Synthesis and evaluation of 2-amino-4-[(18)F]fluoro-2-methylbutanoic acid (FAMB): relationship of amino acid transport to tumor imaging properties of branched fluorinated amino acids.

Radiolabeled amino acids represent a promising class of tumor imaging agents, and the determination of the optimal characteristics of these tracers remains an area of active investigation. A new (18)F-labeled branched amino acid, 2-amino-4-[(18)F]fluoro-2-methylbutanoic acid (FAMB), has been prepared in 36% decay-corrected yield using no-carrier-added [(18)F]fluoride. In vitro uptake assays with rat 9L gliosarcoma cells suggest that [(18)F]FAMB was transported primarily via the L type amino acid transport system. In vivo studies with [(18)F]FAMB demonstrated tumor to normal brain ratios of 14:1 in rats with intracranial 9L gliosarcoma tumors at 60 minutes after injection. Comparison of [(18)F]FAMB with structurally related (18)F-labeled branched amino acids demonstrated that A type transport in vitro was positively correlated with the tumor to brain ratios observed in vivo.