RE-188 LABELED HYDROXYAPATITE AND RE-188 SULFUR COLLOID - IN-VITRO COMPARISON OF 2 AGENTS FOR RADIATION SYNOVECTOMY

Aim: One therapeutic approach to rheumatoid arthritis and other inflam matory arthropathies besides surgical removal of inflamed synovium is radiation synovectomy using beta-emitting radionuclides to destroy the affected synovial tissue. Up to now the major problem associated with the use of labeled particles or colloids has been considerable leakag e of radionuclides from the injected joint coupled with high radiation doses to liver and other non target organs. in this study we compared Re-188 labeled hydroxyapatite particles and Re-188 rhenium sulfur col loid for their potential use in radiation synovectomy. Methods: To thi s end we varied the labeling conditions (concentrations, pH-value, hea ting procedure) and analyzed the labeling yield, radiochemical purity, and in vitro stability of the resulting radiopharmaceutical. Results: After optimizing labeling conditions we achieved a labeling yield of more than 80% for Re-188 hydroxyapatite and more than 90% for the rhen ium sulfur colloid. Both of the radiopharmaceuticals can be prepared u nder aseptic conditions using an autoclav for heating without loss of activity. In vitro stability studies using various challenge solutions (water, normal saline, diluted synovial fluid) showed that Re-188 lab eled hydroxyapatite particles lost about 80% of their activity within 5 d in synovial fluid. Rhenium sulfur colloid on the other hand proved to be very stable with a remaining activity of more than 93% after 5 d in diluted synovial fluid. Conclusion: These in vitro results sugges t that Re-188 labeled rhenium sulfur colloid expects to be more suitab le for therapeutic use in radiation synovectomy than the labeled hydro xyapatite particles.