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 hydroxyalkyl solubilising group and wherein the tissue targeting moiety has binding affinity for the CD22 receptor. Methods of treatment utilising such complexes and methods of formation of such complexes are provided.
