Concept: Protein kinase
Background Patients with acute myeloid leukemia (AML) and a FLT3 mutation have poor outcomes. We conducted a phase 3 trial to determine whether the addition of midostaurin - an oral multitargeted kinase inhibitor that is active in patients with a FLT3 mutation - to standard chemotherapy would prolong overall survival in this population. Methods We screened 3277 patients, 18 to 59 years of age, who had newly diagnosed AML for FLT3 mutations. Patients were randomly assigned to receive standard chemotherapy (induction therapy with daunorubicin and cytarabine and consolidation therapy with high-dose cytarabine) plus either midostaurin or placebo; those who were in remission after consolidation therapy entered a maintenance phase in which they received either midostaurin or placebo. Randomization was stratified according to subtype of FLT3 mutation: point mutation in the tyrosine kinase domain (TKD) or internal tandem duplication (ITD) mutation with either a high ratio (>0.7) or a low ratio (0.05 to 0.7) of mutant to wild-type alleles (ITD [high] and ITD [low], respectively). Allogeneic transplantation was allowed. The primary end point was overall survival. Results A total of 717 patients underwent randomization; 360 were assigned to the midostaurin group, and 357 to the placebo group. The FLT3 subtype was ITD (high) in 214 patients, ITD (low) in 341 patients, and TKD in 162 patients. The treatment groups were well balanced with respect to age, race, FLT3 subtype, cytogenetic risk, and blood counts but not with respect to sex (51.7% in the midostaurin group vs. 59.4% in the placebo group were women, P=0.04). Overall survival was significantly longer in the midostaurin group than in the placebo group (hazard ratio for death, 0.78; one-sided P=0.009), as was event-free survival (hazard ratio for event or death, 0.78; one-sided P=0.002). In both the primary analysis and an analysis in which data for patients who underwent transplantation were censored, the benefit of midostaurin was consistent across all FLT3 subtypes. The rate of severe adverse events was similar in the two groups. Conclusions The addition of the multitargeted kinase inhibitor midostaurin to standard chemotherapy significantly prolonged overall and event-free survival among patients with AML and a FLT3 mutation. (Funded by the National Cancer Institute and Novartis; ClinicalTrials.gov number, NCT00651261 .).
Identification of a systemically acting and universal small molecule therapy for Duchenne muscular dystrophy would be an enormous advance for this condition. Based on evidence gained from studies on mouse genetic models we have identified tyrosine phosphorylation and degradation of β-dystroglycan as a key event in the aetiology of Duchenne muscular dystrophy. Thus preventing tyrosine phosphorylation and degradation of β-dystroglycan presents itself as a potential therapeutic strategy. Using the dystrophic sapje zebrafish we have investigated the use of tyrosine kinase and other inhibitors to treat the dystrophic symptoms in this model of Duchenne muscular dystrophy. Dasatinib, a potent and specific Src tyrosine kinase inhibitor was found to decrease the levels of β-dystroglycan phosphorylation on tyrosine and increase the relative levels of non-phosphorylated β-dystroglycan in sapje zebrafish. Furthermore, dasatinib treatment resulted in the improved physical appearance of the sapje zebrafish musculature and increased swimming ability as measured by both duration and distance of swimming dasatinib treated fish compared to control animals. These data suggest great promise for pharmacological agents that prevent the phosphorylation of β-dystroglycan on tyrosine and subsequent steps in the degradation pathway as therapeutic targets for the treatment of Duchenne muscular dystrophy.
A library of 367 protein kinase inhibitors, the GSK Published Kinase Inhibitor Set (PKIS), which has been annotated for protein kinase family activity and is available for public screening efforts, was assayed against the commonly used luciferase reporter enzymes from the firefly, Photinus pyralis (FLuc) and marine sea pansy, Renilla reniformis (RLuc). A total of 22 compounds (∼6% of the library) were found to inhibit FLuc with 10 compounds showing potencies ≤1 µM. Only two compounds were found to inhibit RLuc, and these showed relatively weak potency values (∼10 µM). An inhibitor series of the VEGFR2/TIE2 protein kinase family containing either an aryl oxazole or benzimidazole-urea core illustrate the different structure activity relationship profiles FLuc inhibitors can display for kinase inhibitor chemotypes. Several FLuc inhibitors were broadly active toward the tyrosine kinase and CDK families. These data should aid in interpreting the results derived from screens employing the GSK PKIS in cell-based assays using the FLuc reporter. The study also underscores the general need for strategies such as the use of orthogonal reporters to identify kinase or non-kinase mediated cellular responses.
There have been few reports of a response to dasatinib or nilotinib after failure of two prior sequential tyrosine kinase inhibitors. We report the outcome of 82 chronic phase patients who received nilotinib or dasatinib as third-line alternative tyrosine kinase inhibitor therapy. Thirty-four patients failed to respond to nilotinib and were started on dasatinib as third-line tyrosine kinase inhibitor therapy while 48 patients were switched to nilotinib after dasatinib failure. Overall, we obtained a cytogenetic response in 32 of 82 patients and major molecular response in 13 patients; disease progression occurred in 12 patients. At last follow up, 70 patients (85.4%) were alive with a median overall survival of 46 months. Our results show that third-line tyrosine kinase inhibitor therapy in chronic myeloid leukemia patients after failure of two prior sequential tyrosine kinase inhibitors may induce a response that, in some instances, could prolong overall survival and affect event-free survival.
To the Editor: Ibrutinib is an oral, small-molecule Bruton’s tyrosine kinase (BTK) inhibitor that has activity in chronic lymphocytic leukemia, mantle-cell lymphoma, and Waldenström’s macroglobulinemia.(1)-(3) We administered single-agent ibrutinib at a dose of 560 mg daily to two heavily pretreated patients who had primary refractory classic Hodgkin’s lymphoma. Patient 1 was a 28-year-old woman who underwent haploidentical allogeneic hematopoietic-cell transplantation after receiving eight prior therapeutic regimens, including autologous hematopoietic-cell transplantation and brentuximab vedotin. Two months after the hematopoietic-cell transplantation, fevers, night sweats, and weight loss developed. Combined positron-emission tomography (PET) and computed tomography (CT) showed relapsed disease above and . . .
Nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) play key roles in physiological and pathological responses in cardiac myocytes. The mechanisms whereby H(2)O(2)-modulated phosphorylation pathways regulate the endothelial isoform of nitric oxide synthase (eNOS) in these cells are incompletely understood. We show here that H(2)O(2) treatment of adult mouse cardiac myocytes leads to increases in intracellular Ca(2+) ([Ca(2+)](i)), and document that activity of the L-type Ca(2+) channel is necessary for the H(2)O(2)-promoted increase in sarcomere shortening and of [Ca(2+)](i). Using the chemical NO sensor Cu(2)(FL2E), we discovered that the H(2)O(2)-promoted increase in cardiac myocyte NO synthesis requires activation of the L-type Ca(2+) channel, as well as phosphorylation of the AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase kinase ½ (MEK1/2). Moreover, H(2)O(2)-stimulated phosphorylations of eNOS, AMPK, MEK1/2, and ERK1/2 all depend on both an increase in [Ca(2+)](i) as well as the activation of protein kinase C (PKC). We also found that H(2)O(2)-promoted cardiac myocyte eNOS translocation from peripheral membranes to internal sites is abrogated by the L-type Ca(2+) channel blocker nifedipine. We have previously shown that kinase Akt is also involved in H(2)O(2)-promoted eNOS phosphorylation. Here we present evidence documenting that H(2)O(2)-promoted Akt phosphorylation is dependent on activation of the L-type Ca(2+) channel, but is independent of PKC. These studies establish key roles for Ca(2+)- and PKC-dependent signaling pathways in the modulation of cardiac myocyte eNOS activation by H(2)O(2).
The Wnt signaling pathways control many critical developmental and adult physiological processes. In vertebrates, one fundamentally important function of Wnts is to provide directional information by regulating the evolutionarily conserved planar cell polarity (PCP) pathway during embryonic morphogenesis. However, despite the critical roles of Wnts and PCP in vertebrate development and disease, little is known about the molecular mechanisms underlying Wnt regulation of PCP. Here we have found that the receptor-like tyrosine kinase (Ryk), a Wnt5a-binding protein required in axon guidance, regulates PCP signaling. We show that Ryk interacts with Vangl2 genetically and biochemically and such interaction is potentiated by Wnt5a. Loss of Ryk in a Vangl2+/- background results in classic PCP defects including open neural tube, misalignment of sensory hair cells in the inner ear and shortened long bones in the limbs. Complete loss of both Ryk and Vangl2 results in more severe phenotypes that resemble the Wnt5a-/- mutant in many aspects, such as shortened anterior-posterior body axis, limb and frontonasal process. Our data identify the Wnt5a-binding protein Ryk as a general regulator of the mammalian Wnt/PCP signaling pathway. We show that Ryk transduces Wnt5a signaling by forming a complex with Vangl2 and that Ryk regulates PCP by promoting Vangl2 stability. As human mutations in WNT5A and VANGL2 are found to cause Robinow syndrome and neural tube defects, respectively, our results further suggest that human mutations in RYK may also be involved in these diseases.
We explored the relation between vasoactive intestinal peptide (VIP), CRTH2, and eosinophil recruitment. It is shown that CRTH2 expression by eosinophils from allergic rhinitis (AR) patients and eosinophils cell line (Eol-1 cells) was up-regulated by VIP treatment. This was functional and resulted into exaggerated migratory response of cells against PGD2. Nasal challenge of AR patients resulted into significant increase of VIP contents in nasal secretion (ELISA), and the immunohistochemical studies of allergic nasal tissues, showed significant expression of VIP in association with intense eosinophil recruitment. Biochemical assays showed that VIP-induced eosinophils chemotaxis from AR patients and Eol-1 cells, was mediated through CRTH2 receptor. Cells migration against VIP was sensitive to protein kinase C (PKC) and protein kinase A (PKA) inhibition, but not to tyrosine kinase or P38 MAP-kinase inhibition, or calcium chelation. Western blot demonstrated a novel CRTH2 mediated cytosol to membrane translocation of PKC-ε, PKC-δ and PKA-α, γ and IIα reg in Eol-1 cells upon stimulation with VIP. Confocal images and FACS demonstrated a strong association and co-localization between VIP peptide and CRTH2 molecules. Further, VIP induced PGD2 secretion from eosinophils. Our results demonstrate the first evidence of association between VIP and CRTH2 in recruiting eosinophils.
Thrombin activates platelets through protease activated receptors (PARs). Mouse platelets express PAR3 and PAR4. PAR3 does not signal in platelets. However, PAR4 is a relatively poor thrombin substrate and requires PAR3 as a cofactor at low thrombin concentrations. In this study we show that PAR3 also regulates PAR4 signaling. In response to thrombin (30-100 nM) or PAR4 activating peptide (AYPGKF), platelets from PAR3(-/-) mice had increased G(q) signaling compared to wild type mice as demonstrated by a 1.6-fold increase in the maximum intracellular calcium (Ca(2+)) mobilization, an increase in phosphorylation level of protein kinase C (PKC) substrates, and a 2-fold increase of Ca(2+) release from intracellular stores. Moreover, platelets from heterozygous mice (PAR3(+/-)) had an intermediate increase in maximum Ca(2+) mobilization. Treatment of PAR3(-/-) mice platelets with P2Y(12) antagonist (2MeSAMP) did not affect Ca(2+) mobilization from PAR4 in response to thrombin or AYPGKF. The activation of RhoA-GTP downstream G(12/13) signaling in response to thrombin was not significantly different between wild type and PAR3(-/-) mice. Since PAR3 influenced PAR4 signaling independent of agonist, we examined the direct interaction between PAR3 and PAR4 with bioluminescence resonance energy transfer (BRET). PAR3 and PAR4 form constitutive homodimers and heterodimers. In summary, our results demonstrate that in addition to enhancing PAR4 activation at low thrombin concentrations, PAR3 negatively regulates PAR4-mediated maximum Ca(2+) mobilization and PKC activation in mouse platelets by physical interaction.
The PACSIN (protein kinase C and casein kinase 2 substrate in neurons) adapter proteins couple components of the clathrin-mediated endocytosis machinery with regulators of actin polymerization and thereby regulate the surface expression of specific receptors. The brain-specific PACSIN 1 is enriched at synapses and has been proposed to affect neuromorphogenesis and the formation and maturation of dendritic spines. In studies of how phosphorylation of PACSIN 1 contributes to neuronal function, we identified serine 358 as a specific site used by casein kinase 2 (CK2) in vitro and in vivo. Phosphorylated PACSIN 1 was found in neuronal cytosol and membrane fractions. This localization could be modulated by trophic factors such as BDNF. We further show that expression of a phospho-negative PACSIN 1 mutant, S358A, or inhibition of CK2 drastically reduces spine formation in neurons. We identified a novel protein complex containing the spine regulator Rac1, its GAP neuron-associated developmentally-regulated protein (NADRIN) and PACSIN 1. CK2 phosphorylation of PACSIN 1 leads to a dissociation of the complex upon BDNF-treatment and induces Rac1-dependent spine formation in dendrites of hippocampal neurons. These findings suggest that upon BDNF signaling PACSIN 1 is phosphorylated by CK2 which is essential for spine formation.