Abstracts

Rationale: Dravet syndrome is a debilitating and often catastrophic childhood epilepsy with unremitting pharmaco-resistant seizures and attendant lifelong cognitive, behavioral and mental health problems. The continued pharmaco-refractory nature of this disorder suggests novel approaches to drug-screening are needed to uncover drugs with new and unexpected mechanisms of action. Our long-term goal is to use zebrafish and mice models of Dravet to uncover new drugs for this patient population. Using zebrafish, we developed a metabolism-based drug screening platform that unbiasedly assays for decreases in metabolic hyperexcitability. Here we compared efficacies of known antiseizure drugs across both Dravet and a more generalizable model of epilepsy (e.g., episodic ataxia with epilepsy), which is more responsive to current therapies. We reasoned that if modulating bioenergetics is indeed a reliable readout for efficacious drugs, then fewer antiseizure drugs should be effective in the Dravet zebrafish versus the episodic ataxia with epilepsy model. To test the translation of our approach, positive hits were validated in Dravet and episodic ataxia with epilepsy mouse models. Methods: We used CRIPSR/cas9 to introduce mutations into the zebrafish ortholog of SCN1A (e.g., scn1lab) and KV1.1 (e.g., kcna1) epilepsy-associated genes to create Dravet and the generalizable episodic ataxia with epilepsy models, respectively. Extensive metabolic profiles of both scn1lab and kcna1 mutant zebrafish were analyzed with XF24^e Seahorse Bioanalyzer. We conducted a shelf screen of twenty-three known antiseizure drugs in both models to test their ability to restore altered metabolic functions. Drugs that restored mitochondrially-mediated bioenergetics to baseline (e.g., wild type) levels were considered efficacious. Furthermore, drugs effective in the zebrafish models were prioritized and validated in Scn1a^+/- Dravet mice using a hyperthermia-induced seizure assay and Kv1.1-null mice using video-EEG. Results: The scn1lab and kcna1 mutant zebrafish exhibited distinct bioenergetics phenotypes for oxidative phosphorylation and glycolysis, including decreases in basal respiration, mitochondrially-mediated respiration, and ATP-linked respiration. On the other hand, the maximum respiratory capacity and non-mitochondria respiration were unchanged. Interestingly, only 8 of 23 antiseizure drugs were effective in the scn1lab mutants, whereas 18 of the 23 drugs were efficacious in the kcna1 mutant zebrafish. Top drugs reduced the frequency of seizures in Kv1.1-null mice and are currently being tested in the Scn1a^+/- Dravet model.   Conclusions: The fewer number of compounds efficacious in the scn1lab Dravet syndrome model is consistent with the pharmaco-refractory nature of this disease and suggests that bioenergetics in a robust and reliable readout to identify new antiseizure drugs.  Funding: This work was funded by Brain Canada Platform Support Grant and Alberta Children’s Hospital Research Institute.