In silico screening of the impact of hERG channel kinetic abnormalities on channel block and susceptibility to acquired long QT syndrome

Abstract

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 of IKr channels. We then screened and identified the properties of IKr blockers that caused acquired long QT and therefore unmasked mutant phenotypes for mild, moderate and severe variants. Mutant IKr channels were incorporated into the O'Hara et al. human ventricular action potential (AP) model and subjected to simulated application of a wide variety of IKr–drug interactions in order to identify the characteristics that selectively exacerbate the AP duration (APD) differences between wild-type and IKr mutated cells. Our results show that drugs with disparate affinities to conformation states of the IKr channel are key to amplify variants underlying susceptibility to acquired long QT syndrome, an effect that is especially pronounced at slow frequencies. Finally, we developed a mathematical formulation of the M54T MiRP1 latent mutation and simulated a provocative test. In this setting, application of dofetilide dramatically amplified the predicted QT interval duration in the M54T hMiRP1 mutation compared to wild-type.

A multiscale computational modelling approach predicts mechanisms of female sex risk in the setting of arousal‐induced arrhythmias

“…An I Kr Markov model (Romero et al 2014) was incorporated into the O'Hara-Rudy human ventricular action potential (AP) model (O'Hara et al 2011) to simulate the effects of dofetilide on I Kr .…”

“…Dofetilide is a prototype of the pro-arrhythmic classassociated with hERG block, QT prolongation and TdP (Van Opstal et al 2001). We recently developed a detailed kinetically based model of the hERG blocker dofetilde by extending the consensus five-state Markov chain model that includes three closed states (C 3 , C 2 and C 1 ), a conducting open state (O) and an inactivation state (I) (Romero et al 2014). The expanded I Kr model that includes dofetilide interactions was incorporated into the O'Hara-Rudy model of the J Physiol 595.14 human ventricular action potential (AP) (O'Hara et al 2011).…”

“…The dofetilide model, described and validated in detail previously (Romero et al 2014), includes the experimentally observed 70-fold preferential binding to the inactivated state relative to the open state (Perrin et al 2008) and mimics the clinically observed 16% prolongation of the QT interval produced by the therapeutic dose 8.22 nM (Demolis et al 1996). The effects of the female hormones 17β-oestradiol (E2) and progesterone (Pg), the male hormone dihydrotestosterone (DHT) and sex-specific genomic-based differences in expression of key cardiac channels on human action potentials from this study and O'Hara et al (2011) and Yang & Clancy (2012) were also incorporated to develop female and male models as described in more details in Methods above.…”

The virtual heart as a platform for screening drug cardiotoxicity

“…Drug molecular binding to channel states with different conformations or a distinct affinity presents complex behaviours. In a recent study, Romero et al (2014) Based on experimental data on the effect of the antipsychotic clozapine on hERG channel blocking and unblocking kinetics, Hill et al (2014) proposed an hERG channel model with kinetically distinct binding states of the drug to open and inactivation states. Their modelling data effectively illustrated the interaction between clozapine and hERG channels in acquired LQT (Hill et al, 2014).…”

Modeling Inherited Arrhythmia Disorders Using Induced Pluripotent Stem Cell-Derived Cardiomyocytes

“…Expression of mutant genes in non-cardiac expression systems has allowed the characterization of the effect of mutations on individual channel function 14,15 . These analyses have been augmented by structural homology modeling 16 and by computational models that integrate individual channel properties into virtual APs 16,17 . Genetically modified mouse, and more recently rabbit and pig, models have been useful to assess the effect of mutations within intact animals 18–20 .…”