Mixed ligand ruthenium(ii) complexes of bis(pyrid-2-yl)-/bis(benzimidazol-2-yl)-dithioether and diimines: Study of non-covalent DNA binding and cytotoxicity

Abstract

A series of mixed ligand ruthenium(II) complexes [Ru(pdto)(diimine)](ClO4)2/(PF6)2 1-3 and [Ru(bbdo)(diimine)](ClO4), 4-6, where pdto is 1,8-bis(pyrid-2-yl)-3,6-dithiooctane, bbdo is 1,8-bis(benzimidazol-2-yl)-3,6-dithiooctane and diimine is 1,10-phenanthroline (phen), dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz), have been isolated and characterised by analytical and spectral methods. The complexes [Ru(pdto)(phen)](PF6)2 la, [Ru(pdto)(dpq)(Cl](PF6) 2a, [Ru(bbdo)(phen)](PF6)2 4a and [Ru(bbdo)(dpq)](ClO4)2 5 have been structurally characterized and their coordination geometries around ruthenium(II) are described as distorted octahedral. In la, 4a and 5 the two thioether sulfur and two py/bzim nitrogen atoms of the tetradentate pdto/bbdo ligand are folded around Ru(II) to give predominantly a "cis-alpha" configuration. (I)H NMR spectral data of the complexes support this configuration in solution. In [Ru(pdto)(dpq)Cl](PF6) 2a with a distorted octahedral coordination geometry, one of the two py nitrogens of pdto is not coordinated. The DNA binding constants (Kb: 2, 2.00 +/- 0.02 x 10(4) M(-1), s = 1.0; 3, 3.00 +/- 0.01 x 10(6) M(-1), s = 1.3) determined by absorption spectral titrations of the complexes with CT DNA reveal that 3 interacts with DNA more tightly than 2 through partial intercalation of the extended planar ring of coordinated dppz with the DNA base stack. The DNA binding affinities of the complexes increase with increase in the number of planar aromatic rings in the co-ligand, and on replacing both the py moieties in pdto complexes (1-3) by bzim moieties to give bbdo complexes (4-6). Upon interaction with CT DNA the complexes 1, 2, 5 and 6 show a decrease in anodic current in the cyclic voltammograms. On the other hand, interestingly, 3 and 4 show an increase in anodic current suggesting their involvement in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 6 alters the superhelicity of DNA upon binding with supercoiled pBR322 DNA. The cytotoxicities of the dppz complexes 3 and 6, which avidly bind to DNA, have been examined by screening them against cell lines of different cancer origins. It is noteworthy that 6 exhibits selectivity with higher cytotoxicity against the melanoma cancer cell line (A375) than other cell lines, potency approximately twice that of cisplatin and toxicity to normal cells 3 and 90 times less than cisplatin and adriamycin respectively.

Synthesis, characterization and cytotoxic activities of the [RuCl2(NO)(dppp)(L)]PF6 complexes

“…This is probably not the case of the nitrosyl complexes in this study since they are hexacoordinated and very stable in incubation solution. Therefore, one possible mechanism to explain the activity of our nitrosyl complexes could be similar to those reported earlier suggesting the intercalation of ruthenium compound containing bidentate ligands with DNA [54][55][56]. However, we do not exclude the possibility of a parallel mechanism involving the dissociation of the NO from the metal center in the nitrosyl complexes, in which this molecule could play a synergistic role inhibiting metalloproteinase enzymes, in particular MMP-2 and MMP-9, as suggested for the complexes [3-pyhaH][trans-RuCl 4 (dmso-S)(3-pyha)] and [4-pyhaH][trans-RuCl 4 (dmso-S)(4-pyha)](X-pyha = X-pyridinehydroxamic acid) in which the NO is generated from the hydroxamic acids, under physiological conditions [57].…”

Cytotoxicity of half sandwich ruthenium(II) complexes with strong hydrogen bond acceptor ligands and their mechanism of action

“…Research groups of Sadler, Dyson, Keppler and Reedijk have synthesized a remarkably large number of Ru(II)/Ru(III) organometallic complexes that are being tested for anticancer activity [1][2][3][4][5][6][7][8][9][10]. Ruthenium complexes are quite cytotoxic but do not affect normal cells significantly [11,12].…”

Crystal structures of o , o ′-( N , N ′-dipicolinyldene)diazadiphenyl disulfide and its copper (II) complex: Antioxidant, antibacterial and DNA-binding properties

“…4 at a constant concentration of compound, 25 lg/ml). Since pyridine moieties are present in the compounds, we expect these compounds to insert partially in the DNA base pairs, leading to a decrease in transition energy, accounting for hypochromism and bathochromism [46][47][48][49]. However, upon incremental addition of DNA to L-L and 1, the bands at 209 and 213 nm underwent hyperchromism and shifted slightly to 2-3 nm (blue shift) (Fig.…”