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 2/2 ) mice was used (n 5 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 2/2 mice was also performed with 99m Tc-B2702p1. The animals were then euthanized, and the biodistribution of 99m Tc-labeled peptides was evaluated by g-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 g-well counting, there was a significant 2.0-fold increase in the 99m Tc-B2702p1 left-to-right carotid artery activity ratio (2.6 6 0.6) and a 3.4-fold increase in the left carotid-to-blood activity ratio (1.4 6 0.4) in comparison to 99m Tc-B2702p (1.3 6 0.2 and 0.4 6 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 6 0.1 vs. 1.0 6 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 6 0.4 vs. 1.4 6 0.3 cpm/mm 2 / injected dose, respectively, P , 0.05). Conclusion: 99m Tc-B2702p1 is a potentially useful radiotracer for the in vivo molecular imaging of VCAM-1 expression in atherosclerotic plaques.

PET/CT Imaging of Chemokine Receptor CCR5 in Vascular Injury Model Using Targeted Nanoparticle

“…Some molecular probes have been developed to image these biomarkers in preclinical atherosclerosis models with promising results. However, their translational potentials remain to be determined (11,12). Although the clinical tracer 18 F-FDG has been widely used to evaluate the elevated metabolic activity in atherosclerosis, it is essentially a nonspecific tracer and has technical challenges to detect the lesions in coronary arteries because of the size of the vessel and myocardial uptake (4,8,13).…”

New radiotracers for imaging of vascular targets in angiogenesis-related diseases

“…The inhibition of leucocyte recruitment by B2702-rp was confirmed by direct interaction with VCAM-1. The derivatives of B2702-p with optimized target-to-background ratio were subsequently developed, generating improved SPECT image quality in atherosclerotic lesions [219]. …”

New Targets of Molecular Imaging in Atherosclerosis: Prehension of Current Status

“…1). 18,19,26 Similarly, VCAM-1 ligand conjugatedGd was also reported for detecting early atherogenesis with MRI ( Table 1, Fig. 1).…”

“…muscle cells during the initiation of atherogenesis. 11,12 This is stage 1 where VCAM-1, ICAM-1, and P-selectin [13][14][15][16][17][18][19] (Table 1) are the main targets for imaging early stage atherosclerosis. At stage 2, fatty streaks formation by macrophages displays scavenger function during immune responses.…”