PET/CT Imaging of Chemokine Receptors in Inflammatory Atherosclerosis Using Targeted Nanoparticles

Luehmann, H. P., Detering, L., Fors, B. P., Pressly, E. D., Woodard, P. K., Randolph, G. J., Gropler, R. J., Hawker, C. J., Liu, Y.
J. Nucl. Med.
57, 1124–1129

Atherosclerosis is inherently an inflammatory process that is strongly affected by the chemokine/chemokine receptors axes regulating the trafficking of inflammatory cells at all stages of the disease. Of the chemokine receptor family, some specifically up-regulated on macrophages play a critical role in plaque development and may have the potential to track plaque progression. However, the diagnostic potential of these chemokine receptors has not been fully realized. Based on our previous work using a broad spectrum peptide antagonist imaging 8 chemokine receptors together, the purpose of this study was to develop a targeted nanoparticle for sensitive and specific detection of these chemokine receptors in both a mouse vascular injury model and a spontaneously developed mouse atherosclerosis model. Methods: The viral macrophage inflammatory protein-II (vMIP-II) was conjugated to a biocompatible poly(methyl methacrylate)-core/polyethylene glycol-shell amphiphilic comb-like nanoparticle through controlled conjugation and polymerization before radiolabeling with 64Cu for PET imaging in an ApoE-/- mouse vascular injury model and a spontaneous ApoE-/- mouse atherosclerosis model. Histology, immunohistochemistry, and real-time reverse transcription polymerase chain reaction (RT-PCR) were performed to assess the plaque progression and up-regulation of chemokine receptors. Results: The chemokine receptors targeted 64Cu-vMIP-II-Comb showed extended blood retention and improved biodistribution. PET imaging showed specific tracer accumulation at plaques in ApoE-/- mice, confirmed by competitive receptor blocking studies and assessment in wild-type mice. Histopathological characterization showed the progression of plaque including size and macrophage population, corresponding to the elevated concentration of chemokine receptors and more importantly increased PET signals. Conclusion:This work provides a useful nanoplatform for sensitive and specific detection of chemokine receptors to assess plaque progression in mouse atherosclerosis models.