Activated platelets in carotid artery thrombosis in mice can be selectively targeted with a radiolabeled single-chain antibody

Background

Activated platelets can be found on the surface of inflamed, rupture-proneand ruptured plaques as well as in intravascular thrombosis. They are keyplayers in thrombosis and atherosclerosis. In this study we describe theconstruction of a radiolabeled single-chain antibody targeting theLIBS-epitope of activated platelets to selectively depict plateletactivation and wall-adherent non-occlusive thrombosis in a mouse model withnuclear imaging using in vitro and ex vivoautoradiography as well as small animal SPECT-CT for invivo analysis.

Methodology/Principal Findings

LIBS as well as an unspecific control single-chain antibody were labeled with¹¹¹Indium (¹¹¹In) via bifunctional DTPA( = ¹¹¹In-LIBS/¹¹¹In-control).Autoradiography after incubation with ¹¹¹In-LIBS on activatedplatelets in vitro (mean 3866±28 DLU/mm²,4010±630 DLU/mm² and 4520±293 DLU/mm²)produced a significantly higher ligand uptake compared to¹¹¹In-control (2101±76 DLU/mm², 1181±96DLU/mm² and 1866±246 DLU/mm²) indicating aspecific binding to activated platelets; P<0.05.Applying these findings to an ex vivo mouse model ofcarotid artery thrombosis revealed a significant increase in ligand uptakeafter injection of ¹¹¹In-LIBS in the presence of small thrombicompared to the non-injured side, as confirmed by histology(49630±10650 DLU/mm² vs. 17390±7470DLU/mm²; P<0.05). These findings couldalso be reproduced in vivo. SPECT-CT analysis of theinjured carotid artery with ¹¹¹In-LIBS resulted in a significantincrease of the target-to-background ratio compared to¹¹¹In-control (1.99±0.36 vs. 1.1±0.24;P<0.01).

Conclusions/Significance

Nuclear imaging with ¹¹¹In-LIBS allows the detection of plateletactivation in vitro and ex vivo with highsensitivity. Using SPECT-CT, wall-adherent activated platelets in carotidarteries could be depicted in vivo. These results encouragefurther studies elucidating the role of activated platelets in plaquepathology and atherosclerosis and might be of interest for furtherdevelopments towards clinical application.