title: Radiosynthesis of [124I]iodometomidate and biological evaluation using small-animal PET.
abstract: OBJECTIVE
  The application of radiolabelled inhibitors of cytochrome P450 enzymes is a novel approach for molecular imaging of adrenocortical masses to detect adrenal tumours. One potential tracer is radiolabelled iodometomidate (IMTO) with a common option for scintigraphic diagnosis and therapeutic applications. The aim of this study was to radiolabel iodometomidate with the positron-emitting radionuclide iodine-124 ((124)I) for the investigation of the biological behaviour and pharmacokinetics with positron emission tomography (PET).
  
  
  METHODS
  [(124)I]IMTO has been synthesized by oxidative radioiodo-destannylation, purified via semi-preparative HPLC and formulated in acetate-buffered saline, which contained ascorbic acid and ethanol to avoid radiolytic decomposition. Biological evaluation was performed in rats which received 5.5 ± 0.7 MBq [(124)I]IMTO in vivo. The radioactivity distribution (n = 3) has been dynamically imaged from 0-120 min after intravenous (i.v.) injection by small-animal PET. Regions of interest have been defined manually in the reconstructed PET images, and the activity concentration was expressed as percent injected dose per gram tissue (%ID/g).
  
  
  RESULTS
  [(124)I]IMTO was prepared with a radiochemical yield of 83 ± 5 % (n = 3) and a radiochemical purity of >97 %. The final formulation of [(124)I]IMTO was stable for up to 48 h at room temperature. Two hours after i.v. administration in rats, radioactivity concentration in the adrenal glands were 2.1 ± 0.3 %ID/g, which was sufficient to achieve highest-contrast adrenal PET images.
  
  
  CONCLUSIONS
  In the present study, the biological characteristics of radioiodinated metomidate were evaluated. [(124)I]IMTO appears as an attractive PET tracer for imaging of adrenals.
authors.affiliation: Division of Nuclear Medicine, Medical University of Graz, Auenbruggerplatz 9, 8036, Graz, Austria, herbert.kvaternik@medunigraz.at.
authors.forename: Herbert
authors.initials: H
authors.lastname: Kvaternik
authors.forename: Thomas
authors.initials: T
authors.lastname: Wanek
authors.forename: Friedrich
authors.initials: F
authors.lastname: Hammerschmidt
authors.forename: Ilse
authors.initials: I
authors.lastname: Zolle
authors.forename: Reingard
authors.initials: R
authors.lastname: Aigner
authors.forename: Claudia
authors.initials: C
authors.lastname: Kuntner
mesh_terms: D000818:Animals; D005045:Etomidate / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D007457:Iodine Radioisotopes / Q000737:chemistry*; D049268:Positron-Emission Tomography / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D007457:Iodine Radioisotopes; C529450:iodophenyl metomidate; D005045:Etomidate