variant alleles was analyzed in genomic DNA from 104 patients with lung cancer and in 197 healthy controls. No statistically significant differences in CYP2C9 genotypes, allele frequencies or predicted phenotypes were observed between overall patients and controls. Unconditional logistic regression for the interaction smoking/genotype indicate P values of 0.66 and 0.62 for carriers of CYP2C9*2 and CYP2C9*3, respectively, versus individuals without these mutations. The P values for the same interaction in carriers of one and two mutated genes were 0.56 and 0.67, respectively, versus individuals homozygous for non-mutated genes. Independent analyses of histological types of lung cancer also indicated the absence of statistically significant differences as compared to healthy subjects. Association between CYP2C9 polymorphism and lung cancer risk was not identified in this study.

Genetic polymorphism of enzymes involved in xenobiotic metabolism and the risk of lung cancer

Chronic inhalation of cigarette smoke is a major risk factor for the development of lung cancer. It has been suggested that genetic susceptibility may contribute to the risk, because only a small portion of smokers develops the disease. Several polymorphisms that involve the metabolic activation or detoxification of carcinogens derived from cigarette smoke have been found to be associated with lung cancer risk. Many studies have focused on the relation between the distribution of polymorphic variants of different forms of the metabolic enzymes and lung cancer susceptibility. In this respect two groups of genetic polymorphisms of enzymes involved in xenobiotic metabolism, cytochrome P450 (CYP) and glutathione S-transferases (GSTs), have been discussed.CYP multigene superfamily consists of 10 subfamilies (CYP1-CYP10). A positive association between development of lung cancer and the mutant homozygous genotype ofCYP1A1 gene has been reported in several Japanese populations but such an association has not been observed in either Caucasians or African-Americans. The relation betweenCYP2D6 and lung cancer remains conflicting and inconclusive. Several polymorphisms have been identified at theCYP2E1 locus. No definitive link between the polymorphisms ofCYP2E1 and the risk of lung cancer has, however, been identified. The role of otherCYP2 isoforms in lung carcinogenesis has not been sufficiently investigated.GSTs form a superfamily of genes consisting of five distinct families, namedGSTA, GSTM, GSTP, GSTT andGSTS. The role ofGSTM, GSTT1 orGSTP1 polymorphism in modifying the lung cancer risk may be more limited than has been so far anticipated.Although some genetic polymorphisms discussed here have not shown significant increases/decreases in risk, individuals with differing genotypes may have different susceptibilities to lung cancer. Hopefully, in future studies it will be possible to screen for lung cancer using specific biomarkers.

Pharmacogenetics: the therapeutic drug monitoring of the future?

Genetic variability in drug response occurs as a result of molecular alterations at the level of drug-metabolising enzymes, drug targets/receptors, and drug transport proteins. In this paper, we discuss the possibility that therapeutic drug monitoring (TDM) in the future will involve not the mere measurement and interpretation of drug concentrations but will include both traditional TDM and pharmacogenetics-oriented TDM. In contrast to traditional TDM, which cannot be performed until after a drug is administered to the patient. pharmacogenetics-oriented TDM can be conducted even before treatment begins. Other advantages of genotyping over traditional TDM include, but are not limited to, the following: (i) it does not require the assumption of steady-state conditions (or patient compliance) for the interpretation of results; (ii) it can often be performed less invasively (with saliva, hair root or buccal swab samples); (iii) it can provide predictive value for multiple drugs [e.g. a number of cytochrome P450 (CYP) 2D6, CYP2C 19 or CYP2C9 substrates] rather than a single drug; (iv) it provides mechanistic, instead of merely descriptive, information; and (v) it is constant over an individual's lifetime (and not influenced by concurrent drug administration, alteration in hormonal levels or disease states). Pharmacogenetic information can be applied a priori for initial dose stratification and identification of cases where certain drugs are simply not effective. However, traditional TDM will still be required for all of the reasons that we use it now. In current clinical practice, pharmacogenetic testing is performed for only a few drugs (e.g. mercaptopurine, thioguanine, azathioprine, trastuzumab and tacrine) and in a limited number of teaching hospitals and specialist academic centres. We propose that other drugs (e.g. warfarin, phenytoin, codeine, oral hypoglycaemics, tricyclic antidepressants, aminoglycosides, digoxin, cyclosporin, cyclophosphamide, ifosfamide, theophylline and clozapine) are potential candidates for pharmacogenetics-oriented TDM. However, prospective studies of phaymacogenetics-oriented TDM must be performed to determine its efficacy and cost effectiveness in optimising therapeutic effects while minimising toxicity. In the future, in addition to targeting a patient's drug concentrations within a therapeutic range, pharmacists are likely to be making dosage recommendations for individual drugs on the basis of the individual patient's genotype. As we enter the era of personalised drug therapy, we will be able to identify not only the best drug to be administered to a particular patient, but also the most effective and safest dosage from the outset of therapy.

Cytochrome P4502C9 (CYP2C9) allele frequencies in Canadian Native Indian and Inuit populations

CYP2C9 is the major P450 2C enzyme in human liver and contributes to the metabolism of a number of clinically important substrate drugs. This polymorphically expressed enzyme has been studied in Caucasian, Asian, and to some extent in African American populations, but little is known about the genetic variation in Native American populations. We therefore determined the 2C9*2 (Arg144Cys) and 2C9*3 (Ile359Leu) allele frequencies in 153 Native Canadian Indian (CNI) and 151 Inuit subjects by PCR-RFLP techniques. We also present genotyping data for two reference populations, 325 Caucasian (white North American) and 102 Chinese subjects. Genotyping analysis did not reveal any 2C9*4 alleles in the CNI, Inuit, Caucasian, or Chinese individuals. The 2C9*2 allele appears to be absent in Chinese and Inuit populations, but was present in CNI and Caucasian subjects at frequencies of 0.03 and 0.08–0.15, respectively. The 2C9*3 allele was not detected in the Inuit group, but occured in the CNI group (f = 0.06) at a frequency comparable to that of other ethnic groups. This group of Inuit individuals are the first population in which no 2C9*2 or *3 alleles have been detected so far. Therefore, these alleles may be extremely rare or absent, and unless other novel polymorphisms exist in this Inuit group one would not anticipate any CYP2C9 poor metabolizer subjects among this population.Key words: CYP2C9, polymorphism, genotyping, ethnic diversity.

Cytochrome P4502C9: an enzyme of major importance in human drug metabolism

Accumulating evidence indicates that CYP2C9 ranks amongst the most important drug metabolizing enzymes in humans. Substrates for CYP2C9 include fluoxetine, losartan, phenytoin, tolbutamide, torsemide, S-warfarin, and numerous NSAIDs. CYP2C9 activity in vivo is inducible by rifampicin. Evidence suggests that CYP2C9 substrates may also be induced variably by carbamazepine, ethanol and phenobarbitone. Apart from the mutual competitive inhibition which may occur between alternate substrates, numerous other drugs have been shown to inhibit CYP2C9 activity in vivo and/or in vitro. Clinically significant inhibition may occur with coadministration of amiodarone, fluconazole, phenylbutazone, sulphinpyrazone, sulphaphenazole and certain other sulphonamides. Polymorphisms in the coding region of the CYP2C9 gene produce variants at amino acid residues 144 (Arg144Cys) and 359 (Ile359Leu) of the CYP2C9 protein. Individuals homozygous for Leu359 have markedly diminished metabolic capacities for most CYP2C9 substrates, although the frequency of this allele is relatively low. Consistent with the modulation of enzyme activity by genetic and other factors, wide interindividual variability occurs in the elimination and/or dosage requirements of prototypic CYP2C9 substrates. Individualisation of dose is essential for those CYP2C9 substrates with a narrow therapeutic index.