OBJECTIVE To investigate the therapeutic efficiency of an endogenous enzyme-NQO1 activated hypericin in photodynamic therapy.METHODS An endogenous enzyme-NQO1 responsive photo sensitizer was designed and synthesized by conjugating aquinonebased ligand to a natural photosensitizer derived from Chinese herb.The photophysical and photochemical properties were investigated through UV-visible and fluorescence spectrophotometer,and the photodynamic activity was evaluated with MTT assay.RESULTS An endogenous enzyme-NQO1 activated hypericin was prepared and fully characterized with various spectroscopic methods.The electronic absorption was almost the same with the free hypericin,indicating the introducing of the ligand to hypericin has little effect to its ground state,while there is almost no detected fluorescence and reactive oxygen species(ROS)generation in PBS solution indicating the introducing of the ligand can effectively quench the fluorescence emission and ROS generation.The in vitro study showed that both compounds have almost no dark toxicity,but they are highlyphotocytoxic with an IC50 less than 1μmol·L-1 against A549 cell lines indicating the modified compound can be activated in the intracellular environment.CONCLUSION A simple and efficient hypericin-based activated photosensitizer was prepared.The ROS generation was quenched in PBS solution and it would be activated inside A549 cell lines.It may be served as apromising tumor selective fluorescent probe and photosensitizer for targeted photodynamic therapy. OBJECTIVE To investigate the therapeutic efficiency of an endogenous enzyme-NQO1 activated endogenous enzyme-NQO1 responsive photic therapy. investigated through UV-visible and fluorescence spectrophotometer, and the photodynamic activity was evaluated with MTT assay. RESULTS An endogenous enzyme-NQO1 activated hypericin was prepared and fully characterized with various spectroscopic methods. the electronic absorption was almost the same with the free hypericin, indicating the introduction of the ligand to hypericin has little effect to its ground state, while there is almost no detected fluorescence and reactive oxygen species (ROS) generation in PBS solution indicating the introduction of the ligand can quench the fluorescence emission and ROS generation. in vitro study showed that both compounds have almost no dark toxicity, but they are highly photocytoxic with an IC50 less than 1 μmol·L-1 against A549 cell lines indicating the modified compound can be activated in the intracellular environment. CONCLUSION A simple and efficient hypericin-based activated photosensitizer was prepared. ROS generation was quenched in PBS solution and it would be activated inside A549 cell lines. It may be served as a promising tumor selective fluorescent probe and photosensitizer for targeted photodynamic therapy.