Human Embryonic and Induced Pluripotent Stem Cell Based Toxicity Testing Models: Future Applications in New Drug Discovery

Transcriptome-based prediction of drugs, inhibiting cardiomyogenesis in human induced pluripotent stem cells

Animal studies for embryotoxicity evaluation of potential therapeutics and environmental factors are complex, costly, and time-consuming. Often, studies are not of human relevance because of species differences. In the present study, we recapitulated the process of cardiomyogenesis in human induced pluripotent stem cells (hiPSCs) by modulation of the Wnt signaling pathway to identify a key cardiomyogenesis gene signature that can be applied to identify compounds and/or stress factors compromising the cardiomyogenesis process. Among the 23 tested teratogens and 16 non-teratogens, we identified three retinoids including 13-cis-retinoic acid that completely block the process of cardiomyogenesis in hiPSCs. Moreover, we have identified an early gene signature consisting of 31 genes and associated biological processes that are severely affected by the retinoids. To predict the inhibitory potential of teratogens and non-teratogens in the process of cardiomyogenesis we established the "Developmental Cardiotoxicity Index" (CDI31g) that accurately differentiates teratogens and non-teratogens to do or do not affect the differentiation of hiPSCs to functional cardiomyocytes.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications-Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications—Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Advanced human developmental toxicity and teratogenicity assessment using human organoid models

Tremendous progress has been made in the field of toxicology leading to the advance of developmental toxicity assessment. Conventional animal models and in vitro two-dimensional models cannot accurately describe toxic effects and predict actual in vivo responses due to obvious inter-species differences between humans and animals, as well as the lack of a physiologically relevant tissue microenvironment. Human embryonic stem cell (hESC)- and induced pluripotent stem cell (iPSC)-derived three-dimensional organoids are ideal complex and multicellular organotypic models, which are indispensable in recapitulating morphogenesis, cellular interactions, and molecular processes of early human organ development. Recently, human organoids have been used for drug discovery, chemical toxicity and safety in vitro assessment. This review discusses the recent advances in the use of human organoid models, (i.e., brain, retinal, cardiac, liver, kidney, lung, and intestinal organoid models) for developmental toxicity and teratogenicity assessment of distinct tissues/organs following exposure to pharmaceutical compounds, heavy metals, persistent organic pollutants, nanomaterials, and ambient air pollutants. Combining next-generation organoid models with innovative engineering technologies generates novel and powerful tools for developmental toxicity and teratogenicity assessment, and the rapid progress in this field is expected to continue.

Human inducible pluripotent stem cells: Realization of initial promise in drug discovery

Over the course of the last decade, the biopharmaceutical industry has slowly adopted human inducible pluripotent stem cell (hiPSC) technology to enable the development of humanized model systems to test new therapeutic molecules and drug modalities. The adoption of hiPSC-based models by the industry has increased appreciably in the past 3-5 years. This increase has paralleled the explosion in availability of high-quality human genetic data to mine for new drug targets and the emergence of human-specific therapeutic modalities.

In vitro and In vivo toxicity analysis of zinc selenium/zinc sulfide (ZnSe/ZnS) quantum dots

Despite the versatility of quantum dots (QDs) in optoelectronics and biomedical field, their toxicity risks remain a considerable hindrance for clinical applications. Cytotoxicity of Cadmium containing QDs is well documented and reveals that they are toxic to cells. Reports suggest that the presence of toxic elements at the QD core (e.g., cadmium, selenium) is responsible for its toxicity in in vivo and in vitro levels. Hence, here the toxicity of heavy metal free ZnSe/ZnS QDs on two scenarios were assessed, (i) HEK cells as in vitro system and (ii) Swiss Albino mice as in vivo model. Before toxicity analysis, QDs subjected to various optical and physico-chemical characterization methods such as absorption and emission spectra analysis, observation under U.V light, TEM, DLS, Zeta potential, FTIR, Raman and XPS spectra, ICP-OES, TGA and DTG curve. It is very necessary to characterize the synthesized QDs because their toxicity greatly influenced by the physico-chemical properties. On checking the vulnerability of HEK cells on exposure to ZnSe/ZnS QDs, the obtained results disclose that ZnSe/ZnS QDs showed merest impact on cellular viability at a concentration less than 100 μg/ml. Acute toxicity of 10 mg/kg ZnSe/ZnS QDs was studied in mice and no clinical or behavioural changes were observed. It did not induce any changes in haematological parameters and any loss of body or organ weight. Moderate pathological changes were evident only in the liver, all others organs like kidney, spleen and brain did not show any manifestations of toxicity. Current work lays substantial bedrock for safe biomedical and environmental application of ZnSe/ZnS QDs in near future.

Human pluripotent stem cell-derived models and drug screening in CNS precision medicine

Development of effective therapeutics for neurological disorders has historically been challenging partly because of lack of accurate model systems in which to investigate disease etiology and test new therapeutics at the preclinical stage. Human stem cells, particularly patient-derived induced pluripotent stem cells (iPSCs) upon differentiation, have the ability to recapitulate aspects of disease pathophysiology and are increasingly recognized as robust scalable systems for drug discovery. We review advances in deriving cellular models of human central nervous system (CNS) disorders using iPSCs along with strategies for investigating disease-relevant phenotypes, translatable biomarkers, and therapeutic targets. Given their potential to identify novel therapeutic targets and leads, we focus on phenotype-based, small-molecule screens employing human stem cell-derived models. Integrated efforts to assemble patient iPSC-derived cell models with deeply annotated clinicopathological data, along with molecular and drug-response signatures, may aid in the stratification of patients, diagnostics, and clinical trial success, shifting translational science and precision medicine approaches. A number of remaining challenges, including the optimization of cost-effective, large-scale culture of iPSC-derived cell types, incorporation of aging into neuronal models, as well as robustness and automation of phenotypic assays to support quantitative drug efficacy, toxicity, and metabolism testing workflows, are covered. Continued advancement of the field is expected to help fully humanize the process of CNS drug discovery.

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

Cardiotoxicity and Heart Failure: Lessons from Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes and Anticancer Drugs

Human-induced pluripotent stem cells (hiPSCs) are discussed as disease modeling for optimization and adaptation of therapy to each individual. However, the fundamental question is still under debate whether stem-cell-based disease modeling and drug discovery are applicable for recapitulating pathological processes under in vivo conditions. Drug treatment and exposure to different chemicals and environmental factors can initiate diseases due to toxicity effects in humans. It is well documented that drug-induced cardiotoxicity accelerates the development of heart failure (HF). Until now, investigations on the understanding of mechanisms involved in HF by anticancer drugs are hindered by limitations of the available cellular models which are relevant for human physiology and by the fact that the clinical manifestation of HF often occurs several years after its initiation. Recently, we identified similar genomic biomarkers as observed by HF after short treatment of hiPSCs-derived cardiomyocytes (hiPSC-CMs) with different antitumor drugs such as anthracyclines and etoposide (ETP). Moreover, we identified common cardiotoxic biological processes and signal transduction pathways which are discussed as being crucial for the survival and function of cardiomyocytes and, therefore, for the development of HF. In the present review, I discuss the applicability of the in vitro cardiotoxicity test systems as modeling for discovering preventive mechanisms/targets against cardiotoxicity and, therefore, for novel HF therapeutic concepts.

Addressing Manufacturing Challenges for Commercialization of iPSC-Based Therapies

The development of reprogramming technology to generate human induced pluripotent stem cells (iPSCs) has tremendously influenced the field of regenerative medicine and clinical therapeutics where curative cell replacement therapies can be used in the treatment of devastating diseases such as Parkinson's disease (PD) and diabetes. In order to commercialize these therapies to treat a large number of individuals, it is important to demonstrate the safety and efficacy of these therapies and ensure that the manufacturing process for iPSC-derived functional cells can be industrialized at an affordable cost. However, there are a number of manufacturing obstacles that need to be addressed in order to meet this vision. It is important to note that the manufacturing process for generation of iPSC-derived specialized cells is relatively long and fairly complex and requires differentiation of high-quality iPSCs into specialized cells in a controlled manner. In this chapter, we have summarized our efforts to address the main challenges present in the industrialization of iPSC-derived cell therapy products with focus on the development of a current Good Manufacturing Practice (cGMP)-compliant iPSC manufacturing process, a comprehensive iPSC characterization platform, long-term stability of cGMP compliant iPSCs, and innovative technologies to address some of the scale-up challenges in establishment of iPSC processing in 3D computer-controlled bioreactors.

Road Map for Development of Stem Cell-Based Alternative Test Methods

Much progress has been made in establishing strategies for differentiation of induced human pluripotent stem cells (hiPSCs). However, differentiated hiPSCs are not yet routinely used for prediction of toxicity. Here, limiting factors are summarised and possibilities for improvement are discussed, with a focus on hepatocytes, cardiomyocytes, tubular epithelial cells, and developmental toxicity. Moreover, we make recommendations for further fine-tuning of differentiation protocols for hiPSCs to hepatocyte-like cells by comparing individual steps of currently available protocols to the mechanisms occurring during embryonic development. A road map is proposed to facilitate test system development, including a description of the most useful performance metrics.

Current Challenges of iPSC-Based Disease Modeling and Therapeutic Implications

Induced pluripotent stem cell (iPSC)-based disease modelling and the cell replacement therapy approach have proven to be very powerful and instrumental in biomedical research and personalized regenerative medicine as evidenced in the past decade by unraveling novel pathological mechanisms of a multitude of monogenic diseases at the cellular level and the ongoing and emerging clinical trials with iPSC-derived cell products. iPSC-based disease modelling has sparked widespread enthusiasm and has presented an unprecedented opportunity in high throughput drug discovery platforms and safety pharmacology in association with three-dimensional multicellular organoids such as personalized organs-on-chips, gene/base editing, artificial intelligence and high throughput "omics" methodologies. This critical review summarizes the progress made in the past decade with the advent of iPSC discovery in biomedical applications and regenerative medicine with case examples and the current major challenges that need to be addressed to unleash the full potential of iPSCs in clinical settings and pharmacology for more effective and safer regenerative therapy.

Derivation of phenotypically diverse neural culture from hESC by combining adherent and dissociation methods

BACKGROUND

Differentiation of human embryonic stem cells (hESCs) into distinct neural lineages has been widely studied. However, preparation of mixed yet neurochemically mature populations, for the study of neurological diseases involving mixed cell types has received less attention.

NEW METHOD

We combined two commonly used differentiation methods to provide robust and reproducible cultures in which a mixture of primarily GABAergic and Glutamatergic neurons was obtained. Detailed characterisation by immunocytochemistry (ICC) and quantitative real-time PCR (qPCR) assessed the neurochemical phenotype, and the maturation state of these neurons.

RESULTS

We found that once neurospheres (NSs) had attached to the culture plates, proliferation of neural stem cell was suppressed. Neuronal differentiation and synaptic development then occurred after 21 days in vitro (DIV). By 49DIV, there were large numbers of neurochemically and structurally mature neurons. The qPCR studies indicated that expression of GABAergic genes increased the most (93.3-fold increase), followed by glutamatergic (51-fold increase), along with smaller changes in expression of cholinergic (3-fold increase) and dopaminergic genes (6-fold increase), as well as a small change in glial cell marker expression (5-fold increase).

COMPARISON WITH EXISTING METHOD (S)

Existing methods isolate hESC-derived neural progenitors for onward differentiation to mature neurons using either migration or dissociative paradigms. These give poor survival or yield. By combining these approaches, we obtain high yields of morphologically and neurochemically mature neurons. These can be maintained in culture for extended periods.

CONCLUSION

Our method provides a novel, effective and robust neural culture system with structurally and neurochemically mature cell populations and neural networks, suitable for studying a range of neurological diseases from a human perspective.

Modelling cadmium-induced cardiotoxicity using human pluripotent stem cell-derived cardiomyocytes

Cadmium, a highly ubiquitous toxic heavy metal, has been widely recognized as an environmental and industrial pollutant, which confers serious threats to human health. The molecular mechanisms of the cadmium-induced cardiotoxicity (CIC) have not been studied in human cardiomyocytes at the cellular level. Here we showed that human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) can recapitulate the CIC at the cellular level. The cadmium-treated hPSC-CMs exhibited cellular phenotype including reduced cell viability, increased apoptosis, cardiac sarcomeric disorganization, elevated reactive oxygen species, altered action potential profile and cardiac arrhythmias. RNA-sequencing analysis revealed a differential transcriptome profile and activated MAPK signalling pathway in cadmium-treated hPSC-CMs, and suppression of P38 MAPK but not ERK MAPK or JNK MAPK rescued CIC phenotype. We further identified that suppression of PI3K/Akt signalling pathway is sufficient to reverse the CIC phenotype, which may play an important role in CIC. Taken together, our data indicate that hPSC-CMs can serve as a suitable model for the exploration of molecular mechanisms underlying CIC and for the discovery of CIC cardioprotective drugs.

A human population-based organotypic in vitro model for cardiotoxicity screening

Assessing inter-individual variability in responses to xenobiotics remains a substantial challenge, both in drug development with respect to pharmaceuticals and in public health with respect to environmental chemicals. Although approaches exist to characterize pharmacokinetic variability, there are no methods to routinely address pharmacodynamic variability. In this study, we aimed to demonstrate the feasibility of characterizing inter-individual variability in a human in vitro model. Specifically, we hypothesized that genetic variability across a population of iPSC-derived cardiomyocytes translates into reproducible variability in both baseline phenotypes and drug responses. We measured baseline and drug-related effects in iPSC-derived cardiomyocytes from 27 healthy donors on kinetic Ca²⁺ flux and high-content live cell imaging. Cells were treated in concentration-response with cardiotoxic drugs: isoproterenol (β-adrenergic receptor agonist/positive inotrope), propranolol (β-adrenergic receptor antagonist/negative inotrope), and cisapride (hERG channel inhibitor/QT prolongation). Cells from four of the 27 donors were further evaluated in terms of baseline and treatment-related gene expression. Reproducibility of phenotypic responses was evaluated across batches and time. iPSC-derived cardiomyocytes exhibited reproducible donor-specific differences in baseline function and drug-induced effects. We demonstrate the feasibility of using a panel of population-based organotypic cells from healthy donors as an animal replacement experimental model. This model can be used to rapidly screen drugs and chemicals for inter-individual variability in cardiotoxicity. This approach demonstrates the feasibility of quantifying inter-individual variability in xenobiotic responses and can be expanded to other cell types for which in vitro populations can be derived from iPSCs.

Organoid technology for brain and therapeutics research

Brain is one of the most complex organs in human. The current brain research is mainly based on the animal models and traditional cell culture. However, the inherent species differences between humans and animals as well as the gap between organ level and cell level make it difficult to study human brain development and associated disorders through traditional technologies. Recently, the brain organoids derived from pluripotent stem cells have been reported to recapitulate many key features of human brain in vivo, for example recapitulating the zone of putative outer radial glia cells. Brain organoids offer a new platform for scientists to study brain development, neurological diseases, drug discovery and personalized medicine, regenerative medicine, and so on. Here, we discuss the progress, applications, advantages, limitations, and prospects of brain organoid technology in neurosciences and related therapeutics.

Human-Induced Pluripotent Stem Cells Manufactured Using a Current Good Manufacturing Practice-Compliant Process Differentiate Into Clinically Relevant Cells From Three Germ Layers

The discovery of reprogramming and generation of human-induced pluripotent stem cells (iPSCs) has revolutionized the field of regenerative medicine and opened new opportunities in cell replacement therapies. While generation of iPSCs represents a significant breakthrough, the clinical relevance of iPSCs for cell-based therapies requires generation of high-quality specialized cells through robust and reproducible directed differentiation protocols. We have recently reported manufacturing of human iPSC master cell banks (MCB) under current good manufacturing practices (cGMPs). Here, we describe the clinical potential of human iPSCs generated using this cGMP-compliant process by differentiating them into the cells from all three embryonic germ layers including ectoderm, endoderm, and mesoderm. Most importantly, we have shown that our iPSC manufacturing process and cell culture system is not biased toward a specific lineage. Following controlled induction into a specific differentiation lineage, specialized cells with morphological and cellular characteristics of neural stem cells, definitive endoderm, and cardiomyocytes were developed. We believe that these cGMP-compliant iPSCs have the potential to make various clinically relevant products suitable for cell therapy applications.

Human Embryonic Kidney 293 Cells: A Vehicle for Biopharmaceutical Manufacturing, Structural Biology, and Electrophysiology

Mammalian cells, e.g., CHO, BHK, HEK293, HT-1080, and NS0 cells, represent important manufacturing platforms in bioengineering. They are widely used for the production of recombinant therapeutic proteins, vaccines, anticancer agents, and other clinically relevant drugs. HEK293 (human embryonic kidney 293) cells and their derived cell lines provide an attractive heterologous system for the development of recombinant proteins or adenovirus productions, not least due to their human-like posttranslational modification of protein molecules to provide the desired biological activity. Secondly, they also exhibit high transfection efficiency yielding high-quality recombinant proteins. They are easy to maintain and express with high fidelity membrane proteins, such as ion channels and transporters, and thus are attractive for structural biology and electrophysiology studies. In this article, we review the literature on HEK293 cells regarding their origins but also stress their advancements into the different cell lines engineered and discuss some significant aspects which make them versatile systems for biopharmaceutical manufacturing, drug screening, structural biology research, and electrophysiology applications.

Concise Review: Optimized Strategies for Stem Cell-Based Therapy in Myocardial Repair: Clinical Translatability and Potential Limitation

Ischemic heart diseases (IHDs) remain major public health problems with high rates of morbidity and mortality worldwide. Despite significant advances, current therapeutic approaches are unable to rescue the extensive and irreversible loss of cardiomyocytes caused by severe ischemia. Over the past 16 years, stem cell-based therapy has been recognized as an innovative strategy for cardiac repair/regeneration and functional recovery after IHDs. Although substantial preclinical animal studies using a variety of stem/progenitor cells have shown promising results, there is a tremendous degree of skepticism in the clinical community as many stem cell trials do not confer any beneficial effects. How to accelerate stem cell-based therapy toward successful clinical application attracts considerate attention. However, many important issues need to be fully addressed. In this Review, we have described and compared the effects of different types of stem cells with their dose, delivery routes, and timing that have been routinely tested in recent preclinical and clinical findings. We have also discussed the potential mechanisms of action of stem cells, and explored the role and underlying regulatory components of stem cell-derived secretomes/exosomes in myocardial repair. Furthermore, we have critically reviewed the different strategies for optimizing both donor stem cells and the target cardiac microenvironments to enhance the engraftment and efficacy of stem cells, highlighting their clinical translatability and potential limitation. Stem Cells 2018;36:482-500.

Neural organoids for disease phenotyping, drug screening and developmental biology studies

Human induced pluripotent stem cells (hiPSCs) can theoretically yield limitless supplies of cells fated to any cell type that comprise the human organism, making them a new tool by which to potentially overcome caveats in current biomedical research. In vitro derivation of central nervous system (CNS) cell types has the potential to provide material for drug discovery and validation, safety and toxicity assays, cell replacement therapy and the elucidation of previously unknown disease mechanisms. However, current two-dimensional (2D) CNS differentiation protocols do not faithfully recapitulate the spatial organization of heterogeneous tissue, nor the cell-cell interactions, cell-extracellular matrix interactions, or specific physiological functions generated within complex tissue such as the brain. In an effort to overcome 2D protocol limitations, there have been advancements in deriving highly complicated 3D neural organoid structures. Herein we provide a synopsis of the derivation and application of neural organoids and discuss recent advancements and remaining challenges on the full potential of this novel technological platform.