Thrombin Supports Colitis and Colitis-Associated Cancer Pathogenesis

Abstract 2237

Chronic inflammation has been recognized as a major factor in the development and progression of multiple cancers. A prime example of this is the strong association between colitis and colon cancer. However, the specific factors that regulate disadvantageous immune processes in the context of inflammation-associated cancers remain poorly defined. Growing evidence suggests that hemostatic system components, traditionally associated with the maintenance of vascular integrity and prevention of blood loss, also directly regulate inflammatory processes. Furthermore, thrombin and several thrombin targets (e.g., PARs, fibrinogen, factor XIII) have been shown to regulate tumor cell proliferation and apoptosis, support metastasis, and protect tumor cells from innate immune surveillance mechanisms in other experimental contexts. A logical extension of these findings is the hypothesis that thrombin, as a master regulator of both inflammatory processes and tumor cell biology, is a major determinant of the progression of inflammation-driven cancers such as colitis-associated colon cancer (CAC). To test this hypothesis, we induced CAC in mice carrying prothrombin levels 50% of normal (fII+/−) and WT mice in parallel using an established two step protocol consisting of azoxymethane (AOM) and dextran sodium sulfate (DSS) exposure. The modest diminution in prothrombin levels imposed by the fII+/− genotype resulted in a dramatic diminution in the number of colonic adenomas formed after AOM/DSS challenge relative to WT mice. In order to determine if the diminution in adenoma formation observed in fII+/− mice was coupled to thrombin function, wildtype mice challenged with AOM/DSS were treated with daily i.p. injections of hirudin, a direct thrombin inhibitor, or saline carrier. Similar to the finding in mice with a genetically-imposed diminution in circulating prothrombin, hirudin treatment significantly blunted adenoma formation. To determine if reduction of thrombin generation improved the inflammation preceding the development of colonic adenomas, we used a novel, highly-specific factor XI antisense oligonucleotide “gapmer” (ISIS Pharmaceuticals) to inhibit hepatic factor XI synthesis prior to DSS challenge. Gapmer-mediated diminution of fXI levels to ∼15% of normal resulted in a dramatic improvement in colitis related symptoms. Gapmer-treated mice had less intestinal bleeding and weight loss associated with DSS challenge relative to mice treated with a control oligonucleotide. Consistent with these gross observations, microscopic analyses of colonic tissue showed that fXI gapmer treatment significantly limited mucosal ulceration. Factor XI gapmer treatment also significantly diminished local levels of several inflammatory cytokines known to play a role in colon cancer progression (i.e., IL-6, IL-1β, IL-12). These results demonstrate that thrombin is a crucial driver of the pathogenesis of colitis-associated colon cancer and suggest that therapies directed at thrombin or thrombin generation could treat or prevent inflammation-driven colon cancer. As pathological inflammation has been estimated to account for as many as 1 in 5 cancer-related deaths, thrombin-directed therapies could have broad applicability to multiple malignancies.