APO866 is a potent inhibitor of
nicotinamide phosphoribosyltransferase (NAMPT), and inhibits
nicotinamide adenine dinucleotide (
NAD) synthesis. Our previous study showed that
APO866 inhibits the proliferation of C6
glioblastoma cells, but failed to induce apoptosis. Since
APO866 inhibits cellular metabolism and such metabolic stress is closely related with autophagy, thus we determined whether
APO866 can induce autophagy in C6
glioblastoma cells and whether the autophagy induced by
APO866 is pro-death or pro-survival. Using LC3 immunofluorescence imaging and transmission electron microscopy detection, we found that
APO866 at 1-100 nM induced autophagy in C6
glioblastoma cells.
APO866 at 1 nM mainly induced initial autophagic vacuoles. Whereas
APO866 at 100 nM induced degrading autophagic vacuoles, as well as induced nuclei malformation and mitochondria swelling. In addition,
APO866 concentration-dependently decreased the cell viability of C6
glioblastoma cells, and this effect was attenuated by autophagy inhibitors, including
3-methyladenine and
LY294002.
APO866 concentration-dependently decreased intracellular
NAD level. Interestingly,
APO866 at 1 nM slightly decreased intracellular
NAD level, but dramatically increased autophagy-positive cells. The dramatical cell viability decreasing required the decreasing of intracellular
NAD level to a very low threshold. Thus, our results indicated that
APO866 induced pro-death autophagy in C6
glioblastoma cells by decreasing intracellular
NAD, and low concentration of
APO866 can be used as an autophagy inducer in autophagic-death sensitive
glioblastoma.