Aref, Sarah; (2020) Characterizing the Mechanisms Underlying Measles Virus Mediated Oncolysis in a Stromal Model of Cellular Transformation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Vaccine strain measles virus (MV) is oncolytic in numerous models of malignancy and is currently being tested in ongoing clinical trials. The mechanism behind the selectivity of MV for tumour cells is poorly understood. To determine the mechanism of selectivity, I used an established step-wise model of cellular transformation, in which progressive oncogenic hits were stably and additively expressed in human bone marrow-derived mesenchymal stromal cells (MSCS) (Funes et al., 2007). Progressive MSC transformation was associated with increased viral infectivity, MV productivity and MV-induced cell killing. This was not explained by differences in MV receptors CD46, SLAM or nectin-4 expression. Investigation of the anti-viral type 1 IFN response 24 and 48 hours post infection demonstrated that IFNb production was delayed and reduced in transformed cells compared to their normal counterparts (hTERT). A similar pattern was observed for STAT1 phosphorylation. Exogenous pre-treatment of the most highly transformed cells (5H) cells with IFNb rendered the cells less susceptible to MV-mediated oncolysis confirming the biological role of IFNb. To identify genetic correlates of MV oncolysis, RNA-seq was performed using mock-infected and MV-infected hTERT and 5H cells, revealing a dampened basal levels of immune-related genes involved in the type 1 IFN pathway, gamma IFN pathway, and antigen presentation and processing pathways. Interferon-inducible transmembrane protein 1 (IFITM1) was the foremost basally downregulated immune gene with a 183-fold downregulation in 5H cells compared to hTERT cells. I therefore attempted to stably overexpress IFITM1 in 5H cells. This resulted in a 50% increase in cell viability and significantly reduced viral replication at 24hpi, newly identifying IFITM1 as a restriction factor for early stages of oncolytic MV infection. I also assessed the impact of MV infection on mitochondrial function and morphology. MV infection altered mitochondrial morphology and 4 significantly affected expression levels of regulators of the mitochondrial fusion-fission cycle in MSCs. Oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were evaluated by the Seahorse extracellular flux analysis. Progressive MSC transformation was associated with increased OCR and ECAR and a reduced spare respiratory capacity, indicating mitochondrial dysfunction. OCR and ECAR levels in MSCs were minimally affected by MV infection. However, viral infection significantly increased SRC in transformed cell lines 4+V and 5H. Finally, to explore the impact of MSC transformation and MV infection on the metabolite pool in hTERT and 5H cells, I performed a global metabolomics experiment, to my knowledge the first global metabolomic analysis after infection with oncolytic MV. MV infection targeted several facets of the host cell metabolome including glycolysis, TCA cycle and the pentose phosphate pathway (PPP). In particular, the host cell’s redox status was targeted by cellular transformation and MV infection. I showed that an intact antioxidant system is a determinant for the tumour selectivity of MV.

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