TY - JOUR

T1 - A New Negative Allosteric Modulator AP14145 for the Study of Small Conductance Calcium-Activated Potassium Channels

AU - Simo Vicens, Rafel

AU - Kirchhoff, Jeppe Egedal

AU - Dolce , Bernardo

AU - Abildgaard, Lea

AU - Speerschneider, Tobias

AU - Sørensen, Ulrik Svane

AU - Grunnet, Morten

AU - Diness, Jonas Goldin

AU - Bentzen, Bo Hjorth

PY - 2017/12/5

Y1 - 2017/12/5

N2 - Background and purpose: Small conductance Ca2+-activated K+ (KCa2) channels represent a promising atrial-selective target for treatment of atrial fibrillation (AF). Here, we establish the mechanism of KCa2 inhibition by the new compound AP14145.Experimental approach: Using site directed mutagenesis binding determinants for AP14145 inhibition were explored. AP14145 selectivity and mechanism of action were investigated by patch clamp recordings of heterologously expressed KCa2 channels. The biological efficacy of AP14145 was assessed by measuring atrial effective refractory period (AERP) prolongation in anaesthetised rats and a beam walk test was performed in mice to determine acute CNS related effects of the drug.Key results: AP14145 was found to be an equipotent negative allosteric modulator of KCa2.2 and KCa2.3 channels (IC50 = 1.1 ± 0.3 μM L-1). The presence of AP14145 (10 μM L-1) increased the EC50 of Ca2+ on KCa2.3 from 0.36 ± 0.02 μM L-1 to 1.2 ± 0.1 μM L-1. The inhibitory effect strongly depended on two amino acids, S508 and A533. AP14145 concentration-dependently prolonged AERP in rats. Moreover, AP14145 (10 mg kg-1) did not trigger any apparent CNS effects in mice.Conclusion and implications: AP14145 is a negative allosteric modulator of KCa2.2 and KCa2.3 that shifts the calcium dependence of channel activation, an effect strongly dependent on two identified amino acids. AP14145 prolongs AERP in rats and does not trigger any acute CNS effects in mice. The understanding of how KCa2 inhibition is accomplished at the molecular level will help future development of drugs targeting KCa2 channels.

AB - Background and purpose: Small conductance Ca2+-activated K+ (KCa2) channels represent a promising atrial-selective target for treatment of atrial fibrillation (AF). Here, we establish the mechanism of KCa2 inhibition by the new compound AP14145.Experimental approach: Using site directed mutagenesis binding determinants for AP14145 inhibition were explored. AP14145 selectivity and mechanism of action were investigated by patch clamp recordings of heterologously expressed KCa2 channels. The biological efficacy of AP14145 was assessed by measuring atrial effective refractory period (AERP) prolongation in anaesthetised rats and a beam walk test was performed in mice to determine acute CNS related effects of the drug.Key results: AP14145 was found to be an equipotent negative allosteric modulator of KCa2.2 and KCa2.3 channels (IC50 = 1.1 ± 0.3 μM L-1). The presence of AP14145 (10 μM L-1) increased the EC50 of Ca2+ on KCa2.3 from 0.36 ± 0.02 μM L-1 to 1.2 ± 0.1 μM L-1. The inhibitory effect strongly depended on two amino acids, S508 and A533. AP14145 concentration-dependently prolonged AERP in rats. Moreover, AP14145 (10 mg kg-1) did not trigger any apparent CNS effects in mice.Conclusion and implications: AP14145 is a negative allosteric modulator of KCa2.2 and KCa2.3 that shifts the calcium dependence of channel activation, an effect strongly dependent on two identified amino acids. AP14145 prolongs AERP in rats and does not trigger any acute CNS effects in mice. The understanding of how KCa2 inhibition is accomplished at the molecular level will help future development of drugs targeting KCa2 channels.

KW - Faculty of Health and Medical Sciences

KW - AP14145

KW - Atrial fibrillation

KW - small conductance calcium-activated potassium channels

KW - Electrophysiology

KW - SK channel

KW - negative allosteric modulator

U2 - 10.1111/bph.14043

DO - 10.1111/bph.14043

M3 - Journal article

C2 - 28925012

VL - 174

SP - 4396

EP - 4408

JO - British Journal of Pharmacology

JF - British Journal of Pharmacology

SN - 0007-1188

IS - 23

ER -