CYP2C9 Ile359 and Leu359 variants: enzyme kinetic study with seven substrates

Roles of Individual Human Cytochrome P450 Enzymes in Drug Metabolism

Our knowledge of the roles of individual cytochrome P450 (P450) enzymes in drug metabolism has developed considerably in the past 30 years, and this base has been of considerable use in avoiding serious issues with drug interactions and issues due to variations. Some newer approaches are being considered for "phenotyping" metabolism reactions with new drug candidates. Endogenous biomarkers are being used for noninvasive estimation of levels of individual P450 enzymes. There is also the matter of some remaining "orphan" P450s, which have yet to be assigned reactions. Practical problems that continue in drug development include predicting drug-drug interactions, predicting the effects of polymorphic and other P450 variations, and evaluating interspecies differences in drug metabolism, particularly in the context of "metabolism in safety testing" regulatory issues ["disproportionate (human) metabolites"]. SIGNIFICANCE STATEMENT: Cytochrome P450 enzymes are the major catalysts involved in drug metabolism. The characterization of their individual roles has major implications in drug development and clinical practice.

The relationship between CYP2C9 gene polymorphisms and azilsartan metabolism in vitro

BACKGROUND

The gene polymorphisms of the CYP2C9, as well as the substrate specificity of the enzyme, result in different clearances for different substrates by CYP2C9 variants.

RESEARCH DESIGNAND METHODS

The CYP2C9 wild type and 38 CYP2C9 variants, expressed in insectmicrosomes, were incubated with azilsartan. The resulting metabolite,O-desethyl azilsartan, was determined by HPLC-MS/MS. The enzyme kineticparameters of the 38 variants were calculated and compared with the wild type.Subsequently, we selected CYP2C9*1, *2, and  *3 as target proteins for molecular docking with azilsartan to elucidate the mechanisms underlying changes in enzyme function.

RESULTS

Compared with CYP2C9*1, three variants (CYP2C9*29, *39, and *49) exhibited markedlyincreased CLint values (from 170%-275%, *p < 0.05), whereas 28 variants exhibited significantly decreased CLint values (from 3-63%,*p < 0.05). The molecular docking results showed that the binding energy of CYP2C9*2 and *3 was lower than that of the wild type.

CONCLUSION

Thisassessment revealed the effect of CYP2C9 gene polymorphisms on azilsartan metabolism, establishing a theoretical basis for further in-vivo studies and clinical applications. This study will help expand the database of CYP2C9 gene-drug pairs and identify appropriate treatment strategies for azilsartan, contributing to the field of precision medicine.

Drug Metabolism: A Half-Century Plus of Progress, Continued Needs, and New Opportunities

The systematic study of drug metabolism began in the 19th Century, but most of what we know now has been learned in the last 50 years. Drug metabolism continues to play a critical role in pharmaceutical development and clinical practice, as well as contributing to toxicology, chemical carcinogenesis, endocrinology, and drug abuse. The importance of the field will continue, but its nature will continue to develop with changes in analytical chemistry, structural biology, and artificial intelligence. Challenges and opportunities include toxicology, defining roles of genetic variations, and application to clinical issues. Although the focus of this Minireview is cytochrome P450, the same principles apply to other enzymes and transporters involved in drug metabolism. SIGNIFICANCE STATEMENT: Progress in the field of drug metabolism over the past 50 years has helped make the pharmaceutical enterprise what it is today. Drug metabolism will continue to be important. Challenges and opportunities for the future are discussed.

Pharmacogenomics of lipid-lowering agents: the impact on efficacy and safety

Hyperlipidemia is a significant risk factor for cardiovascular disease morbidity and mortality. The lipid-lowering drugs are considered the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease. Unfortunately, the lack of efficacy and associated adverse effects, ranging from mild-to-moderate to potentially life-threatening, lead to therapy discontinuation. Numerous reports support the role of gene polymorphisms in drugs' pharmacokinetic parameters and their associated adverse reactions. Therefore, this study aims to understand the pharmacogenomics of lipid-lowering drugs and the impact of genetic variants of key genes on the drugs' efficacy and toxicity. Indeed, genetically guided lipid-lowering therapy enhances overall safety, improves drug adherence and achieves long-term therapy.

Impact of genetic and non-genetic factors on hepatic CYP2C9 expression and activity in Hungarian subjects

CYP2C9, one of the most abundant hepatic cytochrome P450 enzymes, is involved in metabolism of 15–20% of clinically important drugs (warfarin, sulfonylureas, phenytoin, non-steroid anti-inflammatory drugs). To avoid adverse events and/or impaired drug-response, CYP2C9 pharmacogenetic testing is recommended. The impact of CYP2C9 polymorphic alleles (CYP2C9*2, CYP2C9*3) and phenoconverting non-genetic factors on CYP2C9 function and expression was investigated in liver tissues from Caucasian subjects (N = 164). The presence of CYP2C9*3 allele was associated with CYP2C9 functional impairment, and CYP2C9*2 influenced tolbutamide 4′-hydroxylase activity only in subjects with two polymorphic alleles, whereas the contribution of CYP2C8*3 was not confirmed. In addition to CYP2C9 genetic polymorphisms, non-genetic factors (co-medication with CYP2C9-specific inhibitors/inducers and non-specific factors including amoxicillin + clavulanic acid therapy or chronic alcohol consumption) contributed to the prediction of hepatic CYP2C9 activity; however, a CYP2C9 genotype–phenotype mismatch still existed in 32.6% of the subjects. Substantial variability in CYP2C9 mRNA levels, irrespective of CYP2C9 genotype, was demonstrated; however, CYP2C9 induction and non-specific non-genetic factors potentially resulting in liver injury appeared to modify CYP2C9 expression. In conclusion, complex implementation of CYP2C9 genotype and non-genetic factors for the most accurate estimation of hepatic CYP2C9 activity may improve efficiency and safety of medication with CYP2C9 substrate drugs in clinical practice.

Variability in Human In Vitro Enzyme Kinetics

There are many factors which are known to cause variability in human in vitro enzyme kinetic data. Factors such as the source of enzyme and how it was prepared, the genetics and background of the donor, how the in vitro studies are designed, and how the data are analyzed contribute to variability in the resulting kinetic parameters. It is important to consider not only the factors which cause variability within an experiment, such as selection of a probe substrate, but also those that cause variability when comparing kinetic data across studies and laboratories. For example, the artificial nature of the microsomal lipid membrane and microenvironment in some recombinantly expressed enzymes, relative to those found in native tissue microsomes, has been shown to influence enzyme activity and thus can be a source of variability when comparing across the two different systems. All of these factors, and several others, are discussed in detail in the chapter below. In addition, approaches which can be used to visualize the uncertainty arising from the use of enzyme kinetic data within the context of predicting human pharmacokinetics are discussed.

In Vivo Functional Effects of CYP2C9 M1L, a Novel and Common Variant in the Yup'ik Alaska Native Population

Alaska Native people are under-represented in genetic research but have unique gene variation that may critically impact their response to pharmacotherapy. Full resequencing of CYP2C9 in a cross-section of this population identified CYP2C9 Met1Leu (M1L), a novel, relatively common single nucleotide polymorphism hypothesized to confer CYP2C9 poor metabolizer phenotype by disrupting the start codon. M1L is present at a minor allele frequency of 6.3% in Yup'ik Alaska Native people and thus can contribute to the risk of an adverse drug response from narrow-therapeutic-index CYP2C9 substrates such as (S)-warfarin. This study's objective was to characterize the catalytic efficiency of the Leu1 variant enzyme in vivo by evaluating the pharmacokinetic behavior of naproxen, a probe substrate for CYP2C9 activity, in genotyped Yup'ik participants. We first confirmed the selectivity of (S)-naproxen O-demethylation by CYP2C9 using activity-phenotyped human liver microsomes and selective cytochrome P450 inhibitors and then developed and validated a novel liquid chromatography mass spectrometry method for simultaneous quantification of (S)-naproxen, (S)-O-desmethylnaproxen, and naproxen acyl glucuronide in human urine. The average ratio of (S)-O-desmethylnaproxen to unchanged (S)-naproxen in urine was 18.0 ± 8.0 (n = 11) for the homozygous CYP2C9Met1 reference group and 10.3 ± 6.6 (n = 11) for the Leu1 variant carrier group (P = 0.011). The effect of M1L variation on CYP2C9 function and its potential to alter the pharmacokinetics of drugs metabolized by the enzyme has clinical implications and should be included in a variant screening panel when pharmacogenetic testing in the Alaska Native population is warranted. SIGNIFICANCE STATEMENT: The novel CYP2C9 Met1Leu variant in Alaska Native people was recently identified. This study validated (S)-naproxen as a CYP2C9 probe substrate to characterize the in vivo functional activity of the CYP2C9 Leu1 variant. The results of this pharmacogenetic-pharmacokinetic study suggest that the CYP2C9 Leu1 variant exhibits loss of enzyme activity. This finding may be important to consider when administering narrow-therapeutic-index medications metabolized by CYP2C9 and also compels further investigation to characterize novel genetic variation in understudied populations.

Association Between the CYP2C9 Genotype and Hypoglycemia Among Patients With Type 2 Diabetes Receiving Sulfonylurea Treatment: A Meta-analysis

PURPOSE

Two common variants, CYP2C9*2 (Arg144Cys, rs1799853) and CYP2C9*3 (Ile359Leu, rs1057910), are known to reduce the catalytic function of the CYP2C9 enzyme. Because impaired catalytic function is likely to affect sulfonylurea metabolism, it is predictable that CYP2C9 loss-of-function alleles may increase the risk of sulfonylurea-induced hypoglycemia. This systematic review and meta-analysis aimed to assess the association between CYP2C9 genotype and hypoglycemia among patients with type 2 diabetes mellitus (T2DM) receiving sulfonylurea.

METHODS

We searched for studies on the association between CYP2C9 genotype and sulfonylurea-induced hypoglycemia among patients with T2DM, published through August 7, 2020, using PubMed, Web of Science, and EMBASE. Odds ratios (ORs) and 95% CIs were calculated.

FINDINGS

Five cohort studies and 2 case-control studies were included, and the total number of patients analyzed in this meta-analysis was 2769. The CYP2C9 variant alleles were associated with an increase in sulfonylurea-induced hypoglycemia compared with wild-type homozygote (OR = 1.24; 95% CI, 1.03-1.48). Compared with CYP2C9 wild-type homozygotes, CYP2C9*2 allele was associated with increased incidence of hypoglycemia (OR = 1.85; 95% CI, 1.18-2.89), whereas the CYP2C9*3 allele failed to show the statistical significance (OR = 1.67; 95% CI, 0.40-6.86; P = 0.48).

IMPLICATIONS

On the basis of these results, CYP2C9 genotyping may be useful for predicting the risk of hypoglycemia during sulfonylurea treatment for T2DM.

Quantitative Systems Pharmacology Model-Based Predictions of Clinical Endpoints to Optimize Warfarin and Rivaroxaban Anti-Thrombosis Therapy

Background

Tight monitoring of efficacy and safety of anticoagulants such as warfarin is imperative to optimize the benefit-risk ratio of anticoagulants in patients. The standard tests used are measurements of prothrombin time (PT), usually expressed as international normalized ratio (INR), and activated partial thromboplastin time (aPTT).

Objective

To leverage a previously developed quantitative systems pharmacology (QSP) model of the human coagulation network to predict INR and aPTT for warfarin and rivaroxaban, respectively.

Methods

A modeling and simulation approach was used to predict INR and aPTT measurements of patients receiving steady-state anticoagulation therapy. A previously developed QSP model was leveraged for the present analysis. The effect of genetic polymorphisms known to influence dose response of warfarin (CYP2C9, VKORC1) were implemented into the model by modifying warfarin clearance (CYP2C9 *1: 0.2 L/h; *2: 0.14 L/h, *3: 0.04 L/h) and the concentration of available vitamin K (VKORC1 GA: −22% from normal vitamin K concentration; AA: −44% from normal vitamin K concentration). Virtual patient populations were used to assess the ability of the model to accurately predict routine INR and aPTT measurements from patients under long-term anticoagulant therapy.

Results

The introduced model accurately described the observed INR of patients receiving long-term warfarin treatment. The model was able to demonstrate the influence of genetic polymorphisms of CYP2C9 and VKORC1 on the INR measurements. Additionally, the model was successfully used to predict aPTT measurements for patients receiving long-term rivaroxaban therapy.

Conclusion

The QSP model accurately predicted INR and aPTT measurements observed during routine therapeutic drug monitoring. This is an exemplar of how a QSP model can be adapted and used as a model-based precision dosing tool during clinical practice and drug development to predict efficacy and safety of anticoagulants to ultimately help optimize anti-thrombotic therapy.

CYP2 C9 polymorphism among patients with oral squamous cell carcinoma and its role in altering the metabolism of benzo[a]pyrene

OBJECTIVES

The aim of this study was to evaluate the prevalence of CYP2 C9 polymorphism among healthy controls and patients with oral squamous cell carcinoma (OSCC) and to analyze the risk of disease development. We also investigated the interaction between CYP2 C9 wild type and the polymorphic variants with benzo[a]pyrene by using molecular docking analysis.

STUDY DESIGN

The study included 46 patients with OSCC and 46 controls. Amplification of the genomic DNA was done by using allele-specific polymerase chain reaction and then analyzed by using agarose gel electrophoresis. Molecular docking was then carried out to determine the interaction of CYP2 C9*1, CYP2 C9*2, and CYP2 C9*3 with benzo[a]pyrene.

RESULTS

In the OSCC group, CYP2 C9*2 and CYP2 C9*3 polymorphisms were 17.4% and 15.2%, respectively, and in the control group, they were 8.7% and 6.5%, respectively. The OSCC group showed a statistically significant (P = .043) increase in the prevalence of CYP2 C9 polymorphic variants compared with the control group. The docking analysis showed benzo[a]pyrene to bind specifically to the altered single nucleotide catalytic site in the polymorphic CYP2 C9*3 enzyme.

CONCLUSIONS

This study demonstrates that functionally important CYP2 C9 polymorphism exists among patients with OSCC, with a modest increase in the risk of disease development in those individuals who acquire these poor metabolizing variants. The modified docking of CYP2 C9*3 with benzo[a]pyrene signifies altered metabolism in vivo.

The Effect of CYP2C9 Genotype Variants in Type 2 Diabetes on the Pharmacological Effectiveness of Sulfonylureas, Diabetic Retinopathy, and Nephropathy

Aim

Type 2 diabetes (T2D), as a major cause of morbidity and mortality, is predicted to have a prevalence of 629 million by 2045. As diabetic patients show considerable inter-individual variation in response to antidiabetic treatment, this study aimed to investigate the gene polymorphism of cytochrome P450 as well as the effectiveness and safety of glibenclamide and gliclazide for different genotypes of CYP2C9. Besides, the chronic side effects of T2D including retinal microvasculature complications or retinopathy and renal dysfunction due to nephropathy in different genotypes were considered.

Patients and Methods

The participants including 80 T2D patients treated with glibenclamide or gliclazide were recruited from university hospitals of Ahvaz Jundishpur University of Medical Sciences, Ahvaz, in the southwest of Iran. Blood samples were collected from the patients at 2.5h after the morning dose of glibenclamide and 12h after the last dose of gliclazide. Genotyping from the extracted DNA was, then, performed using PCR-RFLP. The plasma level of glibenclamide and gliclazide was, in turn, measured by the reverse-phase high-pressure liquid chromatography.

Results

The results showed that the wild-type allele, i.e., CYP2C9*1, occurred in the highest frequency (0.8), while the frequency rates of the mutant allele, i.e., CYP2C9*2 and CYP2C9*3, were 0.15 and 0.05, respectively. Moreover, no significant association was found between any of the genotypes as well as the clinical and biochemical characteristics of the patients. The findings also showed that the plasma level of sulfonylureas (i.e., glibenclamide and gliclazide) was the highest in the patients with the CYP2C9*3 allele. It was also found that 75.9% of the patients with variant genotypes had experienced hypoglycemia events. Furthermore, in the absence of wild type allele, a significant increase was observed in retinopathy (p=0.039) and nephropathy (p=0.05).

Conclusion

The findings can provide guidelines for the optimal management of the treatment protocols with sulfonylurea intended to control the T2D complications.

Osthole inhibited the activity of CYP2C9 in human liver microsomes and influenced indomethacin pharmacokinetics in rats

Osthol, a pharmacologically active ingredient in various traditional Chinese medicines, is predominantly metabolized by CYP2C9. It may be co-administered with other drugs which are metabolized by CYP2C9 in clinical medicine. However, CYP2C9*1/*2/*3 genotype on the pharmacokinetics of osthole and its metabolic diversity between rat and human are unclear.In this study, we investigated the effects of osthole on enzyme activity of CYP2C11/CYP2C9 in rat liver microsomes (RLMs) and human liver microsomes (HLMs), to distinguish metabolic manner of osthole in different species. Interestingly, we found that osthole inhibits the activity of CYP2C11 in a non-competitive manner in RLMs, while inhibits CYP2C9 activity in a competitive manner in pooled HLMs. Then, the effects of CYP2C9*1/*2/*3 allele on the pharmacokinetics of osthole were identified. In human CYP2C9 isoform, the Ki value of 21.93 μM (CYP2C9*1), 18.10 μM (CYP2C9*2), 13.12 μM (CYP2C9*3) indicate that there are individual differences in the inhibition of osthole on CYP2C9 activity.We investigated how the indomethacin pharmacokinetics was affected by osthole in SD rat. To estimate the area under the curve (AUC), maximum plasma concentration (C_max) and apparent clearance (CL/F), indomethacin (10 mg/kg) was given orally combined with osthole (20 mg/kg) in adult SD rat. We found the value of PK on indomethacin, such as the AUC_0-∞, was from 176.40 ± 17.29 to 173.74 ± 27.69 μg/ml h^-1, C_max from 9.02 ± 1.24 to 9.89 ± 0.82 μg/ml and CL/F from 0.11 ± 0.01 to 0.12 ± 0.04 mg/kg/h which were unsignificantly changed compared with the control groups. However, the T_max was prolonged from 2.00 ± 0.00 h to 7.33 ± 1.15 h, and T_1/2 increased from 8.38 ± 2.30 h to 11.37 ± 2.11 h. These results indicate that osthole could potentially affect the metabolism of indomethacin in vivo.

HLA-B*51:01 and CYP2C9*3 Are Risk Factors for Phenytoin-Induced Eruption in the Japanese Population: Analysis of Data From the Biobank Japan Project

CYP2C9*3 and HLA-B alleles are reportedly associated with phenytoin-induced eruption in some East Asian populations; however, this finding is not readily applicable to the Japanese population. Thus, we aimed to investigate the risk alleles using samples and data from BioBank Japan. A total of 747 patients (24 cases and 723 tolerant controls) were selected for analysis. Case-control association studies were conducted, using CYP2C9*3, CYP2C9*27, CYP2C19*2, CYP2C19*3, and HLA-B allele genotype data. CYP2C9*3 carrier status was significantly associated with phenytoin-induced eruption (P = 0.0022, odds ratio 7.05, 95% confidence interval, 2.44-20.4). HLA-B*51:01 showed the most prominent association (P = 0.010, odds ratio 3.19, 95% confidence interval, 1.37-7.48). Including both of these features improved predictive performance, measured as area under the receiver operating characteristic curve, by 10%. CYP2C9*3 and HLA-B*51:01 allele carrier statuses are significantly associated with phenytoin-induced eruption; thus, checking this carrier status before prescription would decrease the incidence of phenytoin-induced eruption in clinical practice.

Genetic Polymorphisms and In Silico Mutagenesis Analyses of CYP2C9, CYP2D6, and CYPOR Genes in the Pakistani Population

Diverse distributions of pharmacogenetically relevant variants of highly polymorphic CYP2C9, CYP2D6 and CYPOR genes are responsible for some varied drug responses observed across human populations. There is limited data available regarding the pharmacogenetic polymorphisms and frequency distributions of major allele variants in the Pakistani population. The present in silico mutagenesis study conducted on genotype pharmacogenetic variants and comparative analysis with a global population aims to extend the currently limited pharmacogenetic available evidence for the indigenous Pakistani population. Extracted genomic DNA from 244 healthy individuals' venous blood samples were amplified for distinct variant loci in the CYP2C9, CYP2D6 and CYPOR genes. Two-way sequencing results were compared with standard PubMed data and sequence variant loci confirmed by Chromas. This study revealed significant variations in CYP2C9 (rs1799853, rs1057910 and rs72558189), CYP2D6 (rs16947 and rs1135840), and CYPOR (rs1057868, rs781919285 and rs562750402) variants in intraethnic and interethnic frequency distributions. In silico mutagenesis and three-dimensional protein structural alignment analysis approaches clearly exposed the possible varied impact of rare CYPOR (rs781919285 and rs562750402) single nucleotide polymorphisms (SNPs) and confirmed that the influences of CYP2C9 and CYP2D6 variants are consistent with what was found in earlier studies. This investigation highlighted the need to study pharmacogenetic relevance loci and documentation since evidence could be utilized to elucidate genetic backgrounds of drug metabolism, and provide a basis for future pharmacogenomic studies and adequate dose adjustments in Pakistani and global populations.

The Cytochrome P450 Slow Metabolizers CYP2C9*2 and CYP2C9*3 Directly Regulate Tumorigenesis via Reduced Epoxyeicosatrienoic Acid Production

Increased expression of cytochrome P450 CYP2C9, together with elevated levels of its products epoxyeicosatrienoic acids (EET), is associated with aggressiveness in cancer. Cytochrome P450 variants CYP2C9*2 and CYP2C9*3 encode proteins with reduced enzymatic activity, and individuals carrying these variants metabolize drugs more slowly than individuals with wild-type CYP2C9*1, potentially affecting their response to drugs and altering their risk of disease. Although genetic differences in CYP2C9-dependent oxidation of arachidonic acid (AA) have been reported, the roles of CYP2C9*2 and CYP2C9*3 in EET biosynthesis and their relevance to disease are unknown. Here, we report that CYP2C9*2 and CYP2C9*3 metabolize AA less efficiently than CYP2C9*1 and that they play a role in the progression of non-small cell lung cancer (NSCLC) via impaired EET biosynthesis. When injected into mice, NSCLC cells expressing CYP2C9*2 and CYP2C9*3 produced lower levels of EETs and developed fewer, smaller, and less vascularized tumors than cells expressing CYP2C9*1. Moreover, endothelial cells expressing these two variants proliferated and migrated less than cells expressing CYP2C*1. Purified CYP2C9*2 and CYP2C9*3 exhibited attenuated catalytic efficiency in producing EETs, primarily due to impaired reduction of these two variants by NADPH-P450 reductase. Loss-of-function SNPs within CYP2C9*2 and CYP2C9*3 were associated with improved survival in female cases of NSCLC. Thus, decreased EET biosynthesis represents a novel mechanism whereby CYPC29*2 and CYP2C9*3 exert a direct protective role in NSCLC development.Significance: These findings report single nucleotide polymorphisms in the human CYP2C9 genes, CYP2C9*2 and CYP2C9*3, exert a direct protective role in tumorigenesis by impairing EET biosynthesis. Cancer Res; 78(17); 4865-77. ©2018 AACR.

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

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

Presence of a single nucleotide polymorphism (RS3758581) in a boy with DRESS syndrome

Drug rash with eosinophilia and systemic symptoms (DRESS) syndrome is a rare, potentially life-threatening, drug-induced hypersensitivity reaction that includes rash, hematologic abnormalities, lymphadenopathy, and internal organ involvement. The pathogenesis of DRESS syndrome is partially understood. Various medications have been described as the cause of DRESS syndrome. Phenytoin and allopurinol are the most commonly reported culprit drugs, although more than 50 drugs can induce DRESS syndrome. Members of the cytochrome P450 (CYP) superfamily are the most commonly involved enzymes in metabolism of drugs such as phenytoin. This case report addresses the influence of CYP2C9 genetic polymorphism (a single nucleotide polymorphism) on phenytoin drug metabolism, thereby causing DRESS syndrome.

En route to precision medicine through the integration of biological sex into pharmacogenomics

Frequently, pharmacomechanisms are not fully elucidated. Therefore, drug use is linked to an elevated interindividual diversity of effects, whether therapeutic or adverse, and the role of biological sex has as yet unrecognized and underestimated consequences. A pharmacogenomic approach could contribute towards the development of an adapted therapy for each male and female patient, considering also other fundamental features, such as age and ethnicity. This would represent a crucial step towards precision medicine and could be translated into clinical routine. In the present review, we consider recent results from pharmacogenomics and the role of sex in studies that are relevant to cardiovascular therapy. We focus on genome-wide analyses, because they have obvious advantages compared with targeted single-candidate gene studies. For instance, genome-wide approaches do not necessarily depend on prior knowledge of precise molecular mechanisms of drug action. Such studies can lead to findings that can be classified into three categories: first, effects occurring in the pharmacokinetic properties of the drug, e.g. through metabolic and transporter differences; second, a pharmacodynamic or drug target-related effect; and last diverse adverse effects. We conclude that the interaction of sex with genetic determinants of drug response has barely been tested in large, unbiased, pharmacogenomic studies. We put forward the theory that, to contribute towards the realization of precision medicine, it will be necessary to incorporate sex into pharmacogenomics.

Frequencies of CYP2C9 polymorphisms in North Indian population and their association with drug levels in children on phenytoin monotherapy

Background

Phenytoin, mainly metabolized by cytochrome P450 enzyme system, has a narrow therapeutic index and may have adverse effects due to inter-individual variation in the dose requirement and genetic polymorphisms. This cross-sectional study was done to study the prevalence of cytochrome P450 CYP2C9 polymorphisms in Indian epileptic children and to see the effect of polymorphisms on serum levels in epileptic children on phenytoin monotherapy.

Methods

We studied 89 epileptic children of North Indian population, randomly selected, to see the genotypic and allelic frequency of CYP2C9 and its association with drug levels on phenytoin monotherapy. Analysis was done using STATA 9 Software. The results were analyzed as prevalence at 95 % C.I. (Confidence Interval). The difference in mean phenytoin serum levels between wild and mutant alleles was tested using Student`s T test for independent samples. P value less than 0.05 was considered statistically significant.

Results

CYP2C9*1, *2 & *3 allelic frequencies were 85.4, 4.5 and 10.1 % respectively. CYP2C9*3 allelic group showed significantly higher serum phenytoin levels compared to the wild variants (P = 0.009). There was no statistically significant difference in the dose received (P = 0.12) and side effects of CYP2C9*2 and CYP2C9*3 genotypes (P = 0.442 and 0.597 respectively) when compared with wild variant.

Conclusion

CYP2C9*3 is more common than *2 in the present study. All the polymorphisms demonstrated in our study were heterozygous with no homozygosity. Serum phenytoin levels are higher in polymorphic groups (*3) which suggest their poor metabolizing nature. Genotyping may help to avoid toxicity and concentration-dependent adverse effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-016-0603-0) contains supplementary material, which is available to authorized users.

In vitro metabolism of phenytoin in 36 CYP2C9 variants found in the Chinese population

Cytochrome P450 2C9 (CYP2C9) is an important member of the cytochrome P450 enzyme superfamily, with 57 CYP2C9 allelic variants being previously reported. Recently, we identified 22 novel alleles (*36 -*56 and N418T) in the Han Chinese population. This study aims to assess the catalytic activities of wild-type (CYP2C9*1) and 36 CYP2C9 allelic variants found in the Chinese population toward phenytoin (PHT) in vitro. Insect microsomes expressing CYP2C9*1 and 36 CYP2C9 variants were incubated with 1-200 μM phenytoin for 30 min at 37 °C. Then, these products were extracted and the signal detection was performed by HPLC-MS/MS. The intrinsic clearance (Vmax/Km) values of all variants, with the exception of CYP2C9*2, CYP2C9*11, CYP2C9*23, CYP2C9*29, CYP2C9*34, CYP2C9*38, CYP2C9*44, CYP2C9*46 and CYP2C9*48, were significantly different from CYP2C9*1. CYP2C9*27, *40, *41, *47, *49, *51, *53, *54, *56 and N418T variant exhibited markedly larger values than CYP2C9*1 (>152.8%), whereas 17 variants exhibited smaller values (from 48.6% to 99.9%) due to larger Km and/or smaller Vmax values than CYP2C9*1. The findings suggest that more attention should be paid on subjects carrying these infrequent CYP2C9 alleles when administering phenytoin in clinic.

The effect of CYP2C9 and VKORC1 genetic polymorphisms on warfarin dose requirements in a pediatric population

OBJECTIVE

The aim was to investigate the frequency of genetic polymorphisms of cytochrome P4502C9 (CYP2C9) and vitamin K epoxide reductase complex subunit1 (VKORC1) and determine the effect of these polymorphisms on warfarin dose requirements in pediatric patients.

METHODS

Fifty-eight pediatric patients with cardiac disease, thrombophilia, or other conditions, taking a stable warfarin dose, aged 0.2-18 years, and with international normalized ratio (INR) between 2 and 3 and 149 healthy children as a control group were included in this prospective, observational study. Patients receiving drugs that interact with warfarin, having chronic liver or renal disease, obesity, or thyroid dysfunctions were excluded. Polymerase chain reaction (real time and restriction fragment length polymorphism) was used to analyze the CYP2C9*2, CYP2C9*3, and VKORC1 polymorphisms. The ideal warfarin dose was calculated according to the patient's age, height, and the presence of CYP2C9*2, CYP2C9*3, and VKORC1 genetic polymorphisms. The mean daily administered doses and ideal doses were compared. Analysis of variance, Student's t-test, logistic regression analysis, and Pearson's correlation analysis were used for statistical analyses.

RESULTS

The frequency of the CYP2C9 and VKORC1 genetic polymorphisms was determined as CYP2C9*1/*1 (54.6%), *1/*2 (16.4%), *1/*3 (24.2%), *2/*3 (2.9%), *3/*3 (1.9%), wild-type VKORC1 (26.6%), heterozygote alleles (52.7%), and mutant alleles (20.8%). Patients with allelic variants were found to require lower warfarin doses, and a 64.5% correlation was found between the calculated ideal doses and the administered warfarin doses.

CONCLUSION

Considering CYP2C9 and VKORC1 genetic polymorphisms prior to commencing warfarin treatment will make it easier to reach target INRs and reduce the rate of complications.

Genetic Polymorphism of Cytochrome p450 (2C9) Enzyme in Iranian Baluch Ethnic Group

The aim of the present study is to assess and compare the frequencies of the cytochrome P450 CYP2C9 variations in the Baluch ethnic group (n=110) with other ethnic groups. The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 were 80.90%, 11.82% and 7.27%, respectively. 70.90%, 11.82%, 8.18%, 4.55%, 2.73% and 1.82% of subjects were with CYP2C9*1/*1, CYP2C9*1/*2, CYP2C9*1/*3, CYP2C9*2/*2, CYP2C9*2/*3 and CYP2C9*3/*3 genotypes, respectively. Different mutants may effect on prediction of drug dose requirements in different ethnic groups. Thus, CYP2C9 variants to be determined for findings high risk groups use optimal dosage of drugs metabolized by this polymorphic enzyme.

Injectable microspheres for extended delivery of bioactive insulin and salicylic acid

Developing methods for insulin delivery continues to be of great translational research interest as insulin remains one of the most effective and commonly used treatments for diabetes. Bolus insulin injection at frequent intervals or insulin-loaded pumps used to treat diabetic patients have drawbacks including highly uneven kinetics, low patient compliance, enhanced chances of infections and disease transmission, and device fouling. This study evaluates the in vivo effects of insulin-loaded, salicylate-based, biocompatible, biodegradable polymeric microspheres that gradually release salicylic acid and insulin simultaneously. The study is predicated on the knowledge that such a continuous delivery system can release insulin over an extended period of time and overcome the aforementioned issues. Additionally, salicylic acid reduces insulin resistance in type-2 diabetic patients. In this work, we observed that insulin and salicylic acid were detected in serum over an extended period of time (at least 12 h and 4 days, respectively), and mice receiving insulin-loaded microspheres had a blood glucose reduction time frame ⩾12 times that of bolus insulin administration.

Hormonal regulation of hepatic drug biotransformation and transport systems

The human body is constantly exposed to many xenobiotics including environmental pollutants, food additives, therapeutic drugs, etc. The liver is considered the primary site for drug metabolism and elimination pathways, consisting in uptake, phase I and II reactions, and efflux processes, usually acting in this same order. Modulation of biotransformation and disposition of drugs of clinical application has important therapeutic and toxicological implications. We here provide a compilation and analysis of relevant, more recent literature reporting hormonal regulation of hepatic drug biotransformation and transport systems. We provide additional information on the effect of hormones that tentatively explain differences between sexes. A brief discussion on discrepancies between experimental models and species, as well as a link between gender-related differences and the hormonal mechanism explaining such differences, is also presented. Finally, we include a comment on the pathophysiological, toxicological, and pharmacological relevance of these regulations.

The effect of polymorphic metabolism enzymes on serum phenytoin level

Phenytoin has a widespread use in epilepsy treatment and is mainly metabolized by hepatic cytochrome P450 enzymes (CYP). We have investigated CYP2C9*2, CYP2C9*3, CYP2C19*2 and CYP2C19*3 allelic variants in a Turkish population of patients on phenytoin therapy. Patients on phenytoin therapy (n = 102) for the prevention of epileptic seizures were included. Polymorphic alleles were analyzed by restriction fragment length polymorphism method. Serum concentrations of phenytoin were measured by fluorescence polarization immune assay method. The most frequent genotype was detected for CYP2C9 wild-type alleles (78.43 %), whereas CYP2C19*2/*2 (5.88 %) was the least frequent genotype group. According to the classification made with both enzyme polymorphisms, CYP2C9*1/*1-CYP2C19*1/*1 (G1: 41.17 %) genotype group was the most frequent whereas CYP2C9*1/*2-CYP2C19*1/*3 (G7: 0.98 %) was the least frequent one. The highest mean phenytoin level (27.95 ± 1.85 µg/ml) was detected in the G8 genotype group (CYP2C9*1/*3-CYP2C19*2/*3) and the G1 genotype group showed the lowest mean phenytoin level (7.43 ± 0.73 µg/ml). The mean serum concentration of phenytoin of the polymorphic patients with epilepsy was higher than that for the wild-type alleles both in the monotherapy and polytherapy patients. These results show the importance of the genetic polymorphism analysis of the main metabolizing enzyme groups of phenytoin for the dose adjustment.

Effects of amiodarone, thyroid hormones and CYP2C9 and VKORC1 polymorphisms on warfarin metabolism: a review of the literature

OBJECTIVE

To review the literature regarding the interaction among amiodarone therapy, thyroid hormone levels, and warfarin metabolism.

METHODS

A 73-year-old male with type 2 after describing an unusual case of amiodarone-induced thyrotoxicosis (AIT) who experienced a severe rise in international normalized ratio (INR) values after initiating warfarin therapy due to an unusual combination of excessive thyroid hormones, amiodarone therapy, and a genetic abnormality affecting warfarin metabolism.

RESULTS

Genetic analysis revealed that the patient was CYP2C9*2 wild-type, CYP2C9*3/*3 homozygous mutant, and VKORC1*3/*3 homozygous mutant. A review of the literature revealed that both mutations can independently affect warfarin metabolism. In addition, amiodarone therapy and the presence of thyrotoxicosis per se can affect warfarin metabolism and reduce the dose needed to maintain INR in the therapeutic range. The association of the 2 genetic polymorphisms in a patient with AIT is extremely rare and strongly impairs warfarin metabolism, exposing the patient to a high risk of overtreatment.

CONCLUSIONS

In patients with AIT, warfarin therapy should be gradually introduced, starting with a very low dose, because of the significant risk of warfarin overtreatment. Whether the genetic analysis of CYP2C9 and VKORC1 polymorphisms should be routinely performed in AIT patients remains conjectural.

Effect of CYP2A6 genetic polymorphism on the metabolic conversion of tegafur to 5-fluorouracil and its enantioselectivity

Tegafur (FT), a prodrug of 5-fluorouracil, is a chiral molecule, a racemate of R- and S-isomers, and CYP2A6 plays an important role in the enantioselective metabolism of FT in human liver microsomes (R-FT >> S-FT). This study examined the enantioselective metabolism of FT by microsomes prepared from Sf9 cells expressing wild-type CYP2A6 and its variants (CYP2A6*7, *8, *10, and *11) that are highly prevalent in the Asian population. We also investigated the metabolism of coumarin and nicotine, both CYP2A6 probe drugs, in these variants. Enzyme kinetic analyses showed that CYP2A6.7 (I471T) and CYP2A6.10 (I471T and R485L) had markedly lower Vmax values for both enantiomers than wild-type enzyme (CYP2A6.1) and other variant enzymes, whereas Km values were higher in most of the variant enzymes for both enantiomers than CYP2A6.1. The ratios of Vmax and Km values for R-FT to corresponding values for S-FT (R/S ratio) were similar among enzymes, indicating little difference in enantioselectivity among the wild-type and variant enzymes. Similarly, both CYP2A6.7 and CYP2A6.10 had markedly lower Vmax values for coumarin 7-hydroxylase and nicotine C-oxidase activities than CYP2A6.1 and other variant enzymes, whereas Km values were higher in most of the variant enzymes for both activities than CYP2A6.1. In conclusion, the amino acid substitutions in CYP2A6 variants generally resulted in lower affinity for substrates, while Vmax values were selectively reduced in CYP2A6.7 and CYP2A6.10. Consistent R/S ratios among CYP2A6.1 and variant enzymes indicated that the amino acid substitutions had little effect on enantioselectivity in the metabolism of FT.

Search for genetic determinants of sulfonylurea efficacy in type 2 diabetic patients from China

AIMS/HYPOTHESIS

The aim of this study was to investigate whether genetic variance can influence the efficacy of glibenclamide in patients with type 2 diabetes.

METHODS

A total of 747 patients with type 2 diabetes was enrolled from the Xiaoke Pills Clinical Trial, which is a double-blind, randomised controlled trial. All the patients had been treated with glibenclamide for 48 weeks, with strict drug dose adjustment and data collection. Treatment failure was confirmed when patients reached the criteria for terminating their participation in the study (fasting blood glucose level ≥ 7.0 mmol/l on two consecutive tests 4 weeks after reaching the pre-set maximal dose or maximal tolerated dose). Using this cohort, we tested 44 single-nucleotide polymorphisms (SNPs) in 27 gene regions. The genes in our study were involved in the metabolism of sulfonylureas, islet beta cell function, insulin resistance and beta cell growth and differentiation. A logistic regression model was used to evaluate the relationship between genetic variants and treatment failure over a period of 48 weeks.

RESULTS

We found that no SNP reached the significance level of p < 0.00125 if Bonferroni correction was performed for multiple testing in the logistic regression model used in this pharmacogenetic study. Participants with the minor allele C of rs10811661 in CDKN2A/CDKN2B showed a significantly greater reduction in fasting blood glucose (TT vs TC vs CC: 9.3% (0-20.0%) vs 9.2% (0.9-20.5%) vs 12.7% (5.2-24.4%), p = 0.008) after the initial 4 weeks of treatment independent of age, sex and BMI. There was a significant difference in beta cell function among carriers of different genotypes of rs10811661.

CONCLUSIONS/INTERPRETATION

Our study demonstrated that the CDKN2A/CDKN2B gene may be nominally associated with the efficacy of glibenclamide, and that CDKN2A/CDKN2B is associated with beta cell function.

Warfarin Dosing in a Patient with CYP2C9(∗)3(∗)3 and VKORC1-1639 AA Genotypes

Genetic factors most correlated with warfarin dose requirements are variations in the genes encoding the enzymes cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase (VKOR). Patients receiving warfarin who possess one or more genetic variations in CYP2C9 and VKORC1 are at increased risk of adverse drug events and require significant dose reductions to achieve a therapeutic international normalized ratio (INR). A 74-year-old white female with atrial fibrillation was initiated on a warfarin dose of 2 mg PO daily, which resulted in multiple elevated INR measurements and three clinically significant hemorrhagic events and four vitamin K antidote treatments over a period of less than two weeks. Genetic analysis later revealed that she had the homozygous variant genotypes of CYP2C9∗3∗3 and VKORC1-1639 AA. Warfarin dosing was subsequently restarted and stabilized at 0.5 mg PO daily with therapeutic INRs. This is the first case report of a white female with these genotypes stabilized on warfarin, and it highlights the value of pharmacogenetic testing prior to the initiation of warfarin therapy to maximize efficacy and minimize the risk of adverse drug events.

Variability in human in vitro enzyme kinetics

There are many factors which are known to cause variability in human in vitro enzyme kinetic data. Factors such as the source of enzyme and how it was prepared, the genetics and background of the donor, how the in vitro studies are designed, and how the data are analyzed contribute to variability in the resulting kinetic parameters. It is important to consider not only the factors which cause variability within an experiment, such as selection of a probe substrate, but also those that cause variability when comparing kinetic data across studies and laboratories. For example, the artificial nature of the microsomal lipid membrane and microenvironment in some recombinantly expressed enzymes, relative to those found in native tissue microsomes, has been shown to influence enzyme activity and thus can be a source of variability when comparing across the two different systems. All of these factors, and several others, are discussed in detail in the chapter below.

In vitro functional characterization of 37 CYP2C9 allelic isoforms found in Chinese Han population

AIM

Cytochrome P450 2C9 (CYP2C9) is a polymorphic enzyme that is responsible for the metabolism of approximately 15% of clinically important drugs. The aim of this study was to assess the catalytic characteristics of 37 CYP2C9 allelic isoforms found in Chinese Han population on the metabolism of tolbutamide in vitro.

METHODS

The wild-type and 36 CYP2C9 variants were expressed in sf21 insect cells using a baculovirus-mediated expression system. Then the insect microsomes were prepared for assessing the metabolic characteristics of each variant toward the CYP2C9-specific drug substrate tolbutamide.

RESULTS

Of 36 allelic variants tested, the intrinsic clearance values of 2 allelic isoforms (CYP2C9.36 and CYP2C9.51) were much higher than the wild-type CYP2C9.1 protein, 3 allelic isoforms (CYP2C9.11, CYP2C9.56 and N418T) exhibited similar intrinsic clearance values as the wild-type enzyme, whereas the other 31 variants showed significantly reduced intrinsic clearance values, ranging from 0.08% to 66.88%, for tolbutamide.

CONCLUSION

Our study provides the most comprehensive data concerning the enzymatic activity of the CYP2C9 variants that are present in the Chinese Han population, and our data suggest that most of the carriers of these alleles might be paid more attention when using CYP2C9 mediated drugs clinically.

Functional characterization of 32 CYP2C9 allelic variants

Genetic variations in cytochrome P450 2C9 (CYP2C9) contribute to interindividual variability in the metabolism of clinically used drugs such as warfarin and tolbutamide. We functionally characterized 32 types of allelic variant CYP2C9 proteins. Recombinant CYP2C9 proteins generated using a heterologous expression system are useful for comparing functional changes in CYP2C9 variant proteins expressed from low-frequency alleles. Wild-type CYP2C9 and its 31 variants were found to be transiently expressed in COS-7 cells, and the enzymatic activity of the CYP2C9 variants was characterized using S-warfarin as a representative substrate. Among the 32 types of CYP2C9 allelic variants tested, CYP2C9.18, CYP2C9.21, CYP2C9.24, CYP2C9.26, CYP2C9.33 and CYP2C9.35 exhibited no enzyme activity, and 12 types showed significantly decreased enzyme activity. In vitro analysis of CYP2C9 variant proteins should be useful for predicting CYP2C9 phenotypes and for application to personalized drug therapy.

Interaction of cigarette smoking and carcinogen-metabolizing polymorphisms in the risk of colorectal polyps

The causal role of cigarette smoking in the risk of colorectal neoplasm has been suggested but not established. In a case-control study including 2060 colorectal polyp patients and 3336 polyp-free controls, we evaluated 21 functional genetic variants to construct a tobacco-carcinogen-metabolizing genetic risk score. Data regarding cigarette smoking were obtained through telephone interviews. Cigarette smoking was associated with an elevated risk of both adenomas and hyperplastic polyps. The association with smoking was stronger in participants with a high carcinogen-metabolizing risk score than those with a low risk score. Smoking 30 or more cigarettes per day was associated with a 1.7-fold elevated risk of any polyps (95% confidence interval = 1.3-2.2) among those with a low genetic risk score and 2.9-fold elevated risk (95% confidence interval = 1.8-4.8) among those with a high genetic risk score (P interaction = 0.025). A similar pattern of interaction was observed in analyses conducted separately for those with adenomas only (P interaction = 0.039) and hyperplastic polyps only (P interaction = 0.024). Interaction between carcinogen-metabolizing genetic risk and cigarette smoking was found in relation to high-risk adenomas (P interaction = 0.010) but not low-risk adenomas (P interaction = 0.791). No apparent interaction was found for duration of smoking. This study shows that the association between cigarette smoking and colorectal polyp risk is modified by tobacco-carcinogen-metabolizing polymorphisms, providing support for a causal role of cigarette smoking in the etiology of colorectal tumors.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.

Meta-analysis of cytochrome P-450 2C9 polymorphism and colorectal cancer risk

Background

CYP2C9 encodes a member of the cytochrome P450 superfamily of enzymes which play a central role in activating and detoxifying many carcinogens and endogenous compounds thought to be involved in the development of colorectal cancer (CRC). In the past decade, the relationship between CYP2C9 common polymorphisms (R144C and I359L) and CRC has been reported in various ethnic groups; however, these studies have yielded contradictory results. To investigate this inconsistency, we performed this meta-analysis.

Methods

Databases including Pubmed, EMBASE, Web of Science and China National Knowledge Infrastructure (CNKI) were searched to find relevant studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of association.

Results

A total of 13 articles involving 9,463 cases and 11,416 controls were included. Overall, the summary odds ratio of CRC was 0.98 (95% CI: 0.89−1.06) and 0.99 (95% CI: 0.87−1.14) for CYP2C9 144C and 359L alleles, respectively. No significant results were observed using dominant or recessive genetic model for these polymorphisms. In the stratified analyses according to ethnicity and sex, no evidence of any gene-disease association was obtained.

Conclusions

This meta-analysis suggests that the CYP2C9 may not be associated with colorectal cancer development.

Pharmacogenetics of nonsteroidal anti-inflammatory drugs

With the beginning of the Human Genome Project, an emerging field of science was brought to the forefront of the pharmaceutical community. Pharmacogenetics facilitates optimization of the current patient-centered care model and pharmacotherapy as a whole. Utilizing these ever-expanding branches of science to nonsteroidal anti-inflammatory drugs (NSAIDs) can provide novel opportunities to affect patient care. With a wide range of NSAID choices available as treatment options for relieving pain and/or reducing inflammation or fever, a more systematic way of selecting the ideal agent for the patients based upon their genetic information could spare them from a potentially permanent health-care condition. Furthermore, if a patient possesses or lacks certain alleles, serious adverse events can be anticipated and avoided. The tailoring of drug therapy can be achieved using the published data and cutting-edge genetic testing to attain a higher standard of care for patients.

Effect of genetic variants, especially CYP2C9 and VKORC1, on the pharmacology of warfarin

The genes encoding the cytochrome P450 2C9 enzyme (CYP2C9) and vitamin K-epoxide reductase complex unit 1 (VKORC1) are major determinants of anticoagulant response to warfarin. Together with patient demographics and clinical information, they account for approximately one-half of the warfarin dose variance in individuals of European descent. Recent prospective and randomized controlled trial data support pharmacogenetic guidance with their use in warfarin dose initiation and titration. Benefits from pharmacogenetics-guided warfarin dosing have been reported to extend beyond the period of initial dosing, with supportive data indicating benefits to at least 3 months. The genetic effects of VKORC1 and CYP2C9 in African and Asian populations are concordant with those in individuals of European ancestry; however, frequency distribution of allelic variants can vary considerably between major populations. Future randomized controlled trials in multiethnic settings using population-specific dosing algorithms will allow us to further ascertain the generalizability and cost-effectiveness of pharmacogenetics-guided warfarin therapy. Additional genome-wide association studies may help us to improve and refine dosing algorithms and potentially identify novel biological pathways.

Bioinformatics and variability in drug response: a protein structural perspective

Marketed drugs frequently perform worse in clinical practice than in the clinical trials on which their approval is based. Many therapeutic compounds are ineffective for a large subpopulation of patients to whom they are prescribed; worse, a significant fraction of patients experience adverse effects more severe than anticipated. The unacceptable risk-benefit profile for many drugs mandates a paradigm shift towards personalized medicine. However, prior to adoption of patient-specific approaches, it is useful to understand the molecular details underlying variable drug response among diverse patient populations. Over the past decade, progress in structural genomics led to an explosion of available three-dimensional structures of drug target proteins while efforts in pharmacogenetics offered insights into polymorphisms correlated with differential therapeutic outcomes. Together these advances provide the opportunity to examine how altered protein structures arising from genetic differences affect protein-drug interactions and, ultimately, drug response. In this review, we first summarize structural characteristics of protein targets and common mechanisms of drug interactions. Next, we describe the impact of coding mutations on protein structures and drug response. Finally, we highlight tools for analysing protein structures and protein-drug interactions and discuss their application for understanding altered drug responses associated with protein structural variants.

A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II)

Background—

Warfarin is characterized by marked variations in individual dose requirements and a narrow therapeutic window. Pharmacogenetics (PG) could improve dosing efficiency and safety, but clinical trials evidence is meager.

Methods and Results—

A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II) comprised 2 comparisons: (1) a blinded, randomized comparison of a modified 1-step (PG-1) with a 3-step algorithm (PG-2) (N=504), and (2) a clinical effectiveness comparison of PG guidance with use of either algorithm with standard dosing in a parallel control group (N=1866). A rapid method provided same-day CYP2C9 and VKORC1 genotyping. Primary outcomes were percentage of out-of-range international normalized ratios at 1 and 3 months and percentage of time in therapeutic range. Primary analysis was modified intention to treat. In the randomized comparison, PG-2 was noninferior but not superior to PG-1 for percentage of out-of-range international normalized ratios at 1 month and 3 months and for percentage of time in therapeutic range at 3 months. However, the combined PG cohort was superior to the parallel controls (percentage of out-of-range international normalized ratios 31% versus 42% at 1 month; 30% versus 42% at 3 months; percentage of time in therapeutic range 69% versus 58%, 71% versus 59%, respectively, all P <0.001). Differences persisted after adjustment for age, sex, and clinical indication. There were fewer percentage international normalized ratios ≥4 and ≤1.5 and serious adverse events at 3 months (4.5% versus 9.4% of patients, P <0.001) with PG guidance.

Conclusions—

These findings suggest that PG dosing should be considered for broader clinical application, a proposal that is being tested further in 3 major randomized trials. The simpler 1-step PG algorithm provided equivalent results and may be preferable for clinical application.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00927862.