Abstract
AimsSmall conductance Ca2+-activated K+ channels (SK channels, KCa2) are a new target for treatment of atrial fibrillation (AF). AP30663 is a small molecule inhibitor of KCa2 channels that is currently in clinical development for treatment of AF. The aim of this study is to present the electrophysiological profile and mechanism of action of AP30663 and its efficacy in prolonging atrial refractoriness in rodents, and by bioinformatic analysis investigate if genetic variants in KCNN2 or KCNN3 influence the expression level of these in human heart tissue.Methods and ResultsWhole-cell and inside-out patch-clamp recordings of heterologously expressed KCa2 channels revealed that AP30663 inhibits KCa2 channels with minor effects on other relevant cardiac ion channels. AP30663 modulates the KCa2.3 channel by right-shifting the Ca2+-activation curve. In isolated guinea pig hearts AP30663 significantly prolonged the atrial effective refractory period (AERP) with minor effects on the QT-interval corrected for heart rate. Similarly, in anaesthetized rats 5 and 10 mg/kg of AP30663 changed the AERP to 130.7±5.4% and 189.9±18.6 of baseline values. The expression quantitative trait loci analyses revealed that the genome wide association studies for AF SNP rs13376333 in KCNN3 is associated with increased mRNA expression of KCNN3 in human atrial appendage tissue.ConclusionsAP30663 is a novel negative allosteric modulator of KCa2 channels that concentration-dependently prolonged rodent atrial refractoriness with minor effects on the QT-interval. Moreover, AF associated SNPs in KCNN3 influence KCNN3 mRNA expression in human atrial tissue. These properties support continued development of AP30663 for treatment of AF in man.
Highlights
Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting more than 30 million people worldwide, a number that is rising partly because of the aging population and better detection
We first investigate if genetic variants (SNPs) in KCNN2 or KCNN3 found in Genome wide association studies (GWAS) to be associated with AF influence the expression level of KCNN2 or KCNN3 in human atrial or ventricular tissue
The expression quantitative trait loci analyses effects of the AF GWAS associated single nucleotide polymorphisms (SNPs) rs337711 on KCNN2 and SNP rs13376333 on KCNN3 were investigated in the Genotype-Tissue Expression (GTEx) database, release v05-08-15, using default dashboard analytics setup
Summary
Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting more than 30 million people worldwide, a number that is rising partly because of the aging population and better detection. Preclinical studies showed that KCa2 channels during sinus rhythm as well as during AF play a more prominent role in atria as compared to ventricles in several species including man (Tuteja et al, 2005; Li et al, 2009; Diness et al, 2010; Qi et al, 2014; Skibsbye et al, 2014; Haugaard et al, 2015; Diness et al, 2017), thereby exhibiting a functional atrial specificity. We first investigate if genetic variants (SNPs) in KCNN2 or KCNN3 found in GWAS to be associated with AF influence the expression level of KCNN2 or KCNN3 in human atrial or ventricular tissue. We present the ion channel profile, mode of action, and in vitro, ex vivo and in vivo effects of the clinical candidate AP30663
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