RESUMO
Quinolones are known for their antimicrobial and antitumor activities. Gold(III) compounds constitute an emerging class of biologically active substances, of special interest as potential anticancer agents. In this work three gold(III) complexes of the fluoroquinolones antimicrobial agents norfloxacin (NOR), levofloxacin (LEVO) and sparfloxacin (SPAR) were prepared and characterized with physicochemical and spectroscopic techniques. In these complexes, NOR, LEVO and SPAR act as bidentate neutral ligands bound to gold(III) through the nitrogen atoms of the piperazine ring, which is an unusual mode of coordination for this class of compounds. Two chloride ions occupy the remaining coordination sites. The cytotoxic activity of the fluoroquinolones and their gold(III) complexes was tested against the A20 (murine lymphoma), B16-F10 (murine melanoma) and K562 (human myeloid leukemia) tumor cell lines as well as the L919 (murine lung fibroblasts) and MCR-5 (human lung fibroblasts) normal cells lines. All complexes were more active than their corresponding free ligands. Complex [AuCl(2)(LEVO)]Cl was selected for DNA fragmentation and cell cycle analysis. Spectroscopic titration with calf-thymus DNA (CT DNA) showed that the complexes can bind weakly to CT DNA, probably by an external contact (electrostatic or groove binding). The complexes exhibit good binding propensity to bovine serum albumin (BSA) having relatively high binding constant values.
Assuntos
DNA/metabolismo , Fluoroquinolonas/química , Compostos Organoáuricos/metabolismo , Compostos Organoáuricos/farmacologia , Soroalbumina Bovina/metabolismo , Animais , Antineoplásicos/química , Antineoplásicos/metabolismo , Antineoplásicos/farmacologia , Transporte Biológico , Bovinos , Ciclo Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Quelantes/química , Quelantes/metabolismo , Quelantes/farmacologia , Fragmentação do DNA/efeitos dos fármacos , Humanos , Concentração Inibidora 50 , Camundongos , Compostos Organoáuricos/químicaRESUMO
Formation of gold(III) complexes with the synthetic antibiotic norfloxacin (NF) was investigated in aqueous solution at pH 4.0, 7.5 and 10.6, with the ligand in cationic, zwitterionic and anionic forms, respectively. UV-Visible spectroscopy, steady state and time-resolved fluorometry were used to characterize the complexes. Binding sites, association constants and fluorescence lifetimes of the complexes were obtained. Au(3+) binding to zwitterionic NF produced a fluorescence decrease and a small red shift. Fluorescence changes as a function of Au(3+) concentration were fitted using a one-site binding model and the association constant was obtained, K(bzw) = 1.7 X 105 M⻹. The association of Au(3+) with cationic NF was much weaker, the obtained binding constant being K(bcat) = 2.4 X 10³ M⻹. The Au(3+) binding site for these species involves the carboxyl group, in agreement with a much stronger association of the cation with the carboxylate anion than with the neutral acid. Association of Au(3+) with nonfluorescent anionic NF presented a clear evidence of two binding sites. The highest affinity site is the unprotonated piperazinyl group with K(bpip) ≥ 5 X 107 M⻹ , and the low affinity site includes the carboxylate anion. The results point out to important pH dependent differences in complex formation between transition metal ions and fluoroquinolones, leading to different binding sites and association constants that change by several orders of magnitude.