Cell-Based Bioassay to Screen Environmental Chemicals and Human Serum for Total Glucocorticogenic Activity

Glucocorticoids are steroid hormones that have systemic effects that are mediated by the glucocorticoid receptor. Environmental chemicals that disrupt glucocorticoid receptor signaling and/or glucocorticoid homeostasis could adversely affect the health of human and nonhuman vertebrates. A major challenge in identifying environmental chemicals that alter glucocorticoid receptor signaling and/or glucocorticoid homeostasis is a lack of adequate screening methods. We developed a cell-based bioassay to measure total glucocorticogenic activity (TGA) of environmental chemicals and human serum. Human MDA-MB-231 breast cancer cells were stably transfected with a luciferase reporter gene driven by 3 tandem glucocorticoid-response elements. Dose-response curves for 6 glucocorticoids and 4 non-glucocorticoid steroid hormones were generated to evaluate the specificity of the bioassay. Cells were also optimized to measure TGA of 176 structurally diverse environmental chemicals and human serum samples in a high-throughput format. Reporter activity was glucocorticoid-specific and induced 400-fold by 1 μM dexamethasone. Furthermore, 3 of the screened chemicals (3,4,4'-trichlorocarbanilide, isopropyl-N-phenylcarbamate, and benzothiazole derivative 2-[4-chlorophenyl]-benzothiazole) potentiated cortisol-induced glucocorticoid receptor activity. Serum TGA estimates from the bioassay were highly correlated with a cortisol enzyme-linked immunosorbent assay. The present study establishes an in vitro method to rapidly screen environmental chemicals and human serum for altered glucocorticogenic activity. Future studies can utilize this tool to quantify the joint effect of endogenous glucocorticoids and environmental chemicals. Environ Toxicol Chem 2021;40:177-186. © 2020 SETAC.