Abstracts

Rationale: Drug-resistant epilepsy affects ~30% of patients despite over 30 FDA-approved antiseizure medicines (ASMs). Further, no agent has yet been found to prevent the development of epilepsy in at-risk individuals. Historical ASM discovery has primarily relied on demonstration of efficacy in “traditional” acute in vivo seizure models evoked in male, wild-type rodents (e.g. maximal electroshock, subcutaneous pentylenetetrazol, kindling). However, little work has profiled ASM response in female mice with acute or chronic seizures to inform ASM discovery. Therefore, this study aimed to fill this knowledge gap by defining the acute median effective doses (ED50s) of known ASMs (levetiracetam, carbamazepine, valproic acid (VPA), and phenobarbital) in female CF-1 mice using the 6 Hz 32 mA focal seizure model to compare with our established female C57BL/6J data (Lehmann & Barker-Haliski 2023). Further, we assessed whether repeated administration of therapeutic doses of VPA prevented corneal kindling acquisition, a relevant model of epileptogenesis, or modified behavioral comorbidities of epilepsy in female mice. This study informs our future investigational drug screening in female CF-1 mice.

Methods:
Female CF-1 mice were used to quantify of ED50s of candidate ASMs (n=8 mice/ASM dose) in the 6 Hz 32 mA test. Noted motor impairment was recorded via assessment of performance on a fixed-speed rotarod. To assess disease-modifying potential, CF-1 mice (n=22) underwent corneal kindling in the presence or absence of VPA (150 mg/kg, i.p.; 2x daily 3 sec, 2.6 mA, 60 Hz corneal stimulation for approximately 3-4 weeks to achieve kindling criterion). Corneal kindled seizures present along the modified Racine scale; the fully kindled state was defined as the presentation of five consecutive Racine stage 5 seizures. After attaining kindling criterion, mice were challenged in the open field (OF) test to identify anxiety-like behavioral comorbidities of epilepsy.




Results:
The calculated ED50 in female CF-1 mice was consistent versus our previously calculated 6 Hz test ED50s in C57BL/6J female mice for both VPA (100.318 mg/kg [60.5-138.99]) and phenobarbital (18.29 [6.8-30.4]). Carbamazepine exhibited poor tolerability: 87.5% of mice were impaired on a rotarod at high doses, but there were no notable motor impairments for the other ASMs. In our corneal kindling acquisition study, VPA prevented kindling. The number of mice reaching kindling criterion after 3 weeks was significantly lower in VPA-treated mice (2/11 mice) than in VEH-treated mice (8/10 mice; Χ²=8.03, p< 0.005). Mice with repeated VPA treatment spent 25% of total activity in the OF center vs 35% activity in VEH-treated mice.




Conclusions: This study establishes the anticonvulsant properties of conventional ASMs to inform future preclinical drug discovery in female mice, as well as guide additional seizure model selection, e.g. the i.v PTZ test or Theiler’s virus model. Altogether, these studies will support further differentiation of new treatments for epilepsy.

Funding:
This work was supported by R61NS126626 to MBH.