Identification of Human Ether-a-go-go Related Gene Modulators by Three Screening Platforms in an Academic Drug-Discovery Setting

The human Ether-a-go-go related gene (hERG) potassium channel is responsible for the rapid delayed rectifier potassium current that plays a critical role in the repolarization of cardiomyocytes during the cardiac action potential. In humans, inhibition of hERG by drugs can prolong the electrocardiographic QT interval, which, in rare instance, leads to ventricular arrhythmia and sudden cardiac death. As such, several medications that block hERG channels in vitro have been withdrawn from the market due to QT prolongation and arrhythmias. The current FDA guidelines recommend that drug candidates destined for human use be evaluated for potential hERG activity (www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm074963.pdf). Here, we employed automated planar patch clamp (APPC), high-throughput fluorescent Tl+ flux, and moderate-throughput [H-3]dofetilide competition binding assays to characterize a panel of 49 drugs for their activities at the hERG channel. Notably, we used the same HEK293-hERG cell line for all assays, facilitating comparisons of hERG potencies across screening platforms. In general, hERG inhibitors were most potent in APPC assays, intermediate potent in [H-3] dofetilide binding assays, and least potent in Tl+ flux assays. Binding affinity constants (pK(i) values) and Tl+ flux potencies (pEC(50) values) correlated well with APPC pEC(50) values. Further, the inhibitory potencies of many known hERG inhibitors in APPC matched literature values from manual and/or automated patch clamp systems. We also developed a novel fluorescent Tl+ flux assays to measure the effects of drugs that modulate hERG trafficking and surface expression.