Fasting Enhances the Contrast of Bone Metastatic Lesions in 18F-Fluciclovine-PET: Preclinical Study Using a Rat Model of Mixed Osteolytic/Osteoblastic Bone Metastases

F-18-fluciclovine (trans-1-amino-3-F-18-fluorocyclobutanecarboxylic acid) is an amino acid positron emission tomography (PET) tracer used for cancer staging (e.g., prostate and breast). Patients scheduled to undergo amino acid-PET are usually required to fast before PET tracer administration. However, there have been no reports addressing whether fasting improves fluciclovine-PET imaging. In this study, the authors investigated the influence of fasting on fluciclovine-PET using triple-tracer autoradiography with C-14-fluciclovine, [5,6-3H]-2-fluoro-2-deoxy-D-glucose (H-3-FDG), and Tc-99m-hydroxymethylene diphosphonate (Tc-99m-HMDP) in a rat breast cancer model of mixed osteolytic/osteoblastic bone metastases in which the animals fasted overnight. Lesion accumulation of each tracer was evaluated using the target-to-background (muscle) ratio. The mean ratios of C-14-fluciclovine in osteolytic lesions were 4.6 +/- 0.8 and 2.8 +/- 0.6, respectively, with and without fasting, while those for H-3-FDG were 6.9 +/- 2.5 and 5.1 +/- 2.0, respectively. In the peri-tumor bone formation regions (osteoblastic), where Tc-99m-HMDP accumulated, the ratios of C-14-fluciclovine were 4.3 +/- 1.4 and 2.4 +/- 0.7, respectively, and those of 3H-FDG were 6.2 +/- 3.8 and 3.3 +/- 2.2, respectively, with and without fasting. These results suggest that fasting before F-18-fluciclovine-PET improves the contrast between osteolytic and osteoblastic bone metastatic lesions and background, as well as F-18-FDG-PET.