Introduction: Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) offer a novel in vitro platform for pre-clinical cardiotoxicity and pro-arrhythmia screening of drugs in development. To date hiPSC-CMs used for cardiotoxicity testing display an immature, fetal-cardiomyocyte electrophysiological phenotype which has called into question the applicability of hiPSC-CM findings to the adult heart.
Objective: The aim of the current work was to determine the effect of cardiomyocyte maturation state on hiPSC-CM drug responsiveness. To this end, here we developed a high content pro-arrhythmia screening platform consisting of either fetal or mature hiPSC-CM monolayers.
Methods and Results: hiPSC-CM maturation was apparent by assessment of cell shape, cellular hypertrophy, expression of mature ventricular myofilament proteins (β-myosin heavy chain and ventricular myosin light chain) and electrophysiological function. Compounds tested in the screen were selected based on the pro-arrhythmia risk classification (Low risk=tamoxifen and diltiazem; Intermediate risk= cisapride, clozapine and terfenadine; High risk= bepridil, dofetilide, quinidine and E-4031) established recently for the validation of the Comprehensive In vitro Pro-Arrhythmia Assay (CiPA). Other compounds tested include nilotinib, doxorubicin, amiodarone and fluoxetine. A voltage sensitive dye (FluoVolt) was used to quantify compound effects on hiPSC-CM action potential duration recorded using a high speed CCD-camera.
Conclusions: Results indicate that maturation state of hiPSC-CMs determines the absolute pro-arrhythmia risk score calculated for these compounds. Thus, the maturation state of hiPSC-CMs should be considered prior to pro-arrhythmia and cardiotoxicity screening in drug discovery programs.