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

Abstract

Aims: Small conductance Ca 2+ -activated K + channels (SK channels, K Ca 2) are a new target for treatment of atrial fibrillation (AF). AP30663 is a small molecule inhibitor of K Ca 2 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 Results: Whole-cell and inside-out patch-clamp recordings of heterologously expressed K Ca 2 channels revealed that AP30663 inhibits K Ca 2 channels with minor effects on other relevant cardiac ion channels. AP30663 modulates the K Ca 2.3 channel by right-shifting the Ca 2+ -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.Conclusions: AP30663 is a novel negative allosteric modulator of K Ca 2 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.

The KCa2 Channel Inhibitor AP30663 Selectively Increases Atrial Refractoriness, Converts Vernakalant-Resistant Atrial Fibrillation and Prevents Its Reinduction in Conscious Pigs

“…As the first K Ca 2 inhibitor to enter clinical trials, AP30663 was selected to be the lead compound based on a screening of >1,000 compounds in a lead optimization program. AP30663 has consistently shown the wanted technical quality and necessary properties in various in vitro and in vivo models, some of which are presented in Bentzen et al, 2020 In the current study we document a pronounced effect on atrial refractoriness by K Ca 2 inhibition with AP30663. Importantly, we have shown that AP30663 can convert AF to a sinus rhythm in a pig model of AF where existing pharmacotherapy fails.…”

“…An increase of the QT interval would not be improbable, considering that AP30663 was associated with a K V 11.1 IC 50 of 15 and 4 μM in two different analyses (Bentzen et al, 2020).…”

“…The current results support that an AERP increase of ≥30 ms in pigs is a meaningful measure for predicting cardioversion efficacy since infusion of 5 mg/kg AP30663 over 30 min produced a free plasma concentration of 1.14 ± 0.04 μM in our PK pigs which is within the concentration range of 1.0-1.4 μM where conversion to sinus rhythm was observed in the A-TP induced AF pigs. Since cardioversion takes place at a concentration that corresponds to the in vitro K Ca 2 IC 50 value (Bentzen et al, 2020), i.e. when~50% of the I KCa is blocked, it could be speculated that there is room for better effects at higher plasma concentrations of AP30663.…”

“…In the current study we document a pronounced effect on atrial refractoriness by K Ca 2 inhibition with AP30663. It would not be unreasonable to expect some degree of QT prolongation based on both the presence of K Ca 2 mRNA in the ventricles and the fact the AP30663 blocks the hERG channel with an IC 50 of 4-15 μM (Bentzen et al, 2020), but the clinical development program has so far demonstrated minor impact on QT intervals at expected supratherapeutic doses for atrial efficacy.…”

“…Inhibition of K Ca 2 channels with different compounds converted AF and/or protected against its induction in models of AF in isolated perfused hearts from rat, guinea pig, and rabbit as well as in in vivo models of AF in rat, dog, pig, goat, and horse (Diness et al, 2010;Diness et al, 2011;Skibsbye et al, 2011;Qi et al, 2013;Haugaard et al, 2015;Diness et al, 2017;Gatta et al, 2019). The small molecule AP30663 selectively inhibits K Ca 2 channels thereby diminishing the current mediated by them, I KCa (Bentzen et al, 2020). Other small-molecule K Ca 2 channel inhibitors give rise to adverse central nervous effects such as vomiting and tremors (Diness et al, 2017;Simó-Vicens et al, 2017), but this does not seem to be the case with AP30663.…”