Inhibition by bovine endothelial cells of degradation by HT-1080 fibrosarcoma cells of extracellular matrix proteins.

Medium conditioned by bovine arterial endothelial cells inhibited the degradation by human fibrosarcoma cells of living cultures of rat smooth muscle cells or their cell-free extracellular matrices. Endothelial cell-conditioned medium had no effect on the growth kinetics of fibrosarcoma cells, and the inhibitory influence of conditioned medium on matrix degradation was greatest with low numbers of tumor cells. Conditioned medium inhibited the production of tumor cell plasminogen activators, enzymes previously found to play a role in matrix glycoprotein degradation. The endothelial factor was heat- and acid-stable and non-dialyzable, and mixing experiments showed that it did not directly inactivate the tumor cell plasminogen activator. Endothelial cells may therefore modulate the production of proteolytic enzymes important in the implantation stage of tumor metastasis.