Proarrhythmia Risk Assessment in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Using the Maestro MEA Platform

ELM2-SANT Domain-Containing Scaffolding Protein 1 Regulates Differentiation and Maturation of Cardiomyocytes Derived From Human-Induced Pluripotent Stem Cells

BACKGROUND

ELMSAN1 (ELM2-SANT domain-containing scaffolding protein 1) is a newly identified scaffolding protein of the MiDAC (mitotic deacetylase complex), playing a pivotal role in early embryonic development. Studies on Elmsan1 knockout mice showed that its absence results in embryo lethality and heart malformation. However, the precise function of ELMSAN1 in heart development and formation remains elusive. To study its potential role in cardiac lineage, we employed human-induced pluripotent stem cells (hiPSCs) to model early cardiogenesis and investigated the function of ELMSAN1.

METHODS AND RESULTS

We generated ELMSAN1-deficient hiPSCs through knockdown and knockout techniques. During cardiac differentiation, ELMSAN1 depletion inhibited pluripotency deactivation, decreased the expression of cardiac-specific markers, and reduced differentiation efficiency. The impaired expression of genes associated with contractile sarcomere structure, calcium handling, and ion channels was also noted in ELMSAN1-deficient cardiomyocytes derived from hiPSCs. Additionally, through a series of structural and functional assessments, we found that ELMSAN1-null hiPSC cardiomyocytes are immature, exhibiting incomplete sarcomere Z-line structure, decreased calcium handling, and impaired electrophysiological properties. Of note, we found that the cardiac-specific role of ELMSAN1 is likely associated with histone H3K27 acetylation level. The transcriptome analysis provided additional insights, indicating maturation reduction with the energy metabolism switch and restored cell proliferation in ELMSAN1 knockout cardiomyocytes.

CONCLUSIONS

In this study, we address the significance of the direct involvement of ELMSAN1 in the differentiation and maturation of hiPSC cardiomyocytes. We first report the impact of ELMSAN1 on multiple aspects of hiPSC cardiomyocyte generation, including cardiac differentiation, sarcomere formation, calcium handling, electrophysiological maturation, and proliferation.

Low-adhesion culture selection for human iPS cell-derived cardiomyocytes

Despite progress in generating cardiomyocytes from pluripotent stem cells, these populations often include non-contractile cells, necessitating cardiomyocyte selection for experimental purpose. This study explores a novel cardiomyocyte enrichment mechanism: low-adhesion culture selection. The cardiac cells derived from human induced pluripotent stem cells were subjected to a coating-free low-adhesion culture using bovine serum albumin and high molecular weight dextran sulfate. This approach effectively increased the population of cardiac troponin T-positive cardiomyocytes. Similar results were obtained with commercially available low-adhesion culture dishes. Subsequently, we accessed the practicality of selection of cardiomyocytes using this phenomenon by comparing it with established methods such as glucose-free culture and selection based on puromycin resistance genes. The cardiomyocytes enriched through low-adhesion culture selection maintained autonomous pulsation and responsiveness to beta-stimuli. Moreover, no significant differences were observed in the expression of genes related to subtype commitment and maturation when compared to other selection methods. In conclusion, cardiomyocytes derived from pluripotent stem cells were more low-adhesion culture resistant than their accompanying non-contractile cells, and low-adhesion culture is an alternative method for selection of pluripotent stem cell-derived cardiomyocytes.

Enhancing the functional maturity of hiPSC-derived cardiomyocytes to assess inotropic compounds

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) present an attractive in vitro platform to model safety and toxicity assessments-notably screening pro-arrhythmic compounds. The utility of the platform is stymied by a hiPSC-CM contractile apparatus and calcium handling mechanism akin to fetal phenotypes, evidenced by a negative force-frequency relationship. As such, hiPSC-CMs are limited in their ability to assess compounds that modulate contraction mediated by ionotropic compounds (Robertson, Tran, & George, 2013). To address this limitation, we utilize Agilent's xCELLigence Real-Time Cell Analyzer ePacer (RTCA ePacer) to enhance hiPSC-CM functional maturity. A continuous, progressive increase of electrical pacing is applied to hiPSC-CMs for up to 15 days. Contraction and viability are recorded by measurement of impedance using the RTCA ePacer. Our data confirms hiPSC-CMs inherently demonstrate a negative impedance amplitude frequency that is reversed after long-term electrical pacing. The data also indicate positive inotropic compounds increase the contractility of paced cardiomyocytes and calcium handling machinery is improved. Increased expression of genes critical to cardiomyocyte maturation further underscores the maturity of paced cells. In summary, our data suggest the application of continuous electrical pacing can functionally mature hiPSC-CMs, enhancing cellular response to positive inotropic compounds and improving calcium handling. SUMMARY: Long-term electrical stimulation of hiPSC-CM leads to functional maturation enabling predictive assessment of inotropic compounds.

Continuous contractile force and electrical signal recordings of 3D cardiac tissue utilizing conductive hydrogel pillars on a chip

Heart-on-chip emerged as a potential tool for cardiac tissue engineering, recapitulating key physiological cues in cardiac pathophysiology. Controlled electrical stimulation and the ability to provide directly analyzed functional readouts are essential to evaluate the physiology of cardiac tissues in the heart-on-chip platforms. In this scenario, a novel heart-on-chip platform integrating two soft conductive hydrogel pillar electrodes was presented here. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and cardiac fibroblasts were seeded into the apparatus to create 3D human cardiac tissues. The application of electrical stimulation improved functional performance by altering the dynamics of tissue structure and contractile development. The contractile forces that cardiac tissues contract was accurately measured through optical tracking of hydrogel pillar displacement. Furthermore, the conductive properties of hydrogel pillars allowed direct and non-invasive electrophysiology studies, enabling continuous monitoring of signal changes in real-time while dynamically administering drugs to the cardiac tissues, as shown by a chronotropic reaction to isoprenaline and verapamil. Overall, the platform for acquiring contractile force and electrophysiological signals in situ allowed monitoring the tissue development trend without interrupting the culture process and could have diverse applications in preclinical drug testing, disease modeling, and therapeutic discovery.

Does Enhanced Structural Maturity of hiPSC-Cardiomyocytes Better for the Detection of Drug-Induced Cardiotoxicity?

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) are currently used following the Comprehensive in vitro Proarrhythmic Assay (CiPA) initiative and subsequent recommendations in the International Council for Harmonization (ICH) guidelines S7B and E14 Q&A, to detect drug-induced cardiotoxicity. Monocultures of hiPSC-CMs are immature compared to adult ventricular cardiomyocytes and might lack the native heterogeneous nature. We investigated whether hiPSC-CMs, treated to enhance structural maturity, are superior in detecting drug-induced changes in electrophysiology and contraction. This was achieved by comparing hiPSC-CMs cultured in 2D monolayers on the current standard (fibronectin matrix, FM), to monolayers on a coating known to promote structural maturity (CELLvo™ Matrix Plus, MM). Functional assessment of electrophysiology and contractility was made using a high-throughput screening approach involving the use of both voltage-sensitive fluorescent dyes for electrophysiology and video technology for contractility. Using 11 reference drugs, the response of the monolayer of hiPSC-CMs was comparable in the two experimental settings (FM and MM). The data showed no functionally relevant differences in electrophysiology between hiPSC-CMs in standard FM and MM, while contractility read-outs indicated an altered amplitude of contraction but not changes in time course. RNA profiling for cardiac proteins shows similarity of the RNA expression across the two forms of 2D culture, suggesting that cell-to-matrix adhesion differences may explain account for differences in contraction amplitude. The results support the view that hiPSC-CMs in both 2D monolayer FM and MM that promote structural maturity are equally effective in detecting drug-induced electrophysiological effects in functional safety studies.

Precision medicine for long QT syndrome: patient-specific iPSCs take the lead

Long QT syndrome (LQTS) is a detrimental arrhythmia syndrome mainly caused by dysregulated expression or aberrant function of ion channels. The major clinical symptoms of ventricular arrhythmia, palpitations and syncope vary among LQTS subtypes. Susceptibility to malignant arrhythmia is a result of delayed repolarisation of the cardiomyocyte action potential (AP). There are 17 distinct subtypes of LQTS linked to 15 autosomal dominant genes with monogenic mutations. However, due to the presence of modifier genes, the identical mutation may result in completely different clinical manifestations in different carriers. In this review, we describe the roles of various ion channels in orchestrating APs and discuss molecular aetiologies of various types of LQTS. We highlight the usage of patient-specific induced pluripotent stem cell (iPSC) models in characterising fundamental mechanisms associated with LQTS. To mitigate the outcomes of LQTS, treatment strategies are initially focused on small molecules targeting ion channel activities. Next-generation treatments will reap the benefits from development of LQTS patient-specific iPSC platform, which is bolstered by the state-of-the-art technologies including whole-genome sequencing, CRISPR genome editing and machine learning. Deep phenotyping and high-throughput drug testing using LQTS patient-specific cardiomyocytes herald the upcoming precision medicine in LQTS.

In vitro circulation model driven by tissue-engineered dome-shaped cardiac tissue

The heart is an essential organ for animals and humans. With the increased availability of pluripotent stem cells, the use of three-dimensional cardiac tissues consisting of cultured cardiomyocytes in in vitro drug evaluation has been widely studied. Several models have been proposed for the realization of the pump function, which is the original function of the heart. However, there are no models that simulate the human circulatory system using cultured cardiac tissue. This study shows that a dome-shaped cardiac tissue fabricated using the cell sheet stacking technique can achieve a heart-like pump function and circulate culture medium, there by mimicking the human circulatory system. Firstly, human induced pluripotent stem cells were differentiated into autonomously beating cardiomyocytes, and cardiomyocyte cell sheets were created using temperature-responsive culture dishes. A cardiomyocyte sheet and a human dermal fibroblast sheet were stacked using a cell sheet manipulator. This two-layered cell sheet was then inflated to create a dome-shaped cardiac tissue with a base diameter of 8 mm. The volume of the dome-shaped cardiac tissue changed according to the autonomous beating. The stroke volume increased with the culture period and reached 21 ± 8.9 μL (n = 6) on day 21. It also responded to β-stimulant and extracellular calcium concentrations. Internal pressure fluctuations were also recorded under isovolumetric conditions by dedicated culture devices. The peak heights of pulsatile pressure were 0.33 ± 0.048 mmHg (n = 3) under a basal pressure of 0.5 mmHg on day 19. When the tissue was connected to a flow path that had check valves applied, it drove a directional flow with an average flow rate of approximately 1 μL/s. Furthermore, pressure-volume (P-V) diagrams were created from the simultaneous measurement of changes in pressure and volume under three conditions of fluidic resistance. In conclusion, this cardiac model can potentially be used for biological pumps that drive multi-organ chips and for more accurate in vitro drug evaluation using P-V diagrams.

A computational method for identifying an optimal combination of existing drugs to repair the action potentials of SQT1 ventricular myocytes

Mutations are known to cause perturbations in essential functional features of integral membrane proteins, including ion channels. Even restricted or point mutations can result in substantially changed properties of ion currents. The additive effect of these alterations for a specific ion channel can result in significantly changed properties of the action potential (AP). Both AP shortening and AP prolongation can result from known mutations, and the consequences can be life-threatening. Here, we present a computational method for identifying new drugs utilizing combinations of existing drugs. Based on the knowledge of theoretical effects of existing drugs on individual ion currents, our aim is to compute optimal combinations that can ‘repair’ the mutant AP waveforms so that the baseline AP-properties are restored. More specifically, we compute optimal, combined, drug concentrations such that the waveforms of the transmembrane potential and the cytosolic calcium concentration of the mutant cardiomyocytes (CMs) becomes as similar as possible to their wild type counterparts after the drug has been applied. In order to demonstrate the utility of this method, we address the question of computing an optimal drug for the short QT syndrome type 1 (SQT1). For the SQT1 mutation N588K, there are available data sets that describe the effect of various drugs on the mutated K⁺ channel. These published findings are the basis for our computational analysis which can identify optimal compounds in the sense that the AP of the mutant CMs resembles essential biomarkers of the wild type CMs. Using recently developed insights regarding electrophysiological properties among myocytes from different species, we compute optimal drug combinations for hiPSC-CMs, rabbit ventricular CMs and adult human ventricular CMs with the SQT1 mutation. Since the ‘composition’ of ion channels that form the AP is different for the three types of myocytes under consideration, so is the composition of the optimal drug.

Poly-pharmacology (using multiple drugs to treat disease) has been proposed for improving cardiac anti-arrhythmic therapy for at least two decades. However, the specific arrhythmia contexts in which polytherapy is likely to be both safe and effective have remained elusive. Type 1 short QT syndrome (SQT1) is a rare form of cardiac arrhythmia that results from mutations to the human Ether-á-go-go Related Gene (hERG) potassium channel. Functionally, these mutations are remarkably consistent in that they permit the channel to open earlier during each heart beat. While hundreds of compounds are known to inhibit hERG channels, the specific effect of SQT1 mutations that allows for early channel opening also limits the ability of most of those compounds to correct SQT1 dysfunction. Here, we have applied a suite of ventricular cardiomyocyte computational models to ask whether polytherapy may offer a more effective therapeutic strategy in SQT1, and if so, what the likely characteristics of that strategy are. Our analyses suggest that simultaneous induction of late sodium current and partial hERG blockade offers a promising strategy. While no activators of late sodium current have been clinically approved, several experimental compounds are available and may provide a basis for interrogating this strategy. The method presented here can be used to compute optimal drug combinations provided that the effect of each drug on every relevant ion channel is known.

Construction of chamber-specific engineered cardiac tissues in vitro with human iPSC-derived cardiomyocytes and human foreskin fibroblasts

Human-induced pluripotent stem cell (hiPSC) technology and directed cardiac differentiation technology can provide a continuous supply of cells for disease modeling, drug screening, and cell therapy. However, two-dimensional (2D) cells often fail to faithfully reflect the physiological structure and function of the heart. Considering the contractile function is the most critical and easy-to-understand function of cardiomyocytes, the engineered cardiac tissues (ECT) with mechanical properties may serve as an appropriate three-dimensional (3D) platform for drug evaluation. At present, there are various methods to generate ECTs, some of which are quite costly. In the present study, we proposed that human foreskin fibroblast (HFF) cells, as a cost-effective and accessible cell source, can promote the compaction and remodeling of ECTs. The HFFs derived ECTs displayed stable structural and functional characteristics with a higher performance-to-price ratio. Moreover, both ECTs made from atrial and ventricular cardiomyocytes showed an excellent drug response, demonstrating that the ECT with HFFs as an easy and reliable platform for drug evaluation.

A predictive in vitro risk assessment platform for pro-arrhythmic toxicity using human 3D cardiac microtissues

Cardiotoxicity of pharmaceutical drugs, industrial chemicals, and environmental toxicants can be severe, even life threatening, which necessitates a thorough evaluation of the human response to chemical compounds. Predicting risks for arrhythmia and sudden cardiac death accurately is critical for defining safety profiles. Currently available approaches have limitations including a focus on single select ion channels, the use of non-human species in vitro and in vivo, and limited direct physiological translation. We have advanced the robustness and reproducibility of in vitro platforms for assessing pro-arrhythmic cardiotoxicity using human induced pluripotent stem cell-derived cardiomyocytes and human cardiac fibroblasts in 3-dimensional microtissues. Using automated algorithms and statistical analyses of eight comprehensive evaluation metrics of cardiac action potentials, we demonstrate that tissue-engineered human cardiac microtissues respond appropriately to physiological stimuli and effectively differentiate between high-risk and low-risk compounds exhibiting blockade of the hERG channel (E4031 and ranolazine, respectively). Further, we show that the environmental endocrine disrupting chemical bisphenol-A (BPA) causes acute and sensitive disruption of human action potentials in the nanomolar range. Thus, this novel human 3D in vitro pro-arrhythmic risk assessment platform addresses critical needs in cardiotoxicity testing for both environmental and pharmaceutical compounds and can be leveraged to establish safe human exposure levels.

Computational prediction of drug response in short QT syndrome type 1 based on measurements of compound effect in stem cell-derived cardiomyocytes

Short QT (SQT) syndrome is a genetic cardiac disorder characterized by an abbreviated QT interval of the patient's electrocardiogram. The syndrome is associated with increased risk of arrhythmia and sudden cardiac death and can arise from a number of ion channel mutations. Cardiomyocytes derived from induced pluripotent stem cells generated from SQT patients (SQT hiPSC-CMs) provide promising platforms for testing pharmacological treatments directly in human cardiac cells exhibiting mutations specific for the syndrome. However, a difficulty is posed by the relative immaturity of hiPSC-CMs, with the possibility that drug effects observed in SQT hiPSC-CMs could be very different from the corresponding drug effect in vivo. In this paper, we apply a multistep computational procedure for translating measured drug effects from these cells to human QT response. This process first detects drug effects on individual ion channels based on measurements of SQT hiPSC-CMs and then uses these results to estimate the drug effects on ventricular action potentials and QT intervals of adult SQT patients. We find that the procedure is able to identify IC50 values in line with measured values for the four drugs quinidine, ivabradine, ajmaline and mexiletine. In addition, the predicted effect of quinidine on the adult QT interval is in good agreement with measured effects of quinidine for adult patients. Consequently, the computational procedure appears to be a useful tool for helping predicting adult drug responses from pure in vitro measurements of patient derived cell lines.

Micro-electrode channel guide (µECG) technology: an online method for continuous electrical recording in a human beating heart-on-chip

Cardiac toxicity still represents a common adverse outcome causing drug attrition and post-marketing withdrawal. The development of relevant in vitro models resembling the human heart recently opened the path towards a more accurate detection of drug-induced human cardiac toxicity early in the drug development process. Organs-on-chip (OoC) have been proposed as promising tools to recapitulate in vitro the key aspects of the in vivo cardiac physiology and to provide a means to directly analyze functional readouts. In this scenario, a new device capable of continuous monitoring of electrophysiological signals from functional in vitro human hearts-on-chip is here presented. The development of cardiac microtissues was achieved through a recently published method to control the mechanical environment, while the introduction of a technology consisting in micro-electrode coaxial guides (µECG) allowed to conduct direct and non-destructive electrophysiology studies. The generated human cardiac microtissues exhibited synchronous spontaneous beating, as demonstrated by multi-point and continuous acquisition of cardiac field potential, and expression of relevant genes encoding for cardiac ion-channels. A proof-of-concept pharmacological validation on 3 drugs proved the proposed model to potentially be a powerful tool to evaluate functional cardiac toxicity.

Identifying Drug Response by Combining Measurements of the Membrane Potential, the Cytosolic Calcium Concentration, and the Extracellular Potential in Microphysiological Systems

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) offer a new means to study and understand the human cardiac action potential, and can give key insight into how compounds may interact with important molecular pathways to destabilize the electrical function of the heart. Important features of the action potential can be readily measured using standard experimental techniques, such as the use of voltage sensitive dyes and fluorescent genetic reporters to estimate transmembrane potentials and cytosolic calcium concentrations. Using previously introduced computational procedures, such measurements can be used to estimate the current density of major ion channels present in hiPSC-CMs, and how compounds may alter their behavior. However, due to the limitations of optical recordings, resolving the sodium current remains difficult from these data. Here we show that if these optical measurements are complemented with observations of the extracellular potential using multi electrode arrays (MEAs), we can accurately estimate the current density of the sodium channels. This inversion of the sodium current relies on observation of the conduction velocity which turns out to be straightforwardly computed using measurements of extracellular waves across the electrodes. The combined data including the membrane potential, the cytosolic calcium concentration and the extracellular potential further opens up for the possibility of accurately estimating the effect of novel drugs applied to hiPSC-CMs.

Tumorigenic and Immunogenic Properties of Induced Pluripotent Stem Cells: a Promising Cancer Vaccine

Induced pluripotent stem cells (iPSCs) are mainly characterized by their unlimited proliferation abilities and potential to develop into almost any cell type. The creation of this technology has been of great interest to many scientific fields, especially regenerative biology. However, concerns about the safety of iPSC application in transplantation have arisen due to the tumorigenic and immunogenic properties of iPSCs. This review will briefly introduce the developing history of somatic reprogramming and applications of iPSC technology in regenerative medicine. In addition, the review will highlight two challenges to the efficient usage of iPSCs and the underlying mechanisms of these challenges. Finally, the review will discuss the expanding application of iPSC technology in cancer immunotherapy as a potential cancer vaccine and its advantages in auxiliary treatment compared with oncofetal antigen-based and embryonic stem cell (ESC)-based vaccines.

Inotropic assessment in engineered 3D cardiac tissues using human induced pluripotent stem cell-derived cardiomyocytes in the BiowireTM II platform

To develop therapeutics for cardiovascular disease, especially heart failure, translational models for assessing cardiac contractility are necessary for preclinical target validation and lead optimization. The availability of stem cell-derived cardiomyocytes (SC-CM) has generated a great opportunity in developing new in-vitro models for assessing cardiac contractility. However, the immature phenotype of SC-CM is a well-recognized limitation in inotropic evaluation, especially regarding the lack of or diminished positive inotropic response to β-adrenergic agonists. Recent development of 3D engineered cardiac tissues (ECTs) using human induced pluripotent stem cell derived-cardiomyocytes (hiPSC-CM) in the Biowire^TM II platform has shown improved maturation. To evaluate their suitability to detect drug-induced changes in cardiac contractility, positive inotropes with diverse mechanisms, including β-adrenergic agonists, PDE3 inhibitors, Ca²⁺-sensitizers, myosin and troponin activators, and an apelin receptor agonist, were tested blindly. A total of 8 compounds were evaluated, including dobutamine, milrinone, pimobendan, levosimendan, omecamtiv mecarbil, AMG1, AMG2, and pyr-apelin-13. Contractility was evaluated by analyzing the amplitude, velocity and duration of contraction and relaxation. All tested agents, except pyr-apelin-13, increased contractility by increasing the amplitude of contraction and velocity. In addition, myosin and troponin activators increase contraction duration. These results indicate that ECTs generated in the Biowire^TM II platform can identify inotropes with different mechanisms and provides a human-based in-vitro model for evaluating potential therapeutics.

Computational translation of drug effects from animal experiments to human ventricular myocytes

Using animal cells and tissues as precise measuring devices for developing new drugs presents a long-standing challenge for the pharmaceutical industry. Despite the very significant resources that continue to be dedicated to animal testing of new compounds, only qualitative results can be obtained. This often results in both false positives and false negatives. Here, we show how the effect of drugs applied to animal ventricular myocytes can be translated, quantitatively, to estimate a number of different effects of the same drug on human cardiomyocytes. We illustrate and validate our methodology by translating, from animal to human, the effect of dofetilide applied to dog cardiomyocytes, the effect of E-4031 applied to zebrafish cardiomyocytes, and, finally, the effect of sotalol applied to rabbit cardiomyocytes. In all cases, the accuracy of our quantitative estimates are demonstrated. Our computations reveal that, in principle, electrophysiological data from testing using animal ventricular myocytes, can give precise, quantitative estimates of the effect of new compounds on human cardiomyocytes.

An Industry Survey With Focus on Cardiovascular Safety Pharmacology Study Design and Data Interpretation

Introduction:

The Safety Pharmacology Society (SPS) conducted a membership survey to examine industry practices related mainly to cardiovascular (CV) safety pharmacology (SP).

Methods:

Questions addressed nonclinical study design, data analysis methods, drug-induced effects, and conventional and novel CV assays.

Results:

The most frequent therapeutic area targeted by drugs developed by the companies/institutions that employ survey responders was oncology. The most frequently observed drug-mediated effects included an increased heart rate, increased arterial blood pressure, hERG (IKr) block, decreased arterial blood pressure, decreased heart rate, QTc prolongation, and changes in body temperature. Broadly implemented study practices included Latin square crossover study design with n = 4 for nonrodent CV studies, statistical analysis of data (eg, analysis of variance), use of arrhythmia detection software, and the inclusion of data from all study animals when integrating SP studies into toxicology studies. Most responders frequently used individual animal housing conditions. Responders commonly evaluated drug effects on multiple ion channels, but in silico modeling methods were used much less frequently. Most responders rarely measured the J-Tpeak interval in CV studies. Uncertainties relative to Standard for Exchange of Nonclinical Data applications for data derived from CV SP studies were common. Although available, the use of human induced pluripotent stem cell cardiomyocytes remains rare. The respiratory SP study was rarely involved with identifying drug-induced functional issues. Responders indicated that the study-derived no observed effect level was more frequently determined than the no observed adverse effect level in CV SP studies; however, a large proportion of survey responders used neither.

Effects of Electrical Stimulation on hiPSC-CM Responses to Classic Ion Channel Blockers

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) hold great potential for personalized cardiac safety prediction, particularly for that of drug-induced proarrhythmia. However, hiPSC-CMs fire spontaneously and the variable beat rates of cardiomyocytes can be a confounding factor that interferes with data interpretation. Controlling beat rates with pacing may reduce batch and assay variations, enable evaluation of rate-dependent drug effects, and facilitate the comparison of results obtained from hiPSC-CMs with those from adult human cardiomyocytes. As electrical stimulation (E-pacing) of hiPSC-CMs has not been validated with high-throughput assays, herein, we compared the responses of hiPSC-CMs exposed with classic cardiac ion channel blockers under spontaneous beating and E-pacing conditions utilizing microelectrode array technology. We found that compared with spontaneously beating hiPSC-CMs, E-pacing: (1) reduced overall assay variabilities, (2) showed limited changes of field potential duration to pacemaker channel block, (3) revealed reverse rate dependence of multiple ion channel blockers on field potential duration, and (4) eliminated the effects of sodium channel block on depolarization spike amplitude and spike slope due to a software error in acquiring depolarization spike at cardiac pacing mode. Microelectrode array optogenetic pacing and current clamp recordings at various stimulation frequencies demonstrated rate-dependent block of sodium channels in hiPSC-CMs as reported in adult cardiomyocytes. In conclusion, pacing enabled more accurate rate- and concentration-dependent drug effect evaluations. Analyzing responses of hiPSC-CMs under both spontaneously beating and rate-controlled conditions may help better assess the effects of test compounds on cardiac electrophysiology and evaluate the value of the hiPSC-CM model.

Sex-Related Differences in Drug-Induced QT Prolongation and Torsades de Pointes: A New Model System with Human iPSC-CMs

Numerous drugs have the potential to prolong the QT interval and may cause accidental cardiac arrest (torsades de pointes [TdP]). Women are at a higher risk than men for experiencing drug-induced TdP. Due to the lack of appropriate tools, few studies have investigated whether genetic differences between men and women have any effects on drug-induced proarrhythmia. Sex hormones are believed to play a predominant role in the induction of TdP. Recently, progress in induced pluripotent stem cell (iPSC) technologies has made it possible to utilize human iPSC-derived cardiomyocytes (hiPSC-CMs) to investigate the influence of both genetics and sex hormones on cardiac ion channel gene expression and cardiomyocyte function. In this study, we investigated genetic and hormonal effects on sex differences of drug-induced QT prolongation and TdP with hiPSC-CMs from healthy male and female donors. We found that despite batch variations in beating rates and field potential durations (FPD), female-derived hiPSC-CMs showed steeper slopes of FPD to interspike interval ratios and were more sensitive to IKr blocker-induced FPD prolongation. 17β-estradiol increased FPD and 5α-dihydrotestosterone shortened FPD, but the addition of sex hormones had limited effect on the responses of hiPSC-CMs to IKr blockades. The differential expression of KCNE1 gene and reduced repolarization reserve in female-derived hiPSC-CMs compared with male-derived hiPSC-CMs may partially explain why females are more susceptible to proarrhythmias. Human iPSC-CMs can be a useful new model to study mechanisms of sex differences in cardiomyocyte repolarization processes and aid in the prediction of drug-induced proarrhythmias in both men and women.

Assessment of temporal functional changes and miRNA profiling of human iPSC-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been developed for cardiac cell transplantation studies more than a decade ago. In order to establish the hiPSC-CM-based platform as an autologous source for cardiac repair and drug toxicity, it is vital to understand the functionality of cardiomyocytes. Therefore, the goal of this study was to assess functional physiology, ultrastructural morphology, gene expression, and microRNA (miRNA) profiling at Wk-1, Wk-2 & Wk-4 in hiPSC-CMs in vitro. Functional assessment of hiPSC-CMs was determined by multielectrode array (MEA), Ca²⁺ cycling and particle image velocimetry (PIV). Results demonstrated that Wk-4 cardiomyocytes showed enhanced synchronization and maturation as compared to Wk-1 & Wk-2. Furthermore, ultrastructural morphology of Wk-4 cardiomyocytes closely mimicked the non-failing (NF) adult human heart. Additionally, modulation of cardiac genes, cell cycle genes, and pluripotency markers were analyzed by real-time PCR and compared with NF human heart. Increasing expression of fatty acid oxidation enzymes at Wk-4 supported the switching to lipid metabolism. Differential regulation of 12 miRNAs was observed in Wk-1 vs Wk-4 cardiomyocytes. Overall, this study demonstrated that Wk-4 hiPSC-CMs showed improved functional, metabolic and ultrastructural maturation, which could play a crucial role in optimizing timing for cell transplantation studies and drug screening.

Comparison of in vitro and computational experiments on the relation of inter-beat interval and duration of repolarization in a specific type of human induced pluripotent stem cell-derived cardiomyocytes

We compared a published computational model of the action potential of a specific type of human induced pluripotent stem cell -derived cardiomyocytes (hiPSC-CM) with experimental field potential data with regard to their inter-beat interval and the duration of repolarization. In particular, concomitant changes in inter-beat interval and duration of repolarization were calculated after reduction and/or augmentation of specific ion channel conductances as a surrogate for pharmacological manipulation. The observed mismatches between calculations and experimental data indicate that there is information missing about the cellular test system. Based on our results we hypothesize that, among other currents, the actual I_f (“funny current”) may deviate from the prediction. We show that replacement of the I_f formulation by alternative equations causes the model predictions to change qualitatively, however, none of the available formulations is actually achieving a satisfactory match with experimental data. We suggest a strategy to clarify whether the mismatch can be completely resolved at all using single cell models and, if yes, how this goal could be reached.

Pharmacological enhancement of repolarization reserve in human induced pluripotent stem cells derived cardiomyocytes

BACKGROUND

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for many applications including safety pharmacology. However, a deficiency or complete absence of several K⁺ currents suggests repolarization reserve is low in hiPSC-CMs. We determined whether a dual I_to and I_Kr activator can improve repolarization reserve in hiPSC-CMs resulting in a more electrophysiologically mature phenotype.

METHODS AND RESULTS

Human iPSC were maintained on growth factor and differentiated into the cardiac phenotype by addition of selective Wnt molecules. Current and voltage clamp recordings in single cells were made using patch electrodes. Extracellular field potentials were made using a microelectrode array on hiPSC monolayers. Action potential recordings from hiPSC-CMs following application of an I_Kr inhibitor resulted in depolarization of the membrane potential and prolongation of the APD. A flattening of the T-wave was noted on the pseudo-ECG. In contrast, application of the I_Kr and I_to agonist, NS3623, resulted in hyperpolarization of the membrane, slowing of the spontaneous rate and shortening of the APD. Voltage clamp recording showed a significant increase in I_Kr; no enhancement of I_to in hiPSC-CMs was noted. AP clamp experiments revealed that I_Kr plays a role in both phase 3 repolarization and phase 4 depolarization. mRNA analysis revealed that KCNH2 is abundantly expressed in hiPSC-CM, consistent with electrophysiological recordings.

CONCLUSIONS

Although NS3623 is a dual I_to and I_Kr activator in ventricular myocytes, application of this compound to hiPSC-CMs enhanced only I_Kr and no effect on I_to was noted. Our results suggest I_Kr enhancement can improve repolarization reserve in this cell type. The disconnect between a dramatic increase in I_to in adult myocytes versus the lack of effect in hiPSC-CMs suggest that the translation of pharmacological effects in hiPSC-CM to adult myocytes should be viewed with caution.

Cross-Site Reliability of Human Induced Pluripotent stem cell-derived Cardiomyocyte Based Safety Assays Using Microelectrode Arrays: Results from a Blinded CiPA Pilot Study

Recent in vitro cardiac safety studies demonstrate the ability of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to detect electrophysiologic effects of drugs. However, variability contributed by unique approaches, procedures, cell lines, and reagents across laboratories makes comparisons of results difficult, leading to uncertainty about the role of hiPSC-CMs in defining proarrhythmic risk in drug discovery and regulatory submissions. A blinded pilot study was conducted to evaluate the electrophysiologic effects of 8 well-characterized drugs on 4 cardiomyocyte lines using a standardized protocol across 3 microelectrode array platforms (18 individual studies). Drugs were selected to define assay sensitivity of prominent repolarizing currents (E-4031 for IKr, JNJ303 for IKs) and depolarizing currents (nifedipine for ICaL, mexiletine for INa) as well as drugs affecting multichannel block (flecainide, moxifloxacin, quinidine, and ranolazine). Inclusion criteria for final analysis was based on demonstrated sensitivity to IKr block (20% prolongation with E-4031) and L-type calcium current block (20% shortening with nifedipine). Despite differences in baseline characteristics across cardiomyocyte lines, multiple sites, and instrument platforms, 10 of 18 studies demonstrated adequate sensitivity to IKr block with E-4031 and ICaL block with nifedipine for inclusion in the final analysis. Concentration-dependent effects on repolarization were observed with this qualified data set consistent with known ionic mechanisms of single and multichannel blocking drugs. hiPSC-CMs can detect repolarization effects elicited by single and multichannel blocking drugs after defining pharmacologic sensitivity to IKr and ICaL block, supporting further validation efforts using hiPSC-CMs for cardiac safety studies.

Human-induced pluripotent stem cell-derived cardiomyocytes have limited IKs for repolarization reserve as revealed by specific KCNQ1/KCNE1 blocker

Objective

We investigated if there is I_Ks, and if there is repolarization reserve by I_Ks in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs).

Design

We used a specific KCNQ1/KCNE1 channel blocker, L-000768673, with an IC₅₀ of 9 nM, and four hERG-specific blockers, astemizole, cisapride, dofetilide, and E-4031 to investigate the issue.

Results

L-000768673 concentration-dependently prolonged feature point duration (FPD)―a surrogate signal of action potential duration―from 1 to 30 nM without pacing or paced at 1.2 Hz, resulting from I_Ks blockade in hiPSC-CMs. At higher concentrations, the effect of L-000768673 on I_Ks was mitigated by its effect on I_Ca-L, resulting in shortened FPD, reduced impedance amplitude, and increased beating rate at 1 µM and above, recapitulating the self-limiting properties of L-000768673 on action potentials. All four hERG-specific blockers prolonged FPD as expected. Co-application of L-000768673 at sub-threshold (0.1 and 0.3 nM) and threshold (1 nM) concentrations failed to synergistically enhance the effects of hERG blockers on FPD prolongation, rather it showed additive effects, inconsistent with the repolarization reserve role of I_Ks in mature human myocytes that enhanced I_Kr response, implying a difference between hiPSC-CMs used in this study and mature human cardiomyocytes.

Conclusion

There was I_Ks current in hiPSC-CMs, and blockade of I_Ks current caused prolongation of action potential of hiPSC-CMs. However, we could not demonstrate any synergistic effects on action potential duration prolongation of hiPSC-CMs by blocking hERG current and I_Ks current simultaneously, implying little or no repolarization reserve by I_Ks current in hiPSC-CMs used in this study.

Inhibitory effects of class I antiarrhythmic agents on Na+ and Ca2+ currents of human iPS cell-derived cardiomyocytes

INTRODUCTION

Human induced pluripotent stem cells (hiPSCs) harboring cardiac myosin heavy chain 6 promoter can differentiate into functional cardiomyocytes called "iCell cardiomyocytes" under blasticidin treatment condition. While iCell cardiomyocytes are expected to be used for predicting cardiotoxicity of drugs, their responses to antiarrhythmic agents remain to be elucidated. We first examined electrophysiological properties of iCell cardiomyocytes and mRNA levels of ion channels and Ca handling proteins, and then evaluated effects of class I antiarrhythmic agents on their Na+ and Ca2+ currents.

METHODS

iCell cardiomyocytes were cultured for 8-14 days (38-44 days after inducing their differentiation), according to the manufacturer's protocol. We determined their action potentials (APs) and sarcolemmal ionic currents using whole-cell patch clamp techniques, and also mRNA levels of ion channels and Ca handling proteins by RT-PCR. Effects of three class I antiarrhythmic agents, pirmenol, pilsicainide and mexiletine, on Na+ channel current (INa) and L-type Ca2+ channel current (ICaL) were evaluated by the whole-cell patch clamp.

RESULTS

iCell cardiomyocytes revealed sinoatrial node-type (18%), atrial-type (18%) and ventricular-type (64%) spontaneous APs. The maximum peak amplitudes of INa, ICaL, and rapidly-activating delayed-rectifier K+ channel current were -62.7 ± 13.7, -8.1 ± 0.7, and 3.0 ± 1.0 pA/pF, respectively. The hyperpolarization-activated cation channel and inward-rectifier K+ channel currents were observed, whereas the T-type Ca2+ channel or slowly-activating delayed-rectifier K+ channel current was not detectable. mRNAs of Nav1.5, Cav1.2, Kir2.1, HCN4, KvLQT1, hERG and SERCA2 were detected, while that of HCN1, minK or MiRP was not. The class Ia antiarrhythmic agent pirmenol and class Ic agent pilsicainide blocked INa in a concentration-dependent manner with IC50 of 0.87 ± 0.37 and 0.88 ± 0.16 μM, respectively; the class Ib agent mexiletine revealed weak INa block with a higher IC50 of 30.0 ± 3.0 μM. Pirmenol, pilsicainide and mexiletine blocked ICaL with IC50 of 2.00 ± 0.39, 7.7 ± 2.5 and 5.0 ± 0.1 μM, respectively.

CONCLUSIONS

In iCell cardiomyocytes, INa was blocked by the class Ia and Ic antiarrhythmic agents and ICaL was blocked by all the class I agents within the ranges of clinical concentrations, suggesting their cardiotoxicity.

Analysis of time-course drug response in rat cardiomyocytes cultured on a pattern of islands

We previously reported the kinetics analysis of cardiomyocyte beating using scanning electrochemical microscopy (SECM). In this study, a stage-top incubator and a capillary micropipette (MP) for delivering drugs were assembled with an SECM instrument, and the responses of rat cardiomyocytes were analyzed under a culture environment after drug stimulation. When adenosine triphosphate (ATP) was delivered to synchronously beating cardiomyocytes, the beating acceleration effect of ATP was counteracted by the synchronously beating network in the culture dish. In contrast, cardiomyocytes cultured on a pattern of islands in a culture dish showed fluctuations in the duration of beating upon the addition of ATP. We also examined the effect of the cardiotoxic agent astemizole on cardiomyocytes and successfully detected motion fluctuations. Therefore, drug stimulation via MPs and beating measurement by SECM are effective routes for the evaluation of drug candidates through the analysis of time-course beating motion fluctuations of the cardiomyocytes.

Human Cardiac Ventricular-Like Organoid Chambers and Tissue Strips From Pluripotent Stem Cells as a Two-Tiered Assay for Inotropic Responses

Traditional drug discovery is an inefficient process. Human pluripotent stem cell-derived cardiomyocytes can potentially fill the gap between animal and clinical studies, but conventional two-dimensional cultures inadequately recapitulate the human cardiac phenotype. Here, we systematically examined the pharmacological responses of engineered human ventricular-like cardiac tissue strips (hvCTS) and organoid chambers (hvCOC) to 25 cardioactive compounds covering various drug classes. While hvCTS effectively detected negative and null inotropic effects, the sensitivity to positive inotropes was modest. We further quantified the predictive capacity of hvCTS in a blinded screening, with accuracies for negative, positive, and null inotropic effects at 100%, 86%, and 80%, respectively. Interestingly, hvCOC, with a pro-maturation milieu that yields physiologically complex parameters, displayed enhanced positive inotropy. Based on these results, we propose a two-tiered screening system for avoiding false positives and negatives. Such an approach would facilitate drug discovery by leading to better overall success.

Modeling cardiac complexity: Advancements in myocardial models and analytical techniques for physiological investigation and therapeutic development in vitro

Cardiomyopathies, heart failure, and arrhythmias or conduction blockages impact millions of patients worldwide and are associated with marked increases in sudden cardiac death, decline in the quality of life, and the induction of secondary pathologies. These pathologies stem from dysfunction in the contractile or conductive properties of the cardiomyocyte, which as a result is a focus of fundamental investigation, drug discovery and therapeutic development, and tissue engineering. All of these foci require in vitro myocardial models and experimental techniques to probe the physiological functions of the cardiomyocyte. In this review, we provide a detailed exploration of different cell models, disease modeling strategies, and tissue constructs used from basic to translational research. Furthermore, we highlight recent advancements in imaging, electrophysiology, metabolic measurements, and mechanical and contractile characterization modalities that are advancing our understanding of cardiomyocyte physiology. With this review, we aim to both provide a biological framework for engineers contributing to the field and demonstrate the technical basis and limitations underlying physiological measurement modalities for biologists attempting to take advantage of these state-of-the-art techniques.

Application of human pluripotent stem cells and pluripotent stem cell-derived cellular models for assessing drug toxicity

Introduction: Human pluripotent stem cells (hPSCs) are capable of differentiating into all types of cells in the body and so provide suitable toxicology screening systems even for hard-to-obtain human tissues. Since hPSCs can also be generated from differentiated cells and current gene editing technologies allow targeted genome modifications, hPSCs can be applied for drug toxicity screening both in normal and disease-specific models. Targeted hPSC differentiation is still a challenge but cardiac, neuronal or liver cells, and complex cellular models are already available for practical applications. Areas covered: The authors review new gene-editing and cell-biology technologies to generate sensitive toxicity screening systems based on hPSCs. Then the authors present the use of undifferentiated hPSCs for examining embryonic toxicity and discuss drug screening possibilities in hPSC-derived models. The authors focus on the application of human cardiomyocytes, hepatocytes, and neural cultures in toxicity testing, and discuss the recent possibilities for drug screening in a 'body-on-a-chip' model system. Expert opinion: hPSCs and their genetically engineered derivatives provide new possibilities to investigate drug toxicity in human tissues. The key issues in this regard are still the selection and generation of proper model systems, and the interpretation of the results in understanding in vivo drug effects.

Blinded Contractility Analysis in hiPSC-Cardiomyocytes in Engineered Heart Tissue Format: Comparison With Human Atrial Trabeculae

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) may serve as a new assay for drug testing in a human context, but their validity particularly for the evaluation of inotropic drug effects remains unclear. In this blinded analysis, we compared the effects of 10 indicator compounds with known inotropic effects in electrically stimulated (1.5 Hz) hiPSC-CM-derived 3-dimensional engineered heart tissue (EHT) and human atrial trabeculae (hAT). Human EHTs were prepared from iCell hiPSC-CM, hAT obtained at routine heart surgery. Mean intra-batch variation coefficient in baseline force measurement was 17% for EHT and 49% for hAT. The PDE-inhibitor milrinone did not affect EHT contraction force, but increased force in hAT. Citalopram (selective serotonin reuptake inhibitor), nifedipine (LTCC-blocker) and lidocaine (Na+ channel-blocker) had negative inotropic effects on EHT and hAT. Formoterol (beta-2 agonist) had positive lusitropic but no inotropic effect in EHT, and positive clinotropic, lusitropic, and inotropic effects in hAT. Tacrolimus (calcineurin-inhibitor) had a negative inotropic effect in EHTs, but no effect in hAT. Digoxin (Na+-K+-ATPase-inhibitor) showed a positive inotropic effect only in EHTs, but no effect in hAT probably due to short incubation time. Ryanodine (ryanodine receptor-inhibitor) reduced contraction force in both models. Rolipram and acetylsalicylic acid showed noninterpretable results in hAT. Contraction amplitude and kinetics were more stable over time and less variable in hiPSC-EHTs than hAT. HiPSC-EHT faithfully detected cAMP-dependent and -independent positive and negative inotropic effects, but limited beta-2 adrenergic or PDE3 effects, compatible with an immature CM phenotype.

Evaluation of Batch Variations in Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes from 2 Major Suppliers

Drug-induced proarrhythmia is a major safety issue in drug development. Developing sensitive in vitro assays that can predict drug-induced cardiotoxicity in humans has been a challenge of toxicology research for decades. Recently, induced pluripotent stem cell-derived human cardiomyocytes (iPSC-hCMs) have become a promising model because they largely replicate the electrophysiological behavior of human ventricular cardiomyocytes. Patient-specific iPSC-hCMs have been proposed for personalized cardiac drug selection and adverse drug response prediction; however, many procedures are involved in cardiomyocytes differentiation and purification process, which may result in large line-to-line and batch-to-batch variations. Here, we examined the purity, cardiac ion channel gene expression profile, and electrophysiological response of 3 batches of iPSC-hCMs from each of 2 major cell suppliers. We found that iPSC-hCMs from both vendors had similar purities. Most of the cardiac ion channel genes were expressed uniformly among different batches of iCells, while larger variations were found in Cor.4U cells, particularly in the expression of CACNA1C, KCND2, and KCNA5 genes, which could underlie the differences in baseline beating rate (BR) and field potential duration (FPD) measurements. Although, in general, the electrophysiological responses of different batches of cells to Na+, Ca2+, Ikr, and Iks channel blockers were similar, with Ikr blocker-induced proarrhythmia, the sensitivities were depended on baseline BR and FPD values: cells that beat slower had longer FPD and greater sensitivity to drug-induced proarrhythmia. Careful evaluation of the performance of iPSC-hCMs and methods of data analysis is warranted for shaping regulatory standards in qualifying iPSC-hCMs for drug safety testing.

Predicting cardiac safety using human induced pluripotent stem cell-derived cardiomyocytes combined with multi-electrode array (MEA) technology: A conference report

Safety pharmacology studies that evaluate drug candidates for potential cardiovascular liabilities remain a critical component of drug development. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have recently emerged as a new and promising tool for preclinical hazard identification and risk assessment of drugs. Recently, Pluriomics organized its first User Meeting entitled 'Combining Pluricyte® Cardiomyocytes & MEA for Safety Pharmacology applications', consisting of scientific sessions and live demonstrations, which provided the opportunity to discuss the application of hiPSC-CMs (Pluricyte® Cardiomyocytes) in cardiac safety assessment to support early decision making in safety pharmacology. This report summarizes the outline and outcome of this Pluriomics User Meeting, which took place on November 24-25, 2016 in Leiden (The Netherlands). To reflect the content of the communications presented at this meeting we have cited key scientific articles and reviews.

Response of human induced pluripotent stem cell-derived cardiomyocytes to several pharmacological agents when intrinsic syncytial pacing is overcome by acute external stimulation

We challenged human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) syncytia, mainly, CDI iCells with several classes of well-characterized pharmacological agents (including hERG blocker, Nav1.5 blocker, Cav1.2 blocker and opener, β-adrenergic agonist, and I_f blocker) under pacing conditions, utilizing the Cardio-ECR instrument, a non-invasive platform featuring simultaneous and continuous measurement of synchronized beating rate and contractility (both signals were acquired simultaneously and well aligned). We found that: 1) with increasing acute stimulation rates (no pacing; 1, 1.5, and 2Hz), beat interval was gradually shortened mainly in the relaxation phase of each beat cycle; 2) typical responses of iCells hiPSC-CMs to all tested pharmacological agents were either attenuated or even eliminated by pacing, in a concentration- and stimulation rate-dependent manner; and 3) when iCells were influenced by pharmacological agents and cannot follow pacing rates, they still beat regularly at exactly 1/2 or 1/3 of pacing rates. We concluded that when intrinsic syncytial pacing was overcome by faster, external stimulations, beat intervals of hiPSC-CMs were mainly shortened in the relaxation phase, instead of proportionally in each beat cycle, with increasing pacing rates. In addition, in response to pharmacological agents upon pacing, hiPSC-CMs exhibited distinct patterns of refractoriness, manifested by skipped beats in pacing-rate dependent manner, and attenuation (or even abolition) of the typical response evoked under spontaneous beating.

Action Potential Recording and Pro-arrhythmia Risk Analysis in Human Ventricular Trabeculae

To assess drug-induced pro-arrhythmic risk, especially Torsades de Pointe (TdP), new models have been proposed, such as in-silico modeling of ventricular action potential (AP) and stem cell-derived cardiomyocytes (SC-CMs). Previously we evaluated the electrophysiological profile of 15 reference drugs in hESC-CMs and hiPSC-CMs for their effects on intracellular AP and extracellular field potential, respectively. Our findings indicated that SC-CMs exhibited immature phenotype and had the propensity to generate false positives in predicting TdP risk. To expand our knowledge with mature human cardiac tissues for drug-induced pro-arrhythmic risk assessment, human ventricular trabeculae (hVT) from ethically consented organ donors were used to evaluate the effects of the same 15 drugs (8 torsadogenic, 5 non-torsadogenic, and 2 discovery molecules) on AP parameters at 1 and 2 Hz. Each drug was tested blindly with 4 concentrations in duplicate trabeculae from 2 hearts. To identify the pro-arrhythmic risk of each drug, a pro-arrhythmic score was calculated as the weighted sum of percent drug-induced changes compared to baseline in various AP parameters, including AP duration and recognized pro-arrhythmia predictors such as triangulation, beat-to-beat variability and incidence of early-afterdepolarizations, at each concentration. In addition, to understand the translation of this preclinical hVT AP-based model to clinical studies, a ratio that relates each testing concentration to the human therapeutic unbound Cmax (Cmax) was calculated. At a ratio of 10, for the 8 torsadogenic drugs, 7 were correctly identified by the pro-arrhythmic score; 1 was mislabeled. For the 5 non-torsadogenic drugs, 4 were correctly identified as safe; 1 was mislabeled. Calculation of sensitivity, specificity, positive predictive value, and negative predictive value indicated excellent performance. For example, at a ratio of 10, scores for sensitivity, specificity, positive predictive value and negative predictive values were 0.88, 0.8, 0.88 and 0.8, respectively. Thus, the hVT AP-based model combined with the integrated analysis of pro-arrhythmic score can differentiate between torsadogenic and non-torsadogenic drugs, and has a greater predictive performance when compared to human SC-CM models.

Adult Human Primary Cardiomyocyte-Based Model for the Simultaneous Prediction of Drug-Induced Inotropic and Pro-arrhythmia Risk

Cardiac safety remains the leading cause of drug development discontinuation. We developed a human cardiomyocyte-based model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic and pro-arrhythmia risk.

Methods: Adult human primary cardiomyocytes from ethically consented organ donors were used to measure contractility transients. We used measures of changes in contractility parameters as markers to infer both drug-induced inotropic effect (sarcomere shortening) and pro-arrhythmia (aftercontraction, AC); contractility escape (CE); time to 90% relaxation (TR90). We addressed the clinical relevance of this approach by evaluating the effects of 23 torsadogenic and 10 non-torsadogenic drugs. Each drug was tested separately at four multiples of the free effective therapeutic plasma concentration (fETPC).

Results: Human cardiomyocyte-based model differentiated between torsadogenic and non-torsadogenic drugs. For example, dofetilide, a torsadogenic drug, caused ACs and increased TR90 starting at 10-fold the fETPC, while CE events were observed at the highest multiple of fETPC (100-fold). Verapamil, a non-torsadogenic drug, did not change TR90 and induced no AC or CE up to the highest multiple of fETPCs tested in this study (222-fold). When drug pro-arrhythmic activity was evaluated at 10-fold of the fETPC, AC parameter had excellent assay sensitivity and specificity values of 96 and 100%, respectively. This high predictivity supports the translational safety potential of this preparation and of the selected marker. The data demonstrate that human cardiomyocytes could also identify drugs associated with inotropic effects. hERG channel blockers, like dofetilide, had no effects on sarcomere shortening, while multi-ion channel blockers, like verapamil, inhibited sarcomere shortening.

Conclusions: Isolated adult human primary cardiomyocytes can simultaneously predict risks associated with inotropic activity and pro-arrhythmia and may enable the generation of reliable and predictive data for assessing human cardiotoxicity at an early stage in drug discovery.

Frequency-Dependent Multi-Well Cardiotoxicity Screening Enabled by Optogenetic Stimulation

Side effects on cardiac ion channels causing lethal arrhythmias are one major reason for drug withdrawals from the market. Field potential (FP) recording from cardiomyocytes, is a well-suited tool to assess such cardiotoxic effects of drug candidates in preclinical drug development, but it is currently limited to the spontaneous beating of the cardiomyocytes and manual analysis. Herein, we present a novel optogenetic cardiotoxicity screening system suited for the parallel automated frequency-dependent analysis of drug effects on FP recorded from human-induced pluripotent stem cell-derived cardiomyocytes. For the expression of the light-sensitive cation channel Channelrhodopsin-2, we optimised protocols using virus transduction or transient mRNA transfection. Optical stimulation was performed with a new light-emitting diode lid for a 96-well FP recording system. This enabled reliable pacing at physiologically relevant heart rates and robust recording of FP. Thereby we detected rate-dependent effects of drugs on Na⁺, Ca2+ and K⁺ channel function indicated by FP prolongation, FP shortening and the slowing of the FP downstroke component, as well as generation of afterdepolarisations. Taken together, we present a scalable approach for preclinical frequency-dependent screening of drug effects on cardiac electrophysiology. Importantly, we show that the recording and analysis can be fully automated and the technology is readily available using commercial products.

Ajmaline blocks INa and IKr without eliciting differences between Brugada syndrome patient and control human pluripotent stem cell-derived cardiac clusters

The class Ia anti-arrhythmic drug ajmaline is used clinically to unmask latent type I ECG in Brugada syndrome (BrS) patients, although its mode of action is poorly characterised.

Our aims were to identify ajmaline's mode of action in human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs), and establish a simple BrS hiPSC platform to test whether differences in ajmaline response could be determined between BrS patients and controls.

Control hiPSCs were differentiated into spontaneously contracting cardiac clusters. It was found using multi electrode array (MEA) that ajmaline treatment significantly lengthened cluster activation-recovery interval. Patch clamping of single CMs isolated from clusters revealed that ajmaline can block both I_Na and I_Kr.

Following generation of hiPSC lines from BrS patients (absent of pathogenic SCN5A sodium channel mutations), analysis of hiPSC-CMs from patients and controls revealed that differentiation and action potential parameters were similar. Comparison of cardiac clusters by MEA showed that ajmaline lengthened activation-recovery interval consistently across all lines.

We conclude that ajmaline can block both depolarisation and repolarisation of hiPSC-CMs at the cellular level, but that a more refined integrated tissue model may be necessary to elicit differences in its effect between BrS patients and controls.

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hiPSC lines generated and differentiated from BrS patients lacking SCN5A mutations

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Ajmaline lengthens the activation-recovery interval of hPSC cardiac clusters

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Ajmaline effect consistent between BrS patient and control hPSC cardiac clusters

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Patch clamp analysis of hiPSC-CMs reveals ajmaline blocks both I_Na and I_Kr

In silico assessment of the effects of various compounds in MEA/hiPSC-CM assays: Modeling and numerical simulations

We propose a mathematical approach for the analysis of drugs effects on the electrical activity of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) based on multi-electrode array (MEA) experiments. Our goal is to produce an in silico tool able to simulate drugs action in MEA/hiPSC-CM assays. The mathematical model takes into account the geometry of the MEA and the electrodes' properties. The electrical activity of the stem cells at the ion-channel level is governed by a system of ordinary differential equations (ODEs). The ODEs are coupled to the bidomain equations, describing the propagation of the electrical wave in the stem cells preparation. The field potential (FP) measured by the MEA is modeled by the extracellular potential of the bidomain equations. First, we propose a strategy allowing us to generate a field potential in good agreement with the experimental data. We show that we are able to reproduce realistic field potentials by introducing different scenarios of heterogeneity in the action potential. This heterogeneity reflects the differentiation atria/ventricles and the age of the cells. Second, we introduce a drug/ion channels interaction based on a pore block model. We conduct different simulations for five drugs (mexiletine, dofetilide, bepridil, ivabradine and BayK). We compare the simulation results with the field potential collected from experimental measurements. Different biomarkers computed on the FP are considered, including depolarization amplitude, repolarization delay, repolarization amplitude and depolarization-repolarization segment. The simulation results show that the model reflect properly the main effects of these drugs on the FP.

Proarrhythmic risk assessment using conventional and new in vitro assays

Drug-induced QT prolongation is a major safety issue in the drug discovery process. This study was conducted to assess the electrophysiological responses of four substances using established preclinical assays usually used in regulatory studies (hERG channel or Purkinje fiber action potential) and a new assay (human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs)-field potential). After acute exposure, moxifloxacin and dofetilide concentration-dependently decreased I_Kr amplitude (IC₅₀ values: 102 μM and 40 nM, respectively) and lengthened action potential (100 μM moxifloxacin: +23% and 10 nM dofetilide: +18%) and field potential (300 μM moxifloxacin: +76% and 10 nM dofetilide: +38%) durations. Dofetilide starting from 30 nM induced arrhythmia in hiPSC-CMs. Overnight application of pentamidine (10 and 100 μM) and arsenic (1 and 10 μM) decreased I_Kr, whereas they were devoid of effects after acute application. Long-term pentamidine incubation showed a time- and concentration-dependent effect on field potential duration. In conclusion, our data suggest that hiPSC-CMs represent a fully functional cellular electrophysiology model which may significantly improve the predictive validity of in vitro safety studies. Thereafter, lead candidates may be further investigated in patch-clamp assays for mechanistic studies on individual ionic channels or in a multicellular Purkinje fiber preparation for confirmatory studies on cardiac conduction.

Proarrhythmia liability assessment and the comprehensive in vitro Proarrhythmia Assay (CiPA): An industry survey on current practice

INTRODUCTION

The Safety Pharmacology Society (SPS) has conducted a survey of its membership to identify industry practices related to testing considered in the Comprehensive In vitro Proarrhythmia Assay (CiPA).

METHODS

Survey topics included nonclinical approaches to address proarrhythmia issues, conduct of in silico studies, in vitro ion channel testing methods used, drugs used as positive controls during the conduct of cardiac ion channel studies, types of arrhythmias observed in non-clinical studies and use of the anticipated CiPA ion channel assay.

RESULTS

In silico studies were used to evaluate effects on ventricular action potentials by only 15% of responders. In vitro assays were used mostly to assess QT prolongation (95%), cardiac Ca²⁺ and Na⁺ channel blockade (82%) and QT shortening or QRS prolongation (53%). For de-risking of candidate drugs for proarrhythmia, those assays most relevant to CiPA including cell lines stably expressing ion channels used to determine potency of drug block were most frequently used (89%) and human stem cell-derived or induced pluripotent stem cell cardiomyocytes (46%). Those in vivo assays related to general proarrhythmia derisking include ECG recording using implanted telemetry technology (88%), jacketed external telemetry (62%) and anesthetized animal models (53%). While the CiPA initiative was supported by 92% of responders, there may be some disconnect between current practice and future expectations, as explained.

DISCUSSION

Proarrhythmia liability assessment in drug development presently includes study types consistent with CiPA. It is anticipated that CiPA will develop into a workable solution to the concern that proarrhythmia liability testing remains suboptimal.

Induced pluripotent stem cell technology: a decade of progress

Since the advent of induced pluripotent stem cell (iPSC) technology a decade ago, enormous progress has been made in stem cell biology and regenerative medicine. Human iPSCs have been widely used for disease modelling, drug discovery and cell therapy development. Novel pathological mechanisms have been elucidated, new drugs originating from iPSC screens are in the pipeline and the first clinical trial using human iPSC-derived products has been initiated. In particular, the combination of human iPSC technology with recent developments in gene editing and 3D organoids makes iPSC-based platforms even more powerful in each area of their application, including precision medicine. In this Review, we discuss the progress in applications of iPSC technology that are particularly relevant to drug discovery and regenerative medicine, and consider the remaining challenges and the emerging opportunities in the field.