Characterisation of a Neural Teratogenicity Assay Based on Human ESCs Differentiation Following Exposure to Valproic Acid

Teratogenicity is more likely a function of primary and secondary pharmacology than caused by chemically reactive metabolites: a critical evaluation of 40 years of scientific research

The number of therapeutic drugs known to be human teratogens is actually relatively small. This may reflect the rigorous animal testing and well defined labelling. Some of these drugs were identified to have reactive metabolites and this has been postulated, historically, to be their teratogenic mechanism. These drugs include thalidomide, various anticonvulsants and retinoic acid derivatives.Many of these experiments were conducted in a period where chemically reactive metabolites were being intensely investigated and associated with all forms of toxicity. The legacy of this is that these examples are routinely cited as well established mechanisms.Examination of mechanism leads to the conclusion that the teratogenicity in humans of these compounds is likely due to the primary and secondary pharmacology of the parent drug and stable circulating metabolites and that association of reactive metabolites to this toxicity is unwarranted.

Accuracy, discriminative properties and reliability of a human ESC-based in vitro toxicity assay to distinguish teratogens responsible for neural tube defects

The poor correlation of developmental toxicity studies in animals with human outcome data has emphasized the need for complementary assays based on human cells and tissues. As neural tube defects represent an important proportion of congenital malformations, we evaluated here the accuracy of a human embryonic stem cell (hESC)-based assay to predict chemically induced disruption of neural tube formation. As teratogenic compounds, we used cyclopamine (CPA), valproic acid (VPA), ochratoxin A (OTA) and mycophenolic acid (MMF), all suspected or known inducers of human neural tube defects, as well as theophylline and saccharin as negative control compounds. We analyzed their effects on the ability of hES cells to give rise to neural precursors (expressing specific marker Nestin), to form neural tube-like structures (rosettes), and to express specific markers (Sox1, Otx2, Lix1, EvI1, Rspo3) during rosette formation. The results showed that various effects of the selected compounds on early neural development could be specifically revealed in vitro through related alterations of neurogenic differentiation of hESC. Furthermore, it was possible to discriminate toxicants acting at different time points during embryonic development and, therefore, responsible for distinct adverse effects on neural tube formation. By comparing four different hESC lines, we observed a significant (up to fivefold) variability of the line-dependent response to toxicants. We highlight at least two sources of variability: one related to the heterogeneity of hESC lines in culture (stemness/commitment profiles); the second to possible genetically determined differences in individual sensitivity to teratogens.

A genomics-based framework for identifying biomarkers of human neurodevelopmental toxicity

Human embryonic stem cell (hESC) neural differentiation models have tremendous potential for evaluating environmental compounds in terms of their ability to induce neurodevelopmental toxicity. Genomic based-approaches are being applied to identify changes underlying normal human development (in vitro and in vivo) and the effects of environmental exposures. Here, we investigated whether mechanisms that are shared between hESC neural differentiation model systems and human embryos are candidate biomarkers of developmental toxicities for neurogenesis. We conducted a meta-analysis of transcriptomic datasets with the goal of identifying differentially expressed genes that were common to the hESC-model and human embryos. The overlapping NeuroDevelopmental Biomarker (NDB) gene set contained 304 genes which were enriched for their roles in neurogenesis. These genes were investigated for their utility as candidate biomarkers in the context of toxicogenomic studies focused on the effects of retinoic acid, valproic acid, or carbamazepine in hESC models of neurodifferentiation. The results revealed genes, including 13 common targets of the 3 compounds, that were candidate biomarkers of neurotoxicity in hESC-based studies of environmental toxicants.

A method for human teratogen detection by geometrically confined cell differentiation and migration

Unintended exposure to teratogenic compounds can lead to various birth defects; however current animal-based testing is limited by time, cost and high inter-species variability. Here, we developed a human-relevant in vitro model, which recapitulated two cellular events characteristic of embryogenesis, to identify potentially teratogenic compounds. We spatially directed mesoendoderm differentiation, epithelial-mesenchymal transition and the ensuing cell migration in micropatterned human pluripotent stem cell (hPSC) colonies to collectively form an annular mesoendoderm pattern. Teratogens could disrupt the two cellular processes to alter the morphology of the mesoendoderm pattern. Image processing and statistical algorithms were developed to quantify and classify the compounds' teratogenic potential. We not only could measure dose-dependent effects but also correctly classify species-specific drug (Thalidomide) and false negative drug (D-penicillamine) in the conventional mouse embryonic stem cell test. This model offers a scalable screening platform to mitigate the risks of teratogen exposures in human.

Neuronal developmental gene and miRNA signatures induced by histone deacetylase inhibitors in human embryonic stem cells

Human embryonic stem cells (hESCs) may be applied to develop human-relevant sensitive in vitro test systems for monitoring developmental toxicants. The aim of this study was to identify potential developmental toxicity mechanisms of the histone deacetylase inhibitors (HDAC) valproic acid (VPA), suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) relevant to the in vivo condition using a hESC model in combination with specific differentiation protocols and genome-wide gene expression and microRNA profiling. Analysis of the gene expression data showed that VPA repressed neural tube and dorsal forebrain (OTX2, ISL1, EMX2 and SOX10)-related transcripts. In addition, VPA upregulates axonogenesis and ventral forebrain-associated genes, such as SLIT1, SEMA3A, DLX2/4 and GAD2. HDACi-induced expression of miR-378 and knockdown of miR-378 increases the expression of OTX2 and EMX2, which supports our hypothesis that HDACi targets forebrain markers through miR-378. In conclusion, multilineage differentiation in vitro test system is very sensitive for monitoring molecular activities relevant to in vivo neuronal developmental toxicity. Moreover, miR-378 seems to repress the expression of the OTX2 and EMX2 and therefore could be a regulator of the development of neural tube and dorsal forebrain neurons.

Concise review: drug discovery in the age of the induced pluripotent stem cell

For decades, the paradigm of drug discovery and development has relied on immortalized cell lines, animal models of human disease, and clinical trials. With the discovery of induced pluripotent stem cell (iPSC) technology in 2007, a new human in vitro drug testing platform has potentially augmented this set of tools by providing additional ways to screen compounds for safety and efficacy. The growing number of human disease models made with patient-specific iPSCs has made it possible to conduct research on a wide range of disorders, including rare diseases and those with multifactorial origin, as well as to simulate drug effects on difficult-to-obtain tissues such as brain and cardiac muscle. Toxicity and teratogenicity assays developed with iPSC-derived cells can also provide an additional layer of safety before advancing drugs to clinical trials. The incorporation of iPSC technology into drug therapy development holds promise as a more powerful and nuanced approach to personalized medicine.