99mTc-cAbVCAM1-5 Imaging Is a Sensitive and Reproducible Tool for the Detection of Inflamed Atherosclerotic Lesions in Mice

Tc-99m-cAbVCAM1-5, a single-domain antibody fragment directed against mouse or human vascular cell adhesion molecule 1 (VCAM-1), recently has been proposed as a new imaging agent for the detection of inflamed atherosclerotic lesions. Indeed, in a mouse model of atherosclerosis, Tc-99m-cAbVCAM1-5 specifically bound to VCAM-1 positive lesions, thereby allowing their identification on SPECT images. The purpose of the present study was to investigate Tc-99m-cAbVCAM1-5 imaging sensitivity using a reference statin therapy. Methods: Thirty apolipoprotein E deficient mice were fed a western-type diet. First, the relationship between the level of VCAM-1 expression and Tc-99m-cAbVCAM1-5 uptake was evaluated in 18 mice using immunohistochemistry and autoradiography. Second, longitudinal SPECT/CT imaging was performed on control (n = 9) or atorvastatin-treated mice (0.01% w/w, n = 9). Results: Tc-99m-cAbVCAM1-5 uptake in atherosclerotic lesions correlated with the level of VCAM-1 expression (P < 0.05). Atorvastatin exerted significant antiatherogenic effects, and Tc-99m-cAbVCAM1-5 lesion uptake was significantly reduced in 35-wk-old atorvastatin-treated mice, as indicated by ex vivo y-well counting and autoradiography (P < 0.05). SPECT imaging quantification based on contrast-enhanced CT was reproducible (interexperimenter intraclass correlation coefficient, 0.97; intraexperimenter intraclass correlation coefficient, 0.90), and yielded results that were highly correlated with tracer biodistribution (r = 0.83; P < 0.0001). Therefore, reduced Tc-99m-cAbVCAM1-5 uptake in atorvastatin-treated mice was successfully monitored noninvasively by SPECT/CT imaging (0.87 +/- 0.06 vs. 1.11 +/- 0.09 percentage injected dose per cubic centimeter in control group, P < 0.05). Conclusion: Tc-99m-cAbVCAM1-5 imaging allowed the specific, sensitive, and reproducible quantification of VCAM-1 expression in mouse atherosclerotic lesions. Tc-99m-cAbVCAM1-5 therefore exhibits suitable characteristics for the evaluation of novel antiatherogenic agents.