Expert Opinion on Drug Metabolism & Toxicology

doi: 10.1517/17425255.2013.853148pmid: N/A

Campion, Sarah; Aubrecht, Jiri; Boekelheide, Kim; Brewster, David W; Vaidya, Vishal S; Anderson, Linnea; Burt, Deborah; Dere, Edward; Hwang, Kathleen; Pacheco, Sara; Saikumar, Janani; Schomaker, Shelli; Sigman, Mark; Goodsaid, Federico

doi: 10.1517/17425255.2013.827170pmid: 23961847

Introduction: There are significant rates of attrition in drug development. A number of compounds fail to progress past preclinical development due to limited tools that accurately monitor toxicity in preclinical studies and in the clinic. Research has focused on improving tools for the detection of organ-specific toxicity through the identification and characterization of biomarkers of toxicity. Areas covered: This article reviews what we know about emerging biomarkers in toxicology, with a focus on the 2012 Northeast Society of Toxicology meeting titled ‘Translational Biomarkers in Toxicology.' The areas covered in this meeting are summarized and include biomarkers of testicular injury and dysfunction, emerging biomarkers of kidney injury and translation of emerging biomarkers from preclinical species to human populations. The authors also provide a discussion about the biomarker qualification process and possible improvements to this process. Expert opinion: There is currently a gap between the scientific work in the development and qualification of novel biomarkers for nonclinical drug safety assessment and how these biomarkers are actually used in drug safety assessment. A clear and efficient path to regulatory acceptance is needed so that breakthroughs in the biomarker toolkit for nonclinical drug safety assessment can be utilized to aid in the drug development process.

Gautier, Laurent; Taboureau, Olivier; Audouze, Karine

doi: 10.1517/17425255.2013.820704pmid: 23937336

Introduction: The high failure rate of drug candidates due to toxicity, during clinical trials, is a critical issue in drug discovery. Network biology has become a promising approach, in this regard, using the increasingly large amount of biological and chemical data available and combining it with bioinformatics. With this approach, the assessment of chemical safety can be done across multiple scales of complexity from molecular to cellular and system levels in human health. Network biology can be used at several levels of complexity. Areas covered: This review describes the strengths and limitations of network biology. The authors specifically assess this approach across different biological scales when it is applied to toxicity. Expert opinion: There has been much progress made with the amount of data that is generated by various omics technologies. With this large amount of useful data, network biology has the opportunity to contribute to a better understanding of a drug's safety profile. The authors believe that considering a drug action and protein's function in a global physiological environment may benefit our understanding of the impact some chemicals have on human health and toxicity. The next step for network biology will be to better integrate differential and quantitative data.

Yoshizato, Katsutoshi; Tateno, Chise

doi: 10.1517/17425255.2013.826649pmid: 23978259

Introduction: The mouse is a common model used in evaluating drug metabolism and hepatitis infectivity. However, these models have limited value due to species difference in hepatic functions, leading to the creation of the chimeric mouse 12 years ago. These models were unique in that their hepatocytes had been replaced with human (hu) hepatocytes (dubbed the ‘first-generation chimeric mouse'). Since then, the chimeric mouse has become a practical tool for this area of studies. However, some shortcomings have also been recognized. One major shortcoming is that the mouse cannot mimic hu-liver diseases due to immunodeficiency and also it is unable to provide sufficient amounts of blood for analysis compared to the rat. There are also issues around donor-to-donor variability of hu-hepatocytes such as variable engraftment efficiency. Areas covered: This review provides the current status of the first-generation chimeric mouse. Furthermore, the authors review studies intended to create a ‘second-generation of the chimeric mouse' in which inflammation/immune-response cells as well as hepatocytes are humanized. A brief comment is also made on studies aiming at producing chimeric rats. Finally, the authors consider induced pluripotent stem cells (iPS cells) as new sources of hu-hepatocytes. Expert opinion: The authors believe that the current rapid progress in the field of biotechnology should enable us to create a mouse model with a humanized liver that is made by iPS-derived hu-hepatocytes and hu-immune cells. This development will provide researchers with a model that will be able to effectively mimic human liver disease under experimental conditions.

García-Martín, Elena; Canto, Gabriela; Agúndez, José AG

doi: 10.1517/17425255.2013.823400pmid: 23902458

Introduction: The clinical management of allergic diseases involves a number of drugs, most of which are extensively metabolized. This review aims to analyze the metabolism and the clinical implications of altered metabolism for these drugs. Areas covered: The authors present an overview of current knowledge of the metabolism of: antihistamine drugs, glucocorticoids, inhaled β-2 bronchodilators, anticholinergics and other drugs used in allergic diseases, such as cromoglycate, omalizumab, montelukast and epinephrine. Polymorphic drug metabolism is relevant for chlorpheniramine, loratadine and montelukast. Inhibition of drug metabolism is relevant for loratadine, methylprednisolone, fluticasone, mometasone, triamcinolone or prednisolone. Polymorphic pre-systemic metabolism may be relevant to budesonide, fluticasone, beclomethasone, mometasone or salmeterol. The authors also discuss the current information on gene variations according to the 1,000 genomes catalog and other databases. Finally, the authors review the clinical implications of these variations with a particular regard to drugs used in the management of allergic diseases. Expert opinion: Most drugs used in allergic diseases are extensively metabolized. Drug interaction or adverse reactions related to altered metabolism are relevant issues that should be considered in the management of allergic diseases. However, much additional research is required before defining pharmacogenomic biomarkers for the management of drugs used in allergic diseases.

Ande, Anusha; McArthur, Carole; Kumar, Anil; Kumar, Santosh

doi: 10.1517/17425255.2013.816285pmid: 23822755

Introduction: Tobacco smoking is highly prevalent among the HIV-1-infected population. In addition to diminished immune response, smoking has been shown to increase HIV-1 replication and decrease response to antiretroviral therapy, perhaps through drug–drug interaction. However, the mechanism by which tobacco/nicotine increases HIV-1 replication and mediates drug–drug interaction is poorly understood. Areas covered: In this review, the authors discuss the effects of smoking on HIV-1 pathogenesis. Since they propose a role for the cytochrome P450 (CYP) pathway in smoking-mediated HIV-1 pathogenesis, the authors briefly converse the role of CYP enzymes in tobacco-mediated oxidative stress and toxicity. Finally, the authors focus on the role of CYP enzymes, especially CYP2A6, in tobacco/nicotine metabolism and oxidative stress in HIV-1 model systems monocytes/macrophages, lymphocytes, astrocytes and neurons, which may be responsible for HIV-1 pathogenesis. Expert opinion: Recent findings suggest that CYP-mediated oxidative stress is a novel pathway that may be involved in smoking-mediated HIV-1 pathogenesis, including HIV-1 replication and drug–drug interaction. Thus, CYP and CYP-associated oxidative stress pathways may be potential targets to develop novel pharmaceuticals for HIV-1-infected smokers. Since HIV-1/TB co-infections are common, future study involving interactions between antiretroviral and antituberculosis drugs that involve CYP pathways would also help treat HIV-1/TB co-infected smokers effectively.

Harris, Kelly L; Banks, Leah D; Mantey, Jane A; Huderson, Ashley C; Ramesh, Aramandla

doi: 10.1517/17425255.2013.823157pmid: 23898780

Introduction: Bioaccessibility is a growing area of research in the field of risk assessment. As polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, they are the toxicants of focus to establish cancer risks in humans. Orally ingested PAHs also cause toxicity and even affect the pharmacokinetic behavior of some therapeutic agents. Toward this end, bioaccessibility is being used as a tool to assess the risk of PAHs via dietary exposures. Areas covered: This review covers some in vitro bioaccessibility models for PAHs that have been used for the past one-and-a-half decade. This review also considers the factors that influence bioaccessibility and debates the merits and limitations of using a bioaccessibility concept for estimating risk from ingestion of PAH-contaminated soil and food. Finally, the authors discuss the implications of bioaccessibility for PAH-induced toxicity and cancers in the context of risk assessment. Expert opinion: So far, much of the focus on PAH bioaccessibility is centered on soil as a preferential matrix. However, ingestion of PAHs through diet far exceeds the amount accidentally ingested through soil. Therefore, bioaccessibility could be exploited as a tool to assess the relative risk of various dietary ingredients tainted with PAHs. While bioaccessibility is a promising approach for assessing PAH risk arising from various types of contaminated soils, none of the models proposed appears to be valid. Bioaccessibility values, derived from in vitro studies, still require validation from in vivo studies.

Fernández de Gatta, M a del Mar; Martin-Suarez, Ana; Lanao, Jose M

doi: 10.1517/17425255.2013.822486pmid: 23898816

Introduction: Pharmacokinetic variability in critically ill patients is the result of the overlapping of multiple pathophysiological and clinical factors. Unpredictable exposure from standard dosage regimens may influence the outcome of treatment. Therefore, strategies for dosage individualisation are recommended in this setting. Areas covered: The authors focus on several approaches for dosage individualisation that have been developed, ranging from the well-established therapeutic drug monitoring (TDM) up to the innovative application of pharmacogenomics criteria. Furthermore, the authors summarise the specific population pharmacokinetic models for different drugs developed for critically ill patients to improve the initial dosage selection and the Bayesian forecasting of serum concentrations. The authors also consider the use of Monte Carlo simulation for the selection of dosage strategies. Expert opinion: Pharmacokinetic/pharmacodynamics (PK/PD) modelling and dosage individualisation methods based on mathematical and statistical criteria will contribute in improving pharmacologic treatment in critically ill patients. Moreover, substantial effort will be necessary to integrate pharmacogenomics criteria into critical care practice. The lack of availability of target biomarkers for dosage adjustment emphasizes the value of TDM which allows a large part of treatment outcome variability to be controlled.

Mandrioli, Roberto; Mercolini, Laura; Raggi, Maria Augusta

doi: 10.1517/17425255.2013.816675pmid: 23834458

Introduction: Social anxiety disorder (SAD) is an emerging, often invalidating, syndrome with deep personal, social and psychological implications. While multiple treatment strategies exist, presently none of them can be considered superior to all others. Areas covered: The aim of this review is to provide the latest information on sertraline (SRT), one of the most important selective serotonin reuptake inhibitors (SSRIs) currently used for the pharmacological therapy of SAD. A literature search was carried out with the keywords ‘sertraline', ‘social anxiety', ‘social phobia' and ‘clinical trials'. In this process, particular attention is paid to the pharmacokinetic characteristics of the drug and its safety in clinical use. Expert opinion: SRT is an effective drug in the treatment of SAD, especially when used in combination with some form of psychological support. While it does not seem to be significantly more effective than other SSRIs, SRT could offer some peculiar advantages: for example, it has a long half-life, allowing a single daily administration, and seems to be particularly indicated for the control of specific symptoms of SAD.

Prucha, Hanna; Schnopp, Christina; Akdis, Cezmi; Lauener, Roger; Wollenberg, Andreas; Ring, Johannes; Traidl-Hoffmann, Claudia

doi: 10.1517/17425255.2013.819343pmid: 23876065

Introduction: Pimecrolimus, a calcineurin inhibitor, is a non-steroidal treatment option in patients aged ≥ 2 years with mild-to-moderate atopic eczema (AE). It was approved as a viable therapeutic option by the FDA in 2001 and in the European Union a year later in 2002. Calcineurin inhibitors inhibit the synthesis of inflammatory cytokines released from T cells and mast cells. In contrast to corticosteroids, calcineurin inhibitors act specifically on proinflammatory cells. Pimecrolimus shows comparative efficacy to mild topical corticosteroids and a special antipruritic effect. Furthermore, examinations of the systemic absorption of pimecrolimus implicated no systemic immunosuppression. In 2006, the FDA set a black box warning in the packaging materials of pimecrolimus alluding to the risk of skin malignancy or lymphomas due to theoretical consideration. Areas covered: The authors provide a review of pimecrolimus as a treatment for AE. Specifically, the authors present the pharmacokinetic and pharmacodynamic information on pimecrolimus and also review its efficacy. The authors also discuss pimecrolimus' safety and tolerability profile. Expert opinion: Pimecrolimus represents a valuable part of active and proactive therapy in AE. That being said, the long-term safety of topical calcineurin inhibitors remains to be investigated. Given the results from experimental photocarcinogenicity studies, effective sun protection should be employed during the therapy, although an increased risk for skin malignancies and lymphomas was not found in recent studies. Pimecrolimus should be considered as an alternative therapeutic approach in AE treatment management going along with a corticoid-sparing effect.