Dual-Modality Activity-Based Probes as Molecular Imaging Agents for Vascular Inflammation.

Abstract

Macrophages are cellular mediators of vascular inflammation and are involved in the formation of atherosclerotic plaques. These immune cells secrete proteases such as matrix metalloproteinases and cathepsins that contribute to disease formation and progression. Here, we demonstrate that activity-based probes (ABPs) targeting cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes can also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations.

METHODS:

Macrophage-rich carotid lesions were induced in FVB mice fed on a high-fat diet by streptozotocin injection followed by ligation of the left common carotid artery. Mice with carotid atherosclerotic plaques were injected with the optical or dual-modality probes BMV109 and BMV101, respectively, via the tail vein and noninvasively imaged by optical and small-animal PET/CT at different time points. After noninvasive imaging, the murine carotid arteries were imaged in situ and ex vivo, followed by immunofluorescence staining to confirm target labeling. Additionally, human carotid plaques were topically labeled with the probe and analyzed by both sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunofluorescence staining to confirm the primary targets of the probe.

RESULTS:

Quantitative analysis of the signal intensity from both optical and PET/CT imaging showed significantly higher levels of accumulation of BMV109 and BMV101 (P < 0.005 and P < 0.05, respectively) in the ligated left carotid arteries than the right carotid or healthy arteries. Immunofluorescence staining for macrophages in cross-sectional slices of the murine artery demonstrated substantial infiltration of macrophages in the neointima and adventitia of the ligated left carotid arteries compared with the right. Analysis of the human plaque tissues by sodium dodecyl sulfate polyacrylamide gel electrophoresis confirmed that the primary targets of the probe were cathepsins X, B, S, and L. Immunofluorescence labeling of the human tissue with the probe demonstrated colocalization of the probe with CD68, elastin, and cathepsin S, similar to that observed in the experimental carotid inflammation murine model.

CONCLUSION:

We demonstrate that ABPs targeting the cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes could also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations. Therefore, ABPs targeting the cysteine cathepsins are potentially valuable new reagents for rapid and noninvasive imaging of atherosclerotic disease progression and plaque vulnerability.

• Authors: Nimali P Withana, Toshinobu Saito, Xiaowei Ma, Megan Garland, Changhao Liu, Hisanori Kosuge, Myriam Amsallem, Martijn Verdoes, Leslie O Ofori, Michael Fischbein, Mamoru Arakawa, Zhen Cheng, Michael V McConnell, Matthew Bogyo
• Journal: Journal of nuclear medicine : official publication, Society of Nuclear Medicine (J Nucl Med) Vol. 57 Issue 10 Pg. 1583-1590 (Oct 2016) ISSN: 1535-5667 [Electronic] United States
• PMID: 27199363 (Publication Type: Journal Article)
• Copyright: © 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.

Chemical References

• Molecular Probes
• Cathepsins

Topics

• Animals
• Atherosclerosis (diagnostic imaging, metabolism)
• Carotid Arteries (diagnostic imaging, metabolism)
• Cathepsins (metabolism)
• Humans
• Macrophages (metabolism)
• Mice
• Molecular Imaging (methods)
• Molecular Probes (metabolism)
• Positron-Emission Tomography (methods)