High-Affinity Uranyl-Specific Antibodies Suitable for Cellular Imaging

Monoclonal antibodies (mAbs) have proved to be valuable models for the study of protein−metal interactions, and previous reports have described very specific antibodies to chelated metal ions, including uranyl. We raised specific mAbs against UO₂²⁺−DCP-BSA (DCP, 1,10-phenanthroline-2,9-dicarboxylic acid) to generate new sets of antibodies that might cross-react with various complexed forms of uranyl in different environments for further application in the field of toxicology. Using counter-screening with UO₂²⁺−DCP-casein, we selected two highly specific mAbs against uranyl−DCP (K_D 10–100 pM): U04S and U08S. Competitive assays in the presence of different metal ions (UO₂²⁺, Fe³⁺, Zn²⁺, Cu²⁺, and Ca²⁺) showed that uranyl in solution can act as a good competitor, suggesting some antibody ability to cross-react with chelating groups other than DCP in the UO₂²⁺ equatorial coordination plane. Interestingly, one of the antibodies could be used for revealing uranyl cations in cell samples. Fluorescence activated cell sorting analyses after immunolabeling revealed the interaction of uranyl with human kidney cells HK2. The intracellular accumulation of uranyl could be directly visualized by metal-immunostaining using fluorescent-labeled mAb. Our results suggest that U04S mAb epitopes mostly include the uranyl fraction and its paratopes can accommodate a wide variety of chelating groups.