Gallium (III) complexes with the ligands 5-bromosalicylaldehyde-4-hydroxybenzoylhydrazone and 5-bromosalicylaldehyde isonicotinoylhydrazone were synthesized to receive compounds with improved antiproliferative action. Compounds were characterized by elemental analysis, IR, and NMR spectroscopy. Density functional theory calculations with Becke's 3-parameter hybrid functional and 6-31+G(d,p) basis set were carried out to investigate the structural features of the ligands and Ga(III) complexes. Cytotoxic screening by MTT-dye reduction assay was carried out using cisplatin and melphalan as reference cytotoxic agents. A general formula [Ga(HL)2]NO3 for the complexes obtained was suggested. The complexes are mononuclear with the Ga(III) ions being surrounded by two ligands. The ligands acted as monoanionic tridentate (ONO) donor molecules. The analysis revealed coordination binding through deprotonated phenolic-oxygen, azomethine-nitrogen, and amide-oxygen atoms. The bioassay demonstrated that all compounds exhibited concentration-dependent antiproliferative activity at low micromolar concentrations against the acute myeloid leukemia HL-60 and T-cell leukemia SKW-3 cell lines. IC50 values of 5-bromo-derivative ligands and gallium (III) complexes are lower than those of cisplatin and much lower than these of melphalan. The coordination to gallium (III) additionally increased the cytotoxicity compared to the metal-free hydrazones.
Keywords: 5-bromosalicylaldehyde; DFT calculations; cytotoxic activity; gallium (III) complexes; hydrazones.