Promoting the formation and stabilization of human telomeric G-quadruplex DNA, inhibition of telomerase and cytotoxicity by phenanthroline derivatives

Abstract

Four new di-substituted phenanthroline-based compounds a-d have been designed and prepared, and they have been shown to induce the formation of anti-parallel structure of human telomeric G-quadruplex DNA by CD spectra. FRET assay indicates that the melting temperature increases (DT m values) of G-quadruplex in buffer (pH 7.4) containing 100 mM NaCl are 31.6, 34.6, 17.8 and 32.6• C for the compounds (1.0 mM) a, b, c and d, respectively. Competitive FRET assay shows that the four compounds exhibit a high G-quadruplex DNA selectivity over duplex DNA. Three of the compounds are the potent telomerase inhibitors and HeLa cell proliferation inhibitors.

The interactions of phenanthroline compounds with DNAs: Preferential binding to telomeric quadruplex over duplex

“…The melting Table 3). The T m values of the compound/i-motif complexes were lower than those of the compound/G-quadruplex complexes, in which their corresponding T m values were 32.5, 37.6 and 35.4 • C at 5 times excess of compound concentration [26]. The results suggested that three compounds are the potent stabilization agents for G-quadruplex DNA.…”

“…Compounds 1-3 were synthesized according to a previously reported literature [26]. Stock solutions were prepared by dissolving in DMSO at a concentration of 5 mM and kept at −20 • C. Before experiments, the concentrated compound was diluted in buffer solution.…”

“…Then the interactions between compounds 1-3 and quadruplexes were further explored by means of fluorescence titration, thermodynamics and continuous variation titration. In our previous study, the interactions of compounds with G-quadruplex have been investigated by CD spectra and fluorescence resonance energy transfer (FRET) melting assay [26], hence here the conformational effect and stabilizing potential of compounds 1-3 on i-motif were further evaluated using CD spectra and UV-melting experiment, respectively. Finally, the binding selectivity of three compounds to duplex, G-quadruplex and i-motif was evaluated by competition dialysis assay.…”

“…The binding studies were carried out at 293, 295, 298 and 303 K, in which structures of both G-quadruplex and i-motif are fully folded (see UV-melting curves in below and FRET-melting curves in Ref. [26]). The enthalpy change ( H • ) and entropy change ( S • ) were obtained from the slope and intercept of the linear van't Hoff plot based on ln K versus 1/T.…”

“…In our previous studies we found that phenanthroline-based compounds 1-3 ( Fig. 2) could recognize and stabilize selectively human telomeric G-quadruplex DNA in the presence of 10 times excess duplex DNA and induced the formation of the antiparallel structure, hence inhibit significantly telomerase activity and cancer cell proliferation [26]. In order to understand their binding mechanism, herein the interactions between these compounds and G-quadruplex DNA were investigated by absorption, fluorescence and CD spectroscopies and competition dialysis assay.…”