The 103Pd-DOTMP complex for conversion electron and Auger electron therapy of bone metastatic tumor cells

Abstract The radionuclide palladium-103 ( 103 Pd) has significant potential for use in targeted conversion electron and Auger electron radionuclide therapy. In this study, we synthesized a complex of 103 Pd with the macrocyclic ligand DOTMP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephosphonic acid). In the complex, the Pd 2+ ions are coordinated by the macrocyclic nitrogen and phosphonate oxygen atoms. While 103 Pd remains stably bound to the ligand, our results indicate that approximately 10% of the decay product, 103m Rh, is released from the [ 103 Pd]Pd-DOTMP complex in PBS buffer. We evaluated the cytotoxicity of [ 103 Pd]Pd-DOTMP and compared it with those of [ 177 Lu]Lu-DOTMP, which emits β − particles, and [ 161 Tb]Tb-DOTMP, which emits both β − particles and Auger electrons. Since DOTMP complexes do not exhibit internalization and lack nuclear localization within cells, the cytotoxic effect of [ 103 Pd]Pd-DOTMP is significantly lower than that of DOTMP labeled with the beta emitters 177 Lu and 161 Tb, which emit β − particles over a longer range.