title: ¹²⁴I-Epidepride: a PET radiotracer for extended imaging of dopamine D2/D3 receptors.
abstract: OBJECTIVE
  A new radiotracer, ¹²⁴I-epidepride, has been developed for the imaging of dopamine D2/3 receptors (D2/3Rs). ¹²⁴I-Epidepride (half-life of ¹²⁴I=4.2 days) allows imaging over extended periods compared to (18)F-fallypride (half-life of ¹⁸F=0.076 days) and may maximize visualization of D2/3Rs in the brain and pancreas (allowing clearance from adjacent organs). D2/3 Rs are also present in pancreatic islets where they co-localize with insulin to produce granules and may serve as a surrogate marker for imaging diabetes.
  
  
  METHODS
  ¹²⁴I-Epidepride was synthesized using N-[[(2S)-1-ethylpyrrolidin-2-yl]methyl]-5-tributyltin-2,3-dimethoxybenzamide and ¹²⁴I-iodide under no carrier added condition. Rats were used for in vitro and in vivo imaging. Brain slices were incubated with (124)I-epidepride (0.75 μCi/cc) and nonspecific binding measured with 10 μM haloperidol. Autoradiograms were analyzed by OptiQuant. ¹²⁴I-Epidepride (0.2 to 0.3 mCi, iv) was administered to rats and brain uptake at 3 hours, 24 hours, and 48 hours post injection was evaluated.
  
  
  RESULTS
  ¹²⁴I-Epidepride was obtained with 50% radiochemical yield and high radiochemical purity (>95%). (124)I-Epidepride localized in the striatum with a striatum to cerebellum ratio of 10. Binding was displaced by dopamine and haloperidol. Brain slices demonstrated localization of ¹²⁴I-epidepride up until 48 hours in the striatum. However, the extent of binding was reduced significantly.
  
  
  CONCLUSIONS
  ¹²⁴I-Epidepride is a new radiotracer suitable for extended imaging of dopamine D2/3 receptors and may have applications in imaging of receptors in the brain and monitoring pancreatic islet cell grafting.
authors.affiliation: Preclinical Imaging, Department of Radiological Sciences, University of California - Irvine, Irvine, CA 92697, USA.
authors.forename: Suresh
authors.initials: S
authors.lastname: Pandey
authors.affiliation: Preclinical Imaging, Department of Radiological Sciences, University of California - Irvine, Irvine, CA 92697, USA.
authors.forename: Archana
authors.initials: A
authors.lastname: Venugopal
authors.affiliation: Preclinical Imaging, Department of Radiological Sciences, University of California - Irvine, Irvine, CA 92697, USA.
authors.forename: Ritu
authors.initials: R
authors.lastname: Kant
authors.affiliation: Preclinical Imaging, Department of Radiological Sciences, University of California - Irvine, Irvine, CA 92697, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Coleman
authors.affiliation: Preclinical Imaging, Department of Radiological Sciences, University of California - Irvine, Irvine, CA 92697, USA. Electronic address: j.mukherjee@uci.edu.
authors.forename: Jogeshwar
authors.initials: J
authors.lastname: Mukherjee
mesh_terms: D000818:Animals; D001549:Benzamides / Q000737:chemistry / Q000378:metabolism; D007457:Iodine Radioisotopes; D007515:Islets of Langerhans / Q000000981:diagnostic imaging / Q000378:metabolism; D008297:Male; D049268:Positron-Emission Tomography / Q000379:methods*; D011759:Pyrrolidines / Q000737:chemistry / Q000378:metabolism; D011849:Radioactive Tracers; D011854:Radiochemistry; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D050637:Receptors, Dopamine D3 / Q000378:metabolism*
chemical_list: D001549:Benzamides; D007457:Iodine Radioisotopes; D011759:Pyrrolidines; D011849:Radioactive Tracers; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; C063525:epidepride
keywords: Dopamine D2/3 receptor; Epidepride; Fallypride; Iodine-124