There are over 420 human Solute Carrier transporters (SLCs) from 65 families that are expressed ubiquitously in the body. The SLCs mediate the movement of ions, drugs, and metabolites across membranes, and their dysfunction has been associated with a variety of diseases, such as diabetes, cancer, and central nervous system disorders. Thus, the SLCs are emerging as important targets for therapeutic intervention. Recent technological advancements in experimental and computational biology allow better characterization of SLC pharmacology. Here we describe recent approaches to modulate SLC transporter function, with an emphasis on the use of computational approaches and computer-aided drug design to study nutrient transporters. Finally, we discuss future perspectives in the rational design of SLC drugs.

The neutral amino acid transporter alanine serine cysteine transporter 2 (ASCT2) belongs to the solute carrier 1 (SLC1) family of transport proteins and transports neutral amino acids, such as alanine and glutamine, into the cell in exchange with intracellular amino acids. This amino acid transport is sodium dependent, but not driven by the transmembrane Na+ concentration gradient. Glutamine transport by ASCT2 is proposed to be important for glutamine homoeostasis in rapidly growing cancer cells to fulfill the energy and nitrogen demands of these cells. Thus, ASCT2 is thought to be a potential anticancer drug target. However, the pharmacology of the amino acid binding site is not well established. Here, we report on the synthesis and characterization of a novel class of ASCT2 inhibitors based on an amino acid scaffold with a sulfonamide/sulfonic acid ester linker to a hydrophobic group. The compounds were designed based on an improved ASCT2 homology model using the human glutamate transporter hEAAT1 crystal structure as a modeling template. The compounds were shown to inhibit with a competitive mechanism and a potency that scales with the hydrophobicity of the side chain. The most potent compound binds with an apparent affinity, Ki, of 8 ± 4 µM and can block the alanine response with a Ki of 40 ± 23 µM at 200 µM alanine concentration. Computational analysis predicts inhibitor interactions with the binding site through molecular docking. In conclusion, the sulfonamide/sulfonic acid ester scaffold provides facile synthetic access to ASCT2 inhibitors with a potentially large variability in chemical space of the hydrophobic side chain. These inhibitors will be useful chemical tools to further characterize the role of ASCT2 in disease as well as improve our understanding of inhibition mechanisms of this transporter.

The evolutionarily conserved Hippo inhibitory pathway plays critical roles in tissue homeostasis and organ size control, while mutations affecting certain core components contribute to tumorigenesis. Here we demonstrate that proliferation of Hippo pathway mutant human tumor cells exhibiting high constitutive TEAD transcriptional activity was markedly inhibited by dominant negative TEAD4, which did not inhibit the growth of Hippo wild-type cells with low levels of regulatable TEAD-mediated transcription. The tankyrase inhibitor, XAV939, identified in a screen for inhibitors of TEAD transcriptional activity, phenocopied these effects independently of its other known functions by stabilizing angiomotin and sequestering YAP in the cytosol. We also identified one intrinsically XAV939 resistant Hippo mutant tumor line exhibiting lower and less durable angiomotin stabilization. Thus, angiomotin stabilization provides a new mechanism for targeting tumors with mutations in Hippo pathway core components as well as a biomarker for sensitivity to such therapy.

The Alanine-Serine-Cysteine transporter (SLC1A5, ASCT2), is a neutral amino acid exchanger involved in the intracellular homeostasis of amino acids in peripheral tissues. Given its role in supplying glutamine to rapidly proliferating cancer cells in several tumor types such as triple-negative breast cancer and melanoma, ASCT2 has been identified as a key drug target. Here we use a range of computational methods, including homology modeling and ligand docking, in combination with cell-based assays, to develop hypotheses for structure-function relationships in ASCT2. We perform a phylogenetic analysis of the SLC1 family and its prokaryotic homologs to develop a useful multiple sequence alignment for this protein family. We then generate homology models of ASCT2 in two different conformations, based on the human EAAT1 structures. Using ligand enrichment calculations, the ASCT2 models are then compared to crystal structures of various homologs for their utility in discovering ASCT2 inhibitors. We use virtual screening, cellular uptake and electrophysiology experiments to identify a non-amino acid ASCT2 inhibitor that is predicted to interact with the ASCT2 substrate binding site. Our results provide insights into the structural basis of substrate specificity in the SLC1 family, as well as a framework for the design of future selective and potent ASCT2 inhibitors as cancer therapeutics.

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