Subtle Structural Changes of Dyes Lead to Distinctly Different Fluorescent Behaviors in Cellular Context: The Role of G-Quadruplex DNA Interaction Using Coumarin–Quinazolinone Conjugates as a Case Study

Abstract

Fluorogenic organic materials have gained tremendous attention due to their unique properties. However, only a few of them are suitable for bioimaging. Their different behaviors in organic and cellular environments hinder their application in bioimaging. Thus understanding the photoluminescent behaviors of organic materials in a cellular context is particularly important for their rational design. Herein, we describe two coumarin-quinazolinone conjugates: CQ and MeCQ. The high structure similarity makes them possess similar physical and photophysical properties, including bright fluorescence ascribed to the monomer forms in organic solvents and aggregation-caused quenching (ACQ) effect due to self-assembly aggregation in aqueous solution. However, they behave quite differently in cellular context: that is, CQ exhibits bright fluorescence in living cells, while the fluorescence of MeCQ is almost undetectable. The different performance between CQ and MeCQ in living cells is attributed to their different scenario in G-quadruplex (G4) DNA interaction. CQ selectively binds with G4 DNA to recover its fluorescence via aggregation–disaggregation switching in living cells, while MeCQ remained in the aggregate form due to its poor interplay with G4 DNA. Furthermore, CQ is applied as a two-photon fluorescent dye, and its photoswitchable fluorescence capability is exploited for super-resolution imaging of the specific mitochondrial structure in living cells via the STORM technique.

Thionation toward High-Contrast ACQ-DIE Probes by Reprogramming the Aqueous Segregation Behavior: Enlightenment from a Sulfur-Substituted G-Quadruplex Ligand

“…CTQ, as expected, exhibited selectivity toward G4 and an overall preference to parallel and hybrid topology G4s like its precursor CQ. 12 The results can also be confirmed with nakedeye observation (Figure 4C). After a Job's plot for assuring the binding ratio, we checked the data availability, fitted it with a proper equation and the derived energy changes (Figures S24−S25 and Table S5).…”

Crescent‐Shaped Carbazole Derivatives as Light‐Up Fluorescence Probes for G‐Quadruplex DNA and Live Cell Imaging

“…Moreover, the bright fluorescence signal in HepG2 cells is still able to be observed after staining with 4b and 4c for 8 h (Figure S18), suggesting the compounds are stable in cell. It was reported that the lipophilic cationic dyes are easily accumulated in mitochondria, [58] so we speculate the fluorescence signal in cytoplasm maybe come from the mitochondria. Figure 8 shows the CLSM images by the Mito-Tracker dye and the compound co-staining, and it is found that their positions are highly overlapped.…”

“…quadruplex DNA after interacting with the compounds (Figure S15). According to the characteristic of CD signal, bcl-2 [57] and HRCC [58] exhibit a mixed-type conformation, while c-kit 2 [59] and c-myc [60] are a parallel one. HTG shows a hybrid and antiparallel Gquadruplex in buffer containing 100 mM K + and 100 mM Na + , respectively.…”

“…[59] KSS is similar to HTG K + , implying a hybrid conformation. [58] After addition of 1 or 2 mol. equiv.…”

Monitoring and Modulating mtDNA G-Quadruplex Dynamics Reveal Its Close Relationship to Cell Glycolysis

“…To address these challenges related to mtDNA G4s, we reasoned that accurate tracking of such noncanonical structures using small-molecule fluorescent probes in live cells would be a practical and effective first step. To date, several fluorescent probes have been developed to selectively stain mtDNA G4s in cells; however, the fluorescence of the probes is distributed diffusely and uniformly over the mitochondria. − This staining pattern surprisingly differs from the punctate distribution of mtDNA indicated by the commercial dye PicoGreen or by fluorescent protein-tagged mitochondrial transcription factor A (TFAM). − Obviously, a more applicable mtDNA G4-specific fluorescent probe is required to understand the biological roles of mtDNA in greater detail.…”