Novel PET imaging of atherosclerosis with 68Ga-labeled NOTA-Neomannosylated Human Serum Albumin

Abstract Activated macrophages take up 2-deoxy-2-(18)F-fluoro-D-glucose (FDG) via glucose transporters, so this compound is useful for atherosclerosis imaging by positron emission tomography (PET). However, FDG application is limited for imaging of the heart and brain, where glucose uptake is high, and in patients with aberrant glucose metabolism. The aims of this study were to confirm that mannosylated human serum albumin (MSA) specifically binds to the mannose receptor (MR) on macrophages and to test the feasibility of (68)Ga-labeled NOTA-MSA for PET imaging of atherosclerotic plaques. The peritoneal macrophages of C57/B6 mice were collected, incubated with 10 μg/ml RITC-MSA, and evaluated by confocal microscopy and flow cytometry. The same evaluations were performed after pre-incubation of the macrophages with anti-CD206 MR blocking antibodies. NOTA-MSA was synthesized by conjugating 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid to MSA, followed by labeling with (68)Ga. Rabbits with atherosclerotic aorta induced by a 3-month cholesterol diet and chronic inflammation underwent consecutive PET/computed tomography with (18)F-FDG and (68)Ga-NOTA-MSA at 2-day intervals. The binding of MSA to MR, and its dose-dependent reduction by pre-incubation with anti-CD206 MR blocking antibody, were confirmed. Rhodamine B isothiocyanate (RITC) and fluorescein isothiocyanate (FITC) fluorescence co-localized at the atherosclerotic plaque. The (68)Ga-NOTA-MSA standard uptake values of the atherosclerotic aorta were significantly higher than those of the healthy arteries and inferior vena cava, and were comparable to those obtained with (18)F-FDG. These findings suggest that MR-specific (68)Ga-NOTA-MSA is effective for detecting atherosclerosis in the aorta, and is a promising radiopharmaceutical for imaging atherosclerosis because of the presence of M2 macrophages in atherosclerotic plaques.