Pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), an enzyme essential for NAD+ biosynthesis, in human cancer cells: metabolic basis and potential clinical implications.

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.

The Folate Pathway Inhibitor Pemetrexed Pleiotropically Enhances Effects of Cancer Immunotherapy.

PURPOSE: Combination strategies leveraging chemotherapeutic agents and immunotherapy have held the promise as a method to improve benefit for patients with cancer. However, most chemotherapies have detrimental effects on immune homeostasis and differ in their ability to induce immunogenic cell death (ICD). The approval of pemetrexed and carboplatin with anti-PD-1 (pembrolizumab) for treatment of non-small cell lung cancer represents the first approved chemotherapy and immunotherapy combination. Although the clinical data suggest a positive interaction between pemetrexed-based chemotherapy and immunotherapy, the underlying mechanism remains unknown. EXPERIMENTAL DESIGN: Mouse tumor models (MC38, Colon26) and high-content biomarker studies (flow cytometry, Quantigene Plex, and nCounter gene expression analysis) were deployed to obtain insights into the mechanistic rationale behind the efficacy observed with pemetrexed/anti-PD-L1 combination. ICD in tumor cell lines was assessed by calreticulin and HMGB-1 immunoassays, and metabolic function of primary T cells was evaluated by Seahorse analysis. RESULTS: Pemetrexed treatment alone increased T-cell activation in mouse tumors in vivo, robustly induced ICD in mouse tumor cells and exerted T-cell-intrinsic effects exemplified by augmented mitochondrial function and enhanced T-cell activation in vitro. Increased antitumor efficacy and pronounced inflamed/immune activation were observed when pemetrexed was combined with anti-PD-L1. CONCLUSIONS: Pemetrexed augments systemic intratumor immune responses through tumor intrinsic mechanisms including immunogenic cell death, T-cell-intrinsic mechanisms enhancing mitochondrial biogenesis leading to increased T-cell infiltration/activation along with modulation of innate immune pathways, which are significantly enhanced in combination with PD-1 pathway blockade.See related commentary by Buque et al., p. 6890.