Hypoxia-Targeting, Tumor Microenvironment Responsive Nanocluster Bomb for Radical-Enhanced Radiotherapy.

Although ultrasmall metal nanoparticles (NPs) have been used as radiosensitizers to enhance the local damage to tumor tissues while reducing injury to the surrounding organs, their rapid clearance from the circulatory system and the presence of hypoxia within the tumor continue to hamper their further application in radiotherapy (RT). In this study, we report a size tunable nanocluster bomb with a initial size of approximately 33 nm featuring a long half-life during blood circulation and destructed to release small hypoxia microenvironment-targeting NPs (∼5 nm) to achieve deep tumor penetration. Hypoxic profiles of solid tumors were precisely imaged using NP-enhanced computed tomography (CT) with higher spatial resolution. Once irradiated with a 1064 nm laser, CT-guided, local photothermal ablation of the tumor and production of radical species could be achieved simultaneously. The induced radical species alleviated the hypoxia-induced resistance and sensitized the tumor to the killing efficacy of radiation in Akt-mTOR pathway-dependent manner. The therapeutic outcome was assessed in animal models of orthotopical breast cancer and pancreatic cancer, supporting the feasibility of our combinational treatment in hypoxic tumor management.