Hypomethylating Agents In Myelodysplastic Syndromes Research Articles

Acute myeloid leukemia management and research in 2025.

The first 5 decades of research in acute myeloid leukemia (AML) were dominated by the cytarabine plus anthracyclines backbone, with advances in strategies including allogeneic hematopoietic stem cell transplantation, high-dose cytarabine, supportive care measures, and targeted therapies for the subset of patients with acute promyelocytic leukemia. Since 2017, a turning point in AML research, 12 agents have received regulatory approval for AML in the United States: venetoclax (BCL2 inhibitor); gemtuzumab ozogamicin (CD33 antibody-drug conjugate); midostaurin, gilteritinib, and quizartinib (fms-like tyrosine kinase 3 inhibitors); ivosidenib, olutasidenib, and enasidenib (isocitrate dehydrogenase 1 and 2 inhibitors); oral azacitidine (a partially absorbable formulation); CPX351 (liposomal encapsulation of cytarabine:daunorubicin at a molar ratio of 5:1); glasdegib (hedgehog inhibitor); and recently revumenib (menin inhibitor; approved November 2024). Oral decitabine-cedazuridine, which is approved as a bioequivalent alternative to parenteral hypomethylating agents in myelodysplastic syndrome, can be used for the same purpose in AML. Menin inhibitors, CD123 antibody-drug conjugates, and other antibodies targeting CD123, CD33, and other surface markers are showing promising results. Herein, the authors review the frontline and later line therapies in AML and discuss important research directions.

A Phase I/II Study of Venetoclax in Combination with 5-Azacytidine in Treatment-Naïve and Relapsed/Refractory High-Risk Myelodysplastic Syndrome (MDS) or Chronic Myelomonocytic Leukemia (CMML)

A Phase I/II Study of Venetoclax in Combination with 5-Azacytidine in Treatment-Naïve and Relapsed/Refractory High-Risk Myelodysplastic Syndrome (MDS) or Chronic Myelomonocytic Leukemia (CMML)

A Pilot/Safety Study of sEphB4-Hsa in Combination with a Hypomethylating Agent for Patients with Relapsed or Refractory Myelodysplastic Syndrome and Acute Myeloid Leukemia Previously Treated with a Hypomethylating Agent

Background: Myelodysplastic syndrome (MDS) is a clonal hematopoietic neoplasm that results in bone marrow failure and frequently leads to acute myeloid leukemia (AML). Hypomethylating agents (HMA) are the only FDA-approved treatment for MDS and among few options for chemotherapy-ineligible patients with AML. There are limited options for patients in whom HMA therapy fails and who are not candidates for allogeneic stem cell transplant, so therapies that complement or restore sensitivity to HMAs are needed. Studies have shown increases in bone marrow microvessel density (MVD) and angiogenic markers in patients with MDS and AML. A decrease in MVD has been shown to correlate with response to hypomethylating agents in MDS. A receptor-ligand interaction, comprised of receptor EphB4 and membrane localized ligand EphrinB2, mediates angiogenesis in normal tissue and appears to be a target unique to many cancer types. We have previously shown EphB4 to be highly expressed and a driver of leukemic cell survival in a subset of AML patients. Our group has developed a human fusion protein, sEphB4-HSA, that blocks bidirectional signaling induced by EphB4-EphrinB2 interaction to inhibit tumor cell proliferation and angiogenesis. In phase I clinical trials of sEphB4-HSA in various tumor types, there were no myelosuppressive effects and minimal toxicity. Given its safety in phase I and potential to inhibit leukemic cell proliferation and angiogenesis, we proposed a pilot trial to evaluate the safety of sEphB4-HSA in combination with HMAs in MDS and AML patients who have failed treatment with HMAs. Methods: This pilot study was designed to enroll 6 patients with relapsed/refractory intermediate or high-risk MDS and 6 patients with AML refractory to or relapsed to HMA treatment and who are deemed unfit for chemotherapy. Treatment consisted of sEphB4-HSA 15 mg/kg IV every 2 weeks in combination with the FDA-approved HMA most recently or currently being used for treatment (decitabine 20mg/m2 IV/1hr on days 1 to 5 every 28 days or azacitidine 75mg/m2 SC or IV on days 1 to 7 every 28 days). Patients were treated for as long as they were receiving clinical benefit up to 12 months. The primary endpoint was toxicity and tolerability of sEphB4-HSA in combination with HMA. Toxicity was assessed and graded after each cycle according to the CTCAE version 4. Tolerability was defined as the ability to complete two cycles of treatment without the occurrence of dose-limiting toxicity. A secondary efficacy endpoint was to assess best overall response, based on the IWG Working Group Criteria for MDS and AML, during the first two cycles of treatment. Enrollment was stopped after 7 patients due to expiration of funding. Results: Three patients with intermediate-risk MDS were treated for a median duration of 6 cycles (2-12) and 4 patients with AML were treated for 2 cycles. Median age was 75.5 years (67.9-84.8) and 57.1% were male. HMA included azacitadine in 6 patients and decitabine in one patient. There were no dose-limiting toxicities. There were 8 grade 3/4 events attributed to HMA, which included: neutropenia (2), thrombocytopenia (3), and leukopenia (3). There were 3 grade 3/4 events attributed to sEphB4, which included: febrile neutropenia (1), leukopenia (1), and hypertension (1). Of the MDS patients, 2 had stable disease, 1 patient after 2 cycles and 1 patient after 4 cycles. One patient achieved a hematologic improvement-erythroid after 6 cycles. AML patients had no disease response. Reasons for treatment discontinuation were death (1), disease progression (2), patient's decision (1), physician's decision (2), and hospice (1). Notably, a comparison of bone marrow biopsies at baseline and after 8 weeks of treatment demonstrated a decrease in MVD (Figure 1). Discussion: This pilot study found sEphB4 in combination with HMAs to be tolerable with no significant toxicity beyond that expected with HMA therapy and associated with potential clinical benefit in MDS patients. Improvement in abnormal bone marrow MVD may indicate a potential for sEphB4-HSA plus HMA therapy to alter the malignant microenvironment in MDS/AML. Disclosures No relevant conflicts of interest to declare.

Characteristics of Long-Term Survival of Patients with MDS Treated with 5-Azacytidine. Results from the Hellenic 5-Azacytidine Registry

IntroductionThe prognosis of patients with myelodysplastic syndromes (MDS) depends on several disease characteristics such as the cytopenias, the percentage of bone marrow blasts, and the cytogenetic profile of the patients. The use of hypomethylating agents (HMAs) has altered the prognosis of patients with higher risk MDS offering a median survival of around 24 months. Nevertheless, the range of survival is wide, with some patients achieving long remissions and high survival rates irrespective of their initial prognostic characteristics. Long-term survivors after 5-azacytidine administration constitute a large group of patients with potentially special characteristics and needs.AimWe analyzed data from a large cohort of patients with MDS treated with 5-azacytidine to describe the hematologic and prognostic characteristics of long-term survivors and compare them to those of patients with shorter survival.Patients and MethodsWe retrospectively recorded through the Hellenic 5-azacytidine registry the main demographic, hematologic and treatment characteristics of adult patients with MDS treated with 5-azacytidine monotherapy. Patient data from 28 centers meeting the 2008/2016 WHO diagnostic criteria for MDS were recorded during a 7-month period.We defined two groups of long-term survivors based on their survival after initiation of treatment with 5-azacytidine (OST). The first group comprised patients with OST above the third quartile (Q3 or 75th percentile) of the whole group (Q3 group) and the second patients with OST above the 90th percentile of the whole group (P90 group). Correlations were made between long- and short-term survivors for both groups.IBM SPSS statistics, version 23.0 (IBM Corporation, North Castle, NY, USA) was used for the statistical analysis of the results.ResultsData from 626 patients was recorded. The Q3 group comprised 157 patients with an OST longer than 24.5 months (median, 43.3 months) and the P90 group 63 patients with an OST longer than 36.4 months (median, 65.7 months). The detailed characteristics of the two groups along with comparisons with the remaining patients with OST below Q3 and P90 respectively are shown in Table 1. Data analysis revealed that the sex, the age, the type of MDS at diagnosis per the 2008/2016 WHO classification, the presence of excess (≥5%) marrow blasts, the number of cytopenias, the hemoglobin, neutrophil and platelet count, and the transfusion needs were not predictive of long-term survival in neither of the groups. On the other hand, the presence of peripheral blood blasts, the karyotype risk, the IPSS, IPSS-R and WPSS classification and response to treatment were predictive of long term survival in both groups (Table 1). Multivariate analysis revealed that response to 5-azacytidine was the strongest determinant of long-term survival (Kaplan Meier, Log Rank, p<0.0001) in a model comprising IPSS, IPSS-R, WPSS and response to treatment. Nevertheless, patients with stable disease were almost equally distributed in the groups of long- and short-term survivors (p=0.795 for the Q3 group and p=0.310 for the P90 group).DiscussionThe use of HMAs in MDS has increased survival rates, hence long-term survival is now a feasible target when managing such patients. One fourth of the patients of this registry achieved an OST over 24.5 months and 10% over 36.4 months. IPSS, IPSS-R and WPSS are powerful prognostic tools for patients with MDS. Among the prognostic components of IPSS and IPSS-R at diagnosis (cytopenias, bone marrow blast count, karyotype risk), the karyotype risk seems to be the stronger determinant of survival. Nevertheless, among long-term survivors there are patients with adverse prognostic characteristics at diagnosis, whose prognosis is altered by the administration of HMAs. Failure to respond to 5-azacytidine is a major determinant of OST, but stable disease was not correlated to survival in this cohort. This result highlights the importance of continuing treatment with hypomethylating agents in patients not achieving an optimal response (PR, CR, HI), since a significant proportion of them may achieve long survival rates. Further search for new clinical and/or molecular prognostic markers is warranted to identify the prognosis of patients with MDS and define those who would benefit from the use of HMAs or other upcoming treatment choices. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Phase I/IB Study of Azacitidine and Hedgehog Pathway Inhibition in Myeloid Malignancies

Background: Hypomethylating agents (HMA) such as 5-Azacitidine (Aza) have overall responses rate of ~35-50% in acute myeloid Leukemia (AML) and higher risk myelodysplastic syndrome (MDS) patients (pts). However, eventually all pts develop resistance on therapy. To improve upfront response rates and to address HMA failure, we performed genome-scale RNAi screens targeting genes on chromosomes 5 and 7, recurrent cytogenetic abnormalities in AML/MDS. These screens identified Hedgehog pathway (Hh) genes as potentially targetable vulnerabilities with Aza. Combination experiments with smoothened (SMO) inhibitors (SMO is a central activating gene within the Hh pathway) showed pre-clinical synergy. These and additional published data support the Hh pathway as a targetable vulnerability in AML, and provide a rational for a trial.Methods: A phase I/Ib protocol of the oral SMO inhibitor LDE225 (Sonidegib) in combination with Aza in untreated and relapsed/refractory (rel/ref) AML, chronic myelomonocytic leukemia (CMML), MDS, or MDS/myeloproliferative neoplasm overlap pts. Objectives of the phase I part are to determine safety, toxicity and MTD and for the phase Ib part to assess the preliminary overall efficacy. Sonidegib was started at dose level (DL) 0 at 400mg oral daily continuously and Aza at the approved doses (75mg/m2 x 7 days or days 5-2-2) with dose adjustment per label. A classical 3+3 design was used and DLT (CTCAE v4.0) defined as > grade 3 CPK elevation or hepatic or non-hematologic adverse events (AEs) lasting > 7 days or any grade 4 event, except for hematologic toxicities. DLT was assessed after 42 days when steady-state concentrations of Sonidegib were reached. Pharmacokinetic assessments were not performed for this study.Results:Patients and Dose Levels: Between 5/22/2014 and the data cut-off date (7/20/2015), 36 pts were enrolled. Median age was 72 y (range 52-85 y) and 64% were male. Most AML pts (23 of 24) had intermediate or unfavorable cytogenetics and most MDS/CMML pts were in the int.- to high-/very high-risk group (IPSS-R). Six pts were treated at DL-0 of Sonidegib 400mg/day and one DLT of CPK elevation was observed. Another patient had grade 4 neutropenia (which at the time was included in the DLT definition, later removed). Due to overall tolerance of the combination at DL 0 and investigator assessment, despite only 1/6 pts having a formal DLT, DL -1 at Sonidegib 200mg was explored at which 0/3 pts (1 pt non-evaluable) had DLT and the phase Ib portion was opened at DL -1. To date a total of 24 AML (13 newly dx, 11 rel/ref), 11 MDS/CMML (5 newly dx, 6 rel/ref ) and 1 myelofibrosis pt have been enrolled.Safety and Tolerability: An initial safety and efficacy assessment for 25 of the 29 pts treated on the phase Ib (n=26) + the MTD cohort of 200 mg (n=3) and for who at least 2 cycles of treatment follow up was available, showed that all pts experienced at least one grade-3 or 4 hematologic AE with a lower rate in the untreated vs. treated cohort. Other, non-hematologic grade-3 and 4 AEs respectively were seen in 24 and 28% of patients-most commonly hyponatremia and fatigue, known AEs for this drug class. Treatment delays occurred in 28% of pts and Aza or Sonidegib dose reductions in 16%. 23 (79%) pts are alive and 6 have died (21%), with one death while pt was actively treated but was deemed unrelated; 11 pts remain on study, with the remainder showing disease progression (n=3) or taken-off study for other reasons (n=3 each for AEs and did not want further treatment; n=4 other).Efficacy: As of 7/20/15 with a median treatment duration of 2 cycles, 2/5 untreated MDS/CMML pts achieved CR/CRi; 1 HMA rel/ref AML had CR; 1 untreated AML pt each had PR and MLFS. 90% of pts have not progressed. Updated results will be presented at the ASH 2015 meeting; by then all 29 pts will have completed a minimum of 4-6 cycles on study and full efficacy and AE result on all pts will be reported. To date the OS at 6 mo is 77% (95% CI: 44-97%) with a median PFS of 4 mo (range: 2-NR). Many pts in the untreated cohorts have just enrolled.Conclusion: Hh pathway inhibition with the clinically well tolerated SMO inhibitor Sonidegib in combination with Aza in MDS and AML pts is well tolerated with mostly hematologic AEs as expected with early signs of clinical activity in untreated and HMA-failure pts. Full efficacy results of 29 pts and updated safety data will be reported for this first combination trial of a SMO inhibitor in combination with a HMA in MDS and AML pts. DisclosuresMesa:Gilead: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; Incyte Corporation: Research Funding; Genentech: Research Funding; Pfizer: Research Funding; Promedior: Research Funding; NS Pharma: Research Funding; CTI Biopharma: Research Funding. Al-Kali:Novartis: Research Funding.

Effect of Azacytidine on the Hematopoietic Stem and Progenitor Cell Compartments of MDS Mouse Models: Unveiling the Mechanisms of Remission and Relapse

Myelodysplastic syndromes (MDS) are a group of heterogeneous hematopoietic malignancies characterized by the defective production of mature blood cells and the risk of progression to myeloid leukemia. Hypomethylating agents (HMA) are currently the first-line therapy for high-risk MDS and induce hematological improvement in 50% of the patients. However, complete responses occur in less than 20% of these patients, and a majority of MDS patients treated with HMA will eventually relapse, with a subsequently fatal prognosis. Although the presence of mutations in certain genes, such as Tet2, has been reported to predict response to HMA, the causes of resistance and relapse have yet to be described.MDS research has been traditionally a slow-moving field owing to the lack of well-established MDS cell lines and animal models. This landscape recently changed with the development of transgenic mouse models that mirror the phenotype of high-risk MDS patients. In mice from the 4th/5th generations (G4/G5) of our group's telomere-dysfunctional TERTER/ER mouse model, the DNA-damage response triggered by telomere erosion causes profound cell-intrinsic abnormalities in hematopoietic stem and progenitor cells (HSPC) that lead to myeloid-skewed hematopoiesis. These mice exhibit peripheral blood (PB) cytopenias, age-related granulocytosis and myeloid infiltration of the BM and the spleen (Colla et al. Cancer Cell 2015). Similarly, the conditional deletion of Tet2 in mouse hematopoietic cells generates a phenotype of HSC expansion and myeloid skewing of hematopoiesis. These defects, which are also cell-intrinsic, induce progressive PB neutrophilia and granulocytosis, with myeloid infiltration of the bone marrow (BM) and spleen and severe splenomegaly (Moran-Crusio et al. Cancer Cell 2011).Using the TERTER/ER and Tet2-/- mouse models as a platform for cellular and molecular studies, we have investigated the mechanism of action of HMA in MDS, with a focus on the characterization of response by the different HSPC populations and the mechanisms involved in resistance and relapse. Our results show that the administration of the HMA azacytidine (AZA) for 7 days induces in both mouse models a 20-40% drop in white blood cell counts and a 17-24% decrease in hemoglobin levels that mimic patient responses to AZA. After the last day of treatment and during the 3 last weeks of the cycle, cell counts and hemoglobin levels returned to normal values. These changes in PB were explained by an 80-86% decrease in the number of BM common myeloid progenitors (CMP; n = 8, P = 0.0046) and granulo-monocytic progenitors (GMP; n = 8, P <0.0001) after 1 week of AZA treatment, while megakaryocytic-erythroid progenitors remained largely unaffected. However, the number of CMP and GMP in the BM of both G5 and Tet2-/- mice recovered by the end of each cycle, and the characteristic myeloid skewing was not overcome after 2 cycles of treatment, which indicates that AZA cannot reverse the cell-intrinsic defects of these progenitors. Most importantly, BM analysis in both mouse models after one week of treatment and during the recovery period revealed that AZA has no effect on long and short-term HSC populations.To study the effect of AZA in a BM context that mimicked the coexistence of MDS and normal cells in patients, we performed competitive transplantation experiments in both models. Our preliminary results indicate that, in mixed populations, AZA induces a 2.6-fold expansion of the wild type long-term HSC compartment (n = 4, P = 0.0018). The fact that AZA gives a repopulation advantage to normal HSC suggest that, after several cycles, there is a shift in the abundance of normal versus MDS cells in patients BM, and this explains why patients enter morphologic remission. However, in both transgenic mouse models, AZA failed to decrease the size of the MDS-like HSC compartment. This indicates that, although this drug allows a temporary hematologic recovery, it does not eliminate the cell populations that maintain the disease, and therefore it cannot eliminate MDS.Ongoing unbiased transcriptomic and methylomic analyses in the sorted MDS-like HSC that survived AZA treatment will identify the HSC signature of resistance to HMA, and the integration of these results with similar analyses in MDS patients will provide valuable insights into the mechanistic bases of relapse and resistance to HMA and facilitate the design of better combination therapies for high-risk MDS. DisclosuresNo relevant conflicts of interest to declare.

Comparison of Very Low-Dose Decitabine to Standard-Dose Hypomethylating Agents in Myelodysplastic Syndromes (MDS)

▪Background: Aberrant epigenetic modifications, fundamental to the pathogenesis of MDS, provide rationale for the use of the so-called hypomethylating agents, decitabine (DAC) and azacitidine (AZA). As depletion of DNA methyltransferase 1 (DNMT1) by these agents is S-phase dependent, episodic dosing used in common practice (SD-DAC; 20 mg/m2 x 5 days, every 28 days, SD-AZA; 75 mg/m2 x 5-7 days, every 28 days) affects only a fraction of the malignant clones. Alternative dosing schedules of decitabine with lower doses given more frequently (LD-DAC; .1-.2 mg/kg SC once/twice weekly) may decrease toxicity and increase response rates by improved hematopoietic differentiation and DNMT1 depletion while avoiding cytotoxicity. Data comparing use of very low and standard-dose DAC or AZA are lacking.Methods: We compared response, survival, and toxicities of 242 MDS patients (pts) treated at our institution from 9/06-10/13 with LD-DAC (n=39), SD-DAC (n=17), or SD-AZA (n=186). Response was assessed per International Working Group 2006 (IWG) criteria, progression-free (PFS) from date of response, and overall survival (OS) from diagnosis.Results: There were no significant differences in baseline characteristics, including median age (70 vs. 74 years, P=.93), proportion of patients with ≥5% bone marrow blasts (27% vs. 35%, P=.54), high/very high cytogenetic risk by the Revised International Prognostic Scoring System (IPSS-R, 25% vs. 40%, P=.31), number of pts with comorbidities (44% vs. 29%, P=.38), median time from diagnosis to treatment (14.6 vs. 6.4 months, P=.25) or prior MDS treatment (AZA and/or lenalidomide, 46% vs. 53%, P=.17), between the LD-DAC and SD-DAC groups, respectively. Likewise, the LA-DAC and SD-AZA groups were similar with respect to median age (70 vs. 68 years, P=.15), proportion of patients with ≥5% bone marrow blasts (27% vs. 39%, P=.19), and high/very high cytogenetic risk by the IPSS-R (25% vs. 27%, P=.83). However, pts in the SD-AZA group had a shorter median time from diagnosis to treatment (2.9 vs. 14.6 months, P=.009) compared to LD-DAC.Median treatment duration was longer in LD-DAC pts compared to SD-DAC (9.1 vs. 3.1 months, P=.0008) with a median cumulative dose of 8.4 mg/kg (range 1.2-41.2) and 350 mg/m2 (range 175-975) for LD-DAC and SD-DAC, respectively. Compared to SD-DAC, the LD-DAC group required more frequent dose reductions/delays (67% vs. 20%, P=.004) and experienced more hematologic toxicity (85% vs. 29%, P< .0001), respectively.While median time to best response was similar for LD-DAC and SD-DAC (3 vs. 4.1 months, P=.52) there was a trend for higher IWG response rates (30% vs. 18%, P=.06) and lower disease progression rates (18% vs. 41%, P=.06) for LD-DAC compared to SD-DAC. However, this did not translate into a difference in median PFS (11 vs. 7.6 months, P= .34) or OS (23.9 vs. 18.2 months, P=.64, Figure 1). Comparing these results to SD-AZA, while LD-DAC had a longer median treatment duration (9.1 vs. 5.1 months, P=.052) and shorter median time to best response (3 vs. 5.3 months, P=.005) than SD-AZA, response rates were similar (30% vs. 31%, P=.5) and there were no significant differences with respect to median PFS (11 vs. 7.1 months, P=.059) or OS (23.9 vs. 21.1 months, P=.5, Figure 1).Conclusion: Pts treated with the LD-DAC strategy have a response rate at least equivalent to SD-DAC and SD-AZA, though they required more dose adjustments and receive treatment for a longer time period. Survival was similar for all dosing strategies. Very low-dose DAC is an active treatment approach and will be compared to standard-dose DAC and AZA in an upcoming randomized, prospective trial conducted through the MDS Clinical Research Consortium. [Display omitted] DisclosuresOff Label Use: Subcutaneous administration of very low-dose decitabine in treatment of MDS .

Epigenetics of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are clonal diseases of the elderly characterized by chronic cytopenias, dysplasia and a variable risk of progression to acute myeloid leukemia (AML). Aberrant methylation of tumor-suppressor gene promoters has been established for many years and recently tracked to the most immature cells of MDS, suggesting that these alterations are drivers of MDS pathogenesis. In recent years, recurrent somatic mutations in genes encoding proteins involved in DNA methylation and demethylation and in covalent histone modifications have been reported in myeloid malignancies, including MDS. Whole-genome epigenetic profiles of MDS are also emerging. In parallel with these advances in the molecular pathogenesis of MDS, clinical trials have established hypomethylating agents (HMAs) as the mainstay of therapy in the advanced forms of the disease. In this review, we summarize the current understanding of the molecular machinery involved in epigenetic regulation, discuss how epigenetic alterations arise in MDS and contribute to its pathogenesis and then discuss the mode of action of HMAs in MDS.

Guest editorial: Genetic and epigenetic alterations in hematopoietic malignancies

It is now recognized that multiple gene alterations are required for the development of leukemia, as is the case with solid tumors. About a decade ago, these gene alterations were classified into two groups, called class I and class II mutations [1]. Class I mutations include activating mutations of tyrosine kinase receptors such as FLT-3 and c-Kit, tyrosine kinases such as JAK2, oncogenes such as Ras as well as inactivating mutations of tumor suppressors such as p53 and NF-1. Class I mutations induce cell proliferation or block apoptosis. Class II mutations, which include inactivating mutations of transcription factors such as AML1/Runx1 and chromosome modifying enzymes such as MLL, block hemopoietic differentiation. Class II mutations are often caused by chromosomal translocations resulting in fusion proteins such as AML1-ETO, PMLRARa and a variety of MLL-fusions. Combinations of class I and II mutations but not either class I or class II mutations alone induced acute leukemia in mouse models. In addition, both class I and class II mutations frequently coexist in patients’ leukemic cells. Thus, it was assumed that combinations of class I and class II mutations are required for leukemogenesis. On the other hand, class I mutations alone seem to induce myeloproliferative neoplasm (MPN) while class II mutations are associated with myelodysplastic syndromes (MDS), and additional mutations would lead to leukemic transformation of MPN and MDS (Fig. 1). However, recently developed high-speed sequencing and SNP arrays have revealed a variety of novel mutations in hematologic malignancies. Those include mutations of epigenetic regulators, signaling adaptors and proteins involved in splicing [2]. Among these mutations, those in adaptors such as c-Cbl and Lnk may be categorized into class I mutations because mutations of these adaptors with negative signaling roles would lead to autonomous signaling of cytokine receptors. In addition, one of epigenetic regulators mutations, MLLfusions, was categorized with class II mutations. Thus, the ‘‘class I and class II story’’ need to be modified. In this series of Progress in Hematology, four articles review genetic and epigenetic alterations in hematological malignancies. Drs. Tomoki Naoe and Hitoshi Kiyoi briefly summarize the class I and class II story, and then offer an overview of newly identified mutations of epigenetic regulators. They attempt to integrate these mutations, which they call class III, into the class I and class II story. They also discuss driver and passenger mutations as well as background mutations randomly acquired in hematopoietic cells with age and stress [3]. When we think about epigenetic aspects of diseases, MDS is the most prominent because DNA hypomethylating agents are found to be effective in a substantial numbers of patients with MDS. Drs. Jumpei Yamazaki and Jean-Pierre Issa review the basics of epigenetics in cancer and MDS as well as the therapeutic use of DNA hypomethylating agents in MDS and AML. This review update the history as well as the current state of MDS therapy, including a combination therapy of DNA hypomethylating agents and histone deacetylating enzyme (HDAC) inhibitors. Concerning MPN, a class I mutation alone such as BcrAbl and JAK2V617F (activating mutant of JAK2) induces MPN-like diseases in mouse models, and most patients with MPN harbor either Bcr-Abl or JAK2-V617F. Therefore, it was assumed that these mutations are the sole mutations related to MPN and were able to induce MPN by T. Kitamura (&) Division of Cellular Therapy/Division of Stem Cell Signaling, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan e-mail: kitamura@ims.u-tokyo.ac.jp

Optimizing hypomethylating agents in myelodysplastic syndromes

Hypomethylating agents (HMAs) improve the outcome of higher-risk myelodysplastic syndromes (MDS) and provide multilineage response in lower-risk patients but their results must be optimized, especially as the poor outcome of patients after HMA failure is now established. Current efforts include evaluation of novel outpatient administration schedules and routes, improving compliance and drug exposure to reach continuous hypomethylation. Novel combination strategies are emerging, with histone deacetylase inhibitors or immunomodulatory compounds, but none has proven superior to HMA single-agent therapy so far. Improved understanding of the epigenetic deregulation of MDS and of HMA's mode of action has allowed putative biomarkers to emerge, including multiple gene methylation patterns, and gene mutations, notably TET2 mutations. As HMAs may elicit antileukemic immune responses, they are also being evaluated in patients eligible for allogeneic stem cell transplantation. The indication and practical use of HMAs in MDS so far remain those of phase III registration studies, but will hopefully be modified with future results of ongoing clinical and translational research.