Bisquinolinium-fluorescein conjugates as specific fluorescence probes of c-myc Pu22 G-quadruplex and their bioimaging and anticancer activities

Abstract Targeting G-quadruplexes in the c-myc gene promoter region is one of the few therapeutic opportunities through inhibiting the c-myc protein overexpression. However, the design of probes recognizing c-myc G-quadruplexes with high selectivity and specificity and the more evaluation of cellular system still remain a big challenge. Here, two novel bisquinolinium-fluorescein conjugates (1a and 1b) with the alkyl linkers, have been designed and evaluated their selectivity and specificity for parallel c-myc Pu22 G-quadruplex. Compared with conjugate 1b with longer alkyl linker, conjugate 1a with shorter alkyl linker, exhibited higher fluorescence response and specificity towards c-myc Pu22 G-quadruplex than other wild-type c-myc G-quadruplexes, human telomere G-quadruplexes, other G-quadruplexes in the promoter regions and double-stranded DNA. According to the binding mode, the interaction of compound 1a with the 2nd loop around the 3’-end G-quartet through regulating the length of the alkyl linker, excited its fluorescence and enhanced its selectivity towards c-myc Pu22 G-quadruplex. Furthermore, conjugate 1a could selectively recognize c-myc Pu22 G-quadruplex DNA in cells through microscopy experiments, and inhibit cell proliferation possibly by reducing c-myc protein expression in cancer cells. This study provides guidance to design the high-performance fluorescence probes towards c-myc G-quadrulex by regulating the alkyl linker in the conjugate of G-quadruplex binder and fluorescence ligand, and develop anticancer drugs targeting c-myc G-quadruplex.