Non-invasive in vivo imaging of acute thrombosis: development of a novel factor XIIIa radiotracer

Abstract

Aims Cardiovascular thrombosis is responsible a quarter of deaths annually worldwide. Current imaging methods for cardiovascular thrombosis focus on anatomical identification of thrombus but cannot determine thrombus age or activity. Molecular imaging techniques hold promise for identification and quantification of thrombosis in vivo. Our objective was to assess a novel optical and positron-emitting probe targeting Factor XIIIa (ENC2015) as biomarker of active thrombus formation. Methods and results Optical and positron-emitting ENC2015 probes were assessed ex vivo using blood drawn from human volunteers and passed through perfusion chambers containing denuded porcine aorta as a model of arterial injury. Specificity of ENC2015 was established with co-infusion of a factor XIIIa inhibitor. In vivo18F-ENC2015 biodistribution, kinetics, radiometabolism, and thrombus binding were characterized in rats. Both Cy5 and fluorine-18 labelled ENC2015 rapidly and specifically bound to thrombi. Thrombus uptake was inhibited by a factor XIIIa inhibitor. 18F-ENC2015 remained unmetabolized over 8 h when incubated in ex vivo human blood. In vivo, 42% of parent radiotracer remained in blood 60 min post-administration. Biodistribution studies demonstrated rapid clearance from tissues with elimination via the urinary system. In vivo,18F-ENC2015 uptake was markedly increased in the thrombosed carotid artery compared to the contralateral patent artery (mean standard uptake value ratio of 2.40 vs. 0.74, P < 0.0001). Conclusion ENC2015 rapidly and selectively binds to acute thrombus in both an ex vivo human translational model and an in vivo rodent model of arterial thrombosis. This probe holds promise for the non-invasive identification of thrombus formation in cardiovascular disease.

Visualizing thrombosis to improve thrombus resolution

“…Ultrasound imaging can now use microbubbles and other contrast agents coated with specific targeting ligand molecules that bind selectively to the site of interest 14 . Thrombus‐targeted imaging technologies use ligands that are specific either for fibrin, 15 activated platelets expressing the integrin αIIbβ3, 16 or prothrombotic components such as factor XIIIa, 17 tissue factor, von Willebrand factor, or exposed collagen 14 . Noninvasive molecular imaging techniques targeting thrombus components have been used both in disease‐state animal models and in clinical applications.…”

Preclinical dosimetry models and the prediction of clinical doses of novel positron emission tomography radiotracers

“…Analytical HPLC was performed on a Dionex UltiMate 300 using an Agilent Pursuit XRs 5 μm C 18 column (250 × 4 mm). All precursors were purchased from Advanced Biochemical Compounds (ABX), apart from ENC2015 and ENC2018, which were manufactured as described previously 26 . The structures of all radiotracers prepared in this study are shown in Supplementary Figure 1 The radiosynthesis of the Al 18 F-labelled peptides was carried out using an automated synthesis on a GE TRACERlab MX synthesiser.…”

“…[ 18 F]AlF-NOTA-RGDfK was obtained in 11 ± 2% radiochemical yield (starting from 21 ± 2 GBq of [ 18 F]fluoride, n = 18) with a radiochemical purity of > 99%. [ 18 F]ENC2015 radiochemical yield and purity were as previously reported 26 . [ 18 F]ENC2018 was obtained in 10 ± 4% radiochemical yield (starting from 17 ± 0.4 GBq of [ 18 F]fluoride, n = 3) with a radiochemical purity of > 99%.…”

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

“…These typically combine a targeting component, that ideally interacts specifically with the biochemical process being investigated, and an imaging component that can attach to the targeting component without affecting its interaction with the targeted biochemical process (5). In studies of atherosclerosis, unique molecular imaging agents have been developed for the assessment of a wide variety of FIGURE 1 | Molecular and Non-molecular thrombosis imaging strategies in atherosclerosis patients for assessing pathophysiological features related to early thrombosis at the molecular and cellular level (13), including ultrasound molecular imaging (6), magnetic resonance imaging (7), radionuclide imaging (14), optical imaging (15), intravascular ultrasound, optical coherence tomography, CT angiography (16), angioscopy and angiography (17).…”