CD44 and central nervous system cancer: NAMPT mutations319 enhance NAD+ synthesis through other pathways, such as the de novo pathway, upregulate quinolinic acid phosphoribosyltransferase (QAPRT), and enhance amino acid catabolism (for example, tryptophan in the de novo pathway or glutamine in the salvage pathway).320 Moreover, resistance to cancer therapy has been attributed to the self-renewal and dedifferentiation of cancer stem cells (CSCs) residing within the tumor.321 CD133-high/CD44-high populations of glioma cell lines are enriched in NAMPT, correlating with glioma stem cells.