Positive Leukemia Cells Research Articles

Equipping CAR-Modified T Cells with a Brake to Prevent Chronic Adverse Effects

Genetical modification of T lymphocytes by chimeric antigen receptor (CAR), which has the affinity to tumor associated antigen (TAA), can redirect the normal T lymphocytes with tumor specificity. Through optimization of the CAR construct from first generation to third generation, the properties of these CAR-modified T lymphocytes, including, cytokines release, proliferative capacity, in vivo survival time, have been remarkably improved. These improvements accelerate the clinical applications of the CAR-modified T lymphocytes. Due to CD19, and CD20 specificity, CAR-modified T lymphocytes have been clinically used to treat leukemia. Notably, T lymphocytes genetically engineered by Carl June group with CAR targeting to CD19 have expanded more than 1,000 folds by clearing all CD19 positive leukemia cells, even the normal B cells, which infiltrated in bone marrow, and survived for more than 6 months. This encouraging report demonstrates the overwhelming tumor-lytic ability of the CAR-modified T lymphocytes; it also raises the concern about the chronic toxicity. Here, we emphasize the safety concern when using the CAR-modified T lymphocytes. We also summarize strategies exploited to clear the genetically engineered T lymphocytes under an urgent condition, which increases the safety and optimizes the applications of the CAR-modified T lymphocytes.

Problem-solving test: Signal transduction in Philadelphia chromosome positive leukemia cells

Terms to be familiar with before you start to solve the test: reciprocal translocation, proto-oncogene, gene expression, c-Abl, tyrosine protein kinases, transmembrane protein, G protein, Src protein, malignant transformation, transfection, immunoprecipitation, pre-immune serum, [γ-(32)P]ATP, cAMP, SDS-polyacrylamide gel electrophoresis, autoradiography, Western blot (immunoblot), co-immunoprecipitation, expression vector, cDNA, transient transfection, reporter gene, reporter plasmid, promoter, Ras protein, transformed foci, extracellular signal-regulated kinase.

Rac2-MRC-cIII–generated ROS cause genomic instability in chronic myeloid leukemia stem cells and primitive progenitors

AbstractChronic myeloid leukemia in chronic phase (CML-CP) is induced by BCR-ABL1 oncogenic tyrosine kinase. Tyrosine kinase inhibitors eliminate the bulk of CML-CP cells, but fail to eradicate leukemia stem cells (LSCs) and leukemia progenitor cells (LPCs) displaying innate and acquired resistance, respectively. These cells may accumulate genomic instability, leading to disease relapse and/or malignant progression to a fatal blast phase. In the present study, we show that Rac2 GTPase alters mitochondrial membrane potential and electron flow through the mitochondrial respiratory chain complex III (MRC-cIII), thereby generating high levels of reactive oxygen species (ROS) in CML-CP LSCs and primitive LPCs. MRC-cIII–generated ROS promote oxidative DNA damage to trigger genomic instability, resulting in an accumulation of chromosomal aberrations and tyrosine kinase inhibitor–resistant BCR-ABL1 mutants. JAK2(V617F) and FLT3(ITD)–positive polycythemia vera cells and acute myeloid leukemia cells also produce ROS via MRC-cIII. In the present study, inhibition of Rac2 by genetic deletion or a small-molecule inhibitor and down-regulation of mitochondrial ROS by disruption of MRC-cIII, expression of mitochondria-targeted catalase, or addition of ROS-scavenging mitochondria-targeted peptide aptamer reduced genomic instability. We postulate that the Rac2-MRC-cIII pathway triggers ROS-mediated genomic instability in LSCs and primitive LPCs, which could be targeted to prevent the relapse and malignant progression of CML.

Evaluation of deoxyhypusine synthase inhibitors targeting BCR-ABL positive leukemias

Effective inhibition of BCR-ABL tyrosine kinase activity with Imatinib represents a breakthrough in the treatment of patients with chronic myeloid leukemia (CML). However, more than 30 % of patients with CML in chronic phase do not respond adequately to Imatinib and the drug seems not to affect the quiescent pool of BCR-ABL positive leukemic stem and progenitor cells. Therefore, despite encouraging clinical results, Imatinib can still not be considered a curative treatment option in CML. We recently reported downregulation of eukaryotic initiation factor 5A (eIF5A) in Imatinib treated K562 cells. Furthermore, the inhibition of eIF5A by siRNA in combination with Imatinib has been shown to exert synergistic cytotoxic effects on BCR-ABL positive cell lines. Based on the structure of known deoxyhypusine synthase (DHS) inhibitors such as CNI-1493, a drug design approach was applied to develop potential compounds targeting DHS. Here we report the biological evaluation of selected novel (DHSI-15) as compared to established (CNI-1493, deoxyspergualin) DHS inhibitors. We show that upon the compounds tested, DHSI-15 and deoxyspergualin exert strongest antiproliferative effects on BCR-ABL cells including Imatinib resistant mutants. However, this effect did not seem to be restricted to BCR-ABL positive cell lines or primary cells. Both compounds are able to induce apoptosis/necrosis during long term incubation of BCR-ABL positive BA/F3 derivates. Pharmacological synergism can be observed for deoxyspergualin and Imatinib, but not for DHSI-15 and Imatinib. Finally we show that deoxyspergualin is able to inhibit proliferation of CD34+ progenitor cells from CML patients. We conclude that inhibition of deoxyhypusine synthase (DHS) can be supportive for the anti-proliferative treatment of leukemia and merits further investigation including other cancers.

Targeting BCR Tyrosine177 site with novel SH2-DED causes selective leukemia cell death in vitro and in vivo

Emergence of resistance to imatinib mesylate complicates the treatment of chronic myeloid leukemia (CML). Second-generation tyrosine kinase inhibitors are capable to overcome resistance mediated by most mutations except T315I. As this mutation is causative for 20% of clinically observed resistances, the need for novel treatment strategies becomes obvious and urgent. The autophosphorylated BCR/ABL Tyr177 recruits Grb2 via its SH2 domain, which is required for efficient induction of the myeloproliferative disease by BCR/ABL. The death effector domain (DED) is the critical factor for activation of caspase-8 induced apoptosis signal. We thus speculated that transduction of an exogenous SH2-DED (SD) fragment into the CML cells may inhibit the binding of BCR/ABL Tyr177 and Grb2, activate caspase-8 induced apoptosis and serve as a novel CML treatment strategy. The infection of the recombinant adenovirus Ad5/F35-SD was verified to show both cell proliferation-inhibitory and apoptosis-inducing effect. Further exploration into the underlying mechanisms revealed that Ad5/F35-SD exerted its function by binding to the phospho-BCR/ABL Tyr177 site, reducing Ras, MAPK and AKT kinase activities, and activating caspase-8 induced apoptosis signal by DED protein binding to DED domain of precursor caspase-8. Moreover, high anti-proliferative activity of Ad5/F35-SD was observed in nude mice and its leukemia-protective effect was evident in chronic myeloid leukemia model mice injected with BCR/ABL+ BaF3 cells. In conclusion, Ad5/F35-SD exhibits anti-proliferative and pro-apoptotic activity on BCR/ABL positive leukemia cells in vitro and in vivo through disruption of Grb2 SH2-phospho-BCR/ABL Tyr177 complex formation and induction of caspase-8 activation.

Targeting the Oligomerization of BCR/ABL by Membrane Permeable Competitive Peptides Inhibits the Proliferation of Philadelphia Chromosome Positive Leukemic Cells

The BCR/ABL fusion protein is the hallmark of Philadelphia Chromosome positive (Ph+) leukemia. The constitutive activation of the ABL-kinase in BCR/ABL cells induces the leukemic phenotype. Targeted inhibition of BCR/ABL by small molecule inhibitors reverses the transformation potential of BCR/ABL. Recently, we definitively proved that targeting the tetramerization of BCR/ABL mediated by the N-terminal coiled-coil domain (CC) using competitive peptides, representing the helix-2 of the CC, represents a valid therapeutic approach for treating Ph+ leukemia. To further develop competitive peptides for targeting BCR/ABL, we created a membrane permeable helix-2 peptide (MPH-2) by fusing the helix-2 peptide with a peptide transduction tag. In this study, we report that the MPH-2: (i) interacted with BCR/ABL in vivo; (ii) efficiently inhibited the autophosphorylation of BCR/ABL; (iii) suppressed the growth and viability of Ph+ leukemic cells; and (iv) was efficiently transduced into mononuclear cells (MNC) in an in vivo mouse model. This study provides the first evidence that an efficient peptide transduction system facilitates the employment of competitive peptides to target the oligomerization interface of BCR/ABL in vivo.

Targeting Rac2 - Mitochondrial Respiratory Chain Complex III Signaling to Prevent Genomic Instability in Leukemia Stem and Progenitor Cells

Abstract 2736BCR-ABL1 –positive chronic myeloid leukemia in chronic phase (CML-CP) is a leukemia stem cell (LSC)-derived but leukemia progenitor cell (LPC)-driven disease, which may eventually develop resistance to the tyrosine kinase inhibitors (TKIs) and progress to fatal CML blast phase (CML-BP). In CML-CP, LSCs and LPCs reside in the CD34+CD38- and CD34+CD38+ populations, respectively. In addition, majority of LSCs and LPCs belong to quiescent (CFSEmax) and proliferative (CFSElow) populations, respectively. Quiescent LSCs are intrinsically insensitive to TKIs, and LPCs can acquire resistance to TKIs. In the TKI era, these cells may eventually initiate the disease relapse and progression to CML-BP, which is associated with genomic instability manifested by accumulation of a new or additional TKI-resistant BCR-ABL1 kinase mutations and chromosomal aberrations. We reported that BCR-ABL1 –positive leukemia cells contain high levels of the reactive oxygen species (ROS)-induced oxidative DNA damage resulting in genomic instability (Nowicki et al., Blood, 2005; Koptyra et al., Blood, 2006; Koptyra et al., Leukemia, 2008). These studies highlighted the importance of identification of the origin of leukemia cell lineage accumulating genomic instability and the mechanisms responsible for generation of ROS-mediated oxidative DNA damage.Here we show that LSC-enriched CD34+CD38- cells and quiescent LSCs, and also LPC-enriched CD34+CD38+ and proliferating CML-CP cells contain higher levels of ROS (superoxide anion, hydrogen peroxide, and hydroxyl radical) and oxidative DNA lesions (8-oxoG and DNA double-strand breaks) than corresponding cells from healthy donors. Surprisingly, the most primitive quiescent LSCs accumulated the highest levels of ROS and oxidative DNA damage. On the basis of these observations and the studies in murine hematopoietic 32Dcl3 cells expressing TKI-resistant BCR-ABL1 kinase variants (Y253F, T315I, H396P), we would predict that primitive CML-CP cells carrying these mutations would also contain high levels of ROS and oxidative DNA damage. Moreover, inhibition of BCR-ABL1 kinase with imatinib exerted only modest, if any, effect on ROS and oxidative DNA damage in LSCs/LPCs in the presence of growth factors (GFs).Among numerous signaling proteins activated in CML cells, Rac GTPases were potential candidates to regulate production of ROS. Importantly, Rac was stimulated in leukemia cells expressing non-mutated BCR-ABL1 and TKI-resistant kinase mutants and it remained active in CML-CP cells treated with imatinib in the presence of GFs. We used Rac dominant-negative mutant (RacT17N), Rac specific inhibitors (NSC23766 and EHT1864) and Rac1, Rac2 and Rac3 knockout cells to document that Rac2 GTPase is responsible for elevation of ROS and oxidative DNA damage in LSC-enriched CD34+CD38- cells, quiescent LSCs, and also in LPCs. Active Rac2 reduced mitochondrial membrane potential (ΔΨm) and slowed the electron flow between mitochondrial respiratory chain (MRC) complexes I-II and I-III leading to overproduction of ROS. Using cells depleted of functional mitochondria (Rho0 cells), applying specific probes to measure mitochondrial ROS (MitosoxRed and mitochondria matrix-targeted circularly permuted yellow fluorescence protein = mt-cpYFP) and employing a specific inhibitor of mitochondrial ROS (MitoQ) we determined that mitochondria are the main source of ROS causing oxidative DNA damage in CD34+CD38- and quiescent LSCs and in LPCs. Furthermore, using selective inhibitors of various MRC complexes we pinpointed complex III as major producer of ROS in LSCs and LPCs. This conclusion is supported by the observation that BCR-ABL1 –positive cells with genetically inactivated complex III, but not complex I, displayed diminished capability to generate ROS. Targeting Rac2 GTPase by RacT17N and reduction of mitochondrial ROS by mitochondrial-targeted catalase and by mitochondrial-targeted ROS-scavenging peptide aptamers prevented genomic instability.Altogether, Rac2 - MRC-cIII pathway is a major source of ROS-mediated oxidative DNA damage resulting in genomic instability in LSCs and LPCs, which could be targeted to prevent the relapse and malignant progression of CML. We also postulate that similar mechanisms cause genomic instability in FLT3(ITD)-positive acute myeloid leukemia cells and in JAK2(V617F)-positive polycythemia vera cells. Disclosures:Holyoake:Novartis: Consultancy, Research Funding. Valent:Novartis: Consultancy, Honoraria, Research Funding. Hochhaus:Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Hughes:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Pharmacologic Doses of Amiloride Preferentially Induce Apoptosis and Growth Inhibition of Flt3-ITD Mutation Positive Acute Myeloid Leukemia Cell Lines

Abstract 5004 Introduction:Amiloride is an FDA approved potassium-sparing diuretic which targets Na+/H+ exchanger isoform 1 (NHE1). NHE1 is responsible for the regulation of the intracellular pH, as well as cell-cycle and apoptosis. In supra-pharmacologic concentrations, amiloride non-specifically inhibits protein kinases. Recent study demonstrated that proapoptotic effect of amiloride in CML cell lines is linked to the modulation of the alternative splicing of Bcl-x, HIPK3, and BCR/ABL genes and is independent of pHi.Here, we demonstrate that pharmacologic doses of amiloride preferentially induce growth inhibition, cell cycle arrest and apoptosis in Flt3-ITD positive acute myeloid leukemia cell lines as compared to Bcr-Abl positive leukemia cell line. Our data suggests that amiloride may have an effect on Flt3 signaling and that its treatment potential for Flt3-ITD positive acute myeloid leukemia needs to be explored. Methods:MV4-11, MOLM13 and K562 cells lines in log-phase growth were used for the experiments. Analysis of the baseline Flt3 expression and phosphorylation status was assessed via Flt3 immunoprecipitation and Western blotting for Flt3 and phosphotyrosine. Cells were incubated with various amiloride concentrations; equal volume dilutions of DMSO were used for control. Cell counting and trypan blue exclusion viability was performed on TC10 Bio-Rad automated cell counter. The cell cycle analysis was performed applying propidium iodide staining. To assess for apoptosis and cell death, we used annexin V/PI staining kit and flow cytometry. Results:MOLM13 and MV4-11 cell lines carry activating Flt3-ITD mutation. We confirmed the expression and constituative activation of Flt3 in MOLM13 and MV4-11 cells with Western blotting. Flt3 protein was not detectable in K562 cell line. Amiloride at 0.025 mM and 0.05 mM completely inhibited the growth of MV4-11 cells after 24 hrs of treatment with no significant increase in total or live cell numbers at 72 hrs, but only mildly affected K562 cell proliferation. While the above amiloride concentrations caused cell death in MV4-11 and MOLM13 cell lines, there was no increased cell death in K562 cells.Incubation of MOLM13 and MV4-11 cell lines with 0.05 mM amiloride for 20 hrs induced cell cycle arrest. In MV4-11 cell line, the proportion of S phase cells after amiloride treatment was 15.4% (SD=5.4%) as compared to 31.3% (SD=1.4%) in control. MOLM13 cell line demonstrated 15.3% (SD=4.7%) of cells in S after amiloride treatment as compared to 35.3% (SD=2.4%) cells in S phase in control treatment. In K562 cell line, there was less effect with 52% (SD=4.2%) of cells in S phase in control as compared to 37% (SD=8.9%) in amiloride treatment.MV4-11 and MOLM 13 cell lines were more sensitive than K562 cells to amiloride induced apoptosis with 28.8% (control 12.7%) of MV4-11 cells, 11.4% (control 7.4%) of MOLM13 cells, and 11.4% (control 8.6%) of K562 cells being apoptotic after 20 hr treatment with 0.05mM amiloride. At 72 hrs of amiloride treatment 34% (control 1.5%) of MV4-11 cells, 17% (control 5%) of MOLM13 cells and 11% of K562 cells (control 8.9%) were apoptotic. Amiloride had similar effect on the number of dead cells with no increase in total cell death in K562 cell line. Upon treatment with increasing amiloride concentrations, there was dose-dependent increase in cell death and apoptosis in all three cell lines with K562 line showing relative resistance to amiloride. Discussion:Our results demonstrate that amiloride induces cell cycle arrest and inhibits proliferation of Flt3-ITD positive cell lines MV4-11 and MOLM13 as well as K562 cell line at a pharmacologic concentration of 0.05 mM. Both, cell cycle arrest and antiproliferative effect are more pronounced in Flt3-ITD positive cells lines while it is mild in Bcr-Abl positive K562 cell line. Pharmacologic doses of amiloride induce cell death and apoptosis in Flt3-ITD positive cell lines but not in K562 cell line. Both, Bcr-Abl and Flt3 signaling stimulates proliferation and inhibits apoptosis in myeloid leukemia cells. Our study suggests that amiloride may induce cell cycle arrest and apoptosis via modulating Flt3 signaling cascade. We are currently investigating the effects of amiloride on Flt3 phosphorylation. In conclusion, our data suggests that amiloride presents a potential treatment option for Flt3-ITD positive acute myeloid leukemia. Disclosures:No relevant conflicts of interest to declare.

Loss of EZH2 and Aberrant DNA Methylation Account for PKC412 Drug Resistance in the FLT3-ITD Positive Acute Myeloid Leukemia (AML) Cell Line MV4-11,

Abstract 3468The development of drug resistance is a common feature in AML that occurs towards classical cytotoxic drugs as well as novel kinase inhibitors. Mutations in primary drug targets explain a significant fraction of acquired drug resistance but the mechanisms of resistance still remain unknown in most patients. About 20–30% of all AML patients possess the mutant FLT3-ITD leading to a constitutive activation of the FLT3 kinase. Flt3-mutations can be targeted by treatment with tyrosine kinase inhibitors. Resistance to these kinase inhibitors is an increasing phenomenon whose mechanisms are not entirely understood today. As epigenetic mechanisms are shown to play an important role in leukemia pathogenesis they are also likely to influence drug resistance. To elucidate the potential role of epigenetic mechanisms in the development of drug resistance towards kinase inhibitors we used a PKC412 partially resistant clone (MV4-11R) of the AML cell line MV4-11, which harbors a homozygous FLT3 internal tandem duplication (ITD) mutation.An initial screening for histone modifying enzymes revealed a downregulation of EZH2 on mRNA as well as protein level compared with the parental cell line. The reduction of EZH2, a H3K27 methyltransferase, in MV4-11R is furthermore correlating with globally diminished H3K27me3 levels. ChIP-Seq experiments using H3K27me3 antibody revealed differences in histone 3 K27 methylation at specific promoter sites between the parental and resistant MV4-11. To test for an increased drug resistance due to reduced EZH2 protein levels lentiviral knock-down of EZH2 was performed in the MV4-11 parental cell line and three individual knock-down cell clones were investigated for their drug resistance potential. These knock downs all showed elevated IC50 values as well as resistance towards the apoptosis-inducing effects of PKC412 compared with the scrambled shRNA cells. Furthermore, EZH2 protein levels of 5 FLT3-ITD-positive AML patient samples were determined by Western Blot, samples were treated with PKC412 for 3 days and cell survival was assayed. Using this approach higher EZH2 levels in patients could also be associated with a higher sensitivity to PKC412 pointing to a putative role of EZH2 in the development of PKC412 resistance in vivo.As EZH2 has been shown to interact with DNMTs in the context of the Polycomb Repressive Complex 2 and 3 (Viré et al., Nature 2006), we analyzed whether parental and resistant MV4-11 differ in their DNA methylation pattern. To identify hyper-/hypomethylated genes in MV4-11R, we applied the Illumina 27k Methylation BeadChip approach as well as Reduced Representation Bisulfite Sequencing (RRBS) for a genome wide CpG methylation analysis. In particular genes associated with apoptosis pathways and signal transduction were hypermethylated in MV4-11R cells compared to the parental cell line. Based on the observation of DNA methylation changes between the parental cell line and MV4-11R, treatment with the demethylating agent 2-deoxy-5-azacytidine (Aza dC) was conducted to investigate recovery of drug sensitivity. Incubation with 250 nM Aza dC for 5 days could restore the sensitivity of MV4-11R towards PKC412 as shown in proliferation and apoptosis assays. Using the Affymetrix Human Gene 1.0 ST Array platform we identified 110 genes whose expression was reactivated after treatment of MV4-11R with Aza dC, predominantly genes playing a role in signal transduction, apoptosis pathways and cell cycle. A cell cycle analysis of the MV4-11 and MV4-11R cells indeed showed that the resistant cell line is cycling less than the parental one, which possibly also favors the resistance development towards PKC412.Summarized, our data show that a loss of EZH2 accompanied by DNA methylation changes lead to PKC412 resistance in a FLT3-ITD AML cell line model possibly reflecting a way of acquisition of drug resistance in patients. Disclosures:Thiede:Novartis: Lectures, Research Funding. Müller-Tidow:Novartis: Research Funding.

PD0332991, a CDK4/6 Inhibitor, Has An Anti-Leukemic Activity Against Lymphoid Crisis of CML and Ph+ALL Even with T315I Mutation in BCR-Abl; in Vitro Analysis

Abstract 1511Since BCR-ABL plays a central role in cell cycle progression of Philadelphia-chromosome positive (Ph+) leukemia cells and CDK4/6 critically involves in G1-progression of cell cycle, we analyzed sensitivity of Ph+ leukemia cell lines to compounds that act as specific CDK4/6 inhibitors. H3-thymidine uptake assay showed that both PD183812 and CBC219476 significantly inhibited cell growth of Ph+ lymphoid leukemia cell lines (n=9) in comparison with Ph+ myeloid leukemia cell lines (n=7) and Ph- ALL cell lines (n=26). Thus, we next tested the anti-leukemic activity of PD0332991, a potent CDK4/6 inhibitor that is under phase II clinical study for solid tumor patients, and found that 8 of 9 Ph+ lymphoid leukemia cell lines showed extremely higher sensitivity to PD0332991; median IC50 was <25 nM. IC50 of Ph+ lymphoid leukemia cell lines was significantly lower than that of Ph+ myeloid cell lines (200 nM, n=7) and Ph-ALL cell lines (100nM, n=25). PD0332991 effectively dephosphorylated Rb protein (pRb), and subsequently induced G1 arrest on all of Ph+ lymphoid leukemia cell lines. Moreover, PD0332991 gradually induced cell death in 4 Ph+ lymphoid leukemia cell lines. Since CDK4/6 inhibitor acts depending on intact pRb, we analyzed protein and gene expression status of Rb. Of note, all Ph+ lymphoid leukemia cell lines expressed intact pRb except for one cell line that showed relative resistance to PD0332991. In contrast, pRb was almost undetectable in Ph+ myeloid cell lines in spite of comparable level of Rb gene expression, which might be mechanism for resistance to PD0332991. However, most of Ph- ALL cell lines had intact pRb expression in spite of their relative resistance to PD0332991, indicating that Rb status alone did not explain higher PD0332991-sensitivity of Ph+ lymphoid leukemia cell lines. Thus, we assumed that Ph+ lymphoid leukemia cells showed higher PD0332991-sensitivity probably because BCR-ABL regulates CDK4/6 expression for cell cycle progression. To clarify this assumption, we treated Ph+ lymphoid leukemia cell lines with imatinib and performed immunoblot analysis of cell cycle machineries such as CDKs, cyclines, and CDK inhibitors. Of note, CDK4 expression level was frequently downregulated by imatinib in Ph+ lymphoid leukemia cell lines. Moreover, imatinib-induced downregulation of CDK4 in Ph+ lymphoid leukemia cell line was abrogated by the addition of IL-7 and FLT3 ligand, which stimulated cell cycle progression of imatinib-treated Ph+ ALL cell line. LY294002, a PI3K inhibitor, but not U0126, a MAPK inhibitor, and AG490, an inhibitor for JAK/STAT pathway, efficiently downregulated CDK4 expression in Ph+ lymphoid leukemia cell lines. Gene expression level of CDK4 in Ph+ lymphoid leukemia cell lines was downregulated by imatinib, and lactastatin, an inhibitor of protein degradation, partially inhibited imatinib-induced downregulation of CDK4 protein in Ph+ lymphoid leukemia cell lines, indicating that BCR-ABL regulates CDK4 expression both in gene expression level and in protein degradation level. These findings indicated that Ph+ lymphoid leukemia cell lines showed higher sensitivity to PD0332991 since BCR-ABL induces cell cycle progression of Ph+ lymphoid leukemia cells by regulating CDK4 as one of downstream pathways. Accordingly, we tested if PD0332991 shows anti-leukemic activity in Ph+ lymphoid leukemia cells that have a T315I mutation of BCR-ABL. SU/SR is an imatinib-resistant Ph+ ALL cell line with T315I mutation (IC50 for imatinib >10 mM), which was established from SU-Ph2, an imatinib-sensitive Ph+ ALL cell line (IC50 for imatinib <0.1 mM), after long-term culture in the presence of gradually increasing concentration of imatinib. Of note, PD0332991 effectively dephosphorylated pRb and inhibited cell growth of both SU/SR and SU-Ph2. Our findings provide a rationale for efficacy of PD0332991 in the context of anti-leukemic therapy for lymphoid crisis of CML and Ph+ ALL patients even with T315I mutation in BCR-ABL. Disclosures:No relevant conflicts of interest to declare.

DNMT3B Expression Delays Leukemogenesis,

Abstract 3446Acute myeloid leukaemia (AML) is a malignant disease with poor prognosis, which is, among other biological features, characterized by epigenetic changes including alterations in DNA methylation. DNA methyltransferases (DNMT) play an important role in regulation of DNA methylation and mutations of DNMT3A are frequently found in AML. We analyzed the effects of DNMT overexpression on leukemogenesis using an inducible DNMT3B mouse model (Linhart et al., 2007). To analyse the impact of DNMT3B overexpression on leukemia we retrovirally co-transduced lineage-negative bone marrow cells of wildtype and DNMT3Btg mice with a MSCV-cMyc-bcl2 and a MSCV-tTA-GFP containing vector. Under these conditions, doxycycline suppressed DNMT3B expression whereas absence of doxycycline led to overexpression of DNMT3B on the mRNA and protein level. DNMT3B overexpression was not toxic since colony formation in vitro did not differ between DNMT3B expressing and physiologically expressing cells. To analyze leukemogenesis, 5 × 104 sorted GFP-positive cells were transplanted into sublethally irradiated wildtype recipients. Both recipients of transduced wildtype cells and recipients of transduced DNMT3Btg cells developed leukemia with a tendency of delayed leukemogenesis in DNMT3B overexpressing mice. GFP positive leukemic cells were sorted and doxycycline regulated DNMT3B expression was verified by Western blot analysis in vitro. To determine the repopulation capacity of the leukemic cells we performed transplantation of GFP-positive primary leukemia cells into secondary wildtype recipients. Leukemia of both, wildtype and DNMT3B-overexpressing donors was transplantable and lethal. However, DNMT3Btg leukemic cells were severely impaired in leukemia development in secondary recipients. Secondary recipients of leukemic DNMT3Btg cells died significantly later (p= 0.02). Taken together, these findings demonstrate that DNMT3B expression impairs leukemia maintenance. Loss of DNMT activity might contribute to the pool size of leukemia initiating cells. Disclosures:Krug:Boehringer Ingelheim: Research Funding.

Activation of the unfolded protein response in primary acute myeloid leukemia cells

The unfolded protein response (UPR), which plays an important role in maintaining homeostasis of the endoplasmic reticulum (ER), is known to be activated in various solid tumors [1]. The role of the UPR in different forms of cancer or metastasis remains poorly characterized, and it is unclear whether UPR activation in cancer is due solely to microenvironmental stress, or to other mechanisms. The influence of the UPR on leukemogenesis remains largely uninvestigated. We previously reported that the UPR is activated in Philadelphia (Ph)-positive leukemia cells using cell lines and primary cells from Ph-positive acute lymphoid leukemia (ALL) patients [2]. In the present study, we investigated whether the UPR is activated in another type of acute leukemia, primary acute myeloid leukemia (AML).

Characterization of a Monoclonal Antibody Specific for Novel Bcr/Abl Out-of-Frame Fusion Proteins

The new tumor-specific antigens Bcr/Abl-OOF, identified in Philadelphia chromosome (Ph)-positive leukemia cells, are derived from an alternative splicing event involving BCR exons 1, 13, or 14 and ABL exons 4 and 5. The COOH-terminus of these transcription products contain an amino acid portion derived from an out-of-frame (OOF) reading of the ABL gene; these variants are expressed in Ph-positive chronic myelogenous leukemia (CML) and acute lymphocytic leukemia patients. Previously, we confirmed the presence of out-of-frame peptide-specific T cells in the peripheral blood of CML patients with the ability to lyse primary autologous CML cells. We also demonstrated that the out-of-frame Abl portion was immunogenic in HLA-A2.1 transgenic mice. Here we describe the production and characterization of monoclonal antibody 1D8G8, a new tool for localization and functional studies of the tumor antigen Bcr/Abl-OOF. This antibody recognizes the out-of-frame protein portion of the native full-length Bcr/Abl-OOF protein expressed in cells transiently transfected, as demonstrated by immunoprecipitation and immunofluorescence, and binds to a specific epitope of this antigen presented in association with HLA-A2.1 molecules at the surface of these cells, as demonstrated by flow cytometry. Thus this MAb could be useful to better understand how this new protein presents in Ph-positive cells beside the canonical Bcr/Abl fusion proteins.

EVI1‐mediated down regulation of MIR449A is essential for the survival of EVI1 positive leukaemic cells

Chromosomal rearrangements involving the MECOM (MDS1 and EVI1 complex) locus are recurrent genetic events in myeloid leukaemia and are associated with poor prognosis. In this study, we assessed the role of MECOM locus protein EVI1 in the transcriptional regulation of microRNAs (miRNAs) involved in the leukaemic phenotype. For this, we profiled expression of 366 miRNAs in 38 MECOM-rearranged patient samples, normal bone marrow controls and MECOM (EVI1) knock down/re-expression models. Cross-comparison of these miRNA expression profiling data showed that MECOM rearranged leukaemias are characterized by down regulation of MIR449A. Reconstitution of MIR449A expression in MECOM-rearranged cell line models induced apoptosis resulting in a strong decrease in cell viability. These effects might be mediated in part by MIR449A regulation of NOTCH1 and BCL2, which are shown here to be bona fide MIR449A targets. Finally, we confirmed that MIR449A repression is mediated through direct promoter occupation of the EVI1 transcriptional repressor. In conclusion, this study reveals MIR449A as a crucial direct target of the MECOM locus protein EVI1 involved in the pathogenesis of MECOM-rearranged leukaemias and unravels NOTCH1 and BCL2 as important novel targets of MIR449A. This EVI1-MIR449A-NOTCH1/BCL2 regulatory axis might open new possibilities for the development of therapeutic strategies in this poor prognostic leukaemia subgroup.

Sumoylation of MEL1S at lysine 568 and its interaction with CtBP facilitates its repressor activity and the blockade of G-CSF-induced myeloid differentiation

MEL1 (MDS1/EVI1-like gene 1/PRDM16), which was identified as a gene near the chromosomal breakpoint in t(1;3)(p36;q21)-positive human acute myeloid leukemia cells, belongs to the PRDI-BF1-RIZ1 homologous (PR) domain (PRDM) family of transcription repressors. The short form of MEL1 (MEL1S), which lacks the PR-domain at the N-terminus, is the main form expressed in t(1;3)(p36;q21)-positive acute myeloid leukemia cells. The overexpression of MEL1S blocks granulocyte colony-stimulating factor (G-CSF)-induced myeloid differentiation in interleukin-3-dependent murine myeloid L-G3 cells. In this study, we show that treatment with the histone deacetylase inhibitor trichostatin A abolished the blockade of myeloid differentiation in L-G3 cells overexpressing MEL1S. The expression of MEL1S containing mutated CtBP-interacting motif (CIM) in L-G3 cells still blocked the myeloid differentiation induced by G-CSF. We found that the small ubiquitin-related modifier (SUMO) motif (SM) at lysine 568 (VKAE) adjacent to the CIM was necessary to obtain the maximum transcriptional repressor activity of MEL1S. L-G3 cells expressing MEL1S, and bearing mutated CIM and SM differentiated into granulocytes in response to G-CSF; this indicated that both the SUMO modification at lysine 568 and CtBP binding were required for MEL1S-mediated transcriptional repression and blockade of differentiation, which might be relevant for the process of leukemogenesis.

Abstract 2603: Inhibition of Notch and mTOR by nelfinavir as a novel approach for T cell acute lymphoblastic leukemia (T-ALL)

Abstract Background: T-ALL accounts for 10-15% of childhood ALL and 25% of adult ALL. Although intensive chemotherapy improves disease free survival, patients who relapse or progress have a dismal prognosis. Notch1 is a promising target in T-ALL because it is commonly activated, and inhibitors of γ-secretase (GSI), an aspartic protease that processes Notch1, are in clinical trials. Nelfinavir is an HIV protease inhibitor with anti-cancer activity through its inhibition of the Akt/mTOR pathway as well as unknown mechanisms. Because the HIV protease is an aspartic protease, we hypothesized that a target for nelfinavir in cancer cells could be γ-secretase. Methods: Nelfinavir was compared to compound E, a commercially available GSI, in in vitro studies. Notch1 and mTOR signalling was evaluated in human and murine T-ALL cell lines by immunoblotting. γ-secretase activity was assessed in cell-free in vitro assays. Cell death was measured by flow cytometry after annexin V and propidium iodide staining. Nelfinavir was also tested in a transgenic model of T-ALL (established by overexpression of SCL and LMO1 in the mouse thymus) using microCT scans, flow cytometry and IHC. Results: Among 7 HIV protease inhibitors evaluated, only nelfinavir inhibited expression of the Notch1 transmembrane and intracellular domains as well as Hes1 and survivin, well-established downstream targets of Notch1. At clinically achievable concentrations, nelfinavir rapidly inhibited Notch1, which was sustained to 16 hr when death was evident. Cell-free assays showed that although compound E was a more potent inhibitor of γ-secretase, the maximal enzymatic inhibition by nelfinavir was equivalent at higher doses. Nelfinavir was far more effective than compound E in reducing expression of Notch targets such as phospho-Rb, c-Myc, and Hrb, Hes1, and survivin. Nelfinavir induced apoptosis to levels equivalent to 20 µM etoposide, but compound E was only cytostatic. To explore other mechanisms that could explain the decreased protein expression and higher levels of cell death with nelfinavir, we assessed the Akt/mTOR pathway. Nelfinavir rapidly induced AMPK activation and mTOR inhibition, coincident with Notch1 inhibition. In SCL-LMO1 double transgenic mice, nelfinavir decreased thymic size and markedly increased apoptotic cells in the thymus. It also decreased the CD3+ populations in spleen and bone marrow and decreased CD4+CD8+ double positive leukemic cells. Conclusion: These studies show that nelfinavir is superior to a GSI and highly active in preclinical studies of T-ALL. Clinical testing of nelfinavir in T-ALL patients is planned. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2603. doi:10.1158/1538-7445.AM2011-2603

Endoplasmic reticulum stress inducers, but not imatinib, sensitize Philadelphia chromosome-positive leukemia cells to TRAIL-mediated apoptosis

Philadelphia-chromosome (Ph1)-positive leukemia cells frequently express death receptors DR4/DR5 for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and show high TRAIL-sensitivity. It has been reported that imatinib damaged cardiomyocytes by triggering endoplasmic reticulum (ER) stress and that ER stress inducers intensified TRAIL-sensitivity of some cancer cells by upregulating DR4/DR5 expression. In fact, ER stress inducers enhanced TRAIL-sensitivity of Ph1-positive leukemia cells by upregulating DR4/DR5 expression. In contrast, imatinib did not induce ER stress responses and unexpectedly downregulated DR4/DR5 expression, indicating that sensitization of Ph1-positive leukemia cells to TRAIL-mediated cellular immunity by imatinib through upregulation of DR4/DR5 expression is unlikely.

Effective and specific control of aml1/eto gene expression in acute myeloid leukemia cells by lentivector-based RNA-interference

In presented work, new approach for the control of aml1/eto gene expression in t(8;21)(q22;q22)-positive acute myeloid leukemia cells has been developed. The technique is based on using the RNA-interference and lentiviral transduction methodology. Two new lentiviral vector sets for induction of constitutive anti-aml1/eto RNA-interference in acute myeloid leukemia cells have been developed and tested. The first set was based on use of artificial microRNAs (miRNAs) and second one was intended for production of short hairpin RNAs (shRNAs). It was shown that Kasumi-1 and SKNO-1 leukemia cells can be efficiency transduced by each new lentiviral vector. Moreover, the percent of modified leukemia cells that may be easily evaluated in multiplicity of infection (MOI) test achieved more than 90% for Kasumi-1 and SKNO-1 cells at MOI 40 and 20, respectively. Comparative study elucidated that the anti-aml1/eto shRNA-based approach induced a stronger knock-down of aml1/eto gene in Kasumi-1 and SKNO-1 cells than the miRNA-based method did. We hope that the proposed approach may become useful instrument for controlling the aml1/eto gene expression in vitro as well as in vivo investigations of function and biological role of the gene.

Flow cytometric study of potential target antigens (CD19, CD20, CD22, CD33) for antibody-based immunotherapy in acute lymphoblastic leukemia: analysis of 552 cases

Monoclonal antibody (MoAb)-based therapies have opened innovative treatment avenues that have impacted on the management of patients with both neoplastic and non-neoplastic hematological diseases. The aim of our study was to evaluate in a large series of cases of acute lymphoblastic leukemia (ALL) the expression of specific antigens, CD19, CD20, CD22, and CD33, for which MoAbs are available for clinical use. For each antigen, evaluation was based on the percentage of positive leukemic cells and the degree of antigen expression by mean fluorescence intensity (MFI) and antibody binding capacity (ABC) that were correlated with age, immunophenotype, and presence/absence of particular molecular markers. We can document that some of the analyzed antigens showed a degree of expression related to the B-cell maturation profile, and that the antigen expression intensity appeared to vary according to the presence of specific genetic markers. These findings suggest that the possible clinical use of a given MoAb in patients with ALL should take into account both the maturation profile of the leukemic cells and the presence of a given molecular transcript. Only clinical studies will conclusively demonstrate whether the differences in antigenic expression truly correlate with the different therapeutic efficacies of the various clinical grade MoAbs.

Rakicidin A effectively induces apoptosis in hypoxia adapted Bcr‐Abl positive leukemic cells

Treatment with Abl tyrosine kinase inhibitors (TKI) drastically improves the prognosis of chronic myelogenous leukemia (CML) patients. However, quiescent CML cells are insensitive to TKI and can lead to relapse of the disease. Thus, research is needed to elucidate the properties of these quiescent CML cells, including their microenvironment, in order to effectively target them. Hypoxia is known to be a common feature of solid tumors that contributes to therapeutic resistance. Leukemic cells are also able to survive and proliferate in severely hypoxic environments. The hypoxic conditions in the bone marrow (BM) allow leukemic cells that reside there to become insensitive to cell death stimuli. To target leukemic cells in hypoxic conditions, we focused on the hypoxia-selective cytotoxin, Rakicidin A. A previous report showed that Rakicidin A, a natural product produced by the Micromonospora strain, induced hypoxia-selective cytotoxicity in solid tumors. Here, we describe Rakicidin A-induced cell death in hypoxia-adapted (HA)-CML cells with stem cell-like characteristics. Interestingly, apoptosis was induced via caspase-dependent and -independent pathways. In addition, treatment with Rakicidin A in combination with the TKI, imatinib, resulted in synergistic cytotoxicity against HA-CML cells. In conclusion, Rakicidin A is a promising compound for targeting TKI-resistant quiescent CML stem cells in the hypoxic BM environment.