title: Trimeric Radiofluorinated Sulfonamide Derivatives to Achieve In Vivo Selectivity for Carbonic Anhydrase IX-Targeted PET Imaging.
abstract: Carbonic anhydrase IX (CA-IX), a transmembrane enzyme, mediates cell survival under hypoxic conditions and is overexpressed in solid malignancies. In this study, we synthesized four (18)F sulfonamide derivatives and evaluated their potential for imaging CA-IX expression with PET.
  
  
  METHODS
  Azide derivatives of 2 carbonic anhydrase inhibitors, 4-(2-aminoethyl)benzenesulfonamide (AEBS) and 4-aminobenzensulfonamide (ABS), were coupled to radiosynthons with either 1 or 3 alkynes and a pendent ammoniomethyltrifluoroborate (AmBF3) to generate monovalent or trivalent enzyme inhibitors. Binding affinity to CA-IX and other CA isoforms was determined via a stopped-flow, CA-catalyzed CO2 hydration assay. Tracers were radiolabeled via (18)F-(19)F isotope exchange reactions. Imaging/biodistribution studies were performed using HT-29 tumor-bearing immunocompromised mice.
  
  
  RESULTS
  Monomeric AmBF3-AEBS and AmBF3-ABS were obtained in 41% and 40% yields, whereas trimeric AmBF3-(AEBS)3 and AmBF3-(ABS)3 were obtained in 47% and 55% yields, respectively. Derivatives bound CA-I, -II, -IX, and -XII with good affinity (0.49-100.3 nM). (18)F-labeled sulfonamides were obtained in 16.3%-36.8% non-decay-corrected radiochemical yields, with 40-207 GBq/μmol specific activity and greater than 95% radiochemical purity. Biodistribution/imaging studies showed that the tracers were excreted through both renal and hepatobiliary pathways. At 1 h after injection, HT-29 tumor xenografts were clearly visualized in PET images with modest contrast for all 4 tracers. Tumor uptake was 2-fold higher for monovalent tracers (∼0.60 percentage injected dose per gram [%ID/g]) than for trivalent tracers (∼0.30 %ID/g); however, tumor-to-background ratios were significantly better for (18)F-AmBF3-(ABS)3. Preblocking with acetazolamide reduced more than 80% uptake of (18)F-AmBF3-(ABS)3 in HT-29 tumors.
  
  
  CONCLUSIONS
  Our data suggest that trimerization of an otherwise nonspecific CA inhibitor greatly enhances the selectivity for CA-IX in vivo and represents a promising strategy for creating multivalent enzyme inhibitors for selectively imaging extracellular enzyme activity by PET.
authors.affiliation: Department of Molecular Oncology, BC Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Joseph
authors.initials: J
authors.lastname: Lau
authors.affiliation: Chemistry Department, University of British Columbia, Vancouver, British Columbia, Canada; and.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Molecular Oncology, BC Cancer Agency, Vancouver, British Columbia, Canada klin@bccrc.ca dperrin@chem.ubc.ca.
authors.forename: Kuo-Shyan
authors.initials: KS
authors.lastname: Lin
authors.affiliation: Department of Molecular Oncology, BC Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Jinhe
authors.initials: J
authors.lastname: Pan
authors.affiliation: Department of Molecular Oncology, BC Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Zhengxing
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Università degli Studi di Firenze, Dipartimento Neurofarba and Laboratorio di Chimica Bioinorganica, Florence, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Vullo
authors.affiliation: Università degli Studi di Firenze, Dipartimento Neurofarba and Laboratorio di Chimica Bioinorganica, Florence, Italy.
authors.forename: Claudiu T
authors.initials: CT
authors.lastname: Supuran
authors.affiliation: Chemistry Department, University of British Columbia, Vancouver, British Columbia, Canada; and klin@bccrc.ca dperrin@chem.ubc.ca.
authors.forename: David M
authors.initials: DM
authors.lastname: Perrin
authors.affiliation: Department of Molecular Oncology, BC Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Bénard
mesh_terms: D000818:Animals; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D019073:HT29 Cells; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000201:enzymology*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013449:Sulfonamides / Q000138:chemical synthesis / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D013449:Sulfonamides; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; C492796:Car9 protein, mouse
keywords: 18F-AmBF3; carbonic anhydrase IX; hypoxia; one-step 18F-labeling; positron emission tomography