Tissue Factor Detection for Selectively Discriminating Unstable Plaques in an Atherosclerotic Rabbit Model

Abstract

Tissue factor (TF), a transmembrane glycoprotein that acts as an essential cofactor to factor VII/VIIa, initiates the exogenous blood coagulation cascade leading to thrombin generation and subsequent thrombus formation in vivo. TF expression is closely related to plaque vulnerability, and high TF expression is shown in macrophage-rich atheromatous lesions, making TF a potential target for detecting atheromatous lesions in vivo. Thus, we prepared 99m Tc-labeled anti-TF-monoclonal antibody (TF-mAb) IgG as a molecular probe and evaluated its usefulness to achieve TF-specific imaging using myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits. Methods: Anti-TF-mAb was created using a standard hybridoma technique and was labeled by 99m Tc with 6-hydrazinonicotinic acid (HYNIC) as a chelating agent to obtain 99m Tc-TF-mAb. The immunoreactivity of HYNIC-TF-mAb was estimated by flow cytometry. WHHLMI and control rabbits were injected intravenously with 99m Tc-TF-mAb. Twenty-four hours after the injection, the aorta was removed and radioactivity was measured. Autoradiography and histologic studies were performed using serial aorta sections. Subclass matched antibody (IgG 1 ) was used as a negative control. Results: HYNIC-TF-mAb showed 93% immunoreactivity of the anti-TF-mAb. The radioactivity accumulation in WHHLMI aortas was 6.1-fold higher than that of control rabbits. Autoradiograms showed a heterogeneous distribution of radioactivity in the intima of WHHLMI aortas. Regional radioactivity accumulation was positively correlated with TF expression density (R 5 0.64, P , 0.0001). The highest radioactivity accumulation in percentage injected dose · body weight/mm 2 · 10 2 was found in atheromatous lesions (5.2 6 1.9) followed by fibroatheromatous (2.1 6 0.7), collagen-rich (1.8 6 0.7), and neointimal lesions (1.8 6 0.6). In contrast, 99m Tc-IgG 1 showed low radioactivity accumulation in WHHLMI aortas that was independent of the histologic grade of lesions. Conclusion: The TF-detecting ability and preferential accumulation in atheromatous lesions of 99m Tc-TF-mAb were demonstrated, indicating its potential for selective imaging of macrophage-rich atheromatous lesions in vivo.

Quantitative PET Imaging of Tissue Factor Expression Using 18F-Labeled Active Site–Inhibited Factor VII

“…Only a few other studies have focused on TF imaging. Temma et al reported the use of a 99m Tc-labeled anti-TF antibody for ex vivo imaging of macrophage-rich atheromatous lesions in rabbits (22). More recently, Hong et al reported the first use of PET imaging of TF expression in subcutaneous xenograft mouse models using a 64 Cu-labeled anti-TF antibody ( 64 Cu-NOTA-ALT-836) (23).…”

Radioimmunodetection of Atherosclerotic Lesions Focusing on the Accumulation Mechanism of Immunoglobulin G

“…Thus, various PET/SPECT imaging probes targeting biomolecules related to the progression of atherosclerosis have been developed [18]. Among them, some probes are developed with based on monoclonal IgG and have been evaluated in animal models such as mouse and rabbit [19,20]. In those studies, xenogeneic antibodies were used, whose nonspecific accumulation in atherosclerotic lesions was not taken into consideration.…”

<i>In Vivo</i> Molecular Imaging

“…[57][58][59][60][61][62][63][64] Currently, atherosclerotic plaques are diagnosed based on the grade of vascular stenosis measured on angiography. However, vulnerability of plaque cannot be judged on angiography because the vascular lumen volume is not related to plaque stability.…”