Mechanistic Validation

Johns Hopkins University, Bloomberg School of Public Health, CAAT, Baltimore, USA.
ALTEX: Alternativen zu Tierexperimenten (Impact Factor: 5.47). 05/2013; 30(2):119-30.
Source: PubMed


Validation of new approaches in regulatory toxicology is commonly defined as the independent assessment of the reproducibility and relevance (the scientific basis and predictive capacity) of a test for a particular purpose. In large ring trials, the emphasis to date has been mainly on reproducibility and predictive capacity (comparison to the traditional test) with less attention given to the scientific or mechanistic basis. Assessing predictive capacity is difficult for novel approaches (which are based on mechanism), such as pathways of toxicity or the complex networks within the organism (systems toxicology). This is highly relevant for implementing Toxicology for the 21st Century, either by high-throughput testing in the ToxCast/Tox21 project or omics-based testing in the Human Toxome Project. This article explores the mostly neglected assessment of a test's scientific basis, which moves mechanism and causality to the foreground when validating/qualifying tests. Such mechanistic validation faces the problem of establishing causality in complex systems. However, pragmatic adaptations of the Bradford Hill criteria, as well as bioinformatic tools, are emerging. As critical infrastructures of the organism are perturbed by a toxic mechanism we argue that by focusing on the target of toxicity and its vulnerability, in addition to the way it is perturbed, we can anchor the identification of the mechanism and its verification.

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Available from: Thomas Hartung, Sep 27, 2014
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    • "Previously, in Patlewicz et al. (2013), we discussed scientific confidence in the context of two validation frameworks, the IOM Framework (IOM, 2010) and the OECD Validation principles (2004), and adapted these for consideration in HTS/HCS assays. Similarly, Hartung et al. (2013) stated that ''validating the mechanism of a (group of) toxicant(s) is the basis for mechanistic validation of tests that identify those toxicants,'' and proposed that the performance of Tox21 test methods could be addressed through ''mechanistic validation'' which focuses on biological pathways and is carried out in six steps: (1) articulation of the pathway (''the biological/mechanistic circuitry (''in the absence of xenobiotic challenge'') leading to the hazard; (2) documenting the evidence , based on results in validated models, that reference chemicals that cause the hazard ''perturb the biology in question;'' (3) development of test(s) that reflect this biology; (4) verification that toxicants acting by this mechanism also do so in the test(s); (5) verification that antagonism or interference of the mechanism blocks or hinders positive test results. Although not a one-to-one match, this approach is, in essence, very similar to a well-informed adverse outcome pathway (AOP) that includes support for a causal link between the key event and adverse outcome (Ankley et al., 2010). "
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