Primary Acute Myelogenous Leukemia Cells Research Articles

Human acute leukemia uses branched-chain amino acid catabolism to maintain stemness through regulating PRC2 function.

Cancer-specific metabolic activities play a crucial role in the pathogenesis of human malignancies. To investigate human acute leukemia-specific metabolic properties, we comprehensively measured the cellular metabolites within the CD34+ fraction of normal hematopoietic stem progenitor cells (HSPCs), primary human acute myelogenous leukemia (AML), and acute lymphoblastic leukemia (ALL) cells. Here, we show that human leukemia cells are addicted to the branched-chain amino acid (BCAA) metabolism to maintain their stemness, irrespective of myeloid or lymphoid types. Human primary acute leukemias had BCAA transporters for BCAA uptake, cellular BCAA, α-ketoglutarate (α-KG), and cytoplasmic BCAA transaminase-1 (BCAT1) at significantly higher levels than control HSPCs. Isotope-tracing experiments showed that in primary leukemia cells, BCAT1 actively catabolizes BCAA using α-KG into branched-chain α-ketoacids, whose metabolic processes provide leukemia cells with critical substrates for the trichloroacetic acid cycle and the synthesis of nonessential amino acids, both of which reproduce α-KG to maintain its cellular level. In xenogeneic transplantation experiments, deprivation of BCAA from daily diet strongly inhibited expansion, engraftment and self-renewal of human acute leukemia cells. Inhibition of BCAA catabolism in primary AML or ALL cells specifically inactivates the function of the polycomb repressive complex 2, an epigenetic regulator for stem cell signatures, by inhibiting the transcription of PRC components, such as zeste homolog 2 and embryonic ectoderm development. Accordingly, BCAA catabolism plays an important role in the maintenance of stemness in primary human AML and ALL, and molecules related to the BCAA metabolism pathway should be critical targets for acute leukemia treatment.

Simultaneous Inhibition of Ceramide Hydrolysis and Glycosylation Synergizes to Corrupt Mitochondrial Respiration and Signal Caspase Driven Cell Death in Drug-Resistant Acute Myeloid Leukemia.

Acute myelogenous leukemia (AML), the most prevalent acute and aggressive leukemia diagnosed in adults, often recurs as a difficult-to-treat, chemotherapy-resistant disease. Because chemotherapy resistance is a major obstacle to successful treatment, novel therapeutic intervention is needed. Upregulated ceramide clearance via accelerated hydrolysis and glycosylation has been shown to be an element in chemotherapy-resistant AML, a problem considering the crucial role ceramide plays in eliciting apoptosis. Herein we employed agents that block ceramide clearance to determine if such a "reset" would be of therapeutic benefit. SACLAC was utilized to limit ceramide hydrolysis, and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-threo-PDMP) was used to block the glycosylation route. The SACLAC D-threo-PDMP inhibitor combination was synergistically cytotoxic in drug-resistant, P-glycoprotein-expressing (P-gp) AML but not in wt, P-gp-poor cells. Interestingly, P-gp antagonists that can limit ceramide glycosylation via depression of glucosylceramide transit also synergized with SACLAC, suggesting a paradoxical role for P-gp in the implementation of cell death. Mechanistically, cell death was accompanied by a complete drop in ceramide glycosylation, concomitant, striking increases in all molecular species of ceramide, diminished sphingosine 1-phosphate levels, resounding declines in mitochondrial respiratory kinetics, altered Akt, pGSK-3β, and Mcl-1 expression, and caspase activation. Although ceramide was generated in wt cells upon inhibitor exposure, mitochondrial respiration was not corrupted, suggestive of mitochondrial vulnerability in the drug-resistant phenotype, a potential therapeutic avenue. The inhibitor regimen showed efficacy in an in vivo model and in primary AML cells from patients. These results support the implementation of SL enzyme targeting to limit ceramide clearance as a therapeutic strategy in chemotherapy-resistant AML, inclusive of a novel indication for the use of P-gp antagonists.

Dual mTORC1/2 Inhibition Synergistically Enhances AML Cell Death in Combination with the BCL2 Antagonist Venetoclax.

Acute myelogenous leukemia (AML) is an aggressive disease with a poor outcome. We investigated mechanisms by which the anti-AML activity of ABT-199 (venetoclax) could be potentiated by dual mTORC1/TORC2 inhibition. Venetoclax/INK128 synergism was assessed in various AML cell lines and primary patient AML samples in vitro. AML cells overexpressing MCL-1, constitutively active AKT, BAK, and/or BAX knockout, and acquired venetoclax resistance were investigated to define mechanisms underlying interactions. The antileukemic efficacy of this regimen was also examined in xenograft and patient-derived xenograft (PDX) models. Combination treatment with venetoclax and INK128 (but not the mTORC1 inhibitor rapamycin) dramatically enhanced cell death in AML cell lines. Synergism was associated with p-AKT and p-4EBP1 downregulation and dependent upon MCL-1 downregulation and BAK/BAX upregulation as MCL-1 overexpression and BAX/BAK knockout abrogated cell death. Constitutive AKT activation opposed synergism between venetoclax and PI3K or AKT inhibitors, but not INK128. Combination treatment also synergistically induced cell death in venetoclax-resistant AML cells. Similar events occurred in primary patient-derived leukemia samples but not normal CD34+ cells. Finally, venetoclax and INK128 co-treatment displayed increased antileukemia effects in in vivo xenograft and PDX models. The venetoclax/INK128 regimen exerts significant antileukemic activity in various preclinical models through mechanisms involving MCL-1 downregulation and BAK/BAX activation, and offers potential advantages over PI3K or AKT inhibitors in cells with constitutive AKT activation. This regimen is active against primary and venetoclax-resistant AML cells, and in in vivo AML models. Further investigation of this strategy appears warranted.

The RNA m6A Reader YTHDF1 Is Required for Acute Myeloid Leukemia Progression.

The m6A reader YTHDF1 is required for progression of acute myelogenous leukemia and can be targeted with the FDA-approved drug tegaserod to suppress leukemia growth.

Novel Small Molecule and Peptide Inhibitors of CREB in Leukemia Cells

Background: Acute Lymphoblastic Leukemia (ALL) and Acute Myelogenous Leukemia (AML) account for nearly 45% of all childhood cancer. Current therapy for acute leukemia results in significant morbidity and late complications in children. Therefore, more effective and less toxic therapies to treat leukemia are needed. Previous work in our laboratory has identified CREB (cAMP Response Element Binding Protein), a transcription factor that promotes cell proliferation and survival in acute leukemia, is overexpressed in primary ALL and AML cells and is a potential target for therapy. We have investigated small molecules and peptides to inhibit the critical interaction between the phosphorylated KID (Kinase-Inducible) domain of CREB and the KIX (KID-interacting) domain of the coactivator CBP (CREB Binding Protein). Methods: We assessed a library of previously untested alpha-mimetic compounds from ChemDiv designed to mimic interactions between α-helices and protein surfaces for predicted interaction with a shallow hydrophobic groove on the interaction surface of KIX. We interrogated the 24,737 compounds in the library using rigid-receptor ligand docking, followed by induced-fit ligand docking of the top compounds using two different software, MOE and Schrodinger's Bioluminate. The top 50 binding poses from each software's rankings were combined to yield 87 candidate alpha-mimetic molecule inhibitors. In addition to our screen of small molecules, we have designed peptide inhibitors that closely mimic the αB helix of pKID. We investigated two methods to enhance the stability and cell-penetrating ability of our peptides: hydrocarbon stapling and the utilization of a rigid scaffold from the scorpion toxin peptide BmBKTtx1. Based on the calculated binding scores and locations, the most promising chimeric peptide designs were further investigated for binding stability using 500 nanosecond molecular dynamics (MD) simulations modeling their interaction with KIX. Results: The binding poses of the final set of small molecules were visually inspected for occupation of key hotspots on the pKID:KIX interaction surface, including the location of the phosphorylation sight of KID. Of the 87 molecules and their binding poses, only 21 of them (24%) obstructed fewer than two of the three hotspots chosen for the analysis. Moreover, 80 of the molecules (92%) extended into the hydrophobic pocket, the most critical hotspot. The multi-residue construction of this pocket likely contributed to the high similarity in interaction fingerprint between these molecules and pKID; occupation of this pocket can serve as a good indicator of strong ligand binding to KIX in future assays. The most-promising peptide designs using the scorpion toxin scaffold were assessed with MD simulations and compared to a control peptide comprised primarily of the αB helix of pKID. The chimeric peptides showed increased binding stability over the control peptide with an average RMSD of 6.8Å vs. 12.5Å, illustrating the benefits of the stability afforded by the scorpion scaffold design. Several of the hydrocarbon stapled peptides were tested in vitro using fluorescence polarization (FP) assay developed by our lab (Chae et al. Bioorganic & Medicinal Chemistry Letters, 2019) and in AML HL-60 and KG-1 cells and were shown to have growth inhibitory effects by Cell-Titer Glo Assays. Discussion: These small molecules and scorpion toxin-derived peptides represent novel candidate inhibitors of the pKID:KIX interaction implicated in leukemia. Based on promising results from our in silico analyses of these inhibitors, we have obtained ten structurally diverse alpha-mimetic small molecules and three chimeric peptides and aim to test their efficacy in vitro using the FP assay. Furthermore, we will obtain high resolution cryo-EM structures of successful compounds and peptides bound to the KIX domain using a double-shell protein scaffold (Zhang et al. ACS Central Science, 2022), and use these structures for further refinement of the inhibitors. The development of new inhibitors for the pKID:KIX interaction promises to reveal insights into the structural relationship between the two domains and the basis for effective, targeted leukemia therapeutics.

Characterizing Naked Nuclei Frequency and Movement in Primary AML Cell Culture Using an ECM-Based Model

INTRODUCTIONNaked nuclei (NN) are observed upon examining bone marrow aspirate slides from healthy individuals and from those with hematologic malignancies, but are not well understood. Without characteristic findings like cytoplasm or plasma membrane, NN are considered remnants of slide preparation or are discounted as cells of undetermined significance. NN have been associated with poor prognosis in several solid cancers. Understanding the significance of NN in hematologic malignancies such as acute myelogenous leukemia (AML) may elucidate valuable diagnostic and prognostic knowledge. Decellularized Wharton's jelly matrix (DWJM) is an extra cellular matrix (ECM)-based in vitro model that shares similar elements with the bone marrow ECM and can be used as scaffolding to culture leukemia cells. We hypothesize that NN exist in AML and interact with other cells, suggesting potential biological relevance within the bone marrow microenvironment.METHODSPrimary AML samples obtained by leukapheresis were cultured in suspension with growth media or in the presence of DWJM submerged in growth media. In samples grown with DWJM, cells that were non-adherent to the matrix were collected first and then adherent cells were isolated by treating DWJM with collagenase. Live cells were stained with CellVue Maroon (CVM) for membrane, CellTracker Green (CTG) for cytoplasm, and Hoechst 33342 for nucleus, followed by analysis with Amnis/Luminex ImageStream-X imaging flow cytometer (Figure 1A). NN were defined as events positive for nuclear stain and negative for cytoplasmic and membrane stains (Figure 1B). 3-D movement of adherent AML cells in DWJM was captured in real time using confocal microscopy. Fixed cells from leukemia cell line K562 served as a control for movement. NN (Hoechst positive only), non-nucleated (Hoechst negative/CTG positive), and nucleated cells (Hoechst and CTG positive) were identified by fluorescent labeling. NN were also observed after isolation by cell sorting. Cell speed, cell displacement from origin, and change in distance to closest neighboring cell over time were measured. Additionally, flow sorted NN were examined by immunohistochemistry (IHC).RESULTSAdherent populations contained significantly more NN than non-adherent and suspension populations. The frequency of NN in matrix adherent cells ranged from 0.4-2.4% at day 3 and 0.5-5.4% at day 7 of culture (Figure 1C). Through confocal microscopic analysis, we observed NN, nucleated, and non-nucleated cells moving at speeds ranging from 0.002-0.08 µm/sec. Fixed cells showed no discernible movement in DWJM. The average speed of NN [0.019 mm/s, SD 0.011] significantly differed from the average speed of nucleated and non-nucleated cells [0.027 mm/s, SD 0.016] (p=0.004) (Figure 1E). To demonstrate directional movement, we measured change in distance between NN and closest neighboring nucleated or non-nucleated cells over time. Cells (nucleated and non-nucleated) and NN moved closer to each other over time suggesting directional movement (p=0.001) (Figure 1D). NN also showed movement in DWJM after isolation by cell sorting. IHC analysis showed sorted NN stained positive for nuclear lamin A/C, which are considered markers of nuclear membrane (Figure 1F).CONCLUSIONSOur findings confirm that NN are present in primary AML cells cultured in vitro using ourECM-based model and that they can be isolated using flow cytometry. Additionally, NN display directional movement in DWJM suggesting that they interact with other cells and may be biologically relevant structures in the bone marrow microenvironment. [Display omitted] DisclosuresBaran: AstraZeneca/Acerta: Research Funding. Chu: Pfizer: Current equity holder in publicly-traded company; Acerta/AstraZeneca: Research Funding; TG Therapeutics: Research Funding.

Platelet Microparticles Protect Acute Myelogenous Leukemia Cells against Daunorubicin-Induced Apoptosis.

Simple SummaryActivated or apoptotic platelets both shed platelet microparticles that are proven to be internalized by many different cell types, including cancer cells. Here, we have investigated whether platelet microparticles can transfer their contents to the monocytic leukemia cell line THP-1 and if this could change cell activity and resistance to chemotherapy. We show that platelet microparticles were internalized by THP-1 cells and that platelet-associated microRNAs were elevated after a brief co-incubation. Furthermore, differentiation toward macrophages was induced and cell cycle progression, proliferation, and mitochondrial activity were decreased. Co-incubation with platelet microparticles increased chemotherapy resistance, which also was evident in acute myelogenous leukemia cells from patient samples, and it could be explained by the decrease in cell activity. Thus, platelet microparticles may have a role in the evolution of acute myelogenous leukemia and contribute to development of chemotherapy resistance, making them an interesting target for treatment.The role of platelets in cancer development and progression is increasingly evident, and several platelet–cancer interactions have been discovered, including the uptake of platelet microparticles (PMPs) by cancer cells. PMPs inherit a myriad of proteins and small RNAs from the parental platelets, which in turn can be transferred to cancer cells following internalization. However, the exact effect this may have in acute myelogenous leukemia (AML) is unknown. In this study, we sought to investigate whether PMPs could transfer their contents to the THP-1 cell line and if this could change the biological behavior of the recipient cells. Using acridine orange stained PMPs, we demonstrated that PMPs were internalized by THP-1 cells, which resulted in increased levels of miR-125a, miR-125b, and miR-199. In addition, co-incubation with PMPs protected THP-1 and primary AML cells against daunorubicin-induced cell death. We also showed that PMPs impaired cell growth, partially inhibited cell cycle progression, decreased mitochondrial membrane potential, and induced differentiation toward macrophages in THP-1 cells. Our results suggest that this altering of cell phenotype, in combination with decrease in cell activity may offer resistance to daunorubicin-induced apoptosis, as serum starvation also yielded a lower frequency of dead and apoptotic cells when treated with daunorubicin.

Immunoglobulin Superfamily Member 8 Is Indispensable for Myeloid Leukemia Via Wnt/β-Catenin Signaling Pathway

Immunoglobulin superfamily member 8 (IGSF8, also known as EWI-2, PGRL, and CD316), is a cell surface protein containing 4 immunoglobulin domains. IGSF8 directly binds to the tetraspanin molecules, CD9 and CD81, and modulates cell adhesion, migration, and growth. Previous studies demonstrated that IGSF8 was associated with prognosis and metastasis in several solid tumors. However, the role of IGSF8 in normal hematopoiesis and myeloid leukemia is still unclear. First, we examined the expression levels of Igsf8 in various hematopoietic fraction of wild-type murine bone marrow cells, and found that Igsf8 is expressed in all hematopoietic lineages. To investigate hematopoietic functions of Igsf8, we generated hematopoietic cells specific Igsf8 deleted mice (Igsf8fl/fl; Vav-Cre) and tamoxifen induced Igsf8 deleted mice (Igsf8fl/fl; Rosa26-CreERT). Igsf8fl/fl, Vav-Cre (denoted as Igsf8-/-) mice represented normal maturation. Deletion of Igsf8 did not significantly affect adult hematopoiesis in peripheral blood and bone marrow. Igsf8-/- long-term hematopoietic stem cells (LT-HSCs: CD34- Flk2- c-Kit+ Sca-1+ Lineage- cells) reduced colony forming ability in vitro, and serial competitive transplantation assay showed comparable donor chimerism by 3 months, but led to decrease Igsf8-/- donor chimerism at 4 months and those after second transplantation in vivo. These results suggest that Igsf8 does not affect the adult hematopoiesis, but it can affect their proliferative and reconstitutive capacity of HSCs. To investigate the effects of Igsf8 on myeloid leukemia, we generated MLL-AF9 and NRASG12V-driven acute myelogenous leukemia (AML), or BCR-ABL and NUP98-HOXA9-driven blast crisis of chronic myelogenous leukemia (CML-BC) mice models. Igsf8-/- led to a dramatic reduction in the number of leukemic colonies formed in vitro (Figure 1A). Igsf8-/- leukemia mice showed significantly longer survival in vivo (Figure 1B). This effect was also observed by eliminating Igsf8 expression after leukemia establishment using conditionally deletion. Igsf8-/- AML cells showed decreased S phase fraction. Igsf8-/- leukemia stem cells (LSCs: c-Kit+ Lineage- cells) triggered an increment of the apoptosis, which contribute to significantly lower proportion of LSCs in spleen of Igsf8-/- leukemic mice. Given that Igsf8-/- did not affect homing ability of leukemia cells, these results indicate that Igsf8 is required for propagation of myeloid leukemia and maintenance of LSC. To understand the Igsf8-mediated regulation of myeloid leukemia, we conducted RNA sequencing analysis of LT-HSCs, and LSCs of AML and CML-BC. Gene set enrichment analysis exhibited increase apoptosis related genes and decrease Wnt/β-catenin related genes in Igsf8-/- leukemic cells, but not in LT-HSCs (Figure 1C). Increment of pro-apoptosis genes, and decrement of anti-apoptosis genes and Wnt/β-catenin target genes in Igsf8-/- AML stem cells were validated in quantitative polymerase chain reaction analysis. Further, expression levels of β-catenin protein in Igsf8-/- leukemic cells were significantly lower compared to Igsf8+/+ leukemic cells, but not in normal hematopoietic stem and progenitor cells (Figure 1D). These results suggest that Igsf8 might be critical for myeloid leukemia maintenance via Wnt/β-catenin signaling pathway. Then, we investigated the effects of IGSF8 on human myeloid leukemia. We confirmed IGSF8 expression in several human myeloid leukemia cell line and primary patient-derived leukemia cells. Knockdown of IGSF8 by small hairpin RNA in myeloid leukemia cell lines (THP-1, MV4-11, SKM-1, and K562) and primary patient-derived AML cells exhibited reduced numbers of colony forming cells in vitro. Knockdown of IGSF8 also caused decrease expression of β-CATENIN in AML cell lines. These results indicate that IGSF8 is also required for propagation of human myeloid leukemia cells. Taken together, our present study reveals that Igsf8 is indispensable for myeloid leukemia, but not adult hematopoiesis, suggesting that IGSF8 inhibition should be considered for targeting myeloid leukemia. Disclosures Jimbo: Japan Society for the Promotion of Science: Research Funding. Konuma:SGH Foundation: Research Funding; The Japanese Society of Hematology: Research Funding; Institute for Frontier Life and Medical Sciences, Kyoto University: Research Funding. Ito:Institute for Frontier Life and Medical Sciences, Kyoto University: Research Funding.

Inhibition of NF-κB Signaling Alters Acute Myelogenous Leukemia Cell Transcriptomics.

Acute myelogenous leukemia (AML) is an aggressive hematological malignancy. The pathophysiology of the disease depends on cytogenetic abnormalities, gene mutations, aberrant gene expressions, and altered epigenetic regulation. Although new pharmacological agents have emerged during the last years, the prognosis is still dismal and new therapeutic strategies are needed. The transcription factor nuclear factor-κB (NF-κB) is regarded a possible therapeutic target. In this study, we investigated the alterations in the global gene expression profile (GEP) in primary AML cells derived from 16 consecutive patients after exposure to the NF-κB inhibitor BMS-345541. We identified a profound and highly discriminative transcriptomic profile associated with NF-κB inhibition. Bioinformatical analyses identified cytokine/interleukin signaling, metabolic regulation, and nucleic acid binding/transcription among the major biological functions influenced by NF-κB inhibition. Furthermore, several key genes involved in leukemogenesis, among them RUNX1 and CEBPA, in addition to NFKB1 itself, were influenced by NF-κB inhibition. Finally, we identified a significant impact of NF-κB inhibition on the expression of genes included in a leukemic stem cell (LSC) signature, indicating possible targeting of LSCs. We conclude that NF-κB inhibition significantly altered the expression of genes central to the leukemic process.

Targeting the Second Bromodomain (BDII) of BET Family with Abbv-744 Results in Robust Anti-Leukemia Activity in AML Models with Excellent In Vivo Tolerability

The BET family proteins consist of BRD2, BRD3, BRD4 and BRDT, with each of these proteins containing two highly conserved bromodomains (BDI and BDII). First generation BET inhibitors, including ABBV-075, are pan-BET inhibitors that bind with nearly equimolar affinity to BDI and BDII. Pan-BET inhibitors generally block transcription and inhibit the proliferation of a large spectrum of tumor types, but exhibit a narrow therapeutic index. ABBV-744 is a highly selective inhibitor for the BDII of BET family proteins, exhibiting greater than 300-fold more potent binding affinity to the BDII bromodomain of BRD4 relative to BDI (Warren Kati AACR 2018; Xiaoyu Lin AACR 2018). In this study, we evaluated the anti-leukemia activities of ABBV-744 in acute myelogenous leukemia (AML) cell lines and primary samples.In AML cell lines, ABBV-744 induced G1 cell cycle arrest and apoptosis with caspase-3 activation and PAPR cleavage through regulation of the key proteins that are involved in cell cycle and apoptosis pathways (e.g. (BCL-2, BCL-XL, MCL-1, c-Myc). Mechanistically, ABBV-744 displaced BRD4 from the regulatory region of BCL2, RUNX1, BCL2L1 and IL8 genes by ChiP-Seq. MLL-rearranged cells were most sensitive to BDII inhibition, and ABBV-744 displaced both, BRD4 and MLL from the regulatory regions of BCL2 and c-Myc genes in MV4;11 (MLL-AF4) and Nomo-1 (MLL-AF9) cells. We examined anti-leukemia activity of ABBV-744 in 12 primary AML samples with diverse genetic alterations. ABBV-744 inhibited cell growth in 8/12 primary samples (20.2%-77.9%) and induced apoptosis (26.7 ± 9.6% in ABBV-744 group vs 14.1± 3.9% in DMSO group, p=0.007, Fig 1A). We next performed the whole genome transcriptome analysis of pre-treatment AML cells by RNA-sequencing (RNA-seq). The samples which were sensitive to ABBV-744 tend to have higher pro-apoptosis (TXNIP, DR5) and lower anti-apoptosis (BCL2, EXPO) than resistant samples.For efficacy assessment in vivo, we established a patient-derived xenograft (PDX) from an AML patient with FLT3-ITD, DNMT3A, IDH1 and NPM1 mutations in NSG mice. Upon engraftment, mice were randomized to receive vehicle or single agent ABBV-744 at a well-below MTD dose of 9.4 mg/kg for 21 days. The median survival time of mice treated with ABBV-744 (Median survival: 76 days) was significantly higher compared to untreated mice (Median survival: 67.5 days, p=0.007, Fig 1B). Next, the anti-leukemia efficacy of ABBV-744 was tested in 7 additional AML PDX models. NSG mice were injected with 7 AML PDX (one mouse per cohort design). After engraftment was confirmed by retro-orbital bleeding, mice were treated with vehicle or ABBV-744. Circulating tumor burden was measured by flow cytometry in peripheral blood samples from mice collected on indicated days of therapy. In five of the 7 models, ABBV-744 treatment delayed AML progression compared to untreated mice (survival days: 135 vs 105, 205 vs 153, 62 vs 46, 118 vs 77, 97 vs 86). No significant impact on mice' weight was noted (Fig 1C), and no clinical signs of toxicity recorded over the course of therapy.In summary, blockade of BET family bromodomain BDII promotes apoptotic cell death and suppresses proliferation in the majority of primary AML cells. Importantly, ABBV-744 therapy reduced AML tumor burden and extended survival in AML PDX models at a well-below MTD dose. Together, these results provide proof of concept that highly selective inhibitors of the second bromodomain of BET family may maintain robust anti-leukemia efficacy in AML while exhibiting improved tolerability relative to pan-BET inhibitors. [Display omitted] DisclosuresUziel:AbbVie Inc.: Employment. Shen:AbbVie Inc: Employment. Konopleva:Stemline Therapeutics: Research Funding. Lin:AbbVie Inc: Employment. Lu:AbbVie Inc: Employment. Zhang:AbbVie Inc: Employment.

Oroxylin A, a natural compound, mitigates the negative effects of TNFα-treated acute myelogenous leukemia cells.

Tumor necrosis factor alpha (TNFα) is a complicated cytokine which is involved in proliferation and differentiation of acute myelogenous leukemia (AML) cells through a poorly understood mechanism. Mechanistic studies indicate that TNFα induced binding of PI3K subunit p85α to N-terminal truncated nuclear receptor RXRα (tRXRα) proteins, and activated AKT. The activated PI3K/AKT pathway negatively regulated differentiation of AML cells through the upregulation of c-Myc. In addition, TNFα also induced activation of nuclear factor κB (NF-κB), a nuclear transcription factor which was shown to promote cell proliferation. The present study demonstrates that oroxylin A, a natural compound isolated from Scutellariae radix, sensitizes leukemia cells to TNFα and markedly enhances TNFα-induced growth inhibition and differentiation of AML cell including human leukemia cell lines and primary AML cells. Activation of PI3K/AKT pathway could be inhibited by oroxylin A through inhibiting expression of tRXRα in NB4 and HL-60-resistant cells. Furthermore, we found that oroxylin A inhibited the activation of NF-κB and the DNA binding activity by TNFα proved by EMSA in these two AML cell lines. Moreover, in vivo studies showed that treatment with oroxylin A in combination with TNFα decreased AML cell population and prolonged survival in NOD/SCID mice with xenografts of primary AML cells. Overall, our results indicate that oroxylin A is able to inhibit the negative effects of TNFα for AML therapy, suggesting that combination of oroxylin A and TNFα have the potential to delay growth or eliminate the abnormal leukemic cells, thus representing a promising strategy for AML treatment.

Rational Design of a Parthenolide-based Drug Regimen That Selectively Eradicates Acute Myelogenous Leukemia Stem Cells

Although multidrug approaches to cancer therapy are common, few strategies are based on rigorous scientific principles. Rather, drug combinations are largely dictated by empirical or clinical parameters. In the present study we developed a strategy for rational design of a regimen that selectively targets human acute myelogenous leukemia (AML) stem cells. As a starting point, we used parthenolide, an agent shown to target critical mechanisms of redox balance in primary AML cells. Next, using proteomic, genomic, and metabolomic methods, we determined that treatment with parthenolide leads to induction of compensatory mechanisms that include up-regulated NADPH production via the pentose phosphate pathway as well as activation of the Nrf2-mediated oxidative stress response pathway. Using this knowledge we identified 2-deoxyglucose and temsirolimus as agents that can be added to a parthenolide regimen as a means to inhibit such compensatory events and thereby further enhance eradication of AML cells. We demonstrate that the parthenolide, 2-deoxyglucose, temsirolimus (termed PDT) regimen is a potent means of targeting AML stem cells but has little to no effect on normal stem cells. Taken together our findings illustrate a comprehensive approach to designing combination anticancer drug regimens.

The NAE inhibitor pevonedistat interacts with the HDAC inhibitor belinostat to target AML cells by disrupting the DDR

AbstractTwo classes of novel agents, NEDD8-activating enzyme (NAE) and histone deacetylase (HDAC) inhibitors, have shown single-agent activity in acute myelogenous leukemia (AML)/myelodysplastic syndrome (MDS). Here we examined mechanisms underlying interactions between the NAE inhibitor pevonedistat (MLN4924) and the approved HDAC inhibitor belinostat in AML/MDS cells. MLN4924/belinostat coadministration synergistically induced AML cell apoptosis with or without p53 deficiency or FLT3–internal tandem duplication (ITD), whereas p53 short hairpin RNA (shRNA) knockdown or enforced FLT3-ITD expression significantly sensitized cells to the regimen. MLN4924 blocked belinostat-induced antiapoptotic gene expression through nuclear factor–κB inactivation. Each agent upregulated Bim, and Bim knockdown significantly attenuated apoptosis. Microarrays revealed distinct DNA damage response (DDR) genetic profiles between individual vs combined MLN4924/belinostat exposure. Whereas belinostat abrogated the MLN4924-activated intra-S checkpoint through Chk1 and Wee1 inhibition/downregulation, cotreatment downregulated multiple homologous recombination and nonhomologous end-joining repair proteins, triggering robust double-stranded breaks, chromatin pulverization, and apoptosis. Consistently, Chk1 or Wee1 shRNA knockdown significantly sensitized AML cells to MLN4924. MLN4924/belinostat displayed activity against primary AML or MDS cells, including those carrying next-generation sequencing–defined poor-prognostic cancer hotspot mutations, and CD34+/CD38−/CD123+ populations, but not normal CD34+ progenitors. Finally, combined treatment markedly reduced tumor burden and significantly prolonged animal survival (P < .0001) in AML xenograft models with negligible toxicity, accompanied by pharmacodynamic effects observed in vitro. Collectively, these findings argue that MLN4924 and belinostat interact synergistically by reciprocally disabling the DDR in AML/MDS cells. This strategy warrants further consideration in AML/MDS, particularly in disease with unfavorable genetic aberrations.

Regulation of Mitochondrial Morphology Is Important for Leukemia Stem Cell Function

Studies from normal cell biology have demonstrated that mitochondria can switch between fission-active and fusion-active states to dramatically change their morphology during important developmental events such as lineage differentiation and cell division. Further, very recent research has revealed intriguing interactions between mitochondrial morphology regulation and oncogenic signals in cancer. To date however, whether mitochondrial morphology regulation plays a role in cancer stem cell function remains largely unknown.We report, in acute myelogenous leukemia (AML), leukemia stem cells (LSCs), characterized by a low level of reactive oxygen species (ROS), have hyper-active mitochondrial fission regulators as evidenced by higher levels of mitochondrial fission 1 (FIS1) and activating phosphorylation of dynamin-related protein 1 (DRP1), compared to non-LSCs. To directly compare the mitochondrial morphology in LSCs versus non-LSCs, we imaged mitochondrial morphology using transmission electron microscopy. Quantification of the imaging results showed that the LSCs contain an increased number of smaller and globular-shaped mitochondria (see Figure), indicating that they reside in a fission-active state relative to non-LSCs. Inhibition of mitochondrial fission through genetic knock-down of FIS1 (FIS1-KD) induces mitochondrial fusion and dramatically diminishes both colony-forming ability and serial engraftment potential of primary AML cells, suggesting a fission-active state of mitochondrial morphology is critical for LSC function.To dissect the mechanism by which FIS1 regulates primitive leukemia cells, we performed detailed analysis of molecular events following FIS1-KD. We found that AML cells lacking the function of FIS1 up-regulated the expression of mitochondrial oxidative phosphorylation (OXPHOS) proteins, suggesting an increased OXPHOS activity. We then observed through metabolomic studies that knock-down of FIS1 altered the level of metabolites involved in glycolysis and the citric acid cycle (TCA), suggesting that the FIS1-KD-induced change in OXPHOS activity affected other aspects of global cellular energy metabolism as well. Among the metabolic changes seen was an increase in Acetyl-CoA, which plays an important role in epigenetic regulation by serving as the substrate for histone acetylation. Consistently, we observed an increase in H3K27-acetylation in AML cells following FIS-KD, and our transcriptomic analysis using RNA-seq showed that AML cells lacking FIS1 function exhibited global up-regulation of a hematopoietic lineage differentiation gene signature including CD11B, CD14, CD36, and CD68, indicating an induction of differentiation. In addition to affecting energy metabolism and epigenetic landscape, FIS1-KD also increased cellular ROS level in AML cells. This may happen as a consequence of induced OXPHOS activity, since ROS is a major byproduct of oxygen metabolism in OXPHOS machineries.Taken together, our functional studies raise the hypothesis that mitochondrial morphology critically regulates LSC function. Our subsequent molecular studies begin to reveal two major potential mechanisms by which mitochondrial morphology regulators can affect LSC potential. First, FIS1-regulated mitochondrial morphology may sequentially affect mitochondrial OXPHOS activity, global energy metabolism, homeostasis of metabolites such as Acetyl-CoA that can link metabolism to epigenetics, and regulation of the epigenome that is required for sustaining LSCs. Second, FIS1 can also affect cellular ROS, a critical determinant of self-renewal ability of stem cells, to effect LSC function. Overall, our current study elucidates a previously unknown link between the regulation of mitochondrial morphology and LSC function, targeting of which represents a novel therapeutic means to eradicate LSCs. [Display omitted] DisclosuresPollyea:Ariad: Consultancy; GlycoMimetics: Other: Member of data safety monitoring board; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy; Karyopharm: Consultancy.

WTAP is a novel oncogenic protein in acute myeloid leukemia

WTAP is a novel oncogenic protein in acute myeloid leukemia

Activation Of Akt Enhances Ribosomal RNA Synthesis In AML Cells Through a Novel Isoform Of TIF-1A and Inhibition Of Filamin A Cleavage

PI3Kinase/Akt signaling is frequently activated in acute myelogenous leukemia (AML) and inhibitors of this pathway have shown some promise in both pre-clinical and early clinical studies. In particular, much attention has been focused on components of the mTOR complex as downstream effectors of Akt activation that promote cell proliferation and survival in AML and other malignancies. We have discovered a direct effect of activated and phosphorylated Akt in increasing ribosomal RNA (rRNA) synthesis in both leukemic cell lines and primary AML cells by a novel pathway that is independent of mTOR. We have defined TIF-90 as a splice variant of TIF-1A, a molecule that tethers RNA Polymerase I to the ribosomal DNA promoter and is required for rRNA synthesis. TIF-90 is localized in the nucleolus and directly co-locates with Pol I in imaging, pull down, and rDNA promoter occupancy studies. Activation and phosphorylation of Akt correlates with high levels of TIF-90 expression and increased TIF-90 occupancy of the rDNA promoter in primary AML cells, while overexpression of constitutively activated Akt (Akt-Myr) increases rRNA synthesis in a TIF-90-dependent fashion in cell lines. Activation of Akt increases the expression of TIF-90 by inhibiting its ubiquitination and proteasomal degradation by the p53 ubiquitin ligase, Mdm2. Furthermore, activated Akt directly inhibits the cleavage of the actin-binding protein, Filamin A, into a 90 kDa fragment that interacts with TIF-90 and prevents it from occupying the rDNA promoter. Expression of the 90 kDa Filamin A cleavage fragment alone is sufficient to inhibit rRNA synthesis by binding to TIF-90. Thus, inhibition of Filamin A cleavage by Akt is associated with increased rRNA synthesis. The Akt inhibitor AZD8055, but not the mTORC1 inhibitor Rapamycin, promotes the cleavage of filamin A, decreasing both TIF-90 occupancy of the rDNA promoter and rRNA synthesis. Examination of 21 primary AML samples reveals an inverse correlation between the phosphorylation of Akt and the cleavage of Filamin A; conversely, AZD8055 inhibits both Akt phosphorylation and rRNA synthesis in these samples while promoting the cleavage of Filamin A. These data demonstrate a novel pathway by which Akt directly enhances rRNA synthesis. This pathway is active in primary AML cells and in cell lines that have high levels of phosphorylated Akt. Inhibition of rRNA synthesis has been shown to result in nucleolar disruption, cell cycle arrest, and ultimately cell death. Our data support an mTOR-independent effect of Akt activation on cell proliferation that would require direct targeting of PI3Kinase or activated Akt to have a major therapeutic effect in AML. Disclosures:No relevant conflicts of interest to declare.

Panobinostat, An Oral Pan-Histone Deacetylase (HDAC) Inhibitor Activates a Microrna Signature That Targets Rad51 To Attenuate Homologous DNA Repair and Sensitize AML Cells To Sapacitabine

Acute myelogenous leukemia (AML) is characterized by multiple genetic and epigenetic abnormalities including a profound dysregulation of microRNA expression. Specific expression signatures of miRNA are associated with disease behavior and clinical outcome.Effective clinical treatment of AML has largely depended on a class of antimetabolites – the nucleoside analogs. Of these, sapacitabine is a nucleoside analog prodrug that is in development for the therapy of AML. It is converted to its active metabolite 2-C-cyano-2-deoxy-1-β(-D-arabino-pentafuranosyl) cytosine (CNDAC), which interferes with DNA synthesis by initially causing a single stranded DNA break that is converted into a double strand break in the subsequent replicative cycle. Such double strand breaks are primarily repaired by the homologous recombination repair (HR) pathway. Consequently, efficient HR may offer a potential resistance mechanism to therapy with sapacitabine.Panobinostat and vorinostat are pan HDAC inhibitors (HDACi) that modulate gene expression, induce apoptosis, and are clinically active against specific leukemias and lymphomas. In pilot experiments, we identified that exposure of AML cell lines to a combination of panobinostat or vorinostat and sapacitabine had a greater than additive effect on cell viability. Loss of cell survival was preceded by a rapid and marked decline in the levels of Rad51, a protein that is critical in repairing CNDAC-induced damage via the HR repair pathway, both in AML cell lines and primary tumor cells that were exposed to either panobinostat or vorinostat. Therefore, we hypothesized that exposure of AML cells to HDACi would activate the expression of a set microRNAs, that would target Rad51. Loss of Rad51 protein, would in turn impede the successful completion of HR rendering the cells incapable of repairing the damage caused by CNDAC and thus sensitizing them to the nucleoside analog.Our preliminary data using microRNA arrays indicated that exposure of AML cells to panobinostat resulted in the induction of nine microRNA that putatively target Rad51. We then ectopically expressed three of the nine Rad51- directed miRNA and found that miR-182 efficiently targeted the Rad51 protein. Using real time-PCR we found that the levels of miR-182 were significantly lower in primary AML cells when compared to hematopoietic cells from normal donors. Using chromatin immunoprecipitation (ChIP) assays we identified that HDAC1 and HDAC2 were recruited to the miR182 promoter in AML cell lines as well as in primary AML cells, which was probably linked to loss of gene expression. Correspondingly, HDAC inhibition led to the accumulation of activating chromatin modifications at the miR-182 promoter, which was followed by the induction of miR-182 levels in both AML cells lines and primary AML cells. To determine whether HDAC inhibition targets Rad51 via miR-182, we expressed antagomiRs that interfere with the binding of miR-182 to Rad51, and found that the levels of Rad51 were preserved in cells expressing anti-miR182 before being exposed to panobinostat. Finally, we identified that exposure to panobinostat suppressed ongoing HR as measured by the absence of Rad51 foci in cells exposed to this agent, whereas cells exposed to CNDAC alone exhibited robust Rad51 foci formation, indicating an active HR pathway.In conclusion, HDAC inhibition results in the induction of miR-182 which targets Rad51 and attenuates HR to sensitize cells to sapacitabine in AML. This therapeutic strategy may be effective in circumventing potential resistance mechanisms to nucleoside analog therapy in AML. Disclosures:Ewald:Novartis: Employment.

A-Type Proanthocyanidins Prevent Engraftment Of Primary Acute Myelogenous Leukemia Cells In Mice and Exhibit Potentially Novel Anti-Leukemia Mechanisms

Acute myelogenous leukemia (AML) is often a fatal disease where after strong induction therapy most patients relapse and die. AML originates and is maintained by leukemia stem cells (LSCs). Failure to eliminate LSCs by chemotherapy is likely to result in disease relapse. Therefore, it is a priority to identify new therapies that eliminate blasts while ablating LSCs and preventing a relapse.We have found that a unique class of compounds in cranberries (Vaccinium macrocarponAit.), known as A-type proanthocyanidins (A-PACs), were effective against several leukemia cell lines and primary AML samples in vitro. A-PACs consist of monomeric epicatechin units attached to one another by a carbon-carbon bond and a distinctive ether bond that differentiates these compounds from other proanthocyanidins found in nature. Moreover, A-PACs possess ortho-hydroxyl phenolic groups that have the potential to bind to iron and alter redox status.Preliminary work showed that pre-treatment with antioxidants or holo-transferrin (iron-saturated transferrin) partially protected AML cells from A-PAC induced cell death (p<0.01). A-PACs were also found to selectively ablate leukemia stem and progenitor cells, with minimal effects on normal hematopoetic stem cells. Furthermore, AML engraftment of cells treated ex vivo with 62.5 µg/ml A-PACs was decreased (90.6%, n=3, p<0.001), while normal CD34+ cells retained engraftment capability in immunodeficient mice. It was also found that a fraction of A-PACs of up to 7 degree of polymerization was more effective than individual A-PACs. This information prompted us to investigate the in vivo anti-leukemia effects of A-PACs in xenotransplanted mice with primary AML samples, and to further investigate the mechanisms associated with these compounds.Primary AML cells were injected in sub-lethally irradiated NOD/SCID mice. Four weeks after injections, when human leukemia cells have engrafted, intraperitoneal injections of cytarabine (AraC) at 60 mg/kg were given to the mice for 1 week everyday or A-PACs (100 mg/kg dose every 3 days for A-PACs) and vehicle control (1% DMSO in PBS every 3 days) were injected for 2.5 weeks. Mice were sacrificed and leukemia engraftment evaluated using anti-human CD45 and CD33. Moreover, primary cells treated with A-PACs were assessed for effects on iron metabolism, ROS, and survival pathways either by gene expression analysis, flow cytometry or mass spectrometry.Administration of A-PACs to NOD-SCID mice bearing AML tumors reduced tumor burden. Mice that were treated with the vehicle control had engraftment of AML primary cells equivalent to 16.1% (95% CI: -6.0, 38.37; n=4), whereas the mice treated with the A-PACs and AraC showed a level of engraftment of 4.9% (95% CI: 2, 8; n=5) and 5.8% (95% CI: -1.1, 12.7; n=5), respectively. No significant changes in hemoglobin or weight were found between the different treatment groups. Moreover, qPCR analysis of sensitive leukemia cell lines treated with A-PACs showed changes in gene expression of several iron metabolism genes in sensitive leukemia cell lines (up-regulation of ferritin and transferrin receptors 1 and down-regulation of ferroportin) and several ROS-relevant genes (down-regulation of nuclear factor erythroid-2-related factor 2 and glutamate-cysteine ligase regulatory subunit). Mass spectrometry also confirmed that A-PACs bind iron.The results indicate that A-PACs not only target primary AML cells in vitro but are also effective in vivo. Secondary transplants are also being performed to determine the effects on LSC activity. Some of the anti-leukemia mechanisms under investigation include effects related to iron metabolism, ROS or inhibition of survival pathways. Understanding the unique structure and biological effects of A-PACs may provide novel information about pathways involved in the survival of LSCs and provide crucial information in preparation for clinical trials and/or optimal combination drug therapies. Disclosures:Rivella:Novartis: Consultancy; Bayer: Consultancy; Isis: Consultancy, Research Funding; Merganser: Equity Ownership, Research Funding; Biomarin: Consultancy; Alexion: Consultancy; Imago: Consultancy.

The pp90rsk-CREB Signaling Pathway Regulates Apoptosis In Acute Myelogenous Leukemia

CREB (cAMP Response-Element Binding Protein) is a nuclear transcription factor critical for hematopoietic cell proliferation, differentiation, and survival. We previously demonstrated that 60% of patients with Acute Myelogenous Leukemia (AML) overexpress CREB in leukemic blasts, and CREB overexpression in these patients was associated with an increased risk of relapse and decreased event-free survival. Previous studies have suggested that CREB may play an important role in the regulation of apoptosis in a wide variety of cancers. Specifically, CREB has been shown to up-regulate members the anti-apoptotic protein family such as Bcl-2, Bcl-XL and Mcl-1, leading to chemotherapy resistance in vitro. CREB-mediated resistance to apoptosis may underlie the increased rate of relapse and poor survival of AML patients with CREB overexpression. Thus, we hypothesized that targeted inhibition of CREB in AML cells would promote AML cell apoptosis. To test this hypothesis, we developed a small-molecule inhibitor of CREB function, XX-650-23. This molecule disrupts the interaction between CREB and its binding partner CBP (CREB-Binding Protein), which is required for full activation of CREB-mediated gene transcription. Treatment of primary AML patient bone marrow samples with XX-650-23 induced apoptosis and cell death at a dose of 2 uM. The degree of apoptosis varied with the expression level of CREB in primary AML cells tested. Higher CREB levels correlated with higher sensitivity to XX-650-23. In non-leukemic primary patient bone marrow samples, CREB levels were very low, and XX-650-23 did not induce apoptosis in these cells. AML cell lines (KG-1 and HL-60) also underwent apoptosis following CREB inhibition, in proportion to CREB expression level. CREB knockdown or overexpression in KG-1 cells decreased and increased susceptibility to apoptosis, respectively. Mechanistically, the onset of apoptosis in AML cells occurred simultaneously with down-regulation of Bcl-2, a validated CREB-regulated gene. Inhibition of Bcl-2 function using the specific Bcl-2 inhibitor ABT-737 (100 nM) induced apoptosis similar to XX-650-23, indicating that Bcl-2 inhibition alone is sufficient to cause apoptosis. Thus, targeted inhibition of CREB results in Bcl-2 downregulation and is sufficient to induce apoptosis in AML cells. Proteomic analysis using Mass Cytometry-Time of Flight (CyTOF) revealed that one compensatory cellular response to CREB inhibition is increased phosphorylation of CREB. This phosphorylation decreased in the presence of BI-D1870, a specific inhibitor of the pp90RSK kinase (RSK), but not by pharmacologic inhibition of the p38 or ERK kinases, using SB202190 or U0126, respectively. We therefore examined the role of pp90RSK in the regulation of apoptosis in AML cells. Pharmacologic inhibition of RSK independently lead to AML cell apoptosis (BI-D1870, IC50=3.3 uM), in part due to blockade of CREB phosphorylation. In summary, our data provide the first evidence that inhibition of CREB, or its chief activator RSK, is sufficient to induce apoptosis in AML cells. Current work focuses on defining CREB target genes mediating XX-650-23 response using chromatin-immunoprecipitation with massively parallel DNA sequencing (ChIP-Seq), and defining the RSK kinome in AML cells using 2-dimensional gel phosphoprotein profiling. These studies will more fully define the role of the RSK-CREB signaling axis in AML proliferation, survival, and apoptosis. Disclosures:No relevant conflicts of interest to declare.

Targeting Aberrant Glutathione Metabolism to Eradicate Human Acute Myelogenous Leukemia Cells

The development of strategies to eradicate primary human acute myelogenous leukemia (AML) cells is a major challenge to the leukemia research field. In particular, primitive leukemia cells, often termed leukemia stem cells, are typically refractory to many forms of therapy. To investigate improved strategies for targeting of human AML cells we compared the molecular mechanisms regulating oxidative state in primitive (CD34(+)) leukemic versus normal specimens. Our data indicate that CD34(+) AML cells have elevated expression of multiple glutathione pathway regulatory proteins, presumably as a mechanism to compensate for increased oxidative stress in leukemic cells. Consistent with this observation, CD34(+) AML cells have lower levels of reduced glutathione and increased levels of oxidized glutathione compared with normal CD34(+) cells. These findings led us to hypothesize that AML cells will be hypersensitive to inhibition of glutathione metabolism. To test this premise, we identified compounds such as parthenolide (PTL) or piperlongumine that induce almost complete glutathione depletion and severe cell death in CD34(+) AML cells. Importantly, these compounds only induce limited and transient glutathione depletion as well as significantly less toxicity in normal CD34(+) cells. We further determined that PTL perturbs glutathione homeostasis by a multifactorial mechanism, which includes inhibiting key glutathione metabolic enzymes (GCLC and GPX1), as well as direct depletion of glutathione. These findings demonstrate that primitive leukemia cells are uniquely sensitive to agents that target aberrant glutathione metabolism, an intrinsic property of primary human AML cells.