Inhibition Of Histone Deacetylation Research Articles

Enhanced growth inhibition by combined DNA methylation/HDAC inhibitors in lung tumor cells with silenced CDKN2A

Aberrant hypermethylation at CpG sites within the CDKN2A gene is associated with silencing and has been proposed as a target for reactivation using both DNA methylation and histone deacetylation inhibitors. This study investigates the role of selecting tumor samples with a silenced as compared to deleted CDKN2A locus when assessing the efficacy of DNA methyltransferase inhibitor, zebularine, combined with the HDAC inhibitor, depsipeptide. Non-small cell lung cancer cell lines with defined CDKN2A status were analyzed by MTS assay to determine the effect of zebularine or zebularine combined with depsipeptide on tumor cell growth. We observed that zebularine treatment resulted in inhibition of cell growth in 11 out of 12 lung cancer cell lines with silenced CDKN2A, but no cell growth inhibition was detected in the 7 lung cancer cell lines tested with deleted CDKN2A (p>0.001). In addition, we found that the combination of 30 microM zebularine and 6 or 7 nM depsipeptide resulted in a synergistic inhibition of cell growth in tumor cells with silenced CDKN2A (p<0.001, CI=0.70 and 0.57, respectively) but not in tumor cells with deleted CDKN2A. In conclusion, tumor cells with methylated CDKN2A are more sensitive to zebularine than cell lines with deleted CDKN2A and the combination of zebularine/depsipeptide results in a synergistic effect on cell growth inhibition that is also linked with the presence of silenced CDKN2A. Thus, combination of DNA methyltransferase and HDAC inhibitors may be a potential treatment for lung cancer patients, but careful selection of patients will be needed to optimize the benefit of this regimen.

Oncogenic Ras‐mediated downregulation of Clast1/LR8 is involved in Ras‐mediated neoplastic transformation and tumorigenesis in NIH3T3 cells

Oncogenic Ras proteins transform cells by way of multiple downstream signaling pathways that promote the genesis of human cancers. However, the exact cellular mechanisms by which downstream targets are regulated are not fully understood. Here, we show that oncogenic Ras reduced Clast1/LR8 transcript levels in mouse NIH3T3 fibroblasts and human WI38 fibroblasts. Clast1/LR8 transcript was undetectable in H460, A549, and H1299 cells showing high Ras activity, but was relatively abundant in DMS53 cells displaying low Ras activity. We also showed that K-Ras siRNA restored Clast1/LR8 expression in H460 and A549 cells, and that inhibitors of DNA methylation and histone deacetylation reversed oncogenic H-Ras-mediated suppression of Clast1/LR8 transcription. Additionally, ectopic expression of Clast1/LR8 inhibited serum-stimulated phosphorylation of ERK1/2 and Akt in H-RasV12-transformed NIH3T3 cells. We further showed that the expression of Clast1/LR8 interfered with oncogenic Ras-induced NIH3T3 cell transformation and invasion. Finally, our results showed that Clast1/LR8 inhibited Ras-induced proliferation of, and tumor formation by, oncogenic H-RasV12-transformed NIH3T3 cells in vivo. This study identifies the downregulation of Clast1/LR8 as a potentially important mechanism by which oncogenic Ras-mediated neoplastic transformation occurs.

Stable Morphology, but Dynamic Internal Reorganisation, of Interphase Human Chromosomes in Living Cells

Despite the distinctive structure of mitotic chromosomes, it has not been possible to visualise individual chromosomes in living interphase cells, where chromosomes spend over 90% of their time. Studies of interphase chromosome structure and dynamics use fluorescence in-situ hybridisation (FISH) on fixed cells, which potentially damages structure and loses dynamic information. We have developed a new methodology, involving photoactivation of labelled histone H3 at mitosis, to visualise individual and specific human chromosomes in living interphase cells. Our data revealed bulk chromosome volume and morphology are established rapidly after mitosis, changing only incrementally after the first hour of G1. This contrasted with the behaviour of specific loci on labelled chromosomes, which showed more progressive reorganisation, and revealed that “looping out” of chromatin from chromosome territories is a dynamic state. We measured considerable heterogeneity in chromosome decondensation, even between sister chromatids, which may reflect local structural impediments to decondensation and could potentially amplify transcriptional noise. Chromosome structure showed tremendous resistance to inhibitors of transcription, histone deacetylation and chromatin remodelling. Together, these data indicate steric constraints determine structure, rather than innate chromosome architecture or function-driven anchoring, with interphase chromatin organisation governed primarily by opposition between needs for decondensation and the space available for this to happen.

Epigenetic tools in potential anticancer therapy

Human cancer represents a heterogeneous group of diseases that are driven by progressive genetic and epigenetic abnormalities. The latter alterations involve hypermethylation and hypomethylation of DNA, and changed patterns of histone modification, with resultant remodeling of the chromatin structure that cause deregulation of the transcription activity of many genes. Unlike the remarkable progress in understanding the processes by which DNA methyltransferases can regulate gene expression and histone deacetylases can induce alteration of chromatin structure, the roles of epigenetic events in tumors remain insufficiently explained. In contrast to genetic changes, the epigenetic alterations in cancer cells can be reversed by the inhibition of DNA methylation and histone deacetylation. Therefore, many inhibition agents for re-expression, predominantly of tumor-suppressor genes, have been identified and tested in laboratory models and numerous clinical trials. Despite in-vitro evidence that a single drug can lead to reactivation of methylated genes, inhibitors of DNA methyltransferases and histone deacetylases have been investigated in combination, or together with cytotoxic chemotherapy, radiotherapy, immunotherapy, or hormonal therapy to improve the therapeutic effect. Ongoing trials are recognizing that the identification of a target group of patients who are more likely to respond to the epigenetic therapy, defining of an optimal dose and schedule of treatment, and the development of more specific inhibitors with minimal unwanted side effects are necessary. Thus, new combinations of anticancer agents, including epigenetic modulators, may lead to a more effective control of cancer.

Role of Salt-Induced Kinase 1 in Androgen Neuroprotection against Cerebral Ischemia

Androgens within physiological ranges protect castrated male mice from cerebral ischemic injury. Yet, underlying mechanisms are unclear. Here, we report that, after middle cerebral artery occlusion (MCAO), salt-induced kinase 1 (SIK1) was induced by a potent androgen-dihydrotestosterone (DHT) at protective doses. To investigate whether SIK1 contributes to DHT neuroprotection after cerebral ischemia, we constructed lentivirus-expressing small interference RNA (siRNA) against SIK1. The SIK1 knockdown by siRNA exacerbated oxygen-glucose deprivation (OGD)-induced cell death in primary cortical neurons, suggesting that SIK1 is an endogenous neuroprotective gene against cerebral ischemia. Furthermore, lentivirus-mediated SIK1 knockdown increased both cortical and striatal infarct sizes in castrated mice treated with a protective dose of DHT. Earlier studies show that SIK1 inhibits histone deacetylase (HDAC) activities by acting as a class IIa HDAC kinase. We observed that SIK1 knockdown decreased histone H3 acetylation in primary neurons. The SIK1 siRNA also exacerbated OGD-induced neuronal death in the presence of trichostatin A (TSA), an HDAC inhibitor, and decreased histone H3 acetylation at 4 hours reoxygenation in TSA-treated neurons. Finally, we showed that DHT at protective doses prevented ischemia-induced histone deacetylation after MCAO. Our finding suggests that SIK1 contributes to neuroprotection by androgens within physiological ranges by inhibiting histone deacetylation.

Exciting New Targets in Lung Cancer Therapy: ALK, IGF-1R, HDAC, and Hh

The anaplastic lymphoma kinase (ALK) inhibitor crizotinib will become an integral addition to the treatment of patients with non-small cell lung cancer (NSCLC) harboring genetic ALK translocations. The insulin-like growth factor receptor (IGF-1R) monoclonal antibody figitumumab, while initially promising, appears to increase toxicity and death in combination with chemotherapy in the treatment of patients with NSCLC of squamous histology; therefore, clinical development of this class of agents will need to proceed with caution. The histone deacetylation (HDAC) inhibitor vorinostat did not demonstrate an improvement in overall survival (OS) compared with placebo in a large randomized trial, but other agents in this class may have greater selectivity and efficacy. Inhibitors of the hedgehog (Hh) signaling pathways have some early clinical promise in both NSCLC and small cell lung cancer (SCLC), and larger studies using these agents are eagerly anticipated.

AR-42, a novel HDAC inhibitor, exhibits biologic activity against malignant mast cell lines via down-regulation of constitutively activated Kit

Histone hypoacetylation occurs in many cancers and inhibition of histone deacetylation is a promising approach to modulate these epigenetic changes. Our laboratory previously demonstrated that the histone deacetylase inhibitors (HDACis) vorinostat and AR-42 reduced the viability of a canine malignant mast cell line. The purpose of this study was to further investigate the mechanisms of pan-HDAC inhibition in normal and malignant mast cells. Mouse and canine malignant mast cell lines expressing various Kit mutations, normal canine mast cells, and primary canine malignant mast cells were treated with AR-42 (a novel HDACi) and effects on cell viability, cycling, and signaling were evaluated. Treatment with AR-42 induced growth inhibition, cell- cycle arrest, apoptosis, and activation of caspases-3/7. AR-42 promoted hyperacetylation of H3, H4, and alpha-tubulin, and up-regulation of p21. Down-regulation of Kit occurred after AR-42 treatment via inhibition of Kit transcription. Disassociation between Kit and heat shock protein 90 (HSP90) and up-regulation of HSP70 were observed after AR-42 treatment, suggesting potential loss of HSP90 chaperone function. Lastly, AR-42 down-regulated the expression of p-Akt, total Akt, phosphorylated STAT3/5 (pSTAT3/5), and total STAT3/5. In summary, AR-42 exhibits in vitro and ex vivo biologic activity against malignant mast cells, representing a promising therapeutic approach for malignant mast cell disease.

Abstract 5024: Sorafenib in combination with modifiers of epigenetic mechanism induce synergistic cytotoxicity in human liver cancer cell lines

Abstract Background: Hepatocellular carcinoma (HCC) is the third most important cause of cancer death worldwide. Sorafenib, a multikinase inhibitor improved outcomes in patients with hepatocellular carcinoma (HCC) by inhibiting angiogenesis. Epigenetic research suggests that many cancers may not be caused by mutations in genes but by chemical modifications that change how the genes function. DNA methylation and histone deacetylation are two of the more widely studied epigenetic mechanisms. Inhibitors of DNA methylation (Vidaza) and histone deacetylation (SAHA) have shown inhibited cell growth and induced apoptosis in liver cancer cells. We investigated the cytotoxicity of combination of Sorafenib with SAHA or Vidaza in two liver cancer cell lines HepG2 and Hep3B. METHODS: HepG2 and Hep3B cells in log phase growth were treated simultaneously with sorafenib (0.5-10 µM) and/or vidaza (1.25-10 µM) or SAHA (1.25-10 µM) for 72 hours. Following drug treatment, MTS assay was used as the endpoint for cell proliferation and the IC50 values and combination indices (CI) were derived using Calcusyn software (Biosoft, Cambridge, UK). Each combination was repeated at least three times. RESULTS: The mean single agent IC50's for Sorafenib, Vidaza and SAHA were 6.83±0.44 µM, 10.33±2.91µM, and 11.5±4.25 µM, respectively in HepG2 cells and 6.25±0.20 µM, 11.50±0.41 µM, and 4.25±0.20 µM, respectively in Hep3B cells. The combination indices were:CombinationsHepG2Hep3BSorafenib and Vidaza0.72+0.130.73+0.12Sorafenib and SAHA0.77+0.130.68+0.05 CONCLUSIONS: The CI's for both combinations demonstrated synergistic effects in each of the cell lines. The molecular mechanism behind the synergistic effect of sorafenib in combination with vidaza or SAHA in liver cancer in underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5024.

Abstract LB-296: Synergistic anticancer action of inhibitor of DNA methylation 5-aza-2-deocycytidine and EZH2 histone methylase inhibitor 3-deazaneplanocin A

Abstract The purpose of this study was to investigate the antineoplastic action of epigenetic therapy using 5-aza-2′-deoxycytidine (5-AZA-CdR) in combination with 3-deazaneplanocin A (DZNep). Aberrant epigenetic modifications play an important role in oncogenesis. DNA hypermethylation, which can silence tumor suppressor genes (TSGs), can be reversed by treatment with 5-AZA-CdR, a potent inhibitor of DNA methylation. Overexpression of EZH2 methyltransferase (HMT) can also contribute to neoplastic transformation by silencing differentiation genes and TSGs. Recent studies have shown that DZNep, an inhibitor of HMT, can reactivate certain TSGs and has activity as an antineoplastic agent. Inhibitors of DNA methylation and histone deacetylation are reported to produce synergistic reactivation of silent TSGs and synergistic anticancer activity. Our objective was to determine if this type of “cross-talk” also exists between inhibitors of DNA methylation and inhibitors of HMT. Our experimental approach was to treat leukemic and tumor cells with 5-AZA-CdR and/or DZNep and determine cell survival by in vitro colony assays. Treatment of human HL-60 myeloid leukemic cells for 24 h with 50 nM 5-AZA-CdR or 500 nM DZNep produced a loss of clonogenity (LC) of 50.0 ± 5.8% and 75.6 ± 4.15, respectively. 5-AZA-CdR in combination with DZNep at the same concentrations of each agent produced a LC of 99 ± 1% (n =3). The interaction between these two different types of epigenetic agents was clearly synergistic. We also performed colony assays with 5-AZA-CdR plus DZNep on human A549 lung carcinoma cells. These epigenetic agents in combination also produced a synergistic LC on these tumor cells. The epigenetic action of 5-AZA-CdR plus DZNep on malignant cells of different phenotype suggests that this type of treatment may show effectiveness in most types of cancer. Our current objective is to verify the synergistic interaction between inhibitors of DNA methylation and HMT in mouse models with cancer. We are also investigating action of these agents alone and in combination on expression of cancer-related genes in order to understand the molecular basis of the synergistic anticancer activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-296.

Impact of selenate treatment on broccoli glucosinolate profile and bioactivity

Selenium (Se)‐enriched broccoli has potent anticarcinogenic effects, which are suggested to be the result of changes in detoxification enzyme activity, induction of apoptosis, and inhibition of histone deacetylation (HDAC) and angiogenesis. We previously showed that feeding high‐Se broccoli powder (H‐SeB; 4.28 ppm) to male Copenhagen rats induced hepatic ethoxyresorufin‐O‐deethylase (EROD) and NAD(P)H:quinone oxidoreductase (NQO1) activity 1.6 and 1.9‐fold over low‐Se broccoli (L‐SeB; 0.25 ppm), respectively. To elucidate the relative role of Se in induction of these enzymes, mouse hepatoma Hepa‐1c1c7 cells were exposed to aqueous extracts of H‐SeB or L‐SeB. Extracts of H‐SeB increased EROD and NQO1 activity 2.7 and 1.3‐fold, respectively. Adding Se as selenite or Se‐methylselenocysteine (SeMSC) to L‐SeB extracts had no impact on EROD or QR activity. Likewise, Lee et al. reported that SeMSC up to 2.5 mM had no direct effect on HDAC in prostate cancer cells. Selenium‐enrichment of broccoli increased levels of the glucosinolate neoglucobrassicin, the hydrolysis product of which is known to induce EROD activity. We conclude that the increase in detoxification enzyme activity is not a direct effect of Se, but the result of a (plant) metabolite of Se and/or changes in the glucosinolate profile. Supported by grants from USDA/AFRI and the Illinois Council on Food and Agricultural Research.

New directions in cancer therapy ‐ HDAC inhibitors

AbstractThe HDACis (histone deacetylation inhibitors) are an active class of drugs that have been used to treat a wide variety of tumours including breast cancer, prostate cancer, multiple myeloma, thyroid cancer and Hodgkin's and non‐Hodgkin's lymphoma. One HDAC, vorinostat, has been licensed by the FDA, but more work is needed to identify and delineate the histone and nonhistone targets of these agents. In this article, Dr Steve Schey considers the place of HDACis in future cancer therapy. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Downregulation of Rap1GAP through Epigenetic Silencing and Loss of Heterozygosity Promotes Invasion and Progression of Thyroid Tumors

Thyroid cancer is the most common type of endocrine malignancy, encompassing tumors with various levels of invasive growth and aggressiveness. Rap1GAP, a Rap1 GTPase-activating protein, inhibits the RAS superfamily protein Rap1 by facilitating hydrolysis of GTP to GDP. In this study, we analyzed 197 thyroid tumor samples and showed that Rap1GAP was frequently lost or downregulated in various types of tumors, particularly in the most invasive and aggressive forms of thyroid cancer. The downregulation was due to promoter hypermethylation and/or loss of heterozygosity, found in the majority of thyroid tumors. Treatment with demethylating agent 5-aza-deoxycytidine and/or histone deacetylation inhibitor trichostatin A induced gene reexpression in thyroid cells. A genetic polymorphism, Y609C, was seen in 7% of thyroid tumors but was not related to gene downregulation. Loss of Rap1GAP expression correlated with tumor invasiveness but not with specific mutations activating the mitogen-activated protein kinase pathway. Rap1GAP downregulation was required in vitro for cell migration and Matrigel invasion. Recovery of Rap1GAP expression inhibited thyroid cell proliferation and colony formation. Overall, our findings indicate that epigenetic or genetic loss of Rap1GAP is very common in thyroid cancer, where these events are sufficient to promote cell proliferation and invasion.

Identification of phenylbutyrate-generated metabolites in Huntington disease patients using parallel liquid chromatography/electrochemical array/mass spectrometry and off-line tandem mass spectrometry

Oral sodium phenylbutyrate (SPB) is currently under investigation as a histone deacetylation (HDAC) inhibitor in Huntington disease (HD). Ongoing studies indicate that symptoms related to HD genetic abnormalities decrease with SPB therapy. In a recently reported safety and tolerability study of SPB in HD, we analyzed overall chromatographic patterns from a method that employs gradient liquid chromatography with series electrochemical array, ultraviolet (UV), and fluorescence (LCECA/UV/F) for measuring SPB and its metabolite phenylacetate (PA). We found that plasma and urine from SPB-treated patients yielded individual-specific patterns of approximately 20 metabolites that may provide a means for the selection of subjects for extended trials of SPB. The structural identification of these metabolites is of critical importance because their characterization will facilitate understanding the mechanisms of drug action and possible side effects. We have now developed an iterative process with LCECA, parallel LCECA/LCMS, and high-performance tandem MS for metabolite characterization. Here we report the details of this method and its use for identification of 10 plasma and urinary metabolites in treated subjects, including indole species in urine that are not themselves metabolites of SPB. Thus, this approach contributes to understanding metabolic pathways that differ among HD patients being treated with SPB.

Distinct and Temporal Roles of Nucleosomal Remodeling and Histone Deacetylation in the Repression of the hTERT Gene

hTERT, the human telomerase reverse transcriptase, is highly expressed in stem cells and embryonic tissues but undetectable in most adult somatic cells. To understand its repression mechanisms in somatic cells, we investigated the endogenous hTERT gene regulation during differentiation of human leukemic HL60 cells. Our study revealed that silencing of the hTERT promoter was a biphasic process. Within 24 h after initiation of differentiation, hTERT mRNA expression decreased dramatically, accompanied by increased expression of Mad1 gene and disappearance of a nucleosome-free region at the hTERT core promoter. Subsequent to this early repression, nucleosomal remodeling continued at the promoter and downstream region for several days, as demonstrated by micrococcal nuclease and restriction enzyme accessibility assays. This later nucleosomal remodeling correlated with stable silencing of the hTERT promoter. Progressive changes of core histone modifications occurred throughout the entire differentiation process. Surprisingly, inhibition of histone deacetylation at the hTERT promoter did not prevent hTERT repression or nucleosomal deposition, indicating that nucleosomal deposition at the core promoter, but not histone deacetylation, was the cause of transcriptional repression. Our data also suggested that succeeding nucleosomal remodeling and histone deacetylation worked in parallel to establish the stable repressive status of hTERT gene in human somatic cells.

Molecular and Therapeutic Potential and Toxicity of Valproic Acid

Valproic acid (VPA), a branched short-chain fatty acid, is widely used as an antiepileptic drug and a mood stabilizer. Antiepileptic properties have been attributed to inhibition of Gamma Amino Butyrate (GABA) transaminobutyrate and of ion channels. VPA was recently classified among the Histone Deacetylase Inhibitors, acting directly at the level of gene transcription by inhibiting histone deacetylation and making transcription sites more accessible. VPA is a widely used drug, particularly for children suffering from epilepsy. Due to the increasing number of clinical trials involving VPA, and interesting results obtained, this molecule will be implicated in an increasing number of therapies. However side effects of VPA are substantially described in the literature whereas they are poorly discussed in articles focusing on its therapeutic use. This paper aims to give an overview of the different clinical-trials involving VPA and its side effects encountered during treatment as well as its molecular properties.

CBP Histone Acetyltransferase Activity Regulates Embryonic Neural Differentiation in the Normal and Rubinstein-Taybi Syndrome Brain

Increasing evidence indicates that epigenetic changes regulate cell genesis. Here, we ask about neural precursors, focusing on CREB binding protein (CBP), a histone acetyltransferase that, when haploinsufficient, causes Rubinstein-Taybi syndrome (RTS), a genetic disorder with cognitive dysfunction. We show that neonatal cbp(+/-) mice are behaviorally impaired, displaying perturbed vocalization behavior. cbp haploinsufficiency or genetic knockdown with siRNAs inhibited differentiation of embryonic cortical precursors into all three neural lineages, coincident with decreased CBP binding and histone acetylation at promoters of neuronal and glial genes. Inhibition of histone deacetylation rescued these deficits. Moreover, CBP phosphorylation by atypical protein kinase C zeta was necessary for histone acetylation at neural gene promoters and appropriate differentiation. These data support a model in which environmental cues regulate CBP activity and histone acetylation to control neural precursor competency to differentiate, and indicate that cbp haploinsufficiency disrupts this mechanism, thereby likely causing cognitive dysfunction in RTS.

Histone H4 Acetylation is Essential to Proceed from a Histone- to a Protamine-based Chromatin Structure in Spermatid Nuclei of Drosophila melanogaster

In humans, other mammals, and also in Drosophila, the paternal genome in the sperm is highly condensed and organized mainly in a protamine-based chromatin structure. However, the timing and mechanism of the switch from a histone- to the protamine-based chromatin configuration is still poorly understood. We therefore established Drosophila in vitro cultures of cysts with 64 synchronously developing spermatids genetically marked with histone H2AvD-RFP and ProtamineB-eGFP. Live cell imaging showed that the switch from H2AvD-RFP to Protamine-eGFP chromatin takes approximately five hours, with a short but clear overlap of the presence of both histones and protamines. Moreover, cultured pupal testes showed H4 hyperacetylation at the canoe stage shortly before histone removal; a feature previously observed in the intact animal. We then used TSA to inhibit histone deacetylation and found that premature hyperacetylation was already induced at the round nuclei stage of spermatids. However, this premature hyperacetylation did not lead to a premature switch to the protamine-based chromatin structure, showing that histone hyperacetylation is not the sole inducer of the histone to protamine switch. Importantly, we observed that inactivation of histone acetyltransferases by anacardic acid blocks further differentiation and thus prevents the degradation of histones and the switch to a protamine-based chromatin. Thus, we conclude that H4 hyperacetylation is an essential feature but not the sole inducer of the histone to protamine switch during spermiogenesis.

Core promoter acetylation is not required for high transcription from the phosphoenolpyruvate carboxylase promoter in maize

BackgroundAcetylation of promoter nucleosomes is tightly correlated and mechanistically linked to gene activity. However, transcription is not necessary for promoter acetylation. It seems, therefore, that external and endogenous stimuli control histone acetylation and by this contribute to gene regulation. Photosynthetic genes in plants are excellent models with which to study the connection between stimuli and chromatin modifications because these genes are strongly expressed and regulated by multiple stimuli that are easily manipulated. We have previously shown that acetylation of specific histone lysine residues on the photosynthetic phosphoenolpyruvate carboxylase (Pepc) promoter in maize is controlled by light and is independent of other stimuli or gene activity. Acetylation of upstream promoter regions responds to a set of other stimuli which include the nutrient availability of the plant. Here, we have extended these studies by analysing histone acetylation during the diurnal and circadian rhythm of the plant.ResultsWe show that histone acetylation of individual lysine residues is removed from the core promoter before the end of the illumination period which is an indication that light is not the only factor influencing core promoter acetylation. Deacetylation is accompanied by a decrease in gene activity. Pharmacological inhibition of histone deacetylation is not sufficient to prevent transcriptional repression, indicating that deacetylation is not controlling diurnal gene regulation. Variation of the Pepc promoter activity during the day is controlled by the circadian oscillator as it is maintained under constant illumination for at least 3 days. During this period, light-induced changes in histone acetylation are completely removed from the core promoter, although the light stimulus is continuously applied. However, acetylation of most sites on upstream promoter elements follows the circadian rhythm.ConclusionOur results suggest a central role of upstream promoter acetylation in the quantitative regulation of gene expression in this model gene. Induced core promoter acetylation is dispensable for the highest gene expression in the diurnal and circadian rhythm.

Gemcitabine Is An Active Agent in the Treatment of T Cell Non Hodgkin Lymphomas.

Abstract 4771Approximately 12- 15% of non- Hodgkin lynphoma NHL are caused by malignant Tcell lymphocytes. The success of the treatment in the aggressive form has lagged behind that of B -Cell in term of poor resonse and durability. Peripheral T-Cell lymphoma PTCL and cutaneous T-Cell lymphoma CTCL are two major charachterized classifiction in the World Health Organization based on their morphology, growth patern and genetics. Stem cell transplant and high dose chemotherapy have been associated with long term response rate of 45%. However this treatment is not well tolerated and not feasible for many patients. Other theraputic options include cytotoxic drugs CHOP,CVP regimen, purine analogues, Denileukin diftitox, Histone deacetylation inhibitors and novel antifolates drugs. In this abstract we will show our experience with gemcitabin an active antimetabolite as a single agent or in combination with other active drugs. Eight patients with PTCL, five with visceral stage of mycosis fundoides( one patient with HIV infection), two with refractory anaplastic Ki positive NHL and one with angioimmunoblastic type. All patients failed a minimum two lines of therapy. Mean age 58 years( range 28-75). Eight blacks, two whites, four hispanics and one asian. Meduim cycles given are four. The dose range 800-1000 mg/M2, given weekly x3 every 28 days cycle. Overall response rate is 85%. Complete response rate CR in eight patients ( three PTCL, three mycosis fungoides and two anaplastic large cell NHL). Partial response PR in four and stable disease in one. Median duration of response is nine months, range six to two years. Median time for response is six weeks. In conclusion:Gemcitabine is an active drug in T-Cell lymphomas particularly when used in combination with other active agents. Maintenance dosing or retreatment with this drug should be investigated. Disclosures:No relevant conflicts of interest to declare.

DNA methyltransferase inhibitors increase baculovirus-mediated gene expression in mammalian cells when applied before infection

The application of baculovirus as a gene delivery vector for mammalian cells is limited by gene silencing in host cells. Although histone deacetylation inhibitors were known to improve baculovirus-mediated gene expression in mammalian cells, another group of chemicals that induces epigenetic changes, DNA methyltransferase inhibitors (DNMTis), were reported to have no such effect. In the current work, we found that, when added prior to virus inoculation, DNMTis improved baculovirus-mediated gene expression by fourfold or more in all four mammalian cell lines tested. The presence of inhibitors during the period of virus inoculation was important for them to be effective.