Abstracts

Rationale: Despite numerous therapies for the treatment of epilepsy, over 30% of patients remain resistant to available antiseizure drugs (ASDs) and are considered pharmacoresistant. ASD discovery has primarily relied on demonstration of efficacy in acute in vivo seizure models (e.g. 6 Hz) before advancing a compound into etiologically-relevant chronic models of epilepsy. Traditional pharmacoresistant rodent models, such as the focal kainic acid mouse or lamotrigine (LTG)-resistant kindled rat, are labor- and resource-intensive, whereas the 6 Hz seizure model does not exhibit pathophysiological or behavioral alterations associated with chronic seizures. Given that over 30% of patients with epilepsy are currently resistant to available therapies, there is a high unmet need for novel ASDs that are effective in patients with pharmacoresistant epilepsy. The early identification of novel ASDs should thus be conducted in etiologically-relevant models of pharmacoresistant chronic epilepsy.The traditional corneal kindled mouse (CKM) represents a well-characterized preclinical model of chronic seizures that has contributed to the development of numerous ASDs; however, this model is typically not considered pharmacoresistant. To provide a moderate-throughput, etiologically-relevant model that exhibits the behavioral and pathophysiological alterations associated with epilepsy, we developed a pharmacoresistant CKM that is potentially suitable for frontline ASD discovery. Methods: Male CF-1 mice (n = 30/ group) were administered either vehicle (VEH; 0.5% methylcellulose) or LTG (8.5 mg/kg, i.p. b.i.d.) 30 min prior to twice-daily corneal kindling (3 mA, 60 Hz, 3 sec stimulation) until mice achieved kindling criterion (5 consecutive Racine stage 5 seizures). Upon achieving kindling criterion, mice were allowed 5-7 days of washout before determining the response to prototype ASDs: carbamazepine (CBZ); phenytoin (PHT); lamotrigine (LTG); levetiracetam (LEV); valproic acid (VPA); diazepam (DZP); phenobarbital (PB); and retigabine (RTG). Fluoxetine and minocycline were also evaluated as compounds with mechanisms of action of interest to ASD discovery. Results: Administration of LTG did not delay acquisition of the corneal kindled seizure, consistent with the LTG-resistant amygdala-kindled rat. Following the wash-out period, administration of 17 mg/kg (i.p.) LTG did not block the expression of the secondarily generalized kindled seizure in the LTG-kindled mice (mean seizure score (MSS) of 4.9±0.05 SEM), whereas VEH-treated mice were highly sensitive to this dose (MSS: 2.3±0.30; t=10.8, p < 0.0001); thus, confirming LTG-resistance. Furthermore, the seizures of LTG-resistant CKM were resistant to treatment with single i.p. doses of CBZ (20 mg/kg), RTG (10 mg/kg), and VPA (300 mg/kg) that elicited significant reductions in seizure score in VEH-treated kindled mice. The MSS±SEM for VEH- vs. LTG-kindled mice, respectively, at these ASD doses were as follows: CBZ – 3.40±0.29 vs. 4.8±0.17; RTG – 3.2±0.70 vs. 4.7±0.20; VPA – 1.1±0.58 vs 2.6±0.53. The full pharmacological profile, as well as behavioral characterization (e.g. anxiety-like behavior), of this model will be discussed. Conclusions: The pharmacoresistant LTG-resistant corneal kindled mouse provides an early platform to identify compounds before advancing to more resource-intensive models of pharmacoresistant epilepsy. Funding: This work was supported by the University of Washington School of Pharmacy.