Table 1.
Validated assays for Tox21 screening
| Target | Conduit | Pathway | Readout |
|---|---|---|---|
| 5-Hydroxytryptamine receptor 2A | CHO-K1 | GPCR/Ca2+ signaling | Fluorescence |
| Acetylcholinesterase | AChE-SH-SY5Y Biochemical | Stress response/neuronal signaling | Absorbance Fluorescence |
| Acetyl-(E)-2-(4-mercaptostyryl)-1,3,3-trimethyl-3H-indol-1-ium (acetyl-MSTI) binding | Biochemical | Electrophilic binding | Fluorescence |
| Aryl hydrocarbon receptor | AhR-HepG2 | NR signaling | Luminescence |
| Activator protein 1 | AP1-ME180 | Stress response | Fluorescence |
| Androgen receptor (LBD) | AR-HEK293 | NR signaling | Fluorescence |
| Androgen receptor (full) | AR-MDA | NR signaling | Luminescence |
| Antioxidant response element | Nrf2/ARE-HepG2 | Stress response | Fluorescence Luminescence |
| Aromatase | Aromatase-MCF7 | NR signaling | Luminescence |
| Autofluorescence | HEK293 and HepG2 | Autofluorescence | Fluorescence |
| β2-Adrenergic receptor | CHO-K1 | GPCR/cAMP signaling | Fluorescence |
| Constitutive androstane receptor | CAR-HepG2 | NR signaling | Luminescence |
| cAMP response element–binding protein | CREB-HEK293 | Stress response/neuronal signaling | Fluorescence |
| Caspase-3 and caspase-7 | Caspase-3/7-HepG2 | Stress response | Luminescence |
| CYP1A2 | Enzyme | Cytochrome P450 | Luminescence |
| CYP2C9 | Enzyme | Cytochrome P450 | Luminescence |
| CYP2C19 | Enzyme | Cytochrome P450 | Luminescence |
| CYP2D6 | Enzyme | Cytochrome P450 | Luminescence |
| CYP3A4 | Enzyme | Cytochrome P450 | Luminescence |
| Cytotoxicity and viability | HEK293 | Stress response | Fluorescence Luminescence |
| HepG2 | Stress response | Fluorescence Luminescence |
|
| Dopamine receptor D2 | DRD2-HEK293 | GPCR/cAMP signaling | Fluorescence |
| DNA repair, Rad54/ku70 (−/−) | DT40 | Stress response | Luminescence |
| DNA repair, Rev3 (−/−) | DT40 | Stress response | Luminescence |
| DNA repair, wild type | DT40 | Stress response | Luminescence |
| Ether-a-go-go-related gene potassium channel | hERG-U2OS | Cardiology signaling | Fluorescence |
| Estrogen receptor α (LBD) | ERα-HEK293 | NR signaling | Fluorescence |
| Estrogen receptor α (full) | ER-MCF7 | NR signaling | Luminescence |
| Estrogen receptor β | ERβ-HEK293 | NR signaling | Fluorescence |
| Estrogen-related receptor α | ERR-HEK293 | NR signaling | Luminescence |
| PGC/ERR-HEK293 | NR signaling | Luminescence | |
| Endoplasmic reticulum stress response element | ESRE-Hela | Stress response | Fluorescence |
| Farnesoid X receptor | FXR-HEK293 | NR signaling | Fluorescence |
| Glucocorticoid receptor | GR-Hela | NR signaling | Fluorescence |
| Gonadotropin-releasing hormone receptor | GnRHR-HEK293 | GPCR/Ca2+ signaling | Fluorescence |
| H2A histone family member X | CHO | Stress response | Fluorescence Luminescence |
| HDAC I and HDAC II | HCT116 | Epigenetics | Luminescence |
| Hypoxia-inducible factors | HRE-ME180 | Stress response | Fluorescence |
| Heat shock element | HSE-HeLa | Stress response | Fluorescence |
| KISS1 receptor | KISS1-HEK293 | GPCR/Ca2+ signaling | Fluorescence |
| Luciferase | Enzyme | Luciferase inhibition | Luminescence |
| Mitochondrial membrane potential | MMP-HepG2 | Stress response | Fluorescence |
| Muscarinic acetylcholine receptor M1 | M1-CHO-K1 | GPCR/Ca2+ signaling | Fluorescence |
| Nonspecific cAMP signaling | HEK293 | GPCR/cAMP signaling | Fluorescence |
| Nuclear factor κB | NF-κB-ME180 | Stress response | Fluorescence |
| p53 | p53-HCT-116 | Stress response | Fluorescence |
| Peroxisome proliferator-activated receptor δ | PPARδ-HEK293 | NR signaling | Fluorescence |
| Peroxisome proliferator-activated receptor γ | PPARγ-HEK293 | NR signaling | Fluorescence |
| Progesterone receptor | PR-HEK293 | NR signaling | Fluorescence |
| Pregnane X receptor | PXR-HepG2 | NR signaling | Luminescence |
| Retinoic acid–related orphan receptor γ | RORγ-CHO | NR signaling | Luminescence |
| Retinoid X receptor | RXR-HEK293 | NR signaling | Fluorescence |
| Retinol signaling pathway | RAR-C3H10T1/2 | Developmental | Luminescence |
| Sonic Hedgehog pathway | ShhGli1–3T3 | Developmental | Luminescence |
| Smad signaling pathway | SMAD-HEK293 | Developmental | Fluorescence |
| Telomere length regulation protein ELG1 | ELG1-HEK293 | Stress response | Luminescence |
| Thyroid hormone receptor | TRE-GH3 | NR signaling | Luminescence |
| Thyroid-stimulating hormone receptor | TSHR-HEK293 | GPCR/cAMP signaling | Fluorescence |
| Thyrotropin-releasing hormone receptor | TRHR-HEK293 | GPCR/Ca2+ signaling | Fluorescence |
| Vitamin D receptor | VDR-HEK293 | NR signaling | Fluorescence |
Abbreviations: GPCR, G protein–coupled receptor; LBD, ligand-binding domain; NR, nuclear receptor; Tox21, Toxicology in the 21st Century.