2-Deoxy-2-fluoro-D-mannose induces type II cell death in gliomas.

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We have hypothesized that blocking glycolysis, the major energy producing pathway for fast growing, glycolytically depended cancers such as gliomas may be a powerful therapeutic strategy when used alone or in combination therapy to enhance the effects of chemotherapy in energy starved tumors. Our previous studies using the D-glucose antimetabolites 2-deoxy-D-glucose (2-DG) and 2-fluoro-deoxy-D-glucose (2-FG) have demonstrated that such an approach induces autophagic cell death in vitro and antitumor activity in vivo comparable to drugs such as temozolomide in orthotopic glioma models. In this study we investigated a novel glucose analog, 2-deoxy-2-fluoro-D-mannose (2-FM), for its ability to block glycolysis and induce autophagic cell death. Cell viability assays were carried in U87 cells treated for 72h with increasing concentrations of the 2-FM under hypoxic and normoxic conditions. The results showed 2-FM to have comparable cytotoxicity as that demonstrated by 2-DG and 2-FG in U87 cells. The IC50 values for 2-FM in U87 cells treated for 72 hrs were 3 mM in cells treated under normoxic conditions (21% O₂) and 2 mM when cells were under hypoxic conditions (0.1% O₂). To test the ability of the 2-FM to induce autophagic cell death we monitored the increase in acidic vesicular organelles (AVO) using acridine orange staining in U87 cells treated with 5 mM 2-FM for 72 hours. The results showed a significant increase in acridine orange staining indicating autophagic cell death under normoxia. In addition, transmission electron microscopy (TEM) studies of the cells treated with 5 mM 2-FM revealed formation of multilamellar structures, otherwise called autophagosomes, confirming Type II - autophagic cell death in cells treated with 2-FM. Our studies show that 2-FM is an equally potent inhibitor of cell proliferation and an inducer of autophagic cell death in gliomas as are 2-DG and 2-FG, and that targeting energetic metabolism of cancer cells and the autophagic survival response using inhibitors of glycolysis is a promising therapeutic approach to the treatment of cancers that are heavily dependent on glycolysis for survival.