Mishiroku Izumo

Synthesis of 188Re-MDP complex using carrier-free 188Re

Abstract The synthesis of a rhenium-MDP labelled compound using carrier-free 188Re from the 188W/188Re generator was investigated. Stannous chloride was used as the reducing agent for the reduction of rhenium. Dependence of the yield of Re-MDP upon the concentration of reducing agent, reaction time, antioxidant, pH, temperature, ionic strength and adding the carrier was examined. Under optimum conditions, the yields of Re-MDP were 85–89% using carrier-free 188Re and 92–95% using carrier-added 188Re. Furthermore, the stability of Re-MDP at different pHs was studied.

Radioimmunotherapy with 186Re-labeled monoclonal antibody to treat liver metastases of colon cancer cells in nude mice.

The efficacy of radioimmunotherapy (RIT) in the treatment of minimal disease has been previously shown, despite the limitation of beta-emitters suggested by a mathematical model. In the present study, the efficacy of RIT with an anti-colorectal cancer IgG1 A7 conjugated with 186Re was examined in a liver metastasis model established by intrasplenic inoculation of human colon cancer cells. In this model, small metastases of less than 1 mm in diameter can be observed 1 week after cell inoculation. Metastases attain a diameter of several millimeters at 2 weeks. 186Re-A7 accumulated exclusively in metastases, displaying a value of 24.1 +/- 8.7% ID/g 2 days after the injection. 186Re-A7 accumulation in liver metastases increased with decreasing size. RIT with 7 MBq 186Re-A7 at 2 weeks significantly suppressed the growth of metastases; weight of metastases 4 weeks after cell inoculation was 5.96 +/- 0.87 g in nontreated control mice and 1.25 +/- 0.75 g in mice receiving 186Re-A7 RIT (p < 0.0001). RIT at 1 week more effectively inhibited metastatic growth to 0.08 +/- 0.05 g (p < 0.002 vs. RIT at 2 weeks). RIT with a class-matched irrelevant MAb 186Re-HPMS-1 at 1 week after cell inoculation somewhat suppressed metastatic growth, 3.39 +/- 0.25 g at 4 weeks, as compared with the control; however, 186Re-HPMS-1 RIT was far less effective than 186Re-A7 RIT (p < 0.0001). These results support the use of RIT with 186Re-MAb in an adjuvant setting in cases involving minimal disease. Factors such as higher and homogeneous MAb accumulation in small nodules, better perfusion, and subsequent better oxygenation likely compensate for the loss of beta radiation outside small metastases.

TANTALUM-183 : CYCLOTRON PRODUCTION OF A NEUTRON-RICH BIOMEDICAL TRACER

Abstract No-carrier-added tantalum-183 was produced free of radiotantalum impurities by the 186 W(p,α) 183 Ta nuclear reaction using 13.6 MeV protons on thick targets of isotopically enriched 186 WO 3 . The proton energy was optimum for the simultaneous production of 186 Re and 183 Ta. The ALICE code was used to theoretically determine the optimum irradiation conditions for the production of 183 Ta with proton and deuteron nuclear reactions. A Bio-imaging analyser was used to illustrate the migration of 183 Ta species into a grass plant ( Cyperus microiria steud). 183 Ta has potential applications as a tracer for ecotoxicity studies, and for developmental studies for radiotantalum pharmaceuticals.