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Herein, a binuclear ruthenium(II) complex modified by calix[4]arene group has been prepared. The complex as potential inducer and stabilizer of c-myc G-quadruplex DNA and antitumor reagent were studied. Observations revealed that the complex could bind to c-myc Pu27 and Pu22 DNA strongly with constants of 1.18 × 107 (Pu27) and 4.13 × 106 M-1 (Pu22) via groove mode as determined from absorption and luminescence titrations, as well as CD spectra. Results of continuous variation analysis confirmed that the complex interacted with c-myc G-quadruplex DNA through a 1:1 binding stoichiometry. As verified by PCR-stop assay, the replication of c-myc DNA was effectively blocked by the complex with the complete inhibition at the complex concentration of 4.0 μM both for Pu27 and Pu22, suggesting that the complex could efficiently induce the formation of c-myc G-quadruplex DNA. The appearance of blue TMB solution in the visual experiment also proved that the sequences of Pu27 and Pu22 could fold into G-quadruplex under the induction of the complex. Nevertheless, the complex was found to exhibit weak stabilization ability on c-myc G-quadruplex DNA according to FRET assay, which increased the melting point of c-myc DNA only 3-3.5 °C. The experiments on Topoisomerase inhibition and cytotoxicity of the complex showed that it acted as an inhibitor of TopoI and exhibited moderate anticancer activity against MCF-7 and Huh-7 tumor cells.

A polypyridyl ruthenium(II) complex with hydroxyquinoline-derived ligand has been synthesized and characterized. The ability to act as telomeric quadruplex inducer and stabilizer, and quadruplex-binding properties of the complex have been evaluated by absorption and emission analyses, fluorescent intercalator displacement (FID) titrations, circular dichroism (CD) spectroscopy, polymerase chain reaction (PCR) stop assay, color reaction studies, fluorescence resonance energy transfer (FRET) melting assay, Job plot, and molecular modeling. Observations revealed that the complex could well induce and stabilize the formation of antiparallel G-quadruplex of telomeric DNA in the presence or absence of metal cations, and showed superior G-quadruplex selectivity over duplex DNA with remarkable ΔTm value of 18.0 °C even at 50-fold excessive supplies of calf thymus (ct) DNA. The complex exhibited high interaction affinity of 2.56 × 106 M−1 with G-quadruplex DNA and evident luminescence enhancements of 3.1 and 4.2 times for quadruplex binding in Na+ and K+ buffer, respectively. In addition, the 1:1 [quadruplex]/[complex] binding mode ratio was determined. The results suggest that the complex can be developed as potential anticancer reagent through binding and stabilization of G-quadruplex DNA.

Given that recognition and regulation of G-quadruplex nucleic acid structures is an important goal for the development of chemical tools and medicinal agents, a dinuclear ruthenium complex [Ru2(bpy)4(bip-phenol)](ClO4)4 {bpy = 2,2′-bipyridine, bip-phenol = 2,4-bis(1H-imidazo[4,5-f] [1,10] phenanthroline-2-yl)phenol} has been synthesized and characterized, and its interactions with telomeric G-quadruplex DNA have been explored by photophysical and biophysical methods. This complex can induce and stabilize the formation of an antiparallel G-quadruplex of telomeric DNA in the absence of salt, or in the presence of K+/Na+-containing buffer. The complex binds strongly to the telomeric G-quadruplex, with a binding constant Kb > 106 and a 2:1 [complex]/[quadruplex] binding ratio. Fluorescence titrations revealed that the complex behaves as a promising photophysical “light switch” for G-quadruplex DNA, with 8.6- and 8.4-fold fluorescence enhancements in Na+ and K+ buffers, respectively.

A dinuclear ruthenium complex [Ru2(bpy)4(bip-phenol)](ClO4)4 {bpy = 2,2′-bipyridine, bip-phenol = 2,4-bis(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol} has been synthesized and characterized. The calf thymus (ct) DNA binding properties of the complex are investigated by means of DNA viscosity and optical spectroscopic techniques of UV-visible absorption and emission spectral titrations, steady-state emission quenching with ferrocyanide, ethidium bromide competitive binding, DNA thermal denaturation and reverse salt effect, together with molecular simulation technology. The results suggest that the complex is a promising DNA groove binder with a large DNA binding constant on 106 M−1 order of magnitude. The fluorescence of the complex manifests by 6.3-fold upon binding saturately to DNA. The complex is also demonstrated to be an efficient photocleaver of pBR 322 DNA.