Homogeneous Sn-117m Colloid Radiosynovectomy Results in Rat Models of Joint Disease

Objectives Objectives: Late stage osteoarthritic (OA) disease and rheumatoid arthritis (RA) cause severe, chronic joint pain but these conditions can be treated with radiosynovectomy (RSV). A limitation of RSV has been the sub-optimal characteristics of the radiocolloids, with leakage from the joint resulting in irradiation of tissues beyond the synovium. To overcome these limitations we developed a novel Sn-117m homogeneous colloid that has been tested in two animal inflammatory arthritis models for its effects.

Methods Methods: Sn-117m (t½ 14d) decays by isomeric transition, producing both gamma rays at 159 keV, 86% abundant as well as monoenergetic conversion electrons (~140 keV; >110%) with a discreet range of about 290 µm, providing the therapeutic advantage of depositing energy in the synovial wall with minimal or no effect to surrounding tissue. A Sn-117m colloid (Sn-Colloid) with colloid particles between 2µm and 20µm was utilized. The colloid was tested in a collagen induced model of RA (n=40), and an OA model induced by joint laxity and instability (n=90). All rats were treated with a single injection of the Sn-Colloid (doses ranged from 2-50 μCi). Histopathology, autoradiography, blood and bio-distribution measurements were performed at 7, 28, 42 and 70 days after injection.

Results Results: Joint retention of the colloid was typically >99.0% throughout the study. Autoradiography indicated deposition of colloid in the synovium. The measured effects and safety of the microscopic evaluation of the cartilage and synovium will be reported.

Conclusions Conclusions: These results demonstrate that this unique Sn-Colloid delivered intra-articularly has exceptionally high retention in the joint space in OA and RA rat models.