Automated Synthesis of¹⁸F-Fluoropropoxytryptophan for Amino Acid Transporter System Imaging

Abstract

Objective. This study was to develop a cGMP grade of [18F]fluoropropoxytryptophan (18F-FTP) to assess tryptophan transporters using an automated synthesizer. Methods. Tosylpropoxytryptophan (Ts-TP) was reacted with K18F/kryptofix complex. After column purification, solvent evaporation, and hydrolysis, the identity and purity of the product were validated by radio-TLC (1M-ammonium acetate : methanol = 4 : 1) and HPLC (C-18 column, methanol : water = 7 : 3) analyses. In vitro cellular uptake of 18F-FTP and 18F-FDG was performed in human prostate cancer cells. PET imaging studies were performed with 18F-FTP and 18F-FDG in prostate and small cell lung tumor-bearing mice (3.7 MBq/mouse, iv). Results. Radio-TLC and HPLC analyses of 18F-FTP showed that the Rf and Rt values were 0.9 and 9 min, respectively. Radiochemical purity was >99%. The radiochemical yield was 37.7% (EOS 90 min, decay corrected). Cellular uptake of 18F-FTP and 18F-FDG showed enhanced uptake as a function of incubation time. PET imaging studies showed that 18F-FTP had less tumor uptake than 18F-FDG in prostate cancer model. However, 18F-FTP had more uptake than 18F-FDG in small cell lung cancer model. Conclusion. 18F-FTP could be synthesized with high radiochemical yield. Assessment of upregulated transporters activity by 18F-FTP may provide potential applications in differential diagnosis and prediction of early treatment response.

Assessment of Tryptophan Uptake and Kinetics Using 1-(2-18F-Fluoroethyl)-l-Tryptophan and α-11C-Methyl-l-Tryptophan PET Imaging in Mice Implanted with Patient-Derived Brain Tumor Xenografts

“…Several novel 18 F-labeled tryptophan derivatives have been developed and tested as potential PET tracers for tumor imaging (27)(28)(29)(30)(31)(32). Although most compounds showed tumor uptake, they were not designed to target IDO1, IDO12, or TDO2 activity.…”

Upgrades and regulatory aspects of [18F]Fluorodeoxyglucose ([18F]FDG) production using the FASTLab2 synthesizer

“…Generally, cassette-based automated synthesis module is widely used among the centers that routinely produce [ 18 F] FDG for commercial purposes as such systems facilitate compliance with regulatory requirements, specifically current Good Manufacturing Practice (cGMP) and Radiation safety [6,7]. The cassette-based automated synthesis module comprises three main components: hardware, software, and consumables.…”