Glutamate enrichment as new diagnostic opportunity in breast cancer

Abstract

Exogenous glutamine is an important source of energy and molecular building blocks for many tumors. There is a renewed interest in therapeutically targeting glutamine metabolism due to the recent discovery of two novel glutaminase inhibitors. To quantify the dysregulation of the glutamate-glutamine equilibrium in breast cancer, metabolomics analysis of 270 clinical breast cancer samples and 97 normal breast samples was carried out using gas chromatography combined with time-of-flight mass spectrometry. Positive correlation between glutamate and glutamine in normal breast tissues switched to negative correlation between glutamate and glutamine in breast cancer tissues. Compared with the ratio of glutamate to glutamine in normal tissues, we found 56% of the ER1 tumor tissues and 88% of the ER2 tumor tissues glutamate-enriched. The glutamateto-glutamine ratio (GGR) significantly correlated with ER status (p 5 8.0E-09) and with tumor grade (p 5 3.3E-05). Higher levels of GGR were associated with prolonged overall survival in univariate analysis (HR 5 0.77, p 5 0.027) and in multivariate analysis (HR 5 0.73, p 5 0.038). GGR levels were reflected in an unsupervised clustering of metabolomics profiles. In a supervised analysis of metabolomics data and of genome-wide expression data, replacement of GGR by metabolite surrogate markers was feasible, while replacement of GGR by RNA markers had a limited accuracy. Functional analysis of the gene expression data showed negative correlation between glutamate enrichment and activation of peroxisome proliferator-activated receptor (PPAR) pathway. Our findings may have important implications for patient stratification related to utilization of glutaminase inhibitors.Altered energy metabolism is acknowledged as one of the emerging hallmarks of cancer. 1 Recently, there is a renewed interest in the metabolic transformation occurring in cancer cells and in targeting metabolic enzymes for cancer therapy. 2-4 However, the discovery of dysregulated metabolism in tumors dates back to the work of Otto Warburg in the 1920s. Warburg observed that cancer cells exhibit elevated glycolysis and that much of the generated pyruvate is fermented to lactate rather than feed to the TCA cycle and used for oxidative phosphorylation. 5,6 This phenomenon occurs under anaerobic and even under aerobic conditions ("aerobic glycolysis").A second change that occurs in central metabolism of many cancer cells is the alteration of glutamine metabolism. 7-9 Glutamine can be used to replenish the TCA cycle instead of glucose and feed in carbon and nitrogen for synthesis of nucleotides, several amino acids and glutathione. Further, glutamine can be used for energy production and in transformed cultured cells glutamine driven oxidative phosphorylation was recently shown to be the main source of

Combined Label-Free Quantitative Proteomics and microRNA Expression Analysis of Breast Cancer Unravel Molecular Differences with Clinical Implications

“…Recent studies suggest differences in the metabolism of glutamine between ER À and ER þ disease. It has been observed that ER À tumors have a shift in the equilibrium between glutamine and glutamate toward glutamate in the ER À disease (49,50). We found that GLUD1 expression is slightly lower in TNBC tumors, which is consistent with previous reports describing that TNBCs have the lowest GLUD1 protein expression rate of all molecular subtypes, whereas HER2-positive tumors show the highest (51).…”

Metabolomics Biomarkers for Breast Cancer

“…A series of studies using tissue samples was carried using LC-MS [42,43,44,45]. Budczies et al [43] performed a GC-MS study using a large number of BC and normal tissues samples.…”

“…Budczies et al [44] used LC-MS to look at the Gln/Glu ratio in BC. Normal tissues exhibit a positive correlation between Glu and Gln, which switches to a negative correlation in BC tissues.…”

Targeting metabolism in breast cancer: How far we can go?

“…Asiago et al [34] reported that an elevated level of glutamate was associated with disease outcome in breast cancer patients. Metabolomic analysis of 270 clinical breast cancer samples and 97 normal breast samples showed that breast cancer cells had a higher glutamateto-glutamine ratio than normal cells, particularly ERtumor cells [35] . A cell study showed that highly invasive and drug-resistant breast cancer cells were characterized by increased glutamine metabolism with an increased glutamate-to-glutamine ratio and greater expression of glutaminase compared with noninvasive breast cancer cells [36] .…”