Effects of DNA methyltransferase inhibitors (DNMTIs) on MDS-derived cell lines

Pathogenic role of 25-hydroxycholesterol in cancer development and progression

Cholesterol is an essential lipid that serves several important functions, including maintaining the homeostasis of cells, acting as a precursor to bile acid and steroid hormones and preserving the stability of membrane lipid rafts. 25-hydroxycholesterol (25-HC) is a cholesterol derivative that may be formed from cholesterol. 25-HC is a crucial component in various biological activities, including cholesterol metabolism. In recent years, growing evidence has shown that 25-HC performs a critical function in the etiology of cancer, infectious diseases and autoimmune disorders. This review will summarize the latest findings regarding 25-HC, including its biogenesis, immunomodulatory properties and role in innate/adaptive immunity, inflammation and the development of various types of cancer.

Histone deacetylase inhibitor, panobinostat, exerts anti-proliferative effect with partial normalization from aberrant epigenetic states on granulosa cell tumor cell lines

The prognosis of the patients with inoperable or advanced granulosa cell tumors (GCTs) is still poor, and therefore it is important to establish a novel treatment strategy. Here we investigated the in vitro effects of a histone deacetylase inhibitor, panobinostat (PS) on two GCT cell lines (KGN and COV434). GCT cell lines were found to be susceptible to PS treatment and it inhibited cell growth mainly by apoptosis. In cell cycle analysis, PS reduced only the ratio of S phase in GCT cell lines. Combined treatment of PS with a deubiquitinase inhibitor, VLX1570 enhanced the expression of p21, cleaved PARP, cleaved caspase-9, heme oxygenase-1, and the acetylation of histone H4 and α-tubulin, leading to an additive anti-proliferative effect on KGN and COV434. The gene set enrichment analysis revealed that PS treatment suppressed DNA replication- or cell cycle-related gene expression which led to chemotherapeutic cell death and in addition, this treatment induced activation of the gene set of adherens junction towards a normalized direction as well as activation of neuron-related gene sets that might imply unexpected differentiation potential due to epigenetic modification by a HDAC inhibitor in KGN cells. Exposure of KGN and COV434 cells to PS increased the expression of E-cadherin, one of the principal regulators associated with adherens junction in quantitative RT-PCR and immunoblotting analysis. In the present study, we indicate a basis of a novel therapeutic availability of a HDAC inhibitor for the treatment of GCTs and further investigations will be warranted.

Epigenetic Silencing of PTEN and Epi-Transcriptional Silencing of MDM2 Underlied Progression to Secondary Acute Myeloid Leukemia in Myelodysplastic Syndrome Treated with Hypomethylating Agents

In myelodysplastic syndrome (MDS), resistance to hypomethylating agents (HMA) portends a poor prognosis, underscoring the importance of understanding the molecular mechanisms leading to HMA-resistance. In this study, P39 and Kasumi-1 cells and their azacitidine-resistant and decitabine-resistant sublines were evaluated comparatively with transcriptomic and methylomic analyses. Expression profiling and genome-wide methylation microarray showed downregulation of PTEN associated with DNA hypermethylation in P39 cell lines resistant to azacitidine and decitabine. This pattern of PTEN dysregulation was also confirmed in a cohort of patients failing treatment with HMA. DNA hypomethylation of MDM2 was detected with downregulation of MDM2 in HMA resistant cell lines. Long-read sequencing revealed significant RNA hypomethylation of MDM2 resulting in alternative splicing and production of a truncated MDM2 transcript in azacitidine-resistant P39 cells. The expression of this MDM2 truncated transcript was also significantly increased in HMA-resistant patients compared with HMA-responsive patients. In conclusion, epigenetic and epi-transcriptomic dysregulation of PTEN and MDM2 were associated with resistance to hypomethylating agents.

The Differential Expression of CD47 may be Related to the Pathogenesis From Myelodysplastic Syndromes to Acute Myeloid Leukemia

Myelodysplastic syndrome (MDS) can lead to the development of peripheral blood cytopenia and abnormal cell morphology. MDS has the potential to evolve into AML and can lead to reduced survival. CD47, a member of the immunoglobulin family, is one molecule that is overexpressed in a variety of cancer cells and is associated with clinical features and poor prognosis in a variety of malignancies. In this study, we analyzed the expression and function of CD47 in MDS and AML, and further analyzed its role in other tumors. Our analysis revealed significantly low CD47 expression in MDS and significantly high expression in AML. Further analysis of the function or pathway of CD47 from different perspectives identified a relationship to the immune response, cell growth, and other related functions or pathways. The relationship between CD47 and other tumors was analyzed from four aspects: DNA methyltransferase, TMB, MSI, and tumor cell stemness. Changes in gene expression levels have a known association with aberrant DNA methylation, and this methylation is the main mechanism of tumor suppressor gene silencing and clonal variation during the evolution of MDS to AML. Taken together, our findings support the hypothesis that the differential expression of CD47 might be related to the transformation of MDS to AML.

Epigenetic Mechanisms in Memory and Cognitive Decline Associated with Aging and Alzheimer's Disease

Epigenetic mechanisms, which include DNA methylation, a variety of post-translational modifications of histone proteins (acetylation, phosphorylation, methylation, ubiquitination, sumoylation, serotonylation, dopaminylation), chromatin remodeling enzymes, and long non-coding RNAs, are robust regulators of activity-dependent changes in gene transcription. In the brain, many of these epigenetic modifications have been widely implicated in synaptic plasticity and memory formation. Dysregulation of epigenetic mechanisms has been reported in the aged brain and is associated with or contributes to memory decline across the lifespan. Furthermore, alterations in the epigenome have been reported in neurodegenerative disorders, including Alzheimer’s disease. Here, we review the diverse types of epigenetic modifications and their role in activity- and learning-dependent synaptic plasticity. We then discuss how these mechanisms become dysregulated across the lifespan and contribute to memory loss with age and in Alzheimer’s disease. Collectively, the evidence reviewed here strongly supports a role for diverse epigenetic mechanisms in memory formation, aging, and neurodegeneration in the brain.

VLX1570 induces apoptosis through the generation of ROS and induction of ER stress on leukemia cell lines

A novel proteasome deubiquitinase inhibitor, VLX1570, has been highlighted as a promising therapeutic agent mainly for lymphoid neoplasms and solid tumors. We examined in vitro effects of VLX1570 on eight myeloid and three lymphoid leukemia cell lines. From cell culture studies, 10 out of 11 cell lines except K562 were found to be susceptible to VLX1570 treatment and it inhibited cell growth mainly by apoptosis. Next, to identify the signaling pathways associated with apoptosis, we performed gene expression profiling using HL‐60 with or without 50 nmol/L of VLX1570 for 3 hours and demonstrated that VLX1570 induced the genetic pathway involved in “heat shock transcription factor 1 (HSF1) activation”, “HSF1 dependent transactivation”, and “Regulation of HSF1 mediated heat shock response”. VLX1570 increased the amount of high molecular weight polyubiquitinated proteins and the expression of HSP70 as the result of the suppression of ubiquitin proteasome system, the expression of heme oxygenase‐1, and the amount of phosphorylation in JNK and p38 associated with the generation of reactive oxygen species (ROS) induced apoptosis and the amount of phosphorylation in eIF2α, inducing the expression of ATF4 and endoplasmic reticulum (ER) stress dependent apoptosis protein, CHOP, and the amount of phosphorylation slightly in IRE1α, leading to increased expression of XBP‐1s in leukemia cell lines. In the present study, we demonstrate that VLX1570 induces apoptosis and exerts a potential anti‐leukemic effect through the generation of ROS and induction of ER stress in leukemia cell lines.

Synergistic inhibitory effects of low-dose decitabine in combination with bortezomib in the AML cell line Kasumi-1

In the present study, the ability of the proteasome inhibitor bortezomib (BZ), an oxidative stress-inducing agent, to sensitize acute myeloid leukemia (AML) cells to decitabine (Dacogen^®, DAC; a DNA methyltransferase inhibitor), in terms of cell viability and differentiation, was investigated. Kasumi-1 AML (M2) cells were treated with low-dose DAC (10, 50, 100, 200 or 400 nΜ), with or without BZ (10 nM). Apoptosis and the cell cycle were evaluated after 24 h of treatment through fluorescence-assisted cell sorting (FACS) with Annexin V/propidium iodide and DAPI staining, respectively. The expression levels of CD193, CD11b, CD13, CD14, CD15, CD16 and CD117 surface differentiation markers were evaluated by FACS after 6 days of treatment. The results indicated significant alterations in cell death and cell cycle phases in Kasumi-1 cells following DAC and BZ combination treatment compared to untreated cells and cells with single treatments. Low-dose DAC/BZ combinations significantly enhanced apoptosis and decreased the population of live Kasumi-1 cells, with 100 and 200 nM of DAC and 10 nM BZ appearing to have the most potent synergistic effect according to a combination index. Furthermore, cell cycle profiling revealed that DAC/BZ treatment synergistically led to G0/G1- and G2/M-phase arrest. By contrast, DAC appeared to promote monocytic and granulocytic differentiation of Kasumi-1 cells more effectively alone than in combination with BZ. BZ acted synergistically with low-dose DAC in vitro, leading to enhanced apoptosis and G0/G1- and G2/M-phase arrest in AML cells, hence prohibiting either DNA synthesis or mitosis. Although further in vivo investigation is necessary, these results provide a strong rationale for the implementation of a combination treatment with DAC and bortezomib in AML therapy, followed by DAC alone, which may achieve better clinical responses and possibly partially overcome the frequently encountered DAC resistance of patients with AML.

Tumor-derived CK1α mutations enhance MDMX inhibition of p53

Somatic missense mutations of the CSNK1A1 gene encoding casein kinase 1 alpha (CK1α) occur in a subset of myelodysplastic syndrome (MDS) with del(5q) karyotype. The chromosomal deletion causes CSNK1A1 haplo-insufficiency. CK1α mutations have also been observed in a variety of solid and hematopoietic tumors at low frequency. The functional consequence of CK1α mutation remains unknown. Here we show that tumor-associated CK1α mutations exclusively localize to the substrate-binding cleft. Functional analysis of recurrent mutants E98K and D140A revealed enhanced binding to the p53 inhibitor MDMX, increased ability to stimulate MDMX-p53 binding, and increased suppression of p21 expression. Furthermore, E98K and D140A mutants have reduced ability to promote phosphorylation of β-catenin, resulting in enhanced Wnt signaling. The results suggest that the CK1α mutations observed in tumors cause gain-of-function in cooperating with MDMX and inhibiting p53, and partial loss-of-function in suppressing Wnt signaling. These functional changes may promote expansion of abnormal myeloid progenitors in del(5q) MDS, and in rare cases drive the progression of other tumors.

Genomic and epigenomic predictors of response to guadecitabine in relapsed/refractory acute myelogenous leukemia

Background

Guadecitabine is a novel DNA methyltransferase (DNMT) inhibitor with improved pharmacokinetics and clinical activity in a subset of patients with relapsed/refractory acute myeloid leukemia (r/r AML), but identification of this subset remains difficult.

Methods

To search for biomarkers of response, we measured genome-wide DNA methylation, mutations of 54 genes, and expression of a panel of 7 genes in pre-treatment samples from 128 patients treated at therapeutic doses in a phase I/II study.

Results

Response rate to guadecitabine was 17% (2 complete remission (CR), 3 CR with incomplete blood count recovery (CRi), or CR with incomplete platelets recovery (CRp)) in the phase I component and 23% (14 CR, 9 CRi/CRp) in phase II. There were no strong mutation or methylation predictors of response. Gene expression clustering defined a subset of patients (~ 20%) that had (i) high DNMT3B and low CDKN2B, CTCF, and CDA expression; (ii) enrichment for KRAS/NRAS mutations; (iii) frequent CpG island hypermethylation; (iv) low long interspersed nuclear element 1 (LINE-1) hypomethylation after treatment; and (v) resistance to guadecitabine in both phase I (response rate 0% vs. 33%, p = 0.07) and phase II components of the study (response rate 5% vs. 30%, p = 0.02). Multivariate analysis identified peripheral blood (PB) blasts and hemoglobin as predictors of response and cytogenetics, gene expression, RAS mutations, and hemoglobin as predictors of survival.

Conclusions

A subset of patients (~ 20%) with r/r AML is unlikely to benefit from guadecitabine as a single agent. In the remaining 80%, guadecitabine is a viable option with a median survival of 8 months and a 2-year survival rate of 21%.

Trial registration

NCT01261312.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0704-3) contains supplementary material, which is available to authorized users.

Binimetinib, a novel MEK1/2 inhibitor, exerts anti-leukemic effects under inactive status of PI3Kinase/Akt pathway

A MEK1/2 inhibitor, binimetinib is promising as a therapeutic agent for malignant melanoma with N-RAS mutation. We examined in vitro effects of binimetinib on 10 human myeloid/lymphoid leukemia cell lines, and found that three of five cell lines with N-RAS mutation and one of five without N-RAS mutation were responsive to treatment with binimetinib. Binimetinib inhibited cell growth mainly by inducing G₁ arrest and this action mechanism was assisted by gene set enrichment analysis. To identify signaling pathways associated with binimetinib response, we examined the status of MAP kinase/ERK and PI3Kinase/Akt pathways. The basal levels of phosphorylated ERK and Akt varied between the cell lines, and the amounts of phosphorylated ERK and Akt appeared to be reciprocal of each other. Interestingly, most of the binimetinib-resistant cell lines revealed strong Akt phosphorylation compared with binimetinib-sensitive ones. The effect of binimetinib may not be predicted by the presence/absence of N-RAS mutation, but rather by Akt phosphorylation status. Moreover, combination of binimetinib with a PI3K/Akt inhibitor showed additive growth-suppressive effects. These results suggest that binimetinib shows potential anti-leukemic effects and the basal level of phosphorylated Akt might serve as a biomarker predictive of therapeutic effect.

Methylation level of Rap1GAP and the clinical significance in MDS

Previous studies on the pathogenesis of myelodysplastic syndrome (MDS) have identified multiple associated gene mutations, including mutations of tetmethylcytosinedioxygenase 2, isocitrate dehydrogenase [NADP(+)] 1 cytosolic, isocitrate dehydrogenase [NADP(+)] 2 mitochondrial and additional sex combs like 1 transcriptional regulator, all of which may be considered epigenetic regulators. Furthermore, mutations of RAS type GTPase family genes have been identified in 10-15% patients with MDS. The authors' previous study on the gene expression profile of cluster of differentiation 34⁺ cells using microarray analysis identified elevated expression of RAP1GTPase activating protein 1 (Rap1GAP) in patients with MDS compared with that in non-malignant blood diseases (NM) control group. To further investigate the mechanism of increased Rap1GAP expression, the methylation pattern of the promoter of this gene was determined in 86 patients with MDS (n=29), acute myeloid leukemia (AML) (n=31) or NM (n=26) using bisulfite-specific polymerase chain reaction and DNA sequencing. The results demonstrated that the methylation of Rap1GAP occurred in all 29 patients with MDS at multiple CpG sites. The methylation level of Rap1GAP in patients with MDS was decreased compared with that in patients with NM. Significant differences at 4CpG sites (5,7,8 and 12) of Rap1GAP promoter were identified between MDS and NM. Furthermore, based on the present clinical records of the patient cohort, the methylation status of Rap1GAP promoter did not appear to be associated with the clinicopathological characteristics of patients with MDS, including age, gender and International Prognosis Score System. The difference in methylation level at CpG site 8 of Rap1GAP promoter was identified to be significantly increased in patients with MDS-refractory anemia with ring sideroblasts compared with that in the MDS-refractory cytopenia with multilineage dysplasia or MDS-unclassified groups. The results of the present study suggest that patients with MDS exhibit a lower overall methylation level within Rap1GAP promoter compared with patients with NM or AML. In addition, the methylation level at the four identified CpG sites can distinguish between MDS and NM.

Panobinostat inhibits the proliferation of CD34+ CD38- cells under stimulation of hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia

BACKGROUND

Encouraging responses to histone deacetylase inhibitors have been reported for hematologic malignancies. Here, we report effects of panobinostat and 5-azacytidine on the proliferation of juvenile myelomonocytic leukemia (JMML) CD34⁺ cells.

PROCEDURE

We previously reported that stimulation of JMML CD34⁺ cells with stem cell factor and thrombopoietin on irradiated murine AGM-S3 cells led to substantial expansion of JMML CD34⁺ cells that contained leukemic stem cells capable of transplantation into immunodeficient mice. Using this culture system, we evaluated effects of panobinostat and 5-azacytidine on the proliferation of JMML CD34⁺ cells.

RESULTS

Panobinostat dose dependently reduced the numbers of day 7 CD34⁺ cells generated under stimulation of hematopoietic growth factors on AGM-S3 cells in all eight patients with JMML. These patients possessed various genetic and/or karyotypic abnormalities. CD34⁺ CD38^- cells were substantially more sensitive to panobinostat at 10 and 20 nM than CD34⁺ CD38⁺ cells. Panobinostat, however, failed to influence the ability of AGM-S3 cells to stimulate JMML CD34⁺ cell production. In contrast to HL60 cells, apoptosis and cell cycle arrest in panobinostat-mediated inhibition were at low levels in JMML. The inhibitor also suppressed the factor-dependent proliferation of normal CD34⁺ cells on AGM-S3 cells. Meanwhile, no substantial inhibitory effects of 5-azacytidine on the growth of JMML CD34⁺ cells were observed.

CONCLUSIONS

These results demonstrate that panobinostat directly suppresses the growth of JMML CD34⁺ cells, in particular CD34⁺ CD38^- cells, regardless of the genetic abnormality type, suggesting that it is a useful antileukemic drug to target JMML stem cells at a pretransplant stage.

Efficacy of azacitidine is independent of molecular and clinical characteristics - an analysis of 128 patients with myelodysplastic syndromes or acute myeloid leukemia and a review of the literature

Azacitidine is the first drug to demonstrate a survival benefit for patients with MDS. However, only half of patients respond and almost all patients eventually relapse. Limited and conflicting data are available on predictive factors influencing response. We analyzed 128 patients from two institutions with MDS or AML treated with azacitidine to identify prognostic indicators. Genetic mutations in ASXL1, RUNX1, DNMT3A, IDH1, IDH2, TET2, TP53, NRAS, KRAS, FLT3, KMT2A-PTD, EZH2, SF3B1, and SRSF2 were assessed by next-generation sequencing. With a median follow up of 5.6 years median survival was 1.3 years with a response rate of 49%. The only variable with significant influence on response was del(20q). All 6 patients responded (p = 0.012) but survival was not improved. No other clinical, cytogenetic or molecular marker for response or survival was identified. Interestingly, patients from poor-risk groups as high-risk cytogenetics (55%), t-MDS/AML (54%), TP53 mutated (48%) or relapsed after chemotherapy (60%) showed a high response rate. Factors associated with shorter survival were low platelets, AML vs. MDS, therapy-related disease, TP53 and KMT2A-PTD. In multivariate analysis anemia, platelets, FLT3-ITD, and therapy-related disease remained in the model. Poor-risk factors such as del(7q)/-7, complex karyotype, ASXL1, RUNX1, EZH2, and TP53 did not show an independent impact. Thus, no clear biomarker for response and survival can be identified. Although a number of publications on predictive markers for response to AZA exist, results are inconsistent and improved response rates did not translate to improved survival. Here, we provide a comprehensive overview comparing the studies published to date.

Synergistic inhibitory effects of deferasirox in combination with decitabine on leukemia cell lines SKM-1, THP-1, and K-562

A multi-center study from the French Myelodysplastic Syndrome (MDS) Group confirmed that iron chelation therapy is an independent prognostic factor that can increase the survival rate of patients who are suffering from transfusion-dependent low-risk MDS. In this study, we aimed to explore this clinical phenomena in vitro, by exploring the synergistic effect of the iron chelator Deferasirox (DFX) and the DNA methyl transferase inhibitor Decitabine (DAC) in the leukemia cell lines SKM-1, THP-1, and K-562. Treatment with both DFX or DAC promoted apoptosis, induced cell cycle arrest, and inhibited proliferation in all three of these cell lines. The combination of DFX and DAC was much greater than the effect of using either drug alone. DFX showed a synergistic effect with DAC on cell apoptosis in all three cell lines and on cell cycle arrest at the G0/G1 phase in K-562 cells. DFX decreased the ROS levels to varying degrees. In contrast, DAC increased ROS levels and an increase in ROS was also noted when the two drugs were used in combination. Treatment of cells with DAC induced re-expression of ABAT, APAF-1, FADD, HJV, and SMPD3, presumably through demethylation. However the combination of DAC and DFX just had strong synergistic effect on the re-expression of HJV.

Establishment and characterization of hypomethylating agent-resistant cell lines, MOLM/AZA-1 and MOLM/DEC-5

Two hypomethylating agents (HMAs), azacitidine and decitabine, have demonstrated clinical activities in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML); however, potential problems include development of acquired resistance. HMA-resistant patients have very poor prognosis and this cohort of patients constitutes an important area of research. To understand the mechanisms underlying HMA-resistance and to overcome it, we established an azacitidine-resistant cell line, MOLM/AZA-1 and a decitabine-resistant cell line, MOLM/DEC-5 using MOLM-13. For cytogenetic characterization, we performed microarray-based comparative genomic hybridization (array-CGH), which identified a total of 15 copy number alterations (CNAs). Among these CNAs, eight regions in HMA-resistant cell lines showed CNA patterns distinct from the parental MOLM-13 genome. Single nucleotide polymorphism (SNP) microarray was also performed to obtain a more reliable interpretation of the identified CNAs, and all HMA-resistance-specific CNAs except one detected by array-CGH were successfully validated. In addition to CNAs, copy neutral loss of heterozygosity and mosaic loss events were identified in HMA-resistant cell lines. In our resistant cell lines, MDR-1 was not overexpressed, while DNMT3b was upregulated. Azacitidine and decitabine did not inhibit DNMT1, DNMT3a, or DNMT3b in both HMA-resistant cell lines, while they inhibited the enzymes in parental MOLM-13. We also developed mouse xenograft models using MOLM/AZA-1 and MOLM/DEC-5. Our in vitro and in vivo models of HMA-resistant cell lines will provide clues for the elucidation of molecular mechanisms related to the development of resistance to HMA and tools for the application of novel therapeutics for AML and MDS.

Increased IFNγ+ T Cells Are Responsible for the Clinical Responses of Low-Dose DNA-Demethylating Agent Decitabine Antitumor Therapy

Purpose: Low-dose DNA-demethylating agent decitabine therapy is effective in a subgroup of cancer patients. It remains largely elusive for the biomarker to predict therapeutic response and the underlying antitumor mechanisms, especially the impact on host antitumor immunity.Experimental Design: The influence of low-dose decitabine on T cells was detected both in vitro and in vivo Moreover, a test cohort and a validation cohort of advanced solid tumor patients with low-dose decitabine-based treatment were involved. The activation, proliferation, polarization, and cytolysis capacity of CD3⁺ T cells were analyzed by FACS and CCK8 assay. Kaplan-Meier and Cox proportional hazard regression analysis were performed to investigate the prognostic value of enhanced T-cell activity following decitabine epigenetic therapy.Results: Low-dose decitabine therapy enhanced the activation and proliferation of human IFNγ⁺ T cells, promoted Th1 polarization and activity of cytotoxic T cells both in vivo and in vitro, which in turn inhibited cancer progression and augmented the clinical effects of patients. In clinical trials, increased IFNγ⁺ T cells and increased T-cell cytotoxicity predicted improved therapeutic responses and survival in the test cohort and validation cohort.Conclusions: We find that low-dose decitabine therapy promotes antitumor T-cell responses by promoting T-cell proliferation and the increased IFNγ⁺ T cells may act as a potential prognostic biomarker for the response to decitabine-based antitumor therapy. Clin Cancer Res; 23(20); 6031-43. ©2017 AACR.

Withaferin A suppresses the growth of myelodysplasia and leukemia cell lines by inhibiting cell cycle progression

Treatment outcomes for acute myeloid leukemia and myelodysplastic syndromes (MDS) remain unsatisfactory despite progress in various types of chemotherapy and hematopoietic stem cell transplantation. Therefore, there is a need for the development of new treatment options. We investigated the growth‐suppressive effects of withaferin A (WA), a natural plant steroidal lactone, on myelodysplasia and leukemia cell lines. WA exhibited growth‐suppressive effects on the cell lines, MDS‐L, HL‐60, THP‐1, Jurkat and Ramos, and induction of cell cycle arrest at G2/M phase at relatively low doses. Evaluation by annexin V/PI also confirmed the induction of partial apoptosis. Gene expression profiling and subsequent gene set enrichment analysis revealed increased expression of heme oxygenase‐1 (HMOX1). HMOX1 is known to induce autophagy during anticancer chemotherapy and is considered to be involved in the treatment resistance. Our study indicated increased HMOX1 protein levels and simultaneous increases in the autophagy‐related protein LC3A/B in MDS‐L cells treated with WA, suggesting increased autophagy. Combined use of WA with chloroquine, an autophagy inhibitor, enhanced early apoptosis and growth suppression. Together with the knowledge that WA had no apparent suppressive effect on the growth of human normal bone marrow CD34‐positive cells in the short‐term culture, this drug may have a potential for a novel therapeutic approach to the treatment of leukemia or MDS.

Five-aza-2'-deoxycytidine-induced hypomethylation of cholesterol 25-hydroxylase gene is responsible for cell death of myelodysplasia/leukemia cells

DNA methyltransferase inhibitors (DNMT inhibitors) are administered for high-risk MDS, but their action mechanisms are not fully understood. Hence, we performed a genome-wide DNA methylation assay and focused on cholesterol 25-hydroxylase (CH25H) among the genes whose expression was up-regulated and whose promoter region was hypomethylated after decitabine (DAC) treatment in vitro. CH25H catalyzes hydroxylation of cholesterol and produces 25-hydroxycholesterol (25-OHC). Although CH25H mRNA expression level was originally low in MDS/leukemia cell lines, exposure to DNMT inhibitors enhanced CH25H mRNA expression. The promoter region of CH25H was originally hypermethylated in HL-60 and MDS-L cells, but DAC treatment induced their hypomethylation together with increased CH25H mRNA expression, activation of CH25H-oxysterol pathway, 25-OHC production and apoptotic cell death. We further confirmed that normal CD34-positive cells revealed hypomethylated status of the promoter region of CH25H gene. CH25H-knockdown by transfection of shRNA lentiviral vector into the cell lines partially protected the cells from DAC-induced cell death. Exogenous addition of 25-OHC suppressed leukemic cell growth. The present study raises a possibility that DNMT inhibitors activate CH25H-oxysterol pathway by their hypomethylating mechanism and induce leukemic cell death. Further investigations of the promoter analysis of CH25H gene and therapeutic effects of DNMT inhibitors on MDS/leukemia will be warranted.

Rigosertib induces cell death of a myelodysplastic syndrome-derived cell line by DNA damage-induced G2/M arrest

A multi-kinase inhibitor, rigosertib (ON 01910.Na) has recently been highlighted as a novel type of anti-cancer agent for the treatment of the myelodysplastic syndromes (MDS), but its action mechanisms remain to be clarified. We investigated the in vitro effects of rigosertib on an MDS-derived cell line MDS-L and a myeloid leukemia cell line HL-60. Rigosertib suppressed the proliferation of both HL-60 and MDS-L cells and induced apoptosis by inhibition of the PI3 kinase/Akt pathway. As the effects on cell cycle, rigosertib treatment promoted the phosphorylation of histone H2AX and led to the DNA damage-induced G2/M arrest. In addition, an immunofluorescence staining study demonstrated the abnormal localization of aurora A kinase, suggesting that rigosertib causes perturbation of spindle assembly and deregulated mitotic patterns towards cell cycle arrest and apoptosis. We also found that rigosertib exerted growth inhibitory effects on two lymphoid cell lines, Jurkat and Ramos. We further examined the molecular pathways influenced by rigosertib from the gene expression profiling data of MDS-L cells and found a possible involvement of rigosertib treatment in the upregulation of the genes related to microtubule kinetics and the downregulation of the mRNA degradation system. The gene set enrichment analysis showed the suppression of "nonsense-mediated mRNA decay (NMD)" as the most significantly affected gene set. These data provide a new aspect and a potential utility of rigosertib for the treatment of refractory hematopoietic malignancies.

New answers to old questions from genome-wide maps of DNA methylation in hematopoietic cells

DNA methylation is a well-studied epigenetic modification essential for efficient cellular differentiation. Aberrant DNA methylation patterns are a characteristic feature of cancer, including myeloid malignancies such as acute myeloid leukemia. Recurrent mutations in DNA-modifying enzymes were identified in acute myeloid leukemia and linked to distinct DNA methylation signatures. In addition, discovery of Tet enzymes provided new mechanisms for the reversal of DNA methylation. Advances in base-resolution profiling of DNA methylation have enabled a more comprehensive understanding of the methylome landscape in the genome. This review will summarize and discuss the key questions in the function of DNA methylation in the hematopoietic system, including where and how DNA methylation regulates diverse biological processes in the genome as elucidated by recent studies.

Redistribution of H3K27me3 and acetylated histone H4 upon exposure to azacitidine and decitabine results in de-repression of the AML1/ETO target gene IL3

Human acute myeloid leukemia is characterized by a block in maturation caused by genetic and epigenetic alterations. We studied the effects of low concentrations of the DNA methyltransferase (DNMT) inhibitors 5-azacitidine and decitabine on apoptosis and on chromatin remodeling in an AML1/ETO inducible model of human AML. While both DNMT inhibitors induced apoptosis, only azacitidine did so via caspase activation, possibly through its exclusive non-DNA depending effects. We evaluated histone marks for permissive chromatin, H3K4me3, and acetylated histone H4, and for non-permissive chromatin, H3K9me2, and H3K27me3, at the promoter of the IL3 gene, which is under the direct control of AML1/ETO and is critical for myeloid maturation. We observed that low concentrations of DNMT inhibitors induced a loss of H3K27me3 and gain of acetylated histone H4 at the IL3 promoter exclusively in AML1/ETO-positive cells, which was associated with transcriptional reactivation of the IL3 gene.