Microenvironment-triggered dual-activation of a photosensitizer- fluorophore conjugate for tumor specific imaging and photodynamic therapy

Photodynamic therapy is attracting increasing attention, but how to increase its tumor-specificity remains a daunting challenge. Herein we report a theranostic probe (azo-PDT) that integrates pyropheophorbide α as a photosensitizer and a NIR fluorophore for tumor imaging. The two functionalities are linked with a hypoxic-sensitive azo group. Under normal conditions, both the phototoxicity of the photosensitizer and the fluorescence of the fluorophore are inhibited. While under hypoxic condition, the reductive cleavage of the azo group will restore both functions, leading to tumor specific fluorescence imaging and phototoxicity. The results showed that azo-PDT selectively images BEL-7402 cells under hypoxia, and simultaneously inhibits BEL-7402 cell proliferation after near-infrared irradiation under hypoxia, while little effect on BEL-7402 cell viability was observed under normoxia. These results confirm the feasibility of our design strategy to improve the tumor-targeting ability of photodynamic therapy, and presents azo-PDT probe as a promising dual functional agent.