Sequence diversity in CYP3A promoters and characterization of the genetic basis of polymorphic CYP3A5 expression

Past and future applications of CYP450-genetic polymorphisms for biomonitoring of environmental toxicants

Cytochrome P450s (CYPs) are a huge gene superfamily of heme enzymes involved in xenobioitc as well as endobiotic metabolism. They play a critical role in adaptation to environmental changes for survival of living organisms. In addition, the huge environmental loads of human-made chemicals are biotransformed into bioactive or detoxified forms by CYPs. Thus, CYPs have been used for biomonitoring of environmental pollutants, screening of their metabolisms and exploring remedy. In particular, the induction or inhibition of CYPs has been applied to exposure monitoring of environmental toxicants, which are biotransformed by CYPs. This review considers past and future applications of CYP-genetic polymorphisms as susceptibility biomarkers for biomonitoring. Furthermore, we suggest the needs for further understanding of the characteristics of each CYP isozyme, consideration of real-life exposures such as mixed contamination with various chemicals, and incorporation of the presence of other phase I and phase II enzymes, for proper applications of CYP polymorphisms on biomonitoring.

Cloned Enzyme Donor Immunoassay Tacrolimus Assay Compared With High-Performance Liquid Chromatography-Tandem Mass Spectrometry and Microparticle Enzyme Immunoassay in Liver and Renal Transplant Recipients

The immunosuppressant drug tacrolimus has a narrow therapeutic index and is subject to a large variation in individual bioavailability and clearance. With its narrow therapeutic index, therapeutic drug monitoring is standard clinical practice in the management of transplant recipients. In this study, we report the evaluation of the cloned enzyme donor immunoassay (CEDIA) for the determination of whole-blood tacrolimus concentrations compared with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and microparticle enzyme immunoassay (MEIA) using samples obtained from liver (n = 100) and renal (n = 88) transplant recipients. Linear regression analysis showed a relationship of CEDIA = 1.24 HPLC-MS/MS -0.18 (r = 0.81). The mean bias (+/-SEM) for all patients when compared with HPLC-MS/MS was 22.2% (+/-2.1%). The precision of the CEDIA method for all samples showed a root mean square error of 3.1 microg/L. Liver transplant recipient samples showed a mean (+/-SEM) bias compared with HPLC-MS/MS of 12.5% (+/-1.6%). The precision of the CEDIA method for these samples showed a root mean square error of 1.5 microg/L. The data suggest that in the renal transplant group, the CEDIA and MEIA methods have a bias of 33.3% and 20.1%, respectively, compared with HPLC-MS/MS. The CEDIA tacrolimus immunoassay has been shown to be a rapid method for the determination of whole-blood tacrolimus concentrations and may be considered when HPLC-MS/MS is not available. When used in the clinical setting with other parameters, it would be a useful adjunct in the management of liver transplant recipients, but a significant bias in renal transplant patients needs to be further investigated.

Impact of population admixture on the distribution of the CYP3A5*3 polymorphism

Objective: To compare the effectiveness of self-identified ethnic/color and marker-based biogeographical ancestry classifications in genotyping the CYP3A5*3 polymorphism in the Brazilian population. Methods: Individual DNA from 308 healthy Brazilians, self-identified as white, intermediate and black was genotyped for the CYP3A5*3 polymorphism and for a set of insertion–deletion polymorphisms, validated as ancestry informative markers (AIMs). The Structure software was used to analyze the AIMs data and to obtain estimates of the African component of ancestry (ACA). Nonlinear logistic regression modeling was developed to describe the association between the CYP3A5*3 polymorphism and the individual ACA values. Results: The CYP3A5*3 allele and genotype distribution differed significantly across the self-reported 'color’ groups (p < 0.0001, Fisher exact test), with a trend for decreasing frequency of both the CYP3A5*3 allele and the *3/*3 genotype from white to intermediate to black individuals (p < 0.0001, χ2 test for trend in proportions). When the population sample was proportioned in quartiles according to the individual ACA values, the frequency of the CYP3A5*3 allele and the *3/*3 genotype declined progressively from the lowest (<0.25 ACA) to the highest (>0.75 ACA) quartile. Nonlinear logistic regression showed that the odds of having the CYP3A5*3 allele decreases monotonically (p < 0.0001, Wald statistics) with the increase of the ACA, throughout the ACA range (0.15–0.93) observed in the overall population sample. Conclusion: Interethnic admixture is a source of cryptic population structure that may lead to spurious genotype–phenotype associations in pharmacogenetic/-genomic studies. Logistic regression modeling of CYP3A5*3 polymorphism shows that admixture must be dealt with as a continuous variable, rather than proportioned in arbitrary subcategories for the convenience of data quantification and analysis.

Disparity in holoprotein/apoprotein ratios of different standards used for immunoquantification of hepatic cytochrome P450 enzymes

An analysis of reported hepatic abundances of CYP3A4 and 3A5 indicated that values determined by immunoquantification using commercially available, unpurified recombinant enzymes as standards are significantly lower than those determined using purified enzymes or human liver microsomes characterized with lysosomal peptides (CYP3A4: mean 45 versus 121 pmol/mg protein, p < 0.01; CYP3A5: mean 28 versus 83 pmol/mg protein, p < 0.05). When immunoquantifying cytochromes P450 (P450s), it is assumed that the holoprotein (holo)/apoprotein ratio is the same in the samples and the standard. Estimates of holo/apoprotein ratios from data reported for a range of P450s purified from human liver and non-commercial recombinant systems indicated less than complete and variable heme coupling dependent on enzyme and system.

Discovery of osmosensitive transcriptional regulation of human cytochrome P450 3As by the tonicity-responsive enhancer binding protein (nuclear factor of activated T cells 5)

We report the discovery of an osmosensitive transcriptional control of human CYP3A4, CYP3A7, and CYP3A5. Ambient hypertonicity (350-450 mOsmol/kg) increased mRNA expressions of the CYP3A by approximately 10- to 20-fold in human-intestinal C(2)bbe1 cells, followed by an increase of CYP3A protein. Hypotonicity, on the other hand, suppressed CYP3A mRNA levels, indicating that physiological isotonic conditions may regulate the basal expression of CYP3A. Similar responses to ambient tonicity were observed in other human-derived cell lines (intestinal LS180 and hepatic HepG2) and human primary colonic cells. The 11-base pair tonicity-responsive enhancer (TonE) is an osmosensitive regulator that is activated by the transcription factor, the nuclear factor of activated T-cells 5 (NFAT5). Luciferase-based reporter assays of 13 consensus TonE motifs within +/-10 kilobases (kb) from the transcription start sites of CYP3A showed that only the CYP3A7 intron 2 region ( approximately 5 kb downstream from the transcription start site), which contains two TonE motifs (+5076/+5086 and + 5417/+5427), was responsive to hypertonicity stimuli. This observation was confirmed upon cotransfection with an NFAT5 expression vector, small interfering RNA, or dominant-negative NFAT5. Deletion and mutation analyses suggested that the TonE (+5417/+5427) is indispensable for the enhancer activity. NFAT5 binding to the CYP3A7 intron 2 TonE motif was demonstrated with electrophoretic mobility shift assay and in a native cell context by chromatin immunoprecipitation. We conclude that transcription of human CYP3A is influenced by ambient tonicity. The physiological significance of the tonic regulation of CYP3A enzymes remains to be determined.

Characterization of human cytochrome p450 enzymes involved in the metabolism of cilostazol

Cilostazol (OPC-13013; 6-[4-(1-cyclohexl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone) is widely used as an antiplatelet vasodilator agent. In vitro, the hydroxylation of the quinone moiety of cilostazol to OPC-13326 [6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-4-hydroxy-2(1H)-quinolinone], is the predominant route, and the hydroxylation of the hexane moiety to OPC-13217 is the second most predominant route. This study was carried out to identify and kinetically characterize the human cytochrome P450 (P450) isozymes responsible for the formation of the two major metabolites of cilostazol, namely, OPC-13326 and OPC-13217 [3,4-dihydro-6-[4-[1-(cis-4-hydroxycyclohexyl)-1H-tetrazol-5-yl)butoxy]-2(1H)-quinolinone)]. In in vitro studies using 14 recombinant human P450 isozymes, CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP2J2, CYP3A4, CYP3A5, and CYP4A11, cilostazol was metabolized to OPC-13326 mainly by CYP3A4 (K(m) = 5.26 muM, intrinsic clearance (CL(int)) = 0.34 microl/pmol P450/min), CYP1B1 (K(m) = 11.2 microM, CL(int) = 0.03 microl/pmol P450/min), and CYP3A5 (K(m) = 2.89 microM, CL(int) = 0.05 microl/pmol P450/min) and to OPC-13217 mainly by CYP3A5 (K(m) = 1.60 microM, CL(int) = 0.57 microl/pmol P450/min), CYP2C19 (K(m) = 5.95 microM, CL(int) = 0.16 microl/pmol P450/min), CYP3A4 (K(m) = 5.35 microM, CL(int) = 0.10 microl/pmol P450/min), and CYP2C8 (K(m) = 33.8 microM, CL(int) = 0.009 microl/pmol P450/min). The present study showed that the two major metabolites of cilostazol in vitro, namely, OPC-13326 and OPC-13217, are mainly catalyzed by CYP3A4 and CYP3A5, respectively.

Vitamin D receptor haplotypes protect against development of colorectal cancer

OBJECTIVE

We investigated the association of vitamin D receptor polymorphisms and colorectal cancer incidence in a Caucasian population.

METHODS

Frequencies of the vitamin D receptor gene polymorphisms 23005G>A (CDX-2), 27823C>T (FokI), 60890G>A (BsmI), 61050G>A (Tru9I), 61888G>T (ApaI), and 61968T>C (TaqI) were determined in a series of 256 colorectal cancer patients and 256 patients without malignant disease (case-control study) using polymerase chain reaction and restriction fragment length polymorphism genotyping assays (PCR-RFLP). Haplotype analysis based on the six genetic loci was applied to the received genotypes.

RESULTS

Pairwise linkage disequilibrium between BsmI, ApaI, TaqI, and Tru9I was confirmed (P < 0.001). Allele frequencies did not differ between the groups. There was no association between any single variant and colorectal cancer. However, haplotypes BsmI(G)#TaqI(C) and BsmI(A)#TaqI(T) were inversely associated with colorectal cancer incidence (P < 0.001), the odds being 15.0 times smaller [odds ratio (OR) 0.067; 95% confidence interval (CI), 0.016-0.284] and 5.3 times smaller (OR 0.188; 95% CI 0.077-0.461), respectively, compared with noncarriers.

CONCLUSION

Our findings suggest that vitamin D receptor haplotypes BsmI(G)#TaqI(C) and BsmI(A)#TaqI(T) have a protective effect against colorectal cancer in Caucasians.

No association of the CYP3A5*1 allele with blood pressure and left ventricular mass and geometry: the KORA/MONICA Augsburg echocardiographic substudy

A polymorphism in the cytochrome P450 3A CYP3A5 enzyme has been implicated in BP (blood pressure) control and arterial hypertension. Carriers of the CYP3A5*1 allele had high, whereas homozygous carriers of the CYP3A5*3 allele exhibit low, CYP3A5 expression in the kidney, where CYP3A5 represents the major CYP3A enzyme. The aim of the present study was to investigate the association of the CYP3A5*1 allele with BP, arterial hypertension, LVM [(left ventricular) mass] and LV geometry in a large Caucasian-population-based cohort. We compared BP, LVM and the prevalence of hypertension between carriers (CYP3A5*1/*1 and CYP3A5*1/*3 genotypes) and non-carriers (CYP3A5*3/*3 genotype) of the CYP3A5*1 allele in the echocardiographic substudy of the third MONICA (MONItoring trends and determinants in CArdiovascular disease) Augsburg survey. After exclusion of 269 individuals who were taking antihypertensive medication, 530 women and 554 men were available for analysis, revealing allele frequencies of 5.8 and 94.2% for the CYP3A5*1 and CYP3A5*3 alleles respectively. Overall, the presence of the CYP3A5*1 allele exhibited no effect on systolic or diastolic BP in either gender. One-third of the individuals in this cohort were hypertensive (BP > or =140/90 mmHg), and the genotype distribution between normotensive and hypertensive individuals revealed no association between CYP3A5*1 and hypertension after adjustment for age, BMI and gender (odds ratio, 1.02; P=0.92). Moreover, no effect of CYP3A5*1 on LVM, thickness of the septal and posterior wall and LV end-diastolic diameter was found. We conclude that CYP3A5*1 exhibits no significant effect on BP, LVM and LV geometry in the KORA/MONICA echocardiographic substudy.

Pharmacogenetics as a tool for optimising drug therapy in solid-organ transplantation

Existing immunosuppressive therapies used for solid-organ transplantation have narrow therapeutic indices, whereby underdosing is associated with acute immunological rejection of the transplanted organ and overdosing is associated with infections and malignancy, as well as organ-specific toxicities. There is significant inter-individual variation in the pharmacokinetics and pharmacodynamics of these drugs, an issue that has been addressed, in part, by therapeutic drug monitoring. Genetic polymorphisms in drug metabolising enzymes, drug efflux pumps and drug targets which may underly this heterogeneity have been identified and may provide a tool to guide prescribing. There are a number of associations between genotype and pharmacology, but as of now, only thiopurine-S-methyltransferase and cytochrome P450 3A5 have a sufficiently large influence to have potential in guiding therapy. Recent studies have also identified that donor genotype may play a significant role in immunosuppressive drug pharmacokinetics and pharmacodynamics.

Impact of the CYP3A5 genotype on midazolam pharmacokinetics and pharmacodynamics during intensive care sedation

OBJECTIVE

Information is lacking on whether the CYP3A5 genotype affects the disposition and effects of midazolam during the long-term intensive care sedation of patients. This study was undertaken to estimate whether the CYP3A5 genotype can explain a relevant portion of pharmacokinetic interindividual variability.

METHODS

We determined the CYP3A5 genotype in 71 Caucasian patients who underwent long-term sedation during intensive care treatment. We then assessed the relation between the genotype and both the plasma concentrations of midazolam and 1'-OH-midazolam in 645 plasma samples and the simultaneously estimated Ramsay sedation score, both of which were recorded during routine midazolam drug monitoring.

RESULTS

Eight patients had the CYP3A5*1/*3 genotype and 63 patients the CYP3A5*3/*3 genotype. The concentration-dose ratio [C/D; plasma concentration of midazolam (ng/ml) divided by the rate of infusion (mg/h); expressed as the mean (95% confidence interval)] was 87.4 (70.8, 108.9) for the *3/*3 patients and 79.0 (48.9, 129.0) for *1/*3 patients. The corresponding data for infusion rate (IR; in mg/h), Ramsay score (RS) and the ratio 1'-OH-midazolam concentration/midazolam concentration (ROH) for *3/*3 and *1/*3 patients were IR 7.4 (6.2, 8.6) vs. 11.4 (4.9, 17.9), RS 5.4 (5.2, 5.6) vs. 5.3 (4.2, 6.0) and ROH 0.11 (0.09, 0.13) vs. 0.17 (0.11, 0.26), respectively.

CONCLUSIONS

The CYP3A5*1/*3 genotype did not lead to an apparently lower midazolam concentration/dose ratio or Ramsay score values. As the present sedation procedure during intensive care therapy may be described as a physician closed-loop titration towards Ramsay scores of 4 +/- 1, our data do not indicate that prior determination of the genotype will result in better care or economic savings.

Transcription factor binding to a putative double E-box motif represses CYP3A4 expression in human lung cells

Two vital enzymes of the CYP3A subfamily, CYP3A4 and CYP3A5, are differentially expressed in the human lung. However, the molecular mechanisms that regulate tissue-selective expression of the genes are poorly understood. The ability of the 5' upstream promoter region of these two genes to drive luciferase reporter activities in human lung A549 cells was dramatically different. The CYP3A5 promoter region activated luciferase gene expression by 10-fold over the promoterless construct, whereas the CYP3A4 promoter did not drive expression. Sequence comparisons of the promoters identified a 57-base pair insertion in the CYP3A4 promoter region (-71 to -127) that was absent in the CYP3A5 promoter. Deletion of the 57-bp motif from CYP3A4 or insertion into the CYP3A5 promoter, showed that this motif represses CYP3A4 expression in lung. EMSA analysis using nuclear extracts from either A549 cells or human lung tissues showed two specific protein/DNA complexes formed with the (32)P-labeled CYP3A4 57-bp oligonucleotide. EMSA analyses identified two E-box motifs as the minimal specific cis-elements. Supershift assays with antibodies directed against known double- or single-E-box binding factors (TAL1, deltaEF1, E2A, HEB, etc.) failed to identify this factor as a previously characterized trans-acting double E-box binding protein. These results demonstrated that the 5'-upstream region of CYP3A4 contains an active putative double E-box repressor motif, not present in the 5'-upstream region of the CYP3A5 gene, that attenuates CYP3A4 expression in the human lung. We believe that this is the first documented case in which a cytochrome P450 gene is actively repressed in a tissue-specific manner.

Pharmacogenetics of Tacrolimus and Sirolimus in Renal Transplant Patients: From Retrospective Analyses to Prospective Studies

The promises of pharmacogenetics are to elucidate the inherited basis of differences between individual responses to drugs in order to identify the right drug and dose for each patient. The recent identification of genetic polymorphisms in drug-metabolizing enzymes and drug transporters led to the hypothesis that genetic factors may be implicated in the interindividual variability of the pharmacokinetic or pharmacodynamic characteristics of immunosuppressive drugs, major side effects, and efficacy. The purpose of this study was to provide a short overview of recent results obtained in the field of pharmacogenetics of tacrolimus and sirolimus, both substrates of the cytochrome P450 3A (CYP3A) enzymes and of the efflux pump P-glycoprotein, the product of the Multidrug Resistance-1 (MDR1) genes. A number of retrospective studies that demonstrated a link between the polymorphisms governing the CYP3A5 protein expression, with more conflicting results with the MDR1 gene polymorphisms, related to the daily dose necessary to achieve adequate blood tacrolimus levels. The CYP3A5 polymorphisms have also been associated with sirolimus pharmacokinetics. One challenge is to investigate the combined effect of a number of different polymorphisms in various genes to define genetic backgrounds with different pharmacokinetic profiles using high throughput technologies. Another challenge is to move toward prospective randomized studies to explore whether a pharmacogenetic approach, taking into account a limited number of polymorphisms prior to drug treatment, could be used on an individual basis to guide initial dosing of a given drug. The last challenge is based on "target" pharmacogenetics to investigate the role of the polymorphisms of other genes implicated in the efficacy and/or safety of the drug.

Pharmacogenomic associations in ABCB1 and CYP3A5 with acute kidney injury and chronic kidney disease after myeloablative hematopoietic cell transplantation

Renal disease is a major complication in patients following myeloablative allogeneic hematopoietic cell transplantation (HCT). Post-HCT patients receive immunosuppressive regimens containing calcineurin inhibitor (CNIs), cyclosporine or tacrolimus, for graft-versus-host disease prophylaxis. In this retrospective trial, we investigated pharmacogenomic associations in the multidrug resistance (ABCB1) and cytochrome P450 3A5 (CYP3A5) genes and acute kidney injury (AKI) and chronic kidney disease (CKD) in a cohort of 121 patients. ABCB1 and CYP3A5 are responsible for the renal disposition of CNIs, which are known to be nephrotoxic. AKI was defined as doubling of baseline serum creatinine during the first 100 days post-HCT, and CKD as at least one glomerular filtration rate <60 ml/min/m2 between 6 and 18 months post-HCT. Patients were genotyped for CYP3A5*1>*3 and ABCB1 single nucleotide polymorphisms (SNPs) (1199G>A, 1236C>T, 2677G>T/A and 3435C>T). Odds ratios were calculated using logistic regression. Haplotype estimation and univariate association analyses were performed because of strong ABCB1 linkage disequilibrium (LD). AKI occurred in 48 of 121 patients (39.7%) and CKD in 16 of 66 patients (24.2%). No pharmacogenomic associations were found between ABCB1 and CYP3A5 SNPs and the incidences of AKI or CKD. The degree of LD(r2) between ABCB1 SNPs was estimated as follows: 2677G>T/3435C>T (0.44), 1236C>T/3435C>T (0.42) and 1236C>T/2677G>T (0.72). ABCB1 1199G>A showed no LD to other SNPs (<0.05). No associations were found between the most common ABCB1 haplotypes and AKI or CKD. Since no significant pharmacogenomic associations were observed, tailoring CNIs dosing based on these genotypes is unlikely to lower significantly the risk of renal injury following myeloablative HCT.

Genetic polymorphisms of drug-metabolizing enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 in the Greek population

The aim of the present study was to determine the prevalence of the most common allelic variants of the polymorphic cytochrome P450 (CYP) enzymes CYP2D6, CYP2C9, CYP2C19 and CYP3A5 and to predict the genotype frequency for each polymorphism in the Greek population. DNA isolated from peripheral blood samples derived from 283 non-related Greek ethnic subjects was used to determine the frequency of CYP2D6*3, CYP2D6*4, CYP2C9*2, CYP2C9*3 and CYP3A5*3 allelic variants by the polymerase chain reaction (PCR)-restriction fragment length polymorphism method, CYP2C19*2 and CYP2C19*3 with allelic specific amplification (PCR-ASA), and CYP2D6*2 (gene duplications) by long PCR analysis. The allelic frequencies (out of a total of 566 alleles) for CYP2D6*3 and CYP2D6*4, were 2.3% and 17.8%, respectively, while gene duplications (CYP2D6*2) were found in 7.4% of the subjects tested. For CYP2C9*2 and CYP2C9*3 polymorphisms the allelic frequencies were 12.9% and 8.13% respectively. For CYP2C19, the *2 polymorphism was present at an allelic frequency of 13.1%, while no subjects were found carrying the CYP2C19*3 allele. Finally, the CYP3A5*3 allele was abundantly present in the Greek population with an allelic frequency of 94.4%. Overall our results show that the frequencies of the common defective allelic variants of CYP2C9, CYP2C19 and CYP3A5 in Greek subjects are similar to those reported for several other Caucasian populations. Finally, a high prevalence of CYP2D6 gene duplication among Greeks was found, a finding that strengthens the idea that a South/North gradient exists in the occurrence of CYP2D6 ultrarapid metabolizers in European populations.

A pharmacogenomics primer

The human genome project and related research initiatives have enabled the identification of a significant number of genetic variants that are predictive of drug response and outcome (pharmacogenomic biomarkers). As yet, incorporation of routine pharmacogenomic testing into clinical practice has been relatively modest. Potential barriers to adoption include a relative lack of prospective controlled trials establishing the benefits of such testing, economic constraints, and ethical concerns, among others. Clinicians considering the use of pharmacogenomic testing in their practice also may be unfamiliar with the concepts and principles underlying this rapidly evolving discipline. Consequently, the purpose of this review is to provide the clinical pharmacologist with a primer on the principles and molecular mechanisms underlying pharmacogenomics. In addition, the methods currently being used to discover novel pharmacogenomic biomarkers and then apply these to clinical practice will be described.

Advances in the understanding of susceptibility to treatment-related acute myeloid leukaemia

Treatment-related acute myeloid leukaemia (t-AML) is a devastating complication following exposure to the cytotoxic and genotoxic agents used to treat a primary malignancy. Whilst the incidence of t-AML is rising, it still only occurs in a minority of patients who have received chemotherapy and/or radiotherapy treatment and hence it is important to identify factors that may confer susceptibility to the development of the condition. This paper reviews the literature and discusses the advances and limitations in our understanding of susceptibility factors to t-AML. In particular, it concentrates upon genetic polymorphisms in detoxification genes and in genes belonging to the major DNA repair pathways. This review also considers more novel susceptibility factors, such as those proposed to determine stem cell number. Increased understanding of t-AML susceptibility may enable steps to be taken to prevent its development and increase the effectiveness of treatment of the disease.

Interaction between midazolam and clarithromycin in the elderly

AIM

To assess the relative contribution of intestinal and hepatic CYP3A inhibition to the interaction between the prototypic CYP3A substrate midazolam and clarithromycin in the elderly.

METHODS

On day 1, 16 volunteers (eight male, eight female) aged 65-75 years weighing 59-112 kg received simultaneous doses of midazolam intravenously (i.v.) (0.05 mg kg(-1) over 30 min) and orally (p.o.) (3.5 mg of a stable isotope, (15)N(3)-midazolam). Starting on day 2, clarithromycin 500 mg was administered orally twice daily for 7 days. On day eight, i.v. and p.o. doses of midazolam were administered 2 h after the final clarithromycin dose. Serum and urine samples were assayed for midazolam, (15)N(3)-midazolam and metabolites by gas chromatography/mass spectometry.

RESULTS

Men and women exhibited similar i.v. (30.4 vs. 36.0 l h(-1)) and p.o. (119 vs. 124 l h(-1)) clearances of midazolam. Midazolam hepatic availability was significantly (P = 0.006) greater in men [0.79, 95% confidence interval (CI) 0.75, 0.84] than in women (0.66, 95% CI 0.59, 0.73), but midazolam intestinal availability (0.39 vs. 0.55) was not different. Following clarithromycin dosing, a significant decrease in systemic (33.2 l h(-1) to 11.5 l h(-1)) and oral (121 l h(-1) to 17.4 l h(-1)) midazolam clearance occurred. Oral, hepatic and intestinal availability was significantly increased after clarithromycin dosing from 0.34 to 0.72, 0.73 to 0.91 and 0.47 to 0.79, respectively. Clarithromycin administration led to an increase in the AUC of midazolam by 3.2-fold following i.v. dosing and 8.0-fold following p.o. dosing. Similar effects were observed for males and females.

CONCLUSIONS

Intestinal and hepatic CYP3A inhibition by clarithromycin significantly reduces the clearance of midazolam in the elderly.

[Individualized dosage regimen of immunosuppressive drugs based on pharmacokinetic and pharmacodynamic analysis]

The calcineurin inhibitors cyclosporine and tacrolimus are widely used to prevent allograft rejection after transplantation. Since these drugs have narrow therapeutic windows and show considerable pharmacokinetic variability, therapeutic drug monitoring (TDM) is essential to avoid adverse effects such as nephrotoxicity while maximizing immunosuppressive efficacy. On the other hand, some patients experience acute rejection episodes or postoperative complications despite achieving therapeutic blood drug levels. Therefore, pharmacokinetic and pharmacodynamic factors by which to establish individualized dosage adjustment for these drugs should be identified. Recently, it was recognized that pharmacogenomics has the potential to facilitate personalized medicine by translating knowledge of human genome variability into rational therapeutics. In this paper, we review the population pharmacokinetic and pharmacogenomic analysis of tacrolimus, focusing on an efflux transporter P-glycoprotein (multidrug resistance 1 [MDR1/ABCB1]) and drug-metabolizing enzymes cytochrome P450 (CYP) 3A4 and 3A5, and describe Bayesian forecasting to individualize the tacrolimus dose in de novo living-donor liver transplant recipients. Furthermore, the pharmacodynamic properties of tacrolimus and cyclosporine, which were evaluated by measuring calcineurin phosphatase activity in peripheral blood mononuclear cells, are reviewed in relation to an optimal monitoring strategy as well as a rational dosage regimen for these drugs.

Effects of the renin-angiotensin system genes and salt sensitivity genes on blood pressure and atherosclerosis in the total population and patients with type 2 diabetes

Most studies on the genetic determinants of blood pressure and vascular complications of type 2 diabetes have focused on the effects of single genes. These studies often have yielded conflicting results. Therefore, we examined the combined effects of three renin-angiotensin system (RAS) genes and three salt sensitivity genes in relation to blood pressure and atherosclerosis in the total population and type 2 diabetic patients. The study was a part of the Rotterdam Study, a population-based cohort study. We have genotyped three RAS gene polymorphisms and three salt sensitivity gene polymorphisms. Diabetic patients with three risk genotypes of the RAS genes had a 6.9 mmHg higher systolic blood pressure (P for trend = 0.04) and a 6.0 mmHg higher pulse pressure (P for trend = 0.03) than those who did not carry any risk genotypes. Diabetic patients with three risk genotypes of the salt sensitivity genes had a 9.0 mmHg higher systolic blood pressure (P = 0.19) and a 13.1 mmHg higher pulse pressure (P = 0.02). Diabetic patients who carried three risk genotypes for the RAS genes had a higher mean intima-media thickness than those with two risk genotypes (mean difference 0.04 mm, P = 0.02). We found that among type 2 diabetic patients, mean systolic blood pressure, pulse pressure, and risk of hypertension increased with the number of risk genotypes for the RAS genes and the salt sensitivity genes.

Pharmacogenomics of acute leukemia

Pharmacogenomics provides knowledge regarding how genetic polymorphisms affect treatment responses. Such an approach is particularly needed in cancer therapy, as most chemotherapeutics drugs affect both tumor and normal cells, are ineffective in many patients and exhibit serious side effects. Leukemia exists in two different forms, myeloid and lymphoid. Acute lymphoblastic leukemia more frequently occurs in children, whereas the risk of acute myeloid leukemia is more common in adults. Despite significant progress in the treatment of these diseases, therapy is still unsuccessful in many patients. Prognosis is particularly poor in adult acute myeloid leukemia. Treatment failure in childhood acute lymphoblastic leukemia due to drug resistance remains the leading cause of cancer-related death in children. Here, we provide an overview of pharmacogenetics studies carried out in children and adults with acute lymphoblastic leukemia and acute myeloid leukemia, attempting to find the associations between treatment responses and polymorphisms in the genes whose products are needed for metabolism, and effects of drugs used in the treatment of leukemia.

Impact of CYP3A7*1C polymorphism on bone mineral content in postmenopausal women

A CYP3A7-enzim részt vesz a dehidroepiandroszteron-szulfát metabolizációjában. Kimutatták, hogy CYP3A7*1C-mutáció esetén férfiakban alacsonyabb a dehidroepiandroszteron-szulfát-szint, és ismert az is, hogy a dehidroepiandroszteron-szulfát-koncentráció csökkenése csontritkuláshoz vezethet.Célkitűzés:A szerzők a CYP3A7*1C-polimorfizmus, a dehidroepiandroszteron-szulfát-szérumszint és a csont ásványanyag-tartalmának együttes vizsgálatát tűzték ki célul, 319 posztmenopauzás nőben.Eredmények:A homozigóta CYP3A7*1C-genotípus esetén a vad típushoz képest szignifikánsan alacsonyabb lumbális gerinccsontdenzitást tapasztaltak (homozigóta mutáns T-score: –3,27 ± 1,02, vs vad típus: –1,35 ± 1,53;p= 0,041). Szignifikáns maradt a kapcsolat a menopauzális kor, szérum-dehidroepiandroszteron-szulfát-szint, az alkoholfogyasztás, a korábbi szteroidkezelés, dohányzás és megelőző csonttörés figyelembevétele után is. Nem volt viszont összefüggés a CYP3A7-genotípus és a dehidroepiandroszteron-szulfát-koncentráció között.Következtetés:A CYP3A7 polimorfizmusa a lumbális gerincen mért csontsűrűség csökkenéséhez vezet, mely hatás független a szérum-dehidroepiandroszteron-szulfát-szinttől.

GST CYP and PON1 polymorphisms in farmers attributing ill health to organophosphate-containing sheep dip

Previously we reported that in sheep dippers exposed to organophosphates the frequency of paraoxonase (PON1) polymorphisms differed between those with or without self-reported ill health. We have now examined whether polymorphisms in other genes involved in xenobiotic metabolism alter disease risk in this population. There were elevated but non-significant risks associated with the CYP2D6 WT genotype (odds ratio (OR) 1.47, 95% CI 0.83-2.60), or a GSTP1*B or *C allele (OR 1.37, 95% CI 0.88-2.01) or being GSTM1*2/GSTT1*2 homozygous (OR 1.61, 95% CI 0.74-3.48). Similar results were generally obtained after the exclusion of subjects to obtain a more homogenous case-referent population: for double null GSTM1 and GSTT1 homozygotes the OR was 2.06 (95% CI 0.85-2.04). In those also likely to have been exposed to diazinon, risks associated with a GSTP1*B or *C allele (OR 1.82, 95% CI 0.92-3.63) or a GSTM1*2/GSTT1*2 homozygous (OR 2.60, 95% CI 0.72-10.42) were elevated but not to a significant extent. Risk associated with PON1 genotype and phenotype varied with CYP2D6 and GSTP1 genotype but not consistently with a priori hypotheses. Further work is necessary to delineate more clearly pathways of organophosphate activation and non-PON1 pathways of detoxification and to confirm whether CYP and GST polymorphisms alter disease risk in populations exposed to organophosphates.

A phase I study of 17-allylaminogeldanamycin in relapsed/refractory pediatric patients with solid tumors: a Children's Oncology Group study

PURPOSE

To determine the recommended phase 2 dose, dose-limiting toxicities (DLT), pharmacokinetic profile, and pharmacodynamics of the heat shock protein (Hsp) 90 inhibitor, 17-allylaminogeldanamycin (17-AAG).

EXPERIMENTAL DESIGN

17-AAG was administered as a 60-min infusion, on days 1, 4, 8, and 11 of a 21-day cycle at dose levels of 150, 200, 270, and 360 mg/m(2)/dose. Pharmacokinetic studies and evaluations for Hsp72 and Akt levels in peripheral blood mononuclear cells were done during the first course of therapy.

RESULTS

Seventeen patients (7 males), median 7 years of age (range, 1-19 years), were enrolled using a standard dose escalation scheme. No DLTs were observed. Although there were no objective responses, three patients remain on therapy at 6+, 7+, and 9+ months with stable disease. One patient with hepatoblastoma had a reduction in alpha-fetoprotein and stable disease over three cycles. At 270 mg/m(2)/dose, the C(max) and areas under the plasma concentration-time curves of 17-AAG were 5,303 +/- 1,591 ng/mL and 13,656 +/- 4,757 ng/mL h, respectively, similar to the exposure in adults. The mean terminal half-life for 17-AAG was 3.24 +/- 0.80 h. Induction of Hsp72, a surrogate marker for inhibition of Hsp90, was detected at the 270 mg/m(2) dose level.

CONCLUSIONS

Drug exposures consistent with those required for anticancer activity in preclinical models were achieved without DLT. Evidence for drug-induced modulation of Hsp90 systemically was also detected. The recommended phase II dose of 17-AAG is 360 mg/m(2)/d. Non-DMSO-containing formulations may improve acceptance of this drug by children and their families.

Influence of CYP3A5 genotype on the pharmacokinetics and pharmacodynamics of the cytochrome P4503A probes alfentanil and midazolam

The hepatic and first-pass cytochrome P4503A (CYP3A) probe alfentanil (ALF) is also metabolized in vitro by CYP3A5. Human hepatic microsomal ALF metabolism is higher in livers with at least one CYP3A5*1 allele and higher CYP3A5 protein content, compared with CYP3A5*3 homozygotes with little CYP3A5. The influence of CYP3A5 genotype on ALF pharmacokinetics and pharmacodynamics was studied, and compared to midazolam (MDZ), another CYP3A probe. Healthy volunteers (58 men, 41 women) were genotyped for CYP3A5 *1, *3, *6, and *7 alleles. They received intravenous MDZ then ALF, and oral MDZ and ALF the next day. Plasma MDZ and ALF concentrations were determined by mass spectrometry. Dark-adapted pupil diameters were determined coincident with blood sampling. In CYP3A5(*)3/(*)3 (n=62), (*)1/(*)3 (n=28), and (*)1/(*)1 (n=8) genotypes, systemic clearances of ALF were 4.6+/-1.8, 4.8+/-1.7, and 3.9+/-1.7 ml/kg/min and those of MDZ were 7.8+/-2.3, 7.7+/-2.3, and 6.0+/-1.4 ml/kg/min, respectively (not significant), and apparent oral clearances were 11.8+/-7.2, 13.3+/-6.1, and 12.6+/-8.2 ml/kg/min for ALF and 35.2+/-19.0, 36.4+/-15.7, and 29.4+/-9.3 ml/kg/min for MDZ (not significant). Clearances were not different between African Americans (n=25) and Whites (n=68), or between CYP3A5 genotypes within African Americans. ALF pharmacodynamics was not different between CYP3A5 genotypes. There was consistent concordance between ALF and MDZ, in clearances and extraction ratios. Thus, in a relatively large cohort of healthy subjects with constitutive CYP3A activity, CYP3A5 genotype had no effect on the systemic or apparent oral clearances, or pharmacodynamics, of the CYP3A probes ALF and MDZ, despite affecting their hepatic microsomal metabolism.

Increased (R)-methadone plasma concentrations by quetiapine in cytochrome P450s and ABCB1 genotyped patients

Steady-state plasma concentrations of (R)- (ie, the active form), (S)-, and (R,S)-methadone were measured in 14 addict patients in methadone maintenance treatment, before and after introduction of quetiapine, administered at a mean dosage of 138 mg/d (SD, 87 mg/d; median, 125 mg/d; range, 50-300 mg/d) during a mean period of 30 days (SD, 8 days; median, 30 days; range, 20-48 days). Eleven patients were genotyped as being CYP2D6 extensive metabolizers (EMs) and 3 patients as poor metabolizers. Eleven patients had the ABCB1 3435 CT or CC genotypes, and 3 patients had the ABCB1 3435 TT genotype, the latter genotype being associated with lower P-glycoprotein activity. Quetiapine significantly increases (R)-methadone concentration-dose ratios in the whole group [increase for (R)-methadone: mean, +21%; SD, +28%; median, +13%; range, -23% to +85%; P = 0.026], but not for (S)-methadone (mean, +23%; SD, +43%; median, +6%; range, -30% to +115%; P = 0.12) or for (R,S)-methadone (mean, +21%; SD, +34%; median, +9%; range, -21% to +95%; P = 0.064). The mean increases of (R)-methadone concentration-dose ratios were of 7%, 21%, and 30% in the CYP2D6 poor metabolizers, heterozygous EMs, and homozygous EMs, respectively, whereas they were of 3%, 23%, and 33% in the subjects with the ABCB1 3435 TT, CT, and CC genotypes, respectively. Thus, quetiapine increases the plasma concentrations of (R)-methadone, possibly in part by an interaction with CYP2D6 and/or with the P-glycoprotein transporter system. No signs of overmedication caused by increased methadone plasma concentrations were noticed by the staff or reported by the patients.

Genetic polymorphisms of CYP2B6 affect the pharmacokinetics/pharmacodynamics of cyclophosphamide in Japanese cancer patients

OBJECTIVE

To evaluate the effects of genetic polymorphisms of drug metabolizing enzymes on the pharmacokinetics of cyclophosphamide and its active metabolite, 4-hydroxycyclophosphamide, and on the pharmacodynamics.

EXPERIMENTAL DESIGN

One hundred and three Japanese patients with malignant lymphoma or breast cancer treated with cyclophosphamide (500-750 mg/m) participated in this study. The plasma concentrations of cyclophosphamide and 4-hydroxycyclophosphamide were determined by high-performance liquid chromatography, and pharmacokinetic parameters were calculated. The genotypes of CYP2B6, CYP2C19, CYP3A4, CYP3A5, ALDH1A1, GST genes were determined by allele-specific polymerase chain reaction or polymerase chain reaction-restriction-fragment length polymorphism.

RESULTS

A large interindividual difference (54-fold) was observed in the area under the curve ratio of 4-hydroxycyclophosphamide/cyclophosphamide calculated as the metabolic index. We first proved that leukocytopenia and neutropenia were significantly (P<0.01) related to the area under the curve of 4-hydroxycyclophosphamide. We found that the homozygotes of CYP2B6*6 (Q172H and K262R) showed significantly (P<0.05) higher clearance and shorter half-life of cyclophosphamide than heterozygotes and homozygotes of CYP2B6*1. The small sample size, however, limited the impact. On the other hand, it was clearly demonstrated that the patients possessing the single nucleotide polymorphisms of the CYP2B6 gene, g.-2320T>C, g.-750T>C (5'-flanking region), g.15582C>T (intron 3), or g.18492T>C (intron 5), had significantly lower area under the curve ratios of 4-hydroxycyclophosphamide/cyclophosphamide, indicating a decreased cyclophosphamide 4-hydroxylation. Of particular importance was the finding that leukocytopenia was significantly related to the single nucleotide polymorphisms g.-2320T>C, g.-750T>C, and g.18492T>C in CYP2B6 gene, which are highly linked. No relationship was observed between the pharmacokinetics of cyclophosphamide or 4-hydroxycyclophosphamide and genetic polymorphisms of the other enzymes.

CONCLUSIONS

We clarified that the single nucleotide polymorphisms in the promoter region or introns in the CYP2B6 affect the potency of cyclophosphamide activation to 4-hydroxycyclophosphamide. This information would be valuable for predicting adverse reactions and the clinical efficacy of cyclophosphamide.

Molecular mechanism of basal CYP3A4 regulation by hepatocyte nuclear factor 4alpha: evidence for direct regulation in the intestine

Cytochrome P450 3A4 plays an outstanding role in the metabolism of clinically used drugs and shows a marked interindividual variability in expression even in the absence of inducing agents. Thus, regulation of basal expression contributes considerably to variability. The nuclear receptor hepatocyte nuclear factor 4alpha (HNF4alpha) was previously shown to be associated with basal hepatic CYP3A4 expression. As how HNF4alpha regulates basal expression of CYP3A4 still remains elusive, we systematically screened 12.5 kilobase pairs (kb) of the CYP3A4 5' upstream region for activation by the receptor in the human intestinal cell line LS174T. In this study, we newly identified two widely separated regions mediating the activation by HNF4alpha: a far distal region at -9.0 kb and the proximal promoter region at approximately -0.2 kb. By gel shift experiments and transient transfections, we characterized direct repeat (DR) 1-type motifs in both regions as functional HNF4alpha response elements. Cooperation of the two regions was shown to be required for maximal activation by HNF4alpha. The effect of HNF4alpha was antagonized by chicken ovalbumin upstream promoter transcription factor II, which was shown to bind to one of the DR1 motifs. Furthermore, activation of CYP3A4 via the DR1 element in the proximal promoter depends on an additional, yet unknown, factor, which is binding at approximately -189 base pairs. Physiological relevance of this position for activation by HNF4alpha in vivo is suggested by the presence of a binding activity in small intestine similar to that in LS174T cells. In summary, we here have elucidated a molecular mechanism of direct regulation of CYP3A4 by HNF4alpha, which is probably specific for the intestine.

An improved HPLC assay with fluorescence detection for the determination of domperidone and three major metabolites for application to in vitro drug metabolism studies

Domperidone is currently used in Canada and Europe for the treatment of intestinal motility disorders as well as for its antiemetic properties. Recent drug metabolism studies have indicated that domperidone is a substrate of different subtypes of CYP3A family and consequently, the drug requires complete characterization of its metabolism for the identification of major drug-drug interactions. Therefore, the purpose of our studies was to develop a simple, sensitive and rapid HPLC assay for the determination of domperidone and its major metabolites. This assay had to be suitable for the conduct of in vitro drug metabolism study with human liver microsomes. Baseline resolution of internal standard, domperidone and three of its major metabolites was achieved in a run time of less than 15 min using an Ultrasphere ODS column (250 mm x 4.6 mm x 5 microM) and a mobile phase consisting of disodium citrate buffer (10 mM, pH 3.4):methanol:acetonitrile:trietylamine, 54.6:34.7:9.9:0.8 at a flow rate of 1.0 mL/min. Chromatographic separation was executed at room temperature. Quantification was performed by tandem fluorescence (excitation lambda=282 nm and emission lambda=328 nm) and ultraviolet detectors (lambda=254 nm for the quantification of encainide, internal standard). Calibration curves were constructed and showed linearity in the range of 0.1-20 micromol/L and 10-250 micromol/L. Intra- and interday coefficients of variation were less than 8% and 11%, respectively. Mean accuracy was 100.5+/-9.9% and limit of quantification was established at 0.06 micromol/L for domperidone and its metabolites. The assay allows estimation of enzymatic parameters (K(m) and V(max)) of domperidone for the formation of its various metabolites and sensitivity is sufficient for the conduct of inhibition studies with potent CYP3A inhibitors.

A Comparison of the Pharmacokinetics and Pharmacodynamics of Docetaxel between African-American and Caucasian Cancer Patients: CALGB 9871

PURPOSE

Increased clearance of drugs, such as oral cyclosporine, that are CYP3A and/or ABCB1 (P-gp/MDR1) substrates was reported in African-American compared with Caucasian patients. We hypothesized that the pharmacokinetics and pharmacodynamics of docetaxel, an i.v. administered cytotoxic and substrate for CYP3A4, CYP3A5, and ABCB1, would differ between African-American and Caucasian patients.

EXPERIMENTAL DESIGN

We investigated population pharmacokinetics and pharmacodynamics and the pharmacogenetics of CYP3A4, CYP3A5, and ABCB1 in African-American and Caucasian cancer patients who received docetaxel 75 or 100 mg/m(2) as a 1-h i.v. infusion. Plasma docetaxel concentrations were measured by high-performance liquid chromatography. Clinical toxicity and absolute neutrophil count (ANC) were monitored on days 8, 15, and 22 postadministration of docetaxel. Using a limited sampling strategy and nonlinear mixed-effects modeling, each patient's docetaxel clearance was estimated. Genotyping for known polymorphisms in CYP3A4, CYP3A5, and ABCB1 was done.

RESULTS

We enrolled 109 patients: 40 African-Americans (26 males; 14 females), with a median age of 61 years (range, 29-73), and 69 Caucasians (43 males; 26 females), with a median age of 63 years (range, 38-81). There was no difference in the geometric mean docetaxel clearance between African-American patients [40.3 L/h; 95% confidence interval (95% CI), 19.3-84.1] and Caucasian patients (41.8 L/h; 95% CI, 22.0-79.7; P = 0.6). We observed no difference between African-American and Caucasian patients in the percentage decrease in ANC nor were docetaxel pharmacokinetic parameters related to the genotypes studied.

CONCLUSIONS

Docetaxel clearance and its associated myelosuppression were similar in African-American and Caucasian cancer patients.

Minimal effect of MDR1 and CYP3A5 genetic polymorphisms on the pharmacokinetics of indinavir in HIV-infected patients

AIMS

The protease inhibitor indinavir is characterized by an important interindividual pharmacokinetic variability, which results from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A and the multidrug efflux pump P-glycoprotein (P-gp), encoded by MDR1. Using a population pharmacokinetic approach, we investigated the effect of several MDR1 and CYP3A5 polymorphisms on the pharmacokinetic parameters of indinavir in HIV-infected patients.

METHODS

Twenty-eight patients receiving indinavir alone or together with ritonavir were included. Indinavir pharmacokinetics were studied over a 12 h interval. Genetic polymorphisms were assessed by real-time PCR assays and direct sequencing for MDR1 and by PCR-SSCP analysis for CYP3A5.

RESULTS

The pharmacokinetics of indinavir were best described by a one-compartment model with first-order absorption. In the final model, the MDR1 C3435T genotype and ritonavir were identified as statistically significant covariates (P </= 0.001) for the absorption rate constant (95% confidence interval on the difference between CC and CT genotype 0.37, 5.53) and for clearance (95% confidence interval on the difference 5.8, 26.2), respectively. Patients with the CYP3A5*3/*3 genotype receiving indinavir alone had a 31% decrease in the indinavir clearance rate compared with patients carrying the CYP3A5*1/*3 genotype.

CONCLUSIONS

The MDR1 C3435T genotype affects the absorption constant of indinavir suggesting that P-gp may be implicated in its pharmacokinetic variability. Through its inhibition of CYP3A and P-gp, ritonavir could attenuate the pharmacokinetic variability linked to genetic differences, reducing significantly the interindividual variability of indinavir. However, genotyping MDR1 and/or CYP3A5 to optimize protease inhibitor boosted regimens does not seem clinically relevant.

UGT1A1 polymorphism can predict hematologic toxicity in patients treated with irinotecan

PURPOSE

Irinotecan (CPT-11) is approved in metastatic colorectal cancer treatment and can cause severe toxicity. The main purpose of our study was to assess the role of different polymorphisms on the occurrence of hematologic toxicities and disease-free survival in high-risk stage III colon cancer patients receiving 5-fluorouracil (5FU) and CPT-11 adjuvant chemotherapy regimen in a prospective randomized trial.

EXPERIMENTAL DESIGN

Four hundred patients were randomized in a phase III trial comparing LV5FU2 to LV5FU2 + CPT-11. DNA from 184 patients was extracted and genotyped to detect nucleotide polymorphism: 3435C>T for ABCB1, 6986A>G for CYP3A5, UGT1A1*28 and -3156G>A for UGT1A1.

RESULTS

Genotype frequencies were similar in both treatment arms. In the test arm, no significant difference was observed in toxicity or disease-free survival for ABCB1 and CYP3A5 polymorphisms. UGT1A1*28 homozygous patients showed more frequent severe hematologic toxicity (50%) than UGT1A1*1 homozygous patients (16.2%), P = 0.06. Moreover, patients homozygous for the mutant allele of -3156G>A UGT1A1 polymorphism showed more frequent severe hematologic toxicity (50%) than patients homozygous for wild-type allele (12.5%), P = 0.01. This toxicity occurred significantly earlier in homozygous mutant than wild-type homozygous patients (P = 0.043). In a Cox model, the hazard ratio for severe hematologic toxicity is significantly higher for patients with the A/A compared with the G/G genotype [hazard ratio, 8.4; 95% confidence interval, 1.9-37.2; P = 0.005].

CONCLUSIONS

This study supports the clinical utility of identification of UGT1A1 promoter polymorphisms before LV5FU2 + CPT-11 treatment to predict early hematologic toxicity. The -3156G>A polymorphism seems to be a better predictor than the UGT1A1 (TA)(6)TAA>(TA)(7)TAA polymorphism.

Genetic variants of CYP3A5, CYP2D6, SULT1A1, UGT2B15 and tamoxifen response in postmenopausal patients with breast cancer

Introduction

Tamoxifen therapy reduces the risk of recurrence and prolongs the survival of oestrogen-receptor-positive patients with breast cancer. Even if most patients benefit from tamoxifen, many breast tumours either fail to respond or become resistant. Because tamoxifen is extensively metabolised by polymorphic enzymes, one proposed mechanism underlying the resistance is altered metabolism. In the present study we investigated the prognostic and/or predictive value of functional polymorphisms in cytochrome P450 3A5 CYP3A5 (*3), CYP2D6 (*4), sulphotransferase 1A1 (SULT1A1; *2) and UDP-glucuronosyltransferase 2B15 (UGT2B15; *2) in tamoxifen-treated patients with breast cancer.

Methods

In all, 677 tamoxifen-treated postmenopausal patients with breast cancer, of whom 238 were randomised to either 2 or 5 years of tamoxifen, were genotyped by using PCR with restriction fragment length polymorphism or PCR with denaturing high-performance liquid chromatography.

Results

The prognostic evaluation performed in the total population revealed a significantly better disease-free survival in patients homozygous for CYP2D6*4. For CYP3A5, SULT1A1 and UGT2B15 no prognostic significance was observed. In the randomised group we found that for CYP3A5, homozygous carriers of the *3 allele tended to have an increased risk of recurrence when treated for 2 years with tamoxifen, although this was not statistically significant (hazard ratio (HR) = 2.84, 95% confidence interval (CI) = 0.68 to 11.99, P = 0.15). In the group randomised to 5 years' tamoxifen the survival pattern shifted towards a significantly improved recurrence-free survival (RFS) among CYP3A5*3-homozygous patients (HR = 0.20, 95% CI = 0.07 to 0.55, P = 0.002). No reliable differences could be seen between treatment duration and the genotypes of CYP2D6, SULT1A1 or UGT2B15. The significantly improved RFS with prolonged tamoxifen treatment in CYP3A5*3 homozygotes was also seen in a multivariate Cox model (HR = 0.13, CI = 0.02 to 0.86, P = 0.03), whereas no differences could be seen for CYP2D6, SULT1A1 and UGT2B15.

Conclusion

The metabolism of tamoxifen is complex and the mechanisms responsible for the resistance are unlikely to be explained by a single polymorphism; instead it is a combination of several mechanisms. However, the present data suggest that genetic variation in CYP3A5 may predict response to tamoxifen therapy.

CYP3A5 and CYP3A4 but not MDR1 single-nucleotide polymorphisms determine long-term tacrolimus disposition and drug-related nephrotoxicity in renal recipients

The impact of CYP3A and MDR1 gene single-nucleotide polymorphisms on long-term tacrolimus disposition and drug-related toxicity has not been assessed. A study was performed in 95 genotyped recipients by measuring (12 and 4 h) concentration-time curves on day 7; 3, 6 months; 1, 2, 3, 4, and 5 years after transplantation. In contrast to recipients carrying the CYP3A4*1/CYP3A5*1 or CYP3A4*1B/CYP3A5*1 genotypes, dose-corrected tacrolimus exposure almost doubled over 5 years in patients with the CYP3A4*1/ CYP3A5*3 genotype (AUC(0-12 h): from 41.7+/-18.7 to 80+/-39.2 ng h/ml/mg; P<0.05), whereas apparent oral steady-state clearance and dose requirements significantly decreased accordingly. The CYP3A4*1/CYP3A5*1 and CYP3A4*1B/CYP3A5*1 genotypes were significantly more frequently associated with the development of biopsy-proven tacrolimus-related nephrotoxicity than the CYP3A4*1/ CYP3A5*3 genotype (37.5 vs 11.2%; P=0.03 and 42.8 vs 11.2%; P=0.02). The lack of a time-related increase in dose-corrected tacrolimus exposure observed with the CYP3A4*1/CYP3A5*1 and CYP3A4*1B/CYP3A5*1 genotypes is associated with tacrolimus-related nephrotoxicity, possibly as a result of higher concentrations of toxic metabolites.

Reduction of site-specific CYP3A-mediated metabolism for dual angiotensin and endothelin receptor antagonists in various in vitro systems and in cynomolgus monkeys

2-{Butyryl-[2'-(4,5-dimethyl-isoxazol-3-ylsulfamoyl)-biphenyl-4-ylmethyl]-amino}-N-isopropyl-3-methyl-butyramide (BMS-1) is a potent dual acting angiotensin-1 and endothelin-A receptor antagonist. The compound was subject to rapid metabolic clearance in monkey and human liver microsomes and exhibited low systemic exposure and marked interanimal variability in cynomolgus monkeys after p.o. administration. The variability pattern was identical to that of midazolam given p.o. in the same monkeys, as measured by area under the curve and Cmax values, suggesting that CYP3A-mediated metabolism might play a role in the rapid clearance and observed interanimal variability. Subsequent in vitro metabolism studies using human liver microsomes and cDNA-expressed human cytochrome P450 (P450) enzymes revealed that BMS-1 was a CYP3A4 substrate and was not metabolized by other human P450 enzymes. Mass spectral and NMR analyses of key metabolites led to the identification of the dimethyl isoxazole group as a major metabolic soft spot for BMS-1. Replacement of the 4-methyl group on the isoxazole ring with halogens not only improved overall metabolic stability but also decreased CYP3A-mediated hydroxylation of the isoxazole 5-methyl group. As exemplified by 2-{butyryl-[2'-(4-fluoro-5-methyl-isoxazol-3-ylsulfamoyl)-biphenyl-4-ylmethyl]-amino}-N-isopropyl-3-methyl-butyramide (BMS-3), a fluorinated analog of BMS-1, the structural modification resulted in an increase in the systemic exposure relative to previous analogs and a dramatic reduction in interanimal variability in the monkeys after p.o. administration. In addition, BMS-3 could be metabolized by both CYP2C9 and CYP3A4, thus avoiding the reliance on a single P450 enzyme for metabolic clearance. Integration of results obtained from in vitro metabolism studies and in vivo pharmacokinetic evaluations enabled the modulation of site-specific CYP3A-mediated metabolism, yielding analogs with improved overall metabolic profiles.

Sequential metabolism is responsible for diltiazem-induced time-dependent loss of CYP3A

Kinetic parameters (k(inact) and K(I)) obtained in microsomes are often used to predict time-dependent inactivation. We previously reported that microsomal inactivation kinetic parameters of diltiazem underpredicted CYP3A inactivation in hepatocytes. In this study, we evaluated the contributions of inactivation and reversible inhibition of CYP3A by diltiazem and its N-desmethyl (MA) and N,N-didesmethyl (MD) metabolites. In human liver microsomes, MA was a more potent time-dependent inactivator of CYP3A than its parent drug, with apparent k(inact) approximately 4-fold higher than that of diltiazem at a microsomal protein concentration of 0.2 mg/ml. MD did not inactivate CYP3A. Inactivation of CYP3A by diltiazem was dependent on microsomal protein concentration (25, 36, and 41% decrease in CYP3A activity at 0.2, 0.4, and 0.8 mg/ml microsomal protein, respectively, incubated with 10 microM diltiazem over 20 min), whereas inactivation by MA did not seem to be protein concentration-dependent. MA and MD were reversible inhibitors of CYP3A with competitive Ki values of 2.7 and 0.2 microM, respectively. In cryopreserved hepatocytes incubated with diltiazem, time-dependent loss of CYP3A was accompanied by increased formation of MA and MD, with the MA level similar to its K(I) at higher diltiazem concentrations. In addition, the metabolites appeared to be accumulated inside the cells. In summary, time-dependent CYP3A inactivation by MA seems to be the major contributor responsible for the loss of CYP3A in human liver microsomes and human hepatocytes incubated with diltiazem. These findings suggest that prediction of CYP3A loss based solely on microsomal inactivation parameters of parent drug may be inadequate.

Effect of CYP3A5 expression on vincristine metabolism with human liver microsomes

Vincristine is preferentially metabolized to a secondary amine, M1, by CYP3A5 with a 9- to 14-fold higher intrinsic clearance than CYP3A4 using cDNA-expressed enzymes. The genetically polymorphic expression of CYP3A5 may contribute to interindividual variability in vincristine efficacy and toxicity. The current study quantifies the contribution of cytochromes P450 (P450s), including CYP3A4 and CYP3A5, to vincristine metabolism with a bank of human liver microsomes (HLMs). M1 was the major metabolite formed with HLMs, and selective chemical inhibition of P450s confirmed that CYP3A was the major metabolizing subfamily. The liver tissues were genotyped for low expression alleles, CYP3A5*3,*6, and *7, and the HLMs were phenotyped for CYP3A4 and CYP3A5 expression by Western blot. Testosterone 6beta-hydroxylation and itraconazole hydroxylation were used to quantify CYP3A4 activity in the HLMs. For each CYP3A5 high expresser (n=10), the rate of M1 formation from vincristine due to CYP3A5 was quantified by subtracting the CYP3A4 contribution as determined by linear regression with CYP3A5*3/*3 samples. For CYP3A5 high expressers, the contribution of CYP3A5 to the metabolism of vincristine was 54 to 95% of the total activity, and the rate of M1 formation mediated by CYP3A5 correlated with CYP3A5 protein content (r2=0.95). Selective inhibition of CYP3A4 demonstrated that the M1 formation rate with CYP3A5 high expressers was differentially inhibited based on CYP3A4 activity. Using median values, the estimated hepatic clearances were 5-fold higher for CYP3A5 high expressers than low expressers. We conclude that polymorphic expression of CYP3A5 may be a major determinant in the P450-mediated clearance of vincristine.

Influence of the CYP3A5 genotype on tacrolimus pharmacokinetics and pharmacodynamics in young kidney transplant recipients

CYP3A enzyme plays a pivotal role in TAC metabolism. The aim of this study was to analyze retrospectively the influence of CYP3A5 gene polymorphism on TAC pharmacokinetics and pharmacodynamics in 30 teenage kidney transplant recipients. TAC dose, trough blood levels, apparent volume of distribution, as well as blood pressure and antihypertensive therapy obtained at different post-transplant periods, were correlated with the corresponding genotype. Despite a therapeutic monitoring strategy, heterozygotes (CYP3A5*1/*3) displayed a lower TAC blood concentration compared with homozygotes (CYP3A5*3/*3). Therefore, a two-fold increase of the daily TAC dose was required in the heterozygotes to reach the desired therapeutic target level. A significant group by time interaction effect was present for both variables (repeated measures ANOVA: p = 0.002) meaning a significant different pharmacokinetic response in these two cohorts. Mean blood pressure was also elevated in CYP3A5*1/*3 recipients despite similar antihypertensive treatment. This was parallel with an elevated apparent volume of distribution of TAC in this group. Thus, the allele-effect was correlated with one of the most common TAC side-effects suggesting a possible influence of CYP3A5 polymorphism on TAC pharmacodynamics. The authors concluded that a pre-emptive CYP3A5 pharmacogenetic screening could contribute to better individualization of TAC therapy.

Some mutations of exon-7 in cytochrome P450 gene 3A4 and their effect on 6beta-hydroxylation of cortisol

Analysis of variants of exon 7 sequences in cytochrome P450 gene 3A4 in a sample of Caucasoid persons was carried out. The effect of these variants on activity of CYP3A was assessed by the level of cortisol 6beta-hydroxylation. Alleles CYP3A4*5 and *17 were not detected: probably, these mutations are rare and consequently they have little effect on the character of polymorphic distribution of CYP3A4 activity in this population. The incidence of CYP3A4*2 was 5.26%. The 6betaOH-cortisol/cortisol ratio in an individual with CYP3A4*2/*2 genotype was 7.408, which corresponded to "slow metabolizer" phenotype in this sample.

Cytochrome P450 3A5 genotype is associated with verapamil response in healthy subjects

We hypothesized that CYP3A5 genotype contributes to the interindividual variability in verapamil response. Healthy subjects (n=26) with predetermined CYP3A5 genotypes were categorized as expressers (at least one CYP3A5(*)1 allele) and nonexpressers (subjects without a CYP3A5(*)1 allele). Verapamil pharmacokinetics and pharmacodynamics were determined after 7 days of dosing with 240 mg daily. There was a significantly higher oral clearance of R-verapamil (165.1+/-86.4 versus 91.2+/-36.5 l/h; P=0.009) and S-verapamil (919.4+/-517.4 versus 460.2+/-239.7 l/h; P=0.01) in CYP3A5 expressers compared to nonexpressers. Consequently, CYP3A5 expressers had significantly less PR-interval prolongation (19.5+/-12.3 versus 44.0+/-19.4 ms; P=0.0004), and had higher diastolic blood pressure (69.2+/-7.5 versus 61.6+/-5.1 mm Hg; P=0.036) than CYP3A5 nonexpressers after 7 days dosing with verapamil. CYP3A5 expressers display a greater steady-state oral clearance of verapamil and may therefore experience diminished pharmacological effect of verapamil due to a greater steady state oral clearance.

Expression of Cytochromes P450 3A and P-Glycoprotein in Human Large Intestinse in Paired Tumour and Normal Samples

Our objective was to investigate the expression of different cytochromes P450 3A (CYP3A4, CYP3A5, and CYP3A7) and P-glycoprotein (ABCB1) genes along the human large intestine in paired tumour and normal samples. Real-time reverse transcriptase-polymerase chain reaction was used to measure CYP3A4-, CYP3A5-, CYP3A7- and ABCB1-specific mRNA expression, and Western blot analysis was used to measure membrane protein levels of CYP3A4/7, CYP3A5 and P-glycoprotein. Levels of mRNA and membrane protein fractions in the large intestine were compared with those of normal human liver. The mRNA expressions of CYP3A4, CYP3A5, CYP3A7 and ABCB1 in the large intestine were found to be highly variable, but overall the levels were significantly lower than those measured in liver (P < 0.0001, P < 0.001, P < 0.0001 and P < 0.01, respectively). At the membrane protein level, CYP3A4/7 was detected in all large intestine samples examined and the levels were substantially higher than those of the liver (P < 0.01). Although expression of CYP3A5 was detected in all large intestine samples, in most the levels were too low to allow quantification. P-glycoprotein was readily detected at levels slightly higher than those of liver (P < 0.05). Comparison between paired samples of normal and tumour in large intestine showed no significant differences in either the mRNA or membrane protein levels of these genes. In conclusion, this work suggests a potential role of the large intestine in the absorption and metabolism of xenobiotics and nutrients and no difference in the CYP3A and P-glycoprotein membrane protein fractions and mRNA expression between normal and tumour tissues.

The inactivation of cytochrome P450 3A5 by 17alpha-ethynylestradiol is cytochrome b5-dependent: metabolic activation of the ethynyl moiety leads to the formation of glutathione conjugates, a heme adduct, and covalent binding to the apoprotein

17Alpha-ethynylestradiol (EE) inactivates cytochrome P450 3A5 (3A5) in the reconstituted system in a mechanism-based manner. The inactivation is dependent on NADPH, and it is irreversible. The inactivation of 3A5 by EE is also dependent on cytochrome b5 (b5). The values for the K(I) and k(inact) of the 7-benzyloxy-4-(trifluoromethyl)coumarin O-debenzylation activity of 3A5 are 26 microM and 0.06 min(-1), respectively. Incubation of 3A5 with EE resulted in a 62% loss of catalytic activity, 60% loss in the reduced CO difference spectrum, and 40% decrease in native heme with the formation of a heme adduct. The partition ratio was approximately 25, and the stoichiometry of binding was approximately 0.3 mol of EE metabolite bound/mol of P450 inactivated. Four major metabolites were formed during the metabolism of EE by 3A5. SDS-polyacrylamide gel electrophoresis analysis demonstrated that [3H]EE was irreversibly bound to 3A5 apoprotein. Liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS) revealed that two glutathione (GSH) conjugates with m/z values of 620 were formed only in the presence of b5. These two conjugates are formed from the reaction of GSH with the ethynyl group with the oxygen being inserted into either the internal or terminal carbon. A heme adduct with the ion at m/z 927 and two dipyrrole adducts with ions at m/z 579 were detected by LC-MS/MS analysis. In conclusion, 3A5 can activate EE to a 17alpha-oxirene-related reactive species that can then partition the oxygen between the internal and terminal carbons of the ethynyl group to form heme and apoprotein adducts, resulting in the inactivation of P450 3A5.

Dynamically simulating the interaction of midazolam and the CYP3A4 inhibitor itraconazole using individual coupled whole-body physiologically-based pharmacokinetic (WB-PBPK) models

Background

Drug-drug interactions resulting from the inhibition of an enzymatic process can have serious implications for clinical drug therapy. Quantification of the drugs internal exposure increase upon administration with an inhibitor requires understanding to avoid the drug reaching toxic thresholds. In this study, we aim to predict the effect of the CYP3A4 inhibitors, itraconazole (ITZ) and its primary metabolite, hydroxyitraconazole (OH-ITZ) on the pharmacokinetics of the anesthetic, midazolam (MDZ) and its metabolites, 1' hydroxymidazolam (1OH-MDZ) and 1' hydroxymidazolam glucuronide (1OH-MDZ-Glu) using mechanistic whole body physiologically-based pharmacokinetic simulation models. The model is build on MDZ, 1OH-MDZ and 1OH-MDZ-Glu plasma concentration time data experimentally determined in 19 CYP3A5 genotyped adult male individuals, who received MDZ intravenously in a basal state. The model is then used to predict MDZ, 1OH-MDZ and 1OH-MDZ-Glu concentrations in an CYP3A-inhibited state following ITZ administration.

Results

For the basal state model, three linked WB-PBPK models (MDZ, 1OH-MDZ, 1OH-MDZ-Glu) for each individual were elimination optimized that resulted in MDZ and metabolite plasma concentration time curves that matched individual observed clinical data. In vivo K_m and V_max optimized values for MDZ hydroxylation were similar to literature based in vitro measures. With the addition of the ITZ/OH-ITZ model to each individual coupled MDZ + metabolite model, the plasma concentration time curves were predicted to greatly increase the exposure of MDZ as well as to both increase exposure and significantly alter the plasma concentration time curves of the MDZ metabolites in comparison to the basal state curves. As compared to the observed clinical data, the inhibited state curves were generally well described although the simulated concentrations tended to exceed the experimental data between approximately 6 to 12 hours following MDZ administration. This deviations appeared to be greater in the CYP3A5 *1/*1 and CYP3A5 *1/*3 group than in the CYP3A5 *3/*3 group and was potentially the result of assuming that ITZ/OH-ITZ inhibits both CYP3A4 and CYP3A5, whereas in vitro inhibition is due to CYP3A4.

Conclusion

This study represents the first attempt to dynamically simulate metabolic enzymatic drug-drug interactions via coupled WB-PBPK models. The workflow described herein, basal state optimization followed by inhibition prediction, is novel and will provide a basis for the development of other inhibitor models that can be used to guide, interpret, and potentially replace clinical drug-drug interaction trials.

CYP3A5 and ABCB1 genes influence blood pressure and response to treatment, and their effect is modified by salt

The permeability-glycoprotein efflux-transporter encoded by the multidrug resistance 1 (ABCB1) gene and the cytochromes P450 3A4/5 encoded by the CYP3A4/5 genes are known to interact in the transport and metabolism of many drugs. Recent data have shown that the CYP3A5 genotypes influence blood pressure and that permeability-glycoprotein activity might influence the activity of the renin-angiotensin system. Hence, these 2 genes may contribute to blood pressure regulation in humans. We analyzed the association of variants of the ABCB1 and CYP3A5 genes with ambulatory blood pressure, plasma renin activity, plasma aldosterone, endogenous lithium clearance, and blood pressure response to treatment in 72 families (373 individuals; 55% women; mean age: 46 years) of East African descent. The ABCB1 and CYP3A5 genes interact with urinary sodium excretion in their effect on ambulatory blood pressure (daytime systolic: P=0.05; nighttime systolic and diastolic: P<0.01), suggesting a gene-gene-environment interaction. The combined action of these genes is also associated with postproximal tubular sodium reabsorption, plasma renin activity, plasma aldosterone, and with an altered blood pressure response to the angiotensin-converting enzyme inhibitor lisinopril (P<0.05). This is the first reported association of the ABCB1 gene with blood pressure in humans and demonstration that genes encoding for proteins metabolizing and transporting drugs and endogenous substrates contribute to blood pressure regulation.

Effects of genetic polymorphisms on the pharmacokinetics of calcineurin inhibitors

PURPOSE

The effects of genetic polymorphisms on the pharmacokinetics of calcineurin inhibitors were examined.

SUMMARY

The bioavailability and metabolism of cyclosporine and tacrolimus are primarily controlled by efflux pumps and members of the cytochrome P-450 (CYP) isoenzyme system found in the liver and gastrointestinal tract. The number and severity of adverse effects from these drugs are related to the overall exposure, measured by length of therapy and blood drug concentration. One contributing factor to the inconsistent pharmacokinetics of calcineurin inhibitors may be variable expression of functional CYP3A4, CYP3A5, and P-glycoprotein (PGP) efflux pumps, which may be the result of single-nucleotide polymorphisms found on the genes encoding for CYP3A4, CYP3A5, and PGP. CYP3A5*3 and CYP3A5*6 are the most common polymorphisms of CYP3A5. Using genetic markers to adjust initial doses of cyclosporine or tacrolimus may prove difficult, considering the variety of polymorphism known to affect CYP3A4, CYP3A5, and the multidrug resistance-1 (MDR1) gene (the gene that codes for PGP). Studies have found that carriers of CYP3A5*1 consistently have higher clearance rates of tacrolimus than do CYP3A5*3 homozygotes. The influences of CYP3A5 alleles on cyclosporine metabolism and the MDR1 C3435T polymorphism on tacrolimus metabolism remain controversial.

CONCLUSION

For renal transplant recipients receiving tacrolimus as an immunosuppressant, practitioners can expect CYP3A5*1 carriers to have a tacrolimus clearance 25-45% greater than that of CYP3A5*3 homozygotes, with proportional dosing needs to maintain adequate immunosuppression. Since inadequate immunosuppression is linked to graft rejection, evaluation of CYP3A5 polymorphisms may be helpful in determining an appropriate starting dosage, rapidly achieving adequate immunosuppression, and ultimately improving the outcome of renal transplantation.

Toward individualized treatment: prediction of anticancer drug disposition and toxicity with pharmacogenetics

A great deal of effort has been spent in defining the pharmacokinetics and pharmacodynamics of investigational and registered anticancer agents. Often, there is a marked variability in drug handling between individual patients, which contributes to variability in the pharmacodynamic effects of a given dose of a drug. A combination of physiological variables, genetic characteristics (pharmacogenetics) and environmental factors is known to alter the relationship between the absolute dose and the concentration-time profile in plasma. A variety of strategies are now being evaluated in patients with cancer to improve the therapeutic index of anticancer drugs by implementation of pharmacogenetic imprinting through genotyping or phenotyping individual patients. The efforts have mainly focused on variants in genes encoding the drug-metabolizing enzymes thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, members of the cytochrome P450 family, including the CYP2B, 2C, 2D and 3A subfamilies, members of the UDP glucuronosyltransferase family, as well as the ATP-binding cassette transporters ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein). Several of these genotyping strategies have been shown to have substantial impact on therapeutic outcome and should eventually lead to improved anticancer chemotherapy.

Effect of polymorphic CYP3A5 genotype on the single-dose simvastatin pharmacokinetics in healthy subjects

Simvastatin, a cholesterol-lowering agent, is mainly metabolized by CYP3A4/5. The objective of this study was to investigate the effect of CYP3A5*3 genotype on the pharmacokinetics of simvastatin in humans. Twenty-two men with CYP3A5*1/*1 (n = 4), CYP3A5*1/*3 (n = 8), or CYP3A5*3/*3 (n = 10) genotypes were enrolled. Each subject ingested a 20-mg dose of simvastatin, and plasma simvastatin concentrations were measured for 12 hours after dosing. The mean (+/-SD) area under the plasma concentration-time curve for simvastatin in the CYP3A5*1/*1 carriers (4.94 +/- 2.25 ng x h/mL) was significantly lower than CYP3A5*3/*3 carriers (16.35 +/- 6.37 ng x h/mL; P = .013, Bonferroni test). The mean (+/-SD) oral clearance was also significantly different between CYP3A5*1/*1 carriers (4.80 +/- 2.35 L/h) and CYP3A5*3/*3 carriers (1.35 +/- 0.61 L/h; P < .05, Dunn's test). However, other pharmacokinetic parameters including peak plasma concentrations and half-life did not show any difference between genotype groups. These findings suggest that the polymorphic CYP3A5 gene affects the disposition of simvastatin and provides a plausible explanation for interindividual variability of simvastatin disposition.