Leukemia Stem Cells in Acute Myeloid Leukemia

Discovery of JNJ-74856665: A Novel Isoquinolinone DHODH Inhibitor for the Treatment of AML

Acute myelogenous leukemia (AML), a heterogeneous disease of the blood and bone marrow, is characterized by the inability of myeloblasts to differentiate into mature cell types. Dihydroorotate dehydrogenase (DHODH) is an enzyme well-known in the pyrimidine biosynthesis pathway and preclinical findings demonstrated that DHODH is a metabolic vulnerability in AML as inhibitors can induce differentiation across multiple AML subtypes. As a result of virtual screening and structure-based drug design approaches, a novel series of isoquinolinone DHODH inhibitors was identified. Further lead optimization afforded JNJ-74856665 as an orally bioavailable, potent, and selective DHODH inhibitor with favorable physicochemical properties selected for clinical development in patients with AML and myelodysplastic syndromes (MDS).

Interpreting single-cell messages in normal and aberrant hematopoiesis with the Cell Marker Accordion

Single-cell technologies offer a unique opportunity to explore cellular heterogeneity in hematopoiesis, reveal malignant hematopoietic cells with clinically significant features and measure gene signatures linked to pathological pathways. However, reliable identification of cell types is a crucial bottleneck in single-cell analysis. Available databases contain dissimilar nomenclature and non-concurrent marker sets, leading to inconsistent annotations and poor interpretability. Furthermore, current tools focus mostly on physiological cell types, lacking extensive applicability in disease. We developed the Cell Marker Accordion, a user-friendly platform for the automatic annotation and biological interpretation of single-cell populations based on consistency weighted markers. We validated our approach on peripheral blood and bone marrow single-cell datasets, using surface markers and expert-based annotation as the ground truth. In all cases, we significantly improved the accuracy in identifying cell types with respect to any single source database. Moreover, the Cell Marker Accordion can identify disease-critical cells and pathological processes, extracting potential biomarkers in a wide variety of contexts in human and murine single-cell datasets. It characterizes leukemia stem cell subtypes, including therapy-resistant cells in acute myeloid leukemia patients; it identifies malignant plasma cells in multiple myeloma samples; it dissects cell type alterations in splicing factor-mutant cells from myelodysplastic syndrome patients; it discovers activation of innate immunity pathways in bone marrow from mice treated with METTL3 inhibitors. The breadth of these applications elevates the Cell Marker Accordion as a flexible, faithful and standardized tool to annotate and interpret hematopoietic populations in single-cell datasets focused on the study of hematopoietic development and disease.

The Potential Role of 3D In Vitro Acute Myeloid Leukemia Culture Models in Understanding Drug Resistance in Leukemia Stem Cells

The complexity of the bone marrow (BM) microenvironment makes studying hematological malignancies in vitro a challenging task. Three-dimensional cell cultures are being actively studied, particularly due to their ability to serve as a bridge of the gap between 2D cultures and animal models. The role of 3D in vitro models in studying the mechanisms of chemotherapeutic resistance and leukemia stem cells (LSCs) in acute myeloid leukemia (AML) is not well-reviewed. We present an overview of 3D cell models used for studying AML, emphasizing the recent advancements in microenvironment modeling, chemotherapy testing, and resistance.

Recent progress on targeting leukemia stem cells

Leukemia is a type of malignant clonal disease of hematopoietic stem cells (HSCs). A small population of leukemic stem cells (LSCs) are responsible for the initiation, drug resistance, and relapse of leukemia. LSCs have the ability to form tumors after xenotransplantation in immunodeficient mice and appear to be common in most human leukemias. Therefore, the eradication of LSCs is an approach with the potential to improve survival or even to cure leukemia. Using recent research in the field of LSCs, we summarize the targeted therapy approaches for the removal of LSCs through surface markers including immune checkpoint molecules, pathways influencing LSC survival, or the survival microenvironment of LSCs. In addition, we introduce the survival microenvironment and survival regulation of LSCs.

A carboxylic acid isostere screen of the DHODH inhibitor Brequinar

Dihydroorotate dehydrogenase (DHODH) enzymatic activity impacts many aspects critical to cell proliferation and survival. Recently, DHODH has been identified as a target for acute myeloid differentiation therapy. In preclinical models of AML, the DHODH inhibitor Brequinar (BRQ) demonstrated potent anti-leukemic activity. Herein we describe a carboxylic acid isostere study of Brequinar which revealed a more potent non-carboxylic acid derivative with improved cellular potency and good pharmacokinetic properties.

Myeloid translocation gene CBFA2T3 directs a relapse gene program and determines patient-specific outcomes in AML

CBFA2T3 is a master transcriptional coregulator in hematopoiesis. In this study, we report novel functions of CBFA2T3 in acute myeloid leukemia (AML) relapse. CBFA2T3 regulates cell-fate genes to establish gene expression signatures associated with leukemia stem cell (LSC) transformation and relapse. Gene set enrichment analysis showed that CBFA2T3 expression marks LSC signatures in primary AML samples. Analysis of paired primary and relapsed samples showed that acquisition of LSC gene signatures involves cell type-specific activation of CBFA2T3 transcription via the NM_005187 promoter by GCN5. Short hairpin RNA-mediated downregulation of CBFA2T3 arrests G1/S cell cycle progression, diminishes LSC gene signatures, and attenuates in vitro and in vivo proliferation of AML cells. We also found that the RUNX1-RUNX1T1 fusion protein transcriptionally represses NM_005187 to confer t(8;21) AML patients a natural resistance to relapse, whereas lacking a similar repression mechanism renders non-core-binding factor AML patients highly susceptible to relapse. These studies show that 2 related primary AML-associated factors, the expression level of CBFA2T3 and the ability of leukemia cells to repress cell type-specific CBFA2T3 gene transcription, play important roles in patient prognosis, providing a paradigm that differential abilities to repress hematopoietic coregulator gene transcription are correlated with patient-specific outcomes in AML.

CD45dimCD34+CD38-CD133+ cells have the potential as leukemic stem cells in acute myeloid leukemia

Background

Leukemia stem cells (LSCs) in play an important role in the initiation, relapse, and progression of acute myeloid leukemia (AML), and in the development of chemotherapeutic drug resistance in AML. Studies regarding the detection of LSCs and the development of novel therapies for targeting them are extensive. The identification of LSCs and targeting therapies for them has been continuously under investigation.

Methods

We examined the levels of CD45^dimCD34⁺CD38⁻CD133⁺ cells in bone marrow samples from patients with hematological malignancies and healthy controls, using four-color flow cytometry.

Results

Interestingly, the CD45^dimCD34⁺CD38⁻CD133⁺ cells were highly expressed in the bone marrow of patients with AML compared to that in healthy controls (HC). Moreover, the proportions of CD45^dimCD34⁺CD38⁻CD133⁺ cells were also examined in diverse hematological malignancies, including AML, CML, DLBCL, MM, MDS, HL, ALL, and CLL. LSCs were prominently detected in the BMCs isolated from patients with AML and CML, but rarely in BMCs isolated from patients with DLBCL, MM, MDS, ALL, CLL, and HL. Additionally, the high CD45^dimCD34⁺CD38⁻CD133⁺ cell counts in AML patients served as a significantly poor risk factor for overall and event free survival.

Conclusions

Therefore, our results suggest that CD45^dimCD34⁺CD38⁻CD133⁺ cells in AML might potentially serve as LSCs. In addition, this cell population might represent a novel therapeutic target in AML.

Inhibition of Slug effectively targets leukemia stem cells via the Slc13a3/ROS signaling pathway

Leukemia stem cells (LSCs) are the rare populations of acute myeloid leukemia (AML) cells that are able to initiate, maintain, and propagate AML. Targeting LSCs is a promising approach for preventing AML relapse and improving long-term outcomes. While Slug, a zinc-finger transcription repressor, negatively regulates the self-renewal of normal hematopoietic stem cells, its functions in AML are still unknown. We report here that Slug promotes leukemogenesis and its loss impairs LSC self-renewal and delays leukemia progression. Mechanistically, Slc13a3, a direct target of Slug in LSCs, restricts the self-renewal of LSCs and markedly prolongs recipient survival. Genetic or pharmacological inhibition of SLUG or forced expression of Slc13a3 suppresses the growth of human AML cells. In conclusion, our studies demonstrate that Slug differentially regulates self-renewal of LSCs and normal HSCs, and both Slug and Slc13a3 are potential therapeutic targets of LSCs.

Synthesis and biological evaluation of dithiocarbamate esters of parthenolide as potential anti-acute myelogenous leukaemia agents

A series of dithiocarbamate esters of parthenolide (PTL) was designed, synthesised, and evaluated for their anti- acute myelogenous leukaemia (AML) activities. The most promising compound 7l showed greatly improved potency against AML progenitor cell line KG1a with IC₅₀ value of 0.7 μM, and the efficacy was 8.7-folds comparing to that of PTL (IC₅₀ = 6.1 μM). Compound 7l induced apoptosis of total primary human AML cells and leukaemia stem cell (LSCs) of primary AML cells while sparing normal cells. Furthermore, 7l suppressed the colony formation of primary human leukaemia cells. Moreover, compound 12, the salt form of 7l, prolonged the lifespan of mice in two patient-derived xenograft models and had no observable toxicity. The preliminary molecular mechanism study revealed that 7l-mediated apoptosis is associated with mitogen-activated protein kinase signal pathway. On the basis of these investigations, we propose that 12 might be a promising drug candidate for ultimate discovery of anti-LSCs drug.

Survival outcomes of CD34+CD38-LSCs and their expression of CD123 in adult AML patients

Background and aim

Acute myeloid leukemia (AML) is one of the most common leukemias in adults. AML is generally regarded as a stem cell disease characterized by an accumulation of undifferentiated and functionally heterogeneous populations of cells, The aim of the present study was to identify leukemia stem cells in patients with AML and their correlations with treatment outcomes namely remission status, disease free survival, and overall survival.

Results

The mean percentages of CD34⁺CD38^- and CD34⁺CD38^low/−CD123⁺ LSCs were 2.2± 0.4and 22.3± 2.6, respectively. The percentages of CD34⁺cells, CD34⁺CD38^- and CD34⁺CD38^low/−CD123⁺ LSCs were significantly lower in AML patients with complete remission than those without complete response (P<0.001, P<0.004, P<0.001 respectively). The mean OS of all study patients was 20.03±1.2 months while the median OS was 21 months (95% CI=18.32-21.48). The mean DFS was 16.96±1.02 months and the median was 18 months (95% CI=8.9-11.4). DFS and OS were significantly higher among those who achieved CR than those without CR. In addition, there were significant negative effects of WBCs, CD34⁺cells, CD34⁺CD38^- and CD34⁺CD38^-CD123⁺LSCs on DFS and OS.

Patients and methods

We investigated 30 patients with newly diagnosed AML; all patients underwent complete history taking, and thorough physical and clinical examination, complete blood count. Peripheral smears and bone marrow aspirates were also examined. Cytochemistry and immunophenotyping of leukemic cells were performed routinely in bone marrow using monoclonal antibodies. Flow cytometry was used to analyze leukemia stem cells and their expression of CD123.

Conclusion

Our study elucidated that CD34+CD38-LSCs, with or without CD123+LSCs phenotype was present in a significant proportion of AML patients and it could be responsible for resistance to traditional treatments, and high percentage of MRD that was translated into significantly high number of non CR, poor DFS, and OS.

Targeting primary acute myeloid leukemia with a new CXCR4 antagonist IgG1 antibody (PF-06747143)

The chemokine receptor CXCR4 mediates cell anchorage in the bone marrow (BM) microenvironment and is overexpressed in 25–30% of patients with acute myeloid leukemia (AML). Here we have shown that a new CXCR4 receptor antagonist IgG1 antibody (PF-06747143) binds strongly to AML cell lines and to AML primary cells inhibiting their chemotaxis in response to CXCL12. PF-06747143 also induced cytotoxicity in AML cells via Fc-effector function. To characterize the effects of PF-06747143 on leukemia progression, we used two different patient-derived xenograft (PDX) models: Patient 17^CXCR4-low and P15^CXCR4-high models, characterized by relatively low and high CXCR4 expression, respectively. Weekly administration of PF-06747143 to leukemic mice significantly reduced leukemia development in both models. Secondary transplantation of BM cells from PF-06747143-treated or IgG1 control-treated animals showed that leukemic progenitors were also targeted by PF-06747143. Administration of a single dose of PF-06747143 to PDX models induced rapid malignant cell mobilization into the peripheral blood (PB). These findings support evaluation of this antibody in AML therapy, with particular appeal to patients resistant to chemotherapy and to unfit patients, unable to tolerate intensive chemotherapy.

Inhibition of IRE1α-driven pro-survival pathways is a promising therapeutic application in acute myeloid leukemia

Survival of cancer cells relies on the unfolded protein response (UPR) to resist stress triggered by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). The IRE1α-XBP1 pathway, a key branch of the UPR, is activated in many cancers. Here, we show that the expression of both mature and spliced forms of XBP1 (XBP1s) is up-regulated in acute myeloid leukemia (AML) cell lines and AML patient samples. IRE1α RNase inhibitors [MKC-3946, 2-hydroxy-1-naphthaldehyde (HNA), STF-083010 and toyocamycin] blocked XBP1 mRNA splicing and exhibited cytotoxicity against AML cells. IRE1α inhibition induced caspase-dependent apoptosis and G1 cell cycle arrest at least partially by regulation of Bcl-2 family proteins, G1 phase controlling proteins (p21^cip1, p27^kip1 and cyclin D1), as well as chaperone proteins. Xbp1 deleted murine bone marrow cells were resistant to growth inhibition by IRE1α inhibitors. Combination of HNA with either bortezomib or AS₂O₃ was synergistic in AML cytotoxicity associated with induction of p-JNK and reduction of p-PI3K and p-MAPK. Inhibition of IRE1α RNase activity increased expression of many miRs in AML cells including miR-34a. Inhibition of miR-34a conferred cellular resistance to HNA. Our results strongly suggest that targeting IRE1α driven pro-survival pathways represent an exciting therapeutic approach for the treatment of AML.

Understanding of leukemic stem cells and their clinical implications

Since leukemic stem cells (LSCs) or cancer stem cells (CSCs) were found in acute myeloid leukemia (AML) in 1997, extensive studies have been contributed to identification and characterization of such cell populations in various tissues. LSCs are now generally recognized as a heterogeneous cell population that possesses the capacities of self-renewal, proliferation and differentiation. It has been shown that LSCs are regulated by critical surface antigens, microenvironment, intrinsic signaling pathways, and novel molecules such as some ncRNAs. To date, significant progress has been made in understanding of LSCs, leading to the development of numerous LSCs-targeted therapies. Moreover, various novel therapeutic agents targeting LSCs are undergoing clinical trials. Here, we review current knowledge of LSCs, and discuss the potential therapies and their challenges that are being tested in clinical trials for evaluation of their effects on leukemias.

Targeting acute myeloid leukemia stem cell signaling by natural products

Acute myeloid leukemia (AML) is the most commonly diagnosed leukemia in adults (25%) and comprises 15-20% in children. It is a genetically heterogeneous aggressive disease characterized by the accumulation of somatically acquired genetic changes, altering self-renewal, proliferation, and differentiation of hematopoietic progenitor cells, resulting in uncontrolled clonal proliferation of malignant progenitor myeloid cells in the bone marrow, peripheral blood, and occasionally in other body tissues. Treatment with modern chemotherapy regimen (cytarabine and daunorubicin) usually achieves high remission rates, still majority of patients are found to relapse, resulting in only 40-45% overall 5 year survival in young patients and less than 10% in the elderly AML patients. The leukemia stem cells (LSCs) are characterized by their unlimited self-renewal, repopulating potential and long residence in a quiescent state of G0/G1 phase. LSCs are considered to have a pivotal role in the relapse and refractory of AML. Therefore, new therapeutic strategies to target LSCs with limited toxicity towards the normal hematopoietic population is critical for the ultimate curing of AML. Ongoing research works with natural products like parthenolide (a natural plant extract derived compound) and its derivatives, that have the ability to target multiple pathways that regulate the self-renewal, growth and survival of LSCs point to ways for a possible complete remission in AML. In this review article, we will update and discuss various natural products that can target LSCs in AML.

Fibroblast Growth Factor-2 facilitates the growth and chemo-resistance of leukemia cells in the bone marrow by modulating osteoblast functions

Stromal cells and osteoblasts play major roles in forming and modulating the bone marrow (BM) hematopoietic microenvironment. We have reported that FGF2 compromises stromal cell support of normal hematopoiesis. Here, we examined the effects of FGF2 on the leukemia microenvironment. In vitro, FGF2 significantly decreased the number of stromal-dependent and stromal-independent G0-leukemia cells in the stromal layers. Accordingly, CML cells placed on FGF2-treated stromal layers were more sensitive to imatinib. Conversely, FGF2 increased the proliferation of osteoblasts via FGFR1 IIIc, but its effects on osteoblast support of leukemia cell growth were limited. We next treated a human leukemia mouse model with Ara-C with/without systemic FGF2 administration. BM sections from FGF2-treated mice had thickened bone trabeculae and increased numbers of leukemia cells compared to controls. Leukemia cell density was increased, especially in the endosteal region in FGF2/Ara-C -treated mice compared to mice treated with Ara-C only. Interestingly, FGF2 did not promote leukemia cell survival in Ara-C treated spleen. Microarray analysis showed that FGF2 did not alter expression of many genes linked to hematopoiesis in osteoblasts, but modulated regulatory networks involved in angiogenesis and osteoblastic differentiation. These observations suggest that FGF2 promotes leukemia cell growth in the BM by modulating osteoblast functions.

CBFβ-SMMHC creates aberrant megakaryocyte-erythroid progenitors prone to leukemia initiation in mice

Acute myeloid leukemia (AML) arises through multistep clonal evolution characterized by stepwise accumulation of successive alterations affecting the homeostasis of differentiation, proliferation, self-renewal, and survival programs. The persistence and dynamic clonal evolution of leukemia-initiating cells and preleukemic stem cells during disease progression and treatment are thought to contribute to disease relapse and poor outcome. Inv(16)(p13q22) or t(16;16)(p13.1;q22), one of the most common cytogenetic abnormalities in AML, leads to expression of a fusion protein CBFβ-SMMHC (CM) known to disrupt myeloid and lymphoid differentiation. Anemia is often observed in AML but is presumed to be a secondary consequence of leukemic clonal expansion. Here, we show that CM expression induces marked deficiencies in erythroid lineage differentiation and early preleukemic expansion of a phenotypic pre-megakaryocyte/erythrocyte (Pre-Meg/E) progenitor population. Using dual-fluorescence reporter mice in lineage tracking and repopulation assays, we show that CM expression cell autonomously causes expansion of abnormal Pre-Meg/E progenitors with compromised erythroid specification and differentiation capacity. The preleukemic Pre-Meg/Es display dysregulated erythroid and megakaryocytic fate-determining factors including increased Spi-1, Gata2, and Gfi1b and reduced Zfpm1, Pf4, Vwf, and Mpl expression. Furthermore, these abnormal preleukemic Pre-Meg/Es have enhanced stress resistance and are prone to leukemia initiation upon acquiring cooperative signals. This study reveals that the leukemogenic CM fusion protein disrupts adult erythropoiesis and creates stress-resistant preleukemic Pre-Meg/E progenitors predisposed to malignant transformation. Abnormality in Meg/E or erythroid progenitors could potentially be considered an early predictive risk factor for leukemia evolution.

Survival regulation of leukemia stem cells

Leukemia stem cells (LSCs) are a subpopulation cells at the apex of hierarchies in leukemia cells and responsible for disease continuous propagation. In this article, we discuss some cellular and molecular components, which are critical for LSC survival. These components include intrinsic signaling pathways and extrinsic microenvironments. The intrinsic signaling pathways to be discussed include Wnt/β-catenin signaling, Hox genes, Hh pathway, Alox5, and some miRNAs, which have been shown to play important roles in regulating LSC survival and proliferation. The extrinsic components to be discussed include selectins, CXCL12/CXCR4, and CD44, which involve in LSC homing, survival, and proliferation by affecting bone marrow microenvironment. Potential strategies for eradicating LSCs will also discuss.

Regain control of p53: Targeting leukemia stem cells by isoform-specific HDAC inhibition

Leukemia stem cells (LSCs) are self-renewable, leukemia-initiating populations that are often resistant to traditional chemotherapy and tyrosine kinase inhibitors currently used for treatment of acute or chronic myeloid leukemia. The persistence and continued acquisition of mutations in resistant LSCs represent a major cause of refractory disease and/or relapse after remission. Understanding the mechanisms regulating LSC growth and survival is critical in devising effective therapies that will improve treatment response and outcome. Several recent studies indicate that the p53 tumor suppressor pathway is often inactivated in de novo myeloid leukemia through oncogenic-specific mechanisms, which converge on aberrant p53 protein deacetylation. Here, we summarize our current understanding of the various mechanisms underlying deregulation of histone deacetylases (HDACs), which could be exploited to restore p53 activity and enhance targeting of LSCs in molecularly defined patient subsets.

Tissue invasion and metastasis: Molecular, biological and clinical perspectives

Cancer is a key health issue across the world, causing substantial patient morbidity and mortality. Patient prognosis is tightly linked with metastatic dissemination of the disease to distant sites, with metastatic diseases accounting for a vast percentage of cancer patient mortality. While advances in this area have been made, the process of cancer metastasis and the factors governing cancer spread and establishment at secondary locations is still poorly understood. The current article summarizes recent progress in this area of research, both in the understanding of the underlying biological processes and in the therapeutic strategies for the management of metastasis. This review lists the disruption of E-cadherin and tight junctions, key signaling pathways, including urokinase type plasminogen activator (uPA), phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene (PI3K/AKT), focal adhesion kinase (FAK), β-catenin/zinc finger E-box binding homeobox 1 (ZEB-1) and transforming growth factor beta (TGF-β), together with inactivation of activator protein-1 (AP-1) and suppression of matrix metalloproteinase-9 (MMP-9) activity as key targets and the use of phytochemicals, or natural products, such as those from Agaricus blazei, Albatrellus confluens, Cordyceps militaris, Ganoderma lucidum, Poria cocos and Silybum marianum, together with diet derived fatty acids gamma linolenic acid (GLA) and eicosapentanoic acid (EPA) and inhibitory compounds as useful approaches to target tissue invasion and metastasis as well as other hallmark areas of cancer. Together, these strategies could represent new, inexpensive, low toxicity strategies to aid in the management of cancer metastasis as well as having holistic effects against other cancer hallmarks.

Cancer stem cells in haematological malignancies

At least several types of human haematological malignancies can now be seen as 'stem-cell diseases'. The best-studied in this context is acute myeloid leukaemia (AML). It has been shown that these diseases are driven by a pool of 'leukaemia stem cells (LSC)', which remain in the quiescent state, have the capacity to survive and self-renew, and are responsible for the recurrence of cancer after classical chemotherapy. It has been understood that LSC must be eliminated in order to cure patients suffering from haematological cancers. Recent advances in LSC research have allowed for description of LSC phenotype and identification of potential targets for anti-LSC therapies. This concise review summarises the current view on LSC biology and targeted approaches against LSC.

Conditioning regimens in acute myeloid leukemia

Current intensive consolidation chemotherapy for patients with acute myeloid leukemia (AML) produces median remission duration of 12-18 months, with less than 30% of patients surviving 5 years free of disease. Post-remission therapy is necessary to prevent relapse in most patients with AML; therefore, the aim of post-remission treatment is to eradicate the minimal residual disease. Nevertheless, the optimal form of treatment is still under debate. The choice among the possible approaches (intensive chemotherapy, autologous or allogeneic hematopoietic stem cell transplantation) relies on two main factors: the expected risk of relapse, as determined by biological features, and expected morbidity and mortality associated with a specific option. In this review, we focus on the different preparative regimens before autologous and allogeneic hematopoietic stem cell transplantation in patients with AML, stressing the importance of an adequate conditioning regimen as a mandatory element of a successful AML therapy, in both the allogeneic and the autologous transplant setting.

Can systems biology approach help in finding more effective treatment for acute myeloid leukemia?

Acute myeloid leukemia (AML) is a hematological cancer comprising of cancer stem cells (CSCs) that are responsible for the disease progression, drug resistance and post treatment relapses. Advances in genomic technologies have identified AML as a genetically heterogenous disease with dysregulated gene expression networks. Furthermore, observation of intracellular signaling in individual CSCs by mass cytometry has demonstrated the dysregulation of the mitogen associated protein kinase (MAPK) pathways. It has been envisaged that the future treatment for AML would entail upon formulating individualized treatment plans leading to decreased drug related toxicities for patients. However the emerging role of signaling pathways as dynamic molecular switches influencing the cell cycle process, thereby leading to varying stages of cell differentiation, is making community rethink about the current strategies used for the treatment of AML. This commentary will focus on discovering novel biomarkers and identifying new therapeutic targets, to analyze and treat AML, on a platform enabled by systems biology approach.

Synthesis and anticancer activity of all known (-)-agelastatin alkaloids

The full details of our enantioselective total syntheses of (-)-agelastatins A-F (1-6), the evolution of a new methodology for synthesis of substituted azaheterocycles, and the first side-by-side evaluation of all known (-)-agelastatin alkaloids against nine human cancer cell lines are described. Our concise synthesis of these alkaloids exploits the intrinsic chemistry of plausible biosynthetic precursors and capitalizes on a late-stage synthesis of the C-ring. The critical copper-mediated cross-coupling reaction was expanded to include guanidine-based systems, offering a versatile preparation of substituted imidazoles. The direct comparison of the anticancer activity of all naturally occurring (-)-agelastatins in addition to eight advanced synthetic intermediates enabled a systematic analysis of the structure-activity relationship within the natural series. Significantly, (-)-agelastatin A (1) is highly potent against six blood cancer cell lines (20-190 nM) without affecting normal red blood cells (>333 μM). (-)-Agelastatin A (1) and (-)-agelastatin D (4), the two most potent members of this family, induce dose-dependent apoptosis and arrest cells in the G2/M-phase of the cell cycle; however, using confocal microscopy, we have determined that neither alkaloid affects tubulin dynamics within cells.

Proteomic profiling identifies distinct protein patterns in acute myelogenous leukemia CD34+CD38- stem-like cells

Acute myeloid leukemia (AML) is believed to arise from leukemic stem-like cells (LSC) making understanding the biological differences between LSC and normal stem cells (HSC) or common myeloid progenitors (CMP) crucial to understanding AML biology. To determine if protein expression patterns were different in LSC compared to other AML and CD34+ populations, we measured the expression of 121 proteins by Reverse Phase Protein Arrays (RPPA) in 5 purified fractions from AML marrow and blood samples: Bulk (CD3/CD19 depleted), CD34-, CD34+(CMP), CD34+CD38+ and CD34+CD38-(LSC). LSC protein expression differed markedly from Bulk (n=31 cases, 93/121 proteins) and CD34+ cells (n= 30 cases, 88/121 proteins) with 54 proteins being significantly different (31 higher, 23 lower) in LSC than in either Bulk or CD34+ cells. Sixty-seven proteins differed significantly between CD34+ and Bulk blasts (n=69 cases). Protein expression patterns in LSC and CD34+ differed markedly from normal CD34+ cells. LSC were distinct from CD34+ and Bulk cells by principal component and by protein signaling network analysis which confirmed individual protein analysis. Potential targetable submodules in LSC included the proteins PU.1(SP1), P27, Mcl1, HIF1α, cMET, P53, Yap, and phospho-Stats 1, 5 and 6. Protein expression and activation in LSC differs markedly from other blast populations suggesting that studies of AML biology should be performed in LSC.

Lower phosphorylation of p38 MAPK blocks the oxidative stress-induced senescence in myeloid leukemic CD34(+)CD38 (-) cells

Leukemia seems to depend on a small population of "leukemia stem cells (LSCs)" for its growth and metastasis. However, the precise surviving mechanisms of LSCs remain obscure. Cellular senescence is an important obstacle for production and surviving of tumor cells. In this study we investigated the activated state of a pathway, in which reactive oxygen species (ROS) induces cellular senescence through DNA damage and phophorylation of p38 MAPK (p38), in myeloid leukemic CD34(+)CD38(-) cells. Bone marrow samples were obtained from patients with acute myeloid leukemia (AML, n=11) and chronic myeloid leukemia (CML, n=9). CD34(+)CD38(-) cells were isolated from mononuclear cells from these bone marrow samples, and K562 and KG1a cells (two kinds of myeloid leukemia cell lines) by mini-magnetic activated cell sorting. Hematopoietic stem cells (HSCs) from human cord blood served as controls. Intracellular ROS level was detected by flow cytometry. DNA damage defined as the γH2AX level was measured by immunofluorescence staining. Real-time RT-PCR was used to detect the expression of p21, a senescence-associated gene. Western blotting and immunofluorescence staining were employed to determine the p38 expression and activation. The proliferation and apoptosis of CD34(+)CD38(-) cells were detected by MTT assay and flow cytometry. Our results showed that ROS and DNA damage were substantially accumulated and p38 was less phosphorated in myeloid leukemic CD34(+)CD38(-) cells as compared with HSCs and H(2)O(2)-induced senescent HSCs. Furthermore, over-phosphorylation of p38 by anisomycin, a selective activator of p38, induced both the senescence-like growth arrest and apoptosis of CD34(+)CD38(-) cells from K562 and KG1a cell lines. These findings suggested that, although excessive accumulation of oxidative DNA damage was present in LSCs, the relatively decreased phosphorylation of p38 might help leukemic cells escape senescence and apoptosis.

Flow cytometric quantification and immunophenotyping of leukemic stem cells in acute myeloid leukemia

Leukemic stem cells (LSCs) are root of clonal growth in acute myeloid leukemia (AML) and responsible for the propagation of leukemic blasts (LBs). LSCs are considered as CD34 + CD38- population among LBs and often express as CD123, CD44, or CD184, which are rarely expressed on normal hematopoietic stem cells and could be the potential therapeutic targets. Using multi-color flow cytometry, we analyzed the proportions of CD34 + CD38- LSCs and expression of CD123, CD44, and CD184 on LSCs in 63 patients with AML. The median proportion of LSCs was 1.3 % (0.0-33.1 %) at the time of diagnosis. Of all patients, 74.6 % of them had CD123-positive LSCs, all patients had CD44-positive LSCs, and 85.7 % had CD184-positive LSCs, respectively. The proportions of LSCs were significantly lower in the complete remission (CR) group compared with non-CR group (P = 0.006). The lower proportions of LSCs in CR group indicated that measurement of the proportion of LSCs might be helpful to predict the prognosis of AML.

Unique dual targeting of thymidylate synthase and topoisomerase1 by FdUMP[10] results in high efficacy against AML and low toxicity

Acute myeloid leukemia (AML) is an aggressive malignancy that leads to marrow failure and death. There is a desperate need for new therapies. The novel fluoropyrimidine, FdUMP[10], was highly active against both human AML cell lines, (IC(50) values, 3.4nM-21.5nM) and murine lines (IC(50) values, 123.8pM-131.4pM). In all cases, the IC(50) of FdUMP[10] was lower than for cytarabine and ∼ 1000 times lower than 5-fluorouracil (5-FU). FdUMP[10] remained effective against cells expressing the Flt3 internal tandem duplication, BCR-ABL, MN1, and an shRNA against p53. It had activity against patient samples at concentrations that did not affect normal hematopoietic cells. FdUMP[10] inhibited thymidylate synthase (TS) and trapped topoisomerase I cleavage complexes (Top1CCs), leading to DNA damage and apoptosis. All cell lines and nearly all primary AML samples examined expressed both TS and Top1. In vivo, FdUMP[10] was active against a syngeneic AML model with a survival advantage equivalent to doxorubicin plus cytarabine. 5-FU treatment was toxic and did not improve survival. FdUMP[10] was better tolerated than 5-FU or cytarabine plus doxorubicin and did not affect normal HSCs, while 5-FU dramatically impaired their ability to engraft. In summary, FdUMP[10] was highly efficacious and better tolerated than standard therapies.

Resistance of leukemic stem-like cells in AML cell line KG1a to natural killer cell-mediated cytotoxicity

Leukemic stem cells (LSCs) play the central role in the relapse and refractory of acute myeloid leukemia (AML) and highlight the critical need for the new therapeutic strategies to directly target the LSC population. However, relatively little is known about the unique molecular mechanisms of drug and natural killer cells (NK)-killing resistance of LSCs because of very small number of LSCs in bone marrow. In this study, we investigated whether established leukemia cell line contains LSCs. We showed that KG1a leukemia cell line contained leukemic stem-like cells, which have been phenotypically restricted within the CD34(+)CD38(-) fractions. CD34(+)CD38(-) cells could generate CD34(+)CD38(+) cells in culture medium and had renewal function. Moreover, CD34(+)CD38(-) cells had self-renewal potential. We found that leukemic stem-like cells from KG1a cells were resistant to chemotherapy and NK-mediated cytotoxicity. NKG2D ligands involve in protecting LSCs from NK-mediated attack. Taken together, our studies provide a novel cell model for leukemic stem cells research. Our data also shed light on mechanism of double resistant to chemotherapy and NK cell immunotherapy, which was helpful for developing novel effective strategies for LSCs.

Acute myeloid leukemia: update in diagnosis and treatment in Brazil

OBJECTIVE

To identify how the Brazilian hematology centers treated and diagnosed cases of acute myeloid leukemia in 2009.

METHODS

An epidemiological observational multicenter study of 11 listed Brazilian centers that treat acute myeloid leukemia and perform bone marrow transplantation. Data were collected from clinical charts of patients with acute myeloid leukemia treated at the said centers between 2005 and 2009. The availability for immunophenotyping and cytogenetic tests was assessed.

RESULTS

During 2009, a total of 345 new cases of acute myeloid leukemia were diagnosed. Differences were noted in the tests performed between patients who initiated treatment at the center and those referred for treatment. Of the participating centers, 72% conducted some type of molecular study in acute myeloid leukemia upon diagnosis.

CONCLUSION

Treatment for acute myeloid leukemia in Brazil shows significantly inferior results when compared to other centers worldwide.

Acute myeloid leukemia stem cells: seek and destroy

Most adult patients with acute myeloid leukemia (AML) die from their disease. Relapses are frequent even after aggressive multiagent chemotherapy and allogeneic stem cell transplantation. AML is a biologically heterogeneous disease, characterized by frequent cytogenetic abnormalities and an increasing spectrum of genetic mutations and molecular aberrations. Laboratory data suggest that AML originates from a rare population of cells, termed leukemic stem cells (LSCs) or leukemia-initiating cells, which are capable of self-renewal, proliferation and differentiation. These cells may persist after treatment and are probably responsible for disease relapse. This review will describe bench and translational research in LSCs and discuss how the data should be used to change the direction of developmental therapeutics and clinical trials in AML.

High-resolution kinetics of cytokine signaling in human CD34/CD117-positive cells in unfractionated bone marrow

Cytokine-mediated phosphorylation of Erk (pErk), ribosomal S6 (pS6), and Stat5 (pStat5) in CD34(+)/CD117(+) blast cells in normal bone marrow from 9 healthy adult donors were analyzed over 60 minutes. Treatment with stem cell factor (SCF), Flt3-ligand (FL), IL-3, and GM-CSF and measurement by multiparametric flow cytometry yielded distinctive, highly uniform phosphoprotein kinetic profiles despite a diverse sample population. The correlated responses for SCF- and FL-stimulated pErk and pS6 were similar. Half the population phosphorylated Erk in response to SCF between 0.9 and 1.2 minutes, and S6 phosphorylation followed approximately a minute later (t&frac12;(pS6 rise) = 2.2-2.7 minutes). The FL response was equally fast but more variable (t&frac12;(pErk rise) = 0.9-1.3 minutes; t&frac12;(pS6 rise) = 2.5-3.5 minutes). Stat5 was not activated in 97% of the cells by either cytokine. IL-3 and GM-CSF were similar to each other with half of blast cells phosphorylating Stat5 and 15% to 20% responding through Erk and S6. Limited comparison with leukemic blasts confirmed universal abnormal signaling in AML that is significantly different from normal bone marrow blasts. These differences included sustained signals, a larger fraction of responding cells, and amplification of phosphorylation levels for at least one phosphoprotein. These data support the eventual use of this approach for disease diagnosis and monitoring.

Activation of the unfolded protein response in human acute myeloid leukemia

There is accumulating evidence for the involvement of the unfolded protein response (UPR) in the pathogenesis of many tumor types in humans. This is particularly the case in rapidly growing solid tumors in which the demand for oxygen and nutrients can exceed the supply until new tumor-initiated blood vessels are formed. In contrast, the role of the UPR during leukemogenesis remains largely unknown. Acute myeloid leukemia (AML) is a genetically heterogeneous clonal disorder characterized by the accumulation of somatic mutations in hematopoietic progenitor cells that alter the physiological regulation of self-renewal, survival, proliferation, or differentiation. The CCAAT/enhancer-binding protein alpha (CEBPA) gene is a key myeloid transcription factor and a frequent target for disruption in AML. In particular, translation of CEBPA mRNA can be specifically blocked by binding of the chaperone calreticulin (CALR), a well-established effector of the UPR, to a stem loop structure within the 5' region of the CEBPA mRNA. The relevance of this mechanism was first elucidated in certain AML subtypes carrying the gene rearrangements t(3;21) or inv(16). In our recent work, we could demonstrate the induction of key effectors of the UPR in leukemic cells of AML patients comprising all subtypes (according to the French-American-British (FAB) classification for human AML). The formation of the spliced variant of the X-box binding protein (XBP1s) was detectable in 17.4% (17 of 105) of AML patients. Consistent with an activated UPR, this group had significantly increased expression of the UPR target genes CALR, the 78 kDa glucose-regulated protein (GRP78), and the CCAAT/enhancer-binding protein homologous protein (CHOP). Consistently, in vitro studies confirmed that calreticulin expression was upregulated via activation of the ATF6 pathway in myeloid leukemic cells. As a consequence, CEBPA protein expression was inhibited in vitro as well as in leukemic cells from patients with activated UPR. We therefore propose a model of the UPR being involved in leukemogenesis through induction of calreticulin along the ATF6 pathway, thereby ultimately suppressing CEBPA translation and contributing to the block in myeloid differentiation and cell-cycle deregulation which represent key features of the leukemic phenotype. From a more clinical point of view, the presence of activated UPR in AML patient samples was found to be associated with a favorable disease course.

Stem cells in cancer: instigators and propagators?

There is growing realization that many - if not all - cancer-cell populations contain a subpopulation of self-renewing stem cells known as cancer stem cells (CSCs). Unlike normal adult stem cells that remain constant in number, CSCs can increase in number as tumours grow, and give rise to progeny that can be both locally invasive and colonise distant sites - the two hallmarks of malignancy. Immunodeficient mouse models in which human tumours can be xenografted provide persuasive evidence that CSCs are present in human leukaemias and many types of solid tumour. In addition, many studies have found similar subpopulations in mouse tumours that show enhanced tumorigenic properties when they are transplanted into histocompatible mice. In this Commentary, we refer to CSCs as tumour-propagating cells (TPCs), a term that reflects the assays that are currently employed to identify them. We first discuss evidence that cancer can originate from normal stem cells or closely related descendants. We then outline the attributes of TPCs and review studies in which they have been identified in various cancers. Finally, we discuss the implications of these findings for successful cancer therapies.

Cancer stem cells: problems for therapy?

Many, if not all, tumours contain a sub-population of self-renewing and expanding stem cells known as cancer stem cells (CSCs). The symmetric division of CSCs is one mechanism enabling expansion in their numbers as tumours grow, while epithelial-mesenchymal transition (EMT) is an increasingly recognized mechanism to generate further CSCs endowed with a more invasive and metastatic phenotype. Putative CSCs are prospectively isolated using methods based on either a surface marker or an intracellular enzyme activity and then assessed by a 'sphere-forming' assay in non-adherent culture and/or by their ability to initiate new tumour growth when xenotransplanted into immunocompromised mice-hence, these cells are often referred to as tumour-propagating cells (TPCs). Cell sub-populations enriched for tumour-initiating ability have also been found in murine tumours, countering the argument that xenografting human cells merely select human cells with an ability to grow in mice. Cancer progression can be viewed as an evolutionary process that generates new/multiple clones with a fresh identity; this may be a major obstacle to successful cancer stem cell eradication if treatment targets only a single type of stem cell. In this review, we first briefly discuss evidence that cancer can originate from normal stem cells or closely related descendants. We then outline the attributes of CSCs and review studies in which they have been identified in various cancers. Finally, we discuss the implications of these findings for successful cancer therapies, concentrating on the self-renewal pathways (Wnt, Notch, and Hedgehog), aldehyde dehydrogenase activity, EMT, miRNAs, and other epigenetic modifiers as potential targets for therapeutic manipulation.

Fluorouracil selectively enriches stem-like leukemic cells in a leukemic cell line

Recent studies have reported that cancer stem cells (CSCs) could be isolated from solid cancer cell lines, in which the purity of CSCs was higher than that from tumor tissues. Separation of CSCs from leukemic cell lines was rarely reported. In this study, CD34⁺CD38^- stem-like cell subsets in human KG-1a leukemic cell line were enriched by cytotoxic agent 5-fluorouracil (5-FU). After 4 days incubation of KG-1a cell line with 5-FU (50 μg/ml), the CD34⁺CD38^- subpopulation of cell lines was enriched more than 10 times. The enriched cells had proliferate potential in vitro, low level of RNA transcription and Hoechst 33342 dye efflux ability, accompanied by high expression of ATP-binding cassette transporter protein ABCG2. Our findings suggest that treatment with 5-FU offers an easy method to isolate leukemic stem-like subpopulation. It can facilitate studies of leukemic stem cell biology and the development of new therapeutic strategies.

Differential cytogenomics and miRNA signature of the Acute Myeloid Leukaemia Kasumi-1 cell line CD34+38- compartment

The t(8;21) Acute Myeloid Leukaemia (AML) Kasumi-1 cell line with N822K KIT mutation, is a model system for leukemogenesis. As AML initiating cells reside in the CD34(+)CD38(-) fraction, we addressed the refined cytogenomic characterization and miRNA expression of Kasumi-1 cell line and its FACS-sorted subpopulations focussing on this compartment. By conventional cytogenetics, Spectral-Karyotyping and array-CGH the cytogenomic profile of Kasumi-1 cells evidenced only subtle regions differentially represented in CD34(+)CD38(-) cells. Expression profiling by a miRNA platform showed a set of miRNA differentially expressed in paired subpopulations and the signature of miR-584 and miR-182 upregulation in the CD34(+)CD38(-) fraction.

Hematopoietic stem cells and retroviral infection

Retroviral induced malignancies serve as ideal models to help us better understand the molecular mechanisms associated with the initiation and progression of leukemogenesis. Numerous retroviruses including AEV, FLV, M-MuLV and HTLV-1 have the ability to infect hematopoietic stem and progenitor cells, resulting in the deregulation of normal hematopoiesis and the development of leukemia/lymphoma. Research over the last few decades has elucidated similarities between retroviral-induced leukemogenesis, initiated by deregulation of innate hematopoietic stem cell traits, and the cancer stem cell hypothesis. Ongoing research in some of these models may provide a better understanding of the processes of normal hematopoiesis and cancer stem cells. Research on retroviral induced leukemias and lymphomas may identify the molecular events which trigger the initial cellular transformation and subsequent maintenance of hematologic malignancies, including the generation of cancer stem cells. This review focuses on the role of retroviral infection in hematopoietic stem cells and the initiation, maintenance and progression of hematological malignancies.

Fusion of dendritic cells and CD34+CD38- acute myeloid leukemia (AML) cells potentiates targeting AML-initiating cells by specific CTL induction

Distinct leukemia-initiating cells (L-ICs) represent a critical target for therapeutic intervention of acute myeloid leukemia (AML). A potential strategy to eradicate L-ICs is to generate L-IC-specific cytotoxic T lymphocytes (CTLs). However, owing to rarity and immortality of L-ICs, it is difficult for antigen-presenting cells to capture L-ICs for specific antigen presentation. Here, we report a novel approach by fusing allogeneic dendritic cells (DCs) and CD34CD38 AML progenitor cells, through which specific CTLs were effectively induced, leading to the cytolysis to AML-initiating cells. Fusion of either DC/CD34CD38 AML cell or DC/CD34 AML cell could effectively induce the proliferation and activation of CTLs. However, only the former CTLs could effectively attack AML progenitor cells, and result in the unkilled progenitor/initiating cells losing the abilities of active proliferation in vitro and engraftment in NOD-SCID mice. These findings suggest that AML progenitor/initiating cell-specific CTLs may be generated based on allogeneic DC/progenitor cell fusion strategy; the induced CTLs may potentially eradicate AML by targeting L-ICs directly or indirectly.