Tumors show an increased rate of glucose uptake and utilization. For this reason, glucose analogs are used to visualize tumors by the positron emission tomography technique, and inhibitors of glycolytic metabolism are being tested in clinical trials. Upregulation of glycolysis confers several advantages to tumor cells: it promotes tumor growth and has also been shown to interfere with cell death at multiple levels. Enforcement of glycolysis inhibits apoptosis induced by cytokine deprivation. Conversely, antiglycolytic agents enhance cell death induced by radio-and chemotherapy. Synergistic effects are likely due to regulation of the apoptotic machinery, as glucose regulates activation and levels of proapoptotic BH3-only proteins such as Bim, Bad, Puma and Noxa, as well as the antiapoptotic Bcl-2 family of proteins. Moreover, inhibition of glucose metabolism sensitizes cells to death ligands. Glucose deprivation and antiglycolytic drugs induce tumor cell death, which can proceed through necrosis or through mitochondrial or caspase-8-mediated apoptosis. We will discuss how oncogenic pathways involved in metabolic stress signaling, such as p53, AMPK (adenosine monophosphate-activated protein kinase) and Akt/mTOR (mammalian target of rapamycin), influence sensitivity to inhibition of glucose metabolism. Finally, we will analyze the rationale for the use of antiglycolytic inhibitors in the clinic, either as single agents or as a part of combination therapies.

Alveolar and embryonal rhabdomyosarcomas are childhood tumors that do not respond well to current chemotherapies. Here, we report that the glycolytic inhibitor 2-deoxyglucose (2-DG) can efficiently promote cell death in alveolar, but not embryonal, rhabdomyosarcoma cell lines. Notably, 2-DG also induced cell differentiation accompanied by downregulation of PAX3/FOXO1a, the chromosome translocation-encoded fusion protein that is a central oncogenic driver in this disease. Cell death triggered by 2-DG was associated with its ability to activate Bax and Bak. Overexpression of the antiapoptotic Bcl-2 homologues Bcl-x L and Mcl-1 prevented apoptosis, indicating that cell death proceeds through the mitochondrial pathway. Mechanistic investigations indicated that Mcl-1 downregulation and Noxa upregulation were critical for 2-DG-induced apoptosis. In addition, 2-DG promoted eIF2a phosphorylation and inactivation of the mTOR pathway. Mcl-1 loss and cell death were prevented by downregulation of the endoplasmic reticulum (ER) stress-induced protein ATF4 and by incubating cells in the presence of mannose, which reverted 2-DG-induced ER stress but not ATP depletion. Thus, energetic stresses created by 2-DG were not the primary cause of cell death. Together, our findings suggest that glycolysis inhibitors such as 2-DG may be highly effective in treating alveolar rhabdomyosarcoma and that Noxa could offer a prognostic marker to monitor the efficacy of such agents. Cancer Res; 71(21); 6796-806. Ó2011 AACR.

Background: Autophagy is a response to nutrient deprivation. Results: Inhibition of autophagy does not sensitize cells to apoptotic or necrotic cell death induced by glucose starvation. Moreover, glucose deprivation inhibits autophagy. Conclusion: 2-Deoxyglucose, but not glucose deprivation, induces autophagy. Significance: Not all forms of starvation induce cytoprotective autophagy in mammalian cells.

Apoptosis induced by most stimuli proceeds through the mitochondrial pathway. One such stimulus is nutrient deprivation. In this study we studied death induced by glucose deprivation in cells deficient in Bax and Bak. These cells cannot undergo mitochondrial outer membrane permeabilization (MOMP) during apoptosis, but they undergo necrosis when treated with MOMPdependent apoptotic stimuli. We find in these cells that glucose deprivation, rather than inducing necrosis, triggered apoptosis. Cell death required caspase activation as inhibition of caspases with peptidic inhibitors prevented death. Glucose deprivationinduced death displayed many hallmarks of apoptosis, such as caspase cleavage and activity, phosphatidyl-serine exposure and cleavage of caspase substrates. Neither overexpression of Bcl-xL nor knockdown of caspase-9 prevented death. However, transient or stable knockdown of caspase-8 or overexpression of CrmA inhibited apoptosis. Cell death was not inhibited by preventing death receptor-ligand interactions, by overexpression of c-FLIP or by knockdown of RIPK1. Glucose deprivation induced apoptosis in the human tumor cell line HeLa, which was prevented by knockdown of caspase-8. Thus, we have found that glucose deprivation can induce a death receptor-independent, caspase-8-driven apoptosis, which is engaged to kill cells that cannot undergo MOMP. Apoptosis is a form of cell death required for homeostasis of human tissues. Apoptotic cells display several morphological and biochemical changes, which are a consequence of the activity of caspase proteases.1 Caspases are normally inactive in the cytosol, but they become activated by dimerization and/or proteolysis by other caspases. 'Executioner' caspases such as caspase-3 are activated through cleavage by 'initiator' or 'apical' caspases, of which the best characterized are caspases-8 and -9. Caspase-8 is activated by its recruitment to the multimeric DISC (death-inducing signaling complex) in response to extracellular ligands such as Fas/CD95-ligand, TRAIL or TNF; 2 this is the death receptor, or extrinsic pathway of apoptosis. Caspase-9 is activated by dimerization after recruitment to the apoptosome, a complex of APAF1 proteins formed in response to the release of the mitochondrial protein cytochrome c into the cytosol. 3 This caspase activation cascade is called the mitochondrial or intrinsic pathway of apoptosis.The mitochondrial pathway of apoptosis is regulated by proteins of the Bcl-2 family, which regulate the integrity of the mitochondrial outer membrane, thereby controlling cytochrome c and subsequent caspase activation.4 Impairment of the mitochondrial pathway is common in human tumors. Cancer cells frequently overexpress the antiapoptotic proteins Bcl-2, Bcl-xL and Mcl-1, or they lack functional proapoptotic Bcl-2 family members, including Bax, Bak or both. 5 The overexpression of antiapoptotic Bcl-2 proteins not only blocks the morphological features of apoptosis, but also enables clonogenic cell survival. 6 For these reasons, cells from Bax, B...