Myelodysplastic syndrome and histone deacetylase inhibitors: “to be or not to be acetylated”. J Biomed Biotechnol. 2011;2011:214143. [PMID: 21629744 PMCID: PMC3100562 DOI: 10.1155/2011/214143]

The prognostic and therapeutic potential of HO-1 in leukemia and MDS

BACKGROUND

Heme oxygenase-1 (HO-1), a heme-degrading enzyme, is proven to have anti-apoptotic effects in several malignancies. In addition, HO-1 is reported to cause chemoresistance and increase cell survival. Growing evidence indicates that HO-1 contributes to the course of hematological malignancies as well. Here, the expression pattern, prognostic value, and the effect of HO-1 targeting in HMs are discussed.

MAIN BODY

According to the recent literature, it was discovered that HO-1 is overexpressed in myelodysplastic syndromes (MDS), chronic myeloid leukemia (CML), acute myeloblastic leukemia (AML), and acute lymphoblastic leukemia (ALL) cells and is associated with high-risk disease. Furthermore, in addition to HO-1 expression by leukemic and MDS cells, CML, AML, and ALL leukemic stem cells express this protein as well, making it a potential target for eliminating minimal residual disease (MRD). Moreover, it was concluded that HO-1 induces tumor progression and prevents apoptosis through various pathways.

CONCLUSION

HO-1 has great potential in determining the prognosis of leukemia and MDS patients. HO-1 induces resistance to several chemotherapeutic agents as well as tyrosine kinase inhibitors and following its inhibition, chemo-sensitivity increases. Moreover, the exact role of HO-1 in Chronic Lymphocytic Leukemia (CLL) is yet unknown. While findings illustrate that MDS and other leukemic patients could benefit from HO-1 targeting. Future studies can help broaden our knowledge regarding the role of HO-1 in MDS and leukemia. Video abstract.

Prominent Role of Histone Modifications in the Regulation of Tumor Metastasis

Tumor aggressiveness and progression is highly dependent on the process of metastasis, regulated by the coordinated interplay of genetic and epigenetic mechanisms. Metastasis involves several steps of epithelial to mesenchymal transition (EMT), anoikis resistance, intra- and extravasation, and new tissue colonization. EMT is considered as the most critical process allowing cancer cells to switch their epithelial characteristics and acquire mesenchymal properties. Emerging evidence demonstrates that epigenetics mechanisms, DNA methylation, histone modifications, and non-coding RNAs participate in the widespread changes of gene expression that characterize the metastatic phenotype. At the chromatin level, active and repressive histone post-translational modifications (PTM) in association with pleiotropic transcription factors regulate pivotal genes involved in the initiation of the EMT process as well as in intravasation and anoikis resistance, playing a central role in the progression of tumors. Herein, we discuss the main epigenetic mechanisms associated with the different steps of metastatic process, focusing in particular on the prominent role of histone modifications and the modifying enzymes that mediate transcriptional regulation of genes associated with tumor progression. We further discuss the development of novel treatment strategies targeting the reversibility of histone modifications and highlight their importance in the future of cancer therapy.

Molecular regulation of epithelial-to-mesenchymal transition in tumorigenesis (Review)

Numerous studies over the past two decades have focused on the epithelial-to-mesenchymal transition (EMT) and its role in the development of metastasis. Certain studies highlighted the importance of EMT in the dissemination of tumor cells and metastasis of epithelium-derived carcinomas. Tumor metastasis is a multistep process during which tumor cells change their morphology, and start to migrate and invade distant sites. The present review discusses the current understanding of the molecular mechanisms contributing to EMT in embryogenesis, fibrosis and tumorigenesis. Additionally, the signaling pathways that initiate EMT through transcriptional factors responsible for the activation and suppression of various genes associated with cancer cell migration were investigated. Furthermore, the important role of the epigenetic modifications that regulate EMT and the reverse process, mesenchymal-to-epithelial transition (MET) are discussed. MicroRNAs are key regulators of various intracellular processes and current knowledge of EMT has significantly improved due to microRNA characterization. Their effect on signaling pathways and the ensuing events that occur during EMT at the molecular level is becoming increasingly recognized. The current review also highlights the role of circulating tumor cells (CTCs) and CTC clusters, and their ability to form metastases. In addition, the biological properties of different types of circulating cells based on their tumor-forming potential are compared.

Comprehensive immunohistochemical analysis of histone deacetylases in pancreatic neuroendocrine tumors: HDAC5 as a predictor of poor clinical outcome

Epigenetic factors contribute to carcinogenesis, tumor promotion, and chemoresistance. Histone deacetylases (HDACs) are epigenetic regulators that primarily cause chromatin compaction, leading to inaccessibility of promoter regions and eventually gene silencing. Many cancer entities feature overexpression of HDACs. Currently, the role of HDACs in pancreatic neuroendocrine tumors (pNETs) is unclear. We analyzed the expression patterns of all HDAC classes (classes I, IIA, IIB, III, and IV) in 5 human tissue microarrays representing 57 pNETs resected between 1997 and 2013 and corresponding control tissue. All pNET cases were characterized clinically and pathologically according to recent staging guidelines. The investigated cases included 32 (56.1%) female and 25 (43.9%) male pNET patients (total n=57, 47.4% immunohistochemically endocrine positive). Immunohistochemical profiling revealed a significant up-regulation of all HDAC classes in pNET versus control, with different levels of intensity and extensity ranging from 1.5- to >7-fold up-regulation. In addition, expression of several HDACs (HDAC1, HDAC2, HDAC5, HDAC11, and Sirt1) was significantly increased in G3 tumors. Correlation analysis showed a significant association between the protein expression of HDAC classes I, III, and IV and rate of the pHH3/Ki-67-associated mitotic and proliferation index. Furthermore, especially HDAC5 proved as a negative predictor of disease-free and overall survival in pNET patients. Overall, we demonstrate that specific members of all 4 HDAC classes are heterogeneously expressed in pNET. Moreover, expression of HDACs was associated with tumor grading, proliferation markers, and patient survival, therefore representing interesting new targets in pNET treatment.

A Novel High-Content Immunofluorescence Assay as a Tool to Identify at the Single Cell Level γ-Globin Inducing Compounds

The identification of drugs capable of reactivating γ-globin to ameliorate β-thalassemia and Sickle Cell anemia is still a challenge, as available γ-globin inducers still have limited clinical indications. High-throughput screenings (HTS) aimed to identify new potentially therapeutic drugs require suitable first-step-screening methods combining the possibility to detect variation in the γ/β globin ratio with the robustness of a cell line. We took advantage of a K562 cell line variant expressing β-globin (β-K562) to set up a new multiplexed high-content immunofluorescence assay for the quantification of γ- and β-globin content at single-cell level. The assay was validated by using the known globin inducers hemin, hydroxyurea and butyric acid and further tested in a pilot screening that confirmed HDACs as targets for γ-globin induction (as proved by siRNA-mediated HDAC3 knockdown and by treatment with HDACs inhibitors entinostat and dacinostat) and identified Heme-oxygenases as novel candidate targets for γ-globin induction. Indeed, Heme-oxygenase2 siRNA knockdown as well as its inhibition by Tin protoporphyrin-IX (TinPPIX) greatly increased γ-globin expression. This result is particularly interesting as several metalloporphyrins have already been developed for clinical uses and could be tested (alone or in combination with other drugs) to improve pharmacological γ-globin reactivation for the treatment of β-hemoglobinopathies.

Epigenetic Alterations in Fanconi Anaemia: Role in Pathophysiology and Therapeutic Potential

Fanconi anaemia (FA) is an inherited disorder characterized by chromosomal instability. The phenotype is variable, which raises the possibility that it may be affected by other factors, such as epigenetic modifications. These play an important role in oncogenesis and may be pharmacologically manipulated. Our aim was to explore whether the epigenetic profiles in FA differ from non-FA individuals and whether these could be manipulated to alter the disease phenotype. We compared expression of epigenetic genes and DNA methylation profile of tumour suppressor genes between FA and normal samples. FA samples exhibited decreased expression levels of genes involved in epigenetic regulation and hypomethylation in the promoter regions of tumour suppressor genes. Treatment of FA cells with histone deacetylase inhibitor Vorinostat increased the expression of DNM3Tβ and reduced the levels of CIITA and HDAC9, PAK1, USP16, all involved in different aspects of epigenetic and immune regulation. Given the ability of Vorinostat to modulate epigenetic genes in FA patients, we investigated its functional effects on the FA phenotype. This was assessed by incubating FA cells with Vorinostat and quantifying chromosomal breaks induced by DNA cross-linking agents. Treatment of FA cells with Vorinostat resulted in a significant reduction of aberrant cells (81% on average). Our results suggest that epigenetic mechanisms may play a role in oncogenesis in FA. Epigenetic agents may be helpful in improving the phenotype of FA patients, potentially reducing tumour incidence in this population.

Deacetylase inhibitors for the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a diverse group of myeloid disorders, with patients being at risk for cytopenias or progression to acute myeloid leukemia. Several classification and prognostic scoring systems have been developed. High-intensity treatments are not appropriate for all patients. Two demethylating agents, azacitidine and decitabine, are approved for the treatment of MDS, although many patients do not derive long-term benefit and eventually progress. Deacetylase inhibitors have emerged as novel treatment candidates based on mechanistic rationale and preliminary data. This article reviews existing data on MDS treatment and discusses the rationale and potential for combination with deacetylase inhibitors.

Histone deacetylation meets miRNA: epigenetics and post-transcriptional regulation in cancer and chronic diseases

INTRODUCTION

Epigenetic regulation via DNA methylation, histone acetylation, as well as by microRNAs (miRNAs) is currently in the scientific focus due to its role in carcinogenesis and its involvement in initiation, progression and metastasis. While many target genes of DNA methylation, histone acetylation and miRNAs are known, even less information exists as to how these mechanisms cooperate and how they may regulate each other in a specific pathological context. For further development of therapeutic approaches, this review presents the current status of the crosstalk of histone acetylation and miRNAs in human carcinogenesis and chronic diseases.

AREAS COVERED

This article reviews information from comprehensive PubMed searches to evaluate relevant literature with a focus on possible association between histone acetylation, miRNAs and their targets. Our analysis identified specific miRNAs which collaborate with histone deacetylases (HDACs) and cooperatively regulate several relevant target genes.

EXPERT OPINION

Fourteen miRNAs could be linked to the expression of eight HDACs influencing the α-(1,6)-fucosyltransferase, polycystin-2 and the fibroblast-growth-factor 2 pathways. Focusing on the complex linkage of miRNA and HDAC expression could give deeper insights in new 'druggable' targets and might provide possible novel therapeutic approaches in future.

Silencing HO-1 sensitizes SKM-1 cells to apoptosis induced by low concentration 5-azacytidine through enhancing p16 demethylation

Heme oxygenase-1 was reported previously as a resistance target on acute myelocytic leukemia (AML). We found that HO-1 was resistant to 5-azacytidine (AZA) treatment of myelodysplastic syndrome (MDS), and explored further the relative mechanisms. Patient bone marrow mononuclear cells (n=48) diagnosed as different levels of MDS were collected. Cell growth was evaluated by MTT assay; cell cycle and apoptosis were detected by flow cytometry; mRNA expression was assessed by real-time PCR, protein expression was analyzed through western blotting. Methylation was assessed by MSP. The survival time, and weight of mice were recorded. HO-1 overexpression was observed in SKM-1 cells after AZA treatment comparing to other cell lines. The HO-1 expression in MDS patients with high-risk was higher than in low-risk patients. After HO-1 was silenced by lentivirus-mediated siRNA, the proliferation of SKM-1 cells was effectively inhibited by low concentration AZA, and the cell cycle was arrested in the G0/G1 phase. Upregulation of p16 and changing of p16-relative cell cycle protein was observed after silencing HO-1 in AZA treated SKM-1 cells. In addition, DNMT1 was downregulated following the decrease of HO-1 expression. In vivo, silencing HO-1 inhibited SKM-1 cell growth induced by AZA in a NOD/SCID mouse model. Silencing HO-1 sensitized SKM-1 cells toward AZA, which may be attributed to the influence of HO-1 on AZA-induced p16 demethylation. HO-1 may be one of the targets that enhance the therapeutic effects of AZA on MDS malignant transformation inspiring new treatment methods for high-risk and very high-risk MDS patients in clinical practice.

Digging deep into "dirty" drugs - modulation of the methylation machinery

DNA methylation and histone modification are epigenetic mechanisms that result in altered gene expression and cellular phenotype. The exact role of methylation in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) remains unclear. However, aberrations (e.g. loss-/gain-of-function or up-/down-regulation) in components of epigenetic transcriptional regulation in general, and of the methylation machinery in particular, have been implicated in the pathogenesis of these diseases. In addition, many of these components have been identified as therapeutic targets for patients with MDS/AML, and are also being assessed as potential biomarkers of response or resistance to hypomethylating agents (HMAs). The HMAs 5-azacitidine (AZA) and 2'-deoxy-5-azacitidine (decitabine, DAC) inhibit DNA methylation and have shown significant clinical benefits in patients with myeloid malignancies. Despite being viewed as mechanistically similar drugs, AZA and DAC have differing mechanisms of action. DAC is incorporated 100% into DNA, whereas AZA is incorporated into RNA (80-90%) as well as DNA (10-20%). As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis. Herein, we first give an overview of transcriptional regulation, including DNA methylation, post-translational histone-tail modifications, the role of micro-RNA and long-range epigenetic gene silencing. We place special emphasis on epigenetic transcriptional regulation and discuss the implication of various components in the pathogenesis of MDS/AML, their potential as therapeutic targets, and their therapeutic modulation by HMAs and other substances (if known). The main focus of this review is laid on dissecting the rapidly evolving knowledge of AZA and DAC with a special focus on their differing mechanisms of action, and the effect of HMAs on transcriptional regulation.

Epigenetics and pancreatic cancer: Pathophysiology and novel treatment aspects

An improvement in pancreatic cancer treatment represents an urgent medical goal. Late diagnosis and high intrinsic resistance to conventional chemotherapy has led to a dismal overall prognosis that has remained unchanged during the past decades. Increasing knowledge about the molecular pathogenesis of the disease has shown that genetic alterations, such as mutations of K-ras, and especially epigenetic dysregulation of tumor-associated genes, such as silencing of the tumor suppressor p16^ink4a, are hallmarks of pancreatic cancer. Here, we describe genes that are commonly affected by epigenetic dysregulation in pancreatic cancer via DNA methylation, histone acetylation or miRNA (microRNA) expression, and review the implications on pancreatic cancer biology such as epithelial-mesenchymal transition, morphological pattern formation, or cancer stem cell regulation during carcinogenesis from PanIN (pancreatic intraepithelial lesions) to invasive cancer and resistance development. Epigenetic drugs, such as DNA methyltransferases or histone deactylase inhibitors, have shown promising preclinical results in pancreatic cancer and are currently in early phases of clinical development. Combinations of epigenetic drugs with established cytotoxic drugs or targeted therapies are promising approaches to improve the poor response and survival rate of pancreatic cancer patients.

Epigenetic alterations and microRNAs: new players in the pathogenesis of myelodysplastic syndromes

The term epigenetics refers to the heritable changes in gene expression that do not represent changes in DNA sequence. DNA methylation and histone modification are the best studied epigenetic mechanisms. However, microRNAs, which affect gene expression at the posttranscriptional level, should be considered as members of the epigenetic machinery too. Myelodysplastic syndromes (MDS) are clone disorders of the hematopoietic stem cell with increased risk of leukemic transformation. Over the years, increased number of studies indicates the role of epigenetic mechanisms, including microRNAs, in MDS pathogenesis and prognosis. Indeed, epigenetic therapy with demethylating agents has already been applied to MDS. In this review we summarize current knowledge on the role of epigenetic alterations in MDS pathogenesis and treatment.

Vorinostat induces apoptosis and differentiation in myeloid malignancies: genetic and molecular mechanisms

Background

Aberrant epigenetic patterns are central in the pathogenesis of haematopoietic diseases such as myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML). Vorinostat is a HDACi which has produced responses in these disorders. The purpose of this study was to address the functional effects of vorinostat in leukemic cell lines and primary AML and MDS myeloid cells and to dissect the genetic and molecular mechanisms by which it exerts its action.

Methodology/Principal Findings

Functional assays showed vorinostat promoted cell cycle arrest, inhibited growth, and induced apoptosis and differentiation of K562, HL60 and THP-1 and of CD33⁺ cells from AML and MDS patients. To explore the genetic mechanism for these effects, we quantified gene expression modulation by vorinostat in these cells. Vorinostat increased expression of genes down-regulated in MDS and/or AML (cFOS, COX2, IER3, p15, RAI3) and suppressed expression of genes over-expressed in these malignancies (AXL, c-MYC, Cyclin D1) and modulated cell cycle and apoptosis genes in a manner which would favor cell cycle arrest, differentiation, and apoptosis of neoplastic cells, consistent with the functional assays. Reporter assays showed transcriptional effect of vorinostat on some of these genes was mediated by proximal promoter elements in GC-rich regions. Vorinostat-modulated expression of some genes was potentiated by mithramycin A, a compound that interferes with SP1 binding to GC-rich DNA sequences, and siRNA-mediated SP1 reduction. ChIP assays revealed vorinostat inhibited DNA binding of SP1 to the proximal promoter regions of these genes. These results suggest vorinostat transcriptional action in some genes is regulated by proximal promoter GC-rich DNA sequences and by SP1.

Conclusion

This study sheds light on the effects of vorinostat in AML and MDS and supports the implementation of clinical trials to explore the use of vorinostat in the treatment of these diseases.

The pan-deacetylase inhibitor panobinostat modulates the expression of epithelial-mesenchymal transition markers in hepatocellular carcinoma models

Deacetylase inhibitors (DACis) represent a novel therapeutic option for human cancers by classically affecting proliferation or apoptosis. Since transdifferentiation and dedifferentiation play a key role in carcinogenesis, we investigated the epigenetic influence on the molecular differentiation status in human hepatocellular carcinoma (HCC) models. Markers of differentiation, including cytokeratin (Ck) 7, Ck8, Ck18, Ck19, Ck20, vimentin, sonic hedgehog homolog (SHH), smoothened (Smo), patched (Ptc), glioma-associated oncogene homolog 1 (Gli1), CD133, octamer-binding transcription factor 4 (Oct4) and β-catenin, were examined in the human HCC cell lines HepG2 and Hep3B in vitro and in vivo (xenograft model) using quantitative real-time PCR and immunohistochemistry following treatment with the pan-DACi panobinostat (LBH589). Compared to untreated controls, treated HepG2 xenografts, and to a lesser extent cell lines, demonstrated a significant increase of differentiation markers Ck7 and Ck19 (classical cholangiocellular type) and Ck8 and Ck18 (classical HCC type), and a decreased level of dedifferentiation markers vimentin (mesenchymal) and SHH/Ptc (embryonic), paralleled with a more membranous expression of β-catenin. These findings were dose-dependently correlated with tumor size, necrosis rate, microvessel density and mitosis/Ki-67-associated proliferation rate. Our results demonstrate that the differentiation status of human HCC cells is influenced by the pan-DACi panobinostat, indicating that this treatment may influence the epithelial-mesenchymal transition (EMT) status related to metastasis and aggressiveness.

Epigenetic control of epithelial-mesenchymal-transition in human cancer

Development and tissue homeostasis as well as carcinogenesis share the evolutionary conserved process of epithelial-mesenchymal transition (EMT). EMT enables differentiated epithelial cells to trans-differentiate to a mesenchymal phenotype which is associated with diverse cellular properties including altered morphology, migration and invasion and stemness. In physiological development and tissue homeostasis, EMT exerts beneficial functions for structured tissue formation and maintenance. Under pathological conditions, EMT causes uncontrolled tissue repair and organ fibrosis, as well as the induction of tumor growth, angiogenesis and metastasis in the context of cancer progression. Particularly, the metastatic process is essentially linked to diverse EMT-driven functions which give the mesenchymal differentiated tumor cells the capacity to migrate and form micrometastases in distant organs. Recent analyses of the mechanisms controlling EMT revealed a significant epigenetic regulatory impact reflecting the reversible nature of EMTs. As several approaches of epigenetic therapy are already under clinical evaluation, including inhibitors of DNA methyl transferase and histone deacetylase, targeting the epigenetic regulation of EMT may represent a promising therapeutic option in the future. Therefore, we undertook this review to reassess the current knowledge on the roles of epigenetic control in the regulation of EMT in human cancer. These recent findings are discussed in view of their implications on future diagnostic and therapeutic strategies.