The present study compares the uptake of [(18)F]Fluoroazomycinarabinofuranoside ((18)FAZA),
a recently developed hypoxia tracer for PET imaging of tissue hypoxia, with an established
tracer [(18)F]Fluoromisonidazole ((18)FMISO) both in vitro, using Walker 256 rat carcinosarcoma
cells, and in vivo in experimental rat tumors eleven to twelve days after tumor cell
implantation. In vitro studies indicated that hypoxia-selective uptake of both (18)FAZA
and (18)FMISO in tumor cells, 20 and 100 minutes post-incubation was of the same magnitude
(20 min: 1.24 +/- 0.4% ((18)FAZA); 1.19 +/- 0.7% ((18)FMISO); 100 min: 3.6 +/- 1.6%
((18)FAZA); 3.3 +/- 1.7% ((18)FMISO)). PET imaging reflected a similar radiotracer
distribution in rat tumors for (18)FAZA and (18)FMISO one h after radiotracer injection.
The concentration of (18)FAZA in the tumors as measured by PET, however, was lower
in comparison to (18)FMISO (SUV(FAZA) = 0.61 +/- 0.2 vs. SUV(FMISO) = 0.92 +/- 0.3,
p < 0.05) although the tumor to muscle ratios for (18)FAZA and (18)FMISO did not differ
in the PET images that were obtained after one h (SUV(FAZA) = 2.5 +/- 0.5 vs. SUV(FMISO)
= 2.9 +/- 0.7). A comparison of PET data three h post-injection (SUV(FAZA) = 3.0 +/-
0.5 vs. SUV(FMISO) = 4.6 +/- 1.8, p < 0.05) demonstrated a lower (18)FAZA uptake that
indicates a lower sensitivity of (18)FAZA in comparison to (18)FMISO in detecting
hypoxic regions at a longer time in this animal model. However, these data also show
a faster elimination of (18)FAZA from blood, viscera and muscle tissue, via the renal
system. This advantage of a faster reduction of unspecific binding, in light of similar
or marginally lower tumor uptake, warrants further investigation of (18)FAZA as a
marker of regional hypoxia in tumors.