Clinical Pharmacogenetic Studies Research Articles

The expanding role of gene-based prescribing for phase II drug-metabolizing enzymes

Clinical pharmacogenomics has expanded rapidly with the ability to translate evidence from basic science findings into actionable decisions guiding pharmacotherapy in – various disease states. Most findings with potential clinical relevance have been in drug-metabolizing enzymes where variation could cause interindividual differences in response and efficacy. Conventionally, these metabolizing enzymes are classified as Phase I and Phase II enzymes. Although Phase II enzymes are responsible for the metabolism of many drugs, research has focused more on variation in Phase I enzymes. Our aim in this review was to discuss from a historical to present context, the research on key variants in major Phase II enzymes and to summarize clinical pharmacogenetic association studies that could help guide future translation into practice. We evaluated pivotal articles in PubMed (1980–2022) on human pharmacogenomic studies (preclinical and clinical) of N-acetyltransferases (NATs), methyltransferases, glutathione transferases, sulfotransferases, and glucuronosyltransferases for the evidence of clinical applicability and utility. Of the 5 Phase II enzyme superfamilies reviewed, there is presently evidence to support clinical utility for gene-based prescribing for two of them. A third family (NATs) is evaluated as having strong likelihood for future utility in the pharmacological treatment of acquired immunodeficiency syndrome-associated opportunistic infections, tuberculosis, and endemic diseases.

Population genetic polymorphisms of pharmacogenes in Zimbabwe, a potential guide for the safe and efficacious use of medicines in people of African ancestry.

Pharmacogenomics (PGx) is a clinically significant factor in the safe and efficacious use of medicines. While PGx knowledge is abundant for other populations, there are scarce PGx data on African populations and is little knowledge on drug-gene interactions for medicines used to treat diseases common in Africa. The aim of this study was to use a custom-designed open array to genotype clinically actionable variants in a Zimbabwean population. This study also identified some of the commonly used drugs in Zimbabwe and the associated genes involved in their metabolism. A custom-designed open array that covers 120 genetic variants was used to genotype 522 black Zimbabwean healthy volunteers using TaqMan-based single nucleotide polymorphism genotyping. Data were also accessed from Essential Drugs' List in Zimbabwe (EDLIZ), and the medicines were grouped into the associated biomarker groups based on their metabolism. We also estimated the national drug procurement levels for medicines that could benefit from PGx-guided use based on the data obtained from the national authorities in Zimbabwe. The results demonstrate the applicability of an open-array chip in simultaneously determining multiple genetic variants in an individual, thus significantly reducing cost and time to generate PGx data. There were significantly high frequencies of African-specific variants, such as the CYP2D6*17 and *29 variants and the CYP2B6*18 variant. The data obtained showed that the Zimbabwean population exhibits PGx variations in genes important for the safe and efficacious use of drugs approved by the EDLIZ and are procured at significantly large amounts annually. The study has established a cohort of genotyped healthy volunteers that can be accessed and used in the conduct of clinical pharmacogenetic studies for drugs entering a market of people of predominantly African ancestry. Our study demonstrated the potential benefit of integrating PGx in Zimbabwe for the safe and efficacious use of drugs that are commonly used.

Genetic inhibition of NFATC2 attenuates asparaginase hypersensitivity in mice

AbstractThe family of nuclear factor of activated T cells (NFAT) transcription factors plays a critical role in mediating immune responses. Our previous clinical pharmacogenetic studies suggested that NFATC2 is associated with the risk of hypersensitivity reactions to the chemotherapeutic agent L-asparaginase (ASNase) that worsen outcomes during the treatment of pediatric acute lymphoblastic leukemia. We therefore hypothesized that the genetic inhibition of NFATC2 would protect against the development of anti-ASNase antibodies and ASNase hypersensitivity. Our study demonstrates that ASNase-immunized NFATC2-deficient mice are protected against ASNase hypersensitivity and develop lower antigen-specific and total immunoglobulin E (IgE) levels compared with wild-type (WT) controls. Furthermore, ASNase-immunized NFATC2-deficient mice develop more CD4+ regulatory T cells, fewer CD4+ interleukin-4–positive (IL-4+) cells, higher IL-10/TGF-β1 levels, and lower IL-4/IL-13 levels relative to WT mice. Basophils and peritoneal mast cells from ASNase-immunized, but not naïve, NFATC2-deficient mice had lower FcεRI expression and decreased IgE-mediated mast cell activation than WT mice. Furthermore, ASNase-immunized, but not naïve, NFATC2-deficient mice developed less severe shock than WT mice after induction of passive anaphylaxis or direct histamine administration. Thus, inhibition of NFATC2 protects against ASNase hypersensitivity by impairing T helper 2 responses, which may provide a novel strategy for attenuating hypersensitivity and the development of antidrug antibodies, including to ASNase.

Challenges and Opportunities for Clinical Pharmacogenetic Research Studies in Resource-limited Settings: Conclusions From the Council for International Organizations of Medical Sciences–Ibero-American Network of Pharmacogenetics and Pharmacogenomics Meeting

PurposeThe symposium Health and Medicines in Indigenous Populations of America was organized by the Council for International Organizations of Medical Sciences (CIOMS) Working Group on Clinical Research in Resource-Limited Settings (RLSs) and the Ibero-American Network of Pharmacogenetics and Pharmacogenomics (RIBEF). It was aimed to share and evaluate investigators' experiences on challenges and opportunities on clinical research and pharmacogenetics. MethodsA total of 33 members from 22 countries participated in 2 sessions: RIBEF studies on population pharmacogenetics about the relationship between ancestry with relevant drug-related genetic polymorphisms and the relationship between genotype and phenotype in Native Americans (session 1) and case examples of clinical studies in RLSs from Asia (cancer), America (diabetes and women health), and Africa (malaria) in which the participants were asked to answer in free text their experiences on challenges and opportunities to solve the problems (session 2). Later, a discourse analysis grouping common themes by affinity was conducted. FindingsThe main result of session 1 was that the pharmacogenetics-related ancestry of the population should be considered when designing clinical studies in RLSs. In session 2, 21 challenges and 20 opportunities were identified. The social aspects represent the largest proportion of the challenges (43%) and opportunities (55%), and some of them seem to be common. ImplicationsThe main discussion points were gathered in the Declaration of Mérida/T'Hó and announced on the Parliament of Extremadura during the CIOMS-RIBEF meeting in 4 of the major Latin American autochthonous languages (Náhualth, Mayan, Miskito, and Kichwa). The declaration highlighted the following: (1) the relevance of population pharmacogenetics, (2) the sociocultural contexts (interaction with traditional medicine), and (3) the education needs of research teams for clinical research in vulnerable and autochthonous populations.

862 Challenges and Lessons Learned from Opioid Pharmacogenetic Studies in Burn Patients

Abstract Introduction ”One-size fits all” opioid dosing often results in a lack of efficacy or toxic consequences. Patients are heterogeneous; their drug sensitivity varies, potentially impacting therapeutic outcomes. Implementation of pharmacogenetic testing in the clinical setting is needed to improve precision dosing, especially in the critically ill (e.g. burns). However, due to the lack of comprehensive data addressing the functional impact of genetic variants, universal implementation of genetic screening is not yet possible. While animal models provide valuable data, they do not capture the vast heterogeneity and comorbidities of patients. Clinical pharmacogenetic studies are needed to advance our understanding of genetic variability and clinical impacts on opioid efficacy. The purpose of this report is to describe the challenges of clinical opioid pharmacogenetic studies in burn patients. Methods We performed two studies: 1) a pilot study evaluating CYP gene haplotypes in 13 adult burn patients receiving fentanyl using remnant samples and 2) a pediatric burn patient fentanyl pharmacogenetic study. In the pediatric study, we initially screened with a customized 18 gene panel (opioid pathway specific), and later expanded to whole exome analysis. Results We identified 3 adult slow-metabolizers, one with a CYP3A4 and two with CYP2D6 haplotypes and an average of 80+ variants identified in the 18 genes in preliminary analysis of pediatric patients. Multiple challenges were identified in conducting clinical observational studies. Although remnant samples can be hypothesis-generating, clinical data linkage is limited, decreasing the ability for covariate analysis to investigate clinical factors contributing to altered fentanyl metabolism. The use of a commercial haplotype panel, while convenient, only identifies known haplotypes and doesn’t identify all variants in patients. Research protocols must be tailored to clinical workflow. Repeated dosing of fentanyl, which is standard of care but may not be detailed in medical record charting, predisposes research analysis to inaccuracies. Sparse blood sampling, errors in blood draw methodology and loss of vascular access, particularly in pediatrics, can render data sets unanalyzable. Conclusions While we have faced many challenges, overall, these studies have produced valuable data to enable better future clinical research design. Educating bedside nurses on study goals, teaching investigators about clinical workflow, and trouble-shooting proper sample collection and charting are essential elements of a successful study. Finally, minimizing sample volume and optimizing sample time points allows for better study adherence and more accurate analysis. Applicability of Research to Practice Lessons learned from these studies will aid in the optimization of study design of future burns pharmacogenetic clinical studies.

Genetic polymorphisms of CYP3A5, CHRM2, and ZNF498 and their association with epilepsy susceptibility: a pharmacogenetic and case-control study.

BackgroundA total of 50 million persons were diagnosed worldwide with epilepsy. One-third of them are experiencing debilitating seizures despite optimum anti‐epileptic drugs (AEDs) treatment. Several studies have suggested that CYP3A5, CHRM2, and ZNF498 influence the pharmacokinetics of AEDs. Therefore, the severity of the disease as well as the degree of response to the AEDs could be affected by the genetic polymorphisms within these genes.ObjectivesIn this study, we assessed the effect of certain single nucleotide polymorphisms (SNPs) within CYP3A5, CHRM2, and ZNF498 genes on the susceptibility to develop epilepsy and the responsiveness to AEDs treatment.MethodsA case–control and pharmacogenetic study was conducted on samples of 299 healthy individuals in addition to 296 epileptic patients. Genotypic, allelic, and clinical data association were performed for the selected polymorphisms within the (rs324649, rs420817, rs15524, and rs1859690) in the Jordanian population.ResultsThe analysis revealed no significant association of the investigated SNPs with epilepsy in general, partial and generalized epilepsy as well as drug responsiveness. CYP3A5 and ZNF498 were associated with family history (P=0.003 and P=0.002, respectively) and the classification of epilepsy for the ZNF498 variant (P=0.009). On the other hand, CHRM2 was not linked to either disease severity or treatment responsiveness.ConclusionOur results failed to confirm the association of CYP3A5, ZNF498, and CHRM2 variants with either disease development or treatment response. Clinical pharmacogenetic studies may contribute to treatment personalization, appropriate drug dose selection, minimizing drug adverse reactions, increasing drug efficacy, and reducing the costive burdens.

Current Progress in Pharmacogenetics of Second-Line Antidiabetic Medications: Towards Precision Medicine for Type 2 Diabetes

Precision medicine is a scientific and medical practice for personalized therapy based on patients’ individual genetic, environmental, and lifestyle characteristics. Pharmacogenetics and pharmacogenomics are also rapidly developing and expanding as a key element of precision medicine, in which the association between individual genetic variabilities and drug disposition and therapeutic responses are investigated. Type 2 diabetes (T2D) is a chronic metabolic disorder characterized by hyperglycemia mainly associated with insulin resistance, with the risk of clinically important cardiovascular, neurological, and renal complications. The latest consensus report from the American Diabetes Association and European Association for the Study of Diabetes (ADA-EASD) on the management of T2D recommends preferential use of glucagon-like peptide-1 (GLP-1) receptor agonists, sodium-glucose cotransporter-2 (SGLT2) inhibitors, and some dipeptidyl peptidase-4 (DPP-4) inhibitors after initial metformin monotherapy for diabetic patients with established atherosclerotic cardiovascular or chronic kidney disease, and with risk of hypoglycemia or body weight-related problems. In this review article, we summarized current progress on pharmacogenetics of newer second-line antidiabetic medications in clinical practices and discussed their therapeutic implications for precision medicine in T2D management. Several biomarkers associated with drug responses have been identified from extensive clinical pharmacogenetic studies, and functional variations in these genes have been shown to significantly affect drug-related glycemic control, adverse reactions, and risk of diabetic complications. More comprehensive pharmacogenetic research in various clinical settings will clarify the therapeutic implications of these genes, which may be useful tools for precision medicine in the treatment and prevention of T2D and its complications.

Systematic and quantitative assessment of the effect of chronic kidney disease on CYP2D6 and CYP3A4/5.

Recent reviews suggest that chronic kidney disease (CKD) can affect the pharmacokinetics of nonrenally eliminated drugs, but the impact of CKD on individual elimination pathways has not been systematically evaluated. In this study we developed a comprehensive dataset of the effect of CKD on the pharmacokinetics of CYP2D6‐ and CYP3A4/5‐metabolized drugs. Drugs for evaluation were selected based on clinical drug–drug interaction (CYP3A4/5 and CYP2D6) and pharmacogenetic (CYP2D6) studies. Information from dedicated CKD studies was available for 13 and 18 of the CYP2D6 and CYP3A4/5 model drugs, respectively. Analysis of these data suggested that CYP2D6‐mediated clearance is generally decreased in parallel with the severity of CKD. There was no apparent relationship between the severity of CKD and CYP3A4/5‐mediated clearance. The observed elimination‐route dependency in CKD effects between CYP2D6 and CYP3A4/5 may inform the need to conduct clinical CKD studies with nonrenally eliminated drugs for optimal use of drugs in patients with CKD.

Quantitative Analysis of the ABCG2 c.421C > A Polymorphism Effect on In Vivo Transport Activity of Breast Cancer Resistance Protein (BCRP) Using an Intestinal Absorption Model

ABCG2 c.421C>A is one of the most frequent polymorphisms in ABCG2, which encodes the breast cancer resistance protein (BCRP). Clinical pharmacogenetic studies have shown that the plasma area under the concentration-time curve (AUC) values after oral administration of BCRP substrate drugs are significantly higher in subjects homozygous for the c.421C>A polymorphism (421AA) than in wild-type subjects (421CC). The aim of this study was to quantitatively estimate the in vivo decrease of BCRP function caused by the c.421C>A polymorphism based on clinical pharmacokinetic data. Assuming that the pharmacokinetic alteration is accounted for by intestinal BCRP, the ratio of the transport activity of the mutated BCRP to that of the wild-type was optimized by comparing calculations from an intestinal absorption model and clinical pharmacokinetic data. In conclusion, the in vivo intestinal BCRP transport activity in 421AA subjects is estimated to be approximately 23% of that in the 421CC subjects.

Genetics of Cisplatin Ototoxicity: Confirming the Unexplained?

Replication of findings in clinical pharmacogenetic studies is essential but often neglected. The observation that TPMT and COMT genotypes, in combination with ABCC3 genotype, are predictive of ototoxicity following cisplatin treatment has been confirmed. However, translating this observation into a useful preventive strategy requires more mechanistic insight.

Functional polymorphisms of xenobiotics metabolizing enzymes—a research topic

The human genome harbors an impressive number of genes encoding enzymes that primarily metabolize or transport drugs or other xenobiotics (XMEs). Genetic and functional variation in these genes is tremendous and has complex consequences, depending, for example, on whether enzyme structure or expression is affected, or whether the produced metabolite is pharmacologically or toxicologically active or not. Despite numerous impressive examples of the impact of genetic variation on pharmacokinetics and drug response, today's knowledge is incomplete regarding most XME genes and fragmentary even for many well-investigated XMEs. This is one of the reasons why clinical pharmacogenetic studies are often controversial and clinical application in personalized medicine is presently limited. Advanced technology and ongoing large-scale projects are rapidly uncovering the existing genetic variation in all populations on earth, ultimately enabling the personal genome in the very near future. A wealth of mostly rare novel variants is awaiting functional characterization either by high-throughput expression/phenotyping techniques or by prediction using improved algorithms to estimate functional relevance. With this Research Topic we would like to give an up-to-date overview about the current knowledge in this field by covering both, known hard facts as well as cutting-edge advancement in novel genetic and genomic variation of XMEs and their functional consequences. Five major subtopics which include 20 research or review papers are included in this E-book. These are the following: History and current knowledge of XMEs Clinical application of CYP2C19 pharmacogenetics toward more personalized medicine (Lee, 2013, review). Pharmacogenetics of cytochrome P450 2B6 (CYP2B6): advances on polymorphisms, mechanisms, and clinical relevance (Zanger and Klein, 2013, review). Pharmacogenetics of human ABC transporter ABCC11: new insights into apocrine gland growth and metabolite secretion (Ishikawa et al., 2013, review). Pharmacogenomics of cytochrome P450 3A4: recent progress toward the “missing heritability” problem (Klein and Zanger, 2013, review). Clinical implications of XME gene variants ABCB1 4036A>G and 1236C>T polymorphisms affect plasma efavirenz levels in South African HIV/AIDS patients (Swart et al., 2012, research article). Genetic variations in drug-induced liver injury (DILI): resolving the puzzle (Stephens et al., 2012, opinion). MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant? (de la Torre et al., 2012, review). Molecular interactions between NAFLD and xenobiotic metabolism (Naik et al., 2013, review). Toward a clinical practice guide in pharmacogenomics testing for functional polymorphisms of drug-metabolizing enzymes. Gene/drug pairs and barriers perceived in Spain (Agundez et al., 2012, perspective). Inter/intraethnic variability of XME gene variants Characterization of the genetic variation present in CYP3A4 in three South African populations (Drogemoller et al., 2013, research article). Frequencies of 23 functionally significant variant alleles related with metabolism of antineoplastic drugs in the Chilean population: comparison with Caucasian and Asian populations (Roco et al., 2012, research article). Pharmacogenomic diversity among Brazilians: influence of ancestry, self-reported color, and geographical origin (Suarez-Kurtz et al., 2012, review). Regulation of XME gene expression Impact of the interaction between 3′-UTR SNPs and microRNA on the expression of human xenobiotic metabolism enzyme and transporter genes (Wei et al., 2012, research article). Molecular mechanisms of genetic variation and transcriptional regulation of CYP2C19 (Helsby and Burns, 2012, review). Pharmacogenetics in cancer therapy Impact of genetic polymorphisms on chemotherapy toxicity in childhood acute lymphoblastic leukemia (Gervasini and Vagace, 2012, review). Multilocus genotypes of relevance for drug metabolizing enzymes and therapy with thiopurines in patients with acute lymphoblastic leukemia (Stocco et al., 2013, review). Functional polymorphisms in xenobiotic metabolizing enzymes and their impact on the therapy of breast cancer (Vianna-Jorge et al., 2013, review). High-resolution melting analysis of the common c.1905+1G>A mutation causing dihydropyrimidine dehydrogenase deficiency and lethal 5-fluorouracil toxicity (Borras et al., 2013, research article). Polymorphisms of phase I and phase II enzymes and breast cancer risk (Justenhoven, 2012, review). Analysis of the functional polymorphism in the cytochrome P450 CYP2C8 gene rs11572080 with regard to colorectal cancer risk (Ladero et al., 2012, research article).

Proximal Tubular Secretion of Creatinine by Organic Cation Transporter OCT2 in Cancer Patients

Knowledge of transporters responsible for the renal secretion of creatinine is key to a proper interpretation of serum creatinine and/or creatinine clearance as markers of renal function in cancer patients receiving chemotherapeutic agents. Creatinine transport was studied in transfected HEK293 cells in vitro and in wild-type mice and age-matched organic cation transporter 1 and 2-deficient [Oct1/2(-/-)] mice ex vivo and in vivo. Clinical pharmacogenetic and transport inhibition studies were done in two separate cohorts of cancer patients. Compared with wild-type mice, creatinine clearance was significantly impaired in Oct1/2(-/-) mice. Furthermore, creatinine inhibited organic cation transport in freshly isolated proximal tubules from wild-type mice and humans, but not in those from Oct1/2(-/-) mice. In a genetic association analysis (n = 590), several polymorphisms around the OCT2/SLC22A2 gene locus, including rs2504954 (P = 0.000873), were significantly associated with age-adjusted creatinine levels. Furthermore, in cancer patients (n = 68), the OCT2 substrate cisplatin caused an acute elevation of serum creatinine (P = 0.0083), consistent with inhibition of an elimination pathway. Collectively, this study shows that OCT2 plays a decisive role in the renal secretion of creatinine. This process can be inhibited by OCT2 substrates, which impair the usefulness of creatinine as a marker of renal function.

Part 1: Background, Methodology, and Clinical Adoption of Pharmacogenetics

Equivalent drug doses may lead to wide interpatient variability with regard to drug response, reflected by differences in drug activity and normal tissue toxicity. A major factor responsible for this variability is variation among patients in their genetic constitution. Genetic polymorphism may affect the activity of proteins encoded, which in turn may lead to changes in the pharmacokinetic and pharmacodynamic behavior of a drug, observed as differences in drug transport, drug metabolism, and pharmacodynamic drug effects. Recent insights into the functional effect of polymorphism in genes that are involved in the pharmacokinetics and pharmacodynamics of anticancer drugs have provided opportunities for patient-tailored therapy in oncology. Individualized pharmacotherapy based on genotype will help to increase treatment efficacy while reducing unnecessary toxicity, especially of drugs characterized by a narrow therapeutic window, such as anticancer drugs. We provide a series of four reviews aimed at implementing pharmacogenetic-based drug and dose prescription in the daily clinical setting for the practicing oncologist. This first part in the series describes the functional impact of genetic polymorphism and provides a general background to and insight into possible clinical consequences of pharmacogenetic variability. It also discusses different methodologies for clinical pharmacogenetic studies and provides a concise overview about the different laboratory technologies for genetic mutation analysis that are currently widely applied. Subsequently, pharmacogenetic association studies in anticancer drug transport, phase I and II drug metabolism, and pharmacodynamic drug effects are discussed in the rest of the series. Opportunities for patient-tailored pharmacotherapy are highlighted.

Pharmacogenetic Impact of UDP‐Glucuronosyltransferase Metabolic Pathway and Multidrug Resistance—Associated Protein 2 Transport Pathway on Mycophenolic Acid in Thoracic Transplant Recipients: An Exploratory Study

To assess the contribution of polymorphisms in the uridine diphosphate glucuronosyltransferase gene (UGT) and the multidrug resistance-associated protein 2 gene (ABCC2) to mycophenolic acid (MPA) pharmacokinetics and clinical outcomes in thoracic transplant recipients. Open-label, cross-sectional study. Transplant clinic in Vancouver, British Columbia, Canada. Sixty-eight thoracic (36 lung, 32 heart) transplant recipients who were receiving steady-state oral mycophenolate mofetil. Eleven blood samples were obtained from each patient over a 12-hour dosing period. Plasma concentrations of MPA (active metabolite of mycophenolate mofetil), the MPA metabolites 7-Omycophenolic acid glucuronide (MPAG) and acyl glucuronide (AcMPAG), and free MPA were measured, and dose-normalized conventional pharmacokinetic parameters were determined by noncompartmental methods. Genetic polymorphisms in UGT and ABCC2 were determined by sequencing, and their contributions to pharmacokinetic variability were investigated by using multivariate analysis. For both the lung and heart transplant groups, the UGT2B7 variant 802T (Tyr(268) or UGT2B7*2, rs7439366) and the UGT2B7 variant -138A modified AcMPAG exposure (2.5-3.7-fold and 9.3-12.3-fold higher AcMPAG area under the concentration-time curve [AUC] and AcMPAG:MPA ratio, respectively). In an exploratory analysis, occurrences of rejection, infection, anemia, and leukopenia were associated with an AcMPAG AUC greater than 50 μg·hour/ml and an AcMPAG:MPA ratio greater than 2. UGT2B7 is a promising gene candidate that may influence MPA pharmacokinetics clinically; however, larger clinical pharmacogenetic studies in thoracic transplant subpopulations are warranted to corroborate the role of AcMPAG and UGT2B7 variants in optimizing mycophenolate mofetil therapy.

CYP2C9 and VKORC1 genotypes in Puerto Ricans: A case for admixture-matching in clinical pharmacogenetic studies

Admixture is of great relevance to the clinical application of pharmacogenetics and personalized medicine, but unfortunately these studies have been scarce in Puerto Ricans. Besides, allele frequencies for clinically relevant genetic markers in warfarin response (i.e., CYP2C9 and VKORC1) have not yet been fully characterized in this population. Accordingly, this study is aimed at investigating whether a correlation between overall genetic similarity and CYP2C9 and/or VKORC1 genotypes could be established. 98 DNA samples from Puerto Ricans were genotyped for major CYP2C9 and VKORC1 polymorphisms and tested on a physiogenomic (PG)-array to infer population structure and admixture pattern. Analysis affirmed that Puerto Ricans are broadly admixed. A genetic distance dendrogram was constructed by clustering those subjects with similar genetic profiles. Individual VKORC1 and CYP2C9 genotypes were visually overlaid atop the three dendrogram sectors. Sector-1, representing Amerindian ancestry, showed higher VKORC1 -1639G>A variant frequency than the rest of the population (p=0.051). Although CYP2C9*3 allele frequencies matched the expected HapMap values, admixture may explain deviations from published findings regarding VKORC1 -1639G>A and CYP2C9*2 allele frequencies in sector-3. Results suggest that the observed inter-individual variations in ancestral contributions have significant implications for the way each Puerto Rican responds to warfarin therapy. Our findings provide valuable evidence on the importance of controlling for admixture in pharmacogenetic studies of Puerto Rican Hispanics.

Contribution of the Different UDP-Glucuronosyltransferase (UGT) Isoforms to Buprenorphine and Norbuprenorphine Metabolism and Relationship with the Main UGT Polymorphisms in a Bank of Human Liver Microsomes

The goal of this study was to evaluate the specific contribution of individual UDP-glucuronosyltransferase (UGT) isoforms in the metabolism of buprenorphine (BUP) and norbuprenorphine (Nor-BUP), as well as the impact of their genetic variations. The glucuronidation of BUP and Nor-BUP was examined using human liver microsomes (HLMs) and heterologously expressed UGTs. The individual contribution of UGT isoforms was estimated using enzyme kinetic experiments combined with the relative activity factor (RAF). Phenotype-genotype relationships were investigated in a bank of 52 HLMs. Among the six hepatic UGT isoforms tested, UGT1A1, UGT1A3, and UGT2B7 metabolized BUP and Nor-BUP. Using the RAF approach, we found that UGT1A1 and UGT2B7 accounted for approximately 10 and 41% of BUP glucuronidation, respectively. Nor-BUP glucuronidation involved predominantly UGT1A3 (approximately 63%) and UGT1A1 (34%), whereas UGT2B7 had only a minor role. The UGT1A1 promoter (TA)(6/7)TAA mutation (UGT1A1*28) resulted in a 28% decrease of BUP glucuronidation V(max) in pooled HLMs but was not statistically associated with glucuronidation rate in 52 individual HLMs. The presence of the UGT2B7 promoter (G-842A) mutation resulted in higher BUP glucuronidation V(max) in pooled HLMs (+80% on average) and in a significant higher glucuronidation rate in noncarriers (but not in carriers) of the UGT1A1*28 allele (P = 0.0352). This study represents a functional basis for further clinical pharmacogenetic studies.

Cytochrome P450 2C8 Pharmacogenetics: A Review of Clinical Studies

Cytochrome P450 (CYP) 2C8 is responsible for the oxidative metabolism of many clinically available drugs from a diverse number of drug classes (e.g., thiazolidinediones, meglitinides, NSAIDs, antimalarials and chemotherapeutic taxanes). The CYP2C8 enzyme is encoded by the CYP2C8 gene, and several common nonsynonymous polymorphisms (e.g., CYP2C8*2 and CYP2C8*3) exist in this gene. The CYP2C8*2 and *3 alleles have been associated in vitro with decreased metabolism of paclitaxel and arachidonic acid. Recently, the influence of CYP2C8 polymorphisms on substrate disposition in humans has been investigated in a number of clinical pharmacogenetic studies. Contrary to in vitro data, clinical data suggest that the CYP2C8*3 allele is associated with increased metabolism of the CYP2C8 substrates, rosiglitazone, pioglitazone and repaglinide. However, the CYP2C8*3 allele has not been associated with paclitaxel pharmacokinetics in most clinical studies. Furthermore, clinical data regarding the impact of the CYP2C8*3 allele on the disposition of NSAIDs are conflicting and no definitive conclusions can be made at this time. The purpose of this review is to highlight these clinical studies that have investigated the association between CYP2C8 polymorphisms and CYP2C8 substrate pharmacokinetics and/or pharmacodynamics in humans. In this review, CYP2C8 clinical pharmacogenetic data are provided by drug class, followed by a discussion of the future of CYP2C8 clinical pharmacogenetic research.

Genotype-based therapeutic approach for colorectal cancer: state of the art and future perspectives

Background: There is a considerable need to increase efforts in maximizing clinical outcome in the treatment of colorectal cancer, and the identification of genetic factors underlying drug response seems to be one of the most promising areas in this research field. Methods: Clinical trials and pharmacogenetic association studies were reviewed to offer an overview of the most commonly reported polymorphisms in candidate genes critically involved in the response to the chemotherapeutics used at present in the management of colorectal cancer. Results: Several studies investigating the association between genotype and therapeutic results show contrasting data, thus determining increasing uncertainty in the identification of reliable predictive genetic markers of drug response. However, some of the genetic variations identified in genes encoding thymidylate synthase, dihydropyrimidine dehydrogenase, glutathione S-transferase pi, and uridine diphosphate glucosyltransferase 1A1 seem to be promising predictors of drug efficacy and/or toxicity. Conclusion: Additional investigation is needed to validate fully the clinical relevance of individual genetic differences in the variability of drug response. It is hoped that this knowledge base will offer, in the not too distant future, the opportunity to overcome the empirical trial-and-error method in favor of therapeutic drug optimization based on individual genetic make-up.

S.03.05 Clinical pharmacogenetic studies in the treatment of depression

La asenapina, recientemente comercializada en Estados Unidos y pronto en Europa, es un antipsicótico de segunda generación con acción multireceptorial, derivada de su afinidad por múltiples receptores dopaminérgicos (D2, D3 y D4), serotoninérgicos (5HT2A, 5HT2B, 5HT2C, 5HT6 y 5HT7) y adrenérgicos (αa1A, α2A, α2B y α2C). Su administración se realiza por vía sublingual. Tras culminar las fases iniciales de desarrollo, se han realizado diversos ensayos clínicos en dos indicaciones principalmente: esquizofrenia y manía. Este artículo sintetiza la evidencia científica de su eficacia y seguridad en manía aguda y adelanta algunas de sus posibilidades clínicas inmediatas y futuras.La asenapina es eficaz y generalmente bien tolerada en el tratamiento de la manía aguda moderada o grave asociada al trastorno bipolar tipo I. Su administración sublingual plantea el reto de evitar su coadministración con comida u otros fármacos, pero puede suponer una ventaja para la adherencia terapéutica. Por su perfil receptorial, puede asociarse a diversos efectos adversos, pero destaca por la baja intensidad de todos ellos, sin ninguno que destaque por encima de los demás. En Europa está indicada solamente para la manía aguda, pero se están realizando también numerosos ensayos en esquizofrenia y en depresión bipolar.Asenapine, recently marketed in United States and ready to be so in Europe, is a multimodal action second-generation antipsychotic, with high affinity for multiple dopaminergic (D2, D3 y D4), serotonergic (5HT2A, 5HT2B, 5HT2C, 5HT6 and 5HT7) and adrenergic (α1A, α2A, α2B and α2C) receptors. Asenapine has to be administered sublingually. After going through succesfully the preliminary phases of development, several clinical trials have been completed in two main indications: schizophrenia and mania. This article summarizes the available evidence on its safety and efficacy in acute mania and provides some prospect on its clinical immediate and future applications.Asenapine is effective and generally well tolerated in the treatment of moderate-to-severe acute mania associated to bipolar I disorder. The sublingual administration may be a challenge (coadministration with food or other drugs needs to be avoided) but also an opportunity (improved treatment adherence). Due to its multimodal receptor profile, it may cause several side-effects, but most of those are relatively mild, with none being particularly outstanding. In Europe, asenapine is indicated for the treatment of acute mania only, but several trials are being conducted in schizophrenia and bipolar depression.

A review on the design and reporting of studies on drug–gene interaction

Objective Methodological standards for clinical pharmacogenetic studies should be developed to improve reporting of studies and facilitate their inclusion in systematic reviews. The essence of these studies lies within the concept of effect modification. Study Design and Setting A narrative review discussing methodological issues in the design and reporting of pharmacogenetic studies. Results Studying effect modification within a trial leads to the comparison of subgroups based on genotype. Differences in effect based on genotype should preferably be expressed in absolute terms (risk differences) to facilitate clinical decisions on treatment. Information on the distribution of potential effect modifiers or prognostic factors should be available to prevent a biased comparison of differences in effect between genotypes. The distribution of genotypes should also be presented and compared to Hardy–Weinberg equilibrium to check for selection bias. Additional points of interest include the possibility of selective nonavailability of biomaterial and the choice of a statistical model to study effect modification. Conclusion Additional methodological issues should be taken into account when designing and reporting pharmacogenetic studies, to ensure high study quality. We present several important issues for future studies investigating drug–gene interactions that can serve as a basis for further discussion on methodology in pharmacogenetics.