Evaluation of cellular impedance measures of cardiomyocyte cultures for drug screening applications.

Cardiovascular toxicity is a leading contributor to drug withdrawal and late-stage attrition. Earlier and broader screening is a validated approach to build-in cardiovascular safety as demonstrated with human Ether-à-go-go-related gene (hERG) screening to reduce drug-induced arrhythmia. There is an urgent need for novel in vitro assays to address other mechanistic aspects of cardiovascular function, including contractility, heart rate, toxicity, hypertrophy, and non-hERG arrhythmia. Recent advances in label-free cellular impedance technology now enable tracking of spontaneous, synchronized beating of cultured cardiomyocytes. Analysis of beating allows integrated detection that is downstream of electrical and mechanical aspects of contraction. Here, we evaluate impedance-based cardiomyocyte responses against criteria required for drug screening. The throughput and sensitivity allowed for rapid assay development. Critical variables for rat neonatal cardiomyocyte assays included cell density and serum levels. Once optimized, consistent, stable beating for at least 3 days was straight-forward to achieve. In tests of compounds spanning a breadth of target classes, the potency values showed excellent precision, wide dynamic range, and consistency across multiple experiments. Cardiomyocyte impedance assays can extract multiple beat-related parameters. In these experiments, rate, amplitude, and rise slope were examined and each yielded acceptable precision. Potency values calculated by beat rate and amplitude were highly correlated for most compounds although selected compounds displayed unique profiles indicative of different mechanisms. Tests with known cardiovascular active drugs revealed concordance with clinical findings. Thus, impedance assays combine novel features including sensitivity to contractile activity, versatile data analysis, and robust/translatable data in a format with sufficient throughput to become a valuable addition to the cardiovascular in vitro screening arsenal.