Autocrine growth factors and leukaemic haemopoiesis

The cytokine network in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous malignancy of the blood and bone marrow, characterized by clonal expansion of myeloid stem and progenitor cells and rapid disease progression. Chemotherapy has been the first-line treatment for AML for more than 30 years. Application of recent high-throughput next-generation sequencing technologies has revealed significant molecular heterogeneity to AML, which in turn has motivated efforts to develop new, targeted therapies. However, due to the high complexity of this disease, including multiple driver mutations and the coexistence of multiple competing tumorigenic clones, the successful incorporation of these new agents into clinical practice remains challenging. These continuing difficulties call for the identification of innovative therapeutic approaches that are effective for a larger cohort of AML patients. Recent studies suggest that chronic immune stimulation and aberrant cytokine signaling act as triggers for AML initiation and progression, facets of the disease which might be exploited as promising targets in AML treatment. However, despite the greater appreciation of cytokine profiles in AML, the exact functions of cytokines in AML pathogenesis are not fully understood. Therefore, unravelling the molecular basis of the complex cytokine networks in AML is a prerequisite to develop new therapeutic alternatives based on targeting cytokines and their receptors.

G-CSF/GM-CSF-induced hematopoietic dysregulation in the progression of solid tumors

There are two types of abnormal hematopoiesis in solid tumor occurrence and treatment: pathological hematopoiesis, and myelosuppression induced by radiotherapy and chemotherapy. In this review, we primarily focus on the abnormal pathological hematopoietic differentiation in cancer induced by tumor-released granulocyte colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF). As key factors in hematopoietic development, G-CSF/GM-CSF are well-known facilitators of myelopoiesis and mobilization of hematopoietic stem cells (HSCs). In addition, these two cytokines can also promote or inhibit tumors, dependent on tumor type. In multiple cancer types, hematopoiesis is greatly enhanced and abnormal lineage differentiation is induced by these two cytokines. Here, dysregulated hematopoiesis induced by G-CSF/GM-CSF in solid tumors and its mechanism are summarized, and the prognostic value of G-CSF/GM-CSF-associated dysregulated hematopoiesis for tumor metastasis is also briefly highlighted.

Interleukin-8 blockade prevents activated endothelial cell mediated proliferation and chemoresistance of acute myeloid leukemia

One of the greatest challenges in treating acute myeloid leukemia (AML) is chemotherapy refractory disease. Previously, we demonstrated a novel mechanism whereby AML-induced endothelial cell (EC) activation leads to subsequent leukemia cell adherence, quiescence and chemoresistance, identifying activated ECs as potential mediators of relapse. We now show mechanistically that EC activation induces the secretion of interleukin-8 (IL-8) leading to significant expansion of non-adherent AML cells and resistance to cytarabine (Ara-C). Through crystallography and computational modeling, we identified a pocket within IL-8 responsible for receptor binding, screened for small molecules that fit within this pocket, and blocked IL-8 induced proliferation and chemo-protection of AML cells with a hit compound. Results from this study show a new therapeutic strategy for targeting the sanctuary of an activated leukemia microenvironment.

High expression of suppressor of cytokine signaling-2 predicts poor outcome in pediatric acute myeloid leukemia: a report from the Children's Oncology Group

Deregulated cytokine signaling is a characteristic feature of acute myeloid leukemia (AML), and expression signatures of cytokines and chemokines have been identified as a significant prognostic factor in this disease. Given this aberrant signaling, we hypothesized that expression of suppressor of cytokine signaling-2 (SOCS2), a negative regulator of cytokine signaling, might be altered in AML and could provide predictive information. Among 188 participants of the Children's Oncology Group AAML03P1 trial, SOCS2 mRNA levels varied > 6000-fold. Higher (> median) SOCS2 expression was associated with inferior overall (60 ± 10% vs. 75 ± 9%, p = 0.026) and event-free (44 ± 10% vs. 59 ± 10%, p = 0.031) survival. However, these differences were accounted for by higher prevalence of high-risk and lower prevalence of low-risk disease among patients with higher SOCS2 expression, limiting the clinical utility of SOCS2 as a predictive marker. It remains untested whether high SOCS2 expression identifies a subset of leukemias with deregulated cytokine signaling that could be amenable to therapeutic intervention.

Blastic leukaemias (AML): a biologist's view

Acute myeloblastic leukaemia is characterised by the extreme clonal proliferation of haematopoietic precursor cells with abnormal or arrested differentiation. Chemotherapy of acute leukaemia is channelled towards the reduction and eradication of leukaemic cells. However, relapse is generally assumed to occur in residual host cells, which are refractory to or elude therapy. The cancer stem cell hypothesis has gained considerable importance in recent years and could interpret this behaviour. This persuasive theory states that cells within a tumour are organised in a hierarchy similar to that of normal tissues and are maintained by a small subset of cells responsible for tumour dormancy. These cells, defined as 'tumour initiating cells' (TICs), possess several properties of normal tissue stem cells. Recently, the TICs associated with AML have been shown to comprise distinct, hierarchically arranged classes similar to those observed for haematopoietic stem cells. We know now that the growth and survival of blasts in AML are driven by the same growth factors that stimulate normal cells. Furthermore, direct evidence of the role of membrane stem cell factor and its receptor c-Kit in cell-cell interactions and cell survival in primary AML blasts have been provided, defining the importance of juxtacrine stimulation. Inhibition of c-Kit signalling induces combinations of cell death: autophagy (compensatory mechanism towards survival) and apoptosis. While recent work confirmed that c-Kit inhibitors reduce cancer cell proliferation, it also demonstrated that future inappropriate prescriptions could cause normal tissue deterioration. The purpose of this paper was to review some of the salient features of leukaemic blasts in support of the proposal that research into neoplasia be increased. Rather than presenting the details of various studies, I have attempted to indicate general areas in which work has been done or is in progress. It is hoped that this survey of the subject will demonstrate a variety of opportunities for additional research in human neoplasia.

Autocrine GM-CSF transcription in the leukemic progenitor cell line KG1a is mediated by the transcription factor ETS1 and is negatively regulated through SECTM1 mediated ligation of CD7

BACKGROUND

CD7 expression is found on ~30% of acute myeloblastic leukemias (AML). The leukemic progenitor cell line KG1a (CD7+) constitutively expresses GM-CSF while the parental KG1 (CD7-) cell line does not. This study focuses on the molecular basis of CD7 mediated GM-CSF regulation.

METHODS

KG1a cells were treated with recombinant SECTM1-Fc protein, the PI3K kinase inhibitors wortmannin, LY292004, or PI4K activator spermine. Stable KG1-CD7+, KG1a-shCD7, KG1a-shETS1 as well as KG1a-GFP, KG1a-PKCβII-GFP cell lines were generated and the levels of CD7, GM-CSF and ETS-1 mRNA and protein were compared by real-time-PCR, western blotting, flow cytometry and ELISA.

RESULTS

SECTM1 is expressed in Human Bone Marrow Endothelial Cells (HBMEC) and its expression can be upregulated by both IFN-γ. KG1a cells demonstrated high expression levels of CD7 and ETS-1 allowing a constitutative signaling through the PI3K/Atk pathway to promote GM-CSF expression, while KG1 cells with low expression of CD7 and ETS-1 showed low GM-CSF expression. On KG1a cells GM-CSF expression could be negatively regulated by PI3K inhibitors or by recombinant SECTM1-Fc. Overexpression of CD7 in KG1 cells was insufficient to promote GM-CSF expression, while silencing of CD7 or ETS-1 resulted in reduced GM-CSF expression levels. Differentiation capable KG1a cells overexpressing PKCβII illustrated complete loss of CD7, but maintained normal levels of both ETS-1 and GM-CSF expression.

CONCLUSION

These findings add an additional layer to the previously described autocrine/paracrine signaling between leukemic progenitor cells and the bone marrow microenvironment and highlight a role for SECTM1 in both normal and malignant hematopoiesis.

GENERAL SIGNIFICANCE

This work shows that SECTM1 secreted from bone marrow stromal cells may interact with CD7 to influence GM-CSF expression in leukemic cells.

The possible diagnostic and prognostic use of systemic chemokine profiles in clinical medicine—the experience in acute myeloid leukemia from disease development and diagnosis via conventional chemotherapy to allogeneic stem cell transplantation

Chemokines are important regulators of many different biological processes, including (i) inflammation with activation and local recruitment of immunocompetent cells; (ii) angiogenesis as a part of inflammation or carcinogenesis; and (iii) as a bridge between the coagulation system and inflammation/immune activation. The systemic levels of various chemokines may therefore reflect local disease processes, and such variations may thereby be used in the routine clinical handling of patients. The experience from patients with myeloproliferative diseases, and especially patients with acute myeloid leukemia (AML), suggests that systemic plasma/serum cytokine profiles can be useful, both as a diagnostic tool and for prognostication of patients. However, cytokines/chemokines are released by a wide range of cells and are involved in a wide range of biological processes; the altered levels may therefore mainly reflect the strength and nature of the biological processes, and the optimal clinical use of chemokine/cytokine analyses may therefore require combination with organ-specific biomarkers. Chemokine levels are also altered by clinical procedures, therapeutic interventions and the general status of the patients. A careful standardization of sample collection is therefore important, and the interpretation of the observations will require that the overall clinical context is considered. Despite these limitations, we conclude that analysis of systemic chemokine/cytokine profiles can reflect important clinical characteristics and, therefore, is an important scientific tool that can be used as a part of future clinical studies to identify clinically relevant biomarkers.

The inducible tissue-specific expression of the human IL-3/GM-CSF locus is controlled by a complex array of developmentally regulated enhancers

The closely linked human IL-3 and GM-CSF genes are tightly regulated and are expressed in activated T cells and mast cells. In this study, we used transgenic mice to study the developmental regulation of this locus and to identify DNA elements required for its correct activity in vivo. Because these two genes are separated by a CTCF-dependent insulator, and the GM-CSF gene is regulated primarily by its own upstream enhancer, the main objective in this study was to identify regions of the locus required for correct IL-3 gene expression. We initially found that the previously identified proximal upstream IL-3 enhancers were insufficient to account for the in vivo activity of the IL-3 gene. However, an extended analysis of DNase I-hypersensitive sites (DHSs) spanning the entire upstream IL-3 intergenic region revealed the existence of a complex cluster of both constitutive and inducible DHSs spanning the -34- to -40-kb region. The tissue specificity of these DHSs mirrored the activity of the IL-3 gene, and included a highly inducible cyclosporin A-sensitive enhancer at -37 kb that increased IL-3 promoter activity 40-fold. Significantly, inclusion of this region enabled correct in vivo regulation of IL-3 gene expression in T cells, mast cells, and myeloid progenitor cells.

Chromatin mechanisms regulating gene expression in health and disease

It is now well established that the interplay of sequence-specific DNA binding proteins with chromatin components and the subsequent expression of differential genetic programs is the major determinant of developmental decisions. The last years have seen an explosion of basic research that has significantly enhanced our understanding of the basic principles of gene expression control. While many questions are still open, we are now at the stage where we can exploit this knowledge to address questions of how deregulated gene expression and aberrant chromatin programming contributes to disease processes. This chapter will give a basic introduction into the principles of epigenetics and the determinants of chromatin structure and will discuss the molecular mechanisms of aberrant gene regulation in blood cell diseases, such as inflammation and leukemia.

Recurrent expression signatures of cytokines and chemokines are present and are independently prognostic in acute myelogenous leukemia and myelodysplasia

The role of circulating cytokines and chemokines (C&Ckine) in activating signal transduction in leukemic cells is incompletely defined. We hypothesized that comprehensive profiling of C&Ckine expression in leukemia would provide greater insight compared with individual analyses. We used multiplex array technology to simultaneously measure the level of 27 C&Ckines in serum from 176 acute myelogenous leukemia (AML) and 114 myelodysplastic syndrome (MDS) patients and 19 normal controls. C&Ckine levels in AML and MDS differed significantly from normal controls (5 higher, 13 lower) but were similar to each other for 24 of 27 analytes, with interleukin-8 and interleukin-13 higher in AML and vascular endothelial growth factor A higher in MDS. Levels did not correlate with age, gender, infection, or blood counts; however, 3 correlated with specific cytognetic abnormalities in AML. Individually, few cytokines had any correlation with response or survival. In newly diagnosed AML, 8 C&Ckine signatures, distinct from the normal control signature, were observed. These signatures had prognostic impact, affecting remission, primary resistance, relapse rates, and overall survival, individually (P = .003) and in multivariable analysis (P = .004). These patterns suggest specific therapeutic interventions to investigate in subsets of AML patients. In conclusion, C&Ckine expression in AML and MDS differs from normal, is similar with one another, and forms recurrent patterns of expression with prognostic relevance.

JTE-607, a multiple cytokine production inhibitor, ameliorates disease in a SCID mouse xenograft acute myeloid leukemia model

OBJECTIVE

Accumulating findings suggest that in acute myeloid leukemia (AML) patients, proinflammatory cytokines and growth factors play important roles in the proliferation and survival of AML cells in an autocrine and paracrine manner, leading to deterioration of AML. JTE-607 is a multiple cytokine inhibitor that potently suppresses production of proinflammatory cytokines. In the present study, we investigated the potency of JTE-607 as an antileukemic agent by exploiting a SCID mouse acute leukemia model.

METHODS

SCID mice injected with anti-asialo-GM1 antibody were exposed to sublethal total-body irradiation at a dose of 3 Gy and then inoculated intravenously with AML cells. JTE-607 was administered using osmotic minipumps. The effects of JTE-607 on mouse survival time, human interleukin (IL)-8 levels in mouse plasma, and proportion of human CD45(+) cells in the bone marrow were studied.

RESULTS

The survival time of the mice was strictly dependent on the number of U-937 cells proliferating in vivo. Administration of JTE-607 during the initial 7 days significantly prolonged survival of the mice, suggesting killing activity of JTE-607 against AML cells in vivo. Delayed administration of JTE-607 also prolonged the survival of mice bearing established leukemia with an effect comparable to the maximum tolerable dose of cytarabine. Flow cytometer analysis of bone marrow cells revealed decreased number of human CD45(+) cells. Human IL-8 level was also reduced by JTE-607.

CONCLUSION

Our results indicate that JTE-607 has potential to be a new class of antileukemic drug that exerts inhibitory activities against both the proliferation and proinflammatory cytokine production of AML cells.

Effects of all-trans retinoic acid or chemotherapy on the molecular regulation of systemic blood coagulation and fibrinolysis in patients with acute promyelocytic leukemia

We studied the pathogenesis of the bleeding disorder in acute promyelocytic leukemia by measuring procoagulant, profibrinolytic, and proinflammatory mediators in peripheral blood and bone marrow cells from 25 previously untreated patients. Patients were induced with either all-trans retinoic acid (ATRA) or chemotherapy. Plasma levels of fibrinopeptide A (FPA), fibrin d-dimer, thrombin antithrombin (TAT) complex, prothrombin fragment 1.2 (F1.2), urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (t-PA) and plasminogen activator-inhibitor 1 (PAI-1) were measured before and after therapy, as was the cellular expression of the genes for tissue factor (TF) and interleukin-1 beta (IL-1 beta). The mean plasma levels of fibrin d-dimer, F1.2, TAT and FPA were markedly elevated prior to therapy and declined during the first 30 days of treatment with either ATRA or chemotherapy, but more rapidly and to a greater extent in patients treated with ATRA. ATRA treatment was associated with a significant decrease in TF gene expression in bone marrow cells during the first 30 days of treatment, whereas IL-1 beta gene expression, which decreased in the cells of six patients treated with either chemotherapy or ATRA, actually increased in the remaining six patients treated with either chemotherapy or ATRA. In patients with APL, treatment with either chemotherapy or ATRA rapidly ameliorates the coagulopathy, as indicated by an abrupt decline in markers of clotting activation. An increase in cytokine gene expression (e.g. IL-1 beta) may provide an explanation for the persistent hypercoagulability observed in some patients with APL, regardless of therapeutic approach. Our data confirms and extends earlier observations by others that ATRA is more effective than chemotherapy alone in rapidly reducing the procoagulant burden of APL tumor cells. However, our data also suggests that cytokine expression in some patients may be accelerated by either chemotherapy or ATRA. The implications of this observation for understanding the retinoic acid syndrome will require further studies.

Granulocyte-macrophage colony-stimulating factor and interleukin-3 induce cell cycle progression through the synthesis of c-Myc protein by internal ribosome entry site-mediated translation via phosphatidylinositol 3-kinase pathway in human factor-dependent leukemic cells

To investigate the roles of c-myc during hematopoietic proliferation induced by growth factors, we used factor-dependent human leukemic cell lines (MO7e and F36P) in which proliferation, cell cycle progression, and c-Myc expression were strictly regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). In these cell lines, both c-myc mRNA and c-Myc protein stability were not affected by GM-CSF and IL-3, suggesting a regulation of c-Myc protein at the translational level. However, rapamycin, an inhibitor of cap-dependent translation, did not block c-myc induction by GM-CSF and IL-3. Thus, we studied the cap-independent translation, the internal ribosome entry site (IRES), during c-Myc protein synthesis using dicistronic reporter gene plasmids and found that GM-CSF and IL-3 activated c-myc IRES to initiate translation. c-myc IRES activation, c-Myc protein expression, and cell cycle progression were all blocked by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. In another factor-dependent cell line, UT7, we observed the cell cycle progression and up-regulation of c-Myc protein, c-myc mRNA, and c-myc IRES simultaneously, which were all inhibited by LY294002. Results indicate that hematopoietic growth factors induce cell cycle progression via IRES-mediated translation of c-myc though the PI3K pathway in human factor-dependent leukemic cells.

Expression of IL-18 and its receptor in human leukemia cells

The importance of IL-18, although clearly established in solid tumors, has not been fully elucidated in human hematopoietic neoplasms. Here we examined the mRNA and protein for IL-18 in eight human hematopoietic cell lines representing different lineages and neoplasms including leukemia, lymphoma and others. Our results revealed that IL-18 mRNA was expressed in these cells and that the corresponding protein was found in the cytoplasm. Seven of eight cell lines were also found to express two subunits of the IL-18 receptor (IL-18R) at varied levels. Furthermore, 29 out of 51 leukemia patients tested were observed to express IL-18R with 18/29 (62%) co-expression of both receptor and ligand. By blocking the IL-18 loop using specific antisense oligodeoxynucleotide (ASON) for IL-18 mRNA or anti-human IL-18R monoclonal antibody (McAbR), we were not able to demonstrate a marked inhibition on the most leukemic cell lines growth. Moreover, the potential proliferation in vitro of primary AML cells co-expressing IL-18 and its receptor was not significantly enhanced by recombinant human IL-18, suggesting that IL-18 is not apparently implicated in the proliferation of the leukemia cells via an autocrine loop. Additionally, we also found the effective modulating effect of M-CSF, IFN-alpha and TNF-alpha on IL-18R expression, implying an important in vivo effect of cytokines on IL-18-induced reaction. Moreover, the modulation of IL-18R expression was possibly irrelevant to IFN-gamma secretion induced by these cytokines.

A novel predictive model of outcome in de novo AML based on S-phase activity and proliferative response of blast cells to haemopoietic growth factors

This study assesses whether the kinetic response of AML cells to HGFs might help to predict initial clinical outcome of treatment in de novo AML in association with age, FAB type and karyotype. Best subset regression analysis indicated optimal variables to develop models to predict prognosis. High S-phase in surviving cells following 7 days incubation in SFM, resistance to stimulation by G+GM-CSF and poor karyotype taken in combination correctly predicted outcome in 83% of patients. The importance of high SFM S-phase may be to indicate autonomous proliferation therefore a leukemic clone more likely to regenerate following therapy at the expense of normal haemopoiesis. Kinetic studies of AML cells may be a useful predictor of outcome in addition to other more established prognostic factors.

Targeted therapies for high-risk acute myeloid leukemia

Approximately half of children with acute myeloid leukemia (AML) can be cured with contemporary chemotherapy regimens; however, various forms of drug resistance pose considerable obstacles for curing the remaining patients. Recent advances in immunology, cytogenetics, and cellular and molecular biology have provided new insights into fundamental biological differences between leukemic myeloid blasts and their normal counterparts. This article focuses on new technologies involving: (1) antibody- or growth factor-mediated targeting of antigens or growth factor receptors found on AML blasts and restricted sub-groups of normal cells, (2) pharmacologic targeting of the pathologic t(15;17) translocation of acute promyelocytic leukemia with all-trans retinoic acid, (3) pharmacologic and immunologic targeting of mutant RAS oncogenes and related aberrant signaling in AML blasts, and (4) targeting of pathological signaling of the Bcr-Abl oncoprotein and c-kit tyrosine kinase in myeloid leukemias. These advances herald an exciting new era of AML-specific therapies.

SCF, IL-1beta, IL-1ra and GM-CSF in the bone marrow and serum of normal individuals and of AML and CML patients

This study compared cytokine transcript and protein levels in BM cells of normal individuals and leukemic patients. AML differed from normal in that: (1) AML marrow cells contain more IL-1beta protein than normal cells, (2) IL-1ra transcripts are absent from AML marrow cells, (3) AML marrow serum contains less IL-1ra protein than normal, (4) peripheral blood and marrow serum of AML patireents contains more SCF protein than normal serum, and (5) SCF transcripts have been detected in AML marrow biopsies and not in aspirate cells. These data suggest that unbalanced cytokine production may make a significant contribution to the abnormal behaviour of AML cells.

The nucleocapsid protein of murine hepatitis virus type 3 induces transcription of the novel fgl2 prothrombinase gene

Using a set of parental and recombinant murine hepatitis virus strains, we demonstrate that the nucleocapsid protein induces transcription of the novel fgl2 prothrombinase gene and elevated procoagulant activity in those strains that produce fulminant hepatitis. Chinese hamster ovary cells cotransfected with a construct expressing nucleocapsid protein from susceptible strains and with a luciferase reporter construct containing the fgl2 promoter showed a 6-fold increase in luciferase activity compared with nontransfected cells or cells cotransfected with a construct expressing nucleocapsid protein from resistant strains. Two deletions found at coding sites 111-123 and 1143-1145 of structural domains I and III, respectively, of the nucleocapsid gene may account for the differences between pathogenic and nonpathogenic strains. Preliminary mapping of the fgl2 promoter has defined a region from -372 to -306 upstream from the ATG translation initiation site to be responsive to nucleocapsid protein. Hence, mapping of genetic determinants in parental and recombinant strains demonstrates that the nucleocapsid protein of strains that induce fulminant hepatitis is responsible for transcription of the fgl2 prothrombinase gene. These studies provide new insights into the role of the nucleocapsid gene in the pathogenesis of viral hepatitis.

In vitro culture of acute myelogenous leukemia blasts: a comparison of four different culture media

Proliferative responses and cytokine secretion were compared when AML blasts were cultured in the three serum-free media, X-Vivo 10, X-Vivo 15, and defined serum-free medium (IMDM with mercaptoethanol, low-density lipoprotein, albumin, and transferrin) and in media containing 10% inactivated fetal bovine serum (FBS). The following AML blast functions were investigated: (a) constitutive cytokine secretion, (b) autonomous and cytokine-dependent proliferation, and (c) accessory cell function during T cell activation. Constitutive cytokine secretion and accessory cell function differed markedly when using different culture media. For the constitutive AML blast secretion of IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha, no qualitative differences were seen, but quantitative differences were observed with decreased cytokine levels for cells cultured in X-Vivo 10 and X-Vivo 15. The accessory cell function of AML blasts was also decreased in the X-Vivo media, whereas differences were less pronounced when comparing AML blast proliferation. Our results clearly demonstrate that a well-characterized culture system is essential for in vitro studies of AML blast functions.

Hematopoietic growth factors and acute leukemia

Over the past decade, with the advent of hematopoietic growth factors, major strides have been made and multiple studies have attempted to define the use of these cytokines in acute leukemia. It is perhaps disappointing that, after so many studies, so many questions remain. Nevertheless, the role of cytokines in induction therapy seems to be established, although questions remain around the issue of priming therapy. Intriguing data regarding the potential for enhancing antimicrobial function should hopefully be resolved over the next few years. What is perhaps most reassuring is that the issue of safety, which for a considerable period of time precluded the development of clinical trials in acute leukemia, has been firmly laid to rest. The use of growth factors to protect normal stem cells during treatment of leukemia and to induce leukemic cell differentiation has not yet been the subject of many clinical trials. Also, growth factors are likely targets for the interruption of autocrine leukemic blast or progenitor cell growth, but again, few clinical observations are published. With the ongoing cloning of new growth factors active both in normal hematopoiesis and in leukemogenesis, the role of growth factor use in the treatment of AML will likely be the basis for much future preclinical and clinical activity.

Characterization of a unique factor-independent variant derived from human factor-dependent TF-1 cells: a transformed event

A factor-independent variant (TF-1a) has been isolated from the factor-dependent TF-1 cell line. The subline has been grown continuously in culture for > 1.5 years without added cytokines. The cells retain the ability to respond to multicytokines, with a different response pattern from its parental cell line. The TF-1 cells appeared singly in liquid culture. In contrast. TF-1a cells formed aggregates which increased markedly in size and in number upon TGFbeta1 treatment and showed a diminished TGFbeta-mediated growth inhibition. TF-1a, but not TF-1 cells, formed colonies in soft agar culture in the absence of any added growth factors, and developed the capacity to generate an invasive tumor(s) in nude mice. There was a constitutive activation of MAPK and MEK in TF-1a but not in TF-1 cells, which may be one of the mechanisms leading to factor-independent growth of TF-1a cells. Phenotypically, TF-1 cells were CD34+ /CD38+, whereas TF-1a cells were CD34+ /CD38-. This suggests that TF-1a may represent a less mature hematopoietic cell than TF-1. In conclusion, TF-1a is different from TF-1 in many important aspects which are associated with neoplastic transformation. The variant appears to be an excellent model for studying the process of progressive malignant transformation of myeloid cells and for studying signal pathways involved in the spontaneous and factor-induced growth of the cells.

Differential constitutive activation between STAT-related proteins and MAP kinase in primary acute myelogenous leukaemia

Many cytokines and growth factors stimulate multiple signal transduction pathways essential for proliferation in human acute leukaemia cells, including a mitogen-activated protein (MAP) kinase pathway and a Janus kinase (JAK)-STAT (signal transducers and activators of transcription) pathway. We have previously shown constitutive activation of MAP kinase in approximately 50% of acute myelogenous leukaemia (AML) samples. Recently, STAT proteins have been reported to be constitutively activated in 10-20% of AML cases. STAT3 and STAT5 are the main STAT proteins activated in haemopoietic progenitors in response to cytokines such as IL-3, GM-CSF, erythropoietin and thrombopoietin. Although the possibility of STAT1 protein as a substrate for MAP kinase at a serine residue has been suggested, the cross-talk between STATs and MAP kinase pathways in vivo, especially in leukaemia cells, remains unknown. We examined the phosphorylation of STAT 3 and STAT 5 at the tyrosine residues in AML samples in which MAP kinase activity had already been found. 40/50 primary AML cases (80%) exhibited constitutive tyrosine phosphorylation of STAT5. Electrophoretic mobility shift assay showed DNA binding activity of STAT5 correlated with tyrosine phosphorylation of STAT5. Similarly, with respect to STAT3, 17/23 cases examined (74%) showed constitutive tyrosine phosphorylation of STAT3. In addition, we examined the tyrosyl-phosphorylation of STAT5 isoforms, STAT5A and STAT5B, in 20 AML cases, and found selective STAT5B phosphorylation in the absence of STAT5A phosphorylation in three cases. Furthermore, in certain AML cases, constitutive activation of MAP kinase and STAT proteins occurred independently. No significant correlation of MAP kinase activation was observed with either tyrosine phosphorylation of STAT3/STAT5 or positive DNA binding of STAT proteins. These results suggest that constitutive activation of STAT proteins occurs commonly and that the causes of constitutive activation of these two major cascades are heterogeneous in AML.

Cytokine gene activity in AML cells in vivo in patients

The proliferation of acute myelogenous leukemia cells is dependent upon cytokine stimulation. Additionally, there is a body of literature which reports that leukemia cells produce GMCSF, IL6, and other cytokines. The study reported here, using an rt-multiplex polymerase method, determined the presence or absence of transcripts in freshly obtained AML cells for the following cytokine or cytokine-related genes: IL 1beta, IL1ra, TNF alpha, GMCSF, IL6, flt 3, and hSCF. This demonstrated that leukemia cell populations usually contain transcripts for IL1beta, TNF alpha, flt 3 and flt 3 ligand in vivo and that transcripts for the other cytokines only appear after the leukemia cells are processed in vitro. The presence of TNF alpha transcripts appears to be associated with resistance to remission induction therapy. Furthermore, the transcript profile of the leukemia cells can change during remission induction therapy. The data also demonstrate the assessment of cytokine production by leukemia cells after in vitro manipulation should not be extrapolated to the in vivo situation.

Granulocyte-macrophage colony-stimulating factor gene transcription is directly repressed by the vitamin D3 receptor. Implications for allosteric influences on nuclear receptor structure and function by a DNA element

The primary function of activated T lymphocytes is to produce various cytokines necessary to elicit an immune response; these cytokines include interleukin-2 (IL-2), interleukin-4, and granulocyte-macrophage colony-stimulating factor (GMCSF). Steroid hormones and vitamin A and D3 metabolites act to repress the expression of cytokines. 1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) down-modulates activated IL-2 expression at the level transcription, through direct antagonism of the transactivating complex NFAT-1/AP-1 by the vitamin D3 receptor (VDR). We report here that GMCSF transcription in Jurkat T cells is also directly repressed by 1, 25-(OH)2D3 and VDR. Among four NFAT/AP-1 elements in the GMCSF enhancer, we have focused on one such element that when multimerized, is sufficient in mediating both activation by NFAT-1 and AP-1 and repression in response to 1,25-(OH)2D3. Although this element does not contain any recognizable vitamin D response elements (VDREs), high affinity DNA binding by recombinant VDR is observed. In contrast to VDR interactions with positive VDREs, this binding is independent of VDR's heterodimeric partner, the retinoid X receptor. Moreover, VDR appears to bind the GMCSF element as an apparent monomer in vitro. Protease digestion patterns of bound VDR, and receptor mutations affecting DNA binding and dimerization, demonstrate that the receptor binds to the negative site in a distinct conformation relative to a positive VDRE, suggesting that the DNA element itself acts as an allosteric effector of VDR function. This altered conformation may account for VDR's action as a repressing rather than activating factor at this locus.

Interleukin-13 secretion by normal and posttransplant T lymphocytes; in vitro studies of cellular immune responses in the presence of acute leukaemia blast cells

T lymphocyte secretion of interleukin-13 (IL-13) in response to different activation signals was characterized in vitro. IL-13 release was investigated when virus transformed B lymphocytes or acute myelogenous leukaemia (AML) blasts were used as accessory cells during T cell activation. First, a majority of both CD4+ and CD8+ TCR alpha beta + T lymphocyte clones, derived from normal individuals and bone marrow transplant recipients, secreted IL-13 in response to a standardized mitogenic activation signal (phytohaemagglutinin + IL-2 + B lymphocyte accessory cells). The CD4+ cells showed significantly higher IL-13 levels than the CD8+ subsets. Second, when leukaemic accessory cells (more than 95% AML blasts) were used during T cell activation, IL-13 was released both during alloactivation of normal T lymphocytes and during mitogen activation of posttransplant T cells. Third, when normal T lymphocytes were stimulated with allogeneic AML blasts, addition of IL-13-neutralizing monoclonal antibodies decreased interferon gamma levels. Although addition of IL-13-neutralizing antibodies did not alter granulocyte-colony-stimulating factor secretion by allostimulating AML blasts, altered blast proliferation was detected for certain patients. Thus, most T cell clones can release IL-13, and IL-13 can modulate cytokine responses during T cell recognition of allogeneic AML cells.

Expression of Activated Mutants of the Human Interleukin-3/Interleukin-5/Granulocyte-Macrophage Colony-Stimulating Factor Receptor Common β Subunit in Primary Hematopoietic Cells Induces Factor-Independent Proliferation and Differentiation

To date, several activating mutations have been discovered in the common signal-transducing subunit (hβc) of the receptors for human granulocyte-macrophage colony-stimulating factor, interleukin-3, and interleukin-5. Two of these, FIΔ and I374N, result in a 37 amino acid duplication and a single amino acid substitution in the extracellular domain of hβc, respectively. A third, V449E, results in a single amino acid substitution in the transmembrane domain. Previous studies comparing the activity of these mutants in different hematopoietic cell lines imply that the transmembrane and extracellular mutations act by different mechanisms and suggest the requirement for cell type-specific molecules in signalling. To characterize the ability of these mutant hβc subunits to mediate growth and differentiation of primary cells and hence investigate their oncogenic potential, we have expressed all three mutants in primary murine hematopoietic cells using retroviral transduction. It is shown that, whereas expression of either extracellular hβc mutant confers factor-independent proliferation and differentiation on cells of the neutrophil and monocyte lineages only, expression of the transmembrane mutant does so on these lineages as well as the eosinophil, basophil, megakaryocyte, and erythroid lineages. Factor-independent myeloid precursors expressing the transmembrane mutant display extended proliferation in liquid culture and in some cases yielded immortalized cell lines.

Expression of Activated Mutants of the Human Interleukin-3/Interleukin-5/Granulocyte-Macrophage Colony-Stimulating Factor Receptor Common β Subunit in Primary Hematopoietic Cells Induces Factor-Independent Proliferation and Differentiation

To date, several activating mutations have been discovered in the common signal-transducing subunit (hβc) of the receptors for human granulocyte-macrophage colony-stimulating factor, interleukin-3, and interleukin-5. Two of these, FIΔ and I374N, result in a 37 amino acid duplication and a single amino acid substitution in the extracellular domain of hβc, respectively. A third, V449E, results in a single amino acid substitution in the transmembrane domain. Previous studies comparing the activity of these mutants in different hematopoietic cell lines imply that the transmembrane and extracellular mutations act by different mechanisms and suggest the requirement for cell type-specific molecules in signalling. To characterize the ability of these mutant hβc subunits to mediate growth and differentiation of primary cells and hence investigate their oncogenic potential, we have expressed all three mutants in primary murine hematopoietic cells using retroviral transduction. It is shown that, whereas expression of either extracellular hβc mutant confers factor-independent proliferation and differentiation on cells of the neutrophil and monocyte lineages only, expression of the transmembrane mutant does so on these lineages as well as the eosinophil, basophil, megakaryocyte, and erythroid lineages. Factor-independent myeloid precursors expressing the transmembrane mutant display extended proliferation in liquid culture and in some cases yielded immortalized cell lines.

Deoxyribonucleic acid triplex formation inhibits granulocyte macrophage colony-stimulating factor gene expression and suppresses growth in juvenile myelomonocytic leukemic cells

Juvenile myelomonocytic leukemia (JMML) is a severe childhood malignancy. The autocrine production of GMCSF is believed to be responsible for the spontaneous proliferation of JMML cells. A nuclear factor-kappaB (NF-kappaB)/Rel binding site within the GM-CSF gene promoter, termed the kappaB element, plays an important role in controlling transcription from the GM-CSF gene. We investigated the effect of an oligonucleotide GM3, directed to form a DNA triple helix across this kappaB element, on growth and GM-CSF production by JMML cells. Treatment of these cells, either unstimulated or induced by TNFalpha, with GM3 led to a significant and specific inhibition of both GM-CSF production and spontaneous colony formation. This constitutes the first report linking specific triplex-mediated inhibition of gene transcription with a functional outcome; i.e., cell growth. We observed the constitutive presence of NF-kappaB/Rel proteins in the nucleus of JMML cells. The constitutive and TNFalpha-induced NF-kappaB/Rel complexes were identical and were composed mainly of p50 and c-Rel proteins. Treatment of the cells with a neutralizing anti-TNFalpha monoclonal antibody completely abrogated constitutive nuclear expression of NF-kappaB/Rel proteins. These results indicate that the aberrant, constitutive GM-CSF gene activation in JMML is maintained by TNFalpha-mediated activation of NF-kappaB/Rel proteins. Our findings identify the molecular basis for the autocrine TNFalpha activation of the GM-CSF gene in JMML and suggest potential novel and specific approaches for the treatment of this aggressive childhood leukemia.

Effect of conditioned media, nutritive elements, and mitotic synchronization on the accuracy of the cytogenetic analysis in acute nonlymphocytic leukemia patients presenting with inv(16)/t(16;16) or t(15;17)

To improve the yield of the cytogenetic analysis in patients with acute nonlymphocytic leukemia (ANLL), six culture conditions for bone marrow or peripheral blood cells were tested in parallel. Two conditioned media (CM), phytohemagglutinin leukocyte PHA-LCM and 5637 CM, nutritive elements (NE), and methotrexate (MTX) cell synchronization were investigated in 14 patients presenting with either inv(16)/ t(16;16) (group 1, n = 9 patients) or t(15;17) (group 2, n = 5). The criteria used to identify the most favorable culture conditions were the mitotic index (MI), the morphological index (MorI), and the percentage of abnormal metaphases. In the presence of PHA-LCM and 5637 CM, the MI were significantly increased in group 2, whereas in the MTX conditions, MI remained very low in both groups. The values of the MorI did not reveal any significant changes in chromosome resolution between the conditions in either group. The addition of NE did not have a positive effect in quantity or quality of metaphases. Because of the variability of the response of leukemic cells to different stimulations in vitro, several culture conditions in parallel are required to ensure a satisfactory yield of the chromosome analysis in ANLL.

A recombinant fusion toxin targeted to the granulocyte-macrophage colony-stimulating factor receptor

Human granulocyte-macrophage colony stimulating factor (GMCSF) and its high affinity receptor function to regulate the proliferation and differentiation of myeloid lineage hematopoietic cells, and may participate in the pathogenesis of many malignant myeloid diseases. We have used genetic engineering based on the elucidated molecular structures of human granulocyte-macrophage colony-stimulating factor and diphtheria toxin (DT) to produce a recombinant fusion toxin, DTctGMCSF, that targets diphtheria toxin to high affinity GMCSF receptors expressed on the surface of blast cells from a large fraction of patients with acute myeloid leukemia (AML). DTctGMCSF was specifically immunoreactive with antidiphtheria toxin and anti-GMCSF antiseras, and exhibited the characteristic catalytic activity of diphtheria toxin, catalyzing the in vitro ADP-ribosylation of purified elongation factor 2. The cytotoxic effects of DTctGMCSF were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-tetrazolium (MTT) bromide assay of cell viability and in vivo assays of protein synthesis inhibition. DTctGMCSF were specifically cytotoxic to human leukemia cell lines bearing high affinity receptors for human GMCSF with IC50 of 10(-9) to 10(-11) M. It was not toxic to mammalian hematopoietic cell lines lacking human GMCSF (hGMCSF) receptors. In receptor positive cells, cytotoxicity can be specifically blocked by a large excess of hGMCSF, confirming that its cytotoxicity is mediated through the hGMCSF receptor. THough DTctGMCSF inhibited granulocyte-macrophage colony formation by committed myeloid progenitor cells (CFU-GM), it did not significantly affect erythroid burst formation by committed erythroid progenitor cells (BFU-E), or mixed granulocyte-erythroid-macrophage-megakaryocyte colony formation by pluripotent multilineage progenitor cells (CFU-GEMM). DTctGMCSF holds promise for the treatment of myeloid lineage malignancies, and is a useful reagent to study hematopoiesis.

Haemopoietic growth factors

Haemopoietic growth factors are involved in the production of the various blood cells from progenitors in the bone marrow, making them useful in a range of clinical situations. The genes for several of them have been cloned and their production engineered by recombinant technology, making them widely available. Myeloid growth factors are used to support patients in the aftermath of chemotherapy and bone marrow transplantation and have potential application in the treatment of infectious diseases. Erythropoietin is widely used for patients with anaemia due to failure of marrow production, having established its effectiveness in chronic renal failure. Thrombopoietin has recently been described and may provide a means to alleviate thrombocytopenia. Current indications and areas of recent reappraisal are addressed in this review.

Cytokines, molecular biological abnormalities, and acute myelogenous leukemia

Leukemia cell proliferation is dependent upon cytokines produced by the leukemia cells or by the microenvironment under stimulation by leukemia cells. Abnormal expression of the p53, rb, and ras genes is associated with cytokine production, suggesting that abnormal expression can affect leukemia cells by affecting intracellular growth controls and by stimulating cytokine production. While these observations suggest that cytokines can be used to stimulate leukemia proliferation during cytotoxic therapy increasing the sensitivity to treatment, they also suggest that inhibition of cytokine affects could increase clinical responses by reducing leukemia cell regrowth between courses of therapy.

DNA triplex formation selectively inhibits granulocyte-macrophage colony-stimulating factor gene expression in human T cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hemopoietic growth factor that is expressed in activated T cells, fibroblasts, macrophages, and endothelial cells. Although GM-CSF does not appear to be essential for normal hemopoiesis, overexpression of GM-CSF has been implicated in the pathogenesis of some diseases such as myeloid leukemia and chronic inflammation. An NF-kappaB/Rel binding site within the GM-CSF promoter, termed the kappaB element appears to be important for controlling expression in reporter gene assays in response to a number of stimuli in T cells. We investigated oligonucleotide-directed triple helix formation across this regulatory sequence as a potential tool to inhibit GM-CSF gene transcription. A 15-base oligonucleotide, GM3, was targeted to a purine-rich region in the GM-CSF proximal promoter, which overlaps the kappaB element. Gel mobility shift assays and DNase I footprinting demonstrated that GM3 formed a sequence-specific collinear triplex with its double-stranded DNA target. Triplex formation by GM3 blocked recombinant and nuclear NF-kappaB proteins binding to the GM-CSF element. GM3 also caused selective inhibition of the human T-cell lymphotrophic virus-1 Tax transactivator-induced luciferase activity from a reporter construct driven by the GM-CSF promoter in Jurkat T cells. Finally, GM3 greatly reduced the concentration of endogenous GM-CSF mRNA induced by different stimuli in Jurkat T cells but did not affect interleukin 3 mRNA levels in the same cells. We conclude that the kappaB element in the GM-CSF promoter plays a central role in the transcriptional activation of the endogenous GM-CSF gene. Colinear triplex formation acts as a selective transcriptional repressor of the GM-CSF gene and may have potential therapeutic application in cases of undesirable overexpression of this protein.

Abnormalities of retinoblastoma gene expression in hematological malignancies

The human retinoblastoma gene product which is involved in cell cycle control and also acts as a transcriptional repressor of genes involved in growth control, is constitutively expressed as a phosphoprotein in normal hemopoietic cells. Abnormalities of the retinoblastoma gene expression leading to loss of protein expression either due to structural changes, mutations or transcriptional abnormalities have been found in a variety of hematological malignancies. There is evidence that loss of Rb protein expression is particularly associated with tumour progression and an adverse response to therapy which may be linked to the biological effect of Rb protein loss on the growth characteristics of tumour cells.

In vitro autonomous proliferation in ANLL: clinical and biological significance

In acute non-lymphoblastic leukemia (ANLL) progenitor cells frequently display a certain degree of autonomous growth. The aim of the present work was to analyze the autonomous proliferative capacity of leukemic progenitors in both de novo and secondary to myeloproliferative disorders (MPD) and myelodysplastic syndromes (MDS), acute myeloid leukemias and to correlate with clinical and biological characteristics of the disease. Clonogenic assays with and without leukocyte conditioned medium with PHA (LCM-PHA) were performed and the autonomous proliferation index (API) calculated in a series of 50 patients (34 de novo ANLL, eight secondary to MPD and eight secondary to MDS). Patients were divided into two groups according to their API, low (< or = 0.4) or high (> 0.4). Autonomous growth was observed in 84% of cases studied (82% in de novo ANLL, 75% secondary to MDS and 100% secondary to MPD). The group with the highest API (29 patients) had increased levels of hemoglobin (P = 0.006) and platelets (P = 0.01). A high API was also associated with an immature phenotype of blast cells (P = 0.02). Upon analyzing the de novo ANLL separately we observed that a high API correlated with high Hb values (P = 0.02), a lower rate of complete remission (42% vs 61%) and a lower survival rate (medium of 3 vs 10 months). These findings suggest that the capacity for autonomous proliferation can condition the clinical and biological profile of the disease.

Biological features of leukaemic cells associated with autonomous growth and reduced survival in acute myeloblastic leukaemia

The blast cells from up to 70% of patients with acute myeloblastic leukaemia exhibit a variable degree of autonomous growth in vitro, which is related to the production of autocrine growth factors. It has recently been established that patients with autonomous blast cell growth have both a lower remission rate and a higher relapse rate, compared to otherwise comparable patients whose blasts exhibit non-autonomous in vitro growth. In a group of 50 patients the actuarial disease-free survival for the autonomous growth group was 11% at 5 years compared to greater than 50% for the non-autonomous growth group. This data suggests that AML blasts with autocrine growth characteristics may be resistant to cytotoxic drug therapy. Here we present further data demonstrating that AML blasts with autonomous growth are relatively resistant to the induction of programmed cell death (apoptosis) and that this is related to the autocrine production of GM-CSF. Also AML blasts with autonomous growths have aberrant expression of genes associated with resistance to apoptosis induced by cytotoxic drugs. These include high expression of the bcl-2 oncoprotein and abnormalities of expression of the p53 tumour suppressor gene. Furthermore bcl-2 expression was found to be unregulated by both exogenous and autocrine GM-CSF suggesting that the documented negative prognostic effect of autonomous growth on treatment outcome in AML, is in part due to the regulatory effect of autocrine GM-CSF on bcl-2 expression, thus protecting cells from apoptosis induced by cytotoxic drug therapy.

Interleukin-3 is an autocrine growth factor of human megakaryoblasts, the DAMI and MEG-01 cells

Interleukin-3 (IL-3), a cytokine known to be produced by activated T lymphocytes, mast cells, eosinophils and neutrophils, is a potent stimulator of normal haemopoiesis, particularly megakaryocytopoiesis. However, it remains unknown whether leukaemic megakaryoblasts can produce IL-3 and whether IL-3 is involved in the pathological process of megakaryoblastic leukaemia. In this study, several human leukaemia cell lines with or without megakaryocytic features, the DAMI, MEG-01, HEL, K562, HL-60 and U937, were chosen as the models. It was first demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) and indirect immunofluorescence assay that IL-3 was expressed in DAMI and MEG-01 cells, but not in other cell lines, although two erythroleukaemic cells, the HEL and K562, also possess some megakaryocytic features. Interestingly, the mRNA for IL-3 receptor was detected in nearly all the cell lines except K562 cells, suggesting that expression of IL-3 and its receptor may be dissociated in most of the cell lines and that co-expression of IL-3 and its receptor exists in megakaryoblastic cell lines, the DAMI and MEG-01. Of the cell lines which did not express IL-3 under unstimulated condition, only HEL cells were able to express IL-3 mRNA after treatment with PMA for 72 h. Furthermore, the proliferation of DAMI and MEG-01 cells could be enhanced in the presence of IL-3 and suppressed by the anti-IL-3 antibody and the IL-3 antisense oligodexyonucleotides (ODNs). These findings indicate that IL-3, as an autocrine growth factor, is involved in the growth of some megakaryocytic leukaemia cell lines.

All-trans retinoic acid promotes a differential regulation of adhesion molecules on acute myeloid leukaemia blast cells

In the present study we investigated the membrane expression of selectin ligands (CD15/Le(x), CDw65/VIM2, CD15s/sLe(x), beta 2 integrins (CD11a/LFA-1, CD11b/Mac-1) and CD45 phosphatase isoforms (CD45RA, CD45O) on leukaemic cells from 28 patients with acute myeloid malignancies cultured with and without all-trans retinoic acid (ATRA). Within each adhesion system. ATRA was able to differentially regulate distinct molecules. Furthermore, it was able to exert effects specific for acute promyelocytic leukaemia (APL) blast cells, as well as to induce a series of non-cytotype-restricted phenotypic changes. An impressive feature of ATRA induction was a simultaneous increase in the expression of CD15, CDw65 and CD11b on leukaemic promyelocytes. The sialylated antigen CD15s, however, showed results independent from the other two carbohydrates (CD15 and CDw65), suggesting a differential enzymatic regulation within the selectin ligands system. In spite of the well-recognized expression of CD11a throughout all stages of normal myeloid differentiation, APL blast cells were found to virtually lack LFA-1 expression. Moreover, ATRA was unable to promote an up-regulation of this antigen in APL, while inducing a frequent down-modulation in non-APL cases constitutively expressing this antigen. In APL cases ATRA generated an asynchronous phenotype (CD15+, CDw65+, CD11b+, CD11a-), undetectable on normally maturing myeloid cells, but consistent with the concept that incomplete differentiation, in terms of surface molecule expression, can be sufficient to obtain therapeutic results.

Specific human granulocyte-macrophage colony-stimulating factor antagonists

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic hemopoietic growth factor and activator of mature myeloid cell function. We have previously shown that residue 21 in the first helix of GM-CSF plays a critical role in both biological activity and high-affinity receptor binding. We have now generated analogues of GM-CSF mutated at residue 21, expressed them in Escherichia coli, and examined them for binding, agonistic, and antagonistic activities. Binding experiments showed that GM E21A, E21Q, E21F, E21H, E21R, and E21K bound to the GM-CSF receptor alpha chain with a similar affinity to wild-type GM-CSF and had lost high-affinity binding to the GM-CSF receptor alpha-chain-common beta-chain complex. From these mutants, only the charge reversal mutants E21R and E21K were completely devoid of agonistic activity. Significantly we found that E21R and E21K antagonized the proliferative effect of GM-CSF on the erythroleukemic cell line TF-1 and primary acute myeloid leukemias, as well as GM-CSF-mediated stimulation of neutrophil superoxide production. This antagonism was specific for GM-CSF in that no antagonism of interleukin 3-mediated TF-1 cell proliferation or tumor necrosis factor alpha-mediated stimulation of neutrophil superoxide production was observed. E. coli-derived GM E21R and E21K were effective antagonists of both nonglycosylated and glycosylated wild-type GM-CSF. These results show that low-affinity GM-CSF binding can be dissociated from receptor activation and have potential clinical significance for the management of inflammatory diseases and certain leukemias where GM-CSF plays a pathogenic role.

Wild-type p53 is required for apoptosis induced by growth factor deprivation in factor-dependent leukaemic cells

The p53 gene is a growth control gene, abnormalities of which have been implicated in a variety of cancers. Recently wild-type p53 has been shown to exist in two interchangeable conformational variants, which can be distinguished by specific p53 monoclonal antibodies. One conformation acts as a suppressor (PAb240-/PAb1620+) and one acts as a promoter (PAb240+/PAb1620-) of cell proliferation; the latter conformation is also that of mutant p53. We have previously shown that acute myeloblastic leukaemia (AML) blasts which proliferate autonomously in vitro express only p53 in the promoter conformation. In contrast, expression of PAb1620 was found only in blasts with non-autocrine growth in vitro and was diminished following stimulation by exogenous growth factors when there was a switch to p53 in the promoter (PAb240+) conformation. As AML blasts with non-autocrine growth undergo apoptosis when deprived of exogenous growth factors, we studied whether this was mediated by wild-type p53. Antisense oligonucleotides to p53 were used to suppress p53 protein expression in blasts with non-autocrine growth and also the factor-dependent human erythroleukaemia cell line TF-1. Following growth factor deprivation for 48 h, 20.6-53.6% of control blasts were apoptotic and demonstrated a typical 'ladder' on DNA electrophoresis characteristic of internucleosomal degradation of DNA. In the presence of p53 antisense, apoptosis was suppressed despite the absence of growth factor, however cell proliferation was not stimulated. We conclude that apoptosis occurring in factor-dependent AML blasts following growth factor deprivation is mediated by wild-type p53 (PAb1620+), and that conformational change of p53 to the PAb240+ conformation occurring either by mutation or by the action of autocrine growth factors would permit leukaemic cell survival by suppressing apoptosis.