Thrombin and Factor XII Drive Prostate Tumor Growth In Vivo

Several hemostatic factors are known to strongly influence the metastatic process by promoting the survival of early metastases. Despite this consistent phenomenon observed across multiple tumor cell types and multiple procoagulant components of the hemostatic system, the role of hemostasis in the establishment and growth of primary tumors is highly context dependent. One clinically relevant context where coagulation appears to be important for tumor development/outgrowth is prostate cancer. Men on long-term anticoagulation appear to be at significantly lower risk for developing prostate cancer compared to men on short-term anticoagulation or those not on anticoagulation. Here, we report that multiple hemostatic proteases drive prostate tumor growth in vivo. To test the hypothesis that the central hemostatic protease, thrombin, promotes prostate tumor growth, mice with a life-long genetically-imposed diminution in circulating prothrombin levels (fII^Lox/-), or mice administered a prothrombin-specific antisense oligonucleotide (ASO) gapmer that limits prothrombin expression, were inoculated subcutaneously with the murine-derived prostatic adenocarcinoma cell line TRAMP-C2Re3 in parallel with appropriate controls. Genetically or pharmacologically lowering prothrombin expression significantly impeded prostate tumor growth. In complementary experiments, treatment with the prothrombin-specific ASO gapmer significantly impeded the growth of human-derived prostate cancer cells (PC3) in immunodeficient mice. Detailed histological analysis revealed that tumors harvested from mice with diminished prothrombin expression had significantly lower mitotic indices, suggesting that thrombin promotes tumor proliferation in vivo. Lowering prothrombin levels did not affect apoptosis, vascular density, or the presence of tumor-associated macrophages. Previous studies have indicated that tumor cell-associated tissue factor expression is one important mechanism by which cancer cells can locally generate thrombin. However, the relative importance of the contact pathway of coagulation system activation in cancer progression is less defined. In order to determine whether fXII plays a role in prostate cancer growth, mice challenged with prostate cancer were treated with a fXII-specific ASO gapmer or a control oligonucleotide with no homology in the murine genome in parallel. Remarkably, tumors from anti-fXII ASO gapmer treated mice were ~3-fold smaller than those harvested from control animals at the end of the ~3 week experiment. To our knowledge, this finding is the first demonstration that the contact system protease fXII plays a significant role in tumor growth. In sum, these data show that thrombin promotes the growth of prostate cancer, and suggest that contact activation of the coagulation cascade may be a critical factor in prostate cancer growth.