Pathway In Myelodysplastic Syndromes Research Articles

Over expression of mTOR gene predicts overall survival in myelodysplastic syndromes.

Myelodysplastic syndromes (MDS) is defined as heterogenous disease, it contains heterogenous leukemic stem cells with various degree of cell differentiation. The perturbation of genes involved in myeloid progenitor cell growth, differentiation and proliferation lead to morphologic dysplasia, maturation arrest, ineffective hematopoiesis hence the cytopenias and propensity to develop into acute myeloid leukemia (AML). Heterogeneous subsets of MDS patients have been defined by their clinical and biologic abnormalities. These different features lead to the development of different prognostic system; however, these approaches are limited in predicting clinical course, and management of patients remains challenging given the uncertainty of the time course of disease progression. It is of importance to identify transcriptomic marker causing maturational and differentiation arrest which could help in understanding the pathogenesis of disease. We have studied differential gene expression profiles (GEPs) in CD34 + marrow cells from myelodysplastic syndrome (MDS) patients (n = 14) and control CD34 + cells using Affymetrix Human Clariom S microarray with 20,000 well annotated genes. We found 4165 genes significantly (p < 0.05) differentially expressed in MDS. Using stringent bioinformatics analyses, we were able to identify few genes (MAPK8, JUNB, mTOR) which were differentially upregulated i.e. 5.39, 73.61 and 2.7 fold change observed in MDS than control and also validated (n = 60) these genes by RT - qPCR. Kaplan - Meier survival analysis indicated that MAPK8 and JUNB could be poor prognostic marker as patients with increased expression showed poor survival, whereas surprisingly mTOR increased expression proved to be good prognostic marker. The correlation analysis showed that the level of gene (MAPK8, JUNB, mTOR) expression was significantly (p ≤ 0.05) associated with frequency of genetic lesions. Interestingly the increased expression of MAPK8 was significantly accompanied with ASXL1 gene mutation. Our study showed an elevation of TNF and AMPK signalling pathways in MDS. TNF signalling might be mediating the proliferative advantage to myeloid clonal cells (mutation carrying cells) over normal cells, whereas, AMPK signalling could be acting as protector against it (favouring normal cells). Hence it would be interesting to explore the functions and pathways associated with mTOR, AMPK, MAPK8 and JUNB in myelopoiesis related diseases like MDS.

Novel Molecular Mechanism of Lenalidomide in Myeloid Malignancies Independent of Deletion of Chromosome 5q.

Simple SummaryLenalidomide is an immunomodulatory drug (IMiD) that has achieved clinical efficacies in multiple myeloma (MM) and myelodysplastic syndromes (MDS) with a single deletion of chromosome 5q (del(5q)). However, many patients treated with lenalidomide relapse and become resistant. Recent studies have demonstrated that lenalidomide binds a protein called cereblon (CRBN), leading to reduced protein levels of IKZF1 and IKZF3 and casein kinase 1 alpha. We have identified signaling molecules downstream of IKZF1, G protein-coupled receptor 68 (GPR68) and regulator of calcineurin 1 (RCAN1) in myeloid malignancies, including MDS and acute myeloid leukemia (AML) with or without del(5q). This review summarizes how lenalidomide exerts anti-tumor activity and highlights novel therapeutic targets that could enhance the anti-tumor activity of lenalidomide with a focus on myeloid malignancies, especially without del(5q).Lenalidomide as well as other immunomodulatory drugs (IMiDs) have achieved clinical efficacies in certain sub-types of hematologic malignancies, such as multiple myeloma, lower-risk myelodysplastic syndromes (MDS) with a single deletion of chromosome 5q (del(5q)) and others. Despite superior clinical response to lenalidomide in hematologic malignancies, relapse and resistance remains a problem in IMiD-based therapy. The last ten years have witnessed the discovery of novel molecular mechanism of IMiD-based anti-tumor therapy. IMiDs bind human cereblon (CRBN), the substrate receptor of the CRL4 E3 ubiquitin ligase complex. Binding of CRBN with IMiDs leads to degradation of the Ikaros family zinc finger proteins 1 and 3 (IKZF1 and IKZF3) and casein kinase 1 alpha. We have found that lenalidomide-mediated degradation of IKZF1 leads to activation of the G protein-coupled receptor 68 (GPR68)/calcium/calpain pro-apoptotic pathway and inhibition of the regulator of calcineurin 1 (RCAN1)/calcineurin pro-survival pathway in MDS and acute myeloid leukemia (AML). Calcineurin inhibitor Cyclosporin-A potentiates the anti-leukemia activity of lenalidomide in MDS/AML with or without del(5q). These findings broaden the therapeutic potential of IMiDs. This review summarizes novel molecular mechanism of lenalidomide in myeloid malignancies, especially without del(5q), in the hope to highlight novel therapeutic targets.

Clinical and Molecular Insights in Erythropoiesis Regulation of Signal Transduction Pathways in Myelodysplastic Syndromes and β-Thalassemia.

Erythropoiesis regulation is essential in normal physiology and pathology, particularly in myelodysplastic syndromes (MDS) and β-thalassemia. Several signaling transduction processes, including those regulated by inositides, are implicated in erythropoiesis, and the latest MDS or β-thalassemia preclinical and clinical studies are now based on their regulation. Among others, the main pathways involved are those regulated by transforming growth factor (TGF)-β, which negatively regulates erythrocyte differentiation and maturation, and erythropoietin (EPO), which acts on the early-stage erythropoiesis. Also small mother against decapentaplegic (SMAD) signaling molecules play a role in pathology, and activin receptor ligand traps are being investigated for future clinical applications. Even inositide-dependent signaling, which is important in the regulation of cell proliferation and differentiation, is specifically associated with erythropoiesis, with phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI3K) as key players that are becoming increasingly important as new promising therapeutic targets. Additionally, Roxadustat, a new erythropoiesis stimulating agent targeting hypoxia inducible factor (HIF), is under clinical development. Here, we review the role and function of the above-mentioned signaling pathways, and we describe the state of the art and new perspectives of erythropoiesis regulation in MDS and β-thalassemia.

Iron overload regulate the cytokine of mesenchymal stromal cells through ROS/HIF-1α pathway in Myelodysplastic syndromes

Iron overload is a significant feature of myelodysplastic syndromes (MDS) patients due to ineffective hematopoiesis and transfusion dependence. Excess iron results in organ dysfunction through the generation of reactive oxygen species (ROS) which can cause oxidative stress even mutation. Mesenchymal stromal cells (MSCs) are responsible for supporting and regulating hematopoiesis, whether MSCs is involved in the pathogenesis of MDS still need further elucidation. Hypoxia-inducible factors-1 (HIF-1) is an integral signal of inflammation that has been shown to up-regulating in MDS patient. We found that MDS-derived MSC had disorganized clones and increased level of apoptosis (n = 53). Iron transportation-related gene, such as DMT1 and ZIP14, and ROS level were increased in iron overload-MDS-MSC (n = 23). HIF-1a, as a crucial part of HIF-1, was also elevated in iron overload-group and PHD2 involved in the degradation of HIF-1a was reduced. Furthermore, HIF-1 downstream cytokines such IL-6, IL-8, TGF-βand VEGF that were also involved in the pathogenesis of MDS were increased in IO-MDS-MSC. When treated with DFO and NAC for iron chelation and antioxidation, the level of HIF-1a and related cytokines could decrease. We conclude that iron overload regulates the cytokine of mesenchymal stromal cells through ROS/HIF-1α pathway in Myelodysplastic syndromes, result in dysfunction of MSC and damage of microenvironment that may be involved in the pathogenesis of MDS.

Biological basis for efficacy of activin receptor ligand traps in myelodysplastic syndromes.

Signaling by the TGF-β superfamily is important in the regulation of hematopoiesis and is dysregulated in myelodysplastic syndromes (MDSs), contributing to ineffective hematopoiesis and clinical cytopenias. TGF-β, activins, and growth differentiation factors exert inhibitory effects on red cell formation by activating canonical SMAD2/3 pathway signaling. In this Review, we summarize evidence that overactivation of SMAD2/3 signaling pathways in MDSs causes anemia due to impaired erythroid maturation. We also describe the basis for biological activity of activin receptor ligand traps, novel fusion proteins such as luspatercept that are promising as erythroid maturation agents to alleviate anemia and related comorbidities in MDSs and other conditions characterized by impaired erythroid maturation.

The SF3B1 K700E Mutation Induces R-Loop Accumulation and Associated DNA Damage

The myelodysplastic syndromes (MDS) are common myeloid malignancies. Mutations in genes involved in pre-mRNA splicing (SF3B1, SRSF2, U2AF1 and ZRSR2) are the most common mutations found in MDS. There is evidence that some spliceosomal components play a role in the maintenance of genomic stability. Splicing is a transcription coupled process; splicing factor mutations affect transcription and may lead to the accumulation of R-loops (RNA-DNA hybrids with a displaced single stranded DNA). Mutations in the splicing factors SRSF2 and U2AF1 have been recently shown to increase R-loops formation in leukemia cell lines, resulting in increased DNA damage, replication stress and activation of the ATR-Chk1 pathway. SF3B1 is the most frequently mutated splicing factor gene in MDS, but a role for mutated SF3B1 in R-loop accumulation and DNA damage has not yet been reported in hematopoietic cells. We have investigated the effects of the common SF3B1 K700E mutation on R-loop formation and DNA damage response in MDS and leukemia cells. R-loop signals and the DNA damage response were measured by immunofluorescence staining using S9.6 and anti-γ-H2AX antibodies respectively. Firstly, we studied K562 (myeloid leukemia) cells with the SF3B1 K700E mutation and isogenic SF3B1 K700K wildtype (WT) K562 cells. K562 cells with SF3B1 mutation showed a significant increase in the number of S9.6 foci [Fold change (FC) 2.01, p&lt;0.001] and in the number of γ-H2AX foci (FC 2.32, p&lt;0.001), indicating increased R-loops and DNA damage, compared to SF3B1 WT K562 cells. Moreover, we observed increased Chk1 phosphorylation at Ser345, a hallmark of activation of the ATR pathway, in SF3B1 mutant K562 cells. Next, we analyzed induced pluripotent stem cells (iPSCs) that we generated from the bone marrow cells of one SF3B1 mutant MDS patient and of one healthy control. A significant increase in R-loops and DNA damage response was observed in an iPSC clone harboring SF3B1 mutation compared to another iPSC clone without SF3B1 mutation obtained from same MDS patient (S9.6 mean fluorescence intensity - FC 1.72, p&lt;0.001; γ-H2AX foci - FC 1.34, p=0.052) and to iPSCs from the healthy control (S9.6 mean fluorescence intensity - FC 1.53, p&lt;0.001; γ-H2AX foci - FC 1.61, p=0.006). In addition, bone marrow CD34+ cells from a SF3B1 mutant MDS patient showed increased R-loops (as measured by number of S9.6 foci) compared to CD34+ cells from a MDS patient without splicing factor mutations (FC 1.9) and from a healthy control (FC 2.6). To investigate whether the observed DNA damage and ATR activation in SF3B1 mutant K562 cells result from induced R-loops, we overexpressed RNASEH1 (encoding an enzyme that degrades the RNA in RNA:DNA hybrids) to resolve R-loops in these cells. RNASEH1 overexpression significantly reduced the number of S9.6 (FC 0.51, p&lt;0.001) and γ-H2AX foci (FC 0.63, p=0.035) in SF3B1 mutant K562 cells compared to SF3B1 WT K562 cells. RNASEH1 overexpression also resulted in decreased Chk1 phosphorylation, indicating suppression of ATR pathway activation in SF3B1 mutant K562 cells. To determine the functional importance of ATR activation associated with SF3B1 mutation, we evaluated the sensitivity of SF3B1 mutant cells towards the ATR inhibitor VE-821. SF3B1 mutant K562 cells showed preferential sensitivity towards VE-821 compared to SF3B1 WT K562 cells. Chk1 is a critical substrate of ATR, and we next investigated the effects of Chk1 inhibition in SF3B1 mutant cells. Interestingly, SF3B1 mutant K562 cells demonstrated preferential sensitivity towards the Chk1 inhibitor UCN-1 (IC50 61.8 nM) compared to SF3B1 WT K562 cells (IC50 267 nM), suggesting that ATR activation is important for the survival of SF3B1 mutant cells. SF3B1 mutant K562 cells were preferentially sensitive to the splicing modulator Sudemycin D6 (IC50 53.2 nM) compared to SF3B1 WT K562 cells (IC50 130.7 nM). The effects of VE-821 and UCN-1 on SF3B1 mutant K562 cells were enhanced by Sudemycin D6 (Combination index &lt;1), indicating synergy. In summary, our results show that the SF3B1 mutation leads to accumulation of R-loops and associated DNA damage resulting in activation of the ATR pathway in MDS and leukemia cells. Thus different mutated splicing factors have convergent effects on R-loop elevation leading to DNA damage. Moreover, our data suggest that Chk1 inhibition, alone or in combination with splicing modulators, may represent a novel therapeutic strategy to target SF3B1 mutant cells. Disclosures Schuh: Janssen: Speakers Bureau; Verastem: Speakers Bureau; Kite: Speakers Bureau; Gilead: Speakers Bureau; Seattle Genetics: Speakers Bureau; Jazz Pharmaceuticals: Speakers Bureau; Bristol-Myers Squibb: Research Funding; AbbVie: Consultancy, Speakers Bureau; Genentech: Consultancy, Speakers Bureau; Pharmacyclics: Consultancy, Speakers Bureau. Wiseman:Novartis, Celgene: Consultancy, Honoraria.

Activin Receptor II Ligand Traps: New Treatment Paradigm for Low-Risk MDS.

Alleviating cytopenias, namely anemia, is the main goal of therapy in lower-risk myelodysplastic syndromes (MDS). Current available treatment options remain limited. We review the role of TGF-B pathway in MDS, the current available data on luspatercept and sotatercept development. TGF-B pathway is overactivated in MDS contributing to observed myelosuppression. SMADs, the downstream proteins of TGF-B pathway, are upregulated. GDF-11 is a negative regulator of terminal erythroid differentiation and an activin receptor ligand. Sotatercept and luspatercept are fusion ligand trap novel agents for activin II receptors A and B, respectively. Early promising results have been reported with those novel agents for treating anemia in lower-risk MDS patients, and higher responses were observed among patients with ring sideroblasts and SF3B1 mutation. A phase III randomized clinical trial with luspatercept was recently conducted. Activin receptor II ligand traps may represent a new paradigm for anemia treatment in MDS.

BRD4 Inhibition Enhances Azacitidine Efficacy in Acute Myeloid Leukemia and Myelodysplastic Syndromes.

Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell-based disorders characterized by ineffective hematopoiesis, increased genomic instability and a tendency to progress toward acute myeloid leukemia (AML). MDS and AML cells present genetic and epigenetic abnormalities and, due to the heterogeneity of these molecular alterations, the current treatment options remain unsatisfactory. Hypomethylating agents (HMA), especially azacitidine, are the mainstay of treatment for high-risk MDS patients and HMA are used in treating elderly AML. The aim of this study was to investigate the potential role of the epigenetic reader bromodomain-containing protein-4 (BRD4) in MDS and AML patients. We identified the upregulation of the short variant BRD4 in MDS and AML patients, which was associated with a worse outcome of MDS. Furthermore, the inhibition of BRD4 in vitro with JQ1 or shRNA induced leukemia cell apoptosis, especially when combined to azacitidine, and triggered the activation of the DNA damage response pathway. JQ1 and AZD6738 (a specific ATR inhibitor) also synergized to induce apoptosis in leukemia cells. Our results indicate that the BRD4-dependent transcriptional program is a defective pathway in MDS and AML pathogenesis and its inhibition induces apoptosis of leukemia cells, which is enhanced in combination with HMA or an ATR inhibitor.

Selinexor, a First-in-Class XPO1 Inhibitor, Is Efficacious and Tolerable in Patients with Myelodysplastic Syndromes Refractory to Hypomethylating Agents

There is no standard therapy for patients with myelodysplastic syndromes (MDS) refractory to hypomethylating agents (HMA) and the median overall survival (OS) of HMA-refractory MDS patients with IPSS Intermediate-2/High-risk MDS is ~6 months. Here, we present data from a phase 2 clinical trial of selinexor, an oral, first-in-class Selective Inhibitor of Nuclear Export (SINE) compound that inhibits XPO1, in patients with MDS refractory to HMAs. XPO1 is the major nuclear export protein responsible for shuttling many key cellular regulators out of the nucleus and is overexpressed in many cancers. Preclinical studies of selinexor have shown that inhibition of XPO1 causes nuclear retention of wildtype p53 and disruption of the NF-κB pathway, both relevant targets for MDS. Moreover, selinexor has shown promising responses in acute myeloid leukemia, multiple myeloma, and Non-Hodgkin lymphoma. We therefore set out to determine the safety and efficacy of selinexor in MDS, and to study potential molecular correlates of response to selinexor.Patients with MDS or MDS/MPN who were refractory to azacitidine or decitabine were included (defined as either progression after initial response or if no response after >6 cycles). The primary endpoint was overall response rate (ORR = CR + mCR + PR + HI) and secondary endpoints included safety, response duration, and OS. The starting dose was 35 mg/m2 PO twice-weekly in 28-day cycles. Bone marrow biopsies, bone marrow DNA and peripheral blood RNA were collected from serial samples and used for correlative analyses including next-generation targeted gene sequencing, RNA-seq, immunohistochemistry, and proteomics. A total of 25 patients were evaluable for safety and 19 were evaluable for response. Six patients were not evaluable for response based on unrelated death from concurrent illness (n=5) or withdrawal of consent (n=1) before completion of one cycle. The median age was 77 (range, 50-85) and the majority of pts were High- or Very High-risk by IPSS-R (72%) with >10% bone marrow blasts (70%).The ORR was 32% (all mCRs) with an average response duration of 6.8 months. An additional 42% of pts achieved stable disease (SD) for an average response duration of 6.4 months for all patients receiving clinical benefit (Figure A). The median overall survival was 9.7 months with a median follow-up of 2.1 years. Those with mCR or SD had greater survival than non-responders (Figure B). Grade 3 or 4 adverse events (AEs) in the first 3 pts (thrombocytopenia (n=3) and hyponatremia (n=1)) led to reduction of the dose to 60mg flat dose twice-weekly for 2 weeks followed by 1 week off, resulting in significantly improved tolerability. The most frequently occurring AE thereafter was grade 2 or 3 fatigue. All other AEs were manageable with routine supportive care.The presence of an SF3B1 hotspot mutation was significantly associated with response to selinexor (p=0.01; Figure C). No other single mutation had a significant association, although patients with mutated TP53 and those with >3 mutations were numerically higher in the non-responders but did not reach statistical significance. The mRNA levels of a number of transcripts from the NF-κB pathway and of Myc were decreased after treatment with selinexor in responders, albeit with some variability. The levels of XPO1 mRNA increased with treatment within 4 hours of the fist dose, indicative of XPO1 target engagement with selinexor (Figure D). Further analyses are underway to determine if splicing is differentially modulated in SF3B1 mutated patients. Immunohistochemistry and proteomics for protein alterations are also ongoing.These data indicate that selinexor is safe and tolerable in MDS when given at 60mg twice-weekly for 2 weeks with 1 week off with a 32% response rate. Responses appear to be enriched in patients with SF3B1 mutations and selinexor appears to affect pathways that may be activated downstream of mutant-SF3B1, such as NF-κB and Myc. Detailed correlative and pre-clinical analyses are ongoing and should provide further illumination of the biological relevance of these markers, which will be tested prospectively in future clinical trials. Further studies of selinexor combined with targeted agents that disrupt similar or complementary oncogenic pathways in MDS could further improve responses. [Display omitted] DisclosuresRampal:Incyte: Honoraria, Research Funding; Stemline: Research Funding; Jazz: Consultancy, Honoraria; Constellation: Research Funding; Celgene: Honoraria. Park:Adaptive Biotechnologies: Consultancy; Kite Pharma: Consultancy; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Shire: Consultancy; AstraZeneca: Consultancy; Novartis: Consultancy; Juno Therapeutics: Consultancy, Research Funding. Stein:Agios: Consultancy; Bayer: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Daiichi Sankyo: Consultancy; Pfizer: Consultancy. Tallman:AbbVie: Research Funding; Cellerant: Research Funding; ADC Therapeutics: Research Funding; Daiichi-Sankyo: Other: Advisory board; Orsenix: Other: Advisory board; BioSight: Other: Advisory board; AROG: Research Funding.

Functional expression of Tim-3 on blasts and clinical impact of its ligand galectin-9 in myelodysplastic syndromes

T-cell immunoglobulin mucin-3 (Tim-3), an inhibitory immune checkpoint receptor, is highly expressed on acute myeloid leukemia cells and its ligand galectin-9 is reported to drive leukemic progression by binding with Tim-3. However, it remains unclear whether the Tim-3–galectin-9 pathway is associated with the pathophysiology of myelodysplastic syndromes (MDS). Thus, we investigated the expression and function of Tim-3 and the clinical impact of its ligand galectin-9 in MDS. Tim-3 expression levels on MDS blasts by CD45/side-scatter or CD34/CD45 gating were increased as MDS progressed to the advanced stage. Tim-3 expression in the MDS blasts was upregulated in the presence of the cell culture supernatant of human stromal cells or the MDS-related cytokine transforming growth factor-β1. The proliferation of Tim-3+ MDS blasts was inhibited by the blockade of anti-Tim-3 antibody. Furthermore, plasma levels of galectin-9 were elevated as MDS progressed to the advanced stage in 70 MDS/acute leukemia transformed from MDS patients and was a prognostic factor in 40 MDS patients. Our data demonstrated that the Tim-3-galectin-9 pathway is associated with the pathogenesis and disease progression of MDS. These findings provide new insight into potential immunotherapy targeting the galectin-9–Tim-3 pathway in MDS.

Iron overload may promote alteration of NK cells and hematopoietic stem/progenitor cells by JNK and P38 pathway in myelodysplastic syndromes.

The objective of the study was to examine levels of intracellular iron, reactive oxygen species (ROS) and the expression of JNK and p38MAPK in NK cells and hematopoietic stem/progenitor cells (HSPCs) in MDS patients, and explore potential mechanisms by which iron overload (IOL) promotes MDS progression. Thirty-four cases of MDS and six cases of AML transformed from MDS (MDS/AML) were included. HSPCs and NK cells were isolated by magnetic absorption cell sorting. We used flow cytometry to detect the levels of ROS and intracellular JNK and P38 in NK cells and HSPCs. Total RNA and protein were extracted from NK cells and CD34+ cells to examine the expression of JNK and p38MAPK using RT-PCR and Western blotting. Intracellular iron concentration was detected. Data were analyzed by SPSS 21 statistical software. Intracellular iron concentration and ROS were increased in both NK cells and HSPCs in MDS patients with iron overload (P<0.05). MDS patients with iron overload had higher JNK expression and lower p38 expression in NK cells, and higher p38 expression in HSPCs compared with non-iron overload group. IOL may cause alterations in NK cells and HSPCs through the JNK and p38 pathways, and play a role in the transformation to AML from MDS.

Role of Aberrant Splicing in Pathogenesis of Myelodysplastic Syndromes-Review

The spectrum of genetic abnormalities in myelodysplastic syndromes(MDS) has been revealed by high-throughput sequencing. However, the functional role of these mutations in occurrence and development of MDS was not delineated. The mutations in splicing factors have been identified as the commonest gene mutations in MDS. Recently, it was reported that the mutated or dysregulated splicing factors, including SF3B1, SRSF2 and U2AF1, attribute to aberrant mRNA splicing, which leads to hematopoietic dysfunction and drives MDS. These findings will be of great help in searching for candidate therapeutic targets in mis-splicing pathway in MDS. In this review the role of aberrant splicing in pathogenesis of MDS is summarized briefly.

SPAG6 regulates cell apoptosis through the TRAIL signal pathway in myelodysplastic syndromes.

Myelodysplastic syndromes(MDSs) are a group of malignant clone hematopoietic stem-cell diseases, and the evolution and progression of MDS depend on the abnormal apoptosis of bone marrow cells. Our previous studies have indicated that sperm-associated antigen6(SPAG6), located in the uniparental disomy regions of myeloid cells, is overexpressed in patients with MDS as compared to controls, and SPAG6 can inhibit apoptosis of SKM-1. However, the concrete mechanism is still unclear. In the present study, it was found that the TNF-related apoptosis-inducing ligand(TRAIL)signal pathway was activated when the expression of SPAG6 was inhibited by SPAG6-shRNA lentivirus in SKM-1cells. Additionally, the results of flow cytometry, Cell Counting Kit-8 assay and western blot analysis implied that the TRAIL signal pathway could be inhibited by a high expression of SPAG6. However, SPAG6 cannot influence the expression of TRAIL death receptors, except for FADD. Additionally the interaction between FADD and TRAIL death receptors also increased in SKM-1cells infected with SPAG6-shRNA lentivirus. Thus, our study demonstrates that SPAG6 may regulate apoptosis in SKM-1 through the TRAIL signal pathway, indicating that SPAG6 could be a potential therapeutic target.

Functional Consequences of Spliceosome Mutations

Mutations in key factors of the spliceosome occur in over 50% of patients with myelodysplastic syndromes (MDS) and thus splicing represents the most frequently affected pathway in MDS. The vast majority of mutations cluster in four genes: SF3B1, SRSF2, U2AF1, and ZRSR2. Mutations occur in a mutually exclusive manner suggesting a common mechanism by which they cause disease, and yet they segregate to specific subtypes of myeloid malignancies suggesting unique, mutation-specific functions. With the exclusion of ZRSR2, mutations occur at highly restricted residues and are strictly heterozygous, suggestive of gain of function mutations. We and others have shown that mutations affect RNA binding affinity and specificity, and can lead to a variety of outcomes including exon inclusion or skipping, alternative splice site selection, intron retention, and most recently alternative polyadenylation. Overall, these splice changes are subtle: only a small subset of all splice events is affected by these mutations and changes in isoform usage are < 10% for most alternative splice events identified. Furthermore, a direct connection between alternatively spliced transcripts and differentially expressed genes is often not seen. However, these alternative splice events affect genes critical to cellular function and hematopoiesis. Examples include EZH2, ABCB7, macroH2A1, and ATG7. Mutations in SRSF2 result in inclusion of a poison exon in EZH2 resulting in reduced protein levels of this critical epigenetic regulator. Mutations in SF3B1 cause alternative splicing of ABCB7 slating its RNA for non-sense mediated decay. Intriguingly, mutations in U2AF1 promote usage of a distal polyadenylation site in an essential autophagy factor, ATG7, resulting in inefficient translation and decreased protein levels. As a consequence, autophagy is impaired, which can promote cellular transformation, providing a possible explanation for the clonal advantage of cells with splicing factor mutations. Additional research is critical to further determine how alternative splicing contributes to the MDS phenotype with impaired hematopoietic differentiation and cellular function and eventual malignant transformation. Latest findings will be presented here with a focus on mechanistic, functional, and biologic effects of splicing factor mutations. DisclosuresNo relevant conflicts of interest to declare.

Identification of microRNA-regulated pathways using an integration of microRNA-mRNA microarray and bioinformatics analysis in CD34+ cells of myelodysplastic syndromes.

The effect of microRNA (miRNA) and targeted mRNA on signal transduction is not fully understood in myelodysplastic syndromes (MDS). Here, we tried to identify the miRNAs-regulated pathways through a combination of miRNA and mRNA microarray in CD34+ cells from MDS patients. We identified 34 differentially expressed miRNAs and 1783 mRNAs in MDS. 25 dysregulated miRNAs and 394 targeted mRNAs were screened by a combination of Pearson’s correlation analysis and software prediction. Pathway analysis showed that several pathways such as Notch, PI3K/Akt might be regulated by those miRNA-mRNAs pairs. Through a combination of Pathway and miRNA-Gene or GO-Network analysis, miRNAs-regulated pathways, such as miR-195-5p/DLL1/Notch signaling pathway, were identified. Further qRT-PCR showed that miR-195-5p was up-regulated while DLL1 was down-regulated in patients with low-grade MDS compared with normal controls. Luciferase assay showed that DLL1 was a direct target of miR-195-5p. Overexpression of miR-195-5p led to increased cell apoptosis and reduced cell growth through inhibition of Notch signaling pathway. In conclusion, alteration expression of miRNAs and targeted mRNAs might have an important impact on cancer-related cellular pathways in MDS. Inhibition of Notch signaling pathway by miR-195-5p-DLL1 axis contributes to the excess apoptosis in low-grade MDS.

Clinical Significance and Pathopysiological Function of the Tim-3/Galection-9 Pathway in Myelodysplastic Syndromes

Abstract Background: Galectin-9 (Gal-9), a member of the galectin family, plays a crucial role in inflammation and tumorigenesis involving angiogenesis, cell adhesion, immune escape, and cancer cell survival. In acute myeloid leukemia (AML), Gal-9 is highly expressed in some AML cell lines and binds with T-cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) on T cells and leukemic stem cells. The Tim-3/Gal-9 pathway may be associated with disease progression by inducing T-cell dysregulation and mediating autocrine proliferation of leukemic cells. However, the role of the pathway in myelodysplastic syndromes (MDS) remains unclear. In the current study, we investigated the prognostic impact of plasma Gal-9 levels and the pathophysiological roles of Gal-9 and Tim-3 in MDS. Methods and results: 1) To investigate the prognostic impact of Gal-9, plasma Gal-9 levels were measured by ELISA in 92 MDS patients: 30 with refractory anemia (RA); 3 with RA with ringed sideroblasts (RARS); 18 with RA with excess blasts (RAEB); 14 with RAEB in transformation (RAEB-t); and 29 with acute leukemia transformed from MDS (AL-MDS). The plasma Gal-9 level increased with disease progression (mean ± SD: control 3.4 ± 0.9; RA, 9.3 ± 5.7; RARS, 10.2 ± 6.8; RAEB, 9.7 ± 6.5; RAEB-t, 17.2 ± 9.6; AML-MDS, 20.1 ± 14.1 ng/ml). Furthermore, patients with AL-MDS in International Prognostic Scoring System (IPSS) high-risk categories (Intermediate-2/High) had significantly higher Gal-9 levels compared with IPSS low-risk (Low/Intermediate-1) patients (Low/Intermediate-1 vs Intermediate-2/High, p = 0.002; Low/Intermediate-1 vs AML-MDS, p = 0.004). The overall survival of MDS patients with plasma Gal-9 higher than the normal level (10 ng/mL) was significantly shorter than that of other patients (log-rank p &lt; 0.001) even in lower-risk (RA, RARS) cases (log-rank p = 0.0369). Moreover, multivariate analysis showed that a high level of Gal-9 was an independent predictor of shorter survival in MDS patients as well as IPSS. 2) Bone marrow mononuclear cells were isolated from some MDS patients, and Tim-3 expression on granulocytes, monocytes, lymphocytes, and blasts was analyzed using flow cytometry (FCM). Tim-3 expression on blasts tended to be higher in AL-MDS patients than in MDS patients. 3) To investigate whether MDS cells can produce Gal-9, we analyzed Gal-9 levels in supernatants of cell cultures of 3 human AL-MDS cell lines, F-36P, SKM-1, and MDS-L, and MDS blasts obtained from an AL-MDS patient by ELISA. Gal-9 was detected in all cell culture supernatants and its concentration was higher when cultured in medium containing 10% fetal bovine serum (FBS) than in 2.5% FBS medium in F-36P and SKM-1 cells. The concentration of Gal-9 produced from MDS blasts was increased time dependently in 2-6 day culture. Furthermore, recombinant human Gal-9 enhanced the cell proliferation of F-36P cells. 4) After analyzing Tim-3 expression in MDS cell lines using real-time quantitative PCR and FCM, all cell lines expressed relatively low levels of Tim-3 mRNA. Extracellular expression of Tim-3 was detected and induced by adding cell culture supernatants of the human stromal cell line HS-5 in F-36P cells. To elucidate the signaling pathway inducing Tim-3 expression, we investigated Tim-3 mRNA expression in F-36P cells treated with HS-5 supernatant with several signal transduction inhibitors (STAT3 inhibitor, U0126; MAPK/ERK; AG490; JAK2, LY294002; PI3K, PDTC; NF-κB inhibitor). Upregulation of Tim-3 gene expression in F-36P cells treated with HS-5 supernatant was inhibited by the MEK inhibitor U0126. These results suggest that the MAPK/ERK pathway is involved in Tim-3 expression induced by HS-5 supernatant. Conclusions: In MDS, the elevation of plasma Gal-9 levels is associated with disease progression, including leukemic transformation, and with shorter survival. Furthermore, its receptor Tim-3 is upregulated on blasts in AL-MDS patients. Our data suggest that the Gal-9/Tim-3 pathway plays a key role in MDS disease progression. Although further study is required to clarify the detailed functions of the interaction between Gal-9 and Tim-3, the current study could lead to the development of a new immunotherapeutic strategy via the blockade of this pathway in MDS. Disclosures No relevant conflicts of interest to declare.

Genetic and epigenetic pathways in myelodysplastic syndromes: A brief overview

Myelodysplastic syndromes (MDS) are a highly heterogenous group of hematopoietic tumors, mainly due to variable clinical features and diverse set of cytogenetic, molecular genetic and epigenetic lesions. The major clinical features of MDS are ineffective hematopoiesis, peripheral cytopenias, and an increased risk of transformation to acute myeloid leukemias, which in turn is most likely determined by specific genetic abnormalities and other presenting hematologic features. The risk of developing MDS is relatively higher in some genetic syndromes such as Fanconi anemia and receipt of chemotherapy and radiation treatment. In recent years a significant progress has occurred and a vast literatures has become available including the spectrum of cytogenetic abnormalities, gene mutations relating to RNA splicing machinery, epigenetic regulation of gene expression and signaling pathways associated with MDS pathogenesis, which have provided opportunities to understand the molecular mechanisms as well as employ targeted therapeutic approaches to treat MDS. The cytogenetic abnormalities detected in MDS varies from a single abnormality to complex karyotype not easily amenable to conventional cytogenetic analysis. In such cases, array based high resolution genomic analysis detected abnormalities, which are diagnostic as well as prognostic. The most common driver gene mutations detected in patients with MDS include RNA splicing (SF3B1,SRSF2,U2F1,ZRSR2), DNA methylation (TET2,DNMT3A,IDH1/IDH2), chromatin modification (ASXL1,EZH2), transcription regulation (RUNX1,BCOR) and DNA repair control p53. A small subset of MDS arise due to deregulation of RAS pathway, mainly due to NRAS/KRAS/NF1 mutations. Identification of these mutations and pathways have provided opportunities for oncologists to target these patients with specific therapies. Several drugs which either target the spliceosome, oncogenic RAS signaling, or hypomethylating agents have been employed to successfully treat MDS patients.

Senescence of bone marrow mesenchymal stromal cells is accompanied by activation of p53/p21 pathway in myelodysplastic syndromes.

The contribution of bone marrow mesenchymal stromal cells (BMMSCs) to the pathogenesis of myelodysplastic syndrome (MDS) has created controversies. In this study, we confirmed that BMMSCs from MDS patients showed prominent features of senescence, which were characterized by increased cell size, decreased proliferation and colony-forming potential, alteration of cytoskeleton, and increased senescence-associated β-galactosidase (SA-β-Gal) activity. Interestingly, the apoptosis assay results showed that the percentage of apoptosis cells was very low and the difference was not significant between MDS patients and normal controls. Moreover, the osteogenic differentiation potential of BMMSCs from lower risk but not higher risk MDS was impaired, indicated by cytochemical stainings and reduced expressions of RUNX2. In addition, BMMSCs from MDS patients had impaired hematopoietic supporting function. Furthermore, the expression of p53 and p21 which played an important role in regulating the senescence progress of BMMSCs was significantly increased, whereas levels of p16 and pRb expression were not changed in the BMMSCs from MDS patients. Taken together, our comprehensive analysis shows that BMMSCs from MDS patients exhibited senescent behavior and activation of p53/p21 pathway probably played an important role in the senescence process.

Aberration Of SF3B1 Results In Deregulated Splicing Of Key Genes and Pathways In Myelodysplastic Syndromes

The recent discovery of a variety of somatic splicesomal mutations in the myelodysplastic syndromes (MDS) has revealed a new leukaemogenic pathway involving spliceosomal dysfunction. Pre-mRNA splicing proceeds by way of two phosphoester transfer reactions and is catalyzed by the spliceosome, which consists of the U1, U2, U4/U6, and U5 small nuclear ribonucleoproteins (snRNPs) and numerous non-snRNP proteins. The snRNPs are involved in recognising short conserved sequences of the pre-mRNA, including the 5′ and 3′ splice sites and the branch site, and in positioning the reactive nucleotides for catalysis. The spliceosome is a dynamic molecular machine, undergoing several major structural rearrangements during its functional cycle. Mutation of the Splicing Factor 3B, subunit 1 (SF3B1) gene is common in MDS, occurring in over 70% of patients whose disease is characterised by ring sideroblasts (RARS). The close association between SF3B1 mutation and ring sideroblasts is consistent with a causal relationship, and makes this the first gene to be strongly associated with a specific feature of MDS.Sf3b1 heterozygous knockout mice show the presence of ringed sideroblasts. In order to investigate the role of SF3B1 haploinsufficiency in MDS we have silenced SF3B1 using siRNA in the myeloid cell lines K562, TF-1, SKM1, HeL and OCIM2. Cell growth was impaired in all the cell lines with SF3B1 knockdown. Using Flow Cytometry, cell cycle analysis showed a significant increase in cells in the sub-G0 phase as well as G2/M arrest in the cell lines. We also observed impaired erythroid differentiation in hemin treated K562 and TF-1 cell lines with SF3B1 knockdown.Gene expression profiling (GEP) was performed in two cell lines with SF3B1 knockdown (K562 and TF1). Deregulated pathways and gene ontology categories included cell cycle regulation and alternative splicing using Ingenuity Pathway Analysis. We next performed Gene Set Enrichment Analysis (GSEA). The GSEA showed a significant enrichment of nonsense-mediated mRNA decay (NMD) genes that were up-regulated in cells with SF3B1 knockdown, suggesting NMD activation following SF3B1 silencing. We used Human Exon-Junction arrays (Affymetrix) to evaluate global transcript exon usage in the K562 and TF1 cell lines with SF3B1 knockdown. We observed significant differential exon usage in genes involved in RNA degradation, spliceosome, cell cycle and apoptosis. We further observed aberrant splicing of the candidate gene ABCB7 showing exon skipping and TP53 gene showing exon skipping as well as intron retention.We have investigated the changes in the transcriptome in CD34+ cells from MDS patients with SF3B1 mutation by RNA sequencing and found many genes showing significant differential exon usage including CCND1, EIF3B, FKBP1A, BCL2 and RB1. Using Ingenuity Pathway Analysis we identified alternative splicing pattern of genes involved in cell cycle, RNA processing, mTOR signalling and P53 signalling pathways.We have studied CD34+ cells from MDS patients with SF3B1 mutation in vitro and observed impairment in cell growth compared to CD34+ cells from healthy controls or from MDS patients without splicing mutations. In colony forming assays we observed a decrease in the number of erythroid or myeloid colonies derived from CD34+ cells of patients with SF3B1 mutation compared to patient CD34+ cells without splicing factor mutation. The identification of SF3B1 downstream targets in SF3B1 mutant and wild-type erythroid and myeloid colonies from MDS patients is in progress using RNA sequencing.Our results show that knockdown of SF3B1 in haematopoietic cell lines results in impaired cell growth, deregulated global gene expression and aberrant splicing. Studies of the haematopoietic progenitor CD34+ cells of patients with SF3B1 mutation show impaired cell growth and erythroid differentiation as well as deregulation of many pathways including the cell cycle and RNA processing. The identification of the key target genes affected by the common splicing mutations in MDS is critical to our understanding of how the mutations contribute to the pathogenesis of this disorder. Disclosures:Maciejewski:NIH: Research Funding; Aplastic anemia&MDS International Foundation: Research Funding.

Toll-Like Receptor (TLR) Signaling Adaptor Protein MYD88 in Myelodysplastic Syndromes (MDS)

Abstract 556We have documented that deregulation of the Toll-like Receptor 2 (TLR2) centered innate immunity signals contribute to the pathogenesis of myelodysplastic syndromes (MDS). Of relevance, oncogenically active mutations of MYD88, a signal adaptor protein for TLR signal, have recently been identified as recurrent genetic lesions in both B-cell lymphoma and in chronic lymphocytic leukemia (CLL) (Vu N et al. Nature 2010 and Puente et al. Nature 2011). This information further supports the importance of innate immunity deregulation in leukemogenesis. To further characterize this pathway in MDS, we analyzed potential genetic alteration and expression level of MYD88 in patients of MDS. In a cohort of 40 MDS whole bone marrow mononuclear cell DNA, we first performed pyrosequencing analysis focusing on a list of previously reported MYD88 mutations (V217, W218, S219, I220, S222, M232, S243, L265, and T294). We did not detect mutation of any these hotspots on MYD88 in MDS. We then expanded the sequencing efforts to the entire coding region of MYD88 using an approach that combines PCR amplification and massive parallel sequencing. Still, no mutation of MYD88 was detected using this technique. We then examined the expression of MYD88 in CD34+ hematopoietic stem cells from 65 patients with MDS. In comparison to healthy donors, 26% of MDS patients (N=17) presented a more than 2 fold increase of MYD88 RNA, and 15% (N=10) had a 30%–90% increase. In average, MYD88 RNA level was 1.7 fold increased compared to control. Of potential clinical relevance, patients with higher MYD88 RNA expression in bone marrow CD34+ cells (above median value) (N=33) had a propensity of shorter period (24.4 mo) of overall survival (OS) in comparison to patients with lower levels of MYD88 expression (N=32) (32 mo)(P=0.05). We also found that patients with higher levels of MYD88 expression (split at 0.8 fold to controls) tended to have higher WBC (P=0.02). We have previously shown that blockade of the TLR2 mediated innate immunity signaling in MDS CD34+ cells could positively regulate erythroid lineage differentiation. To evaluate the potential of MYD88 blockade, we applied a 26 AA MYD88 inhibitory peptide that blocks its homodimerization (Invivogen, San Diego, CA) on primary CD34+ cells isolated from patients with lower-risk MDS (N=5). Methylcellulose medium supported colony formation assays indicated that the presence of MYD88 inhibitor led to an average of 60% increase for the numbers of erythroid colonies and a 30% increase for the numbers of total colonies. At the same time, we did not observe these effects of MYD88 blockade on the CD34+ cells isolated from the patients of higher-risk MDS (N=3). IL-8 is one of the key downstream transcriptional targets of the TLR-MYD88-NFkB innate immunity signaling that was documented to be elevated in bone marrow plasma of MDS. ELISA assays also indicated that blockade MYD88 in cultured MDS CD34+ cells led to a decrease of IL-8 concentration in medium. Taken together, these results indicated that MYD88 is overexpressed in hematopoietic stem cells of MDS and that blockade of MYD88 mediated innate immunity signaling may have therapeutic potential in treating patients with MDS. Disclosures:Kantarjian:Genzyme: Research Funding.