Strong Persistent Luminescence NaYF4-based Nanoparticles Combined with Manipulated Hyperfractionated Irradiation for X-ray-Excited Photodynamic Therapy Enhancement

X-ray-excited photodynamic therapy (X-PDT), a novel synergistic therapy combining radiotherapy (RT) with photodynamic therapy (PDT), demonstrates not only more effective therapeutic outcomes but also overcomes the limitation of PDT's shallow penetration depth. Persistent luminescence nanoparticles (PLNPs) have been employed in X-PDT due to their unique afterglow emission, which yields more light to achieve more effective PDT outcomes using the same irradiation dose. However, at present, persistent luminescent materials used in X-PDT are mainly bulk crystals characterized by a nonuniform size and morphology, which are not suitable for biomedical applications, and the presence of excessive surface defects reduces the luminescence efficiency and the persistent luminescence duration. Herein, the NaYF4:Tb@NaYF4 core-shell nanoparticles with enhanced luminescence and afterglow performance and uniform morphology were prepared via the optimized solvothermal method. Their X-ray excitation optical luminescence (XEOL) and persistent luminescence (XEPL) intensities were enhanced more than 5.2 times and 3.5 times, respectively. The PLNPs were modified with a water-soluble AEP ligand and piggybacked with the photosensitizer Rose Bengal (RB) to construct an efficient X-PDT nanocoupling system. To fully utilize the afterglow of PLNPs, a unique hyperfractionated irradiation plan was designed, and the ROS yield was increased by nearly 50% at the same irradiation dose. In vivo therapeutic efficacy validation using the B16-F10-bearing C57 mouse model demonstrated that hyperfractionated irradiation combined with PLNPs showed significant therapeutic advantages. At a total dose of 2 Gy, the tumor inhibition rate was enhanced from 67.5% to 85% compared to the conventional irradiation strategy. Pathological analysis showed no significant histological damage in major organs, attesting to its negligible side effects. This study offers a novel modality, with both nanoparticles and irradiation strategy improvement, to further improve the X-PDT therapeutic efficacy and reduce side effects.