Glutamine to proline conversion is associated with response to glutaminase inhibition in breast cancer

• Published in: Breast cancer research : BCR Vol. 21; no. 1; pp. 61 - 13
• Main Authors: Grinde, Maria T., Hilmarsdottir, Bylgja, Tunset, Hanna Maja, Henriksen, Ida Marie, Kim, Jana, Haugen, Mads H., Rye, Morten Beck, Mælandsmo, Gunhild M., Moestue, Siver A.
• Format: Journal Article
• Language: English
• Published: London BioMed Central 14.05.2019; BioMed Central Ltd; BMC
• Subjects: 13C MRS; Addictions; Alanine; Aldehyde dehydrogenase 18 family member A1 (ALDH18A1); Amino acids; Analysis; Animals; Biological markers; Biomarkers; Biomedical and Life Sciences; Biomedicine; Biosynthesis; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Cancer cells; Cancer prevention; Cancer Research; Cancer treatment; CB-839; Cell Line, Tumor; Clinical medical disciplines: 750; Clinical trials; Computational Biology; Disease Models, Animal; DNA microarrays; Enzyme Inhibitors - pharmacology; Enzymes; Female; Gene expression; Gene expression analysis; Gene Expression Profiling; Genes; Genetic aspects; Genetic research; Glutamate; Glutaminase; Glutaminase - antagonists & inhibitors; Glutaminase - metabolism; Glutaminase inhibitor; Glutamine; Glutamine - metabolism; Glutathione; High-resolution magic angle spinning MR spectroscopy (HR MAS MRS); Humans; Immunohistochemistry; Kinases; Klinisk medisinske fag: 750; Lactates; Lactic acid; Magnetic Resonance Spectroscopy; Mammals; Medical disciplines: 700; Medical research; Medisinske Fag: 700; Metabolism; Metabolites; Metabolomics - methods; Mice; Models, Biological; Oncology; Oncology: 762; Onkologi: 762; Patient-derived xenograft (PDX); Patients; Proline; Proline - metabolism; Protein expression; Proteins; Research Article; Spectrum analysis; Surgical Oncology; Tumors; VDP; Xenograft Model Antitumor Assays; Xenografts; Immunohistochemistry; Glutaminase inhibitor; Gene expression analysis; High-resolution magic angle spinning MR spectroscopy (HR MAS MRS); Cancer treatment; Patient-derived xenograft (PDX); Aldehyde dehydrogenase 18 family member A1 (ALDH18A1); CB-839; C MRS; Glutaminase; 13C MRS
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/s13058-019-1141-0

Introduction Glutaminase inhibitors target cancer cells by blocking the conversion of glutamine to glutamate, thereby potentially interfering with anaplerosis and synthesis of amino acids and glutathione. The drug CB-839 has shown promising effects in preclinical experiments and is currently undergoing clinical trials in several human malignancies, including triple-negative breast cancer (TNBC). However, response to glutaminase inhibitors is variable and there is a need for identification of predictive response biomarkers. The aim of this study was to determine how glutamine is utilized in two patient-derived xenograft (PDX) models of breast cancer representing luminal-like/ER+ (MAS98.06) and basal-like/triple-negative (MAS98.12) breast cancer and to explore the metabolic effects of CB-839 treatment. Experimental MAS98.06 and MAS98.12 PDX mice received CB-839 (200 mg/kg) or drug vehicle two times daily p.o. for up to 28 days ( n  = 5 per group), and the effect on tumor growth was evaluated. Expression of 60 genes and seven glutaminolysis key enzymes were determined using gene expression microarray analysis and immunohistochemistry (IHC), respectively, in untreated tumors. Uptake and conversion of glutamine were determined in the PDX models using HR MAS MRS after i.v. infusion of [5- 13 C] glutamine when the models had received CB-839 (200 mg/kg) or vehicle for 2 days ( n  = 5 per group). Results Tumor growth measurements showed that CB-839 significantly inhibited tumor growth in MAS98.06 tumors, but not in MAS98.12 tumors. Gene expression and IHC analysis indicated a higher proline synthesis from glutamine in untreated MAS98.06 tumors. This was confirmed by HR MAS MRS of untreated tumors demonstrating that MAS98.06 used glutamine to produce proline, glutamate, and alanine, and MAS98.12 to produce glutamate and lactate. In both models, treatment with CB-839 resulted in accumulation of glutamine. In addition, CB-839 caused depletion of alanine, proline, and glutamate ([1-13C] glutamate) in the MAS98.06 model. Conclusion Our findings indicate that TNBCs may not be universally sensitive to glutaminase inhibitors. The major difference in the metabolic fate of glutamine between responding MAS98.06 xenografts and non-responding MAS98.12 xenografts is the utilization of glutamine for production of proline. We therefore suggest that addiction to proline synthesis from glutamine is associated with response to CB-839 in breast cancer. Graphical abstract The effect of glutaminase inhibition in two breast cancer patient-derived xenograft (PDX) models. 13 C HR MAS MRS analysis of tumor tissue from CB-839-treated and untreated models receiving 13 C-labeled glutamine ([5- 13 C] Gln) shows that the glutaminase inhibitor CB-839 is causing an accumulation of glutamine (arrow up) in two PDX models representing luminal-like breast cancer (MAS98.06) and basal-like breast cancer (MAS98.12). In MAS98.06 tumors, CB-839 is in addition causing depletion of proline ([5- 13 C] Pro), alanine ([1- 13 C] Ala), and glutamate ([1- 13 C] Glu), which could explain why CB-839 causes tumor growth inhibition in MAS98.06 tumors, but not in MAS98.12 tumors.