METB-09. NICOTINAMIDE PHOSPHORIBOSYLTRANSFERASE (NAMPT) IS REQUIRED TO MAINTAIN CELLULAR METABOLISM IN GLIOBLASTOMA

Nicotinamide adenine dinucleotide (NAD) is central to cellular metabolism, both as a cofactor and as an enzymatic substrate. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate limiting enzyme in the NAD salvage pathway, generating the NAD precursor nicotinamide mononucleotide from nicotinamide. We found that NAMPT expression is higher in glioblastoma (GBM) cell lines compared to normal astrocytes and is expressed at higher levels in GBM tissue samples vs. non-malignant brain. Pharmacological blockade of NAMPT reduced GBM cells viability in a time- and dose-dependent manner. Metabolic analysis of a GBM cell line treated with the NAMPT inhibitor FK866 revealed a profile of induced changes in energy metabolism. In the glycolysis pathway, NAD+is required for GAPDH function. Inhibition of NAMPT resulted in increased metabolites above the GAPDH reaction and and a decrease in metabolites below the GAPDH step. Metabolic flux analysis further demonstrated that GBM cell lines treated with NAMPT inhibitor have decreased glycolytic capacity. In the TCA cycle, NAMPT inhibition resulted in increased metabolites early in the cycle and decreased metabolites late in the cycle, indicating a decreased ability to complete the TCA cycle. As a result, GBM cells treated with a NAMPT inhibitor have severely impaired mitochondrial capacity. NAMPT blockade also protected cells from the effects of glucose withdrawal, indicating a role in metabolic stress. To gain further insight into the mechanisms associated with NAMPT inhibition, RNA-Seq was performed on U-251 GBM cells treated with FK866. Regulation of phosphorylation and kinase activity, cell migration, and gene regulation were among the most down regulated pathways and cell adhesion, apoptosis, gene regulation, and kinase activity were the most upregulated by NAMPT inhibition. These data provide critical insight into the role of NAD synthesis in GBM energy metabolism and the potential for NAMPT inhibition as a therapeutic option for GBM.