Radiosynthesis, In Vivo Biological Evaluation, and Imaging of Brain Lesions with [123I]-CLINME, a New SPECT Tracer for the Translocator Protein

Dis Markers. 2015:2015:729698. doi: 10.1155/2015/729698. Epub 2015 Jun 25.

Abstract

The high affinity translocator protein (TSPO) ligand 6-chloro-2-(4'-iodophenyl)-3-(N,N-methylethyl)imidazo[1,2-a]pyridine-3-acetamide (CLINME) was radiolabelled with iodine-123 and assessed for its sensitivity for the TSPO in rodents. Moreover neuroinflammatory changes on a unilateral excitotoxic lesion rat model were detected using SPECT imaging. [(123)I]-CLINME was prepared in 70-80% radiochemical yield. The uptake of [(123)I]-CLINME was evaluated in rats by biodistribution, competition, and metabolite studies. The unilateral excitotoxic lesion was performed by injection of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid unilaterally into the striatum. The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography. In vivo studies with [(123)I]-CLINME indicated a biodistribution pattern consistent with TPSO distribution and the competition studies with PK11195 and Ro 5-4864 showed that [(123)I]-CLINME is selective for this site. The metabolite study showed that the extractable radioactivity was unchanged [(123)I]-CLINME in organs which expresses TSPO. SPECT/CT imaging on the unilateral excitotoxic lesion indicated that the mean ratio uptake in striatum (lesion:nonlesion) was 2.2. Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography. These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.

MeSH terms

  • Acetamides / chemical synthesis*
  • Acetamides / pharmacokinetics
  • Animals
  • Brain / diagnostic imaging*
  • Carrier Proteins / metabolism*
  • Male
  • Protein Binding
  • Pyridines / chemical synthesis*
  • Pyridines / pharmacokinetics
  • Radiopharmaceuticals / adverse effects
  • Radiopharmaceuticals / chemical synthesis*
  • Radiopharmaceuticals / pharmacokinetics
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, GABA-A / metabolism*
  • Tissue Distribution
  • Tomography, Emission-Computed, Single-Photon*

Substances

  • 2-(6-chloro-2-(4-iodophenyl)-imidazo(1,2-alpha)pyridin-3-yl)-N-ethyl-N-methyl-acetamide
  • Acetamides
  • Carrier Proteins
  • Pyridines
  • Radiopharmaceuticals
  • Receptors, GABA-A
  • Tspo protein, rat