Radiosynthesis and biodistribution of 123I-labeled antagonists of the histamine H3 receptor as potential SPECT ligands

Albert D. Windhorst*, Henk Timmerman, Rob P. Klok, Franciscus G.J. Custers, Wiro M.P.B. Menge, Rob Leurs, Holger Stark, Walter Schunack, Eric G.J. Gielen, Marinus J.P.G. Van Kroonenburgh, Jacobus D.M. Herscheid

*Corresponding author for this work

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We have synthesized three 123I-labeled histamine H3 receptor ligands, i.e., [123I]GR 190028, [123I]FUB 271, and [123I]iodoproxyfan, in moderate to good radiochemical yields via a Cu+-assisted I-for-123I exchange method. Biodistribution in the rat of these compounds revealed high hepatic and pulmonary uptake. Brain uptake was moderate, but for [123I]iodoproxyfan, brain uptake was high enough for a pilot single photon emission computed tomography (SPECT) study in the rabbit. However, for this compound, the cerebral uptake could not be blocked by a pretreatment with [R]-α-methylhistamine, a selective, high-affinity histamine H3 receptor agonist, both in the SPECT study in the rabbit and in the biodistribution study in the rat. Apparently, [123I]iodoproxyfan is binding to a non-H3 receptor binding site. None of the three investigated compounds is suitable for use as a SPECT ligand for the H3 receptor in the brain. Copyright (C) 1999 Elsevier Science Inc.

Original languageEnglish
Pages (from-to)651-659
Number of pages9
JournalNuclear Medicine and Biology
Issue number6
Publication statusPublished - 1 Aug 1999

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