Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first rate-limiting step in converting
nicotinamide to
NAD(+), essential for cellular metabolism, energy production, and DNA repair. NAMPT has been extensively studied because of its critical role in these cellular processes and the prospect of developing
therapeutics against the target, yet how it regulates cellular metabolism is not fully understood. In this study we utilized liquid chromatography-mass spectrometry to examine the effects of FK866, a small molecule inhibitor of NAMPT currently in clinical trials, on glycolysis, the pentose phosphate pathway, the
tricarboxylic acid (TCA) cycle, and
serine biosynthesis in
cancer cells and
tumor xenografts. We show for the first time that NAMPT inhibition leads to the attenuation of glycolysis at the
glyceraldehyde 3-phosphate dehydrogenase step due to the reduced availability of
NAD(+) for the
enzyme. The attenuation of glycolysis results in the accumulation of glycolytic intermediates before and at the
glyceraldehyde 3-phosphate dehydrogenase step, promoting
carbon overflow into the pentose phosphate pathway as evidenced by the increased intermediate levels. The attenuation of glycolysis also causes decreased glycolytic intermediates after the
glyceraldehyde 3-phosphate dehydrogenase step, thereby reducing
carbon flow into
serine biosynthesis and the TCA cycle. Labeling studies establish that the
carbon overflow into the pentose phosphate pathway is mainly through its non-oxidative branch. Together, these studies establish the blockade of glycolysis at the
glyceraldehyde 3-phosphate dehydrogenase step as the central metabolic basis of NAMPT inhibition responsible for
ATP depletion, metabolic perturbation, and subsequent
tumor growth inhibition. These studies also suggest that altered metabolite levels in
tumors can be used as robust pharmacodynamic markers for evaluating NAMPT inhibitors in the clinic.