BACKGROUND AND OBJECTIVE: Oncoprotein Myc is a master transcription factor and plays a crucial role in human cancer pathogenesis and the stem-like phenotype of glioblastoma (GBM). Since dyregulated Myc in cancer drives altered glucose and glutamine metabolism promoting tumor growth, pathways involved in Myc-induced aberrant metabolism could offer therapeutic targets. The coenzyme Nicotinamide Adenine Dinucleotide (NAD+) is essential in redox reactions including glycolysis and the citric acid cycle. We sought to determine whether MYC-amplified GBM, as compared to MYC-non-amplified GBM, utilizes distinct NAD+ biosynthesis pathways and exhibits differential dependence on metabolic pathways that require NAD+. MATERIALS AND METHODS: A total of 11 patient-derived GBM stem-like cell (GSCs) lines established from surgical specimens were used. FISH analysis was performed to determine copy number status of MYC and MYCN. Expression of enzymes involved in NAD+ synthesis [e.g., nicotinamide phosphoribosyltransferase (NAMPT) and nicotinic acid phosphoribosyltransferase (NAPRT-1)] was tested with Western blot. NAD+ levels were measured after treating GSCs with FK866, a potent and specific small molecule inhibitor for NAMPT. The effects of pharmacological inhibition of NAMPT on GSC viability were determined by CellTiter Glo cell viability assay. RESULTS: Five (45.5%) GSCs had MYC (1) or MYCN (4) amplification. FK866 depleted NAD+ levels in GSCs. Treatment with FK866 potently inhibited in vitro growth of all the GSCs that harbored MYC/MYCN amplification with IC50 values in a low-nanomolar range (0.7 - 4.6 nM). In contrast, non-amplified GSCs as well as human normal astrocytes showed resistance to FK866. The MYC/MYCN amplified GSCs expressed low or undetectable levels of NAPRT-1, which is involved in the NAD+ synthesis pathway utilizing nicotinic acid. CONCLUSIONS: MYC/MYCN-amplified GSCs, but not non-amplified GSCs, were exquisitely sensitive to NAMPT inhibition. NAMPT may represent a promising therapeutic target for GBM with MYC amplification.