Unraveling the mechanism and the risk behind seizure liability of lead compounds in a neuroscience project.

Abstract Introduction Several compounds from a neuroscience project induced convulsions in animals, at low exposure levels via a hypothetical off-target mechanism. A set of in vitro and in vivo experiments were conducted in order to 1) identify the mechanism behind convulsions; 2) characterize the convulsions, 3) detect premonitory signs that could be monitored clinically, and 4) assess the development of tolerance after repeat dosing. Methods Patch clamp assays were conducted on 12 different ion channels (e.g. sodium, potassium, calcium, AMPA, NMDA, GABAA and purinergic receptors) known to be associated with seizures, to identify the off-target culprit. A multiphase study was conducted with UCB-A and UCB-B in Beagle dogs telemetered for video EEG/EMG monitoring to further characterize the convulsive pattern. First, both compounds were administered by intravenous constant infusion (dose: 5 mg/kg/h) over 2 h. Thereafter, the same dogs received a daily oral administration of UCB-A (8 mg/kg/day) for 7 days. Results Compounds inducing convulsions showed strong inhibitory activity on GABAA channels (IC50 values Discussion A well-designed set of experiments including electrophysiological assays on seizure-related ion channels and EEG/EMG assessment in telemetered dogs allowed a proper seizure liability risk assessment, leading to a rapid no go decision for the two most advanced leads.