Thrombin inhibition by malignant and normal cells: a cell-bound antithrombin effect

Inhibition of metastases by anticoagulants

Metastasis involves several distinct steps, including one in which the tumor cell, after entry into the bloodstream, comes to rest in a capillary located at the distant site where a metastatic tumor will ultimately form. Components of the blood-clotting pathway may contribute to metastasis by trapping cells in capillaries or by facilitating adherence of cells to capillary walls. Conceivably, anticoagulants could interfere with this step in the metastatic process. In this review, we have summarized current knowledge on the interaction of malignant cells, clotting factors, and anticoagulants. We used computerized (MEDLINE) and manual searches to identify studies done in humans, in animals, and in in vitro systems that were published in English between 1952 and 1998. We found many reports that the formation of metastatic tumors could be inhibited by heparin, a vitamin K antagonist (warfarin), and inhibitors of platelet aggregation (prostacyclin and dipyridamole). Despite these encouraging preliminary results and a compelling biochemical rationale, only limited information exists on the clinical use of anticoagulants for the prevention or treatment of metastatic cancer because there have been so few controlled and prospectively randomized studies on this topic. In view of the preliminary results, anticoagulants may hold promise for the prevention and treatment of metastases. We believe that larger controlled investigations are strongly warranted to evaluate the clinical potential of anticoagulants for the prevention and treatment of metastases in humans.

Thrombin-specific sites of fibrinogen in small cell carcinoma of the lung

Thrombin-generated cleavage sites of human fibrinogen have been identified adjacent to viable tumor cells in fresh frozen sections of small cell carcinoma of the lung (SCCL) by means of immunohistochemical techniques using mouse monoclonal antibodies to the N-terminal peptides of the fibrinogen alpha and beta chains. These results indicate that thrombin is generated in situ in this tumor type. Based on previous evidence for the existence of an initiator of coagulation together with coagulation factor intermediates associated with viable SCCL tumor cells in situ, and also for the favorable effects of anticoagulant therapy with warfarin in SCCL, we postulate that local tumor cell-induced thrombin formation may contribute to self-regulated progression of SCCL through deposition of fibrin and stimulation of cell proliferation. These results suggest novel treatment strategies for this particular tumor type and justify efforts to identify other tumor types in which similar mechanisms exist.

Occurrence of blood coagulation factors in situ in small cell carcinoma of the lung

Through immunohistochemical techniques, blood coagulation factors were identified in situ in fresh frozen sections of small cell carcinoma of the lung. Prothrombin/thrombin, factor VII, factor X, and antithrombin III were present in intercellular spaces and associated with tumor cells. Factor IX, factor XI, prekallikrein, and high molecular weight kininogen were identified as being associated with tumor cells but did not exist in intercellular spaces. Variable connective tissue staining but no tumor-related staining was observed for factor V, factor VIII-related antigen, factor XII, the B subunit of factor XIII, alpha 1-antitrypsin, alpha 2-macroglobulin, or alpha 2-antiplasmin. Neither consecutive tissue nor the tumor manifested platelet Ib and IIbIIIa surface glycoproteins. These divergent staining patterns suggested that the detected clotting factors had not merely diffused from permeabilized blood vessels, but were selectively localized in situ. While conditions may exist within tumor tissue that both retard and promote thrombin generation, we propose that interactions between the observed coagulation factors ultimately lead to local thrombin formation, which is responsible for the conspicuous fibrin deposits already described in small cell carcinoma of the lung. Thrombin formed locally might contribute to progression of this tumor. Inhibition of local thrombin formation by warfarin therapy could explain the beneficial effects of warfarin therapy in treating small cell carcinoma of the lung.

Alpha-1-antitrypsin in human brain tumors

This study was undertaken to confirm the presence of alpha-1-antitrypsin (alpha 1-AT) in human brain tumors and to attempt to elucidate its significance. Seventy-seven consecutive unselected patients with various brain tumors were entered in this study. The alpha 1-AT and alpha 2-macroglobulin contents of the tumor extracts were qualitatively assessed by Ouchterlony immunodiffusion techniques. Plasminogen activator (PA) activity was assayed electrophoretically on sodium dodecyl sulfate gels. The patients were were divided into two groups according to the positivity of their tumors to alpha 1-AT. Sixty-eight percent of the tumors were positive for alpha 1-AT, and all specimens were negative for alpha 2-macroglobulin. Clinical and biological parameters obtained in all study patients failed to show statistically significant differences between the two groups with the exception of PA activity (p = 0.001), the peritumoral edema as seen on computerized tomography, and the preoperative serum fibrinogen level. These three parameters were higher in the group with specimens positive to alpha 1-AT. This study supports the hypothesis that alpha 1-AT is produced primarily by tumor cells in proportion to the regional proteolytic and inflammatory activity, and may protect the tumor cells.

Heparan structure and the modulation of angiogenesis

It is postulated that the angiogenic potential of tissues is influenced by the fine structure of heparan glycosaminoglycans present in the tissues. Possible mechanisms involved are discussed. It is suggested that compounds chemically related to heparans might usefully act as inhibitors of pathological angiogenesis.

Glycosaminoglycans and the control of cell surface proteinase activity

It is postulated that the metabolically variable fine structure of pericellular heparan glycosaminoglycans affects the ability of these molecules to influence cell proliferation-associated proteinase-catalysed reactions occurring at cell surfaces. Evidence suggesting the possibility of a wide repertoire of glycosaminoglycan-mediated positive and negative effects on such reactions is reviewed. It is suggested that clinical administration of compounds related chemically to heparins might usefully modulate cell proliferation-associated proteinase activity.