Energy Metabolism of Leukemia Cells: Glycolysis Vs Oxidative Phosphorylation

Cancer cells are more dependent on glycolysis than oxidative phosphorylation in the mitochondria for generation of ATP as energy source. By using 2-deoxy-D-glucose (2-DG: glycolysis inhibitor) and oligomycin (inhibitor of oxidative phosphorylation), we examined the energy metabolism of various leukemia cell lines. The growth of the cell lines was measured by MTS assay, which detects viable cells in proliferation. 2-DG suppressed the growth of all leukemia cell lines examined in dose-dependent manners. The IC₅₀ of each cell line was as follows: Kasumi-1 0.5±0.1mM, KG-1a 1.8±0.6mM, HL-60 3.3±0.1mM, NB4 3.8±0.4mM, and THP-1 23.1±3.8mM. The concentration of lactic acid (the final product of glycolytic pathway) in the culture supernatant was greatly reduced by the treatment with 0.2mM 2-DG for 24 hours in Kasumi-1 (54.5% of the control), compared with THP-1 (92.2%). It is suggested that the growth of Kasumi-1 was strongly suppressed by 2-DG through inhibition of glycolysis, which is supposed to be a main metabolic pathway in this cell line. On the other hand, treatment with oligomycin (1μg/ml) for 48 hours potently suppressed the growth of THP-1 (44.7%), then Kasumi-1 (72.1%). The growth of NB4, KG-1a and HL-60 was minimally suppressed (more than 90%) by oligomycin. Cell cycle was analyzed after 24 hours treatment with 2-DG or oligomycin. Sub-G1 fraction (apoptosis) was greatly increased by 2-DG (5mM) in Kasumi-1 (56.5%) and NB4 (30.6%), compared with THP-1 (7.6%). The apoptosis inducing effect was confirmed by annexinV staining. Oligomycin treatment (1μg/ml) increased apoptosis (subG1) in THP-1 (35.8%), then Kasumi-1 (16.6%) and NB4 (12.2%). Oligomycin treatment also increased G1 population (G1 arrest) in THP-1 (35.9% to 69.4%). AMP-activated protein kinase (AMPK) is activated by an elevated AMP/ATP ratio, which means the energy-deprived status of the cell. Western blot analysis using phospho-AMPK α (Thr172) antibody revealed that treatment with 2-DG or oligomycin induced prompt (30 min) phosphorylation of AMPK in leukemia cell lines. The extent of AMPK phosphorylation was almost proportional to the suppression of the growth. Collectively, it is suggested that leukemia cells are dependent almost exclusively on either glycolysis or oxidative phosphorylation in the mitochondria for energy production. Then, inhibition of glycolysis by 2-DG or oxidative phosphorylation by oligomycin results in growth suppression by inducing apoptosis and/or cell cycle arrest through activation of AMPK. Our data clarified the characteristics of the energy metabolism of each leukemia cell, and showed the key to produce novel therapeutic approach targeting metabolic pathway.