| Summary: | Mona Ahmed,1,2 Tetyana Tegnebratt,3,4 Thuy A Tran,3,4 Li Lu,3,4 Peter Damberg,3 Anton Gisterå,5 Laura Tarnawski,5 Dianna Bone,1,6 Ulf Hedin,1,7 Per Eriksson,5 Staffan Holmin,3,8 Björn Gustafsson,1,* Kenneth Caidahl1,6,9,10,* 1Department of Molecular Medicine and Surgery, Center for Molecular Medicine, BioClinicum, Karolinska Institutet, Stockholm, SE 17176, Sweden; 2Department of Cardiology, Karolinska University Hospital, Stockholm, SE 17176, Sweden; 3Department of Clinical Neuroscience, BioClinicum, Karolinska Institutet, Stockholm, SE 17176, Sweden; 4Department of Radiopharmacy, Karolinska University Hospital, Stockholm, SE 17176, Sweden; 5Department of Medicine Solna, Center for Molecular Medicine, BioClinicum, Karolinska Institutet, Stockholm, SE 17176, Sweden; 6Department of Clinical Physiology, Karolinska University Hospital, Stockholm, SE 17176, Sweden; 7Department of Vascular Surgery, Karolinska University Hospital, Stockholm, SE 17176, Sweden; 8Department of Neuroradiology, Karolinska University Hospital, Stockholm, SE 17176, Sweden; 9Department of Clinical Physiology, Region Västra Götaland, Sahlgrenska University Hospital, Gothenburg, SE 41345, Sweden; 10Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, SE 41345, Sweden*These authors contributed equally to this work.Correspondence: Mona Ahmed Email mona.ahmed@ki.seBackground: Beyond clinical atherosclerosis imaging of vessel stenosis and plaque morphology, early detection of inflamed atherosclerotic lesions by molecular imaging could improve risk assessment and clinical management in high-risk patients. To identify inflamed atherosclerotic lesions by molecular imaging in vivo, we studied the specificity of our radiotracer based on maleylated (Mal) human serum albumin (HSA), which targets key features of unstable atherosclerotic lesions.Materials and Methods: Mal-HSA was radiolabeled with a positron-emitting metal ion, zirconium-89 (89Zr4+). The targeting potential of this probe was compared with unspecific 89Zr-HSA and 18F-FDG in an experimental model of atherosclerosis (Apoe–/– mice, n=22), and compared with wild-type (WT) mice (C57BL/6J, n=21) as controls.Results: PET/MRI, gamma counter measurements, and autoradiography showed the accumulation of 89Zr-Mal-HSA in the atherosclerotic lesions of Apoe–/– mice. The maximum standardized uptake values (SUVmax) for 89Zr-Mal-HSA at 16 and 20 weeks were 26% and 20% higher (P< 0.05) in Apoe–/– mice than in control WT mice, whereas no difference in SUVmax was observed for 18F-FDG in the same animals. 89Zr-Mal-HSA uptake in the aorta, as evaluated by a gamma counter 48 h postinjection, was 32% higher (P< 0.01) for Apoe–/– mice than in WT mice, and the aorta-to-blood ratio was 8-fold higher (P< 0.001) for 89Zr-Mal-HSA compared with unspecific 89Zr-HSA. HSA-based probes were mainly distributed to the liver, spleen, kidneys, bone, and lymph nodes. The phosphor imaging autoradiography (PI-ARG) results corroborated the PET and gamma counter measurements, showing higher accumulation of 89Zr-Mal-HSA in the aortas of Apoe–/– mice than in WT mice (9.4± 1.4 vs 0.8± 0.3%; P< 0.001).Conclusion: 89Zr radiolabeling of Mal-HSA probes resulted in detectable activity in atherosclerotic lesions in aortas of Apoe–/– mice, as demonstrated by quantitative in vivo PET/MRI. 89Zr-Mal-HSA appears to be a promising diagnostic tool for the early identification of macrophage-rich areas of inflammation in atherosclerosis.Keywords: positron emission tomography, molecular imaging, zirconium, human serum albumin, atherosclerosis, macrophages
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