Comprehensive translational assessment of human-induced pluripotent stem cell derived cardiomyocytes for evaluating drug-induced arrhythmias

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) hold promise for assessment of drug-induced arrhythmias and are being considered for use under the comprehensive in vitro proarrhythmia assay (CiPA). We studied the effects of 26 drugs and 3 drug combinations on 2 commercially available iPSC-CM types using high-throughput voltage-sensitive dye and microelectrode-array assays being studied for the CiPA initiative and compared the results with clinical QT prolongation and torsade de pointes (TdP) risk. Concentration-dependent analysis comparing iPSC-CMs to clinical trial results demonstrated good correlation between drug-induced rate-corrected action potential duration and field potential duration (APDc and FPDc) prolongation and clinical trial QTc prolongation. Of 20 drugs studied that exhibit clinical QTc prolongation, 17 caused APDc prolongation (16 in Cor.4U and 13 in iCell cardiomyocytes) and 16 caused FPDc prolongation (16 in Cor.4U and 10 in iCell cardiomyocytes). Of 14 drugs that cause TdP, arrhythmias occurred with 10 drugs. Lack of arrhythmic beating in iPSC-CMs for the four remaining drugs could be due to differences in relative levels of expression of individual ion channels. iPSC-CMs responded consistently to human ether-a-go-go potassium channel blocking drugs (APD prolongation and arrhythmias) and calcium channel blocking drugs (APD shortening and prevention of arrhythmias), with a more variable response to late sodium current blocking drugs. Current results confirm the potential of iPSC-CMs for proarrhythmia prediction under CiPA, where iPSC-CM results would serve as a check to ion channel and in silico modeling prediction of proarrhythmic risk. A multi-site validation study is warranted

Assessment of an in silico mechanistic model for proarrhythmia risk prediction under the CiPA initiative

International Council on Harmonization S7B and E14 regulatory guidelines are sensitive but not specific for predicting which drugs are proarrhythmic. In response, the Comprehensive In Vitro Proarrhythmia Assay (CiPA) was proposed that integrates multi-ion channel pharmacology data in vitro into a human cardiomyocyte model in silico for proarrhythmia risk assessment. Previously, we reported the model optimization and proarrhythmia metric selection based on CiPA training drugs. In this study, we report the application of the prespecified model and metric to independent CiPA validation drugs. Over two validation datasets, the CiPA model performance meets all pre-specified measures for ranking and classifying validation drugs, and outperforms alternatives, despite some in vitro data differences between the two datasets due to different experimental conditions and quality control procedures This suggests that the current CiPA model/metric is fit for regulatory use, and standard experimental protocols and quality control criteria could increase the model prediction accuracy even further

Assessment of an in silico mechanistic model for proarrhythmia risk prediction under the CiPA initiative

International Council on Harmonization S7B and E14 regulatory guidelines are sensitive but not specific for predicting which drugs are proarrhythmic. In response, the Comprehensive In Vitro Proarrhythmia Assay (CiPA) was proposed that integrates multi-ion channel pharmacology data in vitro into a human cardiomyocyte model in silico for proarrhythmia risk assessment. Previously, we reported the model optimization and proarrhythmia metric selection based on CiPA training drugs. In this study, we report the application of the prespecified model and metric to independent CiPA validation drugs. Over two validation datasets, the CiPA model performance meets all pre-specified measures for ranking and classifying validation drugs, and outperforms alternatives, despite some in vitro data differences between the two datasets due to different experimental conditions and quality control procedures This suggests that the current CiPA model/metric is fit for regulatory use, and standard experimental protocols and quality control criteria could increase the model prediction accuracy even further

Rate-dependent blockade of a potassium current in human atrium by the antihistamine loratadine

1. The antihistamine loratadine is widely prescribed for the treatment of symptoms associated with allergies. Although generally believed to be free of adverse cardiac effects, there are a number of recent reports suggesting that loratadine use may be associated with arrhythmias, in particular atrial arrhythmias. 2. Nothing is known regarding the potassium channel blocking properties of loratadine in human cardiac cells. Using the whole-cell patch clamp technique, the effects of loratadine on the transient outward K current (I(to)), sustained current (I(sus)), and current measured at −100 mV (I(K1) and I(ns)), the major inward and outward potassium currents present in human atrial myocytes, were examined in order to provide a possible molecular mechanism for the observed atrial arrhythmias reported with loratadine use. 3. Loratadine rate-dependently inhibited I(to) at therapeutic concentrations with 10 nM loratadine reducing I(to) amplitude at a pacing rate of 2 Hz by 34.9±6.0%. In contrast, loratadine had no effect on either I(sus) or current measured at −100 mV. 4. These results may provide a possible mechanism for the incidences of supraventricular arrhythmias reported with the use of loratadine

Ths JOURNAL OP PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Characterization of the Sodium Channel Blocking Properties of the Major Metabolites of Cocaine in Single Cardiac Myocytes1

ABSTRACT ABBREVIATIONS: BNZ, benZoylecgonlne; EME, ecgonine methyl ester; Kd,, dissociation constant for binding to inactivated channels; INs, sodium current; ANOVA, analysis of variance. 91

Comprehensive T wave Morphology Assessment in a Randomized Clinical Study of Dofetilide, Quinidine, Ranolazine, and Verapamil

BACKGROUND: Congenital long QT syndrome type 2 (abnormal hERG potassium channel) patients can develop flat, asymmetric, and notched T waves. Similar observations have been made with a limited number of hERG‐blocking drugs. However, it is not known how additional calcium or late sodium block, that can decrease torsade risk, affects T wave morphology. METHODS AND RESULTS: Twenty‐two healthy subjects received a single dose of a pure hERG blocker (dofetilide) and 3 drugs that also block calcium or sodium (quinidine, ranolazine, and verapamil) as part of a 5‐period, placebo‐controlled cross‐over trial. At pre‐dose and 15 time‐points post‐dose, ECGs and plasma drug concentration were assessed. Patch clamp experiments were performed to assess block of hERG, calcium (L‐type) and late sodium currents for each drug. Pure hERG block (dofetilide) and strong hERG block with lesser calcium and late sodium block (quinidine) caused substantial T wave morphology changes (P<0.001). Strong late sodium current and hERG block (ranolazine) still caused T wave morphology changes (P<0.01). Strong calcium and hERG block (verapamil) did not cause T wave morphology changes. At equivalent QTc prolongation, multichannel blockers (quinidine and ranolazine) caused equal or greater T wave morphology changes compared with pure hERG block (dofetilide). CONCLUSIONS: T wave morphology changes are directly related to amount of hERG block; however, with quinidine and ranolazine, multichannel block did not prevent T wave morphology changes. A combined approach of assessing multiple ion channels, along with ECG intervals and T wave morphology may provide the greatest insight into drug‐ion channel interactions and torsade de pointes risk. CLINICAL TRIAL REGISTRATION: URL: http://clinicaltrials.gov/ Unique identifier: NCT01873950