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Toxicology in the 21st Century

Tox21 Operational Model

Tox21’s federal partners include the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA) and NIH, with leadership from NCATS and the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences. These agencies work together to advance in vitro toxicological testing.

Partner Roles

NTP and the National Center for Computational Toxicology in the EPA Office of Research and Development co-fund Tox21. Each partner brings key expertise, including:

The ultimate goal is for the EPA and FDA to apply the knowledge gained from Tox21 research to the products these agencies regulate.

Phase I

The completed first phase of Tox21 involved testing of 2,800 compounds in more than 50 assays using the high-throughput robotic screening system now at NCATS. The resulting data are available in public databases, such as the National Library of Medicine’s PubChem, the EPA’s ToxCast and Aggregated Computation Toxicology Resource, and NTP’s Chemical Effects in Biological Systems.

Phase II

The second phase of Tox21 involves testing a collection of more than 10,000 compounds (Tox21 10K library). The initial focus was on creating assays to test the compounds’ effects on nuclear receptors (AhR, AR, ERα, FXR, GR, PPARδ, PPARγ, TR and VDR) and stress response pathways (p53, NF-κB, pH2AX, endoplasmic reticulum stress, mitochondrial membrane potential, ARE/Nrf-2, heat shock response and DNA damage).

Consortium partners continue to develop a range of secondary and tertiary follow-up assays to further define and characterize activities identified in the initial high-throughput screens. All testing results are made publically available through NIH and EPA chemical toxicity databases. In addition, NCATS created a free Tox21 chemical inventory browser, which provides researchers with additional information about the chemicals.

Phase III

Tox21 leaders have begun to focus on developing a third phase for the program. This phase will involve:

  • Using more physiologically relevant cells (i.e., primary or stem cells) in screening assays.
  • Increasing the number of molecular pathways tested by measuring gene expression.
  • Expanding the compound library to include chemical mixtures and fruit and vegetable extracts.
  • Using Tox21 datasets to build models that predict specific compounds’ effects on human health and using the power of crowdsourcing to enlist the help of the larger scientific community to create these models.

Assay Proposals

Although Tox21 experts optimize internally developed assays and screening methodologies, they also accept and evaluate assay proposals submitted by outside investigators, both within and outside the government. Learn more about submitting an assay.

Last updated: 07-25-2017
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