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, namely NTNO, 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. NTNO was 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 μg mL^-1 and a detection limit of 48 ng mL^-1. Most notably, NTNO has 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.