Imaging the hypoxia surrogate marker CA IX requires expression and catalytic activity for binding fluorescent sulfonamide inhibitors

Ludwig Dubois, Kim Douma, Claudiu T Supuran, Roland K Chiu, Marc A M J van Zandvoort, Silvia Pastoreková, Andrea Scozzafava, Bradly G Wouters, Philippe Lambin

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BACKGROUND AND PURPOSE: Carbonic anhydrase (CA) IX expression is increased in response to hypoxia. Recently, sulfonamide based carbonic anhydrase inhibitors (CAI) showing specificity for CA IX have been designed. Aim was to investigate the CAI binding properties under normoxia, hypoxia and reoxygenation.

MATERIAL AND METHODS: Cells with varying CA IX expression were incubated with fluorescein labeled CAI (1mM) during normoxia, hypoxia (0.2%) and reoxygenation. CA IX expression levels were assessed using Western blotting. CAI binding was determined by immunostaining and flow cytometry.

RESULTS: CAI binding in hypoxic cells was significantly higher compared with normoxic cells and correlated with upregulated CA IX levels. Binding occurred within 15min of hypoxia, but was gradually lost upon reoxygenation. Interestingly, although CA IX levels remained high upon reoxygenation, CAI binding was dramatically reduced and no longer correlated with CA IX expression. Similarly, RCC4 cells, constitutively expressing CA IX, do not bind CAI under normoxic conditions.

CONCLUSIONS: Our results confirm and extend previous results showing that CAI binding occurs only under hypoxia. The inability of CAI to bind CA IX in RCC4 cells and following reoxygenation in other cells demonstrates that formation of the active site not only depends on HIF-1alpha-dependent gene activity, but also on the absence of oxygen per se.

Original languageEnglish
Pages (from-to)367-373
Number of pages7
JournalRadiotherapy and Oncology
Issue number3
Publication statusPublished - Jun-2007
Externally publishedYes


  • Antigens, Neoplasm
  • Binding Sites
  • Binding, Competitive
  • Carbonic Anhydrase IX
  • Carbonic Anhydrase Inhibitors
  • Carbonic Anhydrases
  • Catalysis
  • Cell Hypoxia
  • Cell Line, Tumor
  • Female
  • Fluorescent Antibody Technique
  • HeLa Cells
  • Humans
  • Oxygen
  • Sulfonamides
  • Journal Article
  • Research Support, Non-U.S. Gov't

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