Abstract: Cutting-edge in vitro teratogenicity models represent a significant advancement in drug safety assessment, aimed at reducing the reliance on animal testing while enhancing the predictivity and relevance of human-based assays. Conventional animal embryofetal development (EFD) testing requires the use of a large number of animals and is very time-consuming, making it feasible for only a limited number of drug candidates at a late stage in drug development. In contrast, alternative in vitro models, while promising, face their own challenges. Data from model compounds is mostly based on animal studies, and most recent in vitro alternative models are human-based, which creates a "translational gap" from animal EFD data to human in vitro models. Traditional in-vitro teratogenicity testing relies heavily on the mouse embryonic stem cell test (EST), a validated assay for identifying potential teratogens. However, recent developments using human-based models, such as hiPSC-derived, offer promising alternatives that closely mimic early human embryonic development. Here, we present a comprehensive comparison of the mouse EST and these novel human-based assays, such as the Teratox and gastruloid assays. Validation data are presented using a range of reference compounds known for their teratogenic or non-teratogenic effects. These compounds were tested across all models to evaluate and compare their performance and predictive accuracy. Human-based models align better with known human teratogenic outcomes, showing superior translational potential. Specifically, the Teratox assay exhibited higher sensitivity and specificity in detecting teratogenic effects compared to the mouse EST. In conclusion, these innovative in vitro teratogenicity models represent a shift from traditional animal-based methods to human-relevant assays. These models not only offer ethical benefits but also provide more relevant biological insights, potentially leading to safer and more effective pharmaceuticals. This transition promises improved drug development processes, better safety profiles, and safer therapeutic options for patients.
