Mitochondria-targeting near-infrared ratiometric fluorescent probe for selective imaging of cysteine in orthotopic lung cancer mice

Cysteine (Cys) plays significant roles in many physiological processes, although its normal concentration is maintained at the micromole level. Abnormally high levels of intracellular Cys can lead to many diseases including cancer. Recent years, many effective fluorescent probes have been developed for the selective detection of Cys against other biological thiols. Herein, we synthesized a ratiometric near-infrared (NIR) fluorescent probe Cy-OAcr for selective imaging of intracellular Cys. Cy-OAcr has a lipophilic iminium cation unit as the mitochondrial guider and an acrylate group as the Cys recognition unit as well as a fluorescence modulator for rearranging the conjugated π-electron system of cyanine fluorophore. Upon detection of Cys, there occurs a significant absorption and fluorescence spectral shift, which are desirably beneficial for ratiometric detection. This probe has high sensitivity and selectivity for Cys detection over glutathione (GSH), homocysteine (Hcy), and other biomolecules with a low limit of detection at 0.09 μM. Probe Cy-OAcr is capable to detect and image Cys in three living cancer cell lines and their corresponding tumor-bearing mice models. More importantly, we successfully apply this fluorescent probe to evaluate the level of Cys in orthotopic lung cancer model. Imaging analyses reveal that the probe can discriminate tumor lesions from normal tissues, indicating its significant potential applications for clinical auxiliary diagnosis of cancer.