A novel red-emitting two-photon fluorescent probe for imaging nitroreductases in cancer cells and tumor tissues with hypoxia conditions

Nitroreductases (NTRs) are overexpressed in many cancer cells especially in hypoxia conditions. They have been acted as an essential diagnosis and treatment targets for cancers. In order to detecting NTRs with high signal to background ratios using two-photon manner, it is necessary to explore effective two-photon fluorescent probes with long emission wavelengths. Here, we designed a novel red-emitting two-photon fluorescent probe P1 for tracing NTRs. P1 was constructed based on a two-photon fluorogen P1-OH with red-emission and a NTRs recognition site p-nitrobenzene. In the presence of NTRs, P1 showed strong fluorescence emission at 647 nm. P1 had high selectivity and sensitivity with NTRs (LOD is 0.00245 U/L). Importantly, two-photon action cross section experiments showed that P1 had favorable two-photon property encountering with NTRs and NADH. Furthermore, under hypoxia conditions, P1 has succeeded in imaging NTRs in cancer cells under one- and two-photon manners with hypoxia manner. Besides, by means of three-dimensional high-resolution manner, tumor tissues imaging has been achieved using P1 with two-photon manner. Probe P1 with red-emitting two-photon property may a potential molecular tool for detecting NTRs in living biological systems.