Synthesis and evaluation of an F-labeled boramino acid analog of aminosuberic acid for PET imaging of the antiporter system x<sup/>.

In this study, we synthesized F-ASu-BF, a close boramino acid analog of 5-[F]fluoro-aminosuberic acid (F-ASu), via F-F isotope exchange reaction and evaluated its potential for imaging with positron emission tomography (PET). F-ASu-BF was stable in mouse plasma and taken up into PC3 prostate cancer cells via the system x amino acid transporter. The continuous use of isoflurane for anesthesia during dynamic imaging acquisition slowed down the excretion of F-ASu-BF and enabled visualization of PC3 tumor xenografts in mice. In contrast, no tumor visualization was observed from static images of F-BF-ASu due to its rapid renal excretion mediated in part by the organic anion transporter. Our data indicate that the pharmacokinetics of amino acids could be altered after being converted into their boramino acid analogs. Therefore, care should be taken when using the boramino acid strategy to design and prepare F-labeled tracers for imaging amino acid transporters/receptors with PET.