The characterization of IBF as a new selective dopamine D-2 receptor imaging agent

The in vivo and in vitro studies of a new iodinated benzamide analog, [125I]IBF,5-iodo-7-N-[(1-ethyl-2-pyrrolidinyl)methyl]carboxamido-2,3- dihydrobenzofuran as a potential central nervous system (CNS) D-2 dopamine receptor imaging agent were investigated. In vivo biodistribution of IBF in rat indicated that this agent concentrated in the striatum region and displayed a remarkably high target-to-nontarget ratio (striatum/cerebellum = 48 at 120 min post-injection). The in vitro binding studies suggested that IBF binds selectively to D-2 dopamine receptors with high affinity and low nonspecific binding (Kd = 0.106 +/- 0.015 nM, Bmax = 448 +/- 18.2 fmole/mg protein). Ex vivo autoradiography results in rats further confirmed the high uptake and retention of this agent in the basal ganglia region. The planar images of monkey brains (lateral view of the head) after i.v. injection of [123I]IBF clearly demonstrated that D-2 dopamine receptors can be visualized. With the excellent in vivo stability to deiodination and high target-to-nontarget ratio, [123I]IBF may be useful as a CNS D-2 dopamine receptor imaging agent for single photon emission computed tomography (SPECT) in humans.