Synthesis and characterization of mixed-ligand diimine-piperonal thiosemicarbazone complexes of ruthenium(II): Biophysical investigations and biological evaluation as anticancer and antibacterial agents

We have used a novel microwave-assisted method developed in our laboratories to synthesize a series of ruthenium-thiosemicarbazone complexes. The new thiosemicarbazone ligands are derived from benzo[d][1,3]dioxole-5-carbaldehyde (piperonal) and the complexes are formulated as [(diimine)(2) Ru(TSC)](PF6)(2) (where the TSC is the bidentate thiosemicarbazone ligand). The diimine in the complexes is either 2,2'-bipyridine or 1,10-phenanthroline. The complexes have been characterized by spectroscopic means (NMR, IR and UV-Vis) as well as by elemental analysis. We have studied the biophysical characteristics of the complexes by investigating their anti-oxidant ability as well as their ability to disrupt the function of the human topoisomerase ll enzyme. The complexes are moderately strong binders of DNA with binding constants of 10(4) M-1. They are also strong binders of human serum albumin having binding constants on the order of 10(4) M-1. The complexes show good in vitro anticancer activity against human colon cancer cells, Caco-2 and HCT-116 and indeed show some cytotoxic selectivity for cancer cells. The IC50 values range from 7 to 159 mu M (after 72 h drug incubation). They also have antibacterial activity against Gram-positive strains of pathogenic bacteria with IC50 values as low as 10 mu M: little activity was seen against Gram-negative strains. It has been established that all the compounds are catalytic inhibitors of human topoisomerase II. (C) 2011 Elsevier B.V. All rights reserved.