Radiother Oncol. 2003 Apr;67(1):53-61.  

In vivo colocalization of 2-nitroimidazole EF5 fluorescence intensity and
electron paramagnetic resonance oximetry in mouse tumors.

Mahy P, De Bast M, Gallez B, Gueulette J, Koch CJ, Scalliet P, Gregoire V.

Radiation Oncology Department and Radiobiology Unit, Universite catholique de Louvain, 
St-Luc University Hospital, 10 Avenue Hippocrate, B-1200, Brussels,
Belgium

Background and PURPOSE: The primary objective of this study was to establish in vivo 
the relationship between 2-2-nitro-1H-imidazol-1yl-N-(2,2,3,3,3-pentafluoropropyl)-acetamide 
(EF5) adduct formation and intratumoral oxygen concentrations measured by electron
paramagnetic resonance (EPR) in a tumor model mimicking a clinical situation. The secondary 
objective was an attempt to calibrate in situ the immunofluorescence (IF) signal with EPR oximetry.

Materials and METHODS: IM syngeneic fibrosarcoma (NFSA) bearing C3H mice were used. 
Three days after injection of a paramagnetic charcoal into the tumor, the mice were anesthetized,
injected with the hypoxic marker EF5, and monitored every 20 min for 3 h with a low-frequency 
EPR spectrometer. Animals were allowed to breath either under 21 or 100% O(2). 
Tumors were then harvested, frozen, cut into sections including the charcoal and processed 
for EF5 adducts detection using monoclonal antibodies. Slices were viewed with a fluorescence 
microscope and 190x140 &mgr;m areas surrounding the charcoal were digitized and analyzed with the NIH-Image
and Adobe Photoshop software. The fluorescence intensity (FI) was measured in the whole pictures 
and in strips of 10 &mgr;m around the charcoal.

RESULTS: EF5 binding increased with decreasing pO(2), most substantially at pO(2) below 5 mm Hg. 
Baseline (ambient air) pO(2) reached 3.2+/-2.1 mm Hg in NFSA tumors. It increased to 9.8+/-3.2 mm 
Hg under 100% O(2). A statistically significant correlation was observed on an individual tumor 
basis between the FI in the first 10 &mgr;m strip around the charcoal and the pO(2) determined by 
EPR oximetry (Wilcoxon signed rank test: P<0.001).

CONCLUSIONS: The present study confirms the intrinsic relationship between EF5 adduct 
binding and intratumoral pO(2) in an in vivo environment under biologically-relevant pO(2) values of less
than 10 mm Hg. 

PMID: 12758240 [PubMed - as supplied by publisher]