title: Rapid solid phase synthesis and biodistribution of 18F-labelled linear peptides.
abstract: A rapid method for radiolabelling short peptides with 18F ( t(1/2)=109.7 min) for use in positron emission tomography (PET) was developed. Linear peptides (13mers) were synthesised using solid phase peptide synthesis and 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. The peptides were assembled on a solid-phase polyethylene glycol-polystyrene support using the "hyper acid labile" linker xanthen-2-oxyvaleric acid and were labelled in situ with 4-[19F]- or 4-[18F]fluorobenzoic acid. Optimum coupling of 4-[19F]fluorobenzoic acid to the peptidyl resin was achieved within 2 min using N-[(dimethylamino)-1 H-1,2,3-triazolo[4,5-b]pyridin-1-ylmethylene]- Nmethylmethanaminium hexafluorophosphate N-oxide (HATU/DIPEA), and optimum cleavage was achieved within 7 min using trifluoroacetic acid/phenol/water/Triisopropylsilane at 37 degrees C. The linear peptides were rapidly labelled with 4-[18F]fluorobenzoic acid with an overall radiochemical yield of 80%-90% (decay corrected), a radiochemical purity of >95% without HPLC purification and an overall synthesis time of 20 min. This novel method was used to label peptides containing the arginine-glycine-aspartic acid (RGD) motif, the binding site of many integrins. In vitro studies showed that the fluorobenzoyl prosthetic group had no deleterious effect on the ability of these peptides to inhibit the binding of human cells via integrins. Biodistribution studies in tumour-bearing mice showed that although the linear peptides were rapidly removed from the circulation by the liver and kidneys, there was a transient and non-RGD-dependent accumulation in the tumour of both the test and the control peptides. The use of more selective peptides with a longer half-life in the circulation combined with this rapid labelling technique will significantly enhance the application of peptides in PET.
authors.affiliation: The Clinical PET Centre, Guy's, King's and St.Thomas' School of Medicine, The Lower Ground Floor, Lambeth Wing, St. Thomas' Hospital, Lambeth Palace Road, London, SE1 7EH, UK. julie.l.sutcliffe@kcl.ac.uk
authors.forename: Julie L
authors.initials: JL
authors.lastname: Sutcliffe-Goulden
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Doherty
authors.forename: Paul K
authors.initials: PK
authors.lastname: Marsden
authors.forename: Ian R
authors.initials: IR
authors.lastname: Hart
authors.forename: John F
authors.initials: JF
authors.lastname: Marshall
authors.forename: Sukvinder S
authors.initials: SS
authors.lastname: Bansal
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005462:Fluorine Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics*; D007553:Isotope Labeling / Q000379:methods*; D008657:Metabolic Clearance Rate; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009842:Oligopeptides / Q000138:chemical synthesis / Q000493:pharmacokinetics; D010455:Peptides / Q000138:chemical synthesis* / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed / Q000379:methods
chemical_list: D005462:Fluorine Radioisotopes; D009842:Oligopeptides; D010455:Peptides; D019275:Radiopharmaceuticals; C047981:arginyl-glycyl-aspartic acid