title: Synthesis and characterization of 123I-CMICE-013: a potential SPECT myocardial perfusion imaging agent.
abstract: Coronary artery disease (CAD) is a major cause of death in Canada and the United States. Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is a useful diagnostic test in the management of patients with CAD. The widely used SPECT MPI agents, (99m)Tc sestamibi and (99m)Tc tetrofosmin, exhibit less than ideal pharmacokinetic properties with decreasing uptake with higher flows. (123)I has a similar energy as (99m)Tc, an ideal half life, and is readily available from cyclotrons. The objective of this study was to develop an (123)I labeled MPI agent based on rotenone, a mitochondrial complex I inhibitor, as an alternative to currently available SPECT MPI agents.
  
  
  METHODS
  (123)I-CMICE-013 was synthesized by radiolabeling rotenone with (123)I in trifluoroacetic acid (TFA) with iodogen as the oxidizing agent at 60 °C for 45 min, followed by RP-HPLC purification. The product was formulated in 5% EtOH in 10 mM NaOAc pH 6.5. The inactive analog (127)I-CMICE-013 was isolated and characterized by NMR and mass spectrometry, and the structure determined. Micro-SPECT imaging studies were carried out in normal and infarcted rats. Biodistribution studies were performed in normal rats at 2 h (n=6) and 24 h (n=8) post injection (p.i.).
  
  
  RESULTS
  (123)I-CMICE-013 was isolated with >95% radiochemical purity and high specific activity (14.8-111 GBq/μmol; 400-3000 mCi/μmol). Structural analysis showed that rotenone was iodinated at 7'-position, with removal of the 6',7'-double bond, and addition of a hydroxy group at 6'-position. MicroSPECT images in normal rats demonstrated homogeneous and sustained myocardial uptake with minimal interference from lung and liver. Absent myocardial perfusion was clearly identified in rats with permanent left coronary artery ligation and ischemia-reperfusion injury. In vivo biodistribution studies in normal rats at 2 h p.i. showed significant myocardial uptake (2.01±0.48%ID/g) and high heart to liver (2.98±0.93), heart to lung (4.11±1.04) and heart to blood (8.37±3.97) ratios. At 24 h p.i., the majority of (123)I-CMICE-013 was cleared from tissues, and a significant amount of tracer was found in the thyroid, indicating in vivo deiodination of the tracer.
  
  
  CONCLUSIONS
  (123)I-CMICE-013 is a promising new radiotracer for SPECT MPI with high myocardial uptake, very good target to background ratios and favorable biodistribution characteristics.
authors.affiliation: Nordion Inc., 447 March Road, Ottawa, ON, Canada K2K 1X8. lihui.wei@nordion.com
authors.forename: Lihui
authors.initials: L
authors.lastname: Wei
authors.forename: Corinne
authors.initials: C
authors.lastname: Bensimon
authors.forename: Julia
authors.initials: J
authors.lastname: Lockwood
authors.forename: Xuxu
authors.initials: X
authors.lastname: Yan
authors.forename: Pasan
authors.initials: P
authors.lastname: Fernando
authors.forename: R Glenn
authors.initials: RG
authors.lastname: Wells
authors.forename: Yin
authors.initials: Y
authors.lastname: Duan
authors.forename: Yong-Xiang
authors.initials: YX
authors.lastname: Chen
authors.forename: J Russell
authors.initials: JR
authors.lastname: Redshaw
authors.forename: Peter A
authors.initials: PA
authors.lastname: Covitz
authors.forename: Terrence D
authors.initials: TD
authors.lastname: Ruddy
mesh_terms: D000818:Animals; D002867:Chromones / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D006321:Heart / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D006801:Humans; D007457:Iodine Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics*; D008297:Male; D009203:Myocardial Infarction / Q000000981:diagnostic imaging* / Q000503:physiopathology; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012402:Rotenone / Q000737:chemistry; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: C000599676:CMICE-013; D002867:Chromones; D006576:Heterocyclic Compounds, 4 or More Rings; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D012402:Rotenone