Binding of the urokinase-type plasminogen activator to its cell surface receptor is inhibited by low doses of suramin.

The multipotent drug suramin, which is currently being studied as an anticancer agent, was found to inhibit the interaction between the urokinase-type plasminogen activator (u-PA) and its cellular receptor. 50% inhibition of binding was obtained with a suramin concentration between 30 and 60 micrograms/ml when using U937 cells and a ligand concentration of 0.3 nM. This concentration of the drug is well below the serum levels found in suramin-treated patients. Inhibition of binding was also demonstrated at the molecular level, using chemical cross-linking or an enzyme-linked immunosorbent assay-type technique based on the ligand interaction. The inhibition was not caused by a mere polyanion effect since polysulfates such as heparin, heparan sulfate, and pentosan polysulfate were non-inhibitory or showed only a very weak inhibition. However, polysulfonated compounds with structures resembling suramin (i.e. trypan blue and Evans blue) did prove inhibitory. The inhibition found with suramin showed a concentration dependence consistent with a mixed competitive and noncompetitive mechanism. The off-rate of prebound ligand was accelerated by the drug. It is speculated that the present effect may contribute to the anti-invasive properties of suramin by destroying the cellular potential for localized plasminogen activation and proteolytic matrix degradation.