CHANGES IN COAGULATION AND PERMEABILITY PROPERTIES OF HUMAN ENDOTHELIAL-CELLS IN-VITRO INDUCED BY TNF-ALPHA OR 5,6-MEXAA

5,6 dimethyl xanthenone acetic acid (5,6 MeXAA), an analogue of flavon e acetic acid (FAA), has been shown to be more active against murine t umours than FAA. As both drugs have a vascular component in their mech anism of action similar to that observed for TNF-alpha, we have studie d the effects of 5,6 MeXAA alone and in combination with TNF-alpha on endothelial function in vitro. The changes induced by the drugs on pro coagulant activity and permeability were determined under tumour-simul ated conditions of low oxygen tension and the presence of tumour-secre ted factors. Procoagulant activity was assayed by measuring the time t aken for human umbilical vein endothelial cells (HUVECs) to clot norma l human plasma, increased activity resulting in reduced clotting times . HUVECs incubated under aerobic conditions were more sensitive to TNF -alpha than cells incubated at less than or equal to 0.2% oxygen. Cult ure medium conditioned by the human breast adenocarcinoma cell line MD A-MB-231 strongly upregulated procoagulant activity under both aerobic and hypoxic conditions; clotting times were further reduced by TNF-al pha. Both 5,6 MeXAA and FAA potentiated the effect of TNF-alpha on nor mal hypoxic endothelial cells; however, under all other conditions, ne ither drug in combination with TNF-alpha upregulated clotting activity . The presence of tumour-secreted factors had a far greater effect on upregulating procoagulant activity than did oxygen tension. In contras t to procoagulant activity, permeability was insensitive to TNF-alpha and low concentrations of 5,6 MeXAA also caused no change in permeabil ity.