Etripamil - a multichannel modulator to suppress atrial fibrillation

Abstract Background Etripamil is a novel fast-acting class IV antiarrhythmic agent for the treatment of AV-nodal-dependent tachycardia. More recent trials have also suggested therapeutic potential in rate control of atrial fibrillation (AF). Yet, little is known about etripamil’s precise molecular pharmacodynamics, which may involve other targets besides L-type Ca2+ channels. As with other multi-channel modulators, complete knowledge of etripamil's ion channel inhibition profile is essential to determine its optimal use in clinical practice. Purpose We analysed the effects of etripamil on the electrophysiology of human atrial cardiomyocytes (CMs) to assess its therapeutic potential in AF therapy. Methods Patch-clamp recordings of human atrial CMs were used to study etripamil’s effects on outward K+ currents, inward Na+ current, as well as action potentials (APs). Bulk RNA sequencing of human atrial tissue samples was used to analyse the differential ion channel expression in SR vs. AF. Two electrode voltage clamp (TEVC) experiments were used to study the effects on atrial ion channels heterologously expressed in X. laevis oocytes. In silico docking simulations using AutoDock Vina were performed to identify binding sites on target channels, whose functional significance was subsequently assessed using alanine mutagenesis scanning in TEVC. Computational cardiac modelling was employed to assess the ability of etripamil to achieve cardioversion of AF at the tissue level. Results In patch-clamp measurements of induced APs, treatment with rising concentrations of etripamil (0.25 µM, 2.5 µM and 6.25 µM) caused prolongation of the APD90 in CMs obtained from patients with SR and AF (+43%, p<0.001 and +48%, p=0.052 for 6.25 µM, respectively). Moreover, in voltage clamp recordings of human CMs, we observed significant reductions in the sustained outward K+ current (-0.50 pA/pF, p=0.026) and the inward Na+ current (-5.04 pA/pF, p=0.002) after application of 1 µM etripamil. TEVC studies showed that 100 µM etripamil potently inhibited the KV1.5 (74% block), TASK-1 (70%) and TASK-3 (74%), hERG (82%), Kir3.1/3.4 (59%) and KCNQ1/KCNE1 (71%), and NaV1.5 channels (59%), which was higher than for CaV1.2 (31%), etripamil’s class-defining main target. Additional TEVC studies showed comparatively high affinity for TASK-1 (IC50=18.7 µM). Docking simulations and alanine mutagenesis scanning revealed a direct pore-occluding mechanism similar to other TASK-1 inhibitors (e.g. Doxapram). In silico modelling at the tissue level indicates that etripamil may acutely terminate reentrant activity. Conclusions Our results suggest that etripamil exerts class I and III antiarrhythmic effects in addition to the known class IV effect on human atrial CMs through direct inhibition of atrial K+ and Na+ channels, including TASK-1, whose expression has been shown to be upregulated in AF. Tissue level simulations further support the suitability of etripamil for rhythm control of AF.