X-ray-Triggered Activation of Polyprodrugs for Synergistic Radiochemotherapy

X-ray-induced photodynamic therapy (XPDT) can penetrate deeply into the tumor tissues to overcome the disadvantage of conventional PDT. However, the therapeutic efficacy of XPDT in cancer therapy is still restricted due to the insufficient reactive oxygen species (ROS) generation at a relatively low irradiation dosage. Herein, we present the tumor pH and ROS-responsive polyprodrug micelles to load the X-ray photosensitizer verteporfin (VP) as an ROS production enhancer. The block copolymer polyprodrug consisting of hydrophilic poly(ethylene glycol) (PEG) as well as the segments of thioketal-linked camptothecin (CPT) methacrylate (CPTKMA) and 2-(pentamethyleneimino)ethyl methacrylate (PEMA) (PEG-b-P(CPTKMA-co-PEMA)) can self-assemble into micelles in aqueous solution and encapsulate VP with a high loading efficiency of 67%. Inside tumor tissues, the zeta potential of the micelles can transform from neutral to positive for promoted cellular internalization under tumor acidity. Followed by X-ray irradiation at the dose of 4 Gy, efficient ROS generation in the presence of VP triggers CPT release. The VP-loaded polyprodrug micelles can finally ablate tumors efficiently via synergistic radiochemotherapy due to deep penetration of X-ray inside tumor tissues, ROS generation enhancement, and triggered CPT release. Consequently, this promising strategy represents a robust therapeutic modality for the enhanced radiochemotherapy of cancers.