Comparative analysis of OECD guideline data and Tox21 assays to improve reproductive and developmental toxicity prediction

Reproductive and developmental toxicities pose major challenges in chemical safety evaluation because adverse effects can span generations. Conventional in vivo OECD Test Guideline (TG) assays provide robust hazard characterization but require large animal cohorts and extended study periods. In this study, datasets from OECD TG-compliant studies were compiled to identify the mechanistic drivers of toxicity. To complement these data, we integrated high-throughput in vitro results from the U.S. Tox21 program, which evaluates > 10,000 chemicals in human cell-based assays targeting nuclear receptor modulation, oxidative stress, and DNA damage. By aligning OECD TG outcomes with Tox21 profiles, we assessed the associations between in vivo reproductive/developmental toxicity and in vitro mechanistic endpoints using the Toxicity Predictor program. Our analysis suggested that OECD TG 414-, TG 421-, and TG 422-positive chemicals were negatively associated with thyroid-stimulating hormone receptor (TSHR) antagonists, farnesoid X receptor (FXR) antagonists, peroxisome proliferator-activated receptor delta (PPAR δ) antagonists, transforming growth factor beta (TGFβ) agonists, and endoplasmic reticulum stress response (ERsr) agonists in the Tox21 assays. Conversely, OECD TG 416- and TG 443-positive chemicals showed a positive association with histone deacetylase (HDAC) antagonists. Overall, the regulation of miRNA transcription, nuclear receptor activity, and transcription pathways showed significant associations that may indicate key mechanistic links between in vitro and in vivo datasets. These associations may provide supportive insights for considering how alternative data sources could complement existing regulatory toxicology frameworks.