Acyclovir Has Low but Detectable Influence on HLA-B*57:01 Specificity without Inducing Hypersensitivity

Immune mediated adverse drug reactions (IM-ADRs) remain a significant source of patient morbidity that have more recently been shown to be associated with specific class I and/or II human leukocyte antigen (HLA) alleles. Abacavir-induced hypersensitivity syndrome is a CD8⁺ T cell dependent IM-ADR that is exclusively mediated by HLA-B*57:01. We and others have previously shown that abacavir can occupy the floor of the peptide binding groove of HLA-B*57:01 molecules, increasing the affinity of certain self peptides resulting in an altered peptide-binding repertoire. Here, we have identified another drug, acyclovir, which appears to act in a similar fashion. As with abacavir, acyclovir showed a dose dependent increase in affinity for peptides with valine and isoleucine at their C-terminus. In agreement with the binding studies, HLA-B*57:01 peptide-elution studies performed in the presence of acyclovir revealed an increased number of endogenously bound peptides with a C-terminal isoleucine. Accordingly, we have hypothesized that acyclovir acts by the same mechanism as abacavir, although our data also suggest the overall effect is much smaller: the largest changes of peptide affinity for acyclovir were 2-5 fold, whereas for abacavir this effect was as much as 1000-fold. Unlike abacavir, acyclovir is not known to cause IM-ADRs. We conclude that the modest effect of acyclovir on HLA binding affinity in contrast to the large effect of abacavir is insufficient to trigger a hypersensitivity syndrome. We further support this by functional in vitro studies where acyclovir, unlike abacavir, was unable to produce an increase in IFN-γ upon expansion of HLA-B*57:01⁺ PBMCs from healthy donors. Using abacavir and acyclovir as examples we therefore propose an in vitro pre-clinical screening strategy, whereby thresholds can be applied to MHC-peptide binding assays to determine the likelihood that a drug could cause a clinically relevant IM-ADR.     

Abacavir-Reactive Memory T Cells Are Present in Drug Na?ve Individuals

BackgroundFifty-five percent of individuals with HLA-B*57:01 exposed to the antiretroviral drug abacavir develop a hypersensitivity reaction (HSR) that has been attributed to naïve T-cell responses to neo-antigen generated by the drug. Immunologically confirmed abacavir HSR can manifest clinically in less than 48 hours following first exposure suggesting that, at least in some cases, abacavir HSR is due to re-stimulation of a pre-existing memory T-cell population rather than priming of a high frequency naïve T-cell population.MethodsTo determine whether a pre-existing abacavir reactive memory T-cell population contributes to early abacavir HSR symptoms, we studied the abacavir specific naïve or memory T-cell response using HLA-B*57:01 positive HSR patients or healthy controls using ELISpot assay, intra-cellular cytokine staining and tetramer labelling.ResultsAbacavir reactive CD8+ T-cell responses were detected in vitro in one hundred percent of abacavir unexposed HLA-B*57:01 positive healthy donors. Abacavir-specific CD8+ T cells from such donors can be expanded from sorted memory, and sorted naïve, CD8+ T cells without need for autologous CD4+ T cells.ConclusionsWe propose that these pre-existing abacavir-reactive memory CD8+ T-cell responses must have been primed by earlier exposure to another foreign antigen and that these T cells cross-react with an abacavir-HLA-B*57:01-endogenous peptide ligand complex, in keeping with the model of heterologous immunity proposed in transplant rejection.     

Pharmacogenetic testing: proofs of principle and pharmacoeconomic implications

Several proofs of principle have established that pharmacogenetic testing for mutations altering expression and functions of genes associated with drug disposition and response can decrease the "trial-and-error" dosing and reduce the risk of adverse drug reactions. These proofs of principle include thiopurine methyltransferase and thiopurine therapy, dihydropyrimidine dehydrogenase/thymidylate synthase and 5-fluorouracil therapy, folate enzyme MTHFR and methotrexate therapy, UGT1A1 and irinotecan therapy and CYP450 2C9 and S-warfarin therapy. These evidences advocate for the prospective identification of mutations associated with drug response, serious adverse reactions and treatment failure. More recent evidence with the HLA basis of hypersensitivity to the retroviral agent abacavir demonstrates the potential of pharmacogenetic testing and its pharmacoeconomic implications. With the convergence of rising drug costs and evidence supporting the clinical benefits of pharmacogenetic testing, it will be important to demonstrate the improved net health outcomes attributed to the additional costs for this testing.     

Human genome project: pharmacogenomics and drug development

Now that all 30,000 or so genes that make up the human genome have been deciphered, pharmaceutical industries are emerging to capitalize the custom based drug treatment. Understanding human genetic variation promises to have a great impact on our ability to uncover the cause of individual variation in response to therapeutics. The study of association between genetics and drug response is called pharmacogenomics. The potential implication of genomics and pharmacogenomics in clinical research and clinical medicine is that disease could be treated according to the interindividual differences in drug disposition and effects, thereby enhancing the drug discovery and providing a stronger scientific basis of each patient's genetic constitution. Sequence information derived from the genomes of many individuals is leading to the rapid discovery of single nucleotide polymorphisms or SNPs. Detection of these human polymorphisms will fuel the discipline of pharmacogenomics by developing more personalized drug therapies. A greater understanding of the way in which individuals with a particular genotype respond to a drug allows manufacturers to identify population subgroups that will benefit most from a particular drug. The increasing emphasis on pharmacogenomics is likely to raise ethical and legal questions regarding, among other things, the design of research studies, the construction of clinical trials and the pricing of drugs.     

The Pharmacogenomic HLA Biomarker Associated to Adverse Abacavir Reactions: Comparative Analysis of Different Genotyping Methods

Many pharmacogenomic biomarkers (PGBM) were identified and translated into clinical practice, affecting the usage of drugs via label updates. In this context, abacavir is one of the most brilliant examples of pharmacogenetic studies translated into clinical practice. Pharmacogenetic studies have revealed that abacavir HSRs are highly associated with the major histocompatibility complex class I. Large studies established the effectiveness of prospective HLA-B*57:01 screening to prevent HSRs to abacavir. Accordingly to these results the abacavir label has been modified: the European Medicines Agency (EMA) and the FDA recommend/suggested that the administration of abacavir must be preceded by a specific genotyping test. The HLA locus is extremely polymorphic, exhibiting many closely related alleles, making it difficult to discriminate HLA-B*57:01 from other related alleles, and a number of different molecular techniques have been developed recently to detect the presence of HLA-B*57:01. In this review, we provide a summary of the available techniques used by laboratories to genotype HLA-B*57:01, outlining the scientific and pharmacoeconomics pros and cons.     

药物基因组学在新药临床试验及个体化用药中的应用

药物安全性和有效性评价是药物临床试验和个体化用药的核心,也是药物基因组学研究的主要内容。药物基因组学研究贯穿于药物 研发、上市评价和临床应用整个过程, 根据药物代谢酶、转运体、受体相关基因多态性对用药者进行分层分析,评价与药物体内的处置过程、 安全性、有效性个体差异的相关性。综述药物基因组学在新药临床试验、个体化用药中的应用研究新进展。     

Vitamin Pharmacogenomics: New Insight into Individual Differences in Diseases and Drug Responses

Vitamins are vital to sustain normal physiological function, metabolism, and growth for all living organisms. Being an integral component of coenzyme, vitamins can affect the catalytic activities of many enzymes and the expression of drug transporters. Genetic variations in metabolism and/or transporter genes of drugs can influence the exposure of the human body to drugs and/or their active metabolites, thus contributing to the variations in drug responses and toxicities. Nonetheless, pharmacogenomics studies on nutrients have been rarely summarized. In this article, we reviewed recent progress on vitamin pharmacogenomics, for a better understanding on the influence of vitamin-related gene polymorphisms on inter-individual differences in diseases and drug efficacy and safety.     

Chapter 7: Pharmacogenomics

There is great variation in drug-response phenotypes, and a “one size fits all” paradigm for drug delivery is flawed. Pharmacogenomics is the study of how human genetic information impacts drug response, and it aims to improve efficacy and reduced side effects. In this article, we provide an overview of pharmacogenetics, including pharmacokinetics (PK), pharmacodynamics (PD), gene and pathway interactions, and off-target effects. We describe methods for discovering genetic factors in drug response, including genome-wide association studies (GWAS), expression analysis, and other methods such as chemoinformatics and natural language processing (NLP). We cover the practical applications of pharmacogenomics both in the pharmaceutical industry and in a clinical setting. In drug discovery, pharmacogenomics can be used to aid lead identification, anticipate adverse events, and assist in drug repurposing efforts. Moreover, pharmacogenomic discoveries show promise as important elements of physician decision support. Finally, we consider the ethical, regulatory, and reimbursement challenges that remain for the clinical implementation of pharmacogenomics.

What to Learn in This Chapter

• Interactions between drugs (small molecules) and genes (proteins)
• Methods for pharmacogenomic discovery
  • Association- and expression-based methods
  • Cheminformatics and pathway-based methods
• Database resources for pharmacogenomic discovery and application (PharmGKB)
• Applications of pharmacogenomics into a clinical setting

This article is part of the “Translational Bioinformatics” collection for PLOS Computational Biology.

     

Abacavir Induced T Cell Reactivity from Drug Na?ve Individuals Shares Features of Allo-Immune Responses

Abacavir hypersensitivity is a severe hypersensitivity reaction which occurs exclusively in carriers of the HLA-B*57∶01 allele. In vitro culture of PBMC with abacavir results in the outgrowth of abacavir-reacting CD8⁺ T cells, which release IFNγ and are cytotoxic. How this immune response is induced and what is recognized by these T cells is still a matter of debate. We analyzed the conditions required to develop an abacavir-dependent T cell response in vitro. The abacavir reactivity was independent of co-stimulatory signals, as neither DC maturation nor release of inflammatory cytokines were observed upon abacavir exposure. Abacavir induced T cells arose in the absence of professional APC and stemmed from naïve and memory compartments. These features are reminiscent of allo-reactivity. Screening for allo-reactivity revealed that about 5% of generated T cell clones (n = 136) from three donors were allo-reactive exclusively to the related HLA-B*58∶01. The addition of peptides which can bind to the HLA-B*57∶01-abacavir complex and to HLA-B*58∶01 during the induction phase increased the proportion of HLA-B*58∶01 allo-reactive T cell clones from 5% to 42%. In conclusion, abacavir can alter the HLA-B*57∶01-peptide complex in a way that mimics an allo-allele (‘altered self-allele’) and create the potential for robust T cell responses.     

MicroRNA pharmacogenomics: post-transcriptional regulation of drug response

The field of pharmacogenomics aims to predict which drugs will be most effective and safe for a particular individual based on their genome sequence or expression profile, thereby allowing personalized treatment. The bulk of pharmacogenomic research has focused on the role of single nucleotide polymorphisms, copy number variations or differences in gene expression levels of drug metabolizing or transporting genes and drug targets. In this review paper, we focus instead on microRNAs (miRNAs): small noncoding RNAs, prevalent in metazoans, that negatively regulate gene expression in many cellular processes. We discuss how miRNAs, by regulating the expression of pharmacogenomic-related genes, can play a pivotal role in drug efficacy and toxicity and have potential clinical implications for personalized medicine.     

常用口服降糖药的药物基因组学研究进展

近年来,中国 2 型糖尿病(T2DM)发病率呈快速增长趋势。T2DM 是一种慢性代谢性疾病,涉及全身各个系统,甚至可能引起严 重的并发症。大多数 T2DM 患者需长期口服降糖药物。口服降糖药的药物基因组学研究可指导个体化治疗,改善疗效,降低用药成本,减 少不良反应和并发症风险,已成为当前研究的热点。综述常用口服降糖药药效学和药代动力学参数的相关基因多态性研究进展,为更加合理、 有效地进行糖尿病临床个体化治疗提供参考。     

Applying Pharmacogenomics to Antifungal Selection and Dosing: Are We There Yet?

This review summarizes recent literature for applying pharmacogenomics to antifungal selection and dosing, providing an approach to implementing antifungal pharmacogenomics in clinical practice. The Clinical Pharmacogenetics Implementation Consortium published guidelines on CYP2C19 and voriconazole, with recommendations to use alternative antifungals or adjust voriconazole dose with close therapeutic drug monitoring (TDM). Recent studies demonstrate an association between CYP2C19 phenotype and voriconazole levels, clinical outcomes, and adverse events. Additionally, CYP2C19-guided preemptive dose adjustment demonstrated benefit in two prospective studies for prophylaxis. Pharmacokinetic–pharmacodynamic modeling studies have generated proposed voriconazole treatment doses based on CYP2C19 phenotypes, with further validation studies needed. Sufficient evidence is available for implementing CYP2C19-guided voriconazole selection and dosing among select patients at risk for invasive fungal infections. The institution needs appropriate infrastructure for pharmacogenomic testing, integration of results in the clinical decision process, with TDM confirmation of goal trough achievement, to integrate antifungal pharmacogenomics into routine clinical care.     

Pharmacogenomics in colorectal carcinomas: future perspectives in personalized therapy

The recent introduction of new drugs such as capecitabine, irinotecan, and oxaliplatinum has greatly improved the clinical outcome of patients with advanced/metastatic colorectal cancer. Nevertheless, some patients may suffer from the adverse drug reactions which will probably be the main cause of chemotherapy failure. The goal of pharmacogenomics is to find correlations between therapeutic responses to drugs and the genetic profiles of patients; the different responses to a particular drug are due, in fact, not only to the specific clinico-pathological features of the patient or to environmental factors, but also to the ethnic origins and the particular individual's genetic profile. Genes which codify for the metabolism enzymes, receptor proteins, or protein targets of chemotherapy agents often present various genetic polymorphisms. The main aim of this review is to provide an overview of the known polymorphisms present in the genes which codify for factors (thymidylate synthase dihydropyrimidine dehydrogenase, uridine diphosphate (UDP)-glucuronosyl-transferase 1A1, enzymes implicated in DNA repair) involved in the action mechanisms of the drugs now utilized in chemotherapeutic treatment of colorectal carcinoma, such as fluoropyrimidines, irinotecan, and platinum agents.     

Progress in pharmacogenomics and its promise for medicine

Pharmacogenomics addresses the impacts of diverse and multiple genes in populations as determinants of responses of individual patients to drugs. The field has its roots in basic science, and is pivotal in drug development, elucidation of therapeutic efficacy, and constraining the risks of adverse drug reactions. Regulatory agencies are relying increasingly on pharmacogenomics for identification of patients who are particularly likely to benefit from treatment with specific agents and exclusion of those at risk of adverse drug reactions. Practical applications of pharmacogenomics already abound particularly in the use of drugs acting on the central nervous system and on the cardiovascular system. The Society for Experimental Biology and Medicine (SEBM) is proud and pleased to have devoted its 2008 symposium, presented at the annual Experimental Biology meeting in San Diego on April 6, 2008, to advances in pharmacogenomics with emphasis on drug development, regulatory agency considerations, and clinical applications.     

Assessing Website Pharmacy Drug Quality: Safer Than You Think?

Background

Internet-sourced drugs are often considered suspect. The World Health Organization reports that drugs from websites that conceal their physical address are counterfeit in over 50 percent of cases; the U.S. Food and Drug Administration (FDA) works with the National Association of Boards of Pharmacy (NABP) to regularly update a list of websites likely to sell drugs that are illegal or of questionable quality.

Methods and Findings

This study examines drug purchasing over the Internet, by comparing the sales of five popular drugs from a selection of websites stratified by NABP or other ratings. The drugs were assessed for price, conditions of purchase, and basic quality. Prices and conditions of purchase varied widely. Some websites advertised single pills while others only permitted the purchase of large quantities. Not all websites delivered the exact drugs ordered, some delivered no drugs at all; many websites shipped from multiple international locations, and from locations that were different from those advertised on the websites. All drug samples were tested against approved U.S. brand formulations using Raman spectrometry. Many (17) websites substituted drugs, often in different formulations from the brands requested. These drugs, some of which were probably generics or perhaps non-bioequivalent copy versions, could not be assessed accurately. Of those drugs that could be assessed, none failed from “approved”, “legally compliant” or “not recommended” websites (0 out of 86), whereas 8.6% (3 out of 35) failed from “highly not recommended” and unidentifiable websites.

Conclusions

Of those drugs that could be assessed, all except Viagra® passed spectrometry testing. Of those that failed, few could be identified either by a country of manufacture listed on the packaging, or by the physical location of the website pharmacy. If confirmed by future studies on other drug samples, then U.S. consumers should be able to reduce their risk by relying on credentialing agencies recommended lists and by using common sense when examining packaging and pills.     

Pharmacogenetics and pharmacogenomics in oncology therapeutic antibody development

Pharmacogenetics and pharmacogenomics are keys to the success of personalized medicine, prescribing drugs based on a patient's individual genetic and biological profile. In this review, we will focus on the application of pharmacogenetics and pharmacogenomics in developing monoclonal antibody (MAb) therapeutics in oncology. The significance of pharmacogenomics in MAb therapeutics is highlighted by the association between polymorphisms in Fc receptors and clinical response to anti-CD20 MAb rituximab (Rituxan) or anti-ganglioside GD2 MAb 3F8, as well as the potential link between polymorphisms in HER2 and cardiac toxicity in patients treated with the anti-HER2 MAb trastuzumab (Herceptin). The dependence on gene copy number or expression levels of HER2 and epidermal growth factor receptor (EGFR) for therapeutic efficacy of trastuzumab and cetuximab (Erbitux), respectively, supports the importance of selecting suitable patient populations based on their pharmacogenetic profile. In addition, a better understanding of target mutation status and biological consequences will benefit MAAb development and may guide clinical development and use of these innovative therapeutics. The application of pharmacogenetics and pharmacogenomics in developing MAb therapeutics will be largely dependent on the discovery of novel surrogate biomarkers and identification of disease- and therapeutics-relevant polymorphisms. Challenges and opportunities in biomarker discovery and validation, and in implementing clinical pharmacogenetics and pharmacogenomics in oncology MAb development and clinical practice will also be discussed.     

Impact of pharmacogenomics on clinical practice in oncology

Multiple drug strategies for many cancer types are now readily available and there is a clear need for tools to inform decision making on therapy selection. Although there is still a long way to go before pharmacogenomics achieves the goal of individualized selection of cancer treatment, promising progress is being made. Genetic testing for thiopurine methyltransferase (TPMT) variant alleles in patients prior to mercaptopurine administration, and for UGT1A1*28 in patients prior to administration of irinotecan therapy, along with the instigation of genotype-guided clinical trials (e.g. TYMS) are important advances in cancer pharmacogenomics. Markers for the toxicity and efficacy of many oncology drugs remain unknown; however, the examples highlighted here suggest progress is being made towards the incorporation of pharmacogenomics into clinical practice in oncology.     

Comparison of abacavir-specific effector and proliferating functions of CD8 T cells in abacavir-treated HIV-1 patients

Susceptibility to abacavir hypersensitivity (ABH) in HIV-1-positive patients is strongly linked to the carriage of HLA-B*57:01 and the potential mechanism includes drug-specific activation of cytokine producing CD8 T cells exclusively in individuals carrying HLA-B*57:01. Here, we report a detailed characterization of abacavir-induced functional response of CD8 T cells in HLA-B*57:01^pos individuals. Peripheral blood mononuclear cells (PBMNCs) from HLA-B*57:01^posABH^pos and HLA-B*57:01^negABH^neg individuals were stimulated with abacavir. Multicolor flow cytometry was performed to assess the cytokine (IFNγ) production and degranulation (CD107a expression) after 6–18 hr culture and to enumerate proliferating CD4/CD8 T cells by culturing carboxyfluorescein diacetate succinimidyl ester-loaded PBMNCs for 7 days. CD8 T cells from HLA-B*57:01^posABH^pos individuals were multifunctional: proliferating, IFNγ producing, degranulating (CD107a^pos), and both degranulating and IFNγ producing (CD107a^posIFNγ^pos). Degranulating CD8 T cells in general and both degranulating and IFNγ producing CD8 T cells in particular dominated abacavir-specific immune response. All functional responses were partially blocked by addition of HLA-B*57:01-reactive Bw4 mAb, but not by non-HLA-B*57:01-reactive Bw6 mAb. In conclusion, the study demonstrates that abacavir-specific CD8 T-cell-restricted immune response in HLA-B*57:01^posABH^pos HIV-1 patients has multiple effector and proliferating functions, where the primary effector response appears to be the release of cytolytic granules. The findings have implications for immunotherapy of HLA-related drug hypersensitivities.