Genetic and biochemical evidence for a critical role of Janus kinase (JAK)-3 in mast cell-mediated type I hypersensitivity reactions

The role of peripheral nerve signaling in endometriosis

A hallmark of endometriosis - a chronic debilitating condition whose causes are poorly understood - is neuronal innervation of lesions. Recent evidence demonstrates that the peripheral nervous system plays an important role in the pathophysiology of this disease. Sensory nerves, which surround and innervate endometriotic lesions, not only drive the chronic and debilitating pain associated with endometriosis but also contribute to a pro-growth phenotype by secreting neurotrophic factors and interacting with surrounding immune cells. The diverse array of contributions that neurons play in endometriosis indicate that it should be considered as a nerve-centric disease. This review is focused on the emerging field of exoneural biology and how it applies to the field of endometriosis, in particular the role that peripheral nerves play in driving and maintaining endometriotic lesions. A better understanding of the mechanisms of neuronal contribution to endometriosis, as well as their interactions with accompanying stromal and immune cells, will unearth novel disease-relevant pathways and targets, providing additional, more selective therapeutic horizons.

Discovery of a highly selective JAK3 inhibitor for the treatment of rheumatoid arthritis

Janus tyrosine kinase 3 (JAK3) is expressed in lymphoid cells and is involved in the signalling of T cell functions. The development of a selective JAK3 inhibitor has been shown to have a potential benefit in the treatment of autoimmune disorders. In this article, we developed the 4-aminopiperidine-based compound RB1, which was highly selective for JAK3 inhibition, with an IC₅₀ of value of 40 nM, but did not inhibit JAK1, JAK2 or tyrosine kinase 2 (TYK2) at concentrations up to 5 µM. Furthermore, RB1 also exhibited favourable selectivity against a panel of representative kinases. In a battery of cytokine-stimulated cell-based assays, this potent inhibitor of JAK3 activity with good selectivity against other kinases could potently inhibit JAK3 activity over the activity of JAK1 or JAK2 (over at least 100-fold). A combination of liquid chromatography-mass spectrometry (LC-MS) experiments validated that RB1 covalently modified the unique cysteine 909 residue in JAK3. In vivo, RB1 exerted significantly improved pathology in the joints of a collagen-induced arthritis mouse model. The reasonable pharmacokinetics properties (F = 72.52%, T1/2 = 14.6 h) and favourable results of toxicology experiments (LD₅₀ > 2 g/kg) suggest that RB1 has the potential to be an efficacious treatment for RA.

Selective functional inhibition of JAK-3 is sufficient for efficacy in collagen-induced arthritis in mice

OBJECTIVE

All gamma-chain cytokines signal through JAK-3 and JAK-1 acting in tandem. We undertook this study to determine whether the JAK-3 selective inhibitor WYE-151650 would be sufficient to disrupt cytokine signaling and to ameliorate autoimmune disease pathology without inhibiting other pathways mediated by JAK-1, JAK-2, and Tyk-2.

METHODS

JAK-3 kinase selective compounds were characterized by kinase assay and JAK-3-dependent (interleukin-2 [IL-2]) and -independent (IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF]) cell-based assays measuring proliferation or STAT phosphorylation. In vivo, off-target signaling was measured by IL-22- and erythropoietin (EPO)-mediated models, while on-target signaling was measured by IL-2-mediated signaling. Efficacy of JAK-3 inhibitors was determined using delayed-type hypersensitivity (DTH) and collagen-induced arthritis (CIA) models in mice.

RESULTS

In vitro, WYE-151650 potently suppressed IL-2-induced STAT-5 phosphorylation and cell proliferation, while exhibiting 10-29-fold less activity against JAK-3-independent IL-6- or GM-CSF-induced STAT phosphorylation. Ex vivo, WYE-151650 suppressed IL-2-induced STAT phosphorylation, but not IL-6-induced STAT phosphorylation, as measured in whole blood. In vivo, WYE-151650 inhibited JAK-3-mediated IL-2-induced interferon-gamma production and decreased the natural killer cell population in mice, while not affecting IL-22-induced serum amyloid A production or EPO-induced reticulocytosis. WYE-151650 was efficacious in mouse DTH and CIA models.

CONCLUSION

In vitro, ex vivo, and in vivo assays demonstrate that WYE-151650 is efficacious in mouse CIA despite JAK-3 selectivity. These data question the need to broadly inhibit JAK-1-, JAK-2-, or Tyk-2-dependent cytokine pathways for efficacy.

Recent patents in the discovery of small molecule inhibitors of JAK3

IMPORTANCE OF THE FIELD

Protein kinase enzymes have become increasingly important as the target of many disease modification drug discovery programs. Disruption of JAK3 function results in quantitative and qualitative deficiencies in both B- and T-cell compartments of the immune system of JAK3 deficient mice and development of severe combined immunodeficiency in humans with the JAK3 genetic aberration. JAK3 plays a specific role in immune function and lymphoid development and it only resides in the hematopoietic system, thus the rationale for selective targeting. Inhibitors of JAK3 have shown utility in many different autoimmune disorders, including allograft rejection during transplantation, acute lymphoblastic leukemia, Type 1 diabetes, rheumatoid arthritis and allergic and asthmatic diseases. These inhibitors are making their way into clinical trials with profound effects, thus, validating the target and strategy.

AREAS COVERED IN THIS REVIEW

A review that covers around 90 patents and patent applications made in the last 10 years in the area involving JAK3 inhibitors is provided. Specifically, what this content will provide is the genus, highlighted compounds of particular interest, filing organization and some biological measure of these compounds as inhibitors of this protein kinase or none if it is not provided. Some information from original research articles appearing in peer reviewed literature is provided, but this article is not a review of the literature. Furthermore, an overview of the current clinical status and future outcomes of this field is provided as summary.

WHAT THE READER WILL GAIN

A strong understanding for the current state of the art in patents dealing with inhibitors of JAK3 including genus and species designations, potential commercial interest of this target in the pharmaceutical community, depth of coverage by numbers of examples and selected proof of action against the target. Also, a brief understanding of the biology and pharmacology involved in the processes involving the research, discovery, characterization and clinical status of JAK3 inhibitors.

TAKE HOME MESSAGE

This review is intended for medicinal chemists and patent agents who want to get a quick understanding of the state of the art in the field of JAK3 inhibitors. It further serves as a reference point to go into more depth on any series reported and to be able to evaluate any original research ideas in this area in the future.

Janus kinase-3 dependent inflammatory responses in allergic asthma

Allergic asthma is a chronic inflammatory condition of the lung characterized by reversible airway obstruction, high serum immunoglobulin (Ig) E levels, and chronic airway inflammation. A number of cells including mast cells, T cells, macrophages and dendritic cells play a role in the pathogenesis of the disease. Janus kinase (JAK)-3, a non-receptor protein tyrosine kinase, traditionally known to mediate cytokine signaling, also regulates functional responses of these cells. In this review the role of JAK-3 in regulating various pathogenic processes in allergic asthma is discussed. We propose that targeting JAK-3 is a rationale approach to control the inflammatory responses of multiple cell types responsible for the pathogenesis of allergic asthma.

NSC114792, a novel small molecule identified through structure-based computational database screening, selectively inhibits JAK3

Background

Human or animals lacking either JAK3 or the common gamma chain (γc) expression display severe combined immunodeficiency disease, indicating the crucial role of JAK3 in T-cell development and the homeostasis of the immune system. JAK3 has also been suggested to contribute to the pathogenesis of tumorigenesis. Recent studies identified activating JAK3 mutations in patients with various hematopoietic malignancies, including acute megakaryoblastic leukemia. Importantly, functional analyses of some of those JAK3 mutations have been shown to cause lethal hematopoietic malignancies in animal models. These observations make JAK3 an ideal therapeutic target for the treatment of various human diseases. To identify novel small molecule inhibitors of JAK3, we performed structure-based virtual screen using the 3D structure of JAK3 kinase domain and the NCI diversity set of compounds.

Results

We identified NSC114792 as a lead compound. This compound directly blocked the catalytic activity of JAK3 but not that of other JAK family members in vitro. In addition, treatment of 32D/IL-2Rβ cells with the compound led to a block in IL-2-dependent activation of JAK3/STAT5 but not IL-3-dependent activation of JAK2/STAT5. Consistent with the specificity of NSC114792 for JAK3, it selectively inhibited persistently-activated JAK3, but failed to affect the activity of other JAK family members and other oncogenic kinases in various cancer cell lines. Finally, we showed that NSC114792 decreases cell viability by inducing apoptosis through down-regulating anti-apoptotic gene expression only in cancer cells harboring persistently-active JAK3.

Conclusions

NSC114792 is a lead compound that selectively inhibits JAK3 activity. Therefore, our study suggests that this small molecule inhibitor of JAK3 can be used as a starting point to develop a new class of drugs targeting JAK3 activity, and may have therapeutic potential in various diseases that are caused by aberrant JAK3 activity.

Synthetic staurosporines via a ring closing metathesis strategy as potent JAK3 inhibitors and modulators of allergic responses

The synthesis and biological evaluation of JAK3 based staurosporine compounds is described. The compounds are constructed completely de novo, and a ring closing metathesis strategy is used to assemble the sugar mimetic portion. These analogs show potent JAK3 activity against isolated enzyme and in T-cells. One analog (32) showed unique biological effects during in vitro and in vivo tests including inhibition of STAT5 phosphorylation, blockade of mast cell responses, and reduction of JAK3 based effects in mice models of allergic disease.

Targeting mast cells in endometriosis with janus kinase 3 inhibitor, JANEX-1

Endometriosis (EMS) is a chronic inflammatory disease of multifactorial etiology characterized by implantation and growth of endometrial glands and stroma outside the uterine cavity. EMS is a significant public health issue as it affects 15-20% of women in their reproductive age. Clinical symptoms may include pelvic pain, dysmenorrhea, dyspareunia, pelvic/abdominal masses, and infertility. Symptomatic treatments such as surgical resection and/or hormonal suppression of ovarian function and analgesics are not as effective as desired. Consequently, there is an enormous unmet need to develop effective medical therapy capable of preventing the occurrence and recurrence of EMS without undesirable side-effects. EMS-associated intra-abdominal bleeding episodes, local inflammation, adhesions, and i.p. immunologic dysfunction leads to pelvic nociception and pelvic pain. Increasing evidence supports the involvement of allergic-type inflammation in EMS. Invasion of mast cells, degranulation, and proliferation of interstitial component are observed in endometriotic lesions. Presence of activated and degranulating mast cells within the nerve structures can contribute to the development of pain and hyperalgesia by direct effects on primary nociceptive neurons. Therefore, treatments targeting endometrial mast cells may prove effective in preventing or alleviating EMS-associated symptoms. The Janus kinase 3 (JAK3) is abundantly expressed in mast cells and is required for the full expression of high-affinity IgE receptor-mediated mast cell inflammatory sequelae. JANEX-1/WHI-P131 is a rationally designed novel JAK3 inhibitor with potent anti-inflammatory activity in several cellular and in vivo animal models of inflammation, including mouse models of peritonitis, colitis, cellulitis, sunburn, and airway inflammation with favorable toxicity and pharmacokinetic profile. We hypothesize that JAK3 inhibitors, especially JANEX-1, may prove useful to prevent or alleviate the symptoms of EMS.

Different approaches to study mast cell functions

Mast cells have long been known to play a detrimental role in the pathogenesis of IgE-associated allergic disorders by their ability to release a wide variety of pro-inflammatory mediators. A number of studies, however, have demonstrated that mast cells play a beneficial role in innate host defense against bacterial infections. Since mast cells clearly play both physiological and pathophysiological functions in the body, it is important to learn about the components of mast cells that drive these responses. The functional roles of mast cell in vivo have been principally characterized by comparing the biological responses in mast cell-deficient mice (WBB6F(1)-W/W(v)), their normal wild-type littermates (WBB6F(1)-+/+) and mast cell deficient mice reconstituted locally or systemically with mast cells cultured from the bone marrow cells of WBB6F(1)-+/+ mice (WBB6F(1)-W/W(v)+MC). Recently investigators have demonstrated that mast cell-deficient mice (WBB6F(1)-W/W(v)) can be reconstituted with mast cells derived in vitro from the bone marrow cells of certain gene knock-out mice or genetically-manipulated embryonic stem cells. This novel approach of analyzing the biological consequences of gene mutations in mast cells will help us to better understand the role of individual gene products in mast cell responses. In this review, we discuss these new approaches to investigate the functions of mast cells in vivo.

Simplified staurosporine analogs as potent JAK3 inhibitors

Simplification of bottom ring and regioselective functionalization of the indolocarbazole unit of staurosporine (2) are described. The modification led to a new series of simplified staurosporine analogs, which exhibited significant inhibitory activity against Janus kinase 3 (JAK3). The structure-activity relationships (SAR) are discussed and a proposed binding model is also highlighted.

Gö6976 is a potent inhibitor of the JAK 2 and FLT3 tyrosine kinases with significant activity in primary acute myeloid leukaemia cells

Aberrant activation of Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling is implicated in a number of haematological malignancies and effective JAK inhibitors may be therapeutically useful. We found that Gö6976, an indolocarbazole inhibitor of the calcium-dependent isozymes of protein kinase C (PKC), inhibited interleukin 3/granulocyte-macrophage colony-stimulating factor-induced signalling, proliferation and survival whereas Gö6983, a broad spectrum PKC inhibitor, had no such effects. Gö6976 was found to be a direct and potent inhibitor of JAK2 in vitro. Gö6976 also inhibited signalling, survival and proliferation in cells expressing the leukaemia-associated TEL-JAK2 fusion protein and the myeloproliferative disorder (MPD)-associated JAK2 V617F mutant. In primary acute myeloid leukaemia (AML) cells, incubation with Gö6976 reduced constitutive STAT activity in all cases studied. In addition, Akt and mitogen-activated protein kinase phosphorylation were reduced in 4/5 FLT3-internal tandem duplication (ITD) positive AML cases and 7/13 FLT3-wild-type (WT) cases. Expression of FLT3-WT, ITD and D835Y in 32D cells showed that Gö6976 is also a potent inhibitor of WT and mutant FLT3. In AML cells, Gö6976 reduced the survival to 55 +/- 5% of control in FLT3-ITD cases and to 69 +/- 5% in FLT3-WT samples. These data may help identify clinically useful compounds based on the structure of Gö6976, which can be employed for the treatment of MPDs as well as AML.

Targeting kinases in asthma

Through a regulation cascade via the site-specific phosphorylation of downstream substrates, members of kinase signaling pathways play multiple cellular regulatory roles. Because of the contribution of kinases in a diverse number of cellular processes, members of these pathways have become attractive targets for rational drug design. Members of these kinase signalling families, such as mitogen-activated kinases, tyrosine kinases (receptor and non-receptor) and ras human orthologue kinases among others have been shown to play key roles in the pathogenesis of immune, inflammatory and remodelling events that occur during asthma. This review highlights, through information that has been obtained from transgenic and knockout systems, small-molecule inhibitors and antisense technology, the role of select members of kinase families in the pathogenesis of asthma, and discusses the rationale for developing specific inhibitors of these kinases for the treatment of asthma.

Inhibition of the antigen-induced activation of rodent mast cells by putative Janus kinase 3 inhibitors WHI-P131 and WHI-P154 in a Janus kinase 3-independent manner

We analyzed the effects of the Janus kinase 3 (Jak3)-specific inhibitor WHI-P131 (4-(4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline) and the Jak3/Syk inhibitor WHI-P154 (4-(3'-bromo-4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline) on the antigen-induced activation of mast cells. In the rat mast cell line RBL-2H3, both WHI-P131 and WHI-P154 inhibited the antigen-induced degranulation and phosphorylation of p44/42 mitogen-activated protein kinase (MAPK), p38 MAPK and c-Jun N-terminal kinase (JNK). The phosphorylation of Gab2, Akt and Vav was also inhibited by WHI-P131 and WHI-P154, indicating that these inhibitors suppress the activation of phosphatidylinositol 3-kinase (PI3K). In bone marrow-derived mast cells (BMMCs) from Jak3-deficient (Jak3-/-) mice, degranulation and activation of MAPKs were induced by the antigen in almost the same extent as in BMMCs from wild-type mice. In addition, the antigen-induced degranulation and activation of MAPKs were inhibited by WHI-P131 and WHI-P154 in both groups of BMMCs, indicating that these compounds inhibit a certain step except for Jak3. The antigen-induced increase in the activity of Fyn, a probable tyrosine kinase of Gab2, was also inhibited by WHI-P131 and WHI-P154 in RBL-2H3 cells. In BMMCs from Jak3-/- mice, the antigen stimulation induced tyrosine phosphorylation of Fyn, which was inhibited by WHI-P131, as well as in BMMCs from wild-type mice and in RBL-2H3 cells. These findings suggest that Jak3 does not play a significant role in the antigen-induced degranulation and phosphorylation of MAPKs, and that WHI-P131 and WHI-P154 inhibit the PI3K pathway by preventing the antigen-induced activation of Fyn, thus inhibiting the antigen-induced degranulation and phosphorylation of MAPKs in mast cells.

JAK3 inhibition, a viable new modality of immunosuppression for solid organ transplants

The field of organ transplantation has had tremendous success because of the availability of immunosuppressive drugs that efficiently prevent acute organ rejection. Numerous and severe side effects are, however, associated with all current immunosuppressive therapies and justify a search for drugs with better efficacy and safety profiles. Janus kinase (JAK) 3, a tyrosine kinase that is crucial for mediating signals from the common gamma-chain of cytokine receptors, is peculiar in that its expression, contrarily to the targets of most current immunosuppressive drugs, is limited to cells that actively participate to the immune response to allografts. The recent demonstration in stringent preclinical models that JAK3 inhibition results in efficacy for the prevention of allograft rejection with a narrow side-effect profile might lead to a new era in the field of immunosuppression.

Contribution of mast cells to bacterial clearance and their proliferation during experimental cystitis induced by type 1 fimbriated E. coli

Bacterial infections of the urinary bladder are very common, and the role of mast cells in these infections is invariably thought of as a detrimental one. However, recent studies have shown that mast cells play a key role in host defense against various enterobacterial infections. In this manuscript, using mast cell-deficient (WBB6F1 - W/Wv) and mast cell-sufficient (WBB6F1 - +/+) mice we have investigated the protective role of mast cells in urinary bladder infections in vivo. Our findings show that (i) the mast cells are activated by FimH-expressing E. coli, and release large amount of histamine in the urinary bladder; (ii) the number of surviving bacteria in the urine is dependent on the presence of mast cells, and (iii) mast cell number in the bladder increases following uropathogenic infection in mice which is likely due to an increase in the mast cell growth-promoting cytokine IL-3 in bacteria-activated mast cells. Taken together, these observations suggest a beneficial role of mast cells in urinary bladder infections in mice.

Photochemical preparation of a pyridone containing tetracycle: a Jak protein kinase inhibitor

Jak3 is a protein tyrosine kinase that is associated with the shared gamma chain of receptors for cytokines IL2, IL4, IL7, IL9, and IL13. We have discovered that a pyridone-containing tetracycle (6) may be prepared from trisubstituted imidazole (5) in high yield by irradiation with >350 nm light. Compound 6 inhibits Jak3 with K(I)=5 nM; it also inhibits Jak family members Tyk2 and Jak2 with IC(50)=1 nM and murine Jak1with IC(50)=15 nM. Compound 6 was tested as an inhibitor of 21 other protein kinases; it inhibited these kinases with IC(50)s ranging from 130 nM to >10 microM. Compound 6 also blocks IL2 and IL4 dependent proliferation of CTLL cells and inhibits the phosphorylation of STAT5 (an in vivo substrate of the Jak family) as measured by Western blotting.

CYP1A-mediated metabolism of the Janus kinase-3 inhibitor 4-(4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline: structural basis for inactivation by regioselective O-demethylation

Here we report the phase I metabolism of the rationally designed Janus kinase-3 (JAK) inhibitor 4-(4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P131; JANEX-1). JANEX-1 was metabolized by the cytochrome P450 enzymes CYP1A1 and CYP1A2 in a regioselective fashion to form the biologically inactive 7-O-demethylation product 4-(4'-hydroxyphenyl)-amino-6-methoxy-7-hydroxyquinazoline (JANEX-1-M). Our molecular modeling studies indicated that the CYP1A family enzymes bind and demethylate JANEX-1 at the C-7 position of the quinazoline ring since the alternative binding conformation with demethylation at the C-6 position would result in a severe steric clash with the binding site residues. The metabolism of JANEX-1 to JANEX-1-M in pooled human liver microsomes followed Michaelis-Menten kinetics with V(max) and K(m) values (mean +/- S.D.) of 34.6 +/- 9.8 pmol/min/mg and 107.3 +/- 66.3 microM, respectively. alpha-Naphthoflavone and furafylline, which both inhibit CYP1A2, significantly inhibited the formation of JANEX-1-M in human liver microsomes. There was a direct correlation between CYP1A activities and the magnitude of JANEX-1-M formation in the liver microsomes from different animal species. A significantly increased metabolic rate for JANEX-1 was observed in Aroclor 1254-, beta-naphthoflavone-, and 3-methylcholanthrene-induced microsomes but not in clofibrate-, dexamethasone-, isoniazid-, and phenobarbital-induced microsomes. The formation of JANEX-1-M in the presence of baculovirus-expressed CYP1A1 and 1A2 was consistent with Michaelis-Menten kinetics. The systemic clearance of JANEX-1-M was much faster than that of JANEX-1 (5525.1 +/- 1926.2 ml/h/kg versus 1458.0 +/- 258.6 ml/h/kg). Consequently, the area under the curve value for JANEX-1-M was much smaller than that for JANEX-1 (27.5 +/- 8.0 versus 94.8 +/- 18.4 microM. h; P < 0.001).

Role of STAT6 in IgE receptor/FcepsilonRI-mediated late phase allergic responses of mast cells

In this study we show that IgE receptor engagement triggers activation of STAT6 in mast cells. We sought to determine the role of STAT6 activation in IgE receptor-mediated mast cell responses using STAT6 knockout mice. After IgE receptor engagement, bone marrow mast cells from STAT6(-/-) mice exhibited normal histamine and leukotriene C(4) release, but their cytokine release was markedly reduced. In accordance with these in vitro data, IgE/Ag-challenged STAT6(-/-) mice showed normal early phase, but severely impaired late phase, allergic reactions. These findings provide unprecedented evidence that STAT6 plays a pivotal role in mast cell responses to IgE/Ag stimulation.

Leflunomide metabolite analogue alpha-cyano-beta-hydroxy-beta-methyl-N-[3-(trifluoromethyl)phenyl]propenamide inhibits IgE/FcepsilonRI receptor-mediated mast cell leukotriene release and allergic asthma in mice

Mast cell-derived leukotrienes (LTs) play a critical role in the pathophysiology of allergy and asthma. We synthesized 13 analogues of leflunomide (LFM) and examined their in vitro effects on IgE/FcepsilonRI receptor-mediated mast cell LT release. We observed that the novel LFM analogue, alpha-cyano-beta-hydroxy-beta-methyl-N-[3-(trifluoromethyl) phenyl]propenamide (LFM-A8), is a more potent inhibitor than LFM of IgE/FcepsilonRI receptor-mediated LTC4 release from RBL-2H3 rat mast cells. Notably, LFM-A8 showed promising biologic activity in a mouse model of allergic asthma. Treatment of ovalbumin (OVA)-sensitized mice with LFM-A8 prevented the development of airway hyperresponsiveness to methacholine in a dose-dependent fashion. Furthermore, LFM-A8 inhibited the eosinophil recruitment to the airway lumen after the OVA challenge in a dose-dependent fashion. Therefore further development of compound LFM-A8 may provide the basis for new and effective treatment programs for severe allergic disorders, including allergic asthma.

Role of Janus kinase 3 in mast cell-mediated innate immunity against gram-negative bacteria

Mast cells play a pivotal role in innate host immune response to gram-negative bacteria. We report that Janus kinase 3 plays a role in mast cell-mediated bacterial clearance and neutrophil recruitment by regulating the release of tumor necrosis factor from mast cells. The role of JAK3 in mast cell-facilitated neutrophil recruitment and bacterial clearance was investigated by comparing the neutrophil influxes and bacterial clearance in mast cell-deficient W/W(v) mice reconstituted with JAK3(+/+) or JAK(-/-) mast cells. The neutrophil influx, bacterial clearance, and survival outcome in W/W(v) mice reconstituted with JAK3(+/+) mast cells was better than in W/W(v) mice reconstituted with JAK3(-/-) mast cells. These findings provide evidence that JAK3 is a key regulator of mast cell-mediated innate immunity against gram-negative bacteria.

Prediction of the structure of human Janus kinase 2 (JAK2) comprising the two carboxy-terminal domains reveals a mechanism for autoregulation

The structure of human Janus kinase 2 (JAK2) comprising the two C-terminal domains (JH1 and JH2) was predicted by application of homology modelling techniques. JH1 and JH2 represent the tyrosine kinase and tyrosine kinase-like domains, respectively, and are crucial for function and regulation of the protein. A comparison between the structures of the two domains is made and structural differences are highlighted. Prediction of the relative orientation of JH1 and JH2 was aided by a newly developed method for the detection of correlated amino acid mutations. Analysis of the interactions between the two domains led to a model for the regulatory effect of JH2 on JH1. The predictions are consistent with available experimental data on JAK2 or related proteins and provide an explanation for inhibition of JH1 tyrosine kinase activity by the adjacent JH2 domain.

In vivo pharmacokinetics and anti-anaphylactic activity of the novel mast cell inhibitor 4-(4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P131)

WHI-P131 is a novel dimethoxyquinazoline compound that is a potent inhibitor of Janus kinase-3-(JAK3)-dependent mast cell responses. In the present study, the authors investigated the anti-anaphylactic activity and pharmacokinetics of WHI-P131 in mice. After intraperitoneal (i.p.) administration of two consecutive bolus doses of 25 mg/kg injected 30 min apart at dose level of 25 mg/kg, WHI-P131 was rapidly absorbed with an observed C(max) of 82.6 microM, which is higher than the target concentration of 30 microM, at which WHI-P131 abrogates mast cell responses in vitro and the time to reach the maximum plasma concentration (t(max)) was 10.0+/-2.9 min. At a nontoxic 50 mg/kg dose level, WHI-P131 prevented compound 48/80-induced mast cell histamine release and fatal anaphylaxis in mice. Further development of WHI-P131 may provide the basis for new and effective treatment as well as prevention programs for mast cell mediated allergic reactions in clinical settings.

Targeting Janus kinase 3 in mast cells prevents immediate hypersensitivity reactions and anaphylaxis

Janus kinase 3 (JAK3), a member of the Janus family protein-tyrosine kinases, is expressed in mast cells, and its enzymatic activity is enhanced by IgE receptor/FcepsilonRI cross-linking. Selective inhibition of JAK3 in mast cells with 4-(4'-hydroxylphenyl)-amino-6, 7-dimethoxyquinazoline) (WHI-P131) blocked the phospholipase C activation, calcium mobilization, and activation of microtubule-associated protein kinase after lgE receptor/FcepsilonRI cross-linking. Treatment of IgE-sensitized rodent as well as human mast cells with WHI-P131 effectively inhibited the activation-associated morphological changes, degranulation, and proinflammatory mediator release after specific antigen challenge without affecting the functional integrity of the distal secretory machinery. In vivo administration of the JAK3 inhibitor WHI-P131 prevented mast cell degranulation and development of cutaneous as well as systemic fatal anaphylaxis in mice at nontoxic dose levels. Thus, JAK3 plays a pivotal role in IgE receptor/FcepsilonRI-mediated mast cell responses, and targeting JAK3 with a specific inhibitor, such as WHI-P131, may provide the basis for new and effective treatment as well as prevention programs for mast cell-mediated allergic reactions.