Delayed Repolarization Caused by hERG Block With Different Drug Modalities Can Be Detected in Stem Cell-Derived Cardiomyocytes: Incubation Time Matters.

The intrinsic characteristics of oligonucleotides pose a challenge for their assessment in conventional primary in vitro cardiac models, which were designed for the acute application of small molecule agents and are not suitable for transfection and extended culture periods. Conversely, human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) offer a viable platform for the evaluation of agents over prolonged application and recording times. Our previous experiments demonstrated that a chronic protocol of 48 h is necessary to discern the functional effects of a siRNA targeting hERG in a stable cell line heterologously expressing hERG. To investigate whether a targeted hERG siRNA induces delayed repolarization in hiPSC-CM, we recorded field potentials (FPs) using a multielectrode array. FP duration (FPD) prolongation was noted as early as 10 min after exposure to moxifloxacin, whereas pentamidine required 24 h to induce FPD prolongation. Transfection with hERG-targeting siRNA reduced mRNA expression at 6 h post-transfection. However, FPD prolongation was only observed after 24 h post-transfection, with significantly larger effects at 48 h, which is indicative of the time needed for turnover of the hERG protein on the plasma membrane. Our findings provide compelling evidence that MEA recordings in hiPSC-CM can accurately detect disruptions in cardiac repolarization due to various mechanisms that impair hERG channel function, including direct channel blockade, inhibition of protein trafficking, and gene silencing via siRNA. The findings also indicate that indirect mechanisms of hERG knockdown, including gene silencing, require assessment at least 48 h following treatment to detect delayed repolarization in the hiPSC-CM model.