Effects of JAK3 Inhibition with CP-690,550 on Immune Cell Populations and Their Functions in Nonhuman Primate Recipients of Kidney Allografts

JAK Inhibitors in Solid Organ Transplantation

Janus kinase (JAK) inhibitors are a novel group of immunosuppressive drugs approved to treat certain rheumatic and allergic disorders; however, their efficacy in the regulation of alloimmune responses after solid organ transplantation has not yet been elucidated. In the present review, we have summarized the results of in vitro, in vivo, experimental, and clinical trial studies about the efficacy and safety of JAK inhibitors in improving allograft survival in solid organ transplantations, including kidney, heart, lung, and liver transplants. Moreover, reports on administering JAK inhibitors to steroid-resistant patients with graft versus host disease (GvHD) after solid organ transplantation have been reviewed. Overall findings are suggestive of a beneficial role for JAK inhibitors in organ transplantation: for example, they have been shown to improve allograft function, reduce the rate and score of acute rejection, downregulate the expression of proinflammatory cytokines and adhesion molecules, and decrease oxidative stress. However, the adverse effects of these drugs, in particular bone marrow suppression and infection, remain an obstacle.

Tofacitinib-induced Ramsay- Hunt Syndrome in a Patient with Rheumatoid Arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by joint and systemic involvement. Tofacitinib is a JAK- inhibitor that is an effective agent in the treatment of active RA. Varicella zoster virus(VZV) reactivation is among the most important adverse effects of tofacitinib. Ramsay-Hunt syndrome(RHS) is a rare clinical condition that develops as a result of VZV reactivation and progresses with hearing loss, dizziness, and facial nerve paralysis.

OBJECTIVE

To present a case of Ramsay-Hunt syndrome due to varicella zoster reactivation in a RA patient using tofacitinib.

CASE REPORT

A 63-year-old female RA patient under tofacitinib treatment was admitted to the rheumatology outpatient clinic due to widespread skin rashes on her face and ear, and hearing loss. On inspection widespread erythematous, vesicular rashes on the left side of the face, lips, around the eye and in the ear, and mild facial paralysis on the left side were detected. On laboratory investigations, acute phase reactants were increased. Serological study for specific antibodies against varicella zoster virus showed higher titers. Dermatology and ear nose throat specialist consultations were performed, and varicella zoster lesions on the left inner ear, face, and mild facial paresis were considered. According to clinical and laboratory findings, the patient was diagnosed with RHS triggered by tofacitinib. Tofacitinib and methotrexate were discontinued, and intravenous acyclovir was started. On the control examination, the patient's skin lesions and facial nerve paralysis regressed.

CONCLUSION

Herein, we reported the fırst case of tofacitinib-induced RHS in a patient with RA. This may be another side effect of biologic treatment. New studies are needed on this subject.

Molecular Structure and Function of Janus Kinases: Implications for the Development of Inhibitors

Cytokines can trigger multiple signalling pathways, including Janus tyrosine kinases [JAK] and signal transducers and activators of transcription [STATS] pathways. JAKs are cytoplasmic proteins that, following the binding of cytokines to their receptors, transduce the signal by phosphorylating STAT proteins which enter the nuclei and rapidly target gene promoters to regulate gene transcription. Due to the critical involvement of JAK proteins in mediating innate and adaptive immune responses, these family of kinases have become desirable pharmacological targets in inflammatory diseases, including ulcerative colitis and Crohn's disease. In this review we provide an overview of the main cytokines that signal through the JAK/STAT pathway and the available in vivo evidence on mutant or deleted JAK proteins, and discuss the implications of pharmacologically targeting this kinase family in the context of inflammatory diseases.

Pharmacophore modeling and 3D-QSAR studies of 2,4-disubstituted pyrimidine derivatives as Janus kinase 3 inhibitors

A robust pharmacophore model was developed and the structure-activity relationship was analyzed using 71 pyrimidine derivatives reported for covalent Janus Kinase 3 (JAK3) inhibition. Pharmacophore modeling developed a five featured pharmacophore: one H-bond acceptor, two H-bond donors, one hydrophobic, and one aromatic ring features. The atom-based three-dimensional QSAR models with statistical significance were generated using the training set of 52 compounds. The excellent predictive correlation coefficients were obtained for 3D models determined using a test set of 19 molecules. The generated QSAR model implies that the hydrophobic character is important for the JAK3 inhibitory activity of these compounds. Additionally, electron-withdrawing and hydrogen bond donor groups at specific positions positively contribute to the JAK3 inhibition potency. These results provided essential three-dimensional structural requirements and the crucial binding features of 2,4-disubstituted pyrimidine derivatives, which may direct for the design and discovery of novel potent JAK3 inhibitors.

Tofacitinib Halts Progression of Graft Dysfunction in a Rat Model of Mixed Cellular and Humoral Rejection

BACKGROUND

The progression from acute to chronic antibody-mediated rejection in kidney transplant recipients is usually not prevented by current therapeutic options. Here, we investigated whether the use of tofacitinib (TOFA), a Janus kinase 3 inhibitor, was capable of preventing the progression of allograft dysfunction in a Fisher-to-Lewis rat model of kidney transplantation.

METHODS

Rats were treated from the third week after transplantation to allow the development of rejection. Treatment was based on cyclosporin A, rapamycin or TOFA. Renal function was assessed at 1, 4, 8, and 12 weeks after transplantation, whereas rat survival, histological lesions, and infiltrating lymphocytes were analyzed at 12 weeks.

RESULTS

Tofacitinib prolonged graft survival, preserved tubular and glomerular structures and reduced humoral damage characterized by C4d deposition. Tofacitinib was able to reduce donor-specific antibodies. In addition, T and natural killer cell graft infiltration was reduced in TOFA-treated rats. Although rapamycin-treated rats also showed prolonged graft survival, glomerular structures were more affected. Moreover, only TOFA treatment reduced the presence of T, B and natural killer cells in splenic parenchyma.

CONCLUSIONS

Tofacitinib is able to reduce the immune response generated in a rat model of kidney graft rejection, providing prolonged graft and recipient survival, better graft function, and less histological lesions.

The use of tofacitinib in the treatment of inflammatory bowel disease

Janus kinases (JAK) play a major role in the immunologic pathways and specifically in signal transduction in inflammatory bowel disease. Thus, they can serve as a target for new therapeutic options. Tofacitinib is a novel, first-in-class, pan-Janus kinase inhibitor. It has been found to be effective and safe in the treatment of moderate-to-severe ulcerative colitis. In this review, we will describe the drug's mechanism of action as well as the clinical evidence for its effectiveness in treating patients with inflammatory bowel disease.

Immunologic effects of chronic administration of tofacitinib, a Janus kinase inhibitor, in cynomolgus monkeys and rats - Comparison of juvenile and adult responses

Tofacitinib, an oral Janus kinase (JAK) inhibitor for treatment of rheumatoid arthritis, targets JAK1, JAK3, and to a lesser extent JAK2 and TYK2. JAK1/3 inhibition impairs gamma common chain cytokine receptor signaling, important in lymphocyte development, homeostasis and function. Adult and juvenile cynomolgus monkey and rat studies were conducted and the impact of tofacitinib on immune parameters (lymphoid tissues and lymphocyte subsets) and function (T-dependent antibody response (TDAR), mitogen-induced T cell proliferation) assessed. Tofacitinib administration decreased circulating T cells and NK cells in juvenile and adult animals of both species. B cell decreases were observed only in rats. These changes and decreased lymphoid tissue cellularity are consistent with the expected pharmacology of tofacitinib. No differences were observed between juvenile and adult animals, either in terms of doses at which effects were observed or differential effects on immune endpoints. Lymphomas were observed in three adult monkeys. Tofacitinib impaired the primary TDAR in juvenile monkeys, although a recall response was generated. Complete or partial reversal of the effects on the immune system was observed.

Efficacy and safety at 24 weeks of daily clinical use of tofacitinib in patients with rheumatoid arthritis

Objective

We evaluated the efficacy and safety of tofacitinib in patients with rheumatoid arthritis (RA) in a real-world setting.

Methods

Seventy consecutive patients, for whom tofacitinib was initiated between November 2013 and May 2016, were enrolled. All patients fulfilled the 2010 ACR/EULAR classification criteria for RA. All patients received 5 mg of tofacitinib twice daily and were followed for 24 weeks. Clinical disease activity indicated by disease activity score (DAS)28-ESR, the simplified disease activity index, and the clinical disease activity index as well as adverse events (AEs) were evaluated. Statistical analysis was performed to determine which baseline variables influenced the efficacy of tofacitinib at 24 weeks.

Results

Fifty-eight patients (82.9%) continued tofacitinib at 24 weeks. Clinical disease activity rapidly and significantly decreased, and this efficacy continued throughout the 24 weeks: i.e., DAS28-ESR decreased from 5.04 ± 1.33 at baseline to 3.83 ± 1.11 at 4 weeks and 3.53 ± 1.17 at 24 weeks (P<0.0001, vs. baseline). 15 AEs including 5 herpes zoster infection occurred during tofacitinib treatment. The efficacy of tofacitinib was not changed in patients without concomitant use of methotrexate (MTX) or patients whose treatment with tocilizumab (TCZ) failed. Multivariable logistic analysis showed that the number of biologic DMARDs (bDMARDs) previously used was independently associated with achievement of DAS-low disease activity.

Conclusions

Our present study suggests that tofacitinib is effective in real-world settings even without concomitant MTX use or after switching from TCZ. Our results also suggest that its efficacy diminishes if started after use of multiple bDMARDs.

The use of kinase inhibitors in solid organ transplantation

INTRODUCTION

Despite the efficacy of current immunosuppression regimes used in solid organ transplantation, graft dysfunction, graft lost and antibody-mediated rejection continue to be problematic. As a result, clear attraction in exploiting key potential targets controlled by kinase phosphorylation has led to a number of studies exploring the use of these drugs in transplantation. Aim In this review, we consider the role of tyrosine kinase as a target in transplantation and summarize the relevant studies on kinase inhibitors that have been reported to date.

METHODS

Narrative review of literature from inception to December 2016, using OVID interface searching EMBASE and MEDLINE databases. All studies related to kinase based immunosuppression were examined for clinical relevance with no exclusion criteria. Key ideas were extracted and referenced.

CONCLUSION

The higher incidence of infections when using kinase inhibitors is an important consideration, however the number and range inhibitors and their clinical indications are likely to expand, but their exact role in transplantation is yet to be determined.

A novel JAK inhibitor, peficitinib, demonstrates potent efficacy in a rat adjuvant-induced arthritis model

The Janus kinase (JAK) family of tyrosine kinases is associated with various cytokine receptors. JAK1 and JAK3 play particularly important roles in the immune response, and their inhibition is expected to provide targeted immune modulation. Several oral JAK inhibitors have recently been developed for treating autoimmune diseases, including rheumatoid arthritis (RA). Here, we investigated the pharmacological effects of peficitinib (formerly known as ASP015K), a novel, chemically synthesized JAK inhibitor. We found that peficitinib inhibited JAK1 and JAK3 with 50% inhibitory concentrations of 3.9 and 0.7 nM, respectively. Peficitinib also inhibited IL-2-dependent T cell proliferation in vitro and STAT5 phosphorylation in vitro and ex vivo. Furthermore, peficitinib dose-dependently suppressed bone destruction and paw swelling in an adjuvant-induced arthritis model in rats via prophylactic or therapeutic oral dosing regimens. Peficitinib also showed efficacy in the model by continuous intraperitoneal infusion. Area under the concentration versus time curve (AUC) at 50% inhibition of paw swelling via intraperitoneal infusion was similar to exposure levels of AUC at 50% inhibition via oral administration, implying that AUC might be important for determining the therapeutic efficacy of peficitinib. These data suggest that peficitinib has therapeutic potential for the oral treatment of RA.

EZH2 phosphorylation by JAK3 mediates a switch to noncanonical function in natural killer/T-cell lymphoma

The best-understood mechanism by which EZH2 exerts its oncogenic function is through polycomb repressive complex 2 (PRC2)-mediated gene repression, which requires its histone methyltransferase activity. However, small-molecule inhibitors of EZH2 that selectively target its enzymatic activity turn out to be potent only for lymphoma cells with EZH2-activating mutation. Intriguingly, recent discoveries, including ours, have placed EZH2 into the category of transcriptional coactivators and thus raised the possibility of noncanonical signaling pathways. However, it remains unclear how EZH2 switches to this catalytic independent function. In the current study, using natural killer/T-cell lymphoma (NKTL) as a disease model, we found that phosphorylation of EZH2 by JAK3 promotes the dissociation of the PRC2 complex leading to decreased global H3K27me3 levels, while it switches EZH2 to a transcriptional activator, conferring higher proliferative capacity of the affected cells. Gene expression data analysis also suggests that the noncanonical function of EZH2 as a transcriptional activator upregulates a set of genes involved in DNA replication, cell cycle, biosynthesis, stemness, and invasiveness. Consistently, JAK3 inhibitor was able to significantly reduce the growth of NKTL cells, in an EZH2 phosphorylation-dependent manner, whereas various compounds recently developed to inhibit EZH2 methyltransferase activity have no such effect. Thus, pharmacological inhibition of JAK3 activity may provide a promising treatment option for NKTL through the novel mechanism of suppressing noncanonical EZH2 activity.

Tuberculosis and other opportunistic infections in tofacitinib-treated patients with rheumatoid arthritis

OBJECTIVES

To evaluate the risk of opportunistic infections (OIs) in patients with rheumatoid arthritis (RA) treated with tofacitinib.

METHODS

Phase II, III and long-term extension clinical trial data (April 2013 data-cut) from the tofacitinib RA programme were reviewed. OIs defined a priori included mycobacterial and fungal infections, multidermatomal herpes zoster and other viral infections associated with immunosuppression. For OIs, we calculated crude incidence rates (IRs; per 100 patient-years (95% CI)); for tuberculosis (TB) specifically, we calculated rates stratified by patient enrolment region according to background TB IR (per 100 patient-years): low (≤0.01), medium (>0.01 to ≤0.05) and high (>0.05).

RESULTS

We identified 60 OIs among 5671 subjects; all occurred among tofacitinib-treated patients. TB (crude IR 0.21, 95% CI of (0.14 to 0.30)) was the most common OI (n=26); median time between drug start and diagnosis was 64 weeks (range 15-161 weeks). Twenty-one cases (81%) occurred in countries with high background TB IR, and the rate varied with regional background TB IR: low 0.02 (0.003 to 0.15), medium 0.08 (0.03 to 0.21) and high 0.75 (0.49 to 1.15). In Phase III studies, 263 patients diagnosed with latent TB infection were treated with isoniazid and tofacitinib concurrently; none developed TB. For OIs other than TB, 34 events were reported (crude IR 0.25 (95% CI 0.18 to 0.36)).

CONCLUSIONS

Within the global tofacitinib RA development programme, TB was the most common OI reported but was rare in regions of low and medium TB incidence. Patients who screen positive for latent TB can be treated with isoniazid during tofacitinib therapy.

Anti-inflammatory effect of topical administration of tofacitinib on corneal inflammation

We evaluated an anti-inflammatory effect of topical administration of tofacitinib, janus kinase (JAK) blocker, on corneal inflammation. Topical instillation of either tofacitinib or PBS was applied after wounding BALB/c mice corneas with alkali burn. Topical instillation was performed until day 14 after injury and injured eye was analyzed. The vascularized area in the alkali burned cornea was significantly reduced in the tofacitinib group compared with that in the PBS group. The immunoreactivity of Gr-1, F4/80, IFN-γ, and phosphorylated STAT(signal transducer and activator of transcription)1 in corneal stroma was diminished significantly in the tofacitinib group. Using laser capture microdissection system and quantitative PCR array analysis, the expression levels of CXCL9, CXCL5, CCL7, CCL2, MMP(matrix metalloproteinase)-9, and STAT1 in corneal stroma were down-regulated in the tofacitinib group. In in vitro study, human fibroblast pretreated by IFN-γ showed phosphorylation of STAT1, and this phosphorylation was down-regulated by adding tofacitinib to the culture medium. These results indicate the topical application of JAK inhibitor causes down-regulation of JAK- or IFN-γ-related molecules. Therefore, we deduce that application of JAK inhibitor for topical instillation may contribute to the treatment of corneal inflammation.

Role of Memory T Cells and Perspectives for Intervention in Organ Transplantation

Memory T cells are necessary for protective immunity against invading pathogens, especially under conditions of immunosuppression. However, their presence also threatens transplant survival, making transplantation a great challenge. Significant progress has been achieved in recent years in advancing our understanding of the role that memory T cells play in transplantation. This review focuses on the latest advances in our understanding of the involvement of memory T cells in graft rejection and transplant tolerance and discusses potential strategies for targeting memory T cells in order to minimize allograft rejection and optimize clinical outcomes.

Impact of irradiation and immunosuppressive agents on immune system homeostasis in rhesus macaques

In this study we examined the effects of non-myeloablative total body irradiation (TBI) in combination with immunosuppressive chemotherapy on immune homeostasis in rhesus macaques. Our results show that the administration of cyclosporin A or tacrolimus without radiotherapy did not result in lymphopenia. The addition of TBI to the regimen resulted in lymphopenia as well as alterations in the memory/naive ratio following reconstitution of lymphocyte populations. Dendritic cell (DC) numbers in whole blood were largely unaffected, while the monocyte population was altered by immunosuppressive treatment. Irradiation also resulted in increased levels of circulating cytokines and chemokines that correlated with T cell proliferative bursts and with the shift towards memory T cells. We also report that anti-thymocyte globulin (ATG) treatment and CD3 immunotoxin administration resulted in a selective and rapid depletion of naive CD4 and CD8 T cells and increased frequency of memory T cells. We also examined the impact of these treatments on reactivation of latent simian varicella virus (SVV) infection as a model of varicella zoster virus (VZV) infection of humans. None of the treatments resulted in overt SVV reactivation; however, select animals had transient increases in SVV-specific T cell responses following immunosuppression, suggestive of subclinical reactivation. Overall, we provide detailed observations into immune modulation by TBI and chemotherapeutic agents in rhesus macaques, an important research model of human disease.

Herpes zoster and tofacitinib therapy in patients with rheumatoid arthritis

OBJECTIVE

Patients with rheumatoid arthritis (RA) are at increased risk for herpes zoster (HZ) (i.e., shingles). The aim of this study was to determine whether treatment with tofacitinib increases the risk of HZ in patients with RA.

METHODS

HZ cases were identified as those reported by trial investigators from the databases of the phase II, phase III, and long-term extension (LTE) clinical trials in the Tofacitinib RA Development Program. Crude incidence rates (IRs) of HZ per 100 patient-years (with 95% confidence intervals [95% CIs]) were calculated by exposure group. Logistic regression analyses were performed to evaluate potential risk factors for HZ (e.g., age, prednisone use).

RESULTS

Among 4,789 participants, 239 were identified as having tofacitinib-associated HZ during the phase II, phase III, and LTE trials, of whom 208 (87%) were female and whose median age was 57 years (range 21-75 years). One HZ case (0.4%) was multidermatomal; none of the cases involved visceral dissemination or death. Twenty-four patients with HZ (10%) permanently discontinued treatment with tofacitinib, and 16 (7%) were either hospitalized or received intravenous antiviral drugs. The crude HZ IR across the development program was 4.4 per 100 patient-years (95% CI 3.8-4.9), but the IR was substantially higher within Asia (7.7 per 100 patient-years, 95% CI 6.4-9.3). Older age was associated with HZ (odds ratio 1.9, 95% CI 1.5-2.6), and IRs for HZ were similar between patients receiving 5 mg tofacitinib twice daily (4.4 per 100 patient-years, 95% CI 3.2-6.0) and those receiving 10 mg twice daily (4.2 per 100 patient-years, 95% CI 3.1-5.8). In the phase III trials among placebo recipients, the incidence of HZ was 1.5 per 100 patient-years (95% CI 0.5-4.6).

CONCLUSION

In the Tofacitinib RA Development Program, increased rates of HZ were observed in patients treated with tofacitinib compared with those receiving placebo, particularly among patients within Asia. Complicated HZ among tofacitinib-treated patients was rare.

Protein kinase inhibitors in the treatment of inflammatory and autoimmune diseases

Protein kinases mediate protein phosphorylation, which is a fundamental component of cell signalling, with crucial roles in most signal transduction cascades: from controlling cell growth and proliferation to the initiation and regulation of immunological responses. Aberrant kinase activity is implicated in an increasing number of diseases, with more than 400 human diseases now linked either directly or indirectly to protein kinases. Protein kinases are therefore regarded as highly important drug targets, and are the subject of intensive research activity. The success of small molecule kinase inhibitors in the treatment of cancer, coupled with a greater understanding of inflammatory signalling cascades, has led to kinase inhibitors taking centre stage in the pursuit for new anti-inflammatory agents for the treatment of immune-mediated diseases. Herein we discuss the main classes of kinase inhibitors; namely Janus kinase (JAK), mitogen-activated protein kinase (MAPK) and spleen tyrosine kinase (Syk) inhibitors. We provide a mechanistic insight into how these inhibitors interfere with kinase signalling pathways and discuss the clinical successes and failures in the implementation of kinase-directed therapeutics in the context of inflammatory and autoimmune disorders.

In vivo administration of a JAK3 inhibitor during acute SIV infection leads to significant increases in viral load during chronic infection

The studies reported herein are the first to document the effect of the in vivo administration of a JAK3 inhibitor for defining the potential role of NK cells during acute SIV infection of a group of 15 rhesus macaques (RM). An additional group of 16 MHC/KIR typed RM was included as controls. The previously optimized in vivo dose regimen (20 mg/kg daily for 35 days) led to a marked depletion of each of the major NK cell subsets both in the blood and gastro-intestinal tissues (GIT) during acute infection. While such depletion had no detectable effects on plasma viral loads during acute infection, there was a significant sustained increase in plasma viral loads during chronic infection. While the potential mechanisms that lead to such increased plasma viral loads during chronic infection remain unclear, several correlates were documented. Thus, during acute infection, the administration of the JAK3 inhibitor besides depleting all NK cell subsets also decreased some CD8⁺ T cells and inhibited the mobilization of the plasmacytoid dendritic cells in the blood and their localization to the GIT. Of interest is the finding that the administration of the JAK3 inhibitor during acute infection also resulted in the sustained maintenance during chronic infection of a high number of naïve and central memory CD4⁺ T cells, increases in B cells in the blood, but decreases in the frequencies and function of NKG2a⁺ NK cells within the GIT and blood, respectively. These data identify a unique role for JAK3 inhibitor sensitive cells, that includes NK cells during acute infection that in concert lead to high viral loads in SIV infected RM during chronic infection without affecting detectable changes in antiviral humoral/cellular responses. Identifying the precise mechanisms by which JAK3 sensitive cells exert their influence is critical with important implications for vaccine design against lentiviruses.

In efforts to define the potential role of innate immune effector mechanisms in influencing the course of SIV infection during the acute infection period, our lab utilized the in vivo daily administration of 20 mg/kg orally of a compound called Tofacitinib (a Janus kinase 3 inhibitor) to a group of 15 rhesus macaques starting at day −6 and until day 28 post intravenous SIVmac239 infection. An additional group of 16 similarly SIV infected rhesus macaques served as a placebo control. This drug targets the JAK/STAT pathway that is utilized by cells including the NK cell lineage, a major cell of the innate immune system. The dosage utilized was based on extensive previous PK studies that resulted in a marked depletion of the NK cells. Of interest while such drug administration had no effect on plasma viral loads during acute infection, such drug administration led to significant increases in plasma and gastro-intestinal tissues (GIT) viral loads during chronic infection. A series of phenotypic/functional studies were performed to determine the mechanisms for this delayed effect and the correlates identified. These data are the first to document the effect of JAK-3 inhibitor during acute SIV infection with implications for HIV vaccine design.

Tofacitinab in renal transplantation

Tofacitinib (tositinib, CP-690,550) is a small molecule inhibitor of Janus associated kinases, primarily JAK3 and JAK2, which inhibits cytokine signaling through the IL-2Rγ chain. In this article, we review the mechanism of action of tofacitinib, and pre-clinical and clinical data regarding its use in solid organ transplantation thus far. It is hoped that tofacitinib may form the basis for calcineurin-free immunosuppression, improving renal function while eliminating calcineurin inhibitor renal toxicity. Current studies suggest that tofacitinib is an effective immunosuppressive agent for renal transplantation, but it's use in current protocols carries an increased risk of CMV, BK, and EBV viral infection, anemia and leukopenia, and post-transplant lymphoproliferative disorder.

Fate of lymphocytes after withdrawal of tofacitinib treatment

Tofacitinib (Tofa) is an inhibitor of Janus Kinase 3, developed for the treatment of autoimmune diseases and for the prevention of transplant rejection. Due to its selective action on proliferating cells, Tofa can offer a way to block T cell activation, without toxic effects on resting cells. However, few studies have investigated the effects of Tofa on lymphocyte activation in vitro. Our aim was to study the action of Tofa on different lymphocyte subsets after in vitro stimulation and to track the behaviour of treated cells after interruption of the treatment. Peripheral blood lymphocytes were stimulated in vitro with mitogen and treated with two concentrations of Tofa. After a first period in culture, cells were washed and further incubated for an additional time. Lymphocyte subsets, activation phenotype and proliferation were assessed at the different time frames. As expected, Tofa was able to reduce the activation and proliferation of lymphocytes in the first four days of treatment. In addition the drug led to a relative decrease of Natural Killer, B cells and CD8 T cells compared to CD4 T cells. However, treated cells were still viable after the first period in culture and begun to proliferate, strikingly, in a dose dependent manner when the drug was removed from the environment by replacing the culture medium. This novel data does not necessarily predict a similar behaviour in vivo, but can warn about the clinical use of this drug when a discontinuation of treatment with Tofa is considered for any reason.

CP-690550 Treatment Ameliorates Established Disease and Provides Long-Term Therapeutic Effects in an SKG Arthritis Model

Although pathogenesis of human rheumatoid arthritis (RA) remains unclear, arthritogenic T cells and downstream signaling mediators have been shown to play critical roles. An increasing numbers of therapeutic options have been added for the effective control of RA. Nevertheless, there is still a category of patients that fails treatment and suffers from progressive disease. The recently developed immunosuppressant CP-690550, a small molecule JAK kinase inhibitor, has been implicated as an important candidate treatment modality for autoimmune arthritis. In this study, we evaluated the therapeutic effect of CP-690550 on established arthritis using an SKG arthritis model, a pathophysiologically relevant animal model for human RA. CP-690550 treatment revealed remarkable long-term suppressive effects on SKG arthritis when administered to the well-advanced disease (clinical score 3.5~4.0). The treatment effect lasted at least 3 more weeks after cessation of drug infusion, and suppression of disease was correlated with the reduced pro-inflammatory cytokines, including IL-17, IFN-γ, and IL-6 and increased level of immunoregulatory IL-10.

JAK3 inhibition: what potential for the future?

JAK3 inhibition with the CP-690,550 compound has an immunosuppressive potency in murine models, nonhuman primates and humans. This drug blocks STAT5 activation in most T-cell subpopulations but less effectively in T-regulator cells. In low to moderate risk human kidney transplant recipients, combined with mycophenolate mofetil, steroids and an induction with basiliximab, CP-690,550 proved as effective as calcineurin inhibitors with regard to prevention of acute rejection but better than calcineurin inhibitors with regard to preservation of kidney function and histology. However, at the same time, an increased incidence of overimmunosuppression consequences (cytomegalovirus, BK virus and lymphoproliferation) was observed and led to discontinuation of this specific drug development in kidney transplantation.

In vivo administration of a JAK3 inhibitor to chronically siv infected rhesus macaques leads to NK cell depletion associated with transient modest increase in viral loads

Innate immune responses are reasoned to play an important role during both acute and chronic SIV infection and play a deterministic role during the acute stages on the rate of infection and disease progression. NK cells are an integral part of the innate immune system but their role in influencing the course of SIV infection has been a subject of debate. As a means to delineate the effect of NK cells on SIV infection, use was made of a Janus kinase 3 (JAK3) inhibitor that has previously been shown to be effective in the depletion of NK cells in vivo in nonhuman primates (NHP). Extensive safety and in vitro/in vivo PK studies were conducted and an optimal dose that depletes NK cells and NK cell function in vivo identified. Six chronically SIV infected rhesus macaques, 3 with undetectable/low plasma viral loads and 3 with high plasma viral loads were administered a daily oral dose of 10 mg/kg for 35 days. Data obtained showed that, at the dose tested, the major cell lineage affected both in the blood and the GI tissues were the NK cells. Such depletion appeared to be associated with a transient increase in plasma and GI tissue viral loads. Whereas the number of NK cells returned to baseline values in the blood, the GI tissues remained depleted of NK cells for a prolonged period of time. Recent findings show that the JAK3 inhibitor utilized in the studies reported herein has a broader activity than previously reported with dose dependent effects on both JAK2 and JAK1 suggests that it is likely that multiple pathways are affected with the administration of this drug that needs to be taken into account. The findings reported herein are the first studies on the use of a JAK3 inhibitor in lentivirus infected NHP.

The role of JAK-3 in regulating TLR-mediated inflammatory cytokine production in innate immune cells

The role of JAK-3 in TLR-mediated innate immune responses is poorly understood, although the suppressive function of JAK3 inhibition in adaptive immune response has been well studied. In this study, we found that JAK3 inhibition enhanced TLR-mediated immune responses by differentially regulating pro- and anti- inflammatory cytokine production in innate immune cells. Specifically, JAK3 inhibition by pharmacological inhibitors or specific small interfering RNA or JAK3 gene knockout resulted in an increase in TLR-mediated production of proinflammatory cytokines while concurrently decreasing the production of IL-10. Inhibition of JAK3 suppressed phosphorylation of PI3K downstream effectors including Akt, mammalian target of rapamycin complex 1, glycogen synthase kinase 3β (GSK3β), and CREB. Constitutive activation of Akt or inhibition of GSK3β abrogated the capability of JAK3 inhibition to enhance proinflammatory cytokines and suppress IL-10 production. In contrast, inhibition of PI3K enhanced this regulatory ability of JAK3 in LPS-stimulated monocytes. At the transcriptional level, JAK3 knockout lead to the increased phosphorylation of STATs that could be attenuated by neutralization of de novo inflammatory cytokines. JAK3 inhibition exhibited a GSK3 activity-dependent ability to enhance phosphorylation levels and DNA binding of NF-κB p65. Moreover, JAK3 inhibition correlated with an increased CD4(+) T cell response. Additionally, higher neutrophil infiltration, IL-17 expression, and intestinal epithelium erosion were observed in JAK3 knockout mice. These findings demonstrate the negative regulatory function of JAK3 and elucidate the signaling pathway by which JAK3 differentially regulates TLR-mediated inflammatory cytokine production in innate immune cells.

Targeting kinases: a new approach to treating inflammatory rheumatic diseases

After two decades of research and development activity focussed on orally active kinase inhibitors, the first such drug (the JAK inhibitor Xeljanz, tofacitinib) was approved by the FDA in November 2012 for the treatment of rheumatoid arthritis (RA). There is an intense activity in many companies both on expanding the utility of JAK inhibitors in other auto-immune indications and in discovering inhibitors of the JAK family with different and more selective profiles. Progress is also being made with orally active Syk inhibitors. One such inhibitor (fostamatinib) is currently in large-scale phase 3 trials, and there are others in clinical development. The last two to three years have been transformative for kinase inhibitors in auto-immune diseases, as several inhibitors have finally progressed beyond phase 2 trials after so many failures on other targets. Thus, there are new treatment options for RA patients beyond existing oral DMARDs and parenteral biologics.

Back to the future: oral targeted therapy for RA and other autoimmune diseases

The molecular biology revolution coupled with the development of monoclonal antibody technology enabled remarkable progress in rheumatology therapy, comprising an array of highly effective biologic agents. With advances in understanding of the molecular nature of immune cell receptors came elucidation of intracellular signalling pathways downstream of these receptors. These discoveries raise the question of whether selective targeting of key intracellular factors with small molecules would add to the rheumatologic armamentarium. In this Review, we discuss several examples of this therapeutic strategy that seem to be successful, and consider their implications for the future of immune-targeted treatments. We focus on kinase inhibitors, primarily those targeting Janus kinase family members and spleen tyrosine kinase, given their advanced status in clinical development and application. We also summarize other targets involved in signalling pathways that might offer promise for therapeutic intervention in the future.

JAK inhibitor tofacitinib for treating rheumatoid arthritis: from basic to clinical

Rheumatoid arthritis (RA) is a representative autoimmune disease characterized by chronic and destructive inflammatory synovitis. The multiple cytokines play pivotal roles in RA pathogenesis by inducing intracellular signaling, and members of the Janus kinase (JAK) family are essential for such signal transduction. An orally available JAK3 inhibitor, tofacitinib, has been applied for RA, with satisfactory effects and acceptable safety in multiple clinical examinations. From phase 2 dose-finding studies, tofacitinib 5 mg and 10 mg twice a day appear suitable for further evaluation. Subsequently, multiple phase 3 studies were carried out, and tofacitinib with or without methotrexate (MTX) is efficacious and has a manageable safety profile in active RA patients who are MTX naïve or show inadequate response to methotrexate (MTX-IR), disease-modifying antirheumatic drugs (DMARD)-IR, or tumor necrosis factor (TNF)-inhibitor-IR. The common adverse events were infections, such as nasopharyngitis; increases in cholesterol, transaminase, and creatinine; and decreases in neutrophil counts. Although the mode of action of tofacitinib remains unclear, we clarified that the inhibitory effects of tofacitinib could be mediated through suppression of interleukin (IL)-17 and interferon (IFN)-γ production and proliferation of CD4(+) T cells in the inflamed synovium. Taken together, an orally available kinase inhibitor tofacitinib targeting JAK-mediated signals would be expected to be a new option for RA treatment.

Regulation of inflammatory responses in tumor necrosis factor-activated and rheumatoid arthritis synovial macrophages by JAK inhibitors

OBJECTIVE

JAK inhibitors have been developed as antiinflammatory and immunosuppressive agents and are currently undergoing testing in clinical trials. The JAK inhibitors CP-690,550 (tofacitinib) and INCB018424 (ruxolitinib) have demonstrated clinical efficacy in rheumatoid arthritis (RA). However, the mechanisms that mediate the beneficial actions of these compounds are not known. The purpose of this study was to examine the effects of both JAK inhibitors on inflammatory and tumor necrosis factor (TNF) responses in human macrophages.

METHODS

In vitro studies were performed using peripheral blood macrophages derived from healthy donors and treated with TNF and using synovial fluid macrophages derived from patients with RA. Levels of activated STAT proteins and other transcription factors were detected by Western blotting, and gene expression was measured by real-time polymerase chain reaction analysis. The in vivo effects of JAK inhibitors were evaluated in the K/BxN serum-transfer model of arthritis.

RESULTS

JAK inhibitors suppressed the activation and expression of STAT-1 and downstream inflammatory target genes in TNF-stimulated and RA synovial macrophages. In addition, JAK inhibitors decreased nuclear localization of NF-κB subunits in TNF-stimulated and RA synovial macrophages. CP-690,550 significantly decreased the expression of interleukin-6 in synovial macrophages. JAK inhibitors augmented nuclear levels of NF-ATc1 and cJun, followed by increased formation of osteoclast-like cells. CP-690,550 strongly suppressed K/BxN serum-transfer arthritis, which is dependent on macrophages, but not lymphocytes.

CONCLUSION

Our findings demonstrate that JAK inhibitors suppress macrophage activation and attenuate TNF responses and further suggest that suppression of cytokine/chemokine production and innate immunity contribute to the therapeutic efficacy of JAK inhibitors.

JAK Kinases in Health and Disease: An Update

Janus kinases (Jaks) are critical signaling elements for a large subset of cytokines. As a consequence they play pivotal roles in the patho-physiology of many diseases including neoplastic and autoimmune diseases. Small molecule Jak inhibitors as therapeutic agents have become a reality and the palette of such inhibitors will likely expand. This review will summarize our current knowledge on these key enzymes and their associated pharmaceutical inhibitors.

Jakinibs: a new class of kinase inhibitors in cancer and autoimmune disease

Cytokines are critical for normal cell growth and immunoregulation but also contribute to growth of malignant cells and drive immune-mediated disease. A large subset of immunoregulatory cytokines uses the type I and type II cytokine receptors and pharmacological targeting of these cytokines/cytokines receptors has proven to be efficacious in treating immune and inflammatory diseases. These receptors rely on Janus family of kinases (Jaks) for signal transduction. Recently the first Jak inhibitor (jakinib) has been approved by the FDA and a second has been recommended for approval. Many other Jakinibs are likely to follow and in this brief review, we will discuss the state-of-the art of this new class of pharmacological agents.

JAK and STAT signaling molecules in immunoregulation and immune-mediated disease

The discovery of the Janus kinase (JAK)-signal transducer and activator of transcripton (STAT) signaling pathway, a landmark in cell biology, provided a simple mechanism for gene regulation that dramatically advanced our understanding of the action of hormones, interferons, colony-stimulating factors, and interleukins. As we learn more about the complexities of immune responses, new insights into the functions of this pathway continue to be revealed, aided by technology that permits genome-wide views. As we celebrate the 20(th) anniversary of the discovery of this paradigm in cell signaling, it is particularly edifying to see how this knowledge has rapidly been translated to human immune disease. Not only have genome-wide association studies demonstrated that this pathway is highly relevant to human autoimmunity, but targeting JAKs is now a reality in immune-mediated disease.

Kinase inhibitors in the treatment of immune-mediated disease

Protein kinases are fundamental components of diverse signaling pathways, including immune cells. Their essential functions have made them effective therapeutic targets. Initially, the expectation was that a high degree of selectivity would be critical; however, with time, the use of "multikinase" inhibitors has expanded. Moreover, the spectrum of diseases in which kinase inhibitors are used has also expanded to include not only malignancies but also immune-mediated diseases. At present, thirteen kinase inhibitors have been approved in the United States, all for oncologic indications. However, there are a growing number of molecules, including several Janus kinase inhibitors, that are being tested in clinical trials for autoimmune diseases such as rheumatoid arthritis, psoriasis and inflammatory bowel diseases. It appears likely that this new class of immunomodulatory drugs will have a major impact on the treatment of immune-mediated diseases in the near future.

Janus kinase 3: the controller and the controlled

Janus kinase (JAK)-signal transducer and activators of transcription (STAT) signaling pathways play crucial roles in lymphopoiesis. In particular, JAK3 has unique functions in the lymphoid system such that JAK3 ablation results in phenotypes resembling severe combined immunodeficiency syndrome. This review focuses on the biochemistry, immunological functions, and clinical significance of JAK3. Compared with other members of the JAK family, the biochemical properties of JAK3 are relatively less well characterized and thus largely inferred from studies of JAK2. Furthermore, new findings concerning the cross-talks between Notch and JAK signaling pathways through ubiquitin-mediated protein degradation are discussed in more detail.

Phosphospecific flow cytometry for pharmacodynamic drug monitoring: analysis of the JAK-STAT signaling pathway

Cytokines of the IL-2 receptor family act via activation of the JAK-STAT (janus tyrosine kinase-signal transducer and activator of transcription) signaling pathway. These cytokines are pivotal for the development and function of lymphocyte subsets involved in the immune response after organ transplantation including T, B and natural killer cells. The new small drug molecule and JAK1/3 inhibitor, tofacitinib, is currently being tested in phase II and III clinical trials for rheumatoid arthritis, psoriasis and in organ transplantation. This agent specifically targets the JAK-STAT signaling pathway. Here we discuss phosphospecific flow cytometry as a novel tool to monitor the JAK-STAT signaling pathway in kidney transplant patients and speculate that through the use of this pharmacodynamic tool the efficacy of immunosuppressive drugs can be assessed enabling optimization of the immunosuppressive therapy for individual transplant patients.

The JAK inhibitor tofacitinib regulates synovitis through inhibition of interferon-γ and interleukin-17 production by human CD4+ T cells

OBJECTIVE

Tofacitinib (CP-690,550) is a novel JAK inhibitor that is currently in clinical trials for the treatment of rheumatoid arthritis (RA). The aim of this study was to examine the effects of tofacitinib in vitro and in vivo in RA, in order to elucidate the role of JAK in the disease process.

METHODS

CD4+ T cells, CD14+ monocytes, and synovial fibroblasts (SFs) were purified from the synovium and peripheral blood of patients with RA and were evaluated for the effect of tofacitinib on cytokine production and cell proliferation. For in vivo analysis, synovium and cartilage samples obtained from patients with RA were implanted in immunodeficient mice (SCID-HuRAg mice), and tofacitinib was administered via an osmotic minipump.

RESULTS

Tofacitinib treatment of CD4+ T cells originating from synovium and peripheral blood inhibited the production of interleukin-17 (IL-17) and interferon-γ (IFNγ) in a dose-dependent manner, affecting both proliferation and transcription, but had no effect on IL-6 and IL-8 production. Tofacitinib did not affect IL-6 and IL-8 production by RASFs and CD14+ monocytes. However, conditioned medium from CD4+ T cells cultured with tofacitinib inhibited IL-6 production by RASFs and IL-8 production by CD14+ monocytes. Treatment of SCID-HuRAg mice with tofacitinib decreased serum levels of human IL-6 and IL-8 and markedly suppressed invasion of synovial tissue into cartilage.

CONCLUSION

Tofacitinib directly suppressed the production of IL-17 and IFNγ and the proliferation of CD4+ T cells, resulting in inhibition of IL-6 production by RASFs and IL-8 production by CD14+ cells and decreased cartilage destruction. In CD4+ T cells, presumably Th1 and Th17 cells, JAK plays a crucial role in RA synovitis.

Recent advances in immunosuppressive therapy for prevention of renal allograft rejection

PURPOSE OF REVIEW

Current immunosuppressive therapies are highly successful at regulating acute allograft rejection and inducing long-term transplanted kidney survival; however, currently available medications are associated with generalized immune suppression and drug toxicities, including nephrotoxicity. In recent years, advances in immunosuppression that target specific pathways involved in immune activation have been developed.

RECENT FINDINGS

In particular, promising medications are currently under evaluation that target ischemia-reperfusion injury as well as the cellular and humoral branches of the adaptive immune response. Targets of T-cell-mediated activation include antibodies and fusion proteins interfering with LFA-1/ICAM-1, CD2/LFA-3, CD40/CD154, and CD28/B7.1 and B7.2 interactions. Intracellular targets involved in T- and B-cell activation pathways are being evaluated, including protein kinase C inhibitors, Janus-associated kinase (JAK) inhibitors, and proteasome inhibitors. Several new medications demonstrate promise in inhibiting donor-directed humoral immunity by targeting B-cell-activating factor (BAFF) and complement activation pathways.

SUMMARY

The present review evaluates the recent clinical advances in immunosuppressive therapies for kidney transplantation. Publications regarding advances in immunosuppressive therapies over the past year were evaluated in the context of the specific immune pathways involved in allograft rejection.

Identification of a potent Janus kinase 3 inhibitor with high selectivity within the Janus kinase family

We describe a synthetic approach toward the rapid modification of phenyl-indolyl maleimides and the discovery of potent Jak3 inhibitor 1 with high selectivity within the Jak kinase family. We provide a rationale for this unprecedented selectivity based on the X-ray crystal structure of an analogue of 1 bound to the ATP-binding site of Jak3. While equally potent compared to the Pfizer pan Jak inhibitor CP-690,550 (2) in an enzymatic Jak3 assay, compound 1 was found to be 20-fold less potent in cellular assays measuring cytokine-triggered signaling through cytokine receptors containing the common γ chain (γC). Contrary to compound 1, compound 2 inhibited Jak1 in addition to Jak3. Permeability and cellular concentrations of compounds 1 and 2 were similar. As Jak3 always cooperates with Jak1 for signaling, we speculate that specific inhibition of Jak3 is not sufficient to efficiently block γC cytokine signal transduction required for strong immunosuppression.