Antitumor action of crotalase, a defibrinogenating snake venom enzyme

Recent reports have shown that malignant cells release a variety of factors that modulate the tumor microenvironment. These factors, after release or shedding, work in concert to produce extravasation of fibrinogen from surrounding blood vessels with subsequent fibrin deposition around the tumor cells. This fibrin deposit could act to mask the tumor from the host's immune surveillance system. Fibrin deposits have been observed by investigators in the vicinity of various malignant tumors of man and animals. Although these observations suggest a role for the blood coagulation mechanism in tumor biology, the pathogenesis and significance of fibrin deposits in tumors have not been thoroughly investigated. We have used crotalase, a highly purified defibrinogenating serine proteinase from eastern diamondback rattlesnake venom and a fibrinolytic enzyme from southern copperhead venom to modulate selectively the tumor microenvironment in order to evaluate the role of fibrin(ogen) in tumor growth and dissemination. B16 melanoma, carried in C57BL/6 mice, has been selected as the experimental model system to evaluate the effectiveness of treatment by the venom enzymes. For these studies, solid B16 melanoma was excised from mice and a cell suspension was prepared in serum-free RPMI 1640 medium. Treatment of the cells with crotalase (30 NIH clotting U/ml) produced a dramatic inhibition of growth after subcutaneous injection of cells into C57BL/6 mice. On day 17 after implantation of tumor cells alone, the average tumor weight was 70 mg/mouse. By contrast, mice that received the B16 melanoma cells pretreated with crotalase had an average tumor mass of only 2 mg/mouse.(ABSTRACT TRUNCATED AT 250 WORDS)