Mechanisms of Action of the KCa2-Negative Modulator AP30663, a Novel Compound in Development for Treatment of Atrial Fibrillation in Man.

Aims: Small conductance Ca-activated K channels (SK channels, K2) are a new target for treatment of atrial fibrillation (AF). AP30663 is a small molecule inhibitor of K2 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 or influence the expression level of these in human heart tissue.

Methods And Results: Whole-cell and inside-out patch-clamp recordings of heterologously expressed K2 channels revealed that AP30663 inhibits K2 channels with minor effects on other relevant cardiac ion channels. AP30663 modulates the K2.3 channel by right-shifting the Ca-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 is associated with increased mRNA expression of in human atrial appendage tissue.

Conclusions: AP30663 is a novel negative allosteric modulator of K2 channels that concentration-dependently prolonged rodent atrial refractoriness with minor effects on the QT-interval. Moreover, AF associated SNPs in influence mRNA expression in human atrial tissue. These properties support continued development of AP30663 for treatment of AF in man.