Radiolabeling and Biological Evaluation of 153Sm and 175Yb Zoledronic Acid Complexes

Production of bone pain palliation agents is developing increasingly for handling end-stage cancer patients. 153Sm and 175Yb labelled (1-hydroxy-2-imidazol-1-yl-phosphonoethyl) phosphoric acids can be used in bone pain palliation therapy. In this work, 153Sm and 175Yb labelled zoledronates were prepared using the commercial zoledronate ligand and 153SmCl3 and 175YbCl3 at 60ºC, respectively. 153Sm Cl3 and 175YbCl3 were obtained by thermal neutron irradiation (4×1013 n.cm-2s-1) of the natural metal oxide samples. The radiochemical purities were checked by the instant thin layer chromatography (ITLC) and high performance liquid chromatography (HPLC) methods. The stability studies of the final preparations in the presence of human serum, as well as, hydroxyapatite (HA) binding test were performed (>97%). The biodistribution of 153Sm and 153Sm-zoledronate performed in 2-48 h and for 175Yb and the 175Yb-zoledronate performed in 2-96 h post injection in the Syrian mice. The maximum bone uptake for 153Sm-zoledronate was 4% (48 h), while for 175Yb-zoledronate it was 10% (48 h). The complexes demonstrated satisfactory stability in the presence of human serum and the final formulations. However, the complexes are not appropriate for human studies due to the high liver uptake, possibly due to release of free metal from the complex and/or colloid formation.