Synthesis of [123I]IBZM: a reliable procedure for routine clinical studies

The single photon emission computed tomography (SPECT) D2/D3 receptor radiotracer [123I]IBZM, is prepared by electrophilic radioiodination of the precursor BZM with high-purity sodium [123I]iodide in the presence of diluted peracetic acid. However, in our hands, the most commonly used procedure for this radiosynthesis produced variable and inconsistent labeling yields, to such extent that it became inappropriate for routine clinical studies. Our goal was to modify the labeling procedure, to obtain consistently better labeling and radiochemical yields. The best conditions found for the radioiodination were as follows: 50 microg precursor in 50 microL EtOH mixed with buffer pH 2; Na[123I]I in 0.1 M NaOH (< 180 microL), 50 microL peracetic acid diluted solution, heating at 65 degrees C for 14 min. Purification was achieved by solid phase extraction (SPE) and reverse-phase high performance liquid chromatography (HPLC). Under these conditions, labeling yield average was 76 +/- 4% (n = 31); radiochemical yield was 69 +/- 4% and radiochemical purity was 98 +/- 1%. With larger volumes of the Na[123I]I solution the yields were consistent but lower. For example, for volumes between 417 and 523 microL the labeling yield was 61 +/- 5% (n = 21), radiochemical yield was 56 +/- 5% and radiochemical purity was 98 +/- 1%.