MicroRNA-9 plays a role in interleukin-10-mediated expression of E-cadherin in acute myelogenous leukemia cells.

We previously showed that the CD82/signal transducer and activator of transcription/interleukin-10 (IL-10) axis is activated in CD34+ /CD38- AML cells that favor the bone marrow microenvironment. The present study explored the novel biological function of IL-10 in regulation of expression of adhesion molecules in AML cells and found that exposing AML cells to IL-10 induced expression of E-cadherin, but not other adhesion molecules, including VLA4, CD29, and LFA1. Downregulation of E-cadherin with an siRNA suppressed the adhesion of leukemia cells to bone marrow-derived mesenchymal stem cells and enhanced the anti-leukemia effect of cytarabine. A microRNA (miRNA) database search identified an miR-9 as a candidate miRNA binding onto the 3'-UTR of E-cadherin and regulating its expression. Notably, treatment of leukemia cells with IL-10 decreased miR-9 expression through hypermethylation of the miR-9 CpG islands. In addition, downregulation of DNA methyltransferase 3A by siRNAs decreased E-cadherin expression in parallel with an increase in levels of miR-9 in leukemia cells. Notably, short hairpin RNA-mediated IL-10 downregulation impaired engraftment of human AML cells and enhanced the anti-leukemia effect of cytarabine in conjunction with miR-9 upregulation and E-cadherin downregulation in a human AML xenograft model. Taken together, the IL-10/E-cadherin axis may be a promising therapeutic target for treating AML.

The Fifth Epidermal Growth Factor-like Region of Thrombomodulin Alleviates Murine Graft-versus-Host Disease in a G-Protein Coupled Receptor 15 Dependent Manner.

Thrombomodulin (TM) exerts anti-inflammatory functions. We previously found that recombinant human soluble TM alleviated murine graft-versus-host disease (GVHD). Nevertheless, it is unclear how TM mediates its anti-inflammatory functions in GVHD. Here, we identified G-protein coupled receptor 15 (GPR15) expressed on T cells as a receptor/sensor of TM. The fifth region of epidermal growth factor-like domain of TM (TME5) bound GPR15 in vitro. TME5 prolonged survival of mice undergoing acute GVHD after allogeneic hematopoietic stem cell transplantation (allo-HSCT). TME5 increased regulatory T cells (Tregs) but decreased Th 1 proportions in targeted organs. TME5 suppressed allo-reaction in vitro in association with an increase in the number of induced Tregs. However, the anti-inflammatory function of TME5 was abolished when GPR15 knockout T cells were used as donor T cells. We further found that TME5 suppressed production of IL-6 in T cells, which probably facilitated differentiation of Tregs. Moreover, TME5 reduced activation of bone marrow-derived dendritic cells (BMDCs) and hampered function of BMDCs in inducing allo-reaction in vivo and in vitro. Our findings suggested that inducing Tregs as well as blocking activation of DCs in vivo by using TME5 is a potential therapeutic option for preventing GVHD in allo-HSCT.

Bcr-Abl activates AURKA and AURKB in chronic myeloid leukemia cells via AKT signaling.

This study explored molecular mechanisms by which Bcr-Abl induced expression of Aurora kinase A and B (AURKA and AURKB) in chronic myeloid leukemia cells. Lentiviral transduction of Bcr-Abl into either Ba/F3 or CD34(+) hematopoietic stem/progenitor cells potently increased levels of AURKA and AURKB in association with phosphorylation of AKT and stimulated their proliferation. Bcr-Abl-mediated expression of AURKA and AURKB were decreased in CD34(+) HSPCs when AKT was inactivated by an shRNA against AKT, suggesting that Bcr-Abl induced expression of AURKA and AURKB via AKT signaling. MLN8237, an inhibitor of AURKA, significantly inhibited the proliferation of freshly isolated CD34(+) CML cells in a dose-dependent manner as measured by colony forming assay. Importantly, inhibition of AURKA in CD34(+) leukemia cells freshly isolated from individuals with blast crisis of CML with Bcr-Abl T315I mutant (n = 2) by MLN8237 significantly impaired the engraftment of these cells in severely immunocompromised mice and decreased the weight of spleens. Taken together, Bcr-Abl induces expression of AURKA and AURKB at least in part via AKT. Inhibition of AURKA could be useful to overcome imatinib-resistance mediated by Bcr-Abl mutants.

CD82 regulates STAT5/IL-10 and supports survival of acute myelogenous leukemia cells.

We recently reported that adhesion molecule CD82 is aberrantly expressed in CD34(+) /CD38(-) leukemia stem cells (LSCs). Here, we report the results of a functional analysis of CD82 in CD34(+) /CD38(-) acute myelogenous leukemia (AML) cells. Short hairpin (sh)RNA-mediated downregulation of CD82 resulted in a decrease in the level of IL-10. In contrast, forced expression of CD82 in CD34(+)/CD38(+) AML cells by transduction with CD82-expressing lentiviral particles resulted in an increase in the levels of IL-10. Notably, exposure of CD34(+)/CD38(-) AML cells to IL-10 stimulated clonogenic growth of these cells. Moreover, downregulation of CD82 by a shRNA dephosphorylated STAT5 in CD34(+)/CD38(-) AML cells. On the other hand, forced expression of CD82 resulted in increase in the levels of p-STAT5 in CD34(+)/CD38(+) AML cells. Chromatin immunoprecipitation (ChIP) assay results indicated that STAT5A binds to the promoter region of the IL-10 gene, while reporter gene assay results indicated stimulation of IL-10 expression at the transcriptional level. These results suggest that CD82 positively regulates the STAT5/IL-10 signaling pathway. Moreover, shRNA-mediated downregulation of CD82 expression in CD34(+)/CD38(-) AML cells dephosphorylated STAT5 in immunodeficient mice. Taken together, our data suggest that the CD82/STAT5/IL-10 signaling pathway is involved in the survival of CD34(+)/CD38(-) AML cells and may thus be a promising therapeutic target for eradication of AML LSCs.

Downregulation of miR-217 correlates with resistance of Ph(+) leukemia cells to ABL tyrosine kinase inhibitors.

This study found that long-term exposure of chronic myelogenous leukemia (CML) K562 cells to BCR/ABL thyrosine kinase inhibitors (TKI) caused drug-resistance in association with an increase in levels of DNA methyltransferases (DNMT) and a decrease in levels of microRNA miR-217. These observations are clinically relevant; an increase in levels of DNMT3A in association with downregulation of miR-217 were noted in leukemia cells isolated from individuals with BCR/ABL TKI-resistant Philadelphia chromosome positive acute lymphoblastic leukemia (Ph(+) ALL) and CML. Further studies with TKI-resistant K562 cells found that forced expression of miR-217 inhibited expression of DNMT3A through a miR-217-binding site within the 3'-untranslated region of DNMT3A and sensitized these cells to growth inhibition mediated by the TKI. Of note, long-term exposure of K562 cells to dasatinib (10 nM) together with 5-Aza-2'-deoxycytidine (5-AzadC) (0.1 µM) potently inhibited proliferation of these cells in association with upregulation of miR-217 and downregulation of DNMT3A in vitro. In addition, a decrease in levels of DNMT3A and an increase in levels of miR-217 were noted in K562 tumors growing in immune-deficient mice that were treated with the combination of 5-AzadC and dasatinib. Taken together, Ph(+) leukemia cells acquire TKI resistance via downregulation of miR-217 and upregulation of DNMT3A. Inhibition of DNMT3A by forced expression of miR-217 or 5-AzadC may be useful to prevent drug resistance in individuals who receive TKI.

The combination of IκB kinase ß inhibitor and everolimus modulates expression of interleukin-10 in human T-cell lymphotropic virus type-1-infected T cells.

Adult T-cell leukaemia-lymphoma (ATLL) is an aggressive malignancy of CD4(+)  CD25(+) T lymphocytes, characterized by a severely compromised immunosystem, in which the human T-cell lymphotropic virus type 1 (HTLV-1) has been recognized as the aetiological agent. This study found that an IκB kinase ß (IKKß) inhibitor Bay11-7082 inactivated mammalian target of rapamycin (mTOR), signal transducer and activator of transcription 3 and transcription factor nuclear factor-κB in HTLV-1-infected T cells; this was significantly enhanced in the presence of the mTOR inhibitor everolimus. In addition, Bay11-7082 decreased production of the immunosuppressive cytokine interleukin-10 (IL-10), which was further down-regulated when Bay11-7082 was combined with evelolimus in HTLV-1-infected T and ATLL cells isolated from patients. Interleukin-10 is known to inhibit maturation and the antigen-presenting function of dendritic cells (DCs). The culture media of HTLV-1-infected MT-1 cells, which contained a large amout of IL-10, hampered tumour necrosis factor-α-induced maturation of DCs isolated from healthy volunteers. Culture supernatant of MT-1 cells treated with a combination of Bay11-7082 and everolimus augmented maturation of DCs in association with a decrease in production of IL-10 and enhanced the allostimulatory function of DCs. Similarly, when DCs isolated from patients with ATLL were treated with the combination of Bay11-7082 and everolimus, they were fully matured and their capability to stimulate proliferation of lymphocytes was augmented. Taken together, the combination of Bay11-7082 and everolimus might exhibit immunostimulatory properties in HTLV-1-infected T and ATLL cells isolated from patients, and this combination may be potentially therapeutic to regain the compromised immunosystem in ATLL patients.

CD34⁺/CD38⁻ acute myelogenous leukemia cells aberrantly express Aurora kinase A.

We previously showed that Aurora kinase A (AURKA) is aberrantly expressed in acute myelogenous leukemia (AML) cells when compared to bone marrow mononuclear cells isolated from healthy volunteers. We have also shown that CD34(+) /CD38(-) AML cells, one of compartments enriched for leukemia stem cells in most leukemia subgroups, were relatively resistant to cytarabine-mediated growth inhibition when compared to their CD34(+) /CD38(+) counterparts. Our study attempted to identify therapeutic targets in CD34(+) /CD38(-) AML cells and found that CD34(+) /CD38(-) AML cells isolated from patients (n = 26) expressed larger amounts of AURKA than their CD34(+) /CD38(+) counterparts and CD34(+) normal hematopoietic stem/progenitor cells isolated from healthy volunteers (n = 6), as measured by real-time reverse-transcriptase polymerase chain reaction. Blockade of AURKA by the specific inhibitor MLN8237 or a short hairpin RNA (shRNA) against AURKA significantly inhibited proliferation, impaired self-renewal capability and induced apoptosis of CD34(+) /CD38(-) AML cells, in association with modulation of levels of Bcl-2 family member proteins. Importantly, inhibition of AURKA in CD34(+) /CD38(-) AML cells by MLN8237 or an shRNA significantly impaired engraftment of these cells in severely immunocompromised mice and appeared to prolong their survival. These results suggest that AURKA is a promising molecular target to eliminate chemotherapy-resistant CD34(+) /CD38(-) AML cells.

IL-1ß inhibits self-renewal capacity of dormant CD34⁺/CD38⁻ acute myelogenous leukemia cells in vitro and in vivo.

We previously showed that CD34⁺/CD38⁻ acute myelogenous leukemia (AML) cells, which contain leukemia stem cells, expressed a greater amount of the phosphorylated forms of JAK2 and STAT5 (p-JAK2 and p-STAT5) than their CD34⁺/CD38⁺ counterparts. To identify candidate cytokines that are involved in the activation of JAK2/STAT5 in CD34⁺/CD38⁻ AML cells, we compared the cytokine expression profiles of CD34⁺/CD38⁻ AML cells and their CD34⁺/CD38⁺ counterparts. Interestingly, freshly isolated CD34⁺/CD38⁻ AML cells from patients (n = 17) expressed less interleukin-1ß (IL-1ß) than their CD34⁺/CD38⁺ counterparts and CD34⁺ normal hematopoietic stem/progenitor cells from healthy volunteers (n = 6), as measured by real-time Reverse Transcription-Polymerase Chain Reaction (RT-PCR). Methylation-specific PCR found that IL-1B gene expression was silenced by methylation of the promoter region. Importantly, exposure of CD34⁺/CD38⁻ AML cells to IL-1ß (100 ng/ml) stimulated cell-cycle progression, induced apoptosis and sensitized these cells to growth inhibition by antileukemia agents. These changes occurred in conjunction with the downregulation of cyclin-dependent kinase inhibitor p21waf1, antiapoptotic proteins and p-STAT5. Forced expression of IL-1ß in CD34⁺/CD38⁻ AML cells by lentiviral transduction significantly impaired the self-renewal capacity of the cells and induced apoptosis. Additionally, when these CD34⁺/CD38⁻ AML cells with forced expression of IL-1ß were transplanted into severely immunocompromised mice, the engraftment of the cells and reconstitution of AML were significantly impaired. Taken together, our results indicate that the inhibition of STAT5 by IL-1ß may be a promising treatment strategy to eradicate leukemia stem cells in AML.

CD34⁺/CD38⁻ acute myelogenous leukemia cells aberrantly express CD82 which regulates adhesion and survival of leukemia stem cells.

To identify molecular targets in leukemia stem cells (LSCs), this study compared the protein expression profile of freshly isolated CD34(+) /CD38(-) cells with that of CD34(+) /CD38(+) counterparts from individuals with acute myelogenous leukemia (n = 2, AML) using isobaric tags for relative and absolute quantitation (iTRAQ). A total of 98 proteins were overexpressed, while six proteins were underexpressed in CD34(+) /CD38(-) AML cells compared with their CD34(+) /CD38(+) counterparts. Proteins overexpressed in CD34(+) /CD38(-) AML cells included a number of proteins involved in DNA repair, cell cycle arrest, gland differentiation, antiapoptosis, adhesion, and drug resistance. Aberrant expression of CD82, a family of adhesion molecules, in CD34(+) /CD38(-) AML cells was noted in additional clinical samples (n = 12) by flow cytometry. Importantly, down-regulation of CD82 in CD34(+) /CD38(-) AML cells by a short hairpin RNA (shRNA) inhibited adhesion to fibronectin via up-regulation of matrix metalloproteinases 9 (MMP9) and colony forming ability of these cells as assessed by transwell assay, real-time RT-PCR, and colony forming assay, respectively. Moreover, we found that down-regulation of CD82 in CD34(+) /CD38(-) AML cells by an shRNA significantly impaired engraftment of these cells in severely immunocompromised mice. Taken together, aberrant expression of CD82 might play a role in adhesion of LSCs to bone marrow microenvironment and survival of LSCs. CD82 could be an attractive molecular target to eradicate LSCs.

Over-expression of Mcl-1 impairs the ability of ATRA to induce growth arrest and differentiation in acute promyelocytic leukemia cells.

Exposure of acute promyelocytic leukemia (APL) cells to all-trans retinoic acid (ATRA) increases levels of Mcl-1, however, the implication of ATRA-mediated expressions of Mcl-1 in these cells remains to be fully elucidated. This study found that exposure of NB4 and PL-21 cells to ATRA increased levels of Mcl-1 in association with phosphorylation of c-jun N-terminus kinases. Down-regulation of Mcl-1 by a small interfering (siRNA) or an inhibitor of JNK significantly potentiated the ability of ATRA to induce differentiation and apoptosis in these cells. On the other hand, the anti-leukemia effects of ATRA were blunted when Mcl-1 was forced expressed in NB4 and PL-21 cells as well as leukemia cells isolated from individuals with APL. Furthermore, down-regulation of Mcl-1 by an siRNA sensitized non-APL U937 and KG-1 leukemia cells to ATRA-mediated differentiation and apoptosis. Taken together, inhibition of Mcl-1 might be useful to potentiate the action of ATRA in APL as well as non-APL AML cells.

Synthesis of hexa(furan-2-yl)benzenes and their π-extended derivatives.

The first synthesis of hexa(furan-2-yl)benzene derivatives is described. The RhCl3/i-Pr2NEt-catalyzed cyclotrimerization of di(furan-2-yl)acetylenes was an effective method for constructing hexa(furan-2-yl)benzene derivatives in good yields. Their π-extended derivatives were also synthesized by Suzuki-Miyaura coupling between hexakis(5-Bpinfuran-2-yl)benzene (Bpin = (pinacolato)boryl) and several aryl iodides.

Thrombomodulin protects endothelial cells from a calcineurin inhibitor-induced cytotoxicity by upregulation of extracellular signal-regulated kinase/myeloid leukemia cell-1 signaling.

OBJECTIVE: We have recently reported that recombinant human soluble thrombomodulin (rTM) counteracted capillary leakage associated with engraftment, as well as sinusoidal obstructive syndrome after hematopoietic stem cell transplantation. These observations prompted us to explore whether rTM possessed cytoprotective effects on endothelial cells. METHODS AND RESULTS: Exposure of human umbilical vein endothelial cells to rTM induced expression of antiapoptotic protein myeloid leukemia cell-1 through the activation of extracellular signal-regulated kinase in these cells. Additional studies found that exposure of human umbilical vein endothelial cells to cyclosporine A and FK506, an immunosuppressant used for the individuals receiving hematopoietic stem cell transplantation, induced apoptosis, which was attenuated when human umbilical vein endothelial cells were exposed to these agents in the presence of rTM. Further studies using deletion mutants of thrombomodulin (TM) identified that the epidermal growth factor domain of TM possessed cytoprotective effects. A single nucleotide substitution at codon 376 or 424 of TM, which impairs the ability of TM to produce activated protein C or bind to thrombin, respectively, did not hamper the cytoprotective effects of TM, which suggested that cytoprotective effects of rTM were distinctive from those of activated protein C. CONCLUSIONS: TM may be useful for prevention, as well as treatment of endothelial cell damage after hematopoietic stem cell transplantation.

Long-term exposure of gastrointestinal stromal tumor cells to sunitinib induces epigenetic silencing of the PTEN gene.

Although sunitinib possesses significant clinical effects on imatinib-resistant gastrointestinal stromal tumors (GISTs), the individuals with GIST eventually become resistant to treatment with this tyrosine kinase inhibitor. The mechanism of resistance to sunitinib is still under investigation. To address this issue, we have established sunitinib-resistant GIST-T1 sublines (designated as GIST-T1R) by culturing cells with increasing concentrations of sunitinib. GIST-T1R cells were also resistant to imatinib-mediated growth inhibition. Examination of intracellular signaling found that Akt/ mammalian target of rapamycin (mTOR) signaling remained activated in GIST-T1R but not in parental GIST-T1 cells, after exposure of these cells to sunitinib, as measured by immunoblotting. Further study found that the phosphatase and tensin homolog deleted on chromosome ten (PTEN) gene was silenced by methylation of the promoter region of the gene. Notably, forced-expression of PTEN in GIST-T1R cells negatively regulated the Akt/mTOR pathways and sensitized these cells to sunitinib-mediated growth arrest and apoptosis. Taken together, epigenetic silence of PTEN might be one of the mechanisms which cause drug-resistance in individuals with GIST after exposure to tyrosine kinase inhibitors. Blockade of the PI3K/Akt signaling with the specific inhibitors could be useful in such a case.

Inhibition of signal transducer and activator of transcription 5 by the inhibitor of janus kinases stimulates dormant human leukemia CD34+ /CD38- cells and sensitizes them to antileukemia agents.

To verify molecular mechanisms by which leukemia stem cells (LSCs) maintain a dormant state, we explored the activity of the major prosurvival signal pathways in CD34(+) /CD38(-) compartment, supposed to contain LSCs, and CD34(+) /CD38(+) counterparts from patients with acute myelogenous leukemia (AML, n = 11) by fluorescence-activated cell sorting (FACS). CD34(+) /CD38(-) cells expressed a greater amount of p-janus kinase 2 (JAK2) and p-signal transducer and activator of transcription 5 (STAT5) than CD34(+) /CD38(+) counterparts in all patients except for one case. In addition, we found that CD34(+) /CD38(-) cells were relatively resistant to cytarabine- and the inhibitor of the fms-like tyrosine kinase 3 (FLT3)-mediated growth inhibition, as measured by the clonogenic assay. Interestingly, blockade of JAK2/STAT5 signaling by the specific JAK2 inhibitor AZ960 stimulated cell cycling in CD34(+) /CD38(-) cells in conjunction with downregulation of cyclin-dependent kinase inhibitor p21(waf1) and sensitized these cells to the growth inhibition mediated by cytarabine and the FLT3 kinase inhibitor. Moreover, exposure of CD34(+) /CD38(-) cells to AZ960 potently induced apoptosis in parallel with downregulation of antiapoptotic protein Bcl-xL, as measured by Western blot analysis. Taken together, JAK2/STAT5 signaling may be a promising molecular target to eradicate CD34(+) /CD38(-) leukemia cells in individuals with AML.

Expression of p-JAK2 predicts clinical outcome and is a potential molecular target of acute myelogenous leukemia.

Our study determined if Janus kinase 2 (JAK2) was activated in acute myelogenous leukemia (AML; n = 77, excluding acute promyelocytic leukemia) by immunohistochemistry (IHC) using a phosphor-specific antibody against JAK2. p-JAK2 was detectable in all cases, although its levels varied between patient samples (high levels, n = 31; low levels, n = 46). The quantification of levels of p-JAK2 by IHC was well correlated with that assessed by Western blot analyses and fluorescence-activated cell sorting (FACS). Levels of p-JAK2 were directly correlated with high white blood cell count (52.3 × 10(3) /L in patients with high p-JAK2 vs. 28.3 × 10(3) /L in patients with low p-JAK2, p < 0.01) and were inversely correlated with complete remission rates (45% in patients with high p-JAK2 vs. 78% in patients with low p-JAK2, p < 0.003). In addition, multivariate analysis confirmed that high levels of p-JAK2 remained a significant factor for overall survival (hazard ratio = 2.213; 95% confidence interval, 1.212-4.041, p = 0.023). Moreover, we found that AZ960, a novel and specific inhibitor of the JAK2 kinase, potently inhibited the clonogenic growth and induced apoptosis of freshly isolated AML cells from patients in association with cleavage of caspase 3 and downregulation of anti-apoptotic Bcl-xL proteins. Taken together, JAK2 may be a promising molecular target for treatment of AML.

Inhibition of MEK/ERK signaling induces apoptosis of acute myelogenous leukemia cells via inhibition of eukaryotic initiation factor 4E-binding protein 1 and down-regulation of Mcl-1.

We previously showed that the MEK inhibitor AZD6244 induced apoptosis in acute myelogenous leukemia (AML) HL60 cells. However, the mechanisms of AZD6244 to induce apoptosis remain to be fully elucidated. This study found that exposure of HL60 cells to AZD6244 down-regulated the levels of phosphor (p)-4E-binding protein 1 (4E-BP1), a substrate of mammalian target of rapamycin complex 1 (mTORC1), and anti-apoptotic protein Mcl-1. On the other hand, exposure of EOL-1 and MOLM13 cells to AZD6244 failed to induce apoptosis and levels of p-4E-BP1 and Mcl-1 were not down-regulated in these cells. These observations prompted us to hypothesize that down-regulation od 4E-BP1 and Mcl-1 might play an important role in AZD6244-mediated apoptosis. As expected, down-regulation of 4E-BP1 by an siRNA sensitized EOL-1 cells to AZD6244-mediated apoptosis in parallel with down-regulation of Mcl-1. Moreover, we found that blockade of mTORC1 by RAD001 synergistically enhanced the action of AZD6244 in leukemia cells.

Ki11502, a novel multitargeted receptor tyrosine kinase inhibitor, induces growth arrest and apoptosis of human leukemia cells in vitro and in vivo.

Ki11502 is a novel multitargeted receptor tyrosine kinase (RTK) inhibitor with selectivity against platelet-derived growth factor receptor alpha/beta (PDGFRalpha/beta). Ki11502 (0.1-1 nM, 2 days) profoundly caused growth arrest, G(0)/G(1) cell-cycle arrest, and apoptosis associated with down-regulation of Bcl-2 family proteins in the eosinophilic leukemia EOL-1 cells having the activated FIP1-like 1/PDGFRalpha fusion gene. Ki11502 decreased levels of p-PDGFRalpha and its downstream signals, including p-Akt, p-ERK, and p-STAT5, in EOL-1 cells. Of note, Ki11502 was also active against imatinib-resistant PDGFRalphaT674I mutant. In addition, Ki11502 inhibited proliferation of biphenotipic leukemia MV4-11 and acute myelogenous leukemia MOLM13 and freshly isolated leukemia cells having activating mutations in FMS-like tyrosine kinase 3 (FLT3). This occurred in parallel with the drug inhibiting FLT3 and its downstream signal pathways, as measured by fluorescence-activated cell sorting using the phospho-specific antibodies. In addition, Ki11502 totally inhibited proliferation of EOL-1 cells growing as tumor xenografts in SCID mice without any noticeable adverse effects. Taken together, Ki11502 has profound antiproliferative effects on select subsets of leukemia including those possessing imatinib-resistant mutation.

Analysis of Aurora B kinase in non-Hodgkin lymphoma.

This study explored the levels of Aurora B, a key regulator of mitosis, in 71 lymph nodes and tumor specimens excised operatively from individuals with various types of non-Hodgkin lymphoma (NHLs). Immunohistochemical examination found that diffuse large B-cell lymphoma (10/21, 48%) and Burkitt lymphoma (BL) (6/7, 86%) cells highly (percentage of positive cells, >20%) expressed Aurora B in their nuclei. On the other hand, none of the low-grade B-cell lymphoma (n=20), except for one case of follicular lymphoma, highly expressed this protein kinase, suggesting that levels of Aurora B correlated with histological grade in B-cell NHLs (P<0.01). Exposure of BL/leukemia cells to AZD1152-HQPA in vitro, a selective inhibitor of Aurora B kinase, potently induced growth arrest and apoptosis in a caspase-dependent, as well as -independent manner. Moreover, AZD1152 synergistically enhanced the effects of vincristine (VCR) to induce growth arrest of these cells. Further experiments found that VCR increased levels of the p-Aurora B through the activation of c-Jun N-terminal kinase, which was blocked in the presence of AZD1152-HQPA.

Blockade of MEK signaling potentiates 5-Aza-2'-deoxycytidine-induced apoptosis and upregulation of p21(waf1) in acute myelogenous leukemia cells.

We have recently reported that the mitogen-activated protein kinase/ERK kinase (MEK) inhibitor AZD6244 (ARRY-142886) strikingly potentiated the effects of histone deacetylase inhibitor to induce growth arrest and apoptosis of acute myelogeneous leukemia (AML) cells in association with enhanced upregulation of p21(waf1). This study examined the effects of the MEK inhibitor on the action of DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-AzadC), another epigenetic agent in AML cells. AZD6244 significantly potentiated the ability of 5-AzadC to induce growth arrest and apoptosis of NB4, and freshly isolated AML cells. In parallel, 5-AzadC induced expression of p21(waf1) in AML cells, which was potently enhanced in the presence of AZD6244. Further studies explored the molecular mechanisms by which 5-AzadC induced expression of p21(waf1) and found that a low dose of 5-AzadC (1 microM) induced acetylation of histone H3 on the p21(waf1) gene promoter; however, higher dose of this compound (3 or 5 microM) potently induced DNA damage as assessed by expression of gammaH2AX, in NB4 cells. These effects were strikingly enhanced by concomitant blockade of MEK signaling. Furthermore, knock-down of p21(waf1) by the siRNA rescued NB4 cells from 5-AzadC-mediated growth inhibition. Taken together, combination of 5-AzadC and the MEK inhibitor may be useful for treatment of individuals with a subset of AML.

Inhibition of mammalian target of rapamycin signaling potentiates the effects of all-trans retinoic acid to induce growth arrest and differentiation of human acute myelogenous leukemia cells.

Our study explored the drug interaction of all-trans retinoic acid (ATRA) and RAD001 (everolimus), the inhibitor of mammalian target of rapamycin complex 1 (mTORC1), in acute myelogenous leukemia (AML) NB4 and HL60 cells. RAD001 (10 nM) significantly enhanced the ATRA-induced growth arrest and differentiation of these cells, as measured by colony-forming assay and cell cycle analysis, and expression of CD11b cell surface antigen and nitroblue tetrazolium reduction, respectively. ATRA (0.1-1 microM) upregulated levels of RTP801, a negative regulator of mTORC1, and inhibited mTORC1 signaling as assessed by measurement of the levels of p-p70S6K and p-4E-BP1 in HL60 and NB4 cells. ATRA (0.1-1 microM) in combination with RAD001 (10 nM) strikingly downregulated the levels of p-70S6K and p-4E-BP1 without affecting the total amount of these proteins. Notably, RAD001 (10 nM) significantly augmented ATRA-induced expression of CCAAT/enhancer-binding protein epsilon (C/EBPepsilon) and p27(kip1) and downregulated levels of c-Myc in these cells. Furthermore, RAD001 (5 mg/kg) enhanced the ability of ATRA (10 mg/kg) to inhibit the proliferation of HL60 cells growing as tumor xenografts in immune-deficient nude mice. Taken together, concomitant blockade of the RA and mTORC1 signaling may be a promising treatment strategy for individuals with AML.