Abstract: A tissue-targeting complex comprising a tissue targeting moiety, an octadentate hydroxypyridinone-containing ligand comprising four HOPO moieties and the ion of an alpha-emitting thorium radionuclide, where at least one of the four HOPO moieties is substituted at the N-position with a hydroxyalkyi solubilising group and wherein the tissue targeting moiety has binding affinity for the CD33 receptor. A corresponding pharmaceutical formulation and method and use in treatment, as well as methods of manufacture are provided.