International Multisite Study of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Drug Proarrhythmic Potential Assessment.

To assess the utility of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) as an in vitro proarrhythmia model, we evaluated the concentration dependence and sources of variability of electrophysiologic responses to 28 drugs linked to low, intermediate, and high torsades de pointes (TdP) risk categories using two commercial cell lines and standardized protocols in a blinded multisite study using multielectrode array or voltage-sensing optical approaches. Logistical and ordinal linear regression models were constructed using drug responses as predictors and TdP risk categories as outcomes. Three of seven predictors (drug-induced arrhythmia-like events and prolongation of repolarization at either maximum tested or maximal clinical exposures) categorized drugs with reasonable accuracy (area under the curve values of receiver operator curves ∼0.8). hiPSC-CM line, test site, and platform had minimal influence on drug categorization. These results demonstrate the utility of hiPSC-CMs to detect drug-induced proarrhythmic effects as part of the evolving Comprehensive In Vitro Proarrhythmia Assay paradigm.

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 sarcoplasmic reticulum Ca(2+) flux pathways in cardiomyocytes from rabbits with infarct-induced left-ventricular dysfunction.

The aim of the study was to correlate intracellular Ca(2+) transients with Ca(2+) uptake and efflux characteristics of the sarcoplasmic reticulum (SR) in ventricular myocytes isolated from rabbits with left-ventricular dysfunction (LVD). Chronic (8 weeks) ligation of a coronary artery caused marked LVD in rabbits. Measurements of intracellular [Ca(2+)] were made using Fura-2 on intact, single, left-ventricular myocytes. SR Ca(2+) flux rates associated with sarco-endoplasmic reticulum Ca(2+) ATPase type 2 (SERCA2)-mediated uptake, ryanodine receptor type 2 (RyR2)-mediated Ca(2+) efflux and background SR Ca(2+) leak were measured in suspensions of permeabilised myocytes. Measurements on single, permeabilised myocytes were used to assess the steady-state Ca(2+) content of the SR and the characteristics of spontaneous SR Ca(2+) release. Peak systolic [Ca(2+)] was significantly lower; time-to-peak and Ca(2+) transient duration were significantly longer in LVD myocytes. SERCA2-mediated Ca(2+) uptake was reduced to approximately 50% in myocytes from the LVD group. Ruthenium red (RuR)-sensitive Ca(2+) efflux (mediated by the RyR2) was also reduced in the LVD group by approximately 50%, as was the remaining (RuR-insensitive) background Ca(2+) leak. Measurements from single, permeabilised myocytes showed a lower steady-state SR Ca(2+) content. The frequency and amplitude of spontaneous SR Ca(2+) release from LVD hearts was also reduced. Partial inhibition of SERCA2 by thapsigargin depressed both the amplitude and the frequency of spontaneous release. Partial inhibition of RyR2-mediated-Ca(2+) efflux with tetracaine enhanced spontaneous Ca(2+) release amplitude and decreased frequency. Increased background Ca(2+) leak with ionomycin decreased the frequency of spontaneous release. It is concluded that partial inhibition of SERCA2 mimics some aspects of altered SR function in LVD, but reduced RyR2 function cannot explain the other functional alterations observed. Reduced background Ca(2+) leak from the SR may compensate partly for the reduced Ca(2+) uptake capacity of the SR in the LVD group.