Abstract 1045: Targeting NAMPT in Ewing's sarcoma cells

Abstract

Abstract Ewing Sarcoma (ES) is the second most common bone cancer in children and adolescents with a high metastatic potential. Tumor development is driven by the specific t(11;22)(q24;q12) chromosomal translocation resulting in the generation of the chimeric transcription factor EWS-FLI1. NAD is a key metabolite of energy metabolism being involved in cellular redox reactions, DNA repair, and in the maintenance of genomic stability serving as a donor of ADP-ribose. This study describes targeting NAMPT (nicotinamide phosphoribosyltransferase), the rate-limiting enzyme in salvage generation of NAD, by FK866 in ES cells. Using FK866 has been proposed as a treatment option for various inflammatory diseases as well as cancer, rendering ES cells with high NAMPT expression especially susceptible to FK866-induced cytotoxicity. Here we report that NAMPT inhibition in ES cells leads to exhaustive NAD depletion, followed by a delayed reduction of ATP levels and concomitantly to apoptosis-mediated cell death. These effects can be reversed by nicotinic acid, a substrate for the NAD salvage generation. However, the use of a doxycycline-inducible shRNA against EWS-FLI1 revealed that the cytotoxic activity of NAMPT inhibition is significantly lowered in the absence of EWS-FLI1. EWS-FLI1-low ES cells have higher viability and lower rates of apoptosis throughout inhibitor treatment compared to cells with high EWS-FLI1 expression. Additionally, changes in mitochondrial respiration and glycolytic rate can be observed when comparing untreated versus EWS-FLI1 knockdown ES cells after NAMPT inhibition. Interestingly, loss of EWS-FLI1 leads to elevated NAD levels and results in alteration of RNA expression of some enzymes involved in the NAD synthesis pathway. These results might explain the high susceptibility of Ewing Sarcoma cells to FK866 treatment. Taken together, our data reveal evidence of an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of ES cells and suggests NAMPT inhibition as a potential new treatment approach for Ewing Sarcoma in combination with standard therapies. Supported by the Austrian Science fund, grant I1225-B19; and the Research Manitoba and CancerCare Manitoba Foundation. Citation Format: Cornelia N. Mutz, Raphaela Schwentner, Eric Bouchard, Edgard M. Mejia, Anna M. Katschnig, Maximilian O. Kauer, Dave N.T. Aryee, Antje Garten, Versha Banerji, Heinrich Kovar. Targeting NAMPT in Ewing's sarcoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1045.