Plasminogen activator activity of metastatic variants from a murine fibrosarcoma; effect of thrombin in vitro

In order to investigate the possible correlation between plasminogen activator (PA) activity and metastatic potential of tumour cells, we studied cultured cells from the murine fibrosarcoma mFS6 and from its two sublines M4 and M9 which differ markedly in their capacity to cause spontaneous metastases in the lung. PA activity was detected in all the sublines by an amidolytic method and was almost completely inhibited by treatment with antiurokinase antiserum. No significant differences were shown between mFS6, M4 and M9. Moreover, molecular analysis of PA by SDS-PAGE electrophoresis and fibrin overlay revealed in all the cell types a single species having a mol. wt. of approximately 48,000 daltons. Thrombin treatment dramatically inhibited the amidolytic activity of all cells, suggesting a role for this enzyme in the modulation of fibrin formation and dissolution within the primary neoplasm.