System L amino acid transporter LAT1 accumulates O-(2-fluoroethyl)-L-tyrosine (FET).
O-(2-fluoroethyl)-L-tyrosine (FET) labeled with fluorine-18 is an important and specific tracer for diagnostics of glioblastoma via positron emission tomography (PET). However, the mechanism of its quite specific accumulation in tumor tissue has not been understood so far. In this work we demonstrate that [(3)H]L-tyrosine is primarily transported by the system L transporter LAT1 in human LN229 glioblastoma cells. FET reduced tyrosine transport, suggesting that it shares the same uptake pathway. More importantly, accumulation of FET was significantly reduced after siRNA-mediated downregulation of LAT1. Xenopus laevis oocytes expressing human LAT1 together with the glycoprotein 4F2hc (necessary to pull LAT-1 to the plasma membrane) exhibited a similar accumulation of FET as observed in glioblastoma cells. In contrast, no accumulation was observed in control oocytes, not overexpressing an exogenous transporter. Because LAT1 works exclusively as an exchanger of amino acids, substrates at one side of the membrane stimulate exchange against substrates at the other side. Extracellular FET stimulated the efflux of intracellular [(3)H]L-leucine, demonstrating that FET is indeed an influx substrate for LAT1. However, FET injected into oocytes was not able to stimulate uptake of extracellular [(3)H]L-leucine, indicating that FET is not a good efflux substrate. Our data, therefore, suggest that FET is trapped within cells due to the asymmetry of its intra- and extracellular recognition by LAT1. If also found for other transporters in tumor cells, asymmetric substrate recognition may be further exploited for tumor-specific accumulation of PET-tracers and/or other tumor-related drugs.
Institut of Pharmacology, University Medical Center of the Johannes Gutenberg University, Obere Zahlbacher Straße 67, 55270, Mainz, Germany.
A
A
Habermeier
J
J
Graf
B F
BF
Sandhöfer
J-P
JP
Boissel
F
F
Roesch
Ellen I
EI
Closs
D000818:Animals; D045744:Cell Line, Tumor; D003287:Contrast Media; D027282:Fusion Regulatory Protein 1, Heavy Chain / Q000235:genetics / Q000378:metabolism; D005909:Glioblastoma / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D027283:Large Neutral Amino Acid-Transporter 1 / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D049268:Positron-Emission Tomography; D011859:Radiography; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D014982:Xenopus laevis
D003287:Contrast Media; D027282:Fusion Regulatory Protein 1, Heavy Chain; D027283:Large Neutral Amino Acid-Transporter 1; D009363:Neoplasm Proteins; C117289:O-(2-fluoroethyl)tyrosine; C545989:SLC3A2 protein, human; D014443:Tyrosine