Transcriptional signature of histone deacetylase inhibition in multiple myeloma: biological and clinical implications

Anticancer activities of histone deacetylase inhibitors

Histone deacetylases (HDACs) are enzymes involved in the remodelling of chromatin, and have a key role in the epigenetic regulation of gene expression. In addition, the activity of non-histone proteins can be regulated through HDAC-mediated hypo-acetylation. In recent years, inhibition of HDACs has emerged as a potential strategy to reverse aberrant epigenetic changes associated with cancer, and several classes of HDAC inhibitors have been found to have potent and specific anticancer activities in preclinical studies. However, such studies have also indicated that the effects of HDAC inhibitors could be considerably broader and more complicated than originally understood. Here we summarize recent advances in the understanding of the molecular events that underlie the anticancer effects of HDAC inhibitors, and discuss how such information could be used in optimizing the development and application of these agents in the clinic, either as monotherapies or in combination with other anticancer drugs.

Negative and positive regulation of gene expression by mouse histone deacetylase 1

Histone deacetylases (HDACs) catalyze the removal of acetyl groups from core histones. Because of their capacity to induce local condensation of chromatin, HDACs are generally considered repressors of transcription. In this report, we analyzed the role of the class I histone deacetylase HDAC1 as a transcriptional regulator by comparing the expression profiles of wild-type and HDAC1-deficient embryonic stem cells. A specific subset of mouse genes (7%) was deregulated in the absence of HDAC1. We identified several putative tumor suppressors (JunB, Prss11, and Plagl1) and imprinted genes (Igf2, H19, and p57) as novel HDAC1 targets. The majority of HDAC1 target genes showed reduced expression accompanied by recruitment of HDAC1 and local reduction in histone acetylation at regulatory regions. At some target genes, the related deacetylase HDAC2 partially masks the loss of HDAC1. A second group of genes was found to be downregulated in HDAC1-deficient cells, predominantly by additional recruitment of HDAC2 in the absence of HDAC1. Finally, a small set of genes (Gja1, Irf1, and Gbp2) was found to require HDAC activity and recruitment of HDAC1 for their transcriptional activation. Our study reveals a regulatory cross talk between HDAC1 and HDAC2 and a novel function for HDAC1 as a transcriptional coactivator.

Detection of histone deacetylase inhibition by noninvasive magnetic resonance spectroscopy

Histone deacetylase (HDAC) inhibitors are new and promising antineoplastic agents. Current methods for monitoring early response rely on invasive biopsies or indirect blood-derived markers. Our goal was to develop a magnetic resonance spectroscopy (MRS)-based method to detect HDAC inhibition. The fluorinated lysine derivative Boc-Lys-(Tfa)-OH (BLT) was investigated as a (19)F MRS molecular marker of HDAC activity together with (31)P MRS of endogenous metabolites. In silico modeling of the BLT-HDAC interaction and in vitro MRS studies of BLT cleavage by HDAC confirmed BLT as a HDAC substrate. BLT did not affect cell viability or HDAC activity in PC3 prostate cancer cells. PC3 cells were treated, in the presence of BLT, with the HDAC inhibitor p-fluoro-suberoylanilide hydroxamic acid (FSAHA) over the range of 0 to 10 micromol/L, and HDAC activity and MRS spectra were monitored. Following FSAHA treatment, HDAC activity dropped, reaching 53% of control at 10 micromol/L FSAHA. In parallel, a steady increase in intracellular BLT from 14 to 32 fmol/cell was observed. BLT levels negatively correlated with HDAC activity consistent with higher levels of uncleaved BLT in cells with inhibited HDAC. Phosphocholine, detected by (31)P MRS, increased from 7 to 16 fmol/cell following treatment with FSAHA and also negatively correlated with HDAC activity. Increased phosphocholine is probably due to heat shock protein 90 inhibition as indicated by depletion of client proteins. In summary, (19)F MRS of BLT, combined with (31)P MRS, can be used to monitor HDAC activity in cells. In principle, this could be applied in vivo to noninvasively monitor HDAC activity.

Raf kinases: Oncogenesis and drug discovery

Raf kinase signaling has been thoroughly investigated over the last 20 years. A-Raf, B-Raf and C-Raf, the 3 mammalian members of the Raf family, are involved in a variety of cellular processes such as growth, proliferation, survival, differentiation and transformation. The detection of B-RAF mutations in a wide variety of human cancers, the description of wildtype and mutant B-RAF as tumor antigens in melanoma and the promising outcome of clinical trials evaluating the Raf inhibitor Nexavar (Sorafenib, BAY 43-9006) have sparked a broad interest in the scientific community. After a short historical detour and an introduction into Raf kinase signaling, we are going to discuss here recent outcomes of Raf kinase research with respect to tumor formation and give an overview on current efforts to develop anticancer therapies interfering with aberrant Raf kinase signaling.

Phase I Study of Depsipeptide in Pediatric Patients With Refractory Solid Tumors: A Children's Oncology Group Report

Purpose

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities (DLT), pharmacokinetic profile, and pharmacodynamics of the histone deacetylase inhibitor, depsipeptide, in children with refractory or recurrent solid tumors.

Patients and Methods

Depsipeptide was administered as a 4-hour infusion weekly for 3 consecutive weeks every 28 days at dose levels of 10 mg/m2, 13 mg/m2, 17 mg/m2, and 22 mg/m2. Pharmacokinetics and histone acetylation studies were performed in the first course. The levels of H3 histone and acetyl-H3 histone were evaluated in peripheral blood mononuclear cells (PBMC) using immunofluorescence techniques.

Results

There were 24 patients, and 18 who were assessable were enrolled. DLTs included reversible, asymptomatic T-wave inversions, without any associated changes in troponin levels or evidence of ventricular dysfunction, in the inferior leads in two patients at 22 mg/m2 and in the lateral leads in one patient at 13 mg/m2 (n = 1), and transient asymptomatic sick sinus syndrome and hypocalcemia in one patient at 17 mg/m2. At the MTD (17 mg/m2), the median depsipeptide clearance was 6.8 L/h/m2 with an area under the plasma depsipeptide concentration-time curve from 0 to infinity of 2,414 ng/mL/h, similar to adults. Accumulation of acetylated H3 histones was seen in all patients in a dose independent manner, with maximal accumulation at a median of 4 hours, (range, 0 hours to 20 hours) after the end of the infusion. No objective tumor responses were observed.

Conclusion

Depsipeptide is well tolerated in children with recurrent or refractory solid tumors when administered weekly for 3 consecutive weeks every 28 days and inhibits histone deacetylase activity in PBMC in a dose-independent manner. The recommended phase II dose in children with solid tumors is 17 mg/m2.

The histone deacetylase inhibitor LBH589 is a potent antimyeloma agent that overcomes drug resistance

Multiple myeloma represents an incurable disease, for which development of new therapies is required. Here, we report the effect on myeloma cells of LBH589, a new hydroxamic acid-derived histone deacetylase inhibitor. LBH589 was a potent antimyeloma agent (IC(50) < 40 nmol/L) on both cell lines and fresh cells from multiple myeloma patients, including cells resistant to conventional chemotherapeutic agents. In addition, LBH589 potentiated the action of drugs, such as bortezomib, dexamethasone, or melphalan. Using gene array, quantitative PCR, and Western analyses, we observed that LBH589 affected a large number of genes involved in cell cycle and cell death pathways. LBH589 blocked cell cycle progression, and this was accompanied by p21, p53, and p57 up-regulation. LBH589 induced cell death through an increase in the mitochondrial outer membrane permeability. LBH589 favored apoptosome formation by inducing cytochrome c release, Apaf-1 up-regulation, and caspase-9 cleavage. In addition, LBH589 stimulated a caspase-independent pathway through the release of AIF from the mitochondria. LBH589 down-regulated Bcl-2 and particularly Bcl-X. Moreover, overexpression of Bcl-X in multiple myeloma cells prevented LBH589-induced cell death. All these data indicate that LBH589 could be a useful drug for the treatment of multiple myeloma patients.

Protein lysine acetylation in normal and leukaemic haematopoiesis: HDACs as possible therapeutic targets in adult AML

Several new therapeutic strategies are now considered for acute myelogenous leukaemia (AML), including modulation of protein lysine acetylation through inhibition of histone deacetylases (HDACs): a large group of enzymes that alters the acetylation and, thereby, the function of a wide range of nuclear and cytoplasmic proteins. Firstly, HDACs can deacetylate histones as well as transcription factors, and can modulate gene expression through both these mechanisms. Secondly, acetylation is an important post-translational modulation of several proteins involved in the regulation of cell proliferation, differentiation and apoptosis (e.g., p53, tubulin, heat-shock protein 90). The only HDAC inhibitors that have been investigated in clinical studies of AML are butyrate derivatives, valproic acid and depsipeptide. In the first studies, the drugs have usually been used as continuous therapy for several weeks or months, and in most studies the drugs were used alone or in combination with all-trans retinoic acid for treatment of patients with relapsed or primary resistant AML. Neurological toxicity and gastrointestinal side effects seem to be common for all three drugs. Complete haematological remission lasting for several months has been reported for a few patients (< 5% of included patients), whereas increased peripheral blood platelet counts seem more common and have been described both for patients with AML and myelodysplastic syndromes. Taken together, these studies suggest that HDAC inhibition can mediate antileukaemic effects in AML, but for most patients the clinical benefit seems limited and further studies of combination therapy are required.

Histone deacetylase inhibitors: discovery and development as anticancer agents

Histone deacetylase (HDAC) inhibitors are a new class of targeted anticancer agents. Several HDAC inhibitors are in clinical trials and have shown significant activity against a spectrum of both haematological and solid tumours at doses that are well tolerated by patients. HDACs and histone acetyltransferases can, by reversible acetylation, modify the structure and function of histones and proteins in transcription factor complexes, which are involved in the regulation of gene expression, as well as many non-histone proteins that are involved in regulating cell proliferation and cell death. HDAC inhibitors are a structurally diverse group of molecules; these agents selectively alter the expression of genes. HDAC inhibitors can induce cancer cell death, whereas normal cells are relatively resistant to HDAC inhibitor-induced cell death.

The role of the bone microenvironment in the pathophysiology and therapeutic management of multiple myeloma: interplay of growth factors, their receptors and stromal interactions

The close relationship between the biological behaviour of malignant cells and the local microenvironment where they reside is a feature of diverse neoplasias. Multiple myeloma (MM) is considered a main disease model for the study of such interactions and the mechanisms that can lead to bone-related clinical complications, as well as the role of these interactions in attenuating the activity of conventional anti-MM therapeutics, such as dexamethasone and cytotoxic chemotherapeutics. This review focuses on recent progress in the study of interactions of MM cells with their local microenvironment. Major emphasis is placed on how bone marrow stromal cells (BMSCs) and other normal constituents of the bone marrow milieu promote, through cell adhesion- and cytokine-mediated mechanisms, the ability of MM cells to resist conventional anti-MM therapies. The review also addresses ongoing research into these mechanisms, which has already provided several new molecular targets and corresponding therapeutic strategies, such as the proteasome inhibitor bortezomib and thalidomide derivatives (e.g. lenalidomide), for the management of myeloma.

The molecular classification of multiple myeloma

To better define the molecular basis of multiple myeloma (MM), we performed unsupervised hierarchic clustering of mRNA expression profiles in CD138-enriched plasma cells from 414 newly diagnosed patients who went on to receive high-dose therapy and tandem stem cell transplants. Seven disease subtypes were validated that were strongly influenced by known genetic lesions, such as c-MAF- and MAFB-, CCND1- and CCND3-, and MMSET-activating translocations and hyperdiploidy. Indicative of the deregulation of common pathways by gene orthologs, common gene signatures were observed in cases with c-MAF and MAFB activation and CCND1 and CCND3 activation, the latter consisting of 2 subgroups, one characterized by expression of the early B-cell markers CD20 and PAX5. A low incidence of focal bone disease distinguished one and increased expression of proliferation-associated genes of another novel subgroup. Comprising varying fractions of each of the other 6 subgroups, the proliferation subgroup dominated at relapse, suggesting that this signature is linked to disease progression. Proliferation and MMSET-spike groups were characterized by significant overexpression of genes mapping to chromosome 1q, and both exhibited a poor prognosis relative to the other groups. A subset of cases with a predominating myeloid gene expression signature, excluded from the profiling analyses, had more favorable baseline characteristics and superior prognosis to those lacking this signature.

Acetylation of Stat1 modulates NF-kappaB activity

Acetylation of signaling molecules can lead to apoptosis or differentiation of carcinoma cells. The molecular mechanisms underlying these processes and the biological role of enzymes mediating the transfer or removal of an acetyl-group are currently under intense investigation. Our study shows that Stat1 is an acetylated protein. Stat1 acetylation depends on the balance between Stat1-associated histone deacetylases (HDACs) and histone acetyltransferases (HATs) such as CBP. Remarkably both inhibitors of HDACs and the cytokine interferon alpha alter this equilibrium and induce Stat1 acetylation. The analysis of Stat1 mutants reveals Lys 410 and Lys 413 as acetylation sites. Experiments with Stat1 mutants mimicking either constitutively acetylated or nonacetylated states show that only acetylated Stat1 is able to interact with NF-kappaB p65. As a consequence, p65 DNA binding, nuclear localization, and expression of anti-apoptotic NF-kappaB target genes decrease. These findings show how the acetylation of Stat1 regulates NF-kappaB activity and thus ultimately apoptosis.

Aggresome disruption: a novel strategy to enhance bortezomib-induced apoptosis in pancreatic cancer cells

The proteasome inhibitor bortezomib (formerly known as PS-341) recently received Food and Drug Administration approval for the treatment of multiple myeloma, and its activity is currently being evaluated in solid tumors. Bortezomib triggers apoptosis in pancreatic cancer cells, but the mechanisms involved have not been fully elucidated. Here, we show that pancreatic cancer cells exposed to bortezomib formed aggregates of ubiquitin-conjugated proteins ("aggresomes") in vitro and in vivo. Bortezomib-induced aggresome formation was determined to be cytoprotective and could be disrupted using histone deacetylase (HDAC) 6 small interfering RNA or chemical HDAC inhibitors, which resulted in endoplasmic reticulum stress and synergistic levels of apoptosis in vitro and in an orthotopic pancreatic cancer xenograft model in vivo. Interestingly, bortezomib did not induce aggresome formation in immortalized normal human pancreatic epithelial cells in vitro or in murine pancreatic epithelial cells in vivo. In addition, these cells did not undergo apoptosis following treatment with bortezomib, suberoylanilide hydroxamic acid, or the combination, showing tumor selectivity. Taken together, our study shows that inhibition of aggresome formation can strongly potentiate the efficacy of bortezomib and provides the foundation for clinical trials of bortezomib in combination with HDAC inhibitors for the treatment of pancreatic cancer.

Histone Deacetylase Inhibitors Suppress the Inducibility of Nuclear Factor-κB by Tumor Necrosis Factor-α Receptor-1 Down-regulation

Recently, the inhibition of histone deacetylase (HDAC) enzymes has attracted attention in the oncologic community as a new therapeutic opportunity for hematologic and solid tumors including non-small cell lung cancer (NSCLC). In hematologic malignancies, such as diffuse large B-cell lymphoma, the HDAC inhibitor (HDI), suberoylanilide hydroxamic acid (SAHA), has recently entered phase II and III clinical trials. To further advance our understanding of their action on tumor cells, we investigated the possible effect of HDI treatment on the functionality of the nuclear factor-kappaB (NF-kappaB) pathway in NSCLC. We found that in the NSCLC cell lines, A549 and NCI-H460, the NF-kappaB pathway was strongly inducible, for example, by stimulation with tumor necrosis factor-alpha (TNF-alpha). Incubation of several NSCLC cell lines with HDIs resulted in greatly reduced gene expression of TNF-alpha receptor-1. HDI-treated A549 and NCI-H460 cells down-regulated TNF-alpha receptor-1 mRNA and protein levels as well as surface exposure, and consequently responded to TNF-alpha treatment with reduced IKK phosphorylation and activation, delayed IkappaB-alpha phosphorylation, and attenuated NF-kappaB nuclear translocation and DNA binding. Accordingly, stimulation of NF-kappaB target gene expression by TNF-alpha was strongly decreased. In addition, we observed that SAHA displayed antitumor efficacy in vivo against A549 xenografts grown on nude mice. HDIs, therefore, might beneficially contribute to tumor treatment, possibly by reducing the responsiveness of tumor cells to the TNF-alpha-mediated activation of the NF-kappaB pathway. These findings also hint at a possible use of HDIs in inflammatory diseases, which are associated with the overproduction of TNF-alpha, such as rheumatoid arthritis or Crohn's disease.

Advances in oral therapy for multiple myeloma

Conventional intravenous chemotherapy regimens are toxic, cumbersome, and negatively affect patients' quality of life, with oral treatment preferable to most patients with cancer. Multiple myeloma is the second most common haematological malignant disease, but cannot be cured with conventional and high-dose chemotherapy. New oral treatments that target myeloma cells or bone marrow are being developed that are highly effective yet have low toxic effects, such as the immunomodulatory drugs thalidomide and lenalidomide. Several treatments in early development have shown antimyeloma activity, including: CHIR-258, which inhibits fibroblast growth factor receptor 3; NVP-ADW742, which inhibits insulin-like growth factor receptor 1; and PTK787, which inhibits vascular endothelial growth factor. Additional drugs aimed at switching off silenced genes include histone deacetylase inhibitors. The availability of these various oral treatments is hoped to improve regimens that, if used sequentially or in combination, offer the potential of making multiple myeloma a chronic disease, thereby extending patients' lifespans and improving quality of life.

Histone deacetylase inhibitors: multifunctional anticancer agents

Acetylation and deacetylation of chromatin histone protein by histone deacetylase (HDAC) alters chromatin structure and dynamically affects transcriptional regulation. Many lines of evidence indicate that histone hypo-acetylation induces repression of tumour suppressor gene expression. Small molecule inhibitors of HDAC (HDACI) are highly effective in up-regulating tumour suppressor gene expression, reducing tumour growth and inducing programmed cell death in vitro and in cancer patients in phase I and II clinical trials. HDACI-induced growth inhibition and cytotoxicity have been attributed to acetylation of both histone and non-histone proteins. Less studied, but equally important, is the role of HDAC and HDACI on other components of the malignant phenotype: tumour initiation and progression. In this review, we summarise evidence indicating that the in vivo anti-cancer efficacy of HDACIs is at least in part dependent on suppression of cancer cell migration, invasion, metastasis, blood supply, and angiogenesis. As histone hypo-acetylation is involved in the tumourigenesis of various haematological and solid malignancies, the clinical use of HDACIs in patients at high risk of cancer or with precancerous conditions warrants further investigation.

Suberoylanilide Hydroxamic Acid Potentiates Apoptosis, Inhibits Invasion, and Abolishes Osteoclastogenesis by Suppressing Nuclear Factor-κB Activation

Because of its ability to suppress tumor cell proliferation, angiogenesis, and inflammation, the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) is currently in clinical trials. How SAHA mediates its effects is poorly understood. We found that in several human cancer cell lines, SAHA potentiated the apoptosis induced by tumor necrosis factor (TNF) and chemotherapeutic agents and inhibited TNF-induced invasion and receptor activator of NF-kappaB ligand-induced osteoclastogenesis, all of which are known to require NF-kappaB activation. These observations corresponded with the down-regulation of the expression of anti-apoptotic (IAP1, IAP2, X chromosome-linked IAP, Bcl-2, Bcl-x(L), TRAF1, FLIP, and survivin), proliferative (cyclin D1, cyclooxygenase 2, and c-Myc), and angiogenic (ICAM-1, matrix metalloproteinase-9, and vascular endothelial growth factor) gene products. Because several of these genes are regulated by NF-kappaB, we postulated that SAHA mediates its effects by modulating NF-kappaB and found that SAHA suppressed NF-kappaB activation induced by TNF, IL-1beta, okadaic acid, doxorubicin, lipopolysaccharide, H(2)O(2), phorbol myristate acetate, and cigarette smoke; the suppression was not cell type-specific because both inducible and constitutive NF-kappaB activation was inhibited. We also found that SAHA had no effect on direct binding of NF-kappaB to the DNA but inhibited sequentially the TNF-induced activation of IkappaBalpha kinase, IkappaBalpha phosphorylation, IkappaBalpha ubiquitination, IkappaBalpha degradation, p65 phosphorylation, and p65 nuclear translocation. Furthermore, SAHA inhibited the NF-kappaB-dependent reporter gene expression activated by TNF, TNFR1, TRADD, TRAF2, NF-kappaB-inducing kinase, IkappaBalpha kinase, and the p65 subunit of NF-kappaB. Overall, our results indicated that NF-kappaB and NF-kappaB-regulated gene expression inhibited by SAHA can enhance apoptosis and inhibit invasion and osteoclastogenesis.

Raloxifene-Induced Myeloma Cell Apoptosis: A Study of Nuclear Factor-κB Inhibition and Gene Expression Signature

Because multiple myeloma remains associated with a poor prognosis, novel drugs targeting specific signaling pathways are needed. The efficacy of selective estrogen receptor modulators for the treatment of multiple myeloma is not well documented. In the present report, we studied the antitumor activity of raloxifene, a selective estrogen receptor modulator, on multiple myeloma cell lines. Raloxifene effects were assessed by tetrazolium salt reduction assay, cell cycle analysis, and Western blotting. Mobility shift assay, immunoprecipitation, chromatin immunoprecipitation assay, and gene expression profiling were performed to characterize the mechanisms of raloxifene-induced activity. Indeed, raloxifene, as well as tamoxifen, decreased JJN-3 and U266 myeloma cell viability and induced caspase-dependent apoptosis. Raloxifene and tamoxifen also increased the cytotoxic response to vincristine and arsenic trioxide. Moreover, raloxifene inhibited constitutive nuclear factor-kappaB (NF-kappaB) activity in myeloma cells by removing p65 from its binding sites through estrogen receptor alpha interaction with p65. It is noteworthy that microarray analysis showed that raloxifene treatment decreased the expression of known NF-kappaB-regulated genes involved in myeloma cell survival and myeloma-induced bone lesions (e.g., c-myc, mip-1alpha, hgf, pac1,...) and induced the expression of a subset of genes regulating cellular cycle (e.g., p21, gadd34, cyclin G2,...). In conclusion, raloxifene induces myeloma cell cycle arrest and apoptosis partly through NF-kappaB-dependent mechanisms. These findings also provide a transcriptional profile of raloxifene treatment on multiple myeloma cells, offering the framework for future studies of selective estrogen receptor modulators therapy in multiple myeloma.

Modulation of cellular radiation responses by histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are emerging as a new class of targeted cancer chemotherapeutics. Several HDAC inhibitors are currently in clinical trials and promising anticancer effects at well-tolerated doses have been observed for both hematologic and solid cancers. HDAC inhibitors have been shown to induce cell-cycle and growth arrest, differentiation and in certain cases apoptosis in cell cultures and in vivo. However, it is known that these compounds induce varying responses in different cells and biological settings, and identifying their precise mechanisms of action is an area of great interest. Important findings are continually expanding our understanding of the cellular effects of HDAC inhibitors and recent studies will be briefly outlined in this review. In addition to their intrinsic anticancer properties, numerous studies have demonstrated that HDAC inhibitors can modulate cellular responses to other cytotoxic modalities including ionizing radiation, ultraviolet radiation and chemotherapeutic drugs. Hence, there is a growing interest in potential clinical use of HDAC inhibitors in combination with conventional cancer therapies. In this review, the interaction of HDAC inhibitors with other anticancer agents is discussed. The focus of the article is on the different mechanisms by which HDAC inhibitors enhance the sensitivity of cells to the effects of ionizing radiation.

Valproic acid-induced skeletal malformations: associated gene expression cascades

OBJECTIVES

Valproic acid (VPA) is a widely used anticonvulsant medication with well-known teratogenic effects in both humans and in experimental animal model systems. The most commonly observed malformations induced by VPA in experimental animals include neural and skeletal defects. In this study the potential alterations in somitic tissue gene expression relative to the development of observed axial skeletal defects were examined.

METHODS

SWV mice were treated at 8.5 days post coitum (d.p.c.) with 1.36 mmol/kg or 2.72 mmol/kg VPA by i.p. injection. At 18.5 d.p.c., animals were killed and stained for morphological and skeletal examination. Cervical malformations consisting of vertebral fusions and cervical ribs were consistently observed. Phenotypic analysis confirmed the presence of dose-dependent axial skeletal malformations induced by in-utero VPA-exposure. Using antisense RNA amplification and cDNA microarrays, we examined the expression of approximately 5700 genes in the first six postotic somites of control and treated embryos at 6, 12, 18 and 24 h after the 8.5 d.p.c. VPA treatment.

RESULTS

Analysis indicated that several ontological groups (e.g. histone deacetylase complex, guanosine triphosphatases, cell proliferation and cytoskeletal) have significantly enriched gene expression changes in response to the teratogenic insult. The RNA from 6 h post-treatment was also subjected to a microarray cross-platform validation, and genes identified on both platforms are presented.

CONCLUSION

These data were then used to deduce candidate cellular pathways that may be responsible for the VPA-induced teratogenic skeletal phenotypes.

Targeting epigenetic abnormalities with histone deacetylase inhibitors

BACKGROUND

Alterations in chromosome structure play critical roles in the control of gene transcription. These "epigenetic" alterations include modification of histones and other proteins by acetylation and/or phosphorylation. Normally, these modifications are balanced finely and are highly reversible in normal tissues, but they may be imbalanced and heritable in tumor cells. Histone deacetylase inhibitors increase histone acetylation, thereby modulating the expression of a subset of genes in a coordinated fashion. Several tumor suppressor genes associated with the malignant phenotype are repressed by epigenetic mechanisms in sporadic cancers. Thus, therapy with histone deacetylase inhibitors may alter tumor phenotype to inhibit growth in such tumors.

METHODS

The authors reviewed the rationale for histone deacetylase inhibitors as potential anticancer agents and reviewed some preclinical and early clinical trial data with various classes of histone deacetylase inhibitors.

RESULTS

Preclinical and clinical antitumor activity has been observed. Toxicities include fatigue, myelosuppression, and cardiac abnormalities.

CONCLUSIONS

Histone deacetylase inhibitors have shown promising activity in some solid tumors and hematologic malignancies.

Valproate enhances imatinib-induced growth arrest and apoptosis in chronic myeloid leukemia cells

BACKGROUND

The objective of this study was to evaluate the ability of the clinically available histone deacetylase (HDAC) inhibitor valproate to enhance the cytotoxicity of the Bcr-Abl inhibitor imatinib in imatinib-resistant cell lines.

METHODS

Interactions between imatinib, and valproate have been examined in imatinib-sensitive and -resistant chronic myeloid leukemia (CML)cell lines (K562, KCL-22, CML-T1) and in bone marrow mononuclear cells (MNCs) derived from imatinib-resistant CML patients.

RESULTS

In imatinib-sensitive cell lines, cotreatment with imatinib 0.5 muM and valproate 5 microM for 48 hours potently enhanced imatinib-induced growth arrest and apoptosis. In resistant cell lines and in primary MNCs derived from imatinib-rsistant patients, valproate restored sensitivity to the cytotoxic effects of imatinib. Coexposure of cells to valproate and imatinib was associated with repression of several genes involved in Bcr-Abl transformation. In particular, the combination valproate-imatinib downregulated the expression of Bcr-Abl and the antiapoptotic protein Bcl-2, which is particularly overexpressed in imatinib-resistant clones.

CONCLUSIONS

Data from this study suggested that administration of the clinically available HDAC inhibitor valproate may be a powerful strategy to enhance cytotoxic effects of imatinib in those patient resistant to imatinib or in which complete cytogenetic remission has been not reached.

Histone deacetylase inhibitors and the promise of epigenetic (and more) treatments for cancer

Histone deacetylases (HDACs) are considered to be among the most promising targets in drug development for cancer therapy, and first-generation histone deacetylase inhibitors (HDACi) are currently being tested in phase I/II clinical trials. A wide-ranging knowledge of the role of HDACs in tumorigenesis, and of the action of HDACi, has been achieved. However, several basic aspects are not yet fully understood. Investigating these aspects in the context of what we now understand about HDACi action both in vitro and in vivo will further improve the design of optimized clinical protocols.

Histone deacetylation as a target for radiosensitization

Due to an increase in the understanding of molecular radiobiology, strategies for enhancing tumor radiosensitivity have begun to focus on targeting the molecules and processes that regulate cellular radioresponse. Toward this end, histone acetylation has begun to receive considerable attention as a potential target for radiosensitization. Histone acetylation, which is determined by the competing actions of histone acetylases (HATs) and histone deacetylases (HDACs), plays a role in regulating chromatin structure and gene expression--two parameters that have long been considered determinants of radioresponse. As a means of modifying histone acetylation status, considerable effort has been put into the development of inhibitors of HDAC activity, which is often aberrant in tumor cells. This has led to the generation of a relatively large number of structurally diverse compounds that inhibit HDAC activity and result in histone hyperacetylation, and importantly, are applicable to patient treatment. Whereas a number of these HDAC inhibitors have antitumor activity in preclinical cancer models when delivered as single agents, recent studies have indicated that these compounds also significantly enhance tumor cell radiosensitivity. A structurally diverse set of HDAC inhibitors have been shown to enhance the in vitro radiosensitivity of human tumor cell lines generated from a spectrum of solid tumors. Moreover, HDAC inhibitors increased the radiosensitivity of human tumor xenografts. Although the mechanism responsible for this radiosensitization has not been definitely elucidated, data suggest that inhibiting the repair of radiation-induced DNA damage may be involved. Whereas HDAC inhibitors are currently in clinical trials as single modalities and in combination with chemotherapeutic agents, recent results suggest that these compounds may also enhance the antitumor effectiveness of radiotherapy.

The histone deacetylase inhibitor, suberoylanilide hydroxamic acid, overcomes resistance of human breast cancer cells to Apo2L/TRAIL

While the apoptosis-inducing ligand Apo2L/TRAIL is a promising new agent for the treatment of cancer, the sensitivity of cancer cells for induction of apoptosis by Apo2L/TRAIL varies considerably. Identification of agents that can be used in combination with Apo2L/TRAIL to enhance apoptosis in breast cancer cells would increase the potential utility of this agent as a breast cancer therapeutic. Here, we show that the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), can sensitize Apo2L/TRAIL-resistant breast cancer cells to Apo2L/TRAIL-induced apoptosis. Importantly, neither Apo2L/TRAIL alone, nor in combination with SAHA, affected the viability of normal human cells in culture. Apo2L/TRAIL-resistant MDA-MB-231 breast cancer cells, generated by long-term culture in the continuous presence of Apo2L/TRAIL, were resensitized to Apo2L/TRAIL-induced apoptosis by SAHA. The sensitization of these cells by SAHA was accompanied by activation of caspase 8, caspase 9 and caspase 3 and was concomitant with Bid and PARP cleavage. The expression of the proapoptotic protein, Bax, increased significantly with SAHA treatment and high levels of Bax were maintained in the combined treatment with Apo2L/TRAIL. Treatment with SAHA increased cell surface expression of DR5 but not DR4. Interestingly, SAHA treatment also resulted in a significant increase in cell surface expression of DcR1. Taken together, our findings indicate that the use of these 2 agents in combination may be effective for the treatment of breast cancer.

Green tea component, catechin, induces apoptosis of human malignant B cells via production of reactive oxygen species

PURPOSE

Green tea polyphenol, (-)-epigallocatechin-3-gallate, has been shown to inhibit cellular proliferation and induce apoptosis of various cancer cells. The aim of this study was to investigate the possibility of (-)-epigallocatechin-3-gallate as a novel therapeutic agent for the patients with B-cell malignancies including multiple myeloma.

EXPERIMENTAL DESIGN

We investigated the effects of (-)-epigallocatechin-3-gallate on the induction of apoptosis in HS-sultan as well as myeloma cells in vitro and further examined the molecular mechanisms of (-)-epigallocatechin-3-gallate-induced apoptosis.

RESULTS

(-)-Epigallocatechin-3-gallate rapidly induced apoptotic cell death in various malignant B-cell lines in a dose- and time-dependent manner. (-)-Epigallocatechin-3-gallate-induced apoptosis was in association with the loss of mitochondrial transmembrane potentials (Deltapsim); the release of cytochrome c, Smac/DIABLO, and AIF from mitochondria into the cytosol; and the activation of caspase-3 and caspase-9. Elevation of intracellular reactive oxygen species (ROS) production was also shown during (-)-epigallocatechin-3-gallate-induced apoptosis of HS-sultan and RPMI8226 cells as well as fresh myeloma cells. Antioxidant, catalase, and Mn superoxide dismutase significantly reduced ROS production and (-)-epigallocatechin-3-gallate-induced apoptosis, suggesting that ROS plays a key role in (-)-epigallocatechin-3-gallate-induced apoptosis in B cells. Furthermore, a combination with arsenic trioxide (As2O3) and (-)-epigallocatechin-3-gallate significantly enhanced induction of apoptosis compared with As2O3 alone via decreased intracellular reduced glutathione levels and increased production of ROS.

CONCLUSIONS

(-)-Epigallocatechin-3-gallate has potential as a novel therapeutic agent for patients with B-cell malignancies including multiple myeloma via induction of apoptosis mediated by modification of the redox system. In addition, (-)-epigallocatechin-3-gallate enhanced As2O3-induced apoptosis in human multiple myeloma cells.

Targeted therapy in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is an incurable malignancy. Recent insights into its biology has allowed the use of novel therapies targeting not only the deregulated intracellular signaling in MM cells but also its interaction with the bone marrow microenvironment that confers drug resistance, growth, and survival advantage to the malignant cells.

METHODS

We review and summarize the recent advances in our knowledge of myeloma biology as well as the mechanism of action and clinical efficacy for novel therapeutic agents in clinical trials.

RESULTS

Several novel therapeutic agents are currently in clinical trials. Thalidomide is already established for both initial and salvage treatment. Bortezomib is being tested alone and in combination with conventional chemotherapy in various settings. Other agents are less effective in producing response but have been able to stabilize disease in patients with relapsed and/or refractory disease, such as arsenic trioxide, farnesyltransferase inhibitors, 2-methoxyestradiol, and vascular endothelial growth factor receptor inhibitors. Insights into drug resistance mechanism have also led to the development of novel agents that sensitize myeloma cells to chemotherapy (Bcl-2 antisense). Gene expression studies have in many instances identified pathways other than the intended target of the drug and have provided insights into the therapeutic mechanisms.

CONCLUSIONS

In the future, patients with MM will have more therapeutic options available than ever before. The challenge will be to identify patient subgroups that will benefit most from the different therapies and then determine how these biologically based therapies could be combined and incorporated into the overall management of patients.

Novel biological therapies for the treatment of multiple myeloma

The therapeutic management of multiple myeloma (MM) for the last several decades has mainly involved regimens based on use of glucocorticoids and cytotoxic chemotherapeutics. Despite progress in delineating the activity of such regimens, at either conventional or high doses, MM has remained an incurable disease, without substantial improvement in the median overall survival. This has sparked major interest in the development of novel therapies that in part capitalize on recent advances in our understanding of the biology of MM, including the molecular mechanisms by which MM cell-host bone marrow (BM) interactions regulate tumor-cell growth, survival, and drug resistance in the BM milieu. The development of in vitro and in vivo models of MM-stromal interactions has allowed not only for better characterization of these molecular phenomena but also for identification of specific therapeutic strategies to overcome these interactions and achieve an enhanced anti-MM effect, even against MM resistant to conventional therapies. Herein, we review the latest progress in the development of these novel anti-MM therapies, with major focus on therapies which have translated from preclinical evaluation to clinical application, including thalidomide and its more potent immunomodulatory (IMiD) derivatives, the first-in-class proteasome inhibitor bortezomib (formerly known as PS-341), and arsenic trioxide (As2O3).

Gene expression profiling and multiple myeloma

Gene expression profiling is a powerful tool through which the biology of multiple myeloma can be dissected. We will describe in this chapter how early studies using this technology have provided meaningful insights into myeloma biology, have led to the identification of new therapeutic targets, and have identified powerful prognostic and pharmacogenomic markers. Specifically, we will demonstrate that gene expression profiling can be used to segregate myeloma patients into prognostic categories within which known IgH translocation signatures can be readily defined. We also show that expression signatures can identify patients with chromosome 13 deletion. Finally, we demonstrate that global gene expression signatures can be distilled to short lists of three genes or more which together impart clinical outcome information, which is significantly more powerful than any previously defined prognostic tool. Expression profiling has also led to the identification of a number of new therapeutic targets not only in myeloma cell survival but also in the pathogenesis of the osteolysis which is a hallmark of this disease.

Bortezomib interactions with chemotherapy agents in acute leukemia in vitro

Although there is effective chemotherapy for many patients with leukemia, 20% of children and up to 65% of adults relapse. Novel therapies are needed to treat these patients. Leukemia cells are very sensitive to the proteasome inhibitor bortezomib (VELCADE(R), PS-341), which enhances the in vitro cytotoxic effects of dexamethasone and doxorubicin in multiple myeloma. To determine if bortezomib enhances the cytotoxicity of agents used in leukemia, we employed an in vitro tetrazolium-based colorimetric assay (MTT) to evaluate the cytotoxic effects of bortezomib alone and in combination with dexamethasone, vincristine, doxorubicin, cytarabine, asparaginase, geldanamycin, trichostatin A, and the bcl-2 inhibitor HA14.1. We demonstrated that primary leukemia lymphoblasts and leukemia cell lines are sensitive to bortezomib, with an average IC(50) of 12 nM. Qualitative and quantitative bortezomib-drug interactions were evaluated using the universal response surface approach (URSA). Bortezomib was synergistic with dexamethasone in dexamethasone-sensitive leukemia cells, and additive with vincristine, asparaginase, cytarabine, and doxorubicin. The anti-leukemic activity of bortezomib was also additive with geldanamycin and HA14.1, and additive or synergistic with trichostatin A. These results were compared to analysis using the median-dose effect method, which generated complex drug interactions due to differences in dose-response curve sigmoidicities. These data suggest bortezomib could potentiate the cytotoxic effects of combination chemotherapy in patients with leukemia.

Interpreting epithelial cancer biology in the context of stem cells: tumor properties and therapeutic implications

Over 90% of all human neoplasia is derived from epithelia. Significant progress has been made in the identification of stem cells of many epithelia. In general, epithelial stem cells lack differentiation markers, have superior in vivo and in vitro proliferative potential, form clusters in association with a specialized mesenchymal environment (the 'niche'), are located in well-protected and nourished sites, and are slow-cycling and thus can be experimentally identified as 'label-retaining cells'. Stem cells may divide symmetrically giving rise to two identical stem cell progeny. Any stem cells in the niche, which defines the size of the stem cell pool, may be randomly expelled from the niche due to population pressure (the stochastic model). Alternatively, a stem cell may divide asymmetrically yielding one stem cell and one non-stem cell that is destined to exit from the stem cell niche (asymmetric division model). Stem cells separated from their niche lose their stemness, although such a loss may be reversible, becoming 'transit-amplifying cells' that are rapidly proliferating but have a more limited proliferative potential, and can give rise to terminally differentiated cells. The identification of the stem cell subpopulation in a normal epithelium leads to a better understanding of many previously enigmatic properties of an epithelium including the preferential sites of carcinoma formation, as exemplified by the almost exclusive association of corneal epithelial carcinoma with the limbus, the corneal epithelial stem cell zone. Being long-term residents in an epithelium, stem cells are uniquely susceptible to the accumulation of multiple, oncogenic changes giving rise to tumors. The application of the stem cell concept can explain many important carcinoma features including the clonal origin and heterogeneity of tumors, the occasional formation of tumors from the transit amplifying cells or progenitor cells, the formation of precancerous 'patches' and 'fields', the mesenchymal influence on carcinoma formation and behavior, and the plasticity of tumor cells. While the concept of cancer stem cells is extremely useful and it is generally assumed that such cells are derived from normal stem cells, more work is needed to identify and characterize epithelial cancer stem cells, to address their precise relationship with normal stem cells, to study their markers and their proliferative and differentiation properties and to design new therapies that can overcome their unusual resistance to chemotherapy and other conventional tumor modalities.

Rational Design and Development of Radiation-Sensitizing Histone Deacetylase Inhibitors

Histone deacetylases (HDACs) offer potentially attractive molecular targets for sensitizing cancers to treatment with radiation therapy. By affecting patterns of gene expression, differentiation, apoptosis, and enhanced responses to therapeutic agents may be induced in cancer cells. Here, we review the drug characteristics underlying design and screening of HDAC inhibitors with a focus on radiation-sensitizing properties. Radiation-sensitizing capacities have been observed in three model systems, squamous carcinoma of head and neck origin (SQ-20B), prostate adenocarcinoma (PC-3), and breast adenocarcinoma (MCF7). Cell-type specificities in radiation-sensitizing properties have been observed. Mechanisms underlying specificity are under investigation.

HDACs and the senescent phenotype of WI-38 cells

Background

Normal cells possess a limited proliferative life span after which they enter a state of irreversible growth arrest. This process, known as replicative senescence, is accompanied by changes in gene expression that give rise to a variety of senescence-associated phenotypes. It has been suggested that these gene expression changes result in part from alterations in the histone acetylation machinery. Here we examine the influence of HDAC inhibitors on the expression of senescent markers in pre- and post-senescent WI-38 cells.

Results

Pre- and post-senescent WI-38 cells were treated with the HDAC inhibitors butyrate or trichostatin A (TSA). Following HDAC inhibitor treatment, pre-senescent cells increased p21^WAF1 and β-galactosidase expression, assumed a flattened senescence-associated morphology, and maintained a lower level of proteasome activity. These alterations also occurred during normal replicative senescence of WI-38 cells, but were not accentuated further by HDAC inhibitors. We also found that HDAC1 levels decline during normal replicative senescence.

Conclusion

Our findings indicate that HDACs impact numerous phenotypic changes associated with cellular senescence. Reduced HDAC1 expression levels in senescent cells may be an important event in mediating the transition to a senescent phenotype.

Antimyeloma activity of heat shock protein-90 inhibition

We show that multiple myeloma (MM), the second most commonly diagnosed hematologic malignancy, is responsive to hsp90 inhibitors in vitro and in a clinically relevant orthotopic in vivo model, even though this disease does not depend on HER2/neu, bcr/abl, androgen or estrogen receptors, or other hsp90 chaperoning clients which are hallmarks of tumor types traditionally viewed as attractive clinical settings for use of hsp90 inhibitors, such as the geldanamycin analog 17-AAG. This class of agents simultaneously suppresses in MM cells the expression and/or function of multiple levels of insulin-like growth factor receptor (IGF-1R) and interleukin-6 receptor (IL-6R) signaling (eg, IKK/NF-kappaB, PI-3K/Akt, and Raf/MAPK) and downstream effectors (eg, proteasome, telomerase, and HIF-1alpha activities). These pleiotropic proapoptotic effects allow hsp90 inhibitors to abrogate bone marrow stromal cell-derived protection on MM tumor cells, and sensitize them to other anticancer agents, including cytotoxic chemotherapy and the proteasome inhibitor bortezomib. These results indicate that hsp90 can be targeted therapeutically in neoplasias that may not express or depend on molecules previously considered to be the main hsp90 client proteins. This suggests a more general role for hsp90 in chaperoning tumor- or tissue-type-specific constellations of client proteins with critical involvement in proliferative and antiapoptotic cellular responses, and paves the way for more extensive future therapeutic applications of hsp90 inhibition in diverse neoplasias, including MM.

Histone modifications as a platform for cancer therapy

Tumorigenesis and metastasis are a progression of events resulting from alterations in the processing of the genetic information. These alterations result from stable genetic changes (mutations) involving tumor suppressor genes and oncogenes (e.g., ras, BRAF) and potentially reversible epigenetic changes, which are modifications in gene function without a change in the DNA sequence. Mutations of genes coding for proteins that directly or indirectly influence epigenetic processes will alter the cell's gene expression program. Epigenetic mechanisms often altered in cancer cells are DNA methylation and histone modifications (acetylation, methylation, phosphorylation). This article will review the potential of these reversible epigenetic processes as targets for cancer therapies.

Regulatory cross-talk between lysine acetylation and ubiquitination: role in the control of protein stability

It is now becoming apparent that cross-talk between two protein lysine modifications, acetylation and ubiquitination, is a critical regulatory mechanism controlling vital cellular functions. The most apparent effect is the inhibition of proteasome-mediated protein degradation by lysine acetylation. Analysis of the underlying mechanisms, however, shows that, besides a direct competition between the two lysine modifications, more complex and indirect processes also connect these two signalling pathways. These findings point to protein lysine acetylation as a potential regulator of various cellular functions involving protein ubiquitination.

Identification and Validation of Novel Therapeutic Targets for Multiple Myeloma

In vitro and in vivo models have been developed that have allowed for delineation of mechanisms of multiple myeloma (MM) cell homing to bone marrow (BM); tumor cell adhesion to extracellular matrix proteins and BM stromal cells; and cytokine-mediated growth, survival, drug resistance, and migration within the BM milieu. Delineation of the signaling cascades mediating these sequelae has identified multiple novel therapeutic targets in the tumor cell and its BM microenvironment. Importantly, novel therapies targeting the tumor cell and the BM, as well as those targeting the tumor cell or BM alone, can overcome the growth, survival, conventional drug resistance, and migration of MM cells bound to BM using both in vitro and in vivo severe combined immunodeficiency mouse models of human MM. These studies have translated rapidly from the bench to the bedside in derived clinical trials, and have already led to the United States Food and Drug Administration approval of the novel proteasome inhibitor bortezomib for treatment of relapsed/refractory MM. Novel agents will need to be combined to enhance cytotoxicity, avoid development of drug resistance, and allow for use of lower doses in combination therapies. Genomics, proteomics, and cell signaling studies have helped to identify in vivo mechanisms of sensitivity versus resistance to novel therapies, as well as aiding in the rational application of combination therapies. These studies have therefore provided the framework for a new treatment paradigm targeting the MM cell in its BM milieu to overcome drug resistance and improve patient outcome in MM.

Prognostic and Therapeutic Significance of Myeloma Genetics and Gene Expression Profiling

Molecular diagnostic tools and novel therapeutics now offer the potential for accurate prognostic and personalized treatment road maps for patients with multiple myeloma (MM). We will review the evidence and provide specific recommendations for routine clinical molecular genetic testing and use of such information to guide therapeutic decision making. In particular, the negative prognostic impact of specific IgH translocations such as the t(4;14), t(14;16), chromosome 13 deletion by conventional cytogenetics and loss of 17p13 by interphase fluorescence in situ hybridization are now established. Preliminary gene expression profiling studies have also demonstrated that individual genes (CSK1-B) or groups of genes can define prognosis with greater accuracy than conventional genetic markers and can provide pharmacogenomic and biologic insight into the pathophysiology, therapeutics, and future targets of myeloma. Importantly, we recommend that all clinical trials now adopt routine genetic testing and risk stratification.

Histone Deacetylase Inhibitors: Emerging Anticancer Therapeutic Agents?

Histone deacetylase inhibitors are novel anticancer agents in clinical development that target the family of histone deacetylase (HDAC) enzymes responsible for deacetylating core nucleosomal histones and other proteins. The precise mechanisms resulting in the antiproliferative biologic effects of these agents are not yet known, but there are several proposed mechanistic models, including transcriptional and nontranscriptional processes. Clinical experience with these agents indicates that they are generally well tolerated, and anticancer activity has been observed in early clinical trials in several tumor types including non-small-cell lung cancer. The development of these agents continues, with an emphasis on the discovery of HDAC isoform-selective compounds. Successful future development relies on clearer understanding of the dominant mechanisms involved in the observed antiproliferative effects.

Genomics in multiple myeloma: biology and clinical implications

The advent of new techniques, such as interphase fluorescence in situ hybridization, and, more recently, global array-based gene expression profiling, has accelerated genomic research in myeloma. Distinct biologic subtypes, characterized by unique genetic abnormalities with differing clinical outcomes, have been identified. The identification of these primary genetic defects, and the deregulated oncogenes and pathways in myeloma, has allowed for the development of more targeted therapies. This has led to the discovery of an increased number of active agents in the treatment of myeloma. Genetics also have prognostic importance in myeloma. Recent studies have elucidated a genetic prognostic hierarchy, and have enabled improved definition of the prognostic significance of their interactions. The current challenges are to: improve the dissection of the genetic heterogeneity of the disease; better define progression events; improve the risk stratification of patients; more accurately select patients who will respond well to a particular treatment; and develop more rational combinations of treatment. Genomics will have an important role to play in all of these goals.

Induction of Polyploidy by Histone Deacetylase Inhibitor: A Pathway for Antitumor Effects

Histone deacetylase (HDAC) inhibitors can induce various transformed cells to undergo growth arrest and/or death. Suberoylanilide hydroxamic acid (SAHA) is an HDAC inhibitor which is in phase I/II clinical trials and has shown antitumor activity in hematologic and solid tumors at doses well tolerated by patients. HDAC is the target for SAHA, but the mechanisms of the consequent induced death of transformed cells are not completely understood. In this study, we report that SAHA induced polyploidy in human colon cancer cell line HCT116 and human breast cancer cell lines, MCF-7, MDA-MB-231, and MBA-MD-468, but not in normal human embryonic fibroblast SW-38 and normal mouse embryonic fibroblasts. The polyploid cells lost the capacity for proliferation and committed to senescence. The induction of polyploidy was more marked in HCT116 p21WAF1-/- or HCT116 p53-/- cells than in wild-type HCT116. The development of senescence of SAHA-induced polyploidy cells was similar in all colon cell lines. The present findings indicate that the HDAC inhibitor could exert antitumor effects by inducing polyploidy, and this effect is more marked in transformed cells with nonfunctioning p21WAF1 or p53 genes.

HDAC inhibition prevents NF-kappa B activation by suppressing proteasome activity: down-regulation of proteasome subunit expression stabilizes I kappa B alpha

The short chain fatty acid (SCFA) butyrate (BA) and other histone deacetylase (HDAC) inhibitors can rapidly induce cell cycle arrest and differentation of colon cancer cell lines. We found that butyrate and the specific HDAC inhibitor trichostatin A (TSA) can reprogram the NF-(kappa)B response in colon cancer cells. Specifically, TNF-alpha activation is suppressed in butyrate-differentiated cells, whereas IL-1beta activation is largely unaffected. To gain insight into the relationship between butyrate-induced differentiation and NF-(kappa)B regulation, we determined the impact of butyrate on proteasome activity and subunit expression. Interestingly, butyrate and TSA reduced the cellular proteasome activity in colon cancer cell lines. The drop in proteasome activity results from the reduced expression of the catalytic beta-type subunits of the proteasome at both the protein and mRNA level. The selective impact of HDAC inhibitors on TNF-alpha-induced NF-(kappa)B activation appears to relate to the fact that the TNF-alpha-induced activation of NF-(kappa)B is mediated by the proteasome, whereas NF-kappaB activation by IL-1beta is largely proteasome-independent. These findings indicate that cellular differentation status and/or proliferative capacity can significantly impact proteasome activity and selectively alter NF-(kappa)B responses in colon cancer cells. This information may be useful for the further development and targeting of HDAC inhibitors as anti-neoplastic and anti-inflammatory agents.

Histone deacetylase inhibition down-regulates cyclin D1 transcription by inhibiting nuclear factor-kappaB/p65 DNA binding

Histone deacetylase (HDAC) inhibitors are emerging as a promising new class of cancer therapeutic agents. HDAC inhibitors relieve the deacetylation of histone proteins. However, little is known about the nonhistone targets of HDAC inhibitors and their roles in gene regulation. In this study, we addressed the molecular basis of the down-regulation of the nuclear factor-kappaB (NF-kappaB)-responsive gene cyclin D1 by the HDAC inhibitor trichostatin A in mouse JB6 cells. Cyclin D1 plays a critical role in cell proliferation and tumor progression. Trichostatin A inhibits cyclin D1 expression in a NF-kappaB-dependent manner in JB6 cells. Electrophoretic mobility shift assay studies showed that trichostatin A treatment prevents p65 dimer binding to NF-kappaB sites on DNA. Moreover, a chromatin immunoprecipitation assay shows that trichostatin A treatment inhibits endogenous cyclin D1 gene transcription by preventing p65 binding to the cyclin D1 promoter. However, acetylation of p65 is not affected by trichostatin A treatment. Instead, trichostatin A enhances p52 acetylation and increases p52 protein level by enhancing p100 processing. This is the first report that trichostatin A, a HDAC inhibitor, activates p100 processing and relieves the repression of p52 acetylation. The enhanced acetylation of p52 in the nuclei may operate to cause nuclear retention of p65 by increasing the p52/p65 interaction and preventing IkappaBalpha-p65 binding. The enhanced p52 acetylation coincides with decreased p65 DNA binding, suggesting a potential role of p52 acetylation in NF-kappaB regulation. Together, the results provide the first demonstration that HDAC inhibitor trichostatin A inhibits cyclin D1 gene transcription through targeting transcription factor NF-kappaB/p65 DNA binding. NF-kappaB is therefore identified as a transcription factor target of trichostatin A treatment.

Synergistic apoptosis induction by proteasome and histone deacetylase inhibitors is dependent on protein synthesis

Proteasome inhibitors are able to efficiently induce apoptosis in many tumor cells while leaving quiescent, untransformed cells largely unharmed. Here we investigated the further enhancement of proteasome inhibitor-mediated apoptosis induction in Bcr-Abl positive K562 CML cells by simultaneous treatment with different histone deacetylase inhibitors (HDIs). Combining proteasome and HDIs resulted in rapid hyperacetylation of histone H3 and accumulation of polyubiquitinated proteins and the synergistic induction of apoptosis. Apoptosis induction was associated with caspase 8, 3 and 9 activation, Bid processing, destruction of the mitochondrial membrane potential, cleavage of PARP and lamin B and extensive DNA fragmentation. The pan-caspase inhibitor Z-VAD-FMK and the caspase-8 inhibitor Z-IETD-FMK could inhibit K562 cell apoptosis. Apoptosis was also delayed by overexpression of Bcl-xL, as well as by crmA, a known inhibitor of caspases 1 and 8. Caspase 8 activity could still be detected in the presence of ectopic Bcl-xL, but not in crmA transfected cells. The most striking anti-apoptotic effect though was obtained by the translational inhibitor cycloheximide, which abolished caspase 8 processing, blocked Bid cleavage and maintained the mitochondrial transmembrane potential. Apoptosis by the combination treatment occurred independently from CD95/Fas receptor stimulation. These results demonstrated that transcriptional activation by HDIs combined with proteasome inhibitor mediated posttranslational stabilization of protein(s) results in significantly enhanced CML apoptosis which was striktly dependent on uninterrupted protein synthesis.

Histone deacetylase inhibitors, anticancerous mechanism and therapy for gastrointestinal cancers

Histone acetylation regulates gene transcription. Histone acetylation is a reversible process: histone acetyltransferases (HAT) transfer the acetyl moiety from acetyl coenzyme A to the lysine, and histone deacetylases (HDAC) remove the acetyl groups re-establishing the positive charge in the histones. HDAC inhibitors have antiproliferative activity against human cancer cells via cell cycle arrest, pro-differentiation, and pro-apoptosis. In recent years, many studies have shown that specific HDAC inhibitors are helpful for gastrointestinal cancer therapy.

Valproic acid, in combination with all-trans retinoic acid and 5-aza-2'-deoxycytidine, restores expression of silenced RARbeta2 in breast cancer cells

Epigenetic silencing of tumor suppressor genes has been established as an important process of carcinogenesis. The retinoic acid (RA) receptor beta2 (RARbeta2) gene is one such tumor suppressor gene often silenced during carcinogenesis. The combined use of histone deacetylase and DNA methyltransferase inhibitors has been shown to reverse the epigenetic silencing of numerous growth regulatory genes. Valproic acid (VPA), which has long been used in the treatment of epilepsy, was shown recently to be an effective histone deacetylase inhibitor that can induce differentiation of neoplastically transformed cells. In this study, we show for the first time that VPA, in combination with RA and the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (Aza-dC), can overcome the epigenetic barriers to transcription of a prototypical silenced tumor suppressor gene, RARbeta2, in human breast cancer cells. Chromatin immunoprecipitation assays show that the combination of VPA, RA, and Aza-dC increases histone acetylation at the silenced RARbeta2 promoter of MCF-7 breast cancer cells. Furthermore, reverse transcription-PCR analyses reveal cell type-specific effects in the actions of VPA on RARbeta2 expression in cultured human breast cancer cells. Finally, we show that VPA, in combination with RA and Aza-dC, inhibits the proliferation of both estrogen receptor alpha-positive (MCF-7) and estrogen receptor alpha-negative (MDA-MB-231) breast cancer cell lines. These data suggest that VPA may ultimately be useful in combination therapies in the treatment of human breast cancers.

Preclinical evaluation of the proteasome inhibitor bortezomib in cancer therapy

Bortezomib is a highly selective, reversible inhibitor of the 26S proteasome that is indicated for single-agent use in the treatment of patients with multiple myeloma who have received at least 2 prior therapies and are progressing on their most recent therapy. Clinical investigations have been completed or are under way to evaluate the safety and efficacy of bortezomib alone or in combination with chemotherapy in multiple myeloma, both at relapse and presentation, as well as in other cancer types. The antiproliferative, proapoptotic, antiangiogenic, and antitumor activities of bortezomib result from proteasome inhibition and depend on the altered degradation of a host of regulatory proteins. Exposure to bortezomib has been shown to stabilize p21, p27, and p53, as well as the proapoptotic Bid and Bax proteins, caveolin-1, and inhibitor kappaB-alpha, which prevents activation of nuclear factor kappaB-induced cell survival pathways. Bortezomib also promoted the activation of the proapoptotic c-Jun-NH2 terminal kinase, as well as the endoplasmic reticulum stress response. The anticancer effects of bortezomib as a single agent have been demonstrated in xenograft models of multiple myeloma, adult T-cell leukemia, lung, breast, prostate, pancreatic, head and neck, and colon cancer, and in melanoma. In these preclinical in vivo studies, bortezomib treatment resulted in decreased tumor growth, angiogenesis, and metastasis, as well as increased survival and tumor apoptosis. In several in vitro and/or in vivo cancer models, bortezomib has also been shown to enhance the antitumor properties of several antineoplastic treatments. Importantly, bortezomib was generally well tolerated and did not appear to produce additive toxicities when combined with other therapies in the dosing regimens used in these preclinical in vivo investigations. These findings provide a rationale for further clinical trials using bortezomib alone or in combination regimens with chemotherapy, radiation therapy, immunotherapy, or novel agents in patients with hematologic malignancies or solid tumors.

Molecular characterization of PS-341 (bortezomib) resistance: implications for overcoming resistance using lysophosphatidic acid acyltransferase (LPAAT)-beta inhibitors

PS-341 (bortezomib, Velcadetrade mark) is a promising novel agent for treatment of advanced multiple myeloma (MM); however, 65% of patients with relapsed refractory disease in a phase II study do not respond to PS-341. We have previously shown that lysophosphatidic acid acyltransferase (LPAAT)-beta inhibitor CT-32615 triggers caspase-dependent apoptosis, and can overcome resistance to conventional therapeutics (i.e., dexamethasone, doxorubicin, melphalan) in MM cells. In this study, we therefore determined whether CT-32615 could also overcome resistance to PS-341. We first characterized molecular mechanisms of resistance to PS-341 in DHL-4 cells. DHL-4 cells express low levels of caspase-3 and caspase-8; furthermore, no cleavage in caspase-8, caspase-9, caspase-3, poly ADP-ribose polymerase (PARP), or DNA fragmentation factor 45 was triggered by PS-341 treatment. We have previously shown that PS-341 treatment triggers phosphorylation of c-Jun NH(2)-terminal kinase (JNK), which subsequently induces caspase-dependent apoptosis; conversely, JNK inhibition blocks PS-341-induced apoptosis. We here show that phosphorylation of SEK-1, JNK, and c-Jun are not induced by PS-341 treatment, suggesting that PS-341 does not trigger a stress response in DHL-4 cells. Importantly, CT-32615 inhibits growth of DHL-4 cells in a time- and dose-dependent fashion: a transient G2/M cell cycle arrest induced by CT-32615 is mediated via downregulation of cdc25c and cdc2. CT-32615 triggered swelling and lysis of DHL-4 cells, without caspase/PARP cleavage or TUNEL-positivity, suggesting a necrotic response. Our studies therefore demonstrate that LPAAT-beta inhibitor CT-32615 triggers necrosis, even in PS-341-resistant DHL-4 cells, providing the framework for its evaluation to overcome clinical PS-341 resistance and improve patient outcome.