Idiosyncratic adverse drug reactions: current concepts

Idiosyncratic drug reactions are a significant cause of morbidity and mortality for patients; they also markedly increase the uncertainty of drug development. The major targets are skin, liver, and bone marrow. Clinical characteristics suggest that IDRs are immune mediated, and there is substantive evidence that most, but not all, IDRs are caused by chemically reactive species. However, rigorous mechanistic studies are very difficult to perform, especially in the absence of valid animal models. Models to explain how drugs or reactive metabolites interact with the MHC/T-cell receptor complex include the hapten and P-I models, and most recently it was found that abacavir can interact reversibly with MHC to alter the endogenous peptides that are presented to T cells. The discovery of HLA molecules as important risk factors for some IDRs has also significantly contributed to our understanding of these adverse reactions, but it is not yet clear what fraction of IDRs have a strong HLA dependence. In addition, with the exception of abacavir, most patients who have the HLA that confers a higher IDR risk with a specific drug will not have an IDR when treated with that drug. Interindividual differences in T-cell receptors and other factors also presumably play a role in determining which patients will have an IDR. The immune response represents a delicate balance, and immune tolerance may be the dominant response to a drug that can cause IDRs.

The future of pharmacogenetics for osteoporosis

The possibility to predict the outcome of medical treatments, both in terms of efficacy and development of adverse effects, is the main goal of modern personalized medicine. The principal aim of pharmacogenetics is to design specific predictive genetic tests, to be performed prior to any drug treatment, and to tailor the therapy for each patient based on the results of these tests. Few pharmacogenetic tests are today validated and commonly applied in clinical practice, and none in the area of osteoporosis and bone disorders. Surely, the complex regulation of bone metabolism and the involvement of numerous different molecular pathways makes it difficult to individuate responsible genes and polymorphisms involved in the modulation of anti-osteoporotic drug response and, subsequently, in designing specific predictive analyses.

Genetics of congenital and drug-induced long QT syndromes: current evidence and future research perspectives

The long QT syndrome (LQTS) is a condition characterized by abnormal prolongation of the QT interval with an associated risk of ventricular arrhythmias and sudden cardiac death. Congenital forms of LQTS arise due to rare and highly penetrant mutations that segregate in a Mendelian fashion. Over the years, multiple mutations in genes encoding ion channels and ion channel binding proteins have been reported to underlie congenital LQTS. Drugs are by far the most common cause of acquired forms of LQTS. Emerging evidence suggests that drug-induced LQTS also has a significant heritable component. However, the genetic substrate underlying drug-induced LQTS is presently largely unknown. In recent years, advances in next-generation sequencing technology and molecular biology techniques have significantly enhanced our ability to identify genetic variants underlying both monogenic diseases and more complex traits. In this review, we discuss the genetic basis of congenital and drug-induced LQTS and focus on future avenues of research in the field. Ultimately, a detailed characterization of the genetic substrate underlying congenital and drug-induced LQTS will enhance risk stratification and potentially result in the development of tailored genotype-based therapies.

Personalized medicine - where do we stand? Pouring some water into wine: a realistic perspective

Abstract

Reviewing the past and the present status of personalized medicine, the hope and promise from several years ago was critically compared to what is really achieved to tailor the drug treatment according to the patient’s individuality. The basis for consideration is what we know about the variant of the disease the patient is suffering from, and about the mechanisms influencing the plasma concentration-time profile, such as activity of metabolizing enzymes and transporters. In cancer treatment, drugs are currently selected regarding molecular properties of the cancer tissue, eg, expressing receptors such as HER2 receptor. Currently diagnostic tests are available allowing to detect somatic cell mutations that can be used to guide drug selection. Unfortunately, tumor heterogeneity and developing resistance by further mutations may limit the success of the therapy determined by molecular diagnostics. The present status can be described that in drug kinetics we know the influencing factors and we understand the mechanisms. However, only in a few cases the genetic background is the main determinant of kinetic variability, and environmental and other factors have an additional important role. Therefore, much more has to be done before we can translate the accumulating knowledge into a benefit for the patient. Only then, we can speak about personalized medicine.

Regulation of drug-induced liver injury by signal transduction pathways: critical role of mitochondria

Drugs that cause liver injury often 'stress' mitochondria and activate signal transduction pathways important in determining cell survival or death. In most cases, hepatocytes adapt to the drug-induced stress by activating adaptive signaling pathways, such as mitochondrial adaptive responses and nuclear factor erythroid 2-related factor 2 (Nrf-2), a transcription factor that upregulates antioxidant defenses. Owing to adaptation, drugs alone rarely cause liver injury, with acetaminophen (APAP) being the notable exception. Drug-induced liver injury (DILI) usually involves other extrinsic factors, such as the adaptive immune system, that cause 'stressed' hepatocytes to become injured, leading to idiosyncratic DILI, the rare and unpredictable adverse drug reaction in the liver. Hepatocyte injury, due to drug and extrinsic insult, causes a second wave of signaling changes associated with adaptation, cell death, and repair. If the stress and injury reach a critical threshold, then death signaling pathways such as c-Jun N-terminal kinase (JNK) become dominant and hepatocytes enter a failsafe mode to undergo self-destruction. DILI can be seen as an active process involving recruitment of death signaling pathways that mediate cell death rather than a passive process due to overwhelming biochemical injury. In this review, we highlight the role of signal transduction pathways, which frequently involve mitochondria, in the development of DILI.

Pharmacogenetic Biomarkers as Tools for Pharmacoepidemiology of Severe Adverse Drug Reactions

Preclinical Research

The development of new genomic technologies has led to an exponential increase in the number of biomarkers for drug safety and efficacy. Pharmacogenomics has the potential to impact clinically relevant outcomes in drug dosing, efficacy, toxicity, and prediction of adverse drug reactions (ADRs). Genotype‐based prescribing is anticipated to improve the overall efficacy rates and minimize ADRs, making personalized medicine a reality. Genome‐wide association studies have been increasingly applied to pharmacogenetics. Severe ADRs are a major issue for drug therapy because they can cause serious disorders and can be life threatening. For severe ADRs, significant associations have been reported for drug‐induced liver injury, statin‐induced myopathy, increased risk of hemorrhagic complications of anticoagulant use, drug‐induced torsade de pointes, drug‐induced long QT, and severe cutaneous ADRs. This review summarizes the current position concerning the clinical and pharmacoepidemiological relevance of pharmacogenetic biomarkers in ADR prediction and prevention, with an emphasis on genetic risk factors and biomarkers for three specific severe ADRs.

Human leukocyte antigen-associated drug hypersensitivity

A growing number of associations between adverse drug reactions and alleles of the human leukocyte antigen (HLA) genes are now known. Although several models have been proposed to explain these associations, an underlying molecular basis has only recently been described. The associations between HLA-B*57:01 and abacavir hypersensitivity syndrome, and HLA-B*15:02 and carbamazepine-induced bullous skin disease have provided new insights into the mechanism associated with hypersensitivity reactions to these drugs. Here we discuss recent evidence that small molecules can interact with specific HLA to distort self-peptide presentation leading to autoimmune-like drug hypersensitivities that potentially provide clues to the mechanisms underlying other immunopathologies.

Omics and drug response

A new generation of technologies commonly named omics permits assessment of the entirety of the components of biological systems and produces an explosion of data and a major shift in our concepts of disease. These technologies will likely shape the future of health care. One aspect of these advances is that the data generated document the uniqueness of each human being in regard to disease risk and treatment response. These developments have reemphasized the concept of personalized medicine. Here we review the impact of omics technologies on one key aspect of personalized medicine: the individual drug response. We describe how knowledge of different omics may affect treatment decisions, namely drug choice and drug dose, and how it can be used to improve clinical outcomes.

Hepatic differentiation and maturation of human embryonic stem cells cultured in a perfused three-dimensional bioreactor

Drug-induced liver injury is a serious and frequently occurring adverse drug reaction in the clinics and is hard to predict during preclinical studies. Today, primary hepatocytes are the most frequently used cell model for drug discovery and prediction of toxicity. However, their use is marred by high donor variability regarding drug metabolism and toxicity, and instable expression levels of liver-specific genes such as cytochromes P450. An in vitro model system based on human embryonic stem cells (hESC), with their unique properties of pluripotency and self-renewal, has potential to provide a stable and unlimited supply of human hepatocytes. Much effort has been made to direct hESC toward the hepatic lineage, mostly using 2-dimensional (2D) cultures. Although the results are encouraging, these cells lack important functionality. Here, we investigate if hepatic differentiation of hESC can be improved by using a 3-dimensional (3D) bioreactor system. Human ESCs were differentiated toward the hepatic lineage using the same cells in either the 3D or 2D system. A global transcriptional analysis identified important differences between the 2 differentiation regimes, and we identified 10 pathways, highly related to liver functions, which were significantly upregulated in cells differentiated in the bioreactor compared to 2D control cultures. The enhanced hepatic differentiation observed in the bioreactor system was also supported by immunocytochemistry. Taken together, our results suggest that hepatic differentiation of hESC is improved when using this 3D bioreactor technology as compared to 2D culture systems.

Pharmacogenomics in clinical practice and drug development

Genome-wide association studies (GWAS) of responses to drugs, including clopidogrel, pegylated-interferon and carbamazepine, have led to the identification of specific patient subgroups that benefit from therapy. However, the identification and replication of common sequence variants that are associated with either efficacy or safety for most prescription medications at odds ratios (ORs) >3.0 (equivalent to >300% increased efficacy or safety) has yet to be translated to clinical practice. Although some of the studies have been completed, the results have not been incorporated into therapy, and a large number of commonly used medications have not been subject to proper pharmacogenomic analysis. Adoption of GWAS, exome or whole genome sequencing by drug development and treatment programs is the most striking near-term opportunity for improving the drug candidate pipeline and boosting the efficacy of medications already in use.

Insights from genome-wide association studies of drug response

Early genome-wide association studies (GWAS) using relatively small samples have identified both rare and common genetic variants with large impact on severe adverse drug reactions, dosing, and efficacy. Here we outline the challenges and recent successes of the GWAS approach in disease genetics and the ways in which these can be applied to pharmacogenomics for biological discovery, determination of heritability, and personalized treatment. We highlight that the genetic architecture of drug efficacy reflects a complex trait yet that of adverse drug reactions more closely mirrors the architecture of Mendelian diseases and how this difference affects future study design. Given that multiple layers of biological data are increasingly available on large samples from biorepositories linked to electronic medical records, GWAS will remain a key component of the systems biology approach to uncovering small to moderate genetic determinants of drug response; these discoveries should move us closer to a personalized approach to health care.

Genomic perspectives in inter-individual adverse responses following nanomedicine administration: The way forward

The underlying mechanism of intravenous infusion-related adverse reactions inherent to regulatory-approved nanomedicines still remains elusive. There are substantial inter-individual differences in observed adverse reactions, which may include cardiovascular, broncho-pulmonary, muco-cutaneous, neuro-psychosomatic and autonomic manifestations. Although nanomedicine-mediated triggering of complement activation has been suggested to be a significant contributing factor to these adverse events, complement activation may still proceed in non-responders. Whether these reactions share similar immunological mechanisms and underpinning genetic factors with drug hypersensitivity syndrome remains to be investigated. Genetic association studies could be a powerful tool to dissect causative factors and reveal the multiple molecular pathways that induce infusion related adverse reactions. It is envisaged that such research may lead to the design of reliable in vitro profiling tests for risk assessment and treatment decisions, thereby revolutionizing the practice of medicine with nanopharmaceuticals. Such procedures may further improve regulatory approval processes for nanomedicines currently in the pipeline and decrease the overall cost of health care. Here we discuss some key innate immunity genes and their polymorphisms in relation to nanomedicine infusion-mediated symptomatic responses.

Latest advances in predicting DILI in human subjects: focus on biomarkers

INTRODUCTION

The quest for a biomarker that would reliably identify patients at risk of developing acute drug-induced liver injury (DILI) to a specific agent or class of agents before it occurs, has been underway for years. Historical host factors for DILI, such as older age and female gender, are not considered sufficient to truly predict an individual's inherent risk of DILI. In vitro and animal-based biomarker discoveries, in many instances, have not been considered accurate enough for drug development in human subjects nor for use in clinical practice.

AREAS COVERED

In order to assess the current state of biomarkers to predict idiosyncratic human DILI, the authors utilized the PubMed literature search tool to identify research reports dealing with clinical DILI biomarkers covering the period of 2010 through to June 2012. Studies involving pharmacogenetic, proteomic and toxicogenomic analyses are preferentially reviewed.

EXPERT OPINION

Although acute DILI has been linked to specific genetic associations (e.g., flucloxacillin and HLA-B*5701; and certain polymorphisms seen with anti-TB agent DILI), such predictors have been able to identify only some patients at risk for only a limited number of drugs. Proteomic-based biomarkers from stored sera in the US DILI Network, such as apolipoprotein E, have been identified as potential candidates, but require further study. As it currently stands, the quest for a widely applicable, validated DILI biomarker remains an ongoing clinical challenge.