Abstract
BackgroundOsteosarcoma (OS) is a malignant bone tumor that often develops during the period of rapid growth associated with adolescence. Despite successful primary tumor control accompanied by adjuvant chemotherapy, death from pulmonary metastases occurs in approximately 30% of patients within 5 years. As overall survival in patients remains unchanged over the last 30 years, urgent needs for novel therapeutic strategies exist. Cancer metastasis is characterized by complex molecular events which result from alterations in gene and protein expression/function. Recent studies suggest that metabolic adaptations, or “metabolic reprogramming,” may similarly contribute to cancer metastasis. The goal of this study was to specifically interrogate the metabolic vulnerabilities of highly metastatic OS cell lines in a series of in vitro and in vivo experiments, in order to identify a tractable metabolically targeted therapeutic strategy for patients.MethodsNutrient deprivation and drug treatment experiments were performed in MG63.3, 143B, and K7M2 OS cell lines to identify the impact of glutaminase-1 (GLS1) inhibition and metformin treatment on cell proliferation. We functionally validated the impact of drug treatment with extracellular flux analysis, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry. 13C-glucose and 13C-glutamine tracing was employed to identify specific contributions of these nutrients to the global metabolic profiles generated with GLS1 inhibition and metformin treatment in vivo.ResultsHighly metastatic OS cell lines require glutamine for proliferation, and exposure to CB-839, in combination with metformin, induces both primary tumor growth inhibition and a distinct reduction in metastatic outgrowth in vivo. Further, combination-treated OS cells showed a reduction in cellular mitochondrial respiration, while NMR confirmed the pharmacodynamic effects of glutaminase inhibition in tumor tissues. We observed global decreases in glycolysis and tricarboxylic acid (TCA) cycle functionality, alongside an increase in fatty acid oxidation and pyrimidine catabolism.ConclusionsThis data suggests combination-treated cells cannot compensate for metformin-induced electron transport chain inhibition by upregulating glutaminolysis to generate TCA cycle intermediates required for cell proliferation, translating into significant reductions in tumor growth and metastatic progression. This therapeutic approach could be considered for future clinical development for OS patients presenting with or at high risk of developing metastasis.
Highlights
Osteosarcoma (OS) is a malignant bone tumor that often develops during the period of rapid growth associated with adolescence
Metabolic plasticity may allow metastatic cancer cells to cope with various stressful microenvironmental situations, which are believed to be distinct from those faced by cells during primary tumor formation; as such there is increasing evidence that altered metabolism is a driver of cancer metastasis [5,6,7]
Glutaminase inhibitor CB-839 in combination with metformin inhibits cell growth Given that treatment with a glutaminase inhibitor alone was not sufficient to inhibit OS cell proliferation despite a dependence on glutamine, we examined whether a rational drug combination targeting cellular metabolism would be more effective
Summary
Osteosarcoma (OS) is a malignant bone tumor that often develops during the period of rapid growth associated with adolescence. Osteosarcoma (OS) is a highly aggressive malignancy of bone which affects ~ 900 pediatric and adolescent patients per year in the USA, with the primary cause of death being metastatic progression [5, 8] (https://www.cancer.org/cancer/osteosarcoma/about/key-statistics.html). We hypothesized that highly metastatic cells may have a greater flexibility in managing energetic needs during times of stress and that metastatic success may be linked to cells’ ability to efficiently access and utilize energy. This led us to explore the potential for nutrient targeting as an anti-metastatic approach with potential translational value for OS patients
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
