title: Comparison of 18F-fluoroazomycin-arabinofuranoside and 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) in preclinical models of cancer.
abstract: Hypoxic regions are present in different types of cancer and are a negative prognostic factor for disease progression and response to therapy. (18)F-fluoroazomycin-arabinofuranoside ((18)F-FAZA) and (64)Cu-diacetyl-bis(N4-methylthiosemicarbazone) ((64)Cu-ATSM) have been widely used to visualize hypoxic regions in preclinical and clinical studies. Although both these radioligands have high signal-to-noise ratios, (64)Cu-ATSM may be suitable for use in in vivo imaging and as a radiotherapeutic agent. Despite encouraging results suggesting that it may have a role as a prognostic tracer, (64)Cu-ATSM was recently shown to display cell line-dependent kinetics of oxygen-dependent uptake. We set out to evaluate the kinetics of (64)Cu-ATSM distribution in different cancer models, using (18)F-FAZA as the gold standard.
  
  
  METHODS
  (18)F-FAZA and (64)Cu-ATSM uptake were compared ex vivo using dual-tracer autoradiography and in vivo using PET in different xenograft mouse models (FaDu, EMT-6, and PC-3). (18)F-FAZA uptake was compared with (64)Cu-ATSM uptake in PET studies acquired at early (2 h after injection) and delayed time points (24 h after injection). To evaluate the presence of hypoxia and copper pumps, the tumors from animals submitted to PET were harvested and analyzed by an immunohistochemical technique, using antibodies against carbonic anhydrase IX (CAIX) and copper pumps (Ctr1 and ATP7B).
  
  
  RESULTS
  (64)Cu-ATSM showed a higher tumor-to-muscle ratio than did (18)F-FAZA. In the FaDu mouse model, radioactivity distribution profiles were overlapping irrespective of the hypoxic agent injected or the time of (64)Cu acquisition. Conversely, in the EMT-6 and PC-3 models there was little similarity between the early and delayed (64)Cu-ATSM images, and both the radiotracers showed a heterogeneous distribution. The microscopic analysis revealed that (18)F-FAZA-positive areas were also positive for CAIX immunostaining whereas immunolocalization for copper pumps in the 3 models was not related to radioactivity distribution.
  
  
  CONCLUSIONS
  The results of this study confirm the cell-dependent distribution and retention kinetics of (64)Cu-ATSM and underline the need for proper validation of animal models and PET acquisition protocols before exploration of any new clinical applications.
authors.affiliation: IBFM-CNR, Segrate, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Valtorta
authors.forename: Sara
authors.initials: S
authors.lastname: Belloli
authors.forename: Francesca
authors.initials: F
authors.lastname: Sanvito
authors.forename: Valeria
authors.initials: V
authors.lastname: Masiello
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Di Grigoli
authors.forename: Cristina
authors.initials: C
authors.lastname: Monterisi
authors.forename: Ferruccio
authors.initials: F
authors.lastname: Fazio
authors.forename: Maria
authors.initials: M
authors.lastname: Picchio
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Moresco
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D056831:Coordination Complexes; D003301:Copper Radioisotopes / Q000493:pharmacokinetics; D008657:Metabolic Clearance Rate; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009593:Nitroimidazoles / Q000494:pharmacology*; D009928:Organ Specificity; D009942:Organometallic Compounds / Q000493:pharmacokinetics*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013882:Thiosemicarbazones / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: D056831:Coordination Complexes; D003301:Copper Radioisotopes; D009593:Nitroimidazoles; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone); C498052:fluoroazomycin arabinoside
keywords: 18F-FAZA; 64Cu-ATSM; PET imaging; tumor hypoxia