Optimising the radiolabelling properties of technetium tricarbonyl and His-tagged proteins.

Background: To date, the majority of protein-based radiopharmaceuticals have been radiolabelled using non-site-specific conjugation methods, with little or no control to ensure retained protein function post-labelling. The incorporation of a hexahistidine sequence (His-tag) in a recombinant protein can be used to site-specifically radiolabel with 99mTc-tricarbonyl ([99mTc(CO)3]+). This chemistry has been made accessible via a technetium tricarbonyl kit; however, reports of radiolabelling efficiencies and specific activities have varied greatly from one protein to another.