Epigenetic therapies in haematological malignancies: searching for true targets

Optimization of Epigenetic Modifier Drug Combination for Synergistic Effect against Glioblastoma Multiform Cancer Cell Lines

Glioblastoma multiforme (GBM), is a frequent class of malignant brain tumors. Epigenetic therapy, especially with synergistic combinations is highly paid attention for aggressive solid tumors like GBM. Here, RSM optimization has been used to increase the efficient arrest of U87 and U251 cell lines due to synergistic effects. Cell lines were treated with SAHA, 5-Azacytidine, GSK-126, and PTC-209 individually and then RSM was used to find most effective combinations. Results showed that optimized combinations significantly reduce cell survival and induce cell cycle arrest and apoptosis in both cell lines. Expression of cyclin B1 and cyclin D1 were decreased while caspase3 increased expression.

Epigenetic Regulation of the Wnt/β-Catenin Signaling Pathway in Cancer

Studies over the past four decades have elucidated the role of Wnt/β-catenin mediated regulation in cell proliferation, differentiation and migration. These processes are fundamental to embryonic development, regeneration potential of tissues, as well as cancer initiation and progression. In this review, we focus on the epigenetic players which influence the Wnt/β-catenin pathway via modulation of its components and coordinated regulation of the Wnt target genes. The role played by crosstalk with other signaling pathways mediating tumorigenesis is also elaborated. The Hippo/YAP pathway is particularly emphasized due to its extensive crosstalk via the Wnt destruction complex. Further, we highlight the recent advances in developing potential therapeutic interventions targeting the epigenetic machinery based on the characterization of these regulatory networks for effective treatment of various cancers and also for regenerative therapies.

KDM5A suppresses PML-RARα target gene expression and APL differentiation through repressing H3K4me2

Epigenetic abnormalities are frequently involved in the initiation and progression of cancers, including acute myeloid leukemia (AML). A subtype of AML, acute promyelocytic leukemia (APL), is mainly driven by a specific oncogenic fusion event of promyelocytic leukemia-RA receptor fusion oncoprotein (PML-RARα). PML-RARα was reported as a transcription repressor through the interaction with nuclear receptor corepressor and histone deacetylase complexes leading to the mis-suppression of its target genes and differentiation blockage. Although previous studies were mainly focused on the connection of histone acetylation, it is still largely unknown whether alternative epigenetics mechanisms are involved in APL progression. KDM5A is a demethylase of histone H3 lysine 4 di- and tri-methylations (H3K4me2/3) and a transcription corepressor. Here, we found that the loss of KDM5A led to APL NB4 cell differentiation and retarded growth. Mechanistically, through epigenomics and transcriptomics analyses, KDM5A binding was detected in 1889 genes, with the majority of the binding events at promoter regions. KDM5A suppressed the expression of 621 genes, including 42 PML-RARα target genes, primarily by controlling the H3K4me2 in the promoters and 5' end intragenic regions. In addition, a recently reported pan-KDM5 inhibitor, CPI-455, on its own could phenocopy the differentiation effects as KDM5A loss in NB4 cells. CPI-455 treatment or KDM5A knockout could greatly sensitize NB4 cells to all-trans retinoic acid-induced differentiation. Our findings indicate that KDM5A contributed to the differentiation blockage in the APL cell line NB4, and inhibition of KDM5A could greatly potentiate NB4 differentiation.

Multiple roles of HOX proteins in Metastasis: Let me count the ways

Knowledge of the role of HOX proteins in cancer has been steadily accumulating in the last 25 years. They are encoded by 39 HOX genes arranged in 4 distinct clusters, and have unique and redundant function in all types of cancers. Many HOX genes behave as oncogenic transcriptional factors regulating multiple pathways that are critical to malignant progression in a variety of tumors. Some HOX proteins have dual roles that are tumor-site specific, displaying both oncogenic and tumor suppressor function. The focus of this review is on how HOX proteins contribute to growth or suppression of metastasis. The review will cover HOX protein function in the critical aspects of epithelial-mesenchymal transition, in cancer stem cell sustenance and in therapy resistance, manifested as distant metastasis. The emerging role of adiposity in both initiation and progression of metastasis is described. Defining the role of HOX genes in the metastatic process has identified candidates for targeted cancer therapies that may combat the metastatic process. We will discuss potential therapeutic opportunities, particularly in pathways influenced by HOX proteins.

HDAC8: A Promising Therapeutic Target for Acute Myeloid Leukemia

Histone deacetylase 8 (HDAC8), a class I HDAC that modifies non-histone proteins such as p53, is highly expressed in different hematological neoplasms including a subtype of acute myeloid leukemia (AML) bearing inversion of chromosome 16 [inv(16)]. To investigate HDAC8 contribution to hematopoietic stem cell maintenance and myeloid leukemic transformation, we generated a zebrafish model with Hdac8 overexpression and observed an increase in hematopoietic stem/progenitor cells, a phenotype that could be reverted using a specific HDAC8 inhibitor, PCI-34051 (PCI). In addition, we demonstrated that AML cell lines respond differently to PCI treatment: HDAC8 inhibition elicits cytotoxic effect with cell cycle arrest followed by apoptosis in THP-1 cells, and cytostatic effect in HL60 cells that lack p53. A combination of cytarabine, a standard anti-AML chemotherapeutic, with PCI resulted in a synergistic effect in all the cell lines tested. We, then, searched for a mechanism behind cell cycle arrest caused by HDAC8 inhibition in the absence of functional p53 and demonstrated an involvement of the canonical WNT signaling in zebrafish and in cell lines. Together, we provide the evidence for the role of HDAC8 in hematopoietic stem cell differentiation in zebrafish and AML cell lines, suggesting HDAC8 inhibition as a therapeutic target in hematological malignancies. Accordingly, we demonstrated the utility of a highly specific HDAC8 inhibition as a therapeutic strategy in combination with standard chemotherapy.

Targeting the scaffolding role of LSD1 (KDM1A) poises acute myeloid leukemia cells for retinoic acid-induced differentiation

The histone demethylase LSD1 is deregulated in several tumors, including leukemias, providing the rationale for the clinical use of LSD1 inhibitors. In acute promyelocytic leukemia (APL), pharmacological doses of retinoic acid (RA) induce differentiation of APL cells, triggering degradation of the PML-RAR oncogene. APL cells are resistant to LSD1 inhibition or knockout, but targeting LSD1 sensitizes them to physiological doses of RA without altering of PML-RAR levels, and extends survival of leukemic mice upon RA treatment. The combination of RA with LSD1 inhibition (or knockout) is also effective in other non-APL, acute myeloid leukemia (AML) cells. Nonenzymatic activities of LSD1 are essential to block differentiation, while RA with targeting of LSD1 releases a differentiation gene expression program, not strictly dependent on changes in histone H3K4 methylation. Integration of proteomic/epigenomic/mutational studies showed that LSD1 inhibitors alter the recruitment of LSD1-containing complexes to chromatin, inhibiting the interaction between LSD1 and the transcription factor GFI1.

An epigenetic regulator-related score (EpiScore) predicts survival in patients with diffuse large B cell lymphoma and identifies patients who may benefit from epigenetic therapy

Diffuse large B-cell lymphoma (DLBCL) is the most common form of lymphoma and shows considerable clinical and biological heterogeneity. Much research is currently focused on the identification of prognostic markers for more specific patients’ risk stratification and on the development of therapeutic approaches to improve the long-term outcome. Epigenetic alterations are involved in various cancers, including lymphoma. Interestingly, epigenetic alterations are reversible and drugs to target some of them have been developed. In this study, we demonstrated that the gene expression profile of epigenetic regulators has a prognostic value in DLBCL and identified pathways that could be involved in DLBCL poor outcome. We then designed a new risk score (EpiScore) based on the gene expression level of the epigenetic regulators DNMT3A, DOT1L, SETD8. EpiScore was predictive of overall survival in DLBCL and allowed splitting patients with DLBCL from two independent cohorts (n = 414 and n = 69) in three groups (high, intermediate and low risk). EpiScore was an independent predictor of survival when compared with previously described prognostic factors, such as the International Prognostic Index (IPI), germinal center B cell and activated B cell molecular subgroups, gene expression-based risk score (GERS) and DNA repair score. Immunohistochemistry analysis of DNMT3A in 31 DLBCL samples showed that DNMT3A overexpression (>42% of positive tumor cells) correlated with reduced overall and event-free survival. Finally, an HDAC gene signature was significantly enriched in the DLBCL samples included in the EpiScore high-risk group. We conclude that EpiScore identifies high-risk patients with DLBCL who could benefit from epigenetic therapy.

Revisiting the biology of infant t(4;11)/MLL-AF4+ B-cell acute lymphoblastic leukemia

Infant B-cell acute lymphoblastic leukemia (B-ALL) accounts for 10% of childhood ALL. The genetic hallmark of most infant B-ALL is chromosomal rearrangements of the mixed-lineage leukemia (MLL) gene. Despite improvement in the clinical management and survival (∼85-90%) of childhood B-ALL, the outcome of infants with MLL-rearranged (MLL-r) B-ALL remains dismal, with overall survival <35%. Among MLL-r infant B-ALL, t(4;11)+ patients harboring the fusion MLL-AF4 (MA4) display a particularly poor prognosis and a pro-B/mixed phenotype. Studies in monozygotic twins and archived blood spots have provided compelling evidence of a single cell of prenatal origin as the target for MA4 fusion, explaining the brief leukemia latency. Despite its aggressiveness and short latency, current progress on its etiology, pathogenesis, and cellular origin is limited as evidenced by the lack of mouse/human models recapitulating the disease phenotype/latency. We propose this is because infant cancer is from an etiologic and pathogenesis standpoint distinct from adult cancer and should be seen as a developmental disease. This is supported by whole-genome sequencing studies suggesting that opposite to the view of cancer as a "multiple-and-sequential-hit" model, t(4;11) alone might be sufficient to spawn leukemia. The stable genome of these patients suggests that, in infant developmental cancer, one "big-hit" might be sufficient for overt disease and supports a key contribution of epigenetics and a prenatal cell of origin during a critical developmental window of stem cell vulnerability in the leukemia pathogenesis. Here, we revisit the biology of t(4;11)+ infant B-ALL with an emphasis on its origin, genetics, and disease models.

Redox-Mediated Suberoylanilide Hydroxamic Acid Sensitivity in Breast Cancer

AIMS

Vorinostat (suberoylanilide hydroxamic acid; SAHA) is a histone deacetylase inhibitor (HDACi) approved in the clinics for the treatment of T-cell lymphoma and with the potential to be effective also in breast cancer. We investigated the responsiveness to SAHA in human breast primary tumors and cancer cell lines.

RESULTS

We observed a differential response to drug treatment in both human breast primary tumors and cancer cell lines. Gene expression analysis of the breast cancer cell lines revealed that genes involved in cell adhesion and redox pathways, especially glutathione metabolism, were differentially expressed in the cell lines resistant to SAHA compared with the sensitive ones, indicating their possible association with drug resistance mechanisms. Notably, such an association was also observed in breast primary tumors. Indeed, addition of buthionine sulfoximine (BSO), a compound capable of depleting cellular glutathione, significantly enhanced the cytotoxicity of SAHA in both breast cancer cell lines and primary breast tumors.

INNOVATION

We identify and validate transcriptional differences in genes involved in redox pathways, which include potential predictive markers of sensitivity to SAHA.

CONCLUSION

In breast cancer, it could be relevant to evaluate the expression of antioxidant genes that may favor tumor resistance as a factor to consider for potential clinical application and treatment with epigenetic drugs (HDACis).

Chromatin regulators: weaving epigenetic nets

In multicellular organisms differentiated cells must maintain their cellular memory, which will be faithfully inherited and maintained by their progeny. In addition, these specialized cells are exposed to specific environmental and cell-intrinsic signals and will have to appropriately respond to them. Some of these stimuli lead to changes in a subset of genes or to a genome-wide reprogramming of the cells that will remain after stimuli removal and, in some instances, will be inherited by the daughter cells. The molecular substrate that integrates cellular memory and plasticity is the chromatin, a complex of DNA and histones unique to eukaryotes. The nucleosome is the fundamental unit of the chromatin and nucleosomal organization defines different chromatin conformations. Chromatin regulators affect chromatin conformation and accessibility by covalently modifying the DNA or the histones, substituting histone variants, remodeling the nucleosome position or modulating chromatin looping and folding. These regulators frequently act in multiprotein complexes and highly specific interplays among chromatin marks and different chromatin regulators allow a remarkable array of possibilities. Therefore, chromatin regulator nets act to propagate the conformation of different chromatin regions through DNA replication and mitosis, and to remodel the chromatin fiber to regulate the accessibility of the DNA to transcription factors and to the transcription and repair machineries. Here, the state-of-the-art of the best-known chromatin regulators is reviewed.

Computer-aided Molecular Design of Compounds Targeting Histone Modifying Enzymes

Growing evidences show that epigenetic mechanisms play crucial roles in the genesis and progression of many physiopathological processes. As a result, research in epigenetic grew at a fast pace in the last decade. In particular, the study of histone post-translational modifications encountered an extraordinary progression and many modifications have been characterized and associated to fundamental biological processes and pathological conditions. Histone modifications are the catalytic result of a large set of enzyme families that operate covalent modifications on specific residues at the histone tails. Taken together, these modifications elicit a complex and concerted processing that greatly contribute to the chromatin remodeling and may drive different pathological conditions, especially cancer. For this reason, several epigenetic targets are currently under validation for drug discovery purposes and different academic and industrial programs have been already launched to produce the first pre-clinical and clinical outcomes. In this scenario, computer-aided molecular design techniques are offering important tools, mainly as a consequence of the increasing structural information available for these targets. In this mini-review we will briefly discuss the most common types of known histone modifications and the corresponding operating enzymes by emphasizing the computer-aided molecular design approaches that can be of use to speed-up the efforts to generate new pharmaceutically relevant compounds.

DNA double strand break responses and chromatin alterations within the aging cell

Cellular senescence is a state of permanent replicative arrest that allows cells to stay viable and metabolically active but resistant to apoptotic and mitogenic stimuli. Specific, validated markers can identify senescent cells, including senescence-associated β galactosidase activity, chromatin alterations, cell morphology changes, activated p16- and p53-dependent signaling and permanent cell cycle arrest. Senescence is a natural consequence of DNA replication-associated telomere erosion, but can also be induced prematurely by telomere-independent events such as failure to repair DNA double strand breaks. Here, we review the molecular pathways of senescence onset, focussing on the changes in chromatin organization that are associated with cellular senescence, particularly senescence-associated heterochromatin foci formation. We also discuss the altered dynamics of the DNA double strand break response within the context of aging cells. Appreciating how, mechanistically, cellular senescence is induced, and how changes to chromatin organization and DNA repair contributes to this, is fundamental to our understanding of the normal and premature human aging processes associated with loss of organ and tissue function in humans.

The DNA demethylating agent decitabine activates the TRAIL pathway and induces apoptosis in acute myeloid leukemia

Although epigenetic drugs have been approved for use in selected malignancies, there is significant need for a better understanding of their mechanism of action. Here, we study the action of a clinically approved DNA-methyltransferase inhibitor - decitabine (DAC) - in acute myeloid leukemia (AML) cells. At low doses, DAC treatment induced apoptosis of NB4 Acute Promyelocytic Leukemia (APL) cells, which was associated with the activation of the extrinsic apoptotic pathway. Expression studies of the members of the Death Receptor family demonstrated that DAC induces the expression of TNF-related apoptosis-inducing ligand (TRAIL). Upregulation of TRAIL, upon DAC treatment, was associated with specific epigenetic modifications induced by DAC in the proximity of the TRAIL promoter, as demonstrated by DNA demethylation, increased DNaseI sensitivity and histone acetylation of a non-CpG island, CpG-rich region located 2kb upstream to the transcription start site. Luciferase assay experiments showed that this region behave as a DNA methylation sensitive transcriptional regulatory element. The CpG regulatory element was also found methylated in samples derived from APL patients. These findings have been confirmed in the non-APL, AML Kasumi cell line, suggesting that this regulatory mechanism may be extended to other AMLs. Our study suggests that DNA methylation is a regulatory mechanism relevant for silencing of the TRAIL apoptotic pathway in leukemic cells, and further elucidates the mechanism by which epigenetic drugs mediate their anti-leukemic effects.

Next generation histone deacetylase inhibitors: the answer to the search for optimized epigenetic therapies?

INTRODUCTION

HDAC inhibitors have demonstrated potent anticancer activities in preclinical and clinical studies. Currently, two drugs (SAHA and romidepsin) have gained the FDA approval for the treatment of cutaneous T-cell lymphoma. Clinical efficacy of HDAC inhibitors has been observed in advanced hematological malignancies, while response in other cancers has been in most cases unpredictable and often rather limited. The search for new molecules with the potential to overcome the limitations of the first HDAC inhibitors has become a primary goal in the field of epigenetic drug discovery as well as drugs acting on other chromatin modifying enzymes.

AREAS COVERED

The article shortlists seven new HDAC inhibitors that have recently entered clinical studies as representative examples of next generation drugs. The most recently published preclinical profile is reviewed, together with the first clinical data for these compounds. The article then focuses on challenges faced during the progress of first generation HDAC inhibitors and analyzes whether these new compounds are likely to provide a solution to the existing issues and needs.

EXPERT OPINION

Next generation HDAC inhibitors have the 'best-in-class' potential, particularly regarding potency and in vivo exposure. However, several issues remain unresolved. For example, none of the presented compounds appears to have a significantly different selectivity profile towards various HDAC isoforms and, thus, none of them may provide a further elucidation between the toxicity seen in more advanced HDAC inhibitors and isoform selectivity. Additionally, a need for a continuous effort on target validation is seen as a necessary requirement for further progress in the field.

Interplay between oncogene-induced DNA damage response and heterochromatin in senescence and cancer

Two major mechanisms have been causally implicated in the establishment of cellular senescence: the activation of the DNA damage response (DDR) pathway and the formation of senescence-associated heterochromatic foci (SAHF). Here we show that in human fibroblasts resistant to premature p16(INK4a) induction, SAHF are preferentially formed following oncogene activation but are not detected during replicative cellular senescence or on exposure to a variety of senescence-inducing stimuli. Oncogene-induced SAHF formation depends on DNA replication and ATR (ataxia telangiectasia and Rad3-related). Inactivation of ATM (ataxia telangiectasia mutated) or p53 allows the proliferation of oncogene-expressing cells that retain increased heterochromatin induction. In human cancers, levels of heterochromatin markers are higher than in normal tissues, and are independent of the proliferative index or stage of the tumours. Pharmacological and genetic perturbation of heterochromatin in oncogene-expressing cells increase DDR signalling and lead to apoptosis. In vivo, a histone deacetylase inhibitor (HDACi) causes heterochromatin relaxation, increased DDR, apoptosis and tumour regression. These results indicate that heterochromatin induced by oncogenic stress restrains DDR and suggest that the use of chromatin-modifying drugs in cancer therapies may benefit from the study of chromatin and DDR status of tumours.

Pathology tissue-chromatin immunoprecipitation, coupled with high-throughput sequencing, allows the epigenetic profiling of patient samples

Epigenetic alterations in the pattern of DNA and histone modifications play a crucial role in cancer development. Analysis of patient samples, however, is hampered by technical limitations in the study of chromatin structure from pathology archives that usually consist of heavily fixed, paraffin-embedded material. Here, we present a methodology [pathology tissue-ChIP (PAT-ChIP)] to extract and immunoprecipitate chromatin from paraffin-embedded patient samples up to several years old. In a pairwise comparison with canonical ChIP, PAT-ChIP showed a high reproducibility of results for several histone marks and an identical ability to detect dynamic changes in chromatin structure upon pharmacological treatment. Finally, we showed that PAT-ChIP can be coupled with high-throughput sequencing (PAT-ChIP-Seq) for the genome-wide analysis of distinct chromatin modifications. PAT-ChIP therefore represents a versatile procedure and diagnostic tool for the analysis of epigenetic alterations in cancer and potentially other diseases.

Nature or nurture: let food be your epigenetic medicine in chronic inflammatory disorders

Numerous clinical, physiopathological and epidemiological studies have underlined the detrimental or beneficial role of nutritional factors in complex inflammation related disorders such as allergy, asthma, obesity, type 2 diabetes, cardiovascular disease, rheumatoid arthritis and cancer. Today, nutritional research has shifted from alleviating nutrient deficiencies to chronic disease prevention. It is known that lifestyle, environmental conditions and nutritional compounds influence gene expression. Gene expression states are set by transcriptional activators and repressors and are often locked in by cell-heritable chromatin states. Only recently, it has been observed that the environmental conditions and daily diet can affect transgenerational gene expression via "reversible" heritable epigenetic mechanisms. Epigenetic changes in DNA methylation patterns at CpG sites (epimutations) or corrupt chromatin states of key inflammatory genes and noncoding RNAs, recently emerged as major governing factors in cancer, chronic inflammatory and metabolic disorders. Reciprocally, inflammation, metabolic stress and diet composition can also change activities of the epigenetic machinery and indirectly or directly change chromatin marks. This has recently launched re-exploration of anti-inflammatory bioactive food components for characterization of their effects on epigenome modifying enzymatic activities (acetylation, methylation, phosphorylation, ribosylation, oxidation, ubiquitination, sumoylation). This may allow to improve healthy aging by reversing disease prone epimutations involved in chronic inflammatory and metabolic disorders.

Validation of a novel statistical model for assessing the synergy of combined-agent cancer chemoprevention

Lung cancer is the leading cause of cancer death, developing over prolonged periods through genetic and epigenetic changes induced and exacerbated by tobacco exposure. Many epigenetic changes, including DNA methylation and histone methylation and acetylation, are reversible. The use of agents that can modulate these aberrations are a potentially effective approach to cancer chemoprevention. Combined epigenetic-targeting agents have gained interest for their potential to increase efficacy and lower toxicity. The present study applied recently developed statistical methods to validate the combined effects of the demethylating agent 5-aza-2-deoxycytidine (5-AZA-CdR, or AZA, or decitabine) and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA or vorinostat). This validation compared AZA alone with SAHA alone and with their combinations (at later or earlier time points and in varying doses) for inhibiting the growth of cell lines of an in vitro lung carcinogenesis system. This system comprises isogenic premalignant and malignant cells that are immortalized (earlier premalignant), transformed (later premalignant), and tumorigenic human bronchial epithelial cells [immortalized BEAS-2B and its derivatives 1799 (immortalized), 1198 (transformed), and 1170-I (tumorigenic)]. AZA alone and SAHA alone produced a limited (<50%) inhibition of cell growth, whereas combined AZA and SAHA inhibited cell growth more than either agent alone, reaching 90% inhibition under some conditions. Results of drug interaction analyses in the E(max) model and semiparametric model supported the conclusion that drug combinations exert synergistic effects (i.e., beyond additivity in the Loewe model). The present results show the applicability of our novel statistical methodology for quantitatively assessing drug synergy across a wide range of doses of agents with complex dose-response profiles, a methodology with great potential for advancing the development of chemopreventive combinations.

Histone deacetylases and epigenetic therapies of hematological malignancies

Histone deacetylase inhibitors (HDACi) represent a novel class of targeted drugs which alter the acetylation status of several cellular proteins. These agents, modulating both chromatin structure through histone acetylation, and the activity of several non-histone substrates, are at the same time able to determine changes in gene transcription and to induce a plethora of biological effects ranging from cell death induction, to differentiation, angiogenesis inhibition or modulation of immune responses. The impressive anticancer activity observed in both in vitro and in vivo cancer models, together with their preferential effect on cancer cells, have led to a huge effort into the identification and development of HDACi with different characteristics. To date, several clinical trials of HDACi conducted in solid tumors and hematological malignancies have shown a preferential clinical efficacy of these drugs in hematological malignancies, and in particular in cutaneous T-cell lymphoma (CTCL), peripheral T-cell lymphoma (PTCL), Hodgkin lymphoma (HL) and myeloid malignancies. Several agents are also beginning to be tested in combination therapies, either as chemo sensitizing agents in association with standard chemotherapy drugs or in combination with DNA methyltransferase inhibitors (DNMTi) in the context of the so-called "epigenetic therapies", aimed to revert epigenetic alterations found in cancer cells. Herein, we will review HDACi data in hematological malignancies questioning the molecular basis of observed clinical responses, and highlighting some of the concerns raised on the use of these drugs for cancer therapy.

Distinctive patterns of age-dependent hypomethylation in interspersed repetitive sequences

Interspersed repetitive sequences (IRSs) are a major contributor to genome size and may contribute to cellular functions. IRSs are subdivided according to size and functionally related structures into short interspersed elements, long interspersed elements (LINEs), DNA transposons, and LTR-retrotransposons. Many IRSs may produce RNA and regulate genes by a variety of mechanisms. The majority of DNA methylation occurs in IRSs and is believed to suppress IRS activities. Global hypomethylation, or the loss of genome-wide methylation, is a common epigenetic event not only in senescent cells but also in cancer cells. Loss of LINE-1 methylation has been characterized in many cancers. Here, we evaluated the methylation levels of peripheral blood mononuclear cells of LINE-1, Alu, and human endogenous retrovirus K (HERV-K) in 177 samples obtained from volunteers between 20 and 88 yr of age. Age was negatively associated with methylation levels of Alu (r = -0.452, P < 10(-3)) and HERV-K (r = -0.326, P < 10(-3)) but not LINE-1 (r = 0.145, P = 0.055). Loss of methylation of Alu occurred during ages 34-68 yr, and loss of methylation of HERV-K occurred during ages 40-63 yr and again during ages 64-83 yr. Interestingly, methylation of Alu and LINE-1 are directly associated, particularly at ages 49 yr and older (r = 0.49, P < 10(-3)). Therefore, only some types of IRSs lose methylation at certain ages. Moreover, Alu and HERV-K become hypomethylated differently. Finally, there may be several mechanisms of global methylation. However, not all of these mechanisms are age-dependent. This finding may lead to a better understanding of not only the biological causes and consequences of genome-wide hypomethylation but also the role of IRSs in the aging process.

Epigenetic regulation of WNT signaling in chronic lymphocytic leukemia

Certain WNT and WNT network target genes are expressed at higher or lower levels in chronic lymphocytic leukemia compared with normal B-cells. This includes upregulation of nuclear complex genes, as well as genes for cytoplasmic proteins and WNT ligands and their cognate receptors. In addition, epigenetic silencing of several negative regulators of the WNT pathway have been identified. The balance between epigenetic downregulation of negative effector genes and increased expression of positive effector genes demonstrate that the epigenetic downregulation of WNT antagonists is one mechanism, perhaps the main mechanism, that is permissive to active WNT signaling in chronic lymphocytic leukemia. Moreover, constitutive activation of the WNT network and target genes is likely to impact on additional interacting signaling pathways. Based on published studies, we propose a model of WNT signaling that involves mainly permissive expression, and sometimes overexpression, of positive effectors and downregulation of negative regulators in the network. In this model, DNA methylation, histone modifications and altered expression of microRNA molecules interact to allow continuous WNT signaling.

New trends in the standard of care for initial therapy of acute myeloid leukemia

In younger patients with acute myeloid leukemia (AML), initial treatment has provided very good control of the disease. Induction therapy has used combination chemotherapy, with anthracycline and cytarabine as the foundation. Recent trials support dose intensification of anthracycline in induction. Intensive postremission therapy further contributes to improving survival. The addition of targeted therapy with gemtuzumab ozogamicin to standard therapy has not improved on these outcomes. Newer agents targeted to specific molecular abnormalities or survival mechanisms in the leukemic cell are being studied as future additions to the current standard therapy.