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    • br Acknowledgement This work was supported by National

    2021-12-09


    Acknowledgement This work was supported by National Science Foundation (21475047, 21705051, 21874048), the Science and Technology Planning Project of Guangdong Province (2016B030303010), the Program for the Top Young Innovative Talents of Guangdong Province (2016TQ03N305) and the Foundation for High-level Talents in South China Agricultural University.
    Introducting G-Quadruplex DNAs are tertiary structures that involved in many biological processes and have been emerged as therapeutic targets in oncology [[1], [2], [3], [4], [5]]. The Quadruplex-forming G-rich DNA sequences are present in many regulatory regions including telomeres and oncogene promoters [6,7]. Among them, one important G-Quadruplex forming sequence is found in the nuclease hypersensitive ML-7 hydrochloride (NHE) III1 of the c-myc oncogene, which has been shown to regulate c-myc transcription and cell growth, proliferation [8,9]. Therefore, targeting of the c-myc G-Quadruplex DNA is one of the opportunities that would provide promising avenues in anticancer therapeutics. Recently, the optical technology has attracted considerable attention in various biomedical applications because of its unique characteristics including non-invasive, non-destructive, and non-ionizing [[10], [11], [12]]. In particular, “light-up” fluorescence probes, the emission of which is triggered by the interaction with the substrate, based on the small organic molecules (SOMs) have made significant contributions to our understanding of dynamic and complicated processes in vivo biological processes on a real time scale [[13], [14], [15], [16], [17], [18]]. Commonly, they have two function groups: one is the fluorophore that gives fluorescence emission and acts as signal reporter; the other is the binding ligand that binds specifically to the substrate. Also they are easier to prepare and generally provide high signal-to-noise rations. Along these lines, the development of “light-up” fluorescent probes has blossomed in the last couple of decades. Accompanying these advances has been the development of fluorescent probes that can differentiate the G-Quadruplex from duplex DNA [[19], [20], [21], [22], [23], [24]]. However, G-Quadruplexes are highly polymorphic and it is quite challenging to design fluorescence probes that show selectivity toward a particular G-Quadruplex [[25], [26], [27]]. Furthermore, fluorescent probes exhibiting a red/near-infrared emission were able to reduce the background interference and penetrate into tissue deeper than blue/yellow light, and with large Stokes shift could reduce the self-absorption and auto-fluorescence to improve their detection sensitivity [28]. Benzo [f]quinoline derivatives, which have a large planar chromophore, may allow sufficient overlap with the surface of the G-quartet. In our recent study, we found that conjugated functional side chains in the planar core would increase the binding affinity and selectivity [[29], [30], [31]]. Therefore, we concentrated our efforts on the conjugates of Benzo [f]quinoline with a styryl substituent in order to functionalize it as a potential fluorescent probe towards a special G-Quadruplex DNA. Herein, we report the design, synthesis, evaluation of a benzo(f)quinolinium fused chromophore-based fluorescent probe L-1 for the detection of c-myc G-Quadruplex DNA using N-(2-hydroxyethyl)piperazine moiety as a binding unit. This probe exhibiting a red emission and a large Stocks shift is found to be selective and sensitive for “light-up” detection of c-myc quadruplex DNA over other duplex DNA and other G-Quadruplexes. The detailed binding properties for c-myc G-Quadruplex DNA were examined through both experimental and modeling studies. In addition, the effects on cell permeability and intracellular localization of this probe in living cells were also evaluated.
    Experimental methods
    Results
    Conclusion G-Quadruplex structures are believed to emerge as promising nanostructures in many biological areas. Fluorescence probes based on the small organic molecules have made significant contributions to selectively recognize for the G-Quadruplex over duplex DNA. However, it is quite challenging to design fluorescence probes that show selectivity toward a particular G-Quadruplex among the multitude of potential G-Quadruplex-forming sequences. In this paper, a benzo(f)quinolinium fused chromophore-based fluorescent probe L-1 have be designed and synthesized. L-1 possessed the features of a large Stocks shift, as well as emitting red fluorescence for “light-up” recognition of c-myc G-Quadruplex DNA. Our results demonstrated that L-1 could bind and stabilize c-myc G-quadruplex DNA by inhibiting in vitro DNA synthesis. Detailed binding mechanism studies were performed and indicated that L-1 might interact with c-myc G-Quadruplex DNA mainly through end-stacking on the G-quartet surface. Introduction of hydroxyethyl side chain of the aromatic chromophore is critical in probe-Quadruplex interactions. More importantly, L-1 could enter into the nucleus and interact with DNA generating strong fluorescence emission, which might be suitable for living cells applications on monitoring nucleus activity.