Synthesis, DNA-binding, photocleavage, cytotoxicity, and apoptosis studies of ruthenium(II) complexes containing 3,6-dimethyldipyrido[3,2-a:2′,3′-c]phenazine

Two new ruthenium(II) polypyridyl complexes, [Ru(bpy)(2)(DMDPPZ)](ClO4)(2) (1) (bpy = 2,2'-bipyridine, DMDPPZ = 3,6-dimethyldipyrido[3,2-a:2',3'-c] phenazine) and [Ru(dmb)(2) (DMDPPZ)](ClO4)(2) (2) (dmb = 4,4'-dimethyl-2,2'-bipyridine), have been synthesized and their DNA-binding, photoinduced DNA cleavage, and cell cytotoxicity are studied. The complexes show good binding to calf thymus DNA in the order: 1 > 2. Both complexes exhibit efficient DNA cleavage upon irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The cytotoxic activity of 1 and 2 was tested by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) method. These complexes effectively inhibit the proliferation of tumor cells. The antioxidant activity against hydroxyl radical ((OH)-O-center dot) was also explored.