Radiosynthesis and Biological Evaluation of l- and d-S-(3-[18F]Fluoropropyl)homocysteine for Tumor Imaging Using Positron Emission Tomography
摘要:
Interest in radiolabeled amino acids for metabolic imaging of cancer and limitations with [C-11]methionine has prompted the development of a new F-18-labeled methionine derivative S-(3-[F-18]fluoropropyl)homocysteine ([F-18]FPHCys). The L and D enantiomers of [F-18]FPHCys were prepared from their respective protected S-(3-tosyloxypropyl)homocysteine precursors 1 by [F-18]fluoride substitution using K-2.2.2 and potassium oxalate, followed by acid hydrolysis on a Tracerlab FXFN synthesis module. [F-18]-L-FPHCys and [F-18]-D-FPHCys were isolated in 20 +/- 5% radiochemical yield and >98% radiochemical and enantiomeric purity in 65 mm. Competitive Take studies in A375 and HT29 tumor cells suggest that L- and n-[F-18]FPHCys are taken up by the L-transporter system. [F-18]-L-FPHCys and [F-18]-D-FPHCys displayed good stability In Vivo without incorporation into protein at least 2 h postinjection. Biodistribution studies demonstrate good uptake in A375 tumor-bearing rodents with tumor to blood ratios of 3.5 and 5.0 for [F-18]-L-FPHCys and [F-18]-D-FPHCys, respectively, at 2 h postinjection.