Abstract 1887: Bone marrow-derived stromal cells and hypoxia promote glutamine dependency in leukemias.

Abstract

Abstract Glutamine (Gln) is a versatile non-essential amino acid that plays a unique role in the metabolism of proliferating cancer cells; it provides cells with a variety of essential molecules to sustain cell proliferation, regulates redox homeostasis and modulates activity of signal transduction pathways. Recent data suggest that cancer cells employ multiple mechanisms that regulate Gln and glucose metabolism in a coordinated fashion. Microenvironment is recognized as one of the major factors that modulates glucose, Gln and lipid metabolism in cancer cells; however mechanisms that couple survival of leukemic cells to metabolic processes under different microenvironment conditions have not been elucidated. Leukemic bone marrow exhibits heterogeneous microenvironment niches reminiscent to microenvironment of solid tumor characterized by low oxygen tension, reduced nutrient availability and presence of supporting stromal cells. Our published data demonstrated that co-culture of leukemic cells with bone marrow-derived mesenchymal stromal cells (MSC) promotes mitochondrial dysfunction in myeloid leukemia cells, accumulation of HIF-1α and switch to glycolytic metabolism, all associated with chemoresistance (Cancer Biol Ther 13:858, 2012). Here we report in vitro studies aimed to determine the role of Gln in contributing to the core metabolism of proliferating leukemic cells under hypoxia and upon interaction with MSC. Genome-wide gene expression profiling of OCI-AML3 and REH leukemic cells co-cultured with BM-MSC under hypoxic conditions demonstrated that hypoxia alters metabolic patterns through increased rate of glycolysis and down-regulation of oxidative phosphorylation (oxphos), while MSC co-culture under hypoxia further promoted glycolysis in leukemic cells and induced genes regulating oxphos, TCA cycle and Gln utilization (e.g. GLS1, GOT). GLS1 protein level was also increased under hypoxia. Our in vitro findings further indicate that both acute myeloid leukemia (AML) and acute lymphocytic leukemia (ALL) cell lines rely on Gln as a carbon source under normoxia, while AML cells are more tolerant to Gln deprivation under hypoxia. In turn, inhibition of glutaminase (GLS1), the initial enzyme in glutaminolysis, with a small molecule BPTES decreased leukemia cell growth and increased apoptosis under both, normoxic and hypoxic conditions. MSC reduced BPTES-induced apoptosis in floating AML cells, however failed to protect firmly attached hypoxic AML cells, which are otherwise resistant to chemotherapy-induced cytotoxicity. Unexpectedly, GLS blockade negatively affected growth of MSC under co-culture conditions with leukemia cells. In summary, our results indicate the carbon source flexibility that fuels cancer cell growth in response to changes in microenvironment, and support the key role of glutamine utilization pathway for the survival of hypoxic marrow-resident leukemic cells. Citation Format: Polina Matre, Rodrigo O. Jacamo, Ying Wang, Jing Wang, R Eric Davis, Michael Andreeff, Aaron D. Schimmer, Marina Konopleva. Bone marrow-derived stromal cells and hypoxia promote glutamine dependency in leukemias. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1887. doi:10.1158/1538-7445.AM2013-1887