PET/CT imaging of chemokine receptor CCR5 in vascular injury model using targeted nanoparticle

Inflammation plays important roles at all stages of atherosclerosis. Chemokine systems have major effects on the initiation and progression of atherosclerosis by controlling the trafficking of inflammatory cells in vivo through interaction with their receptors. Chemokine receptor 5 (CCR5) has been reported to be an active participant in the late stage of atherosclerosis and has the potential as a prognostic biomarker for plaque stability. However, its diagnostic potential has not yet been explored. The purpose of this study was to develop a targeted nanoparticle for sensitive and specific PET/CT imaging of the CCR5 receptor in an apolipoprotein E knock-out (ApoE(-/-)) mouse vascular injury model.

Methods: The D-Ala1-peptide T-amide (DAPTA) peptide was selected as a targeting ligand for the CCR5 receptor. Through controlled conjugation and polymerization, a biocompatible poly(methyl methacrylate)-core/polyethylene glycol-shell amphiphilic comblike nanoparticle was prepared and labeled with (64)Cu for CCR5 imaging in the ApoE(-/-) wire-injury model. Immunohistochemistry, histology, and real-time reverse transcription polymerase chain reaction (RT-PCR) were performed to assess the disease progression and upregulation of CCR5 receptor.

Results: The (64)Cu-DOTA-DAPTA tracer showed specific PET imaging of CCR5 in the ApoE(-/-) mice. The targeted (64)Cu-DOTA-DAPTA-comb nanoparticles showed extended blood signal and optimized biodistribution. The tracer uptake analysis showed significantly higher accumulations at the injury lesions than those acquired from the sham-operated sites. The competitive PET receptor blocking studies confirmed the CCR5 receptor-specific uptake. The assessment of (64)Cu-DOTA-DAPTA-comb in C57BL/6 mice and (64)Cu-DOTA-comb in ApoE(-/-) mice verified low nonspecific nanoparticle uptake. Histology, immunohistochemistry, and RT-PCR analyses verified the upregulation of CCR5 in the progressive atherosclerosis model.

Conclusion: This work provides a nanoplatform for sensitive and specific detection of CCR5's physiologic functions in an animal atherosclerosis model.