A fluorescent study of ligands for guanidinobenzoatase, a protease associated with tumour cells. 
We have employed ethanol-fixed wax embedded sections of human breast tumours and smears of rat leukaemia cells to provide test systems with recognisable tumour cells amongst normal cells.  We have used 9-aminoacridine to locate cells possesing guanidinobenzoatase, an enzyme which degrades fibronectin and which binds 9-aminoacridine to its active centre.  The binding of 9-aminoacridine to tumour cells allows these cells to be located by fluorescent microscopy.  Pre-treatment of these sections with BZAR, a known inhibitor of guanidinobenzoatase inhibited the binding of 9-aminoacridine to the tumour cells.  These techniques defined the tumour cells in the sections; we then demonstrated by fluorescent microscopy that both Texas red-agmatine and BZAR also bound to the guanidinobenzoatase of these tumour cells.  These fluorescent probes have been used as model compounds to illustrate the ability of both N-substituted agmatines and N-substituted arginines to deliver desired molecules to an enzyme on the surface of tumour cells.  Replacement of these fluorescent moieties by cytotoxic moieties attached to the same ligands could lead to selective drug delivery to tumour cells.