Potent synergistic interaction between the Nampt inhibitor AP0866 and the apoptosis activator TRAIL in human leukemia cells

Objective The nicotinamide phosphoribosyltransferase (Nampt) inhibitor AP0866 depletes intracellular nicotinamide adenine dinucleotide (NAD(+)) and shows promising anticancer activity in preclinical studies Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) binds to plasma membrane receptors DR4 and DR5 and Induces apoptosis via caspase-8 and 10 Here we have explored the interaction between AP0866 and TRAIL in leukemia cell lines and in primary B cell chronic lymphocytic leukemia cells Materials and Methods Cells were treated with AP0866, TRAIL, or their combination Viability and mitochondrial transmembrane potential (Delta Psi(m)) were determined by cell staining with prom dium iodide and tetramethylrhodamine ethyl ester, respectively, and flow cytometry Nampt and gamma tubulin levels, as well as caspase 3 cleavage were detected by immunoblotting DR4 and DR5 expression were assessed by immunostaining and flow cytometry Caspases were inhibited with zVAD-FMK and zDEVD FMK, autophagy with 3-methyladenine, LY294002, and wortmannin Intracellular NAD(+) and adenosine triphosphate (ATP) were measured by cycling assays and high performance liquid chromatography (HPLC), respectively Results AP0866 induced NAD(+) depletion, Delta Psi(m), dissipation, and ATP shortage in leukemia cells, thereby leading to autophagic cell death TRAIL induced caspase dependent apoptosis TRAIL addition to AP0866 synergistically Increased its activity in leukemia cells by enhancing NAD(+) depletion, Delta Psi(m) dissipation, and ATP shortage No DR5 upregulation at the cell surface in response to AP0866 was observed Remarkably, in healthy leukocytes AP0866 and TRAIL were poorly active and failed to show any cooperation Conclusions Activation of the extrinsic apoptotic cascade with TRAIL selectively amplifies the sequelae of Nampt inhibition in leukemia cells, and appears as a promising strategy to enhance AP0866 activity in hematological malignancies (C) 2010 ISEH Society for Hematology and Stem Cells Published by Elsevier Inc