Potentiation of the lethality of the histone deacetylase inhibitor LAQ824 by the cyclin-dependent kinase inhibitor roscovitine in human leukemia cells

• Published in: Molecular cancer therapeutics 2005-11, Vol.4 (11), p.1772-1785
• Main Authors: Rosato, Roberto R, Almenara, Jorge A, Maggio, Sonia C, Atadja, Peter, Craig, Ruth, Vrana, Julie, Dent, Paul, Grant, Steven
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents - pharmacology; Apoptosis; Apoptosis Inducing Factor - metabolism; Blotting, Western; Cell Cycle; Cell Line, Tumor; Cyclin-Dependent Kinase Inhibitor p21 - metabolism; Cytochromes c - metabolism; Cytosol - metabolism; Down-Regulation; Enzyme Inhibitors - pharmacology; Flow Cytometry; histone deacetylase inhibitor; Histone Deacetylase Inhibitors; HL-60 Cells; Humans; Hydroxamic Acids - pharmacology; Jurkat Cells; LAQ824; Leukemia; Leukemia - drug therapy; Leukemia - enzymology; Membrane Potentials; Mitochondria - pathology; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins - metabolism; Protein Conformation; Protein Kinase Inhibitors - pharmacology; Proto-Oncogene Proteins c-bcl-2 - metabolism; Purines - pharmacology; Reactive Oxygen Species; Reverse Transcriptase Polymerase Chain Reaction; roscovitine; Time Factors; U937 Cells; X-Linked Inhibitor of Apoptosis Protein - metabolism; XIAP
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-05-0157

Interactions between the novel histone deacetylase inhibitor LAQ824 and the cyclin-dependent kinase inhibitor roscovitine were examined in human leukemia cells. Pretreatment (24 hours) with a subtoxic concentration of LAQ824 (30 nmol/L) followed by a minimally toxic concentration of roscovitine (10 μmol/L; 24 hours) resulted in greater than additive effects on apoptosis in U937, Jurkat, and HL-60 human leukemia cells and blasts from three patients with acute myelogenous leukemia. These events were associated with enhanced conformational changes in Bax; mitochondrial release of cytochrome c , Smac/DIABLO, and apoptosis-inducing factor; and a marked increase in caspase activation. LAQ824/roscovitine–treated cells displayed caspase-dependent down-regulation of p21 CIP1 and Mcl-1 and a pronounced caspase-independent reduction in X-linked inhibitor of apoptosis (XIAP) expression. The lethality of this regimen was significantly attenuated by ectopic expression of XIAP, a nuclear localization signal–defective p21 CIP1 mutant, Mcl-1, and Bcl-2. Combined exposure to LAQ824 and roscovitine resulted in a significant reduction in XIAP mRNA levels and diminished phosphorylation of the carboxyl-terminal domain of RNA polymerase II. Notably, roscovitine blocked LAQ824-mediated differentiation. Finally, LAQ824 and roscovitine individually and in combination triggered an increase in generation of reactive oxygen species; moreover, coadministration of the free radical scavenger N -acetylcysteine prevented LAQ824/roscovitine–mediated mitochondrial injury and apoptosis. Collectively, these findings suggest that combined treatment of human leukemia cells with LAQ824 and roscovitine disrupts maturation and synergistically induces apoptosis, lending further support for an antileukemic strategy combining novel histone deacetylase and cyclin-dependent kinase inhibitors.