Abstract 3052: NAMPT inhibition induces mitochondrial dysfunction leading to apoptosis in chronic lymphocytic leukemia cells

We have previously shown that the NAD depletion following inhibition of NAMPT by the NA-mimetic FK866 leads to loss of mitochondrial membrane potential, depletion of cellular ATP, cytochrome C release and caspase activation in primary Chronic Lymphocytic Leukemia (CLL) cells in vitro, and that these events are coupled with an increased production of reactive oxygen species uncharacteristic of metabolic inhibition. In the present study we characterize the effect of NAD depletion on CLL mitochondria and the downstream mechanism of cell death. We profiled the mitochondrial respiration of CLL cells and control B-lymphocytes, by extracellular flux analysis, over the 48 hours following FK866 treatment and found time-dependant inhibition of respiratory capacity consistent with disruption of the electron transport chain (ETC) in CLL cells. This led to suppression of basal respiration concomitant with the rise in ROS and approximately one day before loss of cellular viability. Interestingly, Zap70-positive CLL cells exhibited increased mitochondrial respiration and respiratory capacity over Zap70-negative CLL cells, but responded similarly to NAMPT inhibition. Additionally, mitochondrial respiration was not effected by NAMPT inhibition in control B-lymphocytes. Increase autophagic flux, caspase-dependant apoptosis and mitochondrio-nuclear translocation of Apoptosis Inducing Factor (AIF) were detected by western blot. However, neither pan-caspase inhibition with Z-VAD-fmk nor inhibition of autophagy with 3-methyladenine were sufficient to prevent FK866-induced CLL cell death. We conclude that NAD depletion following inhibition of NAMPT leads to disruption of the mitochondrial ETC in CLL cells, leading to mitochondrial initiation of the intrinsic apoptosis pathway. As healthy B-lymphocytes are resistant to this NAD depletion, these downstream effects are also selective for malignant cells. We are currently working to characterize the roles of NAD and Zap70 in the regulation and function of the CLL ETC. This will not only lead to an improved understanding of CLL metabolism, but will also inform new therapeutic strategies that will effectively employ NAMPT inhibition to treat this yet-incurable disease. Citation Format: Eric DJ Bouchard, Edgard M. Mejia, Iris Gehrke, Armando G. Poeppl, Donna Hewitt, James B. Johnston, Spencer B. Gibson, Grant M. Hatch, Versha Banerji. NAMPT inhibition induces mitochondrial dysfunction leading to apoptosis in chronic lymphocytic leukemi