Predictive Model of Rat Reproductive Toxicity from ToxCast High Throughput Screening

National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
Biology of Reproduction (Impact Factor: 3.32). 05/2011; 85(2):327-39. DOI: 10.1095/biolreprod.111.090977
Source: PubMed


The U.S. Environmental Protection Agency's ToxCast research program uses high throughput screening (HTS) for profiling bioactivity and predicting the toxicity of large numbers of chemicals. ToxCast Phase I tested 309 well-characterized chemicals in more than 500 assays for a wide range of molecular targets and cellular responses. Of the 309 environmental chemicals in Phase I, 256 were linked to high-quality rat multigeneration reproductive toxicity studies in the relational Toxicity Reference Database. Reproductive toxicants were defined here as having achieved a reproductive lowest-observed-adverse-effect level of less than 500 mg kg(-1) day(-1). Eight-six chemicals were identified as reproductive toxicants in the rat, and 68 of those had sufficient in vitro bioactivity to model. Each assay was assessed for univariate association with the identified reproductive toxicants. Significantly associated assays were linked to gene sets and used for the subsequent predictive modeling. Using linear discriminant analysis and fivefold cross-validation, a robust and stable predictive model was produced capable of identifying rodent reproductive toxicants with 77% ± 2% and 74% ± 5% (mean ± SEM) training and test cross-validation balanced accuracies, respectively. With a 21-chemical external validation set, the model was 76% accurate, further indicating the model's potential for prioritizing the many thousands of environmental chemicals with little to no hazard information. The biological features of the model include steroidal and nonsteroidal nuclear receptors, cytochrome P450 enzyme inhibition, G protein-coupled receptors, and cell signaling pathway readouts-mechanistic information suggesting additional targeted, integrated testing strategies and potential applications of in vitro HTS to risk assessment.

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    • "AOP networks can then provide justification and increased confidence for applying these assays to predict toxicity. As an example, Martin et al. linked ToxCast TM Phase I in vitro data of 256 chemicals to rat multigenerational reproductive toxicity studies and built a predictive model capable of identifying rodent reproductive toxicants with an accuracy of around 75% [12] (ToxCast TM is a US Environmental Protection Agency research program that uses automated chemical screening technologies to screen for changes in biological activity in living cells or isolated proteins after exposure to chemicals). ToxCast TM assays important to the model include peroxisome proliferator-activated receptor ␣ and ␥, androgen receptor and estrogen receptor agonist and antagonist assays, as well as cytochrome P450 enzyme inhibition, G protein-coupled receptor and cell signaling pathway assays. "
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    ABSTRACT: Historically, the prediction of reproductive and early developmental toxicity has largely relied on the use of animals. The Adverse Outcome Pathway (AOP) framework forms a basis for the development of new non-animal test methods. It also provides biological context for mechanistic information from existing assays. However, a single AOP may not capture all events that contribute to any relevant toxic effect, even in single chemical exposure scenarios. AOP networks, defined as sets of AOPs sharing at least one common element, are capable of more realistically representing potential chemical effects. They provide information on interactions between AOPs and have the potential to reveal previously unknown links between biological pathways. Analysis of these AOP networks can aid the prioritization of assay development, whether the goal is to develop a single assay with predictive utility of multiple outcomes, or development of assays that are highly specific for a particular mode of action. This paper provides a brief overview of the AOPs related to reproductive and early developmental toxicity currently available in the AOP Wiki (, and gives an example of an AOP network based on five reproductive and early developmental toxicity-related AOPs for fish to illustrate how AOP networks can be used for assay development and refinement. Copyright © 2015. Published by Elsevier Inc.
    Reproductive Toxicology 04/2015; 56. DOI:10.1016/j.reprotox.2015.04.003 · 3.23 Impact Factor
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    • "This includes the development of in vitro testing databases for hundreds of assays and thousands of chemicals in the ToxCast and Tox21 programs (Attene-Ramos et al. 2013; Kavlock et al. 2012). This has fostered development of computational models predicative of in vivo adverse outcomes (Martin et al. 2011; Rotroff et al. 2013; Sipes et al. 2011). The lack of adequate data sets for large numbers of chemicals from in vitro DNT assays has severely hampered the development of computational models. "
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    ABSTRACT: A major problem in developmental neurotoxicity (DNT) risk assessment is the lack of toxicological hazard information for most compounds. Therefore, new approaches are being considered to provide adequate experimental data that allow regulatory decisions. This process requires a matching of regulatory needs on the one hand and the opportunities provided by new test systems and methods on the other hand. Alignment of academically and industrially driven assay development with regulatory needs in the field of DNT is a core mission of the International STakeholder NETwork (ISTNET) in DNT testing. The first meeting of ISTNET was held in Zurich on 23-24 January 2014 in order to explore the concept of adverse outcome pathway (AOP) to practical DNT testing. AOPs were considered promising tools to promote test systems development according to regulatory needs. Moreover, the AOP concept was identified as an important guiding principle to assemble predictive integrated testing strategies (ITSs) for DNT. The recommendations on a road map towards AOP-based DNT testing is considered a stepwise approach, operating initially with incomplete AOPs for compound grouping, and focussing on key events of neurodevelopment. Next steps to be considered in follow-up activities are the use of case studies to further apply the AOP concept in regulatory DNT testing, making use of AOP intersections (common key events) for economic development of screening assays, and addressing the transition from qualitative descriptions to quantitative network modelling.
    Archive für Toxikologie 01/2015; 89(2). DOI:10.1007/s00204-015-1464-2 · 5.98 Impact Factor
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    • "Reproductive and developmental toxicity were even estimated to become the largest animal user for safety testing within REACH (Pedersen et al., 2003; Van der Jagt et al., 2004) since approximately 10,000 chemicals with an annual volume of >100 tonnes would have to be tested on reproductive toxicity. The estimates ranged from 40% to 90% of the total number of animals to comply with REACH that would be needed for reproductive toxicity testing purposes (Van der Jagt et al., 2004; Spielmann and Vogel, 2006; Hartung and Rovida, 2009; Martin et al., 2011). At about the same time, several studies became available that questioned the added value of the second generation (Cooper et al., 2006; Janer et al., 2007a,b; Martin et al., 2009; Piersma et al., 2011) and criticized the limited predictive value of the OECD TG 416 for developmental immunotoxic and neurotoxic parameters (See Section 2.1.). "
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    ABSTRACT: The two-generation study (OECD TG 416) is the standard requirement within REACH to test reproductive toxicity effects of chemicals with production volumes >100 tonnes. This test is criticized in terms of scientific relevance and animal welfare. The Extended One Generation Reproductive Toxicity Study (EOGRTS), incorporated into the OECD test guidelines in 2011 (OECD TG 443) has the potential to replace TG 416, while using only one generation of rats and being more informative. However, its regulatory acceptance proved challenging. This article reconstructs the process of regulatory acceptance and use of the EOGRTS and describes drivers and barriers influencing the process. The findings derive from literature research and expert interviews. A distinction is made between three sub-stages; The stage of Formal Incorporation of the EOGRTS into OECD test guidelines was stimulated by retrospective analyses on the value of the second generation (F2), strong EOGRTS advocates, animal welfare concern and changing US and EU chemicals legislation; the stage of Actual Regulatory Acceptance within REACH was challenged by legal factors and ongoing scientific disputes, while the stage of Use by Industry is influenced by uncertainty of registrants about regulatory acceptance, high costs, the risk of false positives and the manageability of the EOGRTS.
    Regulatory Toxicology and Pharmacology 10/2014; 71(1). DOI:10.1016/j.yrtph.2014.10.012 · 2.03 Impact Factor
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