Mitochondrial gene knockout HL60rho0 cells show preferential differentiation into monocytes/macrophages

Uridine Prevents Negative Effects of OXPHOS Xenobiotics on Dopaminergic Neuronal Differentiation

Neuronal differentiation appears to be dependent on oxidative phosphorylation capacity. Several drugs inhibit oxidative phosphorylation and might be detrimental for neuronal differentiation. Some pregnant women take these medications during their first weeks of gestation when fetal nervous system is being developed. These treatments might have later negative consequences on the offspring's health. To analyze a potential negative effect of three widely used medications, we studied in vitro dopaminergic neuronal differentiation of cells exposed to pharmacologic concentrations of azidothymidine for acquired immune deficiency syndrome; linezolid for multidrug-resistant tuberculosis; and atovaquone for malaria. We also analyzed the dopaminergic neuronal differentiation in brains of fetuses from pregnant mice exposed to linezolid. The drugs reduced the in vitro oxidative phosphorylation capacity and dopaminergic neuronal differentiation. This differentiation process does not appear to be affected in the prenatally exposed fetus brain. Nevertheless, the global DNA methylation in fetal brain was significantly altered, perhaps linking an early exposure to a negative effect in older life. Uridine was able to prevent the negative effects on in vitro dopaminergic neuronal differentiation and on in vivo global DNA methylation. Uridine could be used as a protective agent against oxidative phosphorylation-inhibiting pharmaceuticals provided during pregnancy when dopaminergic neuronal differentiation is taking place.

Chemotherapy-Resistant Human Acute Myeloid Leukemia Cells Are Not Enriched for Leukemic Stem Cells but Require Oxidative Metabolism

Chemotherapy-resistant human acute myeloid leukemia (AML) cells are thought to be enriched in quiescent immature leukemic stem cells (LSC). To validate this hypothesis in vivo, we developed a clinically relevant chemotherapeutic approach treating patient-derived xenografts (PDX) with cytarabine (AraC). AraC residual AML cells are enriched in neither immature, quiescent cells nor LSCs. Strikingly, AraC-resistant preexisting and persisting cells displayed high levels of reactive oxygen species, showed increased mitochondrial mass, and retained active polarized mitochondria, consistent with a high oxidative phosphorylation (OXPHOS) status. AraC residual cells exhibited increased fatty-acid oxidation, upregulated CD36 expression, and a high OXPHOS gene signature predictive for treatment response in PDX and patients with AML. High OXPHOS but not low OXPHOS human AML cell lines were chemoresistant in vivo. Targeting mitochondrial protein synthesis, electron transfer, or fatty-acid oxidation induced an energetic shift toward low OXPHOS and markedly enhanced antileukemic effects of AraC. Together, this study demonstrates that essential mitochondrial functions contribute to AraC resistance in AML and are a robust hallmark of AraC sensitivity and a promising therapeutic avenue to treat AML residual disease.Significance: AraC-resistant AML cells exhibit metabolic features and gene signatures consistent with a high OXPHOS status. In these cells, targeting mitochondrial metabolism through the CD36-FAO-OXPHOS axis induces an energetic shift toward low OXPHOS and strongly enhanced antileukemic effects of AraC, offering a promising avenue to design new therapeutic strategies and fight AraC resistance in AML. Cancer Discov; 7(7); 716-35. ©2017 AACR.See related commentary by Schimmer, p. 670This article is highlighted in the In This Issue feature, p. 653.

Metabolic flexibility and cell hierarchy in metastatic cancer

Cancer is characterized by disturbed homeostasis of self-renewing cell populations, and their ability to seed and grow in multiple microenvironments. This overarching cellular property of metastatic cancer emerges from the contentious cancer stem cell hypothesis that underpins the more generic hallmarks of cancer (Hanahan and Weinberg, 2000) and its subsequent add-ons. An additional characteristic, metabolic flexibility, is related to concepts developed by Warburg and to subsequent work by mid 20th century biochemists who elucidated the bioenergetic workings of mitochondria. Metabolic flexibility may circumvent limitations inherent in the increasingly popular but erroneous view that aerobic glycolysis is a universal property of cancer cells. Cancer research in the second half of the 20th century was largely the domain of geneticists and molecular biologists using reductionist approaches. Integrated approaches that address cancer cell hierarchy and complexity, and how cancer cells adapt their metabolism according to their changing environment are now beginning to emerge, and these approaches promise to address the poor mortality statistics of metastatic cancer.

Glycolytic metabolism confers resistance to combined all-trans retinoic acid and arsenic trioxide-induced apoptosis in HL60rho0 cells

Glycolytic cancers are resistant to many forms of chemotherapy and some respond poorly to differentiation therapies. Here, we investigate the effects of exposure to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) on differentiation and cell survival in the human leukemia cell line, HL60 and its mitochondrial gene knockout mutant, HL60rho0. Glycolytic HL60rho0 cells exposed to single and combined treatments expressed less CD15, in most cases, but produced a stronger respiratory burst than parental HL60 cells. HL60rho0 cells were also significantly more resistant to apoptosis after combined ATO+ATRA treatment compared with HL60 cells, and this was associated with failure to upregulate Fas expression.

Cell surface oxygen consumption: a major contributor to cellular oxygen consumption in glycolytic cancer cell lines

Oxygen consumption for bioenergetic purposes has long been thought to be the prerogative of mitochondria. Nevertheless, mitochondrial gene knockout (rho(0)) cells that are defective in mitochondrial respiration require oxygen for growth and consume oxygen at the cell surface via trans-plasma membrane electron transport (tPMET). This raises the possibility that cell surface oxygen consumption may support glycolytic energy metabolism by reoxidising cytosolic NADH to facilitate continued glycolysis. In this paper we determined the extent of cell surface oxygen consumption in a panel of 19 cancer cell lines. Non-mitochondrial (myxothiazol-resistant) oxygen consumption was demonstrated to consist of at least two components, cell surface oxygen consumption (inhibited by extracellular NADH) and basal oxygen consumption (insensitive to both myxothiazol and NADH). The extent of cell surface oxygen consumption varied considerably between parental cell lines from 1% to 80% of total oxygen consumption rates. In addition, cell surface oxygen consumption was found to be associated with low levels of superoxide production and to contribute significantly (up to 25%) to extracellular acidification in HL60rho(0) cells. In summary, cell surface oxygen consumption contributes significantly to total cellular oxygen consumption, not only in rho(0) cells but also in mitochondrially competent tumour cell lines with glycolytic metabolism.