18F-fluoroacetate: a potential acetate analog for prostate tumor imaging--in vivo evaluation of 18F-fluoroacetate versus 11C-acetate.

UNLABELLED: PET with (11)C-acetate ((11)C-ACE) has a high sensitivity for detection of prostate cancer and several other cancers that are poorly detected with (18)F-FDG. However, the short half-life (20.4 min) of (11)C limits the general availability of (11)C-ACE. (18)F-Fluoroacetate ((18)F-FAC) is an analog of acetate with a longer radioactive half-life ((18)F = 110 min). This study was undertaken to assess the potential usefulness of (18)F-FAC as a prostate tumor imaging agent. METHODS: We developed an efficient radiosynthesis for (18)F-FAC, which has already been adapted to a commercial synthesizer. Biodistribution studies of (18)F-FAC were compared with (11)C-ACE in normal Sprague-Dawley male rats and CWR22 tumor-bearing nu/nu mice. We also performed a small-animal PET study of (18)F-FAC in CWR22 tumor-bearing nu/nu mice and a whole-body PET study in a baboon to examine defluorination. RESULTS: We obtained (18)F-FAC in a radiochemical yield of 55% +/- 5% (mean +/- SD) in approximately 35 min and with a radiochemical purity of >99%. Rat biodistribution showed extensive defluorination, which was not observed in the baboon PET, as indicated by the standardized uptake values (SUVs) (SUVs of iliac bones and femurs were 0.26 and 0.3 at 1 h and 0.22 and 0.4 at 2 h, respectively). CWR22 tumor-bearing nu/nu mice showed tumor uptake (mean +/- SD) of 0.78 +/- 0.06 %ID/g (injected dose per gram of tissue) for (11)C-ACE versus 4.01 +/- 0.32 %ID/g for (18)F-FAC. For most organs-except blood, muscle, and fat-the tumor-to-organ ratios at 30 min after injection were higher with (18)F-FAC, whereas the tumor-to-heart and tumor-to-prostate ratios were similar. CONCLUSION: All of these data indicate that (18)F-FAC may be a useful alternative to (11)C-ACE tracer for the detection of prostate tumors by PET.