Stephanie A. Eytcheson obtained her PhD in environmental toxicology from North Carolina State University in 2018 and is currently an ORISE Postdoctoral Fellow at the US EPA in Duluth, MN. Her areas of interest include investigating endocrine disruption through in vitro screening, in vivo exposures, and targeted gene knockout to tease apart mechanisms of action.
Screening ToxCast Chemical Libraries for Binding to Transthyretin
S.A. Eytcheson1,2, A.D. Zosel2,3, M.W. Hornung2, S.J. Degitz2
1Oak Ridge Institute for Science and Education-Postdoctoral Fellow, Oak Ridge, TN, USA
2U.S. Environmental Protection Agency, Office of Research and Development, Center for Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division, Duluth, MN, USA
3Oak Ridge Associate Universities-Student Services Contractor, Oak Ridge, TN, USA
High-throughput screening (HTS) assays allow for rapidly testing many chemicals for bioactivity at specific molecular targets. One goal of HTS is to reduce the time and cost of generating data to support evaluation of chemicals for potential endocrine disruption. Data from HTS assays can be used to inform QSAR model development to predict activity based on chemical structure. The US EPA’s Toxicity Forecaster (ToxCast) has a library of HTS data which can be used to prioritize chemicals of concern. One gap in thyroid related HTS includes the thyroid hormone carrier protein transthyretin (TTR) as a potential target of thyroid system disruption. TTR plays a role in maintaining the levels of free versus bound thyroid hormone and serves as a circulating transport protein to deliver thyroid hormone to target tissue. To address this gap, a fluorescent high-throughput assay has been developed to assess inhibition of TTR. 8-Anilino-1- naphthalenesulfonic acid ammonium salt (ANSA) fluoresces when bound to TTR; thus, displacement of ANSA from the protein by inhibitory chemicals results in a loss of fluorescence. A two-tiered approach was utilized to rank and prioritize chemicals for further testing. The first tier consisted of screening approximately 1800 chemicals from the ToxCast phase 1, phase 2, and e1k libraries for activity at a single high concentration. There were 888 active chemicals (>20% activity) in single concentration screening. Chemicals with activity above the 85% activity threshold were moved on to concentration response testing to define the IC50 values. Data from the assay were used in the Tox24 Challenge which “crowdsourced” approaches to predict chemical binding to TTR based only on chemical structure data, and additional work to develop a QSAR model to predict chemical binding to TTR is ongoing.
The contents of this abstract neither constitute, nor necessarily reflect, US EPA policy.
