Human acute myeloid leukemia stem cells

Hesperidin/Salinomycin Combination; a Natural Product for Deactivation of the PI3K/Akt Signaling Pathway and Anti-Apoptotic Factors in KG1a Cells

AML is a highly aggressive malignant clonal disease of hematopoietic origin. Hesperidin as a polyphenol glycoside, Activates the apoptotic pathway and salinomycin as a k + selective ionophore. We examined how hesperidin and salinomycin induce pro-apoptotic effects in KG1a cells. Cells were divided into four groups; 1) control cells (CRTL), 2) cells treated with hesperidin 85 μM, 3) cells treated with 2 μM salinomycin, 4) cells treated with combination of salinomycin and hesperidin. The MTT assay was implemented to determine the IC50 of hesperidin and salinomycin in KG1a cell lines. Propidium iodide staining and flow cytometry were used to analyze the distribution of the cell cycle. The level of ROS was evaluated by fluorescent microscopy and spectrophotometry. Additionally, Akt, XIAP, Bad, and FOXO1 gene expression was analyzed by real-time PCR. Hesperidin/Salinomycin decreased the viability of KG1a leukemic cells more than Hesperidin and Salinomycin separately. Changes in the shape of apoptotic cells and rise in ROS levels were detected after Hesperidin/Salinomycin treatment. Our findings showed that following Hesperidin/Salinomycin treatment, the expression of PI3K/AKT signaling pathway related genes (AKT, PTEN and FOXO1), were in line with the destruction of KG-1a cells. Furthermore, XIAP and BAD mRNA were regulated to trigger apoptosis in cancer cells. The study discovered that hesperidin and salinomycin, could effectively hinder the PI3K/Akt signaling pathway in leukemia cancer cells. Also, the combination of hesperidin and salinomycin has the potential to be a treatment option for acute myeloid leukemia.

Doxorubicin-Loaded Polymeric Micelles Conjugated with CKR- and EVQ-FLT3 Peptides for Cytotoxicity in Leukemic Stem Cells

Doxorubicin (Dox) is the standard chemotherapeutic agent for acute myeloblastic leukemia (AML) treatment. However, 40% of Dox-treated AML cases relapsed due to the presence of leukemic stem cells (LSCs). Thus, poloxamer 407 and CKR- and EVQ-FLT3 peptides were used to formulate Dox-micelles (DMs) and DM conjugated with peptides (CKR and EVQ) for improving AML-LSC treatment. Results indicated that DMs with a weight ratio of Dox to P407 of 1:200 had a particle size of 23.3 ± 1.3 nm with a high percentage of Dox entrapment. They were able to prolong drug release and maintain physicochemical stability. Following effective DM preparation, P407 was modified and conjugated with FLT3 peptides, CKR and EVQ to formulate DM-CKR, DM-EVQ, and DM-CKR+DM-EVQ. Freshly synthesized DMs displaying FLT3 peptides showed particle sizes smaller than 50 nm and a high drug entrapment level, comparable with DMs. DM-CKR+DM-EVQ was considerably more toxic to KG-1a (AML LSC-like cell model) than Dox-HCl. These FLT3-targeted DMs could increase drug uptake and induce apoptosis induction. Due to an increase in micelle-LSC binding and uptake, DMs displaying both peptides tended to improve the potency of Dox compared to a single peptide-coupled micelle.

Targeting Mitochondrial Oxidative Phosphorylation Eradicates Acute Myeloid Leukemic Stem Cells

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy characterized by multiple cytogenetic and molecular abnormalities, with a very poor prognosis. Current treatments for AML often fail to eliminate leukemic stem cells (LSCs), which perpetuate the disease. LSCs exhibit a unique metabolic profile, especially dependent on oxidative phosphorylation (OXPHOS) for energy production. Whereas, normal hematopoietic stem cells (HSCs) and leukemic blasts rely on glycolysis for adenosine triphosphate (ATP) production. Thus, understanding the regulation of OXPHOS in LSCs may offer effective targets for developing clinical therapies in AML. This review summarizes these studies with a focus on the regulation of the electron transport chain (ETC) and tricarboxylic acid (TCA) cycle in OXPHOS and discusses potential therapies for eliminating LSCs.

Co-Treatments of Edible Curcumin from Turmeric Rhizomes and Chemotherapeutic Drugs on Cytotoxicity and FLT3 Protein Expression in Leukemic Stem Cells

This study aims to enhance efficacy and reduce toxicity of the combination treatment of a drug and curcumin (Cur) on leukemic stem cell and leukemic cell lines, including KG-1a and KG-1 (FLT3+ LSCs), EoL-1 (FLT3+ LCs), and U937 (FLT3- LCs). The cytotoxicity of co-treatments of doxorubicin (Dox) or idarubicin (Ida) at concentrations of the IC10-IC80 values and each concentration of Cur at the IC20, IC30, IC40, and IC50 values (conditions 1, 2, 3, and 4) was determined by MTT assays. Dox-Cur increased cytotoxicity in leukemic cells. Dox-Cur co-treatment showed additive and synergistic effects in several conditions. The effect of this co-treatment on FLT3 expression in KG-1a, KG-1, and EoL-1 cells was examined by Western blotting. Dox-Cur decreased FLT3 protein levels and total cell numbers in all the cell lines in a dose-dependent manner. In summary, this study exhibits a novel report of Dox-Cur co-treatment in both enhancing cytotoxicity of Dox and inhibiting cell proliferation via FLT3 protein expression in leukemia stem cells and leukemic cells. This is the option of leukemia treatment with reducing side effects of chemotherapeutic drugs to leukemia patients.

Targeting Energy Metabolism in Cancer Stem Cells: Progress and Challenges in Leukemia and Solid Tumors

Malignant stem cells have long been considered a key therapeutic target in leukemia. Therapeutic strategies designed to target the fundamental biology of leukemia stem cells while sparing normal hematopoietic cells may provide better outcomes for leukemia patients. One process in leukemia stem cell biology that has intriguing therapeutic potential is energy metabolism. In this article we discuss the metabolic properties of leukemia stem cells and how targeting energy metabolism may provide more effective therapeutic regimens for leukemia patients. In addition, we highlight the similarities and differences in energy metabolism between leukemia stem cells and malignant stem cells from solid tumors.

The PI3K-Akt-mTOR Signaling Pathway in Human Acute Myeloid Leukemia (AML) Cells

Acute myeloid leukemia (AML) is a heterogeneous group of diseases characterized by uncontrolled proliferation of hematopoietic stem cells in the bone marrow. Malignant cell growth is characterized by disruption of normal intracellular signaling, caused by mutations or aberrant external signaling. The phosphoinositide 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway (PI3K-Akt-mTOR pathway) is among one of the intracellular pathways aberrantly upregulated in cancers including AML. Activation of this pathway seems important in leukemogenesis, and given the central role of this pathway in metabolism, the bioenergetics of AML cells may depend on downstream signaling within this pathway. Furthermore, observations suggest that constitutive activation of the PI3K-Akt-mTOR pathway differs between patients, and that increased activity within this pathway is an adverse prognostic parameter in AML. Pharmacological targeting of the PI3K-Akt-mTOR pathway with specific inhibitors results in suppression of leukemic cell growth. However, AML patients seem to differ regarding their susceptibility to various small-molecule inhibitors, reflecting biological heterogeneity in the intracellular signaling status. These findings should be further investigated in both preclinical and clinical settings, along with the potential use of this pathway as a prognostic biomarker, both in patients receiving intensive curative AML treatment and in elderly/unfit receiving AML-stabilizing treatment.

Distinct roles of mesenchymal stem and progenitor cells during the development of acute myeloid leukemia in mice

Despite increasing evidence for the involvement of bone marrow (BM) hematopoietic stem cell niche in leukemogenesis, how BM mesenchymal stem and progenitor cells (MSPCs) contribute to leukemia niche formation and progression remains unclear. Using an MLL-AF9 acute myeloid leukemia (AML) mouse model, we demonstrate dynamic alterations of BM cellular niche components, including MSPCs and endothelial cells during AML development and its association with AML engraftment. Primary patient AML cells also induced similar niche alterations in xenografted mice. AML cell infiltration in BM causes an expansion of early B-cell factor 2⁺ (Ebf2⁺) MSPCs with reduced Cxcl12 expression and enhanced generation of more differentiated mesenchymal progenitor cells. Importantly, in vivo fate-mapping indicates that Ebf2⁺ MSPCs participated in AML niche formation. Ebf2⁺ cell deletion accelerated the AML development. These data suggest that native BM MSPCs may suppress AML. However, they can be remodeled by AML cells to form leukemic niche that might contribute to AML progression. AML induced dysregulation of hematopoietic niche factors like Angptl1, Cxcl12, Kitl, Il6, Nov, and Spp1 in AML BM MSPCs, which was associated with AML engraftment and partially appeared before the massive expansion of AML cells, indicating the possible involvement of the niche factors in AML progression. Our study demonstrates distinct dynamic features and roles of BM MSPCs during AML development.

Mathematical modeling of bone marrow - peripheral blood dynamics in the disease state based on current emerging paradigms, part II

The cancer stem cell hypothesis has gained currency in recent times but concerns remain about its scientific foundations because of significant gaps that exist between research findings and comprehensive knowledge about cancer stem cells (CSCs). In this light, a mathematical model that considers hematopoietic dynamics in the diseased state of the bone marrow and peripheral blood is proposed and used to address findings about CSCs. The ensuing model, resulting from a modification and refinement of a recent model, develops out of the position that mathematical models of CSC development, that are few at this time, are needed to provide insightful underpinnings for biomedical findings about CSCs as the CSC idea gains traction. Accordingly, the mathematical challenges brought on by the model that mirror general challenges in dealing with nonlinear phenomena are discussed and placed in context. The proposed model describes the logical occurrence of discrete time delays, that by themselves present mathematical challenges, in the evolving cell populations under consideration. Under the challenging circumstances, the steady state properties of the model system of delay differential equations are obtained, analyzed, and the resulting mathematical predictions arising therefrom are interpreted and placed within the framework of findings regarding CSCs. Simulations of the model are carried out by considering various parameter scenarios that reflect different experimental situations involving disease evolution in human hosts. Model analyses and simulations suggest that the emergence of the cancer stem cell population alongside other malignant cells engenders higher dimensions of complexity in the evolution of malignancy in the bone marrow and peripheral blood at the expense of healthy hematopoietic development. The model predicts the evolution of an aberrant environment in which the malignant population particularly in the bone marrow shows tendencies of reaching an uncontrollable equilibrium state. Essentially, the model shows that a structural relationship exists between CSCs and non-stem malignant cells that confers on CSCs the role of temporally enhancing and stimulating the expansion of non-stem malignant cells while also benefitting from increases in their own population and these CSCs may be the main protagonists that drive the ultimate evolution of the uncontrollable equilibrium state of such malignant cells and these may have implications for treatment.

Yi-qi-yang-yin-tang increases the sensitivity of KG1a leukemia stem cells to daunorubicin by promoting cell cycle progression and regulating the expression of PTEN, TOPOII and mTOR

The present study aimed to investigate the effects of serum containing a combination of yi-qi-yang-yin-tang (YQYYT) and daunorubicin (DNR) on multidrug resistance in KG1a leukemia stem cells (LSCs). The effects of YQYYT and DNR on proliferation, cell cycle progression and the expression of phosphatase and tensin homolog (PTEN), topoisomerase II (Topo II) and mechanistic target of rapamycin (mTOR) in KG1a cells were investigated in vitro using cell counting kit-8 assay, flow cytometry, reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. It was revealed that YQYYT-containing serum did not affect proliferation of KG1a cells compared with the blank group. Furthermore, there were no significant differences on the inhibition of proliferation among different groups at various concentrations of YQYYT. Treatment with YQYYT-containing serum (volume, 20 and 40 µl) and DNR was able to significantly inhibit the proliferation of KG1a cells compared with the blank group. The inhibition rate in the treatment group with YQYYT-containing serum (40 µl) and DNR for 48 h (72.5%) was higher compared with treatment for 24 h (60.4%, P<0.01). Treatment with YQYYT-containing serum was able to promote G₀ phase of KG1a cells into cell cycle in a dose- and time-dependent manner, and significantly upregulated the mRNA expression of PTEN and Topo II, but did not affect mTOR expression compared with the blank group. Treatment with serum containing YQYYT alone did not directly affect the proliferation of KG1a cells, but when the cells were treated with a combination of YQYYT-containing serum and DNR, the proliferation of KG1a cells was significantly inhibited in a dose- and time-dependent manner. Furthermore, treatment with YQYYT-containing serum was able to promote cell cycle progression of KG1a cells in the G₀ phase and upregulate the expression of the negative regulatory genes PTEN and Topo II. These results indicated the potential of YQYYT to reverse multidrug resistance in LSCs.

Overexpression of long non-coding RNA zinc finger antisense 1 in acute myeloid leukemia cell lines influences cell growth and apoptosis

The association between long non-coding RNA zinc finger antisense 1 (ZFAS1) and acute myeloid leukemia (AML) has not yet been investigated. The present study aimed to assess the potential role of ZFAS1 in AML cell proliferation and apoptosis. The expression of ZFAS1 mRNA in various AML cell lines (HL-60, KG-1, ML-1 and SKNO-1) was measured by reverse transcription-quantitative polymerase chain reaction. The results showed that ZFAS1 expression was increased in all four human AML cell lines compared with the control cell lines (T lymphocytic leukemia or Burkitt's lymphoma). Transfection with small interfering RNA into human AML cells established ZFAS1 knockdown. A cell-counting kit-8 (CCK-8) assay was used to investigate the effect of ZFAS1 on AML cell proliferation and the effect of ZFAS1 on the cell cycle and cell apoptosis was assessed using flow cytometry. Notably, the CCK-8 assay demonstrated that ZFAS1 knockdown inhibited cell proliferation in HL-60 and SKNO-1 cell lines and flow cytometry analysis indicated that ZFAS1 knockdown induced AML cell cycle G1 phase arrest and triggered cell apoptosis. Therefore, the present study indicated that ZFAS1 promoted the proliferation and inhibited the apoptosis of AML cells.

What roles do colon stem cells and gap junctions play in the left and right location of origin of colorectal cancers?

This "Commentary" examines an important clinical observation that right-sided colorectal cancers appear less treatable than the left-sided cancers. The concepts of (a) the "initiation/promotion/progression" process, (b) the stem cell hypothesis, (c) the role gap junctional intercellular communication, (d) cancer cells lacking GJIC either because of the non-expression of connexin genes or of non-functional gap junction proteins, and (e) the role of the microbiome in promoting initiated colon stem cells to divide symmetrically or asymmetrically are examined to find an explanation. It has been speculated that "embryonic-like" lesions in the ascending colon are initiated stem cells, promoted via symmetrical cell division, while the polyp-type lesions in the descending colon are initiated stem cells stimulated to divide asymmetrically. To test this hypothesis, experiments could be designed to examine if right-sided lesions might express Oct4A and ABCG2 genes but not any connexin genes, whereas the left-sided lesions might express a connexin gene, but not Oct4A or the ABCG2 genes. Treatment of the right sided lesions might include transcriptional regulators, whereas the left-sided lesions would need to restore the posttranslational status of the connexin proteins.

Therapeutic targeting of acute myeloid leukemia stem cells

For more than 50 years, investigators have considered a malignant stem cell as the potential origin of and a key therapeutic target for acute myeloid leukemia (AML) and other forms of cancer.^1-4 The nature and existence of tumor-initiating cells for leukemia and other malignancies have long been the subject of intense and rigorous study; indeed, the promise of the potential to eradicate such cells is clear. However, until recently, deficiencies in our understanding of the nature of these cell populations, coupled with a limited ability to therapeutically exploit their weaknesses, have been limiting factors in realizing the goal of targeting leukemic stem cells (LSCs). Exciting new insights into the fundamental underpinnings of LSCs are now being made in an era in which drug development pipelines offer the potential to specifically target pathways of significance. Therefore, the focus in this new era, characterized by the confluence of understanding LSCs and the ability to target them, is shifting from "if it can be done" to "how it will be done." Moving from a theoretical stage to this hopeful era of possibilities, new challenges expectedly arise, and our focus now must shift to determining the best strategy by which to target LSCs, with their well-documented heterogeneity and readily evident intra- and interpatient variability. The purpose of this review is therefore both to summarize the key scientific findings pertinent to AML LSC targeting and to consider methods of clinical evaluation that will be most effective for identifying successful LSC-directed therapies.

Single-Cell Mass Cytometry of Acute Myeloid Leukemia and Leukemia Stem/Progenitor Cells

Mass cytometry time-of-flight (CyTOF) empowers us to understand acute myeloid leukemia (AML) biology at the single-cell level. This technology, combined with advanced data-analysis methods, enables identification and characterization of the rare AML stem/progenitor cells that play key roles in drug resistance and AML relapse. Here we provide a protocol for AML sample preparation for CyTOF and keynotes emphasizing critical steps in and troubleshooting strategies for this procedure.

Evolution of Microbial Quorum Sensing to Human Global Quorum Sensing: An Insight into How Gap Junctional Intercellular Communication Might Be Linked to the Global Metabolic Disease Crisis

The first anaerobic organism extracted energy for survival and reproduction from its source of nutrients, with the genetic means to ensure protection of its individual genome but also its species survival. While it had a means to communicate with its community via simple secreted molecules (“quorum sensing”), the eventual shift to an aerobic environment led to multi-cellular metazoan organisms, with evolutionary-selected genes to form extracellular matrices, stem cells, stem cell niches, and a family of gap junction or “connexin” genes. These germinal and somatic stem cells responded to extracellular signals that triggered intra-cellular signaling to regulate specific genes out of the total genome. These extra-cellular induced intra-cellular signals also modulated gap junctional intercellular communication (GJIC) in order to regulate the new cellular functions of symmetrical and asymmetrical cell division, cell differentiation, modes of cell death, and senescence. Within the hierarchical and cybernetic concepts, differentiated by neurons organized in the brain of the Homo sapiens, the conscious mind led to language, abstract ideas, technology, myth-making, scientific reasoning, and moral decision–making, i.e., the creation of culture. Over thousands of years, this has created the current collision between biological and cultural evolution, leading to the global “metabolic disease” crisis.

Concurrent targeting Akt and sphingosine kinase 1 by A-674563 in acute myeloid leukemia cells

Akt signaling plays a pivotal role in acute myeloid leukemia (AML) development and progression. In the present study, we evaluated the potential anti-AML activity by a novel Akt kinase inhibitor A-674563. Our results showed that A-674563 dose-dependently inhibited survival and proliferation of U937 AML cells and six lines of human AML progenitor cells, yet sparing human peripheral blood mononuclear leukocytes (PBMCs). A-674563 activated caspase-3/9 and apoptosis in the AML cells. Reversely, the pan-caspase inhibitor z-VAD-CHO dramatically alleviated A-674563-induced AML cell apoptosis and cytotoxicity. For the molecular study, we showed that A-674563 blocked Akt activation in U937 cells and human AML progenitor cells. Further, A-674563 decreased sphingosine kinase 1 (SphK1) activity in above AML cells to deplete pro-survival sphingosine-1-phosphate (S1P) and boost pro-apoptotic ceramide production. Such an effect on SphK1 signaling by A-674563 appeared independent of Akt blockage. Significantly, K6PC-5, a novel SphK1 activator, or supplement with S1P attenuated A-674563-induced ceramide production, and subsequent U937 cell death and apoptosis. Importantly, intraperitoneal injection of A-674563 at well-tolerated doses suppressed U937 leukemic xenograft tumor growth in nude mice, whiling significantly improving the animal survival. The results of the current study demonstrate that A-674563 exerts potent anti-leukemic activity in vitro and in vivo, possibly via concurrent targeting Akt and SphK1 signalings.

Mathematical modeling of bone marrow--peripheral blood dynamics in the disease state based on current emerging paradigms, part I

Stemming from current emerging paradigms related to the cancer stem cell hypothesis, an existing mathematical model is expanded and used to study cell interaction dynamics in the bone marrow and peripheral blood. The proposed mathematical model is described by a system of nonlinear differential equations with delay, to quantify the dynamics in abnormal hematopoiesis. The steady states of the model are analytically and numerically obtained. Some conditions for the local asymptotic stability of such states are investigated. Model analyses suggest that malignancy may be irreversible once it evolves from a nonmalignant state into a malignant one and no intervention takes place. This leads to the proposition that a great deal of emphasis be placed on cancer prevention. Nevertheless, should malignancy arise, treatment programs for its containment or curtailment may have to include a maximum and extensive level of effort to protect normal cells from eventual destruction. Further model analyses and simulations predict that in the untreated disease state, there is an evolution towards a situation in which malignant cells dominate the entire bone marrow - peripheral blood system. Arguments are then advanced regarding requirements for quantitatively understanding cancer stem cell behavior. Among the suggested requirements are, mathematical frameworks for describing the dynamics of cancer initiation and progression, the response to treatment, the evolution of resistance, and malignancy prevention dynamics within the bone marrow - peripheral blood architecture.

Rapid in-vitro testing for chemotherapy sensitivity in leukaemia patients

Bioluminescent bacterial biosensors can be used in a rapid in vitro assay to predict sensitivity to commonly used chemotherapy drugs in acute myeloid leukemia (AML). The nucleoside analog cytarabine (ara-C) is the key agent for treating AML; however, up to 30 % of patients fail to respond to treatment. Screening of patient blood samples to determine drug response before commencement of treatment is needed. To achieve this aim, a self-bioluminescent reporter strain of Escherichia coli has been constructed and evaluated for use as an ara-C biosensor and an in vitro assay has been designed to predict ara-C response in clinical samples. Transposition mutagenesis was used to create a cytidine deaminase (cdd)-deficient mutant of E. coli MG1655 that responded to ara-C. The strain was transformed with the luxCDABE operon and used as a whole-cell biosensor for development an 8-h assay to determine ara-C uptake and phosphorylation by leukemic cells. Intracellular concentrations of 0.025 μmol/L phosphorylated ara-C were detected by significantly increased light output (P < 0.05) from the bacterial biosensor. Results using AML cell lines with known response to ara-C showed close correlation between the 8-h assay and a 3-day cytotoxicity test for ara-C cell killing. In retrospective tests with 24 clinical samples of bone marrow or peripheral blood, the biosensor-based assay predicted leukemic cell response to ara-C within 8 h. The biosensor-based assay may offer a predictor for evaluating the sensitivity of leukemic cells to ara-C before patients undergo chemotherapy and allow customized treatment of drug-sensitive patients with reduced ara-C dose levels. The 8-h assay monitors intracellular ara-CTP (cytosine arabinoside triphosphate) levels and, if fully validated, may be suitable for use in clinical settings.

Ovarian cancer stem cells: Can targeted therapy lead to improved progression-free survival?

Despite significant effort and research funds, epithelial ovarian cancer remains a very deadly disease. There are no effective screening methods that discover early stage disease; the majority of patients are diagnosed with advanced disease. Treatment modalities consist primarily of radical debulking surgery followed by taxane and platinum-based chemotherapy. Newer therapies including limited targeted agents and intraperitoneal delivery of chemotherapeutic drugs have improved disease-free intervals, but failed to yield long-lasting cures in most patients. Chemotherapeutic resistance, particularly in the recurrent setting, plagues the disease. Targeting the pathways and mechanisms behind the development of chemoresistance in ovarian cancer could lead to significant improvement in patient outcomes. In many malignancies, including blood and other solid tumors, there is a subgroup of tumor cells, separate from the bulk population, called cancer stem cells (CSCs). These CSCs are thought to be the cause of metastasis, recurrence and resistance. However, to date, ovarian CSCs have been difficult to identify, isolate, and target. It is felt by many investigators that finding a putative ovarian CSC and a chemotherapeutic agent to target it could be the key to a cure for this deadly disease. This review will focus on recent advances in this arena and discuss some of the controversies surrounding the concept.

Human adult stem cells as the target cells for the initiation of carcinogenesis and for the generation of "cancer stem cells"

The inference to stem cells has been found in ancient myths and the concept of stem cells has existed in the fields of plant biology, developmental biology and embryology for decades. In the field of cancer research, the stem cell theory was one of the earliest hypotheses on the origin of a cancer from a single cell. However, an opposing hypothesis had it that an adult differentiated somatic cell could "de-differentiate" to become a cancer cell. Only within the last decade, via the "cloning" of Dolly, the sheep, did the field of stem cell biology really trigger an exciting revolution in biological research. The isolation of human embryonic stem cells has created a true revolution in the life sciences that has led to the hope that these human stem cells could lead to (a) basic science understanding of gene regulation during differentiation and development; (b) stem cell therapy; (c) gene therapy via stem cells; (d) the use of stem cells for drug discovery; (e) screening for toxic effects of chemicals; and (f) understand the aging and diseases of aging processes.

Expression of CD90, CD96, CD117, and CD123 on different hematopoietic cell populations from pediatric patients with acute myeloid leukemia

BACKGROUND AND AIMS

In trying to contribute to our knowledge on the biology of hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC) from pediatric acute myeloid leukemia (AML), in the present study we analyzed the expression of four cell surface antigens relevant to human hematopoiesis-CD90, CD96, CD117, and CD123-in bone marrow from pediatric AML patients and normal control subjects.

METHODS

CD34(+) CD38(-) cells (enriched for HSC) and CD34(+) CD38(+) cells (enriched for HPC) were resolved on the basis of CD34 and CD38 expression. Concomitantly, expression of CD90 and CD96 or CD117 and CD123 was assessed by multicolor flow cytometry in each cell population.

RESULTS

CD90 and CD117 were expressed in a low proportion of CD34(+) CD38(-) and CD34(+) CD38(+) cells and no significant differences were observed between normal marrow and AML at diagnosis. In contrast, CD96(+) cells and CD123(+) cells were found at significantly higher levels in both cell populations from AML at diagnosis, as compared to normal marrow. Levels of both cell surface markers after treatment remained higher than in normal marrow.

DISCUSSION

These results show an increased frequency of CD96(+) and CD123(+) cells within the CD34(+) cell population from pediatric AML; this is consistent with the findings reported previously for adult AML. Our study supports the notion that expression of such antigens should be explored for their use as markers for diagnosis and prognosis.

Investigation and verification of a bioluminescent biosensor for the quantitation of ara-CTP generation: a biomarker for cytosine arabinoside sensitivity in acute myeloid leukaemia

A novel whole cell bacterial biosensor, which emits light in response to the active metabolite of cytosine arabinoside (ara-C, cytarabine), ara-CTP, has been investigated and verified. The biosensor has been formulated as an ex vivo assay, designed for peripheral blood or bone marrow cells, which can produce a clinical result within a working day. The nucleoside analogue ara-C is a key agent for treatment of acute myeloid leukaemia (AML); treatment decisions are made rapidly with AML, patients often receiving same-day commencement of chemotherapy. Currently no rapid predictive test is available to select appropriate therapy for patients prior to treatment. Experiments were designed to determine optimal assay conditions using leukaemic cell lines. We observed a significant increase (~15 fold) in bioluminescence signal compared to control after 8-h incubation of the biosensor with ara-C. This corresponded to a >2-log increase in light output per bacterial cell. Interestingly, bioluminescence conferred a survival advantage to the bacteria following ara-C treatment. The assay is sensitive (lower limit of quantitation of 0.05 µM), selective, accurate (≤ 15% RE) and precise (≤ 15% coefficient of variation) over a linear concentration range of ara-CTP (0.05-0.5 µM), and detection is independent of reaction volume. Recovery of added standard was tested using ex vivo patient leukaemic cells (n=5). Stability studies on lyophilized bacterial biosensor were performed to ensure maintenance of performance over 12 months. The biosensor assay could be invaluable to the clinician, assisting with treatment selection, and potentially mitigating the risks of resistance and toxicity observed with this drug.

Developmental signaling pathways in cancer stem cells of solid tumors

BACKGROUND

The intricate regulation of several signaling pathways is essential for embryonic development and adult tissue homeostasis. Cancers commonly display aberrant activity within these pathways. A population of cells identified in several cancers, termed cancer stem cells (CSCs) show similar properties to normal stem cells and evidence suggests that altered developmental signaling pathways play an important role in maintaining CSCs and thereby the tumor itself.

SCOPE OF REVIEW

This review will focus on the roles of the Notch, Wnt and Hedgehog pathways in the brain, breast and colon cancers. We describe the roles these pathways play in normal tissue homeostasis through the regulation of stem cell fate in these three tissues, and the experimental evidence indicating that the role of these pathways in cancers of these is directly linked to CSCs.

MAJOR CONCLUSIONS

A large body of evidence is accumulating to indicate that the deregulation of Notch, Wnt and Hedgehog pathways play important roles in both normal and cancer stem cells. We are only beginning to understand how these pathways interact, how they are coordinated during normal development and adult tissue homeostasis, and how they are deregulated during cancer. However, it is becoming increasingly clear that if we are to target CSCs therapeutically, it will likely be necessary to develop combination therapies.

GENERAL SIGNIFICANCE

If CSCs are the driving force behind tumor maintenance and growth then understanding the molecular mechanisms regulating CSCs is essential. Such knowledge will contribute to better targeted therapies that could significantly enhance cancer treatments and patient survival. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Hematopoietic stem cells, progenitor cells and leukemic stem cells in adult myeloproliferative neoplasms

The understanding of myeloproliferative neoplasms has changed dramatically since Dameshek proposed his classification over 50 years ago. Our knowledge of the types of cells which constitute the hematopoietic system and of how they are regulated has also appreciated significantly over this time. This review relates what is currently known about the acquired genetic mutations associated with adult myeloproliferative neoplasms to how they lead to the hematopoietic perturbations of myeloproliferative disease. There is a particular focus on how stem and progenitor cell compartments are affected by BCR-ABL1 and JAK2V617F mutations, and the particular issue of resistance of leukemic stem cells to conventional and targeted therapies.

Engineering a CD123xCD3 bispecific scFv immunofusion for the treatment of leukemia and elimination of leukemia stem cells

Engineered bispecific antibodies that recruit cytotoxic lymphocytes to kill specific tumor cells have been showing promising clinical results. Here, we describe a bispecific single-chain Fv (scFv) immunofusion or BIf to target CD123(+) leukemia, that contains an anti-CD123 scFv fused at the N-terminus of human IgG1 hinge-C(H)2-C(H)3, and an anti-CD3 scFv fused at C-terminus. When expressed from transfected CHO-S cells, CD123xCD3 BIf forms a homodimer that provides a structure of N-terminal tumor-targeting domain that closely resembles natural antibody. The CD123xCD3 dimeric structure also provides binding affinity to CD123(+) tumor cells with a Kd of 10(-10) M, one to two orders of magnitude stronger than traditional bispecific antibody constructs. The location of the anti-CD3 scFv at C-terminus of BIf reduces the binding affinity to CD3(+) T cells by two orders, which could help to prevent non-specific T-cell activation. CD123xCD3 BIf is able to achieve T-cell-mediated target cell killing activities at low pM levels with E/T ratios as low as 2. Overall, the inclusion of human IgG1 constant region in BIf construct increases target cell-binding affinity; potentially increases serum half-life by its larger size and FcRn-mediated salvage system; and includes the abilities to activate the additional antibody-mediated cellular cytotoxicities.

Myeloid translocation gene 16 is required for maintenance of haematopoietic stem cell quiescence

The t(8;21) and t(16;21) that are associated with acute myeloid leukaemia disrupt two closely related genes termed Myeloid Translocation Genes 8 (MTG8) and 16 (MTG16), respectively. Many of the transcription factors that recruit Mtg16 regulate haematopoietic stem and progenitor cell functions and are required to maintain stem cell self-renewal potential. Accordingly, we found that Mtg16-null bone marrow (BM) failed in BM transplant assays. Moreover, when removed from the animal, Mtg16-deficient stem cells continued to show defects in stem cell self-renewal assays, suggesting a requirement for Mtg16 in this process. Gene expression analysis indicated that Mtg16 was required to suppress the expression of several key cell-cycle regulators including E2F2, and chromatin immunoprecipitation assays detected Mtg16 near an E2A binding site within the first intron of E2F2. BrdU incorporation assays indicated that in the absence of Mtg16 more long-term stem cells were in the S phase, even after competitive BM transplantation where normal stem and progenitor cells are present, suggesting that Mtg16 plays a role in the maintenance of stem cell quiescence.

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.

Functional regulation of pre-B-cell leukemia homeobox interacting protein 1 (PBXIP1/HPIP) in erythroid differentiation

Pre-B-cell leukemia homeobox interacting protein 1 or human PBX1 interacting protein (PBXIP1/HPIP) is a co-repressor of pre-B-cell leukemia homeobox 1 (PBX1) and is also known to regulate estrogen receptor functions by associating with the microtubule network. Despite its initial discovery in the context of hematopoietic cells, little is yet known about the role of HPIP in hematopoiesis. Here, we show that lentivirus-mediated overexpression of HPIP in human CD34(+) cells enhances hematopoietic colony formation in vitro, whereas HPIP knockdown leads to a reduction in the number of such colonies. Interestingly, erythroid colony number was significantly higher in HPIP-overexpressing cells. In addition, forced expression of HPIP in K562 cells, a multipotent erythro-megakaryoblastic leukemia cell line, led to an induction of erythroid differentiation. HPIP overexpression in both CD34(+) and K562 cells was associated with increased activation of the PI3K/AKT pathway, and corresponding treatment with a PI3K-specific inhibitor, LY-294002, caused a reduction in clonogenic progenitor number in HPIP-expressing CD34(+) cells and decreased K562 cell differentiation. Combined, these findings point to an important role of the PI3K/AKT pathway in mediating HPIP-induced effects on the growth and differentiation of hematopoietic cells. Interestingly, HPIP gene expression was found to be induced in K562 cells in response to erythroid differentiation signals such as DMSO and erythropoietin. The erythroid lineage-specific transcription factor GATA1 binds to the HPIP promoter and activates HPIP gene transcription in a CCCTC-binding factor (CTCF)-dependent manner. Co-immunoprecipitation and co-localization experiments revealed the association of CTCF with GATA1 indicating the recruitment of CTCF/GATA1 transcription factor complex onto the HPIP promoter. Together, this study provides evidence that HPIP is a target of GATA1 and CTCF in erythroid cells and plays an important role in erythroid differentiation by modulating the PI3K/AKT pathway.

The human stem cell hierarchy is defined by a functional dependence on Mcl-1 for self-renewal capacity

The molecular basis for the unique proliferative and self-renewal properties that hierarchically distinguish human stem cells from progenitors and terminally differentiated cells remains largely unknown. We report a role for the Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) as an indispensable regulator of self-renewal in human stem cells and show that a functional dependence on Mcl-1 defines the human stem cell hierarchy. In vivo pharmacologic targeting of the Bcl-2 family members in human hematopoietic stem cells (HSCs) and human leukemic stem cells reduced stem cell regenerative and self-renewal function. Subsequent protein expression studies showed that, among the Bcl-2 family members, only Mcl-1 was up-regulated exclusively in the human HSC fraction on in vivo regeneration of hematopoiesis. Short hairpin RNA-knockdown of Mcl-1 in human cord blood cells did not affect survival in the HSC or hematopoietic progenitor cell fractions in vitro but specifically reduced the in vivo self-renewal function of human HSCs. Moreover, knockdown of Mcl-1 in ontogenetically primitive human pluripotent stem cells resulted in almost complete ablation of stem cell self-renewal function. Our findings show that Mcl-1 is an essential regulator of stem cell self-renewal in humans and therefore represents an axis for therapeutic interventions.

NCI first International Workshop on the biology, prevention, and treatment of relapse after allogeneic hematopoietic stem cell transplantation: report from the committee on the biological considerations of hematological relapse following allogeneic stem cell transplantation unrelated to graft-versus-tumor effects: state of the science

Hematopoietic malignant relapse still remains the major cause of death following allogeneic hematopoietic stem cell transplantation (HSCT). Although there has been a large focus on the immunologic mechanisms responsible for the graft-versus-tumor (GVT) effect or lack thereof, there has been little attention paid to investigating the biologic basis of hematologic malignant disease relapse following allogeneic HSCT. There are a large number of factors that are responsible for the biologic resistance of hematopoietic tumors following allogeneic HSCT. We have focused on 5 major areas including clonal evolution of cancer drug resistance, cancer radiation resistance, genomic basis of leukemia resistance, cancer epigenetics, and resistant leukemia stem cells. We recommend increased funding to pursue 3 broad areas that will significantly enhance our understanding of the biologic basis of malignant relapse after allogeneic HSCT, including: (1) genomic and epigenetic alterations, (2) cancer stem cell biology, and (3) clonal cancer drug and radiation resistance.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

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.

CXCR4 chemokine receptor antagonists: perspectives in SCLC

Small-cell lung cancer (SCLC) is a particularly aggressive form of lung cancer characterized by early and widespread metastases and the ability to rapidly develop resistance against chemotherapeutic agents. Tumor cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokine receptors and adhesion molecules. SCLC cells express high levels of CXCR4 (CD184), a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the bone marrow microenvironment and at extramedullary sites constitutively secrete stromal cell-derived factor-1 (CXCL12), the ligand for CXCR4. Activation of CXCR4 induces SCLC cell migration and adhesion to stromal cells that secrete CXCL12, which in turn provides growth- and drug resistance-signals to the tumor cells. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogues (TN14003/ BKT140), disrupt CXCR4-mediated SCLC cell-adhesion to stromal cells. In stromal cell co-cultures, CXCR4 antagonists also sensitize SCLC cells to cytotoxic drugs, such as etoposide, and thereby antagonize cell adhesion-mediated drug resistance. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach in SCLC. Here, we summarize preclinical data about CXCR4 in SCLC, and the current status of the preclinical and clinical development of CXCR4 antagonists.

Myeloid leukemic progenitor cells can be specifically targeted by minor histocompatibility antigen LRH-1–reactive cytotoxic T cells

CD8+ T cells recognizing minor histocompatibility antigens (MiHAs) on leukemic stem and progenitor cells play a pivotal role in effective graft-versus-leukemia reactivity after allogeneic stem cell transplantation (SCT). Previously, we identified a hematopoiesis-restricted MiHA, designated LRH-1, which is presented by HLA-B7 and encoded by the P2X5 purinergic receptor gene. We found that P2X5 is significantly expressed in CD34+ leukemic subpopulations from chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) patients. Here, we demonstrate that LRH-1–specific CD8+ T-cell responses are frequently induced in myeloid leukemia patients following donor lymphocyte infusions. Patients with high percentages of circulating LRH-1–specific CD8+ T cells had no or only mild graft-versus-host disease. Functional analysis showed that LRH-1–specific cytotoxic T lymphocytes (CTLs) isolated from 2 different patients efficiently target LRH-1–positive leukemic CD34+ progenitor cells from both CML and AML patients, whereas mature CML cells are only marginally lysed due to down-regulation of P2X5. Furthermore, we observed that relative resistance to LRH-1 CTL-mediated cell death due to elevated levels of antiapoptotic XIAP could be overcome by IFN-γ prestimulation and increased CTL-target ratios. These findings provide a rationale for use of LRH-1 as immunotherapeutic target antigen to treat residual or persisting myeloid malignancies after allogeneic SCT.

Review Paper: Cancer Stem Cells and Cancer Nonstem Cells: From Adult Stem Cells or from Reprogramming of Differentiated Somatic Cells

Two opposing hypotheses of the origin of cancer have existed for many decades. One hypothesis postulates that the adult stem cell is needed to initiate the carcinogenic process, whereas the other claims a somatic differentiated cell can dedifferentiate or be reprogrammed to regain properties associated with cancer cells. Recent reemergence of the cancer stem cell hypothesis and the isolation of presumptive cancer stem cells from many types of cancer have forced a reexamination of these 2 hypotheses of the origin of cancer. In addition, normal embryonic and adult stem cells have now been isolated and partially characterized. Furthermore, the demonstration of embryonic-like stem cells, being isolated from adult-differentiated skin fibroblast cells of mice, monkey, and human beings, provides a newer opportunity to determine which of these 2 hypotheses might explain the cell type for initiating the carcinogenic process. The goal of this review is to integrate these recent findings, concerning the isolation of normal and cancer stem cells, with several of the classical concepts of carcinogenesis (initiation/promotion/progression; mutation/epigenetic; stem cell theory/dedifferentiation hypotheses; oncogenetumor suppressor theory). Although the weight of the evidence in this review seems to support the stem cell hypothesis, only future studies, probably using comparative animal and human oncologic studies, will determine if targeting the cancer stem cell, with individualized medical approaches, will improve cancer prevention and therapy.

CXCR4 antagonists: targeting the microenvironment in leukemia and other cancers

Hematopoietic and epithelial cancer cells express CXCR4, a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the bone marrow microenvironment constitutively secrete stromal cell-derived factor-1 (SDF-1/CXCL12), the ligand for CXCR4. Activation of CXCR4 induces leukemia cell trafficking and homing to the marrow microenvironment, where CXCL12 retains leukemia cells in close contact with marrow stromal cells that provide growth and drug resistance signals. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogs, can disrupt adhesive tumor-stroma interactions and mobilize leukemia cells from their protective stromal microenvironment, making them more accessible to conventional drugs. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach that is explored in ongoing clinical trials in leukemia patients. Initially, CXCR4 antagonists were developed for the treatment of HIV, where CXCR4 functions as a co-receptor for virus entry into T cells. Subsequently, CXCR4 antagonists were noticed to induce leukocytosis, and are currently used clinically for mobilization of hematopoietic stem cells. However, because CXCR4 plays a key role in cross-talk between leukemia cells (and a variety of other tumor cells) and their microenvironment, cancer treatment may become the ultimate application of CXCR4 antagonists. Here, we summarize the development of CXCR4 antagonists and their preclinical and clinical activities, focusing on leukemia and other cancers.

Defective in vitro growth of primitive hematopoietic cells from pediatric patients with acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a neoplastic hematologic disorder that arises at the level of a primitive stem/progenitor cell. Most studies on the biology of the hematopoietic system in AML have focused on cells from adult patients; much less is known about hematopoietic cells from childhood AML.

PROCEDURE

By using a negative immunoselection system, we have obtained a primitive cell population (enriched for CD34(+) Lin(-) cells) from the bone marrow (BM) of 17 pediatric AML patients and characterized its proliferation, expansion, and differentiation potentials in liquid cultures supplemented with a mixture of 8 different recombinant stimulatory cytokines.

RESULTS

The proportion of CD34(+) cells in AML patients was extremely heterogeneous, ranging from 0% to 74%. Regardless of their CD34(+) cell content, and in contrast to normal cells, AML cells showed a deficient capacity to proliferate even in the presence of the stimulatory cytokines. AML progenitors were unable to generate new progenitor cells, indicating their inability to expand. Interestingly, AML cells were able to differentiate in culture, giving rise to morphologically recognizable precursors. A major difference, however, as compared to hematopoietic progenitors from normal subjects, was the fact that whereas in cultures of normal cells both myeloid and erythroid precursors were produced, in AML cultures the vast majority of the cells generated corresponded to myeloid cells, mostly mature macrophages.

CONCLUSION

As compared to their normal counterparts, primitive hematopoietic cells from pediatric patients with AML possess impaired proliferation, expansion, and differentiation potentials in vitro.

Deletion of Mtg16, a target of t(16;21), alters hematopoietic progenitor cell proliferation and lineage allocation

While a number of DNA binding transcription factors have been identified that control hematopoietic cell fate decisions, only a limited number of transcriptional corepressors (e.g., the retinoblastoma protein [pRB] and the nuclear hormone corepressor [N-CoR]) have been linked to these functions. Here, we show that the transcriptional corepressor Mtg16 (myeloid translocation gene on chromosome 16), which is targeted by t(16;21) in acute myeloid leukemia, is required for hematopoietic progenitor cell fate decisions and for early progenitor cell proliferation. Inactivation of Mtg16 skewed early myeloid progenitor cells toward the granulocytic/macrophage lineage while reducing the numbers of megakaryocyte-erythroid progenitor cells. In addition, inactivation of Mtg16 impaired the rapid expansion of short-term stem cells, multipotent progenitor cells, and megakaryocyte-erythroid progenitor cells that is required under hematopoietic stress/emergency. This impairment appears to be a failure to proliferate rather than an induction of cell death, as expression of c-Myc, but not Bcl2, complemented the Mtg16(-/-) defect.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

Xenograft models for the preclinical evaluation of new therapies in acute leukemia

Major advances in understanding the pathophysiology of acute leukemia have resulted in a dramatic increase in the availability of novel compounds for clinical trials. However, since the number of new drugs far exceeds the number of clinical trials that can be conducted because of the availability of eligible patients, there is an urgent need to utilize reliable preclinical models for the prioritization of the most promising potential therapies for those clinical trials. The most widely used preclinical models for the acute leukemias are human tumor xenografts established in immune-deficient mice, and genetically engineered mouse strains. This review summarizes the recent developments and considerations in the use of xenograft models of acute lymphoblastic leukemia, acute myeloid leukemia, and acute promyelocytic leukemia for the preclinical testing of new therapies.