Prediction of in vivo developmental toxicity by combination of Hand1-Luc embryonic stem cell test and metabolic stability test with clarification of metabolically inapplicable candidates

Comprehensive Search for Genes Involved in Thalidomide Teratogenicity Using Early Differentiation Models of Human Induced Pluripotent Stem Cells: Potential Applications in Reproductive and Developmental Toxicity Testing

Developmental toxicity testing is essential to identify substances that may harm embryonic development. This study aimed to establish a protocol for evaluating developmental toxicity using human induced pluripotent stem cells (iPSCs) by analyzing cellular activity and gene expression changes. Two ICH S5(R3) positive substances, valproic acid (VPA), which is a substance previously detected as positive by other test methods, and thalidomide (Thalido), were examined during early trichoderm differentiation without fetal bovine serum. RNA-seq analysis identified seven candidate genes, including TP63, associated with altered expression following exposure to VPA or Thalido. These genes were implicated in pathways related to tissue development, cell growth, and molecular interactions. While the assay effectively detected VPA and Thalido, its limitations include testing only soluble substances and focusing on early differentiation stages. Nevertheless, the protocol demonstrates potential for the classification and evaluation of emerging modality drugs based on physical properties such as solubility, polarity, and pH. Integration with AI analysis may enhance its capacity to uncover genetic variations and evaluate previously uncharacterized substances. This study provides a foundation for alternative developmental toxicity testing methods, with further refinements in the culture method expected to improve accuracy and applicability in regulatory toxicology.

Pluripotent stem cell assays: Modalities and applications for predictive developmental toxicity

This manuscript provides a review focused on embryonic stem cell-based models and their place within the landscape of alternative developmental toxicity assays. Against the background of the principles of developmental toxicology, the wide diversity of alternative methods using pluripotent stem cells developed in this area over the past half century is reviewed. In order to provide an overview of available models, a systematic scoping review was conducted following a published protocol with inclusion criteria, which were applied to select the assays. Critical aspects including biological domain, readout endpoint, availability of standardized protocols, chemical domain, reproducibility and predictive power of each assay are described in detail, in order to review the applicability and limitations of the platform in general and progress moving forward to implementation. The horizon of innovative routes of promoting regulatory implementation of alternative methods is scanned, and recommendations for further work are given.

Establishment of a developmental toxicity assay based on human iPSC reporter to detect FGF signal disruption

The number of man-made chemicals has increased exponentially recently, and exposure to some of them can induce fetal malformations. Because complex and precisely programmed signaling pathways play important roles in developmental processes, their disruption by external chemicals often triggers developmental toxicity. However, highly accurate and high-throughput screening assays for potential developmental toxicants are currently lacking. In this study, we propose a reporter assay that utilizes human-induced pluripotent stem cells (iPSCs) to detect changes in fibroblast growth factor signaling, which is essential for limb morphogenesis. The dynamics of this signaling after exposure to a chemical were integrated to estimate the degree of signaling disruption, which afforded a good prediction of the capacity of chemicals listed in the ECVAM International Validation Study that induce limb malformations. This study presents an initial report of a human iPSC-based signaling disruption assay, which could be useful for the screening of potential developmental toxicants.

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Human iPSC-based FGF signal disruption reporter system was established

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FGF signal disruption was a good indicator of limb malformation-related toxicants

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Integration of dynamic FGF signal disruption results improved assay performance

Integrated fibroblast growth factor signal disruptions in human iPS cells for prediction of teratogenic toxicity of chemicals

The number of man-made chemicals has increased rapidly in recent decades, with certain chemicals potentially causing malformations in fetuses. Although the toxicities of chemicals have been tested in animals, chemicals that are not teratogenic in rodents can cause severe malformations in humans, owing to the differences in the susceptibility to the teratogenicity of chemicals among species. One possible cause of such species differences, other than pharmacokinetics, could be the difference in sensitivity to such chemicals at the cellular level. Therefore, a human cell-based high-throughput assay system is needed for detecting potential teratogenic chemicals. In this study, we proposed a signal reporter assay using human induced pluripotent stem cells (iPSCs). Because developmental processes are governed by highly intricate and precisely programmed signaling pathways, external chemical-induced disruption of these pathways often triggers developmental toxicities. The reporter assay using hiPSCs was used to detect changes in the fibroblast growth factor (FGF) signaling pathway, a pathway essential for limb morphogenesis. The method was based on monitoring and time-accumulation of the signal disruption over time, rather than the classical endpoint detection of the signal disruption. This approach was useful for detecting signal disruptions caused by the malformation chemicals listed in the ICH S5 guideline, including thalidomide. The human iPSC-based signal disruption assay could be a promising tool for the initial screening of developmental toxicants.

An automated and high-throughput-screening compatible pluripotent stem cell-based test platform for developmental and reproductive toxicity assessment of small molecule compounds

The embryonic stem cell test (EST) represents the only validated and accepted in vitro system for the detection and classification of compounds according to their developmental and reproductive teratogenic potency. The widespread implementation of the EST, however, in particular for routine application in pharmaceutical development, has not been achieved so far. Several drawbacks still limit the high-throughput screening of potential drug candidates in this format: The long assay period, the use of non-homogeneous viability assays, the low throughput analysis of marker protein expression and the compatibility of the assay procedures to automation. We have therefore introduced several advancements into the EST workflow: A reduction of the assay period, an introduction of homogeneous viability assays, and a straightforward analysis of marker proteins by flow cytometry and high content imaging to assess the impact of small molecules on differentiation capacity. Most importantly, essential parts of the assay procedure have been adapted to lab automation in 96-well format, thus enabling the interrogation of several compounds in parallel. In addition, extensive investigations were performed to explore the predictive capacity of this next-generation EST, by testing a set of well-known embryotoxicants that encompasses the full range of chemical-inherent embryotoxic potencies possible. Due to these significant improvements, the augmented workflow provides a basis for a sensitive, more rapid, and reproducible high throughput screening compatible platform to predict in vivo developmental toxicity from in vitro data which paves the road towards application in an industrial setting.

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An engineered mouse embryonic stem cell model with survivin as a molecular marker and EGFP as the reporter for high throughput screening of embryotoxic chemicals in vitro

Embryonic stem cell test (EST) is the only generally accepted in vitro method for assessing embryotoxicity without animal sacrifice. However, the implementation and application of EST for regulatory embryotoxicity screening are impeded by its technical complexity, long testing period, and limited endpoint data. In this study, a high throughput embryotoxicity screening based on mouse embryonic stem cells (mESCs) expressing enhanced green fluorescent protein (EGFP) driven by a human survivin promoter and a human cytomegalovirus promoter, respectively, was developed. These EGFP expressing mESCs were cultured in three-dimensional (3D) fibrous scaffolds in microbioreactors on a multiwell plate with EGFP fluorescence signals as cell responses to chemicals monitored noninvasively in a high throughput manner. Nine chemicals with known developmental toxicity were used to validate the survivin-based embryotoxicity assay, which showed that strongly embryotoxic compounds such as 5-fluorouracil, retinoic acid, and methotrexate downregulated survivin expression by more than 50% in 3 days, while weakly embryotoxic compounds such as boric acid, methoxyacetic acid, and tetracyclin showed modest downregulation effect and nonembryotoxic saccharin, penicillin G, and acrylamide had negligible downregulation effect on survivin expression, confirming that survivin can be used as a molecular endpoint for high throughput screening of embryotoxicants. The potential developmental toxicity of three Chinese herbal medicines were also evaluated using this assay, demonstrating its application in in vitro developmental toxicity test for drug safety assessment.

Pluripotent Stem Cells in Developmental Toxicity Testing: A Review of Methodological Advances

Millions of children are born each year with a birth defect. Many of these defects are caused by environmental factors, although the underlying etiology is often unknown. In vivo mammalian models are frequently used to determine if a chemical poses a risk to the developing fetus. However, there are over 80 000 chemicals registered for use in the United States, many of which have undergone little safety testing, necessitating the need for higher-throughput methods to assess developmental toxicity. Pluripotent stem cells (PSCs) are an ideal in vitro model to investigate developmental toxicity as they possess the capacity to differentiate into nearly any cell type in the human body. Indeed, a burst of research has occurred in the field of stem cell toxicology over the past decade, which has resulted in numerous methodological advances that utilize both mouse and human PSCs, as well as cutting-edge technology in the fields of metabolomics, transcriptomics, transgenics, and high-throughput imaging. Here, we review the wide array of approaches used to detect developmental toxicants, suggest areas for further research, and highlight critical aspects of stem cell biology that should be considered when utilizing PSCs in developmental toxicity testing.

[Development of alternatives to animal experiments using pluripotent stem cells]

Animal experiments have occupied an important position in the safety assessment of chemicals. However, due to the rise in animal welfare as seen in the ban of animal experiments in European cosmetic development, the development of alternative methods for animal experiments has become very important in recent years. Development of in vitro tests for local toxicity such as irritation and sensitization tests is preceded. Meanwhile, alternative tests for systemic toxicity such as chronic and developmental toxicities are under development. In developing alternative methods using cultured cells, we have been focusing on pluripotent stem cells such as ES and iPS cells and studying alternatives to developmental toxicity and neurotoxicity. As an alternative test of developmental toxicity, we developed the Hand 1-Luc EST, which is a simple test utilizing cardiomyocyte differentiation process of mouse ES cells, and Tubb 3- and Reln-Luc ESTs using nerve differentiation process. Recently, it was clarified that the combination of the Hand 1-Luc EST and the Tubb 3- and Reln-Luc ESTs improves the prediction of the developmental toxicity. In the study of in vitro neurotoxicity test using neurons derived from mouse ES cells, evaluation methods for neurite outgrowth using high-content imaging technology and for neural function using multi-electrode arrays were developed. In addition, we introduce differentiation methods for retinal tissues from human ES/iPS cells, which are the results as the collaboration with RIKEN and the present state of an in vitro phototoxicity test using retinal pigment epithelial cells (RPE) derived from human ES cells.

Editor's Highlight: Development of Novel Neural Embryonic Stem CellTests for High-Throughput Screening of Embryotoxic Chemicals

There is a great demand for appropriate alternative methods to rapidly evaluate the developmental and reproductive toxicity of a wide variety of chemicals. We used the differentiation of mouse embryonic stem cells (mESCs) into cardiomyocytes as a basis for establishing a rapid and highly reproducible invitro embryotoxicity test known as the Hand1-Luc Embryonic Stem Cell Test (Hand1-Luc EST). In this study, we developed novel neural-Luc ESTs using two marker genes for neural development, tubulin beta-3 (Tubb3) and Reelin (Reln), and evaluated the capacity of these tests to predict developmental toxicity. In addition, we tested whether an integrated approach (a combination of neural-Luc ESTs and the Hand1-Luc EST) improved developmental toxicant detection. To perform our neural-Luc ESTs, we needed to generate stable transgenic mESCs with individual promoters linked to the luciferase gene, and to establish that similar changes in promoter activities and mRNA expression levels occur during neural differentiation. Based on the concentration-response curves of 15 developmental toxicants and 17 non-developmental toxic chemicals, we derived a prediction formula and assessed the capacity of this formula to predict developmental toxicity. Although both were highly sensitive and specific for predicting developmental toxicity, neural-Luc ESTs had similar predictive capacities. In contrast, neural-Luc ESTs and Hand1-Luc EST had significantly different predictive powers. As expected, the combination of these ESTs increased the sensitivity of developmental toxicant detection. These results demonstrate the convenience and the usefulness of this combination of ESTs as an alternative assay system for future toxicological and mechanistic studies of developmental toxicity.