Getting to the stem of chronic myeloid leukaemia

Targeted degradation of oncogenic BCR-ABL by silencing the gene of NEDD8 E3 ligase RAPSYN

Tyrosine kinase inhibitors have been the standard treatment for patients with Philadelphia chromosome-positive (Ph+) leukemia. However, a series of issues, including drug resistance, relapse and intolerance, are still an unmet medical need. Here, we report the targeted siRNA-based lipid nanoparticles in Ph+ leukemic cell lines for gene therapy of Ph+ leukemia, which specifically targets a recently identified NEDD8 E3 ligase RAPSYN in Ph+ leukemic cells to disrupt the neddylation of oncogenic BCR-ABL. To achieve the specificity for Ph+ leukemia therapy, a single-chain fragment variable region (scFv) of anti-CD79B monoclonal antibody was covalently conjugated on the surface of OA2-siRAPSYN lipid nanoparticles to generate the targeted lipid nanoparticles (scFv-OA2-siRAPSYN). Through effectively silencing RAPSYN gene in leukemic cell lines by the nanoparticles, BCR-ABL was remarkably degraded accompanied by the inhibition of proliferation and the promotion of apoptosis. The specific targeting, therapeutic effects and systemic safety were further evaluated and demonstrated in cell line-derived mouse models. The present study has not only addressed the clinical need of Ph+ leukemia, but also enabled gene therapy against a less druggable target.

Prognosis in Chronic Myeloid Leukemia: Baseline Factors, Dynamic Risk Assessment and Novel Insights

The introduction of tyrosine kinase inhibitors (TKIs) has changed the treatment paradigm of chronic myeloid leukemia (CML), leading to a dramatic improvement of the outcome of CML patients, who now have a nearly normal life expectancy and, in some selected cases, the possibility of aiming for the more ambitious goal of treatment-free remission (TFR). However, the minority of patients who fail treatment and progress from chronic phase (CP) to accelerated phase (AP) and blast phase (BP) still have a relatively poor prognosis. The identification of predictive elements enabling a prompt recognition of patients at higher risk of progression still remains among the priorities in the field of CML management. Currently, the baseline risk is assessed using simple clinical and hematologic parameters, other than evaluating the presence of additional chromosomal abnormalities (ACAs), especially those at "high-risk". Beyond the onset, a re-evaluation of the risk status is mandatory, monitoring the response to TKI treatment. Moreover, novel critical insights are emerging into the role of genomic factors, present at diagnosis or evolving on therapy. This review presents the current knowledge regarding prognostic factors in CML and their potential role for an improved risk classification and a subsequent enhancement of therapeutic decisions and disease management.

Therapeutic Benefits of Selenium in Hematological Malignancies

Supplementing chemotherapy and radiotherapy with selenium has been shown to have benefits against various cancers. This approach has also been shown to alleviate the side effects associated with standard cancer therapies and improve the quality of life in patients. In addition, selenium levels in patients have been correlated with various cancers and have served as a diagnostic marker to track the efficiency of treatments or to determine whether these selenium levels cause or are a result of the disease. This concise review presents a survey of the selenium-based literature, with a focus on hematological malignancies, to demonstrate the significant impact of selenium in different cancers. The anti-cancer mechanisms and signaling pathways regulated by selenium, which impart its efficacious properties, are discussed. An outlook into the relationship between selenium and cancer is highlighted to guide future cancer therapy development.

Altered BMP2/4 Signaling in Stem Cells and Their Niche: Different Cancers but Similar Mechanisms, the Example of Myeloid Leukemia and Breast Cancer

Understanding mechanisms of cancer development is mandatory for disease prevention and management. In healthy tissue, the microenvironment or niche governs stem cell fate by regulating the availability of soluble molecules, cell-cell contacts, cell-matrix interactions, and physical constraints. Gaining insight into the biology of the stem cell microenvironment is of utmost importance, since it plays a role at all stages of tumorigenesis, from (stem) cell transformation to tumor escape. In this context, BMPs (Bone Morphogenetic Proteins), are key mediators of stem cell regulation in both embryonic and adult organs such as hematopoietic, neural and epithelial tissues. BMPs directly regulate the niche and stem cells residing within. Among them, BMP2 and BMP4 emerged as master regulators of normal and tumorigenic processes. Recently, a number of studies unraveled important mechanisms that sustain cell transformation related to dysregulations of the BMP pathway in stem cells and their niche (including exposure to pollutants such as bisphenols). Furthermore, a direct link between BMP2/BMP4 binding to BMP type 1 receptors and the emergence and expansion of cancer stem cells was unveiled. In addition, a chronic exposure of normal stem cells to abnormal BMP signals contributes to the emergence of cancer stem cells, or to disease progression independently of the initial transforming event. In this review, we will illustrate how the regulation of stem cells and their microenvironment becomes dysfunctional in cancer via the hijacking of BMP signaling with main examples in myeloid leukemia and breast cancers.

Splenic red pulp macrophages provide a niche for CML stem cells and induce therapy resistance

Disease progression and relapse of chronic myeloid leukemia (CML) are caused by therapy resistant leukemia stem cells (LSCs), and cure relies on their eradication. The microenvironment in the bone marrow (BM) is known to contribute to LSC maintenance and resistance. Although leukemic infiltration of the spleen is a hallmark of CML, it is unknown whether spleen cells form a niche that maintains LSCs. Here, we demonstrate that LSCs preferentially accumulate in the spleen and contribute to disease progression. Spleen LSCs were located in the red pulp close to red pulp macrophages (RPM) in CML patients and in a murine CML model. Pharmacologic and genetic depletion of RPM reduced LSCs and decreased their cell cycling activity in the spleen. Gene expression analysis revealed enriched stemness and decreased myeloid lineage differentiation in spleen leukemic stem and progenitor cells (LSPCs). These results demonstrate that splenic RPM form a niche that maintains CML LSCs in a quiescent state, resulting in disease progression and resistance to therapy.

Influence of Telomere Length on the Achievement of Deep Molecular Response With Imatinib in Chronic Myeloid Leukemia Patients

Tyrosine kinase inhibitors have dramatically changed the outcome of chronic myeloid leukemia (CML), and nowadays, one of the main treatment goals is the achievement of deep molecular responses (DMRs), which can eventually lead to therapy discontinuation approaches. Few biological factors at diagnosis have been associated with this level of response. Telomere length (TL) in peripheral blood cells of patients with CML has been related to disease stage, response to therapy and disease progression, but little is known about its role on DMR. In this study, we analyzed if age-adjusted TL (referred as “delta-TL”) at diagnosis of chronic phase (CP)-CML might correlate with the achievement of DMR under first-line imatinib treatment. TL from 96 CP-CML patients had been retrospectively analyzed at diagnosis by monochrome multiplex quantitative PCR. We observed that patients with longer age-adjusted telomeres at diagnosis had higher probabilities to achieve DMR with imatinib than those with shortened telomeres (P = 0.035 when delta-TL was studied as a continuous variable and P = 0.047 when categorized by the median). Moreover, patients carrying long telomeres also achieved major molecular response significantly earlier (P = 0.012). This study provides proof of concept that TL has a role in CML biology and when measured at diagnosis of CP-CML could help to identify patients likely to achieve DMR to first-line imatinib treatment.

Metoclopramide treatment blocks CD93-signaling-mediated self-renewal of chronic myeloid leukemia stem cells

Self-renewal is a key characteristic of leukemia stem cells (LSCs) responsible for the development and maintenance of leukemia. In this study, we identify CD93 as an important regulator of self-renewal and proliferation of murine and human LSCs, but not hematopoietic stem cells (HSCs). The intracellular domain of CD93 promotes gene transcription via the transcriptional regulator SCY1-like pseudokinase 1 independently of ligation of the extracellular domain. In a drug library screen, we identify the anti-emetic agent metoclopramide as an efficient blocker of CD93 signaling. Metoclopramide treatment reduces murine and human LSCs in vitro and prolongs survival of chronic myeloid leukemia (CML) mice through downregulation of pathways related to stemness and proliferation in LSCs. Overall, these results identify CD93 signaling as an LSC-specific regulator of self-renewal and proliferation and a targetable pathway to eliminate LSCs in CML.

DYRK2 controls a key regulatory network in chronic myeloid leukemia stem cells

Chronic myeloid leukemia is a hematological cancer driven by the oncoprotein BCR-ABL1, and lifelong treatment with tyrosine kinase inhibitors extends patient survival to nearly the life expectancy of the general population. Despite advances in the development of more potent tyrosine kinase inhibitors to induce a durable deep molecular response, more than half of patients relapse upon treatment discontinuation. This clinical finding supports the paradigm that leukemia stem cells feed the neoplasm, resist tyrosine kinase inhibition, and reactivate upon drug withdrawal depending on the fitness of the patient's immune surveillance. This concept lends support to the idea that treatment-free remission is not achieved solely with tyrosine kinase inhibitors and that new molecular targets independent of BCR-ABL1 signaling are needed in order to develop adjuvant therapy to more efficiently eradicate the leukemia stem cell population responsible for chemoresistance and relapse. Future efforts must focus on the identification of new targets to support the discovery of potent and safe small molecules able to specifically eradicate the leukemic stem cell population. In this review, we briefly discuss molecular maintenance in leukemia stem cells in chronic myeloid leukemia and provide a more in-depth discussion of the dual-specificity kinase DYRK2, which has been identified as a novel actionable checkpoint in a critical leukemic network. DYRK2 controls the activation of p53 and proteasomal degradation of c-MYC, leading to impaired survival and self-renewal of leukemia stem cells; thus, pharmacological activation of DYRK2 as an adjuvant to standard therapy has the potential to induce treatment-free remission.

Hydroxychavicol sensitizes imatinib-resistant chronic myelogenous leukemia cells to TRAIL-induced apoptosis by ROS-mediated IAP downregulation

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of cytokine superfamily, induces apoptosis in a number of tumor cells through the activation of extrinsic apoptotic pathway but shows little or no cytotoxicity toward normal cells. However some tumor cells are inherently resistant to TRAIL-mediated apoptosis, which needs to be addressed to establish TRAIL as a potential chemotherapeutic drug. In this study, our aim was to manipulate TRAIL-apoptosis pathway by hydroxychavicol (HCH), a polyphenol from Piper betel leaf, for the induction of apoptosis in TRAIL resistant chronic myeloid leukemia cell. When imatinib-resistant K562 cells were treated with HCH, it made these K562 cells sensitive to TRAIL. It was observed that HCH downregulated antiapoptotic proteins XIAP and FLIP, whereas the expression of TRAIL receptors, DR4 and DR5, remains unchanged. Moreover, we observed that reactive oxygen species or ROS played a crucial role in the downregulation of FLIP and XIAP because ROS scavenger significantly reversed the decrease of XIAP, and FLIP. Ubiquitin-proteasome pathway was observed to play a crucial role in the downregulation of XIAP and FLIP, as proteasomal inhibitor MG132 significantly reversed the downregulation of XIAP and FLIP. In conclusion, this study demonstrates the combinatorial treatment of TRAIL and HCH as promising alternative therapeutic approach to treat the imatinib-resistant leukemia, which are also resistant to TRAIL.

Let-7b regulates the adriamycin resistance of chronic myelogenous leukemia by targeting AURKB in K562/ADM cells

Chronic myeloid leukemia (CML) is a malignant hematological disease, and drug resistance is often related to poor prognosis. MicroRNAs (miRNA) play a pivotal role in transcriptional regulation, cell development, and chemotherapy resistance. Here, we describe the effect of let-7b on resistant leukemia cells and examine the relevance of let-7b as a biomarker for adriamycin resistance. Results showed that let-7b was downregulated in K562/ADM (KA) cells, and the downregulation of let-7b in K562 and KA cells increased ADM resistance. The inhibition of let-7b subsequently induced the upregulation of AURKB. Finally, results proved that the Pi3k/Akt/Erk pathway was related to AURKB-activated resistance. Our research indicated that the underexpression of let-7b and overexpression of AURKB contributed to the resistance of CML, and its function is partly regulated by the Pi3k/Akt/Erk pathway. Thus, our further understand of its inhibitory effect may promise a new therapeutic strategy to overcome chemotherapeutic resistance in CML.

The Hidden Pathogenesis of CML: Is BCR-ABL1 the First Event?

PURPOSE OF REVIEW

Identification of the BCR-ABL1 fusion oncogene in patients diagnosed with chronic myeloid leukemia (CML) led to the development of targeted therapy responsible for the dramatic survival benefits observed in the past two decades. However, despite these revolutionary findings, there remains marked disparity in patient outcomes. Why do some patients present de novo while others evolve to the more aggressive stages of CML? Why can select patients successfully discontinue therapy as part of a treatment-free remission attempt whereas others fail to meet specific molecular milestones?

RECENT FINDINGS

BCR-ABL1 kinase mutations are only identified in approximately 50% of patients with poor responses and disease progression, suggesting the presence of alternative resistance mechanisms. Numerous institutions have identified the presence of additional genomic events in addition to BCR-ABL1 with the increasing availability of next-generation sequencing. We explore the potential pathways and events that may cooperate with BCR-ABL1 to answer these questions but also challenge the fundamental tenet that BCR-ABL1 is always the sole event initiating CML.

Mendonça L, Matos L, Prata MJ, S. Jurado A, Pedroso de Lima MC, Alves S. Lysosomal Storage Disease-Associated Neuropathy: Targeting Stable Nucleic Acid Lipid Particle (SNALP)-Formulated siRNAs to the Brain as a Therapeutic Approach

More than two thirds of Lysosomal Storage Diseases (LSDs) present central nervous system involvement. Nevertheless, only one of the currently approved therapies has an impact on neuropathology. Therefore, alternative approaches are under development, either addressing the underlying enzymatic defect or its downstream consequences. Also under study is the possibility to block substrate accumulation upstream, by promoting a decrease of its synthesis. This concept is known as substrate reduction therapy and may be triggered by several molecules, such as small interfering RNAs (siRNAs). siRNAs promote RNA interference, a naturally occurring sequence-specific post-transcriptional gene-silencing mechanism, and may target virtually any gene of interest, inhibiting its expression. Still, naked siRNAs have limited cellular uptake, low biological stability, and unfavorable pharmacokinetics. Thus, their translation into clinics requires proper delivery methods. One promising platform is a special class of liposomes called stable nucleic acid lipid particles (SNALPs), which are characterized by high cargo encapsulation efficiency and may be engineered to promote targeted delivery to specific receptors. Here, we review the concept of SNALPs, presenting a series of examples on their efficacy as siRNA nanodelivery systems. By doing so, we hope to unveil the therapeutic potential of these nanosystems for targeted brain delivery of siRNAs in LSDs.

Chronic myeloid leukemia stem cells require cell-autonomous pleiotrophin signaling

Tyrosine kinase inhibitors (TKIs) induce molecular remission in the majority of patients with chronic myelogenous leukemia (CML), but the persistence of CML stem cells hinders cure and necessitates indefinite TKI therapy. We report that CML stem cells upregulate the expression of pleiotrophin (PTN) and require cell-autonomous PTN signaling for CML pathogenesis in BCR/ABL+ mice. Constitutive PTN deletion substantially reduced the numbers of CML stem cells capable of initiating CML in vivo. Hematopoietic cell-specific deletion of PTN suppressed CML development in BCR/ABL+ mice, suggesting that cell-autonomous PTN signaling was necessary for CML disease evolution. Mechanistically, PTN promoted CML stem cell survival and TKI resistance via induction of Jun and the unfolded protein response. Human CML cells were also dependent on cell-autonomous PTN signaling, and anti-PTN antibody suppressed human CML colony formation and CML repopulation in vivo. Our results suggest that targeted inhibition of PTN has therapeutic potential to eradicate CML stem cells.

MLL-AF9 initiates transformation from fast-proliferating myeloid progenitors

Cancer is a hyper-proliferative disease. Whether the proliferative state originates from the cell-of-origin or emerges later remains difficult to resolve. By tracking de novo transformation from normal hematopoietic progenitors expressing an acute myeloid leukemia (AML) oncogene MLL-AF9, we reveal that the cell cycle rate heterogeneity among granulocyte-macrophage progenitors (GMPs) determines their probability of transformation. A fast cell cycle intrinsic to these progenitors provide permissiveness for transformation, with the fastest cycling 3% GMPs acquiring malignancy with near certainty. Molecularly, we propose that MLL-AF9 preserves gene expression of the cellular states in which it is expressed. As such, when expressed in the naturally-existing, rapidly-cycling immature myeloid progenitors, this cell state becomes perpetuated, yielding malignancy. In humans, high CCND1 expression predicts worse prognosis for MLL fusion AMLs. Our work elucidates one of the earliest steps toward malignancy and suggests that modifying the cycling state of the cell-of-origin could be a preventative approach against malignancy.

A KLF4-DYRK2-mediated pathway regulating self-renewal in CML stem cells

Leukemia stem cells are a rare population with a primitive progenitor phenotype that can initiate, sustain, and recapitulate leukemia through a poorly understood mechanism of self-renewal. Here, we report that Krüppel-like factor 4 (KLF4) promotes disease progression in a murine model of chronic myeloid leukemia (CML)-like myeloproliferative neoplasia by repressing an inhibitory mechanism of preservation in leukemia stem/progenitor cells with leukemia-initiating capacity. Deletion of the Klf4 gene severely abrogated the maintenance of BCR-ABL1(p210)-induced CML by impairing survival and self-renewal in BCR-ABL1+ CD150+ lineage-negative Sca-1+ c-Kit+ leukemic cells. Mechanistically, KLF4 repressed the Dyrk2 gene in leukemic stem/progenitor cells; thus, loss of KLF4 resulted in elevated levels of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 2 (DYRK2), which were associated with inhibition of survival and self-renewal via depletion of c-Myc protein and p53 activation. In addition to transcriptional regulation, stabilization of DYRK2 protein by inhibiting ubiquitin E3 ligase SIAH2 with vitamin K3 promoted apoptosis and abrogated self-renewal in murine and human CML stem/progenitor cells. Altogether, our results suggest that DYRK2 is a molecular checkpoint controlling p53- and c-Myc-mediated regulation of survival and self-renewal in CML cells with leukemic-initiating capacity that can be targeted with small molecules.

CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML

Purpose

Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1^T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1^T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1^T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro.

Methods

Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and ³H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting.

Findings

HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1^T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1^T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1^T315I-associated TKI resistance.

Interpretation

HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1^T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML.

Funding

This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Management of Chronic Myeloid Leukemia in Advanced Phase

Management of chronic myeloid leukemia (CML) in advanced phases remains a challenge also in the era of tyrosine kinase inhibitors (TKIs) treatment. Cytogenetic clonal evolution and development of resistant mutations represent crucial events that limit the benefit of subsequent therapies in these patients. CML is diagnosed in accelerated (AP) or blast phase (BP) in <5% of patients, and the availability of effective treatments for chronic phase (CP) has dramatically reduced progressions on therapy. Due to smaller number of patients, few randomized studies are available in this setting and evidences are limited. Nevertheless, three main scenarios may be drawn: (a) patients diagnosed in AP are at higher risk of failure as compared to CP patients, but if they achieve optimal responses with frontline TKI treatment their outcome may be similarly favorable; (b) patients diagnosed in BP may be treated with TKI alone or with TKI together with conventional chemotherapy regimens, and subsequent transplant decisions should rely on kinetics of response and individual transplant risk; (c) patients in CP progressing under TKI treatment represent the most challenging population and they should be treated with alternative TKI according to the mutational profile, optional chemotherapy in BP patients, and transplant should be considered in suitable cases after return to second CP. Due to lack of validated and reliable markers to predict blast crisis and the still unsatisfactory results of treatments in this setting, prevention of progression by careful selection of frontline treatment in CP and early treatment intensification in non-optimal responders remains the main goal. Personalized evaluation of response kinetics could help in identifying patients at risk for progression.

Concise Review: Exploiting Unique Biological Features of Leukemia Stem Cells for Therapeutic Benefit

Cancer stem cells play a critical role in disease initiation and insensitivity to chemotherapy in numerous hematologic malignancies and some solid tumors, and these stem cells need to be eradicated to achieve a cure. Key to successful targeting of cancer stem cells is to identify and functionally test critical target genes and to fully understand their associated molecular network in these stem cells. Human chronic myeloid leukemia (CML) is well accepted as one of the typical types of hematopoietic malignancies that are derived from leukemia stem cells (LSCs), serving as an excellent model disease for understanding the biology of LSCs and developing effective, selective, and curative strategies through targeting LSCs. Here, we discuss LSCs in CML with a focus on identification of unique biological features of these stem cells to emphasize the feasibility and significance of specific targeting of LSCs while sparing normal stem cell counterparts in leukemia therapy. stem cells translational medicine2019;8:768&774

Telomere shortening correlates with leukemic stem cell burden at diagnosis of chronic myeloid leukemia

Telomere length (TL) in peripheral blood (PB) cells of patients with chronic myeloid leukemia (CML) has been shown to correlate with disease stage, prognostic scores, response to therapy, and disease progression. However, due to considerable genetic interindividual variability, TL varies substantially between individuals, limiting its use as a robust prognostic marker in individual patients. Here, we compared TL of BCR-ABL^-, nonleukemic CD34⁺CD38^- hematopoietic stem cells (HSC) in the bone marrow of CML patients at diagnosis to their individual BCR-ABL⁺ leukemic stem cell (LSC) counterparts. We observed significantly accelerated telomere shortening in LSC compared with nonleukemic HSC. Interestingly, the degree of LSC telomere shortening was found to correlate significantly with the leukemic clone size. To validate the diagnostic value of nonleukemic cells as internal controls and to rule out effects of tyrosine kinase inhibitor (TKI) treatment on these nontarget cells, we prospectively assessed TL in 134 PB samples collected in deep molecular remission after TKI treatment within the EURO-SKI study (NCT01596114). Here, no significant telomere shortening was observed in granulocytes compared with an age-adjusted control cohort. In conclusion, this study provides proof of principle for accelerated telomere shortening in LSC as opposed to HSC in CML patients at diagnosis. The fact that the degree of telomere shortening correlates with leukemic clone's size supports the use of TL in leukemic cells as a prognostic parameter pending prospective validation. TL in nonleukemic myeloid cells seems unaffected even by long-term TKI treatment arguing against a reduction of telomere-mediated replicative reserve in normal hematopoiesis under TKI treatment.

Tissue "Hypoxia" and the Maintenance of Leukemia Stem Cells

The relationship of the homing of normal hematopoietic stem cells (HSC) in the bone marrow to specific environmental conditions, referred to as the stem cell niche (SCN), has been intensively studied over the last three decades. These conditions include the action of a number of molecular and cellular players, as well as critical levels of nutrients, oxygen and glucose in particular, involved in energy production. These factors are likely to act also in leukemias, due to the strict analogy between the hierarchical structure of normal hematopoietic cell populations and that of leukemia cell populations. This led to propose that leukemic growth is fostered by cells endowed with stem cell properties, the leukemia stem cells (LSC), a concept readily extended to comprise the cancer stem cells (CSC) of solid tumors. Two alternative routes have been proposed for CSC generation, that is, the oncogenic staminalization (acquisition of self-renewal) of a normal progenitor cell (the "CSC in normal progenitor cell" model) and the oncogenic transformation of a normal (self-renewing) stem cell (the "CSC in normal stem cell" model). The latter mechanism, in the hematological context, makes LSC derive from HSC, suggesting that LSC share SCN homing with HSC. This chapter is focused on the availability of oxygen and glucose in the regulation of LSC maintenance within the SCN. In this respect, the most critical aspect in view of the outcome of therapy is the long-term maintenance of the LSC subset capable to sustain minimal residual disease and the related risk of relapse of disease.

Chronic myeloid leukaemia cells require the bone morphogenic protein pathway for cell cycle progression and self-renewal

Leukaemic stem cell (LSC) persistence remains a major obstacle to curing chronic myeloid leukaemia (CML). The bone morphogenic protein (BMP) pathway is deregulated in CML, with altered expression and response to the BMP ligands shown to impact on LSC expansion and behaviour. In this study, we determined whether alterations in the BMP pathway gene signature had any predictive value for therapeutic response by profiling 60 CML samples at diagnosis from the UK SPIRIT2 trial and correlating the data to treatment response using the 18-month follow-up data. There was significant deregulation of several genes involved in the BMP pathway with ACV1C, INHBA, SMAD7, SNAIL1 and SMURF2 showing differential expression in relation to response. Therapeutic targeting of CML cells using BMP receptor inhibitors, in combination with tyrosine kinase inhibitor (TKI), indicate a synergistic mode of action. Furthermore, dual treatment resulted in altered cell cycle gene transcription and irreversible cell cycle arrest, along with increased apoptosis compared to single agents. Targeting CML CD34⁺ cells with BMP receptor inhibitors resulted in fewer cell divisions, reduced numbers of CD34⁺ cells and colony formation when compared to normal donor CD34⁺ cells, both in the presence and absence of BMP4. In an induced pluripotent stem cell (iPSC) model generated from CD34⁺ hematopoietic cells, we demonstrate altered cell cycle profiles and dynamics of ALK expression in CML-iPSCs in the presence and absence of BMP4 stimulation, when compared to normal iPSC. Moreover, dual targeting with TKI and BMP inhibitor prevented the self-renewal of CML-iPSC and increased meso-endodermal differentiation. These findings indicate that transformed stem cells may be more reliant on BMP signalling than normal stem cells. These changes offer a therapeutic window in CML, with intervention using BMP inhibitors in combination with TKI having the potential to target LSC self-renewal and improve long-term outcome for patients.

Parthenolide and DMAPT induce cell death in primitive CML cells through reactive oxygen species

Tyrosine kinase inhibitors (TKI) have become a first-line treatment for chronic myeloid leuakemia (CML). TKIs efficiently target bulk CML cells; however, they are unable to eliminate the leukaemic stem cell (LSC) population that causes resistance and relapse in CML patients. In this study, we assessed the effects of parthenolide (PTL) and dimethyl amino parthenolide (DMAPT), two potent inhibitors of LSCs in acute myeloid leukaemia (AML), on CML bulk and CML primitive (CD34⁺ lin^- ) cells. We found that both agents induced cell death in CML, while having little effect on the equivalent normal hematopoietic cells. PTL and DMAPT caused an increase in reactive oxygen species (ROS) levels and inhibited NF-κB activation. PTL and DMAPT inhibited cell proliferation and induced cell cycle arrest in G₀ and G₂ phases. Furthermore, we found cell cycle inhibition to correlate with down-regulation of cyclin D1 and cyclin A. In summary, our study shows that PTL and DMAPT have a strong inhibitory effect on CML cells. Given that cell cycle arrest was not dependent on ROS induction, we speculate that this effect could be a direct consequence of NF-κB inhibition and if this mechanism was to be evaded, PTL and DMAPT induced cell death would be potentiated.

Differential proteomic profile of leukemic CD34+ progenitor cells from chronic myeloid leukemia patients

Chronic Myeloid Leukemia (CML) is a stem cell disease sustained by a rare population of quiescent cells which are to some extent resistant to tyrosine kinase inhibitors (TKIs). BCR-ABL oncogene activates multiple cross-talking signal transduction pathways (STP), such as RAS/MEK/ERK, PI3K/Akt, Wnt and STAT5, contributing to abnormal proliferation of clonal cells. From this perspective, the aim of this study was to analyze the expression and activation profile of STP involved in the mechanisms of cell proliferation/quiescence and survival of the progenitor CD34+ cells from chronic phase (CP) CML. Our results showed that CP-CML CD34+ progenitors were characterized by significant lower phosphorylation of proteins involved in the regulation of growth and cell survival, such as tyrosine kinases of the Src family and members of STAT family, and by a significant higher phosphorylation of p53 (Ser15), compared to normal CD34+ cells from healthy donors. Consistent with these results, cell cycle analysis demonstrated that CP-CML CD34+ cells were characterized by higher percentage of cells in G0-phase compared to normal CD34+ cells. Analysis of expression profile on proteins involved in the apoptotic machinery revealed that, in addition, CD34+ cells from CP-CML were characterized by a significant lower expression of catalase and higher expression of HSP27 and FADD. In sum, we report that CD34+ cells from CP-CML are characterized by a proteomic and phospho-proteomic profile that promotes quiescence through the inhibition of proliferation and the promotion of survival. This differential signaling activation network may be addressed by novel targeted therapies aimed at eradicating CML stem cells.

Targeting chronic myeloid leukemia stem cells: can transcriptional program be a druggable target for cancers?

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm resulting from acquisition of constitutively active BCR-ABL protein tyrosine kinase in a hematopoietic stem cell (HSC). Though tyrosine kinase inhibitors (TKIs) have changed a fatal disease into manageable disease, most patients cannot discontinue TKI treatment due to persistence of TKI-resistant leukemia stem cells (LSCs). Much effort has been made to find out factors or pathways specifically operating in LSCs to selectively target LSCs, with some promising results at least in preclinical models. In this article, we briefly review the role of Wnt/β-catenin signaling and its related factors in CML LSCs, especially focusing on Tcf1/Lef1 transcription factors, major effectors of Wnt/β-catenin pathway, of which transcriptional program have recently been shown to be targetable with prostaglandin E1.

Arresting of miR-186 and releasing of H19 by DDX43 facilitate tumorigenesis and CML progression

Cancer-testis (CT) antigens, rarely in normal tissues except testis, are expressed in many tumor types. In recent years, DDX43 has been shown to be expressed in several malignancies. However, the role of DDX43 during tumorigenesis is not well established. In the present study, we explored the function of DDX43 in chronic myeloid leukemia (CML). We found that DDX43 overexpression in CML cell lines enhanced survival and colony formation, inhibited cell apoptosis, promoted tumorigenesis, and CML progression. In contrast, silencing of DDX43 inhibited cell survival and tumorigenesis. Upregulated H19 and downregulated miR-186 were identified in DDX43-transfected cells. Furthermore, we demonstrated that miR-186 targeted DDX43, and overexpressed miR-186 increased apoptosis and decreased cell survival. We also showed that DDX43 regulated the expression of H19 through demethylation and silencing H19 inhibited cell survival. Taken together, these results indicate that DDX43 provides critical support to the progression of CML by enhancing cell survival, colony formation, and inhibiting cell apoptosis, thereby implicating DDX43 as a potential therapeutic target in CML.

The BCR-ABL/NF-κB signal transduction network: a long lasting relationship in Philadelphia positive Leukemias

The Nuclear Factor-kappa B (NF-κB) family of transcription factors plays a key role in cancer pathogenesis due to the ability to promote cellular proliferation and survival, to induce resistance to chemotherapy and to mediate invasion and metastasis. NF-κB is recruited through different mechanisms involving either canonical (RelA/p50) or non-canonical pathways (RelB/p50 or RelB/p52), which transduce the signals originated from growth-factors, cytokines, oncogenic stress and DNA damage, bacterial and viral products or other stimuli. The pharmacological inhibition of the NF-κB pathway has clearly been associated with significant clinical activity in different cancers. Almost 20 years ago, NF-κB was described as an essential modulator of BCR-ABL signaling in Chronic Myeloid Leukemia and Philadelphia-positive Acute Lymphoblastic Leukemia. This review summarizes the role of NF-κB in BCR-ABL-mediated leukemogenesis and provides new insights on the long lasting BCR-ABL/NF-κB connection.

Leukotriene signaling via ALOX5 and cysteinyl leukotriene receptor 1 is dispensable for in vitro growth of CD34+CD38- stem and progenitor cells in chronic myeloid leukemia

Tyrosine kinase inhibitors targeting the BCR-ABL oncoprotein in chronic myeloid leukemia (CML) are remarkably effective inducing deep molecular remission in most patients. However, they are less effective to eradicate the leukemic stem cells (LSC), resulting in disease persistence. Therefore, there is great need to develop novel therapeutic strategies to specifically target the LSC. In an experimental mouse CML model system, the leukotriene pathway, and specifically, the expression ALOX5, encoding 5-lipoxygenase (5-LO), has been reported as a critical regulator of the LSC. Based on these results, the 5-LO inhibitor zileuton has been introduced in clinical trials as a therapeutic option to target the LSC although its effect on primary human CML LSC has not been studied. We have here by using multiplex single cell PCR analyzed the expression of the mediators of the leukotriene pathway in bone marrow (BM) BCR-ABL⁺CD34⁺CD38^- cells at diagnosis, and found low or undetectable expression of ALOX5. In line with this, zileuton did not exert significant overall growth inhibition in the long-term culture-initiating cell (LTC-IC) and colony (CFU-C) assays of BM CD34⁺CD38^- cells from 7 CML patients. The majority of the single leukemic BCR-ABL⁺CD34⁺CD38^- cells expressed cysteinyl leukotriene receptors CYSLT1 and CYSLT2. However, montelukast, an inhibitor of CYSLT1, also failed to significantly suppress CFU-C and LTC-IC growth. These findings indicate that targeting ALOX5 or CYSLT1 signaling with leukotriene antagonists, introduced into the clinical practice primarily as prophylaxis and treatment for asthma, may not be a promising pharmacological strategy to eradicate persisting LSC in CML patients.

A novel AHI-1-BCR-ABL-DNM2 complex regulates leukemic properties of primitive CML cells through enhanced cellular endocytosis and ROS-mediated autophagy

Tyrosine kinase inhibitor (TKI) therapies induce clinical remission with remarkable effects on chronic myeloid leukemia (CML). However, very few TKIs completely eradicate the leukemic clone and persistence of leukemic stem cells (LSCs) remains challenging, warranting new, distinct targets for improved treatments. We demonstrated that the scaffold protein AHI-1 is highly deregulated in LSCs and interacts with multiple proteins, including Dynamin-2 (DNM2), to mediate TKI-resistance of LSCs. We have now demonstrated that the SH3 domain of AHI-1 and the proline rich domain of DNM2 are mainly responsible for this interaction. DNM2 expression was significantly increased in CML stem/progenitor cells; knockdown of DNM2 greatly impaired their survival and sensitized them to TKI treatments. Importantly, a new AHI-1-BCR-ABL-DNM2 protein complex was uncovered, which regulates leukemic properties of these cells through a unique mechanism of cellular endocytosis and ROS-mediated autophagy. Thus, targeting this complex may facilitate eradication of LSCs for curative therapies.

Combined inhibition of β-catenin and Bcr-Abl synergistically targets tyrosine kinase inhibitor-resistant blast crisis chronic myeloid leukemia blasts and progenitors in vitro and in vivo

Tyrosine kinase inhibitor (TKI) resistance and progression to blast crisis (BC), both related to persistent β-catenin activation, remain formidable challenges for chronic myeloid leukemia (CML). We observed overexpression of β-catenin in BC-CML stem/progenitor cells, particularly in granulocyte–macrophage progenitors, and highest among a novel CD34⁺CD38⁺CD123^hiTim-3^hi subset as determined by CyTOF analysis. Co-culture with mesenchymal stromal cells (MSCs) induced the expression of β-catenin and its target CD44 in CML cells. A novel Wnt/β-catenin signaling modulator, C82, and nilotinib synergistically killed KBM5^T315I and TKI-resistant primary BC-CML cells with or without BCR–ABL kinase mutations even under leukemia/MSC co-culture conditions. Silencing of β-catenin by short interfering RNA restored sensitivity of primary BCR–ABL^T315I/E255V BC-CML cells to nilotinib. Combining the C82 pro-drug, PRI-724, with nilotinib significantly prolonged the survival of NOD/SCID/IL2Rγ null mice injected with primary BCR–ABL^T315I/E255V BC-CML cells. The combined treatment selectively targeted CML progenitors and inhibited CD44, c-Myc, survivin, p-CRKL and p-STAT5 expression. In addition, pretreating primary BC-CML cells with C82, or the combination, but not with nilotinib alone, significantly impaired their engraftment potential in NOD/SCID/IL2Rγ-null-3/GM/SF mice and significantly prolonged survival. Our data suggest potential benefit of concomitant β-catenin and Bcr–Abl inhibition to prevent or overcome Bcr–Abl kinase-dependent or -independent TKI resistance in BC-CML.

Targeting c-FOS and DUSP1 abrogates intrinsic resistance to tyrosine-kinase inhibitor therapy in BCR-ABL-induced leukemia

Tyrosine kinase inhibitor (TKI) therapy for human cancers is not curative, with relapse due to the continuing presence of tumor cells, referred to as minimal residual disease (MRD) cells. MRD stem or progenitor cells survival in the absence of oncogenic kinase signaling, a phenomenon referred to as intrinsic resistance, depends on diverse growth factors. Here, we report that oncogenic kinase and growth factor signaling converge to induce the expression of the signaling proteins c-Fos and Dusp1. Genetic deletion of c-Fos and Dusp1 suppressed tumor growth in a BCR-ABL-induced mouse model of chronic myeloid leukemia (CML). Pharmacological inhibition of c-Fos, Dusp1 and BCR-ABL eradicated MRD in multiple in vivo models, as well as in primary CML patient xenotransplanted mice. Growth factor signaling also conferred TKI resistance and induced c-FOS and DUSP1 expression in tumor cells modeling other types of kinase-driven leukemias. Our data demonstrate that c-Fos and Dusp1 expression levels determine the threshold of TKI efficacy, such that growth factor-induced expression of c-Fos and Dusp1 confers intrinsic resistance to TKI therapy in a wide-ranging set of leukemias, and may represent a unifying Achilles heel of kinase-driven cancers.

Immunological Analyses of Leukemia Stem Cells

Traditionally, the intracellular localization and expression levels of specific proteins in CML Leukemia stem cells (LSCs) have been evaluated by fluorescence immunohistochemistry (FIHC). More recently, Duolink(®) in situ PLA technology has opened up a new and more quantitative way to evaluate signal transduction, posttranslational modification, and protein-protein interaction at the single-stem-cell level. This novel methodology, which employs two antibody-based probes, has already increased our understanding of the biology of the rare CML LSC population. In the future, the use of this approach may contribute to the development of novel therapeutics aimed at eradicating CML LSCs in CML patients.

Synergistic effects of p53 activation via MDM2 inhibition in combination with inhibition of Bcl-2 or Bcr-Abl in CD34+ proliferating and quiescent chronic myeloid leukemia blast crisis cells

The Bcr-Abl tyrosine kinase regulates several Bcl-2 family proteins that confer resistance to apoptosis in chronic myeloid leukemia (CML) cells. Given p53's ability to modulate the expression and activity of Bcl-2 family members, we hypothesized that targeting Bcr-Abl, Bcl-2, and p53 concomitantly could have therapeutic benefits in blast crisis (BC) CML and in quiescent CML CD34+ cells that are insensitive to tyrosine kinase inhibitors (TKI). We examined the effects of the MDM2 inhibitor nutlin3a and its combination with the dual Bcl-2 and Bcl-xL inhibitor ABT-737, and the Bcr-Abl inhibitor nilotinib on BC CML patient samples. We found that in quiescent CD34+ progenitors, p53 expression is significantly lower, and MDM2 is higher, compared to their proliferating counterparts. Treatment with nutlin3a induced apoptosis in bulk and CD34+CD38- cells, and in both proliferating and quiescent CD34+ progenitor CML cells. Nutlin3a synergized with ABT-737 and nilotinib, in part by inducing pro-apoptotic, and suppressing anti-apoptotic, Bcl-2 proteins. Nilotinib inhibited the expression of Bcl-xL and Mcl-1 in BC CML cells. These results demonstrate that p53 activation by MDM2 blockade can sensitize BC CML cells, including quiescent CD34+ cells, to Bcl-2 inhibitor- and TKI-induced apoptosis. This novel strategy could be useful in the therapy of BC CML.

Tyrosine kinase inhibitor-induced CD70 expression mediates drug resistance in leukemia stem cells by activating Wnt signaling

In chronic myelogenous leukemia (CML), oncogenic BCR-ABL1 activates the Wnt pathway, which is fundamental for leukemia stem cell (LSC) maintenance. Tyrosine kinase inhibitor (TKI) treatment reduces Wnt signaling in LSCs and often results in molecular remission of CML; however, LSCs persist long term despite BCR-ABL1 inhibition, ultimately causing disease relapse. We demonstrate that TKIs induce the expression of the tumor necrosis factor (TNF) family ligand CD70 in LSCs by down-regulating microRNA-29, resulting in reduced CD70 promoter DNA methylation and up-regulation of the transcription factor specificity protein 1. The resulting increase in CD70 triggered CD27 signaling and compensatory Wnt pathway activation. Combining TKIs with CD70 blockade effectively eliminated human CD34(+) CML stem/progenitor cells in xenografts and LSCs in a murine CML model. Therefore, targeting TKI-induced expression of CD70 and compensatory Wnt signaling resulting from the CD70/CD27 interaction is a promising approach to overcoming treatment resistance in CML LSCs.

NUMB inactivation confers resistance to imatinib in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) progresses from a chronic to a blastic phase, where the leukemic cells are proliferative and undifferentiated. The CML is nowadays successfully treated with BCR-ABL kinase inhibitors as imatinib and its derivatives. NUMB is an evolutionary well-conserved protein initially described as a functional antagonist of NOTCH function. NUMB is an endocytic protein associated with receptor internalization, involved in multiple cellular functions. It has been reported that MSI2 protein, a NUMB inhibitor, is upregulated in CML blast crisis, whereas NUMB itself is downregulated. This suggest that NUMB plays a role in the malignant progression of CML. Here we have generated K562 cells (derived from CML in blast crisis) constitutively expressing a dominant negative form of NUMB (dnNUMB). We show that dnNUMB expression confers a high proliferative phenotype to the cells. Importantly, dnNUMB triggers a partial resistance to imatinib in these cells, antagonizing the apoptosis mediated by the drug. Interestingly, imatinib resistance is not linked to p53 status or NOTCH signaling, as K562 lack p53 and imatinib resistance is reproduced in the presence of NOTCH inhibitors. Taken together, our data support the hypothesis that NUMB activation could be a new therapeutic target in CML.

Induction of Chronic Myeloid Leukemia in Mice

Chronic myeloid leukemia (CML) is a myeloproliferative disorder derived from a hematopoietic stem cell (HSC), harboring Philadelphia chromosome (Ph chromosome). Formation of the Ph chromosome is caused by a reciprocal translocation between the chromosomes 9 and 22 t(9;22)(q34;q11), resulting in a fusion protein known as BCR-ABL which has constitutive tyrosine kinase activity and promotes the proliferation of leukemia cells via multiple mechanisms. Studies on CML have led to the identification of the first cancer-associated chromosomal abnormality and the subsequent development of tyrosine kinase inhibitors (TKIs) that inhibit BCR-ABL kinase activity in CML. It has become clear that leukemia stem cells (LSCs) in CML are insensitive to inhibition by TKIs, and eradication of LSCs appears to be difficult. Therefore, some of the major issues in current CML therapy are to understand the biology of LSCs and to investigate why LSCs are insensitive to TKIs for developing curative therapeutic strategies. In this regard, application of mouse models recapitulating human CML disease will be critical. In this chapter, we describe methods for induction of CML in mice with BCR-ABL.

Discovery of 2-Acylaminothiophene-3-Carboxamides as Multitarget Inhibitors for BCR-ABL Kinase and Microtubules

The emergence of drug resistance of the BCR-ABL kinase inhibitor imatinib, especially toward the T315I gatekeeper mutation, poses a great challenge to targeted therapy in treating chronic myeloid leukemia (CML) patients. To discover novel inhibitors against drug-resistant CML bearing T315I mutation, we applied a physics-based hierarchical virtual screening approach to dock a large chemical library against ATP binding pockets of both wild-type (WT) and T315I mutant ABL kinases in a combinatorial fashion. This strategy automatically resulted in 87 compounds satisfying structural and energetic criteria of both WT and T315I mutant kinases. Among them, nine compounds, which share a common thiophene-based scaffold and adopt similar binding poses, were chosen for experimental testing and one of them was shown to have low micromolar inhibition activities against both WT and mutant ABL kinases. Structure-activity relationship analysis with a series of structural modifications based on 2-acylaminothiophene-3-carboxamide scaffold supports our predicted binding mode. Interestingly, the same chemical scaffold was also enriched in our previous virtual screening campaign against colchicine site of microtubules using the same computational protocol, which suggests our virtual screening strategy is capable of discovering small-molecule ligands targeting distinct protein binding sites without sharing any sequential and structural similarity. Furthermore, the multitarget inhibition activity of this class of compounds was assessed in cellular experiments. We expect that the 2-acylaminothiophene-3-carboxamide scaffold may serve as a promising starting point for developing multitarget inhibitors in cancer treatment by targeting both kinases and microtubules.

Epigenetic inactivation of DLX4 is associated with disease progression in chronic myeloid leukemia

Aberrant DNA methylation of various genes has been identified to be associated with disease progression in chronic myeloid leukemia (CML). Our study was intended to investigate DLX4 methylation pattern in different clinical stages of CML and further determine its role in regulating DLX4 expression. Real-time quantitative methylation-specific PCR and bisulfite sequencing PCR were applied to detect DLX4 methylation. 5-aza-2'-deoxycytidine (5-aza-dC) was used for demethylation studies. DLX4 was significantly hypermethylated in CML patients (P = 0.002) especially in blastic phase (BC) stage (P < 0.001) as compared with controls. Moreover, DLX4 methylation level in BC stage was significantly higher than in chronic phase (CP) stage (P < 0.001). DLX4 methylation density was significantly increased during the progression of CML among the tested two patients (P < 0.001). DLX4 hypermethylation occurred with the highest incidence in BC stage (83%), lower incidence in acute phase (AP) stage (43%), and the lowest incidence in CP stage (26%) (P = 0.001). Moreover, t(9; 22) with additional alteration cases had significantly higher frequency of DLX4 hypermethylation compared with the other cytogenetics (P = 0.010). Significantly negative correlation was observed between DLX4 methylation and DLX4-TV2 (the shorter DLX4 isoform) expression (R = -0.382, P = 0.001, n = 78) but not between DLX4 methylation and BP1 (the longer DLX4 isoform) expression (R = 0.134, P = 0.244, n = 78) in CML patients. Both DLX4-TV2 and BP1 mRNA were significantly increased after 5-aza-dC treatment in K562 cell line (P < 0.001). Our study indicated that hypermethylation of DLX4 correlated with disease progression of CML. Moreover, DLX4 expression was regulated by its methylation in CML.

Treatment of chronic myelogenous leukemia by blocking cytokine alterations found in normal stem and progenitor cells

Leukemic cells disrupt normal patterns of blood cell formation, but little is understood about the mechanism. We investigated whether leukemic cells alter functions of normal hematopoietic stem and progenitor cells. Exposure to chronic myelogenous leukemia (CML) caused normal mouse hematopoietic progenitor cells to divide more readily, altered their differentiation, and reduced their reconstitution and self-renewal potential. Interestingly, the normal bystander cells acquired gene expression patterns resembling their malignant counterparts. Therefore, much of the leukemia signature is mediated by extrinsic factors. Indeed, IL-6 was responsible for most of these changes. Compatible results were obtained when human CML were cultured with normal human hematopoietic progenitor cells. Furthermore, neutralization of IL-6 prevented these changes and treated the disease.

Convert and conquer: the strategy of chronic myelogenous leukemic cells

Emerging evidence is contributing to explain how leukemias disrupt normal blood cell production. In this issue of Cancer Cell, Welner and colleagues show that, during the development of chronic myeloid leukemia, mutated cells transform normal hematopoietic progenitors into "leukemic like" cells through IL-6 secretion, proposing a new cellular target.

A novel compound against oncogenic Aurora kinase A overcomes imatinib resistance in chronic myeloid leukemia cells

Drug resistance still represents a major obstacle to successful chronic myeloid leukemia (CML) treatment and novel compounds or strategies to override this challenging problem are urgently required. Here, we evaluated a novel compound AKI603 against oncogenic Aurora kinase A (Aur-A) in imatinib-resistant CML cells. We found that Aur-A was highly activated in imatinib-resistant KBM5-T315I cells. AKI603 significantly inhibited the phosphorylation of Aur-A kinase at Thr288, while had little inhibitory effect on BCR-ABL kinase in both KBM5 and KBM5-T315I cells. AKI603 inhibited cell viability, and induced cell cycle arrest with polyploidy accumulation in KBM5 and KBM5-T315I cells. Moreover, inhibition of Aur-A kinase by AKI603 suppressed colony formation capacity without promoting obvious apoptosis. Importantly, AKI603 promoted cell differentiation in both CML cell types. Thus, our study suggested the potential clinical use of small molecule Aurora kinase inhibitor AKI603 to overcome imatinib resistance in CML treatment.

In vivo selective imaging and inhibition of leukemia stem-like cells using the fluorescent carbocyanine derivative, DiOC5(3)

Elimination of leukemia stem cells (LSCs) is necessary for the destruction of malignant cell populations. Owing to the very small number of LSCs in leukemia cells, xenotransplantation studies are difficult in terms of functionally and pathophysiologically replicating clinical conditions of cell culture experiments. There is currently a limited number of lead compounds that target LSCs. Using the LSC-xenograft zebrafish screening method we previously developed, we found that the fluorescent compound 3,3'-dipentyloxacarbocyanine iodide (DiOC5(3)) selectively marked LSCs and suppressed their proliferation in vivo and in vitro. DiOC5(3) had no obvious toxicity to human umbilical cord blood CD34+ progenitor cells and normal zebrafish. It accumulated in mitochondria through organic anion transporter polypeptides that are overexpressed in the plasma membrane of LSCs, and induced apoptosis via ROS overproduction. DiOC5(3) also inhibited the nuclear translocation of NF-κB through the downregulation of LSC-selective pathways, as indicated from DNA microarray analysis. In summary, DiOC5(3) is a new type of anti-LSC compound available for diagnostic imaging and therapeutics that has the advantage of being a single fluorescent chemical.

Sustained anti-BCR-ABL activity with pH responsive imatinib mesylate loaded PCL nanoparticles in CML cells

IM–chitosan complex encapsulated poly(ε-caprolactone) (PCL) nanoparticles are proposed for their potential in enabling more intelligent controlled release and enhancing chemotherapeutic efficiency of IM.

Unusual case of simultaneous presentation of plasma cell myeloma, chronic myelogenous leukemia, and a jak2 positive myeloproliferative disorder

Background. Multiple articles discuss the rare incidence and potential causes of second hematologic disorders arising after treatment of Chronic Myelogenous Leukemia (CML), leading to the theory of imatinib, the current treatment regimen for CML, as a possible trigger for the development of secondary neoplasms. Our case eliminates the possibility of imatinib as the sole cause since our patient received a diagnosis of simultaneous plasma cell myeloma, CML, and a Jak2 mutation positive myeloproliferative disorder (MPD) arising de novo, prior to any treatment. We will further investigate into alternative theories as potential causes for multiple hematopathologic disorders. Case Report. There are currently no reported cases with the diagnosis of simultaneous plasma cell myeloma, chronic myelogenous leukemia, and Jak2 positive myeloproliferative disorder. We present a case of a 77-year-old male who was discovered to have these three concurring hematopathologic diagnoses. Our review of the literature includes a look at potential associations linking the three coexisting hematologic entities. Conclusion. The mechanism resulting in simultaneous malignancies is most likely multifactorial and potentially includes factors specific to the host, continuous stimulation of the immune system, previous chemotherapy or radiation, a potential common pluripotent stem cell, or, lastly, preexisting myeloma which may increase the susceptibility of additional malignancies.

Re-evaluating the role of BCR/ABL in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) requires the BCR/ABL tyrosine kinase for disease onset and maintenance. As a result, CML can be successfully treated with tyrosine kinase inhibitors (TKIs) such as imatinib. Most patients are maintained in a disease-suppressed state on daily TKI therapy for several years and in many cases this treatment prevents progression to the blast phase. If the TKI is discontinued, CML redevelops in 95% of patients as a result of persisting leukemia initiating cells (LICs). There are several hypotheses that describe the potential mechanism(s) responsible for LIC persistence in CML, but supporting evidence is limited. Furthermore, of the few patients who discontinue TKI therapy and are "cured" (i.e., in treatment-free remission), most have residual BCR/ABL-expressing cells in their hematopoietic tissues. There are also healthy individuals without a CML diagnosis who express the BCR/ABL mutation in a fraction of their hematopoietic cells. Finally, mice that express BCR/ABL from the Bcr locus as a knockin mutation do not develop CML. These mice have lower BCR/ABL levels than retroviral or transgenic models of BCR/ABL that do develop CML. Understanding why mice with BCR/ABL expressed from the Bcr locus and some people that express BCR/ABL are not afflicted with CML will provide insights into therapies to prevent or cure this disease.

Targeting the MYC and PI3K pathways eliminates leukemia-initiating cells in T-cell acute lymphoblastic leukemia

Disease relapse remains the major clinical challenge in treating T-cell acute lymphoblastic leukemia (T-ALL), particularly those with PTEN loss. We hypothesized that leukemia-initiating cells (LIC) are responsible for T-ALL development and treatment relapse. In this study, we used a genetically engineered mouse model of Pten(-/-) T-ALL with defined blast and LIC-enriched cell populations to demonstrate that LICs are responsible for therapeutic resistance. Unlike acute and chronic myelogenous leukemia, LICs in T-ALL were actively cycling, were distinct biologically, and responded differently to targeted therapies in comparison with their differentiated blast cell progeny. Notably, we found that T-ALL LICs could be eliminated by cotargeting the deregulated pathways driven by PI3K and Myc, which are altered commonly in human T-ALL and are associated with LIC formation. Our findings define critical events that may be targeted to eliminate LICs in T-ALL as a new strategy to treat the most aggressive relapsed forms of this disease.