Automated synthesis of the generic peptide labelling agent N-succinimidyl 4-[(18)F]fluorobenzoate and application to (18)F-label the vasoactive transmitter urotensin-II as a ligand for positron emission tomography.
BACKGROUND
The objectives of this work were to develop an automated production of N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]-SFB) and to test whether the vasoactive peptide urotensin-II (U-II) could be labelled by conjugation with [(18)F]-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 [(18)F]-SFB. U-II was subsequently conjugated with [(18)F]-SFB, and the resulting (18)F-labelled peptides were characterised using in vitro ligand binding assays.


RESULTS
[(18)F]-SFB was successfully synthesised in the TRACERlab MX(FDG) in 44.3+/-2.5% (n=25) radiochemical yield in 98 min. [(18)F]-SFB (8-12 GBq) has been produced with specific activities in the range of 250-350 GBq/mumol and a radiochemical purity >95%. [(18)F]-SFB was subsequently used to label U-II. Two radiolabelled products, [(18)F]-(Glu(1))-U-II and [(18)F]-(Lys(8))-U-II, were formed in an isolated radiochemical yield from [(18)F]-SFB of 5.2+/-0.3% and 29.0+/-3.7%, respectively (n=7). Radioligand binding assays revealed that [(18)F]-(Glu(1))-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
[(18)F]-SFB has been synthesised using the TRACERlab MX(FDG) module, allowing production of up to 8-12 GBq of [(18)F]-SFB with specific activities of 250-350 GBq/mumol. [(18)F]-SFB was used for the labelling of U-II. In vitro characterisation demonstrated that [(18)F]-(Glu(1))-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.
Johnström
Peter
P
Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.
Clark
John C
JC
Pickard
John D
JD
Davenport
Anthony P
AP
D001565:Benzoates / Q000737:chemistry*; D005462:Fluorine Radioisotopes / Q000737:chemistry*; D007553:Isotope Labeling / Q000379:methods; D010455:Peptides / Q000737:chemistry*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000737:chemistry*; D012371:Robotics / Q000379:methods*; D013388:Succinimides / Q000737:chemistry*; D014579:Urotensins / Q000737:chemistry*; D014662:Vasoconstrictor Agents / Q000737:chemistry*
D001565:Benzoates; D005462:Fluorine Radioisotopes; D010455:Peptides; D019275:Radiopharmaceuticals; D013388:Succinimides; D014579:Urotensins; D014662:Vasoconstrictor Agents; C075713:N-succinimidyl-4-fluorobenzoate; C029677:urotensin II