Cardiomyocytes from human embryonic stem cells as predictors of cardiotoxicity

Anthracycline Toxicity: Light at the End of the Tunnel?

Anthracycline-induced cardiotoxicity (AIC) is a serious and common side effect of anthracycline therapy. Identification of genes and genetic variants associated with AIC risk has clinical potential as a cardiotoxicity predictive tool and to allow the development of personalized therapies. In this review, we provide an overview of the function of known AIC genes identified by association studies and categorize them based on their mechanistic implication in AIC. We also discuss the importance of functional validation of AIC-associated variants in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to advance the implementation of genetic predictive biomarkers. Finally, we review how patient-specific hiPSC-CMs can be used to identify novel patient-relevant functional targets and for the discovery of cardioprotectant drugs to prevent AIC. Implementation of functional validation and use of hiPSC-CMs for drug discovery will identify the next generation of highly effective and personalized cardioprotectants and accelerate the inclusion of approved AIC biomarkers into clinical practice.

A Human 3D Cardiomyocyte Risk Model to Study the Cardiotoxic Influence of X-rays and Other Noxae in Adults

The heart tissue is a potential target of various noxae contributing to the onset of cardiovascular diseases. However, underlying pathophysiological mechanisms are largely unknown. Human stem cell-derived models are promising, but a major concern is cell immaturity when estimating risks for adults. In this study, 3D aggregates of human embryonic stem cell-derived cardiomyocytes were cultivated for 300 days and characterized regarding degree of maturity, structure, and cell composition. Furthermore, effects of ionizing radiation (X-rays, 0.1–2 Gy) on matured aggregates were investigated, representing one of the noxae that are challenging to assess. Video-based functional analyses were correlated to changes in the proteome after irradiation. Cardiomyocytes reached maximum maturity after 100 days in cultivation, judged by α-actinin lengths, and displayed typical multinucleation and branching. At this time, aggregates contained all major cardiac cell types, proven by the patch-clamp technique. Matured and X-ray-irradiated aggregates revealed a subtle increase in beat rates and a more arrhythmic sequence of cellular depolarisation and repolarisation compared to non-irradiated sham controls. The proteome analysis provides first insights into signaling mechanisms contributing to cardiotoxicity. Here, we propose an in vitro model suitable to screen various noxae to target adult cardiotoxicity by preserving all the benefits of a 3D tissue culture.

Disruption of mitochondrial membrane potential coupled with alterations in cardiac biomarker expression as early cardiotoxic signatures in human ES cell-derived cardiac cells

Cardiotoxicity is one of the most significant reasons of attrition in drug development. The present study assessed the sensitivity of various endpoints for early monitoring of drug-induced cardiotoxicity using human embryonic stem cell-derived cardiac cells, including precursors as well as mature cardiomyocytes, by correlating changes in cardiac biomarker expression. Directed differentiation was induced and cardiac progenitor cell (CPC) population were treated with cardiotoxic drugs, namely, doxorubicin (Dox) and paclitaxel (Pac), and with noncardiotoxic drug, namely penicillin G. To assess cardiac-specific toxicity, the changes in the expression of key markers of cardiac lineage, such as Nkx2.5, Tbx5, α-myosin heavy chain α-MHC, and cardiac troponin T, were studied using quantitative real-time polymerase chain reaction (qRT-PCR) and flow cytometry (FC). The half-maximal inhibition in the expression of these cardiac markers was analyzed from the dose-response curves. We also assessed the half-maximal inhibition (IC₅₀) in cardiac cells using propidium iodide dye (IC₅₀ PI) and by measuring disruption in the mitochondrial membrane potential (IC₅₀ MMP). We observed that the most sensitive marker was α-MHC in the case of both Dox and Pac, and the order of sensitivity of the various prediction assays was MMP > protein expression by FC > gene expression by qRT-PCR > cell viability by PI staining. The results could enrich the screening of drug-induced cardiotoxicity in vitro and propose disruption in MMP along with downregulation of α-MHC protein as a potential biomarker of predicting cardiotoxicity earlier during drug safety evaluation.

hiPSC Modeling of Inherited Cardiomyopathies

OPINION STATEMENT

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful new model system to study the basic mechanisms of inherited cardiomyopathies. hiPSC-CMs have been utilized to model several cardiovascular diseases, achieving the most success in the inherited arrhythmias, including long QT and Timothy syndromes (Moretti et al. N Engl J Med. 363:1397-409, 2010; Yazawa et al. Nature. 471:230-4, 2011) and arrhythmogenic right ventricular dysplasia (ARVD) (Ma et al. Eur Heart J. 34:1122-33, 2013). Recently, studies have applied hiPSC-CMs to the study of both dilated (DCM) (Sun et al. Sci Transl Med. 4:130ra47, 2012) and hypertrophic (HCM) cardiomyopathies (Lan et al. Cell Stem Cell. 12:101-13, 2013; Carvajal-Vergara et al. Nature. 465:808-12, 2010), providing new insights into basic mechanisms of disease. However, hiPSC-CMs do not recapitulate many of the structural and functional aspects of mature human cardiomyocytes, instead mirroring an immature - embryonic or fetal - phenotype. Much work remains in order to better understand these differences, as well as to develop methods to induce hiPSC-CMs into a fully mature phenotype. Despite these limitations, hiPSC-CMs represent the best current in vitro correlate of the human heart and an invaluable tool in the search for mechanisms underlying cardiomyopathy and for screening new pharmacologic therapies.

Screening drug-induced arrhythmia [corrected] using human induced pluripotent stem cell-derived cardiomyocytes and low-impedance microelectrode arrays

BACKGROUND

Drug-induced arrhythmia is one of the most common causes of drug development failure and withdrawal from market. This study tested whether human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) combined with a low-impedance microelectrode array (MEA) system could improve on industry-standard preclinical cardiotoxicity screening methods, identify the effects of well-characterized drugs, and elucidate underlying risk factors for drug-induced arrhythmia. hiPSC-CMs may be advantageous over immortalized cell lines because they possess similar functional characteristics as primary human cardiomyocytes and can be generated in unlimited quantities.

METHODS AND RESULTS

Pharmacological responses of beating embryoid bodies exposed to a comprehensive panel of drugs at 65 to 95 days postinduction were determined. Responses of hiPSC-CMs to drugs were qualitatively and quantitatively consistent with the reported drug effects in literature. Torsadogenic hERG blockers, such as sotalol and quinidine, produced statistically and physiologically significant effects, consistent with patch-clamp studies, on human embryonic stem cell-derived cardiomyocytes hESC-CMs. False-negative and false-positive hERG blockers were identified accurately. Consistent with published studies using animal models, early afterdepolarizations and ectopic beats were observed in 33% and 40% of embryoid bodies treated with sotalol and quinidine, respectively, compared with negligible early afterdepolarizations and ectopic beats in untreated controls.

CONCLUSIONS

We found that drug-induced arrhythmias can be recapitulated in hiPSC-CMs and documented with low impedance MEA. Our data indicate that the MEA/hiPSC-CM assay is a sensitive, robust, and efficient platform for testing drug effectiveness and for arrhythmia screening. This system may hold great potential for reducing drug development costs and may provide significant advantages over current industry standard assays that use immortalized cell lines or animal models.

Concise review: maturation phases of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPS-CM) may offer a number of advantages over previous cardiac models, however, questions of their immaturity complicate their adoption as a new in vitro model. hPS-CM differ from adult cardiomyocytes with respect to structure, proliferation, metabolism and electrophysiology, better approximating fetal cardiomyocytes. Time in culture appears to significantly impact phenotype, leading to what can be referred to as early and late hPS-CM. This work surveys the phenotype of hPS-CM, including structure, bioenergetics, sensitivity to damage, gene expression, and electrophysiology, including action potential, ion channels, and intracellular calcium stores, while contrasting fetal and adult CM with hPS-CM at early and late time points after onset of differentiation.

Induced pluripotent stem cells in cardiovascular drug discovery

The unexpected discovery that somatic cells can be reprogrammed to a pluripotent state yielding induced pluripotent stem cells has made it possible to produce cardiovascular cells exhibiting inherited traits and disorders. Use of these cells in high throughput analyses should broaden our insight into fundamental disease mechanisms and provide many benefits for patients, including new therapeutics and individually tailored therapies. Here we review recent progress in generating induced pluripotent stem cell-based models of cardiovascular disease and their multiple applications in drug development.

High throughput measurement of Ca²⁺ dynamics for drug risk assessment in human stem cell-derived cardiomyocytes by kinetic image cytometry

Current methods to measure physiological properties of cardiomyocytes and predict fatal arrhythmias that can cause sudden death, such as Torsade de Pointes, lack either the automation and throughput needed for early-stage drug discovery and/or have poor predictive value. To increase throughput and predictive power of in vitro assays, we developed kinetic imaging cytometry (KIC) for automated cell-by-cell analyses via intracellular fluorescence Ca²⁺ indicators. The KIC instrument simultaneously records and analyzes intracellular calcium concentration [Ca²⁺](i) at 30-ms resolution from hundreds of individual cells/well of 96-well plates in seconds, providing kinetic details not previously possible with well averaging technologies such as plate readers. Analyses of human embryonic stem cell and induced pluripotent stem cell-derived cardiomyocytes revealed effects of known cardiotoxic and arrhythmogenic drugs on kinetic parameters of Ca²⁺ dynamics, suggesting that KIC will aid in the assessment of cardiotoxic risk and in the elucidation of pathogenic mechanisms of heart disease associated with drugs treatment and/or genetic background.

Production of de novo cardiomyocytes: human pluripotent stem cell differentiation and direct reprogramming

Cardiovascular disease is a leading cause of death worldwide. The limited capability of heart tissue to regenerate has prompted methodological developments for creating de novo cardiomyocytes, both in vitro and in vivo. Beyond uses in cell replacement therapy, patient-specific cardiomyocytes may find applications in drug testing, drug discovery, and disease modeling. Recently, approaches for generating cardiomyocytes have expanded to encompass three major sources of starting cells: human pluripotent stem cells (hPSCs), adult heart-derived cardiac progenitor cells (CPCs), and reprogrammed fibroblasts. We discuss state-of-the-art methods for generating de novo cardiomyocytes from hPSCs and reprogrammed fibroblasts, highlighting potential applications and future challenges.

Primitive cardiac cells from human embryonic stem cells

Pluripotent stem cell-derived cardiomyocytes are currently being investigated for in vitro human heart models and as potential therapeutics for heart failure. In this study, we have developed a differentiation protocol that minimizes the need for specific human embryonic stem cell (hESC) line optimization. We first reduced the heterogeneity that exists within the starting population of bulk cultured hESCs by using cells adapted to single-cell passaging in a 2-dimensional (2D) culture format. Compared with bulk cultures, single-cell cultures comprised larger fractions of TG30(hi)/OCT4(hi) cells, corresponding to an increased expression of pluripotency markers OCT4 and NANOG, and reduced expression of early lineage-specific markers. A 2D temporal differentiation protocol was then developed, aimed at reducing the inherent heterogeneity and variability of embryoid body-based protocols, with induction of primitive streak cells using bone morphogenetic protein 4 and activin A, followed by cardiogenesis via inhibition of Wnt signaling using the small molecules IWP-4 or IWR-1. IWP-4 treatment resulted in a large percentage of cells expressing low amounts of cardiac myosin heavy chain and expression of early cardiac progenitor markers ISL1 and NKX2-5, thus indicating the production of large numbers of immature cardiomyocytes (~65,000/cm(2) or ~1.5 per input hESC). This protocol was shown to be effective in HES3, H9, and, to a lesser, extent, MEL1 hESC lines. In addition, we observed that IWR-1 induced predominantly atrial myosin light chain (MLC2a) expression, whereas IWP-4 induced expression of both atrial (MLC2a) and ventricular (MLC2v) forms. The intrinsic flexibility and scalability of this 2D protocol mean that the output population of primitive cardiomyocytes will be particularly accessible and useful for the investigation of molecular mechanisms driving terminal cardiomyocyte differentiation, and potentially for the future treatment of heart failure.

Pluripotent stem cell models of cardiac disease and their implication for drug discovery and development

Recent advances in pluripotent stem cell biology now make it possible to generate human cardiomyocytes in vitro from both healthy individuals and from patients with cardiac abnormalities. This offers unprecedented opportunities to study cardiac disease development 'in a dish' and establish novel platforms for drug discovery, either to prevent disease progression or to reverse it. In this review paper, we discuss some of the genetic diseases that affect the heart and illustrate how these new paradigms could assist our understanding of cardiac pathogenesis and aid in drug discovery. In particular, we highlight the limitations of other commonly used model systems in predicting the consequences of drug exposure on the human heart.

Present state and future perspectives of using pluripotent stem cells in toxicology research

The use of novel drugs and chemicals requires reliable data on their potential toxic effects on humans. Current test systems are mainly based on animals or in vitro–cultured animal-derived cells and do not or not sufficiently mirror the situation in humans. Therefore, in vitro models based on human pluripotent stem cells (hPSCs) have become an attractive alternative. The article summarizes the characteristics of pluripotent stem cells, including embryonic carcinoma and embryonic germ cells, and discusses the potential of pluripotent stem cells for safety pharmacology and toxicology. Special attention is directed to the potential application of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) for the assessment of developmental toxicology as well as cardio- and hepatotoxicology. With respect to embryotoxicology, recent achievements of the embryonic stem cell test (EST) are described and current limitations as well as prospects of embryotoxicity studies using pluripotent stem cells are discussed. Furthermore, recent efforts to establish hPSC-based cell models for testing cardio- and hepatotoxicity are presented. In this context, methods for differentiation and selection of cardiac and hepatic cells from hPSCs are summarized, requirements and implications with respect to the use of these cells in safety pharmacology and toxicology are presented, and future challenges and perspectives of using hPSCs are discussed.