title: Synthesis and characterization of (18)F-labeled active site inhibited factor VII (ASIS).
abstract: Activated factor VII blocked in the active site with Phe-Phe-Arg-chloromethyl ketone (active site inhibited factor VII (ASIS)) is a 50-kDa protein that binds with high affinity to its receptor, tissue factor (TF). TF is a transmembrane glycoprotein that plays an important role in, for example, thrombosis, metastasis, tumor growth, and tumor angiogenesis. The aim of this study was to develop an (18)F-labeled ASIS derivative to assess TF expression in tumors. Active site inhibited factor VII was labeled using N-succinimidyl-4-[(18)F]fluorobenzoate, and the [(18)F]ASIS was purified on a PD-10 desalting column. The radiochemical yield was 25 ± 6%, the radiochemical purity was >97%, and the pseudospecific radioactivity was 35 ± 9 GBq/µmol. The binding efficacy was evaluated in pull-down experiments, which monitored the binding of unlabeled ASIS and [(18)F]ASIS to TF and to a specific anti-factor VII antibody (F1A2-mAb). No significant difference in binding efficacy between [(18)F]ASIS and ASIS could be detected. Furthermore, [(18)F]ASIS was relatively stable in vitro and in vivo in mice. In conclusion, [(18)F]ASIS has for the first time been successfully synthesized as a possible positron emission tomography tracer to image TF expression levels. In vivo positron emission tomography studies to evaluate the full potential of [(18)F]ASIS are in progress.
authors.affiliation: Department of Clinical Physiology, Nuclear Medicine & PET and Cluster for Molecular Imaging, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Maria
authors.initials: M
authors.lastname: Erlandsson
authors.forename: Carsten H
authors.initials: CH
authors.lastname: Nielsen
authors.forename: Troels E
authors.initials: TE
authors.lastname: Jeppesen
authors.forename: Jesper B
authors.initials: JB
authors.lastname: Kristensen
authors.forename: Lars C
authors.initials: LC
authors.lastname: Petersen
authors.forename: Jacob
authors.initials: J
authors.lastname: Madsen
authors.forename: Andreas
authors.initials: A
authors.lastname: Kjaer
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D020134:Catalytic Domain; D005167:Factor VII / Q000037:antagonists & inhibitors / Q000737:chemistry*; D005462:Fluorine Radioisotopes / Q000737:chemistry; D051379:Mice; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D014018:Tissue Distribution
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; C027587:phenylalanyl-phenylalanyl-arginine chloromethyl ketone; D005167:Factor VII
keywords: 18F; PET; [18F]SFB; active site inhibited factor VII; molecular imaging; protein labeling