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Title: Development of a non-mammalian, pre-clinical screening tool for the predictive analysis of drug toxicity
Author: Saide, Katy
ISNI:       0000 0004 7227 7957
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2018
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The failure to predict drug-induced toxicity reactions is still a major problem contributing to a high attrition rate and tremendous cost in drug development. Xenopus laevis embryos are amenable for the early stage medium to high throughput small molecule screens. We hypothesise Xenopus embryos can assist in vitro drug-induced toxicity safety assessment in the early phases of drug development before moving on to expensive preclinical trials in mammals. The objective of this study was to assess the use of Xenopus laevis embryos for the prediction of organ-specific toxicity. To do this I used drugs known to generate toxicity reactions in humans. First of all I determined that Xenopus embryos treated with a drug from the age of stage 38 until stage 45, was an appropriate assay for the prediction of drug-induced toxicity. The embryos expressed major drug metabolism enzymes including CYP2E1, CYP2D6, CYP3A4 and glutathione S-transferases, sulphotransferases and glucuronosyltransferases. They also expressed KCNH2, which encodes the α-subunit protein of the potassium ion channel KV11.1 that contributes to heart electrophysiology. For drug-induced liver injury, I used paracetamol treatment. Xenopus laevis embryos treated with paracetamol (0-5 mM) generated predicted paracetamol metabolites, had a dose-dependent depletion of free glutathione and increased expression of microRNA-122 (miR-122) in tissue that did not contain the liver. To investigate drug-induced cardiotoxicity, I treated Xenopus embryos with doxorubicin (0-100 μM) and terfenadine (050 μM). Embryo heart rates increased and decreased with these drugs respectively and arrhythmias occurred with both drug treatments. Embryos treated with doxorubicin had an increasing amount of arrhythmia that correlated with an increasing dose of doxorubicin treatment. Terfenadine treatment induced arrhythmia at a rate that was not concentration dependent. Wholemount in situ hybridisation (WISH) revealed the Xenopus embryos also express miR-208 specifically in the heart, similar to mammalian models. We conclude that Xenopus laevis embryos exhibit some similar characterisations of drug-induced hepatotoxicity and cardiotoxicity observed in mammalian models. These data indicate the Xenopus embryo could be a useful model to assess drug-induced toxicity and aid lead compound prioritisation in early drug development.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available