INHIBITION OF A TUMOR PROTEASE WITH 3,4-DICHLOROISOCOUMARIN, PENTAMIDINE-ISETHIONATE AND GUANIDINO DERIVATIVES

Guanidinobenzoatase (GB) is a cell surface proteolytic enzyme capable of degrading fibronectin, and is associated with tumour cells and cell s capable of migration. The location of active GB in sections has been demonstrated with 9-aminoacridine (9-AA), a competitive inhibitor of GB. 3,4-Dichloroisocoumarin (3,4-DCI) and pentamidine isethionate (PI) are inhibitors of trypsin-like enzymes. It has now been demonstrated that 3,4-DCI, PI, and guanidino derivative compounds are significant i nhibitors of GB, on the surfaces of lung squamous cell carcinoma cells in frozen sections and free GB in solution. Dexamethasone acetate (DM A) and medroxy-progesterone (MP) did not show any significant inhibiti on of GB activity. These molecules lack a reactive chloride or guanidi no groups and are thought to react at the nuclear level, rather than d irectly on this cell surface protease. Kinetic studies have shown that 3,4-DCI, PI and guanidino derivatives are reversible competitive inhi bitors of GB, as determined in vitro on the purified enzyme. The inhib ition resulting with 3,4-DCI was a time-dependent process. It is sugge sted that these inhibitors interact with GB by binding to its active s ite, resulting in the formation of enzyme-inhibiter complexes (GB-I). The GB-I complexes can be dissociated with SDS treatment, resulting in the regain of GB activity.