A nitroreductase-responsive near-infrared phototheranostic probe for in vivo imaging of tiny tumor and photodynamic therapy.

The hypoxia-activated and nitroreductase-responsive phototheranostic probe has been developed by incorporating a nitro group into a hemicyanine fluorophore. The probe displays extremely sensitive and selective near-infrared fluorescence enhancement to nitroreductase with the detection limit of 2.10 ng/mL. The detection mechanism relies on the nitroreductase-catalyzed reduction of the nitro group to an amino group, along with the generation of the fluorophore. The availability of the probe in fluorescence imaging and photodynamic therapy was demonstrated at cellular level and in vivo. The probe can image endogenous nitroreductase and the hypoxia status of living cells. The probe also exhibits significant phototoxicity to hypoxia tumor cells under the 660 nm laser irradiation. More importantly, the probe has been successfully utilized in imaging tiny tumor (about 6 mm3) and tumor photodynamic therapy in vivo. The proposed probe integrates accurate near-infrared fluorescence imaging and photodynamic therapy into the same molecule, which probably become a promising agent in the early diagnosis and therapy of tumors.