Potent Transient Inhibition of BCR-ABL by Dasatinib Leads to Complete Cytogenetic Remissions in Patients with Chronic Myeloid Leukemia: Implications for Patient Management and Drug Development.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2166-2166 ◽  
Author(s):  
Neil P. Shah ◽  
John M. Nicoll ◽  
Eric Bleickardt ◽  
Claude Nicaise ◽  
Ronald L. Paquette ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Cell Line ◽  
Cell Biology ◽  
Kinase Activity ◽  
Kinase Inhibition ◽  
Once Daily ◽  
Minute Exposure ◽  
Abl Kinase ◽  
Short Term Exposure ◽  
Dose Modifications

Abstract Dasatinib (Sprycel; formerly BMS-354825) is an oral multi-targeted SRC/ABL tyrosine kinase inhibitor that is approximately 325-fold more potent than imatinib, and has been recently approved by the US FDA for the treatment of imatinib-resistant and -intolerant Philadelphia chromosome-associated leukemias. In contrast to other tyrosine kinase inhibitors, pharmacokinetic analyses reveal that dasatinib has a short half-life (5–6 hours), with near-complete loss of BCR-ABL kinase activity inhibition eight hours after drug administration in patients with CML. Remarkably, patients treated with dasatinib as infrequently as once daily, five days per week, have achieved complete cytogenetic remission (CCyR). We tested transient BCR-ABL inhibition in vitro by assessing the sensitivity of the CML cell line K562 to short-term exposure of dasatinib. After as short as a 20-minute exposure to a clinically-relevant dasatinib concentration (100 nM), the majority of cells undergo apoptosis when analyzed after 48 hours, whereas a clinically-relevant concentration of imatinib (5 uM) failed to result in substantial cytotoxicity under these conditions. When higher concentrations (>=12.5 uM) of imatinib were used that correct for differences in potency between imatinib and dasatinib, cytotoxicity at 48 hours after a 20-minute exposure was similar to that observed with dasatinib. These results exclude SRC family inhibition as a potential mediator of this effect, and were reproducible in a second CML cell line, KU-812. Importantly, cytotoxicity was not observed in BCR-ABL-negative leukemia cell lines under these conditions. Signiificantly, similar phenomenon was observed when an erlotinib-sensitive non-small cell lung cancer was exposed to high concentrations of erlotinib for 20 minutes. We assessed the degree of BCR-ABL kinase inhibition achieved in 20 patients with chronic phase CML who were treated with dasatinib once daily as part of a phase I clinical trial by quantifying the ratio of phospho-CRKL to CRKL (a BCR-ABL substrate) achieved in PBMCs harvested four hours after the first dose of dasatinib. We found a strong correlation between the magnitude of BCR-ABL kinase inhibition and the depth of response achieved. Notably, CCyR was achieved exclusively in four patients who experienced the deepest inhibition of BCR-ABL kinase activity activity. The current medical management of CML involves assessing the degree of cytogenetic response after 6–12 months of imatinib therapy before considering dose modifications of imatinib. While our findings will need to be validated prospectively in larger cohorts of patients, they suggest that it may be feasible to make early dose modifications based upon the degree of target inhibition following the initial dose of dasatinib, and thus maximize the likelihood of clinical benefit. Together, these findings have potentially significant implications not only for the optimal clinical management of CML patients, but also for the rational development of small molecule inhibitors of other cancer-associated tyrosine kinases, as well as our global understanding of cancer cell biology.

The Protein Tyrosine Phosphatase STS-1 Interacts with Bcr-Abl and Impairs the Response of Philadelphia-Positive Acute Lymphoblastic Leukemia (ALL) to Tyrosine Kinase Inhibitors

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3236-3236
Author(s):  
Marcus Liebermann ◽  
Daniela Hoeller ◽  
Susanne Badura ◽  
Tamara Tesanovic ◽  
Hubert Serve ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
B Cell ◽  
Cell Line ◽  
Cell Lines ◽  
Research Funding ◽  
Kinase Activity ◽  
Kinase Inhibitors ◽  
Signalling Pathways ◽  
Abl Kinase ◽  
Clinical Resistance

Abstract Abstract 3236 Bcr-Abl is a leukemogenic fusion gene that by itself is sufficient for cellular transformation (Daley et al.) and is the hallmark of chronic myeloid leukemia and Philadelphia chromosome positive (Ph+) ALL. The Bcr-Abl fusion protein is a constitutively active tyrosine kinase (TK) which disrupts multiple cellular signalling pathways controlling apoptosis, cell cycle, proliferation and DNA repair. In Ph+ ALL, a subtype of ALL with a particularly poor prognosis, targeted inhibition of Bcr-Abl activity by Abl kinase inhibitors such as imatinib has improved treatment outcome but has not abrogated the frequent development of clinical resistance. In addition to mutations in the Bcr-Abl tyrosine kinase domain (TKD), it has become apparent that other resistance mechanisms contribute to disease progression. The activity of proteins involved in the above-mentioned signalling pathways and possibly resistance to TK inhibitors (TKI) is controlled at least partially by posttranslational modifications such as phosphorylation, which is regulated by the balance between kinases and protein tyrosine phosphatases (PTP). We previously showed that PTP1B is a negative regulator of Bcr-Abl-mediated transformation and modulates sensitivity to the TKI imatinib (Koyama et al). We hypothesized that other phosphatases for which Bcr-Abl is a substrate may also contribute to resistance, one candidate being Suppressor of T-cell receptor Signalling 1 (STS-1), which negatively regulates the endocytosis of receptor TK involved in a variety of hematologic malignancies. It was the aim of this study to determine whether: i) Bcr-Abl is a substrate of STS-1 ii) STS-1 is able to dephosphorylate Bcr-Abl iii) expression of STS-1 reduces the proliferation of Bcr-Abl expressing cells by inhibiting Bcr-Abl kinase activity iv) the level of STS-1 expression modulates the sensitivity of Bcr-Abl positive cells to TKI In order to answer these questions, we used 293T cells, a human primary embryonal kidney cell line, and the IL3-dependent murine pro B cell line Ba/F3. Both cell lines were modified with constructs encoding both forms of Bcr-Abl (p185/p210) and Sts-1. For experiments with endogenous Bcr-Abl (p185) and Sts-1 we used Sup B15 cells, a human B cell precursor leukemia, and its TKI-resistant subline (Sup B15 RT), which was generated in our lab and is highly resistant not only to imatinib but also to 2nd generation TKIs (Nilotinib & Dasatinib), with no evidence of TKD mutations or transcriptional up-regulation of Bcr-Abl. In all above described cell lines the interaction between Bcr-Abl and Sts-1 could be shown in an overexpressed system (293T & Ba/F3) and on an endogenous level (Sup B15 & Sup B15 RT) by using co-IPs followed by SDS-PAGE and Western blotting. The functional relevance was examined by testing the ability of Sts-1 to dephosphorylate Bcr-Abl. Complete dephosphorylation of Bcr-Abl was shown for p185bcr-abl and p210bcr-abl in 293T cells. To verify that the functional activity was also present in hematopoietic cells, we analyzed the ability of Sts-1 to dephosphorylate Bcr-Abl in Ba/F3 and Sup B15 cells. Dephosphorylation was observed in both cell lines but was less pronounced than in 293T cells. We therefore more closely examined the most important tyrosine (Tyr) residues of Bcr-Abl and identified Tyr245 and Tyr412 as the major targets of Sts-1. Phosphorylation of Tyr245 and Tyr412 was decreased by ∼60% in Ba/F3 cells and ∼39% in Sup B15 cells. These two residues are known to be important for regulating cell proliferation, survival and cell motility. In a competitive proliferation assay in the absence of IL3, the proliferation rate of BA/F3 cells infected with Bcr-Abl and Sts – 1 was reduced compared to a Bcr-Abl infected control population. When treated with imatinib the Sts-1 expressing cells showed an approximately 5-fold reduced proliferation rate compared to cells lacking Sts-1, or to imatinib-resistant cells harbouring the Bcr-Abl “gatekeeper mutation” T315I. The expression level of Sts-1 was found to be approximately 3-fold lower in the Sup B15 RT compared to the WT cell line. Regulation appeared to occur at the transcriptional level as shown by quantitive RT-PCR. These results show that Bcr-Abl is a substrate of Sts-1, that this phosphatase modulates Bcr-Abl kinase activity and may abrogate the response to TKI. This suggests that phosphatases may contribute to the development of clinical resistance of Ph+ leukemias to TKIs. Disclosures: Ottmann: Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding.

Therapeutically Rewiring Kinase Pathways in BCR-ABL+ Leukemias

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3197-3197
Author(s):  
Louise M Carlson ◽  
Sanjay Bansal ◽  
Kelvin P. Lee
Keyword(s):  
Tyrosine Kinase ◽  
Cell Line ◽  
Signaling Pathway ◽  
Kinase Activity ◽  
Lymphoblastic Leukemia ◽  
Growth Arrest ◽  
Leukemic Cells ◽  
Tyrosine Kinase Activity ◽  
Poor Prognostic Factor ◽  
Abl Kinase

Abstract The central leukemogenic lesion in chronic myeloid leukemia (CML) is the bcr-abl fusion gene, arising from the reciprocal chromosomal translocation t(9;22)(q34;q11) and resulting in the chimeric Bcr-Abl protein with constitutively activate Abl tyrosine kinase activity. Bcr-Abl is also present in 20–40% of adult acute lymphoblastic leukemia (ALL), and represents poor prognostic factor. The tyrosine kinase inhibitor (TKI) imatinib specifically inhibits tyrosine kinase activity of Bcr-Abl and selectively suppresses the growth and induces apoptosis in CML blasts – and has become the paradigm for inhibiting oncogenic signal transduction as a means of altering leukemic blast (and other transformed cells) biology. However, imatinib and other TKIs have been much less effective in accelerated phase/blast crisis CML and BCR-Abl+ ALL due to mutated TKI-resistant enzymes, BCR-Abl overexpression or cellular independence from the pro-survival signals transduced by the oncogenic kinase. We have developed a previously unexplored strategy that utilizes BCR-Abl kinase activity (instead of inhibiting it), in which the oncogenic kinase specifically activates a “prodrug” that subsequently acts as a “suicide” agent, causing leukemic cell differentiation and death. We and others have shown that pharmacologic activation of the serine-threonine kinase protein kinase C (PKC) induces growth arrest, differentiation and apoptosis in CML and AML blasts, and also kills ALL blasts. However, PKC are not tyrosine kinase substrates and are not directly activated by BCR-Abl. However, substitution of a negatively charged “phospho-mimetic” glutamic acid for Ala25 in the pseudo-substrate domain of PKC results in a constitutively active enzyme. We now show that reengineering PKC by “swapping in” the Abl kinase target motif (Ala-X-X-Ile-Tyr25-X-X-Phe/Pro) into the pseudosubstrate domain (A25Y PKC constructs) allows BCR-ABL to phosphorylate the tyrosine at position 25. This phosphorylation activates A25Y PKC specifically in the BCR-Abl+ K562 CML cell line, but not BCR-Abl negative AML KG1 cell line, as detected by PKC translocation from the cytoplasm to the plasma membrane. At a cellular level, this BCR-Abl-mediated activation of A25Y PKC results in a 6 fold reduction in cell growth and 6 fold increase in apoptosis as measured by annexin V staining (wild type PKC 2.9% apoptotic vs. A25Y 17.8% apoptotic). These findings demonstrate that the novel strategy of “rewiring” the pro-survival BCR-Abl signaling pathway into the “pro-death” PKC pathway via kinase activated suicide agents results in PKC-mediated growth arrest/apoptosis in BCR-Abl+ leukemic cells. More broadly, this therapeutic approach using oncogenic signaling pathways to activate prodrug effector molecules specifically within cancer cells may be particularly useful in TKI-resistant malignancies (especially where resistance to tyrosine kinase inhibitors is due to an amplified signal) or particularly in malignancies that may be less dependent on the oncogenic signal for survival (i.e. BCR-Abl+ ALL, EGFR signaling in lung cancer), where the signaling pathway is “on” but blocking it has little effect.

Inhibition of c-kit receptor tyrosine kinase activity by STI 571, a selective tyrosine kinase inhibitor

Blood ◽  
2000 ◽  
Vol 96 (3) ◽  
pp. 925-932 ◽  
Author(s):  
Michael C. Heinrich ◽  
Diana J. Griffith ◽  
Brian J. Druker ◽  
Cecily L. Wait ◽  
Kristen A. Ott ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Map Kinase ◽  
Cell Line ◽  
Cellular Proliferation ◽  
Kinase Activity ◽  
Leukemia Cell ◽  
Myelogenous Leukemia ◽  
Leukemia Cell Line ◽  
Tyrosine Kinase Activity ◽  
Sti 571

Abstract STI 571 (formerly known as CGP 57148B) is a known inhibitor of the c-abl, bcr-abl, and platelet-derived growth-factor receptor (PDGFR) tyrosine kinases. This compound is being evaluated in clinical trials for the treatment of chronic myelogenous leukemia. We sought to extend the activity profile of STI 571 by testing its ability to inhibit the tyrosine kinase activity of c-kit, a receptor structurally similar to PDGFR. We treated a c-kit expressing a human myeloid leukemia cell line, M-07e, with STI 571 before stimulation with Steel factor (SLF). STI 571 inhibited c-kit autophosphorylation, activation of mitogen-activated protein (MAP) kinase, and activation of Akt without altering total protein levels of c-kit, MAP kinase, or Akt. The concentration that produced 50% inhibition for these effects was approximately 100 nmol/L. STI 571 also significantly decreased SLF-dependent growth of M-07e cells in a dose-dependent manner and blocked the antiapoptotic activity of SLF. In contrast, the compound had no effect on MAP kinase activation or cellular proliferation in response to granulocyte-macrophage colony-stimulating factor. We also tested the activity of STI 571 in a human mast cell leukemia cell line (HMC-1), which has an activated mutant form of c-kit. STI 571 had a more potent inhibitory effect on the kinase activity of this mutant receptor than it did on ligand-dependent activation of the wild-type receptor. These findings show that STI 571 selectively inhibits c-kit tyrosine kinase activity and downstream activation of target proteins involved in cellular proliferation and survival. This compound may be useful in treating cancers associated with increased c-kit kinase activity.

Leukemic Stem Cells of Chronic Phase CML Patients Possess Uniquely Elevated BCR-ABL Kinase Activity and Acquire Spontaneous BCR-ABL Kinase Domain Mutations at a High Frequency.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 438-438 ◽  
Author(s):  
Xiaoyan Jiang ◽  
Kyi Min Saw ◽  
Allen Eaves ◽  
Connie Eaves
Keyword(s):  
Stem Cells ◽  
Tyrosine Kinase ◽  
Kinase Activity ◽  
Point Mutations ◽  
Chronic Phase ◽  
Kinase Domain ◽  
Tyrosine Kinase Activity ◽  
Abl Kinase ◽  
Kinase Domain Mutations

Abstract Growing evidence indicates that the therapeutic potential of imatinib mesylate (IM) for the treatment of CML may be limited initially by a relative innate resistance of the leukemic stem cells and eventually by an accumulation of cells with BCR-ABL tyrosine kinase domain mutations. We now show that the amount and tyrosine kinase activity of p210-BCR-ABL in the most primitive and relatively IM-unresponsive lin−CD34+CD38− CML cells is 3 to 10-fold higher than in the majority of the lin−CD34+CD38+ CML progenitors (n=3). These results confirm previous BCR-ABL transcript data and identify elevated p210-BCR-ABL expression to be a likely important factor in the characteristic IM-insensitivity of very primitive CML cells. To determine whether in vivo, CML stem cells also accumulate gene mutations affecting the BCR-ABL kinase domain, cDNAs were prepared from RNA extracts of purified lin−CD34+CD38− cells isolated from 3 chronic phase patients that had not received IM therapy. Bidirectional sequencing of individually cloned cDNAs from these samples revealed BCR-ABL kinase domain mutations in 2 of the 3 patients at frequencies of 10% (1/10), 20% (2*/10,*identical mutations). Incubation of these lin−CD34+CD38− cells in vitro for 2–3 wk ± a high concentration of IM (up to 10 μM, which was sufficient to reduce the tyrosine kinase activity in the input cells by 70±12% and in their 2 wk progeny by 10±5%) selected a subpopulation of more differentiated and completely IM-resistant cells. This was shown in Western blots by the inability of 10 μM IM to reduce either their p210-BCR-ABL tyrosine kinase activity or CrkL phosphorylation and in methylcellulose assays ±5 μM IM. As predicted, IM-selected cells showed a higher frequency of kinase domain mutations (13–20% vs 0–20% of cDNA clones analyzed from 3 wk cells cultured ±IM). Analysis of individual colonies produced from CFCs in the cultured cells showed all (21/21) colonies from IM-selected cells had mutations vs 50% (5/10) in those cultured without IM. The total frequency of mutant cDNAs detected was also increased in the IM-resistant cells (35–55% vs 10–25% mutant cDNAs in selected vs control cells). Interestingly, in most cases, both wild-type and mutant cDNAs were identified in the same colony, indicating de novo generation of mutations in vitro. Overall, >50 different mutations were identified. These included 10 point mutations previously associated with clinical IM resistance (including G250 and T315), another 13 point mutations previously identified in a comprehensive mutational screen, and >20 previously undescribed mutations. Several of the latter affect the critical region of the P loop, the c-helix and the activation loop and would be predicted to confer significant IM resistance. To investigate the possibility that the observed genomic instability of very primitive CML cells might be related to their elevated innate p210-BCR-ABL activity, BCR-ABL transcript levels in individual IM-selected, fully resistant and control (similarly treated but no IM exposure) colonies were compared. This showed that BCR-ABL transcripts were ~20-fold higher (P<0.05) in the resistant colonies (30 assessed from 3 patients). These findings suggest that the increased BCR-ABL expression and activity that uniquely characterizes the most primitive CML cells may contribute not only to their innate insensitivity to IM but also to a deregulation of genomic stability leading to the emergence of IM-resistant mutants and other subclones associated with disease progression.

Blocking of Cytokine Survival Signals along with Intense Bcr-Abl Kinase Inhibition May Eradicate CML Progenitor Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3250-3250
Author(s):  
Devendra K Hiwase ◽  
Deborah L White ◽  
Jason A Powell ◽  
Verity A Saunders ◽  
Stephanie Zrim ◽  
...  
Keyword(s):  
Cell Death ◽  
Cell Lines ◽  
Research Funding ◽  
Kinase Activity ◽  
Short Term ◽  
Kinase Inhibition ◽  
Gm Csf ◽  
Abl Kinase ◽  
Cd34 Cells ◽  
Short Term Culture

Abstract Abstract 3250 Poster Board III-1 Preclinical studies of imatinib set the paradigm of continuous Bcr-Abl kinase inhibition for optimal response in chronic myeloid leukemia (CML). However, the clinical success of once daily dasatinib, despite its short serum half life, implies that intermittent inhibition of Bcr-Abl kinase activity is sufficient for clinical response. In vitro studies also demonstrated that short-term intense (≥90%) Bcr-Abl kinase inhibition triggers cell death in BCR-ABL + cell lines, demonstrating their oncogene addiction. However, the effect of short-term intense kinase inhibition on CD34+ CML progenitors is not studied. Clinical, mathematical modelling and in vitro studies suggest that leukemic stem cells (LSC) are difficult to eradicate and hence the majority of CML patients may not be cured with tyrosine kinase inhibitors (TKI). Inadequate Bcr-Abl kinase inhibition has been postulated to cause refractoriness of LSC to TKI's. This may be due to increased expression of ABCB1 and ABCG2 efflux proteins, or the quiescent state of LSC. However, the phenomenon could be independent of Bcr-Abl kinase activity. In vivo leukemic progenitors live in a cytokine rich environment which may be providing a mechanism for Bcr-Abl independent resistance. We have assessed the impact of short-term intense Bcr-Abl kinase inhibition on CML cell lines and CML CD34+ primary cells in the presence and absence of cytokines. In CML cell lines, short-term (cells were cultured with dasatinib for 30 min and following thorough drug washout, cells were recultured in drug free media for 72 hr) intense Bcr-Abl kinase inhibition with 100 nM dasatinib triggers cell death. In CML-CD34+ cells 30 min of culture with 100 nM dasatinib (n=13) or 30 μM IM (n=7) reduced the level of p-Crkl (surrogate marker of Bcr-Abl kinase activity) by 97±3% and 96±4% respectively. In the presence of either a six growth factors cocktail (6-GF; n=10) or GM-CSF (n=11) or G-CSF (n=4) alone, despite 97% inhibition of p-Crkl, short-term culture with 100 nM dasatinib (D100ST) reduced colony forming cells (CFC) by only 24%, 32% or 5%, respectively. However without cytokines, D100ST reduced CML-CD34+ CFCs by 70%. Consistent with the results observed with dasatinib, short-term culture with 30 μM imatinib (IM) (n=3) also reduced 90% CFC in the absence of cytokines but by only 38% in the presence of 6-GF. These results suggest that in CML-CD34+ cells, GM-CSF, G-CSF or 6-GF mediate Bcr-Abl independent TKI resistance. It is possible that cytokines may be promoting cell survival via signalling pathways that are refractory to dasatinib. To examine this possibility, we assessed the effect of D100ST on p-STAT5 signalling in CML-CD34+ cells, in the presence and absence of GM-CSF, G-CSF or 6-GF. STAT5 was constitutively phosphorylated in CML-CD34+ cells, and in the absence of cytokines, D100ST reduced the p-STAT 5. STAT5 phosphorylation was not inhibited by D100ST when cells were cultured with 6-GFs or GM-CSF however, the combination of D100ST and a Janus kinase (Jak) inhibitor dramatically reduced p-STAT5. Similarly, in the presence of GM-CSF (32.35±5.16% vs. 68.33±14.90%) or G-CSF (58.13±13 vs. 94.68±21.12) combination of D100ST and JAK inhibitor significantly reduced CFC compared to D100ST only. Thus our data suggest that in contrast to CML cell lines, primary CML progenitors may not be completely dependent on the BCR-ABL oncogene and that activation of the cytokine mediated JAK-2/STAT-5 pathway may circumvent the need for BCR-ABL signalling for maintenance of survival. Thus a therapeutic strategy based on short-term intense kinase inhibition may have limited success unless critical redundant cytokine-induced survival pathways are also inhibited. We postulate that blockade of cytokine signalling along with short-term intense Bcr-Abl kinase inhibition with a potent second generation TKI may provide a novel strategy to eradicate primitive CML cells. Fig 1 In CML-CD34+ cells, Jak kinase inhibition abrogates the rescuing effect of cytokines on cell death induced by BCR-ABL blockade: In the absence of cytokines (No GF, n=11) short-term culture with 100 nM dasatinib (D100ST) reduced CFCs by 67% of control, however in the presence of 6-GFs (n=10), GM-CSF (n=10) or G-CSF (n=4) it could reduce CFCs by only 24%, 32% or 5% of control respectively (B) In the presence of GM-CSF (n= 4) or G-CSF (n= 4), combination of Jak inhibition and D100ST reduced CFC compared to dasatinib alone. Fig 1. In CML-CD34+ cells, Jak kinase inhibition abrogates the rescuing effect of cytokines on cell death induced by BCR-ABL blockade: In the absence of cytokines (No GF, n=11) short-term culture with 100 nM dasatinib (D100ST) reduced CFCs by 67% of control, however in the presence of 6-GFs (n=10), GM-CSF (n=10) or G-CSF (n=4) it could reduce CFCs by only 24%, 32% or 5% of control respectively (B) In the presence of GM-CSF (n= 4) or G-CSF (n= 4), combination of Jak inhibition and D100ST reduced CFC compared to dasatinib alone. Disclosures: White: Novartis and Britol-Myers Squibb: Research Funding. Hughes:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Enhanced SH3:Linker Interaction Suppresses Activating Mutations of the c-Abl Protein-Tyrosine Kinase.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1208-1208
Author(s):  
Shoghag Panjarian ◽  
Shugui Chen ◽  
John Engen ◽  
Thomas Smithgall
Keyword(s):  
Tyrosine Kinase ◽  
Myristic Acid ◽  
Protein Tyrosine Kinase ◽  
Kinase Activity ◽  
Binding Pocket ◽  
Sh3 Domain ◽  
Kinase Domain ◽  
Abl Kinase ◽  
Defective Mutant ◽  
T315i Mutation

Abstract Abstract 1208 Bcr-Abl, the chimeric protein-tyrosine kinase expressed as a result of the Philadelphia chromosome translocation, plays a pivotal role in the initiation and maintenance of chronic myelogenous leukemia (CML). Imatinib (Gleevec) is an ATP-competitive Bcr-Abl inhibitor that selectively kills Bcr-Abl+ CML cells. Despite its clinical success, imatinib is less effective in the advanced stages of CML due to the emergence of drug resistance caused by point mutations in the Abl kinase domain. Second generation Bcr-Abl inhibitors such as dasatinib and nilotinib are active against most imatinib-resistant forms of Bcr-Abl, with the exception of the T315I “gatekeeper” mutant. The Abl gatekeeper residue (Thr315) is located between the ATP-binding site and an adjacent hydrophobic pocket, and forms a key hydrogen bond with imatinib. Additionally, the T315I mutation produces a strong activating effect on the downregulated c-Abl “core,” consisting of the myristoylated N-terminal Ncap, tandem SH3 and SH2 regulatory domains, the SH2-kinase linker, which forms a polyproline type II helix for internal SH3 docking, and the tyrosine kinase domain. Using hydrogen-exchange mass spectrometry, we recently found that the T315I mutation not only induced conformational changes in the Abl kinase domain as expected, but also at a distance in the RT-loop of the SH3 domain. Such changes may allosterically contribute to kinase domain activation by disturbing the negative regulatory influence of SH3:linker interaction. Recently, a new class of allosteric Bcr-Abl inhibitors has been reported that targets the myristate-binding pocket of Abl, which localizes to C-lobe of the kinase domain and away from the active site. Together with our finding that the T315I mutation perturbs SH3:linker interaction, these inhibitors support the existence of an extensive network of allosteric interactions that work together to regulate Abl kinase activity. In this project, we investigated whether enhanced SH3:linker interaction can allosterically reverse the activating effects of the T315I imatinib resistance mutation as well as mutations of the N-terminal myristoylation site and myristic acid binding pocket. We created modified versions of Abl [High Affinity Linker proteins (HALs)] by mutating multiple residues within the SH2-kinase linker to proline, thereby enhancing the SH3 domain binding affinity. Using mammalian cell-based expression assays and immunoblotting with phosphospecific antibodies, we identified five of eleven Abl-HAL proteins that did not exhibit changes in basal kinase activity. The Abl-HAL protein with the greatest enhancement of SH3:linker interaction was then combined with the T315I mutation, a myristoylation-defective mutant, and a myristic acid binding pocket mutation. Remarkably, this HAL substitution completely reversed the activating effect of the myristic acid binding pocket mutation, while substantially suppressing the activity of Abl T315I and the myristoylation-defective mutant. These results indicate that stabilization of SH3:linker interaction allosterically represses Abl activation by a wide variety of mechanisms, and suggests a new approach to allosteric control of Bcr-Abl kinase activity. Disclosures: No relevant conflicts of interest to declare.

Inhibition of c-kit receptor tyrosine kinase activity by STI 571, a selective tyrosine kinase inhibitor

Blood ◽  
2000 ◽  
Vol 96 (3) ◽  
pp. 925-932 ◽  
Author(s):  
Michael C. Heinrich ◽  
Diana J. Griffith ◽  
Brian J. Druker ◽  
Cecily L. Wait ◽  
Kristen A. Ott ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Map Kinase ◽  
Cell Line ◽  
Cellular Proliferation ◽  
Kinase Activity ◽  
Leukemia Cell ◽  
Myelogenous Leukemia ◽  
Leukemia Cell Line ◽  
Tyrosine Kinase Activity ◽  
Sti 571

STI 571 (formerly known as CGP 57148B) is a known inhibitor of the c-abl, bcr-abl, and platelet-derived growth-factor receptor (PDGFR) tyrosine kinases. This compound is being evaluated in clinical trials for the treatment of chronic myelogenous leukemia. We sought to extend the activity profile of STI 571 by testing its ability to inhibit the tyrosine kinase activity of c-kit, a receptor structurally similar to PDGFR. We treated a c-kit expressing a human myeloid leukemia cell line, M-07e, with STI 571 before stimulation with Steel factor (SLF). STI 571 inhibited c-kit autophosphorylation, activation of mitogen-activated protein (MAP) kinase, and activation of Akt without altering total protein levels of c-kit, MAP kinase, or Akt. The concentration that produced 50% inhibition for these effects was approximately 100 nmol/L. STI 571 also significantly decreased SLF-dependent growth of M-07e cells in a dose-dependent manner and blocked the antiapoptotic activity of SLF. In contrast, the compound had no effect on MAP kinase activation or cellular proliferation in response to granulocyte-macrophage colony-stimulating factor. We also tested the activity of STI 571 in a human mast cell leukemia cell line (HMC-1), which has an activated mutant form of c-kit. STI 571 had a more potent inhibitory effect on the kinase activity of this mutant receptor than it did on ligand-dependent activation of the wild-type receptor. These findings show that STI 571 selectively inhibits c-kit tyrosine kinase activity and downstream activation of target proteins involved in cellular proliferation and survival. This compound may be useful in treating cancers associated with increased c-kit kinase activity.

Survivin silencing sensitizes imatinib-resistant CML cells to the cytotoxic effect of hydroxyurea

2006 ◽  
Vol 24 (18_suppl) ◽  
pp. 13119-13119
Author(s):  
F. Stagno ◽  
E. Conte ◽  
S. Stella ◽  
E. Tirrò ◽  
L. Manzella ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Cell Lines ◽  
Cytotoxic Effect ◽  
Kinase Activity ◽  
Point Mutations ◽  
Survivin Expression ◽  
Over Expression ◽  
Abl Kinase ◽  
Abl Tyrosine Kinase ◽  
Apoptosis Protein

13119 Background: Imatinib Mesylate (IM), a semi-specific inhibitor of the BCR-ABL tyrosine kinase, is currently the treatment of choice for Chronic Myeloid Leukemia (CML). However, about one third of CML patients treated with IM develop resistance to the drug because of reactivation of BCR-ABL kinase activity. This phenomenon is usually ascribed to the amplification of the BCR-ABL gene or to the selection of leukemic clones harboring point mutations that abrogate IM binding. To identify novel anti-apoptotic signaling pathways employed by BCR-ABL and devise strategies capable of killing IM-resistant CML cells, we investigated the interplay between BCR-ABL and the Inhibitor of Apoptosis Protein Survivin. Methods: Murine hematopoietic cells (32D) transduced with p210 BCR-ABL and human cell lines either positive (K562, KCL22, KYO1 and LAMA84) or negative (HL60) for the BCR-ABL oncoprotein, were analyzed for Survivin expression by western blot before and after IM treatment. Three different pathways (MAPK, PI3K and JAK2/STA3) potentially involved in BCR-ABL-mediated induction of Survivin were studied using inhibitors specific for each signaling cascade. The effect of Survivin on the proliferation and viability of IM-sensitive and IM-resistant CML cells was investigated after silencing Survivin expression with small interfering RNAs. Results: BCR-ABL tyrosine kinase activity induced an over-expression of Survivin in both human and murine hematopoietic cell lines. This over-expression was both at the transcriptional and the translational level and required the JAK2/STAT3 pathway. Survivin silencing by siRNA increased IM cytotoxicity in IM-sensitive cells but failed to restore IM efficacy in IM-resistant cells. However, Survivin silencing sensitized CML cells to the cytotoxic effect of hydroxyurea and enhanced the efficacy of this compound on three different murine cell lines are insensitive to IM because of point mutations in the BCR-ABL kinase domain (Ba/F3p210Y253F, Ba/F3p210D276G and Ba/F3p210T315I). Conclusions: Reduction of Survivin expression improves the efficacy of IM and increases the sensitivity of IM-resistant CML cells to hydroxyurea. Survivin may represent an attractive therapeutic target for both IM-sensitive and IM-resistant CML patients. No significant financial relationships to disclose.

Sign in / Sign up

Export Citation Format

Share Document