panobinostat and Leukemia--Lymphocytic--Chronic--B-Cell

Interleukin-6 (IL-6) is a pleiotropic cytokine produced by a variety of cell types, including fibroblasts, endothelial cells, lymphocytes, and bone marrow stromal cells (BMSCs). Levels of IL-6 are increased in serum of CLL patients and correlated with adverse clinical features and short survival. In our study, we observed that IL-6 induced the resistance of CLL cells to pan-histone deacetylase (HDAC) inhibitors vorinostat (SAHA) and panobinostat (LBH589). Furthermore, low concentrations of SAHA and LBH589 enhanced the activation of the signal transducer and activator of transcription 3 (STAT3) signaling pathway induced by IL-6 in CLL cells. All of these effects were blocked by the STAT3-selective inhibitor, WP1066. Meanwhile, WP1066 decreased the expressions of Mcl-1 and Bcl-xL protein induced by IL-6 with or without low concentrations of HDAC inhibitors. Co-culture of CLL cells with BMSCs could also facilitate the activation of STAT3 and protected CLL cells from apoptosis when treated with HDAC inhibitors, and this cytoprotection was reversed by WP1066. The present study indicated that IL-6 or co-culture with BMSCs prevented HDAC inhibitor-induced apoptosis of CLL cells. This prevention was mediated by activation of the STAT3 signaling pathway. Moreover, WP1066 reversed the resistance of CLL cells to SAHA and LBH589 induced by either IL-6 or co-culture with BMSCs. Our findings suggest that targeting the STAT3 pathway may be a novel way to improve the efficacy of the HDAC inhibitor in CLL patients by overcoming antiapoptotic signaling of the microenvironment.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; bcl-X Protein; Cell Survival; Coculture Techniques; Drug Resistance, Neoplasm; Female; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Indoles; Interleukin-6; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Myeloid Cell Leukemia Sequence 1 Protein; Panobinostat; Phosphorylation; Protein Processing, Post-Translational; Pyridines; STAT3 Transcription Factor; Stromal Cells; Tumor Cells, Cultured; Tyrphostins; Vorinostat

Chronic lymphocytic leukemia (CLL) demonstrates a global down-regulation of miR-15a and miR-16 and a selective silencing of the related miR-29b in aggressive disease. Deletions in chromosome 13 [del(13q14)] partially account for the loss of expression of miR-15a and miR-16, but the mechanisms by which miR-29b becomes silenced is unknown. In the present study, we show that the histone deacetylases (HDACs) are overexpressed in CLL and mediate the epigenetic silencing of miR-15a, miR-16, and miR-29b. HDAC inhibition triggered the accumulation of the transcriptionally activating chromatin modification H3K4me2 and restored the expression of miR-15a, miR-16, and miR-29b in approximately 35% of samples. Ectopic expression of miR-15a and miR-16 and HDAC inhibition-induced expression of miR-15a, miR-16, or miR-29b in primary CLL cells was associated with declines in the levels of Mcl-1, but not Bcl-2, mitochondrial dysfunction, and induction of cell death. Therefore, our results show that HDACs aberrantly silence the expression of the critical tumor suppressors miR-15a, miR-16, and miR-29b in CLL. Deacetylase inhibition may be a therapeutic strategy that restores the expression of these miRs to antagonize Mcl-1, an important survival protein in these cells. Consequently, CLL patients who exhibit such epigenetic silencing may benefit from HDAC inhibitor-based therapy.

Topics: Adult; Benzamides; Female; Gene Expression Regulation, Leukemic; Gene Silencing; Histone Deacetylase Inhibitors; Histone Deacetylases; Humans; Hydroxamic Acids; Indoles; Leukemia, Lymphocytic, Chronic, B-Cell; Male; MicroRNAs; Panobinostat; Primary Cell Culture; Pyridines; Tumor Cells, Cultured

Topics: Adult; Aged; Aged, 80 and over; Biphenyl Compounds; Drug Synergism; Female; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; In Vitro Techniques; Indoles; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Nitrophenols; Panobinostat; Piperazines; Proto-Oncogene Proteins c-bcl-2; Sulfonamides; Tumor Cells, Cultured; Vorinostat

E3 ubiquitin ligases catalyze the final step in the ubiquitylation cascade and therefore determine the specificity of this important cellular metabolic pathway. Although first thought to be constitutively active, increasing evidence demonstrates the existence of a wide variety of posttranslational modifications that regulate the activity of these enzymes. Here we show that upon induction of apoptosis the ubiquitin ligase Itch is processed by caspases both in vitro and ex vivo in cells from patients with chronic lymphocytic leukemia (CLL). The specific cleavage site was mapped to residue Asp240. Interestingly, cleavage of Itch by active caspases does not inhibit the catalytic activity of Itch, but results in the loss of an N-terminal Itch fragment that contains a negative regulatory region. Our data suggests that caspase-dependent Itch cleavage might be an important regulator of Itch at the endogenous level under both physiological and stressed conditions.

Topics: Apoptosis; Caspases; Catalysis; Enzyme Inhibitors; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Indoles; Leukemia, Lymphocytic, Chronic, B-Cell; Panobinostat; Repressor Proteins; Stress, Physiological; Substrate Specificity; Tumor Cells, Cultured; Ubiquitin-Protein Ligases

Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF family, which is being developed as an anti-tumour agent due to its selective toxicity to tumour cells, induces apoptosis by binding to two membrane-bound receptors, TRAIL-R1 and TRAIL-R2. Clinical trials have been initiated with various preparations of TRAIL as well as agonistic monoclonal antibodies to TRAIL-R1 and TRAIL-R2. Previously we reported that prior treatment of primary chronic lymphocytic leukaemia (CLL) cells with histone deacetylase inhibitors was required to sensitize CLL cells to TRAIL and, using various receptor-selective TRAIL mutant ligands, we demonstrated that CLL cells signalled to apoptosis primarily through TRAIL-R1. Some, but not all, agonistic TRAIL-receptor antibodies require cross-linking in order to induce apoptosis. The present study demonstrated that CLL cells can signal to apoptosis through the TRAIL-R2 receptor, but only after cross-linking of the agonistic TRAIL-R2 antibodies, LBY135 and lexatumumab (HGS-ETR2). In contrast, signalling through TRAIL-R1 by receptor-selective ligands or certain agonistic antibodies, such as mapatumumab (HGS-ETR1), occurs in the absence of cross-linking. These results further highlight important differences in apoptotic signalling triggered through TRAIL-R1 and TRAIL-R2 in primary tumour cells. Such information is clearly important for the rational optimisation of TRAIL therapy in primary lymphoid malignancies, such as CLL.

Topics: Aged; Aged, 80 and over; Antibodies, Monoclonal; Antibodies, Monoclonal, Murine-Derived; Apoptosis; Cell Communication; Cell Line, Tumor; Cross-Linking Reagents; Drug Interactions; Ephrins; Female; Humans; Hydroxamic Acids; Indoles; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Panobinostat; Receptors, TNF-Related Apoptosis-Inducing Ligand; TNF-Related Apoptosis-Inducing Ligand