Abstracts

Rationale: Prevention of premature mortality due to sudden unexpected death in epilepsy (SUDEP) is a major unmet need in epilepsy. Most witnessed clinical cases of SUDEP observed generalized seizures that led to respiratory and then cardiac failure. A similar sequence of events is observed in the DBA/1 mouse model of SUDEP. Dravet Syndrome is an intractable form of epilepsy beginning in infancy with an elevated incidence of SUDEP. A recent clinical report indicated that patients with Dravet Syndrome have an improved clinical course when treated with fenfluramine (Ceulemans et al., Epilepsia 57 (7):e129-e134, 2016), a drug that enhances serotonin (5-HT) release.  Fluoxetine, which blocks 5-HT re-uptake, effectively suppresses SUDEP in DBA/1 mice (Faingold et al., Epilepsy Behav. 2011 Oct;22(2):186-90), but not all the drugs that enhance the action of 5-HT are effective. Therefore, this study evaluated whether fenfluramine could prevent seizure-induced respiratory arrest (S-IRA) in the DBA/1mouse SUDEP model. Methods: DBA/1 mice (21-30 days old) were tested for susceptibility to audiogenic S-IRA with 3-4 daily seizures (priming), using an electrical bell at 122 dB SPL (re: 0.0002 dyne/cm2) in a cylindrical chamber. Behaviors were recorded on videotape, and seizure patterns were quantified and statistically compared offline (Wilcoxon signed ranks test). Mice that exhibited S-IRA were resuscitated using a rodent respirator. At least 24 h after the final priming seizure the mice that exhibited S-IRA were given fenfluramine or vehicle (i.p.) to determine if seizure behaviors or susceptibility to S-IRA was affected. Results: Fenfluramine significantly (p < 0.05) reduced the susceptibility of DBA/1 mice to S-IRA 30 min after the 20 (n=6) or 30 (n=5) mg/kg doses. Neither the doses of 5 (n=6) or 10 (n=8) mg/kg of fenfluramine nor the vehicle (n=6) significantly altered seizure behavior or S-IRA incidence. The suppression of S-IRA was still significant at 24 h. Susceptibility to tonic seizures was also significantly (p < 0.05) reduced 30 min after the 20 and 30 mg/kg doses, but the animals continued to exhibit clonic and/or wild running seizure behaviors. Tonic seizure susceptibility returned at 24 h after these doses, but susceptibility to S-IRA remained significantly reduced. Return to S-IRA susceptibility occurred at 48 h after treatment. Conclusions: Fenfluramine, a 5-HT releasing agent, was effective in blocking S-IRA in DBA/1 mice. This action is consistent with the effects previously observed with certain (but not all) 5-HT-enhancing drugs, including fluoxetine, which are also effective in blocking S-IRA in these mice. The prolonged effect of fenfluramine in the present study was not consistently seen with any of the other serotonergic agents. These data provide the first evidence of the therapeutic efficacy of fenfluramine in a mammalian model of epilepsy and SUDEP. Thus, in addition to better seizure control outcomes, fenfluramine may prove effective in prophylaxis of SUDEP in disorders such as Dravet Syndrome. Funding: This research is supported in part by a grant from Zogenix.