Value and limitation of structure-based profilers to characterize developmental and reproductive toxicity potential

Comparative assessment of different alternatives to animal models for developmental toxicity prediction using physiologically based toxicokinetic modelling approach: A case study of hexaconazole, an azole fungicide

The 21st-century risk assessment is gradually moving from animal-based toxicity studies to in vitro alternative assays that are sustainable and ethically acceptable. Alternative assays, such as rat whole embryo culture test (WEC), mouse embryonic stem cell test (EST), zebrafish embryotoxicity test (ZET), and ToxCast assays, are widely used for screening the chemicals for developmental toxicity. However, for use in risk assessment, these assays require integration with the predictive approaches, such as physiologically based toxicokinetic (PBTK) model. Using PBTK-facilitated reverse dosimetry approach, we translated the in vitro assay concentration to human equivalent doses (HEDs) using hexaconazole (HEX, a widely used fungicide) as the model compound. For this, a rat PBTK model was developed and verified using in-house generated toxicokinetic data. Based on the rat model, human PBTK model was developed to translate the in vitro concentrations of various alternative assays into HEDs (0.16-7850 mg/kg/day). These HEDs were compared with the HED derived using the traditional approach based on rat toxicity data. The HEDs derived from the alternative assays (WEC, EST and ZET) showed poor correlation with the HED derived from the traditional approach. However, most of the HEDs derived from the ToxCast assays were close to the traditional HED. This indicated that the PBTK model-facilitated reverse dosimetry approach could derive the HEDs directly from in vitro assays when sufficient animal data is lacking.

Advancing the use of new approach methodologies for assessing teratogenicity: Building a tiered approach

Many New Approach Methodologies (NAMs) have been developed for the safety assessment of new ingredients. Research into reproductive toxicity and teratogenicity is a particularly high priority, especially given their mechanistic complexity. Forty-six non-teratogenic and 39 teratogenic chemicals were screened for teratogenic potential using the in silico DART model from the OECD QSAR Toolbox; the devTox quickPredict™ (devTox assay) test and the Zebrafish Embryotoxicity Test (ZET). The sensitivity and specificity were 94.7% and 84.1%, respectively, for the DART tree (83 chemicals), 86.1% and 35.6% for the devTox (81 chemicals) and 77.8% and 76.7% for the ZET (57 chemicals). Fifty-three chemicals were tested in all three assays and when results were combined and based on a "2 out of 3 rule", the sensitivity and specificity were 96.0% and 71.4%, respectively. The specificity of the devTox assay for a sub-set of 43 chemicals was increased from 26.1% to 82.6% by incorporating human plasma concentrations into the assay interpretation. When all 85 chemicals were assessed in a decision tree approach, there was an excellent predictivity and assay robustness of 90%. In conclusion, all three models exhibited a good sensitivity and specificity, especially when outcomes from all three were combined or used in "2 out of 3" or a tiered decision tree approach. The latter is an interesting predictive approach for evaluating the teratogenic potential of new chemicals. Future investigations will extend the number of chemicals tested, as well as explore ways to refine the results and obtain a robust Integrated Testing Strategy to evaluate teratogenic potential.

Human-Based New Approach Methodologies in Developmental Toxicity Testing: A Step Ahead from the State of the Art with a Feto-Placental Organ-on-Chip Platform

Developmental toxicity testing urgently requires the implementation of human-relevant new approach methodologies (NAMs) that better recapitulate the peculiar nature of human physiology during pregnancy, especially the placenta and the maternal/fetal interface, which represent a key stage for human lifelong health. Fit-for-purpose NAMs for the placental-fetal interface are desirable to improve the biological knowledge of environmental exposure at the molecular level and to reduce the high cost, time and ethical impact of animal studies. This article reviews the state of the art on the available in vitro (placental, fetal and amniotic cell-based systems) and in silico NAMs of human relevance for developmental toxicity testing purposes; in addition, we considered available Adverse Outcome Pathways related to developmental toxicity. The OECD TG 414 for the identification and assessment of deleterious effects of prenatal exposure to chemicals on developing organisms will be discussed to delineate the regulatory context and to better debate what is missing and needed in the context of the Developmental Origins of Health and Disease hypothesis to significantly improve this sector. Starting from this analysis, the development of a novel human feto-placental organ-on-chip platform will be introduced as an innovative future alternative tool for developmental toxicity testing, considering possible implementation and validation strategies to overcome the limitation of the current animal studies and NAMs available in regulatory toxicology and in the biomedical field.