Molecular imaging of vascular cell adhesion molecule-1 expression in experimental atherosclerotic plaques with radiolabelled B2702-p

Purpose VCAM-1 plays a major role in the chronic inflammatory processes present in vulnerable atherosclerotic plaques. The residues 75-84 (B2702-p) and 84-75/75-84 (B2702-rp) of the major histocompatibility complex-1 (MHC-1) molecule B2702 were previously shown to bind specifically to VCAM-1. We hypothesised that radiolabelled B2702-p and B2702-rp might have potential for the molecular imaging of vascular cell adhesion molecule-1 (VCAM-1) expression in atherosclerotic plaques. Methods Preliminary biodistribution studies indicated that I-12-B2702-rp was unsuitable for in vivo imaging owing to extremely high lung uptake. I-123- or Tc-99m-labelled B2702-p was injected intravenously to Watanabe heritable hyperlipidaemic rabbits (WHHL, n=6) and control animals (n=6). After 180 min, aortas were harvested for ex vivo autoradiographic imaging, gamma-well counting, VCAM-1 immunohistology and Sudan IV lipid staining. Results Robust VCAM-1 immunostaining was observed in Sudan IV-positive and to a lesser extent in Sudan IV-negative areas of WHHL animals, whereas no expression was detected in control animals. Significant 2.9-fold and 1.9-fold increases in I-123-B2702-p and Tc-99m-B2702-p aortic-to-blood ratios, respectively, were observed between WHHL and control animals (p<0.05). Tracer uptake on ex vivo images co-localised with atherosclerotic plaques. Image quantification indicated a graded increase in I-123-B2702-p and Tc-99m-B2702-p activities from control to Sudan IV-negative and to Sudan IV-positive areas, consistent with the observed pattern of VCAM-1 expression. Sudan IV-positive to control area tracer activity ratios were 17.0 +/- 9.0 and 5.9 +/- 1.8 for I-123-B2702-p and Tc-99m-B2702-p, respectively. Conclusion Radiolabelled B2702-p is a potentially useful radiotracer for the molecular imaging of VCAM-1 in atherosclerosis.