Rationale:
Dravet syndrome (DS), is a form of epilepsy commonly associated
with heterozygous loss-of-function variants in the sodium voltage-gated channel NaV1.1 gene, scn1a. We have previously shown metabolic deficits in a scn1Lab mutant zebrafish model that closely replicates several phenotypes associated with human DS cases. Furthermore, we identified PK11195 as a potential therapeutic agent that rescues metabolic deficits and seizures in this model (Banerji et. Al., 2021). PK11195 is a ligand of the translocator protein (TSPO) which resides on the outer mitochondrial membrane and has been widely accepted as a biomarker for neuroinflammation. The goal of this study was to evaluate additional TSPO ligands for their therapeutic potential in the scn1lab mutants.Methods:
TSPO ligands were evaluated using the
scn1ab zebrafish model in the Noldus Danio Vision to examine seizure-like swim behavior. Six days post-fertilization (6 dpf) larvae were treated with a TSPO ligand or vehicle (0.1% DMSO) for three hours after a baseline was captured. Criteria for a positive hit were classified at a threshold ≥ 40% change in mean velocity when compared to baseline. A multielectrode analysis system (MEA, Axion Maestro) was used to evaluate the ability of drugs to alter neuronal hyperexcitability.
Results:
TSPO antagonist ligands, Etifoxine (7.5uM) and XBD173 (20uM), significantly reduced seizure-like swim behavior in DS mutants in comparison to their respective vehicles (n=30, replicates=3,
p= < 0.0001 for each). Larval
scn1Lab zebrafish treated with Etifoxine displayed a greater than five fold decrease in neuronal spikes compared to the vehicle (
p < 0.0006; N=21 with replicates=7). Etifoxine also decreased the number of electrographic bursts significantly (
p < 0.0006; N=21 with replicates=7). The positive control, PK11195 (10uM) significantly reduced the number of spikes, and bursts (
p= 0.0029), to a similar extent observed previously using electrophysiology.
Conclusions:
Etifoxine and XBD173 significantly decreased seizure-like behavioral activity. Etifoxine also reduced electrographic spikes and bursts resembling neuronal hyperexcitability. Pending further exploration, our studies suggest that TSPO ligands with antagonistic properties may be novel therapeutic entities for treating drug-refractory epilepsies such as DS.
Funding:
Funded by NIH R01HD102071
Supported by NIH/NCATS Colorado CTSA Grant Number UL1 TR002535