2-Deoxy-d-glucose induces unfolded protein response mediated apoptosis via CHOP/GADD153 in select tumor cells growing under normoxia

4464

Cells growing under hypoxia are solely dependent on glucose metabolism via glycolysis for energy production. Consequently, when this pathway is blocked, with 2-deoxy-D-glucose (2DG), hypoxic cells die. In contrast, when glycolysis is blocked under normoxia most cells survive since fats and proteins can substitute as energy sources to fuel mitochondrial oxidative phosphorylation. However, here we find that under normal oxygen tension, a select number of tumor cell lines undergo an unfolded protein response (UPR) mediated apoptosis via CHOP/GADD153 at a relatively low dose of 2-DG (4 mM). These results coincide with previous studies on viral coat glycoprotein synthesis in which it was shown that 2-DG interferes with the process of N-linked glycosylation, that can be reversed by addition of exogenous mannose. Thus, our results which show that 2-DG toxicity under normoxia can be completely reversed by low dose mannose (1 mM), implicate glycosylation and not glycolysis as the mechanism responsible for this phenomenon. Additionally, 2-fluoro-deoxy-D-glucose (2-FDG) which is more potent than 2-DG in blocking glycolysis and killing these cells when grown under anaerobic conditions, shows little or no toxicity to these same cells under normoxia. Furthermore, the molecular chaperones, GRP 94 and 78, which are known to be induced by an unfolded protein response (UPR) when N-linked glycosylation is altered, were found to be upregulated by 2-DG and this induction could be reversed by mannose. In addition, 2-DG was more potent in inducing UPR in sensitive vs. resistant cells growing under normoxia. Since 2-DG has been shown to be well-tolerated in phase I clinical trials when used in combination with chemotherapeutic agents, our results raise the possibility that in certain tumor cell types, this sugar analog could be used as a single agent to selectively kill both the aerobic (via interference with glycosylation) as well as the hypoxic (via inhibition of glycolysis) cells of a solid tumor.