Interaction of the antitumor drug 9-aminoacridine with guanidinobenzoatase studied by spectroscopic methods:: A possible tumor marker probe based on the fluorescence exciplex emission

Fluorescence spectroscopy, surface-enhanced Raman spectroscopy (SERS), and analytical centrifugation are applied in this work to study the interaction of the antitumor drug 9-aminoacridine (9AA) with a trypsin-like protease, guanidinobenzoatase (GB), extracted from an Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission can be detected at a certain drug and enzyme concentration. The 9AA exciplex emission was also studied for 9AA interacting with others serin proteases: alpha-chymotrypsin, trypsin, and penicillin G-acylase (PGA), as well as with bovine serum albumin (BSA) in order to obtain information about the active center of GB. We have found that the exciplex 9AA emission may be induced by a ring-stacking interaction between the monomeric drug, under the amino form, and an aromatic residue placed in the catalytic site of the protein. The results derived from Raman spectroscopy corroborate this interaction mechanism, as demonstrated by the existence of typical protonated amino 9AA marker bands as well as an important modification of the ring vibrations, thus indicating the existence of an interaction through ring stacking, The analytical centrifugation technique was applied to study the GB association in aqueous solution, demonstrating that the 9AA/GB interaction depends on the enzyme quaternary structure. An interaction of 9AA with an associate form of GB, which may be the actual enzyme active form, is suggested.