The Role of Circulating Pancreatic Stellate Cells and Circulating Tumour Cells in Pancreatic Cancer

Pancreatic cancer (PC) has a dismal prognosis, with an overall 5-year survival of less than 9%. The key determinant of PC outcome is the development of metastasis, not only in newly diagnosed patients, but also in patients who have undergone potentially curative surgery. Thus, there is a need for understanding the pathogenesis of metastasis in PC. The investigations described in this PhD project were driven by the knowledge that: (i) the interactions between PC cells and pancreatic stellate cells (PSCs, which produce the prominent collagenous stroma of PC) facilitate local tumour growth and metastasis; (ii) PSCs from the primary cancer spread to metastatic sites potentially promoting metastasis; and (iii) hepatocyte growth factor (HGF)/c-Met inhibition in combination with gemcitabine effectively suppresses metastasis in PC. It follows that if PSCs can metastasise, circulating PSCs (cPSCs) should be detectable. This led to the hypotheses of this project, namely that PSCs circulate along with PC cells to help create a growth permissive microenvironment at metastatic sites; and that these cells are modulated by treatments which affect PC−PSC interactions, thereby disrupting metastasis. Studies described in this thesis report: (i) the development of techniques for size-based isolation and immunocytochemical identification of cPSCs; (ii) the demonstration of the existence of cPSCs in vivo using an orthotopic mouse model of PC; (iii) the characterisation of cPSCs morphologically and immunocytochemically; (iv) the assessment of the effects of HGF/c-Met inhibition on these cells; and (v) the characterisation of the transcriptome of circulating rare cells in PC (including PSCs) by single cell RNA sequencing. As a corollary, this thesis describes the establishment of a novel PC mouse model of adjuvant treatment, and the use of this model in assessing the effectiveness of adjuvant HGF/c-Met inhibition treatment. As a result, this work has confirmed the effectiveness of HGF/c-Met inhibition not only in the context of unresected PC but has also established it as an adjuvant treatment after resection. These findings significantly add to the understanding of PSC−PC biology and open new dimensions for future investigation of cPSCs in PC