A Novel Approach for Evaluation of Drug-Induced QT Prolongation using Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Abstract

Drug-induced cardiac arrhythmias characterized by QT prolongation have been a major reason for drug withdrawal at late stage of clinical trials. Species difference is a cause of insufficient predictability of current drug safety models. Therefore, human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) have great promise for application of cardiac drug safety testing as a human cardiac model. Our perforated patch-clamp recordings from hiPS-CMs revealed that the cells exhibited diverse shapes of spontaneous action potentials (APs) with relatively small upstroke velocity (∼10V/s) and depolarized maximum diastolic potential (MDP; >-50 mV), which represents rather immature forms of cardiac cells. Actually, a selective hERG blocker, E4031,depolarized significantly MDP and stopped spontaneous beatings on a monolayer of hiPS-CMs, which makes it difficult to evaluate the effects on AP durations.Thus, in order to improve evaluation of risks for drug-induced QT prolongation in hiPS-CMs, we generated ventricular-like hiPS-CMs by over-expressing protein-X into hiPS-CMs and characterized the utility for evaluation of drug effects on cardiac repolarization process. The protein-X over-expression made hiPS-CMs quiescent with hyperpolarized MDP (−67 mV), and were excitable with rapid upstroke velocity (∼95 V/s) by electrical field stimulation. When E4031 was applied to hiPS-CMs overexpressing protein-X, both AP durations of single myocytes and extracellular field potential durations of cardiac sheets were prolonged in a dose dependent manner. These results suggest that hiPS-CMs engineered with gene X would be a novel approach for evaluation of drug-induced alternation of repolarization processes in the human cardiomyocytes.