Effect of Drugs on Repolarization of IPSCD-Cardiomyocytes

The FDA has proposed a Comprehensive in Vitro Pro-Arrhythmia Assay (CiPA Initiative) to address the clinical potential for cardiotoxicity during pre-clinical drug development in part, this involves the use of human-induced pluripotent adult stem cell-derived cardiac myocytes (hiPSC-CM) as a model system to measure the effects of drugs on the cardiac action potential (AP). hiPSC-CMs, however, have little or no IK1, resulting in unstable APs and anomalous behavior in the presence of some drugs. We stabilized APs from hiPSC-CMs through the electronic addition of IK1 via dynamic clamp. hiPSC-CMs (iCell, Inc., WI) were cultured according to manufacturer's instructions, and studied using the Amphotericin B perforated patch technique. Cardiac APs (1.5-2.0 nA stimulus pulse for 1.5 ms, 0.5 Hz) were measured in the absence and presence of increasing drug concentrations. As expected, quinidine, dofetilide, cisapride and sotalol (known IKR blockers) caused dose-dependent increases in APD. In 10 μM quinidine APD90 increased 144±12%; 1420 nM dofetilide increased APD90 128±3%; 103 nM cisapride increased, APD90 170±6%; 324 μM sotalol increased APD90 139±14%). Further, qualitative differences in potentiation were observed in that cisapride and sotalol, but not dofetilide, caused a pronounced flattening in Phase 2 of the AP. Quinidine (10 μM) also decreased dV/dtmax by 68±18%, which is consistent with Na+ channel block. Nifedipine (300nM), a Ca2+ channel blocker, significantly decreased APD90 by 35±1%. The ability to measure stable cardiac APs by the electronic addition of IK1 allows for more accurate comprehensive evaluation of drug effects on the ion channel components comprising the cardiac AP, particularly in the case of sodium channel block, and may aid in the identification of pro-arrhythmic changes in AP morphology.