¹⁸F-fluoroacetate: A potential acetate analog for prostate tumor imaging - In vivo evaluation of ¹⁸F-fluoroacetate versus ¹¹C-acetate

PET with ¹¹C-acetate (¹¹C-ACE) has a high sensitivity for detection of prostate cancer and several other cancers that are poorly detected with ¹⁸F-FDG. However, the short half-life (20.4 min) of ¹¹C limits the general availability of ¹¹C-ACE. ¹⁸F-Fluoroacetate (¹⁸F-FAC) is an analog of acetate with a longer radioactive half-life (¹⁸F = 110 min). This study was undertaken to assess the potential usefulness of ¹⁸F-FAC as a prostate tumor imaging agent. Methods: We developed an efficient radiosynthesis for ¹⁸F-FAC, which has already been adapted to a commercial synthesizer. Biodistribution studies of ¹⁸F-FAC were compared with ¹¹C-ACE in normal Sprague-Dawley male rats and CWR22 tumor-bearing nu/nu mice. We also performed a small-animal PET study of ¹⁸F-FAC in CWR22 tumor-bearing nu/nu mice and a whole-body PET study in a baboon to examine defluorination. Results: We obtained ¹⁸F-FAC in a radiochemical yield of 55% ± 5% (mean ± SD) in ∼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 ¹¹C-ACE versus 4.01 ± 0.32 %ID/g for ¹⁸F-FAC. For most organs - except blood, muscle, and fat - the tumor-to-organ ratios at 30 min after injection were higher with ¹⁸F-FAC, whereas the tumor-to-heart and tumor-to-prostate ratios were similar. Conclusion: All of these data indicate that ¹⁸F-FAC may be a useful alternative to ¹¹C-ACE tracer for the detection of prostate tumors by PET.