Histone deacetylase (HDAC) inhibitor activation of p21WAF1 involves changes in promoter-associated proteins, including HDAC1

Hexamethylbisacetamide remodels the human immunodeficiency virus type 1 (HIV-1) promoter and induces Tat-independent HIV-1 expression but blunts cell activation

Hexamethylbisacetamide (HMBA) induces human immunodeficiency virus type 1 (HIV-1) gene expression in latently infected T-cell and monocytoid cell lines. We find that HMBA activation of viral expression is Tat independent but, like Tat, increases the efficiency of elongation of the HIV-1 promoter (long terminal repeat [LTR]) transcripts. Further, exposure to HMBA induces chromatin remodeling at nucleosome 1 (Nuc-1) near the start site of LTR transcription but does so without increasing histone acetylation or altering histone methylation near Nuc-1. Of note, despite enhanced proviral expression, HMBA suppressed HIV infection ex vivo in primary blood mononuclear cell (PBMC) cultures. Treatment with HMBA did not alter expression of the HIV coreceptors, CCR5 and CXCR4, in PBMCs but down-regulated CD4. Finally, HMBA interferes with cell proliferation and activation; it suppressed expression of Ki67 and CD25 and in PBMCs exposed to mitogen. As HMBA has been tested in oncology trials, its unusual properties make it a useful reagent for future studies of HIV promoter regulation and a novel prototype molecule for therapeutics that abort the latent proviral state of chronic HIV infection.

Suberoylanilide hydroxamic acid is effective in preclinical studies of medulloblastoma

PURPOSE

Suberoylanilide hydroxamic acid (SAHA) has been studied in adult solid and hematologic malignancies. However, little information has been reported on the effects of SAHA on central nervous system (CNS) tumors including medulloblastoma, the most common malignant brain tumor in children. We investigated SAHA in preclinical medulloblastoma models to determine its anti-cancer efficacy as well as its ability to affect intracranial lesions when administered systemically.

EXPERIMENTAL DESIGN AND RESULTS

Tissue culture studies were performed treating primary human fibroblasts, established medulloblastoma cell lines, and primary human medulloblastoma tumors with SAHA. At 10 microM concentration, SAHA had little effect on normal fibroblasts but caused >90% apoptosis in cultured medulloblastoma cells. Primary medulloblastomas from patients were sensitive to SAHA compared to vehicle alone in ex vivo studies. In athymic mice with medulloblastoma xenograft tumors, oral SAHA resulted in apoptosis of tumor tissue and significantly slowed tumor growth. In the ND2:Smo transgenic mouse medulloblastoma model, SAHA treatment caused significant apoptosis in these cerebellar tumors.

CONCLUSIONS

SAHA effectively induces cell death in established medulloblastoma cell lines, human patient primary tumor cultures, medulloblastoma xenografts and intracranial spontaneous medulloblastomas. Fibroblasts in culture and mice treated with SAHA did not reveal prohibitive toxicity profiles. These findings support the advancement of SAHA to pediatric clinical trials.

CpG island methylation and histone modifications: biology and clinical significance

The discovery that drastic changes in DNA methylation and histone modifications are common in human tumors has inspired various laboratories and pharmaceutical companies to develop and study epigenetic drugs. One of the most promising groups of agents is the inhibitors of histone deacetylases (HDACs), which have different biochemical and biologic properties but have a single common activity: induction of acetylation in histones, the key proteins in nucleosome and chromatin structure. HDAC inhibitors may act through the transcriptional reactivation of dormant tumor-suppressor genes. However, their pleiotropic nature leaves open the possibility that their well-known differentiation, cell-cycle arrest, and apoptotic properties are also involved in other functions associated with HDAC inhibition. Many phase I clinical trials indicate that HDAC inhibitors appear to be well-tolerated drugs. Thus, the field is ready for rigorous biologic and clinical scrutiny to validate the therapeutic potential of these drugs. HDAC inhibitors, probably in association with classical chemotherapy drugs or in combination with DNA-demethylating agents, could be promising drugs for cancer patients.

Epigenetic remodeling in colorectal cancer results in coordinate gene suppression across an entire chromosome band

We report a new mechanism in carcinogenesis involving coordinate long-range epigenetic gene silencing. Epigenetic silencing in cancer has always been envisaged as a local event silencing discrete genes. However, in this study of silencing in colorectal cancer, we found common repression of the entire 4-Mb band of chromosome 2q.14.2, associated with global methylation of histone H3 Lys9. DNA hypermethylation within the repressed genomic neighborhood was localized to three separate enriched CpG island 'suburbs', with the largest hypermethylated suburb spanning 1 Mb. These data change our understanding of epigenetic gene silencing in cancer cells: namely, epigenetic silencing can span large regions of the chromosome, and both DNA-methylated and neighboring unmethylated genes can be coordinately suppressed by global changes in histone modification. We propose that loss of gene expression can occur through long-range epigenetic silencing, with similar implications as loss of heterozygosity in cancer.

The role of histone acetylation versus DNA damage in drug-induced senescence and apoptosis

The present study was undertaken to determine the significance of histone acetylation versus DNA damage in drug-induced irreversible growth arrest (senescence) and apoptosis. Cellular treatment with the DNA-damaging drugs doxorubicin and cisplatin or with the histone deacetylase inhibitor trichostatin A, led to the finding that all the three drugs induced senescence at concentrations significantly lower than those required for apoptosis. However, only doxorubicin and cisplatin induced activation of H2AX, a marker for double-strand break formation. Interestingly, this occurred mainly at apoptosis and not senescence-inducing drug concentrations, suggesting that non-DNA-damage pathways may be implicated in induction of senescence by these drugs. In agreement with this, chromatin immunoprecipitation experiments indicated that doxorubicin was able to induce acetylation of histone H3 at the promoter of p21/WAF1 only at senescence-inducing concentrations. Collectively, these findings suggest that alteration of chromatin structure by cytotoxic drugs may represent a key mediator of senescence.

P210 Bcr-abl tyrosine kinase interaction with histone deacetylase 1 modifies histone H4 acetylation and chromatin structure of chronic myeloid leukaemia haematopoietic progenitors

The BCR-ABL fusion gene, originating from the balanced (9;22) translocation, is the molecular hallmark and the causative event of chronic myeloid leukaemia (CML). The interactions of its p210 protein constitutively activated and improperly confined to the cytoplasm with multiple regulatory signals of cell cycle progression, apoptosis and self-renewal, induce the illegitimate enlargement of clonal haematopoiesis and genetic instability that drives its progression towards the fully transformed phenotype of blast crisis. However, its effects on the basic transcription machinery and chromatin remodelling are unknown. Our study underscored histone H4 hyperacetylation associated with p210 tyrosine kinase in vitro and in vivo and its role in BCR-ABL transcription. Histone H4 hyperacetylation proceeds, at least partly, from the 'loss of function' of histone deacetylase 1 protein, a critical component of Rb-mediated transcriptional repression, in consequence of its cytoplasmatic compartmentalisation.

Valproic acid induces growth arrest, apoptosis, and senescence in medulloblastomas by increasing histone hyperacetylation and regulating expression of p21Cip1, CDK4, and CMYC

Valproic acid is a well-tolerated anticonvulsant that has been identified recently as a histone deacetylase inhibitor. To evaluate the antitumor efficacy and mechanisms of action of valproic acid in medulloblastoma and supratentorial primitive neuroectodermal tumor (sPNET), which are among the most common malignant brain tumors in children with poor prognosis, two medulloblastoma (DAOY and D283-MED) and one sPNET (PFSK) cell lines were treated with valproic acid and evaluated with a panel of in vitro and in vivo assays. Our results showed that valproic acid, at clinically safe concentrations (0.6 and 1 mmol/L), induced potent growth inhibition, cell cycle arrest, apoptosis, senescence, and differentiation and suppressed colony-forming efficiency and tumorigenicity in a time- and dose-dependent manner. The medulloblastoma cell lines were more responsive than the sPNET cell line and can be induced to irreversible suppression of proliferation and significantly reduced tumorigenicity by 0.6 and 1 mmol/L valproic acid. Daily i.p. injection of valproic acid (400 mg/kg) for 28 days significantly inhibited the in vivo growth of DAOY and D283-MED s.c. xenografts in severe combined immunodeficient mice. With Western hybridization and real-time reverse transcription-PCR, we further showed that the antitumor activities of valproic acid correlated with induction of histone (H3 and H4) hyperacetylation, activation of p21, and suppression of TP53, CDK4, and CMYC expression. In conclusion, valproic acid possesses potent in vitro and in vivo antimedulloblastoma activities that correlated with induction of histone hyperacetylation and regulation of pathways critical for maintaining growth inhibition and cell cycle arrest. Therefore, valproic acid may represent a novel therapeutic option in medulloblastoma treatment.

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.

Histone deacetylase 1 contributes to cell cycle and apoptosis

Histone deacetylases (HDACs) are generally thought to play important roles in human disease. However, little information is available concerning the specific functions of individual HDACs. We previously reported on transgenic mice that expressed human HDAC1 and experienced steatosis and nuclear pleomorphism in their hepatic tissues. To find out if the over-expression of HDAC1 contributes to the expression of genes related to the cell cycle, apoptosis, and lipid metabolism that eventually contribute to the pathological changes in the livers of the transgenic mice, the expression profiles of the related genes in liver tissues were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. The activated human HDAC1 significantly induced the expression levels of mRNA for p53, PPAR-gamma and Bak and reduced the p21 expression level compared with the levels in control littermates. However, the protein levels of p53 and PPAR-gamma were significantly decreased. In conclusion, our results indicate that HDAC1 can regulate gene expression at the mRNA and protein levels independently and that this may be a potential cytopathic factor for hepatic tissue in transgenic mice that over-express HDAC1.

Sodium butyrate sensitizes human glioma cells to TRAIL-mediated apoptosis through inhibition of Cdc2 and the subsequent downregulation of survivin and XIAP

In TNF-related apoptosis-inducing ligand (TRAIL)-resistant glioma cells, co-treatment with nontoxic doses of sodium butyrate and TRAIL resulted in a marked increase of TRAIL-induced apoptosis. This combined treatment was also cytotoxic to glioma cells overexpressing Bcl-2 or Bcl-xL, but not to normal human astrocytes, thus offering an attractive strategy for safely treating resistant gliomas. Cotreatment with sodium butyrate facilitated completion of proteolytic processing of procaspase-3 that was partially blocked by treatment with TRAIL alone. We also found that treatment with sodium butyrate significantly decreased the protein levels of survivin and X-linked inhibitor of apoptosis protein (XIAP), two major caspase inhibitors. Overexpression of survivin and XIAP attenuated sodium butyrate-stimulated TRAIL-induced apoptosis, suggesting its involvement in conferring TRAIL resistance to glioma cells. Furthermore, the kinase activities of Cdc2 and Cdk2 were significantly decreased following sodium butyrate treatment, accompanying downregulation of cyclin A and cyclin B, as well as upregulation of p21. Forced expression of Cdc2 plus cyclin B, but not Cdk2 plus cyclin A, attenuated sodium butyrate/TRAIL-induced apoptosis, overriding sodium butyrate-mediated downregulation of survivin and XIAP. Therefore, Cdc2-mediated downregulation of survivin and XIAP by sodium butyrate may contribute to the recovery of TRAIL sensitivity in glioma cells.

Selective induction of apoptosis by histone deacetylase inhibitor SAHA in cutaneous T-cell lymphoma cells: relevance to mechanism of therapeutic action

Suberoylanilide hydroxamic acid (SAHA), an orally administered inhibitor of histone deacetylases, is currently in phase II clinical trials for cutaneous T cell lymphomas (CTCL), but the mechanism of SAHA action is unknown. In this study, we investigated the anti-tumor effects of SAHA in CTCL cell lines and freshly isolated peripheral blood lymphocytes (PBL) from CTCL patients with high percentage of circulating malignant T cells. Three cell lines (MJ, Hut78, and HH) and PBL from 11 patients and three healthy donors were treated with SAHA (1, 2.5, and 5 microM) for 24 and/or 48 h. Apoptosis was determined by flow cytometry analysis of sub-G1 hypodiploid nuclei and/or annexin V binding populations. Acetylated histones and apoptosis-associated proteins were detected by Western blotting. SAHA at 1-5 microM for 24 and 48 h induced apoptosis in a concentration- and time-dependent manner in three cell lines: MJ (0%-7% and 1%-32%), Hut78 (4%-36% and 5%-54%), and HH (4%-67% and 8%-81%). SAHA at 1-5 muM for 48 h also induced more apoptosis of patients' PBL than healthy donors' (15%-32%versus 6%-13%, p < 0.05). SAHA treatment caused an accumulation of acetylated histones (H2B, H3, and H4), an increase of p21(WAF1) and bax proteins, a decrease of Stat6 and phospho-Stat6 proteins, and activation of caspase-3 in CTCL cells. Our data suggest that selective induction of malignant T cell apoptosis and modulation of acetylated histones, p21(WAF1), bax, Stat6, and caspase-3 may underlie the therapeutic action of SAHA in CTCL patients.

Inhibition of histone deacetylation blocks cardiac hypertrophy induced by angiotensin II infusion and aortic banding

BACKGROUND

A number of distinct stress signaling pathways in myocardium cause cardiac hypertrophy and heart failure. Class II histone deacetylases (HDACs) antagonize several stress-induced pathways and hypertrophy. However, cardiac hypertrophy induced by transgenic overexpression of the homeodomain only protein, HOP, can be prevented by the nonspecific HDAC inhibitors trichostatin A and valproic acid, suggesting that alternate targets that oppose class II HDAC function might exist in myocardium. We tested the effects of several HDAC inhibitors, including a class I HDAC-selective inhibitor, SK-7041, on cardiac hypertrophy induced by angiotensin II (Ang II) treatment or aortic banding (AB).

METHODS AND RESULTS

Cardiac hypertrophy was induced by chronic infusion of Ang II or by AB in mice or rats and evaluated by determining the ratio of heart weight to body weight or to tibia length, cross-sectional area, or echocardiogram. Cardiac hypertrophy induced by Ang II or AB for 2 weeks was significantly reduced by simultaneous administration of trichostatin A, valproic acid, or SK-7041. Echocardiogram revealed that exaggerated left ventricular systolic dimensions were relieved by HDAC inhibitors. HDAC inhibitors partially reversed preestablished cardiac hypertrophy and improved survival of AB mice. The expressions of atrial natriuretic factor, alpha-tubulin, beta-myosin heavy chain, and interstitial fibrosis were reduced by HDAC inhibition.

CONCLUSIONS

These results suggest that the predominant effect of HDAC inhibition, mainly mediated by class I HDACs, is to prevent cardiac hypertrophy in response to a broad range of agonist and stretch stimuli.

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.

Cancer cells become susceptible to natural killer cell killing after exposure to histone deacetylase inhibitors due to glycogen synthase kinase-3-dependent expression of MHC class I-related chain A and B

We show that histone deacetylase (HDAC) inhibitors lead to functional expression of MHC class I-related chain A and B (MICA/B) on cancer cells, making them potent targets for natural killer (NK) cell-mediated killing through a NK group 2, member D (NKG2D) restricted mechanism. Blocking either apoptosis or oxidative stress caused by HDAC inhibitor treatment did not affect MICA/B expression, suggesting involvement of a separate signal pathway not directly coupled to induction of cell death. HDAC inhibitor treatment induced glycogen synthase kinase-3 (GSK-3) activity and down-regulation of GSK-3 by small interfering RNA or by different inhibitors showed that GSK-3 activity is essential for the induced MICA/B expression. We thus present evidence that cancer cells which survive the direct induction of cell death by HDAC inhibitors become targets for NKG2D-expressing cells like NK cells, gammadelta T cells, and CD8 T cells.

Cell cycle checkpoint signaling involved in histone deacetylase inhibition and radiation-induced cell death

In breast cancer, radiation has a central role in the treatment of brain metastasis, although tumor sensitivity might be limited. The tumor cell defense response to ionizing radiation involves activation of cell cycle checkpoint signaling. Histone deacetylase (HDAC) inhibitors, agents that cause hyperacetylation of histone proteins and thereby aberrations in the chromatin structure, may also override the DNA damage defense response and facilitate the radiation-induced mitotic cell death. In experimental metastasis models, the human breast carcinoma cell line MA-11 invariably disseminates to the central nervous system. We compared profiles of in vitro MA-11 cell cycle response to ionizing radiation and HDAC inhibition. After radiation exposure, the G2-M phase accumulation and the preceding repression of the G2 phase regulatory factors Polo-like kinase-1 and cyclin B1 required intact G2 checkpoint signaling through the checkpoint kinase CHK1, whereas the similar phenotypic changes observed with HDAC inhibition did not. MA-11 cells did not show radiation-induced expression of the G1 cell cycle inhibitor p21, indicative of a defective G1 checkpoint and consistent with a point mutation detected in the tumor suppressor TP53 gene. Increase in the p21 level, however, was observed with HDAC inhibition. Following pretreatment with the HDAC inhibitor, the efficiency of clonogenic regrowth after irradiation was reduced, which is in accordance with the concept of increased probability of mitotic cell death when the chromatin structure is disrupted. Among molecular cell cycle-targeted drugs currently in the pipeline for testing in early-phase clinical trials, HDAC inhibitors may have therapeutic potential as radiosensitizers.

Regulation of the INK4a/ARF locus by histone deacetylase inhibitors

Despite the importance of the INK4a/ARF locus in tumor suppression, its modulation by histone deacetylase inhibitors (HDACis) remains to be characterized. Here, we have shown that the levels of p16INK4a are decreased in human and murine fibroblasts upon exposure to relatively high concentrations of trichostatin A and sodium butyrate. Interestingly, the levels of p19ARF are strongly upregulated in murine cells even at low concentrations of HDACis. Using ARF-deficient cells, we have demonstrated that p19ARF plays an active role in HDACi-triggered cytostasis and the contribution of p19ARF to this arrest is of higher magnitude than that of the well established HDACi target p21Waf1/Cip. Moreover, chemically induced fibrosarcomas in ARF-null mice are more resistant to the therapeutic effect of HDACis than similar tumors in wild type or p21Waf1/Cip-null mice. Together, our results have established the tumor suppressor ARF as a relevant target for HDACi chemotherapy.

Coordinated changes in DNA methylation and histone modifications regulate silencing/derepression of luteinizing hormone receptor gene transcription

We have previously demonstrated that transcription of the luteinizing hormone receptor (LHR) gene is subject to repression by histone deacetylation at its promoter region, where a histone deacetylase (HDAC)/mSin3A complex is anchored at a proximal Sp1 site. The present studies have shown that epigenetic silencing and activation of the LHR gene is achieved through coordinated regulation at both the histone and DNA levels. The HDAC inhibitor trichostatin A (TSA) evoked robust but significantly lower activation of the LHR gene in JAR than in MCF-7 cells. This effect was localized to the 176-bp promoter region, which is highly methylated in JAR and lightly methylated in MCF-7 cells. Consequently, TSA and the DNA demethylating reagent 5-azacytidine (5-AzaC) caused marked synergistic activation of the LHR gene in JAR but not in MCF-7 cells. Multiple site-specific lysine acetylation of H3/H4 is associated with such LHR gene activation. Methylation or acetylation of H3 at K9 is present at the silenced and derepressed LHR promoter, respectively. While DNA methylation levels did not affect the histone code of the LHR gene promoter, demethylation of the promoter CpG sites was necessary for maximal stimulation of this gene. Mechanistically, the combined actions of TSA and 5-AzaC, but not either 5-AzaC or TSA alone, resulted in complete demethylation of the LHR gene promoter in JAR cells. Release of the repressive HDAC/mSin3A complex from the LHR gene promoter in both cell types required both TSA-induced changes of histone modifications and, concurrently, a demethylated promoter. Also, Dnmt1 was largely dissociated from the LHR gene promoter in the presence of TSA or TSA plus 5-AzaC, and binding of MBD2 in JAR cells was diminished upon conversion of the promoter to a demethylated state. Such changes induced a more permissive chromatin where recruitment of polymerase II and TFIIB to the promoter was significantly increased. The activated state of the LHR gene induced by TSA and 5-AzaC in JAR and MCF-7 cells was observed basally in LHR-expressing PLC cells, in which the promoter is unmethylated and associated with hyperacetylated histones. Consequently, PLC cells are unresponsive to drug treatment. These findings have elucidated a regulatory mechanism whereby concurrent dissociation of repressors and association of activators and basal transcriptional components, resulting from coordinated histone hyperacetylation and DNA demethylation, lead to derepression of the LHR gene expression.

Suberoylanilide hydroxamic acid combined with gemcitabine enhances apoptosis in non-small cell lung cancer

BACKGROUND

We have shown that non-small cell lung cancer (NSCLC) is resistant to the histone deacetylase inhibitor (HDI) suberoylanilide hydroxamic acid (SAHA) through upregulation of the antiapoptotic transcription factor nuclear factor-kappaB (NF-kappaB). HDIs also promote chromatin remodeling, potentially making the DNA more accessible to chemotherapy. We hypothesize that combined SAHA and gemcitabine sensitizes NSCLC to apoptosis.

METHODS

Three NSCLC cell lines (A549, H358, H460) were untreated, or treated with SAHA, gemcitabine, or both agents. NF-kappaB-dependent transcription was determined by reporter gene assays, reverse transcriptase-polymerase chain reaction RT-PCR, and Western blot analysis for the NF-kappaB-regulated antiapoptotic gene MnSOD. Survival of NSCLC cells overexpressing Bfl/A1, Bcl-X(L), or MnSOD and treated with SAHA and gemcitabine was determined in the presence or absence of NF-kappaB. Survival of treated cells overexpressing HDAC-1, 2, 3 or p/CAF was determined. Apoptosis was determined by fluorescence-activated cell sorter analysis, DNA fragmentation, and caspase-3 activity. Colony formation assays were performed on cells treated concurrently and sequentially with SAHA and gemcitabine. Assays were performed in triplicate, and the Student t test was applied as appropriate.

RESULTS

SAHA-activated NF-kappaB (P <or= .05) and gemcitabine inhibited these effects (P <or= .01). Increased cell survival was observed after overexpression of antiapoptotic genes, as well as in cells overexpressing HDAC-1, -2, and -3. Fluorescence-activated cell sorter analysis, DNA fragmentation, and caspase-3 assays all showed enhanced apoptosis with combined therapy, compared with single-agent therapy (P <or= .01). Sequential treatment offered no improvement over concurrent treatment.

CONCLUSIONS

Combined SAHA and gemcitabine sensitized NSCLC cells to apoptosis. Potential "proapoptotic" mechanisms for this finding include gemcitabine inhibition of SAHA-induced NF-kappaB activation and chromatin remodeling mediated by the inhibition of histone deacetylases.

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.

Rational development of histone deacetylase inhibitors as anticancer agents: a review

The epigenome is defined by DNA methylation patterns and the associated post-translational modifications of histones. This histone code determines the expression status of individual genes dependent upon their localization on the chromatin. The histone deacetylases (HDACs) play a major role in keeping the balance between the acetylated and deacetylated states of chromatin and eventually regulate gene expression. Recent developments in understanding the cancer cell cycle, specifically the interplay with chromatin control, are providing opportunities for developing mechanism-based therapeutic drugs. Inhibitors of HDACs are under considerable exploration, in part because of their potential roles in reversing the silenced genes in transformed tumor cells by modulating transcriptional processes. This review is an effort to summarize the nonclinical and clinical status of HDAC inhibitors currently under development in anticancer therapy.

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.

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.

Histone modifying and chromatin remodelling enzymes in cancer and dysplastic syndromes

Inactivation of tumour suppressor genes is central to the development of cancer. Although this inactivation was once considered to be secondary to intragenic mutations, it is now clear that silencing of these genes often occurs by epigenetic means. Hypermethylation of CpG islands associated with the tumour suppressor genes was the first manifestation of this phenomenon to be described. It is apparent, however, that this is one of a host of chromatin modifications which characterize gene silencing. Although we know little about what determines which loci are affected, our understanding of the nature of the epigenetic marks and how they are established has blossomed. There is no compelling evidence that cancer ever develops by purely epigenetic means, but it is apparent that perturbations in the apparatus which establish the epigenome may contribute to the development of cancer. This review will focus on the role of two classes of chromatin remodelling enzymes, those that alter histones by the addition or removal of acetyl and methyl groups and those of the SWI/SNF family of proteins that change the topology of the nucleosome and its DNA strand via the hydrolysis of ATP, and we shall examine the consequence of mutations in, or mis-expression of, these factors. In some cases, mutations in these factors appear to play a direct role in cancer development. However, their general role as important intermediaries involved in regulating gene expression makes them attractive therapeutic targets. In exciting developments, it has been shown that inhibition of these factors leads to the reversal of tumour suppressor gene silencing and the inhibition of cancer cell growth.

5-Aza-2'-deoxycytidine (decitabine) can relieve p21WAF1 repression in human acute myeloid leukemia by a mechanism involving release of histone deacetylase 1 (HDAC1) without requiring p21WAF1 promoter demethylation

Decitabine is a potent demethylating agent that exhibits clinical activity against myeloid malignancies. Numerous genes silenced by hypermethylation are reactivated by decitabine through a mechanism involving promoter demethylation with subsequent release of histone deacetylases (HDACs) and accumulation of acetylated histones. Recent studies indicating that decitabine also induces regional chromatin remodeling of some unmethylated genes suggest additional mechanisms of action. Decitabine reactivates unmethylated p21WAF1 in some AML cell lines but the possible occurrence of p21WAF1 methylation in AML in vivo has not been studied in detail and decitabine effects on p21WAF1 chromatin remodeling have not been reported. We found that p21WAF1 mRNA was undetectable in 6 of 24 AML patient samples and 4 of 5 AML cell lines but there was no evidence of p21WAF1 promoter methylation. However, decitabine induced p21WAF1 in AML cell lines KG-1 and KG-1a in association with release of HDAC1 and increased acetylated histone H3 at the unmethylated p21WAF1 promoter. Decitabine effects on p21WAF1 histone acetylation and induction were enhanced by the HDAC inhibitor trichostatin A and were independent of wild type p53. Our findings indicate that decitabine can relieve p21WAF1 repression in AML by a mechanism that involves release of HDAC1 without requiring promoter demethylation. Furthermore, our study provides evidence that combined decitabine and HDAC inhibitor treatment can enhance chromatin remodeling and reactivation of an unmethylated tumor suppressor gene. This latter finding is of relevance to the clinical use of these agents in AML as we found the p21WAF1 promoter to be unmethylated in vivo.

Lost in transcription: p21 repression, mechanisms, and consequences

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 is a major player in cell cycle control and it is mainly regulated at the transcriptional level. Whereas induction of p21 predominantly leads to cell cycle arrest, repression of p21 may have a variety of outcomes depending on the context. In this review, we concentrate on transcriptional repression of p21 by cellular and viral factors, and delve in detail into its possible biological implications and its role in cancer. It seems that the major mode of p21 transcriptional repression by negative regulators is the interference with positive transcription factors without direct binding to the p21 promoter. Specifically, the negative factors may either inhibit binding of positive regulators to the promoter or hinder their transcriptional activity. The ability of p21 to inhibit proliferation may contribute to its tumor suppressor function. Because of this, it is not surprising that a number of oncogenes repress p21 to promote cell growth and tumorigenesis. However, p21 is also an inhibitor of apoptosis and p21 repression may also have an anticancer effect. For example, c-Myc and chemical p21 inhibitors, which repress p21, sensitize tumor cells to apoptosis by anticancer drugs. Further identification of factors that repress p21 is likely to contribute to the better understanding of its role in cancer.

Suberoylanilide hydroxamic acid (SAHA) has potent anti-glioma properties in vitro, ex vivo and in vivo

Current treatment modalities for malignant gliomas do not allow long-term survival. Here, we identify suberoylanilide hydroxamic acid (SAHA), an inhibitor of histone deacetylases (HDAC), as an effective experimental anti-glioma agent. Administration of SAHA to various glioma cell lines obtained from human, rat and mouse inhibited tumour cell growth in a range of 1-10 microm. This anti-glioma property is associated with up-regulation of the cell cycle control protein p21/WAF, as well as the induction of apoptosis. A novel tumour invasion model using slice cultures of rat brain corroborated the anti-glioma properties of SAHA in the organotypic brain environment. In this model, glioma invasion compromised adjacent brain parenchyma, and this tumour-associated cytotoxicity could be inhibited by SAHA. In addition, a 10-fold dose escalation experiment did not challenge the viability of cultured brain slices. In vivo, a single intratumoural injection of SAHA 7 days after orthotopic implantation of glioma cells in syngeneic rats doubled their survival time. These observations identify chromatin-modifying enzymes as possible and promising targets for the pharmacotherapy of malignant gliomas.

Histone deacetylase inhibitors suppress the induction of c-Jun and its target genes including COX-2

Cyclooxygenase-2 (COX-2) is considered to be a target for anticancer therapy. Histone deacetylase (HDAC) inhibitors exhibit antitumor activity, but the mechanisms of action are incompletely understood. We investigated whether HDAC inhibitors blocked AP-1-mediated activation of COX-2 transcription. Trichostatin A and suberoylanilide hydroxamic acid, two structurally related inhibitors of HDAC activity, blocked AP-1-mediated induction of COX-2 expression and prostaglandin E2 biosynthesis. Chromatin immunoprecipitation assays indicated that HDAC inhibitors suppressed c-Jun binding to the COX-2 promoter and thereby blocked transcription. The observed reduction in binding reflected reduced levels of c-Jun. HDAC inhibitors suppressed the induction of c-jun transcription by blocking the recruitment of the preinitiation complex (RNA polymerase II and TFIIB) to the c-jun promoter. HDAC3 but not HDAC1 or HDAC2 was required for AP-1-mediated stimulation of c-jun expression. Because HDAC inhibitors suppressed the induction of c-jun gene expression, resulting in reduced COX-2 transcription, it was important to determine whether other known AP-1 target genes were also modulated. Cyclin D1 and collagenase-1 are AP-1-dependent genes that have been implicated in carcinogenesis. HDAC inhibitors suppressed the induction of both cyclin D1 and collagenase-1 transcription by inhibiting the binding of c-Jun to the respective promoters. Taken together, these results suggest that HDAC inhibitors block the induction of c-jun transcription by inhibiting the recruitment of the preinitiation complex to the c-jun promoter. This led, in turn, to reduced expression of several activator protein-1-dependent genes (COX-2, cyclin D1, collagenase-1). These findings provide new insights into the mechanisms underlying the antitumor activity of HDAC inhibitors.

Hepatic steatosis in transgenic mice overexpressing human histone deacetylase 1

It is generally thought that histone deacetylases (HDACs) play important roles in the transcriptional regulation of genes. However, little information is available concerning the specific functions of individual HDACs in disease states. In this study, two transgenic mice lines were established which harbored the human HDAC1 gene. Overexpressed HDAC1 was detected in the nuclei of transgenic liver cells, and HDAC1 enzymatic activity was significantly higher in the transgenic mice than in control littermates. The HDAC1 transgenic mice exhibited a high incidence of hepatic steatosis and nuclear pleomorphism. Molecular studies showed that HDAC1 may contribute to nuclear pleomorphism through the p53/p21 signaling pathway.

Epigenetic and chromatin modifiers as targeted therapy of hematologic malignancies

Epigenetic regulation of gene expression is mediated through alterations in the DNA methylation status, covalent modifications of core nucleosomal histones, rearrangement of histones, and by RNA interference. It is now abundantly clear that deregulation of epigenetic mechanisms cooperates with genetic alterations in the development and progression of cancer and leukemia. Epigenetic deregulation affects several aspects of tumor cell biology, including cell growth, cell cycle control, differentiation, DNA repair, and cell death. This raises the strong possibility that reversing deregulated epigenetic mechanisms may be an effective treatment strategy for leukemia and cancer. This treatment strategy may either be designed to separately or collectively target the specific perturbations in the epigenetic mechanisms found in human hematologic malignancies. The following review describes our current understanding of the important deregulated epigenetic mechanisms and the preclinical and clinical development of epigenetic and chromatin modifiers in the therapy of these disorders.

Novel Histone Deacetylase Inhibitors in the Treatment of Thyroid Cancer

Histone deacetylases (HDAC) and histone acetyltransferases exert opposing enzymatic activities that modulate the degree of acetylation of histones and other intracellular molecular targets, thereby regulating gene expression, cellular differentiation, and survival. HDAC inhibition results in accumulation of acetylated histones and induces differentiation and/or apoptosis in transformed cells. In this study, we characterized the effect of two HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and m-carboxycinnamic acid bis-hydroxamide, on thyroid carcinoma cell lines, including lines originating from anaplastic and medullary carcinomas. In these models, both SAHA and m-carboxycinnamic acid bis-hydroxamide induced growth arrest and caspase-mediated apoptosis and increased p21 protein levels, retinoblastoma hypophosphorylation, BH3-interacting domain death agonist cleavage, Bax up-regulation, down-regulation of Bcl-2, A1, and Bcl-x(L) expression, and cleavage of poly(ADP-ribose) polymerase and caspase-8, -9, -3, -7, and -2. Transfection of Bcl-2 cDNA partially suppressed SAHA-induced cell death. SAHA down-regulated the expression of the apoptosis inhibitors FLIP and cIAP-2 and sensitized tumor cells to cytotoxic chemotherapy and death receptor activation. Our studies provide insight into the tumor type-specific mechanisms of antitumor effects of HDAC inhibitors and a framework for future clinical applications of HDAC inhibitors in patients with thyroid cancer, including histologic subtypes (e.g., anaplastic and medullary thyroid carcinomas) for which limited, if any, therapeutic options are available.

Increased expression of histone deacetylase 2 is found in human gastric cancer

Accumulated evidence has established that aberrant regulation of histone deacetylases (HDACs) is one of the major causes of the development of human malignancies. Among different iso-enzymes of HDAC and sirtuins grouped as the HDAC super family, little is known as to how histone deacetylase 2 (HDAC2) causes carcinogenesis in solid tumors. Here, in order to investigate the possible role of HDAC2 in gastric carcinogenesis, we analyzed the expression of HDAC2 in 71 gastric adenocarcinomas by immunohistochemistry. Moderate to strong expression of HDAC2 was found in 44 (62%) out of a total of 71 tumors. The majority of positive tumors, which were detected in the nucleus but not in normal gastric epithelium, did not express HDAC2 or showed only weak positive staining. Interestingly, we also noted that HDAC2 expression appeared to be associated with tumor aggressiveness as HDAC2 expression was observed to be statistically significant in advanced gastric cancer (P=0.0023, Chi-square test) and in positive lymph node metastasis (P=0.0713, Chi-square test). Taken together, these results suggest that HDAC2 may play an important role in the aggressiveness of gastric cancer.

Histone deacetylase inhibitors down-regulate bcl-2 expression and induce apoptosis in t(14;18) lymphomas

Histone deacetylase (HDAC) inhibitors are promising antitumor agents, but they have not been extensively explored in B-cell lymphomas. Many of these lymphomas have the t(14;18) translocation, which results in increased bcl-2 expression and resistance to apoptosis. In this study, we examined the effects of two structurally different HDAC inhibitors, trichostatin A (TSA) and sodium butyrate (NaB), on the cell cycle, apoptosis, and bcl-2 expression in t(14;18) lymphoma cells. We found that in addition to potent cell cycle arrest, TSA and NaB also dramatically induced apoptosis and down-regulated bcl-2 expression, and overexpression of bcl-2 inhibited TSA-induced apoptosis. The repression of bcl-2 by TSA occurred at the transcriptional level. Western blot analysis and quantitative chromatin immunoprecipitation (ChIP) assay showed that even though HDAC inhibitors increased overall acetylation of histones, localized histone H3 deacetylation occurred at both bcl-2 promoters. TSA treatment increased the acetylation of the transcription factors Sp1 and C/EBPalpha and decreased their binding as well as the binding of CBP and HDAC2 to the bcl-2 promoters. Mutation of Sp1 and C/EBPalpha binding sites reduced the TSA-induced repression of bcl-2 promoter activity. This study provides a mechanistic rationale for the use of HDAC inhibitors in the treatment of human t(14;18) lymphomas.

Gene expression analysis reveals that histone deacetylation sites may serve as partitions of chromatin gene expression domains

Background

It has been a long-term puzzle whether chromatin can be further divided into distinct gene expression domains. Because histone deacetylation affects chromatin structure, that in turn may affect the expression of nearby genes, histone deacetylation sites may act to partition chromatin into different gene expression domains. In this article, we explore the relationship between histone deacetylation sites and gene expression patterns on the genome scale using different data sources, including microarray data measuring gene expression levels, microarray data measuring histone deacetylation sites, and information on regulatory targets of transcription factors.

Results

Using 269 Saccharomyces cerevisiae microarray datasets, histone deacetylation datasets, and regulatory targets of transcription factors assembled from the Yeast Proteome Database and ChIP-chip data, we found that histone deacetylation sites can reduce the level of co-expression of neighboring genes.

Conclusion

Histone deacetylation sites may serve as possible partition sites for chromatin domains and affect gene expression.

Histone deacetylase inhibitors profoundly decrease proliferation of human lymphoid cancer cell lines

Methylation of tumor suppressor genes is frequently observed in human cancers. These genes are silenced by histone deacetylase (HDAC) recruited by methylated DNA in their promoter regions. HDAC removes acetyl groups from histones and prevents the basic transcriptional machinary access to the target gene, leading to transcriptional repression. HDAC inhibitors (HDACIs) can restore the expression of the tumor suppressor and/or cell cycle regulatory genes in cancer cells and block the cellular proliferation of these cells. In this study, we investigated the in vitro antiproliferative activities of the HDACIs, suberoylanilide hydroxamic acid (SAHA), and valproic acid against 14 human lymphoid cancer cell lines. All of these cell lines were sensitive to the antiproliferative effects of the HDACI. SAHA induced either G1 or G2-M arrest as well as apoptosis. SAHA downregulated cyclin D1 and D2, and upregulated p53, p21, and p27. Chromatin immunoprecipitation analysis revealed a remarkable increase in the level of acetylated histones associated with the p21 promoter after SAHA treatment. In nude mice, SAHA significantly inhibited growth of a mantle cell lymphoma without major toxic side effects. In summary, HDACIs are promising therapeutic agents for human lymphoid cancers.

Drug Insight: histone deacetylase inhibitors—development of the new targeted anticancer agent suberoylanilide hydroxamic acid

This review focuses on the discovery and development of the histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA). Post-translational modifications of the histones of chromatin are important factors in regulating gene expression--so-called epigenetic gene regulation. Acetylation and deacetylation of lysine residues in histone tails, controlled by the activities of HDACs and histone acetyltransferases, are among the most studied post-translational modification of histones. In addition to chromatin protein, transcription factors, cell-signaling regulatory proteins, and proteins regulating cell death are substrates of HDACs and may be altered in function by HDAC inhibitors. HDAC inhibitors have several remarkable aspects. For instance, despite HDACs being ubiquitously distributed through chromatin, SAHA selectively alters the transcription of relatively few genes, and normal cells are at least 10-fold more resistant than transformed cells to SAHA and related HDAC inhibitor-induced cell death. HDAC inhibitors represent a relatively new group of targeted anticancer compounds, which are showing significant promise as agents with activity against a broad spectrum of neoplasms, at doses that are well tolerated by cancer patients. SAHA is one of the HDAC inhibitors most advanced in development. It is in phase I and II clinical trials for patients with both hematologic and solid tumors.

Antileukemia activity of the combination of 5-aza-2'-deoxycytidine with valproic acid

Aberrant DNA methylation of promoter associated CpG islands is a common phenomenon in human leukemias and cooperates with histone code changes in the control of gene expression. 5-Aza-2'-deoxycytidine (DAC) is a hypomethylating agent with significant antileukemia activity in humans. Recently, valproic acid (VPA) has been shown to be a histone deacetylase inhibitor and to have potential antineoplastic activity. In this report, we study the in vitro effects of the combination of DAC and VPA on the leukemic cell lines HL-60 and MOLT4. DAC alone induced growth inhibition and apoptosis at doses of 1 microM, an effect observed with VPA at doses of 1 mM. Each drug alone had the capacity to induce the expression of p57KIP2 and p21CIP1. DAC mediated hypomethylation of p57KIP2 was not required to induce p57KIP2 gene expression, and treatment with DAC resulted in the induction of p21CIP1. VPA induced global histone acetylation, an effect enhanced by the addition of DAC. The combination of DAC and VPA had a synergistic effect in terms of growth inhibition, induction of apoptosis and reactivation of p57KIP2 and p21CIP1. These results suggest that the combination of DAC and VPA could have significant antileukemia activity in vivo.

Proteasome inhibition sensitizes non-small cell lung cancer to histone deacetylase inhibitor-induced apoptosis through the generation of reactive oxygen species

OBJECTIVES

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces apoptosis in some malignancies through mitochondrial injury and generation of reactive oxygen species. Histone deacetylase inhibitors also activate the antiapoptotic transcription factor nuclear factor kappaB. We hypothesize that proteasome inhibition with bortezomib (Velcade; Millennium Pharmaceuticals, Inc, Cambridge, Mass)will inhibit nuclear factor kappaB activation, enhance suberoylanilide hydroxamic acid-induced mitochondrial injury, and sensitize non-small cell lung cancer cells to apoptosis.

METHODS

Four tumorigenic non-small cell lung cancer cell lines were treated with nothing, suberoylanilide hydroxamic acid, bortezomib, or both drugs. Nuclear factor kappaB-dependent transcription was determined by reporter gene assays and endogenous interleukin 8 transcription. Reactive oxygen species were quantified by using the fluorophore H 2 DCFDA. Cell viability was determined on the basis of clonogenic survival, and apoptosis was measured by quantifying caspase-3 activity and DNA fragmentation. Apoptosis and cell-survival assays were repeated in similarly treated cells incubated in the presence or absence of N-acetyl cysteine. Statistical significance was determined by means of analysis of variance.

RESULTS

Suberoylanilide hydroxamic acid significantly enhanced interleukin 8 and nuclear factor kappaB-dependent reporter gene transcription, and these effects were inhibited by bortezomib ( P < or = .01). Combined treatment with suberoylanilide hydroxamic acid and bortezomib induced greater reactive oxygen species generation, more apoptosis ( P < or = .02), and more cell death ( P < or = .001) than either drug alone. N-acetyl cysteine diminished the induction of apoptosis and enhanced cell survival ( P < or = .04).

CONCLUSIONS

Suberoylanilide hydroxamic acid and bortezomib synergistically induce reactive oxygen species generation in non-small cell lung cancer, and this plays a critical role in the induction of apoptosis after treatment. Combined treatment with suberoylanilide hydroxamic acid and bortezomib might be an effective treatment strategy for non-small cell lung cancer.

Role of thioredoxin in the response of normal and transformed cells to histone deacetylase inhibitors

This study examines the basis of resistance and sensitivity of normal and transformed cells to histone deacetylase inhibitor (HDACi)-induced cell death, specifically the role of caspases and thioredoxin (Trx). An important attribute of HDACis is that they induce cancer cell death at concentrations to which normal cells are relatively resistant, making them well suited for cancer therapy. The mechanism underlying this selectivity has not been understood. In this study we found that the HDACi suberoylanilide hydroxamic acid (SAHA) and MS-275, a benzamide, cause an accumulation of reactive oxygen species (ROS) and caspase activation in transformed but not normal cells. Inhibition of caspases does not block HDACi-induced cell death. These studies provide a possible mechanism that can explain why normal but not certain transformed cells are resistant to HDACi-induced cell death. The HDACi causes an increase in the level of Trx, a major reducing protein for many targets, in normal cells but not in transformed cells. The SAHA-induced increase in Trx activity in normal cells is associated with no increase in ROS accumulation. Transfection of transformed cells with Trx small interfering RNA caused a marked decrease in the level of Trx protein with an increase in ROS, a decrease in cell proliferation, and an increase in sensitivity to SAHA-induced cell death. Thus, Trx, independent of the caspase apoptotic pathway, is an important determinant of resistance of cells to HDACi-induced cell death.

Potent stimulation of gene expression by histone deacetylase inhibitors on transiently transfected DNA

Transcription activity of chromatin is associated with histone acetylation which is regulated by recruitment of histone acetyltransferases and deacetylases (HDAC) to specific chromatin regions. We have tested how expression of a transfected or stably introduced gene correlates with histone acetylation. Our results demonstrate that expression of transiently transfected green fluorescence protein (GFP) genes is significantly enhanced by HDAC inhibitors. Although HDAC treatment did not induce noticeable changes in the chromatin structure of genomic DNA, chromatin immunoprecipitation showed that more transiently transfected DNA is assembled into chromatin containing acetylated histones in HDAC inhibitor treated cells when compared to untreated cells. For stably integrated GFP, the expression response to HDAC inhibitors varies between independent stable cell lines. However, there was no difference in histone acetylation associated with the integrated transgene between HDAC inhibitor responsive and non-responsive cells. Furthermore, the overall enhancement of transgene expression by HDAC inhibitors was not as pronounced as in transiently transfected cells.

Histone deacetylase inhibitor, Trichostatin A, activates p21WAF1/CIP1 expression through downregulation of c-myc and release of the repression of c-myc from the promoter in human cervical cancer cells

Histone deacetylase (HDAC) inhibitors have shown promise in clinical cancer therapy and to consistently induce p21WAF1/CIP1 expression in a p53-independent manner and via increased acetylation of the chromatin at the Sp1 sites in the p21WAF1/CIP1 promoter region. However, the exact mechanism by which HDAC inhibitors induce p21WAF1/CIP1 remains unclear. In this study, we observed that Trichostatin A (TSA), a HDAC inhibitor, induced strikingly p21WAF1/CIP1 expression in human cervical cancer (HeLa) cells, and this induction correlated with downregulation of c-myc expression. Coincident with this observation, knock down of c-myc with a c-myc specific small interfering RNA dramatically induced expression of p21WAF1/CIP1 in these cancer cells. These data suggest that c-myc may play a critical role in repression of p21WAF1/CIP1 expression in HeLa cells. More importantly, using chromatin immunoprecipitation assay, we observed for the first time that c-myc bound to the endogenous p21WAF1/CIP1 promoter in untreated HeLa cells, but not in TSA-treated cells. Taken together, TSA induced c-myc downregulation and release from the endogenous p21WAF1/CIP1 promoter contributes, at least partially, to transcriptional activation of the p21WAF1/CIP1 in HeLa cells.

ICI182,780 induces p21Waf1 gene transcription through releasing histone deacetylase 1 and estrogen receptor alpha from Sp1 sites to induce cell cycle arrest in MCF-7 breast cancer cell line

We used the estrogen-responsive MCF-7 breast cancer cell line as a relevant model to study the anti-proliferative effects of ICI182,780 and identified the negative cell cycle regulator p21Waf1 as a specific target of ICI182,780. Furthermore, silencing of the p21Waf1 expression by small interfering RNA overcame the G0/G1 cell cycle arrest induced by ICI182,780, suggesting that the induction of p21Waf1 expression has a direct role in mediating the ICI182,780-induced G0/G1 arrest. We further demonstrated that the induction of p21Waf1 by ICI182,780 is mediated at transcriptional and gene promoter levels through the proximal Sp1 sites located near the transcription start site. Co-immunoprecipitation, DNA "pull-down," and chromatin immunoprecipitation experiments together showed that in cycling cells, estrogen receptor alpha and histone deacetylase 1 (HDAC1) are recruited to the proximal Sp1 sites of the promoter to repress p21Waf1 expression. In the presence of ICI182,780, estrogen receptor alpha and HDACs are dissociated from Sp1, resulting in increased histone acetylation and de-repression of the p21Waf1 promoter and induction of p21Waf1 expression. The fact that p21Waf1 expression is normally repressed by HDAC activity in cycling cells is further demonstrated by the finding that p21Waf1 transcription can be induced by the silencing of HDACs with small interfering RNA or treatment with HDAC inhibitors.

Histone deacetylase inhibitors

The base sequence of DNA provides the genetic code for proteins. The regulation of expression or suppression of gene transcription is largely determined by the structure of the chromatin--referred to as epigenetic gene regulation (Agalioti et al., 2002; Jenuwein and Allis, 2001; Richards and Elgin, 2002; Spotswood and Turner, 2002; Zhang and Reinberg, 2001). Posttranslational modifications of the histones of chromatin play an important role in regulating gene expression. Some of the most extensively studied epigenetic modifications involve acetylation/deacetylation of lysines in the tails of the core histones, which is controlled by the action of histone deacetylases (HDACs) and histone acetyltransferases (HATs). A controlled balance between histone acetylation and deacetylation appears to be essential for normal cell growth (Waterborg, 2002). Alterations in the structure or expression of HATs and HDACs occur in many cancers (Jones and Baylin, 2002; Marks et al., 2001, 2003; Timmermann et al., 2001; Wang et al., 2001). A structurally diverse group of molecules has been developed that can inhibit HDACs (HDACi) (Arts et al., 2003; Bouchain and Delorme, 2003; Curtin and Glaser, 2003; Johnstone and Licht, 2003; Marks et al., 2003; Remiszewski, 2003; Richon et al., 1998; Yoshida et al., 2003). These inhibitors induce growth arrest, differentiation, and?or apoptosis of cancer cells in vitro and in in vivo tumor-bearing animal models. Clinical trials with several of these agents have shown that certain HDACi have antitumor activity against various cancers at doses that are well tolerated by patients (Gottlicher et al., 2001; Kelly et al., 2002a,b; Piekarz et al., 2001; Wozniak et al., 1999).

Neuroprotective effects of phenylbutyrate in the N171-82Q transgenic mouse model of Huntington's disease

Huntington's disease (HD) is caused by an expansion of exonic CAG triplet repeats in the gene encoding the huntingtin protein (Htt), however, the means by which neurodegeneration occurs remains obscure. There is evidence that mutant Htt interacts with transcription factors leading to reduced histone acetylation. We report that administration of the histone deacetylase inhibitor phenylbutyrate after onset of symptoms in a transgenic mouse model of HD significantly extends survival and attenuates both gross brain and neuronal atrophy. Administration of phenylbutyrate increased brain histone acetylation and decreased histone methylation levels as assessed by both immunocytochemistry and Western blots. Phenylbutyrate increased mRNA for components of the ubiquitin-proteosomal pathway and down-regulated caspases implicated in apoptotic cell death, and active caspase 3 immunoreactivity in the striatum. These results show that administration of phenylbutyrate, at doses that are well tolerated in man, exerts significant neuroprotective effects in a transgenic mouse model of HD, and therefore represents a very promising therapeutic approach for HD.

Histone deacetylase inhibitors: understanding a new wave of anticancer agents

Cancer is as much an epigenetic disease as it is a genetic and cytogenetic disease. The discovery that drastic changes in DNA methylation and histone modifications are commonly found in human tumors has inspired various laboratories and pharmaceutical companies to develop and study epigenetic drugs. One of the most promising groups of agents is the inhibitors of histone deacetylases (HDACs), which have different biochemical and biologic properties but have a single common activity: induction of acetylation in histones, the key proteins in nucleosome and chromatin structure. One of the main mechanisms of action of HDAC inhibitors is the transcriptional reactivation of dormant tumor-suppressor genes, such as p21WAF1. However, their pleiotropic nature leaves open the possibility that their well-known differentiation, cell-cycle arrest and apoptotic properties are also involved in other functions associated with HDAC inhibition. Many phase I clinical trials indicate that HDAC inhibitors appear to be well-tolerated drugs. Thus, the field is ready for rigorous biologic and clinical scrutiny to validate the therapeutic potential of these drugs. Our current data indicate that the use of HDAC inhibitors, probably in association with classical chemotherapy drugs or in combination with DNA-demethylating agents, could be promising for cancer patients.

Contribution of disruption of the nuclear factor-kappaB pathway to induction of apoptosis in human leukemia cells by histone deacetylase inhibitors and flavopiridol

Interactions between the cyclin-dependent kinase inhibitor flavopiridol and the histone deacetylase inhibitors (HDACIs) sodium butyrate (NaB) and suberoylanilide hydroxamic acid (SAHA) have been examined in human leukemia cells in relation to effects on nuclear factor kappaB (NF-kappaB) activation. Exposure (24 h) of U937 human leukemia cells to NaB (1 mM) or SAHA (1.5 microM) resulted in a marked increase in NF-kappaB DNA binding, effects that were essentially abrogated by coadministration of flavopiridol (100 nM). These events were accompanied by a marked increase in mitochondrial injury, caspase activation, and apoptosis. Mutant cells expressing an IkappaBalpha super-repressor exhibited impairment of NF-kappaB DNA binding in response to HDACIs and a significant although modest increase in apoptosis. However, disruption of the NF-kappaB pathway also increased mitochondrial injury and caspase activation in response to flavopiridol and to an even greater extent to the combination of flavopiridol and HDACIs. Coadministration of flavopiridol with HDACIs down-regulated the X-linked inhibitor of apoptosis (XIAP), Mcl-1, and p21CIP1/WAF1 and activated c-Jun NH2-terminal kinase; moreover, these effects were considerably more pronounced in IkappaBalpha mutants. Similar responses were observed in U937 mutant cells stably expressing RelA/p65 small interfering RNA. In all cases, flavopiridol was significantly more potent than genetic interruption of the NF-kappaB cascade in promoting HDACI-mediated lethality. Together, these findings are consistent with the notion that although inhibition of NF-kappaB activation by flavopiridol contributes to antileukemic interactions with HDACIs, other NF-kappaB-independent flavopiridol actions (e.g., down-regulation of Mcl-1, XIAP, and p21CIP1/WAF1) play particularly critical roles in this phenomenon.

Trichostatin A-induced histone acetylation causes decondensation of interphase chromatin

The effect of trichostatin A (TSA)-induced histone acetylation on the interphase chromatin structure was visualized in vivo with a HeLa cell line stably expressing histone H2A, which was fused to enhanced yellow fluorescent protein. The globally increased histone acetylation caused a reversible decondensation of dense chromatin regions and led to a more homogeneous distribution. These structural changes were quantified by image correlation spectroscopy and by spatially resolved scaling analysis. The image analysis revealed that a chromatin reorganization on a length scale from 200 nm to >1 microm was induced consistent with the opening of condensed chromatin domains containing several Mb of DNA. The observed conformation changes could be assigned to the folding of chromatin during G1 phase by characterizing the effect of TSA on cell cycle progression and developing a protocol that allowed the identification of G1 phase cells on microscope coverslips. An analysis by flow cytometry showed that the addition of TSA led to a significant arrest of cells in S phase and induced apoptosis. The concentration dependence of both processes was studied.

Activation of the growth-differentiation factor 11 gene by the histone deacetylase (HDAC) inhibitor trichostatin A and repression by HDAC3

Histone deacetylase (HDAC) inhibitors inhibit the proliferation of transformed cells in vitro, restrain tumor growth in animals, and are currently being actively exploited as potential anticancer agents. To identify gene targets of the HDAC inhibitor trichostatin A (TSA), we compared the gene expression profiles of BALB/c-3T3 cells treated with or without TSA. Our results show that TSA up-regulates the expression of the gene encoding growth-differentiation factor 11 (Gdf11), a transforming growth factor beta family member that inhibits cell proliferation. Detailed analyses indicated that TSA activates the gdf11 promoter through a conserved CCAAT box element. A comprehensive survey of human HDACs revealed that HDAC3 is necessary and sufficient for the repression of gdf11 promoter activity. Chromatin immunoprecipitation assays showed that treatment of cells with TSA or silencing of HDAC3 expression by small interfering RNA causes the hyperacetylation of Lys-9 in histone H3 on the gdf11 promoter. Together, our results provide a new model in which HDAC inhibitors reverse abnormal cell growth by inactivation of HDAC3, which in turn leads to the derepression of gdf11 expression.

Comparison of tumor marker CA 242 with CA 19-9 and carcinoembryonic antigen (CEA) in pancreatic cancer

BACKGROUND/AIMS

Although there are a variety of tumor markers used for diagnosis of pancreatic carcinoma, the sensitivity and specificity of those markers have not yet reached an ideal level. The aim of this study was to compare the diagnostic value of CA 242 with CA 19-9 and CEA in the patients with pancreatic cancer.

METHODOLOGY

Serum CA 242, CA 19-9 and CEA levels were determined in 135 subjects in the following groups: Pancreatic cancer (n = 40), cholangiocellular carcinoma (n = 15), hepatocellular carcinoma (n = 10), cirrhosis (n = 7), chronic active hepatitis (n = 7), choledochal stone (n = 12), chronic pancreatitis (n = 9), acute pancreatitis (n = 6), and healthy controls (n = 29).

RESULTS

An elevated serum CA 242 concentration (> 20 U/mL) was found in 30 out of 40 (70%) (mean; 2163 +/- 838 U/mL) patients with pancreas cancer, in 11 out of 15 patients with cholangiocellular carcinoma (93.3%) (mean 916 +/- 529 U/mL), in none of patients with hepatocellular carcinoma and healthy controls. Slightly elevated CA 242 concentration was found in 6 out of 41 patients with benign hepatobiliary and pancreatic disease (range 0.4-97.8 U/mL) (1 acute pancreatitis, 2 chronic pancreatitis, 1 cirrhosis, 2 choledochal stone). Mean serum CA 242, CA 19-9 and CEA levels of the pancreas cancer group were significantly higher than those of the other groups except the cholangiocellular carcinoma group. There was no significant difference between the stage of pancreas cancer regarding mean serum CA 242, CA 19-9 and CEA level. There was positive correlation between serum CA 242 and CA 19-9 level. In the pancreas cancer, the sensitivity of CA 242, CA 19-9 and CEA was 75%, 80%, 40%, respectively and the specificity of those markers was 85.5%, 67.5% and 73%, respectively.

CONCLUSIONS

In conclusion, the advantage of CA 242 compared to CA 19-9 is that its specificity is higher than that of CA 19-9 in the diagnosis of pancreas cancer.