ALBERT

Description: Mutations in the receptor tyrosine kinase Flt3 represent one of the most common known genetic lesions in AML. Internal tandem duplication (ITD) mutations clustered in the juxtamembrane domain are the most frequent and best characterized mutations found in Flt3. We and others have previously reported that oncogenic activation of Flt3 by ITD mutations activate aberrant signaling including activation of STAT5, up-regulation of STAT targets like-Pim and SOCS proteins and repression of the myeloid transcription factors Pu.1 and c/EBP-alpha (Mizuki et al., Blood96: 3907–14, 2000; Mizuki et al., Blood101: 3164–73, 2003). Earlier studies have observed activation of Src and Jak kinases by Flt3-ITD but the mechanisms of STAT5 activation by Flt3-ITD and the role of Src or Jak kinases in this process remains unclear. Using the specific small molecule inhibitors PP-1 and PP-2, we analyzed the role of Src kinases in Flt3-ITD mediated STAT5 activation. Treatment of Flt3-ITD expressing 32D cells with PP-1 and 2 had only marginal effect on Flt3-ITD induced STAT5 activation, which was due to a proportional inhibition of Flt3 kinase by these inhibitors. Similar results were obtained with AG490, reportedly a specific inhibitor of Jak2. However, use of cell a line deficient for all Src family kinases revealed a Src-independent activation of STAT5 by Flt3-ITD. Also, using cell lines deficient for Jak2 or Tyk2 we show that Flt3-ITD induced STAT5 activation independent of Jak2 or Tyk2 kinases. To rule out a possible redundant role of different Jak kinases in Flt3-ITD mediated STAT5 activation, we used SOCS1, a target of STAT5 and a potent molecular inhibitor of all Jak kinases. Surprisingly, retroviral transduction of 32D cells with SOCS1 inhibited IL-3 but not Flt3-ITD mediated proliferation of these cells. Similar results were obtained with SOCS3, another inhibitor of Jak kinases. Detailed signaling analyses of stable 32D cells co-expressing Flt3-ITD and SOCS1 revealed that activation of the STAT5 and up-regulation of STAT5 target gene Pim-2 by Flt3-ITD is completely resistant to SOCS1. In contrast, expression of SOCS1 severely inhibited IL-3 mediated STAT5 activation. Furthermore, using purified recombinant STAT5 and Flt3 kinase in in-vitro kinase assays, we show that STAT5 is indeed a direct target of Flt3. Taken together, our data show that Flt3-ITD directly activates STAT5 independent of Src or Jak kinases, providing the mechanistic basis of Flt3-ITD induced STAT5 activation. Furthermore, our finding that Flt3-ITD up-regulates SOCS proteins but activate STAT5 in a SOCS1 resistant manner may have important implications for Flt3-ITD-mediated modification of cytokine signaling.

Description: 2-Cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) induces differentiation and apoptosis of tumor cells in vitro and in vivo. Here we assessed the effects of CDDO on CCAAT enhancer–binding protein alpha (CEBPA), a transcription factor critical for granulocytic differentiation. In HL60 acute myeloid leukemia (AML) cells, CDDO (0.01 to 2 μM) induces apoptosis in a dose-dependent manner. Conversely, subapoptotic doses of CDDO promote phagocytic activity and granulocytic-monocytic differentiation of HL60 cells through increased de novo synthesis of p42 CEBPA protein. CEBPA translational up-regulation is required for CDDO-induced granulocytic differentiation and depends on the integrity of the CEBPA upstream open reading frame (uORF). Moreover, CDDO increases the ratio of transcriptionally active p42 and the inactive p30 CEBPA isoform, which, in turn, leads to transcriptional activation of CEBPA-regulated genes (eg, GSCFR) and is associated with dephosphorylation of eIF2α and phosphorylation of eIF4E. In concordance with these results, CDDO induces a CEBPA ratio change and differentiation of primary blasts from patients with acute myeloid leukemia (AML). Because AML is characterized by arrested differentiation, our data suggest the inclusion of CDDO in the therapy of AML characterized by dysfunctional CEBPA expression.

Description: Abstract 324 Introduction and classification: This is the largest adult T-ALL cohort treated according to immunologic subtypes. All patients were immunophenotyped in one central lab (Berlin). T-ALL (cyCD3+, CD7+) were subclassified into early T-ALL (sCD3-, CD1a-), thymic T-ALL (sCD3-/+, CD1a+) and mature T-ALL (sCD3+, CD1a-). T-ALL constitutes in 3 consecutive GMALL-studies 24% of ALL patients. Patients and methods: A total of 744 T-ALL pts (15 to 55 yrs) were accrued in 102 hospitals in the GMALL studies 05/93, 06/99 and 07/2003. In GMALL 05/93 239 adult T-ALL patients, were treated according to a multi-agent chemoprotocol. Stem cell transplantation (SCT) was not recommended in CR1. In GMALL studies 06/99 and 07/03 505 T-ALL pts received intensified chemotherapy; particularly with introduction of PEG-asparaginase in induction as well as HDMTX/PEG-Asp consolidation cycles. Based on study 05/93 results, SCT from sibling (Sib) as well as matched unrelated (MUD) donor in CR1 was recommended for all patients with early T-ALL, mature T-ALL and for high-risk (HR) pts with thymic T-ALL (defined as late CR, complex karyotype or MRD positivity (MRD+)). Results: T-ALL subtype distribution in the total cohort of 744 adult T-ALL was early-T 23% (N=170), thymic-T 56% (N=420), mature-T 21% (N=154), without any differences between the studies. GMALL Study 05/93: The overall CR rate was 86% (early-T 72%, thymic-T 93%, mature-T 84%. The lower CR rate in early T-ALL was mainly due to early death (19%). The overall CCR rate was 47% (early-T 45%, thymic-T 54%, mature-T 30%). The overall survival rate at 10 yrs for all pts was 47% (early-T 47%, thymic-T 55%, mature-T 25%). GMALL Study 06/99 and 07/03: Of the 505 patients, 87% achieved CR (early-T 84%, thymic-T 92%, mature-T 77%). PR/Failure was higher in early-T (13%) and mature-T (17%) compared to thymic-T (5%). Early death was 4% and equally distributed. 267 pts (64%) received chemotherapy only and the majority were 229 pts (86%) with thymic T-ALL, not considered for SCT in CR1. The CCR rate was 61%. The few early (n = 15) and mature (n = 23) T-ALL pts, which could not have a transplant in CR1, are a negative selection (e.g. early relapse, comorbidity, no donor) and their CCR rate was 33% and 22% respectively. This was due to a high relapse rate in early T-ALL (60%) and mature-T (74%) compared to 33% in thymic-T. Overall survival rate at 8 yrs for thymic T-ALL with chemotherapy was 68%, for the 77 adolescent pts (15 to 25 yrs) even 76%. Stem cell transplantation: 153 T-ALL pts in studies 06/99 and 07/03 received a SCT in first remission. SCT realisation rate in early T-ALL was 84%, in mature-T 68%. Overall CCR rate was 58% (early-T 47%, HR thymic-T 79%, mature-T 61%). Relapse rate after SCT was in early-T 33% and in mature-T 22%. The overall TRM rate was 18% despite more than half MUD SCT, without any TRM difference between the immunological subtypes. Overall survival rate after SCT in CR1 at 8 yrs was 53%, early-T 44%, thymic-T 67%, mature-T 59%. SCT modalit: 49% received alloSib, 55% alloMUD and 20% auto-SCT. Overall CCR rate after alloSib for the total cohort was 65% (early-T 60%, thymic-T 73% and mature-T 69%); for alloMUD total 55% (early-T 45%, thymic-T 77%, mature-T 61%) and for the small cohort of 20 pts with auto-SCT CCR was 35%. Conclusion: The strategy in three consecutive GMALL studies to stratify and treat adult T-ALL pts according to the immunologic T-subtypes was successful. Overall survival at 5 yrs could be improved to 56% from 44%. There was a particular improvement for mature T-ALL (49% vs. 30%) and early-T (40% vs. 33%). This was mainly due to a high realisation rate of SCT in early T-ALL and mature T-ALL and the substantial better results of SCT. Results of alloMUD SCT were comparable to alloSib SCT. The small cohort of HR thymic T-ALL pts also had a benefit from SCT. The excellent outcome of SR thymic T-ALL (∼ 50% of all T-ALL) with the OS of 68% and 76% in adolescents due to intensified chemo, partic. PEG-Asp, does not suggest SCT in CR1. Several molecular markers, such as ERG, BAALC, WT1, had in a retrospective analysis some prognostic relevance in this pt cohort. The new GMALL study generation will however focus in thymic T-ALL on early evaluation of MRD to decide for SCT (MRD+) or not (MRD-) whereas early/mature T-ALL remain allocated to high risk groups with SCT in CR1. Supported by Deutsche Krebshilfe 702657Ho2 and BMBF 01GI9971/8 Disclosures: No relevant conflicts of interest to declare.

Description: Mutations in the receptor tyrosine kinase Flt3 represent a very common genetic lesion in acute myeloid leukemia (AML). Internal tandem duplication (ITD) mutations clustered in the juxtamembrane domain are the most frequent and best characterized mutations found in Flt3. Oncogenic activation of Flt3 by ITD mutations is known to activate aberrant signaling including activation of STAT5 and repression of myeloid transcription factors Pu.1 and c/EBP-alpha. However, the mechanisms of STAT5 activation by Flt3-ITD remain unclear. Using small molecule inhibitors and cell lines deficient for Src family kinases or Jak2 or Tyk2, here we show that Flt3-ITD–induced STAT5 activation is independent of Src or Jak kinases. Also, overexpression of SOCS1, an inhibitor of Jak kinases, inhibited IL-3– but not Flt3-ITD–mediated STAT5 activation. Furthermore, in vitro kinase assays revealed that STAT5 is a direct target of Flt3. Taken together, our data provide the mechanistic basis of STAT5 activation by Flt3-ITD.

Description: The macrophage colony-stimulating factor receptor (c-Fms) plays an important role in proliferation, differentiation and survival of macrophages and is involved in the regulation of distinct macrophage functions. Interaction with the ligand M-CSF results in activation of the intracellular tyrosine kinase domain and phosphorylation of tyrosine residues, thereby creating binding sites for several molecules containing Src homology 2 (SH2) domains. One such protein is the adaptor Lnk that negatively regulates several hematopoietic cytokine receptors including MPL, EpoR and c-Kit. Lnk belongs to a family of proteins sharing several structural motifs including a SH2 domain and a pleckstrin homology domain. The SH2 domain is known to be essential for its inhibitory effect which can be abolished by the point mutation R392E. In this study, we investigated the ability of Lnk to interact and modulate the function of c-Fms. In order to determine if Lnk can bind to c-Fms, immunoprecipitation was performed with lysates from 293T cells co-transfected with the cDNAs for c-Fms and Lnk. Only after exposure to M-CSF, Lnk bound to c-Fms, and binding was dependent on an intact SH2 domain. To elucidate further if Lnk exhibits biological and functional effects on macrophages, we examined both in-vitro differentiated macrophages derived from the bone marrow and also macrophages harvested from peritoneum from Lnk deleted (KO) and wild type (WT) mice. These cells appeared to be at a similar stage of differentiation because expression levels of myeloid and macrophage surface markers such as F4/80, CD11b and CD11c were the same in both bone marrow-derived and peritoneum-derived macrophages from Lnk KO and WT mice. Clonogenic assays demonstrated that the number of M-CFUs in the bone marrow were elevated in Lnk KO as compared to WT mice. Furthermore, the M-CSF-induced phosphorylation of AKT in these Lnk KO macrophages was increased and prolonged compared to WT macrophages. This was associated with prominent up-regulation of c-Fms in macrophages from Lnk KO mice. We found that Lnk additionally had several functional effects on bone marrow-derived macrophages. Production of reactive oxygen species (ROS) was dramatically increased in a M-CSF-dependent manner in Lnk KO macrophages upon stimulation with zymosan. In addition, knock-out of Lnk led to altered cytokine production of macrophages: Stimulation with zymosan caused increased levels of TNFalpha and IL-6 in the KO cells, while bacterial lipoproteins (Pam3CSK4) decreased levels of TNFalpha in KO compared to WT macrophages. Last, Lnk inhibited M-CSF-induced migration of macrophages in the Boyden chamber as Lnk KO macrophages showed a significantly higher migration capacity than WT macrophages. In summary, we show for the first time that Lnk can bind to c-Fms and can blunt the stimulation of M-CSF. Modulation of levels of Lnk in macrophages may provide a unique therapeutic approach to increase innate host defenses.

Description: Activating mutations in Flt3, N- and K-Ras have been reported in all AML subtypes and represent common molecular defects in de novo AML. We have previously shown that these mutations lead to constitutive AKT phosphorylation and activation. As a consequence, Akt phosphorylation is found in myeloid blasts of the majority of AML patients. We reasoned that constitutively active AKT may contribute to leukemia development, and therefore we assessed the contribution of AKT in oncogenic transformation in vivo. For this purpose, we established an inducible mouse model expressing myristylated AKT1 under the control of the scl-3′ enhancer (MyrAKT1). This system restricts activated AKT1 to endothelium, hematopoietic stem cells and myeloid lineage cells at a low but detectable level. About 40% of induced mice developed a myeloproliferative disorder after latencies of 7 to 22 months. Onset of disease was frequently associated with hemangioma formation, due to endothelial MyrAKT1 expression. The myeloproliferative disorder was associated with splenomegaly with increased extramedullary hematopoiesis, while the peripheral blood contained mature granulocytes. Furthermore, the stem cell and progenitor cell compartment in spleens and bone marrow of these mice was altered compared to control mice. Colony formation assays with MyrAKT1-expressing bone marrow suggested that overactivation of AKT1 enhanced proliferation. The AKT1-induced disease was transplantable by both bone marrow and spleen cells. These findings highlight the oncogenic capacity of constitutively activated AKT1 in vivo and indicate that AKT is an attractive target for therapeutic intervention in AML.

Description: Introduction: Histone deacetylase inhibitors (DACi) have shown promising antileukemic activity by overcoming the differentiation block and inducing apoptosis in AML blasts. Recent data demonstrating enhanced maintenance and functional capacity of normal, but also leukemic hematopoietic progenitor cells (HPC) by the selective class I DACi valproic acid (VPA) have raised concerns about VPA in AML therapy. As more potent pan-DACi have entered clinical trials, we analysed the impact of the hydroxamic acid LAQ824 on phenotype and function of normal and leukemic CD34+ HPC and studied LAQ824- induced gene expression in the most primitive CD34+CD38- population of normal HPC. Methods: Differentiation and proliferation of CD34+ cells of bone marrow of healthy donors and peripheral blood samples of newly diagnosed AML patients were evaluated after one week of culture in presence of SCF, FLT3 ligand, TPO, IL-3 +/− LAQ824. The effect of LAQ824 on gene expression profiles in normal CD34+CD38− cells was assessed in three independent cell samples following incubation with cytokines +/− LAQ824 for 48 hours using Affymetrix GeneChip Human Genome U133 Plus 2.0 and Gene Spring Software. Serial replating of murine Sca1+Lin- HPC was performed in the presence of SCF, G-CSF, GM-CSF, IL-3, IL-6 +/− LAQ824. Results: Treatment of murine Sca1+Lin- HPC with LAQ824 (10 nM) significantly augmented colony numbers (p

Description: Introduction: Febrile neutropenia is a common and potentially fatal consequence of Acute Myeloid Leukemia (AML). We performed a retrospective analysis of 97 adult AML patients (median age 67.6 y (58–78) treated between February 2000 and June 2005. Aim of the study was to evaluate risk factors for infectious complications and to identify underlying causative pathogens during first and second cycle of intensive induction chemotherapy. For statistical evaluation of the results, Students t-test, Fisher’ exact test or Chi square test were performed as appropriate. Results: Of the 97 episodes 64% occurred in male patients at a median age of 67.6 years (58–78). Patients developed fever not related to cytotoxic therapy or transfusion in 77 (80%) and no fever in 20 (20%) of the episodes. Compared to patients without infectious complications patients with fever had significantly more pretreatment comorbidities (0.80±1.20 vs 1.81±1.41, p=0.0042), a prolonged period of severe neutropenia (

Description: Several conflicting options regarding management of adult ALL are currently discussed. One major issue is the indication for SCT depending on risk factors and age, and the other is the recommendation to use unmodified pediatric protocols for “young” adults. Decision making on SCT is generally based on conventional risk factors – mainly disease characteristics – available at diagnosis, and decision making for “pediatric” chemotherapy on age. It is essential to develop more sophisticated criteria – also to reduce the risk of selection in clinical trials. In order to enhance prognostic models and to better address individual patient characteristics and the course of disease we reanalysed conventional prognostic factors together with new patient specific factors in a large cohort of adult ALL patients. A total of 1657 well characterised pts (15–55 yrs) included in the risk stratified protocols of the German Multicenter Study Group (GMALL) 06/99 and 07/03 was analysed. Treatment and risk stratification have been described (Brüggemann, Blood2006: 107;1116). Age remained a highly significant factor for CR, survival (OS) and disease free survival (DFS). OS ranged from 58% for 15–25 yrs, 52% for 26–35 yrs, 43% for 36–45 yrs to 32% for 45–55 yrs (p=.0001). Poorer outcome with increasing age was mainly due to early death (ED) and death in CR. CR, OS (45% c/pre-B, 45% pro-B, 38% early T, 47% mature T and 64% thymic T;p