Specific targeting of atherosclerotic plaques in ApoE(-/-) mice using a new Camelid sdAb binding the vulnerable plaque marker LOX-1.

Abstract

PURPOSE:

Molecular imaging has the potential to provide quantitative information about specific biological aspects of developing atherosclerotic lesions. This requires the generation of reliable, highly specific plaque tracers. This study reports a new camelid single-domain antibody fragment (sdAb) targeting the Lectin-like oxidized low-density lipoprotein receptor (LOX-1), a biomarker for the detection and molecular phenotyping of vulnerable atherosclerotic plaques.

PROCEDURES:

A camelid sdAb was generated and selected for high affinity binding to LOX-1. Ex vivo biodistribution and in vivo single photon emission computed tomography (SPECT)/computed tomography (CT) imaging studies were performed in wild-type mice and in fat-fed atherosclerotic apolipoprotein E-deficient mice with (99m)Tc-labeled sdAbs. Gamma-counting and autoradiography analyses were performed on dissected aorta segments with different degrees of plaque burden. The specificity of the LOX-1-targeting sdAb was evaluated by blocking with unlabeled sdAb or by comparison with a nontargeting (99m)Tc-labeled control sdAb.

RESULTS:

We generated a sdAb binding LOX-1 with a KD of 280 pM ± 62 pM affinity. After (99m)Tc-labeling, the tracer had radiochemical purity higher then 99 % and retained specificity in in vitro binding studies. Tracer blood clearance was fast with concomitant high kidney retention. At 3 h after injection, uptake in tissues other than plaques was low and not different than background, suggesting a restricted expression pattern of LOX-1. Conversely, uptake in aortic segments increased with plaque content and was due to specific LOX-1 binding. In vivo SPECT/CT imaging 160 min after injection in atherosclerotic mice confirmed specific targeting of LOX-1-expressing aortic plaques.

CONCLUSIONS:

The LOX-sdAb specifically targets LOX-1-expressing atherosclerotic plaques within hours after injection. The possibility to image LOX-1 rapidly after administration combined with the favourable biodistribution of a sdAb are beneficial for molecular phenotyping of atherosclerotic plaques and the generation of a future prognostic tracer.

• Authors: Jens De Vos, Iris Mathijs, Catarina Xavier, Sam Massa, Ulrich Wernery, Luc Bouwens, Tony Lahoutte, Serge Muyldermans, Nick Devoogdt
• Journal: Molecular imaging and biology (Mol Imaging Biol) Vol. 16 Issue 5 Pg. 690-8 (Oct 2014) ISSN: 1860-2002 [Electronic] United States
• PMID: 24687730 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Apolipoproteins E
• Biomarkers
• Scavenger Receptors, Class E
• Single-Domain Antibodies
• Technetium

Topics

• Amino Acid Sequence
• Animals
• Aorta (metabolism, pathology)
• Apolipoproteins E (deficiency)
• Biomarkers (metabolism)
• CHO Cells
• Camelus
• Cricetinae
• Cricetulus
• Female
• Mice, Inbred C57BL
• Molecular Sequence Data
• Plaque, Atherosclerotic (metabolism, pathology)
• Protein Binding
• Scavenger Receptors, Class E (metabolism)
• Single-Domain Antibodies (chemistry, immunology)
• Technetium
• Tissue Distribution