Therapeutic Targeting of Tumour Hypoxia through the Unfolded Protein Response and Autophagy Pathways

Low oxygenation, or hypoxia, is prevalent in human solid tumours and is a known contributor to therapy resistance. Pancreatic cancer is characterized by a poorly perfused, hypoxic microenvironment which contributes to poor treatment response and dismal patient survival rates. We have interrogated the role of key cellular pathways that have been implicated in the survival of cancer cells in hypoxia, and their potential as new therapeutic targets. The unfolded protein response (UPR) is a three-arm adaptive signalling pathway activated in response to endoplasmic reticulum stress, which is induced by conditions of extreme hypoxia. Using genetic and pharmacological approaches, we demonstrated that the PERK signalling arm of the UPR was uniquely responsible for the protection of hypoxic cells, and that inhibition of this pathway caused selective cytotoxicity of hypoxic cells. We also demonstrated that PERK signalling led to the induction and activation of the mammalian autophagy protein kinase ULK1 during hypoxia. Autophagy is a pro-survival molecular mechanism that degrades cellular components and provides nutrients to cells exposed to stressful environments. ULK1 is essential for autophagy initiation and we demonstrated that ULK1 was essential for the survival of pancreatic cancer cell lines. ULK1 depletion led to an expansion of the endoplasmic reticulum (ER), induction of ER stress, and cell death under hypoxic environments. Furthermore, we uncovered a mechanism through which ULK1 can modify steady state oxygenation levels within tumours by regulating the mitochondrial content and oxygen consumption. We found that loss of ULK1 led to a progressive increase in mitochondrial content, and subsequent increased oxygen consumption. This consequential rise in oxygen demand exacerbated the development of hypoxia in tumours. However, at the same time ULK1 loss sensitized cells to hypoxia leading to increased cell death. Increased hypoxia sensitivity and tumour hypoxia resulted in dramatic tumour regression of pancreatic cancer xenografts. Inhibition of ULK1 patient-derived tumour organoids, using genetic and pharmacologic means, significantly decreased organoid formation efficiency in hypoxia. Taken together, this data established ULK1 as a potential therapeutic target in pancreatic cancer.Ph.D.2019-03-01 00:00:0