Justus Duyster

Universitätsklinikum Freiburg, Freiburg an der Elbe, Lower Saxony, Germany

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Publications (154)1207.67 Total impact

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    ABSTRACT: IL-33 binding to the receptor suppression of tumorigenicity 2 (ST2) produces pro-inflammatory and anti-inflammatory effects. Increased levels of soluble ST2 (sST2) are a biomarker for steroid-refractory GVHD and mortality. However, whether sST2 has a role as an immune modulator or only as a biomarker during GVHD was unclear. We show increased IL-33 production by non-hematopoietic cells in the GI tract in mice post-conditioning and patients during GVHD. Exogenous IL-33 administration during the peak inflammatory response worsened GVHD. Conversely, GVHD lethality and TNF-α production was significantly reduced in il33(-/-) recipients. ST2 was upregulated on murine and human alloreactive T cells and sST2 increased as experimental GVHD progressed. Concordantly, st2(-/-) versus wildtype donor T cells had a marked reduction in GvHD lethality and GI histopathology. Alloantigen-induced IL-18 receptor upregulation was lower in st2(-/-) T cells, and linked to reduced IFN-γ production by st2(-/-) versus wildtype T cells during GVHD. Blockade of IL-33/ST2 interactions during allo-hematopoietic cell transplantation by exogenous ST2-Fc infusions had a marked reduction in GVHD lethality indicating a role of ST2 as a decoy receptor modulating GVHD. Together, these studies point to targeting of the IL-33/ST2 axis as a novel and potent target for GVHD therapy. Copyright © 2015 American Society of Hematology.
    Blood 03/2015; DOI:10.1182/blood-2014-10-606830
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    ABSTRACT: FIP1L1-PDGFRA is a constitutively-activated kinase described in chronic eosinophilic leukemia,and hypereosinophilic syndrome. Imatinib is clinically active in FIP1L1-PDGFRA-positive diseases. Using in vitro screening to identify imatinib-resistant mutations, we most frequently detected a Phe to Ser exchange at position 604 (F604S) of FIP1L1-PDGFRA alone or in combination with other exchanges. Surprisingly, FIP1L1-PDGFRA/F604S did not increase the biochemical or cellular IC50 value of imatinib when compared with unmutated FIP1L1-PDGFRA. However, FIP1L1-PDGFRA/F604S more efficiently induced growth factor independence in cell lines and primary mouse bone marrow cells. Pulse chase analysis revealed that the F604S exchange strongly stabilized FIP1L1-PDGFRA/F604S. The F604S mutation creates a binding site for the phosphatase domain of SHP-2 leading to lower autophosphorylation of FIP1L1-PDGFRA/F604S. This is associated with a reduced activation of SRC and CBL by FIP1L1-PDGFRA/F604S compared to the unmutated oncogene. Since SRC inhibition and knock-down resulted in FIP1L1-PDGFRA stabilization this explains the extended half life of FIP1L1-PDGFRA/F604S. Interestingly, FIP1L1-PDGFRA/L629P, a recently identified mutation in an imatinib-resistant CEL patient, also showed protein stabilization similar to that observed with FIP1L1-PDGFRA/F604S. Therefore, resistance mutations in FIP1L1-PDGFRA that do not interfere with drug binding but rather increase target protein stability seem to be one of the drug-resistance mechanism in FIP1L1-PDGFRA-positive disease.Leukemia accepted article preview online, 12 March 2015. doi:10.1038/leu.2015.70.
    Leukemia 03/2015; DOI:10.1038/leu.2015.70
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    ABSTRACT: ABL tyrosine kinase inhibitors (TKI) like Imatinib, Dasatinib and Nilotinib are the gold standard in conventional treatment of CML. However, the emergence of resistance remains a major problem. Alternative therapeutic strategies of ABL TKI-resistant CML are urgently needed. We asked whether dual inhibition of BCR-ABL and Aurora kinases A-C could overcome resistance mediated by ABL kinase mutations. We therefore tested the dual ABL and Aurora kinase inhibitors PHA-739358 and R763/AS703569 in Ba/F3- cells ectopically expressing wild type (wt) or TKI-resistant BCR-ABL mutants. We show that both compounds exhibited strong anti-proliferative and pro-apoptotic activity in ABL TKI resistant cell lines including cells expressing the strongly resistant T315I mutation. Cell cycle analysis indicated polyploidisation, a consequence of continued cell cycle progression in the absence of cell division by Aurora kinase inhibition. Experiments using drug resistant variants of Aurora B indicated that PHA-739358 acts on both, BCR-ABL and Aurora Kinase B, whereas Aurora kinase B inhibition might be sufficient for the anti-proliferative activity observed with R763/AS703569. Taken together, our data demonstrate that dual ABL and Aurora kinase inhibition might be used to overcome ABL TKI resistant CML.
    PLoS ONE 11/2014; 9(11):e112318. DOI:10.1371/journal.pone.0112318
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    ABSTRACT: Multiple myeloma (MM) is a plasma cell neoplasm that results from clonal expansion of an Ig-secreting terminally differentiated B cell. Advanced MM is characterized by tissue damage that involves bone, kidney, and other organs and is typically associated with recurrent genetic abnormalities. IL-6 signaling via the IL-6 signal transducer GP130 has been implicated as an important driver of MM pathogenesis. Here, we demonstrated that ectopic expression of constitutively active GP130 (L-GP130) in a murine retroviral transduction-transplantation model induces rapid MM development of high penetrance. L-GP130-expressing mice recapitulated all of the characteristics of human disease, including monoclonal gammopathy, BM infiltration with lytic bone lesions, and protein deposition in the kidney. Moreover, the disease was easily transplantable and allowed different therapeutic options to be evaluated in vitro and in vivo. Using this model, we determined that GP130 signaling collaborated with MYC to induce MM and was responsible and sufficient for directing the plasma cell phenotype. Accordingly, we identified Myc aberrations in the L-GP130 MM model. Evaluation of human MM samples revealed recurrent activation of STAT3, a downstream target of GP130 signaling. Together, our results indicate that deregulated GP130 activity contributes to MM pathogenesis and that pathways downstream of GP130 activity have potential as therapeutic targets in MM.
    Journal of Clinical Investigation 11/2014; 124(12). DOI:10.1172/JCI69094
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    ABSTRACT: Patients with BRAFV600E/K-driven melanoma respond to the BRAF inhibitor vemurafenib due to subsequent deactivation of the proliferative RAS/RAF/MEK/ERK pathway. In BRAF WT cells and those with mutations that activate or result in high levels of the BRAF activator RAS, BRAF inhibition can lead to ERK activation, resulting in tumorigenic transformation. We describe a patient with malignant melanoma who developed chronic lymphocytic leukemia (CLL) in the absence of RAS mutations during vemurafenib treatment. BRAF inhibition promoted patient CLL proliferation in culture and in murine xenografts and activated MEK/ERK in primary CLL cells from additional patients. BRAF inhibitor-driven ERK activity and CLL proliferation required B cell antigen receptor (BCR) activation, as inhibition of the BCR-proximal spleen tyrosine kinase (SYK) reversed ERK hyperactivation and proliferation of CLL cells from multiple patients, while inhibition of the BCR-distal Bruton tyrosine kinase had no effect. Additionally, the RAS-GTP/RAS ratio in primary CLL cells exposed to vemurafenib was reduced upon SYK inhibition. BRAF inhibition increased mortality and CLL expansion in mice harboring CLL xenografts; however, SYK or MEK inhibition prevented CLL proliferation and increased animal survival. Together, these results suggest that BRAF inhibitors promote B cell malignancies in the absence of obvious mutations in RAS or other receptor tyrosine kinases and provide a rationale for combined BRAF/MEK or BRAF/SYK inhibition.
    Journal of Clinical Investigation 10/2014; 124(11). DOI:10.1172/JCI76539
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    ABSTRACT: The SH2-containing adaptor protein Grb10 was first identified in a yeast-screen as a new binding partner for BCR-ABL and associates with BCR-ABL in a tyrosine-dependent manner. However, its function in BCR-ABL-mediated leukemogenesis in vivo is still unknown. Here we describe an important role of Grb10 in BCR-ABL-induced leukemia by using a versatile system for efficient oncogene expression and simultaneous Grb10-knockdown from a single vector. Primary BM cells coexpressing Grb10-miR/BCR-ABL showed a significant decrease in colony formation and cell cycle progression. Transplantation of Grb10miR/BCR-ABL- or control-miR/BCR-ABL transduced BM lead to a CML/B-ALL-like phenotype with significantly delayed disease onset and progression resulting in prolonged overall survival in Grb10-miR transplanted mice. Methylcellulose experiments exhibit additive effects of Imatinib treatment and Grb10-knockdown. Cell Cycle analysis suggests an antiproliferative effect of Grb10-knockdown in BCR-ABL(+) primary BM cells. However, Grb10 abrogation was not capable of completely abolishing the BCR-ABL-induced disease. Our findings were confirmed in the human BCR-ABL(+) cell-line K562, where we demonstrate reduced viability, cell cycle progression and induction of apoptosis by stable Grb10 microRNA expression. Taken together, our results suggest, that Grb10-knockdown in vivo leads to impaired proliferation, longer survival and reduced colony-formation suggesting an important role of Grb10 in BCR-ABL-mediated leukemogenesis.Leukemia accepted article preview online, 24 September 2014. doi:10.1038/leu.2014.283.
    Leukemia 09/2014; 29(4). DOI:10.1038/leu.2014.283
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    ABSTRACT: Acute graft-versus-host disease (GvHD) limits the success of allogeneic hematopoietic cell transplantation (allo-HCT), therefore a better understanding of its biology may improve therapeutic options. We observed miR-146a upregulation in T cells of mice developing acute GvHD compared to untreated mice. Transplanting miR-146a(-/-) T cells caused increased GvHD severity, elevated TNF serum levels and reduced survival. TNF receptor-associated factor 6(TRAF6), a verified target of miR-146a, was upregulated in miR-146a(-/-) T cells following alloantigen stimulation. Higher TRAF6 levels translated into increased NF-κB activity and TNF production in miR-146a(-/-) T cells. Conversely, the detrimental effect of miR-146a deficiency in T cells was antagonized by TNF blockade, while phytochemical induction of miR-146a or its overexpression using a miR-146a mimic reduced GvHD severity. In humans, the minor genotype of the SNP rs2910164 in HCT donors, which reduces expression of miR-146a, was associated with severe acute GvHD (grade III/IV). We show that miR-146a functions as a negative regulator of donor T cells in GvHD by targeting TRAF6, leading to reduced TNF transcription. Since miR-146a expression can be exogenously enhanced, our results provide a novel, targeted molecular approach to mitigate GvHD.
    Blood 09/2014; DOI:10.1182/blood-2014-04-569046
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    ABSTRACT: The spleen tyrosine kinase (SYK) was identified as an oncogenic driver in a broad spectrum of hematologic malignancies. The in vivo comparison of three SYK containing oncogenes, SYK(wt), TEL-SYK and IL-2-inducible T-cell kinase (ITK)-SYK revealed a general myeloexpansion and the establishment of three different hematologic (pre)diseases. SYK(wt) enhanced the myeloid and T-cell compartment, without leukemia/lymphoma development. ITK-SYK caused lethal T-cell lymphomas and the cytoplasmic TEL-SYK fusion induced an acute panmyelosis with myelofibrosis-type acute myeloid leukemia (AML) with up to 50% immature megakaryoblasts infiltrating bone marrow, spleen and liver, additional MPN features (myelofibrosis and granulocyte expansion) and MDS stigmata with megakaryocytic and erythroid dysplasia. LKS cells were reduced and all subsets (LT/ST/MPP) showed reduced proliferation rates. SYK inhibitor treatment (R788) of diseased TEL-SYK mice reduced leukocytosis, spleen and liver infiltration, enhanced the hematocrit and prolonged survival time, but could not significantly reduce myelofibrosis. Stat5 was identified as a major downstream mediator of TEL-SYK in vitro as well as in vivo. Consequently, targeted deletion of Stat5 in vivo completely abrogated TEL-SYK-induced AML and myelofibrosis development, proving Stat5 as a major driver of SYK-induced transformation. Our experiments highlight the important role of SYK in AML and myelofibrosis and prove SYK and STAT5 inhibitors as potent treatment options for those diseases.
    Blood Cancer Journal 08/2014; 4:e240. DOI:10.1038/bcj.2014.53
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    ABSTRACT: Almost 30% of all acute myeloid leukemias (AML) are associated with an internal tandem duplication (ITD) in the juxtamembrane domain of FLT3. Patients with FLT3-ITD mutations tend to have a poor prognosis. MicroRNAs (miRNAs) play a pivotal role in myeloid differentiation and leukemia. miR-155 was found to be upregulated in FLT3-ITD associated AMLs. In this study, we discovered that FLT3-ITD signaling induces the oncogenic miR-155. We show in vitro and in vivo that miR-155 expression is regulated by FLT3-ITD downstream targets NF-κB (p65) and STAT5. Further, we demonstrate that miR-155 targets the myeloid transcription factor PU.1. Knockdown of miR-155 or overexpression of PU.1 blocks proliferation and induces apoptosis of FLT3-ITD associated leukemic cells. Our data demonstrate a novel network in which FLT3-ITD signaling induces oncogenic miR-155 by p65 and STAT5 in acute myeloid leukemia thereby targeting transcription factor PU.1.Leukemia accepted article preview online, 5 August 2014; doi:10.1038/leu.2014.231.
    Leukemia 08/2014; DOI:10.1038/leu.2014.231
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    ABSTRACT: BACKGROUND Little is known about the factors that predict for gastrointestinal stromal tumor (GIST) recurrence in patients treated with adjuvant imatinib.METHODS Risk factors for GIST recurrence were identified, and 2 risk stratification scores were developed using the database of the Scandinavian Sarcoma Group (SSG) XVIII trial, where 358 patients with high-risk GIST with no overt metastases were randomly assigned to adjuvant imatinib 400 mg/day either for 12 or 36 months after surgery. The findings were validated in the imatinib arm of the American College of Surgeons Oncology Group Z9001 trial, where 359 patients with GIST were randomized to receive imatinib and 354 were to receive placebo for 12 months.RESULTSFive factors (high tumor mitotic count, nongastric location, large size, rupture, and adjuvant imatinib for 12 months) were independently associated with unfavorable recurrence-free survival (RFS) in a multivariable analysis in the SSGXVIII cohort. A risk score based on these 5 factors had a concordance index with GIST recurrence of 78.9%. When a simpler score consisting of the 2 strongest predictive factors (mitotic count and tumor site) was devised, the groups with the lowest, intermediate high, and the highest risk had 5-year RFS of 76.7%, 47.5%, and 8.4%, respectively. Both scores were strongly associated with RFS in the validation cohort (P < .001 for each comparison).CONCLUSIONS The scores generated were effective in stratifying the risk of GIST recurrence in patient populations treated with adjuvant imatinib. Patients with nongastric GIST with a high mitotic count are at a particularly high risk for recurrence. Cancer 2014 © 2014 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.
    Cancer 08/2014; 120(15). DOI:10.1002/cncr.28669
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    ABSTRACT: FLT3 is the most frequently mutated kinase in acute myeloid leukemia (AML). Internal tandem duplications (ITDs) in the juxta-membrane region constitute the majority of activating FLT3 mutations. Several FLT3 kinase inhibitors were developed and tested in the clinic with significant success. However, recent studies have reported the development of secondary drug resistance in patients treated with FLT3 inhibitors. Since FLT3-ITD is an HSP90 client kinase, we here explored if targeting the stability of drug-resistant FLT3 mutant protein could be a potential therapeutic option. We observed that HSP90 inhibitor treatment resulted in the degradation of inhibitor-resistant FLT3-ITD mutants and selectively induced toxicity in cells expressing FLT3-ITD mutants. Thus, HSP90 inhibitors provide a potential therapeutic choice to overcome secondary drug resistance following TKI treatment in FLT3-ITD positive AML.
    PLoS ONE 05/2014; 9(5):e97116. DOI:10.1371/journal.pone.0097116
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    ABSTRACT: Acute graft-versus-host disease (GVHD) considerably limits wider usage of allogeneic hematopoietic cell transplantation (allo-HCT). Antigen-presenting cells and T cells are populations customarily associated with GVHD pathogenesis. Of note, neutrophils are the largest human white blood cell population. The cells cleave chemokines and produce reactive oxygen species, thereby promoting T cell activation. Therefore, during an allogeneic immune response, neutrophils could amplify tissue damage caused by conditioning regimens. We analyzed neutrophil infiltration of the mouse ileum after allo-HCT by in vivo myeloperoxidase imaging and found that infiltration levels were dependent on the local microbial flora and were not detectable under germ-free conditions. Physical or genetic depletion of neutrophils reduced GVHD-related mortality. The contribution of neutrophils to GVHD severity required reactive oxygen species (ROS) because selective Cybb (encoding cytochrome b-245, beta polypeptide, also known as NOX2) deficiency in neutrophils impairing ROS production led to lower levels of tissue damage, GVHD-related mortality and effector phenotype T cells. Enhanced survival of Bcl-xL transgenic neutrophils increased GVHD severity. In contrast, when we transferred neutrophils lacking Toll-like receptor-2 (TLR2), TLR3, TLR4, TLR7 and TLR9, which are normally less strongly activated by translocating bacteria, into wild-type C57BL/6 mice, GVHD severity was reduced. In humans, severity of intestinal GVHD strongly correlated with levels of neutrophils present in GVHD lesions. This study describes a new potential role for neutrophils in the pathogenesis of GVHD in both mice and humans.
    Nature Medicine 05/2014; 20(6). DOI:10.1038/nm.3517
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    ABSTRACT: Graft-versus-host-disease (GvHD) is a severe complication of allogeneic hematopoietic cell transplantation (allo-HCT) characterized by the production of high levels of pro-inflammatory cytokines. Activated Janus kinases (JAKs) are required for T effector cell responses in different inflammatory diseases and their blockade could potently reduce acute GvHD. We observed that inhibition of JAK1/2 signaling resulted in reduced proliferation of effector T cells and suppression of pro-inflammatory cytokine production in response to alloantigen in mice. In vivo JAK 1/2 inhibition improved survival of mice developing acute GvHD and reduced histopathologic GvHD grading, serum levels of pro-inflammatory cytokines and expansion of alloreactive luc-transgenic T cells. Mechanistically, we could show that ruxolitinib impaired differentiation of CD4(+) T cells into IFN-γ and IL17A-producing cells, both T cell phenotypes are linked to GvHD. Conversely, ruxolitinib treatment in allo-HCT recipients increased FoxP3(+) regulatory T cells, which are linked to immunological tolerance. Based on these results, we treated 6 patients suffering from steroid-refractory GvHD with ruxolitinib. All patients responded with respect to clinical GvHD symptoms and serum levels of pro-inflammatory cytokines. In summary, ruxolitinib represents a novel targeted approach in GvHD by suppression of pro-inflammatory signaling that mediates tissue damage and by promotion of tolerogenic Treg cells.
    Blood 04/2014; 123(24). DOI:10.1182/blood-2013-12-543736
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    ABSTRACT: Lung cancer is the leading cause of cancer-related deaths worldwide. Recently, we have shown that Notch1 inhibition resulted in substantial cell death of non-small cell lung cancer (NSCLC) cells in vitro. New compounds targeting Notch signal transduction have been developed and are now being tested in clinical trials. However, the tumorigenic role of individual Notch receptors in vivo remains largely unclear. Using a Kras(G12D)-driven endogenous NSCLC mouse model, we analyzed the effect of conditional Notch1 and Notch2 receptor deletion on NSCLC tumorigenesis. Notch1 deficiency led to a reduced early tumor formation and lower activity of MAPK compared with the controls. Unexpectedly, Notch2 deletion resulted in a dramatically increased carcinogenesis and increased MAPK activity. These mice died significantly earlier due to rapidly growing tumor burden. We found that Notch1 regulates Ras/MAPK pathway via HES1-induced repression of the DUSP1 promoter encoding a phosphatase specifically suppressing pERK1/2. Interestingly, Notch1 but not Notch2 ablation leads to decreased HES1 and DUSP1 expression. However, Notch2-depleted tumors showed an appreciable increase in β-catenin expression, a known activator of HES1 and important lung cancer oncogene. Characteristically for β-catenin upregulation, we found that the majority of Notch2-deficient tumors revealed an undifferentiated phenotype as determined by their morphology, E-Cadherin and TTF1 expression levels. In addition, these carcinomas showed aggressive growth patterns with bronchus invasion and obstruction. Together, we show that Notch2 mediates differentiation and has tumor suppressor functions during lung carcinogenesis, whereas Notch1 promotes tumor initiation and progression. These data are further supported by immunohistochemical analysis of human NSCLC samples showing loss or downregulation of Notch2 compared with normal lung tissue. In conclusion, this is the first study characterizing the in vivo functions of Notch1 and Notch2 in Kras(G12D)-driven NSCLC tumorigenesis. These data highlight the clinical importance of a thorough understanding of Notch signaling especially with regard to Notch-targeted therapies.Oncogene advance online publication, 10 February 2014; doi:10.1038/onc.2013.592.
    Oncogene 02/2014; DOI:10.1038/onc.2013.592
  • Annals of Hematology 12/2013; 93(8). DOI:10.1007/s00277-013-1987-7
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    ABSTRACT: The success of allogeneic hematopoietic cell transplantation is limited by acute graft-versus-host disease (GvHD), a severe complication accompanied by high mortality rates. Yet, the molecular mechanisms initiating this disease remain poorly defined. In this study, we show that, after conditioning therapy, intestinal commensal bacteria and the damage-associated molecular pattern uric acid contribute to Nlrp3 inflammasome-mediated IL-1β production and that gastrointestinal decontamination and uric acid depletion reduced GvHD severity. Early blockade of IL-1β or genetic deficiency of the IL-1 receptor in dendritic cells (DCs) and T cells improved survival. The Nlrp3 inflammasome components Nlrp3 and Asc, which are required for pro-IL-1β cleavage, were critical for the full manifestation of GvHD. In transplanted mice, IL-1β originated from multiple intestinal cell compartments and exerted its effects on DCs and T cells, the latter being preferentially skewed toward Th17. Compatible with these mouse data, increased levels of active caspase-1 and IL-1β were found in circulating leukocytes and intestinal GvHD lesions of patients. Thus, the identification of a crucial role for the Nlrp3 inflammasome sheds new light on the pathogenesis of GvHD and opens a potential new avenue for the targeted therapy of this severe complication.
    Journal of Experimental Medicine 08/2013; 210(10). DOI:10.1084/jem.20130084
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    ABSTRACT: PURPOSEThe prognosis of elderly patients with acute myeloid leukemia (AML) is still dismal even with intensive chemotherapy. In this trial, we compared the antileukemic activity of standard induction and consolidation therapy with or without the addition of the kinase inhibitor sorafenib in elderly patients with AML. PATIENTS AND METHODS All patients received standard cytarabine and daunorubicin induction (7+3 regimen) and up to two cycles of intermediate-dose cytarabine consolidation. Two hundred one patients were equally randomly assigned to receive either sorafenib or placebo between the chemotherapy cycles and subsequently for up to 1 year after the beginning of therapy. The primary objective was to test for an improvement in event-free survival (EFS). Overall survival (OS), complete remission (CR) rate, tolerability, and several predefined subgroup analyses were among the secondary objectives.ResultsAge, sex, CR and early death (ED) probability, and prognostic factors were balanced between both study arms. Treatment in the sorafenib arm did not result in significant improvement in EFS or OS. This was also true for subgroup analyses, including the subgroup positive for FLT3 internal tandem duplications. Results of induction therapy were worse in the sorafenib arm, with higher treatment-related mortality and lower CR rates. More adverse effects occurred during induction therapy in the sorafenib arm, and patients in this arm received less consolidation chemotherapy as a result of higher induction toxicity.DiscussionIn conclusion, combination of standard induction and consolidation therapy with sorafenib in the schedule investigated in our trial is not beneficial for elderly patients with AML.
    Journal of Clinical Oncology 07/2013; 31(25). DOI:10.1200/JCO.2012.46.4990
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    ABSTRACT: In gastrointestinal stromal tumor (GIST), there is no biomarker available that indicates success or failure of therapy. We hypothesized that tumor specific CKIT or PDGFRA mutant DNA fragments can be detected and quantified in plasma samples of GIST patients. We prospectively collected 291 plasma samples from 38 subjects with GIST harbouring activating mutations of CKIT or PDGFRA detected in tumor tissue, irrespective of current disease status or treatment. We used allele-specific Ligation PCR to detect mutant free circulating (fc)DNA. We were able to detect fcDNA harbouring the tumor mutation in 15 out of 38 patients. Patients with active disease displayed significantly higher amounts of mutant fcDNA compared to patients in CR. The amount of mutant fcDNA correlated with disease course. We observed repeated positive test results or an increase of mutant fcDNA in five patients with progressive disease or relapse. A decline of tumor fcDNA or conversion from positive to negative was seen in five patients responding to treatment. A negative to positive conversion was seen in two patients with relapse and one patient with progression. In two cases, we aimed to identify additional mutations, and found four additional exchanges, including mutations not known from sequentially performed tumor biopsies. Our results indicate that free circulating DNA harbouring tumor specific mutations in the plasma of patients with GIST can be used as tumor-specific biomarker. The detection of resistance mutations in plasma samples might allow earlier treatment changes and obviates the need for repeated tumor biopsies.
    Clinical Cancer Research 07/2013; 19(17). DOI:10.1158/1078-0432.CCR-13-0765
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    ABSTRACT: The role of HSP90 in stabilization of oncogenic tyrosine kinases made it an attractive therapeutic target for treating cancer but the molecular basis underlying the interaction between the HSP90 chaperone and client kinases is not elucidated yet. Using kinase inhibitors we show that the inactive conformation of ERBB2 does not interact with HSP90 chaperone and is thus not amenable to degradation upon HSP90 inhibitor treatment, while active ERBB2 kinase conformation promotes interaction with the HSP90 machinery and thus is degraded upon HSP90 inhibitor treatment. Interestingly, the kinase-chaperone interaction is disrupted in case of BCR-ABL and FLT3-ITD when bound to inhibitors irrespective of whether they block the kinase in an active or inactive conformation and thus our results indicate that the stability of the active kinase conformation varies between different kinases.
    PLoS ONE 07/2013; 8(7):e68394. DOI:10.1371/journal.pone.0068394
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    ABSTRACT: BACKGROUND: Formation of asymmetric kinase dimers is required for wt-EGFR activation upon ligand stimulation. The role of receptor dimerization in oncogenic EGFRvIII mutant activation is not completely understood and the molecular details of EGFRvIII interactions within homo-dimers and hetero-dimers are not elucidated yet. FINDINGS: By employing mutations that disrupt the asymmetric kinase dimer interface in EGFRvIII, we demonstrate that the mechanism of oncogenic EGFRvIII mutant activation is similar to that of the full-length wild-type EGFR. Surprisingly, the monomeric EGFRvIII lacks autophosphorylation and the formation of asymmetric kinase dimers is indispensable for oncogenic kinase activation. In addition, we show that ERBB3 can act as an activator of EGFRvIII by forming asymmetric kinase dimer in a ligand-independent manner. Interestingly, we found that the formation of asymmetric kinase dimer is dispensable for ERBB3 phosphorylation by the activated EGFR kinase as well as the ERBB2 kinase thus revealing a novel model for receptor function. CONCLUSIONS: Lateral signaling is a novel mechanism of signal propagation via ERBB3 upon activation by EGFR/ERBB2 kinase even in the absence of their ability to form asymmetric kinase dimers.
    Cell Communication and Signaling 06/2013; 11(1):39. DOI:10.1186/1478-811X-11-39

Publication Stats

5k Citations
1,207.67 Total Impact Points

Institutions

  • 2013–2015
    • Universitätsklinikum Freiburg
      • Department of Internal Medicine I
      Freiburg an der Elbe, Lower Saxony, Germany
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 1998–2013
    • Technische Universität München
      • Medizinische Klinik und Poliklinik III - Hämatologie/Onkologie
      München, Bavaria, Germany
  • 2003–2007
    • St. Jude Children's Research Hospital
      Memphis, Tennessee, United States
  • 2005
    • Memorial Sloan-Kettering Cancer Center
      New York, New York, United States
  • 2003–2005
    • Technische Universität Dresden
      Dresden, Saxony, Germany
  • 2004
    • Johannes Gutenberg-Universität Mainz
      • III. Department of Medicine
      Mayence, Rheinland-Pfalz, Germany
  • 2000–2001
    • Robert-Bosch Krankenhaus
      Stuttgart, Baden-Württemberg, Germany
    • Institut für klinische Pharmakologie
      Stuttgart, Baden-Württemberg, Germany
  • 1998–2000
    • Universität Ulm
      • Department of Internal Medicine
      Ulm, Baden-Württemberg, Germany
  • 1993
    • Evangelische Hochschule Freiburg, Germany
      Freiburg, Baden-Württemberg, Germany