Abstracts

Rationale: Dravet Syndrome (DS) is a calamitous genetic encephalopathy linked to over 300 de novo mutations in a neuronal voltage-gated sodium channel (SCN1A) and associated with childhood epilepsy, seizures, and early fatality. Antiepileptic drugs do not adequately control seizures in most DS patients, making discovery of new drug candidates a critical unmet need. To this end, we developed a high-throughput phenotype-based in vivo drug screening assay using a simple vertebrate (zebrafish) with a mutation in scn1Lab that recapitulates the relevant phenotypes associated with DS.Methods: scn1Lab Zebrafish (didys552) were identified in a large-scale mutagenesis screen (Schoonheim et al. 2010). Heterozygous adults were mated and their homozygous mutant larvae were used at 5 days post-fertilization (dpf) to blindly screen a commercially available re-purposed library (Pharmakon1600). Ten-minute locomotion plots were obtained and analyzed for one fish per well (6 fish per drug), measuring distance and velocity in addition to scoring seizures on a three-stage scale (Baraban et al. 2005). Compounds of interest were further screened using electrophysiology with a field-recording electrode placed in the forebrain or optic tectum of agar-immobilized fish (3 to 6 fish per drug).Results: First, we used automated locomotion tracking to perform a phenotypic screen for compounds reducing scn1Lab mutant swim velocity to levels seen in normal untreated zebrafish; high velocity movements in these locomotion plots correspond to convulsions consistently seen in mutant larvae but not in age-matched wild-type siblings. We found 22 of the 1014 screened compounds significantly inhibited spontaneous seizure behavior in scn1Lab mutants; re-testing them yielded 8 compounds having consistent effects. Second, we used these 8 drugs for electrophysiology testing at higher concentrations; 2 of the 8 drugs, dimethadione and propofol, were shown to suppress burst discharge activity in scn1Lab mutant larvae at a concentration of 1 mM.Conclusions: A zebrafish SCN1A mutant was used to identify antiepileptic compounds in a high-throughput drug screening approach. Quantifying seizure behaviors and electrographic discharges using this zebrafish model demonstrated a rapid and sensitive method for finding drugs that could produce antiepileptic effects desired in clinical treatments of DS. Our approach offers a unique resource for future drug discovery in an era of personalized medicine.