Differences in structure, physiological stability, electrochemistry, cytotoxicity, DNA and protein binding properties between two Ru(III) complexes

A novel Ru(III) complex, mer-[RuCl3(CH3CN)(dpq)] (1), has been synthesized and characterized by X-ray diffraction, where dpq = dipyrido[3,2-d:2',3'-f]quinoxaline. Its chemical and biological properties have been intensively compared with those of mer-[RuCl3(DMSO)(dpq)] (DMSO = dimethyl sulfoxide) (2). It has been found that the stability in buffered solutions and the reduction potential for the Ru-III/Ru-II couple can be modulated by changing the small molecule bonded to the Ru(III) center. Interactions of 1 with DNA have been investigated by DNA melting experiments, DNA competitive binding with EB (ethidium bromide), plasmid DNA cleavage experiments and viscosity measurements. The interaction of 1 and 2 with BSA (bovine serum albumin) has also been studied using fluorescent quenching method. The experimental results show that 1 exerts higher affinity towards DNA and BSA than 2 does. The cytotoxicity of 1 has been evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method, and 2 shows slightly higher anticancer potency than 1 does against all the cell lines screened. Attempts are made to clarify the possible antitumor mechanisms of these two complexes by analyzing the experimental results presented. (c) 2007 Elsevier Inc. All rights reserved.