Citation:

Wang, J., A. Richard, A. Murr, A. Buckalew, R. Lougee, Mahmoud A. Shobair, D. Hallinger, S. Laws, AND T. Stoker. Expanded High-Throughput Screening and Chemotype-Enrichment Analysis of the Phase II:e1k ToxCast Library for Human Sodium-Iodide Symporter (NIS) Inhibition. Archives of Toxicology. Springer, New York, NY, 95(5):1723-1737, (2021). https://doi.org/10.1007/s00204-021-03006-2

Impact/Purpose:

The use of hNIS-HEK293T-EPA cells in the NIS-mediated iodide uptake and cell viability assays provide the U.S.EPA with a rapid approach for identifying chemicals that have the potential to disrupt a key molecular step essential for the synthesis of thyroid hormones. This manuscript demonstrates that the application of this approach in an expanded screening of NIS inhibitors in the ToxCast e1k library, and the further application of a chemotype enrichment analysis in identifying chemical structural features associated with NIS inhibition activity. This study screened a total of 804 unique ToxCast e1k substances for RAIU inhibition. The 143 chemicals that were active in the RAIU assay were ranked based on potency, effects on cell viability, and normalized to perchlorate. A total of 55 chemicals actively inhibited RAIU without cytotoxicity. Most of the active chemicals had weak RAIU inhibition, and only 5 chemicals scored within a factor of 2 of the sodium perchlorate. Four chemicals were further validated using our secondary FRTL-5 based RAIU assay. The present results were then combined with the previous PhII (ph1_v2 and ph2) library screening results to produce two sets of binary hit-calls for 1771 unique chemicals, consisting of 400 positives exhibiting significant RAIU inhibition, and 112 positives following application of a cell viability filter. A ToxPrint chemotype-enrichment analysis were used to compare changes in enriched chemical structures upon significant expansion of the chemical library from 1000 (PhII) to ~1800 (PhII+e1k) chemicals. This analysis is also applied to the entire combined PhII+e1k library and compare the resulting enriched chemical structures to those derived previously, both for the cytotoxicity unfiltered and filtered activity datasets. The results from this study conclude the screening of the current ToxCast library and represent the largest source of in vitro screening data for NIS inhibitors. The NIS assay results and chemotype enrichment results presented herein for the combined PhII+e1k library of approximately 1800 chemicals, spanning many chemicals of biological interest and environmental concern, should provide a valuable resource for future research investigations, as well as improve the understanding of local structure-activity determinants and mechanisms potentially impacting thyroid function.

Description:

The sodium-iodide symporter (NIS) mediates the uptake of iodide into the thyroid. Inhibition of NIS function by xenobiotics has been demonstrated to suppress circulating thyroid hormones and perturb related physiological functions. Until recently, few environmental chemicals had been screened for NIS inhibition activity. We previously screened over 1000 chemicals from the ToxCast Phase II (ph1v2 and ph2) libraries using an in vitro radioactive iodide uptake (RAIU) with the hNIS-HEK293T cell line to identify NIS inhibitors. Here, we broaden the chemical space by expanding screening to include the ToxCast e1k library (804 unique chemicals) with initial screening for RAIU at 1 × 10–4 M. Then 209 chemicals demonstrating > 20% RAIU inhibition were further tested in multiple-concentration, parallel RAIU and cell viability assays. This identified 55 chemicals as active, noncytotoxic RAIU inhibitors. Further cytotoxicity-adjusted potency scoring (with NaClO4 having a reference score of 200) revealed five chemicals with moderate to strong RAIU inhibition (scored > 100). These data were combined with our previous PhII screening data to produce binary hit-calls for ~ 1800 unique chemicals (PhII + e1k) with and without cytotoxicity filtering. Results were analyzed with a ToxPrint chemotype-enrichment workflow to identify substructural features significantly enriched in the NIS inhibition hit-call space. We assessed the applicability of enriched PhII chemotypes to prospectively predict NIS inhibition in the e1k dataset. Chemotype enrichments derived for the combined ~ 1800 dataset also identified additional enriched features, as well as chemotypes affiliated with cytotoxicity. These enriched chemotypes provide important new information that can support future data interpretation, structure–activity relationship, chemical use, and regulation. Access provided by U.S. Environmental Protection Agency Multi-Site Li

URLs/Downloads:

Record Details: