Visualization\nof Mitochondrial DNA G‑Quadruplexes with Isaindigotone Derived\nNear-Infrared Fluorogenic Probe

Mitochondrial DNA G-quadruplexes (mtDNA G4s) play potential\nregulatory roles in mitochondrial functions. Fluorescent probes for\nimaging mtDNA G4s may provide useful information to unveil their regulating\ndynamics and functions. However, the existing probes for mtDNA G4s\nstill exhibit short absorption and emission wavelengths and limited\nsensitivity. Here, we develop a new isaindigotone-derived near-infrared\n(NIR) fluorogenic probe for imaging mtDNA G4s in live cells and in\nvivo. Different fluorescent probes are engineered by conjugating the\nisaindigotone scaffold with varying electron-donating groups. It is\nshown that the probe ISAP using dimethylaminophenyl as the electron-donating\ngroup exhibits near-infrared absorption/emission and a high fluorescence\nactivation fold in response to G4s. Molecular docking simulations\nreveal that ISAP binds to <i>c</i>-Myc G4 via multiple π–π\nstacking and hydrogen-bond interaction. Cellular studies show that\nISAP exhibits an excellent mitochondrial targeting ability and allows\nspecific imaging of mtDNA G4s. We further employed ISAP to image the\ndynamics of mtDNA G4s under glycolysis and oxidative stresses in live\ncells. Its capability to mtDNA G4s in vivo is showcased using a tumor-bearing\nmice model. This probe may serve as a useful tool to image mtDNA G4s\nand interrogate their biological roles in living systems.