177Lu-labeled cyclic polyaminophosphonates as potential agents for bone pain palliation

177Lu (T1/2=6.71 d, Eβ(max)=497 keV) has radionuclidic properties suitable for use in palliative therapy of bone pain due to metastasis. 177Lu was produced in high-specific activity (3–4 TBq/g) and excellent radionuclidic purity (100%) by thermal neutron bombardment of natural Lu target. Two cyclic tetraaminomethylene phosphonate ligands, namely DOTMP and CTMP were synthesized and radiolabeled with 177Lu. The 177Lu-DOTMP complex was formed with very high yield (>99%) and showed excellent stability (up to 40 d at room temperature). Biodistribution of 177Lu-DOTMP was carried out in Wistar rats and the complex showed significant bone uptake (4.23%/g in femur and 5.23% in tibia at 3 h p. i.), rapid clearance from blood (no activity at 3 h p. i.) and minimum uptake in soft tissues.