Small Molecule Fluorescent Probes for Sensing and Bioimaging of Nitroreductase

Abstract Hypoxia is a condition caused by a decrease in oxygen and is often seen in cases of cardiac ischemia, solid tumors, inflammation, and other diseases. Tumor hypoxia can result in cancer invasion, metastasis, decreased apoptosis, and resistance to various therapies (chemotherapy, immunotherapy, and radiotherapy), ultimately reducing overall survival rates. These effects of hypoxia underline the need to monitor hypoxia‐associated specific markers for more effective therapeutic intervention. Nitroreductase (NTR) is a common biomarker of hypoxia, via its reduction activity with nitroaromatic compounds to corresponding amino derivatives using NADH and NADPH as cofactor. The NTR expression level can be correlated to cellular hypoxia. Therefore, developing a diagnostic tool for measuring NTR activity is of immense importance for improving treatment efficacies. To leverage NTR activity as a proxy of hypoxia, small molecule based fluorescent probes have been developed as quantifiable probes. To date, several NTR‐sensitive fluorescent probes have been reported. This review is focuses on the advances in these fluorescent NTR probes over the last five years.