Aluminum fluoride-18 labeled folate enables in vivo detection of atherosclerotic plaque inflammation by positron emission tomography

Abstract

Inflammation plays an important role in the development of atherosclerosis and its complications. Because the folate receptor β (FR-β) is selectively expressed on macrophages, an FR targeted imaging agent could be useful for assessment of atherosclerotic inflammation. We investigated aluminum fluoride-18-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate (¹⁸F-FOL) for the detection of atherosclerotic plaque inflammation. We studied atherosclerotic plaques in mice, rabbits, and human tissue samples using ¹⁸F-FOL positron emission tomography/computed tomography (PET/CT). Compound 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) was used as a comparison. Firstly, we found that the in vitro binding of ¹⁸F-FOL co-localized with FR-β-positive macrophages in carotid endarterectomy samples from patients with recent ischemic symptoms. We then demonstrated specific accumulation of intravenously administered ¹⁸F-FOL in atherosclerotic plaques in mice and rabbits using PET/CT. We noticed that the ¹⁸F-FOL uptake correlated with the density of macrophages in plaques and provided a target-to-background ratio as high as ¹⁸F-FDG, but with considerably lower myocardial uptake. Thus, ¹⁸F-FOL PET/CT targeting of FR-β-positive macrophages presents a promising new tool for the in vivo imaging of atherosclerotic inflammation.