title: Investigation of hypoxia and carbonic anhydrase IX expression in a renal cell carcinoma xenograft model with oxygen tension measurements and ¹²⁴I-cG250 PET/CT.
abstract: OBJECTIVE
  In tumors, hypoxia stimulates angiogenesis and correlates with treatment resistance and poor prognosis. We have previously demonstrated hypoxia in human renal cell carcinoma (RCC) via direct oxygen probe measurements. Carbonic anhydrase IX (CA IX) is a protein stimulated by hypoxia and involved in angiogenesis, and is a potential tumor target for imaging and therapies using cG250, a monoclonal antibody that recognizes CAIX. Our objectives were to characterize intratumoral hypoxia in a human RCC xenograft model using oxygen probe measurements; investigate if (124)I-cG250 targets RCC correlating uptake on noninvasive positron emission tomography-computerized tomography (PET-CT) against traditional biodistribution studies, and investigate CAIX expression in this RCC model.
  
  
  METHODS
  BALB/c nude mice had human RCC (SK-RC-52) subcutaneously xenografted with oxygen levels measured by probe. Positron emission tomography (PET/CT) and biodistribution studies ((124)I-cG250) were correlated with oxygen measurements. Immunohistochemistry and autoradiography were performed on selected tumors to confirm CAIX expression.
  
  
  RESULTS
  Oxygen tension in normal tissue (muscle) was 35.08 ± 2.41 mmHg (mean ± 95% CI), significantly greater compared to xenograft SK-RC-52 tumors at 5.02 ± 1.12 mmHg. Biodistribution studies of (124)I-cG250 demonstrated isotope uptake in SK-RC-52 xenografts peaking at 23.45 ± 5.07% ID/g (mean ± SD) 48 hours after antibody injection, which was maintained for a further 2 days (19.43 ± 4.31 and 10.64 ± 5.64 % ID/g, respectively). PET studies demonstrated excellent localization of (124)I-cG250 in tumor, and a significant correlation between SUVmean, SUVmax, and %/ID (124)I-cG250. CAIX expression was present in all groups studied but there was no significant correlation between it and any oxygen parameter studied.
  
  
  CONCLUSIONS
  Intratumoral hypoxia does exist within a human RCC xenograft model using invasive oxygen probe measurements. (124)I-cG250 targets RCC with correlation between uptake on noninvasive PET-CT studies and traditional biodistribution studies opening the possibility of using PET/CT in future studies. Finally, CAIX expression was not related to hypoxia in this model, supporting the hypothesis that cell lines may subvert known hypoxia mechanisms in hypoxic environments.
authors.affiliation: University of Melbourne Department of Surgery, Austin Hospital, Melbourne, Victoria, Australia. nathan.lawrentschuk@uhn.on.ca
authors.forename: Nathan
authors.initials: N
authors.lastname: Lawrentschuk
authors.forename: Fook T
authors.initials: FT
authors.lastname: Lee
authors.forename: Gareth
authors.initials: G
authors.lastname: Jones
authors.forename: Angela
authors.initials: A
authors.lastname: Rigopoulos
authors.forename: Angela
authors.initials: A
authors.lastname: Mountain
authors.forename: Graeme
authors.initials: G
authors.lastname: O'Keefe
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Papenfuss
authors.forename: Damien M
authors.initials: DM
authors.lastname: Bolton
authors.forename: Ian D
authors.initials: ID
authors.lastname: Davis
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Scott
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000493:pharmacokinetics; D000951:Antigens, Neoplasm / Q000096:biosynthesis*; D001345:Autoradiography; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000096:biosynthesis*; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D006801:Humans; D000860:Hypoxia; D007150:Immunohistochemistry; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010100:Oxygen / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000379:methods*; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; C106533:G250 monoclonal antibody; D007457:Iodine Radioisotopes; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D010100:Oxygen