MicroRNA-29b induces global DNA hypomethylation and tumor suppressor gene reexpression in acute myeloid leukemia by targeting directly DNMT3A and 3B and indirectly DNMT1

Aberrant DNA hypermethylation contributes to myeloid leukemogenesis by silencing structurally normal genes involved in hematopoiesis. MicroRNAs (miRNAs) are noncoding RNAs that regulate gene expression by targeting protein-coding mRNAs. Recently, miRNAs have been shown to play a role as both targets and effectors in gene hypermethylation and silencing in malignant cells. In the current study, we showed that enforced expression of miR-29b in acute myeloid leukemia cells resulted in marked reduction of the expression of DNA methyltransferases DNMT1, DNMT3A, and DNMT3B at both RNA and protein levels. This in turn led to decrease in global DNA methylation and reexpression of p15(INK4b) and ESR1 via promoter DNA hypomethylation. Although down-regulation of DNMT3A and DNMT3B was the result of a direct interaction of miR-29b with the 3' untranslated regions of these genes, no predicted miR-29b interaction sites were found in the DNMT1 3' untranslated regions. Further experiments revealed that miR-29b down-regulates DNMT1 indirectly by targeting Sp1, a transactivator of the DNMT1 gene. Altogether, these data provide novel functional links between miRNAs and aberrant DNA hypermethylation in acute myeloid leukemia and suggest a potentially therapeutic use of synthetic miR-29b oligonucleotides as effective hypomethylating compounds.

Inhibition of KSP by ARRY-520 induces cell cycle block and cell death via the mitochondrial pathway in AML cells

Kinesin spindle protein (KSP), a microtubule-associated motor protein essential for cell cycle progression, is overexpressed in many cancers and is a potential anti-tumor target. We found that inhibition of KSP by a selective inhibitor, ARRY-520, blocked cell cycle progression, leading to apoptosis in acute myeloid leukemia cell lines that express high levels of KSP. Knockdown of p53, overexpression of XIAP and mutation in caspase-8 did not significantly affect sensitivity to ARRY-520, suggesting that the response is independent of p53, XIAP and the extrinsic apoptotic pathway. Although ARRY-520 induced mitotic arrest in both HL-60 and Bcl-2-overexpressing HL-60Bcl-2 cells, cell death was blunted in HL-60Bcl-2 cells, suggesting that the apoptotic program is executed through the mitochondrial pathway. Accordingly, inhibition of Bcl-2 by ABT-737 was synergistic with ARRY-520 in HL-60Bcl-2 cells. Furthermore, ARRY-520 increased Bim protein levels prior to caspase activation in HL-60 cells. ARRY-520 significantly inhibited tumor growth of xenografts in SCID mice and inhibited AML blast but not normal colony formation, supporting a critical role for KSP in proliferation of leukemic progenitor cells. These results demonstrate that ARRY-520 potently induces cell cycle block and subsequent death in leukemic cells via the mitochondrial pathway and has the potential to eradicate AML progenitor cells.

Phase I/II study of idarubicin (Ida), high-dose ara-C, and sorafenib (S) in patients (pts) younger than 65 years with acute myeloid leukemia (AML)

7018

Background: S is an oral multi-kinase inhibitor with activity against the Raf/ERK/MEK pathway and FLT3. It selectively induces apoptosis in FLT3-mutant human AML cell lines at nM concentrations. Methods: Objectives of this study are to determine the tolerability and efficacy of combination of S with chemotherapy. Ara-C 1.5 g/m2 over 24 hrs daily x 4 (x 3 for pts over 60) and Ida 12 mg/m2 daily x 3 are administered with S. In the phase I part, pts with relapsed AML were treated with escalating doses of S (400 mg qod, 400 mg daily, 400 mg bid) for 7 days during induction, and 400 mg bid was established as safe. Pts achieving CR receive up to 5 courses of consolidation with Ida 8 mg/m2 daily x 2 and Ara-C 0.75 g/m2 daily x 3 in addition to S 400 mg bid for up to 28 days per cycle repeated every 4 to 6 weeks. Maintenance is with S 400 mg bid for up to a year. Results: 10 pts (median age 34, range 21–58) with relapsed AML (median prior therapy 2, range 1–6) were treated in the phase I . 7 were FLT3-ITD positive. 4 achieved CR; 6 failed. In the phase II part, 45 pts (12 with FLT3-ITD and 2 with FLT3-TKD) were treated. Median age is 53 (range 18 - 65). Cytogenetics were diploid in 19, +8 in 5, -5/-7 in 5, 11q23 in 2, other in 14. Median presentation WBC was 4.9 x 109/L (range 0.6 - 122.7 x 109/L). 8 pts were FLT3-ITD+/NPM1-. 40 pts are evaluable for response and 85% achieved CR (n = 30) or CRp (n = 4) (13 of 14 FLT3 mutated pts); 5 pts are too early (1 FLT3 mutated). Most frequent grade 3 and higher related adverse events: hyperbilirubinemia (5), rash and hand-foot syndrome (3), raised transaminases (2), diarrhea (2), hypertension (2). With a median f/u of 5.4 mo (range, 0.5 - 11.3), the probability of survival at 6 mo is 81.6%. 5 pts have relapsed; median CR duration has not been reached, (range; 0.2+ - 10.6+ mo). Among pts with FLT3 mutation, 4 have relapsed and 9 remain in CR. Plasma inhibitory assay was performed using day 7 samples from 10 pts; mutant FLT3 was suppressed by all with 5-fold more potent suppression against mutant versus wild-type FLT3. Conclusions: S can be safely combined with IA; it has a high CR rate in frontline therapy of younger pts with AML, in particular those with FLT3 mutations. Correlative studies confirm potent activity of S against FLT3 signaling.

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Mesenchymal stem cell transition to tumor-associated fibroblasts contributes to fibrovascular network expansion and tumor progression

Background

Tumor associated fibroblasts (TAF), are essential for tumor progression providing both a functional and structural supportive environment. TAF, known as activated fibroblasts, have an established biological impact on tumorigenesis as matrix synthesizing or matrix degrading cells, contractile cells, and even blood vessel associated cells. The production of growth factors, cytokines, chemokines, matrix-degrading enzymes, and immunomodulatory mechanisms by these cells augment tumor progression by providing a suitable environment. There are several suggested origins of the TAF including tissue-resident, circulating, and epithelial-to-mesenchymal-transitioned cells.

Methodology/Principal Findings

We provide evidence that TAF are derived from mesenchymal stem cells (MSC) that acquire a TAF phenotype following exposure to or systemic recruitment into adenocarcinoma xenograft models including breast, pancreatic, and ovarian. We define the MSC derived TAF in a xenograft ovarian carcinoma model by the immunohistochemical presence of 1) fibroblast specific protein and fibroblast activated protein; 2) markers phenotypically associated with aggressiveness, including tenascin-c, thrombospondin-1, and stromelysin-1; 3) production of pro-tumorigenic growth factors including hepatocyte growth factor, epidermal growth factor, and interleukin-6; and 4) factors indicative of vascularization, including alpha-smooth muscle actin, desmin, and vascular endothelial growth factor. We demonstrate that under long-term tumor conditioning in vitro, MSC express TAF–like proteins. Additionally, human MSC but not murine MSC stimulated tumor growth primarily through the paracrine production of secreted IL6.

Conclusions/Significance

Our results suggest the dependence of in vitro Skov-3 tumor cell proliferation is due to the presence of tumor-stimulated MSC secreted IL6. The subsequent TAF phenotype arises from the MSC which ultimately promotes tumor growth through the contribution of microvascularization, stromal networks, and the production of tumor-stimulating paracrine factors.

Mitotic deregulation by survivin in ErbB2-overexpressing breast cancer cells contributes to Taxol resistance

PURPOSE

Taxol resistance remains a major obstacle to improve the benefit of breast cancer patients. Here, we studied whether overexpression of ErbB2 may lead to mitotic deregulation in breast cancer cells via up-regulation of survivin that confers Taxol resistance.

EXPERIMENTAL DESIGN

ErbB2-overexpressing and ErbB2-low-expressing breast cancer cell lines were used to compare their mitotic exit rate, survivin expression level, and apoptosis level in response to Taxol. Survivin was then down-regulated by antisense oligonucleotides to evaluate its contribution to mitotic exit and Taxol resistance in ErbB2-overexpressing breast cancer cells. At last, specific PI3K/Akt and Src inhibitors were used to investigate the involvement of these two pathways in ErbB2-mediated survivin up-regulation and Taxol resistance.

RESULTS

We found that ErbB2-overexpressing cells expressed higher levels of survivin in multiple breast cancer cell lines and patient samples. ErbB2-overexpressing cells exited M phase faster than ErbB2-low-expressing cells, which correlated with the increased resistance to Taxol-induced apoptosis. Down-regulation of survivin by antisense oligonucleotide delayed mitotic exit of ErbB2-overexpressing cells and also sensitized ErbB2-overexpressing cells to Taxol-induced apoptosis. Moreover, ErbB2 up-regulated survivin at translational level and PI3K/Akt and Src activation are involved. In addition, combination treatment of Taxol with PI3K/Akt and Src inhibitor led to increased apoptosis in ErbB2-overexpressing breast cancer cells than single treatment.

CONCLUSIONS

Survivin up-regulation by ErbB2 is a critical event in ErbB2-mediated faster mitotic exit and contributes to Taxol resistance.

Cyclin-dependent kinase 1 inhibitor RO-3306 enhances p53-mediated Bax activation and mitochondrial apoptosis in AML

Cyclin-dependent kinase (CDK) 1 and the murine double minute 2 homolog (MDM2)-p53 interaction are potential therapeutic targets in cancer, and their inhibition has been reported to be more proapoptotic in malignant cells compared to normal cells. We investigated the effect of CDK1 inhibition on p53 signaling after simultaneous dual blockade using the CDK1 inhibitor RO-3306 and the MDM2 inhibitor Nutlin-3 in AML. Treatment of growing AML cells with RO-3306 induced G2/M-phase cell cycle arrest and apoptosis in a dose- and time-dependent manner. We found that RO-3306 acts cooperatively with Nutlin-3 to induce mitochondrial apoptosis in a cell cycle-independent fashion. RO-3306 downregulated expression of the antiapoptotic proteins Bcl-2 and survivin and blocked p53-mediated induction of p21 and MDM2. CDK1 siRNA experiments showed that reduced CDK1 expression affects p53-induced p21 transactivation. We suggest that RO-3306 actively enhances downstream p53 signaling to promote apoptosis and that a combination strategy aimed at both inhibiting CDK1 and activating p53 signaling is potentially effective in AML, where TP53 mutations are rare and downstream p53 signaling is intact.

Mitochondrial uncoupling and the Warburg effect: molecular basis for the reprogramming of cancer cell metabolism

The precise mitochondrial alterations that underlie the increased dependence of cancer cells on aerobic glycolysis for energy generation have remained a mystery. Recent evidence suggests that mitochondrial uncoupling-the abrogation of ATP synthesis in response to mitochondrial membrane potential-promotes the Warburg effect in leukemia cells, and may contribute to chemoresistance. Intriguingly, leukemia cells cultured on bone marrow-derived stromal feeder layers are more resistant to chemotherapy, increase the expression of uncoupling protein 2, and decrease the entry of pyruvate into the Krebs cycle-without compromising the consumption of oxygen, suggesting a shift to the oxidation of nonglucose carbon sources to maintain mitochondrial integrity and function. Because fatty acid oxidation has been linked to chemoresistance and mitochondrial uncoupling, it is tempting to speculate that Warburg's observations may indeed be the result of the preferential oxidation of fatty acids by cancer cell mitochondria. Therefore, targeting fatty acid oxidation or anaplerotic pathways that support fatty acid oxidation may provide additional therapeutic tools for the treatment of hematopoietic malignancies.

Therapeutic targeting of microenvironmental interactions in leukemia: mechanisms and approaches

In hematological malignancies, there are dynamic interactions between leukemic cells and cells of the bone marrow microenvironment. Specific niches within the bone marrow microenvironment provide a sanctuary for subpopulations of leukemic cells to evade chemotherapy-induced death and allow acquisition of a drug-resistant phenotype. This review focuses on molecular and cellular biology of the normal hematopoietic stem cell and the leukemia stem cell niche, and of the molecular pathways critical for microenvironment/leukemia interactions. The key emerging therapeutic targets include chemokine receptors (CXCR4), adhesion molecules (VLA4 and CD44), and hypoxia-related proteins HIF-1alpha and VEGF. Finally, the genetic and epigenetic abnormalities of leukemia-associated stroma will be discussed. This complex interplay provides a rationale for appropriately tailored molecular therapies targeting not only leukemic cells but also their microenvironment to ensure improved outcomes in leukemia.

Functional proteomic profiling of AML predicts response and survival

Because protein function regulates the phenotypic characteristics of cancer, a functional proteomic classification system could provide important information for pathogenesis and prognosis. With the goal of ultimately developing a proteomic-based classification of acute myeloid leukemia (AML), we assayed leukemia-enriched cells from 256 newly diagnosed AML patients, for 51 total and phosphoproteins from apoptosis, cell-cycle, and signal-transduction pathways, using reverse-phase protein arrays. Expression in matched blood and marrow samples were similar for 44 proteins; another 7 had small fold changes (8%-55%), suggesting that functional proteomics of leukemia-enriched cells in the marrow and periphery are similar. Protein expression patterns were independent of clinical characteristics. However, 24 proteins were significantly different between French-American-British subtypes, defining distinct signatures for each. Expression signatures for AML with cytogenetic abnormalities involving -5 or -7 were similar suggesting mechanistic commonalities. Distinct expression patterns for FMS-like tyrosine kinase 3-internal tandem duplication were also identified. Principal component analysis defined 7 protein signature groups, with prognostic information distinct from cytogenetics that correlated with remission attainment, relapse, and overall survival. In conclusion, protein expression profiling patterns in AML correlate with known morphologic features, cytogenetics, and outcome. Confirmation in independent studies may also provide pathophysiologic insights facilitating triage of patients to emerging targeted therapies.

A phase I study of the pan bcl-2 family inhibitor obatoclax mesylate in patients with advanced hematologic malignancies

PURPOSE

The outcome of patients with refractory leukemia and myelodysplasia is poor, and new therapies are needed. The antiapoptotic proteins of the Bcl-2 family are overexpressed in these malignancies and are potential therapeutic targets. Therefore, we conducted a phase I clinical trial of the small-molecule pan-Bcl-2 inhibitor, obatoclax mesylate, in patients with refractory leukemia and myelodysplasia to assess its safety and define its optimal dose.

EXPERIMENTAL DESIGN

Forty-four patients with refractory leukemia or myelodysplasia were treated with obatoclax mesylate by continuous intravenous infusion at increasing doses and frequencies.

RESULTS

A total of 306 infusions of obatoclax mesylate were administered with a median of 5 infusions per patient. The study drug was well tolerated up to the highest dose planned without dose-limiting toxicity. Grade 1/2 central nervous system symptoms were the most common adverse events attributable to the study drug. One patient with acute myeloid leukemia with mixed lineage leukemia t(9;11) rearrangement achieved a complete remission, which lasted 8 months. Three of 14 patients with myelodysplasia showed hematologic improvement with RBC or platelet transfusion independence.

CONCLUSIONS

Obatoclax mesylate is well tolerated and these results support its further investigation in patients with leukemia and myelodysplasia.

Radiosynoviorthesis (RSO): influencing factors and therapy monitoring

OBJECTIVE

To evaluate the effectiveness of radiosynoviorthesis (RSO) in relation to joint type and underlying disease by both self-assessment of patients and scintigraphic assessment to determine conditions under which RSO might be preferable to the sole intra-articular corticoid injection.

METHODS

Radiosynoviorthesis was performed on 136 patients for 424 joints [242 small, 130 medium-sized, and 52 large joints; 313 with rheumatoid arthritis (RA) and 111 with osteoarthritis (OA)]. The success of RSO was evaluated after 12 months by patients' estimation, and in 35 patients for 157 joints additionally by two-phase bone scintigraphy. The relative change in the scintigraphic uptake was compared with the patients' estimation.

RESULTS

The subjectively estimated success rates for the small, medium-sized, and large joints were 89% (215/242), 86% (112/130), and 79% (41/52), and for RA and OA 89% (280/313) and 79% (88/111), respectively. The scintigraphically determined response rates for small and medium-sized joints were 81% (86/106) and 69% (35/51), respectively. There was a mismatch between patients' assessment and scintigraphic assessments in 18% (28/157) with 6 false-negative and 22 false-positive estimations using scintigraphy as the standard of reference.

CONCLUSIONS

The success of RSO is higher in patients with RA than in patients with OA. For the finger, ankle, and wrist joints in RA, RSO is so promising that we would like to advocate its preference over the sole intraarticular corticoid injection. Perfusion bone scintigraphy can be used for therapy monitoring and earlier switching to RSO by showing that other therapies have failed.

Ceramide promotes apoptosis in chronic myelogenous leukemia-derived K562 cells by a mechanism involving caspase-8 and JNK

Ceramide is a sphingolipid that activates stress kinases such as p38 and c-JUN N-Terminal Kinase (JNK). Though Chronic Myelogenous Leukemia (CML) derived K562 cells resist killing by short chain C2-ceramide, we report here that longer chain C6-ceramide promotes apoptosis in these cells. C6-ceramide induces cleavage of Caspase-8 and Caspase-9, but only Caspase-8 is required for apoptosis. The sphingolipid killed CML derived KBM5 cells and, to a lesser extent, imatinib-resistant KBM5-STI cells suggesting that BCR-ABL can not completely block C6-ceramide-induced apoptosis but the kinase may regulate the process. BCR-ABL is known to suppress Protein Phosphatase 2A (PP2A) in CML cells. While C6-ceramide can activate PP2A in acute leukemia cells, the sphingolipid did not activate the phosphatase in K562 cells. C6-ceramide did not activate p38 kinase but did promote JNK activation and phosphorylation of JUN. Inhibition of JNK by pharmacological agent protected K562 cells from C6-ceramide suggesting that JNK plays an essential role in C6-ceramide mediated apoptosis. Furthermore, the sphingolipid promoted MCL-1 phosphorylation by a mechanism that, at least in part, involves JNK. The findings presented here suggest that Caspase-8, JNK, and perhaps MCL-1 may play important roles in regulating cell death and may represent new targets for therapeutic strategies for CML.

The dual PI3 kinase/mTOR inhibitor PI-103 prevents p53 induction by Mdm2 inhibition but enhances p53-mediated mitochondrial apoptosis in p53 wild-type AML

Activation of the phosphatidylinositol-3 kinase/Akt/mammalian target of the rapamycin (PI3K/Akt/mTOR) pathway and inactivation of wild-type p53 by murine double minute 2 homologue (Mdm2) overexpression are frequent molecular events in acute myeloid leukemia (AML). We investigated the interaction of PI3K/Akt/mTOR and p53 pathways after their simultaneous blockade using the dual PI3K/mTOR inhibitor PI-103 and the Mdm2 inhibitor Nutlin-3. We found that PI-103, which itself has modest apoptogenic activity, acts synergistically with Nutlin-3 to induce apoptosis in a wild-type p53-dependent fashion. PI-103 synergized with Nutlin-3 to induce Bax conformational change and caspase-3 activation, despite its inhibitory effect on p53 induction. The PI-103/Nutlin-3 combination caused profound dephosphorylation of 4E-BP1 and decreased expression of many proteins including Mdm2, p21, Noxa, Bcl-2 and survivin, which can affect mitochondrial stability. We suggest that PI-103 actively enhances downstream p53 signaling and that a combination strategy aimed at inhibiting PI3K/Akt/mTOR signaling and activating p53 signaling is potentially effective in AML, where TP53 mutations are rare and downstream p53 signaling is intact.

Inhibition of mitochondrial metabolism by methyl-2-cyano-3,12-dioxooleana-1,9-diene-28-oate induces apoptotic or autophagic cell death in chronic myeloid leukemia cells

The initial success of the first synthetic bcr-abl kinase inhibitor imatinib has been dampened by the emergence of imatinib-resistant disease in blast crisis chronic myeloid leukemia. Here, we report that the novel triterpenoid methyl-2-cyano-3,12-dioxooleana-1,9-diene-28-oate (CDDO-Me) potently induced cytotoxicity in imatinib-resistant KBM5 cells expressing the T315I mutation of bcr-abl (24-h EC50, 540 nmol/L). In long-term culture, CDDO-Me abrogated the growth of human parental KBM5 and KBM5-STI cells with 96-h IC50 of 205 and 221 nmol/L, respectively. In addition, CDDO-Me rapidly decreased the viability of murine lymphoid Ba/F3 cells expressing wild-type p210 as well as the imatinib-resistant E255K and T315I mutations of bcr-abl. The low-dose effects of CDDO-Me are associated with inhibition of mitochondrial oxygen consumption, whereas the cytotoxic effects appear to be mediated by a rapid and selective depletion of mitochondrial glutathione that accompanies the increased generation of reactive oxygen species and mitochondrial dysfunction. Interestingly, the mitochondriotoxic effects of CDDO-Me are followed by the rapid autophagocytosis of intracellular organelles or the externalization of phosphatidylserine in different cell types. We conclude that alterations in mitochondrial function by CDDO-Me can result in autophagy or apoptosis of chronic myeloid leukemia cells regardless of the mutational status of bcr-abl. CDDO-Me is in clinical trials and shows signs of clinical activity, with minimal side effects and complete lack of cardiotoxicity. Studies in leukemias are in preparation.

Bcl-B expression in human epithelial and nonepithelial malignancies

PURPOSE

Apoptosis plays an important role in neoplastic processes. Bcl-B is an antiapoptotic Bcl-2 family member, which is known to change its phenotype upon binding to Nur77/TR3. The expression pattern of this protein in human malignancies has not been reported.

EXPERIMENTAL DESIGN

We investigated Bcl-B expression in normal human tissues and several types of human epithelial and nonepithelial malignancy by immunohistochemistry, correlating results with tumor stage, histologic grade, and patient survival.

RESULTS

Bcl-B protein was strongly expressed in all normal plasma cells but found in only 18% of multiple myelomas (n = 133). Bcl-B immunostaining was also present in normal germinal center centroblasts and centrocytes and in approximately half of diffuse large B-cell lymphoma (n = 48) specimens, whereas follicular lymphomas (n = 57) did not contain Bcl-B. In breast (n = 119), prostate (n = 66), gastric (n = 180), and colorectal (n = 106) adenocarcinomas, as well as in non-small cell lung cancers (n = 82), tumor-specific overexpression of Bcl-B was observed. Bcl-B expression was associated with variables of poor prognosis, such as high tumor grade in breast cancer (P = 0.009), microsatellite stability (P = 0.0002), and left-sided anatomic location (P = 0.02) of colorectal cancers, as well as with greater incidence of death from prostate cancer (P = 0.005) and shorter survival of patients with small cell lung cancer (P = 0.009). Conversely, although overexpressed in many gastric cancers, Bcl-B tended to correlate with better outcome (P = 0.01) and more differentiated tumor histology (P < 0.0001).

CONCLUSIONS

Tumor-specific alterations in Bcl-B expression may define subsets of nonepithelial and epithelial neoplasms with distinct clinical behaviors.

The warburg effect in leukemia-stroma cocultures is mediated by mitochondrial uncoupling associated with uncoupling protein 2 activation

In 1956, Otto Warburg proposed that the origin of cancer cells was closely linked to a permanent respiratory defect that bypassed the Pasteur effect (i.e., the inhibition of anaerobic fermentation by oxygen). Since then, permanent defects in oxygen consumption that could explain the dependence of cancer cells on aerobic glycolysis have not been identified. Here, we show that under normoxic conditions exposure of leukemia cells to bone marrow-derived mesenchymal stromal cells (MSC) promotes accumulation of lactate in the culture medium and reduces mitochondrial membrane potential (DeltaPsiM) in both cell types. Notably, the consumption of glucose was not altered in cocultures, suggesting that the accumulation of lactate was the result of reduced pyruvate metabolism. Interestingly, the decrease in DeltaPsiM was mediated by mitochondrial uncoupling in leukemia cells and was accompanied by increased expression of uncoupling protein 2 (UCP2). HL60 cells fail to increase UCP2 expression, are not uncoupled after coculture, and do not exhibit increased aerobic glycolysis, whereas small interfering RNA-mediated suppression of UCP2 in OCI-AML3 cells reversed mitochondrial uncoupling and aerobic glycolysis elicited by MSC. Taken together, these data suggest that microenvironment activation of highly conserved mammalian UCPs may facilitate the Warburg effect in the absence of permanent respiratory impairment.

HOX expression patterns identify a common signature for favorable AML

Deregulated HOX expression, by chromosomal translocations and myeloid-lymphoid leukemia (MLL) rearrangements, is causal in some types of leukemia. Using real-time reverse transcription-PCR, we examined the expression of 43 clustered HOX, polycomb, MLL and FLT3 genes in 119 newly diagnosed adult acute myeloid leukemias (AMLs) selected from all major cytogenetic groups. Downregulated HOX expression was a consistent feature of favorable AMLs and, among these cases, inv(16) cases had a distinct expression profile. Using a 17-gene predictor in 44 additional samples, we observed a 94.7% specificity for classifying favorable vs intermediate/unfavorable cytogenetic groups. Among other AMLs, HOX overexpression was associated with nucleophosmin (NPM) mutations and we also identified a phenotypically similar subset with wt-NPM. In many unfavorable and other intermediate cytogenetic AMLs, HOX levels resembled those in normal CD34+ cells, except that the homogeneity characteristic of normal samples was not present. We also observed that HOXA9 levels were significantly inversely correlated with survival and that BMI-1 was overexpressed in cases with 11q23 rearrangements, suggesting that p19(ARF) suppression may be involved in MLL-associated leukemia. These results underscore the close relationship between HOX expression patterns and certain forms of AML and emphasize the need to determine whether these differences play a role in the disease process.

Mechanisms of antileukemic activity of the novel Bcl-2 homology domain-3 mimetic GX15-070 (obatoclax)

In this study, we investigated the mechanism of apoptosis induction of obatoclax (GX15-070), a novel Bcl-2 homology domain-3 (BH3) mimetic, in acute myeloid leukemia (AML) cell lines and primary AML samples. Obatoclax inhibited cell growth of HL-60, U937, OCI-AML3, and KG-1 cell lines. Apoptosis induction contributed to the observed antiproliferative effects at concentrations of this agent that mirror its affinity for antiapoptotic Bcl-2 proteins. We show that obatoclax can promote the release of cytochrome c from isolated leukemia cell mitochondria and that apoptosis induced by this agent is preceded by the release of Bak from Mcl-1, liberation of Bim from both Bcl-2 and Mcl-1, and the formation of an active Bak/Bax complex. Notably, apoptosis was diminished, but not fully prevented, in the absence of Bak/Bax or Bim, suggesting that obatoclax has additional targets that contribute to its cytotoxicity. At growth inhibitory doses that did not induce apoptosis or decrease viability, obatoclax induced an S-G(2) cell-cycle block. Obatoclax induced apoptosis in AML CD34+ progenitor cells with an average IC(50) of 3.59 +/- 1.23 micromol/L although clonogenicity was inhibited at concentrations of 75 to 100 nmol/L. Obatoclax synergized with the novel BH3 mimetic ABT-737 to induce apoptosis in OCI-AML3 cells and synergistically induced apoptosis in combination with AraC in leukemic cell lines and in primary AML samples. In conclusion, we show that obatoclax potently induces apoptosis and decreases leukemia cell proliferation and may be used in a novel therapeutic strategy for AML alone and in combination with other targeted agents and chemotherapeutics.

MicroRNAs and noncoding RNAs in hematological malignancies: molecular, clinical and therapeutic implications

MicroRNAs (miRNAs) are a family of 19-24 nucleotide noncoding RNAs (ncRNAs) with posttranscriptional regulatory functions. Increasing evidences from the literature show that miRNAs play a pivotal role in human tumorigenesis. Many studies have addressed the role of miRNAs in normal hematopoiesis, giving an interpretative key to the aberrancies of expression observed in human hematological malignancies. Moreover, the recent demonstration that other ncRNAs, the ultraconserved genes (UCGs) or transcribed ultraconserved regions (T-UCRs), are involved in human cancerogenesis, suggests that the wider family of ncRNAs (including both miRNAs and UCGs) could contribute to the development of the malignant phenotype. Here we review the main studies investigating the role of miRNAs and UCRs in both normal hemopoiesis and hematological malignancies, and identify the molecular, clinical and therapeutic implications of these recent findings.

TGF-beta receptor kinase inhibitor LY2109761 reverses the anti-apoptotic effects of TGF-beta1 in myelo-monocytic leukaemic cells co-cultured with stromal cells

Transforming growth factor beta1 (TGF-beta1) is an essential regulator of cell proliferation, survival and apoptosis, depending on the cellular context. TGF-beta1 is also known to affect cell-to-cell interactions between tumour cells and stromal cells. We investigated the role of TGF-beta1 in the survival of myelo-monocytic leukaemia cell lines co-cultured with bone marrow (BM)-derived mesenchymal stem cells (MSC). Treatment with recombinant human (rh)TGF-beta1 inhibited spontaneous and cytarabine-induced apoptosis in U937 cells, most prominently in U937 cells directly attached to MSCs. Conversely, the pro-survival effects of TGF-beta1 were inhibited by LY2109761 or TGF-beta1 neutralizing antibody. rhTGF-beta1 increased pro-survival phosphorylation of Akt, which was inhibited by LY2109761. The combination of rhTGF-beta1 and MSC co-culture induced significant upregulation of C/EBPbeta gene (CEBPB) and protein expression along with increased C/EBPbeta liver-enriched activating protein: liver-enriched inhibitory protein ratio, suggesting the novel role of C/EBPbeta in TGF-beta1-mediated U937 cell survival in the context of stromal cell support. In summary, these results indicate that TGF-beta1 produced by BM stromal cells promotes the survival and chemoresistance of leukaemia cells under the direct cell-to-cell interactions. The blockade of TGF-beta signalling by LY2109761, which effectively inhibited the pro-survival signalling, may enhance the efficacy of chemotherapy against myelo-monocytic leukaemic cells in the BM microenvironment.