Interactions And Anticancer Activity Of Naphthalene Diimide Ligands And G-Quadruplexes

G-quadruplexes,which are formed by G-rich DNA in the presence of K+ and Na+,are a special structure in DNA secondary structure at human telomeres or oncogene promoters,and they are involved in regulating biological processes,including carcinogenesis and cell aging.Telomeres are special structures at the end of linear chromosomes in eukaryotes,which are mainly composed of a repeated guanine(G)-rich sequence.For example,the repeat DNA sequence in human telomere is(TTAGGG)n,which can form G-quadruplex.G-quadruplexes have gained attention in recent years owing to their critical roles in the regulation of cancer growth and proliferation.It will be helpful for designing ligands targeting GQs and for developing new strategies toward GQ stabilization in tumor therapy.Here,naphthalimide(NDI)was selected to design the ligand and introduce the chiral center to form the enantiomer.By FL、UV-vis、circular dichroism、NMR spectroscopy、gel electrophoresis and immunofluorescence methods,we study the interaction between NDI ligands and G-quadurplex.The main results may be summarized as following:1.First,ligands were designed with the chiral center,and we expected the enantiomers can show selectivity differences in DNA samples.Unfortunately,we did not observe the expected results in the spectral experiments.However,a new phenomenon was discovered that NDI ligands can induce the conformational conversion of human telomeric DNA G-quadruplex under certain conditions.2.Then,we studied the transformation process of human telomeric G-quadruplex induced by NDI ligands,and found that the parallel G-quadruplex was more stable than initial hybrid G-quadruplex even at 90℃.Moreover,the induced conversion by NDI ligand can be processed at the cellular physiological temperature(37℃),even in a buffer or under mimetic cellular crowding conditions created by Ficoll 70,which indicats that NDI ligands have potential to be used in vivo.In addition,NDI-induced topological conversion of Tel23 may be through hairpinlike and triplex-like intermediate states.And there are differences between the topological conversion process induced by NDI ligands from hybridⅠ and hybrid Ⅱ,respectively.These results indicate that different topological structure of G-quadruplex can be regulated during the transformational coversion,which will provide a new idea for the precisely regulated drugs targeting G-quadruplex3.Squaraine ligand can specifically interact with parallel G-quadruplex,and we expected that NDI ligands and squaraine ligands could be synergized with cells to detect the topological transformation of G-quadruplex in living cells.In our work,SQ1 could not only recognize the parallel G-quadruplex induced by NDI in vitro,but also act synergistically with NDI on cancer cells to effectively improve the anticancer activity.In addition,NDI ligands can be localized in the nucleus through the living cell membranes.SQ1 cannot penetrate into the living cell membrane.However,in the presence of NDI ligand,NDI can assist SQ1 to enter living cells,and they can induce cell apoptosis and inhibit the cell cycle.And we can observe a significant increase in the content of G-quadruplex in cells through immunofluorescence,which indicates that the synergistic effect of the two ligands can stabilize the intracellular G-quadruplex.The synergistic effect of the two ligands can effectively improve the biological activity,which provides a new direction for drug design targeting G-quadruplex.4.Squaraine ligand SQ1 can not only recognize the parallel configuration of G-quadruplex induced by NDI ligand,but also can synergize with NDI ligand to effectively improve anticancer activity.The synergistic effect of the two ligands can improve biological activity,which provides a new direction for drug design targeting G-quadruplex.In conclusion,NDI ligands can not only specifically interact with human telomere G-tetrastrand in vitro,and induce the conformational conversion of human telomere G-quadruplex from hybrid to parallel topology,but also has strong anticancer activity and synergistic effect with square acid ligands on cells,with the content of G-quadruplex increasing in cells.It may provide new possibility for the design of anti-cancer drugs targeting G-quadruplex.