title: Evaluation and immunohistochemical qualification of carbogen-induced ΔR₂ as a noninvasive imaging biomarker of improved tumor oxygenation.
abstract: OBJECTIVE
  To evaluate and histologically qualify carbogen-induced ΔR2 as a noninvasive magnetic resonance imaging biomarker of improved tumor oxygenation using a double 2-nitroimidazole hypoxia marker approach.
  
  
  METHODS
  Multigradient echo images were acquired from mice bearing GH3 prolactinomas, preadministered with the hypoxia marker CCI-103F, to quantify tumor R2 during air breathing. With the mouse remaining positioned within the magnet bore, the gas supply was switched to carbogen (95% O2, 5% CO2), during which a second hypoxia marker, pimonidazole, was administered via an intraperitoneal line, and an additional set of identical multigradient echo images acquired to quantify any changes in tumor R2. Hypoxic fraction was quantified histologically using immunofluorescence detection of CCI-103F and pimonidazole adduct formation from the same whole tumor section. Carbogen-induced changes in tumor pO2 were further validated using the Oxylite fiberoptic probe.
  
  
  RESULTS
  Carbogen challenge significantly reduced mean tumor R2 from 116 ± 13 s(-1) to 97 ± 9 s(-1) (P<.05). This was associated with a significantly lower pimonidazole adduct area (2.3 ± 1%), compared with CCI-103F (6.3 ± 2%) (P<.05). A significant correlation was observed between ΔR2 and Δhypoxic fraction (r=0.55, P<.01). Mean tumor pO2 during carbogen breathing significantly increased from 6.3 ± 2.2 mm Hg to 36.0 ± 7.5 mm Hg (P<.01).
  
  
  CONCLUSIONS
  The combined use of intrinsic susceptibility magnetic resonance imaging with a double hypoxia marker approach corroborates carbogen-induced ΔR2 as a noninvasive imaging biomarker of increased tumor oxygenation.
authors.affiliation: Cancer Research UK & EPSRC Cancer Imaging Centre, Division of Radiotherapy and Imaging, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Surrey, UK. lauren.baker@icr.ac.uk
authors.forename: Lauren C J
authors.initials: LC
authors.lastname: Baker
authors.forename: Jessica K R
authors.initials: JK
authors.lastname: Boult
authors.forename: Yann
authors.initials: Y
authors.lastname: Jamin
authors.forename: Lesley D
authors.initials: LD
authors.lastname: Gilmour
authors.forename: Simon
authors.initials: S
authors.lastname: Walker-Samuel
authors.forename: Jake S
authors.initials: JS
authors.lastname: Burrell
authors.forename: Margaret
authors.initials: M
authors.lastname: Ashcroft
authors.forename: Franklyn A
authors.initials: FA
authors.lastname: Howe
authors.forename: John R
authors.initials: JR
authors.lastname: Griffiths
authors.forename: James A
authors.initials: JA
authors.lastname: Raleigh
authors.forename: Albert J
authors.initials: AJ
authors.lastname: van der Kogel
authors.forename: Simon P
authors.initials: SP
authors.lastname: Robinson
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000378:metabolism*; D015687:Cell Hypoxia; D007150:Immunohistochemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D009593:Nitroimidazoles / Q000008:administration & dosage / Q000378:metabolism*; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism*; D010101:Oxygen Consumption; D010313:Partial Pressure; D010911:Pituitary Neoplasms / Q000378:metabolism*; D015175:Prolactinoma / Q000378:metabolism*; D005466:Fluorocarbons
chemical_list: D015415:Biomarkers; D002245:Carbon Dioxide; D009593:Nitroimidazoles; D010100:Oxygen; C049948:CCI 103F; D005466:Fluorocarbons; C033815:pimonidazole; C011700:carbogen