THE THROMBOSIS PATHWAY PROMOTES PANCREATIC CANCER GROWTH AND METASTASIS
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Pancreatic ductal adenocarcinoma (PDAC) is an incredibly lethal disease with a 5-year survival rate of less than 8 percent in the United States due to a lack of viable treatment options. The failures of chemo- and radiotherapies have been linked to the heterogeneous nature of the tumor microenvironment which forms a hypovascular, immunosuppressive and high coagulation activity tissue. Indeed, PDAC patients have one of the highest rates of thrombosis complications among all cancer types. The expression of two key coagulation factors, Tissue Factor (TF) and Protease Activated Receptor 1 (PAR-1), have been associated with poor patient prognosis and aggressive cancer progression. However, the molecular roles/mechanisms of TF and PAR-1 in PDAC progression are not known. To establish how clotting factors (PAR-1, TF) influence PDAC tumor progression, I utilized a genetically modified mouse model (KPC) where KRasG12D and TRP53R172H mutations were specifically introduced into mouse pancreas acinar cells to initiate PDAC progression. Multiple primary mouse PDAC cell lines were generated and characterized. TF and PAR-1 were highly expressed in primary KPC pancreatic lesions, in PDAC tumors, and in KPC-derived cell lines, an expression profile that is also observed in PDAC patient biopsies. In allograft studies, tumor growth and metastatic potential were significantly diminished by shRNA reduction of TF or PAR-1 in cancer cells or by genetic or pharmacological reduction of the coagulation zymogen prothrombin in mice. Notably, PAR-1 deleted KPC cells (KPC-Par-1KO) failed to generate sizable tumors; a phenotype completely rescued by restoration of PAR-1 expression. To test the significance of targeting PAR-1 in a clinical setting, PAR-1 expression was withdrawn from established tumors to mimic a potential inhibitory effect of PAR-1 on solid PDAC tumors. Removal of PAR-1 from tumors (11 days post injection) yielded a diverse effect on tumor growth which can be categorized into (i) a decline in tumor growth; (ii) continued tumor growth; and (iii) stagnant tumor growth. Immunohistochemistry analysis of KPC2 shCon vs. shPar-1 subcutaneous allograft tumor samples revealed a massive immune cell infiltration in KPC2 shPAR-1 tumors when compared to KPC2 shCon control tumors. Accordingly, KPC-Par-1KO cells failed to form tumors in immune-competent mice but displayed robust tumor growth in immune-compromised NSG mice, providing the first evidence of a PAR-1 mediated tumor immune evasion pathway operating in PDAC.
Together, these results demonstrate that PDAC disease is driven by activation of the coagulation system through tumor cell-derived TF, circulating prothrombin, and tumor cell-derived PAR-1. These studies also highlight a novel mechanism by which thrombin/PAR-1-mediated tumor growth involves suppression of anti-tumor immunity in the tumor microenvironment.