Abstracts

Rationale: An increasing number of de novo SCN8A mutations have been identified in patients with catastrophic, treatment-resistant childhood epilepsy. Interestingly, de novo SCN8A mutations have also been found in patients with autism, intellectual disability and developmental delay but with less severe epilepsy. Since SCN8A-associated epilepsy mutations have only recently been identified, it is unclear which treatments are the most efficacious for these patients. Furthermore, attempts at seizure control are not always effective at improving behavioral outcomes and can sometimes exacerbate behavioral abnormalities. Recent clinical trials demonstrate that cannabidiol (CBD) significantly reduces seizure frequency in patients with Dravet syndrome and Lennox-Gastuat syndrome. It is hypothesized that the antiepileptic effects of CBD may be mediated, in part, by reducing resurgent sodium currents. In HEK293T cells, CBD was shown to reduce resurgent current in both wild-type (WT) Na_v1.6 and mutant Na_v1.6 channels, suggesting that CBD may be beneficial in SCN8A-associated disease.

Methods: Using CRISPR/Cas9 technology, the human SCN8A R1620L mutation was knocked into the corresponding position in the mouse Scn8a gene. We previously showed that heterozygous mutants (RL/+) exhibit increased seizure susceptibility and a range of behavioral abnormalities, including learning and memory deficits and abnormal social behavior. Thus, to evaluate whether CBD could protect against induced seizures, RL/+ mutants and WT littermates were administered 200-360 mg/kg CBD and seizures were induced using the 6 Hz paradigm and pentylenetetrazole (PTZ). To determine whether CBD could improve behavior, RL/+ mutants and WT mice were administered 10-100 mg/kg CBD two hours prior to behavioral testing. The mice were subjected to a battery of behavioral assessments to evaluate locomotor activity, motor coordination, and social behavior. We are currently testing the effect of CBD on spontaneous seizures and sleep architecture.

Results: Using the 6 Hz seizure induction paradigm, we found that 320 mg/kg CBD was the minimum dose required to observe a statistically significant increase in seizure protection in the RL/+ mutants (N = 10-12/dose). CBD (200 mg/kg) was able to increase resistance to PTZ-induced seizures in WT littermates; however, a higher dose of CBD (360 mg/kg) was required to significantly increase resistance in the RL/+ mutants (N = 9/group). We previously demonstrated that RL/+ mutants are hyperactive and exhibit deficits in social behavior. CBD was able to reduce locomotor activity and restore normal social behavior in the RL/+ mutants at doses of 100 mg/kg and 10 mg/kg, respectively (N = 12-13/group).

Conclusions: Our results demonstrate that CBD can significantly increase seizure resistance and improve social behavior in an Scn8a mouse model. These findings suggest that the clinical use of CBD may be therapeutic in patients with SCN8A-associated disease.

Funding: Please list any funding that was received in support of this abstract.: This work was supported by National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (JCW, R21NS114795-01).