For generation of energy, cancer cells utilize glycolysis more vigorously than oxidative phosphorylation in mitochondria (Warburg effect). We examined the energy metabolism of four leukemia cell lines by using glycolysis inhibitor, 2-deoxy-d-glucose (2-DG) and inhibitor of oxidative phosphorylation, oligomycin. NB4 was relatively sensitive to 2-DG (IC(50): 5.75 mM), consumed more glucose and produced more lactate (waste product of glycolysis) than the three other cell lines. Consequently, NB4 was considered as a "glycolytic" leukemia cell line. Dependency on glycolysis in NB4 was confirmed by the fact that glucose (+) FCS (-) medium showed more growth and survival than glucose (-) FCS (+) medium. Alternatively, THP-1, most resistant to 2-DG (IC(50): 16.14 mM), was most sensitive to oligomycin. Thus, THP-1 was recognized to be dependent on oxidative phosphorylation. In THP-1, glucose (-) FCS (+) medium showed more growth and survival than glucose (+) FCS (-) medium. The dependency of THP-1 on FCS was explained, at least partly, by fatty acid oxidation because inhibitor of fatty acid β-oxidation, etomoxir, augmented the growth suppression of THP-1 by 2-DG. We also examined the mechanisms by which THP-1 was resistant to, and NB4 was sensitive to 2-DG treatment. In THP-1, AMP kinase (AMPK), which is activated when ATP becomes limiting, was rapidly phosphorylated by 2-DG, and expression of Bcl-2 was augmented, which might result in resistance to 2-DG. On the other hand, AMPK phosphorylation and augmentation of Bcl-2 expression by 2-DG were not observed in NB4, which is 2-DG sensitive. These results will facilitate the future leukemia therapy targeting metabolic pathways.

BackgroundLike normal hematopoietic stem cells, leukemia cells proliferate in bone marrow, where oxygen supply is limited. However, the growth and energy metabolism of leukemia cells under hypoxia have not been well understood. Although it has been known that reactive oxygen species (ROS) is generated under hypoxic conditions, normal and leukemia stem cells were characterized by relatively low levels of ROS. Roles of ROS on leukemia cells under hypoxia also have not been well understood.MethodsFour Leukemia cell lines were cultured under normoxia (21% O2) or hypoxia (1% O2), where NB4 and THP-1 were most extensively studied. To evaluate energy metabolism, we estimated whole cell number or apoptotic cells with or without a glycolysis inhibitor or an oxidative phosphorylation (OXPHOS) inhibitor. Glucose consumption and lactate production were also measured. To evaluate oxidative stress in hypoxic condition, the ROS level and GSH (reduced glutathione) / GSSG (oxidized glutathione) ratio was measured. In addition, pyruvate dehydrogenase kinase 1 (PDK1) and cytochrome c oxidase subunit 4 (COX4) were examined by western blotting or RT-PCR.ResultsNB4, which grows well under normoxia depending on glycolysis, demonstrated prominent apoptosis and growth suppression after 48 hours culture under hypoxia. NB4 cells cultured under hypoxia showed significantly increased ROS. Culture with a ROS scavenger resulted in decrease of apoptotic cell death of NB4 under hypoxia. NB4 cells cultured for longer period (7 days) under hypoxia did not come to extinction, but grew slowly by upregulating GSH synthesis to protect from ROS generated in hypoxic condition. By contrast, THP-1, which largely depends on OXPHOS in mitochondria under normoxia, demonstrated more growth under hypoxia by changing metabolism from OXPHOS to glycolysis through upregulating PDK1. Moreover, THP-1 avoided ROS generation by substituting COX 4 subunit (from COX 4–1 to COX 4–2) through upregulation of LON, a mitochondrial protease under hypoxia.ConclusionsWe showed that leukemia cells survive and adapt to the hypoxic condition through various pathways. Our results will help understanding energy metabolism of leukemia cells and creating novel therapeutics.

Some cancer cells depend on glutamine despite of pronounced glycolysis. We examined the glutamine metabolism in leukemia cells, and found that HL-60 cells most depended on glutamine in the 4 acute myelogenous leukemia (AML) cell lines examined: growth of HL-60 cells was most suppressed by glutamine deprivation and by inhibition of glutaminolysis, which was rescued by tricarboxylic acid (TCA) cycle intermediate, oxaloacetic acid. Glutamine is also involved in antioxidant defense function by increasing glutathione. Glutamine deprivation suppressed the glutathione content and elevated reactive oxygen species most evidently in HL-60 cells. Glutamine metabolism might be a therapeutic target in some leukemia.

Summary Several anti‐angiogenic drugs have recently been clinically tested for haematological malignancies. To improve the efficacy of molecular target therapy against angiogenic molecules in acute myeloid leukaemia (AML), we examined the dependency of AML cells on the vascular endothelial growth factor (VEGF)/VEGF receptor type2 (VEGFR2) system by using VEGFR2 kinase inhibitor. Nineteen patient AML samples were cultured with or without VEGFR2 kinase inhibitor. All four t(8;21) viable AML cells showed significant reductions when treated with VEGFR2 kinase inhibitor, although VEGFR2 kinase inhibitor did not affect the cell proliferation of five t(15;17) AML samples. Other AML cases showed variable responses. VEGFR2 kinase inhibitor greatly suppressed the growth of Kasumi‐1, a t(8;21) cell line in a dose‐dependent manner through induction of apoptosis, but did not show any significant influence on NB4, a t(15;17) cell line. In addition, VEGFR2 kinase inhibitor potentiated the growth inhibitory effect of cytarabine in Kasumi‐1. Finally, it was shown that the Akt phosphorylation was augmented by VEGF165 in Kasumi‐1, which was abrogated by VEGFR2 kinase inhibitor. NB4 showed undetectable Akt phosphorylation even with VEGF165. These data demonstrated that t(8;21) AML cells are dependent on VEGF through VEGFR2, resulting in the phosphorylation of Akt.

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In this study, we established and analyzed a novel human myeloid leukemia cell line, AMU-AML1, from a patient with acute myeloid leukemia with multilineage dysplasia before the initiation of chemotherapy. AMU-AML1 cells were positive for CD13, CD33, CD117, and HLA-DR by flow cytometry analysis and showed a single chromosomal abnormality, 46, XY, t(12;22)(p13;q11.2), by G-banding and spectral karyotyping. Fluorescent in situ hybridization analysis indicated that the chromosomal breakpoint in band 12p13 was in the sequence from the 5 0 untranslated region to intron 1 of TEL and that the chromosomal breakpoint in band 22q11 was in the 3 0 untranslated region of MN1. The chimeric transcript and protein of MN1-TEL could not be detected by reverse-transcriptase polymerase chain reaction or Western blot analysis. However, the MN1 gene was amplified to three copies detected by array comparative genomic hybridization analysis, and the expression levels of the MN1 transcript and protein were high in AMU-AML1 cells when compared with other cell lines with t(12;22)(p13;q11-12). Our data showed that AMU-AML1 cells contain t(12;22)(p13;q11.2) without chimeric fusion of MN1 and TEL. The AMU-AML1 cells gained MN1 copies and had high expression levels of MN1. Thus, the AMU-AML1 cell line is useful for studying the biological consequences of t(12;22)(p13;q11.2) lacking chimeric MN1-TEL.

4861 In cancer cells, glucose uptake is elevated and glycolysis persists even under aerobic conditions (Warburg effect). Glutamine metabolism is another target for alteration in cancer development. Glutaminolysis (catabolism of glutamine to generate ATP) is known to increase in tumors. We examined the dependency of the leukemia cells (Kasumi-1, THP-1, HL-60 and NB4) on glucose or glutamine by measuring the growth (MTS count) in glucose- or glutamine-deprived condition. Glucose withdrawal greatly suppressed the growth of all 4 cell lines. However, glutamine withdrawal showed different growth suppressive effects among the cell lines (Kasumi-1: 55% of control, THP-1: 60%, HL-60: 39%, NB4: 70%). HL-60 was most sensitive to glutamine deprivation. The growth suppression of HL-60 due to glutamine withdrawal was partially rescued by oxaloacetate (OAA), a TCA cycle metabolite, while the growth of other cell lines was not rescued by OAA. In the course of glutamine catabolism, ammonia is liberated. Although basal level of the ammonia concentration was not so different among each cell line, glycolysis inhibitor (2-deoxyglucose) treatment enhanced the ammonia generation in HL-60 (Kasumi-1: 2.8% increased, THP-1: 1.7%, HL-60: 6.1%, NB4: 2.8%). Glutaminase, an enzyme converting glutamine to glutamate, is most abundantly expressed in HL-60 in western blot analysis. In addition, HL-60 was most sensitive to the treatment with aminooxyacetate, an inhibitor of glutamate-dependent transaminases that convert glutamate into a-ketoglutarate in the glutaminolytic pathway (Kasumi-1: 86% of control, THP-1: 97%, HL-60: 79%, NB4: 83%). Taken together, HL-60 was considered as glutamine dependent cell line. Therapies targeting glutamine metabolism, such as glutamine depletion or use of inhibitor of glutaminolytic pathway, might be effective against some leukemia. Disclosures: No relevant conflicts of interest to declare.