CHEMISTRY AND BIOLOGICAL BEHAVIOR OF SM-153 AND RHENIUM-186-LABELED HYDROXYAPATITE PARTICLES - POTENTIAL RADIOPHARMACEUTICALS FOR RADIATIONSYNOVECTOMY

Hydroxyapatite (HA), a natural constituent of bone, was studied as a p articulate carrier for beta-emitting radionuclides in radiation synove ctomy. Particles were radiolabeled with Sm-153 or Re-186 and their in vivo safety was investigated following intra-articular injection into knees of normal rabbits and rabbits with antigen-induced arthritis (AI A). Radiolabeling efficiency was greater than 95%; in vitro studies sh owed minimal (less-than-or-equal-to 1%) loss of activity from particle s over a 6-day period with Sm-153-labeled HA and about 5% loss of acti vity over a 5-day period with Re-186-labeled HA. The total cumulative extra-articular leakage of Sm-153 over 6 days was 0.28% in normal rabb its and 0.09% in AIA rabbits. Leakage of Re-186 from the joint was 3.0 5% over a 4-day period with 80% of extra-articular activity found in t he urine. Histopathological evaluation of treated knees showed that HA particles are distributed throughout the synovium, embedded in the sy novial fat pad. The ease and efficiency with which this HA carrier is labeled, coupled with observed extremely low leakage rates from the jo int, make radiolabeled HA particles an attractive candidate as a radia tion synovectomy agent for evaluation in rheumatoid arthritis patients .