Interaction of the antitumor drug 9-aminoacridine with guanidinobenzoatasestudied 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 ce rtain drug and enzyme concentration. The 9AA exciplex emission was also stu died for 9AA interacting with others serin proteases: alpha-chymotrypsin, t rypsin, and penicillin G-acylase (PGA), as well as with bovine serum albumi n (BSA) in order to obtain information about the active center of GB. We ha ve found that the exciplex 9AA emission may be induced by a ring-stacking i nteraction between the monomeric drug, under the amino form, and an aromati c residue placed in the catalytic site of the protein. The results derived from Raman spectroscopy corroborate this interaction mechanism, as demonstr ated by the existence of typical protonated amino 9AA marker bands as well as an important modification of the ring vibrations, thus indicating the ex istence of an interaction through ring stacking, The analytical centrifugat ion 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.