Abstract 504: Cardiac Safety Profile of Etamicastat, a Novel Peripheral Selective Dopamine-ß-Hydroxylase Inhibitor, in the Dog

Abstract

Etamicastat, a peripheral reversible dopamine-ß-hydroxylase inhibitor, blocked the hERG current amplitude with an IC50 value of 35.4 μg/ml in HEK 293 cells. At 0.3 and 3 μg/ml, etamicastat had no effects on the action potential (AP) in dog Purkinje fibers. At 30 μg/ml, etamicastat significantly affected resting membrane potential (+4%), AP amplitude (-4%), AP duration at 60% (-14%) and AP duration at 90% (+5%) repolarization, and AP triangulation (+79%). In the telemetered conscious dog, etamicastat (up to 20 mg/kg) had no effects on arterial blood pressure, heart rate and the PR interval. At 10 and 20 mg/kg, the QTc interval was slightly prolonged (8 to 9% max, P < 0.05). No arrhythmia or other changes in the morphology of the ECG were observed. The maximum observed plasma concentrations (Cmax) of etamicastat (i.e. 3h post administration) were 1.4 and 3.7 μg/ml at 10 and 20 mg/kg, respectively. No deleterious effects, including ECG disturbance were observed in male and female dogs dosed by gavage with etamicastat (up to 20 mg/kg/day) for 28 days. Mean plasma Cmax etamicastat levels ranged between 2.4 and 6.3 μg/ml on Day 1 and Day 28 of treatment, respectively. It is concluded that the blockade of the delayed rectifier potassium channels by etamicastat together with the QTc interval prolongation observed in conscious dogs can be considered as modest with respect to the measured plasmatic concentrations. These findings suggest that etamicastat is not likely to prolong the QT interval at therapeutic doses (~ 0.2 μg/ml).