Abstract 1043: Targeting ASCT2-mediated glutamine uptake and metabolism in breast cancer
Authors: van Geldermalsen Michelle , Wang Qian , Holst Jeff 
Published: July 2016

Although a nonessential amino acid in normal cell growth, the demand for glutamine is dramatically increased throughout malignant transformation to provide catabolic substrates for ATP production and anabolic substrates for macromolecule biosynthesis. To maintain glutamine availability for these metabolic processes, cancer cells overexpress cell surface transporters that function to exchange amino acids across the plasma membrane. One such transporter is ASCT2 (alanine, serine, cysteine-preferring transporter 2; SLC1A5), a sodium-dependent symporter that mediates uptake of small, neutral amino acids, including glutamine.

Blocking ASCT2 to prevent glutamine uptake and glutaminolysis has been shown to successfully prevent tumor cell proliferation in melanoma, non-small cell lung cancer, prostate cancer and acute myeloid leukaemia. We recently showed that in breast cancer, although ASCT2 is highly expressed in most tumor subtypes, only aggressive triple-negative (TN) breast cancer cells require ASCT2-mediated uptake of glutamine to sustain cell growth in vitro and in vivo. Gene expression analysis of xenograft-derived tumor tissue and TN patient samples suggested coordinate regulation of ASCT2 and other glutamine metabolism-related genes, such as glutaminase (GLS) and glutamate-ammonia ligase (GLUL), with global activation of glutaminolytic energy production pathways in these tumors. The metabolism-regulating transcription factors, MYC and ATF4, were significantly correlated with these genes, suggesting a dynamic MYC and ATF4-driven transcriptional program in TN breast cancer. We therefore hypothesized that highly proliferative TN breast cancers that are sensitive to ASCT2 inhibition may have unique metabolic signatures that could be additionally exploited for therapeutic purposes.

We developed a targeted metabolomics approach that combined labelled substrate tracing, liquid chromatography coupled tandem-mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS) to analyze intracellular levels of key tricarboxylic acid (TCA) cycle intermediates, glycolytic metabolites, fatty acid precursors, and amino acids in human breast cancer cell lines. These analyses revealed distinct metabolic effects when ASCT2 transporter function was blocked in vitro by pharmacological inhibitors or inducible shRNA knockdown, in combination with CB-839, a GLS inhibitor in Phase I clinical trials. To confirm the clinical utility of these findings, we also determined mRNA and protein expression of glutamine metabolism-related genes in tissue microarrays of TN patient samples. These data suggest a reliance on glutamine availability in TN breast cancers and reinforce the link between increased glutamine metabolism and clinically aggressive breast cancers, thus highlighting the therapeutic potential of targeting the ASCT2 glutamine uptake and metabolism pathway in these patients.

Citation Format: Michelle van Geldermalsen, Qian Wang, Jeff Holst. Targeting ASCT2-mediated glutamine uptake and metabolism in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1043.