Identification of novel treatments for epilepsy

Abstract

Epilepsy is one of the most common neurological disorders, affecting ~65 million people. About 30% of patients do not respond to currently available medication. Despite new drug releases to the market, patient responsiveness to medication has not changed in the past 30 years. This thesis explores the utility of the vinegar fly, Drosophila melanogaster, as a model organism to study the neuronal basis of seizure and to identify novel antiepileptic drugs (AEDs) and/or targets. This thesis has three overarching aims: 1) to characterise and compare several well-established Drosophila seizure models to identify common characteristics that might be exploitable for high-throughput screening for AEDs, 2) to characterise two specific fly seizure mutations, modelling two distinct human epilepsy syndromes, and their responsiveness to AEDs, 3) to investigate the mode of action of two novel anticonvulsive compounds. Chapter 2 characterises six seizure-prone fly models, at the two stages of development: larva and adult. It reveals that seizure can be successfully induced in all the lines, but that of the differing induction methods, larval electroshock was the most reliable method tested. In addition, changes in locomotion at either developmental stage were not predictive of seizure-susceptibility or uniform enough to be used for screening. Finally, extracellular recordings showed elongated burst firing in central neurons at larval stage, but this was not directly correlated with seizure-susceptibility or severity. Chapter 3 explores two humanized epilepsy syndrome models: Genetic Epilepsy with Febrile Seizures Plus (GEFS+) and Dravet Syndrome (DS). Both fly models have mutations in voltage-gated sodium channel (NaV). Responsiveness of the models to AEDs is varied. AED effectiveness on GEFS+ is similar in adults and larvae, but for DS, phenytoin, a NaV blocker, showed reduced seizures in adults and heightened seizures in larvae. This was followed up by sodium current (INa) recordings. At the larval stage, neither of the models replicate the changes of INa reported in adults. In Chapter 4, a well-established epilepsy model is used to investigate the mode of action for two novel anticonvulsive compounds RAB102 and RAB216. The compounds are derivatives of avobenzone, which alters INa and exerts its effects through a transcriptional repressor Pumilio. In larva, pumilio overexpression reduces seizure duration and pumilio knockdown increases seizures. Mode of action for RAB102 involves Pumilio, as it loses anticonvulsive effect in pumilio knockdown. In conclusion, Drosophila seizure mutants are diverse and distinct, yet suitable to decipher mode of action for novel compounds.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rasmus Petersen (Supervisor) & Richard Baines (Supervisor)