Validation of an in vitro human thyroid microtissue model for chemical screening
Current regulatory decision-making for potential thyroid-disrupting chemicals is based on in vivo apical endpoints, such as alterations in thyroid hormone levels. New approach methodologies (NAMs) to complement or replace traditional in vivo tests are being developed to enable higher-throughput mechanistic understanding of potential endocrine-disrupting chemicals.
A key element in the acceptance of NAMs in regulatory contexts is to establish confidence through validation studies that evaluate a NAM’s reliability and relevance for a specific application. NICEATM coordinated an interlaboratory validation study of the utility of a thyroid 3D microtissue model for evaluating chemical effects on thyroid hormone synthesis and tissue viability. The lead laboratory was within the EPA Office of Research and Development, with three agrochemical industry and commercial laboratories participating in the transferability phase (Deisenroth et al. 2026). Goals of this effort included (1) development of the study design, (2) test method harmonization and standardization and demonstration of intralaboratory reproducibility, and (3) method transferability, reference chemical testing, and demonstration of interlaboratory reproducibility. Reference chemical selection was based on previous work demonstrating disruption of thyroid hormone synthesis. These included one “true negative” and three “true positive” compounds. The study established standard operating procedures that were successfully transferred to multiple laboratories with no experience conducting the assay. Consistent results were generated among the testing laboratories using the same four blinded reference chemicals and among the three donor pairs. Independent human thyrocyte donors were matched between a testing laboratory and the lead laboratory to account for biological variability. In addition to the publication describing the study, a detailed report of the study is being prepared. A follow-up study to test the model with a larger chemical set and potentially improve replicability is currently being designed.