Stabilization of an (211)At-Labeled Antibody with Sodium Ascorbate

[Image: see text] (211)At, an α-particle emitter, has recently attracted attention for radioimmunotherapy of intractable cancers. However, our sodium dodecyl sulfate polyacrylamide gel electrophoresis and flow cytometry analyses revealed that (211)At-labeled immunoconjugates are easily disrupted. Luminol assay revealed that reactive oxygen species generated from radiolysis of water caused the disruption of (211)At-labeled immunoconjugates. To retain their functions, we explored methods to protect (211)At-immunoconjugates from oxidation and enhance their stability. Among several other reducing agents, sodium ascorbate most safely and successfully protected (211)At-labeled trastuzumab from oxidative stress and retained the stability of the (211)At-labeled antibody and its cytotoxicity against antigen-expressing cells for several days.