In vitro activity: Eleclazine hydrochloride (also known as GS-6615) is a novel late Na+ current inhibitor with IC50 value of 0.7 uM. Enhanced late Na+ current (late INa ) in the myocardium is pro-arrhythmic. Inhibition of this current is a promising strategy to stabilize ventricular repolarization and suppress arrhythmias. Eleclazine was a selective inhibitor of late INa , stabilizes the ventricular repolarization and suppresses arrhythmias in a model of LQT3. The concentrations at which the electrophysiological effects of Eleclazine were observed are comparable to plasma levels associated with QTc shortening in patients with LQT3, indicating that these effects are clinically relevant.

Kinase Assay: Eleclazine is currently in clinical development for the treatment of long QT syndrome 3 (LQT3). Eleclazine hydrochloride inhibits ATX-II enhanced late INa in ventricular myocytes, shorten the ATX-II induced prolongation of APD, MAPD, QT interval, and decreased spatiotemporal dispersion of repolarization and ventricular arrhythmias. Inhibition by GS-6615 of ATX-II enhanced late INa is strongly correlated with shortening of myocyte APD and isolated heart MAPD

Cell Assay: GS-6615 inhibited ATX-II enhanced late INa in ventricular myocytes (IC50 = 0.7 μM), shortened the ATX-II induced prolongation of APD, MAPD, QT interval, and decreased spatiotemporal dispersion of repolarization and ventricular arrhythmias. Inhibition by GS-6615 of ATX-II enhanced late INa was strongly correlated with shortening of myocyte APD and isolated heart MAPD (R2 = 0.94 and 0.98 respectively). In contrast to flecainide, GS-6615 had the minimal effects on peak INa . GS-6615 did not decrease the maximal upstroke velocity of the action potential (Vmax) nor widen QRS intervals.