Hypoxia imaging in living cells, tissues and zebrafish with a nitroreductase-specific fluorescent probe

Hypoxia in solid tumors is directly linked to the elevated levels of endogenous nitroreductase (NTR). We present a novel fluorescent probe, namelyNTNO, for nitroreductase-specific detection based on the NTR-catalyzed reduction of the nitro unit to an amine functionality, and demonstrated its application for hypoxia imaging.NTNOwas designed by incorporating a nitro unit as the NTR response site into a benzothiazole derivative. Upon reacting with NTR in the presence of reduced nicotinamide adenine dinucleotide (NADH), the fluorescence of the probe was strongly and sensitively turned on, with a good linearity in the NTR concentration range of 0.5-8.0 mu g mL(-1)and a detection limit of 48 ng mL(-1). Most notably,NTNOhas been successfully used for imaging hypoxia levels in living cells, tumor tissues and zebrafish, making it of great potential to monitor NTR in biological systems.