A novel off-on fluorescent probe for sensitive imaging of mitochondria-specific nitroreductase activity in living tumor cells.

Sensitive and selective detection and imaging of nitroreductase (NTR) in cancer cells is of great importance for better understanding their biological functions. Since there are a few fluorescent probes concerning NTR activity specifically located in mitochondria, we developed a novel fluorescent benzoindocyanine probe (BICP) for mitochondrial NTR activity monitoring and imaging via extending a benzoindole moiety into a benzoindocyanine based fluorophore (BICF) with a strong intramolecular charge transfer (ICT) effect and incorporating 4-nitrobenzyl as a fluorescence-quenching and enzyme-responsive moiety. Live cell imaging of HeLa and A549 demonstrates that the developed BICP is able to realize sensitive and selective mitochondrial NTR activity probing with high-contrast "off-on" fluorescence. These findings implied the great potential of the developed probe for monitoring mitochondrial-specific NTR activities in living cells and related applications in cell biology.