Investigating Heterogeneity in Tumour-Stroma Interactions in Pancreatic Ductal Adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a dismal disease with extremely poor survival rates and few treatment options. It is increasing appreciated that PDAC displays a high degree of intra-tumoural heterogeneity, meaning tumours are comprised of phenotypically diverse sub-clones. Such heterogeneity poses a challenge to the efficacy of targeted therapies since sub-clones may exhibit different molecular dependencies. It is also recognized that the extensive stromal reaction, characteristic of PDAC, regulates many aspects of tumour behaviour including progression and response to therapy. However, the extent to which genetically heterogeneous tumour cells might interact with stromal cells in distinct ways is relatively unexplored. Here I present data supporting that PDAC sub-clones interact with stromal fibroblasts in a clone-specific manner. Co-culture of phenotypically distinct tumour sub-clones with fibroblasts leads to reprogramming of fibroblasts to a number of phenotypes, in particular an -SMA high, myo-fibroblastic or IL6-expressing immunogenic phenotype. This suggests that tumour sub-clones can uniquely shape their microenvironment and that heterogeneity in the tumour cancer-cell compartment can perpetuate into the stroma. Furthermore, gene expression analysis of tumour sub-clones isolated from direct co-culture with fibroblasts reveals that tumour sub-clones undergo different transcriptional responses to reciprocal signals, resulting in the adoption of new phenotypes. Moreover, sub-clone grouping according to their transcriptional response reveals the same groups as those identified based on fibroblast reprogramming. These differential responses are corroborated by signalling experiments, finding that groups of sub-clones show distinct oncogenic pathway engagement in response to fibroblasts, in particular differential engagement of the AKT and MAPK pathways. Finally, striking coordination in cell-autonomous phenotype, fibroblast reprogramming and reciprocal signalling responses by tumour sub-clones lead me to hypothesise that these processes were co-ordinately regulated, possibly by oncogenic KRAS levels which were elevated in a subset of the clones. This was investigated in two additional cohorts of cells, however the principles derived from the original sub-clone model did not explain tumour-stroma interactions in wider cohorts of cells.

Date of Award	13 May 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Tim Somervaille (Co Supervisor) & Claus Jorgensen (Main Supervisor)