Desmoplastic stromal cells modulate tumour cell behaviour in pancreatic cancer
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Pancreatic ductal adenocarcinoma (PDAC) is characterised by an intense desmoplastic stromal response that can comprise 60 to 80% of tumour volume and has been implicated to be a factor in promoting tumour invasiveness and the poor prognosis associated with this cancer type. It is now well established that pancreatic stellate cells, which are vitamin A storing cells found in the periacinar spaces of the stroma in the normal gland, are primarily responsible for this desmoplastic reaction. Studying the interaction between stellate cells and cancer cells could provide for a better understanding of the disease process. During the evolution of PDAC, the stromal proportion increases from 4% in the normal gland to up to 80%. We hypothesised that there is an optimal proportion of stellate cells and cancer cells that modulates tumour behaviour and we attempted to dissect out this probable ‘tipping point’ for stromal composition upon cancer cell behaviour using a well-‐established in vitro organotypic culture model of pancreatic cancer. The cancer cell-‐stromal cell interaction led to extra-‐cellular matrix contraction and stiffening; and an increase in cancer cell number. The stromal stellate cells conferred a pro-‐survival and pro-‐ invasive effect on cancer cells which was most pronounced at a stellate cell proportion of 0.66-‐0.83. The expression of key molecules involved in EMT and metastasis such as E-‐Cadherin and β-‐catenin showed a reduction and this was found to be most significant again at a stellate cell proportion of 0.66-‐0.83. Stellate cells altered the genetic profile of cancer cells leading to differential expression of genes involved in key cellular pathways such as cell-‐cycle and proliferation, cell movement and death, cell-‐cell signalling, and inflammatory response. qRT-‐PCR confirmed the differential expression of the top differentially expressed genes and protein validation by immunofluorescence staining using PIGR as a candidate molecule confirmed the experimental findings in human PDAC specimens.This study demonstrates that the progressive accumulation of desmoplastic stromal cells has a tumour progressive (pro-‐survival, pro-‐invasive) effect on cancer cells in addition to stiffening (contraction) of the extracellular matrix (maximum effect when the stromal cell proportion is 60-‐ 80%). This is mediated through a number of signalling cascades and molecular targets. Dampening this tumour-‐promoting interaction between cancer and stromal cells by ‘multi-‐targeting’ agents may allow traditional chemo-‐ and/or radiotherapy to be effective.
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