Hypoxia-activated NIR photosensitizer anchoring in the mitochondria for photodynamic therapy.

Photodynamic therapy is considered as a promising treatment for cancer, but still faces several challenges. The hypoxic environment in solid tumors, imprecise tumor recognition and the lack of selectivity between normal and cancer cells extremely hinder the applications of photodynamic therapy in clinics. Moreover, the "always on" property of photosensitizers also increases the toxicity to normal tissues when exposed to light irradiation. In this study, a hypoxia-activated NIR photosensitizer was synthesized and successfully applied for cancer treatment. is in the inactivated state with low fluorescence whereas its NIR emission ( = 716 nm) was induced reduction caused by nitroreductase at the tumor site. In addition, the reduced product was specially located in the mitochondria and demonstrated a high singlet oxygen production under 660 nm light irradiation, which efficiently induced cell apoptosis (IC = 0.63 μM). The studies carried out in Balb/c mice indicated that was suitable for precise tumor hypoxia imaging and can work as an efficient photosensitizer for restraining tumor growth through the PDT process.