Janus kinase 3 inhibitor WHI-P131/JANEX-1 prevents graft-versus-host disease but spares the graft-versus-leukemia function of the bone marrow allografts in a murine bone marrow transplantation model

JAK inhibitors for the treatment of myeloproliferative neoplasms and other disorders

JAK inhibitors have been developed following the discovery of the JAK2V617F in 2005 as the driver mutation of the majority of non- BCR-ABL1 myeloproliferative neoplasms (MPNs). Subsequently, the search for JAK2 inhibitors continued with the discovery that the other driver mutations ( CALR and MPL) also exhibited persistent JAK2 activation. Several type I ATP-competitive JAK inhibitors with different specificities were assessed in clinical trials and exhibited minimal hematologic toxicity. Interestingly, these JAK inhibitors display potent anti-inflammatory activity. Thus, JAK inhibitors targeting preferentially JAK1 and JAK3 have been developed to treat inflammation, autoimmune diseases, and graft-versus-host disease. Ten years after the beginning of clinical trials, only two drugs have been approved by the US Food and Drug Administration: one JAK2/JAK1 inhibitor (ruxolitinib) in intermediate-2 and high-risk myelofibrosis and hydroxyurea-resistant or -intolerant polycythemia vera and one JAK1/JAK3 inhibitor (tofacitinib) in methotrexate-resistant rheumatoid arthritis. The non-approved compounds exhibited many off-target effects leading to neurological and gastrointestinal toxicities, as seen in clinical trials for MPNs. Ruxolitinib is a well-tolerated drug with mostly anti-inflammatory properties. Despite a weak effect on the cause of the disease itself in MPNs, it improves the clinical state of patients and increases survival in myelofibrosis. This limited effect is related to the fact that ruxolitinib, like the other type I JAK2 inhibitors, inhibits equally mutated and wild-type JAK2 (JAK2WT) and also the JAK2 oncogenic activation. Thus, other approaches need to be developed and could be based on either (1) the development of new inhibitors specifically targeting JAK2V617F or (2) the combination of the actual JAK2 inhibitors with other therapies, in particular with molecules targeting pathways downstream of JAK2 activation or the stability of JAK2 molecule. In contrast, the strong anti-inflammatory effects of the JAK inhibitors appear as a very promising therapeutic approach for many inflammatory and auto-immune diseases.

Therapeutics for Graft-versus-Host Disease: From Conventional Therapies to Novel Virotherapeutic Strategies

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has a curative potential for many hematologic malignancies and blood diseases. However, the success of allo-HSCT is limited by graft-versus-host disease (GVHD), an immunological syndrome that involves inflammation and tissue damage mediated by donor lymphocytes. Despite immune suppression, GVHD is highly incident even after allo-HSCT using human leukocyte antigen (HLA)-matched donors. Therefore, alternative and more effective therapies are needed to prevent or control GVHD while preserving the beneficial graft-versus-cancer (GVC) effects against residual disease. Among novel therapeutics for GVHD, oncolytic viruses such as myxoma virus (MYXV) are receiving increased attention due to their dual role in controlling GVHD while preserving or augmenting GVC. This review focuses on the molecular basis of GVHD, as well as state-of-the-art advances in developing novel therapies to prevent or control GVHD while minimizing impact on GVC. Recent literature regarding conventional and the emerging therapies are summarized, with special emphasis on virotherapy to prevent GVHD. Recent advances using preclinical models with oncolytic viruses such as MYXV to ameliorate the deleterious consequences of GVHD, while maintaining or improving the anti-cancer benefits of GVC will be reviewed.

WHI-131 Promotes Osteoblast Differentiation and Prevents Osteoclast Formation and Resorption in Mice

The small molecule WHI-131 is a potent therapeutic agent with anti-inflammatory, antiallergic, and antileukemic potential. However, the regulatory effects of WHI-131 on osteoblast and osteoclast activity are unclear. We examined the effects of WHI-131 on osteoblast and osteoclast differentiation with respect to bone remodeling. The production of receptor activator of nuclear factor kappa-B ligand (RANKL) by osteoblasts in response to interleukin (IL)-1 or IL-6 stimulation decreased by 56.8% or 50.58%, respectively, in the presence of WHI-131. WHI-131 also abrogated the formation of mature osteoclasts induced by IL-1 or IL-6 stimulation. Moreover, WHI-131 treatment decreased RANKL-induced osteoclast differentiation of bone marrow-derived macrophages, and reduced the resorbing activity of mature osteoclasts. WHI-131 further decreased the mRNA and protein expression levels of c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) by almost twofold, and significantly downregulated the mRNA expression of the following genes: tartrate-resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR), DC-STAMP, OC-STAMP, ATP6v0d2, and cathepsin K (CtsK) compared with the control group. WHI-131 further suppressed the phosphorylation of protein kinase B (Akt) and degradation of inhibitor of kappa B (IκB); Ca(2+) oscillation was also affected, and phosphorylation of the C-terminal Src kinase (c-Src)-Bruton agammaglobulinemia tyrosine kinase (Btk)-phospholipase C gamma 2 (PLCγ2) (c-Src-Btk-PLCg2 calcium signaling pathway) was inhibited following WHI-131 treatment. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway was activated by WHI-131, accompanied by phosphorylation of STAT3 Ser727 and dephosphorylation of STAT6. In osteoblasts, WHI-131 caused an approximately fourfold increase in alkaline phosphatase activity and Alizarin Red staining intensity. Treatment with WHI-131 increased the mRNA expression levels of genes related to osteoblast differentiation, and induced the phosphorylation of Akt, p38, and Smad1/5/8. Furthermore, 5-week-old ICR mice treated with WHI-131 exhibited antiresorbing effects in a lipopolysaccharide-induced calvaria bone loss model in vivo and increased bone-forming activity in a calvarial bone formation model. Therefore, the results of this study show that WHI-131 plays a dual role by inhibiting osteoclast differentiation and promoting osteoblast differentiation. Thus, WHI-131 could be a useful pharmacological agent to treat osteoporosis by promoting bone growth and inhibiting resorption.

The role of chemokines in mediating graft versus host disease: opportunities for novel therapeutics

Bone marrow transplantation (BMT) is the current therapy of choice for several malignancies and severe autoimmune diseases. Graft versus host disease (GVHD) is the major complication associated with BMT. T lymphocytes and other leukocytes migrate into target organs during GVHD, become activated and mediate tissue damage. Chemokines are well known inducers of leukocyte trafficking and activation and contribute to the pathogenesis of GVHD. Here, we review the major animal models used to study GVHD and the role of chemokines in mediating tissue damage in these models. The role of these molecules in promoting potential beneficial effects of the graft, especially graft versus leukemia, is also discussed. Finally, the various pharmacological strategies to block the chemokine system or downstream signaling events in the context of GVHD are discussed.

The use of structural biology in Janus kinase targeted drug discovery

The Janus kinases (or Jak kinases) mediate cytokine and growth factor signal transduction. Acquired or inherited Jak mutations can result in dysregulation of Jak-mediated signal transduction and can be critical to disease acquisition in neoplasias including acute myeloid, acute lymphoblastic and acute megakaryoblastic leukemias, and in rare X-linked severe combined immunodeficiency. The discovery of an acquired Jak2 point mutation, V617F, in significant numbers of patients with classical myeloproliferative disorders has increased the interest in development of Jak2-specific tyrosine kinase inhibitors and consequently there are now over 20 publically available structures of Jak kinase domains that describe all four family members, Jak1, Jak2, Jak3, and Tyk2. Here we review the recent advances in understanding the druggable structure and function of the Jak family, with a focus on the structural biology of the Jak kinase domain. We will discuss how these advances impact the development of Jak-targeted therapeutics.

CP-690550, a Janus kinase inhibitor, suppresses CD4+ T-cell-mediated acute graft-versus-host disease by inhibiting the interferon-γ pathway

BACKGROUND

Acute graft-versus-host disease (GVHD) is a critical obstacle to bone marrow transplantation. Although numerous studies have described immunosuppression protocols to mitigate acute GVHD, the need still exists for a more efficient immunosuppressant with fewer side effects. Here, we evaluated the protective effect of CP-690550, a newly developed Janus kinase inhibitor, in an acute GVHD model.

METHODS

CP-690550 was chemically synthesized. Acute GVHD was induced through the transfer of parent B6 (H-2) bone marrow and CD4 T cells into lethally irradiated (B6×bm12)F1 (H-2) mice. RESULTS.: CP-690550 treatments confined to days -3 to 11 of GVHD induction provided full protection against allogeneic, acute GVHD-related lethality and histopathology. An analysis of the initial donor-derived CD4 T-cell responses revealed that the inhibitory effects of CP-690550 were largely related to the suppression of donor CD4 T-cell-mediated interferon (IFN)-γ production. Enhanced inhibition of T helper 1 cell differentiation, rather than the inhibition of allogeneic CD4 T-cell proliferation or T helper 17 cell differentiation, was also confirmed in allogeneic mixed lymphocyte reactions. Because lethality was considerably delayed by the systemic blockade of IFN-γ, the principal protective effect of CP-690550 occurred through the modulation of IFN-γ production.

CONCLUSION

The targeting of Janus kinase with a sensitive and specific inhibitor, CP-690550, conferred effective protection from acute GVHD induced by a semiallogeneic major histocompatibility complex class II-disparate combination. Protection from acute GVHD was largely mediated by the inhibition of IFN-γ production.

Immunomodulation and pharmacological strategies in the treatment of graft-versus-host disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation offers great promise for the treatment of a variety of diseases including malignancies and other diseases of hematopoietic origin. However, morbidity and mortality due to graft-versus-host disease (GVHD) remain a major barrier to its application.

OBJECTIVE

This review will provide an overview of the pathophysiology of GVHD and discuss the recent advances in GVHD management in both preclinical and clinical studies.

METHODS

An extensive literature search on PubMed from 1995 to 2008 was performed.

RESULTS/CONCLUSION

There has been much progress in our understanding of GVHD and finding new means to control acute GVHD. While these approaches hold promise, as yet none has been able to replace the standard methods we may use routinely to decrease the incidence of the condition.

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.

Drug insight: novel small molecules and drugs for immunosuppression

Gastrointestinal diseases can result from the inadequate or excessive response of the immune system to self or innocuous antigens. Moreover, the physiologic activation of the immune system against non-self antigens is a major clinical problem in liver organ transplantation. At present, many drugs are available that suppress the activation of the immune system, although most of the currently used immunosuppressive drugs lack specificity in terms of their molecular targets and, therefore, have the potential to generate numerous side effects. The advances that have been made in understanding the molecular events that underlie the activation of the immune system have led to the development of a new generation of 'small molecules' that are endowed with immunosuppressive properties and can serve as immunomodulatory agents. Among these new small molecules, inhibitors of Janus kinase 3, p21-Rac1 and p38 mitogen-activated protein kinase represent the most innovative approach to immunosuppression, and could be a promising alternative to current immunosuppressive therapies. Here, we report on the progress that has been made in the development of small molecules in the field of gastroenterology.

Janus tyrosine kinases and signal transducers and activators of transcription regulate critical functions of T cells in allograft rejection and transplantation tolerance

Full activation of T cells requires three sequential signals. Engagement by antigen presenting cells (APC) delivers signals 1/2, whereas signal 3 is delivered by multiple cytokines to regulate the immune homeostasis by influencing proliferation, differentiation, and survival/death. Signaling by cytokines acting through their receptors is delivered by two major molecular families, namely Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Findings obtained from mice genetically deficient in Jaks and Stats suggest that these molecules may serve as therapeutic targets to prevent allograft rejection, induce transplantation tolerance, and inhibit autoimmune disease and lymphoid-derived tumors. This review describes the role of Jak tyrosine kinases and Stat transcription factors and their putative function in regulating T and B cell activity.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Bone marrow transplantation and approaches to avoid graft-versus-host disease (GVHD)

Haematopoietic stem cell transplantation (HSCT) offers promise for the treatment of haematological and immune disorders, solid tumours, and as a tolerance inducing regimen for organ transplantation. Allogeneic HSCTs engraftment requires immunosuppression and the anti-tumour effects are dependent upon the immune effector cells that are contained within or generated from the donor graft. However, significant toxicities currently limit its efficacy. These problems include: (i) graft-versus-host disease (GVHD) in which donor T cells attack the recipient resulting in multi-organ attack and morbidity, (ii) a profound period of immune deficiency following HSCT, and (iii) donor graft rejection. Currently available methods to prevent or treat GVHD with systemic immunosuppression can lead to impaired immune recovery, increased opportunistic infections, and higher relapse rates. This review will provide an overview of GVHD pathophysiology and discuss the roles of various cells, pathways, and factors in the GVHD generation process and in the preservation of graft-versus-tumour effects. Variables that need to be taken into consideration in attempting to extrapolate preclinical results to the clinical paradigm will be highlighted.

Janus kinase 3: a novel target for selective transplant immunosupression

Existing immunosuppressants inhibit lymphocyte activation and T cell cytokine signal transduction pathways, reducing the rate of acute rejection episodes to < 10%. However, the widespread tissue distribution of their molecular targets engenders pleiotropic toxicities. One strategy to address this problem seeks to identify compounds that selectively inhibit a target restricted in distribution to the lymphoid system. Janus kinase (Jak) 3 is such a molecule; it mediates signal transduction via the gamma common chain of lymphokine surface receptors. Disruption of this lymphoid-restricted enzyme would not be predicted to produce collateral damage in other organ systems. Development of selective Jak3 inhibitors has been difficult due to crossreactivity with its homologue, Jak2. In contrast to all other putative antagonists, which are discussed in detail herein, one Jak3 inhibitor, NC1153, shows at least 40-fold greater selective inhibition for Jak3 than for Jak2, is robustly synergistic with calcineurin antagonists, and, either alone or in combination with cyclosporin, produces no adverse effects in rodents preconditioned to be at heightened risk for nephrotoxicity, bone marrow suppression, or altered lipid metabolism.

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.

Janus kinase-3 (JAK3) inhibition: a novel immunosuppressive option for allogeneic transplantation

Current immunosuppressive therapy in clinical organ transplantation is based on drugs that suppress various functions of immunocompetent cells but still affect cells and organ compartments other than the immune system. Hence, these drugs have considerable side effects which lead to increased morbidity and reduced life-quality of transplant recipients. A major step forward in the rationale design of clinical immunosuppression resides in the elucidation of molecular targets that play a critical role specifically within the immune system. Recently, Janus kinase 3 (JAK3) has been identified as such a molecule. Genetic absence or ablation of this tyrosine kinase is associated with defective T-cell immunity that results in severe combined immunodeficiency (SCID) without apparent changes in other organ systems. Furthermore, pharmacological inhibition has significantly prolonged allograft survival in several experimental models of organ transplantation. The present review provides an overview of the emerging role of JAK3 in the immune system and the development of JAK3-inhibiting drugs. The potential clinical application of JAK3 inhibitors in organ transplantations is discussed in the light of a recent series of successful kidney transplantations in non-human primates immunosuppressed solely with a novel JAK3 inhibitor.

Dual targeting of Bruton's tyrosine kinase and Janus kinase 3 with rationally designed inhibitors prevents graft-versus -host disease (GVHD) in a murine allogeneic bone marrow transplantation model

The purpose of the present study was to evaluate the effectiveness of targeting Bruton's tyrosine kinase (BTK) with a specific BTK inhibitor, alpha-cyano-beta-hydroxy-beta-methyl-N-(2,5-dibromophenyl)-propenamide (LFM-A13), for prevention of acute fatal graft-versus-host disease (GVHD) in a murine model of allogeneic bone marrow transplantation (BMT). Vehicle-treated control C57BL/6 mice receiving bone marrow/splenocyte grafts from allogeneic BALB/c donors developed severe multi-organ acute GVHD and died after a median survival time (MST) of 40 d. LFM-A13 treatment (25 mg/kg/d) significantly prolonged the MST of the BMT recipients to 47 d. The probability of survival at 2 months after BMT was 2 +/- 2% for vehicle-treated control mice and 22 +/- 6% for mice treated with LFM-A13 (P = 0.0008). Notably, the combination regimen of LFM-A13 plus the standard anti-GVHD drug methotrexate (MTX) (10 mg/m(2)/d) was more effective than LFM-A13 alone, while the combination regimen of LFM-A13 plus the novel anti-GVHD drug JANEX-1 (60 mg/kg/d), targeting Janus kinase 3, was more effective than LFM-A13, JANEX-1 or MTX alone. More than 70% of recipients receiving this most effective GVHD prophylaxis (LFM-A13 + JANEX-1) remained alive throughout the 80-d observation period with an MST of >80 d. Taken together, these results indicate that targeting BTK with the chemical inhibitor LFM-A13 may attenuate the severity of GVHD, especially when it is combined with other anti-GVHD drugs, such as MTX and JANEX-1.

The Mortimer M. Bortin lecture

The graft-versus-leukemia effect of allogeneic blood or marrow transplantation is a dramatic example of the power of the immune system to eradicate malignant disease. In this personal essay, adapted from the inaugural Mortimer M. Bortin Lecture presented at the 2004 Tandem BMT Meetings, the author recounts early efforts by Bortin and others to manipulate the graft-versus-leukemia effect and separate it from the potentially fatal complications of graft-versus-host disease.

The Role of Signal Transducer and Activator of Transcription Factors in Leukemogenesis

Human leukemias are frequently associated with the aberrant expression of activated fusion tyrosine kinases or activated protein tyrosine kinases carrying insertional or point mutations. The activated kinase enzymes typically phosphorylate one or more signal transducer and activator of transcription (STAT) factors, which translocate to the cell nucleus and regulate the expression of genes associated with survival and proliferation. The phosphorylation and activation of STAT family members has been described in a wide range of human leukemias. Furthermore, animal models of leukemia have demonstrated the pivotal contribution of STAT activation to leukemic pathogenesis. This review discusses evidence for the functional importance of STAT activation in the biology of leukemia and current opportunities for modulating STAT proteins in the therapy of this group of diseases.

Prevention of organ allograft rejection by a specific Janus kinase 3 inhibitor

Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings.

Prevention of CD40-triggered dendritic cell maturation and induction of T-cell hyporeactivity by targeting of Janus kinase 3

Pharmacological targeting of Janus kinase 3 (JAK3) has been employed successfully to control allograft rejection and graft-vs.-host disease (GVHD). Recent evidence suggests that in addition to its involvement in common-gamma chain (cgamma) signaling of cytokine receptors, JAK3 is also engaged in the CD40 signaling pathway of peripheral blood monocytes. In this study, we assessed the consequences of JAK3 inhibition during CD40-induced maturation of myeloid dendritic cells (DCs), and tested the impact thereof on the induction of T-cell alloreactivity. Dendritic cells triggering through CD40 induced JAK3 activity, the expression of costimulatory molecules, production of IL-12, and potent allogeneic stimulatory capacity. In contrast, JAK3 inhibition with the rationally designed JAK3 inhibitor WHI-P-154 prevented these effects arresting the DCs at an immature level. Interestingly, DCs exposed to the JAK3-inhibitor during CD40-ligation induced a state of hyporeactivity in alloreactive T cells that was reversible upon exogenous IL-2 supplementation to secondary cultures. These results suggest that immunosuppressive therapies targeting the tyrosine kinase JAK3 may also affect the function of myeloid cells. This property of JAK3 inhibitors therefore represents a further level of interference, which together with the well-established suppression of cgamma signaling could be responsible for their clinical efficacy.

Suppression of early T-cell-receptor-triggered cellular activation by the Janus kinase 3 inhibitor WHI-P-154

BACKGROUND

Therapeutic targeting of Janus kinase 3 (JAK3) has received particular attention, because it is associated with the common gamma signaling of cytokine receptors and thus vitally influences T-cell growth and survival. Recent evidence, however, indicates a critical role for JAK3 in signaling linked to the T-cell antigen receptor.

METHODS

In this study we investigated whether targeting JAK3 with a rationally designed inhibitor affects early T-cell activation events. T cells were stimulated by CD3 and CD28 cross-linking, and interleukin (IL)-2 production, activation marker expression, increase of free intracellular Ca2+ concentration, activation of the extracellular-related kinase, and nuclear translocation of transcription factors were evaluated.

RESULTS

We found that JAK3 inhibitor treatment dramatically impaired T-cell-receptor (TCR)-induced IL-2 production, surface activation marker expression (CD69, CD154), and homotypic T-cell aggregation. Accordingly, mRNA production of IL-2, interferon-gamma, and IL-10 was profoundly inhibited. Molecular analysis revealed that TCR-triggered phosphorylation of phospholipase C-gamma1, increase in cytoplasmic Ca2+ concentration, and activation of extracellular-related kinase were markedly reduced by the JAK3 inhibitor, resulting in substantially decreased DNA binding of nuclear factor of activated T cells and alkaline phosphatase-1 and subsequent IL-2 promoter activation. Remarkably, on TCR-independent stimulation, IL-2 production, CD69 expression, and blast formation were completely insensitive to JAK3 inhibitor treatment.

CONCLUSION

These data indicate that pharmacologic targeting of JAK3 uncouples early TCR-triggered signaling from essential downstream events, which may have important implications for the use of such compounds in T-cell-mediated disorders such as allograft rejection or graft-versus-host disease.

Targeting JAK3 with JANEX-1 for prevention of autoimmune type 1 diabetes in NOD mice

Here we show that Janus kinase (JAK) 3 is an important molecular target for treatment of autoimmune insulin-dependent (type 1) diabetes mellitus. The rationally designed JAK3 inhibitor JANEX-1 exhibited potent immunomodulatory activity and delayed the onset of diabetes in the NOD mouse model of autoimmune type 1 diabetes. Whereas 60% of vehicle-treated control NOD mice became diabetic by 25 weeks, the incidence of diabetes at 25 weeks was only 9% for NOD females treated with daily injections of JANEX-1 (100 mg/kg/day) from Week 10 through Week 25 (P = 0.007). Furthermore, JANEX-1 prevented the development of insulitis and diabetes in NOD-scid/scid females after adoptive transfer of splenocytes from diabetic NOD females. Chemical inhibitors such as JANEX-1 may provide the basis for effective treatment modalities against human type 1 diabetes. To our knowledge, this is the first report of the immunosuppressive activity of a JAK3 inhibitor in the context of an autoimmune disease.

New strategies for prevention and treatment of graft-versus-host disease and for induction of graft-versus-leukemia effects

Graft-versus-host disease (GVHD) continues to be a problem in allogeneic hemopoietic stem cell transplantation; however, our understanding of the basic pathophysiology of GVHD has improved. Although not all data obtained from murine or other animal models can be extrapolated to the clinic, there are leads that deserve to be pursued. The skin, intestinal tract, and liver are the 3 major target organs of GVHD and share the feature of presenting a barrier to the "environment" of the host. There is evidence that the damage inflicted to these organs, the epithelial and endothelial cells in particular, by the conditioning regimen causes a release of various cytokines and a penetration of endotoxin into the systemic circulation. According to these observations, the nonimmunologic aspects of GVHD have been likened to an inflammatory process. If this characterization is valid, blocking these nonspecific inflammatory changes would ameliorate GVHD without interfering with the graft-versus-leukemia (GVL) reaction. In fact, one study has shown a substantial amelioration of GVHD with a molecule that directly blocks endotoxin. Clinical data also suggest that patients with organ dysfunction early after transplantation that is presumed to be treatment related may benefit from preemptive interventions aimed at controlling GVHD. Furthermore, there is growing evidence that the mechanisms involved in GVHD may differ from organ to organ (for example, Fas/Fas-ligand interactions in the liver versus tumor necrosis factor alpha/receptor interactions in the intestinal tract), and from a therapeutic point of view, the time of onset of clinical GVHD may be important in choosing the appropriate therapy. Thus, combinations of interventions chosen and timed appropriately may be more effective in preventing and managing GVHD than are the standard across-the-board approaches that have been used so far. Such a strategy may also be successful in maintaining a GVL effect and possibly in incorporating direct antileukemic therapy, such as the use of cytotoxic T-cells directed at minor histocompatibility antigens, without increasing the risk of GVHD. The development of nonmyeloablative conditioning regimens and the observations on GVHD kinetics and the progression or eradication of leukemia with that strategy are likely to add new insights into how one can optimally combine various modalities to achieve engraftment, prevent GVHD, and at the same time maintain a GVL effect.