Abstract 2913: Glutamate-enriched breast cancer as new entity and target for metabolic drugs
Authors: Budczies Jan , Pfitzner Berit M. , Winzer Klaus-Jürgen , Radke Cornelia , Dietel Manfred , Fiehn Oliver , Denkert Carsten 
Published: May 2015

In many tumor cells, glutamine in addition to glucose serves as important source of energy and molecular building blocks. The first step of glutamine utilization is conversion of glutamine to glutamate by one of the glutaminase isoenzymes. Recently, two new allosteric inhibitors of glutaminase activity, BPTES and 968, have been discovered and described in the literature. Metabolic drugs developed as chemical analogs of these agents are planned to enter clinical trials in 2014. To quantify the activation of glutamine metabolism and to define a preferential target population for the new metabolic drugs, we analyzed glutamine and glutamate in a large cohort of breast carcinomas.

Glutamine and glutamate were quantified in a training set of 224 fresh-frozen breast cancer tissues and an independent validation set of 143 fresh-frozen breast cancer tissues using gas chromatography combined with time-of-flight mass spectrometry (GC-TOFMS). Glutamate was strongly increased in cancer tissues compared to normal tissues in the training set (fold change=8.2, p=7.3E-24), while glutamine did not change significantly. The strong increase of glutamate in cancer tissues could be validated in the validation set (fold change=6.8, p=4.0E-28). Comparing ER- breast cancer with ER+ breast cancer, glutamate was increased with fold change 1.4 (p=4.7E-05), while glutamine was decreased with fold change -1.7 (p=0.0026) in the training set. Both changes could be validated in the validation set (glutamate: fold change=1.7, p=4.1E-07, glutamine: fold change=-2.6, p=0.00055).

In the following, we used the glutamate/glutamine ratio (GGR) as biomarker for the activation of glutamine catabolism. In the training set, GGR was significantly higher in ER+ tumors compared to normal tissues (fold change=5.4, p=4.0E-21) and significantly higher in ER- tumors compared to ER+ tumors (fold change=2.4, p=8.5E-05). This pattern of deregulation could be validated in the validation set (fold change=7.3, p=4.0E-14 and fold change=4.4, p=1.9E-05). Higher GGR borderline significantly shortened overall survival in the training set (HR=1.31, p=0.09) and in the validation set (HR=1.32, p=0.13). In the combined set, correlation of overall survival and GGR was significant (HR=1.30, p=0.027).

Using the training set data, we determined a cutoff value GGR=2 by requiring all normal tissues to be below the cutoff. In the validation set, only 2 of the 55 normal tissues (3.6%) were above the cutoff. In the combined set, the percentage of tissues above the cutoff increased from 2.2% in normal tissues via 57.1% and 55.5% in ER+/HER+ and ER+/HER2- tumors to 93.8% and 86.0% in ER-/HER+2 and ER-/HER2- tumors.

In summary, we found an activated glutamine metabolism in about 90% of the ER- tumors and about 55% of the ER- tumors. These tumor populations showed an enrichment of glutamate relative to glutamine and represent a preferential target population for treatment with the newly developed glutaminase inhibitors.

Citation Format: Jan Budczies, Berit M. Pfitzner, Klaus-Jürgen Winzer, Cornelia Radke, Manfred Dietel, Oliver Fiehn, Carsten Denkert. Glutamate-enriched breast cancer as new entity and target for metabolic drugs. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2913. doi:10.1158/1538-7445.AM2014-2913