Studies On Molecular Mechanism Of The Anti-HepG2 Cell Proliferation Of Phenanthroline Derivatives Targeting G-quadruplex DNAs

As previous study, phenanthroline derivatives 1 and 2 could specifically induce and stabilize the G-quadruplex conformation of human telomere (h-telo), and they could also recognise and stabilize the conformation of c-myc G-quadruplexes in vitro. In this study, further investigations were proformed to determine the molecular mechanism on the antiproliferative properties of both ligands to HepG2 cells through various molecular biology methods. The main results are as follows:(1) The thermodynamic datas were calculated based on the UV-vis absorption titration assay, the results indicated that the interations between h-telo or c-myc G-quadruplexes and ligand 1 were exothermic reaction, and the main interaction force may be hydrogen bond or Van der Waals forces. Nevertheless, the interactions between ligand 2 and G-quadruplexes were endothermic reaction drived by entrogy, and hydrophobic force played a major role.(2) MTT, Cell cycle, and cell apoptosis experiments showed that both ligands could inhibit the proliferation of HepG2 cells, and the IC50 values were 1.26 and 0.5 μM, respectively. Ligand 1 could arrest cells in S and G2/M phases while ligand 2 could arrest cells in GO/M phase in a dose-dependent manner. Forthermore, both ligands could induce HepG2 cell apoptosis in a dose-dependent and time-dependent manner, and ligand 2 performed higher apoptosis-inducing activity than ligand 1.(3) RT-PCR and Western Blot assays indicated that both ligands had the character to induce down-regulation of the expression of c-myc and hTERT, while they only could induce the down-regulation of the transcription of c-myc in a dose-dependent manner in HepG2 cells.(4) The long-term cell growth inhibition and TRF expriments confirmed that the proliferation of HepG2 cell was inhibited by both ligands after incubating for 17-20 days, and the inhibitory activity of ligand 2 is higher than ligand 1, while both ligands had no effect on the length of telomeres.In short, the apoptosis induction might be due to the down-regulation of the expression of c-myc and/or hTERT. In addition, it was possible that the change of human telomere structure induced the DNA damage response, which would lead to cell death.