Although a nonessential amino acid in normal cells, the demand for glutamine is dramatically increased in cancer to support metabolic demands. These include the provision of catabolic substrates for ATP production and anabolic substrates for the citric acid cycle and subsequent macromolecule biosynthesis, as well as potentiating the uptake of other critical amino acids by acting as an obligate exchange substrate. Elevated expression of glutamine metabolism-related genes, MYC-driven transcriptional events, and increased consumption and reliance on glutamine are all associated with aggressive breast cancers, including the high-risk triple-negative (TN) subtype. We recently showed that in breast cancer cells, glutamine uptake by the small neutral amino acid transporter, ASCT2, is required to sustain TN cell growth in vitro and in vivo. We therefore hypothesised 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.
Using metabolomics, we undertook 13C- and 15N-labelled substrate tracing to analyse intracellular levels of key tricarboxylic acid (TCA) cycle intermediates, glycolytic metabolites, fatty acid precursors, nucleotides, and amino acids in human breast cancer cell lines in vitro and ex vivo. These analyses revealed distinct metabolic effects across cell lines representing different subtypes of breast cancer, both at baseline and when glutamine uptake was blocked. These data confirm a broad reliance on glutamine availability in TN breast cancers, where glutamine is rapidly shunted through the TCA cycle, a phenomenon that was virtually absent in the Luminal A subtype. Analysis of gene expression data (METABRIC and TCGA patient datasets; CCLE cell line dataset), showed upregulation of glutamine metabolism enzymes in TN breast cancer patient samples and cell lines compared to the Luminal A subtype. These data suggest a rewiring of glutamine metabolism in TN breast cancer that utilises their glutamine addiction to fuel growth. These data providing an additional suite of glutamine metabolic enzymes that may be therapeutically targeted to treat TN breast cancer.