Comparative studies of 177Lu–EDTMP and 177Lu–DOTMP as potential agents for palliative radiotherapy of bone metastasis

177Lu is presently considered as an excellent radionuclide for developing bone pain palliation agents owing to its suitable nuclear decay characteristics [T1/2=6.73 d, Eβ(max)=497 keV, Eγ=113 keV (6.4%) and 208 keV (11%)] and large-scale production feasibility with adequate specific activity using moderate flux research reactors. Multidentate polyaminophosphonic acids have already been proven as the carrier molecule of choice for radiolanthanides and similar +3 metal ions in designing agents for palliative radiotherapy of bone pain due to skeletal metastases. The present paper describes a comparison between 177Lu complexes of two potential polyaminophosphonic acid ligands, namely Ethylenediaminetetramethylene phosphonic acid (EDTMP) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene phosphonic acid (DOTMP) with respect to their radiochemical and in-vivo biological characteristics. Although both the agents have exhibited promising features, the study reveals that 177Lu–EDTMP has marginally higher skeletal accumulation in comparison to that of 177Lu–DOTMP, while the latter has slightly faster blood clearance along with lower retention in liver and kidneys in animal models.