Chiral Ruthenium(II) Polypyridyl Complexes: Stabilization of G-Quadruplex DNA, Inhibition of Telomerase Activity and Cellular Uptake

Two ruthenium(II) complexes, Lambda-[Ru(phen)(2)(p-HPIP)](2+) and Delta-[Ru(phen)(2)(p-HPIP)](2+), were synthesized and characterized via proton nuclear magnetic resonance spectroscopy, electrospray ionization-mass spectrometry, and circular dichroism spectroscopy. This study aims to clarify the anticancer effect of metal complexes as novel and potent telomerase inhibitors and cellular nucleus target drug. First, the chiral selectivity of the compounds and their ability to stabilize quadruplex DNA were studied via absorption and emission analyses, circular dichroism spectroscopy, fluorescence-resonance energy transfer melting assay, electrophoretic mobility shift assay, and polymerase chain reaction stop assay. The two chiral compounds selectively induced and stabilized the G-quadruplex of telomeric DNA with or without metal cations. These results provide new insights into the development of chiral anticancer agents for G-quadruplex DNA targeting. Telomerase repeat amplification protocol reveals the higher inhibitory activity of Lambda-[Ru(phen)(2)(p-HPIP)](2+) against telomerase, suggesting that Lambda-[Ru(phen)(2)(p-HPIP)](2+) may be a potential telomerase inhibitor for cancer chemotherapy. MTT assay results show that these chiral complexes have significant antitumor activities in HepG2 cells. More interestingly, cellular uptake and laser-scanning confocal microscopic studies reveal the efficient uptake of Lambda-[Ru(phen)(2)(p-HPIP)](2+) by HepG2 cells. This complex then enters the cytoplasm and tends to accumulate in the nucleus. This nuclear penetration of the ruthenium complexes and their subsequent accumulation are associated with the chirality of the isomers as well as with the subtle environment of the ruthenium complexes. Therefore, the nucleus can be the cellular target of chiral ruthenium complexes for anticancer therapy.