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 RuIII/RuII 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.