Stabilization of G-quadruplex DNA, inhibition of telomerase activity and live cell imaging studies of chiral ruthenium(II) complexes.

Telomerase inhibition is an attractive strategy for cancer chemotherapy. In the current study, we have synthesized and characterized two chiral ruthenium(II) complexes, namely, Λ-Ru(phen)(2)(p-MOPIP) and Δ-Ru(phen)(2)(p-MOPIP), where phen is 1,10-phenanthroline and p-MOPIP is 2-(4-methoxyphenyl)-imidazo[4,5f][1,10]phenanthroline. The chiral selectivity of the compounds and their ability to discriminate quadruplex DNA were investigated by using UV/Vis, fluorescence spectroscopy, circular dichroism spectroscopy, fluorescence resonance energy transfer melting assay, polymerase chain reaction stop assay and telomerase repeat amplification protocol. The results indicate that the two chiral compounds could induce and stabilize the formation of antiparallel G-quadruplexes of telomeric DNA in the presence or absence of metal cations. We report the remarkable ability of the two complexes Λ-Ru(phen)(2)(p-MOPIP) and Δ-Ru(phen)(2)(p-MOPIP) to stabilize selectively G-quadruplex DNA; the former is a better G-quadruplex binder than the latter. The anticancer activities of these complexes were evaluated by using the MTT assay. Interestingly, the antiproliferative activity of Λ-Ru(phen)(2)(p-MOPIP) was higher than that of Δ-Ru(phen)(2)(p-MOPIP), and Λ-Ru(phen)(2)(p-MOPIP) showed a significant antitumor activity in HepG2 cells. The status of the nuclei in Λ/Δ-Ru(phen)(2) (p-MOPIP)-treated HepG2 cells was investigated by using real-time living cell microscopy to determine the effects of Λ/Δ-Ru(phen)(2)(p-MOPIP) on intracellular accumulation. The results show that Λ/Δ-Ru(phen)(2)(p-MOPIP) can be taken up by HepG2 cells and can enter into the cytoplasm as well as accumulate in the nuclei; this suggests that the nuclei were the cellular targets of Λ/Δ-Ru(phen)(2)(p-MOPIP).