Protease inhibitors suppress fibrinolytic activity of herpesvirus-transformed cells

Previous studies in this laboratory have quantified the fibrinolytic activity of herpesvirus-transformed cell lines and implicated the proteolytic capacity of cloned cell lines in the formation of primary and metastatic tumours. Because of the involvement of proteases in tumourigenesis in this system, we examined the effect of various protease inhibitors (alpha-1-antitrypsin, leupeptin and alpha-2-macroglobulin), as well as hamster serum containing acute phase proteins generated in response to physiological trauma, on the fibrinolytic capacity of a herpes simplex virus type 2-transformed hamster cell line. The effects of the various inhibitors on cell growth, fibrinolysis in vitro and tumourigenesis were examined. Leupeptin, alpha-1-antitrypsin, alpha-2-macroglobulin and hamster serum containing acute phase proteins were capable of inhibiting fibrinolysis in vitro, were not toxic to the cells and their action was reversible, while rejection of a mixture of protease inhibitor and transformed cells resulted in delayed tumour development.