Proteolytic degradation of Smad4 in extracts of AML blasts

Loss of transforming growth factor (TGF) beta signaling has been implicated in malignant transformation of various tissues. To investigate a potential role of Smad4 in acute myeloid leukemia (AML), the expression of Smad4 was determined in blast cells from AML patients. Western analysis of nuclear extracts of nine AML samples indicated the absence of Smad4 protein in two cases. Smad4 RT-PCR analysis of these cases indicated normal Smad4 mRNA expression, and sequencing of one of these cases revealed no mutations as compared to wild type Smad4. Next, it was investigated whether Smad4 protein from these AML cases was subject to proteolytic degradation by incubating cell extracts of these Smad4-negative AML cells with extracts from COS-7 cells in which a tagged Smad4 was overexpressed. Inhibitor studies indicated that the extracts of AML blasts lacking Smad4 possessed a serine-dependent proteolytic activity, capable of degrading Smad4. Transfection studies using an SBE containing reporter construct as well as RT-PCR analysis of endogenous TGFbeta1 responsive genes indicated that the AML blasts were still able to respond to TGFbeta1, despite the observed degradation of Smad4. It was, therefore, concluded that the degradation of Smad4 was possibly AML subtype-dependent, in vitro phenomenon, occurring during the preparation of nuclear and cellular extracts despite the addition of a protease inhibitor cocktail. The results indicate that care should be taken when interpreting data obtained from protein expression studies using AML blast cells.

Interaction between nitric oxide and subsets of human T lymphocytes with differences in glutathione metabolism

Nitric oxide (NO) modulates human T-lymphocyte responses through several mechanisms. In the current study we show that interactions between NO and glutathione (GSH) metabolism are related to the selective persistent inhibition of interferon-gamma (IFN-gamma) production by NO, which we previously identified. T cells were exposed to NO using the NO-donor compound Spermine-nonoate (Sper) and activated using anti-CD3 plus anti-CD28 monoclonal antibodies. Persistent inhibition of IFN-gamma by Sper was prevented by addition of the GSH precursor l-cysteine, which inhibits Sper induced GSH depletion. Subsets of cells were either susceptible (GSH(low)) or resistant (GSH(high)) to NO-induced GSH depletion. The GSH(low) subset was characterized by enhanced numbers of CD4+ cells, reduced numbers of activated cells as characterized by CD25 and CD69, and reduced numbers of memory (CD45RO+) cells relative to the GSH(high) population. Rather than directly affecting susceptibility to NO, these surface markers reflected different expression patterns. Particularly, the GSHlow subset was further characterized by decreased activity of the GSH synthesis related enzymes multi-drug resistance related protein (MRP)-1 and gamma-glutamyltranspeptidase (gamma-GT). Blocking gamma-GT, using acivicin was shown to exacerbate NO-induced GSH depletion and NO-induced apoptosis. Since NO induced apoptosis selectively affects IFN-gamma production these findings implicate GSH metabolism in the modulation and maintenance of the T helper (Th)1/Th2 balance.

Interleukin-6 promotes the production of interleukin-4 and interleukin-5 by interleukin-2-dependent and -independent mechanisms in freshly isolated human T cells

T helper 2 (Th2) cytokines [interleukin (IL)-4 and IL-5] play a central role in the development of allergic immune responses. After allergen provocation, the expression of Th2 cytokines is rapidly up-regulated in atopy and asthma. IL-6 is a multifunctional cytokine that is able to direct Th2 immune responses and is secreted by multiple tissue cell types. This study shows that IL-6 induces up-regulation of IL-4 and IL-5 after short (5 min) preincubation periods in freshly isolated, alpha-CD3/alpha-CD28-stimulated T cells. After longer preincubation periods with IL-6 (12 and 24 hr), the priming effect on IL-4 production gradually disappears, whereas the effect on IL-5 becomes more pronounced. In contrast, a small but significant inhibitory effect is found on the production of the Th1 cytokine interferon-gamma. Additional experiments indicate that the long-term priming effect of IL-6 on IL-5 production is dependent on IL-2 signalling. This is not the case for the short-term IL-6 effect on IL-5 secretion, where the p38 mitogen-activated protein kinase-dependent induction of activator protein-1 DNA-binding activity is involved, independent of signal transducer and activator of transcription 3 phosphorylation. In summary, these data demonstrate that the short-term and long-term priming effects of IL-6 on Th2 cytokine production are regulated by different mechanisms.

Fever and neutropenia in cancer patients: the diagnostic role of cytokines in risk assessment strategies

Cancer patients treated with chemotherapy are susceptible to bacterial infections. Therefore, all neutropenic cancer patients with fever receive standard therapy consisting of broad-spectrum antibiotics and hospitalization. However, febrile neutropenia in cancer patients is often due to other causes than bacterial infections. Therefore, standard therapy should be re-evaluated and new treatment strategies for patients with variable risk for bacterial infection should be considered. This paper reviews the changing spectrum of microorganisms and resistance of microorganisms to antibiotics in infection during neutropenia and discusses new strategies for the selection of patients with low-risk for bacterial infection using clinical and biochemical parameters such as acute phase proteins and cytokines. These low-risk patients may be treated with alternative therapies such as oral antibiotics, early discharge from the hospital or outpatient treatment.

Myeloma clonotypic B cells are hampered in their ability to undergo B-cell differentiation in vitro

In the peripheral blood (PB) of multiple myeloma (MM) patients, clonotypic B cells are present that express the identical V(D)J rearrangements as the malignant plasma cells in the bone marrow. In the present study, the proliferative capacity of clonotypic B cells from MM patients (n = 10) and the ability to differentiate in vitro was determined using the CD40-culturing system. For six patients, the presence of clonotypic B cells expressing variant immunoglobulin (Ig) isotypes was assessed by Ig isotype-specific allele-specific oligonucleotide reverse transcription polymerase chain reaction (ASO-RT-PCR) after culturing with CD40L and interleukin 4 (IL-4). In three out of six patients, clonotypic B cells expressing variant isotypes were detected both before and after culturing. The ability of clonotypic B cells to undergo B-cell differentiation was studied by abrogating CD40 signalling accompanied by IL-10 and IL-2 stimulation, enhancing differentiation towards Ig-secreting cells. The numbers of clonotypic B cells were determined by quantitative ASO-PCR. An increase in cell number was observed upon CD40L and IL-4 stimulation, whereas the relative number of clonotypic B cells was unaltered. In contrast, upon B-cell differentiation the relative number of clonotypic B cells decreased. In conclusion, clonotypic B cells can be cultured and isolated in vitro using the CD40 system. Clonotypic B cells responded to CD40 triggering in a similar fashion as to non-clonotypic normal B cells. However, the ability of clonotypic B cells to undergo in vitro activation and differentiation into Ig-secreting cells is hampered.

New vessel formation and aberrant VEGF/VEGFR signaling in acute leukemia: does it matter?

Although many patients with acute leukemia achieve a hematological complete remission with aggressive intensive therapy protocols, a large proportion shows reoccurrence of disease. Novel strategies are warranted. In acute leukemia new vessel formation is observed. New vessel formation is the result of angiogenesis and vasculogenesis. The degree of neovascularization in the bone marrow is correlated with vascular endothelial growth factor (VEGF) expression in the leukemic cells. The present review discusses the impact of new vessel formation related to acute leukemia, the relation with various angiogenic factors and will focus on VEGF/VEGF receptor signaling.

A genetic and genomic analysis identifies a cluster of genes associated with hematopoietic cell turnover

Hematopoietic stem cells from different strains of mice vary widely with respect to their cell cycle activity. In the present study we used complementary genetic and genomic approaches to identify molecular pathways affecting this complex trait. We identified a major quantitative trait locus (QTL) associated with variation in cell proliferation in C57BL/6 and DBA/2 mice to a 10 centimorgan (cM) region on chromosome 11. A congenic mouse model confirmed that a genomic interval on chromosome 11 in isolation confers the proliferation phenotype. To detect candidate genes we performed subtractive hybridizations and gene arrays using cDNA from highly enriched stem cells from parental strains. Intriguingly, a disproportionate number of differentially expressed genes mapped to chromosome 11 and, more specifically, these transcripts occurred in 3 distinct clusters. The largest cluster colocalized exactly with the cell cycling QTL. Such clustering suggested the involvement of genetic variation that affects higher-order chromosomal organization. This hypothesis was reinforced by the fact that differentially expressed genes mapped to recombination "coldspots," as a consequence of which clustered genes are collectively inherited. These findings suggest the functional interdependence of these closely linked genes. Our data are consistent with the hypothesis that this isolated cell cycle QTL does not result from a mutation in a single gene but rather is a consequence of variable expression of a collection of highly linked genes.

AL amyloidosis treated with induction chemotherapy with VAD followed by high dose melphalan and autologous stem cell transplantation

High dose melphalan (HDM) followed by reinfusion of autologous blood stem cells (ASCT) has been applied in AL amyloidosis. Vincristine, doxorubicin, and dexamethasone (VAD) rapidly decrease light chain production in multiple myeloma. In a Phase I/II study of VAD followed by HDM and ASCT in AL amyloidosis, toxicity, feasibility, and response to this regimen were evaluated. Over a 5-year period 38 patients with AL amyloidosis were seen of which 12 out of 18 eligible patients participated in the study. VAD induced a distinct clonal response in 50% (6/12) of the patients, but without clinical improvement. In 11 patients HDM and ASCT was applied. Six months after ASCT 78% (7/9) of the surviving patients showed partial clonal response and none responded completely. Clinical condition evidently improved in 67% (6/9) of survivors, whereby clonal response, clinical response, performance score, and SAP scintigraphs were concordant. Therefore a complete clonal response is not a prerequisite for clinical improvement. With median follow-up after ASCT of 25 months, 75% of the study group patients were alive. Mortality was strongly depending on the number of organs involved Patients treated with HDM and ASCT had better survival than those not eligible (P < 0.0005).

Prostaglandin-E2 enhances EPO-mediated STAT5 transcriptional activity by serine phosphorylation of CREB

Erythroid colony formation in response to erythropoietin (EPO) stimulation is enhanced by costimulating the cells with prostaglandin-E2 (PGE2). The present study further analyzed the underlying mechanisms and demonstrated that EPO-mediated STAT5 transactivation in the erythroid AS-E2 cell line was enhanced 6-fold by PGE2 (10 microM), without affecting the STAT5 tyrosine phosphorylation or STAT5-DNA binding. Moreover, the PGE2-enhancing effect was independent of STAT5 serine phosphorylation. In AS-E2 cells STAT5 is constitutively phosphorylated on Ser780 (STAT5A) and EPO-dependently phosphorylated on Ser726/731 (STAT5A/STAT5B), but overexpression of STAT5 serine mutants did not affect STAT5 transactivation. In addition, PGE2 did not affect STAT5 serine phosphorylation. Instead, the stimulatory effect of PGE2 on STAT5 signaling could be mimicked by dibutyryl-cyclic adenosine monophosphate (cAMP) and the phosphodiesterase inhibitor IBMX, suggesting that the effect was mediated by cAMP. Activation of the cAMP pathway resulted in cAMP-response element binding protein (CREB) phosphorylation, which was sustained in the presence of EPO plus PGE2 and transient on EPO stimulation alone. The costimulatory effect of PGE2 on EPO-mediated STAT5 transactivation was inhibited by overexpression of serine-dead CREB or protein kinase A (PKA) inhibitor (PKI), in contrast to EPO-mediated transactivation, which was PKA independent. Furthermore, CREB-binding protein (CBP)/p300 was shown to be involved in EPO-mediated STAT5 transactivation, and a CBP mutant with increased affinity for CREB resulted in an additional enhancement of the PGE2 effect. Finally, we demonstrated that the STAT5 target genes Bcl-X, SOCS2, and SOCS3 were up-regulated by costimulation with PGE2. In summary, these studies demonstrate that PGE2 enhancement of EPO-induced STAT5 transactivation is mediated by the cAMP/PKA/CREB pathway.

Growth factor treatment prior to low-dose total body irradiation increases donor cell engraftment after bone marrow transplantation in mice

Low-toxicity conditioning regimens prior to bone marrow transplantation (BMT) are widely explored. We developed a new protocol using hematopoietic growth factors prior to low-dose total body irradiation (TBI) in recipients of autologous transplants to establish high levels of long-term donor cell engraftment. We hypothesized that treatment of recipient mice with growth factors would selectively deplete stem cells, resulting in successful long-term donor cell engraftment after transplantation. Recipient mice were treated for 1 or 7 days with growth factors (stem cell factor [SCF] plus interleukin 11 [IL-11], SCF plus Flt-3 ligand [FL], or granulocyte colony-stimulating factor [G-CSF]) prior to low-dose TBI (4 Gy). Donor cell chimerism was measured after transplantation of congenic bone marrow cells. High levels of donor cell engraftment were observed in recipients pretreated for 7 days with SCF plus IL-11 or SCF plus FL. Although 1-day pretreatments with these cytokines initially resulted in reduced donor cell engraftment, a continuous increase in time was observed, finally resulting in highly significantly increased levels of donor cell contribution. In contrast, G-CSF treatment showed no beneficial effects on long-term engraftment. In vitro stem cell assays demonstrated the effect of cytokine treatment on stem cell numbers. Donor cell engraftment and number of remaining recipient stem cells after TBI were strongly inversely correlated, except for groups treated for 1 day with SCF plus IL-11 or SCF plus FL. We conclude that long-term donor cell engraftment can be strongly augmented by treatment of recipient mice prior to low-dose TBI with hematopoietic growth factors that act on primitive cells.

Dose-finding study of valspodar (PSC 833) with daunorubicin and cytarabine to reverse multidrug resistance in elderly patients with previously untreated acute myeloid leukemia

INTRODUCTION

This trial was designed to determine the maximum tolerated dose of intravenous daunorubicin (DNR) in combination with valspodar and to test the feasibility of P-glycoprotein modulation using valspodar in elderly patients with previously untreated acute myelogenous leukemia receiving standard induction chemotherapy.

METHODS

Patients > or =60 years of age with previously untreated AML received valspodar (10 mg/kg/24 h by continuous intravenous infusion [CIV] on days 1-4 with a 2-mg/kg loading dose on day 1) in conjunction with two cycles of induction chemotherapy consisting of cytarabine (200 mg/m(2) CIV on days 1-7), and DNR (35 mg/m(2) [cohort 1] or 45 mg/m(2) [cohort 2] on days 1-3, intravenous bolus). Patients were assessed for dose-limiting toxicities (DLT), response rate, event-free and overall survival, and pharmacokinetics of valspodar and DNR.

RESULTS

Valspodar was well tolerated at the lower DNR dose level (ie, 35 mg/m(2)) resulting in a 21% rate of DLT and only three toxic deaths. Treatment-related mortality was unacceptably high at the 45 mg/m(2) DNR dose level. The complete response rate was 49% overall and similar in both cohorts. The median overall survival of patients was 333 days in cohort 1 compared to 98 days in cohort 2. At baseline, 70% of assessable patients were P-glycoprotein positive.

CONCLUSION

Substantial inhibition of P-glycoprotein activity can be achieved in this patient population at clinically tolerable doses of valspodar and DNR. The maximum tolerated dose of DNR was established as 35 mg/m(2). This regimen is being further evaluated in phase III trials.

Peripheral blood stem cells differ from bone marrow stem cells in cell cycle status, repopulating potential, and sensitivity toward hyperthermic purging in mice mobilized with cyclophosphamide and granulocyte colony-stimulating factor

Peripheral blood stem cells (PBSCs) are increasingly used in autologous stem cell transplantations. We investigated the mobilizing effect of a combined cyclophosphamide (CTX) and granulocyte colony-stimulating factor (G-CSF) treatment on progenitor cells (STRA) and primitive stem cells (LTRA) in normal and splenectomized CBA/H mice. This combined treatment not only resulted in mobilization but also in expansion of hematopoietic stem cell subsets. The latter phenomenon was somewhat suppressed in splenectomized animals, but in these mice an enhanced mobilization of STRA and LTRA cells into the peripheral blood was observed. Furthermore, we studied the engraftment potential of mobilized PBSCs. Mice transplanted with PBSCs engrafted significantly better compared to mice transplanted with bone marrow stem cells from control and mobilized mice. The repopulation curve was characterized by a less-deep nadir indicating that the differences occur during the initial phase after transplantation. Contamination of autologous PBSC transplants with malignant cells is noticed frequently and is the basis for urging the use of purging modalities. Here we used hyperthermia and found that the mobilized progenitor cells in peripheral blood are more resistant to hyperthermia than those in the bone marrow (i.e., a survival of 11 +/- 5% after 90 min at 43 degrees C for peripheral blood progenitors, compared to 0.5 +/- 0.4% in bone marrow of mobilized animals and 1.6 +/- 0.5% in normal animals, respectively). Hyperthermic purging does not eliminate the superior repopulating features of a PBSC graft, as is demonstrated by an increased median survival time of lethally irradiated mice transplanted with purged PBSCs. In conclusion, our data demonstrate that CTX + G-CSF-mobilized PBSCs have an enhanced engraftment potential concomitantly with a decreased cycling activity and hence a decreased hyperthermic sensitivity. These findings support the use of these mobilized PBSCs for autologous stem cell transplantation and strengthen the basis for using hyperthermia as a purging modality.

Evaluation assays measuring platelet kinetics in bone marrow and peripheral blood. An overview

Platelets play an important role in haemostasis and thrombosis. For an understanding of the pathophysiology and treatment of thrombocytopenia, it is not sufficient to measure only the platelet count. Platelet kinetic parameters, such as platelet survival and turnover, might be useful because many thrombocytopenia related disorders result from the interaction between production, utilization or destruction, and sequestration of platelets. Therefore, measuring platelet turnover with radiolabelled platelets could be a sensitive and qualitative tool for clinicians. However, the method does not enjoy widespread use because it has some serious drawbacks, such as the problems associated with the manipulation of blood and platelets, and the use of radioactivity. Recently, other useful assays for measuring platelet fluxes have been described in the literature, including plasma thrombopoietin and glycocalicin. In this review, these new tests will be described, compared with the classical method using radiolabelled platelets, and finally evaluated for their usefulness in clinical practice.

Expression and activity of breast cancer resistance protein (BCRP) in de novo and relapsed acute myeloid leukemia

Overexpression of the breast cancer resistance protein (BCRP) efflux pump in human cancer cell lines results in resistance to a variety of cytostatic agents. The aim of this study was to analyze BCRP protein expression and activity in acute myeloid leukemia (AML) samples and to determine whether it is up-regulated due to clonal selection at relapse/refractory disease. BCRP protein expression was measured flow cytometrically with the monoclonal antibodies BXP-34 and BXP-21 in 20 paired samples of de novo and relapsed/refractory AML. BXP-34/immunoglobulin G1 ratios were observed of 1.6 +/- 0.5 (mean +/- SD, range 0.8-2.7) and BXP-21/immunoglobulin G2a ratios of 4.9 +/- 3.0 (range 1.1-14.5) in the patient samples versus 9.8 +/- 6.8 and 6.5 +/- 2.4, respectively, in the MCF-7 cell line. BCRP activity was determined flow cytometrically by measuring mitoxantrone accumulation in absence and presence of the inhibitor fumitremorgin C. Mitoxantrone accumulation, expressed as mean fluorescence intensity (MFI), varied between 44 and 761 MFI (227 +/- 146 MFI) and correlated inversely with BCRP expression (r = -0.58, P <.001). Addition of fumitremorgin C showed a small increase in mitoxantrone accumulation (11 +/- 29 MFI, n = 40) apart from the effect of PSC833 and MK-571. No consistent up-regulation of BCRP expression or activity was observed at relapse/refractory disease; some cases showed an increase and other cases a decrease at relapse. Relatively high BCRP expression correlated with immature immunophenotype, as determined by expression of the surface marker CD34 (r = 0.54, P =.001). In conclusion, this study shows that BCRP protein is expressed at low but variable levels in AML, especially in immature CD34(+) cells. BCRP was not consistently up-regulated in relapsed/refractory AML.

The role of drug efflux pumps in acute myeloid leukemia

A major problem in the treatment of patients with acute myeloid leukemia (AML) is the occurrence of resistance to structurally and functionally unrelated chemotherapeutic agents, called multidrug resistance (MDR). One of the known MDR mechanisms is the overexpression of adenosine triphosphate (ATP)-dependent efflux pumps. Permeability-glycoprotein (P-gp), the best characterized of the human drug efflux pumps, has been shown to be associated with poor treatment outcome in AML patients. Besides P-gp, in addition the multidrug resistance protein 1 (MRP1) appeared to contribute to the observed resistance in AML. Alternative transporter proteins, such as the MRP1 homologues MRP2, MRP3, MRP5 and MRP6, and the breast cancer resistance protein (BCRP), have been shown to be expressed at variable levels in AML patient cells. The latter proteins have been described to confer resistance to chemotherapeutic agents, such as daunorubicin, mitoxantrone, etoposide and 6-mercaptopurine, which are generally used in the treatment of AML patients; however, theyhave not yet proven to play a role in drug resistance in AML. The present review gives an overview of the current knowledge concerning these drug transporters, with a focus on the role of the transporter proteins in AML.

Co-expression of CD30 ligand and interleukin 4 (IL-4) receptors by acute myeloid leukaemia blasts is associated with the expansion of IL-4-producing CD30+ normal T cells

CD30 ligand (CD30L), but not its cognate receptor CD30, is frequently expressed on acute myeloid leukaemia (AML) blasts. In the present study, we found that leukaemic blasts presenting surface CD30L displayed a characteristic cytokine-receptor pattern that makes them ideal targets for those cytokines usually produced by Th2-type cell subsets. In particular, even though a broad distribution of Th2 cytokine receptors by AML blasts was shown, we demonstrated the almost exclusive expression of interleukin 4 (IL-4) receptor (R), in the absence of its cognate cytokine, by CD30L+ AML. Furthermore, a number of Th2-associated markers, including CD30, IL-4 and GATA-3, were expressed by residual T cells derived from CD30L+ AML but not from CD30L- AML, in which the presence of the Th1-associated marker LAG-3 was documented in some cases. The production of IL-4 in the absence of interferon gamma (IFN-gamma) was also detected in CD3+/CD30+ T cells from CD30L+ AML. These results, along with the shift toward IL-4-producing specific T-cell clones observed in CD30L+ AML samples by enzyme-linked Immunospot (ELISpot) assay, were consistent with the hypothesis of a Th2 polarization taking place in T cells from CD30L+ AML. The notion that IL-4 was able to enhance in vitro proliferation of CD30L+/IL-4R+ purified leukaemic blasts suggests that the selective interaction of IL-4-producing CD30+ T cells with CD30L+ leukaemic progenitors may have a role in the progression of this particular AML subset.

Downregulation of IL-6-induced STAT3 tyrosine phosphorylation by TGF-beta1 is mediated by caspase-dependent and -independent processes

To explore the possible cross-talk between the IL-6 and TGF-beta1 pathways in AML blast cells, the effect of TGF-beta1 pretreatment on IL-6-induced STAT3 tyrosine phosphorylation was studied. A reduction of STAT3 tyrosine phosphorylation after TGF-beta1 pretreatment was observed in four out of 40 AML cases (10%), although all of the AML cases responded to TGF-beta1 by means of SMAD3 translocation. The reduced IL-6-mediated STAT3 tyrosine phosphorylation after pre-treatment with TGF-beta1 was associated with apoptosis and coincided with the degradation of certain cellular proteins, including JAK1 and -2 and Tyk2, without affecting the ERK expression and phosphorylation. Furthermore, treatment of AML blasts with the cytostatic agent VP16, as an alternative way to induce apoptosis, resulted in a similar degree of degradation of JAK kinases and concomitant reduction of IL-6-mediated STAT3 tyrosine phosphorylation. Although degradation of JAK kinases could be rescued by incubating the cells with the pan-caspase inhibitor Z-VAD-fmk, the attenuating effect of TGF-beta1 treatment on the STAT3 tyrosine phosphorylation was still partly present. It was shown that in AML cells cultured in the presence of Z-VAD-fmk, TGF-beta1 pretreatment resulted in a reduction of JAK1 phosphorylation upon IL-6 stimulation. Expression of SOCS1 and -3 could be ruled out as a possible cause of reduced JAK1 phosphorylation levels in the investigated AML case.

In vitro megakaryocyte expansion in patients with delayed platelet engraftment after autologous stem cell transplantation

Increasing the number of megakaryocytic cells in stem cell transplants by ex vivo expansion culture may provide an approach to accelerate platelet engraftment after high-dose chemotherapy. However, it is unknown if a relationship exists between the expansion potential of progenitor cells and the time to platelet engraftment in vivo. Therefore, we questioned if those patients who potentially would benefit most from expanded cell supplements are able to generate megakaryocytic cells efficiently in vitro. The in vitro megakaryocyte proliferation was analyzed from 19 leukapheresis samples from a group of multiple myeloma patients who all showed rapid neutrophil engraftment, but varied from 7 to 115 days post-transplant to achieve platelet levels >20x10(9)/l. CD34+ cells were isolated and analyzed for their potential to form megakaryocytic colonies (CFU-Mk) in colony assays and megakaryocytic (CD61+) cells in suspension cultures. The frequency and size of CFU-Mk and the expansion potential of CD61+ cells varied eightfold between individual patients. A similar range was found with CD34+ cells isolated from normal bone marrow (n=9). Rapid platelet engraftment occurred in patients receiving both high or low CFU-Mk doses and with high and low expansion of CD61+ cells. Four patients who experienced prolonged (>3 weeks) thrombocytopenia received low CFU-Mk doses, but the expansion potential was around median values or higher. Therefore, we conclude that the megakaryocyte proliferation is not impaired and that in vitro expansion could increase the number of megakaryocytic cells, although other factors could be more relevant in platelet engraftment in this group of patients.

LIF-induced STAT3 signaling in murine versus human embryonal carcinoma (EC) cells

Self-renewal and the maintenance of pluripotency of mouse embryonal stem (ES) cells in vitro requires exogenous leukemia inhibitory factor (LIF). Mouse ES cells can be cultured and kept undifferentiated in the absence of embryonal feeder-cell layers when exogenous LIF concentrations are maintained above a threshold concentration. An important downstream target of LIF signal transduction in mouse ES cells is the transcription factor signal transducer and activator of transcription 3 (STAT3). In contrast to mouse ES cells, human ES cells are unresponsive to LIF and depend on feeder cells for undifferentiated growth. Here, we investigated the activation patterns of LIF-downstream effectors in mouse and human embryonal carcinoma (EC) cells. We report that LIF induces both ERK-1 as well as STAT3 activation in mouse P19 EC cells. LIF enhances the proliferation rate of P19 EC cells, which depends on ERK activity but does not require activation of STAT3. In contrast, LIF does not activate STAT3, ERK, or the gp130 receptor in human N tera-2/D1 EC cells, although all receptor components are expressed. The negative feedback protein suppressor of cytokine signaling 1 (SOCS-1) is constitutively expressed in N tera-2/D1 EC cells, suggesting that LIF signal transduction is inhibited by elevated levels of SOCS-1 expression.

Identification of LIL-STAT in monocytic leukemia cells and monocytes after stimulation with interleukin-6 or interferon gamma

In acute myelogenous leukemia (AML) and adult T-cell leukemia, it has been demonstrated that the transcription factor LIL-STAT is constitutively activated. To identify and characterize this unknown LIL-STAT protein, electrophoretic mobility shift assay (EMSA) and oligoprecipitation assays were performed by using lipopolysaccharide/interleukin-1 (IL-1)-responsive element (LILRE) oligonucleotide probes. EMSA demonstrated a significant increase in LIL-STAT binding to the LILRE oligonucleotides after interferon gamma (IFN-gamma) and IL-6 stimulation of THP-1 cells. In unstimulated THP-1 and AML cells, LILRE oligonucleotide probes bound only to STAT1 alpha and beta isoforms. The LILRE element showed a significant increase in binding of both alpha and beta isoforms of STAT1 and STAT3 upon IFN-gamma and IL-6 stimulation. Similar results were observed with human monocytes upon IL-6 or IFN-gamma stimulation. These studies indicate that LIL-STAT consists of STAT1 and STAT3 proteins that bind to the LILRE DNA consensus site in a stimulus-dependent way.

Effects of prednisone and splenectomy in patients with idiopathic thrombocytopenic purpura: only splenectomy induces a complete remission

Idiopathic thrombocytopenic purpura (ITP) is a heterogeneous disease, whereby it is unclear if and in which way prednisone and splenectomy affect the platelet kinetics leading to a complete remission. To determine the effects of prednisone and splenectomy on the mean platelet life (MPL) and platelet production, platelet kinetic studies with Indium-111 tropolonate-labeled autologous platelets were performed in patients with ITP ( n=41). In 17 patients platelet kinetic studies were performed before and during prednisone treatment, and in 24 patients before and after splenectomy. MPL increased after prednisone therapy only in patients ( n=13) with a full recovery (FR, platelets >150 x 10(9)/l) and partial recovery (PR, 50 x 10(9)/l <platelets <150 x 10(9)/l) from 2.1+/-1.5 days to 4.9+/-1.3 days in FR patients (p=0.03) and from 1.1+/-0.8 days to 2.4+/-1.1 days in PR patients, which is significantly shorter than in normal controls (9.2+/-1.2, p<0.0001). The platelet production demonstrated an impressive increase (threefold) during prednisone treatment in all responding and nonresponding patients. These results suggest that the clinical response to prednisone is more related to the effect on MPL than on platelet production. In contrast, the group of splenectomized patients showed that a full recovery of platelet count was associated with near normalization of the MPL (2.4+/-1.6 days vs 8+/-1.4 days) and platelet production (119+/-60 vs 162+/-35 x 10(9)/day). These results demonstrate that prednisone as well as splenectomy increase MPL and production in patients with ITP. However, only after splenectomy is a complete remission obtained, defined as a normal platelet count, mean platelet life, and platelet production.

Regulation of constitutive STAT5 phosphorylation in acute myeloid leukemia blasts

In the present study, we examined the underlying mechanism, which causes the constitutive tyrosine phosphorylation of signal transducer and activator of transcription 5 (STAT5) in acute myeloid leukemia (AML) blasts. Constitutive STAT5 phosphorylation was observed in 18 of 26 (69%) patients with AML. The constitutive STAT5 phosphorylation was caused by different mechanisms. In the majority of the investigated cases (71% (12 of 17)) constitutive STAT5 phosphorylation was associated with autophosphorylation of the type III receptor tyrosine kinase Flt3. In 47% (eight of 17) of these cases autophosphorylation of Flt3 coincided with tandem duplications of the Flt3 gene, resulting in constitutive phosphorylation of the receptor, while 24% (four of 17) of the cases demonstrated STAT5 phosphorylation and Flt3 autophosphorylation without mutations. In addition, a subset of AML cases (29% (five of 17)) had no autophosphorylation of the Flt3 receptor, but demonstrated constitutive STAT5 phosphorylation, which was partly due to autocrine growth factor production. All AML cases with high STAT5 and Flt3 phosphorylation demonstrated, in general, a lower percentage of spontaneous apoptosis, compared to AML blasts with no spontaneous STAT5 phosphorylation. Addition of the receptor tyrosine III kinase inhibitor AG1296 strongly inhibited STAT5 phosphorylation and enhanced the percentage of apoptotic cells without modulating the Bcl-xl protein levels. These data indicate that in the majority of AML cases the constitutive STAT5 phosphorylation is caused by Flt3 phosphorylation mostly due to mutations in the receptors and associated with a low degree of spontaneous apoptosis.

A possible role for spontaneous interleukin-8 production by acute myeloid leukemic cells in angiogenesis related processes: work in progress

BACKGROUND

Recently, the role of inter-leukin-8 (IL-8) in angiogenesis was reported. We consequently addressed here the question whether IL-8 produced by acute myeloid leukemia (AML) blasts might have a comparable function.

PROCEDURE

In 21 pediatric patients with AML the role of AML derived IL-8 in angiogenesis related processes were investigated. Therefore, IL-8 protein and mRNA expression were measured and endothelial cell (EC) migration and proliferation assays were performed. In addition, bFGF and VEGF mRNA expression were measured by RT-PCR.

RESULTS

In the supernatant of the AML blasts, IL-8 protein was present in a varying amount (median 0.86 microg/L, range: 0.1-320 microg/L) and confirmed by RT-PCR. Normal bone marrow mononuclear cells secreted a significant lower amount of IL-8 protein (median: 0.053 microg/L, range: 0.023-0.055 microg/L, P = 0.007). Seven of the 17 tested AML supernatants induced a varying low amount of EC proliferation compared to control media, which was not inhibited by anti-IL-8 antibodies. In contrast, in the EC migration assay, 15 out of the 17 AML supernatants tested, showed an increased EC migration (median fold increase: 1.97, range: 0.66-6.36, P = 0.002) compared to control medium. The increase in EC migration could partially be blocked by anti-IL-8 in 59% of the cases (18% decrease, range 0-62%, P = 0.003). Other contributors for the increase in EC migration were also determined. Vascular endothelial growth factor (VEGF) transcripts by RT-PCR were demonstrated in six out of the nine tested AML cases, while no transcripts for basic fibroblast growth factor (VEGF) could be shown.

CONCLUSIONS

Neutralizing anti IL-8 antibodies inhibit EC migration when stimulated with AML supernatant. This suggests a facilitating role for AML-derived IL-8 in an important step in angiogenesis.

Effects of overexpression of the SH2-containing inositol phosphatase SHIP on proliferation and apoptosis of erythroid AS-E2 cells

Previous studies have demonstrated that SH2-containing inositol phosphatase (SHIP) is involved in the control of B cell, myeloid cell and macrophage activation and proliferation. The goal of the present study was to examine the role of SHIP during proliferation and apoptosis in cells of the erythroid lineage. Wild-type and catalytically inactive SHIP proteins were overexpressed in the erythropoietin (EPO)-dependent cell line AS-E2. Stable overexpression of catalytically inactive SHIP decreased proliferation and resulted in prolonged activation of the extracellular signal-regulated protein kinases ERK1/2 and protein kinase B (PKB), while wild-type SHIP did not affect EPO-mediated proliferation or phosphorylation of ERK and PKB. When AS-E2 cells were EPO deprived a significant increase in apoptosis was observed in clones overexpressing wild type. Mutational analysis showed that this increase in apoptosis was independent of the enzymatic activity of SHIP. The enhanced apoptosis due to overexpression of SHIP was associated with an increase in caspase-3 and -9 activity, without a distinct effect on caspase-8 activity or mitochondrial depolarization. Moreover, in cells overexpressing SHIP apoptosis could be reduced by a caspase-3 inhibitor. These data demonstrate that in the erythroid cell line AS-E2 overexpression of catalytically inactive SHIP reduced proliferation, while overexpression of wild-type SHIP had no effect. Furthermore, overexpression of SHIP enhanced apoptosis during growth factor deprivation by inducing specific caspase cascades, which are regulated independently of the 5-phosphatase activity of SHIP.

Mobilized human CD34+ hematopoietic stem cells enhance tumor growth in a nonobese diabetic/severe combined immunodeficient mouse model of human non-Hodgkin's lymphoma

Autologous peripheral blood stem cell mobilization is increasingly applied in the treatment of hematological malignancies. Despite the frequent clinical use in a setting of residual disease, it is not known whether mobilization of hematopoietic stem cells might facilitate tumor outgrowth in vivo. In the bone marrow, a bipotential precursor for hematopoietic and endothelial cells called hemangioblast exists. This hemangioblast, characterized by the expression of CD34 and vascular endothelial growth factor receptor (VEGFR)-2, is released from the bone marrow by mobilization and might be able to result in not only the generation of peripheral blood cells but vasculogenesis due to differentiation of the hemangioblast along the endothelial lineage [in addition to VEGFR-2 expression, angiopoietin-2 (ANG-2) expression can also be found in this stage]. New vessel formation in the tumor is critical for tumor growth. A xenotransplant model was established with 10 x 10(6) Daudi cells (non-Hodgkin's lymphoma) s.c. injected in the neck region of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, who were sublethally irradiated with 2 Gy. At day 10 after tumor inoculation, half of the mice were given 0.5 x 10(6) human CD34+ cells i.v., whereas the other half were given PBS i.v. The human CD34+ cells were obtained from leukapheresis samples of myeloma patients undergoing autologous peripheral blood stem cell mobilization. We compared tumor growth and human-specific VEGFR-2 and ANG-2 expression in the two groups. Tumor growth is enhanced 2-fold when mobilized hematopoietic human CD34+ cells are given compared with PBS controls (P = 0.004). In addition, the human-specific VEGFR-2 and ANG-2 reverse transcription-PCR was only positive in the tumors of mice i.v. injected with human CD34+ cells. This indicates that the injected human CD34+ cells home to the tumors and differentiate along the endothelial lineage. In the present study, we demonstrate that mobilized human CD34+ hematopoietic cells injected i.v. might facilitate the outgrowth of tumors in the setting of minimal residual disease. Malignant tumors are capable of incorporating human CD34+ hematopoietic cells. This study questions the safety of leukapheresis in patients with (residual) tumor and has important implications for further development of intensive chemotherapy protocols with autologous stem cell rescue.