THE ROLE OF TUMOUR-ASSOCIATED MACROPHAGES IN PANCREATIC CANCER
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Pancreatic ductal adenocarcinoma is a highly desmoplastic tumour, and non-malignant stromal cells contribute to progression and treatment resistance. Inflammatory cells in particular are known drivers of carcinogenesis, and macrophages are one of the most abundant inflammatory leucocytes. Therefore, exploring how macrophages drive tumour progression in pancreatic cancer would not only aid in understanding disease biology but could also offer insight to novel treatment strategies. Results presented in this thesis show macrophages secrete factors that drive epithelial-to-mesenchymal transition, promote invasion and lead to expression of checkpoint inhibitors. To determine what factors were driving this phenotype, the serine protease inhibitor SerpinB3 was initially explored, as it was highly upregulated in cancer cells cultured with conditioned media from macrophages. However, SerpinB3 gene overexpression and knockdown did not confirm a direct role for this gene in mediating migration and invasion. Further investigation revealed macrophages were secreting the cytokine oncostatin M, which was driving a metastatic phenotype through activation of the STAT3 pathway. Expression of oncostatin M receptor was upregulated in cancer cells following culture with macrophage conditioned media and conferred a worse prognosis in patient samples. STAT3 pathway activation by oncostatin M led to increased invasion in vitro, particularly of the highly tumourigenic cancer stem cell population, and increased metastasis in vivo. Moreover, oncostatin M mediated expression of the immune ‘checkpoint’ inhibitors on the surface of pancreatic cancer cells. Using antibody and small molecule inhibitors, reversion of these signalling pathway effects were seen and preliminary data from in vivo assays showed decreased metastasis formation with cytokine receptor antibody inhibition. Overall, the findings in this thesis contribute to emerging knowledge of how tumour associated macrophages drive tumour progression in pancreatic adenocarcinoma. Not only do they promote invasion and metastatic potential through oncostatin M secretion, but also potentiate inherent biological properties of cancer stem cells and assist in immune tolerance. In addition, results provide preliminary data to support a rationale for clinical targeting of macrophage-derived oncostatin M in pancreatic cancer.
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