Development of New CCR2 PET Tracer Imaging Atherosclerosis

Introduction: CC chemokine receptor type 2 (CCR2) is a promising biomarker for the diagnosis and treatment of inflammation and tumor. A diagnostic tool capable of assessing CCR2 abundance while predicting and monitoring treatment response will be invaluable. Therefore, Based on CCR2 targeting PET radiotracer (⁶⁴Cu-DOTA-ECL1i), we developed a new tracer (⁶⁴Cu-DOTA-DR-1) through molecular modeling and evaluated its specificity in vitro, and sensitivity in pre-clinical mouse models.

Methods: DR-1 peptide was developed by docking method. DOTA-DR-1 peptide was synthesized using solid phase Fmoc synthesis and conjugated to DOTA. The DOTA-DR-1 conjugate (1.0 μg) was radiolabeled with 37 MBq of ⁶⁴Cu in 0.1M NH₄OAc buffer (pH 5.5) at 45^oC for 40 min. THP-1 cells were used for cell binding and IC₅₀ testing in vitro. PET/CT imaging using CCR2 targeted ⁶⁴Cu-DOTA-DR-1 was performed at 1 h post injection in apolipoprotein E-deficient (Apoe^-/-) mouse (12 weeks on high fat diet (HFD) model and compared to wild type mice.

Results: The binding affinity of DR-1 peptide to CCR2 receptor was -89.5 kJ·mol^-1, while the binding affinity of ECL1i was -72.3 kJ·mol^-1 calculated by docking method. The radiolabeling specific activity was measured as 4.89×10¹⁰MBq·mol^-1. In THP-1 cells, the IC₅₀ of ⁶⁴Cu-DOTA-DR-1 was determined as 3.1×10^-8 M. Biodistribution in wild type mice showed low blood retention and rapid renal clearance. In Apoe^-/-mice at 12 weeks post HFD, ⁶⁴Cu-DOTA-DR-1 was clearly visualized at atherosclerosis lesions while little PET signal was detected in the wild type control mice.

Conclusions: This study demonstrated the success of molecular modeling in radiotracer development for CCR2 imaging. ⁶⁴Cu-DOTA-DR-1 is a promising tracer for CCR2 PET imaging. The sensitive and specific detection of CCR2 warrants its further investigation of macrophages in other inflammatory diseases with PET/CT.