title: Development of a screening approach to detect thyroid disrupting chemicals that inhibit the human sodium iodide symporter (NIS).
abstract: The U.S. EPA's Endocrine Disruptor Screening Program aims to use high-throughput assays and computational toxicology models to screen and prioritize chemicals that may disrupt the thyroid signaling pathway. Thyroid hormone biosynthesis requires active iodide uptake mediated by the sodium/iodide symporter (NIS). Monovalent anions, such as the environmental contaminant perchlorate, are competitive inhibitors of NIS, yet limited information exists for more structurally diverse chemicals. A novel cell line expressing human NIS, hNIS-HEK293T-EPA, was used in a radioactive iodide uptake (RAIU) assay to identify inhibitors of NIS-mediated iodide uptake. The RAIU assay was optimized and performance evaluated with 12 reference chemicals comprising known NIS inhibitors and inactive compounds. An additional 39 chemicals including environmental contaminants were evaluated, with 28 inhibiting RAIU over 20% of that observed for solvent controls. Cell viability assays were performed to assess any confounding effects of cytotoxicity. RAIU and cytotoxic responses were used to calculate selectivity scores to group chemicals based on their potential to affect NIS. RAIU IC50values were also determined for chemicals that displayed concentration-dependent inhibition of RAIU (≥50%) without cytotoxicity. Strong assay performance and highly reproducible results support the utilization of this approach to screen large chemical libraries for inhibitors of NIS-mediated iodide uptake.
authors.affiliation: Endocrine Toxicology Branch, Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Hallinger
authors.affiliation: Endocrine Toxicology Branch, Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Ashley S
authors.initials: AS
authors.lastname: Murr
authors.affiliation: Endocrine Toxicology Branch, Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Angela R
authors.initials: AR
authors.lastname: Buckalew
authors.affiliation: National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Steven O
authors.initials: SO
authors.lastname: Simmons
authors.affiliation: Endocrine Toxicology Branch, Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States. Electronic address: stoker.tammy@epa.gov.
authors.forename: Tammy E
authors.initials: TE
authors.lastname: Stoker
authors.affiliation: Endocrine Toxicology Branch, Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States. Electronic address: laws.susan@epa.gov.
authors.forename: Susan C
authors.initials: SC
authors.lastname: Laws
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D052244:Endocrine Disruptors / Q000633:toxicity*; D057166:High-Throughput Screening Assays; D006801:Humans; D007454:Iodides / Q000378:metabolism*; D007457:Iodine Radioisotopes; D027981:Symporters / Q000037:antagonists & inhibitors* / Q000235:genetics; D013961:Thyroid Gland / Q000378:metabolism; D000099209:Sodium-Iodide Symporters
chemical_list: D052244:Endocrine Disruptors; D007454:Iodides; D007457:Iodine Radioisotopes; D027981:Symporters; D000099209:Sodium-Iodide Symporters
keywords: Chemical screening; Endocrine disruptors; Sodium iodide symporter; Thyroid