TY - JOUR T1 - Defining Substrate and Blocker Activity of Alanine Serine Cysteine Transporter 2 (ASCT2) Ligands with Novel Serine Analogs JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.111.075648 SP - mol.111.075648 AU - Thomas Albers AU - William Marsiglia AU - Taniya Thomas AU - Armanda Gameiro AU - Christof Grewer Y1 - 2011/11/23 UR - http://molpharm.aspetjournals.org/content/early/2011/11/23/mol.111.075648.abstract N2 - The neutral amino acid transporter ASCT2 belongs to the SLC1 family of solute transporters and transports small, neutral amino acids across the membrane, including the physiologically important and ubiquitous amino acid glutamine. Our understanding of the involvement of ASCT2 in the physiological processes involving glutamine is hampered by a lack of understanding of its pharmacology and the absence of high-affinity inhibitors. In this study, we combined an in-silico docking approach with experimental investigation of binding parameters to develop new ASCT2 inhibitors and substrates, a series of serine esters, and to determine structural parameters that govern their functional effects. The series of compounds was synthesized using standard methods and exhibited a range of properties, from inhibitors to partial substrates, and full substrates. Our results suggest that amino acid derivatives with small side-chain volume and low side chain hydrophobicity interact strongly with the closed-loop form of the binding site, in which reentrant loop 2, the presumed extracellular gate for the substrate binding site, is closed off. However, these derivatives bind weakly to the open-loop form (external gate open to the extracellular side), acting as transported substrates. In contrast, inhibitors bind preferentially to the open-loop form. An aromatic residue in the side-chain is required for high-affinity interaction. One of the compounds, the L-serine ester serine biphenyl-4-carboxylate reversibly inhibits ASCT2 function with an apparent affinity of 30 μM. ER -