Synthesis, structure, and anticancer activity of gallium(III) complexes with asymmetric tridentate ligands: growth inhibition and apoptosis induction of cisplatin-resistant neuroblastoma cells

Five gallium(III) complexes described as [Ga(III)(LX)2]ClO4, where (LX)- is the deprotonated form of a series of asymmetric ligands containing pyridine and 4,6-substituted phenol moieties, were synthesized and characterized by spectroscopic and spectrometric methods. Phenol substituents encompass the electron-withdrawing and electron-donating methoxy (1), nitro (2), chloro (3), bromo (4), and iodo (5) groups. Complexes 1 and 3 have had their molecular structure solved by X-ray crystallography and show distinct coordination modes. Complexes 1-5 were tested for growth-inhibition activity on cisplatin-resistant human neuroblastoma cells; those containing halogen substituents on the phenolate rings, i.e., 3-5, showed activity superior to that observed for cisplatin and induced apoptosis of neuroblastoma cells. Nitro-containing 2 suppressed proliferation of the neuroblastoma cells but induced apoptosis less effectively.