Jak2 deficiency defines an essential developmental checkpoint in definitive hematopoiesis

Momelotinib inhibits ACVR1/ALK2, decreases hepcidin production, and ameliorates anemia of chronic disease in rodents

Patients with myelofibrosis (MF) often develop anemia and frequently become dependent on red blood cell transfusions. Results from a phase 2 study for the treatment of MF with the Janus kinase 1/2 (JAK1/2) inhibitor momelotinib (MMB) demonstrated that MMB treatment ameliorated anemia, which was unexpected for a JAK1/2 inhibitor, because erythropoietin-mediated JAK2 signaling is essential for erythropoiesis. Using a rat model of anemia of chronic disease, we demonstrated that MMB treatment can normalize hemoglobin and red blood cell numbers. We found that this positive effect is driven by direct inhibition of the bone morphogenic protein receptor kinase activin A receptor, type I (ACVR1), and the subsequent reduction of hepatocyte hepcidin production. Of note, ruxolitinib, a JAK1/2 inhibitor approved for the treatment of MF, had no inhibitory activity on this pathway. Further, we demonstrated the effect of MMB is not mediated by direct inhibition of JAK2-mediated ferroportin (FPN1) degradation, because neither MMB treatment nor myeloid-specific deletion of JAK2 affected FPN1 expression. Our data support the hypothesis that the improvement of inflammatory anemia by MMB results from inhibition of ACVR1-mediated hepcidin expression in the liver, which leads to increased mobilization of sequestered iron from cellular stores and subsequent stimulation of erythropoiesis.

The Promotion of Erythropoiesis via the Regulation of Reactive Oxygen Species by Lactic Acid

The simultaneous increases in blood lactic acid and erythrocytes after intense exercise could suggest a link between lactate and the erythropoiesis. However, the effects of lactic acid on erythropoiesis remain to be elucidated. Here, we utilized a mouse model to determine the role of lactic acid in this process in parallel with studies using leukaemic K562 cells. Treatment of K562 cells in vitro with lactic acid increased the mRNA and protein expression of haemoglobin genes and the frequency of GPA⁺ cells. Also, increases in haematocrit and CD71⁻/Ter119⁺ erythroid cells were observed in lactic acid-treated mice, which showed a physiological increase in blood lactate. Mouse bone marrow CD34⁺/CD117⁻ cells showed an increase in erythroid burst-forming units after stimulation with lactic acid in vitro. Furthermore, lactic acid increased the intracellular reactive oxygen species (ROS) content in bone marrow and in K562 cells. Erythroid differentiation induced in Haematopoietic Stem Cells (HSCs) and K562 cells by lactic acid was abolished by reducing ROS levels with SOD or 2-mercaptoethanol, which suggests that ROS is a critical regulator of this process. These findings provide a better understanding of the role of lactic acid in cellular metabolism and physiological functions.

Canonical and Non-Canonical Aspects of JAK-STAT Signaling: Lessons from Interferons for Cytokine Responses

Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal transduction mediates cytokine responses. Canonical signaling is based on STAT tyrosine phosphorylation by activated JAKs. Downstream of interferon (IFN) receptors, activated JAKs cause the formation of the transcription factors IFN-stimulated gene factor 3 (ISGF3), a heterotrimer of STAT1, STAT2 and interferon regulatory factor 9 (IRF9) subunits, and gamma interferon-activated factor (GAF), a STAT1 homodimer. In recent years, several deviations from this paradigm were reported. These include kinase-independent JAK functions as well as extra- and intranuclear activities of U-STATs without phosphotyrosines. Additionally, transcriptional control by STAT complexes resembling neither GAF nor ISGF3 contributes to transcriptome changes in IFN-treated cells. Our review summarizes the contribution of non-canonical JAK-STAT signaling to the innate antimicrobial immunity imparted by IFN. Moreover, we touch upon functions of IFN pathway proteins beyond the IFN response. These include metabolic functions of IRF9 as well as the regulation of natural killer cell activity by kinase-dead TYK2 and different phosphorylation isoforms of STAT1.

STATs in NK-Cells: The Good, the Bad, and the Ugly

Natural killer (NK)-cells are major players in the fight against viral infections and transformed cells, but there is increasing evidence attributing a disease-promoting role to NK-cells. Cytokines present in the tumor microenvironment shape NK-cell maturation, function, and effector responses. Many cytokines signal via the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway that is also frequently altered and constitutively active in a broad range of tumor cells. As a consequence, there are currently major efforts to develop therapeutic strategies to target this pathway. Therefore, it is of utmost importance to understand the role and contributions of JAK-STAT molecules in NK-cell biology-only this knowledge will allow us to predict effects of JAK-STAT inhibition for NK-cell functions and to successfully apply precision medicine. We will review the current knowledge on the role of JAK-STAT signaling for NK-cell functions and discuss conditions involved in the switch from NK-cell tumor surveillance to disease promotion.

Jak2a regulates erythroid and myeloid hematopoiesis during zebrafish embryogenesis

Zebrafish (Danio rerio) are an attractive vertebrate model for the molecular dissection of disease mechanisms. Janus kinase (JAK)/signal transducer and activator of transcription (stat) has been defined through studies of cytokine signaling pathways in mammals. Here, we examined the expression level of Jak2a, which is a homolog of mammalian jak2 in zebrafish, by quantitative reverse transcriptase (RT)-PCR, and the peak of mRNA expression occurred at 3.75 hours post fertilization (hpf). The overexpression of Jak2a was proven by real-time Q-PCR and Western blot in 1-4-cell stage embryos injected with 400 ng/µl full-length jak2a mRNA as well as gfi1.1, gata1, mpo and β-embryonic hemoglobin as detected by real-time Q-PCR. Moreover, jak2a mRNA significantly increased the GFP⁺ population in the transgenic zebrafish lines Tg (gata1: gfp) (uninjected embryos: 17.22±1.70%; embryos injected with jak2a mRNA: 21.31±2.11%, p<0.01) and Tg (mpo: gfp) (uninjected embryos: 3.86±1.94; embryos injected with jak2a mRNA: 6.64±1.30%, p<0.01) compared with the control group. Thus, our data indicate that Jak2a plays an important role in erythropoiesis and myeloid hematopoiesis.

Modeling myeloproliferative neoplasms: From mutations to mouse models and back again

Myeloproliferative neoplasms (MPNs) are defined according to the 2008 World Health Organization (WHO) classification and the recent 2016 revision. Over the years, several genetic lesions have been associated with the development of MPNs, with important consequences for identifying unique biomarkers associated with specific neoplasms and for developing targeted therapies. Defining the genotype-phenotype relationship in MPNs is essential to identify driver somatic mutations that promote MPN development and maintenance in order to develop curative targeted therapies. While studies with human samples can identify putative driver mutations, murine models are mandatory to demonstrate the causative role of mutations and for pre-clinical testing of specific therapeutic interventions. This review focuses on MPN mouse models specifically developed to assess the pathogenetic roles of gene mutations found in human patients, as well as murine MPN-like phenotypes identified in genetically modified mice.

IL-12 Signals through the TCR To Support CD8 Innate Immune Responses

CD8 T cells must integrate antigenic and inflammatory signals to differentiate into efficient effector and memory T cells able to protect us from infections. The mechanisms by which TCR signaling and proinflammatory cytokine receptor signaling cooperate in these processes are poorly defined. In this study, we show that IL-12 and other proinflammatory cytokines transduce signals through the TCR signalosome in a manner that requires Fyn activity and self-peptide-MHC (self-pMHC) interactions. This mechanism is crucial for CD8 innate T cell functions. Loss of Fyn activity or blockade of self-pMHC interactions severely impaired CD8 T cell IFN-γ and NKG2D expression, proliferation, and cytotoxicity upon cytokine-mediated bystander activation. Most importantly, in the absence of self-pMHC interactions, CD8 memory T cells fail to undergo bystander activation upon an unrelated infection. Thus, CD8 T cell bystander activation, although independent of cognate Ag, still requires self-pMHC and TCR signaling.

Safety, tolerability, efficacy and pharmacodynamics of the selective JAK1 inhibitor GSK2586184 in patients with systemic lupus erythematosus

We aimed to evaluate the pharmacodynamics, efficacy, safety and tolerability of the JAK1 inhibitor GSK2586184 in adults with systemic lupus erythematosus (SLE). In this adaptive, randomized, double-blind, placebo-controlled study, patients received oral GSK2586184 50-400 mg, or placebo twice daily for 12 weeks. Primary endpoints included interferon-mediated messenger RNA transcription over time, changes in Safety of Estrogen in Lupus National Assessment-SLE Disease Activity Index score, and number/severity of adverse events. A pre-specified interim analysis was performed when ≥ 5 patients per group completed 2 weeks of treatment. In total, 84-92% of patients were high baseline expressors of the interferon transcriptional biomarkers evaluated. At interim analysis, GSK2586184 showed no significant effect on mean interferon transcriptional biomarker expression (all panels). The study was declared futile and recruitment was halted at 50 patients. Shortly thereafter, significant safety data were identified, including elevated liver enzymes in six patients (one confirmed and one suspected case of Drug Reaction with Eosinophilia and Systemic Symptoms), leading to immediate dosing cessation. Safety of Estrogen in Lupus National Assessment-SLE Disease Activity Index scores were not analysed due to the small number of patients completing the study. The study futility and safety data described for GSK2586184 do not support further evaluation in patients with SLE. Study identifiers: GSK Study JAK115919; ClinicalTrials.gov identifier: NCT01777256.

Regulation of skeletal growth and mineral acquisition by the GH/IGF-1 axis: Lessons from mouse models

The growth hormone (GH) and its downstream mediator, the insulin-like growth factor-1 (IGF-1), construct a pleotropic axis affecting growth, metabolism, and organ function. Serum levels of GH/IGF-1 rise during pubertal growth and associate with peak bone acquisition, while during aging their levels decline and associate with bone loss. The GH/IGF-1 axis was extensively studied in numerous biological systems including rodent models and cell cultures. Both hormones act in an endocrine and autocrine/paracrine fashion and understanding their distinct and overlapping contributions to skeletal acquisition is still a matter of debate. GH and IGF-1 exert their effects on osteogenic cells via binding to their cognate receptor, leading to activation of an array of genes that mediate cellular differentiation and function. Both hormones interact with other skeletal regulators, such as sex-steroids, thyroid hormone, and parathyroid hormone, to facilitate skeletal growth and metabolism. In this review we summarized several rodent models of the GH/IGF-1 axis and described key experiments that shed new light on the regulation of skeletal growth by the GH/IGF-1 axis.

Defining the functional binding sites of interleukin 12 receptor β1 and interleukin 23 receptor to Janus kinases

Stimulation of cells with the IL-12–type cytokine IL-12 or IL-23 results in activation of receptor-associated Janus kinases (Jak) and phosphorylation of STAT proteins in target cells. Functional association of IL 12Rβ1 with tyrosine kinase 2 and IL-23R with Jak2 is mandatory for IL-12 and/or IL-23 signaling.

The interleukin (IL)-12–type cytokines IL-12 and IL-23 are involved in T-helper (Th) 1 and Th17 immunity, respectively. They share the IL-12 receptor β1 (IL-12Rβ1) as one component of their receptor signaling complexes, with IL-12Rβ2 as second receptor for IL-12 and IL-23R for IL-23 signal transduction. Stimulation with IL-12 and IL-23 results in activation of receptor-associated Janus kinases (Jak) and phosphorylation of STAT proteins in target cells. The Janus kinase tyrosine kinase (Tyk) 2 associates with IL-12Rβ1, whereas Jak2 binds to IL-23R and also to IL-12Rβ2. Receptor association of Jak2 is mediated by Box1 and Box2 motifs located within the intracellular domain of the receptor chains. Here we define the Box1 and Box2 motifs in IL-12Rβ1 and an unusual Jak2-binding site in IL-23R by the use of deletion and site-directed mutagenesis. Our data show that nonfunctional box motifs abolish IL-12– and IL-23–induced STAT3 phosphorylation and cytokine-dependent proliferation of Ba/F3 cells. Coimmunoprecipitation of Tyk2 by IL-12Rβ1 and Jak2 by IL‑23R supported these findings. In addition, our data demonstrate that association of Jak2 with IL-23R is mandatory for IL-12 and/or IL-23 signaling, whereas Tyk2 seems to be dispensable.

Janus Kinase 1 Is Essential for Inflammatory Cytokine Signaling and Mammary Gland Remodeling

Despite a wealth of knowledge about the significance of individual signal transducers and activators of transcription (STATs), essential functions of their upstream Janus kinases (JAKs) during postnatal development are less well defined. Using a novel mammary gland-specific JAK1 knockout model, we demonstrate here that this tyrosine kinase is essential for the activation of STAT1, STAT3, and STAT6 in the mammary epithelium. The loss of JAK1 uncouples interleukin-6-class ligands from their downstream effector, STAT3, which leads to the decreased expression of STAT3 target genes that are associated with the acute-phase response, inflammation, and wound healing. Consequently, JAK1-deficient mice exhibit impaired apoptosis and a significant delay in mammary gland remodeling. Using RNA sequencing, we identified several new JAK1 target genes that are upregulated during involution. These include Bmf and Bim, which are known regulators of programmed cell death. Using a BMF/BIM-double-knockout epithelial transplant model, we further validated that the synergistic action of these proapoptotic JAK1 targets is obligatory for the remodeling of the mammary epithelium. The collective results of this study suggest that JAK1 has nonredundant roles in the activation of particular STAT proteins and this tyrosine kinase is essential for coupling inflammatory cytokine signals to the cell death machinery in the differentiated mammary epithelium.

Myocardial Hypertrophic Remodeling and Impaired Left Ventricular Function in Mice with a Cardiac-Specific Deletion of Janus Kinase 2

The Janus kinase (JAK) system is involved in numerous cell signaling processes and is highly expressed in cardiac tissue. The JAK isoform JAK2 is activated by numerous factors known to influence cardiac function and pathologic conditions. However, although abundant, the role of JAK2 in the regulation or maintenance of cardiac homeostasis remains poorly understood. Using the Cre-loxP system, we generated a cardiac-specific deletion of Jak2 in the mouse to assess the effect on cardiac function with animals followed up for a 4-month period after birth. These animals had marked mortality during this period, although at 4 months mortality in male mice (47%) was substantially higher compared with female mice (30%). Both male and female cardiac Jak2-deleted mice had hypertrophy, dilated cardiomyopathy, and severe left ventricular dysfunction, including a marked reduction in ejection fractions as assessed by serial echocardiography, although the responses in females were somewhat less severe. Defective cardiac function was associated with altered protein levels of sarcoplasmic reticulum calcium-regulatory proteins particularly in hearts from male mice that had depressed levels of SERCA2 and phosphorylated phospholamban. In contrast, SERCA2 was unchanged in hearts of female mice, whereas phosphorylated phospholamban was increased. Our findings suggest that cardiac JAK2 is critical for maintaining normal heart function, and its ablation produces a severe pathologic phenotype composed of myocardial remodeling, heart failure, and pronounced mortality.

Tofacitinib in ulcerative colitis

Cytokines orchestrate immune and inflammatory responses involved in the pathogenesis of ulcerative colitis (UC). Protein kinases are essential for signal transduction in eukaryotic cells. Janus kinases (JAKs) are a family of protein tyrosine kinases that play a pivotal role in cytokine receptor signaling. Indeed, a major subgroup of cytokines use Type I and II cytokine receptors which signal via the activation of JAKs. Tofacitinib is an oral JAK inhibitor that has been studied in autoimmune pathologies, including UC and rheumatoid arthritis with good overall efficacy and acceptable safety profile. This literature review was performed with the goal of summarizing the knowledge on JAK inhibitors in UC treatment.

The Structural Basis for Class II Cytokine Receptor Recognition by JAK1

JAK1 is a member of the Janus kinase (JAK) family of non-receptor tyrosine kinases that are activated in response to cytokines and interferons. Here, we present two crystal structures of the human JAK1 FERM and SH2 domains bound to peptides derived from the class II cytokine receptors IFN-λ receptor 1 and IL-10 receptor 1 (IFNLR1 and IL10RA). These structures reveal an interaction site in the JAK1 FERM that accommodates the so-called "box1" membrane-proximal receptor peptide motif. Biophysical analysis of the JAK1-IFNLR1 interaction indicates that the receptor box1 is the primary driver of the JAK1 interaction, and identifies residues conserved among class II receptors as important for binding. In addition, we demonstrate that a second "box2" receptor motif further stabilizes the JAK1-IFNLR1 complex. Together, these data identify a conserved JAK binding site for receptor peptides and elucidate the mechanism by which class II cytokine receptors interact with JAK1.

Risk of Infectious Complications in Hemato-Oncological Patients Treated with Kinase Inhibitors

Infectious complications are a major cause of morbidity and mortality in patients with hemato-oncological diseases. Although disease-related immunosuppression represents one factor, aggressive treatment regimens, such as chemotherapy, stem cell transplantation, or antibody treatment, account for a large proportion of infectious side effects. With the advent of targeted therapies affecting specific kinases in malignant diseases, the outcome of patients has further improved. Nonetheless, dependent on the specific pathway targeted or off-target activity of the kinase inhibitor, therapy-associated infectious complications may occur. We review the most common and approved kinase inhibitors targeting a variety of hemato-oncological malignancies for their immunosuppressive potential and evaluate their risk of infectious side effects based on preclinical evidence and clinical data in order to raise awareness of the potential risks involved.

Pharmacokinetics and Pharmacokinetic/Pharmacodynamic Modeling of Filgotinib (GLPG0634), a Selective JAK1 Inhibitor, in Support of Phase IIB Dose Selection

Background and Objectives

Filgotinib (GLPG0634) is a selective inhibitor of Janus kinase 1 (JAK1) currently in development for the treatment of rheumatoid arthritis and Crohn’s disease. While less selective JAK inhibitors have shown long-term efficacy in treating inflammatory conditions, this was accompanied by dose-limiting side effects. Here, we describe the pharmacokinetics of filgotinib and its active metabolite in healthy volunteers and the use of pharmacokinetic–pharmacodynamic modeling and simulation to support dose selection for phase IIB in patients with rheumatoid arthritis.

Methods

Two trials were conducted in healthy male volunteers. In the first trial, filgotinib was administered as single doses from 10 mg up to multiple daily doses of 200 mg. In the second trial, daily doses of 300 and 450 mg for 10 days were evaluated. Non-compartmental analysis was used to determine individual pharmacokinetic parameters for filgotinib and its metabolite. The overall pharmacodynamic activity for the two moieties was assessed in whole blood using interleukin-6-induced phosphorylation of signal-transducer and activator of transcription 1 as a biomarker for JAK1 activity. These data were used to conduct non-linear mixed-effects modeling to investigate a pharmacokinetic/pharmacodynamic relationship.

Results

Modeling and simulation on the basis of early clinical data suggest that the pharmacokinetics of filgotinib are dose proportional up to 200 mg, in agreement with observed data, and support that both filgotinib and its metabolite contribute to its pharmacodynamic effects. Simulation of biomarker response supports that the maximum pharmacodynamic effect is reached at a daily dose of 200 mg filgotinib.

Conclusion

Based on these results, a daily dose range up to 200 mg has been selected for phase IIB dose-finding studies in patients with rheumatoid arthritis.

Integrating Immunologic Signaling Networks: The JAK/STAT Pathway in Colitis and Colitis-Associated Cancer

Cytokines are believed to be crucial mediators of chronic intestinal inflammation in inflammatory bowel diseases (IBD) such as Crohn's disease (CD) and ulcerative colitis (UC). Many of these cytokines trigger cellular effects and functions through signaling via janus kinase (JAK) and signal transducer and activator of transcription (STAT) molecules. In this way, JAK/STAT signaling controls important events like cell differentiation, secretion of cytokines or proliferation and apoptosis in IBD in both adaptive and innate immune cells. Moreover, JAK/STAT signaling, especially via the IL-6/STAT3 axis, is believed to be involved in the transition of inflammatory lesions to tumors leading to colitis-associated cancer (CAC). In this review, we will introduce the main cellular players and cytokines that contribute to pathogenesis of IBD by JAK/STAT signaling, and will highlight the integrative function that JAK/STATs exert in this context as well as their divergent role in different cells and processes. Moreover, we will explain current concepts of the implication of JAK/STAT signaling in CAC and finally discuss present and future therapies for IBD that interfere with JAK/STAT signaling.

Molecular targets of quercetin with anti-inflammatory properties in atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disease. Over the past few decades, AD has become more prevalent worldwide. Quercetin, a naturally occurring polyphenol, shows antioxidant, anti-inflammatory, and antiallergic activities. Several recent clinical and preclinical findings suggest quercetin as a promising natural treatment for inflammatory skin diseases. Significant progress in elucidating the molecular mechanisms underlying the anti-AD properties of quercetin has been achieved in the recent years. Here, we discuss the use of quercetin as treatment for AD, with a particular focus on the molecular basis of its effect. We also briefly discuss the approaches to improve the bioavailability of quercetin.

Structure-Based Design and Synthesis of 3-Amino-1,5-dihydro-4H-pyrazolopyridin-4-one Derivatives as Tyrosine Kinase 2 Inhibitors

We report herein the discovery and optimization of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one TYK2 inhibitors. High-throughput screening against TYK2 and JAK1-3 provided aminoindazole derivative 1 as a hit compound. Scaffold hopping of the aminoindazole core led to the discovery of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one derivative 3 as a novel chemotype of TYK2 inhibitors. Interestingly, initial SAR study suggested that this scaffold could have a vertically flipped binding mode, which prompted us to introduce a substituent at the 7-position as a moiety directed toward the solvent-exposed region. Introduction of a 1-methyl-3-pyrazolyl moiety at the 7-position resulted in a dramatic increase in TYK2 inhibitory activity, and further optimization led to the discovery of 20. Compound 20 inhibited IL-23-induced IL-22 production in a rat PD assay, as well as inhibited IL-23 signaling in human PBMC. Furthermore, 20 showed selectivity for IL-23 signaling inhibition against GM-CSF, demonstrating the unique cytokine selectivity of the novel TYK2 inhibitor.

The common γ-chain cytokine receptor: tricks-and-treats for T cells

Originally identified as the third subunit of the high-affinity IL-2 receptor complex, the common γ-chain (γc) also acts as a non-redundant receptor subunit for a series of other cytokines, collectively known as γc family cytokines. γc plays essential roles in T cell development and differentiation, so that understanding the molecular basis of its signaling and regulation is a critical issue in T cell immunology. Unlike most other cytokine receptors, γc is thought to be constitutively expressed and limited in its function to the assembly of high-affinity cytokine receptors. Surprisingly, recent studies reported a series of findings that unseat γc as a simple housekeeping gene, and unveiled γc as a new regulatory molecule in T cell activation and differentiation. Cytokine-independent binding of γc to other cytokine receptor subunits suggested a pre-association model of γc with proprietary cytokine receptors. Also, identification of a γc splice isoform revealed expression of soluble γc proteins (sγc). sγc directly interacted with surface IL-2Rβ to suppress IL-2 signaling and to promote pro-inflammatory Th17 cell differentiation. As a result, endogenously produced sγc exacerbated autoimmune inflammatory disease, while the removal of endogenous sγc significantly ameliorated disease outcome. These data provide new insights into the role of both membrane and soluble γc in cytokine signaling, and open new venues to interfere and modulate γc signaling during immune activation. These unexpected discoveries further underscore the perspective that γc biology remains largely uncharted territory that invites further exploration.

Tyrosine kinase 2 - Surveillant of tumours and bona fide oncogene

Tyrosine kinase 2 (TYK2) is a member of the Janus kinase (JAK) family, which transduces cytokine and growth factor signalling. Analysis of TYK2 loss-of-function revealed its important role in immunity to infection, (auto-) immunity and (auto-) inflammation. TYK2-deficient patients unravelled high similarity between mice and men with respect to cellular signalling functions and basic immunology. Genome-wide association studies link TYK2 to several autoimmune and inflammatory diseases as well as carcinogenesis. Due to its cytokine signalling functions TYK2 was found to be essential in tumour surveillance. Lately TYK2 activating mutants and fusion proteins were detected in patients diagnosed with leukaemic diseases suggesting that TYK2 is a potent oncogene. Here we review the cell intrinsic and extrinsic functions of TYK2 in the characteristics preventing and enabling carcinogenesis. In addition we describe an unexpected function of kinase-inactive TYK2 in tumour rejection.

Inhibition of JAK2 Reverses Paclitaxel Resistance in Human Ovarian Cancer Cells

OBJECTIVE

Resistance to chemotherapy is a major factor that limits the postsurgical survival of ovarian cancer patients. Janus-activated kinase 2 (JAK2) has been implicated in cancer cell survival and the development of drug resistance in ovarian cancers. In the present study, we sought to determine whether inhibition of JAK2 reverses drug resistance in OC3/TAX300 cells, a paclitaxel-resistant human ovarian cancer cell line previously established in our laboratory.

METHODS

OC3/TAX300 cells were transduced with lentivirus expressing small interference RNA (siRNA) against JAK2 and treated with JAK2 kinase inhibitor AG490.

RESULTS

Treatment with JAK2-siRNA markedly decreased the messenger RNA and protein of JAK2 as determined by real-time polymerase chain reaction and Western blot analysis. OC3/TAX300 cells treated with JAK2-siRNA exhibited stalled growth, increased cell cycle arrest in G2/M phase, and enhanced apoptosis in response to paclitaxel. In keeping with this, JAK2-siRNA also inhibited the expression of multidrug resistance protein 1. To determine whether JAK2 promotes paclitaxel resistance via phosphorylation of signal transducer and activator of transcription 3 (STAT3), a transcription factor known to be involved in resistance to chemotherapy, we treated OC3/TAX300 cells with JAK2 kinase inhibitor AG490. Of note, AG490 reduced the level of p-STAT3 and inhibited the expression of multidrug resistance protein 1 in a dose-dependent manner.

CONCLUSIONS

Collectively, we conclude that the JAK2-STAT3 pathway promotes the development of paclitaxel resistance via upregulating the expression of prosurvival and antiapoptotic genes. Targeting this pathway may be effective in reversing resistance to chemotherapy in ovarian cancers.

Intracellular Signaling Pathways Involved in Childhood Acute Lymphoblastic Leukemia; Molecular Targets

Acute lymphoblastic leukemia (ALL) is a malignant disease characterized by an uncontrolled proliferation of immature lymphoid cells. ALL is the most common hematologic malignancy in early childhood, and it reaches peak incidence between the ages of 2 and 3 years. The prognosis of ALL is associated with aberrant gene expression, in addition to the presence of numerical or structural chromosomal alterations, age, race, and immunophenotype. The Relapse rate with regard to pharmacological treatment rises in childhood; thus, the expression of biomarkers associated with the activation of cell signaling pathways is crucial to establish the disease prognosis. Intracellular pathways involved in ALL are diverse, including Janus kinase/Signal transducers and transcription activators (JAK-STAT), Phosphoinositide-3-kinase-protein kinase B (PI3K-AKT), Ras mitogen-activated protein kinase (Ras-MAPK), Glycogen synthase kinase-3β (GSK-3β), Nuclear factor-kappa beta (NF-κB), and Hypoxia-inducible transcription factor 1α (HIF-1α), among others. In this review, we present several therapeutic targets, intracellular pathways, and molecular markers that are being studied extensively at present.

LIF signaling in stem cells and development

Leukemia inhibitory factor (LIF) is a member of the interleukin-6 (IL-6) cytokine family. All members of this family activate signal transducer and activator of transcription 3 (STAT3), a transcription factor that influences stem and progenitor cell identity, proliferation and cytoprotection. The role of LIF in development was first identified when LIF was demonstrated to support the propagation of mouse embryonic stem cells. Subsequent studies of mice deficient for components of the LIF pathway have revealed important roles for LIF signaling during development and homeostasis. Here and in the accompanying poster, we provide a broad overview of JAK-STAT signaling during development, with a specific focus on LIF-mediated JAK-STAT3 activation.

A comprehensive review of pacritinib in myelofibrosis

The first-in-class JAK1/JAK2 inhibitor ruxolitinib inhibits JAK/STAT signaling, inducing durable reductions in splenomegaly and constitutional symptoms in patients with myelofibrosis. However, the association of ruxolitinib therapy with myelosuppression indicates the continued need for optimal treatment choices in myelofibrosis. Pacritinib, a dual JAK2 and FLT3 inhibitor, improves disease-related symptoms and signs with manageable gastrointestinal toxicity in patients with myelofibrosis with splenomegaly and high-risk features, without causing overt myelosuppression, and therefore may provide an important treatment option for a range of patients with myelofibrosis. This article examines the role of JAK2 and FLT3 signaling in myelofibrosis and provides an overview of the clinical development of pacritinib as a new therapy for myelofibrosis.

Pathogenesis of myeloproliferative neoplasms

Major progress has been recently made in understanding the molecular pathogenesis of myeloproliferative neoplasms (MPN). Mutations in one of four genes-JAK2, MPL, CALR, and CSF3R-can be found in the vast majority of patients with MPN and represent driver mutations that can induce the MPN phenotype. Hyperactive JAK/STAT signaling appears to be the common denominator of MPN, even in patients with CALR mutations and the so-called "triple-negative" MPN, where the driver gene mutation is still unknown. Mutations in epigenetic regulators, transcription factors, and signaling components modify the course of the disease and can contribute to disease initiation and/or progression. The central role of JAK2 in MPN allowed development of small molecular inhibitors that are in clinical use and are active in almost all patients with MPN. Advances in understanding the mechanism of JAK2 activation open new perspectives of developing the next generation of inhibitors that will be selective for the mutated forms of JAK2.

VX-509 (decernotinib) is a potent and selective janus kinase 3 inhibitor that attenuates inflammation in animal models of autoimmune disease

Cytokines, growth factors, and other chemical messengers rely on a class of intracellular nonreceptor tyrosine kinases known as Janus kinases (JAKs) to rapidly transduce intracellular signals. A number of these cytokines are critical for lymphocyte development and mediating immune responses. JAK3 is of particular interest due to its importance in immune function and its expression, which is largely confined to lymphocytes, thus limiting the potential impact of JAK3 inhibition on nonimmune physiology. The aim of this study was to evaluate the potency and selectivity of the investigational JAK3 inhibitor VX-509 (decernotinib) [(R)-2-((2-(1H-pyrrolo[2,3-b]pyridin-3-yl)pyrimidin-4-yl)amino)-2-methyl-N-(2,2,2-trifluoroethyl)butanamide] against JAK3 kinase activity and inhibition of JAK3-mediated signaling in vitro and JAK3-dependent physiologic processes in vivo. These results demonstrate that VX-509 potently inhibits JAK3 in enzyme assays (Ki = 2.5 nM + 0.7 nM) and cellular assays dependent on JAK3 activity (IC50 range, 50-170 nM), with limited or no measurable potency against other JAK isotypes or non-JAK kinases. VX-509 also showed activity in two animal models of aberrant immune function. VX-509 treatment resulted in dose-dependent reduction in ankle swelling and paw weight and improved paw histopathology scores in the rat collagen-induced arthritis model. In a mouse model of oxazolone-induced delayed-type hypersensitivity, VX-509 reduced the T cell-mediated inflammatory response in skin. These findings demonstrate that VX-509 is a selective and potent inhibitor of JAK3 in vitro and modulates proinflammatory response in models of immune-mediated diseases, such as collagen-induced arthritis and delayed-type hypersensitivity. The data support evaluation of VX-509 for treatment of patients with autoimmune and inflammatory diseases such as rheumatoid arthritis.

In vivo regulation of erythropoiesis by chemically inducible dimerization of the erythropoietin receptor intracellular domain

Erythropoietin (Epo) and its receptor (EpoR) are required for the regulation of erythropoiesis. Epo binds to the EpoR homodimer on the surface of erythroid progenitors and erythroblasts, and positions the intracellular domains of the homodimer to be in close proximity with each other. This conformational change is sufficient for the initiation of Epo-EpoR signal transduction. Here, we established a system of chemically regulated erythropoiesis in transgenic mice expressing a modified EpoR intracellular domain (amino acids 247-406) in which dimerization is induced using a specific compound (chemical inducer of dimerization, CID). Erythropoiesis is reversibly induced by oral administration of the CID to the transgenic mice. Because transgene expression is limited to hematopoietic cells by the Gata1 gene regulatory region, the effect of the CID is limited to erythropoiesis without adverse effects. Additionally, we show that the 160 amino acid sequence is the minimal essential domain of EpoR for intracellular signaling of chemically inducible erythropoiesis in vivo. We propose that the CID-dependent dimerization system combined with the EpoR intracellular domain and the Gata1 gene regulatory region generates a novel peroral strategy for the treatment of anemia.

Critical role of Jak2 in the maintenance and function of adult hematopoietic stem cells

Jak2, a member of the Janus kinase family of nonreceptor protein tyrosine kinases, is activated in response to a variety of cytokines, and functions in survival and proliferation of cells. An activating JAK2V617F mutation has been found in most patients with myeloproliferative neoplasms, and patients treated with Jak2 inhibitors show significant hematopoietic toxicities. However, the role of Jak2 in adult hematopoietic stem cells (HSCs) has not been clearly elucidated. Using a conditional Jak2 knockout allele, we have found that Jak2 deletion results in rapid loss of HSCs/progenitors leading to bone marrow failure and early lethality in adult mice. Jak2 deficiency causes marked impairment in HSC function, and the mutant HSCs are severely defective in reconstituting hematopoiesis in recipient animals. Jak2 deficiency also causes significant apoptosis and loss of quiescence in HSC-enriched LSK (Lin(-)Sca-1(+)c-Kit(+)) cells. Jak2-deficient LSK cells exhibit elevated reactive oxygen species levels and enhanced p38 MAPK activation. Mutant LSK cells also show defective Stat5, Erk, and Akt activation in response to thrombopoietin and stem cell factor. Gene expression analysis reveals significant downregulation of genes related to HSC quiescence and self-renewal in Jak2-deficient LSK cells. These data suggest that Jak2 plays a critical role in the maintenance and function of adult HSCs.

Jak-2 positive myeloproliferative neoplasms

Originally described by Dameshek in 1951, myeloproliferative disorders are today classified as myeloproliferative Neoplasms (MPNs) in WHO's Classification of Tumors of Hematopoietic and Lymphoid Tissues. The term includes a range of conditions, [ie, BCR-ABL-positive chronic myelogenous leukemia (CML), chronic neutrophilic leukemia (CNL), polycythemia vera (PV), primary myelofibrosis (PMF), essential thromobocythemia (ET), chronic eosinophilic leukemia not otherwise specified (CEL-NOS), mastocytosis, and unclassifiable myeloproliferative neoplasm]. In the specific case of CML, a better understanding of the pathogenesis and pathophysiology of the disease has led to a targeted therapy. The presence of chromosome Philadelphia, t(9;22)(q34;11) results in the oncogene BCR-ABL, which characterizes the disease; this molecular rearrangement gives rise to a tyrosine-kinase, which in turn triggers the proliferation of the myeloid line through the activation of the signaling pathways downstream. Tyrosine-kinase inhibitors (TKIs) have altered the therapy and monitoring of CML patients and improved both their prognosis and quality of life. In 2005, various groups of investigators described a new point mutation of the gene JAK2 associated to MPNs. Although the presence of this mutation has led to a modification in the diagnostic criteria of these conditions, the impact of the use of JAK2 inhibitors on the prognosis and course of the disease continues to be controversial.

Epo-induced erythroid maturation is dependent on Plcγ1 signaling

Erythropoiesis is a tightly regulated process. Development of red blood cells occurs through differentiation of hematopoietic stem cells (HSCs) into more committed progenitors and finally into erythrocytes. Binding of erythropoietin (Epo) to its receptor (EpoR) is required for erythropoiesis as it promotes survival and late maturation of erythroid progenitors. In vivo and in vitro studies have highlighted the requirement of EpoR signaling through Janus kinase 2 (Jak2) tyrosine kinase and Stat5a/b as a central pathway. Here, we demonstrate that phospholipase C gamma 1 (Plcγ1) is activated downstream of EpoR-Jak2 independently of Stat5. Plcγ1-deficient pro-erythroblasts and erythroid progenitors exhibited strong impairment in differentiation and colony-forming potential. In vivo, suppression of Plcγ1 in immunophenotypically defined HSCs (Lin(-)Sca1(+)KIT(+)CD48(-)CD150(+)) severely reduced erythroid development. To identify Plcγ1 effector molecules involved in regulation of erythroid differentiation, we assessed changes occurring at the global transcriptional and DNA methylation level after inactivation of Plcγ1. The top common downstream effector was H2afy2, which encodes for the histone variant macroH2A2 (mH2A2). Inactivation of mH2A2 expression recapitulated the effects of Plcγ1 depletion on erythroid maturation. Taken together, our findings identify Plcγ1 and its downstream target mH2A2, as a 'non-canonical' Epo signaling pathway essential for erythroid differentiation.

Designed Macrocyclic Kinase Inhibitors

Cancer continues to present as an increasing and serious global unmet medical need in today's aging population.1 Macrocyclic kinase inhibitors have reached advanced clinical testing and are making an impact in oncologic conditions including myelofibrosis, lymphomas and leukemias. Rheumatoid arthritis (RA) is also beginning to be impacted with the first macrocycle having entered Phase I clinical evaluation in healthy volunteers. Increasing reports of innovative macrocycles in preclinical research are appearing in the literature. Desirable, selective, multi-kinase inhibitory profiles against specific kinases known to be abrogated in cancer, RA, and other diseases have been achieved in a first generation series of clinical stage compact small molecule macrocyclic kinase inhibitors. Herein we discuss their design, synthesis, structure activity relationships and assessment of the latest clinical data in a range of oncologic conditions. Macrocyclic kinase inhibitors have the potential to offer new hope to patients and their families.

The molecular regulation of Janus kinase (JAK) activation

The JAK (Janus kinase) family members serve essential roles as the intracellular signalling effectors of cytokine receptors. This family, comprising JAK1, JAK2, JAK3 and TYK2 (tyrosine kinase 2), was first described more than 20 years ago, but the complexities underlying their activation, regulation and pleiotropic signalling functions are still being explored. Here, we review the current knowledge of their physiological functions and the causative role of activating and inactivating JAK mutations in human diseases, including haemopoietic malignancies, immunodeficiency and inflammatory diseases. At the molecular level, recent studies have greatly advanced our knowledge of the structures and organization of the component FERM (4.1/ezrin/radixin/moesin)-SH2 (Src homology 2), pseudokinase and kinase domains within the JAKs, the mechanism of JAK activation and, in particular, the role of the pseudokinase domain as a suppressor of the adjacent tyrosine kinase domain's catalytic activity. We also review recent advances in our understanding of the mechanisms of negative regulation exerted by the SH2 domain-containing proteins, SOCS (suppressors of cytokine signalling) proteins and LNK. These recent studies highlight the diversity of regulatory mechanisms utilized by the JAK family to maintain signalling fidelity, and suggest alternative therapeutic strategies to complement existing ATP-competitive kinase inhibitors.

Preclinical evaluation of bortezomib/dipyridamole novel combination as a potential therapeutic modality for hematologic malignancies

Novel combinations aiming at maximizing the efficacy of bortezomib are highly valued in the clinic. Therefore the current study investigated the outcomes of combining bortezomib with dipyridamole, a well-known antiplatelet. The co-treatment exerted a synergistic lethality in a panel of human leukemia/lymphoma cell lines of different origin. Mechanistically, dipyridamole did not modulate the proteasome inhibitory activity of bortezomib. However, dipyridamole triggered an endoplasmic reticulum (ER) stress, and co-treatment with bortezomib resulted in higher levels of ER stress than either monotherapies. Relieving ER stress with the protein translation inhibitor, cycloheximide suppressed cell death. Moreover, the enhanced ER stress by the co-treatment was associated with an aggravation of reactive oxygen species (ROS) generation and glutathione (GSH) depletion. Replenishing GSH pools significantly scavenged ROS and rescued the cells. Importantly, the cytotoxicity of the co-treatment was executed mainly via the mitochondrial apoptotic pathway with an efficient suppression of the key anti-apoptotic regulators, Mcl-1, Bcl-xl, Bcl-2 and XIAP, driving the independence of the co-treatment-induced apoptosis of a single apoptotic trigger. Furthermore, the intrinsic potential of bortezomib to inhibit important pro-survival pathways was enhanced by dipyridamole in a GSH/ROS-dependent manner. Interestingly, dipyridamole abrogated JAK2 phosphorylation indirectly and selectively in cancer cells, and the co-treatment-induced cytotoxicity was preserved in a model of stromal-mediated chemoresistance. In nude mice, the antitumor activity of the co-treatment surpassed that of bortezomib monotherapy despite that synergy was lacking. In summary, findings of the present study provided a preclinical rationale which warrants further clinical evaluation of bortezomib/dipyridamole novel combination in hematologic malignancies.