Study Of New Methods For Screening G-quadruplex Ligands

The end of eukaryotic chromosomes is compromised of specialized structures known as telomeres,which contain short guanine-rich DNA repeats.Telomere can control cell aging because it gets shorter everytime the cell reduplicates.However,telomerase can provide a compensatory mechanism by adding DNA repeats onto the end of telomere and so the cell becomes immortal and transforms into malignant phenotype.Thus the inhibition of the telomerase activity has potential to halt tumor growth.The G-rich telomeres can form structures known as quadruplexes,which can prevent telomerase to get in touch with the end of telomere and elongate it.Small molecules.which can promote and stabilize the formation of G-quadruplex,are potential anticancer drugs.Therefore,developing efficient mechanism to detect and screen G-quadruplex ligands arouse considerable interest.In this paper,we design two kind of methods,based on the transformation of G-quadruplex structure,to screen small molecules,which can stablize G-quadrupelx and these methods have the potential to be used in clinical application in the future.1.A simple and fast electrochemical technique for screening of G-quadruplex ligands based on the transformation of G-quadruplexstructureIn this part of the work,we developed a simple and fast electrochemical technique for screening of G-quadruplex ligands based on the transformation of G-quadruplex structure leading to change in electrical signal.[Ru(NH3)6]3+is chosen as the electrochemical indicator,since[Ru(NH3)6]3+may bind through electrostatic attractions with the phosphate groups of DNA molecules.However,the electron transfer of[Ru(NH3)6]3+to electrode surface will be sharply inhibited when G-quadruplex-ligand complex forms.Firstly,quadruplex forming sequence(QFS)is immobilized on the surface of gold electrode.When a kind of small molecule with ability to stabilize G-quadruplex is incubated with QFS,SWV wave of[Ru(NH3)6]3+will be changed significantly.As a proof of concept,two types of well-studied G-quadruplex ligands,TMPyP4 and BRACO-19,are chosen as model targets.Experimental results demonstrate that this electrochemical approach may provide a simple,high-efficient method for screening ligands bound to quadruplex with potential therapy in tumor treatment.2.A simple and fast colorimetric technique for screening of G-quadruplex ligands based on the transformation of G-quadruplex structureIn this part of the work,we designed a simple and fast colorimetric technique for screening of G-quadruplex ligands based on the transformation of G-quadruplex structure based on the transformation of G-quadruplex structure leading to change of solution color.We incubate AuNPs with G-quadruplex forming DNA.When there is no existence of quadruplex ligand,G-quadruplex forming DNA is in the form of single chain and can bind to AuNPs and stabilize them,thus the solution is still red However,with the presence of ligands,the single chain transforms to quadruplex structure and leaves AuNPs surface so that AuNPs aggregate leading to color change of solution.Compared to other methods,this technique is very simple and there is no need for labeling.In addition,the results can be observed with naked eyes and this method provides a new way for screening G-quadruplex ligands.