Detection of activated platelets in a mouse model of carotid artery thrombosis with18 F-labeled single-chain antibodies

Abstract Introduction Activated platelets are key players in thrombosis and inflammation. We previously generated single-chain antibodies (scFv) against ligand-induced binding sites (LIBS) on the highly abundant platelet glycoprotein integrin receptor IIb/IIIa. The aim of this study was the construction and characterisation of a novel18 F PET radiotracer based on this antibody. Methods ScFvanti-LIBS and control antibody mut-scFv were reacted with N-succinimidyl-4-[18 F]fluorobenzoate (S[18 F]FB). Radiolabeled scFv was incubated with in vitro formed platelet clots and injected into mice with FeCl3 induced thrombus in the left carotid artery. Clots were imaged in the PET scanner and amount of radioactivity measured using an ionization chamber and image analysis. Assessment of vessel injury as well as the biodistribution of the radiolabeled scFv was studied. Results After incubation with increasing concentrations of18 F-scFvanti-LIBS clots had retained significantly higher amounts of radioactivity compared to clots incubated with radiolabeled18 F-mut-scFv (13.3 ± 3.8 vs. 3.6 ± 1 KBq, p < 0.05, n = 9, decay corrected). In the in vivo experiments we found an high uptake of the tracer in the injured vessel compared with the non-injured vessel, with 12.6 ± 4.7% injected dose per gram (ID/g) uptake in the injured vessel and 3.7 ± 0.9% ID/g in the non-injured vessel 5 minutes after injection (p < 0.05, n = 6). Conclusions Our results show that the novel antibody radiotracer18 F-scFvanti-LIBS is useful for the sensitive detection of activated platelets and thrombosis. Advances in knowledge and implications for patient care We describe the first18 F variant of a scFvanti-LIBS against activated platelets. This diagnostic agent could provide a powerful tool for the assessment of acute thrombosis and inflammation in patients in the future.