SnWO₄-based nanohybrids with full energy transfer for largely enhanced photodynamic therapy and radiotherapy

The "partial matching" between upconversion nanoparticle (UCNP) emission and absorption by photosensitizers (PSs) often leads to a theoretically reduced therapeutic efficiency in UC-based photodynamic therapy (PDT) strategies in which the chosen PSs have limited capabilities and are unable to utilize all the near-infrared-upconverted light. In this study, needle-like SnWO₄ nanocrystals (SWs) with a broad UV-vis absorption region were synthesized to solve the problem. After covalent conjugation with UCNPs, all the UCNP-emitted light was effectively absorbed by SWs, triggering the type-I PDT process to activate ROS maxima. The unique nanostructure of the as-formed UCNP-SnWO₄ nanohybrids (USWs) also enhanced the receiving light intensities of SW, which further boosted the antitumor efficacy. Meanwhile, the strong X-ray attenuation capacity of both tungsten and tin elements qualified the USWs as excellent radio-sensitizers for radiotherapy (RT) enhancement, which played a complementary role with PDT treatment because PDT-mediated induction arrested the cells in the G0-G1 cell cycle phase, and RT was more damaging toward cells in the G2/M phase. The remarkably enhanced UC-PDT/RT efficiency of USWs was next validated in vitro and in vivo, and the combined NIR light and ionizing irradiation treatment completely suppressed tumor growth, revealing its great potential as an efficient anticancer therapeutic agent against solid tumors.