L‐type amino acid transporter 1 as a potential molecular target in human astrocytic tumors

Abstract

L-type amino acid transporter 1 (LAT1) is a Na 1 -independent neutral amino acid transport agency and essential for the transport of large neutral amino acids. LAT1 has been identified as a light chain of the CD98 heterodimer from C6 glioma cells. LAT1 also corresponds to TA1, an oncofetal antigen that is expressed primarily in fetal tissues and cancer cells. We have investigated for the first time, the expression of the transporter in the human primary astrocytic tumor tissue from 60 patients. LAT1 is unique because it requires an additional single membrane spanning protein, the heavy chain of 4F2 cell surface antigen (4F2hc), for its functional expression. 4F2hc expression was also determined by immunohistochemistry. Kaplan-Meier analyses demonstrated that high LAT1 expression correlated with poor survival for the study group as a whole (p < 0.0001) and for those with glioblastoma multiforme in particular (p 5 0.0001). Cox regression analyses demonstrated that LAT1 expression was one of significant predictors of outcome, independent of all other variables. On the basis of these findings, we also investigated the effect of the specific inhibitor to LAT1, 2-aminobicyclo-2 (2,2,1)-heptane-2-carboxylic acid (BCH), on the survival of C6 glioma cells in vitro and in vivo using a rat C6 glioma model. BCH inhibited the growth of C6 glioma cells in vitro and in vivo in a dose-dependent manner. KaplanMeier survival data of rats treated with BCH were significant. These findings suggest that LAT1 could be one of the molecular targets in glioma therapy. ' 2006 Wiley-Liss, Inc.

Radiosynthesis and biological evaluation of alpha-[F-18]fluoromethyl phenylalanine for brain tumor imaging

“…[ 18 F]fluoride was produced using an RDS-11 cyclotron in the Washington University Cyclotron Facility using [ 18 18 F was achieved by heating the reaction mixture in an oil bath (105 °C) for 15 min. Incorporation of [ 18 F]fluoride was estimated using radiometric thin layer chromatography (radio-TLC) analysis with silica gel TLC plates developed using, 1:1 methanol:water.…”

“…The racemic final product [ 18 F]9 was purified by chiral HPLC using an Chirobiotic Tag column (5μm × 25cm × 10.0mm) eluted with 92% CH 3 CN, 8% water for 10 min, then changed to 85% CH 3 CN, 15% water at a flow rate of 3 mL/min. The radioactive peaks corresponding to the single enantiomers of [ 18 The radiochemical and enantiomeric purity and specific activity of the final product were assessed using chiral analytical HPLC (Chirobiotic Tag column 150 mm × 4.6 mm, 20 μ, 80:20 CH 3 CN: water, 1 mL/min, 220 nm). The mass associated with the 18 F-labeled product determined by comparison of the integrated UV absorbance with a calibrated mass/UV absorbance standard curve of non-radioactive (R,S)-9.…”

“…Based on radiometric TLC monitoring, the fluorine-18 incorporation step showed >90% yield of the presumed 18 …”

“…Previous work has demonstrated that the 18 F-labeled α,α-dialkyl amino acids 2-amino-3-[ 18 F]fluoro-2-methyl propanoic acid (FAMP) and its N-methyl analogue MeFAMP can be labeled in very high yield (up to ~80% decay corrected yield) and radiochemical purity through cyclic sulfamidate precursors. These tracers are analogues of α-aminoisobutyric acid and are substrates for system A transport.…”

“…First, the ability to prepare 18 Flabeled system L transport substrates in very high radiochemical yield through a simple and reliable radiosynthesis using nucleophilic [ 18 F]fluorination would facilitate batch productions and dissemination of these tracers to other sites. Second, using the α-fluoromethyl group as the site of labeling frees the phenyl ring for structural modifications.…”