An improved method for rapid and efficient radioiodination of iodine-123-IQNB

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