Venetoclax and dexamethasone synergize with inotuzumab ozogamicin-induced DNA damage signaling in B-lineage ALL.

Adult patients with relapsed B-cell precursor acute lymphoblastic leukemia (BCP-ALL) have a dismal prognosis. To improve pharmacotherapy, we analyzed induction of apoptosis by venetoclax and inotuzumab ozogamicin in terms of cytotoxicity and mode of action. Flow cytometry-based analyses of mitochondrial outer membrane permeabilization (MOMP) and ataxia telangiectasia mutated activation demonstrate rapid induction of MOMP by venetoclax and DNA damage signaling by inotuzumab ozogamicin, respectively. In primary ALL samples and patient-derived xenograft (PDX) models, venetoclax and inotuzumab ozogamicin cooperated and synergized in combination with dexamethasone in vitro in all tested samples of ALL. In murine PDX models, inotuzumab ozogamicin, but not venetoclax, induced complete remission in a dose-dependent manner but constantly failed to achieve relapse-free survival. In contrast, combination therapy with venetoclax, dexamethasone, and inotuzumab ozogamicin induced long-term leukemia-free survival and treatment-free survival in all 3 ALL-PDX models tested. These data demonstrate synergistic and highly efficient pharmacotherapy in preclinical models that qualify for evaluation in clinical trials.

Increased prostaglandin-D2 in male STAT3-deficient hearts shifts cardiac progenitor cells from endothelial to white adipocyte differentiation.

Cardiac levels of the signal transducer and activator of transcription factor-3 (STAT3) decline with age, and male but not female mice with a cardiomyocyte-specific STAT3 deficiency conditional knockout (CKO) display premature age-related heart failure associated with reduced cardiac capillary density. In the present study, isolated male and female CKO-cardiomyocytes exhibit increased prostaglandin (PG)-generating cyclooxygenase-2 (COX-2) expression. The PG-degrading hydroxyprostaglandin-dehydrogenase-15 (HPGD) expression is only reduced in male cardiomyocytes, which is associated with increased prostaglandin D2 (PGD2) secretion from isolated male but not female CKO-cardiomyocytes. Reduced HPGD expression in male cardiomyocytes derive from impaired androgen receptor (AR)-signaling due to loss of its cofactor STAT3. Elevated PGD2 secretion in males is associated with increased white adipocyte accumulation in aged male but not female hearts. Adipocyte differentiation is enhanced in isolated stem cell antigen-1 (SCA-1)+ cardiac progenitor cells (CPC) from young male CKO-mice compared with the adipocyte differentiation of male wild-type (WT)-CPC and CPC isolated from female mice. Epigenetic analysis in freshly isolated male CKO-CPC display hypermethylation in pro-angiogenic genes (Fgfr2, Epas1) and hypomethylation in the white adipocyte differentiation gene Zfp423 associated with up-regulated ZFP423 expression and a shift from endothelial to white adipocyte differentiation compared with WT-CPC. The expression of the histone-methyltransferase EZH2 is reduced in male CKO-CPC compared with male WT-CPC, whereas no differences in the EZH2 expression in female CPC were observed. Clonally expanded CPC can differentiate into endothelial cells or into adipocytes depending on the differentiation conditions. ZFP423 overexpression is sufficient to induce white adipocyte differentiation of clonal CPC. In isolated WT-CPC, PGD2 stimulation reduces the expression of EZH2, thereby up-regulating ZFP423 expression and promoting white adipocyte differentiation. The treatment of young male CKO mice with the COX inhibitor Ibuprofen or the PGD2 receptor (DP)2 receptor antagonist BAY-u 3405 in vivo increased EZH2 expression and reduced ZFP423 expression and adipocyte differentiation in CKO-CPC. Thus, cardiomyocyte STAT3 deficiency leads to age-related and sex-specific cardiac remodeling and failure in part due to sex-specific alterations in PGD2 secretion and subsequent epigenetic impairment of the differentiation potential of CPC. Causally involved is the impaired AR signaling in absence of STAT3, which reduces the expression of the PG-degrading enzyme HPGD.

Neuraminidase-1 promotes heart failure after ischemia/reperfusion injury by affecting cardiomyocytes and invading monocytes/macrophages.

Neuraminidase (NEU)1 forms a multienzyme complex with beta-galactosidase (ß-GAL) and protective-protein/cathepsin (PPC) A, which cleaves sialic-acids from cell surface glycoconjugates. We investigated the role of NEU1 in the myocardium after ischemia/reperfusion (I/R). Three days after inducing I/R, left ventricles (LV) of male mice (3 months-old) displayed upregulated neuraminidase activity and increased NEU1, ß-GAL and PPCA expression. Mice hypomorphic for neu1 (hNEU1) had less neuraminidase activity, fewer pro-inflammatory (Lin-CD11b+F4/80+Ly-6Chigh), and more anti-inflammatory macrophages (Lin-CD11b+F4/80+Ly-6Clow) 3 days after I/R, and less LV dysfunction 14 days after I/R. WT mice transplanted with hNEU1-bone marrow (BM) and hNEU1 mice with WT-BM showed significantly better LV function 14 days after I/R compared with WT mice with WT-BM. Mice with a cardiomyocyte-specific NEU1 overexpression displayed no difference in inflammation 3 days after I/R, but showed increased cardiomyocyte hypertrophy, reduced expression and mislocalization of Connexin-43 in gap junctions, and LV dysfunction despite a similar infarct scar size to WT mice 14 days after I/R. The upregulation of NEU1 after I/R contributes to heart failure by promoting inflammation in invading monocytes/macrophages, enhancing cardiomyocyte hypertrophy, and impairing gap junction function, suggesting that systemic NEU1 inhibition may reduce heart failure after I/R.

LEF-1 is crucial for neutrophil granulocytopoiesis and its expression is severely reduced in congenital neutropenia.

We demonstrate here that lymphoid enhancer-binding factor 1 (LEF-1) mediates the proliferation, survival and differentiation of granulocyte progenitor cells. We initially documented the importance of this transcription factor in the bone marrow of individuals with severe congenital neutropenia (CN) with a 'differentiation block' at the promyelocytic stage of myelopoiesis. LEF-1 expression was greatly reduced or even absent in CN arrested promyelocytes, resulting in defective expression of the LEF-1 target genes CCND1, MYC and BIRC5, encoding cyclin D1 (ref. 2), c-Myc and survivin, respectively. In contrast, healthy individuals showed highest LEF-1 expression in promyelocytes. Reconstitution of LEF-1 in early hematopoietic progenitors of two individuals with CN corrected the defective myelopoiesis and resulted in the differentiation of these progenitors into mature granulocytes. Repression of endogenous LEF-1 by specific short hairpin RNA inhibited proliferation and induced apoptosis of CD34(+) progenitors from healthy individuals and of cells from two myeloid lines (HL-60 and K562). C/EBPalpha, a key transcription factor in granulopoiesis, was directly regulated by LEF-1. These observations indicate that LEF-1 is an instructive factor regulating neutrophilic granulopoiesis whose absence plays a critical role in the defective maturation program of myeloid progenitors in individuals with CN.

NK-like homeodomain proteins activate NOTCH3-signaling in leukemic T-cells.

BACKGROUND: Homeodomain proteins control fundamental cellular processes in development and in cancer if deregulated. Three members of the NK-like subfamily of homeobox genes (NKLs), TLX1, TLX3 and NKX2-5, are implicated in T-cell acute lymphoblastic leukemia (T-ALL). They are activated by particular chromosomal aberrations. However, their precise function in leukemogenesis is still unclear. Here we screened further NKLs in 24 T-ALL cell lines and identified the common expression of MSX2. The subsequent aim of this study was to analyze the role of MSX2 in T-cell differentiation which may be disturbed by oncogenic NKLs. METHODS: Specific gene activity was examined by quantitative real-time PCR, and globally by expression profiling. Proteins were analyzed by western blot, immuno-cytology and immuno-precipitation. For overexpression studies cell lines were transduced by lentiviruses. RESULTS: Quantification of MSX2 mRNA in primary hematopoietic cells demonstrated higher levels in CD34+ stem cells as compared to peripheral blood cells and mature CD3+ T-cells. Furthermore, analysis of MSX2 expression levels in T-cell lines after treatment with core thymic factors confirmed their involvement in regulation. These results indicated that MSX2 represents an hematopoietic NKL family member which is downregulated during T-cell development and may functionally substituted by oncogenic NKLs. For functional analysis JURKAT cells were lentivirally transduced, overexpressing either MSX2 or oncogenic TLX1 and NKX2-5, respectively. These cells displayed transcriptional activation of NOTCH3-signaling, including NOTCH3 and HEY1 as analyzed by gene expression profiling and quantitative RT-PCR, and consistently attenuated sensitivity to gamma-secretase inhibitor as analyzed by MTT-assays. Furthermore, in addition to MSX2, both TLX1 and NKX2-5 proteins interacted with NOTCH-pathway repressors, SPEN/MINT/SHARP and TLE1/GRG1, representing a potential mechanism for (de)regulation. Finally, elevated expression of NOTCH3 and HEY1 was detected in primary TLX1/3 positive T-ALL cells corresponding to the cell line data. CONCLUSION: Identification and analysis of MSX2 in hematopoietic cells implicates a modulatory role via NOTCH3-signaling in early T-cell differentiation. Our data suggest that reduction of NOTCH3-signaling by physiological downregulation of MSX2 expression during T-cell development is abrogated by ectopic expression of oncogenic NKLs, substituting MSX2 function.

Lentivirus-mediated antagomir expression for specific inhibition of miRNA function.

Micro RNAs (miRNA) regulate gene expression by hybridization and recruitment of multi-protein complexes to complementary mRNA target sequences. miRNA function can transiently be antagonized by antagomirs-chemically modified oligonucleotides complementary to individual miRNAs. Here, we describe the induction of stable loss-of-function phenotypes for specific miRNAs by lentivirus-mediated antagomir expression. Lentivirally expressed antagomirs are transcribed from a H1-promoter located within the lentiviral 3'LTR and were directed against miRNAs encoded on the polycistronic miR17-92 transcript. Functional silencing of miR-18a, miR-19b and miR-20a by the corresponding antagomirs specifically relieves miRNA-mediated reporter gene repression. Inhibition of miRNA function correlates to reduction of 'miRNA' amplification by miRNA-specific quantitative RT-PCR. Furthermore, protein expression of E2F-1, a known miR-20 target, is enhanced by lentivirally expressed anti-miR-20 antagomirs in a dose-dependent manner, whereas over-expression of miR-20a reduces E2F-1 levels. Finally, combined over-expression of specific miRNAs and antagomirs reveals individual and complementary functions of miR-18a and miR-20a and demonstrates specific miRNA impact on cell proliferation in a cell culture model.

Optimized induction of mitochondrial apoptosis for chemotherapy-free treatment of BCR-ABL+acute lymphoblastic leukemia.

BCR-ABL+acute lymphoblastic leukemia (ALL) in adults has a poor prognosis with allogeneic stem cell transplantation (SCT) considered the best curative option for suitable patients. We here characterize the curative potential of BH3-mimetics differentially targeting mitochondrial BCL2-family members using a combination therapy approach with dexamethasone and tyrosine kinase inhibitors targeting BCR-ABL. In BCR-ABL + ALL BH3-mimetics act by redistribution of mitochondrial activator BIM, which is strongly required for cytotoxicity of the BCL2-specific BH3-mimetic ABT-199, tyrosine kinase inhibitors (TKIs) and dexamethasone. BIM expression is enhanced by dexamethasone and TKIs and both synergize with ABT-199 in BCR-ABL + ALL. Triple combinations with ABT-199, dexamethasone and TKIs efficiently attenuate leukemia progression both in tissue culture and in primary cell xenotransplantation models. Notably, the dasatinib-containing combination led to treatment- and leukemia-free long-term survival in a BCR-ABL + mouse model. Finally, response to BH3-mimetics can be predicted for individual patients in a clinically relevant setting. These data demonstrate curative targeted and chemotherapy-free pharmacotherapy for BCR-ABL + ALL in a preclinical model. Clinical evaluation, in particular for patients not suitable for allogeneic SCT, is warranted.

miR-125b regulates chemotaxis and survival of bone marrow derived granulocytes in vitro and in vivo.

The evolutionary conserved miR-125b is highly expressed in hematopoietic stem cells (HSC) enhancing self-renewal and survival. Accordingly, over-expression of miR-125b in HSC may induce myeloproliferative neoplasms and leukemia with long latency. During hematopoietic cell maturation miR-125b expression decreases, and the function of miR-125b in mature granulocytes is not yet known. We here use transplantation of miR-125b over-expressing HSC into syngeneic hosts to generate and analyse miR-125b over-expressing granulocytes. Under steady state conditions, miR-125b over-expression inhibits granulocytic chemotaxis and LPS- but not PMA- and TNFα- induced cell death. Inflammatory signals modulate the effects of miR-125b over-expression as demonstrated in a sterile peritonitis and a polymicrobial sepsis model. In particular, survival of mice with miR-125b over-expressing granulocytes is significantly reduced as compared to controls in the polymicrobial sepsis model. These data demonstrate inflammation dependent effects of miR-125b in granulocytes and may point to therapeutic intervention strategies in the future.

A positive feedback loop between IL-1ß, LPS and NEU1 may promote atherosclerosis by enhancing a pro-inflammatory state in monocytes and macrophages.

Inflammation plays an important role in atherosclerosis, a notion supported by the beneficial effects of the IL-1ß inhibitor canakinumab in the CANTOS trial. Sialic acids (Sias), components of the surface glycocalyx, regulate intercellular and intermolecular interactions. We investigated the expression of the Sia cleaving enzyme neuraminidase-1 (NEU1) in atherosclerotic plaques and its potential role in inflammatory processes. In isolated mononuclear blood cells from patients with myocardial infarction, NEU1 expression was increased compared to healthy controls. High expression of NEU1 in macrophages located on the intima layer, in calcified regions and the adventitia of the plaque was observed in human carotid arteries' atherectomies. IL-1ß and LPS induced NEU1 expression in THP-1 monocytic cells. Lentiviral NEU1-overexpression in THP-1-cells enhanced expression of CD80, TNF-α, IL-1ß, number of multinuclear cells, phagocytosis and chemotaxis indicative for M1 monocyte/macrophage polarization. CRISPR/Cas9-mediated knock-out of NEU1 in THP-1-cells did not affect differentiation of monocytes to macrophages but attenuated LPS- and IL-1ß -induced TNF-α and IL-1ß expression. SiRNA-mediated knock-down of NEU1 in M1-macrophages differentiated from primary human CD14+ monocytes reduced the expression of TNF-α and IL-1ß. Thus, in monocytes/macrophages, LPS, NEU1 and IL-1ß act in a positive feedback loop as enhancers of inflammation and may therefore promote atherosclerosis and plaque instability.

Comparison between molecularly defined and conventional therapeutics in a conditional BCR-ABL cell culture model.

Accumulating knowledge about the molecular mechanisms causing human diseases can support the development of targeted therapies such as imatinib, a BCR-ABL-specific tyrosine kinase inhibitor to treat chronic myeloid leukemia (CML). Here, we use lentivirus-mediated RNA interference (RNAi) targeting BCR-ABL and the downstream signaling molecules SHP2, STAT5, and Gab2 to compare the efficacy and specificity of molecularly defined therapeutics with that of conventional cytotoxic drugs (cytarabine, doxorubicin, etoposide) in a conditional BCR-ABL cell culture model. IC(50) values were determined for each drug in TonB cells cultured either with interleukin-3 (IL-3) or BCR-ABL, and molecularly defined therapies were studied using lentivirally expressed shRNAs. We demonstrate that conventional anti-leukemic drugs have small or no differential effects under different cell culture conditions, whereas both imatinib and specific RNAi significantly inhibit proliferation of TonB cells in the presence of BCR-ABL but not IL-3. To study molecularly defined combination therapy, we evaluated either imatinib in TonB cells with target-specific RNAi or we used lentiviral vectors to induce combinatorial RNAi through simultaneous expression of two shRNAs. These combination therapies result in increased efficacy without loss in specificity. Interestingly, combinatorial RNAi can specifically deplete TonB cell cultures in the presence of BCR-ABL, even without targeting the oncogene itself. This model provides a tool to evaluate potential therapeutic targets and to quantify efficacy and specificity preclinically of new combination therapies in BCR-ABL-positive cells.

NKL homeobox gene activities in hematopoietic stem cells, T-cell development and T-cell leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) cells represent developmentally arrested T-cell progenitors, subsets of which aberrantly express homeobox genes of the NKL subclass, including TLX1, TLX3, NKX2-1, NKX2-5, NKX3-1 and MSX1. Here, we analyzed the transcriptional landscape of all 48 members of the NKL homeobox gene subclass in CD34+ hematopoietic stem and progenitor cells (HSPCs) and during lymphopoiesis, identifying activities of nine particular genes. Four of these were expressed in HSPCs (HHEX, HLX1, NKX2-3 and NKX3-1) and three in common lymphoid progenitors (HHEX, HLX1 and MSX1). Interestingly, our data indicated downregulation of NKL homeobox gene transcripts in late progenitors and mature T-cells, a phenomenon which might explain the oncogenic impact of this group of genes in T-ALL. Using MSX1-expressing T-ALL cell lines as models, we showed that HHEX activates while HLX1, NKX2-3 and NKX3-1 repress MSX1 transcription, demonstrating the mutual regulation and differential activities of these homeobox genes. Analysis of a public T-ALL expression profiling data set comprising 117 patient samples identified 20 aberrantly activated members of the NKL subclass, extending the number of known NKL homeobox oncogene candidates. While 7/20 genes were also active during hematopoiesis, the remaining 13 showed ectopic expression. Finally, comparative analyses of T-ALL patient and cell line profiling data of NKL-positive and NKL-negative samples indicated absence of shared target genes but instead highlighted deregulation of apoptosis as common oncogenic effect. Taken together, we present a comprehensive survey of NKL homeobox genes in early hematopoiesis, T-cell development and T-ALL, showing that these genes generate an NKL-code for the diverse stages of lymphoid development which might be fundamental for regular differentiation.

Modulation of gene expression by lentiviral-mediated delivery of small interfering RNA.

RNA interference (RNAi) mediates sequence-specific posttranscriptional gene silencing triggered by double-stranded RNA. RNAi is an effective tool for functional genomics in C. elegans, whereas biochemical characteristics of RNAi hamper its use in mammalian cells. We here analyze kinetic and quantitative aspects of mammalian RNAi in different cell lines using novel lentiviral constructs with double H1-shRNA expression cassettes located in the U3 region of the LTR. Using enhanced green fluorescence protein (EGFP) as a target gene for RNAi and red fluorescence protein (RFP) as surrogate marker for intracellular siRNA expression, we show that long-term siRNA expression mediates stable RNAi. Furthermore, RNAi-induced gene silencing varies from minimal to complete loss-of-function phenotypes within homogeneous and between different cell populations. Interestingly, the extent of gene silencing correlates to lentiviral integrations as well as siRNA expression levels in target cells. Finally, we demonstrate functional gene silencing of a cytokine receptor gene in normal CD34+ hematopoietic progenitor cells. These data suggest that the use of suitable lentiviral constructs to quantify siRNA expression in living cells may allow analysis of loss-of-function phenotypes in a dose-dependent manner in a wide variety of target cells.

High-level transduction and gene expression in hematopoietic repopulating cells using a human immunodeficiency [correction of imunodeficiency] virus type 1-based lentiviral vector containing an internal spleen focus forming virus promoter.

Prolonged exposure of human hematopoietic stem cells (HSC) to growth factors for efficient transduction by murine oncoretroviral vectors has major detrimental effects on repopulating activity. In this study, we have used a vesicular stomatitis virus G envelope protein (VSV-G)-pseudotyped human immunodeficiency virus type 1 (HIV-1) lentiviral-based vector system to transduce cord blood (CB) CD34+ cells over a limited time period (< or =24 hours). Under these conditions, significant gene marking was observed in engrafted human lymphoid, myeloid, and progenitor cells in all transplanted Severe Combined Immunodeficient (SCID) mice. To enhance the level of gene expression in hematopoietic cells, we also generated a series of lentiviral vectors incorporating the spleen focus forming virus (SFFV) long terminal repeat (LTR) sequences, and the Woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). By including the central polypurine tract (cPPT) sequence of HIV-1 we were then able to achieve high levels of transduction (over 80%) and gene expression in vivo after a single exposure to viral supernatant. These results demonstrate that lentiviral vectors are highly effective for gene transfer to human HSC, and that SFFV regulatory sequences can be successfully incorporated to enhance the long-term expression of a transgene in primary human hematopoietic cells in vivo.

Inhibition of GM-CSF receptor function by stable RNA interference in a NOD/SCID mouse hematopoietic stem cell transplantation model.

RNA interference (RNAi) describes a highly conserved mechanism of sequence-specific posttranscriptional gene silencing triggered by double-stranded RNA (dsRNA). Whereas RNAi is applied to study gene function in different organisms and in variant cell types, little is known about RNAi in human hematopoietic stem and progenitor cells and their myeloid progeny. To address this issue, short hairpin RNAs (shRNA) were designed to target the common beta-chain of the human receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 (betaGMR). These receptors regulate proliferation, survival, differentiation, and functional activity of hematopoietic cells. In addition to markedly inhibiting mRNA and protein expression, anti-beta-GMR shRNAs were also found to inhibit receptor function in a cell culture model. Furthermore, lentiviral gene transfer of shRNA expression cassettes into primary normal CD34+ cells selectively inhibited colony formation of transduced progenitors when stimulated with GM-CSF/IL-3 but not when stimulated with cytokines that do not signal via beta-GMR. Finally, anti-beta-GMR shRNAs had no detectable effect on engraftment or lineage composition of lentivirally transduced human CD34+ cells transplanted into NOD/SCID mice. However, the growth defect of transduced colony-forming cells under stimulation with GM-CSF/IL-3 remains unchanged in bone marrow cells harvested from individual NOD/SCID mice 6 weeks after transplantation. These data indicate that lentiviral gene transfer of shRNA expression cassettes may be used to induce long-term RNAi in human hematopoietic stem and progenitor cells for functional genetics and potential therapeutic intervention.

BCR-ABL affects STAT5A and STAT5B differentially.

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors linking extracellular signals to target gene transcription. Hematopoietic cells express two highly conserved STAT5-isoforms (STAT5A/STAT5B), and STAT5 is directly activated by JAK2 downstream of several cytokine receptors and the oncogenic BCR-ABL tyrosine kinase. Using an IL-3-dependent cell line with inducible BCR-ABL-expression we compared STAT5-activation by IL-3 and BCR-ABL in a STAT5-isoform specific manner. RNAi targeting of STAT5B strongly inhibits BCR-ABL-dependent cell proliferation, and STAT5B but not STAT5A is essential for BCL-XL-expression in the presence of BCR-ABL. Although BCR-ABL induces STAT5-tyrosine phosphorylation independent of JAK2-kinase activity, BCR-ABL is less efficient in inducing active STAT5A:STAT5B-heterodimerization than IL-3, leaving constitutive STAT5A and STAT5B-homodimerization unaffected. In comparison to IL-3, nuclear accumulation of a STAT5A-eGFP fusion protein is reduced by BCR-ABL, and BCR-ABL tyrosine kinase activity induces STAT5A-eGFP translocation to the cell membrane and co-localization with the IL-3 receptor. Furthermore, BCR-ABL-dependent phosphorylation of Y682 in STAT5A was detected by mass-spectrometry. Finally, RNAi targeting STAT5B but not STAT5A sensitizes human BCR-ABL-positive cell lines to imatinib-treatment. These data demonstrate differences between IL-3 and BCR-ABL-mediated STAT5-activation and isoform-specific effects, indicating therapeutic options for isoform-specific STAT5-inhibition in BCR-ABL-positive leukemia.

Expression of the miR-17-92 polycistron in chronic myeloid leukemia (CML) CD34+ cells.

Aberrant micro RNA (miRNA) expression has been described in human malignancies including B-cell lymphomas. We here report BCR-ABL- and c-MYC-dependent regulation of miRNA expression in chronic myeloid leukemia (CML) using microarray analysis (miCHIP) and miRNA-specific quantitative real-time reverse transcriptase-polymerase chain reaction (miR-qRT-PCR). In 3 bcr-abl-positive cell lines, expression of miRNAs encoded within the polycistronic miR-17-92 cluster is specifically down-regulated (2- to 5-fold) by both imatinib treatment and anti-BCR-ABL RNA interference (RNAi). In addition, anti-c-MYC RNAi reduces miR-17-92 expression in K562 cells in which miRNAs can specifically repress reporter gene expression, as demonstrated by specific miRNA inhibition with antagomirs. Furthermore, lentivirus-mediated overexpression of polycistronic miRNAs in K562 cells confers increased proliferation, partial resistance against anti-c-MYC RNAi, and enhanced sensitivity to imatinib-induced cell death. Finally, we determined miR-17-92 expression in purified normal (n = 4), early chronic-phase (CP) (n = 24), and blast-crisis (BC) (n = 7) CML CD34(+) cells and found up-regulation of polycistronic pri-miRNA transcripts in CML and mature miRNAs in CP but not in BC CML. These data are in accordance with a BCR-ABL-c-MYC-miR-17-92 pathway that mediates enhanced miRNA expression in CP but not BC CML CD34(+) cells. Altered miRNA expression may contribute to the pathophysiology of the disease and may provide potential targets for therapeutic intervention.

Enhanced sensitivity to inhibition of SHP2, STAT5, and Gab2 expression in chronic myeloid leukemia (CML).

Although targeting the BCR-ABL tyrosine kinase activity by imatinib mesylate has rapidly become first-line therapy in chronic myeloid leukemia (CML), drug resistance suggests that combination therapy directed to a complementing target may significantly improve treatment results. To identify such potential targets, we used lentivirus-mediated RNA interference (RNAi) as a tool for functional genomics in cell lines as well as primary normal and CML CD34+ cells. In a conditional cell culture model, we demonstrate that RNAi-mediated reduction of SHP2, STAT5, and Gab2 protein expression inhibits BCR-ABL-dependent but not cytokine-dependent proliferation in a dose-dependent manner. Similarly, colony formation of purified primary CML but not of normal CD34+ colony-forming cells is specifically reduced by inhibition of SHP2, STAT5, and Gab2 expression, respectively. In addition, coexpression of both anti-BCR-ABL and anti-SHP2 shRNAs from a single lentiviral vector induces stronger inhibition of colony formation as compared to either shRNA alone. The data indicate that BCR-ABL expression may affect the function of normal signaling molecules. Targeting these molecules may harbor significant therapeutic potential for the treatment of patients with CML.

Specific inhibition of bcr-abl gene expression by small interfering RNA.

Small interfering RNAs (siRNAs) were designed to target the bcr-abl oncogene, which causes chronic myeloid leukemia (CML) and bcr-abl-positive acute lymphoblastic leukemia (ALL). Chemically synthesized anti-bcr-abl siRNAs were selected using reporter gene constructs and were found to reduce bcr-abl mRNA up to 87% in bcr-abl-positive cell lines and in primary cells from CML patients. This mRNA reduction was specific for bcr-abl because c-abl and c-bcr mRNA levels remained unaffected. Furthermore, protein expression of BCR-ABL and of laminA/C was reduced by specific siRNAs up to 80% in bcr-abl-positive and normal CD34(+) cells, respectively. Finally, anti-bcr-abl siRNA inhibited BCR-ABL-dependent, but not cytokine-dependent, proliferation in a bcr-abl-positive cell line. These data demonstrate that siRNA can specifically and efficiently interfere with the expression of an oncogenic fusion gene in hematopoietic cells.

Lentiviral gene transfer into peripheral blood-derived CD34+ NOD/SCID-repopulating cells.

This study reports a lentiviral gene transfer protocol for efficient transduction of adult human peripheral blood (PB)-derived CD34+ NOD/SCID-repopulating cells (SRCs) using vesicular stomatitis virus-G protein (VSV-G)-pseudotyped lentiviruses encoding for enhanced green fluorescence protein (eGFP). Lentiviral stocks were concentrated by anion exchange chromatography, and transduction was performed under serum-free conditions at a multiplicity of infection (MOI) between 3 and 50. Similar transduction efficiencies were achieved in the presence and absence of cytokines. Transduction of PB-derived CD34+ cells at a MOI of 3 resulted in gene transfer efficiencies into SRCs of 9.2% and 12.0% in the absence and presence of cytokines, respectively. Using improved lentiviral vectors, transduction frequency varied between 42.0% (MOI 10) and 36.0% (MOI 50) with multilineage transgene expression within SRC-derived myeloid and lymphoid cells. The protocol described can be adapted for clinical application of lentiviral gene transfer into PB-derived CD34+ cells from adult patients.