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Review

l-[ methyl-11C]Methionine

Kam Leung  1
In: Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004.
[updated ].
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Review

l-[ methyl-11C]Methionine

Kam Leung.
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Excerpt

A variety of [11C] and [18F] labeled amino acids have been studied for potential use in positron emission tomography (PET) oncology (1, 2). Most brain tumors show an increased uptake of amino acids as compared with normal brain (3). These amino acids are composed of naturally occurring amino acids such as, L-[11C]leucine, L-[11C]methionine (MET), and L-[11C]tyrosine and non-natural amino acids such as [11C]aminoisobutyric acid, [11C]1-aminocyclopentane-1-carboxylic acid, and [11C]1-aminocyclobutane-1-carboxylic acid. There are also 123I-labeled amino acids used in imaging in oncology (1, 4, 5).

Some 20 amino acid transporter systems have been identified (1). Most of the amino acids are taken up by tumor cells through an energy-independent L-type amino acid transporter system and a sodium-dependent transporter system A but also a Na+-dependent system B0 (6). They are retained in tumor cells due to their higher metabolic activities including incorporation into proteins than most normal cells (1). Malignant transformation increases the use of amino acids for energy, protein synthesis and cell division. Tumor cells were found to have over-expressed transporter systems (7). L-[11C]MET, [18F]fluorotyrosine, L-[11C]leucine, and [18F]fluoro-α-methyl tyrosine have been widely used in detection of tumors (2, 6) but are not approved by the United States Food and Drug Administration. They are moved into cells by various amino acid transporters and are incorporated into proteins. The fraction of radiolabeled amino acid that is incorporated into protein is usually small compared to the total amount taken up into the cell. These natural amino acid images are based on amino acid transport and protein incorporation.

[11C]MET has been widely used in detection of brain, head and neck, lung, and breast cancer as well as lymphomas [PubMed]. It can cross the blood-brain barrier. It is incorporated mainly into proteins but also into lipid, RNA, and DNA. [11C]MET PET imaging is more sensitive to radiotherapy compared to FDG and is useful for monitoring treatment of cancer.

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References

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