A new fluorescent probe with a large turn-on signal for imaging nitroreductase in tumor cells and tissues by two-photon microscopy

Hypoxia is the important characteristic of solid tumors, and it may cause the bioactivity of nitroreductase (NTR) to display an elevated level. Hence, the development of effective monitoring methods of NTR in living systems is of great importance for detecting the occurrence and progress of tumors. Toward this goal, a novel two-photon fluorescence turn-on NTR probe GCTPOC-HY, based on the two-photon platform GCTPOC and the NTR recognition site p-nitrobenzyl ether, is designed and synthesized. The probe GCTPOC-HY exhibits eminent properties such as high sensitivity and selectivity, highly stable photo-stability, and low cytotoxicity. Besides, the probe responds to 1.5μg/mL NTR with a 130-fold fluorescence enhancement, which is larger than the reported two-photon fluorescent NTR probes. Moreover, the probe GCTPOC-HY is suitable for fluorescence imaging of NTR in living cells by one- and two-photon modes. Importantly, the probe GCTPOC-HY is successfully applied to monitor NTR in the tumor tissues with a significant fluorescence signal and a penetration depth of 70µm by using two-photon microscopy.