Automated synthesis of the generic peptide labelling agent N-succinimidyl 4-[18F]fluorobenzoate and application to 18F-label the vasoactive transmitter urotensin-II as a ligand for positron emission tomography

Johnström, Peter; Clark, John C.; Pickard, John D.; Davenport, Anthony P.

doi:10.1016/j.nucmedbio.2008.04.005

« PreviousNuclear Medicine and Biology
Volume 35, Issue 6 , Pages 725-731, August 2008

Automated synthesis of the generic peptide labelling agent N-succinimidyl 4-[¹⁸F]fluorobenzoate and application to ¹⁸F-label the vasoactive transmitter urotensin-II as a ligand for positron emission tomography

Peter Johnström
- Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
- Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
John C. Clark
- Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
John D. Pickard
- Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
Anthony P. Davenport
- Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
- Corresponding author. Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Centre for Clinical Investigation, Box 110, Addenbrooke's Hospital, Cambridge, CB2 2QQ, UK. Tel.: +44 1223 336899; fax: +44 1223 762576.

Received 13 March 2008; accepted 14 April 2008. published online 18 June 2008.

Abstract

Introduction

The objectives of this work were to develop an automated production of N-succinimidyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]-SFB) and to test whether the vasoactive peptide urotensin-II (U-II) could be labelled by conjugation with [¹⁸F]-SFB.

Methods

A TRACERlab MX_FDG synthesizer including an HPLC unit was used. The MS Excel synthesis sequence and the standard disposable FDG cassette were modified to allow the synthesis of [¹⁸F]-SFB. U-II was subsequently conjugated with [¹⁸F]-SFB, and the resulting ¹⁸F-labelled peptides were characterised using in vitro ligand binding assays.

Results

[¹⁸F]-SFB was successfully synthesised in the TRACERlab MX_FDG in 44.3±2.5% (n=25) radiochemical yield in 98 min. [¹⁸F]-SFB (8–12 GBq) has been produced with specific activities in the range of 250–350 GBq/μmol and a radiochemical purity >95%. [¹⁸F]-SFB was subsequently used to label U-II. Two radiolabelled products, [¹⁸F]-(Glu¹)-U-II and [¹⁸F]-(Lys⁸)-U-II, were formed in an isolated radiochemical yield from [¹⁸F]-SFB of 5.2±0.3% and 29.0±3.7%, respectively (n=7). Radioligand binding assays revealed that [¹⁸F]-(Glu¹)-U-II had retained subnanomolar affinity. Binding to human skeletal muscle (n=3) was concentration dependent and saturable with K_d=0.84±0.51 nM, B_max=0.69±0.14 fmol/mg protein and Hill slope (nH)=1.03±0.12.

Conclusions

[¹⁸F]-SFB has been synthesised using the TRACERlab MX_FDG module, allowing production of up to 8–12 GBq of [¹⁸F]-SFB with specific activities of 250–350 GBq/μmol. [¹⁸F]-SFB was used for the labelling of U-II. In vitro characterisation demonstrated that [¹⁸F]-(Glu¹)-U-II had retained desirable binding properties and may be suitable as a positron emission tomography radioligand for the imaging of the U-II receptor.

Keywords: TRACERlab MX_FDG, Urotensin, UT receptors, PET, Peptide labelling, ¹⁸F