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

(18)F-fluciclovine (trans-1-amino-3-(18)F-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 (14)C-fluciclovine, [5,6-(3)H]-2-fluoro-2-deoxy-d-glucose ((3)H-FDG), and (99m)Tc-hydroxymethylene diphosphonate ((99m)Tc-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 (14)C-fluciclovine in osteolytic lesions were 4.6 ± 0.8 and 2.8 ± 0.6, respectively, with and without fasting, while those for (3)H-FDG were 6.9 ± 2.5 and 5.1 ± 2.0, respectively. In the peri-tumor bone formation regions (osteoblastic), where (99m)Tc-HMDP accumulated, the ratios of (14)C-fluciclovine were 4.3 ± 1.4 and 2.4 ± 0.7, respectively, and those of (3)H-FDG were 6.2 ± 3.8 and 3.3 ± 2.2, respectively, with and without fasting. These results suggest that fasting before (18)F-fluciclovine-PET improves the contrast between osteolytic and osteoblastic bone metastatic lesions and background, as well as (18)F-FDG-PET.