In silico screening of the impact of hERG channel kineticabnormalities on channel block and susceptibility to acquired long QTsyndrome

摘要

Accurate diagnosis of predisposition to long QT syndrome is crucial for reducing the risk of cardiac arrhythmias. In recent years, drug-induced provocative tests have proved useful to unmask some latent mutations linked to cardiac arrhythmias. In this study we expanded this concept by developing a prototype for a computational provocative screening test to reveal genetic predisposition to acquired long-QT syndrome (aLQTS). We developed a computational approach to reveal the pharmacological properties of IKr blocking drugs that are most likely to cause aLQTS in the setting of subtle alterations in IKr channel gating that would be expected to result from benign genetic variants. We used the model to predict the most potentially lethal combinations of kinetic anomalies and drug properties. In doing so, we also implicitly predicted ideal inverse therapeutic properties of K channel openers that would be expected to remedy a specific defect. We systematically performed “in silico mutagenesis” by altering discrete kinetic transition rates of the Fink et al. Markov model of human IKr channels, corresponding to activation, inactivation, deactivation and recovery from inactivation ofIKr channels. We then screened and identified the properties ofIKr blockers that caused acquired long QT and therefore unmaskedmutant phenotypes for mild, moderate and severe variants. Mutant IKrchannels were incorporated into the O'Hara et al. human ventricularaction potential (AP) model and subjected to simulated application of a widevariety of IKr–drug interactions in order to identify thecharacteristics that selectively exacerbate the AP duration (APD) differencesbetween wild-type and IKr mutated cells. Our results show that drugswith disparate affinities to conformation states of the IKr channelare key to amplify variants underlying susceptibility to acquired long QTsyndrome, an effect that is especially pronounced at slow frequencies. Finally,we developed a mathematical formulation of the M54T MiRP1 latent mutation andsimulated a provocative test. In this setting, application of dofetilidedramatically amplified the predicted QT interval duration in the M54T hMiRP1mutation compared to wild-type.