title: In vivo molecular imaging of atherosclerotic lesions in ApoE-/- mice using VCAM-1-specific, 99mTc-labeled peptidic sequences.
abstract: Vascular cell adhesion molecule 1 (VCAM-1) plays a major role in the chronic inflammatory processes involved in vulnerable atherosclerotic plaque development. We previously showed that the (99m)Tc-labeled major histocompatibility complex 1-derived peptide B2702p bound specifically to VCAM-1 and allowed the ex vivo imaging of atherosclerotic lesions in Watanabe heritable hyperlipidemic rabbits. However, B2702p target-to-background ratio was suboptimal for the in vivo imaging of VCAM-1 expression in atherosclerotic lesions. To improve the target-to-background ratio, 20 derivatives of B2702p (B2702p1-B2702p20) were synthesized using the alanine scan methodology. We hypothesized that (99m)Tc-radiolabeled B2702p derivatives might allow the molecular imaging of VCAM-1 expression in an experimental model of atherosclerosis.
  
  
  METHODS
  A mouse model of focal atherosclerotic plaque development induced by left carotid artery ligation in apolipoprotein E double-knockout (ApoE(-/-)) mice was used (n = 82). (99m)Tc-B2702p and (99m)Tc-B2702p1-(99m)Tc-B2702p20 were injected intravenously in anesthetized animals 3 wk after the ligation. Whole-body planar imaging was performed for 3 h. SPECT imaging of 6 additional ligated ApoE(-/-) mice was also performed with (99m)Tc-B2702p1. The animals were then euthanized, and the biodistribution of (99m)Tc-labeled peptides was evaluated by γ-well counting of excised organs. Expression of VCAM-1 in the ligated and contralateral carotid arteries was evaluated by immunohistology.
  
  
  RESULTS
  Robust VCAM-1 immunostaining was observed in the left carotid atherosclerotic lesions as a consequence of artery ligation, whereas no VCAM-1 expression was detected in the contralateral carotid artery. Among all evaluated peptides, (99m)Tc-B2702p1 exhibited the most favorable properties. By γ-well counting, there was a significant 2.0-fold increase in the (99m)Tc-B2702p1 left-to-right carotid artery activity ratio (2.6 ± 0.6) and a 3.4-fold increase in the left carotid-to-blood activity ratio (1.4 ± 0.4) in comparison to (99m)Tc-B2702p (1.3 ± 0.2 and 0.4 ± 0.1, respectively, P < 0.05 for both comparisons). Similarly, planar image quantification indicated a higher left-to-right carotid activity ratio in (99m)Tc-B2702p1- than in (99m)Tc-B2702p-injected mice (1.2 ± 0.1 vs. 1.0 ± 0.0, respectively, P < 0.05). Finally, a significantly higher (99m)Tc-B2702p1 activity in the left than in the right carotid artery was observed by SPECT imaging (2.2 ± 0.4 vs. 1.4 ± 0.3 cpm/mm(2)/injected dose, respectively, P < 0.05).
  
  
  CONCLUSIONS
  (99m)Tc-B2702p1 is a potentially useful radiotracer for the in vivo molecular imaging of VCAM-1 expression in atherosclerotic plaques.
authors.affiliation: INSERM, U1039, Radiopharmaceutiques Biocliniques, Grenoble, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Dimastromatteo
authors.forename: Alexis
authors.initials: A
authors.lastname: Broisat
authors.forename: Pascale
authors.initials: P
authors.lastname: Perret
authors.forename: Mitra
authors.initials: M
authors.lastname: Ahmadi
authors.forename: Didier
authors.initials: D
authors.lastname: Boturyn
authors.forename: Pascal
authors.initials: P
authors.lastname: Dumy
authors.forename: Daniel
authors.initials: D
authors.lastname: Fagret
authors.forename: Laurent M
authors.initials: LM
authors.lastname: Riou
authors.forename: Catherine
authors.initials: C
authors.lastname: Ghezzi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency*; D005260:Female; D007700:Kinetics; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D010446:Peptide Fragments / Q000737:chemistry / Q000493:pharmacokinetics; D058226:Plaque, Atherosclerotic / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000378:metabolism*; D013667:Technetium; D015899:Tomography, Emission-Computed, Single-Photon; D019010:Vascular Cell Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001057:Apolipoproteins E; D010446:Peptide Fragments; D019010:Vascular Cell Adhesion Molecule-1; D013667:Technetium
keywords: VCAM-1; molecular imaging; vulnerable atherosclerotic plaque