Near-Infrared Light-Initiated Molecular Superoxide Radical Generator: Rejuvenating Photodynamic Therapy against Hypoxic Tumors

Hypoxia, a quite universal feature in most solid tumors, has been considered as the "Achilles' heel" of traditional photodynamic therapy (PDT) and substantially impairs the overall therapeutic efficacy. Herein, we develop a near-infrared (NIR) light-triggered molecular superoxide radical (O₂-•) generator (ENBS-B) to surmount this intractable issue, also reveal its detailed O₂-• action mechanism underlying the antihypoxia effects, and confirm its application for in vivo targeted hypoxic solid tumor ablation. Photomediated radical generation mechanism study shows that, even under severe hypoxic environment (2% O₂), ENBS-B can generate considerable O₂-• through type I photoreactions, and partial O₂-• is transformed to high toxic OH· through SOD-mediated cascade reactions. These radicals synergistically damage the intracellular lysosomes, which subsequently trigger cancer cell apoptosis, presenting a robust hypoxic PDT potency. In vitro coculture model shows that, benefiting from biotin ligand, ENBS-B achieves 87-fold higher cellular uptake in cancer cells than normal cells, offering opportunities for personalized medicine. Following intravenous administration, ENBS-B is able to specifically target to neoplastic tissues and completely suppresses the tumor growth at a low light-dose irradiation. As such, we postulated this work will extend the options of excellent agents for clinical cancer therapy.