Defined Solution Corrects Phenotypic Response and Improves Detection Accuracy of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes to the 28 Comprehensive In Vitro Proarrhythmia Assay Standards

Abstract

We reported that blockade of Ca2+ channel increased beating rate on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) when in hiPSC-CM culture media, but decreased beating rate if extracellular potassium concentration was elevated above certain threshold. When hiPSC-CMs are used for cardiac safety assessment of drug candidates, a corrected phenotype of Ca2+ channel blockade, particularly for drug candidates possessing multiple cardiac ion channel activities, is expected to minimize exaggerated mitigation of human ether-à-go-go-related gene channel blockage and yield improved accuracy. To further demonstrate this concept, we tested the 28 Comprehensive in vitro Proarrhythmia Assay standards using 10 mM K+ defined solution, and compared the results with data from study using hiPSC-CM culture media. Identical test standard dimethyl sulfoxide stocks, experimental procedure, and data analysis method were used to reduce unrelated variation. We found that in the high-risk category, under 10 mM K+ condition, the early afterdepolarization (EAD)-causing concentrations for azimilide, D, l-sotalol, disopyramide, dofetilide, ibutilide, quinidine, and vandetanib were 14-fold, 0.7-fold, 14-fold, 1.6-fold, 0.01-fold, 3.2-fold, and 33-fold of their respective clinical free therapeutic concentrations. For intermediate-risk standards, 10 mM K+ condition still made hiPSC-CMs more sensitive to detect EADs in cases of cisapride, domperidone, droperidol, and pimozide. Also, the net effect of clozapine was shown to be due to Ca2+ channel blockade. The low-risk standards, metoprolol, mexiletine, and ranolazine no longer stopped hiPSC-CMs beating in 10 mM K+ condition. We conclude that 10 mM K+ condition improved detection accuracy for high- and intermediate-risk compounds, without overestimating torsadogenic risk of low-risk standards. Finally, we proposed an empirical proarrhythmic score system, helping to evaluate torsadogenic liability of drug candidates tested with hiPSC-CMs.