Investigating convulsion triggers in canine toxicity study for preclinical compound: A case study

Convulsions are a serious side effect of pharmaceuticals, and it is crucial to assess the convulsion risk of new drug candidates before clinical trials to ensure the creation of safe drugs. In a repeated toxicity study in dogs, our preclinical compound (CH-X) induced convulsions which were not observed in rats. The convulsions were considered to be induced by off-target effects because target information indicated the low possibility of on-target toxicity. Upon checking the metabolites in each animal species, metabolites (M1 and M2) that are produced more in dogs than in rats were found. The following evaluations were conducted to elucidate the mechanism of the convulsions observed in dogs. 1) Off target panel assay: Several off targets were detected, and among them, monoamine transporters (MAT) were identified as potential targets. The compounds inhibited the function of dopamine transporter in a concentration dependent manner. As for other MAT, the compounds showed different inhibitory profile. 2) In vitro microelectrode array (MEA) assay using human iPS-derived neurons: CH-X, M1 and M2 affected the electrophysiological parameters of neural activity. Total spikes and synchronous burst firings were decreased by the compounds. As a result of PCA analysis, CH-X, M1 and M2 caused changes similar to those of monoamine transporter inhibitors. 3) Metabolic enzyme inhibition study in dogs: Convulsions in dogs occurred even under the condition that systemic exposure of M1 and M2 was suppressed by metabolic enzyme inhibitor, indicating that the metabolites may not be the major cause of the convulsion. The series of mechanistic investigation approach demonstrated in this study provided valuable insights into the mechanisms of drug-induced convulsions.