Polycomb Target Genes Are Silenced in Multiple Myeloma

Multiple myeloma (MM) is a genetically heterogeneous disease, which to date remains fatal. Finding a common mechanism for initiation and progression of MM continues to be challenging. By means of integrative genomics, we identified an underexpressed gene signature in MM patient cells compared to normal counterpart plasma cells. This profile was enriched for previously defined H3K27-tri-methylated genes, targets of the Polycomb group (PcG) proteins in human embryonic fibroblasts. Additionally, the silenced gene signature was more pronounced in ISS stage III MM compared to stage I and II. Using chromatin immunoprecipitation (ChIP) assay on purified CD138+ cells from four MM patients and on two MM cell lines, we found enrichment of H3K27me3 at genes selected from the profile. As the data implied that the Polycomb-targeted gene profile would be highly relevant for pharmacological treatment of MM, we used two compounds to chemically revert the H3K27-tri-methylation mediated gene silencing. The S-adenosylhomocysteine hydrolase inhibitor 3-Deazaneplanocin (DZNep) and the histone deacetylase inhibitor LBH589 (Panobinostat), reactivated the expression of genes repressed by H3K27me3, depleted cells from the PRC2 component EZH2 and induced apoptosis in human MM cell lines. In the immunocompetent 5T33MM in vivo model for MM, treatment with LBH589 resulted in gene upregulation, reduced tumor load and increased overall survival. Taken together, our results reveal a common gene signature in MM, mediated by gene silencing via the Polycomb repressor complex. The importance of the underexpressed gene profile in MM tumor initiation and progression should be subjected to further studies

A Potent, Selective and Cell-Active Allosteric Inhibitor of Protein Arginine Methyltransferase 3 (PRMT3)

PRMT3 catalyzes the asymmetric dimethylation of arginine residues of various proteins. It is essential for maturation of ribosomes, may have a role in lipogenesis, and is implicated in several diseases. A potent, selective, and cell- active PRMT3 inhibitor would be a valuable tool for further investigating PRMT3 biology. Here we report the discovery of the first PRMT3 chemical probe, SGC707, by structure-based optimization of the allosteric PRMT3 inhibitors we reported previously, and thorough characterization of this probe in biochemical, biophysical, and cellular assays. SGC707 is a potent PRMT3 inhibitor (IC50 = 31 ± 2 nm, KD = 53 ± 2 nm) with outstanding selectivity (selective against 31 other methyltransferases and more than 250 non-epigenetic targets). The mechanism of action studies and crystal structure of the PRMT3-SGC707 complex confirm the allosteric inhibition mode. Importantly, SGC707 engages PRMT3 and potently inhibits its methyltransferase activity in cells. It is also bioavailable and suitable for animal studies. This well- characterized chemical probe is an excellent tool to further study the role of PRMT3 in health and disease

DNA microarray profiling of genes differentially regulated by the histone deacetylase inhibitors vorinostat and LBH589 in colon cancer cell lines

<p>Abstract</p> <p>Background</p> <p>Despite the significant progress made in colon cancer chemotherapy, advanced disease remains largely incurable and novel efficacious chemotherapies are urgently needed. Histone deacetylase inhibitors (HDACi) represent a novel class of agents which have demonstrated promising preclinical activity and are undergoing clinical evaluation in colon cancer. The goal of this study was to identify genes in colon cancer cells that are differentially regulated by two clinically advanced hydroxamic acid HDACi, vorinostat and LBH589 to provide rationale for novel drug combination partners and identify a core set of HDACi-regulated genes.</p> <p>Methods</p> <p>HCT116 and HT29 colon cancer cells were treated with LBH589 or vorinostat and growth inhibition, acetylation status and apoptosis were analyzed in response to treatment using MTS, Western blotting and flow cytometric analyses. In addition, gene expression was analyzed using the Illumina Human-6 V2 BeadChip array and Ingenuity^®Pathway Analysis.</p> <p>Results</p> <p>Treatment with either vorinostat or LBH589 rapidly induced histone acetylation, cell cycle arrest and inhibited the growth of both HCT116 and HT29 cells. Bioinformatic analysis of the microarray profiling revealed significant similarity in the genes altered in expression following treatment with the two HDACi tested within each cell line. However, analysis of genes that were altered in expression in the HCT116 and HT29 cells revealed cell-line-specific responses to HDACi treatment. In addition a core cassette of 11 genes modulated by both vorinostat and LBH589 were identified in both colon cancer cell lines analyzed.</p> <p>Conclusion</p> <p>This study identified HDACi-induced alterations in critical genes involved in nucleotide metabolism, angiogenesis, mitosis and cell survival which may represent potential intervention points for novel therapeutic combinations in colon cancer. This information will assist in the identification of novel pathways and targets that are modulated by HDACi, providing much-needed information on HDACi mechanism of action and providing rationale for novel drug combination partners. We identified a core signature of 11 genes which were modulated by both vorinostat and LBH589 in a similar manner in both cell lines. These core genes will assist in the development and validation of a common gene set which may represent a molecular signature of HDAC inhibition in colon cancer.</p

Molecular analyses of cellular replicative senescence

Bibliography: p. 212-238

Molecular and cellular basis for the anti-proliferative effects of the HDAC inhibitor LAQ824.

We have developed a cinnamic hydroxamic class of histone deacetylase inhibitors of which a prototype was designated as NVP-LAQ824. NVP-LAQ824, inhibits histone deacetylase enzymatic activities in vitro and transcriptionally activated the p21 promoter in reporter gene assays. When tested on a variety of solid tumour cell lines, NVP-LAQ824 exhibited selective anti-proliferative effects, inducing cell growth inhibition in some, while inducing cell death in others. To induce cell death, a minimum of 16 h exposure to NVP-LAQ824 is required. Flow cytometry studies revealed that both tumour cell lines and normal diploid fibroblasts arrested in the G2/M phase of the cell cycle after compound treatment. However, an increased sub-G1 population at 48 h (reminiscent of apoptotic cells) was only observed in the cancer cell lines. Annexin V staining data confirmed that NVP-LAQ824 induced apoptosis in tumour cells, but not in normal cells. To relate HDAC inhibition to the anti-proliferative effects of NVP-LAQ824, expression of HDAC 1 was inhibited using antisense and this was sufficient to activate p21 expression, hypophosphorylate Rb and inhibit cell growth. Furthermore, tumour cells treated with NVP-LAQ824 caused acetylation of HSP90 and degradation of its cargo oncoproteins. Finally, NVP-LAQ824 exhibited antitumour effects in a xenograft animal model. To determine if NVP-LAQ824 inhibited histone deacetylases in vivo, tumours treated with the drug were immunoblotted with an antibody specific for acetylated histones H3 and H4 and the results indicated increased histone H3 and 114 acetylation levels in NVP-LAQ824 treated cancer cells. Together, our data indicated that the activity of NVP-LAQ824 was consistent with its intended mechanism of action. This novel HDAC inhibitor is currently in clinical trials as an anticancer agent

A histone deacetylase inhibitor LBH589 downregulates XIAP in mesothelioma cell lines which is likely responsible for increased apoptosis with TRAIL

PURPOSE: Tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) is a member of tumor necrosis factor family and it is important for ligand induced apoptosis in tumor cells. TRAIL has been shown to be synergistic with a variety of chemotherapies and targeted agents. In the study, a combination of TRAIL and a histone deacetylase inhibitor LBH589 was studied in mesothelioma cell lines. EXPERIMENTAL DESIGN: Five mesothelioma cell lines and two normal cell lines were tested for cell growth inhibition and apoptosis using high-throughput assays in the presence of LBH589, TRAIL and a combination of the two. Caspase induction was studied and levels of X-linked inhibitor of apoptosis (XIAP) were tested using Western blotting. A combination of a direct inhibitor of XIAP was also tested in combination with TRAIL. RESULTS: In mesothelioma cell lines, a combination of LBH589 and TRAIL markedly increased cell growth inhibition and apoptosis when compared with the effect on normal cell lines. LBH589 and TRAIL appeared to induce higher levels of caspase 3 and 7 and this appeared to be closely related to ability of LBH589 to degrade XIAP. In addition, a direct inhibitor of XIAP was also sensitized cells to TRAIL apoptosis, providing an indirect confirmation for XIAP degradation as a possible mechanism of synergy. CONCLUSIONS: In mesothelioma cell lines, LBH589 increases the sensitivity to TRAIL. In addition, at least partly, the mechanism of this induction of TRAIL sensitivity is due to LBH589 related degradation of XIAP. These results provide initial evidence for testing this combination in clinical trials

Role of acetylation and extracellular location of heat shock protein 90alpha in tumor cell invasion.

Heat shock protein (hsp) 90 is an ATP-dependent molecular chaperone that maintains the active conformation of client oncoproteins in cancer cells. An isoform, hsp90alpha, promotes extracellular maturation of matrix metalloproteinase (MMP)-2, involved in tumor invasion and metastasis. Knockdown of histone deacetylase (HDAC) 6, which deacetylates lysine residues in hsp90, induces reversible hyperacetylation and attenuates ATP binding and chaperone function of hsp90. Here, using mass spectrometry, we identified seven lysine residues in hsp90alpha that are hyperacetylated after treatment of eukaryotic cells with a pan-HDAC inhibitor that also inhibits HDAC6. Depending on the specific lysine residue in the middle domain involved, although acetylation affects ATP, cochaperone, and client protein binding to hsp90alpha, acetylation of all seven lysines increased the binding of hsp90alpha to 17-allyl-amino-demethoxy geldanamycin. Notably, after treatment with the pan-HDAC inhibitor panobinostat (LBH589), the extracellular hsp90alpha was hyperacetylated and it bound to MMP-2, which was associated with increased in vitro tumor cell invasiveness. Treatment with antiacetylated hsp90alpha antibody inhibited in vitro invasion by tumor cells. Thus, reversible hyperacetylation modulates the intracellular and extracellular chaperone function of hsp90, and targeting extracellular hyperacetylated hsp90alpha may undermine tumor invasion and metastasis