The Histone Deacetylase Inhibitor LAQ824 Induces Human Leukemia Cell Death through a Process Involving XIAP Down-Regulation, Oxidative Injury, and the Acid Sphingomyelinase-Dependent Generation of Ceramide

• Published in: Molecular pharmacology 2006-01, Vol.69 (1), p.216-225
• Main Authors: Rosato, Roberto R, Maggio, Sonia C, Almenara, Jorge A, Payne, Shawn G, Atadja, Peter, Spiegel, Sarah, Dent, Paul, Grant, Steven
• Format: Article
• Language: English
• Subjects: Apoptosis - drug effects; Ceramides - biosynthesis; Down-Regulation; Enzyme Inhibitors - pharmacology; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids - pharmacology; Jurkat Cells; Leukemia - pathology; Oxidative Stress; Reverse Transcriptase Polymerase Chain Reaction; Sphingomyelin Phosphodiesterase - metabolism; U937 Cells; X-Linked Inhibitor of Apoptosis Protein - physiology
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.105.017145

Determinants of differentiation and apoptosis induction by the novel histone deacetylase inhibitor (HDACI) LAQ824 were examined in human leukemia cells (U937 and Jurkat). Exposure of U937 cells to a low concentration of LAQ824 (30 nM) resulted in a delayed (2 h) increase in reactive oxygen species (ROS), induction of p21 WAF1/CIP1 , pRb dephosphorylation, growth arrest of cells in G 0 /G 1 phase, and differentiation. On the other hand, exposure of cells to a higher concentration of LAQ824 (75 nM) resulted in the early (30 min) generation of ROS, arrest of cells in G 2 /M phase, down-regulation of XIAP (at the transcriptional level) and Mcl-1 (through a caspase-mediated process), the acid sphingomyelinase-dependent generation of ceramide, and profound mitochondrial injury, caspase activation, and apoptosis. LAQ824-induced lethality in U937 cells did not involve the extrinsic apoptotic pathway, nor was it associated with death receptor up-regulation; instead, it was markedly inhibited by ectopic expression of Bcl-2, Bcl-x L , XIAP, and Mcl-1. The free radical scavenger N -acetyl cysteine blocked LAQ824-mediated ROS generation, mitochondrial injury, Mcl-1 down-regulation, ceramide generation, and apoptosis, suggesting a primary role for oxidative injury in LAQ824 lethality. Together, these findings indicate that LAQ824-induced lethality represents a multifactorial process in which LAQ824-mediated ROS generation is necessary but not sufficient to induce apoptosis, and that the degree of XIAP and Mcl-1 down-regulation and ceramide generation determines whether this agent engages a maturation rather than an apoptotic program.