Ru/Fe bimetallic complexes: Synthesis, characterization, cytotoxicity and study of their interactions with DNA/HSA and human topoisomerase IB.

Three ruthenium/iron-based compounds, 1: [Ru(MIm)(bipy)(dppf)]PF6 (MIm = 2-mercapto-1-methylimidazole anion), 2: [RuCl(Im)(bipy)(dppf)]PF6 (Im = imidazole), and 3: [Ru(tzdt)(bipy)(dppf)]PF6 (tzdt = 1,3-thiazolidine-2-thione anion) (dppf = 1,1'-bis(diphenylphosphine)ferrocene and bipy = 2,2'-bipyridine), were synthesized, and characterized by elemental analyses, conductivity, UV/Vis, IR, 1H, 13C and 31P{1H} NMR spectroscopies, and by electrochemical technique. The complex 3 was also characterized by single-crystal X-ray. The three ruthenium(II) complexes show cytotoxicity against DU-145 (prostate carcinoma cells) and A549 (lung carcinoma cells) tumor cells. The free ligands do not exhibit any cytotoxic activity, such as evident by the IC50 values higher than 200 µM. UV/Vis and viscosity experiments showed that the complexes interact weakly with the DNA molecule, via electrostatic forces. The interaction of the complexes 1-3 with the HSA is moderate, with Kb values in range of 105-107 M-1, presenting a static mechanism of interaction stabilized by hydrophobic. Complexes 2 and 3 showed high affinity for the FA7 HSA site as evidenced by fluorescence spectroscopy and molecular docking. Complexes 1-3 were tested as potential human Topoisomerase IB inhibitors by analysing the different steps of the enzyme catalytic cycle. The results indicate that all compounds efficiently inhibit the DNA relaxation and the cleavage reaction, in which the effect increases upon pre-incubation. Complexes 1 and 2 are also able to slow down the religation reaction.