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The majority of acute myeloid leukemia (AML) patients suffer from relapse and the exact etiology of AML remains unclear. The aim of this study was to gain comprehensive insights into the activity of signaling pathways in AML. In this study, using a high-throughput PepChip™ Kinomics microarray system, pediatric AML samples were analyzed to gain insights of active signal transduction pathway. Unsupervised hierarchical cluster analysis separated the AML blast profiles into two clusters. These two clusters were independent of patient characteristics, whereas the cumulative incidence of relapse (CIR) was significantly higher in the patients belonging to cluster-2. In addition, cluster-2 samples showed to be significantly less sensitive to various chemotherapeutic drugs. The activated peptides in cluster-1 and cluster-2 reflected the activity of cell cycle regulation, cell proliferation, cell differentiation, apoptosis, PI3K/AKT, MAPK, metabolism regulation, transcription factors and GPCRs signaling pathways. The difference between two clusters might be explained by the higher cell cycle arrest response in cluster-1 patients and higher DNA repair mechanism in cluster-2 patients. In conclusion, our study identifies different signaling profiles in pediatric AML in relation with CIR involving DNA damage response and repair.

Acute myeloid leukemia (AML) is characterized by uncontrolled proliferation and accumulation of immature myeloblasts, which impair normal hematopoiesis. While this definition categorizes the disease into a distinctive group, the large number of different genetic and epigenetic alterations actually suggests that AML is not a single disease, but a plethora of malignancies. Still, most AML patients are not treated with targeted medication but rather by uniform approaches such as chemotherapy. The identification of novel treatment options likely requires the identification of cancer cell vulnerabilities that take into account the different genetic and epigenetic make-up of the individual tumors. Here we show that STK3 depletion by knock-down, knock-out or chemical inhibition results in apoptotic cells death in some but not all AML cell lines and primary cells tested. This effect is mediated by a premature activation of cyclin dependent kinase 1 (CDK1) in presence of elevated cyclin B1 levels. The anti-leukemic effects seen in both bulk and progenitor AML cells suggests that STK3 might be a promising target in a subset of AML patients.

Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is one of the most common genetic lesions in acute myeloid leukemia patients (AML). Although FLT3 tyrosine kinase inhibitors initially exhibit clinical activity, resistance to treatment inevitably occurs within months. PIM kinases are thought to be major drivers of the resistance phenotype and their inhibition in relapsed samples restores cell sensitivity to FLT3 inhibitors. Thus, simultaneous PIM and FLT3 inhibition represents a promising strategy in AML therapy. For such reasons, we have developed SEL24-B489 - a potent, dual PIM and FLT3-ITD inhibitor. SEL24-B489 exhibited significantly broader on-target activity in AML cell lines and primary AML blasts than selective FLT3-ITD or PIM inhibitors. SEL24-B489 also demonstrated marked activity in cells bearing FLT3 tyrosine kinase domain (TKD) mutations that lead to FLT3 inhibitor resistance. Moreover, SEL24-B489 inhibited the growth of a broad panel of AML cell lines in xenograft models with a clear pharmacodynamic-pharmacokinetic relationship. Taken together, our data highlight the unique dual activity of the SEL24-B489 that abrogates the activity of signaling circuits involved in proliferation, inhibition of apoptosis and protein translation/metabolism. These results underscore the therapeutic potential of the dual PIM/FLT3-ITD inhibitor for the treatment of AML.

// Min Huang 1 , Li Zhu 2 , Jacqueline S. Garcia 3 , Michael X. Li 4 , Andrew J. Gentles 5 and Beverly S. Mitchell 1 1 Department of Medicine, Stanford Cancer Institute, Stanford University, Stanford, California, USA 2 Department of Pathology, Stanford University School of Medicine, Stanford, California, USA 3 Department of Medicine, Dana-Farber Cancer Institute, Boston, Massachusetts, USA 4 Department of Electrical Engineering and Computer Science, College of Engineering, Oregon State University, Corvallis, Oregon, USA 5 Department of Medicine, Biomedical Informatics Research, Stanford University, Stanford, California, USA Correspondence to: Beverly S. Mitchell, email: bmitchell@stanford.edu Keywords: Brd4; autophagy; AML; Keap1 Received: October 26, 2017 Accepted: January 19, 2018 Published: February 07, 2018 ABSTRACT We have recently reported that activation of Brd4 is associated with the presence of autophagy in NPMc+ and MLL AML cells. In order to determine the mechanisms underlying this relationship, we have examined the role of Brd4 in regulating the expression of several genes that are central to the process of autophagy. We found that Brd4 binds to the promoters of ATG 3, 7 and CEBPβ, and expression of these genes is markedly reduced by inhibitors of Brd4, as well as by Brd4-shRNA and depletion of CEBPβ. Inhibitors of Brd4 also dramatically suppress the transcription of Keap1, thereby increasing the expression of anti-oxidant genes through the Nrf2 pathway and reducing the cytotoxicity induced by Brd4 inhibitors. Elimination of ATG3 or KEAP1 expression using CRISPR-cas9 mediated genomic editing markedly reduced autophagy. We conclude that Brd4 plays a significant role in autophagy activation through the direct transcriptional regulation of genes essential for it, as well as through the Keap1-Nrf2 axis in NPMc+ and MLL-fusion AML cells.

Acute myeloid leukemia (AML) is the second most common type of leukemia in adults. Incidence of AML increases with age with a peak incidence at 67 years. Patients older than 60 years have an unfavorable prognosis due to resistance to conventional chemotherapy. Volasertib (BI 6727) is a cell-cycle regulator targeting polo-like kinase which has been evaluated in clinical trials in AML. We evaluated effects of volasertib in primary patient samples and NK cells. At equivalent doses, volasertib is cytotoxic to AML blasts but largely spares healthy NK cells. We then evaluated the effect of volasertib treatment in combination with BI 836858 on primary AML blast samples using antibody-dependent cellular cytotoxicity (ADCC) assays. Volasertib treatment of NK cells did not impair NK function as evidenced by comparable levels of BI 836858 mediated ADCC in both volasertib-treated and control-treated NK cells. In summary, volasertib is cytotoxic to AML blasts while sparing NK cell viability and function. Higher BI 836858 mediated ADCC was observed in patient samples pretreated with volasertib. These findings provide a strong rationale to test combination of BI 836858 and volasertib in AML.

// Hamid Sayar 1,* , Yan Liu 4,* , Rui Gao 4 , Mohammad Abu Zaid 1 , Larry D. Cripe 1 , Jill Weisenbach 5 , Katie J. Sargent 5 , Mehdi Nassiri 2 , Lang Li 3 , Heiko Konig 1 , Attaya Suvannasankha 1 , Feng Pan 4 , Rajasubramaniam Shanmugam 1,7 , Chirayu Goswami 3 , Reuben Kapur 4 , Mingjiang Xu 4 and H. Scott Boswell 1,6 1 Indiana University Melvin and Bren Simon Cancer Center, Department of Medicine, Hematology/Oncology Division, Indiana University School of Medicine, Indianapolis, IN, USA 2 Department of Hematopathology, Indiana University School of Medicine, Indianapolis, IN, USA 3 Biostatistics and Computational Biology, Indiana University School of Medicine, Indianapolis, IN, USA 4 Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA 5 Indiana University Health Systems, Indianapolis, IN, USA 6 Veterans Affairs Medical Center, Indianapolis, IN, USA 7 ICMR, National Institute for Research in Tribal Health, Jabalpur, India * These authors contributed equally to this work Correspondence to: Hamid Sayar, email: // Yan Liu, email: // Keywords : AML; sorafenib; vorinostat; bortezomib; epigenetics Received : August 25, 2017 Accepted : October 25, 2017 Published : December 25, 2017 Abstract Co-occurrence of Flt3ITD and TET2 mutations provoke an animal model of AML by epigenetic repression of Wnt pathway antagonists, including RUNX3, and by hyperexpression of ID1, encoding Wnt agonist. These affect HOXA over-expression and treatment resistance. A comparable epigenetic phenotype was identified among adult AML patients needing novel intervention. We chose combinations of targeted agents acting on distinct effectors, at the levels of both signal transduction and chromatin remodeling, in relapsed/refractory AML’s, including Flt3ITD+ve, described with a signature of repressed tumor suppressor genes, involving Wnt antagonist RUNX3 , occurring along with ID1 and HOXA over-expressions. We tracked patient response to combination of Flt3/Raf inhibitor, Sorafenib, and Vorinostat, pan-histone deacetylase inhibitor, without or with added Bortezomib, in consecutive phase I trials. A striking association of rapid objective remissions (near-complete, complete responses) was noted to accompany induced early pharmacodynamic changes within patient blasts in situ, involving these effectors, significantly linking RUNX3 /Wnt antagonist de-repression (80%) and ID1 downregulation (85%), to a response, also preceded by profound HOXA9 repression. Response occurred in context of concurrent TET2 mutation/hypomorphy and Flt3ITD+ve mutation (83% of complete responses). Addition of Bortezomib to the combination was vital to attainment of complete response in Flt3ITD+ve cases exhibiting such Wnt pathway dysregulation.

This study was performed to assess if a recently recommended genomic classification is predictive in patients with normal-karyotype (NK) acute myeloid leukemia (AML). A total of 393 patients were included. Analysis of genetic mutations was performed using targeted resequencing with an Illumina Hiseq 2000. We identified driver mutations across 40 genes, with one or more driver mutations identified in 95.7% of patients. The molecular subclassification was as follows: 34.6% patients (n = 136) with AML with the NPM1 mutation, 10.7% (n = 42) with AML with mutated chromatin or RNA-splicing genes or both, 1.5% (n = 6) with AML with TP53 mutations, 13.5% (n = 53) with AML with biallelic CEBPA mutations, 2.0% (n = 8) with AML with IDH2-R172 mutations and no other class-defining lesion, 29.5% (n = 116) with AML with driver mutations but no detected class-defining lesion, 4.3% (n = 17) with AML with no detected driver mutation, and 3.8% (n = 15) patients with AML who met the criteria for ≥2 genomic subgroups. The 5-year overall survival and relapse rate of subgroup in AML with mutated chromatin, RNA-splicing genes, or both was 11.6% (95% CI = 1.4–21.8%) and 71.4% (95% CI = 45.7–86.5%), respectively. This study suggests that the recently recommended genomic classification is an appropriate and replicable categorization system in the NK AML population. The subgroup of AML with mutated chromatin, RNA-splicing genes, or both showed extremely poor survival in NK-AML; thus, a novel approach is needed to improve their prognosis.

Using next generation sequencing we have systematically analyzed a large cohort of 489 patients with bone marrow failure (BMF), including myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), aplastic anemia (AA), and related conditions for the presence of germline (GL) alterations in Fanconi Anemia (FA) and telomerase genes. We have detected an increased frequency of heterozygous FA gene mutations in MDS and to lesser degree in AML suggesting that the presence of one normal allele may not be completely protective and indeed heterozygous FA lesions may have a long latency period before hematologic manifestation. In contrast, GL telomerase gene mutations were not associated with increased disease risk. When compared to large control cohorts, we have not detected an increased frequency of damaging variants among telomerase complex genes, including those previously believed to be involved in the pathogenesis of AA. Our results may suggest that while low penetrance and delayed disease onset can confound identification of genetic predisposition factors, GL FA alterations can be also associated with MDS.

Azacitidine (AZA) for higher risk MDS patients is a standard therapy with limited durability. To monitor mutation dynamics during AZA therapy we utilized massive parallel sequencing of 54 genes previously associated with MDS/AML pathogenesis. Serial sampling before and during AZA therapy of 38 patients (reaching median overall survival 24 months (Mo) with 60% clinical responses) identified 116 somatic pathogenic variants with allele frequency (VAF) exceeding 5%. High accuracy of data was achieved via duplicate libraries from myeloid cells and T-cell controls. We observed that nearly half of the variants were stable while other variants were highly dynamic. Patients with marked decrease of allelic burden upon AZA therapy achieved clinical responses. In contrast, early-progressing patients on AZA displayed minimal changes of the mutation pattern. We modeled the VAF dynamics on AZA and utilized a joint model for the overall survival and response duration. While the presence of certain variants associated with clinical outcomes, such as the mutations of CDKN2A were adverse predictors while KDM6A mutations yield lower risk of dying, the data also indicate that allelic burden volatility represents additional important prognostic variable. In addition, preceding 5q- syndrome represents strong positive predictor of longer overall survival and response duration in high risk MDS patients treated with AZA. In conclusion, variants dynamics detected via serial sampling represents another parameter to consider when evaluating AZA efficacy and predicting outcome.

// Huda Salman 1, 2 , Xiao Shuai 2, 3, * , Anh Thu Nguyen-Lefebvre 1, * , Banabihari Giri 1 , Mingqiang Ren 1 , Michael Rauchman 4 , Lynn Robbins 4 , Wei Hou 2 , Hasan Korkaya 1 and Yupo Ma 2 1 Georgia Regent University Cancer Center, Augusta, GA, USA 2 Present address: Stony Brook University Cancer Center, Stony Brook, NY, USA 3 Department of Hematology, West China hospital of Sichuan University, Chengdu, P.R. China 4 Department of Nephrology, Saint Louis University, St Louis, MO, USA * These authors contributed equally to this work Correspondence to: Huda Salman, email: huda.salman@stonybrookmedicine.edu Keywords: SALL1; AML Received: August 18, 2017 Accepted: October 25, 2017 Published: December 15, 2017 ABSTRACT Similar signaling pathways could operate in both normal hematopoietic stem and progenitor cells (HSPCs) and leukemia stem cells (LSCs). Thus, targeting LSCs signaling without substantial toxicities to normal HSPCs remains challenging. SALL1, is a member of the transcriptional network that regulates stem cell pluripotency, and lacks significant expression in most adult tissues, including normal bone marrow (NBM). We examined the expression and functional characterization of SALL1 in NBM and in acute myeloid leukemia (AML) using in vitro and in vivo assays. We showed that SALL1 is expressed preferentially in LSCs- enriched CD34+CD38- cell subpopulation but not in NBM. SALL1 inhibition resulted in decreased cellular proliferation and in inferior AML engraftment in NSG mice and it was also associated with upregulation of PTEN and downregulation of m-TOR, β-catenin, and NF- қB expression. These findings suggest that SALL1 inhibition interrupts leukemogenesis. Further studies to validate SALL1 as a potential biomarker for minimal residual disease (MRD) and to determine SALL1’s role in prognostication are ongoing. Additionally, pre-clinical evaluation of SALL1 as a therapeutic target in AML is warranted.

PTPN11 gain-of-function mutation is the most common mutation found in patients with juvenile myelomonocytic leukemia and DNMT3A loss occurs in over 20% of acute myeloid leukemia patients. We studied the combined effect of both Ptpn11 gain-of-function mutation (D61Y) and Dnmt3a haploinsufficiency on mouse hematopoiesis, the presence of which has been described in both juvenile myelomonocytic leukemia and acute myeloid leukemia patients. Double mutant mice rapidly become moribund relative to any of the other genotypes, which is associated with enlargement of the spleen and an increase in white blood cell counts. An increase in the mature myeloid cell compartment as reflected by the presence of Gr1+Mac1+ cells was also observed in double mutant mice relative to any other group. Consistent with these observations, a significant increase in the absolute number of granulocyte macrophage progenitors (GMPs) was seen in double mutant mice. A decrease in the lymphoid compartment including both T and B cells was noted in the double mutant mice. Another significant difference was the presence of extramedullary erythropoiesis with increased erythroid progenitors in the spleens of Dnmt3a+/-;D61Y mice relative to other groups. Taken together, our results suggest that the combined haploinsufficiency of Dnmt3a and presence of an activated Shp2 changes the composition of multiple hematopoietic lineages in mice relative to the individual heterozygosity of these genes.

// Rodica P. Bunaciu 1 , Robert J. MacDonald 1 , Feng Gao 1, 4, 5 , Lynn M. Johnson 3 , Jeffrey D. Varner 4 , Xin Wang 5 , Sarah Nataraj 2 , Monica L. Guzman 2 and Andrew Yen 1 1 Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA 2 Division of Hematology and Medical Oncology, Department of Medicine, Weill Cornell Medical College, New York, NY, USA 3 Cornell Statistical Unit, Cornell University, Ithaca, NY, USA 4 Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA 5 Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China Correspondence to: Andrew Yen, email: ay13@cornell.edu , rpb78@cornell.edu Keywords: retinoic acid; c-Raf; c-Cbl; AML; precision oncology Received: October 16, 2017 Accepted: December 09, 2017 Published: December 23, 2017 ABSTRACT Acute myeloid leukemia (AML) has high mortality rates, perhaps reflecting a lack of understanding of the molecular diversity in various subtypes and a lack of known actionable targets. There are currently 12 open clinical trials for AML using combination therapeutic modalities including all- trans retinoic acid (RA). Mutant nucleophosmin-1, proposed as a possible marker for RA response, is the criterion for recruiting patients in three active RA phase 3 clinical trials. We tested the ability of RA alone or in combination with either bosutinib (B) or 6-formylindolo(3,2-b) carbazole (F) to induce conversion of 12 de novo AML samples toward a more differentiated phenotype. We assessed levels of expression of cell surface markers associated with differentiation, aldehyde dehydrogenase activity, and glucose uptake activity. Colony formation capacity was reduced with the combined treatment of RA and B or F, and correlated with modulation of a c-Cbl/Lyn/c-Raf-centered signalsome. Combination treatment was in most cases more effective than RA alone. Based on their responses to the treatments, some primary leukemic samples cluster closer to HL-60 cells than to other primary samples, suggesting that they may represent a hitherto undefined AML subtype that is potentially responsive to RA in a combination differentiation therapy.

Dormant leukaemia initiating cells in the bone marrow niche are a crucial therapeutic target for total eradication of acute myeloid leukaemia. To study this cellular subset we created and validated an in vitro model employing the cell line TF-1a, treated with Transforming Growth Factor β1 (TGFβ1) and a mammalian target of rapamycin inhibitor. The treated cells showed decreases in total RNA, Ki-67 and CD71, increased aldehyde dehydrogenase activity, forkhead box 03A (FOX03A) nuclear translocation and growth inhibition, with no evidence of apoptosis or differentiation. Using human genome gene expression profiling we identified a signature enriched for genes involved in adhesion, stemness/inhibition of differentiation and tumour suppression as well as canonical cell cycle regulation. The most upregulated gene was the osteopontin-coding gene SPP1. Dormant cells also demonstrated significantly upregulated beta 3 integrin (ITGB3) and CD44, as well as increased adhesion to their ligands vitronectin and hyaluronic acid as well as to bone marrow stromal cells. Immunocytochemistry of bone marrow biopsies of AML patients confirmed the positive expression of osteopontin in blasts near the para-trabecular bone marrow, whereas osteopontin was rarely detected in mononuclear cell isolates. Unsupervised hierarchical clustering of the dormancy gene signature in primary acute myeloid leukaemia samples from the Cancer Genome Atlas identified a cluster enriched for dormancy genes associated with poor overall survival.

The bone marrow microenvironment protects acute myeloid leukemia (AML) cells during chemotherapy and is a major factor in relapse. Here, we examined which type(s) of bone marrow cells are responsible for the relapse of AML following treatment with cytarabine (Ara-C), and we identified a means to inhibit this protection. To determine the protective cell type(s), AML cells were treated with Ara-C, and AML cell survival in the presence or absence of osteoblast lineage cells was assessed. Cultured AML cells and patient bone marrow isolates were each significantly protected from Ara-C-induced apoptosis by co-culture with differentiating osteoblasts. Moreover, pretreating differentiating osteoblasts with the histone deacetylase inhibitors (HDACi) vorinostat and panobinostat abrogated the ability of the differentiating osteoblasts to protect AML cells. Together, our results indicate that differentiating osteoblasts have the potential to promote residual AML in the bone marrow following standard chemotherapy and act via a mechanism requiring HDACi-sensitive gene expression. Using HDACi to target the leukemic microenvironment in combination with Ara-C could potentially improve treatment of AML. Moreover, other strategies for manipulating bone marrow osteoblasts may also help eradicate AML cells and reduce relapse.

// Julia K. Herzig 1 , Lars Bullinger 1 , Alpaslan Tasdogan 2, 6 , Philipp Zimmermann 1 , Martin Schlegel 1 , Veronica Teleanu 1 , Daniela Weber 1 , Frank G. Rucker 1 , Peter Paschka 1 , Anna Dolnik 1 , Edith Schneider 1 , Florian Kuchenbauer 1 , Florian H. Heidel 4, 5 , Christian Buske 3 , Hartmut Dohner 1 , Konstanze Dohner 1, * and Verena I. Gaidzik 1, * 1 Department of Internal Medicine III, University Hospital of Ulm, Ulm, Germany 2 Institute of Immunology, Ulm University, Ulm, Germany 3 Institute of Experimental Cancer Research, University Hospital of Ulm, Ulm, Germany 4 Leibniz Institute on Aging–Fritz Lipmann Institute, Jena, Germany 5 Innere Medizin II, Hamatologie und Onkologie, Universitatsklinikum Jena, Jena, Germany 6 Current/Present address: Children’s Medical Center Research Institute, UT Southwestern, Dallas, TX, USA * These authors contributed equally to this work Correspondence to: Verena I. Gaidzik, email: Verena.Gaidzik@uniklinik-ulm.de Keywords: AML, gene deletion, 3p, PPP4R2, DNA repair Received: June 16, 2017 Accepted: September 03, 2017 Published: September 21, 2017 ABSTRACT We have previously identified a recurrent deletion at chromosomal band 3p14.1-p13 in patients with acute myeloid leukemia (AML). Among eight protein-coding genes, this microdeletion affects the protein phosphatase 4 regulatory subunit 2 ( PPP4R2 ), which plays an important role in DNA damage response (DDR). Investigation of mRNA expression during murine myelopoiesis determined that Ppp4r2 is higher expressed in more primitive hematopoietic cells. PPP4R2 expression in primary AML samples compared to healthy bone marrow was significantly lower, particularly in patients with 3p microdeletion or complex karyotype. To identify a functional role of PPP4R2 in hematopoiesis and leukemia, we genetically inactivated Ppp4r2 by RNAi in murine hematopoietic stem and progenitor cells and murine myeloid leukemia. Furthermore, we ectopically expressed PPP4R2 in a deficient human myeloid leukemic cell line. While PPP4R2 is involved in DDR of both hematopoietic and leukemic cells, our findings indicate that PPP4R2 deficiency impairs de-phosphorylation of phosphorylated key DDR proteins KRAB-domain associated protein 1 (pKAP1), histone variant H2AX (γH2AX), tumor protein P53 (pP53), and replication protein A2 (pRPA2). Potential impact of affected DNA repair processes in primary AML cases with regard to differential PPP4R2 expression or 3p microdeletion is also supported by our results obtained by gene expression profiling and whole exome sequencing. Impaired DDR and increased DNA damage by PPP4R2 suppression is one possible mechanism by which the 3p microdeletion may contribute to the pathogenesis of AML. Further studies are warranted to determine the potential benefit of inefficient DNA repair upon PPP4R2 deletion to the development of therapeutic agents.

// Hasan Mahmud 1, 2 , Frank J.G. Scherpen 1 , Tiny Meeuwsen de Boer 1 , Harm-Jan Lourens 1 , Caroline Schoenherr 3 , Matthias Eder 3 , Michaela Scherr 3 , Victor Guryev 4 and Eveline S. De Bont 1 1 Department of Pediatric Oncology/Hematology, Beatrix Children’s Hospital, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands 2 Stephenson Cancer Center, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA 3 Department of Hematology, Hemostasis, Oncology and Stem Cell Transplantation, Hannover Medical School, Hannover, Germany 4 Laboratory of Genome Structure and Aging, European Research Institute for the Biology of Aging, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands Correspondence to: Eveline S. De Bont, email: e.s.j.m.de.bont@umcg.nl Keywords: AML, leukemia, t(8;21), PLC-γ1, peptide microarray Received: February 21, 2017 Accepted: May 01, 2017 Published: June 27, 2017 ABSTRACT The t(8;21) (q22;q22) chromosomal translocation is one of the most frequent genetic alterations in acute myeloid leukemia (AML) which has a need for improved therapeutic strategies. We found PLC-γ1 as one of the highest phosphorylated peptides in t(8;21) AML samples compared to NBM or CN-AML in our previous peptide microarray. PLC-γ1 is known to play a role in cancer progression, however, the impact of PLC-γ1 in AML is currently unknown. Therefore, we aimed to study the functional role of PLC-γ1 by investigating the cellular growth, survival and its underlying mechanism in t(8;21) AML. In this study, PLC-γ1 expression was significantly higher in t(8;21) AML compared to other karyotypes. The PLC-γ1 protein expression was suppressed in AML1-ETO knock down cells indicating that it might induce kasumi-1 cell death. ShRNA-mediated PLC-γ1 knockdown in kasumi-1 cells significantly blocked cell growth, induced apoptosis and cell cycle arrest which was explained by the increased activation of apoptotic related and cell cycle regulatory protein expressions. Gene expression array analysis showed the up-regulation of apoptotic and DNA damage response genes together with the downregulation of cell growth, proliferation and differentiation genes in the PLC-γ1 suppressed kasumi-1 cells, consistent with the observed phenotypic effects. Importantly, PLC-γ1 suppressed kasumi-1 cells showed higher chemosensitivity to the chemotherapeutic drug treatments and lower cell proliferation upon hypoxic stress. Taken together, these in vitro finding strongly support an important role for PLC-γ1 in the survival of t(8;21) AML mimicking kasumi-1 cells and identify PLC-γ1 as a potential therapeutic target for t(8;21) AML treatment.

// Yoshiya Adachi 1 , Yuichi Ishikawa 1 and Hitoshi Kiyoi 1 1 Department of Hematology and Oncology, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan Correspondence to: Yuichi Ishikawa, email: yishikaw@med.nagoya-u.ac.jp Keywords: AML, PLK1 inhibitor, volasertib, resistance, MDR1 Received: March 06, 2017 Accepted: July 03, 2017 Published: July 26, 2017 ABSTRACT Volasertib, a selective PLK1 inhibitor, was effective for acute myeloid leukemia (AML) patients in clinical trials. However, its efficacy was limited in mono-therapy, and a higher incidence of fatal events was revealed in the combination with low-dose cytarabine. Thus, optimization of combination therapy with volasertib and other agents is necessary for its clinical development, and the predictive factors for response or resistance to volasertib remain largely unknown. In this study, we investigated the resistance mechanism in volasertib-resistant cell lines and the combination effects with other agents, such as azacitidine (AZA), on AML cells. We identified that mutations in the ATP-binding domain of PLK1 and expression of MDR1 conferred resistance to volasertib. In the combination therapy, the effects of AZA differed among cells, but were prominent in the cells with higher GI 50 values of volasertib in mono-therapy. Furthermore, we identified that the cells in G2/M phase were more sensitive to volasertib, and the PI3K/AKT pathway was up-regulated upon administration of volasertib. Combination therapies with the agents that caused cell cycle accumulation in G2/M phase or with PI3K inhibitor were highly potent against AML cells. Our findings provide strategies for further clinical development of volasertib and PLK inhibitors for AML.

Cytogenetics and European Leukemia Net (ELN) genetic classification predict patients at increased risk of relapse in acute myeloid leukemia (AML) except in the intermediate risk group for which further prognostic determinants are required. We have previously shown that Natural Killer (NK) cell defects in AML are predictors of poor overall survival (OS). This study aimins at validating NKp30, a receptor that mediates NK activation, as a prognostic biomarker for AML patients with intermediate prognosis. NKp30 expression was prospectively assessed at diagnosis on NK cells from peripheral blood by flow cytometry (N = 201 patients). Clinical outcome was evaluated with regard to NKp30 status. In patients with intermediate cytogenetic (N = 162), NKp30high phenotype at diagnosis was predictive of better OS (HR = 0.26; 95%CI = [0.14-0.50]; P < 0.0001) and relapse-free survival (RFS) (HR = 0.21; 95%CI = [0.08-0.52]; P = 0.0007). In patients with intermediate ELN (N = 116), NKp30high phenotype at diagnosis was predictive of better OS (HR = 0.33; 95%CI = [0.16–0.67]; P = 0.0019) and RFS (HR = 0.24; 95%CI = [0.08-0.67]; P = 0.0058). In multivariate analysis, high NKp30 expression independently predicted improved OS (HR = 0.56, P = 0.046) and RFS (HR = 0.37, P = 0.048). Consistently, cumulative incidence of relapse (CIR) was lower in patients with high NKp30 expression (HR = 0.37, P = 0.026). In conclusion, we propose NKp30 status as a simple and early prognostic biomarker that identifies intermediate-risk patients with poor prognosis who otherwise may not be identified with existing risk stratification systems.

// Tomasz Rzymski 1, * , Michal Mikula 2, * , Eliza Żylkiewicz 1 , Agnieszka Dreas 1 , Katarzyna Wiklik 1 , Aniela Golas 1 , Katarzyna Wojcik 1 , Magdalena Masiejczyk 1 , Anna Wrobel 1 , Izabela Dolata 1 , Agata Kitlinska 1 , Malgorzata Statkiewicz 2 , Urszula Kuklinska 2 , Krzysztof Goryca 2 , Łukasz Sapala 1 , Aleksandra Grochowska 3 , Aleksandra Cabaj 2, 4 , Malgorzata Szajewska-Skuta 1 , Ewelina Gabor-Worwa 1 , Katarzyna Kucwaj 1 , Arkadiusz Bialas 1 , Adam Radzimierski 1 , Michal Combik 1 , Jakub Woyciechowski 1 , Maciej Mikulski 1 , Renata Windak 1 , Jerzy Ostrowski 2, 3 and Krzysztof Brzozka 1 1 R&D Department, Selvita S.A., Krakow, Poland 2 Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center, Warsaw, Poland 3 Department of Gastroenterology, Hepatology and Clinical Oncology, Medical Center for Postgraduate Education, Warsaw, Poland 4 Laboratory of Bioinformatics, Nencki Institute of Experimental Biology, Warsaw, Poland * These authors have contributed equally to this work Correspondence to: Krzysztof Brzozka, email: krzysztof.brzozka@selvita.com Keywords: CDK8 mediator, kinase inhibitor, STAT5, AML, leukemia stem cells Received: August 04, 2016 Accepted: March 09, 2017 Published: April 04, 2017 ABSTRACT Inhibition of oncogenic transcriptional programs is a promising therapeutic strategy. A substituted tricyclic benzimidazole, SEL120-34A, is a novel inhibitor of Cyclin-dependent kinase 8 (CDK8), which regulates transcription by associating with the Mediator complex. X-ray crystallography has shown SEL120-34A to be a type I inhibitor forming halogen bonds with the protein’s hinge region and hydrophobic complementarities within its front pocket. SEL120-34A inhibits phosphorylation of STAT1 S727 and STAT5 S726 in cancer cells in vitro . Consistently, regulation of STATs- and NUP98-HOXA9- dependent transcription has been observed as a dominant mechanism of action in vivo . Treatment with the compound resulted in a differential efficacy on AML cells with elevated STAT5 S726 levels and stem cell characteristics. In contrast, resistant cells were negative for activated STAT5 and revealed lineage commitment. In vivo efficacy in xenotransplanted AML models correlated with significant repression of STAT5 S726. Favorable pharmacokinetics, confirmed safety and in vivo efficacy provide a rationale for the further clinical development of SEL120-34A as a personalized therapeutic approach in AML.

Azacitidine (AZA), the reference treatment for most higher-risk myelodysplastic (MDS) patients can also improve overall survival (OS) in elderly acute myeloid leukemia (AML) patients ineligible for intensive chemotherapy, but reliable biological markers predicting response and OS in patients treated with AZA are lacking. In a preliminary study, we found that an increase of the percentage of BCL2L10, an anti-apoptotic member of the bcl-2 family, was correlated with AZA resistance. In this study, we assessed prospectively by flow cytometry the prognostic value of BCL2L10 positive bone marrow mononuclear cells in 70 patients (42 MDS and 28 AML), prior to AZA treatment. In patients with baseline marrow blasts below 30%, the baseline percentage of bone marrow BCL2L10 positive cells inversely correlated with response to AZA and OS independently of the International Prognostic Scoring System (IPSS) and IPSS-revised (IPSS-R). Specifically, OS was significantly lower in patients with more than 10% BCL2L10 positive cells (median 8.3 vs 22.9 months in patients with less than 10% positivity, p = 0,001). In summary, marrow BCL2L10 positive cells may be a biomarker for azacitidine response and OS, with a potential impact in clinical practice.

// Emily-Marie Latuske 1 , Hauke Stamm 1 , Marianne Klokow 1 , Gabi Vohwinkel 1 , Jana Muschhammer 1 , Carsten Bokemeyer 1 , Manfred Jucker 2 , Maxim Kebenko 1 , Walter Fiedler 1 , Jasmin Wellbrock 1 1 Department of Oncology, Hematology and Bone Marrow Transplantation with Section Pneumology, Hubertus Wald University Cancer Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany 2 Institute of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Hamburg, Germany Correspondence to: Walter Fiedler, email: fiedler@uke.de Keywords: Hedgehog, non-canonical, GLI, FLT3, AML Received: July 22, 2016 Accepted: February 20, 2017 Published: March 16, 2017 ABSTRACT Activation of the Hedgehog pathway has been implicated in the pathogenesis of several tumor types including myeloid leukemia. Previously we demonstrated that overexpression of Hedgehog downstream mediators GLI1/2 confers an adverse prognosis to patients with acute myeloid leukemia (AML) and is correlated with a FLT3 mutated status. To analyze a possible non-canonical activation of the Hedgehog pathway via FLT3 and PI3K, we performed blocking experiments utilizing inhibitors for FLT3 (sunitinib), PI3K (PF-04691502) and GLI1/2 (GANT61) in FLT3-mutated and FLT3 wildtype AML cell lines and primary blasts. Combination of all three compounds had stronger anti-leukemic effects in FLT3-mutated compared to FLT3 wildtype AML cells in vitro . Interestingly, the colony growth of normal CD34 + cells from healthy donors was not impeded by the triple inhibitor combination possibly opening a therapeutic window for the clinical use of inhibitor combinations. Besides, combined treatment with sunitinib, PF-04691502 and GANT61 significantly prolonged the survival of mice transplanted with FLT3-mutated MV4-11 cells compared to the single agent treatments. Furthermore, the inhibition of FLT3 and PI3K resulted in reduced GLI protein expression and promotor activity in FLT3-mutated but not in FLT3 wildtype AML cell lines in western blotting and GLI1/2 promoter assays supporting our hypothesis of non-canonical GLI activation via FLT3. In summary, FLT3-mutated in contrast to FLT3 wildtype cells or normal human hematopoietic progenitor cells are exquisitely sensitive to combined inhibition by FLT3, PI3K and GLI1/2 overcoming some of the limitations of current FLT3 directed therapy in AML. The development of GLI1/2 inhibitors is highly desirable.

// Christina Krupka 1, 2, 3 , Felix S. Lichtenegger 1, 2, 3 , Thomas Kohnke 1, 2, 3 , Jan Bogeholz 4 , Veit Bucklein 1, 2, 3 , Michael Roiss 1, 2, 3 , Torben Altmann 1, 2, 3 , To Uyen Do 5 , Rachel Dusek 5 , Keith Wilson 5, * , Arnima Bisht 5 , Jon Terrett 6, * , Dee Aud 6, * , Esteban Pombo-Villar 5, * , Christian Rohlff 5 , Wolfgang Hiddemann 1 , Marion Subklewe 1, 2, 3 1 Department of Internal Medicine III, Klinikum of The LMU Munich, Munich, Germany 2 Clinical Cooperation Group Immunotherapy at The Helmholtz Institute Munich, Munich, Germany 3 Laboratory of Translational Cancer Immunology, Gene Center Munich, Ludwig-Maximilians-University, Munich, Germany 4 Department of Hematology, University Hospital Zurich, Zurich, Switzerland 5 Independent consultant Oxford BioTherapeutics Ltd, Abingdon, United Kingdom and San Jose, CA, USA 6 CRISPR Therapeutics, Cambridge, MA, USA * Were employed at Oxford Biotherapeutics at the time the data was generated Correspondence to: Subklewe Marion, email: Marion.Subklewe@med.uni-muenchen.de Keywords: AML, Immunotherapy, CD157, Antibody, Fc-engineering Received: November 01, 2016 Accepted: February 27, 2017 Published: March 09, 2017 ABSTRACT Antibody-based immunotherapy represents a promising strategy to eliminate chemorefractory leukemic cells in acute myeloid leukemia (AML). In this study, we evaluated a novel Fc-engineered antibody against CD157 (MEN1112) for its suitability as immunotherapy in AML. CD157 was expressed in 97% of primary AML patient samples. A significant, albeit lower expression level of CD157 was observed within the compartment of leukemia-initiating cells, which are supposed to be the major source of relapse. In healthy donor bone marrow, CD157 was expressed on CD34 + cells. In ex vivo assays, MEN1112 triggered natural killer (NK) cell-mediated cytotoxicity against AML cell lines and primary AML cells. Compared to its parental analogue, the Fc-engineered antibody exhibited higher antibody dependent cellular cytotoxicity responses. Using NK cells from AML patients, we observed heterogeneous MEN1112-mediated cytotoxicity against AML cells, most likely due to well-documented defects in AML-NK cells and corresponding inter-patient variations in NK cell function. Cytotoxicity could not be correlated to the time after completion of chemotherapy. In summary, we could demonstrate that CD157 is strongly expressed in AML. MEN1112 is a promising antibody construct that showed high cytotoxicity against AML cells and warrants further clinical testing. Due to variability in NK-cell function of AML patients, the time of application during the course of the disease as well as combinatorial strategies might influence treatment results.

// Dominik Schnerch 1 , Julia Schuler 2 , Marie Follo 1 , Julia Felthaus 1 , Dagmar Wider 1 , Kathrin Klingner 2 , Christine Greil 1 , Justus Duyster 1 , Monika Engelhardt 1 , Ralph Wasch 1 1 Department of Hematology, Oncology and Stem Cell Transplantation, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany 2 Oncotest GmbH, Freiburg, Germany Correspondence to: Ralph Wasch, email: ralph.waesch@uniklinik-freiburg.de Keywords: AML, antimitotic therapy, APC/C, mitotic slippage, proteasome inhibition Received: December 22, 2016 Accepted: February 07, 2017 Published: February 18, 2017 ABSTRACT Elderly and frail patients, diagnosed with acute myeloid leukemia (AML) and ineligible to undergo intensive treatment, have a dismal prognosis. The small molecule inhibitor volasertib induces a mitotic block via inhibition of polo-like kinase 1 and has shown remarkable anti-leukemic activity when combined with low-dose cytarabine. We have demonstrated that AML cells are highly vulnerable to cell death in mitosis yet manage to escape a mitotic block through mitotic slippage by sustained proteasome-dependent slow degradation of cyclin B. Therefore, we tested whether interfering with mitotic slippage through proteasome inhibition arrests and kills AML cells more efficiently during mitosis. We show that therapeutic doses of bortezomib block the slow degradation of cyclin B during a volasertib-induced mitotic arrest in AML cell lines and patient-derived primary AML cells. In a xenotransplant mouse model of human AML, mice receiving volasertib in combination with bortezomib showed superior disease control compared to mice receiving volasertib alone, highlighting the potential therapeutic impact of this drug combination.

The type III receptor tyrosine kinase FLT3 is one of the most commonly mutated oncogenes in acute myeloid leukemia (AML). Inhibition of mutated FLT3 in combination with chemotherapy has displayed promising results in clinical trials. However, one of the major obstacles in targeting FLT3 is the development of resistant disease due to secondary mutations in FLT3 that lead to relapse. FLT3 and its oncogenic mutants signal through associating proteins that activate downstream signaling. Thus, targeting proteins that interact with FLT3 and their downstream signaling cascades can be an alternative approach to treat FLT3-dependent AML. We used an SH2 domain array screen to identify novel FLT3 interacting proteins and identified ABL2 as a potent interacting partner of FLT3. To understand the role of ABL2 in FLT3-mediated biological and cellular events, we used the murine pro-B cell line Ba/F3 as a model system. Overexpression of ABL2 in Ba/F3 cells expressing an oncogenic mutant of FLT3 (FLT3-ITD) resulted in partial inhibition of FLT3-ITD-dependent cell proliferation and colony formation. ABL2 expression did not alter the kinase activity of FLT3, its ubiquitination or its stability. However, it partially blocked FLT3-induced AKT phosphorylation without affecting ERK1/2 and p38 activation. Taken together our data suggest that ABL2 acts as negative regulator of signaling downstream of FLT3.

// Jae-Sook Ahn 1, 2 , Hyeoung-Joon Kim 1, 2 , Yeo-Kyeoung Kim 1, 2 , Seung-Shin Lee 1 , Seo-Yeon Ahn 1 , Sung-Hoon Jung 1 , Deok-Hwan Yang 1 , Je-Jung Lee 1 , Hee Jeong Park 2 , Seung Hyun Choi 2 , Chul Won Jung 3 , Jun-Ho Jang 3 , Hee Je Kim 4 , Joon Ho Moon 5 , Sang Kyun Sohn 5 , Jong-Ho Won 6 , Sung-Hyun Kim 7 , Szardenings Michael 8 , Mark D. Minden 9 , Dennis Dong Hwan Kim 9 1 Hematology-Oncology, Chonnam National University Hwasun Hospital, Jeollanam-do, Republic of Korea 2 Genomic Research Center for Hematopoietic Diseases, Chonnam National University Hwasun Hospital, Jeollanam-do, Republic of Korea 3 Division of Hematology-Oncology, Samsung Medical Center, Seoul, Republic of Korea 4 Department of Hematology, Cancer Research Institute, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea 5 Department of Hematology-Oncology, Kyungpook National University Hospital, Daegu, Republic of Korea 6 Department of Hematology-Oncology, Soon Chun Hyang University Hospital, Seoul, Republic of Korea 7 Department of Hematology-Oncology, Dong-A University College of Medicine, Busan, Republic of Korea 8 Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany 9 Department of Medical Oncology and Hematology, Princess Margaret Cancer Centre, University of Toronto, Toronto, Canada Correspondence to: Hyeoung-Joon Kim, email: hjoonk@chonnam.ac.kr Keywords: TET2 , IDH1/2, 5hmC, normal karyotype, AML Received: July 25, 2016 Accepted: November 24, 2016 Published: December 26, 2016 ABSTRACT Stem cells display remarkably high levels of 5-hydroxymethylcytosine (5hmC). Both TET2 and IDH1/2 mutations can impair the production of 5hmC, thus decreasing 5hmC levels. TET2 or IDH1/2 mutations are commonly observed in acute myeloid leukemia (AML). However, the implications of 5hmC on survival in normal karyotype AML patients have not been fully evaluated. The 5hmC levels were analyzed in 375 patients using ELISA. The levels of 5hmC in DNA samples were converted to a log scale for the analysis and correlations with TET2 and/or IDH1/2 mutations were evaluated. The median 5hmC level was 0.065% (range 0.001–0.999). Mutation rates were 13.1% for TET2 mut , 6.7% for IDH1 mut , and 13.9% for IDH2 mut . The prevalence of TET2 and/or IDH1/2 was 33.1% (124/375). TET2 and IDH1 / 2 mutated patients had significantly lower levels of log(5hmC) compared with patients without TET2 or IDH1/2 mutations ( p 0.05). To identify its prognostic value, we sub-classified the levels of 5hmC into tertiles for 5hmC values. However, there was no significant association between the categories of 5hmC levels and survival or relapse risk (all p >0.05). Patients with TET2 or IDH1/2 mutations had lower levels of 5hmC. The 5hmC levels may not be predictive of survival in patients with normal karyotype AML.

Inversion of chromosome 16 (inv(16)) generates the CBFβ-SMMHC fusion protein and is found in nearly all patients with acute myeloid leukemia subtype M4 with Eosinophilia (M4Eo). Expression of CBFβ-SMMHC is causative for leukemia development, but the molecular mechanisms underlying its activity are unclear. Recently, there have been important advances in defining the role of CBFβ-SMMHC and its binding partners, the transcription factor RUNX1 and the histone deacetylase HDAC8. Importantly, initial trials demonstrate that small molecules targeting these binding partners are effective against CBFβ-SMMHC induced leukemia. This review will discuss recent advances in defining the mechanism of CBFβ-SMMHC activity, as well as efforts to develop new therapies for inv(16) AML.

// Pasqualina Liana Scognamiglio 1, 5, * , Concetta Di Natale 1, * , Marilisa Leone 2 , Roberta Cascella 3 , Cristina Cecchi 3 , Lisa Lirussi 4, 6 , Giulia Antoniali 4 , Domenico Riccardi 1 , Giancarlo Morelli 1 , Gianluca Tell 4 , Fabrizio Chiti 3 , Daniela Marasco 1 1 Department of Pharmacy, CIRPEB: Centro Interuniversitario di Ricerca sui Peptidi Bioattivi-University of Naples “Federico II”, DFM-Scarl, 80134, Naples, Italy 2 Institute of Biostructures and Bioimaging - CNR, 80134, Naples, Italy 3 Section of Biochemistry, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, 50134, Florence, Italy 4 Laboratory of Molecular Biology and DNA repair, Department of Medical and Biological Sciences, University of Udine, 33100, Udine, Italy 5 Permanent address: Center for Advanced Biomaterials for Health Care@CRIB Istituto Italiano di Tecnologia, 80125, Napoli, Italy 6 Permanent address: Department of Clinical Molecular Biology, University of Oslo and Akershus University Hospital, Nordbyhagen, 1474, Norway * Co-first authors Correspondence to: Daniela Marasco, email: daniela.marasco@unina.it Keywords: helical peptides, aggregation phenomena, AML, CD spectroscopy Received: November 02, 2015 Accepted: July 17, 2016 Published: August 01, 2016 ABSTRACT Nucleophosmin (NPM1) is a multifunctional protein that is implicated in the pathogenesis of several human malignancies. To gain insight into the role of isolated fragments of NPM1 in its biological activities, we dissected the C-terminal domain (CTD) into its helical fragments. Here we focus the attention on the third helix of the NPM1-CTD in its wild-type (H3 wt) and AML-mutated (H3 mutA and H3 mutE) sequences. Conformational studies, by means of CD and NMR spectroscopies, showed that the H3 wt peptide was partially endowed with an α-helical structure, but the AML-sequences exhibited a lower content of this conformation, particularly the H3 mutA peptide. Thioflavin T assays showed that the H3 mutE and the H3 mutA peptides displayed a significant aggregation propensity that was confirmed by CD and DLS assays. In addition, we found that the H3 mutE and H3 mutA peptides, unlike the H3 wt, were moderately and highly toxic, respectively, when exposed to human neuroblastoma cells. Cellular localization experiments confirmed that the mutated sequences hamper their nucleolar accumulation, and more importantly, that the helical conformation of the H3 region is crucial for such a localization.

// Xiao-Qing Yuan 1, 2 , Dao-Yu Zhang 1, 2 , Han Yan 1, 2 , Yong-Long Yang 3 , Ke-Wei Zhu 1, 2 , Yan-Hong Chen 1, 2 , Xi Li 1, 2 , Ji-Ye Yin 1, 2 , Xiao-Lin Li 4 , Hui Zeng 4 , Xiao-Ping Chen 1, 2, 5 1 Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha 410008, P. R. China 2 Institute of Clinical Pharmacology, Central South University, Hunan Key Laboratory of Pharmacogenetics, Changsha 410078, P. R. China 3 Department of Pharmacy, Haikou People’s Hospital and Affiliated Haikou Hospital of Xiangya Medical School, Central South University, Haikou 570311, P. R. China 4 Department of Hematology, Xiangya Hospital, Central South University, Changsha 410008, P. R. China 5 Hunan Province Cooperation Innovation Center for Molecular Target New Drug Study, Hengyang 421001, P. R. China Correspondence to: Xiao-Ping Chen, email: chenxp74@hotmail.com Hui Zeng, email: androps2011@hotmail.com Keywords: DNMT3A, polymorphism, AML, chemosensitivity, prognosis Received: January 15, 2016 Accepted: July 26, 2016 Published: August 09, 2016 ABSTRACT DNMT3A mutation is known as a recurrent event in acute myelogenous leukemia (AML) patients. However, association between DNMT3A genetic polymorphisms and AML patients’ outcomes is unknown. DNMT3A 11 SNPs (rs11695471, rs2289195, rs734693, rs2276598, rs1465825, rs7590760, rs13401241, rs7581217, rs749131, rs41284843 and rs7560488) were genotyped in 344 diagnostic non-FAB-M3 AML patients from southern China. Patients underwent combined chemotherapy with cytarabine and anthracyclines. DNMT3A mRNA expression was analyzed in PBMCs from randomly selected AML patients. Multivariate analysis and combined genotype analysis showed that rs2276598 was associated with increased while rs11695471 and rs734693 were associated with decreased chemosensitivity ( P

// Lei Qin 1, 2 , Donye Dominguez 2 , Siqi Chen 2 , Jie Fan 2 , Alan Long 2 , Minghui Zhang 1, 2 , Deyu Fang 3 , Yi Zhang 1 , Timothy M. Kuzel 2 , Bin Zhang 1, 2 1 Biotherapy Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450052, Henan, China 2 Robert H. Lurie Comprehensive Cancer Center, Department of Medicine-Division of Hematology/Oncology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA 3 Department of Pathology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA Correspondence to: Bin Zhang, email: bin.zhang@northwestern.edu Keywords: IL-33, ST2, tolerance, AML, CD8 + T cells Received: February 11, 2016 Accepted: July 27, 2016 Published: August 10, 2016 ABSTRACT Emerging studies suggest that dominant peripheral tolerance is a major mechanism of immune escape in disseminated leukemia. Using an established murine acute myeloid leukemia (AML) model, we here show that systemic administration of recombinant IL-33 dramatically inhibits the leukemia growth and prolongs the survival of leukemia-bearing mice in a CD8 + T cell dependent manner. Exogenous IL-33 treatment enhanced anti-leukemia activity by increasing the expansion and IFN-γ production of leukemia-reactive CD8 + T cells. Moreover, IL-33 promoted dendritic cell (DC) maturation and activation in favor of its cross presentation ability to evoke a vigorous anti-leukemia immune response. Finally, we found that the combination of PD-1 blockade with IL-33 further prolonged the survival, with half of the mice achieving complete regression. Our data establish a role of exogenous IL-33 in reversing T cell tolerance, and suggest its potential clinical implication into leukemia immunotherapy.

Treatment of acute promyelocytic leukemia (APL) with all-trans retinoic acid (ATRA) is the first example of targeted therapy. In fact, the oncogenic fusion-protein (PML-RAR) typical of this leukemia contains the retinoid-nuclear-receptor RARalpha. PML-RAR is responsible for the differentiation block of the leukemic blast. Besides PML-RAR, two endogenous RARalpha proteins are present in APL blasts, i.e. RARalpha1 and RARalpha2. We developed different cell populations characterized by PML-RAR, RARalpha2 and RARalpha1 knock-down in the APL-derived NB4 cell-line. Unexpectedly, silencing of PML-RAR and RARalpha2 results in similar increases in the constitutive expression of several granulocytic differentiation markers. This is accompanied by enhanced expression of the same granulocytic markers upon exposure of the NB4 blasts to ATRA. Silencing of PML-RAR and RARalpha2 causes also similar perturbations in the whole genome gene-expression profiles of vehicle and ATRA treated NB4 cells. Unlike PML-RAR and RARalpha2, RARalpha1 knock-down blocks ATRA-dependent induction of several granulocytic differentiation markers. Many of the effects on myeloid differentiation are confirmed by over-expression of RARalpha2 in NB4 cells. RARalpha2 action on myeloid differentiation does not require the presence of PML-RAR, as it is recapitulated also upon knock-down in PML-RAR-negative HL-60 cells. Thus, relative to RARalpha1, PML-RAR and RARalpha2 exert opposite effects on APL-cell differentiation. These contrasting actions may be related to the fact that both PML-RAR and RARalpha2 interact with and inhibit the transcriptional activity of RARalpha1. The interaction surface is located in the carboxy-terminal domain containing the D/E/F regions and it is influenced by phosphorylation of Ser-369 of RARalpha1.

// Sausan A. Moharram 1, 2 , Rohit A. Chougule 1, 2 , Xianwei Su 4, 5 , Tianfeng Li 5 , Jianmin Sun 1, 2, 6 , Hui Zhao 5 , Lars Ronnstrand 1, 2, 3 , Julhash U. Kazi 1, 2 1 Division of Translational Cancer Research, Department of Laboratory Medicine, Lund University, Lund, Sweden 2 Lund Stem Cell Center, Department of Laboratory Medicine, Lund University, Lund, Sweden 3 Translational Cancer Research, Lund University, Skane University Hospital, Department of Oncology, Lund, Sweden 4 Department of Surgery, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong 5 School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong 6 Department of Pathogen Biology and Immunology, School of Basic Medical Sciences, Ningxia Medical University, Yinchuan, P. R. China Correspondence to: Julhash U. Kazi, email: kazi.uddin@med.lu.se Keywords: SLA2, Ba/F3, 32D, AML, AKT Received: May 27, 2016 Accepted: July 13, 2016 Published: July 21, 2016 ABSTRACT Fms-like tyrosine kinase (FLT3) is a frequently mutated oncogene in acute myeloid leukemia (AML). FLT3 inhibitors display promising results in a clinical setting, but patients relapse after short-term treatment due to the development of resistant disease. Therefore, a better understanding of FLT3 downstream signal transduction pathways will help to identify an alternative target for the treatment of AML patients carrying oncogenic FLT3. Activation of FLT3 results in phosphorylation of FLT3 on several tyrosine residues that recruit SH2 domain-containing signaling proteins. We screened a panel of SH2 domain-containing proteins and identified SLAP2 as a potent interacting partner of FLT3. We demonstrated that interaction occurs when FLT3 is activated, and also, an intact SH2 domain of SLAP2 is required for binding. SLAP2 binding sites in FLT3 mainly overlap with those of SRC. SLAP2 over expression in murine proB cells or myeloid cells inhibited oncogenic FLT3-ITD-mediated cell proliferation and colony formation in vitro , and tumor formation in vivo . Microarray analysis suggests that higher SLAP2 expression correlates with a gene signature similar to that of loss of oncogene function. Furthermore, FLT3-ITD positive AML patients with higher SLAP2 expression displayed better prognosis compared to those with lower expression of SLAP2. Expression of SLAP2 blocked FLT3 downstream signaling cascades including AKT, ERK, p38 and STAT5. Finally, SLAP2 accelerated FLT3 degradation through enhanced ubiquitination. Collectively, our data suggest that SLAP2 acts as a negative regulator of FLT3 signaling and therefore, modulation of SLAP2 expression levels may provide an alternative therapeutic approach for FLT3-ITD positive AML.

// Fangli Chen 1 , Yuichi Ishikawa 1 , Akimi Akashi 1 , Tomoki Naoe 2 and Hitoshi Kiyoi 1 1 Department of Hematology and Oncology, Nagoya University Graduate School of Medicine, Nagoya, Japan 2 Department of Hematology/Oncology Research, National Hospital Organization, Nagoya Medical Center, Nagoya, Japan Correspondence to: Yuichi Ishikawa, email: // Keywords : AML, FLT3 inhibitor, resistance, Wt-FLT3, FLT3 ligand Received : May 11, 2016 Accepted : June 09, 2016 Published : June 17, 2016 Abstract FLT3 mutation is found in about 30% of acute myeloid leukemia (AML) patients and is associated with a poor prognosis. Several FLT3 inhibitors are undergoing investigation, while their clinical efficacies were lower than expected and several resistant mechanisms to FLT3 inhibitors have been demonstrated. Although most AML cells harboring FLT3 mutation co-express wild-type (Wt)-FLT3, it is not fully understood how Wt-FLT3 expression is associated with the resistance to FLT3 inhibitors. In this study, we elucidated a resistant mechanism by which FL-dependent Wt-FLT3 activation reduced inhibitory effects of FLT3 inhibitors. We demonstrated that FL-stimulation much more strongly reduced growth inhibitory effects of FLT3 inhibitors on Wt- and mutant-FLT3 co-expressing cells than sole mutant-FLT3 expressing cells both in vitro and in vivo. It was also confirmed that FL impaired the anti-leukemia effects of FLT3 inhibitors on primary AML cells. We elucidated that FL impeded the inhibitory effects of FLT3 inhibitors mainly through the activation of Wt-FLT3, but not mutated FLT3, in the Wt- and ITD-FLT3 co-expressing cells. Furthermore, FL-induced activation of Wt-FLT3-MAPK axis was the dominant pathway for the resistance, and the glycosylation of Wt-FLT3 was also vital for FL-dependent kinase activation and following resistance to FLT3 inhibitors. Thus, we clarified the importance of co-expressing Wt-FLT3 in resistance to FLT3 inhibitors. These findings provide us with important implications for clinical application and new strategies to improve clinical outcomes of FLT3 inhibitors .

CDK4/CDK6 and RB proteins drive the progression through the G1 phase of the cell cycle. In acute myeloid leukemia (AML), the activity of the CDK/Cyclin D complex is increased. The mechanism involved is unknown, as are the respective roles played by CDK4 or CDK6 in this process. Here, we report that AML cells carrying FLT3-ITD mutations are dependent on CDK6 for cell proliferation while CDK4 is not essential. We showed that FLT3-ITD signaling is responsible for CDK6 overexpression, through a pathway involving the SRC-family kinase HCK. Accordingly, FLT3-ITD failed to transform primary hematopoietic progenitor cells from Cdk6-/- mice. Our results demonstrate that CDK6 is the primary target of CDK4/CDK6 inhibitors in FLT3-ITD positive AML. Furthermore, we delineate an essential protein kinase pathway -FLT3/HCK/CDK6- in the context of AML with FLT3-ITD mutations. This project was supported by La Ligue Contre le Cancer (Equipe labelisee) and a grant from the Fondation ARC pour la Recherche sur le Cancer.

Although conventional therapies for acute myeloid leukemia (AML) and diffuse large B-cell lymphoma (DLBCL) are effective in inducing remission, many patients relapse upon treatment. Hence, there is an urgent need for novel therapies. PIM kinases are often overexpressed in AML and DLBCL and are therefore an attractive therapeutic target. However, in vitro experiments have demonstrated that intrinsic resistance to PIM inhibition is common. It is therefore likely that only a minority of patients will benefit from single agent PIM inhibitor treatment. In this study, we performed an shRNA-based genetic screen to identify kinases whose suppression is synergistic with PIM inhibition. Here, we report that suppression of p38α (MAPK14) is synthetic lethal with the PIM kinase inhibitor AZD1208. PIM inhibition elevates reactive oxygen species (ROS) levels, which subsequently activates p38α and downstream AKT/mTOR signaling. We found that p38α inhibitors sensitize hematological tumor cell lines to AZD1208 treatment in vitro and in vivo. These results were validated in ex vivo patient-derived AML cells. Our findings provide mechanistic and translational evidence supporting the rationale to test a combination of p38α and PIM inhibitors in clinical trials for AML and DLBCL.

// Raffaella Pippa 1 , Ana Dominguez 1 , Raquel Malumbres 1 , Akinori Endo 2 , Elena Arriazu 1, 3 , Nerea Marcotegui 1, 3 , Elizabeth Guruceaga 1 and Maria D. Odero 1, 3, 4 1 Hematology/Oncology Program, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain 2 Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK 3 Instituto de Investigacion Sanitaria de Navarra (IdiSNA), Pamplona, Spain 4 Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain Correspondence to: Maria D. Odero, email: modero@unav.es Raffaella Pippa, email: raffa80@gmail.com Keywords: SET, PP2A, AML, MYC, RUNX1 Received: January 11, 2016 Accepted: May 22, 2016 Published: June 06, 2016 ABSTRACT The SET (I2PP2A) oncoprotein is a potent inhibitor of protein phosphatase 2A (PP2A) that regulates many cell processes and important signaling pathways. Despite the importance of SET overexpression and its prognostic impact in both hematologic and solid tumors, little is known about the mechanisms involved in its transcriptional regulation. In this report, we define the minimal promoter region of the SET gene, and identify a novel multi-protein transcription complex, composed of MYC, SP1, RUNX1 and GATA2, which activates SET expression in AML. The role of MYC is crucial, since it increases the expression of the other three transcription factors of the complex, and supports their recruitment to the promoter of SET . These data shed light on a new regulatory mechanism in cancer, in addition to the already known PP2A-MYC and SET-PP2A. Besides, we show that there is a significant positive correlation between the expression of SET and MYC , RUNX1 , and GATA2 in AML patients, which further endorses our results. Altogether, this study opens new directions for understanding the mechanisms that lead to SET overexpression, and demonstrates that MYC, SP1, RUNX1 and GATA2 are key transcriptional regulators of SET expression in AML.

Phosphoinositide-3-kinase (PI3K) is an enzyme group, known to regulate key survival pathways in acute myeloid leukaemia (AML). It generates phosphatidylinositol-3,4,5-triphosphate, which provides a membrane docking site for protein kinaseB activation. PI3K catalytic p110 subunits are divided into 4 isoforms; α,β,δ and γ. The PI3Kδ isoform is always expressed in AML cells, whereas the frequency of PI3Kγ expression is highly variable. The functions of these individual catalytic enzymes have not been fully resolved in AML, therefore using the PI3K p110δ and p110γ-targeted inhibitor IPI-145 (duvelisib) and specific p110δ and p110γ shRNA, we analysed the role of these two p110 subunits in human AML blast survival. The results show that PI3Kδ and PI3Kγ inhibition with IPI-145 has anti-proliferative activity in primary AML cells by inhibiting the activity of AKT and MAPK. Pre-treatment of AML cells with IPI-145 inhibits both adhesion and migration of AML blasts to bone marrow stromal cells. Using shRNA targeted to the individual isoforms we demonstrated that p110δ-knockdown had a more significant anti-proliferative effect on AML cells, whereas targeting p110γ-knockdown significantly inhibited AML migration. The results demonstrate that targeting both PI3Kδ and PI3Kγ to inhibit AML-BMSC interactions provides a biologic rationale for the pre-clinical evaluation of IPI-145 in AML.

Complete remission by induction therapy in acute myelogenous leukemia (AML) can be achieved due to improvements in supportive and optimized therapy. However, more than 20% of patients will still need to undergo salvage therapy, and most will have a poor prognosis. Determining the specificity of drugs to leukemia cells is important since this will maximize the dose of chemotherapeutic agents that can be administered to AML patients. In turn, this would be expected to lead to reduced drug toxicity and its increased efficacy. We targeted Notch-1 positive AML cells utilizing fucose-bound liposomes, since activation of Notch-1 is required for O-fucosylation. Herein, we report that intravenously injected, L-fucose-bound liposomes containing daunorubicin can be successfully delivered to AML cells that express fucosylated antigens. This resulted in efficient tumor growth inhibition in tumor-bearing mice and decreased proliferation of AML patient-derived leukemia cells. Thus, biological targeting by fucose-bound liposomes that takes advantage of the intrinsic characteristics of AML cells could be a promising new strategy for Notch-1 positive-AML treatment.

// Paul Takam Kamga 1 , Giulio Bassi 1 , Adriana Cassaro 1 , Martina Midolo 1 , Mariano Di Trapani 1 , Alessandro Gatti 1 , Roberta Carusone 1 , Federica Resci 1 , Omar Perbellini 1 , Michele Gottardi 2 , Massimiliano Bonifacio 1 , Armel Herve Nwabo Kamdje 3 , Achille Ambrosetti 1 and Mauro Krampera 1 1 Stem Cell Research Laboratory, Section of Hematology, Department of Medicine, University of Verona, Verona, Italy 2 Division of Hematology, Ca’ Foncello Hospital, Treviso, Italy 3 Department of Biomedical Sciences, University of Ngaoundere-Cameroon, Cameroon Correspondence to: Mauro Krampera, email: // Keywords : AML, MSC, Notch, chemoresistance Received : February 10, 2016 Accepted : February 25, 2016 Published : March 07, 2016 Abstract Both preclinical and clinical investigations suggest that Notch signalling is critical for the development of many cancers and for their response to chemotherapy. We previously showed that Notch inhibition abrogates stromal-induced chemoresistance in lymphoid neoplasms. However, the role of Notch in acute myeloid leukemia (AML) and its contribution to the crosstalk between leukemia cells and bone marrow stromal cells remain controversial. Thus, we evaluated the role of the Notch pathway in the proliferation, survival and chemoresistance of AML cells in co-culture with bone marrow mesenchymal stromal cells expanded from both healthy donors (hBM-MSCs) and AML patients (hBM-MSCs*). As compared to hBM-MSCs, hBM-MSCs* showed higher level of Notch1, Jagged1 as well as the main Notch target gene HES1. Notably, hBM-MSCs* induced expression and activation of Notch signalling in AML cells, supporting AML proliferation and being more efficientin inducing AML chemoresistance than hBM-MSCs*. Pharmacological inhibition of Notch using combinations of Notch receptor-blocking antibodies or gamma-secretase inhibitors (GSIs), in presence of chemotherapeutic agents, significant lowered the supportive effect of hBM-MSCs and hBM-MSCs* towards AML cells, by activating apoptotic cascade and reducing protein level of STAT3, AKT and NF-κB. These results suggest that Notch signalling inhibition, by overcoming the stromal-mediated promotion of chemoresistance,may represent a potential therapeutic targetnot only for lymphoid neoplasms, but also for AML.

// Josep Maria Cornet-Masana 1 , Daniel Moreno-Martinez 1 , Maria Carmen Lara-Castillo 1 , Meritxell Nomdedeu 1,2 , Amaia Etxabe 1 , Niccolo Tesi 1 , Marta Pratcorona 1,2 , Jordi Esteve 1,2 and Ruth M. Risueno 1 1 Josep Carreras Leukaemia Research Institute, Barcelona, Spain 2 Department of Hematology, Hospital Clinic, Institut d’Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Barcelona, Spain Correspondence to: Ruth M. Risueno, email: // Keywords : AML, emetine, anti-leukemia drug Received : February 24, 2016 Accepted : February 28, 2016 Published : March 15, 2016 Abstract Acute myeloid leukemia (AML) is an hematologic neoplasia characterized by the accumulation of transformed immature myeloid cells in bone marrow. Although the response rate to induction therapy is high, survival rate 5-year after diagnosis is still low, highlighting the necessity of new novel agents. To identify agents with the capability to abolish the self-renewal capacity of AML blasts, an in silico screening was performed to search for small molecules that induce terminal differentiation. Emetine, a hit compound, was validated for its anti-leukemic effect in vitro , ex vivo and in vivo . Emetine, a second-line anti-protozoa drug, differentially reduced cell viability and clonogenic capacity of AML primary patient samples, sparing healthy blood cells. Emetine treatment markedly reduced AML burden in bone marrow of xenotransplanted mice and decreased self-renewal capacity of the remaining engrafted AML cells. Emetine also synergized with commonly used chemotherapeutic agents such as ara-C. At a molecular level, emetine treatment was followed by a reduction in HIF-1α protein levels. This study validated the anti-leukemiceffect of emetine in AML cell lines, a group of diverse AML primary samples, and in a human AML-transplanted murine model, sparing healthy blood cells. The selective anti-leukemic effect of emetine together with the safety of the dose range required to exert this effect support the development of this agent in clinical practice.

GADS is a member of a family of SH2 and SH3 domain-containing adaptors that functions in tyrosine kinase-mediated signaling cascades. Its expression is largely restricted to hematopoietic tissues and cell lines. Therefore, GADS is mainly involved in leukocyte-specific protein tyrosine kinase signaling. GADS is known to interact with tyrosine-phosphorylated SHC, BCR-ABL and KIT. The SH2 domain of GADS has a similar binding specificity to that of GRB2 but its SH3 domain displays a different binding specificity, and thus it is involved in other downstream signaling pathways than GRB2. In the present study, we examined the role of GADS in FLT3 signaling. FLT3 is a type III receptor tyrosine kinase, which is mutated in more than 30% of acute myeloid leukemia (AML) and the most common mutations is the internal tandem duplication (ITD) mutations. We observed that expression of GADS enhanced oncogenic FLT3-ITD-induced cell proliferation and colony formation in vitro. In a mouse xenograft model, GADS accelerated FLT3-ITD-dependent tumor formation. Furthermore, expression of GADS induced a transcriptional program leading to upregulation of MYC and mTORC1 target genes. GADS localizes to the cell membrane and strongly binds to ligand-stimulated wild-type FLT3 or is constitutively associated with the oncogenic mutant FLT3-ITD. We mapped the binding sites in FLT3 to pY955 and pY969 which overlaps with the GRB2 binding sites. Expression of GADS enhanced FLT3-mediated phosphorylation of AKT, ERK1/2, p38 and STAT5. Taken together, our data suggests that GADS is an important downstream component of FLT3 signaling and expression of GADS potentiates FLT3-mediated mitogenic signaling.

Tefinostat (CHR-2845) is a novel monocyte/macrophage-targeted histone deacetylase (HDAC) inhibitor which is cleaved into its active acid by the intracellular\ud esterase human carboxylesterase-1 (hCE-1). The in vitro efficacy of tefinostat was characterised in cell lines and in a cohort of 73 primary AML and CMML samples. Dose-dependent induction of apoptosis and significant growth inhibitory effects were seen in myelomonocytic (M4), monocytic/monoblastic (M5) and CMML samples in comparison to non-monocytoid AML sub-types (p = 0.007). Importantly, no growth inhibitory effects were seen in normal bone marrow CD34+ cells exposed to AML-toxic doses of tefinostat in clonogenic assays. Expression of hCE-1 was measured by\ud intracellular flow cytometry and immunoblotting across the cohort, with highest levels seen in M5 AML patients. hCE-1 levels correlated with significantly increased tefinostat sensitivity (low EC50) as measured by growth inhibition assays (p = 0.001)and concomitant elevation of the mature monocytoid marker CD14+. Strong induction of intracellular histone protein acetylation was observed in tefinostat-responsive samples, as were high levels of the DNA damage sensor γ-H2A.X, highlighting potential biomarkers of patient responsiveness. Synergistic interaction between\ud tefinostat and the current standard treatment cytarabine was demonstrated in dose response and clonogenic assays using simultaneous drug addition in primary samples\ud (median Combination Index value = 0.51). These data provide a strong rationale for the further clinical evaluation of tefinostat in monocytoid-lineage haematological neoplasms including CMML and monocyte-lineage AMLs.

Acute myeloid leukaemia (AML) cells often up-regulate pro-survival members of the BCL-2 protein family, such as BCL-2 and MCL-1, to avoid apoptosis. Venetoclax (ABT-199) targets BCL-2 and has shown promising efficacy in AML but over-expression of MCL-1 can cause resistance. A co-operative approach, targeting both BCL-2 and MCL-1 may therefore prove beneficial. This study investigated the potential synergistic relationship between Venetoclax and the MCL-1 inhibitor S63845 in AML cells. We treated MV4-11 cells and primary AML samples for 4 hours with Venetoclax, S63845 or the combination. We used a short-term flow cytometric technique to assess synergy using cytochrome C release as a read out of response. The combination of Venetoclax and S63845 produced a synergistic apoptotic response in MV4-11 cells and primary samples, including the leukaemia re-populating leukaemic stem cell (LSC) population, in 92% of the samples. Known molecular biomarkers of response to BCL-2 and MCL-1 targeting agents were corroborated, and augmented, with the short-term functional assay. The assay also predicted potential biomarkers of response to the combination of BCL-2 and MCL-1 targeting agents. Primary samples with an IDH2_140 mutation were more sensitive to Venetoclax as a single agent whereas samples with a FLT3-ITD mutation were more resistant. This resistance could be reversed when combined with S63845. All FLT3-ITD and NPM1 mutated samples were sensitive to the combination of drugs. We report that co-operatively targeting BCL-2 and MCL-1 may be beneficial in AML and a short-term in vitro assay can identify patients who might best respond to this combination.

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults, affecting approximately 21,000 people annually (nearly 11,000 deaths) in the United States. B-cell lymphoma 2 (BCL-2) family proteins, notably myeloid cell leukemia-1 (MCL-1), have been associated with both the development and persistence of AML. MCL-1 is one of the predominant BCL-2 family members expressed in samples from patients with untreated AML. MCL-1 is a critical cell survival factor for cancer and contributes to chemotherapy resistance by directly affecting cell death pathways. Here, we review the role of MCL-1 in AML and the mechanisms by which the potent cyclin-dependent kinase 9 inhibitor alvocidib, through regulation of MCL-1, may serve as a rational therapeutic approach against the disease.