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Title: Using Caenorhabditis elegans to identify succinimide-based neuroprotective compounds and their mechanisms of action
Author: Wong, Shi Quan
ISNI:       0000 0004 7428 4691
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Neurodegenerative diseases such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) are associated with a significant socioeconomic burden. As age is a major risk factor for the development of these conditions, coupled with the fact that no disease-modifying treatments exist, the predicted ageing population growth in the next few decades is only expected to exacerbate this burden. The antiepileptic drug (AED) ethosuximide is a first-line treatment for absence seizures which exhibited neuroprotective and lifespan-extending effects in various models of neurodegeneration in Caenorhabditis elegans and rodents, making it a promising repurposing candidate for treating neurodegenerative diseases. As its molecular mechanism of action (MMOA) remains unclear despite being an established AED, delineating its MMOA may provide useful insights into the pathogenesis processes of these diseases. A most direct and informative strategy is to deconvolute the drug's molecular target(s), and this is classically performed with affinity-type binding approaches such as affinity chromatography, which requires appropriate drug derivatisation for subsequent immobilisation onto an affinity matrix. However, drug repurposing and target identification may prove difficult or unfeasible due to suggestive low potency from high therapeutic concentrations and doses required in models and humans. To improve the prospects of both approaches, the aim of the current project is to develop compounds with enhanced neuroprotective potency from ethosuximide as an alternative strategy. Using chemistry approaches, a selection of structurally-similar compounds to the drug were selected and screened for anticonvulsant activity in a C. elegans seizure model. This facilitated in-house insights into the structure-activity relationship (SAR) of the drug, which informs about appropriate molecular modifications on ethosuximide and/or its derivatives for further potency enhancement and for target identification studies. Furthermore, screens identified a candidate molecule with a two-fold enhanced anticonvulsant potency than the drug. This molecule, referred to as compound 9, was further verified for its neuroprotective and lifespan-extending properties in a C. elegans ALS model whereby it ameliorated locomotion defects, extended the reduced lifespan, and conferred direct protection against neurodegeneration. Comparable extent of protection was exerted at a 160-fold lower externally-administered concentration than ethosuximide. Further 1H nuclear magnetic resonance (NMR) spectroscopy analysis of treated worms suggest that compound 9 had bioaccumulated below the detection limit of 5 µM whereas the internal concentration of ethosuximide was determined to be 143.8 µM, excluding improved bioaccumulation as an unlikely contributing factor towards the enhanced potency of the compound. Finally, both compounds required the DAF-16 forkhead box O (FOXO) transcription factor to exert protection in the ALS worms, demonstrating similar aspects of their MMOAs. Taken together, the current study has established important contributions towards expediting translational efforts for treating neurodegenerative diseases through the identification of compound 9.
Supervisor: Morgan, Alan ; Burgoyne, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral