Predicting drug-induced changes in QT interval and arrhythmias: QT-shortening drugs point to gaps in the ICHS7B Guidelines

Congenital short QT syndrome: A review focused on electrocardiographic features

Congenital short QT syndrome is a very low prevalence inherited primary arrhythmia syndrome first reported in 2000 by Gussak et al., who described two families with a short QT interval, syncope, and sudden cardiac death. In 2004, Ramon Brugada et al. identified the first genetic type of this entity. To date, a total of nine genotypes have been described. The diagnosis is easy from the electrocardiogram (ECG), not only due to the short QT duration, but also based on other aspects covered in this review. During 24-h Holter monitoring, paroxysmal atrial fibrillation spontaneously converting to sinus rhythm may be found. Even though the T wave may appear symmetric on the ECG, the T loop of the vectorcardiogram confirms that the T wave is constantly asymmetric due to the presence of dashes closer to each other in the efferent branch. In this review, we also describe the minus-plus T wave sign that we have described in a previously published article. In addition to congenital causes, we briefly highlight the existence of numerous acquired causes of short QT interval.

Effects of nicorandil on QT prolongation and myocardial damage caused by citalopram in rats

Citalopram is a selective serotonin re-uptake inhibitor (SSRI) antidepressant; it exhibits the greatest cardiotoxic effect among SSRIs. Citalopram can cause drug-induced long QT syndrome (LQTS) and ventricular arrhythmias. We investigated the protective effect of nicorandil, a selective mitochondrial KATP (mito-KATP) channel opener, on LQTS and myocardial damage caused by citalopram in male rats. In a preliminary study, we determined that the minimum citalopram dose that prolonged the QT interval was 102 mg/kg injected intraperitoneally. For the main study, rats were divided randomly into five experimental groups: untreated control, normal saline + citalopram, nicorandil + citalopram, 5-hydroxydecanoate (5-HD) + citalopram, 5-HD + nicorandil + citalopram. Biochemical and histologic data from blood and heart tissue samples from six untreated control rats were evaluated. Electrocardiographic parameters including QRS duration, QT interval, corrected QT interval (QTc) and heart rate (HR) were assessed, and biochemical parameters including malondialdehyde, reduced glutathione, glutathione peroxidase, superoxide dismutase were measured. We also performed histomorphologic and immunohistochemical examination of heart tissue. Citalopram prolonged QT-QTc intervals significantly and increased significantly the histomorphologic score and proportion of apoptotic cells, but produced no differences in the oxidant and antioxidant parameters. Nicorandil did not prevent citalopram induced QT-QTc interval prolongation and produced no significant changes in oxidant and antioxidant parameters; however, it did reduce histologic damage and apoptosis caused by citalopram.

Index of cardiac-electrophysiological balance in relapsing-remitting multiple sclerosis patients treated with fingolimod

BACKGROUND

Fingolimod is indicated for the treatment of relapsing-remitting multiple sclerosis (RRMS) and also targets cardiovascular system due to receptors on cardiomyocytes. Results of previous studies are controversial for the effect of fingolimod in terms of ventricular arrhythmias. Index of cardio-electrophysiological balance (iCEB) is a risk marker for predicting malignant ventricular arrhythmia. There is no evidence on the effect of fingolimod on iCEB in patients with relapsing-remitting multiple sclerosis (RRMS). The aim of this study was to evaluate iCEB in patients with RRMS treated with fingolimod .

METHODS

A total of 86 patients with RRMS treated with fingolimod were included in the study. All patients underwent a standard 12-lead surface electrocardiogram at initiation of treatment and 6 h after treatment. Heart rate, RR interval, QRS duration, QT, QTc (heart rate corrected QT), T wave peak-to-end (Tp-e) interval, Tp-e/QT, Tp-e/QTc, iCEB (QT/QRS) and iCEBc (QTc/QRS) ratios were calculated from the electrocardiogram. QT correction for heart rate was performed using both the Bazett and Fridericia formulas. Pre-treatment and post-treatment values were compared.

RESULTS

Heart rate was significantly lower after fingolimod treatment (p< 0.001). While the post-treatment values of RR and QT intervals were significantly longer (p< 0.001) and post-treatment iCEB was higher (median [Q1-Q3], 4.23 [3.95-4.50] vs 4.53 [4.18-5.14]; p< 0.001), it was found that there was no statistically significant change in iCEB and other study parameters derived using QT after correcting for heart rate using both of two formulas.

CONCLUSIONS

In this study, it was found that fingolimod did not statistically significantly change any of the heart rate-corrected ventricular repolarization parameters, including iCEBc, and it is safe in terms of ventricular arrhythmia.

Effect of the selective mitochondrial KATP channel opener nicorandil on the QT prolongation and myocardial damage induced by amitriptyline in rats

OBJECTIVES

The aim of this study is to evaluate the protective effect of nicorandil, a selective mitochondrial KATP channel opener, on QT prolongation and myocardial damage induced by amitriptyline.

METHODS

The dose of amitriptyline (intraperitoneal, i.p.) that prolong the QT interval was found 75 mg/kg. Rats were randomized into five groups the control group, amitriptyline group, nicorandil (selective mitochondrial KATP channel opener, 3 mg/kg i.p.) + amitriptyline group, 5-hdyroxydecanoate (5-HD, selective mitochondrial KATP channel blocker, 10 mg/kg i.p.) + amitriptyline group and 5-HD + nicorandil + amitriptyline group. Cardiac parameters, biochemical and histomorphological/immunohistochemical examinations were evaluated. p < 0.05 was accepted as statistically significant.

KEY FINDINGS

Amitriptyline caused statistically significant prolongation of QRS duration, QT interval and QTc interval (p < 0.05). It also caused changes in tissue oxidant (increase in malondialdehyde)/anti-oxidant (decrease in glutathione peroxidase) parameters (p < 0.05), myocardial damage and apoptosis (p < 0.01 and p < 0.001). While nicorandil administration prevented amitriptyline-induced QRS, QT, QTc prolongation (p < 0.05), myocardial damage and apoptosis (p < 0.05), it did not affect the changes in oxidative parameters (p > 0.05).

CONCLUSIONS

Our results suggest that nicorandil, a selective mitochondrial KATP channel opener, plays a protective role in amitriptyline-induced QT prolongation and myocardial damage. Mitochondrial KATP channel opening and anti-apoptotic effects may play a role in the cardioprotective effect of nicorandil.

Pharmacological activation of the hERG K + channel for the management of the long QT syndrome: A review

In the human heart, the rapid delayed rectifier K⁺ current (I_Kr) contributes significantly to ventricular action potential (AP) repolarization and to set the duration of the QT interval of the surface electrocardiogram (ECG). The pore‐forming (α) subunit of the I_Kr channel is encoded by KCNH2 or human ether‐à‐go‐go‐related gene 1 (hERG1). Impairment of hERG function through either gene mutation (congenital) or pharmacological blockade by diverse drugs in clinical use (acquired) can cause a prolongation of the AP duration (APD) reflected onto the surface ECG as a prolonged QT interval or Long QT Syndrome (LQTS). LQTS can increase the risk of triggered activity of ventricular cardiomyocytes and associated life‐threatening arrhythmia. Current treatments all focus on reducing the incidence of arrhythmia or terminating it after its onset but there is to date no prophylactic treatment for the pharmacological management of LQTS. A new class of hERG modulators (agonists) have been suggested through direct interaction with the hERG channel to shorten the action potential duration (APD) and/or increase the postrepolarisation refractoriness period (PRRP) of ventricular cardiomyocytes protecting thereby against triggered activity and associated arrhythmia. Although promising drug candidates, there remain major obstacles to their clinical development. The aim of this review is to summarize the latest advances as well as the limitations of this proposed pharmacotherapy.

Identifying Acute Cardiac Hazard in Early Drug Discovery Using a Calcium Transient High-Throughput Assay in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Introduction: Early identification of cardiac risk is essential for reducing late-stage attrition in drug development. We adapted the previously published cardiac hazard risk-scoring system using a calcium transient assay in human stem cell-derived CMs for the identification of cardiac risks recorded from the new hiPSC-CM line and investigated its predictivity and translational value based on the screening of a large number of reference and proprietary compounds. Methods: Evaluation of 55 reference drugs provided the translation of various pharmacological effects into a single hazard label (no, low, high, or very high hazard) using a Ca²⁺-sensitive fluorescent dye assay recorded by -by FDSS/µCell Functional Drug Screening System (Hamamatsu on hiPSC-CM line (FCDI iCell Cardiomyocytes²). Results: Application of the adapted hazard scoring system in the Ca²⁺ transient assay, using a second hiPS-CM line, provided comparable scoring results and predictivity of hazard, to the previously published scoring approach, with different pharmacological drug classes, as well as screening new chemical entities (NCE's) using a single hazard label from four different scoring levels (no, low, high, or very high hazard). The scoring system results also showed minimal variability across three different lots of hiPSC-CMs, indicating good reproducibility of the cell line. The predictivity values (sensitivity and specificity) for drug-induced acute cardiac risk for QT-interval prolongation and Torsade de pointes (TdPs) were >95% and statistical modeling confirmed the prediction of proarrhythmic risk. The outcomes of the NCEs also showed consistency with findings in other well-established in vitro and in vivo cardiac risk assays. Conclusion: Evaluation of a large list of reference compounds and internal NCEs has confirmed the applicability of the adaptations made to the previously published novel scoring system for the hiPSC-CMs. The validation also established the predictivity for drug-induced cardiac risks with good translation to other established preclinical in vitro and in vivo assays, confirming the application of this novel scoring system in different stem cell-CM lines for early cardiac hazard identification.

Deriving waveform parameters from calcium transients in human iPSC-derived cardiomyocytes to predict cardiac activity with machine learning

Human induced pluripotent stem cell-derived cardiomyocytes have been established to detect dynamic calcium transients by fast kinetic fluorescence assays that provide insights into specific aspects of clinical cardiac activity. However, the precise derivation and use of waveform parameters to predict cardiac activity merit deeper investigation. In this study, we derived, evaluated, and applied 38 waveform parameters in a novel Python framework, including (among others) peak frequency, peak amplitude, peak widths, and a novel parameter, shoulder-tail ratio. We then trained a random forest model to predict cardiac activity based on the 25 parameters selected by correlation analysis. The area under the curve (AUC) obtained for leave-one-compound-out cross-validation was 0.86, thereby replicating the predictions of conventional methods and outperforming fingerprint-based methods by a large margin. This work demonstrates that machine learning is able to automate the assessment of cardiovascular liability from waveform data, reducing any risk of user-to-user variability and bias.

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An open-source algorithm was developed to derive parameters from waveform data

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A machine learning model was trained to predict cardiac activity of compounds

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Three parameters for peak width, height, and shape were found to be most predictive

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The model can facilitate the assessment of cardiovascular liability

OUP accepted manuscript

The content of this article derives from a Health and Environmental Sciences Institute (HESI) consortium with a focus to improve cardiac safety during drug development. A detailed literature review was conducted to evaluate the concordance between nonclinical repolarization assays and the clinical thorough QT (TQT) study. Food and Drug Administration and HESI developed a joint database of nonclinical and clinical data, and a retrospective analysis of 150 anonymized drug candidates was reviewed to compare the performance of 3 standard nonclinical assays with clinical TQT study findings as well as investigate mechanism(s) potentially responsible for apparent discrepancies identified. The nonclinical assays were functional (I_Kr) current block (Human ether-a-go-go related gene), action potential duration, and corrected QT interval in animals (in vivo corrected QT). Although these nonclinical assays demonstrated good specificity for predicting negative clinical QT prolongation, they had relatively poor sensitivity for predicting positive clinical QT prolongation. After review, 28 discordant TQT-positive drugs were identified. This article provides an overview of direct and indirect mechanisms responsible for QT prolongation and theoretical reasons for lack of concordance between clinical TQT studies and nonclinical assays. We examine 6 specific and discordant TQT-positive drugs as case examples. These were derived from the unique HESI/Food and Drug Administration database. We would like to emphasize some reasons for discordant data including, insufficient or inadequate nonclinical data, effects of the drug on other cardiac ion channels, and indirect and/or nonelectrophysiological effects of drugs, including altered heart rate. We also outline best practices that were developed based upon our evaluation.

Perspectives of future lung toxicology studies using human pluripotent stem cells

The absence of in vitro platforms for human pulmonary toxicology studies is becoming an increasingly serious concern. The respiratory system has a dynamic mechanical structure that extends from the airways to the alveolar region. In addition, the epithelial, endothelial, stromal, and immune cells are highly organized in each region and interact with each other to function synergistically. These cells of varied lineage, particularly epithelial cells, have been difficult to use for long-term culture in vitro, thus limiting the development of useful experimental tools. This limitation has set a large distance between the bench and the bedside for analyzing the pathogenic mechanisms, the efficacy of candidate therapeutic agents, and the toxicity of compounds. Several researchers have proposed solutions to these problems by reporting on methods for generating human lung epithelial cells derived from pluripotent stem cells (PSCs). Moreover, the use of organoid culture, organ-on-a-chip, and material-based techniques have enabled the maintenance of functional PSC-derived lung epithelial cells as well as primary cells. The aforementioned technological advances have facilitated the in vitro recapitulation of genetic lung diseases and the detection of ameliorating or worsening effects of genetic and chemical interventions, thus indicating the future possibility of more sophisticated preclinical compound assessments in vitro. In this review, we will update the recent advances in lung cell culture methods, principally focusing on human PSC-derived lung epithelial organoid culture systems with the hope of their future application in toxicology studies.

Simultaneous measurement of contractile force and field potential of dynamically beating human iPS cell-derived cardiac cell sheet-tissue with flexible electronics

Human induced pluripotent stem (iPS) cell-derived cardiomyocytes are used for in vitro pharmacological and pathological studies worldwide. In particular, the functional assessment of cardiac tissues created from iPS cell-derived cardiomyocytes is expected to provide precise prediction of drug effects and thus streamline the process of drug development. However, the current format of electrophysiological and contractile assessment of cardiomyocytes on a rigid substrate is not appropriate for cardiac tissues that beat dynamically. Here, we show a novel simultaneous measurement system for contractile force and extracellular field potential of iPS cell-derived cardiac cell sheet-tissues using 500 nm-thick flexible electronic sheets. It was confirmed that the developed system is applicable for pharmacological studies and assessments of excitation-contraction coupling-related parameters, such as the electro-mechanical window. Our results indicate that flexible electronics with cardiac tissue engineering provide an advanced platform for drug development. This system will contribute to gaining new insight in pharmacological study of human cardiac function.

Experimental evidence for proarrhythmic effects of nonsteroidal anti-inflammatory drugs in a sensitive whole-heart model

BACKGROUND

Previous studies have raised serious concerns on cardiovascular safety of widely prescribed nonsteroidal anti-inflammatory drugs (NSAIDs). Therefore, the aim of this study was to characterize the electrophysiological effects of certain NSAIDs in an established whole heart model of proarrhythmia.

METHODS AND RESULTS

Thirty-eight hearts of New Zealand White rabbits were harvested and retrogradely perfused employing a Langendorff setup, and electrophysiology studies were performed to investigate action potential duration at 90% of repolarization (APD₉₀ ), QT intervals, and effective refractory period (ERP). After generating baseline data, hearts were perfused with ibuprofen (Group 1, n = 12; 10 and 30 μM), indomethacin (Group 2, n = 13; 10 and 20 μM) and diclofenac (Group 3, n = 13; 10 and 20 μM), respectively, and the pacing protocols were repeated for each concentration. In all groups, perfusion with the NSAIDs resulted in a significant and reproducible shortening of APD₉₀ and QT interval. In all groups, the arrhythmia susceptibility was significantly raised as occurrence of monomorphic ventricular tachycardia under programmed ventricular stimulation was significantly increased under perfusion with ibuprofen, indomethacin and diclofenac in all concentrations.

CONCLUSION

The perfusion with ibuprofen, indomethacin and diclofenac in commonly used doses raised the arrhythmia susceptibility in an established rabbit whole-heart model while APD shortening and shortened ERP seem to be crucial for arrhythmogenesis.

Role of the rabbit whole-heart model for electrophysiologic safety pharmacology of non-cardiovascular drugs

Plenty of non-cardiovascular drugs alter cardiac electrophysiology and may ultimately lead to life-threatening arrhythmias. In clinical practice, measuring the QT interval as a marker for the repolarization period is the most common tool to assess the electrophysiologic safety of drugs. However, the sole measurement of the QT interval may be insufficient to determine the proarrhythmic risk of non-cardiovascular agents. Several other markers are considered in pre-clinical safety testing to determine potential harm on cardiac electrophysiology. Besides measuring typical electrophysiologic parameters such as repolarization duration, whole-heart models allow the determination of potential predictors for proarrhythmia. Spatial and temporal heterogeneity as well as changes of shape of the action potential can be easily assessed. In addition, provocation manoeuvers (either by electrolyte imbalances or programmed pacing protocols) may induce sustained arrhythmias and thereby determine ventricular vulnerability to arrhythmias. Compared with the human heart, the rabbit heart possesses a similar distribution of ion currents that govern cardiac repolarization, resulting in a rectangular action potential configuration in both species. In addition, similar biophysical properties of rabbit and human cardiac ion channels lead to a comparable pharmacologic response in human and rabbit hearts. Of note, arrhythmia patterns resemble in both species due to the similar effective size of human and rabbit hearts. Thus, the rabbit heart is particularly suitable for testing the electrophysiologic safety of drugs. Several experimental setups have been developed for studying cardiac electrophysiology in rabbits, ranging from single cell to tissue preparations, whole-heart setups, and in vivo models.

Zebrafish, an In Vivo Platform to Screen Drugs and Proteins for Biomedical Use

The nearly simultaneous convergence of human genetics and advanced molecular technologies has led to an improved understanding of human diseases. At the same time, the demand for drug screening and gene function identification has also increased, albeit time- and labor-intensive. However, bridging the gap between in vitro evidence from cell lines and in vivo evidence, the lower vertebrate zebrafish possesses many advantages over higher vertebrates, such as low maintenance, high fecundity, light-induced spawning, transparent embryos, short generation interval, rapid embryonic development, fully sequenced genome, and some phenotypes similar to human diseases. Such merits have popularized the zebrafish as a model system for biomedical and pharmaceutical studies, including drug screening. Here, we reviewed the various ways in which zebrafish serve as an in vivo platform to perform drug and protein screening in the fields of rare human diseases, social behavior and cancer studies. Since zebrafish mutations faithfully phenocopy many human disorders, many compounds identified from zebrafish screening systems have advanced to early clinical trials, such as those for Adenoid cystic carcinoma, Dravet syndrome and Diamond-Blackfan anemia. We also reviewed and described how zebrafish are used to carry out environmental pollutant detection and assessment of nanoparticle biosafety and QT prolongation.

Cardiac hERG K+ Channel as Safety and Pharmacological Target

The human ether-á-go-go related gene (hERG, KCNH2) encodes the pore-forming subunit of the potassium channel responsible for a fast component of the cardiac delayed rectifier potassium current (I_Kr). Outward I_Kr is an important determinant of cardiac action potential (AP) repolarization and effectively controls the duration of the QT interval in humans. Dysfunction of hERG channel can cause severe ventricular arrhythmias and thus modulators of the channel, including hERG inhibitors and activators, continue to attract intense pharmacological interest. Certain inhibitors of hERG channel prolong the action potential duration (APD) and effective refractory period (ERP) to suppress premature ventricular contraction and are used as class III antiarrhythmic agents. However, a reduction of the hERG/I_Kr current has been recognized as a predominant mechanism responsible for the drug-induced delayed repolarization known as acquired long QT syndromes (LQTS), which is linked to an increased risk for "torsades de pointes" (TdP) ventricular arrhythmias and sudden cardiac death. Many drugs of different classes and structures have been identified to carry TdP risk. Hence, assessing hERG/I_Kr blockade of new drug candidates is mandatory in the drug development process according to the regulatory agencies. In contrast, several hERG channel activators have been shown to enhance I_Kr and shorten the APD and thus might have potential antiarrhythmic effects against pathological LQTS. However, these activators may also be proarrhythmic due to excessive shortening of APD and the ERP.

Core battery safety pharmacology testing - An assessment of its utility in early drug development

Requirements for safety pharmacology testing have been in place since the issue of initial regulatory guidance over 20 years ago. An evaluation of such testing, supporting first clinical entry of 105 small molecule drug candidates over the last decade, showed that a "core battery" of in vitro electrophysiological (hERG), conscious non-rodent telemetry cardiovascular, rodent central nervous system (CNS) (modified Irwin's or functional observational battery [FOB] test) and respiratory function (plethysmography) studies was performed. Routine use of the latter 2 studies appears to have limited utility, with only 21% and 28% of studies, respectively, giving findings of which none were identified as of obvious concern to moving the affected drugs into the clinic. The use of a stand-alone hERG assay does not appear to be particular sensitive in predicting proarrythmic risk as a tool by itself. Telemetry study testing had utility especially for identifying effects on QTc interval (about 10% of studies), resulting on some occasions in a lower clinical starting dose and/or increased awareness for potential effects on the cardiovascular system in the Phase I study. Overall, this investigation provides information supporting an overhaul of the current "box ticking" core battery approach used for safety pharmacology testing. However, in order to achieve a more focused examination to investigate potential undesirable pharmacodynamic effects of a new candidate drug and also support 3Rs (Replacement, Reduction and Refinement) thinking in performing unnecessary studies, there will not only need to be a sea change by drug developers but also a change in current regulatory guidance.

Improving reliability and reducing costs of cardiotoxicity assessments using laser-induced cell poration on microelectrode arrays

Drug-induced cardiotoxicity is a major barrier to drug development and a main cause of withdrawal of marketed drugs. Drugs can strongly alter the spontaneous functioning of the heart by interacting with the cardiac membrane ion channels. If these effects only surface during in vivo preclinical tests, clinical trials or worse after commercialization, the societal and economic burden will be significant and seriously hinder the efficient drug development process. Hence, cardiac safety pharmacology requires in vitro electrophysiological screening assays of all drug candidates to predict cardiotoxic effects before clinical trials. In the past 10 years, microelectrode array (MEA) technology began to be considered a valuable approach in pharmaceutical applications. However, an effective tool for high-throughput intracellular measurements, compatible with pharmaceutical standards, is not yet available. Here, we propose laser-induced optoacoustic poration combined with CMOS-MEA technology as a reliable and effective platform to detect cardiotoxicity. This approach enables the acquisition of high-quality action potential recordings from large numbers of cardiomyocytes within the same culture well, providing reliable data using single-well MEA devices and single cardiac syncytia per each drug. Thus, this technology could be applied in drug safety screening platforms reducing times and costs of cardiotoxicity assessments, while simultaneously improving the data reliability.

Utility of Zebrafish Models of Acquired and Inherited Long QT Syndrome

Long-QT Syndrome (LQTS) is a cardiac electrical disorder, distinguished by irregular heart rates and sudden death. Accounting for ∼40% of cases, LQTS Type 2 (LQTS2), is caused by defects in the Kv11.1 (hERG) potassium channel that is critical for cardiac repolarization. Drug block of hERG channels or dysfunctional channel variants can result in acquired or inherited LQTS2, respectively, which are typified by delayed repolarization and predisposition to lethal arrhythmia. As such, there is significant interest in clear identification of drugs and channel variants that produce clinically meaningful perturbation of hERG channel function. While toxicological screening of hERG channels, and phenotypic assessment of inherited channel variants in heterologous systems is now commonplace, affordable, efficient, and insightful whole organ models for acquired and inherited LQTS2 are lacking. Recent work has shown that zebrafish provide a viable in vivo or whole organ model of cardiac electrophysiology. Characterization of cardiac ion currents and toxicological screening work in intact embryos, as well as adult whole hearts, has demonstrated the utility of the zebrafish model to contribute to the development of therapeutics that lack hERG-blocking off-target effects. Moreover, forward and reverse genetic approaches show zebrafish as a tractable model in which LQTS2 can be studied. With the development of new tools and technologies, zebrafish lines carrying precise channel variants associated with LQTS2 have recently begun to be generated and explored. In this review, we discuss the present knowledge and questions raised related to the use of zebrafish as models of acquired and inherited LQTS2. We focus discussion, in particular, on developments in precise gene-editing approaches in zebrafish to create whole heart inherited LQTS2 models and evidence that zebrafish hearts can be used to study arrhythmogenicity and to identify potential anti-arrhythmic compounds.

Drug Screening with Genetically Encoded Fluorescent Sensors: Today and Tomorrow

Genetically-encoded fluorescent sensors have been actively developed over the last few decades and used in live imaging and drug screening. Real-time monitoring of drug action in a specific cellular compartment, organ, or tissue type; the ability to screen at the single-cell resolution; and the elimination of false-positive results caused by low drug bioavailability that is not detected by in vitro testing methods are a few of the obvious benefits of using genetically-encoded fluorescent sensors in drug screening. In combination with high-throughput screening (HTS), some genetically-encoded fluorescent sensors may provide high reproducibility and robustness to assays. We provide a brief overview of successful, perspective, and hopeful attempts at using genetically encoded fluorescent sensors in HTS of modulators of ion channels, Ca2+ homeostasis, GPCR activity, and for screening cytotoxic, anticancer, and anti-parasitic compounds. We discuss the advantages of sensors in whole organism drug screening models and the perspectives of the combination of human disease modeling by CRISPR techniques with genetically encoded fluorescent sensors for drug screening.

Myocardial slices come to age: an intermediate complexity in vitro cardiac model for translational research

Although past decades have witnessed significant reductions in mortality of heart failure together with advances in our understanding of its cellular, molecular, and whole-heart features, a lot of basic cardiac research still fails to translate into clinical practice. In this review we examine myocardial slices, a novel model in the translational arena. Myocardial slices are living ultra-thin sections of heart tissue. Slices maintain the myocardium's native function (contractility, electrophysiology) and structure (multicellularity, extracellular matrix) and can be prepared from animal and human tissue. The discussion begins with the history and current advances in the model, the different interlaboratory methods of preparation and their potential impact on results. We then contextualize slices' advantages and limitations by comparing it with other cardiac models. Recently, sophisticated methods have enabled slices to be cultured chronically in vitro while preserving the functional and structural phenotype. This is more timely now than ever where chronic physiologically relevant in vitro platforms for assessment of therapeutic strategies are urgently needed. We interrogate the technological developments that have permitted this, their limitations, and future directions. Finally, we look into the general obstacles faced by the translational field, and how implementation of research systems utilizing slices could help in resolving these.

Toward a Structural View of hERG Activation by the Small-Molecule Activator ICA-105574

Outward current conducted by human ether-à-go-go-related gene type 1 (hERG1) K+ channels is important for action potential repolarization in the human ventricle. Rapid, voltage-dependent inactivation greatly reduces outward currents conducted by hERG1 channels and involves conformational changes in the ion selectivity filter (SF). Recently, compounds have been found that activate hERG1 channel function by modulating gating mechanisms such as reducing inactivation. Such activating compounds could represent a novel approach to prevent arrhythmias associated with prolonged ventricular repolarization associated with inherited or acquired long QT syndrome. ICA-105574 (ICA), a 3-nitro-n-(4-phenoxyphenyl) benzamide derivative activates hERG1 by strongly attenuating pore-type inactivation. We previously mapped the putative binding site for ICA to a hydrophobic pocket located between two adjacent subunits. Here, we used the recently reported cryoelectron microscopy structures of hERG1 to elucidate the structural mechanisms by which ICA influences the stability of the SF. By combining molecular dynamics simulations, voltage-clamp electrophysiology, and the synthesis of novel ICA derivatives, we provide atomistic insights into SF dynamics and propose a structural link between the SF and S6 segments. Further, our study highlights the importance of the nitro moiety, at the meta position of the benzamide ring, for the activity of ICA and reveals that the (bio)isosteric substitution of this side chain can switch the activity to weak inhibitors. Our findings indicate that ICA increases the stability of the SF to attenuate channel inactivation, and this action requires a fine-tuned compound geometry.

Human Induced Pluripotent Stem Cells Derived from a Cardiac Somatic Source: Insights for an In-Vitro Cardiomyocyte Platform

Reprogramming of adult somatic cells into induced pluripotent stem cells (iPSCs) has revolutionized the complex scientific field of disease modelling and personalized therapy. Cardiac differentiation of human iPSCs into cardiomyocytes (hiPSC-CMs) has been used in a wide range of healthy and disease models by deriving CMs from different somatic cells. Unfortunately, hiPSC-CMs have to be improved because existing protocols are not completely able to obtain mature CMs recapitulating physiological properties of human adult cardiac cells. Therefore, improvements and advances able to standardize differentiation conditions are needed. Lately, evidences of an epigenetic memory retained by the somatic cells used for deriving hiPSC-CMs has led to evaluation of different somatic sources in order to obtain more mature hiPSC-derived CMs.

Investigating the utility of adult zebrafish ex vivo whole hearts to pharmacologically screen hERG channel activator compounds

There is significant interest in the potential utility of small-molecule activator compounds to mitigate cardiac arrhythmia caused by loss of function of hERG1a voltage-gated potassium channels. Zebrafish (Danio rerio) have been proposed as a cost-effective, high-throughput drug-screening model to identify compounds that cause hERG1a dysfunction. However, there are no reports on the effects of hERG1a activator compounds in zebrafish and consequently on the utility of the model to screen for potential gain-of-function therapeutics. Here, we examined the effects of hERG1a blocker and types 1 and 2 activator compounds on isolated zkcnh6a (zERG3) channels in the Xenopus oocyte expression system as well as action potentials recorded from ex vivo adult zebrafish whole hearts using optical mapping. Our functional data from isolated zkcnh6a channels show that under the conditions tested, these channels are blocked by hERG1a channel blockers (dofetilide and terfenadine), and activated by type 1 (RPR260243) and type 2 (NS1643, PD-118057) hERG1a activators with higher affinity than hKCNH2a channels (except NS1643), with differences accounted for by different biophysical properties in the two channels. In ex vivo zebrafish whole hearts, two of the three hERG1a activators examined caused abbreviation of the action potential duration (APD), whereas hERG1a blockers caused APD prolongation. These data represent, to our knowledge, the first pharmacological characterization of isolated zkcnh6a channels and the first assessment of hERG enhancing therapeutics in zebrafish. Our findings lead us to suggest that the zebrafish ex vivo whole heart model serves as a valuable tool in the screening of hKCNH2a blocker and activator compounds.

Development of a Human iPSC Cardiomyocyte-Based Scoring System for Cardiac Hazard Identification in Early Drug Safety De-risking

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have emerged as a promising cardiac safety platform, demonstrated by numerous validation studies using drugs with known cardiac adverse effects in humans. However, the challenge remains to implement hiPSC-CMs into cardiac de-risking of new chemical entities (NCEs) during preclinical drug development. Here, we used the calcium transient screening assay in hiPSC-CMs to develop a hazard score system for cardiac electrical liabilities. Tolerance interval calculations and evaluation of different classes of cardio-active drugs enabled us to develop a weighted scoring matrix. This approach allowed the translation of various pharmacological effects in hiPSC-CMs into a single hazard label (no, low, high, or very high hazard). Evaluation of 587 internal NCEs and good translation to ex vivo and in vivo models for a subset of these NCEs highlight the value of the cardiac hazard scoring in facilitating the selection of compounds during early drug safety screening.

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Scoring system identifies different degrees of cardiac hazard

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Can be applied within R&D to cardiac safety screening of NCEs

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Controls and reference drugs are essential for development of scoring matrix

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Analysis can be applied to other in vitro drug safety assays

Assessing Drug-Induced Long QT and Proarrhythmic Risk Using Human Stem-Cell-Derived Cardiomyocytes in a Ca2+ Imaging Assay: Evaluation of 28 CiPA Compounds at Three Test Sites

The goal of this research consortium including Janssen, MSD, Ncardia, FNCR/LBR, and Health and Environmental Sciences Institute (HESI) was to evaluate the utility of an additional in vitro assay technology to detect potential drug-induced long QT and torsade de pointes (TdP) risk by monitoring cytosolic free Ca2+ transients in human stem-cell-derived cardiomyocytes (hSC-CMs). The potential proarrhythmic risks of the 28 comprehensive in vitro proarrhythmia assay (CiPA) drugs linked to low, intermediate, and high clinical TdP risk were evaluated in a blinded manner using Ca2+-sensitive fluorescent dye assay recorded from a kinetic plate reader system (Hamamatsu FDSS/µCell and FDSS7000) in 2D cultures of 2 commercially available hSC-CM lines (Cor.4U and CDI iCell Cardiomyocytes) at 3 different test sites. The Ca2+ transient assay, performed at the 3 sites using the 2 different hSC-CMs lines, correctly detected potential drug-induced QT prolongation among the 28 CiPA drugs and detected cellular arrhythmias-like/early afterdepolarization in 7 of 8 high TdP-risk drugs (87.5%), 6 of 11 intermediate TdP-risk drugs (54.5%), and 0 of 9 low/no TdP-risk drugs (0%). The results were comparable among the 3 sites and from 2 hSC-CM cell lines. The Ca2+ transient assay can serve as a user-friendly and higher throughput alternative to complement the microelectrode array and voltage-sensing optical action potential recording assays used in the HESI-CiPA study for in vitro assessment of drug-induced long QT and TdP risk.

Naturally-Derived Biomaterials for Tissue Engineering Applications

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Stem cell models as an in vitro model for predictive toxicology

Adverse drug reactions (ADRs) are the unintended side effects of drugs. They are categorised as either predictable or unpredictable drug-induced injury and may be exhibited after a single or prolonged exposure to one or multiple compounds. Historically, toxicology studies rely heavily on animal models to understand and characterise the toxicity of novel compounds. However, animal models are imperfect proxies for human toxicity and there have been several high-profile cases of failure of animal models to predict human toxicity e.g. fialuridine, TGN1412 which highlight the need for improved predictive models of human toxicity. As a result, stem cell-derived models are under investigation as potential models for toxicity during early stages of drug development. Stem cells retain the genotype of the individual from which they were derived, offering the opportunity to model the reproducibility of rare phenotypes in vitro Differentiated 2D stem cell cultures have been investigated as models of hepato- and cardiotoxicity. However, insufficient maturity, particularly in the case of hepatocyte-like cells, means that their widespread use is not currently a feasible method to tackle the complex issues of off-target and often unpredictable toxicity of novel compounds. This review discusses the current state of the art for modelling clinically relevant toxicities, e.g. cardio- and hepatotoxicity, alongside the emerging need for modelling gastrointestinal toxicity and seeks to address whether stem cell technologies are a potential solution to increase the accuracy of ADR predictivity in humans.

Electrophysiological and Pharmacological Characterization of Human Inwardly Rectifying Kir2.1 Channels on an Automated Patch-Clamp Platform

Inwardly rectifying I_K1 potassium currents of the heart control the resting membrane potential of ventricular cardiomyocytes during diastole and contribute to their repolarization after each action potential. Mutations in the gene encoding K_ir2.1 channels, which primarily conduct ventricular I_K1, are associated with inheritable forms of arrhythmias and sudden cardiac death. Therefore, potential iatrogenic inhibition of K_ir2.1-mediated I_K1 currents is a cardiosafety concern during new drug discovery and development. K_ir2.1 channels are part of the panel of cardiac ion channels currently considered for refined early compound risk assessment within the Comprehensive in vitro Proarrhythmia Assay initiative. In this study, we have validated a cell-based assay allowing functional quantification of K_ir2.1 inhibitors using whole-cell recordings of Chinese hamster ovary cells stably expressing human K_ir2.1 channels. We reproduced key electrophysiological and pharmacological features known for native I_K1, including current enhancement by external potassium and voltage- and concentration-dependent blockade by external barium. Furthermore, the K_ir inhibitors ML133, PA-6, and chloroquine, as well as the multichannel inhibitors chloroethylclonidine, chlorpromazine, SKF-96365, and the class III antiarrhythmic agent terikalant demonstrated slowly developing inhibitory activity in the low micromolar range. The robustness of this assay authorizes medium throughput screening for cardiosafety purposes and could help to enrich the currently limited K_ir2.1 pharmacology.

Utility of the JT Peak Interval and the JT Area in Determining the Proarrhythmic Potential of QT-Shortening Agents

Drug-induced long QT increases the risk of ventricular tachyarrhythmia known as torsades de pointes (TdP). Many biomarkers have been used to predict TdP. At present, however, there are few biomarkers for arrhythmias induced by QT-shortening drugs. The objective of the present study was to identify the best biomarkers for predicting arrhythmias caused by the 4 potassium channel openers ICA-105574, NS-1643, R-L3, and pinacidil. Our results showed that, at higher concentrations, all 4 potassium channel openers induced ventricular tachycardia (VT) and ventricular fibrillation (VF) in Langendorff-perfused guinea pig hearts, but not in rabbit hearts. The electrocardiography parameters were measured including QT/QTc, JT peak, Tp-e interval, JT area, short-term beat-to-beat QT interval variability (STV), and index of cardiac electrophysiological balance (iCEB). We found that the potassium channel openers at test concentrations shortened the QT/QTc and the JT peak interval and increased the JT area. Nevertheless, even at proarrhythmic concentrations, they did not always change STV, Tp-e, or iCEB. Receiver operating characteristic curve analysis showed that the JT peak interval representing the early repolarization phase and the JT area reflecting the dispersion of ventricular repolarization were the best predictors of VT/VF. Action potential recordings in guinea pig papillary muscle revealed that except for pinacidil, the potassium channel openers shortened APD₃₀ in a concentration-dependent manner. They also evoked early or delayed afterdepolarizations at fast pacing rates. Patch-clamp recordings in guinea pig ventricular cardiomyocytes showed that the potassium channel openers enhanced the total outward currents during the early phase of action potential repolarization, especially at proarrhythmic concentrations. We concluded that the JT peak interval and the JT area are surrogate biomarkers identifying the risk of proarrhythmia associated with the administration of QT-shortening agents. The acceleration of early-phase repolarization and the increased dispersion of ventricular repolarization may contribute to the occurrence of arrhythmias.

Evaluation of cardiac arrhythmic risks using a rabbit model of left ventricular systolic dysfunction

Patients with heart disease have a higher risk to develop cardiac arrhythmias, either spontaneously or drug-induced. In this study, we have used a rabbit model of myocardial infarction (MI) with severe left ventricular systolic dysfunction (LVSD) to study potential drug-induced cardiac risks with N-(piperidin-2-ylmethyl)-2,5-bis(2,2,2-trifluoroethoxy)benzamide (flecainide). Upon ligation of the left circumflex arteries, male New Zealand White rabbits developed a large MI and moderate or severe LVSD 7 weeks after surgery, in comparison to SHAM-operated animals. Subsequently, animals were exposed to escalating doses of flecainide (0.25-4 mg/kg) or solvent. Electrocardiograms (ECG) were recorded before surgery, 1 and 7 weeks after surgery and continuously during the drug protocol. The ECG biomarker iCEB (index of Cardio-Electrophysiological Balance = QT/QRS ratio) was calculated. During the ECG recording at week 1 and week 7 post MI, rabbits had no spontaneous cardiac arrhythmias. When rabbits were exposed to escalating doses of flecainide, 2 out of 5 rabbits with MI and moderate LVSD versus 0 out of 5 solvent-treated rabbits developed arrhythmias, such as ventricular tachycardia/ventricular fibrillation. These were preceded by a marked decrease of iCEB just before the onset (from 4.09 to 2.42 and from 5.56 to 2.25, respectively). Furthermore, 1 out of 5 MI rabbits with moderate LVSD and 1 out of 7 MI rabbits with severe LVSD developed total atrioventricular block after flecainide infusion and died. This rabbit model of MI and severe LVSD may be useful for preclinical evaluation of drug (similar mechanism as flecainide)-induced arrhythmic risks, which might be predicted by iCEB.

Reflective lens-free imaging on high-density silicon microelectrode arrays for monitoring and evaluation of in vitro cardiac contractility

The high rate of drug attrition caused by cardiotoxicity is a major challenge for drug development. Here, we developed a reflective lens-free imaging (RLFI) approach to non-invasively record in vitro cell deformation in cardiac monolayers with high temporal (169 fps) and non-reconstructed spatial resolution (352 µm) over a field-of-view of maximally 57 mm². The method is compatible with opaque surfaces and silicon-based devices. Further, we demonstrated that the system can detect the impairment of both contractility and fast excitation waves in cardiac monolayers. Additionally, the RLFI device was implemented on a CMOS-based microelectrode array to retrieve multi-parametric information of cardiac cells, thereby offering more in-depth analysis of drug-induced (cardiomyopathic) effects for preclinical cardiotoxicity screening applications.

Cardiac Arrhythmias and Antiarrhythmic Drugs: An Autophagic Perspective

Degradation of cellular material by lysosomes is known as autophagy, and its main function is to maintain cellular homeostasis for growth, proliferation and survival of the cell. In recent years, research has focused on the characterization of autophagy pathways. Targeting of autophagy mediators has been described predominantly in cancer treatment, but also in neurological and cardiovascular diseases. Although the number of studies is still limited, there are indications that activity of autophagy pathways increases under arrhythmic conditions. Moreover, an increasing number of antiarrhythmic and non-cardiac drugs are found to affect autophagy pathways. We, therefore, suggest that future work should recognize the largely unaddressed effects of antiarrhythmic agents and other classes of drugs on autophagy pathway activation and inhibition.

Have the Findings from Clinical Risk Prediction and Trials Any Key Messages for Safety Pharmacology?

Anti-arrhythmic drugs are a mainstay in the management of symptoms related to arrhythmias, and are adjuncts in prevention and treatment of life-threatening ventricular arrhythmias. However, they also have the potential for pro-arrhythmia and thus the prediction of arrhythmia predisposition and drug response are critical issues. Clinical trials are the latter stages in the safety testing and efficacy process prior to market release, and as such serve as a critical safeguard. In this review, we look at some of the lessons to be learned from approaches to arrhythmia prediction in patients, clinical trials of drugs used in the treatment of arrhythmias, and the implications for the design of pre-clinical safety pharmacology testing.

CSAHi study-2: Validation of multi-electrode array systems (MEA60/2100) for prediction of drug-induced proarrhythmia using human iPS cell-derived cardiomyocytes: Assessment of reference compounds and comparison with non-clinical studies and clinical information

With the aim of reconsidering ICH S7B and E14 guidelines, a new in vitro assay system has been subjected to worldwide validation to establish a better prediction platform for potential drug-induced QT prolongation and the consequent TdP in clinical practice. In Japan, CSAHi HEART team has been working on hiPS-CMs in the MEA (hiPS-CMs/MEA) under a standardized protocol and found no inter-facility or lot-to-lot variability for proarrhythmic risk assessment of 7 reference compounds. In this study, we evaluated the responses of hiPS-CMs/MEA to another 31 reference compounds associated with cardiac toxicities, and gene expression to further clarify the electrophysiological characteristics over the course of culture period. The hiPS-CMs/MEA assay accurately predicted reference compounds potential for arrhythmogenesis, and yielded results that showed better correlation with target concentrations of QTc prolongation or TdP in clinical setting than other current in vitro and in vivo assays. Gene expression analyses revealed consistent profiles in all samples within and among the testing facilities. This report would provide CiPA with informative guidance on the use of the hiPS-CMs/MEA assay, and promote the establishment of a new paradigm, beyond conventional in vitro and in vivo assays for cardiac safety assessment of new drugs.

Application of optical action potentials in human induced pluripotent stem cells-derived cardiomyocytes to predict drug-induced cardiac arrhythmias

INTRODUCTION

Human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) are emerging as new and human-relevant source in vitro model for cardiac safety assessment that allow us to investigate a set of 20 reference drugs for predicting cardiac arrhythmogenic liability using optical action potential (oAP) assay.

METHODS

Here, we describe our examination of the oAP measurement using a voltage sensitive dye (Di-4-ANEPPS) to predict adverse compound effects using hiPS-CMs and 20 cardioactive reference compounds. Fluorescence signals were digitized at 10kHz and the records subsequently analyzed off-line. Cells were exposed to 30min incubation to vehicle or compound (n=5/dose, 4 doses/compound) that were blinded to the investigating laboratory. Action potential parameters were measured, including rise time (T_rise) of the optical action potential duration (oAPD).

RESULTS

Significant effects on oAPD were sensitively detected with 11 QT-prolonging drugs, while oAPD shortening was observed with I_Ca-antagonists, I_Kr-activator or ATP-sensitive K⁺ channel (K_ATP)-opener. Additionally, the assay detected varied effects induced by 6 different sodium channel blockers. The detection threshold for these drug effects was at or below the published values of free effective therapeutic plasma levels or effective concentrations by other studies.

DISCUSSION

The results of this blinded study indicate that OAP is a sensitive method to accurately detect drug-induced effects (i.e., duration/QT-prolongation, shortening, beat rate, and incidence of early after depolarizations) in hiPS-CMs; therefore, this technique will potentially be useful in predicting drug-induced arrhythmogenic liabilities in early de-risking within the drug discovery phase.

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.

[Antiemetics and cardiac effects potentially linked to prolongation of the QT interval: Case/non-case analysis in the national pharmacovigilance database]

OBJECTIVES

Observational retrospective studies have linked domperidone and prolonged QT interval, ventricular arrhythmias and risk of sudden death. Since then, antiemetic prescription was applied to other molecules (including metopimazine). The aim of this study was to evaluate the profile of adverse cardiac effects associated with QT prolongation for each antiemetic available in France.

METHODS

We conducted disproportionality analyses (case/non-case method), based on the observations recorded consecutively in the French national pharmacovigilance database between 2004 and 2013. Cases were defined by following MedDRA terms: prolongation of the QT interval, syncope, sudden death, cardiac arrest, ventricular arrhythmias including torsades de pointes; non-cases were other adverse events reported during the same period. We analyzed the presence of each antiemetic among cases and non-cases and measured the disproportionality by reporting odds ratios (ROR). We validate the assay with a positive control (methadone) and a negative control (acetaminophen).

RESULTS

We compared 2093 cases (94 with antiemetics) to 253,665 non-cases (7015 with antiemetics). Among antiemetics, adverse cardiac effects studied were more frequently found with notifications including domperidone (ROR=2.0, 95% CI=[1.3; 3.0]), ondansetron (ROR=1.8, 95% CI=[1.3; 2.6]) and granisetron (ROR=3.4, 95% CI=[1.5; 7.6]). Metopimazine was not statistically associated with that risk (ROR=2.0; 95% CI=[0.8; 4.8]).

CONCLUSION

We confirmed a risk of cardiac adverse event related to prolongation of the QT interval with domperidone and setrons. These results suggest caution when prescribing antiemetics and encourage systematic reporting of adverse cardiac effects observed with these molecules.

Assessment of drug-induced proarrhythmia: The importance of study design in the rabbit left ventricular wedge model

In the present study, we investigated an impact of the stimulation rate on the detection of the proarrhythmic potential of 10 reference compounds with effects on different cardiac ion channels in the isolated arterially-perfused rabbit left ventricular wedge preparation. The compounds were tested in the wedge model using two distinct protocols; including baseline stimulation at 1-Hz followed by a brief period at 0.5-Hz, either without an additional brief period of 2-Hz stimulation (i.e. Protocol 1) or with 2-Hz stimulation (i.e. Protocol 2). As expected, QT-prolonging drugs (ibutilide and quinidine) prolonged the QT interval, similarly increased the Torsades de Pointes (TdP) score, and elicited early afterdepolarizations (EADs) in both protocols. HMR1556 and JNJ-303 (IKs blockers) also prolonged the QT interval up to 1μM similarly in both protocols. Nifedipine (Ca(2+) antagonist) shortened the QT interval, and reduced force of contraction similarly in both protocols. However, Na(+) channel blockers (Ia, Ib, Ic) widened the QRS duration more in Protocol 2 than in Protocol 1. Furthermore, it was only possible to detect non-TdP-like ventricular tachycardia/fibrillation (VT/VF) induced by Na(+) blockers and by QT-shortening drugs (levcromakalim and mallotoxin) using the 2-Hz stimulation (Protocol 2). Our data suggest that the inclusion of a brief period of fast stimulation at 2Hz is critical for detecting drug-induced slowing of conduction (QRS widening), QT shortening and associated (non-TdP-like) VT/VF, which are distinct from the QT prolongation/TdP proarrhythmia in isolated, arterially-perfused rabbit left ventricular wedges.

Safety pharmacology studies using EFP and impedance

INTRODUCTION

While extracellular field potential (EFP) recordings using multi-electrode arrays (MEAs) are a well-established technique for monitoring changes in cardiac and neuronal function, impedance is a relatively unexploited technology. The combination of EFP, impedance and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) has important implications for safety pharmacology as functional information about contraction and field potentials can be gleaned from human cardiomyocytes in a beating monolayer. The main objectives of this study were to demonstrate, using a range of different compounds, that drug effects on contraction and electrophysiology can be detected using a beating monolayer of hiPSC-CMs on the CardioExcyte 96.

METHODS

hiPSC-CMs were grown as a monolayer on NSP-96 plates for the CardioExcyte 96 (Nanion Technologies) and recordings were made in combined EFP and impedance mode at physiological temperature. The effect of the hERG blockers, E4031 and dofetilide, hERG trafficking inhibitor, pentamidine, β-adrenergic receptor agonist, isoproterenol, and calcium channel blocker, nifedipine, was tested on the EFP and impedance signals.

RESULTS

Combined impedance and EFP measurements were made from hiPSC-CMs using the CardioExcyte 96 (Nanion Technologies). E4031 and dofetilide, known to cause arrhythmia and Torsades de Pointes (TdP) in humans, decreased beat rate in impedance and EFP modes. Early afterdepolarization (EAD)-like events, an in vitro marker of TdP, could also be detected using this system. Isoproterenol and nifedipine caused an increase in beat rate. A long-term study (over 30h) of pentamidine, a hERG trafficking inhibitor, showed a concentration and time-dependent effect of pentamidine.

DISCUSSION

In the light of the new Comprehensive in Vitro Proarrhythmia Assay (CiPA) initiative to improve guidelines and standardize assays and protocols, the use of EFP and impedance measurements from hiPSCs may become critical in determining the proarrhythmic risk of potential drug candidates. The combination of EFP offering information about cardiac electrophysiology, and impedance, providing information about contractility from the same area of a synchronously beating monolayer of human cardiomyocytes in a 96-well plate format has important implications for future cardiac safety testing.

Functional and Transcriptional Characterization of Histone Deacetylase Inhibitor-Mediated Cardiac Adverse Effects in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Histone deacetylase (HDAC) inhibitors possess therapeutic potential to reverse aberrant epigenetic changes associated with cancers, neurological diseases, and immune disorders. Unfortunately, clinical studies with some HDAC inhibitors displayed delayed cardiac adverse effects, such as atrial fibrillation and ventricular tachycardia. However, the underlying molecular mechanism(s) of HDAC inhibitor-mediated cardiotoxicity remains poorly understood and is difficult to detect in the early stages of preclinical drug development because of a delayed onset of effects. In the present study, we show for the first time in human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) that HDAC inhibitors (dacinostat, panobinostat, vorinostat, entinostat, and tubastatin-a) induce delayed dose-related cardiac dysfunction at therapeutic concentrations associated with cardiac adverse effects in humans. HDAC inhibitor-mediated delayed effects on the beating properties of hiPS-CMs developed after 12 hours by decreasing the beat rate, shortening the field potential duration, and inducing arrhythmic behavior under form of sustained contractions and fibrillation-like patterns. Transcriptional changes that are common between the cardiotoxic HDAC inhibitors but different from noncardiotoxic treatments identified cardiac-specific genes and pathways related to structural and functional changes in cardiomyocytes. Combining the functional data with epigenetic changes in hiPS-CMs allowed us to identify molecular targets that might explain HDAC inhibitor-mediated cardiac adverse effects in humans. Therefore, hiPS-CMs represent a valuable translational model to assess HDAC inhibitor-mediated cardiotoxicity and support identification of better HDAC inhibitors with an improved benefit-risk profile.

SIGNIFICANCE

Histone deacetylase (HDAC) inhibitors are a promising class of drugs to treat certain cancers, autoimmune, and neurodegenerative diseases. However, treated patients can experience various cardiac adverse events such as hearth rhythm disorders. This study found that human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) can predict cardiac adverse events in patients caused by HDAC inhibitors. Furthermore, transcriptional changes at the level of gene expression supported the effects on the beating properties of hiPS-CMs and highlight targets that might cause these cardiac adverse effects. hiPS-CMs represent a valuable translational model to assess HDAC inhibitor-mediated cardiotoxicity and to support development of safer HDAC inhibitors.

Impaired Inactivation of L-Type Ca2+ Current as a Potential Mechanism for Variable Arrhythmogenic Liability of HERG K+ Channel Blocking Drugs

The proarrhythmic effects of new drugs have been assessed by measuring rapidly activating delayed-rectifier K⁺ current (I_Kr) antagonist potency. However, recent data suggest that even drugs thought to be highly specific I_Kr blockers can be arrhythmogenic via a separate, time-dependent pathway such as late Na⁺ current augmentation. Here, we report a mechanism for a quinolone antibiotic, sparfloxacin-induced action potential duration (APD) prolongation that involves increase in late L-type Ca²⁺ current (I_CaL) caused by a decrease in Ca²⁺-dependent inactivation (CDI). Acute exposure to sparfloxacin, an I_Kr blocker with prolongation of QT interval and torsades de pointes (TdP) produced a significant APD prolongation in rat ventricular myocytes, which lack I_Kr due to E4031 pretreatment. Sparfloxacin reduced peak I_CaL but increased late I_CaL by slowing its inactivation. In contrast, ketoconazole, an I_Kr blocker without prolongation of QT interval and TdP produced reduction of both peak and late I_CaL, suggesting the role of increased late I_CaL in arrhythmogenic effect. Further analysis showed that sparfloxacin reduced CDI. Consistently, replacement of extracellular Ca²⁺ with Ba²⁺ abolished the sparfloxacin effects on I_CaL. In addition, sparfloxacin modulated I_CaL in a use-dependent manner. Cardiomyocytes from adult mouse, which is lack of native I_Kr, demonstrated similar increase in late I_CaL and afterdepolarizations. The present findings show that sparfloxacin can prolong APD by augmenting late I_CaL. Thus, drugs that cause delayed I_CaL inactivation and I_Kr blockage may have more adverse effects than those that selectively block I_Kr. This mechanism may explain the reason for discrepancies between clinically reported proarrhythmic effects and I_Kr antagonist potencies.

Comparison of electrophysiological effects of calcium channel blockers on cardiac repolarization

Dihydropyridine (DHP) calcium channel blockers (CCBs) have been widely used to treat of several cardiovascular diseases. An excessive shortening of action potential duration (APD) due to the reduction of Ca²⁺ channel current (I_Ca) might increase the risk of arrhythmia. In this study we investigated the electrophysiological effects of nicardipine (NIC), isradipine (ISR), and amlodipine (AML) on the cardiac APD in rabbit Purkinje fibers, voltage-gated K⁺ channel currents (I_Kr, I_Ks) and voltage-gated Na⁺ channel current (I_Na). The concentration-dependent inhibition of Ca²⁺ channel currents (I_Ca) was examined in rat cardiomyocytes; these CCBs have similar potency on I_Ca channel blocking with IC₅₀ (the half-maximum inhibiting concentration) values of 0.142, 0.229, and 0.227 nM on NIC, ISR, and AML, respectively. However, ISR shortened both APD₅₀ and APD₉₀ already at 1 µM whereas NIC and AML shortened APD₅₀ but not APD₉₀ up to 30 µM. According to ion channel studies, NIC and AML concentration-dependently inhibited I_Kr and I_Ks while ISR had only partial inhibitory effects (<50% at 30 µM). Inhibition of I_Na was similarly observed in the three CCBs. Since the I_Kr and I_Ks mainly contribute to cardiac repolarization, their inhibition by NIC and AML could compensate for the AP shortening effects due to the block of I_Ca.

Cardiotoxicity screening: a review of rapid-throughput in vitro approaches

Cardiac toxicity represents one of the leading causes of drug failure along different stages of drug development. Multiple very successful pharmaceuticals had to be pulled from the market or labeled with strict usage warnings due to adverse cardiac effects. In order to protect clinical trial participants and patients, the International Conference on Harmonization published guidelines to recommend that all new drugs to be tested preclinically for hERG (Kv11.1) channel sensitivity before submitting for regulatory reviews. However, extensive studies have demonstrated that measurement of hERG activity has limitations due to the multiple molecular targets of drug compound through which it may mitigate or abolish a potential arrhythmia, and therefore, a model measuring multiple ion channel effects is likely to be more predictive. Several phenotypic rapid-throughput methods have been developed to predict the potential cardiac toxic compounds in the early stages of drug development using embryonic stem cells- or human induced pluripotent stem cell-derived cardiomyocytes. These rapid-throughput methods include microelectrode array-based field potential assay, impedance-based or Ca(2+) dynamics-based cardiomyocytes contractility assays. This review aims to discuss advantages and limitations of these phenotypic assays for cardiac toxicity assessment.