Chemokines and their receptors in the metastatic behaviour of human pancreatic ductal adenocarcinoma.

Abstract

The aim of this thesis was to investigate the role of chemokines and their receptors in human pancreatic adenocarcinoma and to explore whether chemokine receptors and their ligands are involved in tumor dissemination. The repertoire of chemokine receptors expressed in 11 pancreatic adenocarcinoma cell lines tested included CXCR4 and CX3CR1. Their significance was therefore further investigated. Expression of CXCR4 was higher in lines derived from metastases. The chemokine CXCL12 induced chemotaxis in CXCR4-positive cell lines, which was inhibited by an anti-CXCR4 specific antibody and by the antagonist AMD3100. Transendothelial migration, Matrigel invasion and activation of matrix metalloproteases were also enhanced by CXCL12. Proliferation was stimulated by CXCL12 in CXCR4-positive cell lines and partially inhibited by the inhibitor AMD3100, indicating an autocrine loop. The addition of exogenous CXCL12 inhibited apoptosis induced by serum starvation. These data demonstrate that autocrine or paracrine loops centred on the CXCR4/CXCL12 axis promote pancreatic cancer cell migration, matrix degradation and invasion, proliferation and survival. The function of the chemokine receptor CX3CR1 was investigated in the context of the peculiar propensity o f pancreatic cancer to disseminate and grow along nerve fibers, as its chemokine ligand Fractalkine/Neurotactin/CX3CLl is expressed by neuronal structures. CX3CR1-positive tumour cells migrated in a dose-dependent manner to CX3CL1 and this effect was blocked by specific anti-CX3CRl antibodies. CX3CR1-positive tumour cells adhered to endothelial and neuronal cells stimulated with TNFa/IFNy, known to induce Fractalkine expression. Neuronal derived Fractalkine elicited migration of CX3CR1-positive pancreatic tumour cells. The CX3CL1 chemokine was detected in vivo in surgical sections of pancreatic cancer nerve metastasis. These results suggest that the CX3CR1/Fractalkine axis could be involved in the dissemination of pancreatic tumour cells via nerve structures. In conclusion, the data presented here support the hypothesis that a selected set of chemokine receptors are expressed in carcinoma of the pancreas and are involved in tumour cell migration and invasion. For CXCR4, promotion o f cell survival and proliferation was observed. For CX3CR1, a role in perineural tropism is suggested