(211)At-labeled immunoconjugate via a one-pot three-component double click strategy: practical access to α-emission cancer radiotherapeutics

α-Emission radiotherapeutics has potential to be one of most effective cancer therapeutics. Herein, we report a facile synthesis of an (211)At-labeled immunoconjugate for use as an α-emission molecular targeting therapy. We synthesized a tetrazine probe modified with closo-decaborate(2-), a prosthetic group that forms a bioavailable stable complex with (211)At. Our one-pot three-component double-click labeling method was used to attach decaborate to trastuzumab (anti-HER2 antibody) using decaborate-tetrazine and TCO-aldehyde probes without reducing the antibody binding affinity. Labeling the decaborate-attached trastuzumab with (211)At produced in the cyclotron at the RIKEN Nishina Center, at which highly radioactive (211)At can be produced, readily furnished the (211)At-labeled trastuzumab with a maximum specific activity of 15 MBq μg(–1) and retention of the native binding affinity. Intratumor injection of the (211)At-labeled trastuzumab in BALB/c nude mice implanted with HER2-expressing epidermoid cancer cells yielded efficient accumulation at the targeted tumor site as well as effective suppression of tumor growth.