Facile Method To Radiolabel Glycol Chitosan Nanoparticles with 64Cu via Copper-Free Click Chemistry for MicroPET Imaging

An efficient and straightforward method for radiolabeling nanoparticles is urgently needed to understand the in vivo biodistribution of nanoparticles. Herein, we investigated a facile and highly efficient strategy to prepare radiolabeled glycol chitosan nanoparticles with Cu-64 via a strain promoted azide-alkyne cycloaddition strategy, which is often referred to as click chemistry. First, the azide (N-3) group, which allows for the preparation of radiolabeled nanoparticles by copper-free click chemistry, was incorporated to 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 preradiolabeled alkyne complex with Cu-64 radionuclide. Following incubation with the Cu-64-radiolabeled DBCO complex (DBCO-PEG(4)-Lys-DOTA-Cu-64 with high specific activity, 18.5 GBq/mu mol), the azide-functionalized CNPs were radiolabeled successfully with Cu-64, 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 mm, with great efficiency in aqueous conditions In addition, we found that the Cu-64-radiolabeled CNPs (Cu-64-CNPs) did not show any significant effect on the physicochemical properties, such as size, zeta potential, or spherical morphology. After Cu-64-CNPs were intravenously administered to tumor bearing mice, the real-time, in vivo biodistribution and tumor targeting ability of Cu-64-CNPs were quantitatively evaluated by microPET images of tumor bearing mice. These results demonstrate the benefit of copper free click chemistry as a facile, preradiolabeling approach to conveniently radiolabel nanoparticles for evaluating the real-time in vivo biodistribution of nanoparticles.