Simplified multidose preparation of iodine-123-beta-CIT: a marker for dopamine transporters.

UNLABELLED Iodine-123-beta-CIT is a SPECT radioligand for dopamine and 5-HT transporters with potential use in Parkinson's disease, schizophrenia and cocaine addiction studies. At present, preparation of no-carrier-added (NCA) [123I] beta-CIT is achieved by iododestannylation of a trialkylstannyl precursor with sodium [123I]iodide in the presence of oxidizing agent, followed by preparative HPLC. The purpose of this study was to develop a faster and simpler method for the routine preparation of this radiopharmaceutical. METHODS Purification of the labeled compound was accomplished by solid phase extraction (SPE) with a C-18 Sep-Pak Light cartridge, which removed unreacted iodide, reaction reagents, polar side products and tributylstannyl precursor. The tributylstannyl precursor was preferred as starting material over the trimethylstannyl precursor due to its higher lipophilicity, allowing better separation of the labeled product and precursor. A TLC method was developed to assess the radiochemical purity of the final product. RESULTS The method produced [123I] beta-CIT in high radiochemical yields (75% +/- 4%), with high radiochemical purity (> or = 98%) and specific activity (> 67000 Ci/mmole), in 1.5 hr. The final formulation was sterile and pyrogen free. CONCLUSION The results obtained by solid phase extraction are consistent with those obtained by the HPLC method; with the advantage that the SPE method does not require solvent extraction, evaporation under reduced pressure or HPLC purification.