(188)Re radiopharmaceuticals for radiosynovectomy: evaluation and comparison of tin colloid, hydroxyapatite and tin-ferric hydroxide macroaggregates

BACKGROUND: Radiosynovectomy is a therapy used to relieve pain and inflammation from rheumatoid arthritis and related diseases. In this study three (188)Re particulate compounds were characterized according to their physico-chemical properties and their biological behavior in rabbits. The results were compared in order to establish which was the radiopharmaceutical that better fits the requirements of this kind of radiotherapy. METHODS: Three radiopharmaceutical formulations, tin colloid, hydroxyapatite particles (HA) and ferric hydroxide macroaggregates coated with tin colloid (FHMA), were physically characterized (number, volume and surface of the particles). For this purpose laser diffraction methodology was used. To evaluate cavity leakage of activity the following studies in New Zealand rabbits were performed: scintigraphic images for 48 hr after intraarticular injection of each radiopharmaceutical, biodistribution at 48 hr and urine samples collection during the first 24 hr post-radiopharmaceutical administration. RESULTS: Labeling procedures for (188)Re-HA and (188)Re-Sn-FHMA were labour intensive while (188)Re-Sn was easily prepared. Furthermore, (188)Re-Sn colloid offered the greatest surface area in the 2–10 microm range and was obtained with a radiochemical purity over 95%, while percentage of bound activity for (188)Re-HA and (188)Re-Sn-FHMA were 55% and 92% respectively. Stability was verified for the three radiopharmaceuticals for 24 hr. Scintigraphic studies and biodistribution in rabbits after intraarticular administration of the radiopharmaceuticals showed relevant activity only in the knee, this being over 90% of the residual activity in the whole body at 48 hr in every case. Renal elimination of (188)Re-Sn colloid and (188)Re-Sn-FHMA was detected by activity measurements in urine samples, during the first 12 hr post-radiopharmaceutical injection. The percentage of activity retained in the knee was 69.1% for (188)Re-Sn colloid, 55.1% for (188)Re-Sn-FHMA and 33.6% for (188)Re-HA. CONCLUSION: The (188)Re-Sn colloid was easy to prepare, minimum facilities were required, was stable for 24 hr and showed minimal leakage from the joint after intraarticular injection into the rabbit's knee. Furthermore, (188)Re-Sn colloid has greater retention in the knee when it is compared with the other radiopharmaceuticals, so it could provide the best therapeutic effect/absorbed dose ratio for the patient.