A Radioluminescent Metal-Organic Framework for Monitoring 225 Ac in Vivo .

Ac is considered as one of the most promising radioisotopes for alpha-therapy because its emitted high-energy α-particles can efficiently damage tumor cells. However, it also represents a significant threat to healthy tissues owing to extremely high radiotoxicity if targeted therapy fails. This calls for a pressing requirement of monitoring the biodistribution of Ac during the treatment of tumors. However, the lack of imageable photons or positrons from therapeutic doses of Ac makes this task currently quite challenging. We report here a nanoscale luminescent europium-organic framework (EuMOF) that allows for fast, simple, and efficient labeling of Ac in its crystal structure with sufficient Ac-retention stability based on similar coordination behaviors between Ac and Eu. After labeling, the short distance between Ac and Eu in the structure leads to exceedingly efficient energy transduction fromAc-emitted α-particles to surrounding Eu ions, which emits red luminescence through a scintillation process and produces sufficient photons for clearcut imaging. The intensity distribution of radioluminescence signal originating from the Ac-labeled EuMOF is consistent with the dose of Ac dispersed among the various organs determined by the radioanalytical measurement , certifying the feasibility of directly monitoring Ac using optical imaging for the first time. In addition, Ac-labeled EuMOF displays notable efficiency in treating the tumor. These results provide a general design principle for fabricating Ac-labeled radiopharmaceuticals with imaging photons and propose a simple way to track radionuclides with no imaging photons, including but not limited to Ac.