Leung Kam
National Center for Biotechnology Information, NLM, NIH, Bethesda, MD
A variety of [C] and [F] 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-[C]leucine, L-[C]methionine (MET), and L-[C]tyrosine and non-natural amino acids such as [C]aminoisobutyric acid, [C]1-aminocyclopentane-1-carboxylic acid, and [C]1-aminocyclobutane-1-carboxylic acid. There are also I-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 B (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-[C]MET, [F]fluorotyrosine, L-[C]leucine, and [F]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. [C]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. [C]MET PET imaging is more sensitive to radiotherapy compared to FDG and is useful for monitoring treatment of cancer.
人们对多种碳（[C]）和氟（[F]）标记的氨基酸进行了研究，以探讨其在正电子发射断层扫描（PET）肿瘤学中的潜在应用（1, 2）。与正常脑组织相比，大多数脑肿瘤对氨基酸的摄取增加（3）。这些氨基酸包括天然存在的氨基酸，如L-[C]亮氨酸、L-[C]蛋氨酸（MET）和L-[C]酪氨酸，以及非天然氨基酸，如[C]氨基异丁酸、[C]1-氨基环戊烷-1-羧酸和[C]1-氨基环丁烷-1-羧酸。肿瘤学成像中也使用碘（I）标记的氨基酸（1, 4, 5）。已鉴定出约20种氨基酸转运系统（1）。大多数氨基酸通过能量非依赖型L型氨基酸转运系统、钠依赖型转运系统A以及钠依赖型系统B被肿瘤细胞摄取（6）。由于它们的代谢活性较高，包括比大多数正常细胞更多地掺入蛋白质，因此它们被保留在肿瘤细胞中（1）。恶性转化增加了氨基酸在能量、蛋白质合成和细胞分裂中的使用。研究发现肿瘤细胞中转运系统过度表达（7）。L-[C]MET、[F]氟酪氨酸、L-[C]亮氨酸和[F]氟-α-甲基酪氨酸已广泛用于肿瘤检测（2, 6），但未获美国食品药品监督管理局批准。它们通过各种氨基酸转运体进入细胞并掺入蛋白质中。与细胞摄取的总量相比，掺入蛋白质中的放射性标记氨基酸的比例通常较小。这些天然氨基酸图像基于氨基酸转运和蛋白质掺入。[C]MET已广泛用于脑、头颈部、肺和乳腺癌以及淋巴瘤的检测[医学期刊数据库]。它可以穿过血脑屏障。它主要掺入蛋白质，但也掺入脂质、RNA和DNA。与氟代脱氧葡萄糖（FDG）相比，[C]MET PET成像对放疗更敏感，可用于监测癌症治疗。
