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A systems approach to understanding mechanisms of drug Induced mitochondrial toxicity

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Title: A systems approach to understanding mechanisms of drug Induced mitochondrial toxicity
Authors: Broom, Ashley
Item Type: Thesis or dissertation
Abstract: Mitochondria are important to the pharmaceutical industry. Mitochondrial perturbation is central to the aetiology of many poorly treated human diseases (e.g. neurodegenerative diseases, diabetes and cancer) and hence mitochondria are increasingly becoming therapeutic targets. However, drug-induced mitochondrial toxicity (DIMT) has also gained recognition as a significant cause of safety related attrition (including multiple post-market withdrawals). The present work ultimately aimed to discern the mechanisms downstream of DIMT in vitro and in vivo with two tool compounds which act via inhibition of the mitochondrial electron transport chain (ETC) (GSK932121A) or via uncoupling of mitochondrial oxidative phosphorylation (GSK2617971A). The first objective was to compare mitochondrial functional responses between in vitro (treatment of mitochondria isolated from control animals or in vitro cell lines) and in vivo scenarios using oxygen consumption rate (OCR) and calcium retention capacity (CRC) assays. The direction of change in these assays was often different between the in vitro and in vivo situation. Whilst seemingly contradictory, these differences reflect an adapted state in vivo which results from the initial insult in combination with compensatory changes made by the tissue to maintain energy production. In contrast, only the initial, unconfounded, response to treatment is observable in vitro. Integration of both is key to the future risk assessment of mitochondrially-active drug candidates. The second objective was to use a systems approach to build candidate adverse outcome pathways (AOP)/modes of action (MOA) for both tool compounds. AOP/MOAs were constructed based on key events observed in vivo. With both compounds, effect on body temperature, increased lactate/pyruvate ratio, gene expression changes indicative of a fasted state (induction of gluconeogenic genes) and mitochondrial ultrastructure effects were key events observed in the adverse outcome. Future work using additional compounds with mitochondrial activities would help validate the proposed AOP/MOAs. The third objective was to highlight markers of underlying mitochondrial perturbation with utility for future pre-clinical monitoring in the absence of overt DIMT. A number of mitochondrial functional changes (e.g. effect on CRC) were observed prior to the onset of overt toxicity in vivo, with both compounds and these endpoints have potential use in tailored future studies with mitochondrially-active drug candidates. These findings add to the knowledgebase on DIMT, particularly with regard to the candidate AOP/MOAs which have been postulated. This will facilitate the selection of more sensitive and functional endpoints for use in future toxicology studies with drugs where mitochondrial impairment is suspected.
Content Version: Open Access
Issue Date: Aug-2015
Date Awarded: Feb-2016
URI: http://hdl.handle.net/10044/1/38408
DOI: https://doi.org/10.25560/38408
Supervisor: Boobis, Alan
Sponsor/Funder: Medical Research Council (Great Britain)
Department: Department of Medicine
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Medicine PhD theses

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