Feasibility of labeled alpha-acetamido-aminoisobutyric acid as new tracer compound for kinetic labeling of neutral amino acid transport: preparation of alpha-(N-[1-11C]acetyl)- and alpha-(N-[1-14C]acetyl)-aminoisobutyric acid

Carbon-11 and Fluorine-18 Labeled Amino Acid Tracers for Positron Emission Tomography Imaging of Tumors

Tumor cells have an increased nutritional demand for amino acids (AAs) to satisfy their rapid proliferation. Positron-emitting nuclide labeled AAs are interesting probes and are of great importance for imaging tumors using positron emission tomography (PET). Carbon-11 and fluorine-18 labeled AAs include the [1-¹¹C] AAs, labeling alpha-C- AAs, the branched-chain of AAs and N-substituted carbon-11 labeled AAs. These tracers target protein synthesis or amino acid (AA) transport, and their uptake mechanism mainly involves AA transport. AA PET tracers have been widely used in clinical settings to image brain tumors, neuroendocrine tumors, prostate cancer, breast cancer, non-small cell lung cancer (NSCLC) and hepatocellular carcinoma. This review focuses on the fundamental concepts and the uptake mechanism of AAs, AA PET tracers and their clinical applications.

Radiosynthesis and biological evaluation of N-[18F]labeled glutamic acid as a tumor metabolic imaging tracer

We have previously reported that N-(2-[¹⁸F]fluoropropionyl)-L-methionine ([¹⁸F]FPMET) selectively accumulates in tumors. However, due to the poor pharmacokinetics of [¹⁸F]FPMET in vivo, the potential clinical translation of this observation is hampered. In this study, we rationally designed and synthesized [¹⁸F] or [¹¹C]labeled N-position L-glutamic acid analogues for tumor imaging. N-(2-[¹⁸F]fluoropropionyl)-L-glutamic acid ([¹⁸F]FPGLU) was synthesized with a 30±10% (n = 10, decay-corrected) overall radiochemical yield and a specific activity of 40±25 GBq/μmol (n = 10) after 130 min of radiosynthesis. In vitro cell experiments showed that [¹⁸F]FPGLU was primarily transported through the X_AG^– system and was not incorporated into protein. [¹⁸F]FPGLU was stable in urine, tumor tissues, and blood. We were able to use [¹⁸F]FPGLU in PET imaging and obtained high tumor to background ratios when visualizing tumors tissues in animal models.