A fluorescent turn-on probe for nitroreductase imaging in living cells and tissues under hypoxia conditions

Nitroreductase (NTR) plays momentous roles in biomedicine and the toxic degradation of organic nitrogen compounds mediated by cells. Numerous NTR is generated in tumor tissue due to the hypoxic conditions. The detection and monitoring of NIR in living cells and tissues can be utilized to the early diagnosis of tumors. In this paper, we developed a novel turn on fluorescent probe KC-NTR for nitroreductase detection. Taking advantage of the reducibility of nitroreductase, this probe can be transformed into the fluorescent compound KC-2 in the presence of NADH via the cascade cyclization reaction within 20 min. Our probe exhibited satisfactory sensitivity and good selectivity to NTR. A good linearity between the fluorescent intensity and the concentration of NTR ranged 0–10 μg/mL was observed, and the detection limit towards NTR was calculated to be 11 ng/mL. Furthermore, this probe was successfully employed in imaging living HepG2 cells and tumor tissues under hypoxia conditions with low cytotoxicity, indicating probe KC-NTR has great potential to monitor the NTR in the biological system.