Plasminogen Activator (PA) Activity In Metastatic Cells: An Amidolytic Approach

It has been proposed that fibrinolytic activity can play an important role in the process of metastasis formation. Nevertheless, it is not yet clear in which phase of the tumor growth and dissemination this activity is involved. We measured the fibrinolytic activity of cells from primary tumor and metastatic nodules of 3LL, an i.m. implanted murine tumor which selectively metastasizes to the lungs. Tumor cells have been studied both immediately after mechanical disruption of tumor tissue and after in vitro culturing to confluence. Their P.A. activity was tested by an amidolytic assay in which cells were incubated with purified plasminogen (3CU/ml) and 4mM S-2251 (Kabi Diagnostica, Stockholm, Sweden), a plasmin specific chromogenic substrate. After 3 hour incubation at 37°C, the reaction was stopped with acetic acid and absorbance read at 405 nm.

Cells from the primary tumor and metastatic nodules showed a similar fibrinolytic activity, which was in both cases in- increased 3 to 4 fold in cell extracts obtained after preincubation with TRITON X-100. A dose-response curve plotted with increasing urokinase concentrations showed a parallel course. This data suggests that, in the 3LL model, PA activity is not one of the properties characterizing the selection of metastatic cells.

On the other hand,cultured cells presented consistently higher levels of PA than their native counterparts, suggesting that adhesion of cells in culture may stimulate PA production or, alternatively, that cultured cells are a selected population in comparison to the overall number of native cells.