I-ADAM SPECT in Healthy Nonhuman Primates: A Preliminary Report

Received 1/9/2002; revised 2/27/2002; accepted 3/6/2002. For correspondence or reprints contact: Wen-Sheng Huang, M.D., Department of Nuclear Medicine, Tri-Service General Hospital, 325 Section 2, Cheng-Kung Road, Taipei 114, Taiwan, R.O.C. Tel: (886)2-87927374, Fax: (886)2-87927217, E-mail: [email protected] Background: Serotonin transporter (SERT) plays a major role in modulating serotonergic neuronal function and is the target of many antidepressant drugs used in neurophychiatric disorders. I-ADAM (2-([2-([dimethylamino]methyl)phenoxyl]thio)-5-[I] iodophenylamine) has been reported as a potential SERT imaging agent. The study was undertaken to in vivo image central SERT using I-ADAM SPECT in non-human primates. Methods: Two female monkeys (Macaca cyclopis) were studied. Eight 30-min brain SPECT after injection of 185 MBq (5 mCi) of I-ADAM were obtained by a dualhead gamma camera equipped with ultra-high-resolution fan-beam collimators (GE, Millennium VG). In addition to visual inspection, the radiouptake and specific uptake ratio (SUR) of midbrain (MB), striatum (ST) and thalamus (TH) in reference to the corresponding MRI at the 8 time points were measured. The SUR of MB, using cerebellum (CB) as the reference tissue, was calculated as following: (MB-CB)/CB in mean counts/pixel. The SUR of ST and TH were also measured in the same method. Results: By visual inspection, there was discernable uptake of I-ADAM in the ST, TH, and MB. Little uptake was found in the CB. The image of MB was easily identified at the 30 min-time point. The SUR of MB reached equilibrium around 210 min after injection. No remarkable adverse reactions were found during and after imaging. Conclusion: The brain distribution of I-ADAM in the monkeys appeared consistent with the known distribution of SERT. In conjunction with a high SUR in MB, we speculate that I-ADAM may be a potential radioligand for human SERT SPECT.