title: A novel method of 18F radiolabeling for PET.
abstract: Small biomolecules are typically radiolabeled with (18)F by binding it to a carbon atom, a process that usually is designed uniquely for each new molecule and requires several steps and hours to produce. We report a facile method wherein (18)F is first attached to aluminum as Al(18)F, which is then bound to a chelate attached to a peptide, forming a stable Al(18)F-chelate-peptide complex in an efficient 1-pot process.
  
  
  METHODS
  For proof of principle, this method was applied to a peptide suitable for use in a bispecific antibody pretargeting method. A solution of AlCl(3).6H(2)O in a pH 4.0 sodium-acetate buffer was mixed with an aqueous solution of (18)F to form the Al(18)F complex. This was added to a solution of IMP 449 (NOTA-p-Bn-CS-d-Ala-d-Lys(HSG)-d-Tyr-d-Lys(HSG)-NH(2)) (NOTA-p-Bn-CS is made from S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid; HSG is histamine-succinyl-glycine) and heated to 100 degrees C for 15 min. In vitro and in vivo stability and targeting ability of the Al(18)F-IMP 449 were examined in nude mice bearing LS174T human colonic tumors pretargeted with an anti-CEACAM5 bispecific antibody (TF2).
  
  
  RESULTS
  The radiolabeled peptide was produced in 5%-20% yield with an estimated specific activity of 18,500-48,100 GBq (500-1,300 Ci)/mmol. The Al(18)F-IMP 449 was stable for 4 h in serum in vitro, and in animals, activity isolated in the urine 30 min after injection was bound to the peptide. Nonchelated Al(18)F had higher tissue uptake, particularly in the bones, than the chelated Al(18)F-IMP 449, which cleared rapidly from the body by urinary excretion. Tumor uptake was 30-fold higher with TF2-pretargeted Al(18)F-IMP 449 than with the peptide alone. Dynamic PET showed tumor localization within 30 min and rapid and thorough clearance from the body.
  
  
  CONCLUSIONS
  The ability to bind highly stable Al(18)F to metal-binding ligands is a promising new labeling method that should be applicable to a diverse array of molecules for PET.
authors.affiliation: Immunomedics, Inc., 300 American Way, Morris Plains, NJ 07950, USA. bmcbride@immunomedics.com
authors.forename: William J
authors.initials: WJ
authors.lastname: McBride
authors.forename: Robert M
authors.initials: RM
authors.lastname: Sharkey
authors.forename: Habibe
authors.initials: H
authors.lastname: Karacay
authors.forename: Christopher A
authors.initials: CA
authors.lastname: D'Souza
authors.forename: Edmund A
authors.initials: EA
authors.lastname: Rossi
authors.forename: Peter
authors.initials: P
authors.lastname: Laverman
authors.forename: Chien-Hsing
authors.initials: CH
authors.lastname: Chang
authors.forename: Otto C
authors.initials: OC
authors.lastname: Boerman
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D007553:Isotope Labeling; D013058:Mass Spectrometry; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D014018:Tissue Distribution
chemical_list: D005462:Fluorine Radioisotopes