laq824 and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

In a variety of malignant cells the prostate-apoptosis-response-gene-4 (Par-4) induces increased sensitivity towards chemotherapeutic agents by down-regulating anti-apoptotic B-cell lymphoma-gene 2 (Bcl-2). Hypothesizing that Par-4 also influences apoptosis in myeloid cell lines, we tested this hypothesis by stably transfecting bcr-abl transformed-K562 cells with a Par-4-expressing vector. Here we demonstrate that over-expression of Par-4 in K562 cells up-regulates expression levels of Bcl-2 and death-associated protein (Daxx). Upon treatment with different chemotherapeutic agents, Fas- or TRAIL agonistic antibodies, Par-4-positive cells did not exhibit an increased rate of apoptosis as compared to Par-4-negative control cells. However, incubation with histone deacetylase (HDAC)-inhibitors Trichostatin A (TSA) and LAQ824 or the tyrosinkinase inhibitor Imatinib (STI571) increased the rate of apoptosis in Par-4-positive K562 cells. Assessing the underlying molecular mechanisms for the Par-4-induced response to HDAC-inhibitors and STI571 we provide evidence, that these effects are associated with a down-regulation of Daxx, enforced activation of caspases and enhanced cleavage of cellular inhibitor of apoptosis (cIAP)-1 and -2.

Topics: Adaptor Proteins, Signal Transducing; Antibodies; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Benzamides; Carrier Proteins; Caspases; Co-Repressor Proteins; Down-Regulation; Drug Screening Assays, Antitumor; Enzyme Inhibitors; fas Receptor; Fusion Proteins, bcr-abl; Gene Expression; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Imatinib Mesylate; Inhibitor of Apoptosis Proteins; Intracellular Signaling Peptides and Proteins; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Membrane Glycoproteins; Molecular Chaperones; Myeloid Cells; Nuclear Proteins; Piperazines; Proteins; Proto-Oncogene Proteins c-bcl-2; Pyrimidines; TNF-Related Apoptosis-Inducing Ligand; Tumor Necrosis Factor-alpha; Up-Regulation

Treatment with LAQ824 (Novartis Pharmaceutical, Inc.), a cinnamyl hydroxamic acid analogue inhibitor of histone deacetylases, depleted the mRNA and protein expression of Bcr-Abl in human chronic myeloid leukemia blast crisis (CML-BC) cells. Exposure to LAQ824 induced the expression of the cell cycle-dependent kinase inhibitors p21 and p27 and caused cell cycle G(1)-phase accumulation and apoptosis of CML-BC cells. LAQ824 also induced acetylation of heat shock protein 90. This inhibited the chaperone association of Bcr-Abl with heat shock protein 90, thereby promoting the proteasomal degradation of Bcr-Abl. Cotreatment with LAQ824 increased imatinib mesylate-induced apoptosis of CML-BC cells. Additionally, LAQ824 down-regulated the levels of mutant Bcr-Abl possessing the T315I point mutation, as well as induced apoptosis of imatinib-refractory primary CML-BC cells. Therefore, LAQ824 may be a promising therapeutic agent in the treatment of imatinib-sensitive or -refractory human leukemia.

Topics: Acetylation; Antineoplastic Agents; Apoptosis; Benzamides; Blast Crisis; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Cysteine Endopeptidases; Drug Resistance, Neoplasm; Enzyme Inhibitors; Fusion Proteins, bcr-abl; G1 Phase; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Microfilament Proteins; Multienzyme Complexes; Muscle Proteins; Piperazines; Promoter Regions, Genetic; Proteasome Endopeptidase Complex; Pyridones; Pyrimidines; Tumor Cells, Cultured