Metabolites in safety testing: metabolite identification strategies in discovery and development

The publication of the FDA MIST guidelines in 2008, together with the acknowledged importance of metabolism data for the progression of novel compounds through drug discovery and drug development, has resulted in a renewed focus on the metabolite identification strategies utilised throughout the pharmaceutical industry. With the plethora of existing and emerging technologies available to the metabolite identification scientist, it is argued that increased diligence should be applied to metabolism studies in the early stages of both drug discovery and drug development, in order to more routinely impact chemical design and to comply with the concepts of the MIST guidance without re‐positioning the definitive radiolabelled studies from there typical place in late development. Furthermore, these strategic elements should be augmented by a broad and thorough understanding of the impact of the derived metabolism data, most notably considerations of absolute abundance, structure and pharmacological activity, such that they can be put into proper context as part of a holistic safety strategy. The combination of these approaches should ensure a metabolite identification strategy that successfully applies the principles of the MIST guidance throughout the discovery/development continuum and thereby provides appropriate confidence in support of human safety. Copyright © 2009 John Wiley & Sons, Ltd.     

Drug metabolites in safety testing

This report summarizes the deliberations of a multidisciplinary committee, sponsored by the Pharmaceutical Research and Manufacturers of America, on current "best practices" within the U.S. pharmaceutical industry in assessing the role of drug metabolites as potential mediators of the toxicity of new drug products. Input to the document was obtained from numerous sources, including members of the pharmaceutical industry, academic investigators, and representatives of regulatory agencies who attended a workshop on the subject in November 2000. The overall goal of the paper is to define practical and scientifically based approaches to the use of metabolite data that address contemporary issues in the safety evaluation of drug candidates. Although there remains a lack of consensus on how best to deal with several aspects of this complex subject, this paper raises a number of points to consider, which emphasize the need to treat drug metabolite issues on a case-by-case basis. It is hoped that the discussion will promote continued dialog among industrial scientists and regulators charged with ensuring the clinical safety of new therapeutic agents.     

Preclinical safety assessment: in vitro -- in vivo testing

In vitro--and in vivo preclinical safety tests on drug candidates needed before first dose in man and before marketing authorisation are as follows: The acute and repeated dose toxicity studies, the reproductive toxicity studies, the genotoxicity studies, the carcinogenicity studies and finally the safety pharmacology studies. The Safety Assessment of the results with respect to predictability for humans is discussed, as well as new tests under validation. Suggestions for changes in the future of Non-Clinical Safety tests are mentioned.     

Use of monkey neonatal neurobehavioral test batteries in safety testing protocols

Developmental neurobehavioral test batteries are important in assessing potential reproductive and developmental toxicity of new chemicals and drugs. They provide a broad-based evaluation of a range of nervous system functions at a period of life when learning and adaptation are particularly critical. Nonhuman primates are an especially appropriate test species because of their similarities to humans in complexity of brain function and prolonged intrauterine brain development. Problems arise, however, in the analysis and interpretation of data bases generated when a relatively small number of animals are tested on a relatively large number of items. A 2-week neonatal test battery for rhesus monkey infants is described along with approaches to experimental design and statistical analyses that are helpful in providing sound and useful interpretation.     

Application of cardiac electrophysiology simulations to pro-arrhythmic safety testing

Concerns over cardiac side effects are the largest single cause of compound attrition during pharmaceutical drug development. For a number of years, biophysically detailed mathematical models of cardiac electrical activity have been used to explore how a compound, interfering with specific ion-channel function, may explain effects at the cell-, tissue- and organ-scales. With the advent of high-throughput screening of multiple ion channels in the wet-lab, and improvements in computational modelling of their effects on cardiac cell activity, more reliable prediction of pro-arrhythmic risk is becoming possible at the earliest stages of drug development. In this paper, we review the current use of biophysically detailed mathematical models of cardiac myocyte electrical activity in drug safety testing, and suggest future directions to employ the full potential of this approach.

LINKED ARTICLE

This article is commented on by Gintant, pp. 929–931 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.02096.x     

线粒体毒性评价及其在创新药物安全性评价中的意义

线粒体是细胞内能量和活性氧自由基(ROS)的主要来源,在病理条件下对细胞的存活与死亡具有十分重要的调控作用。线粒体是药物毒性作用的重要靶标。一些抗病毒药物、抗肿瘤药物和抗生素等可显著诱导肝脏和心脏等靶器官线粒体损伤。药物诱导的线粒体损伤可能涉及多条途径和多种机制。近年来研究表明,线粒体毒性可能是多种已上市药物被迫撤市或受到美国FDA"黑框"警告以及候选药物研发失败的重要原因。因此,在创新药物研发过程中,开展线粒体毒性评价具有十分重要的意义。     

Corneal epithelial testing strategies for safety evaluation of ophthalmic formulations

The toxicity of an ophthalmic formulation was tested both in vivo and in vitro. Initial tests on transformed human corneal epithelial (HCE-T) cells in monolayer cultures resulted in adverse effects on cell morphology. The adverse effects were unexpected since the formulation caused no damage to the cornea in vivo. These results suggested HCE-T monolayers do not adequately model the intact corneal epithelium. Therefore, further in vitro studies were conducted to investigate reversibility of morphologic changes, proliferation, cell viability, and effects on corneal epithelial barrier function. These tests showed that the formulation had no adverse effects on cell viability and proliferation. Multilayered cultures of HCE-T cells at an air interface provide a morphologic and physiologic model more relevant to the in vivo cornea. This study demonstrates the importance of selecting appropriate models when conducting in vitro toxicity studies so that potentially effective ophthalmic formulations are not rejected based on false positive in vitro endpoints.     

An integrated chemical environment with tools for chemical safety testing

Moving toward species-relevant chemical safety assessments and away from animal testing requires access to reliable data to develop and build confidence in new approaches. The Integrated Chemical Environment (ICE) provides tools and curated data centered around chemical safety assessment. This article describes updates to ICE, including improved accessibility and interpretability of in vitro data via mechanistic target mapping and enhanced interactive tools for in vitro to in vivo extrapolation (IVIVE). Mapping of in vitro assay targets to toxicity endpoints of regulatory importance uses literature-based mode-of-action information and controlled terminology from existing knowledge organization systems to support data interoperability with external resources. The most recent ICE update includes Tox21 high-throughput screening data curated using analytical chemistry data and assay-specific parameters to eliminate potential artifacts or unreliable activity. Also included are physicochemical/ADME parameters for over 800,000 chemicals predicted by quantitative structure-activity relationship models. These parameters are used by the new ICE IVIVE tool in combination with the U.S. Environmental Protection Agency's httk R package to estimate in vivo exposures corresponding to in vitro bioactivity concentrations from stored or user-defined assay data. These new ICE features allow users to explore the applications of an expanded data space and facilitate building confidence in non-animal approaches.     

Preclinical safety testing of species-specific proteins produced with recombinant DNA-technqiues

Summary Preclinical toxicity studies in animals with species-specific recombinant DNA products have now been performed for several years. An interim statement on the significance of these animal tests and their ability to predict adverse effects in humans therefore appears indicated, with the aim of deducing future testing strategies. The experience accumulated so far shows that the animal models have failed to predict adverse effects subsequently observed in man. Immunogenicity of these proteins further restricted the usefulness of standard toxicity tests. There is also increasing evidence that animal tests on the toxic potential of impurities contained in the products are markedly inferior in sensitivity to analytical and quality control methods.Thus, modified testing programs are proposed to demonstrate safety rather than target organ toxicity using rodents and small non-rodent species and restricted dosing; furthermore the study duration should be limited by the detection of immunogenic responses.Working Group Participants: K. Hoffmann, G. Schlueter, H. D. Schlumberger, E.-A. Loebbecke, Bayer AG; H. Ronneberger, Behringwerke AG; H. Stoetzer, Boehringer Ingelheim KG; R. Ziel, P. Graepel, Ciba-Geigy AG; H. H. Donaubauer, D. Mayer, Hoechst AG; K. Teelmann, E. Theiss, F. Hoffmann-La Roche & Co AG; R. Omilian-Rosso, B. Ryffel, Sandoz AG; Ch. Hohbach, H. Lehmann, M. Baumeister, L. Luetzen, Thomae GmbH     

Nonclinical safety testing of imaging agents,contrast agents and radiopharmaceuticals

Drug development includes imaging agents, contrast agents and radiopharmaceuticals; these materials differ from therapeutic drugs in that they are largely used to diagnose and/or monitor diseases and not treat them. Consequently, nonclinical safety testing needs are different. An examination of testing packages supporting clinical entry and/or marketing of these materials has shown a common approach to some study types (eg, imaging, biodistribution and toxicity testing). Recent regulatory guidelines to support development are the United States Food and Drug Administration (FDA)’s “Guidance for Industry Microdose Radiopharmaceutical Diagnostic Drugs: Nonclinical Study Recommendations” and the European Medicines Agency (EMA)’s “Guideline on the Non‐Clinical Requirements for Radiopharmaceuticals” (currently draft). It is hoped that these documents will allow developers to only perform nonclinical studies that are necessary to support functionality, follow distribution of the material and examine general safety/toxicity. However, as they are mainly focused on radiopharmaceuticals, companies are likely to apply knowledge of established testing packages to other new imaging agents and/or follow principles given in older regulatory guidelines, namely FDA’s “Guidance for Industry Developing Medical Imaging Drug and Biological Products Part I Conducting Safety Assessments”. Thus, in some cases, the need for regulatory agency interaction is still vital to avoid development surprises and delays due to an incomplete or badly performed testing package.     

Developmental immunotoxicity (DIT) in drug safety testing: matching DIT testing to adverse outcomes and childhood disease risk

Developmental immunotoxicity (DIT) recently emerged as a significant concern for drug safety and was the topic of several recent scientific forums in Europe, North America and Asia. The heightened concern is based on several observations: 1) many childhood diseases with recent increases in prevalence, such as asthma, allergic disease, leukemia and certain infections, have clear linkages to the immune system and immune dysfunction, 2) the developing immune system has been shown to be a particularly sensitive target for xenobiotic-induced adverse outcomes, 3) immunotoxicity assessment following adult exposure to xenobiotics is ineffective for predicting immunotoxic risk in the non-adult and 4) in several cases developmental immunotoxicity to low-level xenobiotic exposure can take the form of immune dysfunction in the absence of readily detected morphometric/histological alterations. The present review examines harmonized preclinical drug safety guidelines for immunotoxicity in light of environmentally-mediated childhood disease trends as well as research-based mechanisms for DIT. Because none of the guidelines was designed to address risk of DIT, suggestions are offered for closing the early-life immune dysfunction data gap. A longer-term goal is to help narrow the difference between current guideline expectations and the known sensitivity of the developing immune system for potential adverse outcomes.     

Study designs for the nonclinical safety testing of new vaccine products

During the development of a new vaccine, the purpose of nonclinical studies is to provide safety information to support the clinical development and licensure of the product. In this article the study designs currently accepted for the nonclinical safety testing of new vaccines are described for single dose, local tolerance, repeat dose toxicity and safety pharmacology studies; these studies together form the basis of a typical nonclinical safety evaluation dossier. The detailed design of the preclinical package must take account of the intended clinical use, patient population, route of administration, formulation, dose level and immunisation schedule. The test item that is used for these studies must be adequately representative of the intended clinical formulation. The animal model used for these studies must be selected on criteria of relevance. Single dose toxicity studies provide information on acute actions or the potential effect of accidental overdose, but this information is often available from the repeat dose toxicity study, obviating the need for the acute study. Local tolerance studies provide information on tissue reactions at the site of administration. Evaluation of the findings must distinguish between normal tissue responses to injected material and findings indicative of undesirable pathological changes. The repeated dose toxicity studies are the principal studies that support the safety profile of the vaccines. The design of these studies must take full account of the features of the vaccine in the choice of treatment regime, dose levels, pharmacodynamic monitoring and timing of investigations and sacrifice. Safety pharmacology studies are performed to evaluate the potential for undesirable secondary pharmacological actions of vaccines if there is data to suggest that such studies are needed; this evaluation is made on a case by case basis. In the absence of specific guidance the design of studies for therapeutic vaccines follows the same general principles as those for anti-infective vaccines.