An oxygen-generating metal organic framework nanoplatform as a “synergy motor” for extricating dilemma over photodynamic therapy

Abstract

Photodynamic therapy, a non-invasive tumor treatment method, selectively kills tumor cells through reactive oxygen species (ROS) generated by photosensitizers. However, traditional photodynamic therapy merely utilizes the limited oxygen in the tumor microenvironment as the source of ROS, resulting in insufficient ROS for activating the eradication of tumors. Meanwhile, given that most photosensitizers bear potently hydrophobic planar conjugate structures which are prone to aggregate spontaneously in water, the efficiency of producing ROS will be reduced upon aggregation caused quenching (ACQ). Thereby, the development of photodynamic therapy is limited by the above two bottlenecks. Metal organic frameworks (MOFs) were reported to possess ample potential for photodynamic therapy in cancer treatment, where diverse metal ions converted the overexpressed endogenous hydrogen peroxide in tumor tissues into ROS via Fenton reactions/Fenton-like reactions, which effectively surmounted the hypoxic environment of tumors and avoided the immunosuppression and treatment resistance in such a state. Moreover, the unique pores of MOFs could inhibit the ACQ effect of photosensitizers in the physiological environment via steric effects, ultimately improving the efficacy of photodynamic therapy. Furthermore, MOFs could co-load photosensitizers and chemotherapeutic drugs, which will release both counterparts to synergistically kill tumor cells after the degradation of MOFs in the tumor microenvironment. In general, MOFs are a promising “synergy motor” nanoplatform for overcoming the bottleneck issues of photodynamic therapy. We believe that this work will provide a new insight into tumor photodynamic therapy.