PET/MR Imaging of Malondialdehyde-Acetaldehyde Epitopes With a Human Antibody Detects Clinically Relevant Atherothrombosis

Abstract

BACKGROUND Oxidation-specific epitopes (OSEs) are proinflammatory, and elevated levels in plasma predict cardiovascular events. OBJECTIVES The purpose of this study was to develop novel positron emission tomography (PET) probes to noninvasively image OSE-rich lesions. METHODS An antigen-binding fragment (Fab) antibody library was constructed from human fetal cord blood. After multiple rounds of screening against malondialdehyde-acetaldehyde (MAA) epitopes, the Fab LA25 containing minimal nontemplated insertions in the CDR3 region was identified and characterized. In mice, pharmacokinetics, biodistribution, and plaque specificity studies were performed with Zirconium-89 (89Zr)-labeled LA25. In rabbits, 89Zr-LA25 was used in combination with an integrated clinical PET/magnetic resonance (MR) system. 18F-fluorodeoxyglucose PET and dynamic contrast-enhanced MR imaging were used to evaluate vessel wall inflammation and plaque neovascularization, respectively. Extensive ex vivo validation was carried out through a combination of gamma counting, near infrared fluorescence, autoradiography, immunohistochemistry, and immunofluorescence. RESULTS LA25 bound specifically to MAA epitopes in advanced and ruptured human atherosclerotic plaques with accompanying thrombi and in debris from distal protection devices. PET/MR imaging 24 h after injection of 89Zr-LA25 showed increased uptake in the abdominal aorta of atherosclerotic rabbits compared with nonatherosclerotic control rabbits, confirmed by ex vivo gamma counting and autoradiography. 18F-fluorodeoxyglucose PET, dynamic contrast-enhanced MR imaging, and near-infrared fluorescence signals were also significantly higher in atherosclerotic rabbit aortas compared with control aortas. Enhanced liver uptake was also noted in atherosclerotic animals, confirmed by the presence of MAA epitopes by immunostaining. CONCLUSIONS 89Zr-LA25 is a novel PET radiotracer that may allow noninvasive phenotyping of high-risk OSE-rich lesions.

Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

“…The E06-scFv expressed in these mice lacks Fc effector functions of antibodies, and therefore, its impact was caused solely by blocking biological effects of OxPL. Translational applications of E06 or similar anti-OxPL antibodies to humans, as well as antibodies to other OSE 29,30 , in which more traditional IgG isotypes are more likely to be used, will need to decipher any potential additional roles of various Fc effector functions.…”

Recent Advances in the Molecular Imaging of Atherosclerosis

“…Additionally, if the developed diagnostic agents were to reach the clinics, the use of humanlike antibodies should limit the risk of immunogenicity, saving the time that would be required for humanization of murine antibodies. HuAbs, 174 humanized, or human antibody fragments 124,152,157,162,177,189 therefore represent a class of ligands that will be theoretically safer to transfer to the clinics.…”

“…More recently, Senders et al developed novel PET probes making use of an Fab, Fab LA25, obtained from an antibody library constructed from human fetal cord blood. 177 This antibody was selected against MDA-acetaldehyde (MAA) epitopes. Using PET/MRI, the authors observed an approximately 32% increase in 89 Zr-LA25 uptake in the abdominal aorta of atherosclerotic rabbits relative to nonatherosclerotic rabbits.…”

Radionuclide Imaging of Atherothrombotic Diseases

“…During the process of LDL oxidation, various by-products are generated that have proinflammatory chemical modifications of lipid and protein moieties that are known as oxidation-specific epitopes (OSEs), which could signal dangerously high levels of inflammation in plaque [51]. Therefore, Senders et al [52] investigated the utility of a novel PET probe, 89 Zr-LA25, that targeted malondialdehydeacetaldehyde epitopes and found that 89 Zr-LA25 specifically co-localized to advanced and ruptured atherosclerotic plaques that had accompanying thrombi. Recent work by Sasaki and colleagues [53] has further demonstrated the potential of molecular imaging of oxLDL in atherosclerosis by developing a PET targeted probe, 64 Cu-3H3-scFv, targeting the B2-glycoprotein/oxLDL complex, with the probe showing colocalization to lipid deposits in atherosclerotic lesions in a rabbit model of hyperlipidemia.…”