Chemistry and biological behavior of samarium-153 and rhenium-186-labeled hydroxyapatite particles: potential radiopharmaceuticals for radiation synovectomy.

Hydroxyapatite (HA), a natural constituent of bone, was studied as a particulate carrier for beta-emitting radionuclides in radiation synovectomy. Particles were radiolabeled with 153Sm or 186Re and their in vivo safety was investigated following intra-articular injection into knees of normal rabbits and rabbits with antigen-induced arthritis (AIA). Radiolabeling efficiency was greater than 95%; in vitro studies showed minimal (< or = 1%) loss of activity from particles over a 6-day period with 153Sm-labeled HA and about 5% loss of activity over a 5-day period with 186Re-labeled HA. The total cumulative extra-articular leakage of 153Sm over 6 days was 0.28% in normal rabbits and 0.09% in AIA rabbits. Leakage of 186Re from the joint was 3.05% over a 4-day period with 80% of extra-articular activity found in the urine. Histopathological evaluation of treated knees showed that HA particles are distributed throughout the synovium, embedded in the synovial fat pad. The ease and efficiency with which this HA carrier is labeled, coupled with observed extremely low leakage rates from the joint, make radiolabeled HA particles an attractive candidate as a radiation synovectomy agent for evaluation in rheumatoid arthritis patients.