Radiolabelling of poly(histidine) derivatized biodegradable microspheres with the 188Re tricarbonyl complex [188Re(CO)3(H2O)3]+

OBJECTIVES: Many radiopharmaceuticals have been studied as radiation synovectomy agents. In this study, we developed a new potential agent for radiation synovectomy: poly(lactic acid)-histidine (PLA-his) microspheres radiolabelled with [188Re(CO)3(H2O)3]+. METHODS: The reaction conditions for the chelation of [188Re(CO)3(H2O)3]+ and the radiolabelling of PLA microspheres were optimized and the stabilities for both steps tested in vitro. RESULTS: The chelation efficiency of [188Re(CO)3(H2O)3]+ reached 93.12 +/- 1.82% with >95% radiochemical purity once the colloidal and free 188Re were removed by a small Sep-Pak column (Plus QMA). More than 90% of radioactivity stayed in the [188Re(CO)3(H2O)3]+ form over 5 h. The radiolabelling efficiency of PLA-his microspheres with [188Re(CO)3(H2O)3]+ was above 92%. After 3 days incubation at 37 degrees C in calf serum, more than 80% of the radioactivity was still bound to the microspheres. CONCLUSION: Such microspheres are potentially useful as a radiation synovectomy agent for the treatment of chronically inflamed arthritic joints. Furthermore, they might be valuable in cancer brachytherapy.