LOCATION OF TUMOR-CELLS IN COLON TISSUE BY TEXAS RED LABELED PENTOSANPOLYSULFATE, AN INHIBITOR OF A CELL-SURFACE PROTEASE

Pentosan polysulphate (PPS), a highly negatively charged polysaccharid e, is a significant inhibitor of an isoenzymic form of a cell surface protease referred to as guanidinobenzoatase GB, associated with coloni c carcinoma tissues in frozen sections and free GB in solution, in a c oncentration-dependent manner. However PPS failed to recognise and bin d to the isoenzymic form of GB associated with normal colon epithelial cell surfaces. Texas red labelled PPS (TR-PPS) binds to the tumour ce ll surfaces of colonic carcinoma and colonic polyps and these cells fl uoresce red, whilst the normal colon cell surfaces failed to bind the TR-PPS, and hence lacked red fluorescence. Polysulphonated suramin als o selectively recognised and inhibited the colonic carcinoma GB isoenz yme. The kinetic data indicated that this inhibition was not caused by a mere polyanionic effect, since highly sulphated heparin failed to s how a significant inhibition of colonic carcinoma GB, however trypan b lue did show 50% inhibition. Kinetic studies have also shown that PPS is a non-competitive, reversible inhibitor of colonic carcinoma GB, wi th an apparent K-m, 6.8 x 10(-7) M. Gel analysis has shown that PPS bi nds to another site, distinct from the active centre, and after bindin g PPS changed the conformation of GB. These studies suggest that TR-PP S is a potent inhibitor of colonic carcinoma GB, and can be used as a novel fluorescent probe for the location of tumour cells in frozen sec tions of human colon tissues. PSS could also have potential as a vehic le for the transport of cytotoxic compounds to carcinoma cells of the colon.