StemPanTox: A fast and wide-target drug assessment system for tailor-made safety evaluations using personalized iPS cells

An alternative model that reliably predicts human-specific toxicity is necessary because the translatability of effects on animal models for human disease is limited to context. Previously, we developed a method that accurately predicts developmental toxicity based on the gene networks of undifferentiated human embryonic stem (ES) cells. Here, we advanced this method to predict adult toxicities of 24 chemicals in six categories (neurotoxins, cardiotoxins, hepatotoxins, two types of nephrotoxins, and non-genotoxic carcinogens) and achieved high predictability (AUC = 0.90-1.00) in all categories. Moreover, we screened for an induced pluripotent stem (iPS) cell line to predict the toxicities based on the gene networks of iPS cells using transfer learning of the gene networks of ES cells, and predicted toxicities in four categories (neurotoxins, hepatotoxins, glomerular nephrotoxins, and non-genotoxic carcinogens) with high performance (AUC = 0.82-0.99). This method holds promise for tailor-made safety evaluations using personalized iPS cells.

The DevTox Germ Layer Reporter Platform: An Assay Adaptation of the Human Pluripotent Stem Cell Test

Environmental chemical exposures are a contributing factor to birth defects affecting infant morbidity and mortality. The USA EPA is committed to developing new approach methods (NAMs) to detect chemical risks to susceptible populations, including pregnant women. NAM-based coverage for cellular mechanisms associated with early human development could enhance identification of potential developmental toxicants (DevTox) for new and existing data-poor chemicals. The human pluripotent stem cell test (hPST) is an in vitro test method for rapidly identifying potential human developmental toxicants that employs directed differentiation of embryonic stem cells to measure reductions in SOX17 biomarker expression and nuclear localization. The objective of this study was to expand on the hPST principles to develop a model platform (DevTox GLR) that utilizes the transgenic RUES2-GLR cell line expressing fluorescent reporter fusion protein biomarkers for SOX17 (endoderm marker), BRA (mesoderm marker), and SOX2 (ectoderm and pluripotency marker). Initial assay adaption to definitive endoderm (DevTox GLR-Endo) was performed to emulate the hPST SOX17 endpoint and enable comparative evaluation of concordant chemical effects. Assay duration was reduced to two days and screening throughput scaled to 384-well format for enhanced speed and efficiency. Assay performance for 66 chemicals derived from reference and training set data resulted in a balanced accuracy of 72% (79% sensitivity and 65% specificity). The DevTox GLR-Endo assay demonstrates successful adaptation of the hPST concept with increased throughput, shorter assay duration, and minimal endpoint processing. The DevTox GLR model platform expands the in vitro NAM toolbox to rapidly identify potential developmental hazards and mechanistically characterize toxicant effects on pathways and processes associated with early human development.

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.

The Human Induced Pluripotent Stem Cell Test as an Alternative Method for Embryotoxicity Testing

The evaluation of substances for their potency to induce embryotoxicity is controlled by safety regulations. Test guidelines for reproductive and developmental toxicity rely mainly on animal studies, which make up the majority of animal usage in regulatory toxicology. Therefore, there is an urgent need for alternative in vitro methods to follow the 3R principles. To improve human safety, cell models based on human cells are of great interest to overcome species differences. Here, human induced pluripotent stem cells (hiPSCs) are an ideal cell source as they largely recapitulate embryonic stem cells without bearing ethical concerns and they are able to differentiate into most cell types of the human body. Here, we set up and characterized a fetal bovine serum (FBS)-free hiPSC-based in vitro test method, called the human induced pluripotent stem cell test (hiPS Test), to evaluate the embryotoxic potential of substances. After 10 days in culture, hiPSCs develop into beating cardiomyocytes. As terminal endpoint evaluations, cell viability, qPCR analyses as well as beating frequency and area of beating cardiomyocytes by video analyses are measured. The embryotoxic positive and non-embryotoxic negative controls, 5-Fluorouracil (5-FU) and Penicillin G (PenG), respectively, were correctly assessed in the hiPS Test. More compounds need to be screened in the future for defining the assay’s applicability domain, which will inform us of the suitability of the hiPS Test for detecting adverse effects of substances on embryonic development.

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

Large-scale data analysis for robotic yeast one-hybrid platforms and multi-disciplinary studies using GateMultiplex

BACKGROUND

Yeast one-hybrid (Y1H) is a common technique for identifying DNA-protein interactions, and robotic platforms have been developed for high-throughput analyses to unravel the gene regulatory networks in many organisms. Use of these high-throughput techniques has led to the generation of increasingly large datasets, and several software packages have been developed to analyze such data. We previously established the currently most efficient Y1H system, meiosis-directed Y1H; however, the available software tools were not designed for processing the additional parameters suggested by meiosis-directed Y1H to avoid false positives and required programming skills for operation.

RESULTS

We developed a new tool named GateMultiplex with high computing performance using C++. GateMultiplex incorporated a graphical user interface (GUI), which allows the operation without any programming skills. Flexible parameter options were designed for multiple experimental purposes to enable the application of GateMultiplex even beyond Y1H platforms. We further demonstrated the data analysis from other three fields using GateMultiplex, the identification of lead compounds in preclinical cancer drug discovery, the crop line selection in precision agriculture, and the ocean pollution detection from deep-sea fishery.

CONCLUSIONS

The user-friendly GUI, fast C++ computing speed, flexible parameter setting, and applicability of GateMultiplex facilitate the feasibility of large-scale data analysis in life science fields.

Stem Cell Based Preclinical Drug Development and Toxicity Prediction

Stem cell based toxicity prediction plays a very important role in the development of the drug. Unexpected adverse effects of the drugs during clinical trials are a major reason for the termination or withdrawal of drugs. Methods for predicting toxicity employ in vitro as well as in vivo models; however, the major drawback seen in the data derived from these animal models is the lack of extrapolation, owing to interspecies variations. Due to these limitations, researchers have been striving to develop more robust drug screening platforms based on stem cells. The application of stem cells based toxicity testing has opened up robust methods to study the impact of new chemical entities on not only specific cell types, but also organs. Pluripotent stem cells, as well as cells derived from them, can be evaluated for modulation of cell function in response to drugs. Moreover, the combination of state-of-the -art techniques such as tissue engineering and microfluidics to fabricate organ- on-a-chip, has led to assays which are amenable to high throughput screening to understand the adverse and toxic effects of chemicals and drugs. This review summarizes the important aspects of the establishment of the embryonic stem cell test (EST), use of stem cells, pluripotent, induced pluripotent stem cells and organoids for toxicity prediction and drug development.

A novel screening test to predict the developmental toxicity of drugs using human induced pluripotent stem cells

In vitro human induced pluripotent stem (iPS) cells testing (iPST) to assess developmental toxicity, e.g., the induction of malformation or dysfunction, was developed by modifying a mouse embryonic stem cell test (EST), a promising animal-free approach. The iPST evaluates the potential risks and types of drugs-induced developmental toxicity in humans by assessing three endpoints: the inhibitory effects of the drug on the cardiac differentiation of iPS cells and on the proliferation/survival of iPS cells and human fibroblasts. In the present study, the potential developmental toxicity of drugs was divided into three classes (1: non-developmentally toxic, 2: weakly developmentally toxic and 3: strongly developmentally toxic) according to the EST criteria. In addition, the type of developmental toxicity of drugs was grouped into three types (1: non-effective, 2: embryotoxic [inducing growth retardation/dysfunction]/deadly or 3: teratogenic [inducing malformation]/deadly) by comparing the three endpoints. The present study was intended to validate the clinical predictability of the iPST. The traditionally developmentally toxic drugs of aminopterin, methotrexate, all-trans-retinoic acid, thalidomide, tetracycline, lithium, phenytoin, 5-fluorouracil, warfarin and valproate were designated as class 2 or 3 according to the EST criteria, and their developmental toxicity was type 3. The non-developmentally toxic drugs of ascorbic acid, saccharin, isoniazid and penicillin G were designated as class 1, and ascorbic acid, saccharin and isoniazid were grouped as type 1 while penicillin G was type 2 but not teratogenic. These results suggest that the iPST is useful for predicting the human developmental toxicity of drug candidates in a preclinical setting.

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.

Graphical abstract

Preconditioning the Initial State of Feeder-free Human Pluripotent Stem Cells Promotes Self-formation of Three-dimensional Retinal Tissue

A three-dimensional retinal tissue (3D-retina) is a promising graft source for retinal transplantation therapy. We previously demonstrated that embryonic stem cells (ESCs) can generate 3D-retina in vitro using a self-organizing stem cell culture technique known as SFEBq. Here we show an optimized culture method for 3D-retina generation from feeder-free human pluripotent stem cells (hPSCs). Although feeder-free hPSC-maintenance culture was suitable for cell therapy, feeder-free hPSC-derived aggregates tended to collapse during 3D-xdifferentiation culture. We found that the initial hPSC state was a key factor and that preconditioning of the hPSC state by modulating TGF-beta and Shh signaling improved self-formation of 3D-neuroepithelium. Using the preconditioning method, several feeder-free hPSC lines robustly differentiated into 3D-retina. In addition, changing preconditioning stimuli in undifferentiated hPSCs altered the proportions of neural retina and retinal pigment epithelium, important quality factors for 3D-retina. We demonstrated that the feeder-free hiPSC-derived 3D-retina differentiated into rod and cone photoreceptors in vitro and in vivo. Thus, preconditioning is a useful culture methodology for cell therapy to direct the initial hPSC state toward self-organizing 3D-neuroepithelium.

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.

Exposure-Based Validation of an In Vitro Gastrulation Model for Developmental Toxicity Assays

Establishment of effective non-animal alternatives for developmental toxicity screening assays is desirable to ensure maternal and fetal health outcomes. Validation of such assays requires a comparison between the in vitro responses to chemical exposures and the in vivo impacts of the corresponding compounds at equivalent concentrations. Here, we investigated how the P19C5 gastrulation model responds to 24 compounds at specific concentrations, some of which are categorized as positive exposures based on previously observed detrimental effects on development in vivo, whereas others are categorized as negative exposures due to lack of effects in vivo. The P19C5 gastrulation model consists of in vitro morphogenesis of mouse stem cells aggregated into embryoid bodies (EBs), which recapitulates growth and axial elongation of early embryos during four days of three-dimensional culture. Adverse impacts of chemical exposures were defined as: death, impaired growth, and altered axial elongation of EBs. Ten out of 17 positive exposures caused adverse impacts on EBs. In contrast, only three out of 17 negative exposures adversely affected EBs, although two of the three diminished viability of somatic cell lines (NIH/3T3, HEK293, and JEG3), suggesting general cytotoxicity. Overall, the study showed that 24 out of 34 exposures impacted EB development in a manner concordant with the in vivo developmental effects. Validation of other alternative assays using the same set of chemical exposures will provide information on the strengths and weaknesses of each assay, and should help determine the most effective ensemble of assays to detect a wide range of developmentally toxic exposures.

[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.

Developmental toxicity assessment of common excipients using a stem cell-based in vitro morphogenesis model

Various chemical compounds can inflict developmental toxicity when sufficiently high concentrations are exposed to embryos at the critical stages of development. Excipients, such as coloring agents and preservatives, are pharmacologically inactive ingredients that are included in various medications, foods, and cosmetics. However, concentrations that may adversely affect embryo development are largely unknown for most excipients. Here, the lowest observed adverse effect level (LOAEL) to inflict developmental toxicity was assessed for three coloring agents (allura red, brilliant blue, and tartrazine) and three preservatives (butylated hydroxyanisole, metabisulfite, and methylparaben). Adverse impact of a compound exposure was determined using the stem cell-based in vitro morphogenesis model, in which three-dimensional cell aggregates, or embryoid bodies (EBs), recapitulate embryonic processes of body axis elongation and patterning. LOAEL to impair EB morphogenesis was 200 μM for methylparaben, 400 μM for butylated hydroxyanisole, 600 μM for allura red and brilliant blue, and 1000 μM for metabisulfite. Gene expression analyses of excipient-treated EBs revealed that butylated hydroxyanisole and methylparaben significantly altered profiles of developmental regulators involved in axial elongation and patterning of the body. The present study may provide a novel in vitro approach to investigate potential developmental toxicity of common excipients with mechanistic insights.

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.

Adverse effect of valproic acid on an in vitro gastrulation model entails activation of retinoic acid signaling

Valproic acid (VPA), an antiepileptic drug, is a teratogen that causes neural tube and axial skeletal defects, although the mechanisms are not fully understood. We previously established a gastrulation model using mouse P19C5 stem cell embryoid bodies (EBs), which exhibits axial patterning and elongation morphogenesis in vitro. Here, we investigated the effects of VPA on the EB axial morphogenesis to gain insights into its teratogenic mechanisms. Axial elongation and patterning of EBs were inhibited by VPA at therapeutic concentrations. VPA elevated expression levels of various developmental regulators, including Cdx1 and Hoxa1, known transcriptional targets of retinoic acid (RA) signaling. Co-treatment of EBs with VPA and BMS493, an RA receptor antagonist, partially rescued axial elongation as well as gene expression profiles. These results suggest that VPA requires active RA signaling to interfere with EB morphogenesis.

A Developmental Toxicology Assay Platform for Screening Teratogenic Liability of Pharmaceutical Compounds

Increasing need for proactive safety optimization of pharmaceutical compounds has led to generation and/or refinement of in vitro developmental toxicology assays. Our laboratory has developed three in vitro developmental toxicology assays to assess teratogenic liability of pharmaceutical compounds. These assays included a mouse molecular embryonic stem cell assay (MESCA), a dechorionated zebrafish embryo culture (ZEC) assay, and a streamlined rat whole embryo culture (rWEC) assay. Individually, the assays presented good (73-82%) predictivity. However, it remains to be determined whether combining or tiering the assays could enhance performance. Seventy-three compounds representing a broad spectrum of pharmaceutical targets and chemistry were evaluated across the assays to generate testing strategies that optimized performance. The MESCA and ZEC assays were found to have two limitations: compound solubility and frequent misclassification of compounds with H1 receptor or GABAnergic activity. The streamlined rWEC assay was found to be a cost-effective stand-alone assay for supporting poorly soluble compounds and/or ones with H1 or GABAnergic activity. For all other compounds, a tiering strategy using the MESCA and ZEC assays additionally optimized throughput, cost, and minimized animal use. The tiered strategy resulted in improved performance achieving 88% overall predictivity and was comparable with 89% overall predictivity achieved with frequency analysis (final teratogenic classification made from most frequent teratogenic classification from each individual assay). Furthermore there were 21 compounds in the test set characterized as definitive or suspect human teratogens and the multiassay approach achieved 95 and 91% correct classification using the tiered or frequency screening approach, respectively.

Evaluation of biological effects of intermediate frequency magnetic field on differentiation of embryonic stem cell

The embryotoxic effect of intermediate frequency (IF) magnetic field (MF) was evaluated using murine embryonic stem (ES) cells and fibroblast cells based on the embryonic stem cell test (EST). The cells were exposed to 21 kHz IF-MF up to magnetic flux density of 3.9 mT during the cell proliferation process (7 days) or the cell differentiation process (10 days) during which an embryonic body differentiated into myocardial cells. As a result, there was no significant difference in the cell proliferation between sham- and IF-MF-exposed cells for both ES and fibroblast cells. Similarly, the ratio of the number of ES-derived cell aggregates differentiated to myocardial cells to total number of cell aggregates was not changed by IF-MF exposure. In addition, the expressions of a cardiomyocytes-specific gene, Myl2, and an early developmental gene, Hba-x, in the exposed cell aggregate were not altered. Since the magnetic flux density adopted in this study is much higher than that generated by an inverter of the electrical railway, an induction heating (IH) cooktop, etc. in our daily lives, these results suggested that IF-MF in which the public is exposed to in general living environment would not have embryotoxic effect.

Hand1-Luc embryonic stem cell test (Hand1-Luc EST): a novel rapid and highly reproducible in vitro test for embryotoxicity by measuring cytotoxicity and differentiation toxicity using engineered mouse ES cells

The embryonic stem cell test (EST) is a promising alternative method for evaluating embryotoxicity of test chemicals by measuring cytotoxicity and differentiation toxicity using mouse ES cells. Differentiation toxicity is analyzed by microscopically counting the beating of embryonic bodies after 10 days of culture. However, improvements are necessary to reduce the laborious manipulations involved and the time required to obtain results. We have previously reported the successful stable transfection of ES cells (ES-D3) with the heart and neural crest derivatives expressed transcript 1 (Hand1) gene and the establishment of a 96-well multi-plate-based new EST with luciferase reporter assay 6 days after treatment with test chemicals. Now, we propose an even more rapid and easier EST, named Hand1-Luc EST. We established another cell line to monitor the Hand1 gene expression via a luciferase reporter gene. By mRNA analysis and luciferase assay, we examined in detail the luciferase activity during cell differentiation, which allowed us to reduce the time of measurement from day 6 to day 5 (120 hr). Furthermore, the protocol was improved, with, among others, the measurement of cytotoxicity and differentiation toxicity taking place in the same 96-well round bottom plate instead of two different plates. With the positive control, 5-fluorouracil (5-FU), and 9 test chemicals, data with high reproducibility and very low variation (CV < 50%) in the relevant endpoints were obtained. This study shows that the Hand1-Luc EST could provide an accurate and sensitive short-term test for prediction of embryotoxicants by measuring cytotoxicity and differentiation toxicity from the same sample.

RNA transcripts for the quantification of differentiation allow marked improvements in the performance of embryonic stem cell test (EST)

Embryonic stem cell test (EST) is an in vitro validated assay for testing embryotoxicity. The EST needs improvements before being used for regulatory purposes, but also needs technical simplification for use in high throughput screenings. We propose the quantification in alterations of the differentiation of D3 monolayer cells cultures through the expression of biomarker genes in a shorter (5-day) and technically simpler (we use only monolayer cultures) test. We have defined a set of sixteen different genes biomarkers of ectoderm (Nrcam, Nes, Shh and Pnpla6), endoderm formation (Flk1 and Afp), mesoderm formation (Mesp1, Vegfa, Myo1e and Hdac7) and general cellular processes (Cdk1, Myc, Jun, Mixl, Cer and Wnt3). These, together with alterations in the viability of D3 and 3T3 cells and the prediction model of a classic EST, enhance the features of EST determinations to 100% concordance between in vivo-in vitro predictions with a set of seven different chemicals used in the validation of a classic EST. In conclusion, the proposed changes implemented in the classic EST confer it more reliability, speed and technical simplicity, which brings the EST closer to high throughput processes and regulatory purposes.

Effects of valproic acid on gene expression during human embryonic stem cell differentiation into neurons

The widely used antiepileptic drug valproic acid (VPA) is known to exhibit teratogenicity in the form of a failure of the neural tube in humans. Embryonic stem cells (ESCs) are reported to be a promising cell source for evaluating chemical teratogenicity, because they are capable of reproducing embryonic developmental model and enable reduction in the number of experimental animals used. We previously investigated 22 genes for which expressions are altered by teratogens, specifically focusing on neural differentiation of mouse ESCs. In the present study, expressions of the investigated genes were evaluated by quantitative real-time PCR and compared during differentiation of human ESCs into neurons with or without VPA. Under the conditions, almost all gene expressions significantly changed in VPA-containing culture. Specifically, in neural development-related genes such as DCX, ARX, MAP2, and NNAT, more than 2-fold expression was observed. The findings suggest that the genes focused on in this study may help to elucidate the teratogenic effects of VPA and might be a useful tool to analyze embryotoxic potential of chemicals in humans.

Organophosphorus pesticide chlorpyrifos and its metabolites alter the expression of biomarker genes of differentiation in D3 mouse embryonic stem cells in a comparable way to other model neurodevelopmental toxicants

There are discrepancies about whether chlorpyrifos is able to induce neurodevelopmental toxicity or not. We previously reported alterations in the pattern of expression of biomarker genes of differentiation in D3 mouse embryonic stem cells caused by chlorpyrifos and its metabolites chlorpyrifos-oxon and 3,5,6-trichloro-2-pyridinol. Now, we reanalyze these data comparing the effects on these genes with those caused in the same genes by retinoic acid, valproic acid, and penicillin-G (model compounds considered as strong, weak, and non-neurodevelopmental toxicants, respectively). We also compare the effects of chlorpyrifos and its metabolites on the cell viability of D3 cells and 3T3 mouse fibroblasts with the effects caused in the same cells by the three model compounds. We conclude that chlorpyrifos and its metabolites act, regarding these end-points, as the weak neurodevelopmental toxicant valproic acid, and consequently, a principle of caution should be applied avoiding occupational exposures in pregnant women. A second independent experiment run with different cellular batches coming from the same clone obtained the same result as the first one.

Assessment of Developmental Toxicants using Human Embryonic Stem Cells

Embryonic stem (ES) cells have potential for use in evaluation of developmental toxicity because they are generated in large numbers and differentiate into three germ layers following formation of embryoid bodies (EBs). In earlier study, embryonic stem cell test (EST) was established for assessment of the embryotoxic potential of compounds. Using EBs indicating the onset of differentiation of mouse ES cells, many toxicologists have refined the developmental toxicity of a variety of compounds. However, due to some limitation of the EST method resulting from species-specific differences between humans and mouse, it is an incomplete approach. In this regard, we examined the effects of several developmental toxic chemicals on formation of EBs using human ES cells. Although human ES cells are fastidious in culture and differentiation, we concluded that the relevancy of our experimental method is more accurate than that of EST using mouse ES cells. These types of studies could extend our understanding of how human ES cells could be used for monitoring developmental toxicity and its relevance in relation to its differentiation progress. In addition, this concept will be used as a model system for screening for developmental toxicity of various chemicals. This article might update new information about the usage of embryonic stem cells in the context of their possible ability in the toxicological fields.

Evaluation of developmental toxicity using undifferentiated human embryonic stem cells

An embryonic stem cell test (EST) has been developed to evaluate the embryotoxic potential of chemicals with an in vitro system. In the present study, novel methods to screen toxic chemicals during the developmental process were evaluated using undifferentiated human embryonic stem (hES) cells. By using surface marker antigens (SSEA-4, TRA-1-60 and TRA-1-81), we confirmed undifferentiated conditions of the used hES cells by immunocytochemistry. We assessed the developmental toxicity of embryotoxic chemicals, 5-fluorouracil, indomethacin and non-embryotoxic penicillin G in different concentrations for up to 7 days. While expressions of the surface markers were not significantly affected, the embryotoxic chemicals influenced their response to pluripotent ES cell markers, such as OCT-4, NANOG, endothelin receptor type B (EDNRB), secreted frizzled related protein 2 (SFRP2), teratocarcinoma-derived growth factor 1 (TDGF1), and phosphatase and tensin homolog (PTEN). Most of the pluripotent ES cell markers were down-regulated in a dose-dependent manner after treatment with embryotoxic chemicals. After treatment with 5-fluorouracil, indomethacin and penicillin G, we observed a remarkable convergence in the degree of up-regulation of development, cell cycle and apoptosis-related genes by gene expression profiles using an Affymetrix GeneChips. Taken together, these results suggest that embryotoxic chemicals have cytotoxic effects, and modulate the expression of ES cell markers as well as development-, cell cycle- and apoptosis-related genes that have pivotal roles in undifferentiated hES cells. Therefore, we suggest that hES cells may be useful for testing the toxic effects of chemicals that could impact the embryonic developmental stage.

Establishment of a molecular embryonic stem cell developmental toxicity assay

The mouse embryonic stem cell test (EST) is a 10-day screen for teratogenic potential developed to reduce animal use for embryotoxicity testing of chemicals (Spielmann, 2005; Spielmann et al., 1997). In this study, we used the cytotoxicity IC(50) values and transcriptional expression changes as primary endpoints in a shorter 4-day version of the EST, the molecular embryonic stem cell assay. Mouse D3 embryonic stem cells were used for cytotoxicity assessment (monolayers) or grown as embryoid bodies in low attachment plates for transcriptional profiling. Sixty-five compounds with known in vivo teratogenicity (33 teratogens and 32 nonteratogens) were evaluated to develop a model for classifying compounds with teratogenic potential. The expression of 12 developmentally regulated gene targets (nanog, fgf5, gsc, cd34, axin2, apln, chst7, lhx1, fgf8, sox17, foxa2, and cxcr4) was measured following exposure of embryoid bodies to a single compound concentration (0.1 × the cytotoxicity IC(20)) for 4 days. In the decision-tree model, compounds with IC(50) values < 22 µM were categorized as teratogens, whereas compounds in the two groups with IC(50) values between 22-200 µM and > 200 µM were categorized as teratogens if ≥ 8 and 12 genes, respectively, were deregulated by at least 10%. Forty-seven of 65 compounds of the training set were correctly identified (72% total concordance). In a test set of 12 additional compounds (5 teratogens, 7 nonteratogens), 10 were correctly classified by this approach (83% concordance). The false positive rate in the training and test sets was 24 and 0%, respectively, indicating that this assay has potential to identify teratogens.