Ruthenium polypyridyl complexes and their modes of interaction with DNA: Is there a correlation between these interactions and the antitumor activity of the compounds?

Abstract

Various interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy)L₁L₂]⁽²⁻ⁿ⁾⁺, and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}₂{μ-H₂N(CH₂)₆NH₂}]⁴⁺. The ligand tpy is 2,2′:6′,2″-terpyridine and the ligand L₁ is a bidentate ligand, namely, apy (2,2′-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L₂ is a labile monodentate ligand, being Cl⁻, H₂O, or CH₃CN. All six species containing a labile L₂ were found to be able to coordinate to the DNA model base 9-ethylguanine by ¹H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds.