Induction of a Fibrin-Gel Investment: An Early Event in Line 10 Hepatocarcinoma Growth Mediated by Tumor-Secreted Products

Abstract

Within a few hours of implantation in the subcutaneous space of strain 2 guinea pigs syngeneic line 10 tumors became invested in a fibrin-gel. We hypothesized that tumors might induce and modulate this fibrin-gel by secreting molecules capable of activating the host's clotting and fibrinolytic systems. To test this possibility, line 10 tumor cells, and several non-neoplastic control cells, were cultured for 2 to 4 hr in serum-free medium and the culture supernatants were assayed for their capacity to activate host inflammatory pathways. Four distinct mediator activities were recognized in line 10 tumor cell culture supernatants: a vascular permeability factor (VPF), a procoagulant (PC), a plasminogen activator (PA), and a macrophage-migration inhibitory activity (MIF). Nonmalignant control cells secreted none of these activities with the exception of rabbit kidney cells that not unexpectedly released a PA activity, presumably urokinase. Based on conditions of culture, physical and chemical properties, inhibitor studies, and kinetics of secretion, it is likely that four distinct molecules are responsible for these activities. The complexity of the culture medium was not critical but low pH was an important variable favoring PA secretion. Secretion of all mediators was inhibited by cold and that of VPF and PA by puromycin. Cytochalasin B and EDTA caused significant increases in PA secretion. The line 10 PA, like that from other sources, was irreversibly inactivated by diisopropyl fluorophosphate and is probably a serine esterase. The capacity to secrete mediators that activate important host inflammatory pathways provides tumors with a mechanism for stroma induction and may be an important factor in determining a tumor's histologic pattern and degree of malignancy.