Intracellular Protein Tyrosine Kinase Research Articles

FLT4 Mutations Are Associated with Segmental Lymphatic Dysfunction and Initial Lymphatic Aplasia in Patients with Milroy Disease.

This study explored mutations in the Fms-related tyrosine kinase 4/vascular endothelial growth factor receptor 3 gene (FLT4) and lymphatic defects in patients with Milroy disease (MD). Twenty-nine patients with lower limb lymphedema were enrolled. Sixteen patients had a familial history of MD, while 13 patients exhibited sporadic MD. Clinical signs, FLT4 mutations, indocyanine green (ICG) lymphography findings, and skin tissue immunohistochemical staining results were evaluated. Twenty-eight variants in FLT4 were identified. Twelve of these have previously been reported, while 16 are novel. Of the 28 variants, 26 are missense mutations, and the remaining two comprise a splicing mutation and a non-frame shift mutation. Twenty-five variants are located in the intracellular protein tyrosine kinase domain; three are located in the extracellular immunoglobulin domain. Substantially delayed contrast-enhanced tortuous lymphatic vessels were visualized to the ankle or knee level in 15 of 23 patients who underwent ICG lymphography. No initial lymphatic vessels were visualized in skin specimens from four patients who did not exhibit lymphatic vessels during imaging analyses. No specific variant was identified in relation to the unique clinical phenotype. Segmental dysfunction of lymphatic vessels and initial lymphatic aplasia are present in MD patients with FLT4 mutations.

TYK2 as a therapeutic target in the treatment of autoimmune and inflammatory diseases.

JAKs are intracellular protein tyrosine kinases that, through activation of STATs, are responsible for signal transduction pathways that regulate cellular responses to numerous cytokines, growth factors and hormones in many different cells. JAK-STAT signaling plays a key role in regulating immune function, and cytokines - such as IL-23, IL-12 and type I interferons - are central to the pathogenesis of autoimmune diseases, including psoriasis, inflammatory bowel disease and systemic lupus erythematosus. Herethe authors review the evidence for targeting TYK2 as a more specific approach to treating these conditions. TYK2 inhibitors are clinically effective in autoimmune and inflammatory diseases and may avoid some of the complications reported with nonselective JAK inhibitors.

Design, synthesis and structure-activity relationship study of aminopyridine derivatives as novel inhibitors of Janus kinase 2

Janus Kinase 2 (JAK2) is a kind of intracellular non-receptor protein tyrosine kinase and has been certified as an important target for the treatment of myeloproliferative neoplasms and rheumatoid arthritis. However, the low selectivity and potential safety issues restrict the clinical applications of JAK2 inhibitors. Here we found that crizotinib showed good inhibitory activity against JAK2 by enzymatic assays (IC50 = 27 nM). Then we carried out structure-based drug design and synthesized a series of compounds with an aminopyridine scaffold. Finally, compound 12k and 12l were identified as the promising inhibitors of JAK2, which exhibited high inhibitory activity (IC50 = 6 nM and 3 nM, respectively) and selectivity for JAK2 over JAK1 and JAK3, and showed potent antiproliferative activities toward HEL human erythroleukemia cells. Moreover, 12k suppressed symptoms of the collagen-induced arthritis (CIA) model in rats.

QSAR modeling, pharmacophore-based virtual screening, and ensemble docking insights into predicting potential epigallocatechin gallate (EGCG) analogs against epidermal growth factor receptor

Epigallocatechin gallate (EGCG) is a major polyphenols of green tea may have the possibility to inhibit epidermal growth factor receptor (EGFR) activity and lead to reduce non-small cell lung cancer (NSCLC) progression. However, EGCG has some toxic features; moreover, there is a lack of explorations into the molecular interaction mechanisms of EGCG and the EGFR. In this examination, integration of quantitative structure–activity relationship (QSAR) modeling, pharmacophore-based virtual screening, and ensemble docking approaches were used to predict potential novel EGCG analogs as effective EGFR inhibitors. QSAR modeling of logP and logS predictions and toxicity endpoint investigation for a set of 82 compounds were shown good predictive ability and robustness from the applicability domain and confusion matrix elucidations. Virtual screening and docking studies revealed that seven high potential EGCG analogs as strong EGFR binders. Molecular interactions interpretations indicated some insights into the structural features of ligands that efficiently interfere with mutation possible residues (Gly719 and Thr790) of the EGFR. The hydrogen bonds, hydrophobic interactions, atomic π-cation interactions and salt bridges of ligands are contributing additional stability to receptor structure, which can lead to blocking the intracellular protein-tyrosine kinase activity, including EGFR associated pathways activation in NSCLC. Therefore, this can characterize as a block-cluster mechanism between EGCG analogs and EGFR complexes. In silico anti-EGFR and anticancer activity predictions suggested that, ligands could act as promising pharmacological, anticancer, and drug-like templates of EGFR towards moderating the NSCLC progressions. These results and provided pinpoints could be beneficial to recognize probable therapeutic targets for NSCLC therapy.

Triggering of organ-specific autoimmunity through synergy of defects in key tolerance checkpoints

Abstract Studies of genetic factors associated with human autoimmunity suggest a multigenic origin of autoimmune susceptibility. To address how defects in different immune tolerance pathways cooperate to result in disease, we investigated whether genetic alterations in two such pathways might synergize to produce autoimmunity in mice. The intracellular protein tyrosine kinase Lyn is critical for inhibitory receptor function in innate immune cells and B cells. Lyn-deficient mice develop systemic but not organ-specific autoimmunity. In contrast, Autoimmune Regulator (Aire) promotes expression of tissue-specific antigens by thymic epithelial cells and T-cell negative selection. Aire-deficient mice develop multiorgan autoimmunity, including autoimmune uveitis, due to lack of thymic expression of the retina-specific interphotoreceptor retinoid binding protein (IRBP). AireGW/+ knockin mice express a dominant negative allele of Aire, have low but detectable thymic expression of IRBP and do not develop uveitis. To determine whether lack of Lyn inhibitory pathways could cooperate with a partial defect in T cell central tolerance, we generated AireGW/+ Lyn−/− double mutants. Remarkably, over 50% of these mice developed severe uveitis that was accompanied by a rise in anti-IRBP antibodies and an expansion of IRBP-specific CD4 T cells. To determine the contribution of different Lyn-expressing cell subsets to uveitis, we crossed AireGW/+ mice to a panel of Cre lines with an inducible Lyn knockout allele. Deletion of Lyn selectively in dendritic cells (DCs) was sufficient to drive disease, suggesting that Lyn-deficient DCs may have increased ability to prime IRBP-specific T cells that have escaped negative selection in the AireGW/+ thymus.

Cbl-b and c-Cbl negatively regulate osteoblast differentiation by enhancing ubiquitination and degradation of Osterix

E3 ubiquitin ligase Cbl-b and c-Cbl play important roles in bone formation and maintenance. Cbl-b and c-Cbl regulate the activity of various receptor tyrosine kinases and intracellular protein tyrosine kinases mainly by regulating the degradation of target proteins. However, the precise mechanisms of how Cbl-b and c-Cbl regulate osteoblast differentiation are not well known. In this study, we investigated potential targets of Cbl-b and c-Cbl. We found that Cbl-b and c-Cbl inhibit BMP2-induced osteoblast differentiation in mesenchymal cells. Among various osteogenic transcription factors, we identified that Cbl-b and c-Cbl suppress the protein stability and transcriptional activity of Osterix. Our results suggest that Cbl-b and c-Cbl inhibit the function of Osterix by enhancing the ubiquitin–proteasome-mediated degradation of Osterix. Taken together, we propose novel regulatory roles of Cbl-b and c-Cbl during osteoblast differentiation in which Cbl-b and c-Cbl regulate the degradation of Osterix through the ubiquitin–proteasome pathway.

Coarse-Grained Molecular Simulation of Epidermal Growth Factor Receptor Protein Tyrosine Kinase Multi-Site Self-Phosphorylation

Upon the ligand-dependent dimerization of the epidermal growth factor receptor (EGFR), the intrinsic protein tyrosine kinase (PTK) activity of one receptor monomer is activated, and the dimeric receptor undergoes self-phosphorylation at any of eight candidate phosphorylation sites (P-sites) in either of the two C-terminal (CT) domains. While the structures of the extracellular ligand binding and intracellular PTK domains are known, that of the ∼225-amino acid CT domain is not, presumably because it is disordered. Receptor phosphorylation on CT domain P-sites is critical in signaling because of the binding of specific signaling effector molecules to individual phosphorylated P-sites. To investigate how the combination of conventional substrate recognition and the unique topological factors involved in the CT domain self-phosphorylation reaction lead to selectivity in P-site phosphorylation, we performed coarse-grained molecular simulations of the P-site/catalytic site binding reactions that precede EGFR self-phosphorylation events. Our results indicate that self-phosphorylation of the dimeric EGFR, although generally believed to occur in trans, may well occur with a similar efficiency in cis, with the P-sites of both receptor monomers being phosphorylated to a similar extent. An exception was the case of the most kinase-proximal P-site-992, the catalytic site binding of which occurred exclusively in cis via an intramolecular reaction. We discovered that the in cis interaction of P-site-992 with the catalytic site was facilitated by a cleft between the N-terminal and C-terminal lobes of the PTK domain that allows the short CT domain sequence tethering P-site-992 to the PTK core to reach the catalytic site. Our work provides several new mechanistic insights into the EGFR self-phosphorylation reaction, and demonstrates the potential of coarse-grained molecular simulation approaches for investigating the complexities of self-phosphorylation in molecules such as EGFR (HER/ErbB) family receptors and growth factor receptor PTKs in general.

Reduction of Brain Barrier Tight Junctional Proteins by Lead Exposure: Role of Activation of Nonreceptor Tyrosine Kinase Src via Chaperon GRP78

Lead (Pb) has long been recognized as a neurodevelopmental toxin. Developing blood-brain barrier (BBB) is known to be a target of Pb neurotoxicity; however, the underlying mechanisms are still unclear. Recent evidence suggests that intracellular nonreceptor protein tyrosine kinase Src regulates tight junctional proteins (TJPs). This study was designed to investigate whether Pb acted on the Src-mediated cascade event leading to an altered TJP expression at BBB. Rats aged 20-22 days were exposed to Pb in drinking water (0, 100, 200, and 300 ppm Pb) for eight weeks. Electron microscopic and Western blot analyses revealed a severe leakage of BBB and significantly decreased expressions of TJP occludin and ZO-1. When cultured brain endothelial RBE4 cells were exposed to 10μM Pb for 24 h, expressions of phosphor-Src and an upstream regulator GRP78 were significantly increased by 6.42-fold and 8.29-fold (p < 0.01), respectively. Inactivation of Src pathway by a Src-specific inhibitor reversed Pb-induced downregulation of occludin, but not ZO-1; small interfering RNA knockdown of GRP78 attenuated Pb-induced Src phosphorylation and occludin reduction. Furthermore, Pb exposure caused redistribution of GRP78 from endoplasmic reticulum to cytosol and toward cell member. However, the data from immunoneutralization studies did not show the involvement of cell-surface GRP78 in regulating Src phosphorylation upon Pb exposure, suggesting that the cytosolic GRP78, rather than cell-surface GRP78, was responsible to Pb-induced Src activation and ensuing occludin reduction. Taken together, this study provides the evidence of a novel linkage of GRP78, Src activation to downregulation of occludin, and BBB disruption during Pb exposure.

PTK6 Activation at the Membrane Regulates Epithelial–Mesenchymal Transition in Prostate Cancer

The intracellular tyrosine kinase protein tyrosine kinase 6 (PTK6) lacks a membrane-targeting SH4 domain and localizes to the nuclei of normal prostate epithelial cells. However, PTK6 translocates from the nucleus to the cytoplasm in human prostate tumor cells. Here, we show that while PTK6 is located primarily within the cytoplasm, the pool of active PTK6 in prostate cancer cells localizes to membranes. Ectopic expression of membrane-targeted active PTK6 promoted epithelial-mesenchymal transition in part by enhancing activation of AKT, thereby stimulating cancer cell migration and metastases in xenograft models of prostate cancer. Conversely, siRNA-mediated silencing of endogenous PTK6 promoted an epithelial phenotype and impaired tumor xenograft growth. In mice, PTEN deficiency caused endogenous active PTK6 to localize at membranes in association with decreased E-cadherin expression. Active PTK6 was detected at membranes in some high-grade human prostate tumors, and PTK6 and E-cadherin expression levels were inversely correlated in human prostate cancers. In addition, high levels of PTK6 expression predicted poor prognosis in patients with prostate cancer. Our findings reveal novel functions for PTK6 in the pathophysiology of prostate cancer, and they define this kinase as a candidate therapeutic target. Cancer Res; 73(17); 5426-37. ©2013 AACR.

Mammalian colonocytes possess a carrier-mediated mechanism for uptake of vitamin B3 (niacin): studies utilizing human and mouse colonic preparations

Niacin (vitamin B3; nicotinic acid) plays an important role in maintaining redox state of cells and is obtained from endogenous and exogenous sources. The latter source has generally been assumed to be the dietary niacin, but another exogenous source that has been ignored is the niacin that is produced by the normal microflora of the large intestine. For this source of niacin to be bioavailable, it needs to be absorbed, but little is known about the ability of the large intestine to absorb niacin and the mechanism involved. Here we addressed these issues using the nontransformed human colonic epithelial NCM460 cells, native human colonic apical membrane vesicles (AMV) isolated from organ donors, and mouse colonic loops in vivo as models. Uptake of ³H-nicotinic acid by NCM460 cells was: 1) acidic pH (but not Na⁺) dependent; 2) saturable (apparent Km = 2.5 ± 0.8 μM); 3) inhibited by unlabeled nicotinic acid, nicotinamide, and probenecid; 4) neither affected by other bacterially produced monocarboxylates, monocarboxylate transport inhibitor, or by substrates of the human organic anion transporter-10; 5) affected by modulators of the intracellular protein tyrosine kinase- and Ca²⁺-calmodulin-regulatory pathways; and 6) adaptively regulated by extracellular nicotinate level. Uptake of nicotinic acid by human colonic AMV in vitro and by mouse colonic loops in vivo was also carrier mediated. These findings report, for the first time, that mammalian colonocytes possess a high-affinity carrier-mediated mechanism for nicotinate uptake and show that the process is affected by intracellular and extracellular factors.

Spleen Tyrosine Kinase Is Important in the Production of Proinflammatory Cytokines and Cell Proliferation in Human Mesangial Cells following Stimulation with IgA1 Isolated from IgA Nephropathy Patients

IgA immune complexes are capable of inducing human mesangial cell (HMC) activation, resulting in release of proinflammatory and profibrogenic mediators. The subsequent inflammation, cellular proliferation, and synthesis of extracellular matrix lead to the progression of IgA nephropathy (IgAN). Spleen tyrosine kinase (SYK) is an intracellular protein tyrosine kinase involved in cell signaling downstream of immunoreceptors. In this study, we determined whether SYK is involved in the downstream signaling of IgA1 stimulation in HMC, leading to production of proinflammatory cytokines/chemokines and cell proliferation. Incubation of HMC with IgA1 purified from IgAN patients significantly increased the synthesis of MCP-1 in a dose-dependent manner. There was also significantly increased production of IL-6, IL-8, IFN-γ-inducible protein-10, RANTES, and platelet-derived growth factor-BB. Stimulation of HMC with heat-aggregated IgA1 purified from IgAN patients induced significantly increased HMC proliferation. Both pharmacological inhibition of SYK and knockdown of SYK by small interfering RNA significantly reduced the synthesis of these mediators and inhibited HMC proliferation. Moreover, positive immunostaining for total and phospho-SYK in glomeruli of kidney biopsies from IgAN patients strongly suggests the involvement of SYK in the pathogenesis of IgAN. To our knowledge, we demonstrate, for the first time, the involvement of SYK in the downstream signaling of IgA1 stimulation in HMC and in the pathogenesis of IgAN. Hence, SYK represents a potential therapeutic target for IgAN.

Tryptic peptide screening for primary immunodeficiency disease by LC/MS‐MS

Early diagnosis of primary immunodeficiency disorders (PIDDs) is critical for maximizing patient survival and clinical outcomes. Consequently, there is significant interest in developing broad-based, high-throughput, screening approaches capable of utilizing small blood volumes to identify patients with PIDD. We developed a novel proteomic screening approach using tandem mass spectrometry to simultaneously identify specific signature peptides derived from the transmembrane protein cluster of differentiation 3 (CD3)ɛ and the intracellular proteins Wiskott-Aldrich syndrome protein (WASP) and Bruton's tyrosine kinase (BTK) as markers of three life-threatening PIDDs; severe combined immunodeficiency, Wiskott-Aldrich syndrome, and X-linked Agammaglobulinemia. Signature peptides were analyzed by LC/MS-MS in proteolytically digested lysates from cell lines and white blood cells (WBCs). The amount of each peptide was determined by the ratio of the signature peptide peak area to that of a known amount of labeled standard peptide. Peptide concentrations were normalized to actin. We show that signature peptides from CD3ɛ, WASP, and BTK were readily detected in proteolytically digested cell lysate and their absence could correctly identify PIDD patients. This proof of concept study demonstrates the applicability of this approach to screen for PIDD and raises the possibility that it could be further multiplexed to identify additional PIDDs and potentially other disorders.

A net-like structure with pores is observed during cell fusion induced by the receptor FGFRL1

FGFRL1 is the fifth member of the fibroblast growth factor receptor (FGFR) family. Similar to the other members, it harbors three Ig loops in its extracellular domain, but in contrast to the other receptors, it lacks the intracellular protein tyrosine kinase domain that would be required for signaling by transphosphorylation. FGFRL1 is mainly found in the musculoskeletal system, where it appears to inhibit cell proliferation but to induce cell adhesion and differentiation. Mice with a targeted disruption of the FGFRL1 gene die during birth due to a malformed diaphragm muscle, which is not strong enough to inflate the lungs after birth. Expression of FGFRL1 is highly up-regulated during the differentiation of myoblasts to multinucleated myotubes, suggesting an important role for FGFRL1 in cell-cell fusion. Recently we showed that FGFRL1 does indeed induce fusion of cultured cells into large syncytia. A reporter gene assay demonstrated that the third Ig domain and the transmembrane domain of FGFRL1 are both necessary and sufficient to fuse CHO cells into syncytia comprising several hundred nuclei. At the contact site, the fusing cells reveal a peculiar net-like structure with pores of about 1 μm diameter. It is possible that these structures represent membrane areas with fusion pores that set in motion the cell-cell fusion process. FGFRL1 is the first mammalian protein that is capable of triggering cell-cell fusion in vitro.

Small Molecule Inhibitor of ITK Disrupts TCR Signaling and Demonstrates Anti-Tumor Efficacy

AbstractAbstract 3932ITK (Interluekin-2 Inducible Tyrosine Kinase) is a member of the TEC family of intracellular protein tyrosine kinases. ITK is highly expressed in T cells and NK cells, with expression detected in mast cells. ITK plays a key role in several aspects of T cell biology, including T cell development, differentiation, migration, proliferation and activation. The function of ITK in immunity and allergy is well documented. T cells from ITK knock out mice show several developmental and functional defects, including defective signal transduction, altered CD4+ to CD8+ T cells ratios, reduced Th2 lineage differentiation, diminished IL4 and IL2 production and reduced T cell proliferation. Importantly ITK deficient mice fail to mount an immune response to infection and show reduced allergic asthma reactions.In contrast to its well described role in immune function, ITK's function in cancer biology is still emerging. Recent studies had reported enhanced ITK expression and activation of the ITK pathway in several types of leukemias and lymphomas. In addition, the dependence of T cell malignancies on an ITK-regulated pathway, namely the IL2/IL2R (CD25) pathway, has also been observed. Taken together, this information indicates that ITK is a therapeutic target, with applicability in leukemias and lymphomas.MannKind scientists have developed a series of selective small molecule ITK inhibitors, including the orally available tool compound described within, and evaluated their activity in enzyme, cell-based and in vivo studies. In cellular assays, the compounds showed significant inhibition of the T cell-receptor mediated activation of the ITK pathways and related downstream cytokine production. In addition to inhibiting the phosphorylation of ITK and its downstream mediator, PLCg, our tool compounds inhibited the production of IL2 and expression of CD25 in a dose dependent manner. Importantly, our compound regulated the in vitro growth of tumor T cells but not that of unrelated control cells. In vivo studies revealed that the tool compounds inhibited the growth and progression of patient derived ATL tumors in a xenograft pre-clinical model, and prolonged the survival of treated mice in a dose dependent manner, in addition to regulating cytokine production in vivo. In summary, our team has identified ITK selective compounds with demonstrated on-target and anti-tumor activity in vitro and preclinical T cell tumor models, and validated this pathway relative to T cell malignancies. This effort provides a platform for further compound optimization and evaluation for hematologic malignancies. Disclosures:Faris:MannKind Corp: Employment. Malyankar:MannKind Corp: Employment. Zeng:MannKind Corp: Employment. Kertesz:Mannkind Corporation: Employment, Equity Ownership. Vuga:MannKind Corp.: Employment. Rosario:MannKind Corp: Employment. Bot:MannKind Corp: Employment.

Brk/PTK6 &amp; Bcl-x Proteins Contribute to Reduced Sensitivity to Chemotherapy.

Abstract Background: Brk/PTK6 is an intracellular protein tyrosine kinase which is frequently overexpressed in the majority of breast cancers and has been shown to increase the anchorage-independent survival of breast cancer cell lines by altering Bcl-xL:Bcl-xS ratios. A Brk binding partner has also been found to modulate the alternative splicing of the Bcl-x gene, and altered Bcl-xL/xS levels are implicated in cell sensitivity to chemotherapeutic agents. We hypothesised that Brk may decrease cell response to chemotherapy through regulation of Bcl-x.Materials &amp; Methods: To determine the clinical relevance and coexpression of Brk and Bcl-xL/S, quantitative PCR was performed on a clinical breast cancer biopsy material (n= 46). Gene knockdown studies using siRNA for either Brk or Bcl-xL were performed in T47D breast cancer cell line. Cells were subsequently cultured onto a 96 well plate in quadruplicate and subject to dose range of the chemotherapeutic drug, doxorubicin or paclitaxel for 72 hours before being tested for viability using the MTT assay. Protein levels for Brk, Bcl-xL/xS in response to siRNA treatments were determined using western blotting.Results: Quantitative PCR analysis of clinical breast cancer series reveal that Bcl-xL and Bcl-xS expression were associated with high grade tumours (p=0.028 and p=0.009 respectively). Moreover, both Bcl-xL and Bcl-xS were found to be significantly associated with Brk expression within these clinical samples (p&amp;lt;0.0001 and p=0.0026 respectively). T47D breast cancer cells with suppressed Brk levels showed a significant increase in sensitivity to doxorubicin and paclitaxel compared to control cultures (p=0.035 for doxorubicin and p&amp;lt;0.05 for paclitaxel at 0.625μM and 0.25nM respectively). Reduced Brk levels in T47D cells resulted in reduced levels of Bcl-xL protein. T47D cells with suppressed Bcl-xL levels also showed a significant increase in the sensitivity to doxorubicin compared to control cultures (p=0.039 at 0.31μM).Conclusion: These data suggests that Brk expression decreases the sensitivity of currently used chemotherapies through a mechanism that may involve regulation of Bcl-xL/xS protein levels. Thus targeting Brk may represent an important strategy for improving patient responses to chemotherapy. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5068.

Abstract C206: In vivo activity of SGI-1252, a potent, small-molecule dual inhibitor of JAK2 and ALK2

Abstract Activation of JAK2, an intracellular protein tyrosine kinase, is known to induce cell proliferation and apoptosis and it has been shown to be mediated by pro-inflammatory cytokines. JAK2 dysregulation is implicated in myeloproliferative disorders, solid tumor malignancies, and autoimmune diseases. Utilizing our proprietary CLIMB™ technology, a computationally driven drug discovery process, we have rapidly designed and developed, SGI-1252, a potent oral inhibitor which exhibits low nanomolar in vitro activity against all of the JAK kinase family, except JAK3. Additionally, it has low nanomolar activity against ALK2, a high-affinity binding receptor for bone morphogenic protein. As predicted from computational models, SGI-1252 is well tolerated across several rodent species and demonstrates a wide safety margin in both short- and long-term toxicity studies. Acute maximum tolerated doses of greater than 900 mg/kg are observed in mice and rats dosed orally with SGI-1252. Over a 5-week period, daily oral dosing of up to 200 mg/kg SGI-1252 shows no hematological toxicity and no body weight loss in mice. Pharmacokinetic studies of SGI-1252 in rodents also demonstrate excellent systemic exposure, with oral bioavailabilities of greater than 50% in mice and rats. Because inflammatory cytokines are known to play a role in the pathogenesis of pancreatic and lung cancers, tumor xenograft models of those cell lines were evaluated. In BxPC3 and A549 xenografts, three weeks of daily oral dosing of 200 mg/kg SGI-1252 demonstrate exceptional activity, with tumor inhibitions of greater than 50% in both models. Pharmacodynamic studies were also performed to further elucidate the effect of SGI-1252 on pro-inflammatory cytokines related to these models. In several acute-phase mouse models, where turpentine-oil injection are utilized for cytokine stimulation, SGI-1252 is observed to down-regulate IL-6 and VEGF expression 16–24 hours after dosing. In summary, SGI-1252 is a potent oral inhibitor that is well tolerated in rodent models, provides excellent PK exposure, and demonstrates tumor growth inhibition as well as modulation of pro-inflammatory cytokines. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C206.

Mutation Analysis of JAK-1, 2 and 3 in Children with Down Syndrome and Acute Leukemia.

Abstract 5035Children with Down Syndrome (DS) have an increased risk of developing leukemia, including both acute myeloid (ML-DS), as well as acute lymphoblastic leukemia (DS-ALL). ML-DS can be preceded by a pre-leukemic clone in newborns (transient leukemia-TL), which in most cases resolves spontaneously. Janus Kinase (JAK) 1-3 belongs to a family of intracellular non-receptor protein tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. JAK plays an important role in regulating the processes of cell proliferation, differentiation and apoptosis in response to cytokines and growth factors. Mullighan et al. described JAK 1-3 mutations in non-DS high-risk childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL; PNAS, 2009). In T-ALL, JAK-1 mutations are a frequent event (∼25%) as reported among others by Jeong et al (Clinical Cancer Research, 2008). Mutations in JAK-2 and JAK-3 have been described in TL and ML-DS. Bercovich et al. recently reported mutations within the pseudokinase domain of JAK-2 in DS-ALL patients (Lancet 2008). This activating JAK-2 mutation differs from the V617F exon 14 mutation found in myeloproliferative diseases. However, JAK-1 has never been investigated in Down syndrome leukemias. Therefore we performed mutational analysis of the pseudokinase and kinase domains of JAK-1, 2 and 3 by direct sequencing in 8 TL, 16 ML-DS and 35 DS-ALL samples taken at initial diagnosis. The TL and ML-DS samples were unpaired. In the ML-DS group, 12 patients were classified as FAB M7, 3 as FAB M0 and 1 as FAB M6; all 35 DS-ALL patients were classified as BCP-ALL. Mutations in JAK-1 were found in 1 ML-DS patient (D625R) and in 1 DS-ALL patient (V651M). These mutations were localised in the same region of the pseudokinase domain, but not identical to the activating mutations in JAK1 described in high-risk ALL (Mullighan et al., PNAS 2009). The JAK-1 mutated ML-DS patient had a complex karyogram, and the DS ALL patient a normal karyotype. No events occurred in either of the patients with a follow-up of 2.4 and 3.1 years, respectively. JAK-2 activating mutations at position R683 were found in 5/35 (14.3%) of the DS-ALL patients. These patients had diverse cytogenetic aberrations, and had no events at a median follow up of 4.4 years. In the TL and ML-DS patients no mutations were identified in JAK-2. For JAK-3, 1 TL-patient (13%) and 1 ML-DS patient (6.3%) harboured the A573V-mutation. This activating mutation is previously described in ML-DS patients and the megakaroyblastic cell line CMY ((Kiyoi et al, Leukemia 2007). Because the mutations occur in both TL and ML-DS, this suggests that they do not play a role in the clonal progression model from TL to ML-DS. A mutation at JAK3 R1092C, which to our knowledge has never been reported before, was found in 1 DS-ALL patient. This patient had a deletion on chromosome 12 (p11p13), and was in CCR with a follow up of 5 years. In conclusion, JAK-mutations are rare in DS-leukemias, except for JAK-2 mutations in DS-ALL, which occur in approximately 15% of cases. The rarity of JAK-1 mutations in DS is in accordance with the rarity of T-ALL in DS. Of interest, none of the DS ALL cases with a JAK-2 mutation relapsed so far, which differs from the patients with JAK-2 mutations that were recently in high-risk BCP-ALL. Hence, JAK-2 may be an interesting novel therapeutic target. DisclosuresNo relevant conflicts of interest to declare.

Inhibition of Pyk2 Blocks Airway Inflammation and Hyperresponsiveness in a Mouse Model of Asthma

The objective of this investigation was to determine the role of Pyk2, an intracellular nonreceptor protein tyrosine kinase for postadhesive inflammatory cell migration, on airway inflammation and hyperresponsiveness in immune-sensitized mice. Blockade of Pyk2 was effected by intraperitoneal administration of dominant-negative C-terminal Pyk2 fused to a TAT protein transduction domain (TAT-Pyk2-CT). Ovalbumin challenge elicited infiltration of both eosinophils and lymphocytes into airways, increased mucus-containing epithelial cells, and caused increased airway hyperresponsiveness to methacholine in immune-sensitized mice. Pretreatment with 10 mg/kg TAT-Pyk2-CT intraperitoneally blocked all of these effects and further decreased secretion of Th2 cytokine IL-4, IL-5, and IL-13 into the bronchoalveolar lavage fluid. Intranasal administration of IL-5 caused eosinophil migration into the airway lumen, which was attenuated by systemic pretreatment with TAT-Pyk2-CT. In each paradigm, treatment with control protein TAT-GFP had no blocking effect. We conclude that Pyk2, which is essential for inflammatory cell migration in vitro, regulates airway inflammation, Th2 cytokine secretion, and airway hyperresponsiveness in the ovalbumin-sensitized mice during antigen challenge in vivo.

Tyrosine kinases and their substrates in B lymphocytes

Gene-targeting experiments have highlighted the importance of the intracellular protein tyrosine kinases, Lyn, Syk, and Btk, in B-cell receptor-mediated phospholipase C gamma 2 and phosphoinositide 3-kinase activation. In linking such tyrosine kinases with effector enzymes, an important role has emerged for adapter molecules. Adapter proteins nucleate formation of distinct signaling complexes in a specific location within the cell and facilitate the interaction between these signaling components in this particular subcellular compartment, which, in turn, contribute to the qualitative and quantitative control of B-cell signaling.

The Prognostic Value of JAK2 Exon 16 Mutations in Children with Down Syndrome and Acute Lymphoblastic Leukemia.

Children with Down Syndrome (DS) have an increased risk of developing leukemia, including both acute myeloid (ML DS), as well as acute lymphoblastic leukemia (DSALL). Recently, Izraeli et al. reported on an activating mutation (R683) localized in exon 16 of the Janus Kinase 2 (JAK2) gene, in 18% of DS-ALL (n=16) patients collected from 9 European study groups (ASH 2007). Screening of other leukemia subsets showed that this mutation was exclusive for DS-ALL patients. This JAK2 mutation differs from the V617F exon 14 mutation found in myeloproliferative diseases. JAK2 is located on chromosome 9p24, and belongs to a family of intracellular non-receptor protein tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. It plays an important role in regulating the processes of cell proliferation, differentiation and apoptosis in response to cytokines and growth factors. Between 1991 and 2007, 45 children with DS ALL were treated in the Netherlands, according to the DCOG protocols ALL 7–10. Of 36 children samples were available in the DCOG cell bank, on which we performed JAK2 mutation screening of the pseudokinase and kinase domains of JAK2 by direct sequencing. All 36 patients were classified as BCP-ALL. Mutations in JAK2 exon 16 were identified in 6 (16.6%) DS-ALL patients. In five patients a point mutation resulted in substitution of Arginine at position 683, the same as was described by Izraeli et al. In one patient an insertion was found. JAK2 mutated patients did not differ in age at diagnosis (3.3 vs. 5.1 years, p=0.08) or in sex (p= 0.8) compared to non-mutated DSALL patients. The diagnostic WBC for DS-ALL patients with a JAK2 exon 16 mutation was lower than for non-mutated patients (3.6×109/L vs. 12.1×109/L; p=0.04). Ploidy status based on karyotyping was known in 29/36 patients. None of the JAK2 mutated samples was hyperdiploid (>52 chromosomes) vs. one in the non-mutated samples (p=0.89). TEL/AML rearrangements were screened in 23/36 samples, and 3/23 (13%) samples showed a TEL-AML rearrangement. None of the JAK2 mutated samples was TEL-AML rearranged (p= 0.76). One JAK2 mutated patient had a normal karyotype, the other JAK2 mutated patients had random cytogenetic abnormalities. We next analyzed the prognostic significance of JAK2 mutated DS-ALL children versus the other patients. The median follow up time for all patients was 3.1 years (range 0.1–15.1 years). Interestingly, none of the JAK2 mutated patients relapsed, versus 4/30 wild type JAK2 patients. The differences between pOS (100% vs. 83.3% p=0.41), pEFS (100% vs. 80%, p=0.38) and pDFS (100% vs. 82.8%, p=0.44) were not statistically significant, probably due to small numbers. Since DS-ALL children are more sensitive to the side effects of chemotherapy, and have relatively high toxic mortality rates, reduction of therapy intensity might be an option for DS-ALL children with a JAK2 exon 16 mutation, if our results could be confirmed in larger series. The development of specific JAK2 inhibitors may allow further reduction of chemotherapy.