Iodine-123 labeled nor-β-CIT as a potential tracer for serotonin transporter imaging in the human brain with single-photon emission tomography

Abstract.

Iodine-123 labelled 2β-carbomethoxy-3β-(4-iodophenyl) (nor-β-CIT) is an analogue of β-CIT, which has high affinity to the serotonin transporter. Initial single-photon emission tomography (SPET) studies with [¹²³I]nor-β-CIT were performed in five healthy volunteers. In addition, its metabolism in plasma was investigated with gradient high performance liquid chromatography. [¹²³I]nor-β-CIT was prepared by a method which gave a specific radioactivity of more than 180 GBq/μmol. Unchanged [¹²³I]nor-β-CIT in plasma accounted for 43% and 19% of total radioactivity after 30 and 180 min, respectively. The dynamic SPET studies demonstrated a high and rapid uptake of radioactivity in the brain (6%/ID at 30 min). Highest accumulation was observed in the striatum, the mid-brain and the thalamus. The specific binding in the mid-brain was 33% higher compared with that of [¹²³I]β-CIT. The high radioactivity in the mid-brain is assumed to represent the accumulation of [¹²³I]nor-β-CIT in the serotonin transporter-rich regions, which indicates that [¹²³I]nor-β-CIT might be a potential tracer for visualization of serotonin transporter sites in the human brain with SPET.