Drug-metabolizing enzymes: Evidence for clinical utility of pharmacogenomic tests

Genotyping genetic variants of CYP2C19 for precision antiplatelet dosing: state of the art and future perspectives

INTRODUCTION

Clopidogrel is the only antiplatelet agent whose activity is significantly affected by CYP2C19 polymorphism.

AREAS COVERED

This review has summarized the available evidence on the clinically significant association between CYP2C19 polymorphism and clopidogrel-based therapy; reviewed the current recommendations for clinical use of CYP2C19 genotype test results in patients on clopidogrel treatment; and discussed possible pitfalls of routine application, and future perspectives of antiplatelets pharmacogenetics.

EXPERT OPINION

The available body of evidence, reflected in several meta-analyses and high-quality clinical practice guidelines, shows that the presence of CYP2C19 LOF alleles, especially CYP2C19*2, correlates with impaired activation of clopidogrel and variable platelet inhibition, followed by minimal or no antiplatelet effect, and higher risk of treatment failure. In combination with other known risk factors, CYP2C19 genetic testing could be very valuable in predicting low clopidogrel efficacy. At the same time, it could be very successful in selecting patients who will most probably benefit from the clopidogrel-based therapy, thus decreasing the pool of those who might need more expensive and otherwise riskier antiplatelet alternatives.

Pharmacogenetic profiling and individualised therapy in the treatment of degenerative spinal conditions

Patients presenting with degenerative spinal changes are often poor surgical candidates due to associated co-morbidities, frailty, or sarcopenia. Additionally, surgeries of a degenerative spine can prove difficult due to the distortion of normal surgical anatomy. Therefore, many patients are managed conservatively with a variety of modalities, including over-the-counter and prescription medications. Nevertheless, several patients do not experience adequate relief from pain with analgesic medications, precipitating multiple hospital visits, and usage of resources. As a result, back pain is regarded as a major economic burden, with total costs of associated treatment exceeding $100 billion annually. Pharmacogenetics is a relatively novel method of evaluating an individual's response to analgesic medications, through analysis of germline polymorphisms. It entails obtaining a genetic sample, often via buccal swab or peripheral blood sample, and genetic analysis achieved through either polymerase chain reaction +/- Sanger sequencing, microassays, restriction length fragment polymorphism analysis, or genetic library preparation and next generation sequencing. The potential efficacy of pharmacogenetic analysis has been highlighted across several specialities to date. However, a paucity of evidence exists regarding spine surgery populations. Nevertheless, regular prospective pharmacogenetic analysis may ultimately prove beneficial when concerning degenerative spinal cohorts due to aforementioned surgical and economic considerations. The purpose of this narrative review is to outline how metaboliser profile variants affect the pharmacokinetics of specific analgesia used to treat back pain, and to discuss the current potential and limitations of employing regular pharmacogenetic analysis for spine surgery populations with degenerative conditions.

CYP2D6 Genotyping and Antipsychotic-Associated Extrapyramidal Adverse Effects in a Randomized Trial of Aripiprazole Versus Quetiapine Extended Release in Children and Adolescents, Aged 12-17 Years, With First Episode Psychosis

PURPOSE/BACKGROUND

The aim of this study was to examine the association between genetically predicted CYP2D6 phenotypes and extrapyramidal symptoms (EPSs).

METHODS/PROCEDURES

Data from the Tolerability and Efficacy of Antipsychotics trial of adolescents with first-episode psychosis randomized to aripiprazole versus quetiapine extended release were studied. Extrapyramidal symptom assessments included the Simpson-Angus Scale and the Barnes Akathisia Rating Scale. Patients were CYP2D6 genotyped. Plasma concentrations of antipsychotics and antidepressants were analyzed.

FINDINGS/RESULTS

One hundred thirteen youths (age, 12-17 years; males, 30%; antipsychotic naive, 51%) were enrolled. Poor metabolizers had a significantly higher dose-adjusted aripiprazole plasma concentration (±SD) compared with normal metabolizers at week 4 (24.30 ± 6.40 ng/mL per milligram vs 14.85 ± 6.15 ng/mL per milligram; P = 0.019), but not at week 12 (22.15 ± 11.04 ng/mL per milligram vs 14.32 ± 4.52 ng/mL per milligram; P = 0.067). This association was not found in the quetiapine extended release group. No association between CYP2D6 genotype groups and global Barnes Akathisia Rating Scale score or Simpson-Angus Scale score was found in any of the treatment arms.

IMPLICATIONS/CONCLUSIONS

Our results do not support routine use of CYP2D6 testing as a predictor of drug-induced parkinsonism or akathisia risk in clinical settings. Further studies with larger samples of CYP2D6 poor metabolizers are needed.

Influence of CYP2D6 gene polymorphisms on the pharmacokinetics of aripiprazole in healthy Chinese subjects

Background: Pharmacogenetics study was added into 2 bioequivalence trials of aripiprazole. The correlation between CYP2D6 polymorphisms and aripiprazole pharmacokinetics (PK) was analyzed. Materials & methods: A total of 140 subjects were included. A total of 26 CYP2D6 gene alleles were detected. The plasma concentration of aripiprazole was measured by liquid chromatography-tandem mass spectrometry. SPSS Statistics 21 was used to analyze the correlation between CYP2D6 polymorphisms and aripiprazole PK parameters. Results: All of the four PK parameters were significantly influenced by CYP2D6 rs1058164 and rs28371699. t_1/2 and area under the concentration-time curve exhibited significant difference between CYP2D6 extensive metabolizers and intermediate metabolizers. Conclusion: Aripiprazole PK was greatly influenced by CYP2D6. Attention should be paid to the possible dose adjustment for CYP2D6 intermediate metabolizer population when the drug is used in Chinese patients.

CYP2C19*2 and Other Allelic Variants Affecting Platelet Response to Clopidogrel Tested by Thrombelastography in Patients with Acute Coronary Syndrome

Background:

To investigate the contributions of CYP2C19 polymorphisms to the various clopidogrel responses tested by thrombelastography (TEG) in Chinese patients with the acute coronary syndrome (ACS).

Methods:

Patients were screened prospectively with ACS diagnose and were treated with clopidogrel and aspirin dual antiplatelet therapy. CYP2C19 loss of function (LOF) and gain of function (GOF) genotype, adenosine 5′-diphosphate (ADP)-channel platelet inhibition rate (PIR) tested by TEG and the occurrence of 3-month major adverse cardiovascular events and ischemic events were assessed in 116 patients.

Results:

High on-treatment platelet reactivity (HTPR) prevalence defined by PIR <30% by TEG in ADP-channel was 32.76% (38/116). With respect to the normal wild type, CYP2C19*2, and *3 LOF alleles, and *17 GOF alleles, patients were classified into three metabolism phenotypes: 41.38% were extensive metabolizers (EMs), 56.90% were intermediate metabolizers (IMs), and 1.72% were poor metabolizers (PMs). Of the enrolled patients, 31.47%, 5.17%, and 0.43%, respectively, were carriers of *2, *3, and *17 alleles. The HTPR incidence differed significantly according to CYP2C19 genotypes, accounting for 18.75%, 41.54%, and 100.00% in EMs, IMs, and PMs, respectively. Eighteen (17.24%) ischemic events occurred during the 3-month follow-up, and there was a significant difference in ischemic events between HTPR group and nonhigh on-treatment platelet reactivity group.

Conclusions:

Genetic CYP2C19 polymorphisms are relative to the inferior, the antiplatelet activity after clopidogrel admission and may increase the incidence of ischemic events in patients with ACS.

Disclosure of individual pharmacogenomic results in research projects: when and what kind of information to return to research participants

In the growing field of genomics, the utility of returning certain research results to participants has become a highly debated issue. Existing guidelines are not explicit as to the kind of genomic information that should be returned to research participants. Moreover, very few current recommendations and articles in the literature address the return of pharmacogenomic results. Although genetics and pharmacogenomics have many similarities, the circumstances in which disclosure could have a benefit for the participants are different. This review aims to describe the conditions in which disclosure of pharmacogenomic results is appropriate.

Cytochrome P450-mediated changes in oxycodone pharmacokinetics/pharmacodynamics and their clinical implications

In recent years the use of the opioid oxycodone has increased markedly and replacing morphine as the first-line choice of opioid in several countries. There are formulations for oral immediate, oral extended release and intravenous use. The bioavailability is higher than for morphine and less variable. Oxycodone is primarily metabolized in the liver by the cytochrome P450 (CYP) enzymes with CYP3A as the major metabolic pathway and CYP2D6 as the minor metabolic pathway to noroxycodone, oxymorphone and noroxymorphone. Oxycodone exerts its analgesic effect via the µ-opioid receptor. The metabolism of CYP2D6 substrates varies to a large degree between individuals as a result of allele functionality. Poor metabolizers (PM) have two non-functional alleles, extensive metabolizers (EM) are homozygous with two functional alleles or heterozygous with one functional allele and ultrarapid metabolizers (UM) have more than two functional alleles. There are pronounced interethnic differences in the allele distribution. On the basis of studies performed thus far, oxycodone concentrations in comparison with EM are similar in PM and reduced in UM. The pharmacokinetics in UM are insufficiently investigated. Simultaneous inhibition of both CYP3A and CYP2D6 results in increased oxycodone concentrations and such a combination should be avoided. A similar effect is to be expected with use of a CYP3A inhibitor in CYP2D6 PM. Concomitant use of enzyme inducers such as rifampicin, St John's wort and carbamazepine should be avoided because of the risk of subtherapeutic concentrations of oxycodone. When the dosage of morphine may result in unpredictable bioavailability, like in patients with severe hepatic cirrhosis, oxycodone might be beneficial because it has higher and less variability in bioavailability between patients than morphine.

Clopidogrel metaboliser status based on point-of-care CYP2C19 genetic testing in patients with coronary artery disease

We compared results obtained with the Nanosphere Verigene® System, a novel point-of-care (POC) genetic test capable of analysing 11 CYP2C19 variants within 3 hours, to an established, validated genotyping method (Affymetrix™ DMET+; reference assay) for identifying extensive and reduced metabolisers of clopidogrel. Based on genotyping, patients (N=82) with stable coronary artery disease on clopidogrel 75 mg daily were defined as extensive metabolisers (*1/*1, *1/*17, *17/*17), reduced metabolisers (*1/*2, *1/*8, *2/*2, *2/*3), or of indeterminate metaboliser status (*2/*17). Pharmacokinetic exposure to clopidogrel's active metabolite and pharmacodynamic measures with P2Y12 reaction units (PRU) (VerifyNow®P2Y12 assay) and VASP PRI (PRI) were also assessed. There was a 99.9% overall concordance of marker-level data between the Nanosphere Verigene and DMET+ systems in identifying the CYP2C19 variants and 100% agreement in classifying the patients as extensive (n=59) or reduced metabolisers (n=15). Extensive metabolisers had significantly higher active metabolite exposure than reduced metabolisers (LS means 12.6 ng*h/ml vs 7.7 ng*h/ml; p<0.001). Extensive metabolisers also had lower PRU (LS means 158 vs 212; p=0.003) and VASP PRI (LS means 48% vs 63%, p=0.01) compared to reduced metabolisers. Rates of high on-treatment platelet reactivity were higher in reduced metabolisers compared to extensive metabolisers (VASP PRI ≥ 50%: 79% vs 47%; PRU >235: 33% vs 16%). The Nanosphere Verigene CBS system identified 11 CYP2C19 alleles in less than 3 hours with a high degree of accuracy when compared to a conventional method, and was further validated against pharmacokinetic and pharmacodynamic phenotypes.

Nifedipine pharmacokinetics are influenced by CYP3A5 genotype when used as a preterm labor tocolytic

OBJECTIVE

To characterize the pharmacokinetics and pharmacogenetics of nifedipine in pregnancy.

STUDY DESIGN

Pregnant women receiving oral nifedipine underwent steady-state pharmacokinetic testing over one dosing interval. DNA was obtained and genotyped for cytochrome P450 (CYP) 3A5 and CYP3A4*1B. Nifedipine and oxidized nifedipine concentrations were measured in plasma, and pharmacokinetic parameters were compared between those women who expressed a CYP3A5*1 allele and those who expressed only variant CYP3A5 alleles (*3,*6, or *7).

RESULTS

Fourteen women had complete data to analyze. Four women (29%) expressed variant CYP3A5; three of these women were also CYP3A4*1B allele carriers. The mean half-life of nifedipine was 1.68 ± 1.56 hours. The area under the curve from 0 to 6 hours for the women receiving nifedipine every 6 hours was 207 ± 138 µg·h /L. Oral clearance was different between high expressers and low expressers (232.0 ± 37.8 µg/mL versus 85.6 ± 45.0 µg/mL, respectively; p = 0.007).

CONCLUSION

CYP3A5 genotype influences the oral clearance of nifedipine in pregnant women.

Establishment of a CYP2C19 genotyping assay for clinical use

Conversion of clopidogrel (Plavix) to its active metabolite is catalyzed largely by the P450 enzyme 2C19 (CYP2C19). Numerous allelic variants of CYP2C19 exist. The *1 allele is considered wild type, whereas the *2 and *3 alleles have no in vivo enzymatic activity. Conversely, the *17 allele has increased expression, resulting in increased clopidogrel activation. Poor metabolizers (*2/*2 and *2/*3 genotypes) experience higher rates of therapeutic failure. For this reason, we have validated a CYP2C19 genotyping assay for the *1, *2, *3, and *17 alleles. Genomic DNA extracted from 30 deidentified EDTA whole-blood samples from patients was analyzed at 2 independent facilities using specific TaqMan realtime polymerase chain reaction primers and probes. Concordant genotypes were generated on all samples tested. Of the 30 samples, 15 were CYP2C19*1/*1, 8 were CYP2C19*1/*17, 5 were CYP2C19*1/*2, and 2 were CYP2C19*2/*17. There were no CYP2C19*3 alleles or *2/*2 homozygous genotypes detected. This CYP2C19 genotyping assay is appropriate for clinical testing, demonstrating excellent interlaboratory concordance, enabling the selection of the most effective clopidogrel treatment regimen for patients undergoing percutaneous coronary intervention.

Novel drug metabolism indices for pharmacogenetic functional status based on combinatory genotyping of CYP2C9, CYP2C19 and CYP2D6 genes

AIMS

We aim to demonstrate clinical relevance and utility of four novel drug-metabolism indices derived from a combinatory (multigene) approach to CYP2C9, CYP2C19 and CYP2D6 allele scoring. Each index considers all three genes as complementary components of a liver enzyme drug metabolism system and uniquely benchmarks innate hepatic drug metabolism reserve or alteration through CYP450 combinatory genotype scores.

METHODS

A total of 1199 psychiatric referrals were genotyped for polymorphisms in the CYP2C9, CYP2C19 and CYP2D6 gene loci and were scored on each of the four indices. The data were used to create distributions and rankings of innate drug metabolism capacity to which individuals can be compared. Drug-specific indices are a combination of the drug metabolism indices with substrate-specific coefficients.

RESULTS

The combinatory drug metabolism indices proved useful in positioning individuals relative to a population with regard to innate drug metabolism capacity prior to pharmacotherapy. Drug-specific indices generate pharmacogenetic guidance of immediate clinical relevance, and can be further modified to incorporate covariates in particular clinical cases.

CONCLUSIONS

We believe that this combinatory approach represents an improvement over the current gene-by-gene reporting by providing greater scope while still allowing for the resolution of a single-gene index when needed. This method will result in novel clinical and research applications, facilitating the translation from pharmacogenomics to personalized medicine, particularly in psychiatry where many drugs are metabolized or activated by multiple CYP450 isoenzymes.

A comparison of the acid-inhibitory effects of esomeprazole and rabeprazole in relation to pharmacokinetics and CYP2C19 polymorphism

BACKGROUND

Esomeprazole and rabeprazole are metabolised in the liver by means of the CYP2C19 enzyme, which has several functional genetic polymorphisms. Among Caucasians, 70% of the population has a fast metaboliser phenotype, 25-30% an intermediate and 2-5% a slow metaboliser phenotype. It is unknown whether different PPIs are affected to the same extent by these phenotypic differences.

AIM

To compare the acid-inhibitory effects of esomeprazole 40 mg and rabeprazole 20 mg in relation to CYP2C19 genotype and pharmacokinetics.

METHODS

Eighteen healthy Helicobacter pylori-negative Caucasian subjects with CYP2C19*2-*6 and *17 genotype were included in a randomised investigator-blinded crossover study with esomeprazole 40 mg and rabeprazole 20 mg. Intragastric 24-h pH-monitoring was performed on days 0, 1 and 5 of oral dosing.

RESULTS

Onset of acid inhibition during the first 4 h after administration did not differ significantly between PPIs. During the upright period, the proportion of time with pH >4 was significantly higher with esomeprazole compared to rabeprazole (52.2 vs. 40.3%, P = 0.003). At day 1 and 5, acid inhibition was significantly greater with esomeprazole than with rabeprazole (median intragastric pH: day 1: 3.7 vs. 3.0, P = 0.008; day 5: 4.7 vs. 3.8, P < 0.001; percentage of time pH >4: day 1: 45 vs. 39%, P = 0.054; day 5: 65 vs. 48%, P < 0.001). Differences in acid inhibition between wt/wt and wt/*2 genotype were significant for both PPIs.

CONCLUSIONS

Once-daily dosing with esomeprazole 40 mg provides a more effective and faster acid-inhibitory effect than rabeprazole 20 mg. The acid-inhibitory effect of esomeprazole and rabeprazole are both influenced by CYP2C19 polymorphism.

Does the medication pattern reflect the CYP2D6 genotype in patients with diagnoses within the schizophrenic spectrum?

BACKGROUND

Cytochrome P450 2D6 enzyme (CYP2D6) is an important metabolic pathway for many antipsychotics. Its genetic polymorphism causes pharmacokinetic variability that might lead to adverse drug reactions or treatment failure unless countered by appropriate dose adjustments or shift to CYP2D6-independent antipsychotics.

PURPOSE

To investigate the clinical impact of CYP2D6 genotype in patients with a diagnosis within the schizophrenic spectrum using medication pattern as proxy for therapeutic and side effect.

METHODS

The study was conducted in patients genotyped during an inpatient stay (N = 576). Continuous antipsychotic, adjuvant, and anticholinergic drug regimens were registered retrospectively in a cross-sectional manner before genotyping. Antipsychotics were divided into CYP2D6 dependent and independent, and dose equivalents were calculated as chlorpromazine equivalents (CPZEq).

RESULTS

Poor metabolizers and ultrarapid metabolizers were treated with significantly higher median CPZEq doses (625.8; inter quartile range [IQR], 460.4-926.7; and 550; IQR, 199.8-1049) than extensive metabolizers (EMs) and intermediate metabolizers (IMs) (384; IQR, 150-698; and 446; IQR, 150-800) (P = 0.018). Logistic regression showed no association between anticholinergic treatment and CYP2D6 genotype or concomitant treatment with CYP2D6 inhibitors (P = 0.79 and P = 0.46, respectively).

CONCLUSIONS

Our results indicate that CYP2D6 genotype has no sufficient clinical impact that poor metabolizers and ultrarapid metabolizers are easily clinically identified with.

Pharmacogenomics of human ABC transporter ABCC11 (MRP8): potential risk of breast cancer and chemotherapy failure

Some genetic polymorphisms of human ABC transporter genes are reportedly related to the risk of certain diseases and patients’ responses to medication. Human ABCC11 functions as an ATP-dependent efflux pump for amphipathic anions. One non-synonymous SNP 538G>A (Gly180Arg) has been found to greatly affect the function and stability of de novo synthesized ABCC11 (Arg180) variant protein. The SNP variant lacking N-linked glycosylation is recognized as a misfolded protein in the endoplasmic reticulum (ER) and readily undergoes proteasomal degradation. This ER-associated degradation of ABCC11 protein underlies the molecular mechanism of affecting the function of apocrine glands. On the other hand, the wild type (Gly180) of ABCC11 is associated with wettype earwax, axillary osmidrosis, colostrum secretion from the mammary gland, and the potential susceptibility of breast cancer. Furthermore, the wild type of ABCC11 reportedly has ability to efflux cyclic nucleotides and nucleoside-based anticancer drugs. The SNP (538G>A) of the ABCC11 gene is suggested to be a clinical biomarker for prediction of chemotherapeutic efficacy. Major obstacle to the successful chemotherapy of human cancer is development of resistance, and nucleoside-based chemotherapy is often characterized by inter-individual variability. This review provides an overview about the discovery and the genetic polymorphisms in human ABCC11. Furthermore, we focus on the impact of ABCC11 538G>A on the apocrine phenotype, patients’ response to nucleoside-based chemotherapy, and the potential risk of breast cancer.

Do guidelines recommending pharmacogenetic testing of psychiatric patients affect treatment costs and the use of healthcare services?

Aim: To identify the effects of local recommendations of pharmacogenetic testing in psychiatry with respect to treatment costs. Methods: Based on Danish patient registers, individual treatment costs within a 365-day period at three psychiatric hospitals recommending and using pharmacogenetic testing is compared retrospectively with treatment costs at other Danish psychiatric hospitals using alternate treatment strategies. Primary outcome of interest is total direct costs analyzed by multilevel modelling. Secondary outcome measures are healthcare consumption within specific sectors analyzed by Tobitregressions. Results: Costs among patients treated at hospitals recommending and using pharmacogenetic testing were not found to be statistically significantly different from costs among patients treated at sites using alternate treatment strategies. In spite of recommendations to test all patients the uptake of the test was, however, low (26—31 %). Treatment practice using routine therapeutic drug monitoring (in Ãrhus) shows a trend towards lower costs. Conclusions: Based on this natural experiment we were not able to document statistically significant differences in total costs between treatment sites that had guidelines recommending pharmacogenetic testing, relative to sites without such guidelines, over a period of one year. However, guidelines of pharmacogenetic testing and possibly also therapeutic drug monitoring seem to lead to reductions in costs for primary care services. In the case of the former, reductions do, however, seem to be outweighed by increases in costs for psychiatric and non-psychiatric inpatient stays. In conclusion, no statistically significant differences in total direct costs across sites with different treatment strategies were found.

Characterization of the genetic profile of CYP2C19 in two South African populations

AIMS

This study was aimed at elucidating the common sequence variation present in the CYP2C19 gene within the South African Xhosa population and comparing it with the Cape Mixed Ancestry (CMA) population for possible future pharmacogenetic applications.

MATERIALS & METHODS

Common sequence variation was identified through the resequencing of 15 Xhosa individuals. The detected variants were prioritized for genotyping in an additional 85 Xhosa and 75 CMA individuals, while 5 -upstream variants were analyzed using dual luciferase reporter assays.

RESULTS

Resequencing of the Xhosa population revealed 30 variants, including the novel CYP2C19*27 and CYP2C19*28 alleles. CYP2C19*27, characterized by -1041G>A, caused a twofold decrease in luciferase activity, while CYP2C19*28 is characterized by the nonsynonymous V374I variant. In addition, the previously characterized variants, CYP2C19*2, CYP2C19*9 and CYP2C19*17, were present in both populations, while CYP2C19*3 was only observed in the CMA population.

CONCLUSION

Our data demonstrate that both the Xhosa and CMA populations exhibit unique genetic profiles that could influence the outcome of drug therapy in these populations.

Pharmacotherapy and pregnancy: highlights from the Second International Conference for Individualized Pharmacotherapy in Pregnancy

To address provider struggles to provide evidence-based, rational drug therapy to pregnant women, a second conference was convened to highlight the current research in the field. Speakers from academic centers and institutions spoke about: the unique physiology and pathology of pregnancy; pharmacokinetic changes in pregnancy; thyroid disorders in pregnancy; pharmacogenetics in pregnancy; the role of CYP2D6 in pregnancy; treating addiction in pregnancy; the power of teratology networks to inform clinical decisions; the use of anti-depressants in pregnancy; and how to utilize computer-based modeling to aid with individualized pharmacotherapy in pregnancy. The Conference highlighted several areas of collaboration with the current Obstetrics Pharmacology Research Units Network (OPRU) and hoped to stimulate further collaboration and knowledge in the area with the common goal to improve the ability to safely and effectively use individualized pharmacotherapy in pregnancy.

Decision criteria for rational selection of homogeneous genotyping platforms for pharmacogenomics testing in clinical diagnostics

BACKGROUND

Genotyping is crucial for the identification of genetic markers underlying the development of neoplastic diseases and for determining individual variations in response to specific drugs. Technologies which can accurately identify genetic polymorphisms will dramatically affect routine diagnostic processes and future therapeutic developments in personalized medicine. However, such methods need to fulfill the principles of analytical validation to determine their suitability to assess nucleotide polymorphisms in target genes.

APPROACH

This article reviews recent developments in homogeneous technologies for the genotyping of single nucleotide polymorphisms. Here, homogeneous methods essentially refer to "single-tube" assays performed in a liquid phase. For the appropriate choice of any method, several criteria must be considered: 1) detection of known genetic variations; 2) analytical performance including specificity, sensitivity and robustness of the method; 3) availability of large platforms and required equipment; 4) suitability of platforms and tests for routine diagnostics; 5) suitability for high throughput implementation.

CONTENT

This review is intended to provide the reader with an understanding of these various technologies for pharmacogenomic testing in the routine clinical laboratory. A brief overview is provided on the available technologies for the detection of known mutations, a specific description of the homogeneous platforms currently employed in genotyping analysis, and considerations regarding the proper assessment of the analytical performance of these methods. Based on the criteria proposed here, potential users may evaluate advantages and limitations of the various analytical platforms and identify the most appropriate platform according to their specific setting and diagnostic needs.

Rapid and cost-effective SNP detection method: application of SmartAmp2 to pharmacogenomics research

Pharmacogenomics data can facilitate our understanding of the sources of variability in drug response, which can potentially lead to improved safety and efficacy of drug therapy for individual patients. A key requirement for the development of individualized medicine or personalized therapy is the ability to rapidly and conveniently test patients for genetic polymorphisms and/or mutations. However, in today's world, genotyping technology remains a bottleneck in clinical applications because of its slow speed and high cost. Therefore, we have recently developed a rapid and cost-effective method for SNP detection, named Smart Amplification Process 2 (SmartAmp2), which enables us to detect genetic polymorphisms or mutations in 30-45 min under isothermal conditions without DNA isolation and PCR amplification. This article presents the SNP detection method and its underlying molecular mechanism as well as clinical research applications.

Economic opportunities and challenges for pharmacogenomics

Economic evaluation provides health care decision makers with a powerful tool for resource allocation decisions because it offers a framework for comparing the costs and benefits of competing interventions or options. This paper reviews how economic analyses have been applied to the field of pharmacogenomics, both by the pharmaceutical industry to inform investment decisions and by payers to make coverage decisions. There is much anticipation that pharmacogenomic testing is likely to be cost-effective because it uses genomic information to improve drug effectiveness and reduce toxicity both in the drug development process and at the bedside. However, the demonstration of economic benefits first requires that pharmacogenomic testing show evidence of clinical effectiveness. This will only be achieved by greater participation of pharmacogenomics experts in comparative effectiveness research and additional emphasis on including costs in the determination of the relative value of pharmacogenomic testing to the health care system.

Impact of CYP2C19 polymorphisms on the antiplatelet effect of clopidogrel in an actual clinical setting in Japan

BACKGROUND

The P2Y(12) adenosine diphosphate (ADP) receptor blocker, clopidogrel, an essential drug for the prevention of stent thrombosis after percutaneous coronary intervention (PCI), is a prodrug that requires CYP2C19- and CYP3A4-mediating activation. CYP2C19*2 and *3 polymorphisms are known to lack enzymatic activity. CYP2C19 polymorphisms have been reported to exhibit weaker antiplatelet response to clopidogrel in healthy subjects. The effect of polymorphisms of CYP2C19, CYP3A4 and P2Y(12) on the antiplatelet effect of clopidogrel in clinical patients was examined in the present study.

METHODS AND RESULTS

Single nucleotide polymorphisms of CYP2C19*2, *3, CYP3A4 (IVS10 +12G>A) and P2Y(12) (T744C) were determined in 25 PCI-scheduled patients who had been systematically analyzed for the antiplatelet effect of clopidogrel in a previous study. On the basis of CYP2C19 genotype, 11 patients (44%) were classified as extensive metabolizers (EMs), 8 (32%) as intermediate metabolizers (IMs) and 6 (24%) as poor metabolizers (PMs). The rates of inhibition of 5 micromol/L ADP-induced platelet aggregation by clopidogrel intake at 48 h were 31.6 +/-14.3% in EMs, 18.4 +/-10.0% in IMs (P=0.04 vs EMs) and 16.0 +/-13.0% in PMs (P=0.02 vs EMs).

CONCLUSIONS

CYP2C19 polymorphisms are frequent in Japanese, and the antiplatelet effect of clopidogrel is strongly affected by them in the real-world clinical setting.

Circulating microparticles and endogenous estrogen in newly menopausal women

BACKGROUND

Estrogen modulates antithrombotic characteristics of the vascular endothelium and the interaction of blood elements with the vascular surface. A marker of these modulatory activities is formation of cell-specific microparticles. This study examined the relationship between blood-borne microparticles and endogenous estrogen at menopause.

METHODS

Platelet activation and plasma microparticles were characterized from women being screened (n = 146) for the Kronos Early Estrogen Prevention Study. Women were grouped according to serum estrogen (< 20 pg/ml; low estrogen, n = 21 or > 40 pg/ml; high estrogen, n = 11).

RESULTS

Age, body mass index, blood pressure and blood chemistries were the same in both groups. No woman was hypertensive, diabetic or a current smoker. Platelet counts, basal and activated expression of P-selectin on platelet membranes were the same, but activated expression of glycoprotein IIb/IIIa was greater in the high-estrogen group. Numbers of endothelium-, platelet-, monocyte- and granulocyte-derived microparticles were greater in the low-estrogen group. Of the total numbers of microparticles, those positive for phosphatidylserine and tissue factor were also greater in the low-estrogen group.

CONCLUSION

These results suggest that, with declines in endogenous estrogen at menopause, numbers of procoagulant microparticles increase and thus may provide a means to explore mechanisms for cardiovascular risk development in newly menopausal women.

Estimating the Danish populations' preferences for pharmacogenetic testing using a discrete choice experiment. The case of treating depression

OBJECTIVE

The objective is to estimate willingness-to-pay (WTP) for pharmacogenetic testing in the treatment of depression.

METHODS

In a web-based discrete choice questionnaire, four attributes were included: 1) number of changes in antidepressants before symptom relief; 2) time with dosage adjustments due to adverse side effects and/or lack of effects; 3) cost of pharmacogenetic testing; 4) probability of benefits from pharmacogenetic testing. Respondents were asked to choose between two scenarios; 1) pharmacogenetic testing; and 2) an opt-out option reflecting a scenario without pharmacogenetic testing. The indirect utility model was assumed to be multiplicative in probability of benefits and reduced time with dosage adjustments as well as reduced number of antidepressant changes.

RESULTS

Most coefficients had the expected signs and were statistically significant. WTP for avoidance of one change in antidepressant medication is 1571 Danish Krone (DKK), whereas WTP for reducing the period with dosage-adjustments by 1 month is DKK604. Both were statistically significantly different from zero.

CONCLUSION

If diagnosed with depression, peoples' WTP for pharmacogenetic testing appears to exceed its price as long as there is a reasonable probability for improvements in treatment (in the present case 10%). Utility is associated with outcomes only. Hence, other modes of provision of similar improvements in treatment may be valued equally highly. WTP estimates and the associated policy implications appear to be robust because they were unaffected by estimation model.

A regulatory science perspective on warfarin therapy: a pharmacogenetic opportunity

Warfarin is a challenging drug to accurately dose, both initially and for maintenance, because of its narrow therapeutic range, wide interpatient variability, and long list of factors that can influence dosing. Two million people in the United States are initiated on warfarin therapy annually, and this number is steadily increasing because of the increase in number of eligible patients. Recently, warfarin was reported to be the fourth leading cause of adverse events. The U.S. Food and Drug Administration recognizes that the adverse event rate of warfarin can be improved through better initial dosing, because many of the serious adverse events of warfarin occur soon after starting treatment. A substantial number of studies demonstrate that common variants of two genes, VKORC1 and CYP2C9, along with other nongenetic factors, correlate significantly with warfarin dosing. The genotypes of VKORC1 and CYP2C9 alone account for nearly 3 times more of the variability ( approximately 30%) in warfarin dosing than do age, weight, gender, and other clinical factors combined ( approximately 12%). Therefore, the purpose of this report is to review the current recommendations for warfarin therapy that involve genetic testing.

Review article: amphetamines and related drugs of abuse

Acute amphetamine toxicity is a relatively common clinical scenario facing the Australasian emergency medicine physician. Rates of use in Australasia are amongst the highest in the world. Clinical effects are a consequence of peripheral and central adrenergic stimulation producing a sympathomimetic toxidrome and a spectrum of central nervous system effects. Assessment aims to detect the myriad of possible complications related to acute amphetamine exposure and to institute interventions to limit associated morbidity and mortality. Meticulous supportive care aided by judicial use of benzodiazepines forms the cornerstone of management. Beta blockers are contraindicated in managing cardiovascular complications. Agitation and hyperthermia must be treated aggressively. Discharge of non-admitted patients from the emergency department should only occur once physiological parameters and mental state have returned to normal. All patients should receive education regarding the dangers of amphetamine use.

Pharmacogenetics: from description to prediction

Many of the complexities of human drug response are sufficiently well understood to transform the field of pharmacogenetics from a descriptive science to a predictive science. Clinical application of these markers is currently limited by lack of knowledge about the effects of modifying genes, about their prevalence and risk contribution in different ethnogeographic populations, and by fragmentary information about how genetic factors interact with physiologic or pathologic and other environmental factors. Nevertheless, progress has been notable, as exemplified in the identification of genetic markers predictive of pharmacokinetic variation, and in markers predictive of outcome and therapeutic benefit in the treatment of cancer.

Pharmacogenomics, evidence, and the role of payers

Initial enthusiasm for the potential of pharmacogenomics (PGx) to transform medical practice has been tempered by the reality that the process of biomarker discovery, validation, and clinical qualification has been disappointingly slow, with a limited number of PGx tests entering the marketplace since the initial publication of the human genome sequence. Reasons for the delays include the complexity of the underlying science as well as clinical, economic, and organizational barriers to the effective delivery of personalized health care. Nevertheless, payers are interested in using PGx services to ensure that drug use is safer and more effective, particularly in the settings of medications that are widely used, have significant risks of serious adverse events, have poor or highly variable drug response, or are very expensive. However, public and private payers have specific evidence requirements for new health care technologies that must be met prior to obtaining favorable coverage and reimbursement status. These evaluation criteria are frequently more rigorous than the current level of evidence required for regulatory approval of new PGx tests or PGx-related drug labeling. To support payer decision-making, researchers will need to measure the impact of PGx testing on clinical and economic outcomes and demonstrate the net benefit of PGx testing as compared to usual care. By linking payer information needs with the current PGx research agenda, there is the opportunity to develop the data required for informed decision-making. This strategy will increase the likelihood that PGx services will be both reimbursed and used appropriately in clinical practice.

Cytochrome P450 2C19 polymorphism in young patients treated with clopidogrel after myocardial infarction: a cohort study

BACKGROUND

Clopidogrel and low-dose aspirin have become the mainstay oral antiplatelet regimen to prevent recurrent ischaemic events after acute coronary syndromes or stent placement. The frequent genetic functional variant 681 G>A (*2) of cytochrome P450 2C19 (CYP2C19) is an important contributor to the wide variability between individuals of the antiplatelet effect of clopidogrel. We assessed whether the CYP2C19*2 polymorphism affected long-term prognosis of patients who were chronically treated with clopidogrel.

METHODS

Between April 1, 1996, and April 1, 2008, 259 young patients (aged <45 years) who survived a first myocardial infarction and were exposed to clopidogrel treatment for at least a month, were enrolled in a multicentre registry and underwent CYP2C19*2 determination. The primary endpoint was a composite of death, myocardial infarction, and urgent coronary revascularisation occurring during exposure to clopidogrel. Follow-up was every 6 months. The key secondary endpoint was stent thrombosis proven by angiography.

FINDINGS

Median clopidogrel exposure time was 1.07 years (IQR 0.28-3.0). Baseline characteristics were balanced between carriers (heterozygous *1/*2, n=64; homozygous *2/*2, n=9) and non-carriers (n=186) of CYP2C19*2 variant. The primary endpoint occurred more frequently in carriers than in non-carriers (15 vs 11 events; hazard ratio [HR] 3.69 [95% CI 1.69-8.05], p=0.0005), as did stent thrombosis (eight vs four events; HR 6.02 [1.81-20.04], p=0.0009). The detrimental effect of the CYP2C19*2 genetic variant persisted from 6 months after clopidogrel initiation up to the end of follow-up (HR 3.00 [1.27-7.10], p=0.009). After multivariable analysis, the CYP2C19*2 genetic variant was the only independent predictor of cardiovascular events (HR 4.04 [1.81-9.02], p=0.0006).

INTERPRETATION

The CYP2C19*2 genetic variant is a major determinant of prognosis in young patients who are receiving clopidogrel treatment after myocardial infarction.

Increased carrier prevalence of deficient CYP2C9, CYP2C19 and CYP2D6 alleles in depressed patients referred to a tertiary psychiatric hospital

OBJECTIVE

This study compared the types and carrier prevalences of clinically significant DNA polymorphisms in the cytochrome P450 (CYP450) genes CYP2C9, CYP2C19 and CYP2D6 in major depressive disorder patients with a control group of nonpsychiatrically ill, medical outpatients.

METHOD

We conducted a case-control study using 73 psychiatric outpatients diagnosed with depression and referred to a tertiary center, The Institute of Living (Hartford, CT, USA), for treatment resistance or intolerable side-effects to psychotropic drugs. The controls were 120 cardiovascular patients from Hartford Hospital being treated for dyslipidemia but otherwise healthy and not psychiatrically ill. DNA typing to detect polymorphisms in the genes CYP2C9, CYP2C19 and CYP2D6 was accomplished with the Tag-It™ mutation detection assay and the Luminex xMAP^® system.

RESULTS

The percentage of individuals in psychiatric versus control groups with two wild-type alleles for CYP2C9, CYP2C19 and CYP2D6 genes, were 50 versus 74% (p < 0.001), 71 versus 73% (not statistically significant) and 36 versus 43% (trend, p < 0.2), respectively. Within the psychiatric population, 57% of individuals were carriers of non-wild-type alleles for 2-3 genes, compared with 36% in the control population (p < 0.0001). The balance, 43% in the psychiatric population and 64% in the control, were carriers of non-wild-type alleles for none or one gene.

CONCLUSIONS

These findings reveal that clinically relevant CYP2C9 polymorphisms occur more frequently in depressed psychiatric patients than in nonpsychiatric controls. The same trend was found for polymorphisms in the CYP2D6 gene. We found a significant cumulative metabolic deficiency in the psychiatric population for combinations of the CYP2C9, CYP2C19 and CYP2D6 genes. The significant enrichment of CYP2C9-deficient alleles in the psychiatric population validates a previously reported association of this gene with the risk for depression disorders. The high prevalence of carriers with deficient and null alleles suggests that CYP450 DNA typing may play a role in the management of psychiatric patients at tertiary care institutions.

Global pharmacogenetics: genetic substructure of Eurasian populations and its effect on variants of drug-metabolizing enzymes

AIMS

To study the frequency distribution of cytochrome P450 (CYP) functional genetic variants in five Eurasian populations from the territory of Siberia in Russia.

MATERIALS & METHODS

Unrelated healthy Tuvinians, Buryats, Altaians, Yakuts and Russians (n = 87-88) were genotyped for CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3 and CYP3A5*6. Standard pairwise genetic distances, locus-specific and global Fst statistics were calculated.

RESULTS

CYP allele and genotype frequencies demonstrated significant variability. Overall, the degree of between-population variance displayed by CYP SNPs was lower than that recorded from neutral short tandem repeats and Alu-insertion polymorphism, indicating evolutionary conservation of CYP polymorphisms. CYP-based genetic distances were well correlated with the geographic distances across populations (r = 0.822, p = 0.008).

CONCLUSIONS

Although the tested variants were present in the neighboring, yet secluded, populations at the expected range of frequencies, the observed frequencies were significantly variable across Eurasian populations, indicating potential relevance to clinical decision making.

Characterization of blood borne microparticles as markers of premature coronary calcification in newly menopausal women

While the risk for symptomatic atherosclerotic disease increases after menopause, currently recognized risk factors do not identify ongoing disease processes in low-risk women. This study tested the hypothesis that circulating cell-derived microparticles may reflect disease processes in women defined as low risk by the Framingham risk score. The concentration and phenotype of circulating microparticles were evaluated in a cross-sectional study of apparently healthy menopausal women, screened for enrollment into the Kronos Early Estrogen Prevention Study. Microparticles were evaluated by flow cytometry, and coronary artery calcification (CAC) was scored using 64-slice computed tomography scanners. The procoagulant activity of isolated microparticles was determined with a sensitive fluorescent thrombin generation assay. Chronological age, body mass index, serum lipids, systolic blood pressure (Framingham risk score < 10%, range 1-3%), and high-sensitivity C-reactive protein did not differ significantly among women with low (0 < 35; range, 0.3-32 Agatston units) or high (>50; range, 93-315 Agatston units) CAC compared with women without calcification. The total concentration and percentage of microparticles derived from platelets and endothelial cells were greatest in women with high CAC scores. The thrombin-generating capacity of the isolated microparticles correlated with phosphatidylserine expression, which also was greatest in women with high CAC scores. The percentages of microparticles expressing granulocyte and monocyte markers were not significantly different among groups. Therefore, the characterization of platelet and endothelial microparticles may identify early menopausal women with premature CAC who would not otherwise be identified by the usual risk factor analysis.

The role of ethnicity in variability in response to drugs: focus on clinical pharmacology studies

Ethnicity is one factor that may account for the observed differences in both pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, resulting in variability in response to drug therapy. Given that the applicability of clinical study results to the treatment of an individual patient is a critical consideration in a physician's choice of drug therapy, drug development should seek to ensure that a clinical pharmacologic evaluation includes a population that is representative of the target therapeutic population. Ethnic diversity in drug response with respect to safety and efficacy and the resulting differences in recommended doses have been well described for some drugs. Some of these differential responses may be related to the pharmacogenomics of a particular drug. Pharmacogenomic techniques have recently enjoyed widespread use in studies of drug exposure and response. The clinical relevance of variability in drug response due to pharmacogenomics of drug-metabolizing enzymes was considered at a September 2004 workshop cosponsored by the US Food and Drug Administration (FDA), Johns Hopkins University, and the Pharmaceutical Research and Manufacturers of America (http://www.fda.gov/cder/Offices/OCPB/workshops.htm).

PhRMA white paper on ADME pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross-industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003-2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug-metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.

CYP2C9, CYP2C19 and CYP2D6 allele frequencies in the Ashkenazi Jewish population

OBJECTIVE

To determine and compare the cytochrome P450 (CYP)2C9, CYP2C19 and CYP2D6 allele and genotype frequencies in the Ashkenazi Jewish (AJ) population with other populations.

METHODS

CYP2C9, CYP2C19 and CYP2D6 genotypes were determined in 250 anonymous, unrelated, healthy AJ individuals from the greater New York (USA) metropolitan area. Genotyping was performed using the Tag-Ittrade mark Mutation Detection system and the recently redefined CYP2D6*41A allele was identified by a restriction fragment length polymorphism assay.

RESULTS

Among the 250 AJ individuals, the CYP2C9*1, *2, *3 and *5 allele frequencies were 0.772, 0.140, 0.086 and 0.002, respectively, and the genotypes were distributed into extensive- (60.8%), intermediate- (32.8%) and poor- (6.4%) metabolizer phenotypes. The CYP2C19*1, *2 and *4 allele frequencies were 0.830, 0.152 and 0.018, respectively, and the genotypes were distributed into extensive (69.2%), intermediate (27.6%) and poor (3.2%) metabolizers. The most common CYP2D6 alleles identified were *1, *2A, *4 and *41A, and their frequencies were 0.286 0.152 0.226 and 0.140, respectively. The CYP2D6 genotypes were distributed into ultrarapid- (8.8%), extensive- (70.0%), intermediate- (16.0%) and poor- (5.2%) metabolizer phenotypes.

CONCLUSION

Although the CYP2C9 allele and genotype frequencies in the AJ subjects were similar to those in other North American Caucasian populations, genotyping the CYP2C19*4 and CYP2D6*41A alleles in the AJ population resulted in the clinically relevant reclassification of the predicted metabolizer phenotypes. Inclusion of CYP2C19*4 reclassified individuals from either extensive- or intermediate- to the intermediate- or poor-metabolizer phenotypes, respectively. Inclusion of the redefined CYP2D6*41A allele increased the ultrarapid-, intermediate- and poor-metabolizer phenotype combined frequencies to 30%, indicating that approximately one in three AJ individuals may benefit from genotype-based drug selection and dosage. In addition, the ultrarapid CYP2D6 genotype frequency in the AJ population (8.8%) was approximately twofold higher than that in other North American Caucasians.

Defining drug disposition determinants: a pharmacogenetic-pharmacokinetic strategy

In preclinical and early clinical drug development, information about the factors influencing drug disposition is used to predict drug interaction potential, estimate and understand population pharmacokinetic variability, and select doses for clinical trials. However, both in vitro drug metabolism studies and pharmacogenetic association studies on human pharmacokinetic parameters have focused on a limited subset of the proteins involved in drug disposition. Furthermore, there has been a one-way information flow, solely using results of in vitro studies to select candidate genes for pharmacogenetic studies. Here, we propose a two-way pharmacogenetic-pharmacokinetic strategy that exploits the dramatic recent expansion in knowledge of functional genetic variation in proteins that influence drug disposition, and discuss how it could improve drug development.