Electron Transfer Mediator Modulates Type II Porphyrin-Based Metal-Organic Framework Photosensitizers for Type I Photodynamic Therapy.

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS-based metal-organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia-tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin-based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF-1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF-1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS-based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.