Design,Synthesis And Antitumor Activity Of Nitrogen-containing Heterocycles As G-Quadruplex Ligand

G-quadruplexes(G4s)are non-canonical secondary nucleic acid structures which are involved in the regulation of many physiological processes,including transcription and translation of cancer-related genes,and have been visualized in human cells.Thus,targeting G4s have become a promising strategy for anti-cancer therapy.At present,the study of G4 ligands has attracted much attention in the world.In this paper,the interaction between aromatic heterocycte ligands and G4s was studied by fluorescence spectrum,circular dichroism spectrum,gel electrophoresis,cytotoxicity,confocal fluorescence imaging,etc.,and it proved that the ligand can stabilize the structure of G4s in cells,influence cell cycles,induce apoptosis,and inhibit proliferation of cancer cells.The results of the thesis were summarized as following:1.Hydrogen-bond-driven dimers of naphthyridine derivatives selectively identified DNA G-quadruplex and inhibited the proliferation of tumor cells.Circular dichroism,fluorescence spectroscopies,and NMR experiment revealed that the hydrogen-bonded dimeric ligands,which were based on naphthyridine,induced the conformational conversion of hybrid G4s and improved the thermal stability of hybrid G4s with an increase of the melting temperature.Through fluorescence spectroscopy experiments,we found that the ligands could selectively bind with G4s,of which L1 was better than other ligands in selectivity.Apoptosis,cell cycle,immunofluorescence imaging,and other experiments were used to investigate the biological activity of ligands.According to the assays,L1 and L3 induced apoptosis in HeLa cells and exhibited moderate cytotoxicity.Cell cycle and immunofluorescence imaging showed that L1 and L3 could selectively bind with G4s in the nucleus,which caused stabilization of DNA G4s,and induced cell cycle arrest.2.Oxidation-based responsive ligand of pyridine derivative stabilized of telomere G-quadruplex and selectively inhibited the proliferation of tumor cells.In the Tris buffer,PDS-B had little effect on the thermal stability of G4s.However,PDS-B could be oxidized and decomposed into PDS-S in the presence of H2O2,which can significantly improve the thermal stability of G4s.The ligand PDS-B exhibited different cytotoxicity against tumor cells and normal cells.In the case of HepG2 and L02 cells,the IC50 value of PDS-B to LO2 cells was about three times as much as HepG2 cells.But PDS-S was much more toxic to LO2 cells than HepG2 cells.The ligand induced tumor cells apoptosis and affected cell cycle,but displayed negligible effect on normal cells.3.A naphthyridine-indole ligand induced conformational conversion of hybrid topology and inhibited the proliferation of tumor cells.The circular dichroism spectra revealed that the L5-DA induced the conformational conversion from hybrid topologies to parallel topologies with a melting temperature increase of more than 30℃.According to Forster resonance energy transfer assays,the presence of excess duplex competitor had no effect on the ligand-induced stabilization of the hybrid topology,confirming the L5-DA’s selectivity for G4s over ds26.With IC50 values of 4.3 μM,the ligand showed significant cytotoxicity against HeLa cells and effectively induced growth inhibition and apoptosis in HeLa cells.Immunofluorescence microscopy revealed an increase in BG4 foci in the presence of the L5-DA,confirming ligand-induced stabilization of G4s in HeLa cells.