Evaluation of the binding characteristics of [18F]fluoroproxyfan in the rat brain for in vivo visualization of histamine H3 receptor

Histamine H3 receptors play an important role in biological functions. The aim of this research was to examine whether histamine H3 receptors can be visualized in vivo and in vitro with [18F]3-(1H-imidazol-4-yl)propyl 4-fluorobenzyl ether (fluoroproxyfan). [18F]Fluoroproxyfan was synthesized with high specific activity using [18F]benzyl bromide. The binding of [18F]fluoroproxyfan to rat brain homogenates was higher in the striatum and thalamus and was lowest in the cerebellum. The in vitro autoradiographic study successfully demonstrated the specific binding of [18F]fluoroproxyfan to the H3 receptor in the rat brain. In accordance with the in vitro bindings, the in vivo distribution of [18F]fluoroproxyfan was heterogeneous in the rat brain. In the blocking experiments, the heterogeneous distribution disappeared in the presence of large amounts of fluoroproxyfan. These data suggest that [18F]fluoroproxyfan can be potentially useful to image histamine H3 receptor noninvasively in the human brain by positron emission tomography.