Glutaminase inhibitor CB-839 increases radiation sensitivity of lung tumor cells and human lung tumor xenografts in mice

Abstract

Purpose: The purpose of this study was to translate our in vitro therapy approach to an in vivo model. Increased glutamine uptake is known to drive cancer cell proliferation, making tumor cells glutamine-dependent. Studying lymph-node aspirates containing malignant lung tumor cells showed a strong correlation between glutamine consumption and glutathione (GSH) excretion. Subsequent experiments with A549 and H460 lung tumor cell lines provided additional evidence for glutamine’s role in driving synthesis and excretion of GSH. Using stable-isotope-labeled glutamine as a tracer metabolite, we demonstrated that the glutamate group in GSH is directly derived from glutamine, linking glutamine utilization intimately to GSH syntheses.

Materials and methods: To understand the possible mechanistic link between glutamine consumption and GSH excretion, we studied GSH metabolism in more detail. Inhibition of glutaminase (GLS) with BPTES, a GLS-specific inhibitor, effectively abolished GSH synthesis and excretion. Since our previous work, several novel GLS inhibitors became available and we report herein effects of CB-839 in A427, H460 and A549 lung tumor cells and human lungtumor xenografts in mice.

Results: Inhibition of GLS markedly reduced cell viability, producing ED₅₀ values for inhibition of colony formation of 9, 27 and 217 nM in A427, A549 and H460, respectively. Inhibition of GLS is accompanied by ∼30% increased response to radiation, suggesting an important role of glutamine-derived GSH in protecting tumor cells against radiation-induced injury. In subsequent mouse xenografts, short-term CB-839 treatments reduced serum GSH by >50% and increased response to radiotherapy of H460-derived tumor xenografts by 30%.

Conclusion: The results support the proposed mechanistic link between GLS activity and GSH synthesis and suggest that GLS inhibitors are effective radiosensitizers.

Keywords:

• Glutathione
• glutaminase
• lung cancer
• radiation therapy
• CB-839

Acknowledgments

The authors are grateful to Calithera Biosciences for providing CB-839.

Disclosure statement

Drs. Boysen and Griffin are actively developing GLS inhibitors as radio sensitizers and have filed patent applications related to the same.

Additional information

Funding

This work was supported in part by the National Institutes of Health (NIH) Clinical and Translational Science Award (CTSA) program, grants UL1TR000039 and KL2TR000063, the Arkansas Bioscience Institute, and the Envoys, an advocacy group of the UAMS Cancer Institute Foundation. We thank Calithera Bioscience, Inc CA USA for providing CB-839.

Notes on contributors

Gunnar Boysen

Gunnar Boysen PhD, is associate professor of Environmental and Occupational Health at the University of Arkansas for Medical Sciences. His group applies targeted and un-targeted mass spectrometry-based metabolomics approaches to improve diagnosis and treatment of lung cancer.

Azemat Jamshidi-Parsian

Azemat Jamshidi-Parsian, PhD, is a research associate in Department of Radiation Oncology at University of Arkansas for Medical Sciences. She has nearly 30 years of experience in area of biomedical research including cell & molecular biology protocols, high quality cell culture and laboratory operations.

Mary A. Davis

Mary A. Davis is a doctoral student at the University of Arkansas for Medical Sciences and Pharmacology and Toxicology training program.

Eric R. Siegel

Eric Siegel B.S. has practiced Biostatistics for almost 20 years at the University of Arkansas for Medical Sciences.

Christine M. Simecka

Christine Simecka DMV, is assistant professor of Division of Laboratory Animal Science, University of Arkansas for Medical Sciences. Her interest is in utilization of advance animal models to improve drug and therapy development.

Rajshekhar A. Kore

Rajshekhar A. Kore, PhD, is a post-doctoral fellow in the Department of Internal Medicine, Cardiovascular Division. His research interests lie in deciphering intercellular communication influenced by hypoxia and inflammation in tissue microenvironments.

Ruud P. M. Dings

Ruud P. M. Dings, PhD, is assistant professor in the Department of Radiation Oncology at the University of Arkansas for Medical Sciences. His research group specializes in delineating tumor microenvironment modulation during carcinogenesis and therapeutic intervention.

Robert J. Griffin

Robert J. Griffin, PhD, is professor of Radiation Biology at the University of Arkansas for Medical Sciences. His research group studies response of living tissue to radiotherapy and/or targeted drug delivery.