title: Development of carbon-11 labeled acryl amides for selective PET imaging of active tissue transglutaminase.
abstract: BACKGROUND
  Tissue transglutaminase (TG2) is a ubiquitously expressed enzyme capable of forming metabolically and mechanically stable crosslinks between the γ-carboxamide of a glutamine acyl-acceptor substrate and the ε-amino functionality of a lysine acyl-donor substrate resulting in protein oligomers. High TG2 crosslinking activity has been implicated in the pathogenesis of various diseases including celiac disease, cancer and fibrotic and neurodegenerative diseases. Development of a PET tracer specific for active TG2 provides a novel tool to further investigate TG2 biology in vivo in disease states. Recently, potent irreversible active site TG2 inhibitors carrying an acrylamide warhead were synthesized and pharmacologically characterized.
  
  
  METHODS
  Three of these inhibitors, compound 1, 2 and 3, were successfully radiolabeled with carbon-11 on the acrylamide carbonyl position using a palladium mediated [(11)C]CO aminocarbonylation reaction. Ex vivo biodistribution and plasma stability were evaluated in healthy Wistar rats. Autoradiography was performed on MDA-MB-231 tumor sections.
  
  
  RESULTS
  [(11)C]1, -2 and -3 were obtained in decay corrected radiochemical yields of 38-55%. Biodistribution showed low uptake in peripheral tissues, with the exception of liver and kidney. Low brain uptake of <0.05% ID/g was observed. Blood plasma analysis demonstrated that [(11)C]1 and [(11)C]2 were rapidly metabolized, whereas [(11)C]3 was metabolized at a more moderate rate (63.2 ± 6.8 and 28.7 ± 10.8% intact tracer after 15 and 45 min, respectively). Autoradiography with [(11)C]3 on MDA-MB-231 tumor sections showed selective and specific binding of the radiotracer to the active state of TG2.
  
  
  CONCLUSIONS
  Taken together, these results identify [(11)C]3 as the most promising of the three compounds tested for development as PET radiotracer for the in vivo investigation of TG2 activity.
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands; Departments of Anatomy & Neurosciences, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: b.vanderwildt@vumc.nl.
authors.forename: Berend
authors.initials: B
authors.lastname: van der Wildt
authors.affiliation: Departments of Anatomy & Neurosciences, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Micha M M
authors.initials: MM
authors.lastname: Wilhelmus
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Jonne
authors.initials: J
authors.lastname: Bijkerk
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Lizeth Y F
authors.initials: LY
authors.lastname: Haveman
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Esther J M
authors.initials: EJ
authors.lastname: Kooijman
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Schuit
authors.affiliation: Departments of Anatomy & Neurosciences, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: John G J M
authors.initials: JG
authors.lastname: Bol
authors.affiliation: Departments of Anatomy & Neurosciences, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Cornelis A M
authors.initials: CA
authors.lastname: Jongenelen
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Adriaan A
authors.initials: AA
authors.lastname: Lammertsma
authors.affiliation: Departments of Anatomy & Neurosciences, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Drukarch
authors.affiliation: Departments of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Albert D
authors.initials: AD
authors.lastname: Windhorst
mesh_terms: D000577:Amides / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D002250:Carbon Radioisotopes; D045744:Cell Line, Tumor; D004355:Drug Stability; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D049268:Positron-Emission Tomography / Q000379:methods*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011854:Radiochemistry; D051381:Rats; D017208:Rats, Wistar; D014018:Tissue Distribution; D011503:Transglutaminases / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000577:Amides; D002250:Carbon Radioisotopes; D004791:Enzyme Inhibitors; C000717609:Tgm2 protein, rat; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins
keywords: Carbon-11; Carbonylation; MDA-MB-231; TG2; Tissue transglutaminase; [(11)C]acryl amides