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ICCVAM Biennial Report 2018-2019

Biennial Progress Report 2018-2019 Interagency Coordinating Committee on the Validation of Alternative Methods

Performance-based Validation of Tox21 Assays

To use data generated by HTS initiatives such as Tox21 and the EPA ToxCast program in regulatory applications, the assays and models built from the assays must be validated based on their performance against the biological targets they query. This requires developing sets of reference chemicals that consistently yield reproducible results when assayed for these biological targets. A process also needs to be established for assessing and reporting the performance evaluation of an assay in a standardized format that provides consumers of the data the ability to interpret the appropriate context for use of the assay. Finally, both the development of reference chemical sets and the validation process need to be streamlined and rapid enough to manage the tens to hundreds of assays that can help inform regulatory toxicity endpoints. To address these needs, scientists at EPA and NIEHS developed a process to identify reference chemicals that consistently produce positive or negative results when assayed in defined assays (Judson et al 2019). Additional work under this project has focused on identifying chemicals that consistently produce false signals by interfering with specific technology types and backgrounds. Models to predict interferent chemicals for luciferase inhibition and autofluorescence are available on the NTP website. Current efforts are focused on using these data to identify reference chemicals and establish protocols for evaluating the performance of specific Tox21 and ToxCast assays.