Tox21 Projects

Tox21 projects are made possible by new technologies and new discoveries in gene expression analysis, culture of human tissue stem cells and integrated pathway information.

Cross-Partner Projects

To accommodate the expanded strategic direction and focus of the Tox21 collaboration, a central functional group called the cross-partner project was created in 2018. See the current Tox21 cross-partner projects.


Through this project, Tox21 researchers are working to annotate pathways by source, species, biological function/process, disease/toxicity relevance and availability of probing assays using data from the PubChem and ToxCast databases. The BioPlanet database currently hosts  approximately 1,700 unique human pathways that have been thoroughly curated. A public web browser enables easy pathway visualization and analysis. Continued development of this resource will include compound activity data, sequence data, gene/protein expression data and pathway data from non-human species, in addition to organizing assays according to pathways/diseases/toxicity end points. This integrated platform will facilitate systematic analysis and modeling of toxicity responses.


Tox21 researchers work on a variety of different assays:

  • Phenotypic readouts
    • Cytotoxicity assays (i.e., cell viability [measures ATP], kinetic measurement of cytotoxicity and viability in cells)
    • Apoptosis assays (i.e., caspase assays [measures activity of caspase 3/7, 8, 9])
    • Membrane integrity assays (i.e., LDH and protease release)
    • Mitochondrial toxicity assays (i.e., mitochondrial membrane potential)
    • Gene toxicity assays
      • Differential cytotoxicity (DNA damage repair gene–deficient cell lines, DT40 and mouse cell lines)
      • ATADS (ELG1)
      • Micronucleus assay
    • Phospholipidosis assays
    • Genetic variation (more than 1,000 HapMap lines)
  • Pathway-specific toxicological mechanisms
    • Pathway assays using reporters (e.g., luciferase, β-lactamase) measuring hypoxia, ER stress, NF-κB*, p53*, ARE/Nrf2*, HSE, CREB, AP-1, STAT, NFAT, HIF-1α*, ESRE*, real time cytotoxicity and viability*
    • Developmental pathway assays (retinol signaling*, Hedgehog/Gli* and SBE/SMAD*)
  • Target-specific toxicological mechanisms
    • Nuclear receptor assays, including AR*, AhR*, ERα/β*, FXR*, GR*, LXR, PPARδ*, PPARγ*, PR*, PXR*, RXR*, TRβ*, VDR*, RORγ, CAR*, ERR*
    • G-protein-coupled receptor signaling assays, including TRHR* and TSHR*
    • Enzyme activity assays, including AChE*
    • hERG channel assay
    • Cytokine assays including IL-8 and TNFα

*Assays screened against the Tox21 10K library

Neuronal Toxicity

Tox21 researchers are developing cellular models and methods to assess neurodegenerative and neurodevelopmental toxicities. Stem cell–derived, LUHMES immortalized and 3-D cultured neuronal models are included. Screening methods include neurite growth measurements and toxicant-chemical interaction “Toxmatrix” screening.