AN IMPROVED METHOD FOR RAPID AND EFFICIENT RADIOIODINATION OF IODINE-123-IQNB

The SPECT radioligand, 3-quinuclidinyl-4-[I-123]iodobenzilate ([I-123] IQNB), binds to muscarinic receptors and has generated interest as a p otential agent for clinical SPECT. Unfortunately, cumbersome and ineff icient radioiodination procedures have limited the practicality of [I- 123]IQNB SPECT imaging. Methods: We report a rapid (5 min) and simple radioiodination procedure for preparing [I-123]IQNB from a tri-n-butyl stannyl precursor in a no-carrier-added reaction that yields high spec ific activity with radiochemical yield exceeding 60%. The radiochemica l purity of the final product exceeds 95%. Results: We have used this procedure to radioiodinate the four stereoisomers of [I-123]IQNB. The procedure is highly reliable and reproducible. SPECT studies on a heal thy human volunteer at 1, 2, 6 and 24 hr after injection of each of th e four stereoisomers reveal expected differences in the kinetic and bi nding characteristics of the four stereoisomers. (R,S)-[I-123]IQNB app ears to be the SPECT agent of choice. Conclusion: Radioiodination of [ I-123]IQNB from our tri-n-butylstannyl precursor is simpler, more effi cient and less expensive than previous techniques. The potential exist s for a ''kit'' which would be practical in a typical clinical setting .