Primary Chronic Myelogenous Leukemia Research Articles

A Deeply Quiescent Subset of CML LSC depend on FAO yet Avoid Deleterious ROS by Suppressing Mitochondrial Complex I.

Disease relapse and therapy resistance remain serious impediments to treating cancer. Leukemia stem cells (LSC) are therapy resistant and the cause of relapse. A state of deep quiescence appears to enable cancer stem cells (CSC) to acquire new somatic mutations essential for disease progression and therapy resistance. Both normal hematopoietic stem cells (HSC) and LSC share many common features, thereby complicating the safe elimination of LSC. A recent study demonstrated that long lived normal oocytes exist without mitochondrial complex I (MC-1), expressing it in a developmentally regulated fashion, thereby mitigating their vulnerability to ROS. Quiescent CSC rely on mitochondrial FAO, without complex I expression, thereby avoiding the generation of damaging ROS, similar to long lived normal human stem cells. A deeper understanding of the biology of therapy resistance is important for the development of optimal strategies to attain complete leukemia cures. Here, using scRNA-sequencing and ATAC-seq on primary chronic myelogenous leukemia (CML) patient samples, combined with bioinformatics analyses, we further examine the heterogeneity of a previously characterized in vitro imatinib-selected CD34-CD38- CML LSC population. We utilized a series of functional analyses, including single-cell metabolomic and Seahorse analyses, to validate the existence of the deepest quiescent leukemia initiators (LI) subset. Current study revealed heterogeneity of therapy resistant LSC in CML patients and their existence of two functionally distinct states. The most deeply quiescent LI suppress the expression of MC-1, yet are highly dependent on fatty acid oxidation (FAO) for their metabolic requirements and ATAC-seq demonstrated increased chromatin accessibility in this population, all consistent with an extremely primitive, quiescent stemness transcriptional signature. Importantly, the specific CREB binding protein (CBP)/β-catenin antagonist ICG-001 initiates the differentiation of LSC, including LI, decreases chromatin accessibility with differentiation and increasing expression of MC-1, CD34, CD38 and BCR-ABL1, thereby resensitizing them to imatinib. We investigated the biological aspects related to LSC heterogeneity in CML patients and demonstrated the ability of specific small molecule CBP/β-catenin antagonists to safely eliminate deeply quiescent therapy resistant CSC. These observations may represent an attractive generalizable therapeutic strategy that could help develop better protocols to eradicate the quiescent LSC population.

Primary Chronic Myelogenous Leukemia Blast Crisis with Precursor B Lymphoblastic Leukemia, a Case Report

Abstract Introduction/Objective Primary chronic myelogenous leukemia (CML) blast crisis at the initial disease presentation is rare. Most CML blast crisis cases present with increased myeloblasts with a minority of patients showing lymphoblastic leukemia. Differentiating primary CML lymphoblast crisis from de novo acute lymphoblastic leukemia may represent a diagnostic challenge to both pathologists and treating clinicians. This distinction is important as it has significant implications on patient management. Methods/Case Report A 15-year-old male patient was admitted to our University Hospital for hyperleukocytosis. Patient reportedly had weight loss with occasional sweats and cervical lymphadenopathy. She was found to have massive splenomegaly. Peripheral blood showed hyperleukocytosis with predominance of granulocytes at all maturation stages ranging from blast to segmented neutrophils with increased blasts. Subsequent bone marrow findings were consistent with extensive involvement by B-lymphoblastic leukemia. Ten-color Flow cytometry showed approximately 30% blasts with rare lymphocytes and monocytes. The blasts revealed precursor B-lymphoblastic immunophenotypic expression of CD45, CD10, CD19, CD20, CD22, CD34, CD38, CD200, HLA-DR and TdT expression. The results were similar to that of peripheral blood. Granulocytes showed abnormal maturation pattern with increased immature precursors and partial expression of CD4 and CD56 with no abnormalities detected in lymphocytes. In this case, while the bone marrow findings are consistent with B-lymphoblastic leukemia, the peripheral blood findings are consistent with blast phase of chronic myeloid leukemia. Further evaluation by cytogenetic and molecular studies confirmed the presence of Philadelphia chromosome, p210 transcripts, and rearrangement of BCR-ABL1, which supported the impression of precursor B-lymphoblastic leukemia in primary blast phase of CML. The patient was treated with tyrosine kinase inhibitor combined chemotherapy and went into remission. She has been followed up without significant complications for a year. Results (if a Case Study enter NA) NA. Conclusion The diagnosis of CML in primary lymphoblastic crisis is rare and needs to be systemically excluded before giving the diagnosis of de novo BCR-ABL1-positive acute lymphoblastic leukemia. If the patient does not have splenomegaly or previous leukocytosis, it needs cytological examination and extensive molecular analyses.

Abstract 3775: Inhibition of mitochondrial translation by the marine natural product elatol shows potent antileukemia activity

Abstract Targeted signaling inhibitors for hematologic malignancies may lead to limited clinical efficacy due to the outgrowth of subpopulations with alternative pathways independent of the drug target. Recent studies have shown that some forms of hematologic malignancies (Ashton et al., 2018) and solid tumors (Molina et al., 2018) have an energy metabolism highly dependent on mitochondrial oxidative phosphorylation. Tigecycline, a US FDA approved antibiotic, has been shown to inhibit synthesis of mitochondrion-encoded proteins leading to selective lethality in hematologic malignancies reliant on oxidative phosphorylation (Norberg et al., 2017). Combination treatment with the tyrosine-kinase inhibitor (TKI) imatinib and tigecycline eradicated therapy-resistant chronic myelogenous leukemia (CML), both in vitro and in vivo (Kuntz et al., 2017). We have previously reported that elatol, the major compound from algae Laurencia microcladia, is effective against several non-Hodgkin lymphomas and primary CML cells (Peters et al., 2018). In vitro studies showed that elatol inhibits eIF4A1 helicase activity, suppressing cytoplasmic cap-dependent translation initiation. Further assessments using 35-S-methionine incorporation in HEK293T cells treated with single-digit micromolar concentrations of elatol for short periods revealed strong downregulation of mitochondrion-encoded proteins (no transcriptional effect). This was confirmed in CML and acute lymphoblastic leukemia (ALL) cell lines whose 24-hour elatol LD50 ranged from high nanomolar to low micromolar concentrations. This potency was 2-10x higher than for tigecycline in side-by-side comparisons across several leukemia cell lines. Through sedimentation property analysis using sucrose gradients, we established that elatol does not affect integrity of small and large mitochondrial ribosomal units. Although the specific target on the mitochondrial translation apparatus remains elusive, we have uncovered that its mechanism of action differs from that of chloramphenicol, which inhibits translation elongation. Moreover, elatol treatment leads to activation of the integrated stress response (ISR) evidenced by induction of ATF4 and CHOP. We found that elatol activates the ISR through mitochondrial stress in which cleaved DELE1 binds to HRI to phosphorylate eIF2α, a mechanism described in Fessler et al., 2020. In summary, we have performed proof-of-concept studies using HEK293T and HeLa cell lines, isolated mitochondria, and CML and ALL cell lines to reveal that elatol is a potent inhibitor of mitochondrial protein synthesis and mechanistically different from chloramphenicol. Tigecycline’s compelling preclinical data in combination with TKI informed design of a pending clinical trial (NCT02883036). Elatol’s greatly improved potency provides a potential starting point for further optimization of this paradigm. Citation Format: Tyler A. Cunningham, Priyanka Maiti, Antonio Barrientos, Jonathan H. Schatz. Inhibition of mitochondrial translation by the marine natural product elatol shows potent antileukemia activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3775.

Inhibition of Mitochondrial Translation By the Marine Natural Product Elatol Shows Potent Antileukemia Activity

Targeted signaling inhibitors for hematologic malignancies may lead to limited clinical efficacy due to the outgrowth of subpopulations with alternative pathways independent of the drug target. Relapse/refractory disease that results from treatment with targeted signaling inhibitors is a major hurdle in obtaining curative responses. Interestingly, work over the past decade or more has shown that chronic myelogenous leukemia (CML) stem cells (CD34+CD38-) are resistant to targeted signaling inhibitors, such as the BCR-ABL kinase class of inhibitors, often a problematic source of resistance leading to residual disease that may precipitate later progression (Hamilton et al., 2012).Recent studies have shown that some forms of lymphoma and leukemia cell have an energy metabolism highly dependent on mitochondrial oxidative phosphorylation (Ashton et al., 2018). Tigecycline, a US FDA approved antibiotic, has been shown to inhibit synthesis of mitochondrion-encoded proteins due to the similarity of bacterial and mitochondrial ribosomes, leading to selective lethality in hematologic malignancies reliant on enhanced oxidative phosphorylation (Norberg et al., 2017). Indeed, it was established that CML stem cells are reliant on upregulated oxidative phosphorylation, and combination treatment with the tyrosine-kinase inhibitor (TKI) imatinib and tigecycline eradicated therapy-resistant CML, both in vitro and in animal models (Kuntz et al., 2017).We have previously reported that elatol, the major compound from the red alga Laurencia microcladia, is effective against several non-Hodgkin lymphomas and primary chronic myelogenous leukemia cells (Peters et al., 2018). In vitro studies showed that elatol inhibits eIF4A1 helicase activity, suppressing cytoplasmic cap-dependent translation initiation. Further assessments using 35-S-methionine incorporation in HEK293T cells with or without single-digit micromolar concentrations of elatol for short time periods revealed strong downregulation of mitochondrion-encoded proteins as in Figure 1, (with no effect on mitochondrial transcription). This was confirmed in CML and acute lymphoblastic leukemia (ALL) cell lines whose 24-hour elatol LD50 ranged from high nanomolar to low micromolar concentrations. This potency was 10-40x higher than for tigecycline in side-by-side comparisons across several leukemia cell lines when compared at 72h. Additionally, we established that elatol does not affect integrity of small and large mitochondrial ribosomal units through sedimentation property analysis using sucrose gradients. Although the specific target on the mitochondrial translation apparatus remains elusive, we have uncovered that its mechanism of action differs from that of chloramphenicol, which inhibits translation elongation.In summary, we have performed proof-of-concept studies using HEK293T and HeLa cell lines, isolated mitochondria from HEK293T, and CML and ALL cell lines to reveal that elatol is a potent inhibitor of mitochondrial protein synthesis at concentrations that do not affect cytoplasmic protein synthesis and that this mechanism differs from chloramphenicol. Tigecycline's compelling preclinical data in combination with TKI informed design of a pending clinical trial (NCT02883036). Elatol's greatly improved potency provide a potential starting point for further optimization of this paradigm. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A 14q32.31 Genomic-Imprinted DLK1-DIO3 microrna promotes Leukemogenesis By Inducing Stem Cell Quiescence and Inhibiting NK Cell Anti-Cancer Immunity

Leukemia emergence, maintenance, relapse and/or progression are causally linked to the presence of drug-resistant leukemia-initiating cells and impaired natural killer (NK) cell anti-tumor immune-response. Bone marrow microenvironment (BMM)- and/or leukemia-derived signals induce aberrant non-coding RNA expression and inhibit protein phosphatase 2A (PP2A) tumor suppressor activity. PP2A loss-of-function is essential for NK cell activity and leukemic but not normal stem and progenitor cell proliferation and survival. The human MIR300 gene is an intergenic miRNA that belongs to the 14q32.31 DLK1-DIO3 genomic-imprinted tumor suppressor miRNA cluster B. MIR300 was found involved in loss-of heterozygosity, inhibited in several tumor types with high mitotic index and during epithelial-to-mesenchymal transition (EMT), and associated with a cancer stem cell phenotype. By using primary cells from Philadelphia-positive (Ph+) chronic myelogenous leukemia (CML) in chronic (CP) and blastic (BC) phase, and complex karyotype (CK) acute myeloid leukemia (AML) patients, as paradigmatic examples of stem cell-derived neoplasms characterized by constitutive expression of oncogenic kinases, PP2A loss-of-function, altered microRNA expression and impaired NK cell proliferation and cytotoxicity, we found that MIR300 is a cell context-independent tumor suppressor with anti-proliferative and PP2A-dependent pro-apoptotic activities which are sequentially activated in a MIR300 dose-dependent manner through inhibition of CCND2/CDK6 and SET (PP2A inhibitor), respectively. To prevent PP2A-induced apoptosis, MIR300 is inhibited by oncogenic signals in CD34+CML (CP and BC) and CK-AML progenitors. Conversely, tumor-naïve BMM-induced C/EBPbeta-mediated signals (hypoxia and MSC exosomes) markedly upregulate MIR300 expression in primary CML and AML CD34+CFSEmax leukemic stem (LSC) and CD56+CD3-NK cells to induce/maintain quiescence (increased CD34+leukemic blasts in G0) and impair immune-response (suppression of NK cell proliferation and cytotoxic activity toward CD34+ leukemic blasts and CFSEmaxCD34+ CML-BC quiescent LSCs), respectively. Inhibition of MIR300 expression/activity rescues NK cell proliferation and anti-tumor cytotoxicity and prevented MSC- and hypoxia-induced growth-suppression of CD34+leukemic blasts by inhibiting degradation of MIR300 targets (e.g. SET, CCND2). We found that CML and AML LSCs escape MIR300-induced PP2A-mediated apoptosis through the hypoxia- and tumor-dependent TGFb1-FoxM1-mediated upregulation of TUG1 lncRNA. TUG1 is an oncogenic lncRNA described as a MIR300sponge and found upregulated in solid tumors, in which it has strong diagnostic, prognostic and therapeutic relevance and is associated with cancer stem cell maintenance and EMT. In quiescent CML and AML LSCs, TUG1 uncouples and limits MIR300 tumor suppressor functions to cytostasis by maintaining unbound MIR300 at levels sufficient to inhibit CCND2 and CDK6 but not SET expression. Exposure to clinically-relevant CpG-modified oligonucleotides modulating MIR300levels and/or inhibiting TUG1 MIR300-sponging activity, restores NK cell proliferation and cytotoxic activity, and suppresses human leukemic but not normal hematopoiesis by eradicating nearly all (> 95% reduction) CFSEmaxCD34+ and CD45+CD34+CD38-CD90+ LSCs and CD34+leukemic CML (CP and BC) and CK-AML blasts in vitro (CFCs, LTC-IC, and CFSEmaxCD34+cell tracking) and/or in NRG-SGM3 PDX mouse models of acute and chronic myeloid leukemias. Altogether, this work highlights the therapeutic importance of altering MIR300 expression in anti-LSC and NK cell-based approaches for myeloid leukemias, and indicates that tumor-naïve BMM-induced MIR300 tumor suppressor anti-proliferative and PP2A-activating functions may support leukemogenesis by promoting the formation and initial expansion of the quiescent LSC pool through the induction of LSC dormancy and inhibition of quiescent LSC killing by cytokine-activated NK cells, respectively. (G.S. and R.T. equally contributed to this work) Disclosures Stagno: BMS: Honoraria; Incyte: Honoraria; Pfizer: Honoraria; Novartis: Honoraria. Deininger:TRM: Consultancy; Sangoma: Consultancy; Incyte: Honoraria; Novartis: Honoraria; Sangamo: Consultancy; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Humana: Honoraria; Ascentage Pharma: Consultancy, Honoraria; Blueprint: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Research Funding; Fusion Pharma: Consultancy; Adelphi: Consultancy. Milojkovic:BMS: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau. Apperley:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Baer:Takeda: Research Funding; Incyte: Research Funding; Kite: Research Funding; Forma: Research Funding; AI Therapeutics: Research Funding; Abbvie: Research Funding; Astellas: Research Funding.

The Embryonic Program Activated during Blast Crisis of Chronic Myelogenous Leukemia (CML) Implicates a TCF7L2 and MYC Cooperative Chromatin Binding and Represents a Druggable Target

Chronic myeloid leukemia (CML) is characterized by an inherent genetic instability, which contributes to the progression of the disease towards accelerated and blast crisis (BC). The occurrence of the latter has been hampered by the use of tyrosine kinase inhibitors (TKI), which changed this natural progression, but BC still occurs in patients resistant to TKI. Several cytogenetic (major and minor routes) and genomic (TP53 mutation, p16/INK4A deletions, DNA repair abnormalities such as BRCA1, DNA-PKcs, hnRNP metabolism) events have been reported in the progression towards BC. Previous data have also suggested the involvement of embryonic stem cell program activated in BC cells such as Lin28A. In this work, we have taken advantage of the previously reported gene profiling of BC in a large cohort of patients (Radich et al. 2006) and found a correlation between blast numbers and the involvement of the Transcription Factor 7 like 2 (TCF7L2) in BC. TFC7L2 is a member of the TCF family of proteins that are known to activate WNT target genes such as Cyclin D1. TCF7L2 has been shown to be overexpressed in acute myeloid leukemia (AML) and represents a druggable target (Saenz et al Leukemia 2019). The involvement of TCF7L2 in CML-BC and its interaction with the epigenetic regulators has not been studied so far. The gene correlation study that we have performed using the blast numbers and the expression of TCF7L2 in CD34+ CML cells was found to be highly significant (Pearson test, r = 0.56, p-value=5.2e-4) (Fig.1A). TCF7L2 promoter was classed as active in K562 with ChromHMM Functional genomic analysis. K562 epigenetics peaks of TCF7L2 CHIP-seq were found principally mapped in proximal promoters (39% of the peaks, -3000pb upstream Transcription Starting Sites (TSS), Fig. 1B) and 183 unique peaks matched with promoter of 144 unique genes found to be correlated to the blast number in blood of the CML patients during BC (Fig 1C). This TCF7L2-dependent BC program was characterized to be active because promoters were also found positive for H3K27Ac and negative for H3K27Me3 histone marks, and functionally enriched with binding sites for MYC/MAX interactions (p=1.15e-6). The analysis of CHIP-sequencing of MYC revealed a significant overlapping of TCF7L2 epigenetic program with MYC (fold enrichment: 20.81, p < 2.2e-16). Surprisingly, the TCF7L2 program was found independent of RUNX1 and GATA2 transcriptional program. To determine these potential interactions, we have designed experiments in K562 cell line using the b-catenin activator Lithium Chloride (LiCL2) and the Myc/Max dimerization inhibitor 10058-F4. K562 cells were cultured in the presence of LiCL2 (10mM & 24hours) and the compound 10058-F4 (64µM & 48hours) and the expression of three epigenetic targets was analyzed by Q-RT-PCR in the presence of DMSO controls. The three targets chosen were protein arginine N-methyltransferase (PRMT1), the ATPase/Helicase RUVBL1 and the WD-repeat containing protein WDR77. As expected, after culture with LiCL2, the expression of PRMT1 was increased x 6.3 fold (p=8.49e-13) , that of RUVBL1 by x 1.66 Fold (p=1.67e-6) and that of WDR77 by x 2 fold (p=4.97e) (Fig.1D). On the contrary, the culture of K562 cells in the presence of MYC/MAX inhibitor 10058-F4, decreased the expression of 3 targets as compared to DMSO controls (x 1.6 fold for PRMT1, p=6.52e-5; x2 fold reduction for RUVBL1, p-value=2.71e-5; and x 1.4 fold for WDR77, p =0.0000643). These results show for the first time a cooperative role of TCF7L2 and MYC during blast crisis of CML and provide mechanistic insights into the interactions for the role of MYC in CML blast crisis. In addition they strengthen previous data showing a possible embryonic footprint in the blast development over the hematopoietic differentiation program during progression of the disease and provide a rationale for the pharmacological targeting of BC by the use of MYC/MAX inhibitors such as 10058-F4. Experiments are underway to evaluate the role of these factors and the MYC/MAX inhibitors in primary CML samples. Reference : Radich JP, Dai H, Mao M, Oehler V, Schelter J, Druker B, Sawyers C, Shah N, Stock W, Willman CL, Friend S, Lindsey PS.(2006) :Gene Expression Changes Associated with Progression and Response in Chronic Myeloid Leukemia. Proceedings of the National Academy of Sciences of the United States of America 103 (8): 2794-99. Disclosures Turhan: Incyte: Consultancy, Honoraria; novartis: Honoraria, Research Funding.

Lncrna RP1-68D18.2 Promotes K562 Cell Line Resistance to Imatinib through CD44 and Its Downstream Signal Molecules

As the first-generation tyrosine kinase inhibitor specifically targeting the BCR-ABL oncoprotein, imatinib has been successfully used in the therapy for chronic myelogenous leukemia (CML) with a significant response and good compliance. However, imatinib resistance becomes the main reason for failure of the treatment of CML. In addition to the common BCR-ABL dependence of imatinib resistance, e.g. BCR-ABL kinase domain mutations and BCR-ABL gene amplification, BCR-ABL independence also plays important roles, which involves alteration of dynamics of drug import and efflux, persistent or compensatory activation of signaling pathways etc. Recently, several studies have reported the correlation of lncRNA with resistance of chemotherapeutic drugs in many cancers. Here, we report, for the first time, discernible overexpression of lncRNARP1-68D18.2 and CD44 mRNA in the imatinib resistant chronic myelogenous leukemia cell line K562R, using lncRNA and mRNA microarray, and further verify it using qPCR. Knockdown of RP1-68D18.2 in K562R cell lines increased their sensitivity to imatinib, and simultaneously caused a decrease in CD44 and c-Myc protein levels. Correspondingly, overexpression of RP1-68D18.2 in K562, a sensitive cell line, led to a slightly decrease in imatinib sensitivity and partially reverse downregulation of c-Myc, p-ERK and p-MEK caused by imatinib treatment. Analysis of correlations revealed positive correlation between RP1-68D18.2 and CD44 mRNA expression in the primary CML blasts and hematological malignant cell lines. We conclude that overexpression of RP1-68D18.2 could promote imatinib resistance in the K562R cell line through the regulation of CD44 and its downstream signal molecules. DisclosuresNo relevant conflicts of interest to declare.

Inhibition of ER stress-related IRE1α/CREB/NLRP1 pathway promotes the apoptosis of human chronic myelogenous leukemia cell

Endoplasmic reticulum (ER) stress is induced in chronic myelogenous leukemia (CML) cells. As an important sensor of ER stress, inositol-requiring protein-1α (IRE1α) promotes the survival of acute myeloid leukemia. NLRP1 inflammasome activation promotes metastatic melanoma growth and that IRE1α can increase NLRP1 inflammasome gene expression. This study aimed to investigate the role and molecular mechanism of IRE1α in CML cell growth. We found that overexpression of IRE1α or NLRP1 significantly promoted the proliferation and decreased the apoptosis of CML cells, whereas downregulation of these two genes showed the opposite effects. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, reduced the expression of IRE1α and NLRP1. IRE1α elevated NLRP1 expression via cAMP responsive element binding protein (CREB) phosphorylation. NLRP1 inflammasome was activated in CML cells and its activation partly reversed ER stress inhibitor-induced cell apoptosis. Furthermore, inhibition of IRE1α/NLRP1 pathway sensitized CML cells to imatinib-mediated apoptosis. Additionally, IRE1α expression was elevated and NLRP1 inflammasome was activated in primary cells from CML patients. Downregulation of IRE1α or NLRP1 suppressed the proliferation and elevated the apoptosis of primary CML cells. Collectively, this study demonstrated that the IRE1α/CREB/NLRP1 pathway contributes to the progression of CML and the development of imatinib resistance. Hence, targeting ER stress-related IRE1α expression or NLRP1 inflammasome activation may block CML development.

PTEN Is Fundamental for Elimination of Leukemia Stem Cells Mediated by GSK126 Targeting EZH2 in Chronic Myelogenous Leukemia.

Purpose: Leukemia stem cells (LSCs) are an important source of tyrosine kinase inhibitor resistance and disease relapse in patients with chronic myelogenous leukemia (CML). Targeting LSCs may be an attractive strategy to override this thorny problem. Given that EZH2 was overexpressed in primary CML CD34+ cells, our purpose in this study was to evaluate the effects of targeting EZH2 on CML LSCs and clarify its underlying mechanism.Experimental Design: Human primary CML CD34+ cells and retrovirally BCR-ABL-driven CML mouse models were employed to evaluate the effects of suppression of EZH2 by GSK126- or EZH2-specific shRNA in vitro and in vivo Recruitment of EZH2 and H3K27me3 on the promoter of tumor-suppressor gene PTEN in CML cells was measured by chromatin immunoprecipitation assay.Results: Our results showed that pharmacologic inhibition of EZH2 by GSK126 not only elicited apoptosis and restricted cell growth in CML bulk leukemia cells, but also decreased LSCs in CML CD34+ cells while sparing those from normal bone marrow CD34+ cells. Suppression of EZH2 by GSK126 or specific shRNA prolonged survival of CML mice and reduced the number of LSCs in mice. EZH2 knockdown resulted in elevation of PTEN and led to impaired recruitment of EZH2 and H3K27me3 on the promoter of PTEN gene. The effect of EZH2 knockdown in the CML mice was at least partially reversed by PTEN knockdown.Conclusions: These findings improve the understanding of the epigenetic regulation of stemness in CML LSCs and warrant clinical trial of GSK126 in refractory patients with CML. Clin Cancer Res; 24(1); 145-57. ©2017 AACR.

Chk1 inhibitors overcome imatinib resistance in chronic myeloid leukemia cells

Drug resistance to tyrosine kinase inhibitors (TKIs) is currently a clinical problem of chronic myelogenous leukemia (CML). Bcr-Abl protein depletion is considered as a way to overcome drug resistance to TKIs. In our study, Chk1 inhibitors, AZD7762 and MK-8776, had strong antitumor effects on CML cell line KBM5 and imatinib-resistant form KBM5T315I. Moreover, Chk1 inhibitors showed a strong cytotoxic effect on leukemia cells from primary CML and imatinib-resistance CML patients, but low cytotoxic effect on normal human mononuclear cells. Then, we found that Chk1 inhibitors induced apoptosis and increased DNA damage in CML cell lines with the degradation of the Bcr-Abl protein. Using the proteasome inhibitor and an immunoprecipitation assay, we found that Chk1 inhibitors triggered the degradation of Bcr-Abl through ubiquitination, which is depending on E3 ubiquitin ligase CHIP. At last, MK-8776 showed a significant tumor-suppressive effect of KBM5T315I cell in xenograft tumor models. Taking together, these findings suggest that targeting Chk1 may overcome TKIs resistance for the treatment of CML.

Selective surface marker and miRNA profiles of CD34+ blast-derived microvesicles in chronic myelogenous leukemia.

The present study aimed at investigating the selective enrichment of surface marker and functional microRNA (miRNA) profiles of cluster of differentiation (CD)34+ blast-derived microvesicles (MVs) from parental cells in chronic myelogenous leukemia (CML), thus providing an experimental basis for MVs to be used to predict characteristics of CD34+ blasts. Magnetic activated cell sorting and continuous differential centrifugation were used to isolate primary CML CD34+ blasts and MVs, in addition to utilizing flow cytometry to identify surface markers of CD34+ blasts and blast-derived MVs. Microarray analysis and the reverse transcription-quantitative polymerase chain reaction were performed to analyze miRNA profiles of CD34+ blasts and MVs. The results of the present study indicated that primary CML CD34+ blasts were able to release MVs, which were selectively enriched with the surface markers CD34 and CD123, and functional miRNAs from parental cells. A total of 15 miRNAs were upregulated in CD34+ blast derived-MVs compared with in CD34+ cells. Distinct Kyoto Encyclopedia of Genes and Genomes pathways and Gene Ontology terms characterized by altered gene expression and potentially associated miRNA were identified. Upregulated miRNAs in MVs were associated with cell development, tumorigenesis and signaling pathways involving ErbB and phosphoinositide 3-kinase/protein kinase B. The present study provides evidence, which increases the understanding of physiological functions of cancer-derived MVs, and aids the understanding of the roles of CD34+ blast-derived MVs in CML-associated processes.

Gas6/AXL Signaling Regulates Self-Renewal of Chronic Myelogenous Leukemia Stem Cells by Stabilizing β-Catenin.

Purpose: Quiescent leukemia stem cells (LSC) are important resources of resistance and relapse in chronic myelogenous leukemia (CML). Thus, strategies eradicating CML LSCs are required for cure. In this study, we discovered that AXL tyrosine kinase was selectively overexpressed in primary CML CD34+ cells. However, the role of AXL and its ligand Gas6 secreted by stromal cells in the regulation of self-renewal capacity of LSCs has not been well investigated.Experimental Design: The function of CML CD34+ cells was evaluated by flow cytometer, CFC/replating, long-term culture-initiating cells (LTC-IC), CML mouse model driven by human BCR-ABL gene and NOD-scid-IL2Rg-/- (NSI) mice.Results: AXL was selectively overexpressed in primary CML CD34+ cells. AXL knockdown reduced the survival and self-renewal capacity of human CML CD34+ cells. Pharmacologic inhibition of AXL reduced the survival and self-renewal capacity of human CML LSCs in vitro and in long-term grafts in NSI mice. Human CML CD34+ cells conscripted bone marrow-derived stromal cells (BMDSC) and primary mesenchymal stem cells (MSC) to secrete Gas6 to form a paracrine loop that promoted self-renewal of LSCs. Suppression of AXL by shRNA and inhibitor prolonged survival of CML mice and reduced the growth of LSCs in mice. Gas6/AXL ligation stabilizes β-catenin in an AKT-dependent fashion in human CML CD34+ cells.Conclusions: Our findings improve the understanding of LSC regulation and validate Gas6/AXL as a pair of therapeutic targets to eliminate CML LSCs. Clin Cancer Res; 23(11); 2842-55. ©2016 AACR.

Anthelmintic Niclosamide Disrupts the Interplay of p65 and FOXM1/β-catenin and Eradicates Leukemia Stem Cells in Chronic Myelogenous Leukemia.

Leukemia stem cells (LSC), which are insensitive to tyrosine kinase inhibitors (TKI), are an important source of TKI resistance and disease relapse in chronic myelogenous leukemia (CML). Obstacles to eradicating LSCs include limited understanding of the regulation network of LSCs. The current study aimed to examine the interplay between NF-κB and FOXM1/β-catenin, and the effect of its chemical intervention on CML LSCs. The interplay between NF-κB and FOXM1/β-catenin was analyzed by reciprocal coimmunoprecipitation (co-IP) and chromatin immunoprecipitation (ChIP) assay in CML cells. The effect of disturbing NF-κB and FOXM1/β-catenin by niclosamide on the self-renewal capacity and survival of LSCs was evaluated in vitro in human primary CML CD34+ cells and in vivo in CML mice. Reciprocal co-IP experiments showed physical interaction of p65 and FOXM1. p65 promoted transcription of FOXM1 gene. ChIP assay revealed recruitment of p65 on the promoter of FOXM1 gene. Conversely, FOXM1 and β-catenin positively regulated the nuclear translocation and transcriptional activity of NF-κB in CML cells. Niclosamide disrupted the positive feedback loop between NF-κB and FOXM1/β-catenin, thereby impairing the self-renewal capacity and survival of CML LSCs. Niclosamide decreased the long-term engraftment of human CML LSCs in NOD-SCID IL2Rγ chain-deficient (NOG) mice, and prolonged the survival of CML mice. Interaction of p65 with FOXM1/β-catenin is critical in CML and its disruption by niclosamide eradicates LSCs. These findings may improve the understanding of a self-renewal regulatory mechanism of LSCs and offer a rationale-based approach to eliminate LSCs in CML. Clin Cancer Res; 23(3); 789-803. ©2016 AACR.

Revealing stiffening and brittling of chronic myelogenous leukemia hematopoietic primary cells through their temporal response to shear stress

Cancer cell transformation is often accompanied by a modification of their viscoelastic properties. When capturing the stress-to-strain response of primary chronic myelogenous leukemia (CML) cells, from two data sets of CD34+ hematopoietic cells isolated from healthy and leukemic bone marrows, we show that the mean shear relaxation modulus increases upon cancer transformation. This stiffening of the cells comes along with local rupture events, detected as reinforced sharp local maxima of this modulus, suggesting that these cancer cells respond to a local mechanical stress by a cascade of local brittle failure events.

Identification of CD25 as STAT5-Dependent Growth Regulator of Leukemic Stem Cells in Ph+ CML.

In chronic myelogenous leukemia (CML), leukemic stem cells (LSC) represent a critical target of therapy. However, little is known about markers and targets expressed by LSCs. The aim of this project was to identify novel relevant markers of CML LSCs. CML LSCs were examined by flow cytometry, qPCR, and various bioassays. In addition, we examined the multipotent CD25(+)CML cell line KU812. In contrast to normal hematopoietic stem cells, CD34(+)/CD38(-)CML LSCs expressed the IL-2 receptor alpha chain, IL-2RA (CD25). STAT5 was found to induce expression of CD25 in Lin(-)/Sca-1(+)/Kit(+)stem cells in C57Bl/6 mice. Correspondingly, shRNA-induced STAT5 depletion resulted in decreased CD25 expression in KU812 cells. Moreover, the BCR/ABL1 inhibitors nilotinib and ponatinib were found to decrease STAT5 activity and CD25 expression in KU812 cells and primary CML LSCs. A CD25-targeting shRNA was found to augment proliferation of KU812 cellsin vitroand their engraftmentin vivoin NOD/SCID-IL-2Rγ(-/-)mice. In drug-screening experiments, the PI3K/mTOR blocker BEZ235 promoted the expression of STAT5 and CD25 in CML cells. Finally, we found that BEZ235 produces synergistic antineoplastic effects on CML cells when applied in combination with nilotinib or ponatinib. CD25 is a novel STAT5-dependent marker of CML LSCs and may be useful for LSC detection and LSC isolation in clinical practice and basic science. Moreover, CD25 serves as a growth regulator of CML LSCs, which may have biologic and clinical implications and may pave the way for the development of new more effective LSC-eradicating treatment strategies in CML.

Knockdown (KD) of Mir-126 Expression Enhances Tyrosine Kinase Inhibitor (TKI)-Mediated Targeting of Chronic Myelogenous Leukemia (CML) Stem Cells

BCR-ABL tyrosine kinase inhibitors (TKI), although highly effective in inducing remission and improving survival in CML patients, fail to eliminate leukemia stem cells (LSC), which remain a potential source of relapse. The long-term goal of our research is to improve the understanding of molecular mechanisms regulating LSC growth and develop effective mechanism-based therapeutic strategies to target LSC in CML. MicroRNAs (miRNAs) are short non-coding RNAs that regulate translation of target protein-coding messenger RNAs (mRNAs) and levels of the corresponding encoded proteins. Among distinct miRNAs, miR-126-3p (miR-126) is expressed in normal hematopoietic stem cells (HSCs) and early hematopoietic progenitor cells (HPCs) and plays a pivotal role in restraining cell-cycle progression of HSC in vitro and in vivo (Cell Stem Cell, 2012). We previously reported that miR-126 expression varies among AML patients; higher level of miR-126 associated with poor outcome, a LSC-associated gene expression signature and increased LSC quiescence; and miR-126 down-regulation decreased LSC self-renewal activity in serial transplant experiments (Leukemia, 2015). Here, we report that the more primitive LSK (Lin-Sca-1+Kit+) from SCL-tTA-BCR/ABL mouse model of CML had higher miR-126 expression compared to more differentiated subpopulations, i.e. common myeloid progenitors (CMP) (3.2 fold) and granulocyte-macrophage progenitors (GMP) (6.4 fold). Among LSK subpopulations, LSC (Flt3-CD150+CD48- LSK) demonstrated the highest miR-126 levels (P<0.01). Furthermore, quiescent (Hoechst-Pyronin-) LSC demonstrated higher miR-126 expression (2.6 fold, p<0.01), generated significantly higher long-term engraftment of donor CML cells in recipient mice (58.6±4.4% vs 33±3.4% in BM at 16 wks after transplanted with 100 LSC/mouse, p=0.003) and enhanced leukemogenic capacity (5 out of 9 mice receiving quiescent LSC developed CML within 14 wks after transplantation vs. none of 10 mice receiving proliferating LSC) compared with proliferating (Hoechst+/-Pyronin+) LSC. Human primary untreated chronic phase (CP) CML CD34+CD38- primitive progenitors also showed higher miR-126 expression compared with CD34+CD38+ committed progenitors. KD of miR-126 in LSK cells of CML mouse model and in primary CML CD34+CD38- cells by using either miRZip-126-3p anti-miR lentivirus (System Biosciences) or a novel, myeloid cell-specific CpG-miR-126 oligonucleotide (ODN) inhibitor increased LSC cell-cycle entry as demonstrated by increased Ki67 staining (p<0.05) and EdU labeling (p<0.05), but affected apoptosis only slightly compared to scramble-treated controls. More importantly, miR-126 KD either by lentivirus or CpG-miR-126 ODN inhibitor combined with Nilotinib (NIL) significantly increased apoptosis of LSC compared with NIL alone (34% vs 19%; p=0.01 for lentivirus KD; and 40% vs 35%; p=0.03 for CpG-miR-126 inhibitor KD), resulting in significant reduction of cell growth and colony forming cell (CFC) frequency in methylcellulose progenitor assays. Conversely, enforced miR-126 expression by miR-126 precursor lentivirus (System Biosciences) impaired cell-cycle entry (28% vs 33%; p=0.05) and led to significantly reduced apoptosis (27% vs 19%; P=0.01) in NIL (5µM) treated CML CD34+CD38- cells compared to cells treated with control lentivirus and NIL. We further investigated the effect of miR-126 KD on growth of primary CML LSC and therapeutic response in vivo. CP CML CD34+ cells were cultured with CpG-scrambled RNA or CpG-miR-126 ODN inhibitor (500nM), in the presence or absence of NIL (5µM) for 4 days, and then transplanted into irradiated NSG mice. While the experiment is still ongoing, we have already observed a significantly reduced engraftment in blood at 4 wks in recipient mice receiving cells treated with CpG-miR-126 inhibitor and NIL compared with those receiving cells treated with CpG-scrambled RNA and NIL (0.16±0.03% vs 0.4±0.04%; P=0.01). Final results of this in vivo experiment and in vivo treatment of SCLtTA/BCR-ABL mice with CpG-miR-126 inhibitor and NIL will be reported at the meeting. Altogether, these observations suggest that miR-126 play a role in CML LSC homeostasis and down-regulation of miR-126 may decrease CML LSC quiescence, increase LSC proliferation and in turn enhance their sensitivity to TKI. miR-126 therefore may represent a novel therapeutic target in CML. DisclosuresStein:Amgen: Speakers Bureau. Snyder:BMS: Membership on an entity's Board of Directors or advisory committees; Ariad: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees. Forman:Mustang: Research Funding; Amgen: Consultancy.

USP47 Is a New Target in Chronic Myelogenous Leukemia

Despite of the great success of tyrosine kinase inhibitor in the therapy of chronic myelogenous leukemia (CML), CML is still not curable. Further investigation on the molecular mechanism of CML pathogenesis and identification of novel therapeutic target are required. In this study, we found that overexpression of CML characterized Bcr/Abl oncoprotein could significantly upregulate the expression of ubiquitin-specific protease Usp47. Also, increased expression of Usp47 was observed in primary CML cells and its expression was associated with the treatment response of imatinib, the first generation of tyrosine kinase inhibitor. Furthermore, Usp47 knockdown could inhibit the proliferation of K562 cells in vitro and in vivo. P22077, a Usp47 inhibitor, could inhibit the proliferation of CML cell lines, which comprise BCR/ABL mutation, including the T315I mutation. P22077 inhibits the proliferation of primary CML cells sensitive or resistant to imatinib. The colony forming activity of CD34+ from CML primary cells but not from normal cord blood cells were also inhibited by P22077. We further demonstrated that inactivation of STAT5 significantly reduce the expression of Usp47, indicating that BCR/ABL-induced upregulation of Usp47 is mediated by STAT5 activition. Interestingly, Usp47 could interact with Sirt1, another STAT5 target gene. Inactivation of Usp47 reduces the expression of Sirt1 in CML cell lines and primary CML cells. Taken together, we demonstrated that Usp47 plays an critical role in CML, revealing a novel BCR/ABL/STAT5/Usp47/Sirt1 signaling pathway in CML, providing a potential target to overcome tyrosine kinase inhibitor resistance. DisclosuresNo relevant conflicts of interest to declare.

Identification of the Epigenetic Reader BRD4 As a Novel Potential Target in Ph+ CML

Chronic myelogenous leukemia (CML) is a bone marrow-derived hematopoietic neoplasm in which BCR/ABL1 acts as a major driver of proliferation, differentiation and survival of leukemic cells. In a majority of all patients with CML, leukemic cells can be kept under control by BCR/ABL1 tyrosine kinase inhibitors (TKI), including imatinib, nilotinib, dasatinib, bosutinib, and ponatinib. Nevertheless, resistance or intolerance against one or more of these TKI may occur. Therefore, current research is focusing on novel potential drug targets in CML. A promising class of targets may be epigenetic regulators of cell growth, such as members of the bromodomain and extra-terminal domain (BET) family. The epigenetic reader and BET family member BRD4 has recently been identified as a novel potential drug target in acute myeloid leukemia (AML). However, so far, little is known about the expression and function of BRD4 in CML cells. The aims of the present study were to determine the expression of BRD4 and its downstream target MYC in CML cells and to explore whether BRD4 can serve as a novel drug target in this disease. As determined by qPCR, primary CML cells (chronic phase patients, n=7) as well as the CML cell lines KU812 and K562 expressed BRD4 mRNA. In addition, both CML cell lines stained positive for BRD4 in our immunocytochemistry staining experiments. In one patient with accelerated phase CML, putative leukemic (CD34+/CD38-) stem cells were sorted to near homogeneity and found to express BRD4 mRNA by qPCR. In order to examine the functional role of BRD4 in CML cells, a BRD4-specific shRNA was applied. In these experiments, the shRNA-induced knockdown of BRD4 in KU812 cells and K562 resulted in reduced growth compared to a control shRNA. Furthermore, the BRD4-targeting drug JQ1 was found to inhibit 3H-thymidine uptake and thus proliferation in KU812 cells in a dose-dependent manner (IC50: 0.25-0.75 µM). In addition, we were able to show that JQ1 inhibits growth of primary CML cells with variable IC50 values (0.1-5 µM). However, no substantial growth-inhibitory effects of JQ1 were seen in K562 cells (IC50: >5 µM). As determined by Annexin V/PI staining, JQ1 induced apoptosis in KU812 cells whereas no apoptosis-inducing effect of JQ1 was observed in K562 cells. Nevertheless, we were able to show that both CML cell lines as well as primary CML cells express MYC mRNA, and treatment of KU812 cells or K562 cells with JQ1 resulted in a decreased expression of MYC mRNA and MYC protein. Next, we analyzed whether MYC expression in CML cells can be blocked by BCR/ABL1 TKI. We found that imatinib, nilotinib, dasatinib, and ponatinib decrease MYC mRNA- and MYC protein expression in KU812 and K562 cells. Finally, we found that JQ1 cooperates with imatinib, nilotinib, ponatinib and dasatinib in inhibiting the proliferation of KU812 and K562 cells. Together, our data show that BRD4 serves as a potential new target in CML cells, and that the BRD4 blocker JQ1 cooperates with BCR/ABL1 TKI in inducing growth-inhibition. Whether BRD4 inhibition is a pharmacologically meaningful approach in patients with TKI-resistant CML remains to be determined in clinical trials. DisclosuresSperr:Ariad: Consultancy; Celgene: Consultancy. Zuber:Mirimus Inc.: Consultancy, Other: Stock holder; Boehringer Ingelheim: Research Funding. Valent:Novartis: Consultancy, Honoraria, Research Funding; Ariad: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Pfizer: Honoraria; Celgene: Honoraria.

WT1-mediated repression of the proapoptotic transcription factor ZNF224 is triggered by the BCR-ABL oncogene

The Kruppel-like protein ZNF224 is a co-factor of the Wilms' tumor 1 protein, WT1. We have previously shown that ZNF224 exerts a specific proapoptotic role in chronic myelogenous leukemia (CML) K562 cells and contributes to cytosine arabinoside-induced apoptosis, by modulating WT1-dependent transcription of apoptotic genes. Here we demonstrate that ZNF224 gene expression is down-regulated both in BCR-ABL positive cell lines and in primary CML samples and is restored after imatinib and second generation tyrosine kinase inhibitors treatment. We also show that WT1, whose expression is positively regulated by BCR-ABL, represses transcription of the ZNF224 gene. Finally, we report that ZNF224 is significantly down-regulated in patients with BCR-ABL positive chronic phase-CML showing poor response or resistance to imatinib treatment as compared to high-responder patients. Taken as a whole, our data disclose a novel pathway activated by BCR-ABL that leads to inhibition of apoptosis through the ZNF224 repression. ZNF224 could thus represent a novel promising therapeutic target in CML.

Tyrosine kinase inhibition in leukemia induces an altered metabolic state sensitive to mitochondrial perturbations.

Although tyrosine kinase inhibitors (TKI) can be effective therapies for leukemia, they fail to fully eliminate leukemic cells and achieve durable remissions for many patients with advanced BCR-ABL(+) leukemias or acute myelogenous leukemia (AML). Through a large-scale synthetic lethal RNAi screen, we identified pyruvate dehydrogenase, the limiting enzyme for pyruvate entry into the mitochondrial tricarboxylic acid cycle, as critical for the survival of chronic myelogenous leukemia (CML) cells upon BCR-ABL inhibition. Here, we examined the role of mitochondrial metabolism in the survival of Ph(+) leukemia and AML upon TK inhibition. Ph(+) cancer cell lines, AML cell lines, leukemia xenografts, cord blood, and patient samples were examined. We showed that the mitochondrial ATP-synthase inhibitor oligomycin-A greatly sensitized leukemia cells to TKI in vitro. Surprisingly, oligomycin-A sensitized leukemia cells to BCR-ABL inhibition at concentrations of 100- to 1,000-fold below those required for inhibition of respiration. Oligomycin-A treatment rapidly led to mitochondrial membrane depolarization and reduced ATP levels, and promoted superoxide production and leukemia cell apoptosis when combined with TKI. Importantly, oligomycin-A enhanced elimination of BCR-ABL(+) leukemia cells by TKI in a mouse model and in primary blast crisis CML samples. Moreover, oligomycin-A also greatly potentiated the elimination of FLT3-dependent AML cells when combined with an FLT3 TKI, both in vitro and in vivo. TKI therapy in leukemia cells creates a novel metabolic state that is highly sensitive to particular mitochondrial perturbations. Targeting mitochondrial metabolism as an adjuvant therapy could therefore improve therapeutic responses to TKI for patients with BCR-ABL(+) and FLT3(ITD) leukemias.