Patient/Disease-specific Pharmacological Screening Utilizing a Human Induced Pluripotent Stem Cells Model of CPVT2

Background: Catecholaminergic polymorphic ventricular tachycardia type-2 (CPVT2) is an autosomal recessive disorder due to mutations in the cardiac calsequestrin (CASQ2) genecausing abnormal calcium (Ca²⁺) handling, ventricular arrhythmias, and sudden cardiac death.Objectives: To establish a patient-specific human induced pluripotent stem cells (hIPSC) model of CPVT2 and utilize the generated hiPSC-derived cardiomyocytes (hiPSC-CMs) for pharmacological screening.

Methods and Results: hiPSCs were derived from a CPVT2-patient inflicted with the D307H-CASQ2 mutation. Detailed laser-confocal Ca²⁺ imaging studies revealed significant Ca²⁺ handling abnormalities in 69% of CPVT2-hiPSC-CMs (in contrast to 15% in healthy-controls) including local Ca²⁺ release events (“Ca²⁺-sparks”) and arrhythmias ranging from single triggered beats to multiple Ca²⁺ release events. Isoproterenol elicited arrhythmias in the remaining CPVT2-CMs, but not in controls. Store-overload–induced Ca²⁺ release (SOICR) events were identified in the hiPSCs-CMs with a reduced threshold in the CPVT2-CMs. Detailed pharmacological studies revealed: (1) that beta adrenergic blockers (carvedilol, propranolol) prevented isoproterenol-induced arrhythmias; (2) that carvedilol, but not other beta- or alpha/beta-blockers, exhibited a direct anti-arrhythmic action in CPVT2-CMs suppressing arrhythmias in the absence of adrenergic stimulation; (3) that other suggested agents, hypothesized to be beneficial in CPVT, reduced arrhythmogenicity in the CPVT2-hiPSC-CMs including JTV-519, flecainide, and riluzole. Investigating the mechanism of the anti-arrhythmic effects, we noted that while carvedilol suppressed SOICR, triggered activity (TA) and diastolic Ca²⁺ release (DCR) events in CPVT2-CMs, flecainide at clinically relevant concentrations suppressed TA formation but not SOICR or DCR events. These findings suggest that the direct anti-arrhythmic effect of carvedilol in CPVT2 may be mediated via reduction of diastolic Ca²⁺ leak while flecainide, at clinically relevant concentrations, probably exerts its anti-arrhythmic effect in CPVT2 by increasing TA-threshold.

Conclusion: Our results demonstrate the ability of the hiPSC model to recapitulate CPVT2 phenotype in vitro, to provide novel insights into disease and drug therapy mechanisms, and potentially to individualize patient-specific therapy.