Scientific Resources

A variety of nonmalignant cells present in the tumor microenvironment promotes tumorigenesis by stimulating tumor cell growth and metastasis or suppressing host immunity. The role of such stromal cells in T-cell lymphoproliferative disorders is incompletely understood. Monocyte-derived cells (MDCs),including professional antigen-presenting cells such as dendritic cells (DCs),play a central role in T-cell biology. Here,we provide evidence that monocytes promote the survival of malignant T cells and demonstrate that MDCs are abundant within the tumor microenvironment of T cell-derived lymphomas. Malignant T cells were observed to remain viable during in vitro culture with autologous monocytes,but cell death was significantly increased after monocyte depletion. Furthermore,monocytes prevent the induction of cell death in T-cell lymphoma lines in response to either serum starvation or doxorubicin,and promote the engraftment of these cells in nonobese diabetic/severe combined immunodeficient mice. Monocytes are actively recruited to the tumor microenvironment by CCL5 (RANTES),where their differentiation into mature DCs is impaired by tumor-derived interleukin-10. Collectively,the data presented demonstrate a previously undescribed role for monocytes in T-cell lymphoproliferative disorders. View Publication

Platelets have a crucial role in the maintenance of hemostasis as well as in thrombosis and vessel occlusion,which underlie stroke and acute coronary syndromes. Anucleate platelets contain mRNAs and are capable of protein synthesis,raising the issue of how these mRNAs are regulated. Here we show that human platelets harbor an abundant and diverse array of microRNAs (miRNAs),which are known as key regulators of mRNA translation in other cell types. Further analyses revealed that platelets contain the Dicer and Argonaute 2 (Ago2) complexes,which function in the processing of exogenous miRNA precursors and the control of specific reporter transcripts,respectively. Detection of the receptor P2Y(12) mRNA in Ago2 immunoprecipitates suggests that P2Y(12) expression may be subjected to miRNA control in human platelets. Our study lends an additional level of complexity to the control of gene expression in these anucleate elements of the cardiovascular system. View Publication

Up to now,no lentiviral vector (LV) tool existed to govern efficient and stable gene delivery into quiescent B lymphocytes,which hampers its application in gene therapy and immunotherapy areas. Here,we report that LVs incorporating measles virus (MV) glycoproteins,H and F,on their surface allowed transduction of 50% of quiescent B cells,which are not permissive to VSVG-LV transduction. This high transduction level correlated with B-cell SLAM expression and was not at cost of cell-cycle entry or B-cell activation. Moreover,the naive and memory phenotypes of transduced resting B cells were maintained. Importantly,H/F-LVs represent the first tool permitting stable transduction of leukemic cancer cells,B-cell chronic lymphocytic leukemia cells,blocked in G(0)/G(1) early phase of the cell cycle. Thus,H/F-LV transduction overcomes the limitations of current LVs by making B cell-based gene therapy and immunotherapy applications feasible. These new LVs will facilitate antibody production and the study of gene functions in these healthy and cancer immune cells. View Publication

Human breast tumors contain a breast cancer stem cell (BCSC) population with properties reminiscent of normal stem cells. We found 37 microRNAs that were differentially expressed between human BCSCs and nontumorigenic cancer cells. Three clusters,miR-200c-141,miR-200b-200a-429,and miR-183-96-182 were downregulated in human BCSCs,normal human and murine mammary stem/progenitor cells,and embryonal carcinoma cells. Expression of BMI1,a known regulator of stem cell self-renewal,was modulated by miR-200c. miR-200c inhibited the clonal expansion of breast cancer cells and suppressed the growth of embryonal carcinoma cells in vitro. Most importantly,miR-200c strongly suppressed the ability of normal mammary stem cells to form mammary ducts and tumor formation driven by human BCSCs in vivo. The coordinated downregulation of three microRNA clusters and the similar functional regulation of clonal expansion by miR-200c provide a molecular link that connects BCSCs with normal stem cells. View Publication

Off-patent drugs with previously unrecognized anticancer activity could be rapidly repurposed for this new indication. To identify such compounds,we conducted 2 independent cell-based chemical screens and identified the antimicrobial ciclopirox olamine (CPX) in both screens. CPX decreased cell growth and viability of malignant leukemia,myeloma,and solid tumor cell lines as well as primary AML patient samples at low-micromolar concentrations that appear pharmacologically achievable. Furthermore,oral CPX decreased tumor weight and volume in 3 mouse models of leukemia by up to 65% compared with control without evidence of weight loss or gross organ toxicity. In addition,oral CPX prevented the engraftment of primary AML cells in nonobese diabetic/severe combined immunodeficiency mouse models,thereby establishing its ability to target leukemia stem cells. Mechanistically,CPX bound intracellular iron,and this intracellular iron chelation was functionally important for its cytotoxicity. By electron paramagnetic resonance,CPX inhibited the iron-dependent enzyme ribonucleotide reductase at concentrations associated with cell death. Thus,in summary,CPX has previously unrecognized anticancer activity at concentrations that are pharmacologically achievable. Therefore,CPX could be rapidly repurposed for the treatment of malignancies,including leukemia and myeloma. View Publication

Acute myelogenous leukemia is driven by leukemic stem cells (LSCs) generated by mutations that confer (or maintain) self-renewal potential coupled to an aberrant differentiation program. Using retroviral mutagenesis,we identified genes that generate LSCs in collaboration with genetic disruption of the gene encoding interferon response factor 8 (Irf8),which induces a myeloproliferation in vivo. Among the targeted genes,we identified Mef2c,encoding a MCM1-agamous-deficiens-serum response factor transcription factor,and confirmed that overexpression induced a myelomonocytic leukemia in cooperation with Irf8 deficiency. Strikingly,several of the genes identified in our screen have been reported to be up-regulated in the mixed-lineage leukemia (MLL) subtype. High MEF2C expression levels were confirmed in acute myelogenous leukemia patient samples with MLL gene disruptions,prompting an investigation of the causal interplay. Using a conditional mouse strain,we demonstrated that Mef2c deficiency does not impair the establishment or maintenance of LSCs generated in vitro by MLL/ENL fusion proteins; however,its loss led to compromised homing and invasiveness of the tumor cells. Mef2c-dependent targets included several genes encoding matrix metalloproteinases and chemokine ligands and receptors,providing a mechanistic link to increased homing and motility. Thus,MEF2C up-regulation may be responsible for the aggressive nature of this leukemia subtype. View Publication

The role of miRNAs in regulating megakaryocyte differentiation was examined using bipotent K562 human leukemia cells. miR-34a is strongly up-regulated during phorbol ester-induced megakaryocyte differentiation,but not during hemin-induced erythrocyte differentiation. Enforced expression of miR-34a in K562 cells inhibits cell proliferation,induces cell-cycle arrest in G(1) phase,and promotes megakaryocyte differentiation as measured by CD41 induction. miR-34a expression is also up-regulated during thrombopoietin-induced differentiation of CD34(+) hematopoietic precursors,and its enforced expression in these cells significantly increases the number of megakaryocyte colonies. miR-34a directly regulates expression of MYB,facilitating megakaryocyte differentiation,and of CDK4 and CDK6,to inhibit the G(1)/S transition. However,these miR-34a target genes are down-regulated rapidly after inducing megakaryocyte differentiation before miR-34a is induced. This suggests that miR-34a is not responsible for the initial down-regulation but may contribute to maintaining their suppression later on. Previous studies have implicated miR-34a as a tumor suppressor gene whose transcription is activated by p53. However,in p53-null K562 cells,phorbol esters induce miR-34a expression independently of p53 by activating an alternative phorbol ester-responsive promoter to produce a longer pri-miR-34a transcript. View Publication

The phosphatidylinositide 3-kinase pathway is frequently deregulated in human cancers and inhibitors offer considerable therapeutic potential. We previously described the promising tricyclic pyridofuropyrimidine lead and chemical tool compound PI-103. We now report the properties of the pharmaceutically optimized bicyclic thienopyrimidine derivatives PI-540 and PI-620 and the resulting clinical development candidate GDC-0941. All four compounds inhibited phosphatidylinositide 3-kinase p110alpha with IC(50) textless or = 10 nmol/L. Despite some differences in isoform selectivity,these agents exhibited similar in vitro antiproliferative properties to PI-103 in a panel of human cancer cell lines,with submicromolar potency in PTEN-negative U87MG human glioblastoma cells and comparable phosphatidylinositide 3-kinase pathway modulation. PI-540 and PI-620 exhibited improvements in solubility and metabolism with high tissue distribution in mice. Both compounds gave improved antitumor efficacy over PI-103,following i.p. dosing in U87MG glioblastoma tumor xenografts in athymic mice,with treated/control values of 34% (66% inhibition) and 27% (73% inhibition) for PI-540 (50 mg/kg b.i.d.) and PI-620 (25 mg/kg b.i.d.),respectively. GDC-0941 showed comparable in vitro antitumor activity to PI-103,PI-540,and PI-620 and exhibited 78% oral bioavailability in mice,with tumor exposure above 50% antiproliferative concentrations for textgreater8 hours following 150 mg/kg p.o. and sustained phosphatidylinositide 3-kinase pathway inhibition. These properties led to excellent dose-dependent oral antitumor activity,with daily p.o. dosing at 150 mg/kg achieving 98% and 80% growth inhibition of U87MG glioblastoma and IGROV-1 ovarian cancer xenografts,respectively. Together,these data support the development of GDC-0941 as a potent,orally bioavailable inhibitor of phosphatidylinositide 3-kinase. GDC-0941 has recently entered phase I clinical trials. View Publication

To date,studies on T cells in acute myeloid leukemia (AML) have been limited to flow cytometric analysis of whole peripheral blood mononuclear cell (PBMC) specimens or functional work looking at the impact of AML myeloblasts on normal or remission T cells. This lack of information on T cells at the time of presentation with disease is due in part to the difficulty in isolating sufficiently pure T cells from these specimens for further study. Negative immunomagnetic selection has been the method of choice for isolating immune cells for functional studies due to concerns that binding antibodies to the cell surface may induce cellular activation,block ligand-receptor interactions or result in immune clearance. In order specifically to study T cells in presentation AML specimens,we set out to develop a method of isolating highly pure CD4 and CD8 T cells by negative selection from the peripheral blood (PB) of newly diagnosed AML patients. This technique,unlike T cell selection from PB from normal individuals or from patients with chronic lymphocytic leukaemia,was extremely problematic due to properties of the leukaemic myeloblasts. A successful method was eventually optimized requiring the use of a custom antibody cocktail consisting of CD33,CD34,CD123,CD11c and CD36,to deplete myeloblasts. View Publication

Loss-of-function mutations in the NF1 tumor suppressor result in deregulated Ras signaling and drive tumorigenesis in the familial cancer syndrome neurofibromatosis type I. However,the extent to which NF1 inactivation promotes sporadic tumorigenesis is unknown. Here we report that NF1 is inactivated in sporadic gliomas via two mechanisms: excessive proteasomal degradation and genetic loss. NF1 protein destabilization is triggered by the hyperactivation of protein kinase C (PKC) and confers sensitivity to PKC inhibitors. However,complete genetic loss,which only occurs when p53 is inactivated,mediates sensitivity to mTOR inhibitors. These studies reveal an expanding role for NF1 inactivation in sporadic gliomagenesis and illustrate how different mechanisms of inactivation are utilized in genetically distinct tumors,which consequently impacts therapeutic sensitivity. View Publication

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that is overexpressed in many types of tumors,including pancreatic cancer,and plays an important role in cell adhesion and survival signaling. Pancreatic cancer is a lethal disease and is very resistant to chemotherapy,and FAK has been shown recently to assist in tumor cell survival. Therefore,FAK is an excellent potential target for anti-cancer therapy. We identified a novel small molecule inhibitor (1,2,4,5-Benzenetetraamine tetrahydrochloride,that we called Y15) targeting the main autophosphorylation site of FAK and hypothesized that it would be an effective treatment strategy against human pancreatic cancer. Y15 specifically blocked phosphorylation of Y397-FAK and total phosphorylation of FAK. It directly inhibited FAK autophosphorylation in a dose- and time-dependent manner. Furthermore,Y15 increased pancreatic cancer cell detachment and inhibited cell adhesion in a dose-dependent manner. Y15 effectively caused human pancreatic tumor regression in vivo,when administered alone and its effects were synergistic with gemcitabine chemotherapy. This was accompanied by a decrease in Y397-phosphorylation of FAK in the tumors treated with Y15. Thus,targeting the Y397 site of FAK in pancreatic cancer with the small molecule inhibitor,1,2,4,5-Benzenetetraamine tetrahydrochloride,is a potentially effective treatment strategy in this deadly disease. View Publication

As a member of the class III histone deacetylases,Sirtuin-2 (SIRT2) is critical in cell cycle regulation which makes it a potential target for cancer therapeutics. In this study,we identified a novel SIRT2 inhibitor,AC-93253,with IC(50) of 6 microM in vitro. The compound is selective,inhibiting SIRT2 7.5- and 4-fold more potently than the closely related SIRT1 and SIRT3,respectively. AC-93253 significantly enhanced acetylation of tubulin,p53,and histone H4,confirming SIRT2 and SIRT1 as its cellular targets. AC-93253 as a single agent exhibited submicromolar selective cytotoxicity towards all four tumor cell lines tested with a therapeutic window up to 200-fold,comparing to any of the three normal cell types tested. Results from high content analysis suggested that AC-93253 significantly triggered apoptosis. Taken together,SIRT2 selective inhibitor AC-93253 may serve as a novel chemical scaffold for structure-activity relationship study and future lead development. View Publication