Background Advances in immunology and cell-based therapies are creating a need to track individual cell types, such as immune cells (neutrophils, eosinophils, chimeric antigen receptor (CAR) T cells, etc.) and stem cells. As the fate of administered cells remains largely unknown, nuclear imaging could determine the migration and survival of cells in patients. [ 89 Zr]Zr(oxinate) 4 , or [ 89 Zr]Zr-oxine, is a radiotracer for positron emission tomography (PET) that has been evaluated in preclinical models of cell tracking and could improve on [ 111 In]In-oxine, the current gold standard radiotracer for cell tracking by scintigraphy and single-photon emission computed tomography (SPECT), because of the better sensitivity, spatial resolution and quantification of PET. However, a clinically usable formulation of [ 89 Zr]Zr-oxine is lacking. This study demonstrates a 1-step procedure for preparing [ 89 Zr] Zr-oxine and evaluates it against [ 111 In]In-oxine in white blood cell (WBC) labelling. Methods Commercial [ 89 Zr]Zr-oxalate was added to a formulation containing oxine, a buffering agent, a base and a surfactant or organic solvent. WBC isolated from 10 human volunteers were radiolabelled with [ 89 Zr]Zr-oxine following a clinical radiolabelling protocol. Labelling efficiency, cell viability, chemotaxis and DNA damage were evaluated in vitro , in an intra-individual comparison against [ 111 In]In-oxine. Results An optimised formulation of [ 89 Zr]Zr-oxine containing oxine, polysorbate 80 and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) was developed. This enabled 1-step radiolabelling of oxine with commercial [ 89 Zr]Zr-oxalate (0.1–25 MBq) in 5 min and radiotracer stability for 1 week. WBC labelling efficiency was 48.7 ± 6.3%, compared to 89.1 ± 9.5% ( P < 0.0001, n = 10) for [ 111 In]In-oxine. Intracellular retention of 89 Zr and cell viability after radiolabelling were comparable to 111 In. There were no significant differences in leukocyte chemotaxis or DNA damage between [ 89 Zr]Zr-oxine or [ 111 In]In-oxine. Conclusions, advances in knowledge and implications for patient care Our results demonstrate that [ 89 Zr]Zr-oxine is a suitable PET alternative to [ 111 In]In-oxine for WBC imaging. Our formulation allows rapid, stable, high-yield, single-step preparation of [ 89 Zr]Zr-oxine fro...

Extracellular vesicles (EVs) such as exosomes and microvesicles have gained recent attention as potential biomarkers of disease as well as nanomedicinal tools, but their behaviour in vivo remains mostly unexplored. In order to gain knowledge of their in vivo biodistribution it is important to develop imaging tools that allow us to track EVs over time and at the whole-body level. Radionuclide-based imaging (PET and SPECT) have properties that allow us to do so efficiently, mostly due to their high sensitivity, imaging signal tissue penetration, and accurate quantification. Furthermore, they can be easily translated from animals to humans. In this review, we summarise and discuss the different studies that have used PET or SPECT to study the behaviour of EVs in vivo . With a focus on the different radiolabelling methods used, we also discuss the advantages and disadvantages of each one, and the challenges of imaging EVs due to their variable stability and heterogeneity.

Exosomes or small extracellular vesicles (sEVs) are increasingly gaining attention for their potential as drug delivery systems and biomarkers of disease. Therefore, it is important to understand their in vivo biodistribution using imaging techniques that allow tracking over time and at the whole-body level. Positron emission tomography (PET) allows short-and long-term wholebody tracking of radiolabeled compounds in both animals and humans and with excellent quantification properties compared to other nuclear imaging techniques. In this report, we explored the use of [ 89 Zr]Zr(oxinate) 4 (a cell and liposome radiotracer) for direct and intraluminal radiolabeling of several types of sEVs, achieving high radiolabeling yields. The radiosynthesis and radiolabeling protocols were optimized for sEV labeling, avoiding sEV damage, as demonstrated using several characterizations (cryoEM, nanoparticle tracking analysis, dot blot, and flow cytometry) and in vitro techniques. Using pancreatic cancer sEVs (PANC1) in a healthy mouse model, we showed that it is possible to track 89 Zrlabeled sEVs in vivo using PET imaging for at least up to 24 h. We also report differential biodistribution of intact sEVs compared to intentionally heat-damaged sEVs, with significantly reduced spleen uptake for the latter. Therefore, we conclude that 89 Zr-labeled sEVs using this method can reliably be used for in vivo PET tracking and thus allow efficient exploration of their potential as drug delivery systems.

89Zr]Zr(oxinate)4 allows direct radiolabelling of exosomes/small extracellular vesicles (sEVs) and in vivo PET-CT imaging

89Zr]Zr(oxinate)4 allows direct radiolabelling of exosomes/small extracellular vesicles (sEVs) and in vivo PET-CT imaging

89Zr]Zr(oxinate)4 allows direct radiolabelling of exosomes/small extracellular vesicles (sEVs) and in vivo PET-CT imaging

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