ALBERT

Description: Abstract 255 Introduction: Standard treatment of acute myeloid leukemia (AML) comprises one or two cycles of chemotherapy to induce complete remission (CR) followed by postremission treatment in order to prevent relapse of the disease (consolidation therapy). In 2003, we initiated a prospective multicenter randomized trial to investigate the impact of different consolidation strategies on long-term outcome in AML patients ≤ 60 years. Consolidation options comprised upfront allogeneic stem cell transplantation (allo SCT) in aplasia after induction therapy, autologous SCT, and three cycles of standard high-dose-cytarabine-based consolidation. For patients receiving high-dose cytarabine, the main study aim was to evaluate the benefit of adding additional mitoxantrone and amsacrine to cytarabine consolidation. Design: From 2003 to 2009, 1182 patients (median age, 48 years; range 16–60 years) with untreated AML were randomly assigned at diagnosis to different consolidation strategies after classical 7+3 induction. According to the risk-adapted treatment strategy of the trial, cytogenetically or molecular intermediate-risk (IR) and adverse-risk (AR) patients should receive an allo SCT as consolidation treatment if an HLA-identical-sibling donor (IR) or HLA-matched related or unrelated donor (AR) was available. IR and AR patients with no available donor should receive autologous SCT. All favorable risk patients and patients with no available donor were scheduled for high-dose cytarabine based consolidation. Half of the patients were randomized for high dose cytarabine based consolidation. Half of the patients were randomized for high dose cytarabine alone while the other half received high dose cytarabine with the addition of amsacrine and mitoxantrone. Standard chemotherapy consisted of three cycles with high dose cytarabine (2 × 3 g/m2, day 1,3,5) whereas combined consolidation contained two cycles of MAC (cytarabine 2 × 1g/m2, day 1–6, mitoxantrone 10 mg/m2, day 4–6) plus one cycle of MAMAC (cytarabine 2 × 1 g/m2, day 1–5, amsacrine 100 mg/m2, day 1–5). In order to evaluate the effect of the two cytarabine based consolidation strategies, we determined overall survival (OS) and event free survival (EFS) using the method of Kaplan Meyer. Survival distributions were compared using the log rank test. Results: 1182 patients were randomized for further intervention (Arm A+B: n=582, 49.3%; Arm C+D: n=600, 50.7 %). Median follow-up was 41.4 months (95%-CI 39.3–43.6). A total number of 375 patients received allogeneic (n=322) or autologous SCT (n=53) and 807 patients were consolidated with cytarabine. Of these patients, 407 were randomized for cytarabine alone and 400were randomized to receive cytarabine plus mitoxantrone and amsacrine (MAC/MAC/MAMAC). Complete remission rate (CR) after second induction therapy was 59.1% (n=698). Between the four arms, there were no significant differences of the CR rates. Five-year OS of patients receiving high dose cytarabine alone was 47.1% (95%-CI 42.0–52.2%), for patients receiving MAC/MAMAC as consolidation therapy it was 46.8% (95%-CI 42.3–51.3%; p = 0.610). Three-year event free survival (EFS) was also not significant with 30.5% (95%-CI 26.6–34.4%) for patients receiving high dose cytarabine alone and 35.6% (95%-CI 31.7–39.5%; p = 0.059) for patients receiving MAC/MAMAC. Conclusions: According to our data, the addition of mitoxantrone and amsacrine to high dose cytarabine consolidation confers no benefit for treatment outcome in younger AML patients. Disclosures: No relevant conflicts of interest to declare.

Description: Key Points Integrin signaling promotes proliferative signals in AML cells that are mediated by the kinase Syk and the transcription factors STAT3 and STAT5.

Description: Management of patients with refractory and relapsed AML needs optimization. We performed a prospective study in these patients aiming at 1) the definition of the anti-leukemic efficacy of the S-HAI regimen; and 2) the evaluation of the prognostic impact of cytogenetic aberrations at relapse in the context of other prognostic parameters. Treatment consisted of AraC 1 g/sqm q 12 h days 1, 2, 8, and 9 and idarubicin 10 mg/sqm days 3, 4, 10, and 11. AraC was given at 3 g/sqm in patients under age 60 with refractory AML or relapse after CR1

Description: The receptor tyrosine kinases FLT3 and KIT are highly expressed on the surface of leukemic blasts in most patients with acute myeloid leukemia. Although about one third of patients display activating mutations in FLT3 (and more rarely in KIT), the majority of patients have no mutations in FLT3 or KIT. Previously, we demonstrated that Cbl functions as the E3 ligase for both FLT3 and KIT, and that ligase-inactivating mutations of Cbl stabilize FLT3 and KIT on the cell surface by preventing endocytosis and degradation (Sargin et al, Blood 2007). Furthermore, we demonstrated that expression of E3-ligase deficient Cbl mutants led to the development of a myeloproliferative disease in a murine bone marrow transplantation model (Bandi et al, Blood 2009). However, Cbl mutations are rarely found in AML. Here, we investigated the role of the Cbl regulators suppressors of T-cell signaling 1 and 2(STS1 and STS2) in stabilizing wild-type FLT3 and KIT on the cell surface of hematopoietic stem and progenitor cells (HSPCs). STS1 is ubiquitously expressed, while STS2 expression is restricted to the hematopoietic tissue. STS1 and STS2 constitutively bind to Cbl, while their binding to FLT3 and KIT is dependent on ligand-activation by FL and SCF, respectively. Interestingly, STS1 (but not STS2) functions as a tyrosine phosphatase for both ligand-activated FLT3 and KIT. This required the PGM domain of STS1, as PGM point mutant of STS1 did not dephosphorylate FLT3 or KIT. In line with this, knockdown of STS1 using stably expressing shRNA constructs showed a significant hyperphosphorylation of FLT3 and KIT. By using STS1/STS2 single and double knockout mice, we analyzed the effects of STS1 and STS2 on hematopoietic stem and progenitor cells in vivo. We found that deficiency of STS1 causes an increase of both absolute number and frequency of LSK (lineage marker-, KIT+, Sca1+) cells, which contain HSPCs. This phenotype was even more pronounced in STS1 and STS2 double knockout (dKO) mice, and is mainly attributable to the short term hematopoietic stem cell (ST-HSC) and multipotent progenitor (MPP) cell population, as defined by both standard and SLAM markers. Colony assays using primary bone marrow cells revealed a significantly higher colony forming ability in STS1-KO and dKO cells compared to wild type (wt) cells, particularly after serial replating. A careful analysis of the cells derived from methylcellulose culture revealed an increased proportion of immature (Mac1- CD48+ CD16/32-) cells in STS1-KO and dKO cells. Competitive repopulation assays showed an advantage for dKO cells when compared to wt, suggesting that the LT-HSC compartment is also affected. Even more pronounced were the differences in CFU-S assays (colony forming units spleen), displaying significantly more colonies of dKO compared to wt donor cells, functionally demonstrating a significantly increased ST-HSC / MPP population in dKO donors. A detailed analysis of the downstream signaling events demonstrated that loss of STS1 specifically causes an activated PI3-Kinase / AKT pathway. In summary, our data demonstrates that STS1 functions as a phosphatase of FLT3 and KIT and, using genetic mouse models, indicates a critical role in the maintenance and proliferation of long-term and short-term hematopoietic stem cells. This may also affect sensitivity to kinase inhibitors. Disclosures: No relevant conflicts of interest to declare.

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: Key Points RUNX1 inhibits erythroid differentiation by downregulation of the erythroid gene expression program. RUNX1 can act as an activator and repressor during megakaryocytic differentiation and counteracts the activity of TAL1.

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 FIP1L1-PDGFRA fusion is seen in a fraction of cases with a presumptive diagnosis of hypereosinophilic syndrome (HES). However, because most HES patients lack FIP1L1-PDGFRA, we studied whether they harbor activating mutations of the PDGFRA gene. Sequencing of 87 FIP1L1-PDGFRA–negative HES patients revealed several novel PDGFRA point mutations (R481G, L507P, I562M, H570R, H650Q, N659S, L705P, R748G, and Y849S). When cloned into 32D cells, N659S and Y849S and—on selection for high expressors—also H650Q and R748G mutants induced growth factor–independent proliferation, clonogenic growth, and constitutive phosphorylation of PDGFRA and Stat5. Imatinib antagonized Stat5 phosphorylation. Mutations involving positions 659 and 849 had been shown previously to possess transforming potential in gastrointestinal stromal tumors. Because H650Q and R748G mutants possessed only weak transforming activity, we injected 32D cells harboring these mutants or FIP1L1-PDGFRA into mice and found that they induced a leukemia-like disease. Oral imatinib treatment significantly decreased leukemic growth in vivo and prolonged survival. In conclusion, our data provide evidence that imatinib-sensitive PDGFRA point mutations play an important role in the pathogenesis of HES and we propose that more research should be performed to further define the frequency and treatment response of PDGFRA mutations in FIP1L1-PDGFRA–negative HES patients.