In vitro evaluation of (S)-2-amino-3-[3-(2-18F-fluoroethoxy)-4-iodophenyl]-2-methylpropanoic acid (18F-FIMP) as a positron emission tomography probe for imaging amino acid transporters

• Published in: EJNMMI research Vol. 13; no. 1; p. 36
• Main Authors: Nozaki, Satoshi, Nakatani, Yuka, Mawatari, Aya, Hume, William Ewan, Doi, Hisashi, Watanabe, Yasuyoshi
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 28.04.2023; Springer Nature B.V; SpringerOpen
• Subjects: Affinity; Alanine; Amino acid transporter; Amino acids; Bioaccumulation; Cardiac Imaging; Fluorine isotopes; Imaging; Inhibitors; Isobutyric acid; L-type amino acid transporter 1; Medical imaging; Medicine; Medicine & Public Health; Nuclear Medicine; Oncology; Original Research; Orthopedics; Positron emission; Positron emission tomography; Radiology; Ribonucleic acid; RNA; Substrates; Tumor; Tumors; Amino acid transporter; Tumor; L-type amino acid transporter 1; Positron emission tomography
• ISSN: 2191-219X; 2191-219X
• DOI: 10.1186/s13550-023-00988-1

Background ( S )-2-amino-3-[3-(2- 18 F-fluoroethoxy)-4-iodophenyl]-2-methylpropanoic acid ( 18 F-FIMP) as a promising PET probe for imaging the tumor-specific L-type amino acid transporter (LAT) 1. Our previous study revealed that 18 F-FIMP had a higher affinity for LAT1 than for LAT2 abundantly expressed even in normal cells. 18 F-FIMP showed high accumulation in LAT1-positive tumor tissues and low accumulation in inflamed lesions in tumor-bearing mice. However, the affinity of 18 F-FIMP for other amino acid transporters was not determined yet. Here, we aimed to determine whether 18 F-FIMP has affinity for other tumor-related amino acid transporters, such as sodium- and chloride-dependent neutral and basic amino acid transporter B(0 +) (ATB 0,+ ), alanine serine cysteine transporter 2 (ASCT2), and cystine/glutamate transporter (xCT). Procedures Cells overexpressing LAT1, ATB 0,+ , ASCT2, or xCT were established by the transfection of expression vectors for LAT1, ATB 0,+ , ASCT2, or xCT. Protein expression levels were determined by western blot and immunofluorescent analyses. Transport function was evaluated by a cell-based uptake assay using 18 F-FIMP and 14 C-labeled amino acids as substrates. Results Intense signals were observed only for expression vector-transfected cells on western blot and immunofluorescent analyses. These signals were strongly reduced by gene-specific small interfering ribonucleic acid treatment. The uptake values for each 14 C-labeled substrate were significantly higher in the transfected cells than in the mock-transfected cells and were significantly inhibited by the corresponding specific inhibitors. The 18 F-FIMP uptake values were significantly higher in the LAT1- and ATB 0,+ -overexpressing cells than in the corresponding mock cells, but no such increase was seen in the ASCT2- or xCT-overexpressing cells. These 18 F-FIMP uptake values were significantly decreased by the specific inhibitors for LAT1- and ATB 0,+ . Conclusions We demonstrated that 18 F-FIMP has affinity not only for LAT1, but also for ATB 0,+ . Our results may be helpful for understanding the mechanisms of the whole-body distribution and tumor accumulation of 18 F-FIMP.