Zonghui Ding

Warburg effect is a dominant phenotype of most cancer cells. Here we show that this phenotype depends on its environment. When cancer cells are under regular culture condition, they show Warburg effect; whereas under lactic acidosis, they show a nonglycolytic phenotype, characterized by a high ratio of oxygen consumption rate over glycolytic rate, negligible lactate production and efficient incorporation of glucose carbon(s) into cellular mass. These two metabolic modes are intimately interrelated, for Warburg effect generates lactic acidosis that promotes a transition to a nonglycolytic mode. This dual metabolic nature confers growth advantage to cancer cells adapting to ever changing microenvironment.

Solid tumours are dependent on glucose, but are generally glucose-deprived due to poor vascularization. Nevertheless, cancer cells can generally survive glucose deprivation better than their normal counterparts. Thus, to render cancer cells sensitive to glucose depletion may potentially provide an effective strategy for cancer intervention. We propose that lactic acidosis, a tumour microenvironment factor, may allow cancer cells to develop resistance to glucose deprivation-induced death, and that disruption of lactic acidosis may resume cancer cells' sensitivity to glucose depletion. Lactic acidosis, lactosis, or acidosis was generated by adding pure lactic acid, sodium lactate, or HCl to the culture medium. Cell death, cell cycle, autophagy, apoptosis, and gene expression profiling of the surviving cancer cells under glucose deprivation with lactic acidosis were determined. Under glucose deprivation without lactic acidosis, 90% of 4T1 cancer cells died within a single day; in a sharp contrast, under lactic acidosis, 90% of 4T1 cells died in a period of 10 days, with viable cells identified even 65 days after glucose was depleted. Upon glucose restoration, surviving cells resumed proliferation. Lactic acidosis also significantly extended survival of other cancer cells under glucose deprivation. G1/G0 arrest, autophagy induction, and apoptosis inhibition were tightly associated with lactic acidosis-mediated resistance to glucose deprivation. Lactosis alone had no effect on cell survival under glucose deprivation; acidosis alone can prolong cell survival time but is not as potent as lactic acidosis. Thus, the ability of cancer cells to resist glucose deprivation-induced cell death is conferred, at least in part, by lactic acidosis, and we envision that disrupting the lactic acidosis may resume the sensitivity of cancer cells to glucose deprivation.

BACKGROUND: Cancer stem cells (CSCs) play a critical role in tumor development and progression and are involved in cancer metastasis. The role of reactive oxygen species (ROS) in CSCs and cancer metastasis remains controversial. The aim of the present study was to investigate the correlation between ROS level of CSCs and cancer metastasis and to explore the possible underlying molecular mechanisms. METHODS: Four different cell lines were used to isolate tumor spheres and to analyze intrinsic properties of tumor sphere cells including proliferation, self-renewal potential, differentiation, drug-resistance and cancer metastasis in vitro and in vivo. ROS assays were used to detect the intracellular ROS level of tumor spheres cells. Gene expression analysis and western blot were used to investigate the underlying mechanisms of ROS in regulating cancer metastasis. RESULTS: Tumor spheres possessed the characteristic features of CSCs, and ROS-high tumor spheres (RH-TS) displayed elevated mitochondrial ROS level exclusively drove metastasis formation. The gene expression analysis showed elevated fatty acid β-oxidation, downregulation of epithelial marker upregulation of mesenchymal markers, and the activation of MAP kinase cascades. Furthermore, 14 up-regulated genes in RH-TS cells were associated with reduced overall survival of different cancer patients. CONCLUSIONS: Our findings demonstrate that CSCs characterized by elevated mitochondrial ROS level potentiate cancer metastasis. Mechanistically, elevated mitochondrial ROS via fatty acid β-oxidation, activates the MAPK cascades, resulting in the epithelial-mesenchymal transition (EMT) process of RH-TS cells, thereby potentiating caner invasion and metastasis. Therefore, targeting mitochondrial ROS might provide a promising approach to prevent and alleviate cancer metastasis induced by RH-TS cells.

Abstract The presence of FMS-like receptor tyrosine kinase-3 internal tandem duplication (FLT3-ITD) mutations in patients with acute myeloid leukemia (AML) is associated with poor clinical outcome. FLT3 tyrosine kinase inhibitors (TKIs), although effective in kinase ablation, do not eliminate primitive FLT3-ITD+ leukemia cells, which are potential sources of relapse. Thus, understanding the mechanisms underlying FLT3-ITD+ AML cell persistence is essential to devise future AML therapies. Here, we show that expression of protein arginine methyltransferase 1 (PRMT1), the primary type I arginine methyltransferase, is increased significantly in AML cells relative to normal hematopoietic cells. Genome-wide analysis, coimmunoprecipitation assay, and PRMT1-knockout mouse studies indicate that PRMT1 preferentially cooperates with FLT3-ITD, contributing to AML maintenance. Genetic or pharmacological inhibition of PRMT1 markedly blocked FLT3-ITD+ AML cell maintenance. Mechanistically, PRMT1 catalyzed FLT3-ITD protein methylation at arginine 972/973, and PRMT1 promoted leukemia cell growth in an FLT3 methylation–dependent manner. Moreover, the effects of FLT3-ITD methylation in AML cells were partially due to cross talk with FLT3-ITD phosphorylation at tyrosine 969. Importantly, FLT3 methylation persisted in FLT3-ITD+ AML cells following kinase inhibition, indicating that methylation occurs independently of kinase activity. Finally, in patient-derived xenograft and murine AML models, combined administration of AC220 with a type I PRMT inhibitor (MS023) enhanced elimination of FLT3-ITD+ AML cells relative to AC220 treatment alone. Our study demonstrates that PRMT1-mediated FLT3 methylation promotes AML maintenance and suggests that combining PRMT1 inhibition with FLT3 TKI treatment could be a promising approach to eliminate FLT3-ITD+ AML cells.