The Radiopharmaceutical Chemistry of the Halogen Radionuclides
Radiohalogens are far fewer in number than radiometals, yet they have been important in radiopharmaceutical therapy since the very beginning. Indeed, radionuclides of the three heaviest naturally occurring halogens-bromine, iodine, and astatine-provide radiochemists with attractive options for the development of radiotherapeutics. Unlike labeling with metallic radionuclides, labeling with radiohalogens involves the formation of covalent bonds, generally via electrophilic or nucleophilic substitution. In this chapter, we shall describe the current state of the art for constructing radiohalogen-based therapeutics and theranostics. We will begin by discussing the isotopes of iodine-the most commonly studied of the radiohalogen family-and then show how concepts used for radioiodination have been adapted for therapeutic isotopes of both astatine and bromine. Applications of these labeling strategies to organic molecules, peptides, and proteins will also be discussed. Finally, we shall speculate on the future role of radiohalogens in radiopharmaceutical therapy, which appears to be particularly bright when considering small protein scaffolds and the alpha-particle emitter 211At.
