Targeted ED-B fibronectin SPECT in vivo imaging in experimental atherosclerosis.

Aim. The extracellular matrix protein ED-B fibronectin (ED-B) is upregulated in inflammatory atherosclerotic lesions. However, functional in vivo imaging of ED-B-containing plaques has not been explored. This study evaluated whether [Tc-99m]-conjugated AP39 ([Tc-99m]-AP39), a single-chain antibody specific to ED-B, can be used for in vivo detection of atherosclerotic plaques in Western diet (WD)-fed, apolipoprotein E-deficient (apoE(-/-)) mice as compared to wildtype (WT) control mice. Methods. Using SPECT, 12-month-old WD-fed apoE(-/-) and WT mice were studied 4 hours after injecting [Tc-99m]-AP39 (148 MBq). Subsequently, mice were sacrificed, thoracic aortas measured in a gamma-counter, and plaques analyzed using histology, immuno-histochemistry, autoradiography, and morphometry. Results. In vivo [Tc-99m]-AP39-SPECT imaging of apoE(-/-) mice demonstrated a significant signal activity in the plaque-ridden thoracic aorta (52.236 +/- 40.646 cpm/cm(3)) that co-localized with the aortic arch and the supra-aortic arteries in MM scans. Low signal activity (9.468 +/- 4.976 cpm/cm(3)) was observed in WT mice. In apoE(-/-) mice, the strongest signals were detected in the aortic root, aortic arch and along the abdominal aorta. Autoradiography analysis of aortas from apoE(-/-) mice confirmed the in vivo observation by demonstrating signal localization in atherosclerotic plaques. The size of autoradiography-positive plaque areas correlated significantly with the size of ED-B-positive (r=0.645, P=0.044) or macrophage-infiltrated (r=0.84, P<0.002) plaques. A significant correlation was found between the sizes of ED-B-positive and macrophage-infiltrated plaque areas (r=0.93, P<0.01). Conclusion. [Tc-99m]-AP39-SPECT in vivo imaging detects inflammatory plaque lesions in WD-fed apoE(-/-) mice.