DNA Binding and Anti-Cancer Activity of Redox-Active Heteroleptic Piano-Stool Ru(II), Rh(III), and Ir(III) Complexes Containing 4-(2-Methoxypyridyl)phenyldipyrromethene

The synthesis of four novel heteroleptic dipyrrinato complexes [(eta(6)-arene)RuCl(2-pcdpm)] (eta(6)-arene = C6H6, 1; C10H14, 2) and [(eta(5)-C5Me5)MCl(2-pcdpm)] (M = Rh, 3; Ir, 4) containing a new chelating ligand 4-(2-methoxypyridyl)-phenyldipyrromethene (2-pcdpm) have been described. The complexes 1-4 have been fully characterized by various physicochemical techniques, namely, elemental analyses, spectral (ESI-MS, IR, H-1, C-13 NMR, UV/vis) and electrochemical studies (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)). Structures of 3 and 4 have been determined crystallographically. In vitro antiproliferative and cytotoxic activity of these complexes has been evaluated by trypan blue exclusion assay, cell morphology, apoptosis, acridine orange/ethidium bromide (AO/EtBr) fluorescence staining, and DNA fragmentation assay in Dalton lymphoma (DL) cell lines. Interaction of 1-4 with calf thymus DNA (CT DNA) has also been supported by absorption titration and electrochemical studies. Our results suggest that in vitro antitumor activity of 1-4 lies in the order 2 > 1 > 4 > 3.