Thromboplastin release, but not content, correlates with spontaneous metastasis of cancer cells

Targeting clotting proteins in cancer therapy - progress and challenges

Cancer-associated thrombosis remains a significant complication in the clinical management of cancer and interactions of the hemostatic system with cancer biology continue to be elucidated. Here, we review recent progress in our understanding of tissue factor (TF) regulation and procoagulant activation, TF signaling in cancer and immune cells, and the expanding roles of the coagulation system in stem cell niches and the tumor microenvironment. The extravascular functions of coagulant and anti-coagulant pathways have significant implications not only for tumor progression, but also for the selection of appropriate target specific anticoagulants in the therapy of cancer patients.

Downregulation of tissue factor by RNA interference in human melanoma LOX-L cells reduces pulmonary metastasis in nude mice

Tissue factor (TF) is the membrane receptor of the serine protease coagulation factor VIIa (FVIIa). Formation of the TF/FVIIa complex initiates the coagulation cascade. We used short hairpin RNA (shRNA)-mediated RNA interference to knock down TF expression in the human metastatic melanoma cell line LOX-L. After transfection with the shRNA construct, 3 stable clones with significantly downregulated TF expression were established. They exhibited decreased proliferation in vitro as determined by (14)C thymidine incorporation and soft agar assay. The in vivo metastatic potential was assessed in an experimental pulmonary metastasis model in which cells from different clones were injected into the tail vein of nude mice. The incidence of pulmonary tumors was significantly lower in mice receiving shRNA-expressing cells (33% +/- 15%) than in control mice injected with wild-type cells or cells stably transfected with empty expression vector (90% +/- 10%). The mice injected with TF-downregulated cells had markedly longer survival time (69 +/- 17 days) compared to the control mice (35.6 +/- 5 days; p = 0.03). Thus, reduction of TF levels in LOX-L cells significantly delayed and reduced lung tumor formation. As a first step in elucidating the molecular basis for this effect, we compared the global gene expression profile in TF-downregulated cells and control cells by using cDNA microarray analysis. Forty-four known human genes were found to be significantly upregulated (> 2-fold; p < 0.05) and 228 genes significantly downregulated (>or= 3-fold; p < 0.05) in TF-downregulated cells compared to control cells. The differentially expressed genes encode proteins functioning in transcription, translation, cell communication and cell growth/death. The results provide a basis for investigating molecular mechanisms underlying the effects of TF on the metastatic capacity of LOX-L melanoma cells.

Expression of tissue factor and vascular endothelial growth factor is associated with angiogenesis in colorectal cancer

We examined the expression of tissue factor (TF) and vascular endothelial growth factor (VEGF) and the microvessel density (MVD) in 100 patients with colorectal cancer, and we investigated the relationship of the expression of TF or VEGF with angiogenesis. TF antigen was positive in 57.0% of all specimens. Incidence of TF expression was 41.2%, 45.5%, 52.6%, 84.6%, and 81.3% in tumors from patients in clinical stages I, II, IIIA, IIIB, and IV, respectively. TF expression was correlated with the Dukes' classification (P = 0.01) and the clinical stage of colorectal cancer (P = 0.02). VEGF antigen was positive in 64.0% of all specimens. Incidence of VEGF expression was 41.2%, 57.6%, 73.7%, 84.6%, and 75.0% in tumors from patients in clinical stages I, II, IIIA, IIIB, and IV, respectively. VEGF expression was correlated with the Dukes' classification (P = 0.01) but showed a weak association with the clinical stage (P = 0.08). MVD was significantly associated with the depth of invasion (P = 0.01), lymph node metastasis (P = 0.001), and liver metastasis (P = 0.02). The mean values of MVD were 7.5 +/- 2.8, 10.1 +/- 5.7, 14.6 +/- 5.8, 13.5 +/- 3.9, and 15.9 +/- 4.2 in tumors from patients in clinical stages I, II, IIIA, IIIB, and IV, respectively. A close relationship between VEGF and MVD (P < 0.001) and a significant correlation between TF expression and MVD were observed (P = 0.02). TF-positive carcinomas presented high MVD and VEGF expression (P < 0.001) more frequently than did TF-negative tumors. These results suggest that involvement of TF in the process of metastasis and progression of colorectal cancer may depend on increased angiogenesis.

Tissue factor as a tumor procoagulant

Tissue factor is a cell surface glycoprotein responsible for initiating the extrinsic pathway of coagulation. Many tumor cell homogenates and intact tumor cells have been shown to contain tissue factor activity. Immunohistochemical studies show that many tumors associated with Trousseau's syndrome express tissue factor on their cell surfaces. Tumor cells shed membrane fragments which carry tissue factor that can account for the activation of the clotting system. Tumor cells also produce soluble substances that can induce tissue factor expression on host cells, such as endothelium and monocytes, at sites distant from the tumor. Although, all the functional TF molecules are localized on the outer cell membrane in many tumor cells, the procoagulant activity on the intact cell surface is largely dormant and can be greatly enhanced upon cell injury or damage. Tissue factor procoagulant activity on the cell surface can be modulated by alterations in the plasma membrane without loss of cell viability. Tissue factor activity on cell surfaces is largely regulated by a plasma inhibitor, tissue factor pathway inhibitor. This inhibitor binds to both functional and non-functional tissue factor/VIIa complexes on the cell surface and prevents non-functional tissue factor/VIIa complexes from becoming functional after cell injury or lysis. Heparin, but not warfarin, therapy is effective in preventing the occurrence of devastating thrombotic events in patients with Trousseau's syndrome and the reason(s) for this are still unknown.

Immunohistochemical identification of tissue factor in solid tumors

Patients with cancer experience a much higher than expected incidence of thromboembolic disorders, commonly referred as Trousseau syndrome. Although this association has been well documented, the etiology of the hypercoagulable state is not known. The expression on tumor cells of tissue factor (TF), a membrane-bound lipoprotein that functions as a cofactor to factor VIIa in the initiation of the extrinsic pathway of blood coagulation, has been postulated as a possible mechanism. Whereas the distribution of TF in normal tissues is known, no large survey of TF expression in malignant tissues has been reported. In this study a polyclonal, monospecific rabbit anti-human TF IgG was used for immunohistochemical localization of TF antigen in 85 different tumor specimens. In general, cell types which normally express TF continued to do so after malignant transformation (41 of 60 epithelial tumor specimens were positive for TF). Tumors of nonepithelial origin frequently lacked TF, with only 3 of 19 specimens containing evidence of TF antigen. In addition five of six benign tumors did not express TF. Many tumor types commonly associated with Trousseau syndrome, for example lung, pancreatic, breast, colon and gastric carcinomas, stained positively for TF. Based on this survey, it appears that TF expression by tumors may be an important factor in the pathogenesis of a hypercoagulable state in some patients with cancer.