Human induced pluripotent stem cells and their use in drug discovery for toxicity testing. Toxicol Lett. 2013;219:49-58. [PMID: 23470867 DOI: 10.1016/j.toxlet.2013.02.020]

Immunotoxicity, genotoxicity and epigenetic toxicity of nanomaterials: New strategies for toxicity testing?

The unique properties of nanomaterials (NMs) are beneficial in numerous industrial and medical applications. However, they could also induce unintended effects. Thus, a proper strategy for toxicity testing is essential in human hazard and risk assessment. Toxicity can be tested in vivo and in vitro; in compliance with the 3Rs, alternative strategies for in vitro testing should be further developed for NMs. Robust, standardized methods are of great importance in nanotoxicology, with comprehensive material characterization and uptake as an integral part of the testing strategy. Oxidative stress has been shown to be an underlying mechanism of possible toxicity of NMs, causing both immunotoxicity and genotoxicity. For testing NMs in vitro, a battery of tests should be performed on cells of human origin, either cell lines or primary cells, in conditions as close as possible to an in vivo situation. Novel toxicity pathways, particularly epigenetic modification, should be assessed along with conventional toxicity testing methods. However, to initiate epigenetic toxicity screens for NM exposure, there is a need to better understand their adverse effects on the epigenome, to identify robust and reproducible causal links between exposure, epigenetic changes and adverse phenotypic endpoints, and to develop improved assays to monitor epigenetic toxicity.

A human induced pluripotent stem cell-based in vitro assay predicts developmental toxicity through a retinoic acid receptor-mediated pathway for a series of related retinoid analogues

The relative developmental toxicity potency of a series of retinoid analogues was evaluated using a human induced pluripotent stem (iPS) cell assay that measures changes in the biomarkers ornithine and cystine. Analogue potency was predicted, based on the assay endpoint of the ornithine/cystine (o/c) ratio, to be all-trans-retinoic acid>TTNPB>13-cis-retinoic acid≈9-cis-retinoic acid>acitretin>etretinate>retinol. These rankings correlate with in vivo data and demonstrate successful application of the assay to rank a series of related toxic and non-toxic compounds. The retinoic acid receptor α (RARα)-selective antagonist Ro 41-5253 inhibited the cystine perturbation caused by all-trans-retinoic acid, TTNPB, 13-cis-retinoic acid, 9-cis-retinoic acid, and acitretin. Ornithine was altered independent of RARα in all retinoids except acitretin. These results suggest a role for an RARα-mediated mechanism in retinoid-induced developmental toxicity through altered cystine metabolism.

A pump-free microfluidic 3D perfusion platform for the efficient differentiation of human hepatocyte-like cells

The practical application of microfluidic liver models for in vitro drug testing is partly hampered by their reliance on human primary hepatocytes, which are limited in number and have batch-to-batch variation. Human stem cell-derived hepatocytes offer an attractive alternative cell source, although their 3D differentiation and maturation in a microfluidic platform have not yet been demonstrated. We develop a pump-free microfluidic 3D perfusion platform to achieve long-term and efficient differentiation of human liver progenitor cells into hepatocyte-like cells (HLCs). The device contains a micropillar array to immobilize cells three-dimensionally in a central cell culture compartment flanked by two side perfusion channels. Constant pump-free medium perfusion is accomplished by controlling the differential heights of horizontally orientated inlet and outlet media reservoirs. Computational fluid dynamic simulation is used to estimate the hydrostatic pressure heads required to achieve different perfusion flow rates, which are experimentally validated by micro-particle image velocimetry, as well as viability and functional assessments in a primary rat hepatocyte model. We perform on-chip differentiation of HepaRG, a human bipotent progenitor cell, and discover that 3D microperfusion greatly enhances the hepatocyte differentiation efficiency over static 2D and 3D cultures. However, HepaRG progenitor cells are highly sensitive to the time-point at which microperfusion is applied. Isolated HepaRG cells that are primed as static 3D spheroids before being subjected to microperfusion yield a significantly higher proportion of HLCs (92%) than direct microperfusion of isolated HepaRG cells (62%). This platform potentially offers a simple and efficient means to develop highly functional microfluidic liver models incorporating human stem cell-derived HLCs. Biotechnol. Bioeng. 2017;114: 2360-2370. © 2017 Wiley Periodicals, Inc.

Heart-on-a-Chip: An Investigation of the Influence of Static and Perfusion Conditions on Cardiac (H9C2) Cell Proliferation, Morphology, and Alignment

Lab-on-a-chip systems are increasingly used as tools for cultures and investigation of cardiac cells. In this article, we present how the geometry of microsystems and microenvironmental conditions (static and perfusion) influence the proliferation, morphology, and alignment of cardiac cells (rat cardiomyoblasts-H9C2). Additionally, studies of cell growth after incubation with verapamil hydrochloride were performed. For this purpose, poly(dimethylsiloxane) (PDMS)/glass microfluidic systems with three different geometries of microchambers (a circular chamber, a longitudinal channel, and three parallel microchannels separated by two rows of micropillars) were prepared. It was found that static conditions did not enhance the growth of H9C2 cells in the microsystems. On the contrary, perfusion conditions had an influence on division, morphology, and the arrangement of the cells. The highest number of cells, their parallel orientation, and their elongated morphology were obtained in the longitudinal microchannel. It showed that this kind of microsystem can be used to understand processes in heart tissue in detail and to test newly developed compounds applied in the treatment of cardiac diseases.

Idiosyncratic Drug-Induced Liver Injury (IDILI): Potential Mechanisms and Predictive Assays

Idiosyncratic drug-induced liver injury (IDILI) is a significant source of drug recall and acute liver failure (ALF) in the United States. While current drug development processes emphasize general toxicity and drug metabolizing enzyme- (DME-) mediated toxicity, it has been challenging to develop comprehensive models for assessing complete idiosyncratic potential. In this review, we describe the enzymes and proteins that contain polymorphisms believed to contribute to IDILI, including ones that affect phase I and phase II metabolism, antioxidant enzymes, drug transporters, inflammation, and human leukocyte antigen (HLA). We then describe the various assays that have been developed to detect individual reactions focusing on each of the mechanisms described in the background. Finally, we examine current trends in developing comprehensive models for examining these mechanisms. There is an urgent need to develop a panel of multiparametric assays for diagnosing individual toxicity potential.

The C. elegans model in toxicity testing

Caenorhabditis elegans is a small nematode that can be maintained at low cost and handled using standard in vitro techniques. Unlike toxicity testing using cell cultures, C. elegans toxicity assays provide data from a whole animal with intact and metabolically active digestive, reproductive, endocrine, sensory and neuromuscular systems. Toxicity ranking screens in C. elegans have repeatedly been shown to be as predictive of rat LD50 ranking as mouse LD50 ranking. Additionally, many instances of conservation of mode of toxic action have been noted between C. elegans and mammals. These consistent correlations make the case for inclusion of C. elegans assays in early safety testing and as one component in tiered or integrated toxicity testing strategies, but do not indicate that nematodes alone can replace data from mammals for hazard evaluation. As with cell cultures, good C. elegans culture practice (GCeCP) is essential for reliable results. This article reviews C. elegans use in various toxicity assays, the C. elegans model's strengths and limitations for use in predictive toxicology, and GCeCP. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Journal of Applied Toxicology published by John Wiley & Sons Ltd.

Phenotypic assays for analyses of pluripotent stem cell-derived cardiomyocytes

Stem cell-derived cardiomyocytes (CMs) hold great hopes for myocardium regeneration because of their ability to produce functional cardiac cells in large quantities. They also hold promise in dissecting the molecular principles involved in heart diseases and also in drug development, owing to their ability to model the diseases using patient-specific human pluripotent stem cell (hPSC)-derived CMs. The CM properties essential for the desired applications are frequently evaluated through morphologic and genotypic screenings. Even though these characterizations are necessary, they cannot in principle guarantee the CM functionality and their drug response. The CM functional characteristics can be quantified by phenotype assays, including electrophysiological, optical, and/or mechanical approaches implemented in the past decades, especially when used to investigate responses of the CMs to known stimuli (eg, adrenergic stimulation). Such methods can be used to indirectly determine the electrochemomechanics of the cardiac excitation-contraction coupling, which determines important functional properties of the hPSC-derived CMs, such as their differentiation efficacy, their maturation level, and their functionality. In this work, we aim to systematically review the techniques and methodologies implemented in the phenotype characterization of hPSC-derived CMs. Further, we introduce a novel approach combining atomic force microscopy, fluorescent microscopy, and external electrophysiology through microelectrode arrays. We demonstrate that this novel method can be used to gain unique information on the complex excitation-contraction coupling dynamics of the hPSC-derived CMs.

Pluripotent stem cells: the last 10 years

Pluripotent stem cells (PSCs) can differentiate into virtually any cell type in the body, making them attractive for both regenerative medicine and drug discovery. Over the past 10 years, technological advances and innovative platforms have yielded first-in-man PSC-based clinical trials and opened up new approaches for disease modeling and drug development. Induced PSCs have become the foremost alternative to embryonic stem cells and accelerated the development of disease-in-a-dish models. Over the years and with each new discovery, PSCs have proven to be extremely versatile. This review article highlights key advancements in PSC research, from 2006 to 2016, and how they will guide the direction of the field over the next decade.

Human Umbilical Cord Blood-Derived Neural Stem Cell Line as a Screening Model for Toxicity

The aim was to investigate whether a human neural stem cell (NSC) line derived from human umbilical cord blood (hUCB) can be used for toxicity study. Toxicity of both neurotoxic environmental xenobiotics, methyl mercury chloride (CH₃HgCl), lead acetate (CH₃COOPb), and chlorpyrifos (CP), and non-neurotoxic insecticide, dichlorvos, as well as non-neurotoxic drugs, theophylline and acetaminophen were assessed. Additionally, differentiation of neuronal and glial cell lines derived from hUCB was elucidated. It was observed that CH₃HgCl was more toxic to human NSCs in comparison to CH₃COOPb and CP. The minimum inhibitory concentration (MIC) value against NSCs was 3, 10, and 300 mg/L, in each staining process, acridine orange/ethidium bromide (AO/EB) staining, 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay, and Hoechst staining, for CH₃HgCl, CP, and CH₃COOPb, respectively. CH₃HgCl had the LC₂₅ value as 10.0, 14.4, and 12.7 mg/L, by staining method mentioned in succession. CP had the LC₂₅ value as 21.9, 23.7, and 18.4 mg/L; similarly, CH₃COOPb had LC₂₅ values, successively as 616.9, 719.2, and 890.3 mg/L. LC₅₀ values ranged from 18.2 to 21.7 mg/L for CH₃HgCl, 56.4 to 60.2 mg/L for CP, and 1000 to 1460.1 for CH₃COOPb. Theophylline, acetaminophen, and dichlorvos had no impact on the viability of NSCs. This work justified that hUCB-NSC model can be used for toxicity study.

Establishment of a translational endothelial cell model using directed differentiation of induced pluripotent stem cells from Cynomolgus monkey

Due to their broad differentiation potential, pluripotent stem cells (PSCs) offer a promising approach for generating relevant cellular models for various applications. While human PSC-based cellular models are already advanced, similar systems for non-human primates (NHPs) are still lacking. However, as NHPs are the most appropriate animals for evaluating the safety of many novel pharmaceuticals, the availability of in vitro systems would be extremely useful to bridge the gap between cellular and animal models. Here, we present a NHP in vitro endothelial cell system using induced pluripotent stem cells (IPSCs) from Cynomolgus monkey (Macaca fascicularis). Based on an adapted protocol for human IPSCs, we directly differentiated macaque IPSCs into endothelial cells under chemically defined conditions. The resulting endothelial cells can be enriched using immuno-magnetic cell sorting and display endothelial marker expression and function. RNA sequencing revealed that the differentiation process closely resembled vasculogenesis. Moreover, we showed that endothelial cells derived from macaque and human IPSCs are highly similar with respect to gene expression patterns and key endothelial functions, such as inflammatory responses. These data demonstrate the power of IPSC differentiation technology to generate defined cell types for use as translational in vitro models to compare cell type-specific responses across species.

Comprehensive in vitro cardiac safety assessment using human stem cell technology: Overview of CSAHi HEART initiative

Recent increasing evidence suggests that the currently-used platforms in vitro I_Kr and APD, and/or in vivo QT assays are not fully predictive for TdP, and do not address potential arrhythmia (VT and/or VF) induced by diverse mechanisms of action. In addition, other cardiac safety liabilities such as functional dysfunction of excitation-contraction coupling (contractility) and structural damage (morphological damage to cardiomyocytes) are also major causes of drug attrition, but current in vitro assays do not cover all these liabilities. We organized the Consortium for Safety Assessment using Human iPS cells (CSAHi; http://csahi.org/en/), based on the Japan Pharmaceutical Manufacturers Association (JPMA), to verify the application of human iPS/ES cell-derived cardiomyocytes in drug safety evaluation. The main goal of the CSAHi HEART team has been to propose comprehensive screening strategies to predict a diverse range of cardiotoxicities by using recently introduced platforms (multi-electrode array (MEA), patch clamp, cellular impedance, motion field imaging [MFI], and Ca transient systems) while identifying the strengths and weaknesses of each. Our study shows that hiPS-CMs used in these platforms have pharmacological responses more relevant to humans in comparison with existent hERG, APD or Langendorff (MAPD/contraction) assays, and not only MEA but also other methods such as impedance, MFI, and Ca transient systems would offer paradigm changes of platforms for predicting drug-induced QT risk and/or arrhythmia or contractile dysfunctions. Furthermore, we propose a potential multi-parametric platform in which field potential (MEA)-Ca transient-contraction (MFI) could be evaluated simultaneously as an ideal novel platform for predicting a diversity of cardiac toxicities, namely whole effects on the excitation-contraction cascade.

Human ex-vivo action potential model for pro-arrhythmia risk assessment

While current S7B/E14 guidelines have succeeded in protecting patients from QT-prolonging drugs, the absence of a predictive paradigm identifying pro-arrhythmic risks has limited the development of valuable drug programs. We investigated if a human ex-vivo action potential (AP)-based model could provide a more predictive approach for assessing pro-arrhythmic risk in man. Human ventricular trabeculae from ethically consented organ donors were used to evaluate the effects of dofetilide, d,l-sotalol, quinidine, paracetamol and verapamil on AP duration (APD) and recognized pro-arrhythmia predictors (short-term variability of APD at 90% repolarization (STV(APD90)), triangulation (ADP90-APD30) and incidence of early afterdepolarizations at 1 and 2Hz to quantitatively identify the pro-arrhythmic risk. Each drug was blinded and tested separately with 3 concentrations in triplicate trabeculae from 5 hearts, with one vehicle time control per heart. Electrophysiological stability of the model was not affected by sequential applications of vehicle (0.1% dimethyl sulfoxide). Paracetamol and verapamil did not significantly alter anyone of the AP parameters and were classified as devoid of pro-arrhythmic risk. Dofetilide, d,l-sotalol and quinidine exhibited an increase in the manifestation of pro-arrhythmia markers. The model provided quantitative and actionable activity flags and the relatively low total variability in tissue response allowed for the identification of pro-arrhythmic signals. Power analysis indicated that a total of 6 trabeculae derived from 2 hearts are sufficient to identify drug-induced pro-arrhythmia. Thus, the human ex-vivo AP-based model provides an integrative translational assay assisting in shaping clinical development plans that could be used in conjunction with the new CiPA-proposed approach.

How Microelectrode Array-Based Chick Forebrain Neuron Biosensors Respond to Glutamate NMDA Receptor Antagonist AP5 and GABAA Receptor Antagonist Musimol

We have established a long-term, stable primary chick forebrain neuron (FBN) culture on a microelectrode array platform as a biosensor system for neurotoxicant screening and for neuroelectrophysiological studies for multiple purposes. This paper reports some of our results, which characterize the biosensor pharmacologically. Dose-response experiments were conducted using NMDA receptor antagonist AP5 and GABA_A receptor agonist musimol (MUS). The chick FBN biosensor (C-FBN-biosensor) responds to the two agents in a pattern similar to that of rodent counterparts; the estimated EC₅₀s (the effective concentration that causes 50% inhibition of the maximal effect) are 2.3 μM and 0.25 μM, respectively. Intercultural and intracultural reproducibility and long-term reusability of the C-FBN-biosensor are addressed and discussed. A phenomenon of sensitization of the biosensor that accompanies intracultural reproducibility in paired dose-response experiments for the same agent (AP5 or MUS) is reported. The potential application of the C-FBN-biosensor as an alternative to rodent biosensors in shared sensing domains (NMDA receptor and GABA_A receptor) is suggested.

Microcarrier-based platforms for in vitro expansion and differentiation of human pluripotent stem cells in bioreactor culture systems

Human pluripotent stem cells (hPSC) have attracted a great attention as an unlimited source of cells for cell therapies and other in vitro biomedical applications such as drug screening, toxicology assays and disease modeling. The implementation of scalable culture platforms for the large-scale production of hPSC and their derivatives is mandatory to fulfill the requirement of obtaining large numbers of cells for these applications. Microcarrier technology has been emerging as an effective approach for the large scale ex vivo hPSC expansion and differentiation. This review presents recent achievements in hPSC microcarrier-based culture systems and discusses the crucial aspects that influence the performance of these culture platforms. Recent progress includes addressing chemically-defined culture conditions for manufacturing of hPSC and their derivatives, with the development of xeno-free media and microcarrier coatings to meet good manufacturing practice (GMP) quality requirements. Finally, examples of integrated platforms including hPSC expansion and directed differentiation to specific lineages are also presented in this review.

Impedimetric real-time monitoring of neural pluripotent stem cell differentiation process on microelectrode arrays

In today's neurodevelopment and -disease research, human neural stem/progenitor cell-derived networks represent the sole accessible in vitro model possessing a primary phenotype. However, cultivation and moreover, differentiation as well as maturation of human neural stem/progenitor cells are very complex and time-consuming processes. Therefore, techniques for the sensitive non-invasive, real-time monitoring of neuronal differentiation and maturation are highly demanded. Using impedance spectroscopy, the differentiation of several human neural stem/progenitor cell lines was analyzed in detail. After development of an optimum microelectrode array for reliable and sensitive long-term monitoring, distinct cell-dependent impedimetric parameters that could specifically be associated with the progress and quality of neuronal differentiation were identified. Cellular impedance changes correlated well with the temporal regulation of biomolecular progenitor versus mature neural marker expression as well as cellular structure changes accompanying neuronal differentiation. More strikingly, the capability of the impedimetric differentiation monitoring system for the use as a screening tool was demonstrated by applying compounds that are known to promote neuronal differentiation such as the γ-secretase inhibitor DAPT. The non-invasive impedance spectroscopy-based measurement system can be used for sensitive and quantitative monitoring of neuronal differentiation processes. Therefore, this technique could be a very useful tool for quality control of neuronal differentiation and moreover, for neurogenic compound identification and industrial high-content screening demands in the field of safety assessment as well as drug development.

Pluripotent stem cells: An in vitro model for nanotoxicity assessments

The advent of technology has led to an established range of engineered nanoparticles that are used in diverse applications, such as cell-cell interactions, cell-material interactions, medical therapies and the target modulation of cellular processes. The exponential increase in the utilization of nanomaterials and the growing number of associated criticisms has highlighted the potential risks of nanomaterials to human health and the ecosystem. The existing in vivo and in vitro platforms show limitations, with fluctuations being observed in the results of toxicity assessments. Pluripotent stem cells (PSCs) are viable source of cells that are capable of developing into specialized cells of the human body. PSCs can be efficiently used to screen new biomaterials/drugs and are potential candidates for studying impairments of biophysical morphology at both the cellular and tissue levels during interactions with nanomaterials and for diagnosing toxicity. Three-dimensional in vitro models obtained using PSC-derived cells would provide a realistic, patient-specific platform for toxicity assessments and in drug screening applications. The current review focuses on PSCs as an alternative in vitro platform for assessing the hazardous effects of nanomaterials on health systems and highlights the importance of PSC-derived in vitro platforms. Copyright © 2016 John Wiley & Sons, Ltd.

Stable engineered vascular networks from human induced pluripotent stem cell-derived endothelial cells cultured in synthetic hydrogels

Here, we describe an in vitro strategy to model vascular morphogenesis where human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) are encapsulated in peptide-functionalized poly(ethylene glycol) (PEG) hydrogels, either on standard well plates or within a passive pumping polydimethylsiloxane (PDMS) tri-channel microfluidic device. PEG hydrogels permissive towards cellular remodeling were fabricated using thiol-ene photopolymerization to incorporate matrix metalloproteinase (MMP)-degradable crosslinks and CRGDS cell adhesion peptide. Time lapse microscopy, immunofluorescence imaging, and RNA sequencing (RNA-Seq) demonstrated that iPSC-ECs formed vascular networks through mechanisms that were consistent with in vivo vasculogenesis and angiogenesis when cultured in PEG hydrogels. Migrating iPSC-ECs condensed into clusters, elongated into tubules, and formed polygonal networks through sprouting. Genes upregulated for iPSC-ECs cultured in PEG hydrogels relative to control cells on tissue culture polystyrene (TCP) surfaces included adhesion, matrix remodeling, and Notch signaling pathway genes relevant to in vivo vascular development. Vascular networks with lumens were stable for at least 14days when iPSC-ECs were encapsulated in PEG hydrogels that were polymerized within the central channel of the microfluidic device. Therefore, iPSC-ECs cultured in peptide-functionalized PEG hydrogels offer a defined platform for investigating vascular morphogenesis in vitro using both standard and microfluidic formats.

STATEMENT OF SIGNIFICANCE

Human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) cultured in synthetic hydrogels self-assemble into capillary networks through mechanisms consistent with in vivo vascular morphogenesis.

Toxicity testing and drug screening using iPSC-derived hepatocytes, cardiomyocytes, and neural cells

Unexpected toxicity in areas such as cardiotoxicity, hepatotoxicity, and neurotoxicity is a serious complication of clinical therapy and one of the key causes for failure of promising drug candidates in development. Animal studies have been widely used for toxicology research to provide preclinical security evaluation of various therapeutic agents under development. Species differences in drug penetration of the blood-brain barrier, drug metabolism, and related toxicity contribute to failure of drug trials from animal models to human. The existing system for drug discovery has relied on immortalized cell lines, animal models of human disease, and clinical trials in humans. Moreover, drug candidates that are passed as being safe in the preclinical stage often show toxic effects during the clinical stage. Only around 16% drugs are approved for human use. Research on induced pluripotent stem cells (iPSCs) promises to enhance drug discovery and development by providing simple, reproducible, and economically effective tools for drug toxicity screening under development and, on the other hand, for studying the disease mechanism and pathways. In this review, we provide an overview of basic information about iPSCs, and discuss efforts aimed at the use of iPSC-derived hepatocytes, cardiomyocytes, and neural cells in drug discovery and toxicity testing.

Long-term maintenance of human induced pluripotent stem cells by automated cell culture system

Pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem (iPS) cells, are regarded as new sources for cell replacement therapy. These cells can unlimitedly expand under undifferentiated conditions and be differentiated into multiple cell types. Automated culture systems enable the large-scale production of cells. In addition to reducing the time and effort of researchers, an automated culture system improves the reproducibility of cell cultures. In the present study, we newly designed a fully automated cell culture system for human iPS maintenance. Using an automated culture system, hiPS cells maintained their undifferentiated state for 60 days. Automatically prepared hiPS cells had a potency of differentiation into three germ layer cells including dopaminergic neurons and pancreatic cells.

Human induced pluripotent stem cells in Parkinson's disease: A novel cell source of cell therapy and disease modeling

Human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs) are two novel cell sources for studying neurodegenerative diseases. Dopaminergic neurons derived from hiPSCs/hESCs have been implicated to be very useful in Parkinson's disease (PD) research, including cell replacement therapy, disease modeling and drug screening. Recently, great efforts have been made to improve the application of hiPSCs/hESCs in PD research. Considerable advances have been made in recent years, including advanced reprogramming strategies without the use of viruses or using fewer transcriptional factors, optimized methods for generating highly homogeneous neural progenitors with a larger proportion of mature dopaminergic neurons and better survival and integration after transplantation. Here we outline the progress that has been made in these aspects in recent years, particularly during the last year, and also discuss existing issues that need to be addressed.

Use of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) to Monitor Compound Effects on Cardiac Myocyte Signaling Pathways

There is a need to develop mechanism-based assays to better inform risk of cardiotoxicity. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are rapidly gaining acceptance as a biologically relevant in vitro model for use in drug discovery and cardiotoxicity screens. Utilization of hiPSC-CMs for mechanistic investigations would benefit from confirmation of the expression and activity of cellular pathways that are known to regulate cardiac myocyte viability and function. This unit describes an approach to demonstrate the presence and function of signaling pathways in hiPSC-CMs and the effects of treatments on these pathways. We present a workflow that employs protocols to demonstrate protein expression and functional integrity of signaling pathway(s) of interest and to characterize biological consequences of signaling modulation. These protocols utilize a unique combination of structural, functional, and biochemical endpoints to interrogate compound effects on cardiomyocytes.

A novel two-dimensional liquid chromatographic system for the online toxicity prediction of pharmaceuticals and related substances

In this study, a novel two-dimensional liquid chromatographic (2D-LC) system was developed for simultaneous separation and toxicity prediction of pharmaceutical and its related substances. A conventional ODS column was used on the 1st-D to separate the sample; while, bio-partitioning micellar chromatography served as the 2nd-D to predict toxicity of the components. The established system was tested for the toxicity of ibuprofen and its impurities with known toxicity. With only one injection, ibuprofen and its impurities were separated on the 1st-D; and LC50 values of individual impurity were obtained based on the quantitative retention-activity relationships, which agreed well with the reported data. Furthermore, LC50 values of photolysis transformation products (TPs) of carprofen, ketoprofen and diclofenac acid (as unknown compounds) were screened in this 2D-LC system, which could be an indicator of the toxicity of these TPs and was meaningful for the environmental monitoring and drinking water treatment. The established 2D-LC system was cost-effective, time-saving and reliable, and was promising for fast online screening of toxicity of known and unknown analytes in the complex sample in a single step. It may find applications in environment, pharmaceutical and food, etc.

Induced Pluripotent Stem Cell Models to Enable In Vitro Models for Screening in the Central Nervous System

There is great need to develop more predictive drug discovery tools to identify new therapies to treat diseases of the central nervous system (CNS). Current nonpluripotent stem cell-based models often utilize non-CNS immortalized cell lines and do not enable the development of personalized models of disease. In this review, we discuss why in vitro models are necessary for translational research and outline the unique advantages of induced pluripotent stem cell (iPSC)-based models over those of current systems. We suggest that iPSC-based models can be patient specific and isogenic lines can be differentiated into many neural cell types for detailed comparisons. iPSC-derived cells can be combined to form small organoids, or large panels of lines can be developed that enable new forms of analysis. iPSC and embryonic stem cell-derived cells can be readily engineered to develop reporters for lineage studies or mechanism of action experiments further extending the utility of iPSC-based systems. We conclude by describing novel technologies that include strategies for the development of diversity panels, novel genomic engineering tools, new three-dimensional organoid systems, and modified high-content screens that may bring toxicology into the 21st century. The strategic integration of these technologies with the advantages of iPSC-derived cell technology, we believe, will be a paradigm shift for toxicology and drug discovery efforts.

Importance of being Nernst: Synaptic activity and functional relevance in stem cell-derived neurons

Functional synaptogenesis and network emergence are signature endpoints of neurogenesis. These behaviors provide higher-order confirmation that biochemical and cellular processes necessary for neurotransmitter release, post-synaptic detection and network propagation of neuronal activity have been properly expressed and coordinated among cells. The development of synaptic neurotransmission can therefore be considered a defining property of neurons. Although dissociated primary neuron cultures readily form functioning synapses and network behaviors in vitro, continuously cultured neurogenic cell lines have historically failed to meet these criteria. Therefore, in vitro-derived neuron models that develop synaptic transmission are critically needed for a wide array of studies, including molecular neuroscience, developmental neurogenesis, disease research and neurotoxicology. Over the last decade, neurons derived from various stem cell lines have shown varying ability to develop into functionally mature neurons. In this review, we will discuss the neurogenic potential of various stem cells populations, addressing strengths and weaknesses of each, with particular attention to the emergence of functional behaviors. We will propose methods to functionally characterize new stem cell-derived neuron (SCN) platforms to improve their reliability as physiological relevant models. Finally, we will review how synaptically active SCNs can be applied to accelerate research in a variety of areas. Ultimately, emphasizing the critical importance of synaptic activity and network responses as a marker of neuronal maturation is anticipated to result in in vitro findings that better translate to efficacious clinical treatments.

Differences in the Epigenetic Regulation of Cytochrome P450 Genes between Human Embryonic Stem Cell-Derived Hepatocytes and Primary Hepatocytes

Human pluripotent stem cell-derived hepatocytes have the potential to provide in vitro model systems for drug discovery and hepatotoxicity testing. However, these cells are currently unsuitable for drug toxicity and efficacy testing because of their limited expression of genes encoding drug-metabolizing enzymes, especially cytochrome P450 (CYP) enzymes. Transcript levels of major CYP genes were much lower in human embryonic stem cell-derived hepatocytes (hESC-Hep) than in human primary hepatocytes (hPH). To verify the mechanism underlying this reduced expression of CYP genes, including CYP1A1, CYP1A2, CYP1B1, CYP2D6, and CYP2E1, we investigated their epigenetic regulation in terms of DNA methylation and histone modifications in hESC-Hep and hPH. CpG islands of CYP genes were hypermethylated in hESC-Hep, whereas they had an open chromatin structure, as represented by hypomethylation of CpG sites and permissive histone modifications, in hPH. Inhibition of DNA methyltransferases (DNMTs) during hepatic maturation induced demethylation of the CpG sites of CYP1A1 and CYP1A2, leading to the up-regulation of their transcription. Combinatorial inhibition of DNMTs and histone deacetylases (HDACs) increased the transcript levels of CYP1A1, CYP1A2, CYP1B1, and CYP2D6. Our findings suggest that limited expression of CYP genes in hESC-Hep is modulated by epigenetic regulatory factors such as DNMTs and HDACs.

CiPA: Ongoing testing, future qualification procedures, and pending issues

INTRODUCTION

The comprehensive in vitro proarrhythmia assay (CiPA) is a nonclinical, mechanism-based paradigm for assessing drug proarrhythmic liability.

TOPICS COVERED

The first CiPA assay determines effects on cloned human cardiac ion channels. The second investigates whether the latter study-generated metrics engender proarrhythmic markers on a computationally reconstructed human ventricular action potential. The third evaluates conclusions from, and searches possibly missed effects by in silico analysis, in human stem cell-derived cardiomyocytes (hSC-CMs). CiPA ad hoc Expert-Working Groups have proposed patch clamp protocols for seven cardiac ion channels, a modified O'Hara-Rudy model for in silico analysis, detailed procedures for field (MEA) and action potential (VSD) measurements in hSC-CMs, and 29 reference drugs for CiPA assay testing and validation.

DISCUSSION

CiPA adoption as drug development tool for identifying electrophysiological mechanisms conferring proarrhythmic liability to candidate drugs is a complex, multi-functional task requiring significant time, reflection, and efforts to be fully achieved.

The application of engineered liver tissues for novel drug discovery

INTRODUCTION

Drug-induced liver injury remains a major cause of drug attrition. Furthermore, novel drugs are being developed for treating liver diseases. However, differences between animals and humans in liver pathways necessitate the use of human-relevant liver models to complement live animal testing during preclinical drug development. Microfabrication tools and synthetic biomaterials now allow for the creation of tissue subunits that display more physiologically relevant and long-term liver functions than possible with declining monolayers.

AREAS COVERED

The authors discuss acellular enzyme platforms, two-dimensional micropatterned co-cultures, three-dimensional spheroidal cultures, microfluidic perfusion, liver slices and humanized rodent models. They also present the use of cell lines, primary liver cells and induced pluripotent stem cell-derived human hepatocyte-like cells in the creation of cell-based models and discuss in silico approaches that allow integration and modeling of the datasets from these models. Finally, the authors describe the application of liver models for the discovery of novel therapeutics for liver diseases.

EXPERT OPINION

Engineered liver models with varying levels of in vivo-like complexities provide investigators with the opportunity to develop assays with sufficient complexity and required throughput. Control over cell-cell interactions and co-culture with stromal cells in both two dimension and three dimension are critical for enabling stable liver models. The validation of liver models with diverse sets of compounds for different applications, coupled with an analysis of cost:benefit ratio, is important for model adoption for routine screening. Ultimately, engineered liver models could significantly reduce drug development costs and enable the development of more efficacious and safer therapeutics for liver diseases.

Enhancing the functional maturity of induced pluripotent stem cell-derived human hepatocytes by controlled presentation of cell-cell interactions in vitro

Induced pluripotent stem cell-derived human hepatocyte-like cells (iHeps) could provide a powerful tool for studying the mechanisms underlying human liver development and disease, testing the efficacy and safety of pharmaceuticals across different patients (i.e., personalized medicine), and enabling cell-based therapies in the clinic. However, current in vitro protocols that rely upon growth factors and extracellular matrices (ECMs) alone yield iHeps with low levels of liver functions relative to adult primary human hepatocytes (PHHs). Moreover, these low hepatic functions in iHeps are difficult to maintain for prolonged times (weeks to months) in culture. Here, we engineered a micropatterned coculture (iMPCC) platform in a multiwell format that, in contrast to conventional confluent cultures, significantly enhanced the functional maturation and longevity of iHeps in culture for at least 4 weeks in vitro when benchmarked against multiple donors of PHHs. In particular, iHeps were micropatterned onto collagen-coated domains of empirically optimized dimensions, surrounded by 3T3-J2 murine embryonic fibroblasts, and then sandwiched with a thin layer of ECM gel (Matrigel). We assessed iHep maturity by global gene expression profiles, hepatic polarity, secretion of albumin and urea, basal cytochrome P450 (CYP450) activities, phase II conjugation, drug-mediated CYP450 induction, and drug-induced hepatotoxicity.

CONCLUSION

Controlling both homotypic interactions between iHeps and heterotypic interactions with stromal fibroblasts significantly matures iHep functions and maintains them for several weeks in culture. In the future, iMPCCs could prove useful for drug screening, studying molecular mechanisms underlying iHep differentiation, modeling liver diseases, and integration into human-on-a-chip systems being designed to assess multiorgan responses to compounds.

Human iPSC-based cardiac microphysiological system for drug screening applications

Drug discovery and development are hampered by high failure rates attributed to the reliance on non-human animal models employed during safety and efficacy testing. A fundamental problem in this inefficient process is that non-human animal models cannot adequately represent human biology. Thus, there is an urgent need for high-content in vitro systems that can better predict drug-induced toxicity. Systems that predict cardiotoxicity are of uppermost significance, as approximately one third of safety-based pharmaceutical withdrawals are due to cardiotoxicty. Here, we present a cardiac microphysiological system (MPS) with the attributes required for an ideal in vitro system to predict cardiotoxicity: i) cells with a human genetic background; ii) physiologically relevant tissue structure (e.g. aligned cells); iii) computationally predictable perfusion mimicking human vasculature; and, iv) multiple modes of analysis (e.g. biological, electrophysiological, and physiological). Our MPS is able to keep human induced pluripotent stem cell derived cardiac tissue viable and functional over multiple weeks. Pharmacological studies using the cardiac MPS show half maximal inhibitory/effective concentration values (IC₅₀/EC₅₀) that are more consistent with the data on tissue scale references compared to cellular scale studies. We anticipate the widespread adoption of MPSs for drug screening and disease modeling.

Prediction of Drug-Induced Liver Injury in Micropatterned Co-cultures Containing iPSC-Derived Human Hepatocytes

Primary human hepatocytes (PHHs) are a limited resource for drug screening, their quality for in vitro use can vary considerably across different lots, and a lack of available donor diversity restricts our understanding of how human genetics affect drug-induced liver injury (DILI). Induced pluripotent stem cell-derived human hepatocyte-like cells (iPSC-HHs) could provide a complementary tool to PHHs for high-throughput drug screening, and ultimately enable personalized medicine. Here, we hypothesized that previously developed iPSC-HH-based micropatterned co-cultures (iMPCCs) with murine embryonic fibroblasts could be amenable to long-term drug toxicity assessment. iMPCCs, created in industry-standard 96-well plates, were treated for 6 days with a set of 47 drugs, and multiple functional endpoints (albumin, urea, ATP) were evaluated in dosed cultures against vehicle-only controls to enable binary toxicity decisions. We found that iMPCCs correctly classified 24 of 37 hepatotoxic drugs (65% sensitivity), while all 10 non-toxic drugs tested were classified as such in iMPCCs (100% specificity). On the other hand, conventional confluent cultures of iPSC-HHs failed to detect several liver toxins that were picked up in iMPCCs. Results for DILI detection in iMPCCs were remarkably similar to published data in PHH-MPCCs (65% versus 70% sensitivity) that were dosed with the same drugs. Furthermore, iMPCCs detected the relative hepatotoxicity of structural drug analogs and recapitulated known mechanisms of acetaminophen toxicity in vitro. In conclusion, iMPCCs could provide a robust tool to screen for DILI potential of large compound libraries in early stages of drug development using an abundant supply of commercially available iPSC-HHs.

Establishment of a Long-Term Chick Forebrain Neuronal Culture on a Microelectrode Array Platform

The biosensor system formed by culturing primary animal neurons on a microelectrode array (MEA) platform is drawing an increasing research interest for its power as a rapid, sensitive, functional neurotoxicity assessment, as well as for many other electrophysiological related research purposes. In this paper, we established a long-term chick forebrain neuron culture (C-FBN-C) on MEAs with a more than 5 month long lifespan and up to 5 month long stability in morphology and physiological function; characterized the C-FBN-C morphologically, functionally, and developmentally; partially compared its functional features with rodent counterpart; and discussed its pros and cons as a novel biosensor system in comparison to rodent counterpart and human induced pluripotent stem cells (hiPSCs). Our results show that C-FBN-C on MEA platform 1) can be used as a biosensor of its own type in a wide spectrum of basic biomedical research; 2) is of value in comparative physiology in cross-species studies; and 3) may have potential to be used as an alternative, cost-effective approach to rodent counterpart within shared common functional domains (such as specific types of ligand-gated ion channel receptors and subtypes expressed in the cortical tissues of both species) in large-scale environmental neurotoxicant screening that would otherwise require millions of animals.

Nonclinical Safety and Toxicology

Nonclinical safety pharmacology and toxicology testing of drug candidates assess the potential adverse effects caused by the drug in relation to its intended use in humans. Hazards related to a drug have to be identified and the potential risks at the intended exposure have to be evaluated in comparison to the potential benefit of the drug. Preclinical safety is thus an integral part of drug discovery and drug development. It still causes significant attrition during drug development.Therefore, there is a need for smart selection of drug candidates in drug discovery including screening of important safety endpoints. In the recent years,there was significant progress in computational and in vitro technology allowing in silico assessment as well as high-throughput screening of some endpoints at very early stages of discovery. Despite all this progress, in vivo evaluation of drug candidates is still an important part to safety testing. The chapter provides an overview on the most important areas of nonclinical safety screening during drug discovery of small molecules.

Assessment of cardiomyocyte contraction in human-induced pluripotent stem cell-derived cardiomyocytes

Functional changes to cardiomyocytes are a common cause of attrition in preclinical and clinical drug development. Current approaches to assess cardiomyocyte contractility in vitro are limited to low-throughput methods not amenable to early drug discovery. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) were used to assess their suitability to detect drug-induced changes in cardiomyocyte contraction. Application of field stimulation and measurement of cardiac contraction (IonOptix edge detection) and Ca(2+) transients confirmed hiPS-CMs to be a suitable model to investigate drug-induced changes in cardiomyocyte contractility. Using a live cell, fast kinetic fluorescent assay with a Ca(2+) sensitive dye to test 31 inotropic and 20 non-inotropic compounds in vivo, we report that hiPS-CMs provide a high-throughput experimental model to detect changes in cardiomyocyte contraction that is applicable to early drug discovery with a sensitivity and specificity of 87% and 70%, respectively. Moreover, our data provide evidence of the detection of this liability at therapeutically relevant concentrations with throughput amenable to influencing chemical design in drug discovery. Measurement of multiple parameters of the Ca(2+) transient in addition to the number of Ca(2+) transients offered no insight into the mechanism of cardiomyocyte contraction.

New easy-to-use hybrid system for extracellular potential and impedance recordings

The need for predictive, in vitro cardiac safety screening drives further development of automated, high-throughput-compatible drug evaluation based on cardiac cell preparations. Recently, pluripotent stem cells are evaluated as a new, more predictive model for cardiovascular risk assessment pertaining to in vitro assays. We present a new screening platform, the CardioExcyte 96, a hybrid instrument that combines impedance (cell contractility) with extracellular field potential (EFP) recordings. The electrophysiological measurements are noninvasive, label free and have a temporal resolution of 1 ms. This hybrid technology addresses the lack of easy-to-use high-throughput screening for in vitro assays and permits the reliable investigation of short- and long-term pharmacological effects. Several models of cardiomyocyte preparations were successfully validated for use with the CardioExcyte96. Furthermore, the pharmacological effects of a number of reference compounds were evaluated. Compound effects on cell monolayers of human-induced pluripotent stem cell-derived cardiomyocytes are evaluated using a quasi-simultaneous hybrid recording mode that combines impedance and EFP readouts. A specialized software package for rapid data handling and real-time analysis was developed, which allows for comprehensive investigation of the cellular beat signal. Combining impedance readouts of cell contractility and EFP (microelectrode array-like) recordings, the system opens up new possibilities in the field of in vitro cardiac safety assessment.

Therapeutic translation of iPSCs for treating neurological disease

Somatic cellular reprogramming is a fast-paced and evolving field that is changing the way scientists approach neurological diseases. For the first time in the history of neuroscience, it is feasible to study the behavior of live neurons from patients with neurodegenerative diseases, such as Alzheimer's and Parkinson's disease, and neuropsychiatric diseases, such as autism and schizophrenia. In this Perspective, we will discuss reprogramming technology in the context of its potential use for modeling and treating neurological and psychiatric diseases and will highlight areas of caution and opportunities for improvement.

Integrated platform for production and purification of human pluripotent stem cell-derived neural precursors

Human pluripotent stem cells (hPSCs) are a promising source of cells for clinical applications, such as transplantation of clinically engineered tissues and organs, and drug discovery programs due to their ability to self-renew and to be differentiated into cells from the three embryonic germ layers. In this study, the differentiation of two hPSC-lines into neural precursors (NPs) was accomplished with more than 80% efficiency, by means of the dual-SMAD inhibition protocol, based on the use of two small molecules (SB431542 and LDN193189) to generate Pax6 and Nestin-positive neural entities. One of the major hurdles related to the in vitro generation of PSC-derived populations is the tumorigenic potential of cells that remain undifferentiated. These remaining hPSCs have the potential to generate teratomas after being transplanted, and may interfere with the outcome of in vitro differentiation protocols. One strategy to tackle this problem is to deplete these "contaminating" cells during the differentiation process. Magnetic activated cell sorting (MACS) was used for the first time for purification of hPSC-derived NPs after the neural commitment stage using anti-Tra-1-60 micro beads for negative selection of the unwanted hPSCs. The depletion had an average efficiency of 80.4 ± 5% and less than 1.5% of Tra-1-60 positive cells were present in the purified populations. After re-plating, the purified neural precursors maintained their phenotype, and the success of the preparative purification with MACS was further confirmed with a decrease of 94.3% in the number of Oct4-positive proliferating hPSC colonies. Thus, the integration of the MACS depletion step with the neural commitment protocol paves the way towards the establishment of a novel bioprocess for production of purified populations of hPSC-derived neural cells for different applications.

Exposure to benzidine caused apoptosis and malformation of telencephalon region in zebrafish

Exposure to benzidine has been known to induce human cancers, particularly bladder carcinomas. In this study, the zebrafish model was used to investigate the developmental toxicity of benzidine. Embryos at 6 h postfertilization (hpf) that were exposed to benzidine exhibited embryonic death in a dose- and time-dependent manner. Benzidine induced malformations in zebrafish, such as small brain development, shorter axes, and a slight pericardial edema. High concentrations (50, 100, and 200 µM) of benzidine triggered widespread apoptosis in the brain and dorsal neurons, as evidenced by acridine orange and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays. Real-time polymerase chain reaction analysis also showed that benzidine treatment affected p53, bax, and noxa expression. Decreases in specific brain markers, such as emx1 in the telencephalon, ngn1 in differentiated neurons, and otx2 in the midbrain, were observed in benzidine-treated embryos at 24 hpf. Conversely, no overt changes to pax2.1 expression in the midbrain-hindbrain boundary were found. Moreover, the use of Tg(HuC:GFP) zebrafish showed that benzidine caused a malformation of the telencephalon region. Our findings show that benzidine exposure triggers widespread apoptosis in the zebrafish brain and dorsal neurons, resulting in the development of an abnormal telencephalon.

mRNA-based therapeutics--developing a new class of drugs

In vitro transcribed (IVT) mRNA has recently come into focus as a potential new drug class to deliver genetic information. Such synthetic mRNA can be engineered to transiently express proteins by structurally resembling natural mRNA. Advances in addressing the inherent challenges of this drug class, particularly related to controlling the translational efficacy and immunogenicity of the IVTmRNA, provide the basis for a broad range of potential applications. mRNA-based cancer immunotherapies and infectious disease vaccines have entered clinical development. Meanwhile, emerging novel approaches include in vivo delivery of IVT mRNA to replace or supplement proteins, IVT mRNA-based generation of pluripotent stem cells and genome engineering using IVT mRNA-encoded designer nucleases. This Review provides a comprehensive overview of the current state of mRNA-based drug technologies and their applications, and discusses the key challenges and opportunities in developing these into a new class of drugs.

A cellular genetics approach identifies gene-drug interactions and pinpoints drug toxicity pathway nodes

New approaches to toxicity testing have incorporated high-throughput screening across a broad-range of in vitro assays to identify potential key events in response to chemical or drug treatment. To date, these approaches have primarily utilized repurposed drug discovery assays. In this study, we describe an approach that combines in vitro screening with genetic approaches for the experimental identification of genes and pathways involved in chemical or drug toxicity. Primary embryonic fibroblasts isolated from 32 genetically-characterized inbred mouse strains were treated in concentration-response format with 65 compounds, including pharmaceutical drugs, environmental chemicals, and compounds with known modes-of-action. Integrated cellular responses were measured at 24 and 72 h using high-content imaging and included cell loss, membrane permeability, mitochondrial function, and apoptosis. Genetic association analysis of cross-strain differences in the cellular responses resulted in a collection of candidate loci potentially underlying the variable strain response to each chemical. As a demonstration of the approach, one candidate gene involved in rotenone sensitivity, Cybb, was experimentally validated in vitro and in vivo. Pathway analysis on the combined list of candidate loci across all chemicals identified a number of over-connected nodes that may serve as core regulatory points in toxicity pathways.

Long-term effects of chromatin remodeling and DNA damage in stem cells induced by environmental and dietary agents

The presence of histones acts as a barrier to protein access; thus chromatin remodeling must occur for essential processes such as transcription and replication. In conjunction with histone modifications, DNA methylation plays critical roles in gene silencing through chromatin remodeling. Chromatin remodeling is also interconnected with the DNA damage response, maintenance of stem cell properties, and cell differentiation programs. Chromatin modifications have increasingly been shown to produce long-lasting alterations in chromatin structure and transcription. Recent studies have shown environmental exposures in utero have the potential to alter normal developmental signaling networks, physiologic responses, and disease susceptibility later in life during a process known as developmental reprogramming. In this review we discuss the long-term impact of exposure to environmental compounds, the chromatin modifications that they induce, and the differentiation and developmental programs of multiple stem and progenitor cell types altered by exposure. The main focus is to highlight agents present in the human lifestyle that have the potential to promote epigenetic changes that impact developmental programs of specific cell types, may promote tumorigenesis through altering epigenetic marks, and may be transgenerational, for example, those able to be transmitted through multiple cell divisions.