Abstract
The rupture of vulnerable atherosclerotic plaques that lead to stroke and myocardial infarction may be induced by macrophage infiltration, and augmented by the expression of integrin αvβ3 Indeed, atherosclerotic angiogenesis may be a promising marker of inflammation. In this study, an engineered integrin αvβ3 integrin targeting positron emission tomography (PET) probe, 64Cu-NOTA-3-4A, derived from a divalent knottin miniprotein was evaluated in a mouse model for carotid atherosclerotic plaques. Methods: Atherosclerotic plaques in BALB/C mice, maintained on a high fat diet, were induced with streptozotocin injection and carotid artery ligation, and verified by magnetic resonance imaging (MRI). Knottin 3-4A was synthesized by solid phase peptide synthesis chemistry, and coupled to 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) prior to radiolabeling with 64Cu. PET probe stability in mouse serum was evaluated. Mice with carotid atherosclerotic plaques were tail-vein injected with 64Cu-NOTA-3-4A or 18F-FDG followed by small animal PET/CT imaging at different time points. Receptor targeting specificity of the probe was verified by co-injection of c(RGDyK) administered in molar excess. Subsequently, carotid artery dissection and immunofluorescence staining were performed to evaluate target expression. Results: 64Cu-NOTA-3-4A was synthesized in high radiochemical purity and yield, and demonstrated molecular stablilty in both PBS and mouse serum at 4 h. Small animal PET/CT showed that 64Cu-NOTA-3-4A accumulated at significantly higher levels in the neovasculature of carotid atherosclerotic plaques (7.41 ± 1.44 %ID/g vs. 0.67 ± 0.23 %ID/g, P<0.05) compared to healthy or normal vessels at 1 h postinjection (p.i.). 18F-FDG also accumulated in atherosclerotic lesions at 0.5 and 1 h p.i., but at lower plaque-to-normal tissue ratios compared to 64Cu-NOTA-3-4A. For example, plaque-to-normal carotid artery ratios for 18F-FDG and 64Cu-NOTA-3-4A at 1 h p.i. were 3.75 and 14.71 (P<0.05), respectively. Furthermore, uptake of 64Cu-NOTA-3-4A in atherosclerotic plaques was effectively blocked (~90% at 1 h p.i.) by co-injection of c(RGDyK). Immunostaining confirmed integrin αvβ3 expression in both the infiltrating macrophages and the neovasculature of atherosclerotic plaques. Conclusion: 64Cu-NOTA-3-4A demonstrates specific accumulation in carotid atherosclerotic plaques where macrophage infiltration and angiogenesis are responsible for elevated integrin αvβ3 levels. Therefore, 64Cu-NOTA-3-4A may demonstrate clinical utility as a PET probe for atherosclerosis imaging, or for the evaluation of therapies used to treat atherosclerosis.
- Cardiology (basic/technical)
- Molecular Imaging
- PET
- αvβ3 integrin
- 64Cu
- Knottin
- PET/CT
- atherosclerotic plaque
- Copyright © 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.