CXCR4-binding PET tracers link monocyte recruitment and endothelial injury in murine atherosclerosis

Viral macrophage inflammatory protein 2 (vMIP-II/vCCL2) binds to multiple chemokine receptors, and vMIP-II based PET tracer ( 64 Cu-DOTA-vMIP-II: vMIP-II tracer) accumulates at atherosclerotic lesions in mice. The magnitude of 64 Cu-DOTA-vMIP-II accumulation correlated with monocyte recruitment, as Apoe -/- mice treated with AAV-mApoE showed PET signal declining as monocyte recruitment subsided. Unexpectedly, monocytes themselves were not the major target of the 64 Cu-DOTA-vMIP-II tracer. Using fluorescence-tagged vMIP-II tracer, competitive receptor blocking with CXCR4 antagonists, CXCR4-specific tracer 64 Cu-DOTA-FC131, or CXCR4 staining during disease progression and regression, endothelial cell expression of CXCR4 proved to be the main target of 64 Cu-DOTA-vMIP-II imaging. Expression of CXCR4 was low in non-plaque areas, but strongly detected on endothelium at the edges of progressing plaques, corresponding to a population of proliferating endothelium and to the location in plaques where monocyte recruitment occurred. Thus, endothelial injury status of plaques is marked by CXCR4 expression and that this injury correlates with the tendency of such plaques to recruit monocytes. Furthermore, our findings suggest PET tracers that, through binding CXCR4, may be useful to monitor plaque injury status.