Preparation and evaluation of a new radiopharmaceutical for radiosynovectomy, 111Ag-labelled hydroxyapatite (HA) particles

Many radionuclides, namely, 166Ho, 90Y, 165Dy, 32P, 198Au, 186Re, etc. have been used for radio-synovectomy. Silver-111 (T1/2 7.45 d) can be produced in a nuclear reactor and is a potential therapeutic radionuclide decaying by β− emission (92% Eβmax=1.037 MeV and 8% by β− decay associated with emission of γ-rays (Eγ=245.4 keV, Iγ=1.33%; Eγ=342.1 keV, Iγ=6.7%)). Because of the production feasibility and favourable nuclear properties, 111Ag may find use as a suitable radionuclide for radio-synovectomy. Hydroxyapatite (HA), Ca10(PO4)6(OH)2 is one of the preferred particulates for this application. In this work, [111Ag]Ag-HA particulates were successfully prepared with high-labelling yield (∼97%) at various pH values. The radiochemical purity of the [111Ag]Ag-HA particles was 99.9%. Stability studies for 7 days showed that the [111Ag]Ag-HA particles retained their stability. γ camera images at 15 min, 24 h and 5 d after injection of the particles into rabbits revealed the retention of the activity in the synovial joints of the knee, thereby indicating excellent in vivo stability of [111Ag]Ag-HA particles. Therefore, [111Ag]Ag-HA particles would be a potential therapeutic agent in the management of arthritis.