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Decreased defluorination by using the novel beta cell imaging agent [18F]FE-DTBZ-d4 in pigs examined by PET
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Oncology, Radiology and Clinical Immunology, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Clinical Immunology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Introduction: Fluorine-18 DTBZ-analogues, which selectively targets the vesicular monoamine transporter 2 (VMAT2), have been extensively studied for in vivo quantification of beta cell mass by positron emission tomography (PET).  This study describes a novel deuterated radioligand [18F]FE-(+)-DTBZ-d4, aimed to increase the stability against in vivo defluorination previously observed for [18F]FE-(+)-DTBZ.

Methods: [18F]FE-(+)-DTBZ-d4 was synthesized by alkylation of desmethyl -(+)-DTBZ precursor with deuterated  [18F]fluoroethyl bromide ([18F]FCD2CD2Br). Radioligand affinity and specificity to VMAT2 was assessed by an in vitro saturation homogenate binding assay using human endocrine and exocrine pancreatic tissues. In vivo PK/PD was studied in a porcine model by PET/CT. The rate of defluorination was quantified by compartmental modeling and contrasted against defluorination of the non-deuterated analogue.

Results: [18F]FE-DTBZ-d4 was produced in good radiochemical yield (3.0-1.7 GBq) in 100 min. Radiochemical purity of the formulated product was > 98% for up to 5h. The in vitro Binding Potential (BP) for VMAT2 in islet tissue was 27.0±8.8. The BP was lower in exocrine tissue (1.7±1.0) in addition to a close to three-fold decrease in specificity. The rate of in vivo defluorination was decreased significantly (kdefluorination= 0.0016±0.0007) compared to the non-deuterated analogue (kdefluorination= 0.012±0.002), resulting in a more than six-fold increase in half-life stability.

Conclusion: [18F]FE-(+)-DTBZ-d4 has favorable pharmacokinetic (PK) properties for VMAT2 imaging, in addition to gaining significantly increased stability against defluorination. The in vitro islet BP and specificity was lower compared to a non-deuterated analogue but the islet/exocrine BP ratio was unchanged, potentially allowing for improved target tissue discrimination.

National Category
Immunology in the medical area
URN: urn:nbn:se:uu:diva-136370OAI: oai:DiVA.org:uu-136370DiVA: diva2:376640
Available from: 2010-12-12 Created: 2010-12-12 Last updated: 2012-02-29
In thesis
1. Imaging Islets of Langerhans by Positron Emission Tomography: Quantification of Beta-Cell Mass in the Native Pancreas and the Islet Graft
Open this publication in new window or tab >>Imaging Islets of Langerhans by Positron Emission Tomography: Quantification of Beta-Cell Mass in the Native Pancreas and the Islet Graft
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Type 1 and 2 Diabetes Mellitus are a growing health problem throughout the world. There is an increasing  need for methodologies, which are both reliable and non-invasive to measure the amount of insulin-producing tissue (Beta-cell mass, or BCM), as well as rapidly quantify changes in the BCM due to the onset of disease, beta-cell replacement therapy, or other treatments.

Positron Emission Tomography (PET) is a non-invasive, quantitative functional imaging technique which can be used to study dynamical or static processes inside the body.

In this thesis, we present a study protocol for in vivo imaging of the most common form of beta- cell replacement therapy; islet transplantation. Islets were labeled with the PET tracer, 2-deoxy-2[18F]fluoro-D-glucose ([18F]FDG), and administered intra-portally, while the recipient was monitored by PET/CT. The hepatic distribution of the islets was highly heterogeneous, and around 25% (human) or 50% (porcine) of the administered islets could not be found in the liver after completed transplantation, confirming previous reports of considerable cell injury during the procedure leading to low hepatic engraftment.

Native BCM in the pancreas can potentially be quantified using a PET tracer with sufficiently high specificity, but the major obstacle is the relative low amounts of insulin producing tissue (only 1-2% of the pancreatic volume). Two tetrabenazine analogues, [18F]FE-(+)-DTBZ and [18F]FE-(+)-DTBZ-d4, are ligands to VMAT2, which is expressed in islet tissue. Both analogues were investigated and characterized as potential BCM imaging agents both in vitro and in vivo.  Both tracers exhibited high preferential binding to islet tissue compared to exocrine pancreatic tissue. However, the specificity was not high enough to overcome the obscuring exocrine signal in vivo (7-10% of the signal originating from specific islet tracer uptake).

This thesis demonstrates that it is possible to quantitatively assess islet transplantation by PET imaging. In vivo determination of native pancreatic BCM is, in theory, possible with both [18F]FE-(+)-DTBZ and [18F]FE-(+)-DTBZ-d4, but tracer analogues with higher islet specificity is needed for quantification of smaller BCM changes with physiological impact.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 67 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 635
Positron Emission Tomography, [18F]FDG, dihydrotetrabenazine, Islet transplantation, IBMIR, beta-cell mass
National Category
Medical and Health Sciences
urn:nbn:se:uu:diva-136372 (URN)978-91-554-7978-7 (ISBN)
Public defence
2011-02-04, Rosénsalen, Akademiska Sjukhuset, Ingång 95/96, Uppsala, 09:15 (English)
Available from: 2011-01-14 Created: 2010-12-12 Last updated: 2011-03-11

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