ADAMS et al COAGULATION FACTORS IN COLON CANCER 1 Colon cancer growth and dissemination relies upon thrombin, stromal PAR-1 and fibrinogen

Running title: Coagulation factors in colon cancer growth and dissemination Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect those of the Pelotonia Fellowship Program. Conflict-of-interest disclosure: The authors have no competing financial interests. Précis: Colon cancers may exhibit a special reliance on hemostatic factors such as thrombin, which appears to act as a multifaceted positive modifier of primary tumor growth, invasion and metastasis, with immediate therapeutic implications for the clinical exploration of inhibitors of thrombin or thrombin generation in this disease setting. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. ABSTRACT Thrombin-mediated proteolysis is a major determinant of metastasis, but is not universally important for primary tumor growth. Here we report that colorectal adenocarcinoma represents one important exception whereby thrombin-mediated functions support both primary tumor growth and metastasis. In contrast to studies of multiple non-gastrointestinal cancers, we found that the growth of primary tumors formed by murine and human colon cancer cells was reduced in mice by genetic or pharmacological reduction of circulating prothrombin. Reduced prothrombin expression associated with lower mitotic indices and invasion of surrounding tissue. Mechanistic investigations revealed that thrombin-driven colonic adenocarcinoma growth relied upon at least two targets of thrombin-mediated proteolysis, protease-activated receptor-1 (PAR-1) expressed by stromal cells, and the extracellular matrix protein, fibrinogen. Colonic adenocarcinoma growth was reduced in PAR-1-deficient mice, implicating PAR-1 as a stromal cell target for thrombin important for tumor outgrowth. Furthermore, tumor growth was dramatically impeded in fibrinogen-deficient mice, offering the first direct evidence of a critical functional role for fibrinogen in malignant tumor growth. Tumors harvested from fibrinogen-deficient mice displayed a relative reduction in cell proliferative indices, as well as increased tumor necrosis and decreased tumor vascular density. Collectively, our findings established a functional role for thrombin and its targets PAR-1 and fibrinogen in the pathogenesis of colonic adenocarcinoma, supporting tumor growth as well as local invasion and metastasis. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.