An Efficient and Straightforward Method for Radiolabeling of Nanoparticles with ⁶⁴Cu via Click Chemistry

Recently, nanoparticles have received a great deal of interest in diagnosis and therapy applications. Since nanoparticles possess intrinsic features that are often required for a drug delivery system and diagnosis, they have potential to be used as platforms for integrating imaging and therapeutic functions, simultaneously. Intrinsic issues that are associated with theranostic nanoparticles, particularly in cancer treatment, include an efficient and straightforward radiolabeling method for understanding the in vivo biodistribution of nanoparticles to reach the tumor region, and monitoring therapeutic responses. Herein, we investigated a facile and highly efficient strategy to prepare radiolabeled nanoparticles with ⁶⁴Cu via a strain-promoted azide, i.e., an alkyne cycloaddition strategy, which is often referred to as click chemistry. First, the azide (N3) group, which allows for the preparation of radiolabeled nanoparticles by copper-free click chemistry, was incorporated into glycol chitosan nanoparticles (CNPs). Second, the strained cyclooctyne derivative, dibenzyl cyclooctyne (DBCO) conjugated with a 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid (DOTA) chelator, was synthesized for preparing the pre-radiolabeled alkyne complex with ⁶⁴Cu radionuclide. Following incubation with the ⁶⁴Cu-radiolabeled DBCO complex (DBCO-PEG4-Lys-DOTA-⁶⁴Cu with high specific activity, 18.5 GBq/μ mol), the azide-functionalized CNPs were radiolabeled successfully with ⁶⁴Cu, with a high radiolabeling efficiency and a high radiolabeling yield (>98%). Importantly, the radiolabeling of CNPs by copper-free click chemistry was accomplished within 30 min, with great efficiency in aqueous conditions. After ⁶⁴Cu-CNPs were intravenously administered to tumor-bearing mice, the real time, in vivo biodistribution and tumor-targeting ability of ⁶⁴Cu-CNPs were quantitatively evaluated by micro-PET images of tumor-bearing mice. These results demonstrate the benefit of copper-free click chemistry as a facile, pre-radiolabeling approach to Medical sciences conveniently radiolabel nanoparticles for evaluating the real-time in vivo biodistribution of nanoparticles. (authors)