123I-ADAM SPECT in healthy nonhuman primates: A preliminary report

Background: Serotonin transporter(SERT)plays amajor role in modulating serotonergic neuronal function and is the target of many antidepressant drugs used in neurophychiatric disorders.123I-ADAM(2-([2-([dimethylamino]methyl)phenoxyl]thio)-5-[123I]iodophenylamine)has been reported as a potential SERT imaging agent. The study was undertaken to in vivo image central SERT using 123I-ADAM SPECT in non-human primates. Methods: Two female monkeys(Macaca cyclopis) were studied. Eight 30-min brain SPECT after injection of185MBq(5mCi)of 123I-ADAM were obtained by a dualhead gamma camera equipped with ultra-high-resolution fan-beam collimators(GE, Millennium VG).In additionto visual inspection,the radiouptake and specificuptake 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 123I-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 afterimaging. Conclusion: The brain distribution of 123I-ADAM in the monkeys appeared consistent with the known distribution of SERT. In conjunction with a high SUR in MB, we speculate that 123I-ADAM may be a potential radioligand for human SERT SPECT.

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