Using Onset-Of-Block Kinetic Analysis Of Herg1 Current With A Markov Model To Improve In Silico Proarrhythmogenic Risk Prediction

The comprehensive in vitro pro-arrhythmia assay (CiPA) in silico working group developed a computational assay for proarrhythmogenic risk prediction based on numeric integration runs of the O’Hara-Rudy 2011 human ventricular cardiomyocyte mathematical model (with default parameters for subendocardial cardiomyocytes), including a Markov model for hERG channels (human ether-à-go-go related gene) that conduct the rapid delayed rectifier K+ current IKr (named ORd-IKr dynamic model, Li et al. 2017 Circ Arrhythm Electrophysiol. 10(2):e004628). A subsequent study (Dutta et al. 2017 Front Physiol. 8:616) used the ORd-IKr dynamic model with pharmacological inhibition data for a panel of 12 drugs with low, intermediate, and high proarrhythmogenic risk to assess the effectiveness of multiple proarrhythmogenic risk predictors based on action potential (AP) and intracellular calcium dynamics during AP, as well as the newly defined predictors cQinward and Qnet, concluding that Qnet represents the most reliable predictor. We reproduced these simulations for the 12-compound panel based on published pharmacological inhibition data using the ORd model with default parameters for midmyocardial cardiomyocytes. Using the classical (Hodgkin-Huxley-type) IKr model we found good predictability of early afterdepolarizations (EADs) development (their detection can be itself a good predictor), while with the Markov IKr model no EADs were detected in the range 1-25x Cmax (maximal therapeutic plasma concentration), except for dofetilide. Therefore we modified the hERG blocking and unblocking rates for cisapride, quinidine, terfenadine and bepridil according to our own experimental pharmacology results in whole-cell patch-clamp experiments on HEK293 cells stably transfected with hERG1, applying an onset-of-block kinetics analysis of the currents recorded with a simplified Milnes protocol with 10-s depolarizing steps to 0 mV repeated at 35-s intervals, obtaining direct EAD generation for all these compounds with the ORd-IKr dynamic model.