0000000000277420
AUTHOR
Boyka Markova
showing 9 related works from this author
Novel pathway in Bcr-Abl signal transduction involves Akt-independent, PLC-γ1-driven activation of mTOR/p70S6-kinase pathway
2009
In chronic myeloid leukemia, activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway is crucial for survival and proliferation of leukemic cells. Essential downstream molecules involve mammalian target of rapamycin (mTOR) and S6-kinase. Here, we present a comprehensive analysis of the molecular events involved in activation of these key signaling pathways. We provide evidence for a previously unrecognized phospholipase C-gamma1 (PLC-gamma1)-controlled mechanism of mTOR/p70S6-kinase activation, which operates in parallel to the classical Akt-dependent machinery. Short-term imatinib treatment of Bcr-Abl-positive cells caused dephosphorylation of p70S6-K and S6-protein without inactivat…
The JAK2 Kinase Inhibitor LS104 Induces Growth-Arrest and Apoptosis in JAK2V617F Positive Cells.
2007
Abstract The JAK2V617F-mutation (V617F) is a novel, highly prevalent molecular marker in Ph-negative myeloproliferative disease (MPD). In vitro, the V617F mutation confers cytokine independent growth of Ba/F3 cells expressing erythropoietin receptor (EpoR) and constitutive activation of the JAK2 kinase and of the JAK-STAT pathway. In a murine bone-marrow transplant model the V617F-mutation alone is sufficient to induce a polycythemia vera-like phenotype. Therefore, mutant JAK2 kinase is a promising target for kinase inhibitor development. In this report, we characterize the small molecule LS104 (previously CR4; Grunberger et al., Blood 2003) as a novel non-ATP-competitive JAK2V617F kinase i…
LS104, a non-ATP-competitive small-molecule inhibitor of JAK2, is potently inducing apoptosis in JAK2V617F-positive cells
2008
Abstract The activating JAK2V617F mutation has been described in the majority of patients with BCR-ABL-negative myeloproliferative disorders (MPD). In this report, we characterize the small-molecule LS104 as a novel non-ATP-competitive JAK2 inhibitor: Treatment of JAK2V617F-positive cells with LS104 resulted in dose-dependent induction of apoptosis and inhibition of JAK2 autophosphorylation and of downstream targets. Activation of these targets by JAK2 was confirmed in experiments using small interfering RNA. LS104 inhibited JAK2 kinase activity in vitro. This effect was not reversible using elevated ATP concentrations, whereas variation of the kinase substrate peptide led to modulation of …
Identification of a novel type of ITD mutations located in nonjuxtamembrane domains of the FLT3 tyrosine kinase receptor
2009
Abstract In acute myeloid leukemia (AML), internal tandem duplications (ITDs) of the juxtamembrane (JM) of FLT3 have been shown to play a crucial role in driving proliferation and survival of the leukemic clone. Here, we report the identification of FLT3_ITD mutations located in non-JM domains of the FLT3-receptor. This novel type of FLT3_ITD mutation was found in 216 of 753 (28.7%) of unselected FLT3_ITD-positive AML cases. An FLT3 receptor harbouring a prototypic non-JM ITD (FLT3_ITD627E) mediated constitutive phosphorylation of FLT3 and of STAT5, suggesting that non-JM ITDs confer constitutive activation of the receptor. FLT3_ITD627E induced transformation of hematopoietic 32D cells and …
The kinase inhibitor LS104 induces apoptosis, enhances cytotoxic effects of chemotherapeutic drugs and is targeting the receptor tyrosine kinase FLT3…
2008
Activating mutations of FLT3 are found in approximately one-third of acute myeloid leukemia (AML)-cases and are considered to represent an attractive therapeutic target. In this study, we report that the hydroxystyryl-acrylonitrile compound LS104 inhibits proliferation and induces potent cytotoxic effects in FLT3 expressing leukemic cells in vitro. Immunoblot and phosphoprotein-FACS analysis demonstrated inhibiton of phosphorylation of FLT3-ITD and of its downstream targets. In pharmacokinetic studies, a rapid and dose dependent cellular uptake of LS104 lasting up to 11h could be demonstrated. Combination of LS104 with chemotherapeutic agents markedly enhanced cytotoxic effects. Recently, a…
In Situ Detection of Phosphorylated Platelet-derived Growth Factor Receptor β Using a Generalized Proximity Ligation Method
2007
Improved methods are needed for in situ characterization of post-translational modifications in cell lines and tissues. For example, it is desirable to monitor the phosphorylation status of individual receptor tyrosine kinases in samples from human tumors treated with inhibitors to evaluate therapeutic responses. Unfortunately the leading methods for observing the dynamics of tissue post-translational modifications in situ, immunohistochemistry and immunofluorescence, exhibit limited sensitivity and selectivity. Proximity ligation assay is a novel method that offers improved selectivity through the requirement of dual recognition and increased sensitivity by including DNA amplification as a…
A novel molecular mechanism of primary resistance to FLT3-kinase inhibitors in AML
2009
Abstract Currently, FLT3 tyrosine kinase inhibitors (TKIs) are emerging as the most promising drug therapy to overcome the dismal prognosis of acute myelogenous leukemia (AML) patients harboring internal tandem duplications (ITDs) of FLT3. However, up-front drug resistance occurs in approximately 30% of patients, and molecular mechanisms of resistance are poorly understood. Here, we have uncovered a novel mechanism of primary resistance to FLT3 TKIs in AML: an FLT3 receptor harboring a nonjuxtamembrane ITD atypically integrating into the β-2 sheet of the first kinase domain (FLT3_ITD627E) induces dramatic up-regulation of the anti-apoptotic myeloid cell leukemia 1 protein (MCL-1). Using RNA…
Identification of a Novel Pathway in BCR/ABL Signal Transduction Involving Akt-Independent Activation of PLC-gamma/mTOR/p70-S6K.
2006
Abstract In BCR/ABL positive CML, defining new, additional therapeutic targets in the pathways, activated by BCR/ABL is critical for the development of new treatment strategies, especially for patients resistant or refractory to Imatinib. While studying the involvement of PI3K/Akt/mTOR signaling pathway in the development of such resistance we have uncovered the existence of additional, Akt-independent mechanism of activation of mTOR/p70-S6 Kinase pathway. Short term treatment with Imatinib (1μM, 4 hours) of the BCR/ABL-positive cell lines LAMA84, AR320, KCL22, K562, Ba/F3-BCR/ABL caused downregulation of p70-S6K phosphorylation and of S6 ribosomal protein phosphorylation without decreasing…
3,4-Diarylmaleimides Effectively Inhibit Proliferation of FLT3-ITD-Positive Leukemic Cells, Induce Apoptosis and Show Additive Effects in Combination…
2007
Abstract Internal tandem duplication (ITD) mutations of FLT3 are present in leukemic blasts of approximately 30% of AML patients. ITD-mutations of FLT3 confer a worse prognosis and decreased overall survival. Therefore, FLT3-tyrosine kinase is considered an attractive drug target in AML and several FLT3-tyrosine kinase inhibitors (TKIs) are currently being tested in clinical trials (CEP701, MLN518, Sorafenib, PKC412). However, using these drugs as monotherapy, against the setting of remarkable efficacy has emerged the problem of short duration of remission indicating rapid development of secondary resistance. In addition, up to 30% of patients may show primary resistance to currently availa…