DNA Interaction, Photocleavage and Topoisomerase I Inhibition by Ru(II) Complex with a New Ligand Possessing Phenazine Unit

Ruthenium(II) complexes as mitochondrial inhibitors of topoisomerase induced A549 cell apoptosis

Two new ruthenium(II) complexes [Ru(dip)2(PPβC)]PF6 (Ru1, dip = 4,7-diphenyl-1,10-phenanthroline, PPβC = N-(1,10-phenanthrolin-5-yl)-1-phenyl-9H-pyrido[3,4-b]indole-3-carboxamide) and [Ru(phen)2(PPβC)]PF6 (Ru2, phen = 1, 10-phenanthroline) with β-carboline derivative PPβC as the primary ligand, were designed and synthesized. Ru1 and Ru2 displayed higher antiproliferative activity than cisplatin against the test cancer cells, with IC50 values ranging from 0.5 to 3.6 μM. Moreover, Ru1 and Ru2 preferentially accumulated in mitochondria and caused a series of changes in mitochondrial events, including the depolarization of mitochondrial membrane potential, the damage of mitochondrial DNA, the depletion of cellular ATP, and the elevation of intracellular reactive oxygen species levels. Then, it induced caspase-3/7-mediated A549 cell apoptosis. More importantly, both complexes could act as topoisomerase I catalytic inhibitors to inhibit mitochondrial DNA synthesis. Accordingly, the developed Ru(II) complexes hold great potential to be developed as novel therapeutics for cancer treatment.

Comparative studies on the binding interaction of two chiral Ru(II) polypyridyl complexes with triple- and double-helical forms of RNA

Two chiral Ru(II) polypyridyl complexes, Δ-[Ru(bpy)₂(6-F-dppz)]²⁺ (Δ-1; bpy = 2,2'-bipyridine, 6-F-dppz = 6-fluorodipyrido[3,2-a:2',3'-c]phenazine) and Λ-[Ru(bpy)₂(6-F-dppz)]²⁺ (Λ-1), have been synthesized and characterized as binders for the RNA poly(U)•poly(A)*poly(U) triplex and poly(A)•poly(U) duplex in this work. Analysis of the UV-Vis absorption spectra and fluorescence emission spectra indicates that the binding of intercalating Δ-1 with the triplex and duplex RNA is greater than that of Λ-1, while the binding affinities of the two enantiomers to triplex structure is stronger than that of duplex structure. Fluorescence titrations show that the two enantiomers can act as molecular "light switches" for triple- and double-helical RNA. Thermal denaturation studies revealed that that the two enantiomers are more stable to Watson-Crick base-paired double strand of the triplex than the Hoogsteen base-paired third strand, but their stability and selectivity are different. For Δ-enantiomer, the increase of the thermal stability of the Watson-Crick base-paired duplex (13 °C) is slightly stronger than of the Hoogsteen base-paired strand (10 °C), displaying no obvious selectivity. However, compared to the Hoogsteen base-paired strand (5 °C), the stability of the Λ-enantiomer to the Watson-Crick base-paired duplex (13 °C) is more significant, which has obvious selectivity. The overall increase in viscosity of the RNA-(Λ-1) system and its curve shape are similar to that of the RNA-(Δ-1) system, suggesting that the binding modes of two enantiomers with RNA are intercalation. The obtained results in this work may be useful for understanding the binding differences in chiral Ru(II) polypyridyl complexes toward RNA triplex and duplex.

Efficient energy transfer between coronene-modified permethyl-β-cyclodextrins and porphyrin for light induced DNA cleavage

A novel supramolecular assembly was constructed by the noncovalent complexation of hexa-cata-hexabenzocoronene modified permethyl-β-cyclodextrins with tetrasodium tetraphenylporphyrintetrasulfonate in water, exhibiting highly efficient excited energy transfer behaviors and a promising DNA photocleavage ability.

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 K_b 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.