First-in-man study of ACT-709478, a novel selective triple T-type calcium channel blocker

Increased activity of T-type Ca²⁺ channels is linked to idiopathic generalized epilepsies, thus blocking these channels may be a new treatment option. ACT-709478 is an orally available triple T-type Ca²⁺ channel blocker. The aim of this first-in-man study was to investigate the pharmacokinetics, pharmacodynamics, tolerability, and safety of single doses of ACT-709478 in healthy subjects.

This double-blind, placebo-controlled, randomized study included 65 healthy male subjects. Ascending single oral doses of 1-400 mg ACT-709478 or placebo were administered to sequential groups of eight subjects (6 on active, 2 on placebo). Effect of food was tested in a crossover part at 60 mg. Blood and saliva sampling for pharmacokinetic evaluations and safety assessments was performed regularly. Effects on the central nervous system were assessed with a battery of pharmacodynamic tests.

The maximum plasma concentration (C_max ) was reached within 3 to 4 hours (≤60 mg) and within 20 to 28 hours (>60 mg), and across all dose levels the terminal half-life (95% confidence interval) ranged from 36 (29-45) to 43 (22-86) hours. Multiple peaks were observed and C_max and area under the plasma concentration-time curve (AUC)_0-∞ increased in a less than dose-proportional manner. A 1.6-fold increase in C_max and no change in AUC_0-∞ was observed in fed compared to fasted conditions. A significant correlation (P < 0.0001) between plasma and saliva concentrations was established using linear regression. All adverse events were transient and of mild or moderate intensity. No treatment-related effects on vital signs, clinical laboratory, telemetry, or electrocardiography were detected. The results of pharmacodynamic tests did not show relevant mean changes compared to baseline or placebo.

ACT-709478 exhibits good tolerability and safety after single-dose administration and its pharmacokinetic and pharmacodynamic properties warrant further investigations.