Metabolic Modulators of Soft Tissue Sarcomas

Abstract

This investigation characterizes the metabolic dependencies of soft tissue sarcomas and evaluates potential therapeutic implications for radiation therapy. Mice were genetically engineered to utilize the Cre/LoxP system, with Cre fused to the estrogen receptor and expressed from the Pax7 promoter in muscle satellite cells. Intramuscular delivery of 4-hydroxytamoxifen to the gastrocnemius muscle enabled Cre to translocate to the nucleus to delete the Trp53 tumor suppressor and activate oncogenic Nras to generate sarcomas. Infusions with 13C-labeled nutrients in tumor-bearing mice revealed glutamine and glucose to be the primary substrates for the Tricarboxylic Acid Cycle in sarcomas. However, metabolomic analysis post-radiation treatment indicated that radiation response in sarcomas was characterized by a shift away from glucose consumption and towards glutamine metabolism. Inhibition of glutamine catabolism in sarcoma cell lines via nutrient restriction, pharmacological blockade, and genetic deletion impaired tumor proliferation. Clonogenic assays demonstrated that glutamine restriction also reduced in vitro survival following radiation exposure. To validate these phenotypes in vivo, the Cre/LoxP system was used to generate mice with sarcomas deficient in glutaminase (Gls), the enzyme governing the rate-limiting reaction for glutamine catabolism. Cohorts of tumor-bearing irradiated and untreated mice were then followed to evaluate the effect of Gls deletion on survival. Collectively, the results from this study demonstrate that (1) glutamine is critical for sarcoma cell growth in vitro and in vivo and (2) inhibition of Gls has the potential to enhance the radiosensitivity of sarcomas.