PROTAC-based nanoassemblies targeting BRD4 for potentiate FLASH radiosensitization therapy

Ultrahigh dose-rate radiotherapy (FLASH-RT) represents a rapidly emerging radiotherapy modality with improved normal tissue protection. However, tumor radioresistance remains a major obstacle limiting its clinical potential. To address this, we developed a novel redox-responsive, PROTAC-based nanoplatform (APF) formed by the self-assembly of folate-conjugated PEG₂₀₀₀-ARV-771 (FA-PEG₂₀₀₀-ARV-771). Following FA-mediated targeting and endocytic uptake by tumor cells, APF nanoparticles underwent glutathione-triggered cleavage in the reductive tumor microenvironment, releasing ARV-771 which promoted the proteasomal degradation of BRD4. The reduction of BRD4 disrupted the BRD4-c-Myc-RAD51AP1 signaling pathway and damaged the DNA repair pathway that resulting in a significant sensitizing effect of FLASH radiotherapy using Petal Accelerator platform. Both in vitro and in vivo experiments demonstrated that APF-assisted FLASH-RT markedly induced tumor cell apoptosis and necrosis, effectively inhibiting the malignant progression of tumors. Additionally, APF significantly enhanced FLASH-RT-induced tumor cell killing by promoting intracellular reactive oxygen species (ROS) generation and exacerbating DNA double-strand breaks. Transcriptomic analysis further revealed that APF-mediated BRD4 degradation suppressed key DNA repair-related genes. As a result, the APF@FLASH-RT combination achieved superior tumor inhibition in vivo with minimal systemic toxicity. This work provides a promising nanomedicine strategy for enhancing FLASH radiotherapy efficacy through targeted protein degradation.