Defining the Limits of Stem-Cell Derived Cardiomyocytes (SC-CMS) to Detect Cardiac Proarrhythmic Liabilities

Abstract

Extracellular Field Potential (FP) and impedance recordings of SC-CMs are currently used to detect drug induced cardiac arrhythmia liabilities. Major endpoints include the field potential duration (FPD), the duration of the impedance twitch, and the presence of proarrhythmic markers including early and delayed afterdepolarizations and fibrillations. We used the cardioECR instrument (ACEA Biosciences) and iCell2 cardiomyocytes (Cellular Dynamics International) to 1) identify the FP parameter that best captures the intrinsic frequency-dependence of repolarization and, 2) assess the extent the system can detect the mitigating effect of drugs with multiple ion channels effects (MICE) on proarrhythmic activity. Cardiac repolarization in FP recordings is encapsulated by one positive (T3) and two negative (T1, T2) peaks. We detected a linear relationship with comparable slopes of 0.133 and 0.129 respectively (n=2) between T2 and T3 durations and beat period in the spontaneous frequency range. T1 shows a shallower slope (0.031) suggesting that the parameter does not follow closely the repolarization process and consistent with its limited response to drugs that prolong the FPD. MICE effects were investigated by assessing the effect of different combinations of pure hERG (E-4031) and hCav1.2 (nifedipine) channel blockers designed to simulate distinct IC50 hERG/IC50 hCav1.2 ratios (HCR). The functional relationship between the number of wells showing proarrhythmic markers and log (HCR) was fitted to a logistic function with an inflection point at −0.148 and a HCR of 0.71. Notably, this ratio is comparable to the 0.89 cutoff for torsadogenic drugs in the clinic (Kramer, Obejero-Paz et al., 2013). SC-CMs are useful tools to investigate the cardiac risks of drugs by using T2 and T3 to evaluate changes in cardiac repolarization and HCR values (≤ 0.71) to determine proarrhythmic activity.