Modulation of innate and adaptive immune responses by tofacitinib (CP-690,550)

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.

Tyrphostin AG490 agent modestly but significantly prevents onset of type 1 in NOD mouse; implication of immunologic and metabolic effects of a Jak-Stat pathway inhibitor

Previously, we have reported that the Jak-Stat signaling pathway is defective in NOD mice. In this study, prediabetic female NOD mice (4 weeks) were treated by intraperitoneal injection either with AG490 or DMSO three times per week for 4 consecutive weeks, followed by once a week for an additional 6 weeks. The onset of diabetes was attenuated in NOD mice treated with AG490 relative to DMSO treated control mice (p < 0.02). From an immunological standpoint, AG490 induced the expression of Foxp3 in CD4(+)CD25(-) T-cells and down-regulated expression of co-stimulatory molecules in dendritic cells (DC) both in vitro and in vivo. AG490 treated CD4+CD25- T-cells and DC in vitro, acquired regulatory functions; namely, the ability to suppress proliferation of a responding cell population in vitro. AG490 treatment resulted in significant reduction of blood glucose values and increased expression of PPARγ in splenocytes and markedly increased expression PPARγ2 but not PPARγ1 in adipocyte in vitro. Presence of multiple Stat5 DNA binding consensus sequences within the promoter region of the PPARγ gene in human and in mouse suggests that PPARγ is downstream to the Jak-Stat signaling pathway. This study highlights a critical role of the Jak-Stat signaling pathway in the pathogenesis of T1D and suggests that blocking the Jak-Stat signaling pathway by AG490 as a tyrosine kinase inhibitor may provide an effective means for preventing autoimmune T1D via both immunological and metabolic effects.

JAK inhibition for the treatment of rheumatoid arthritis: a new era in oral DMARD therapy

INTRODUCTION

In rheumatoid arthritis (RA) there is a significant medical need for safe and effective oral disease-modifying anti-rheumatic drugs (DMARDs) for patients who respond inadequately to methotrexate, the first-line therapy in RA. Oral agents targeting Janus-associated kinases (JAKs) are the most promising new agents in clinical development. This review describes the preclinical and clinical activities of the most advanced JAK inhibitors with different JAK selectivity profiles.

AREAS COVERED

This review first describes the current treatment landscape and the pathophysiology of RA. Role for cytokines in the disease pathogenesis followed by significance of JAK/STAT pathway in cytokine signaling are discussed. Available chemical description and enzymatic data on the most advanced JAK inhibitors in clinical development are provided. Preclinical and clinical results that are publicly available are summarized. Review of literature was conducted using National Library of Medicine (NLM) database, 'PubMed'. In addition, all publicly disclosed data from companies that are developing the JAK inhibitors was researched to obtain the most up-to-date information of the compounds discussed in this report.

EXPERT OPINION

Emerging clinical results demonstrate that JAK inhibition is a validated new mechanism for the development of oral DMARD agents that is likely to join the armamentarium against RA in the near future.

Minimum significant ratio of selectivity ratios (MSRSR) and confidence in ratio of selectivity ratios (CRSR): quantitative measures for selectivity ratios obtained by screening assays

Development of inhibitor compounds selective against undesirable targets is critical in drug discovery. Selectivity ratios for candidate compounds are evaluated by dividing potencies from two assays assessing the off-target and target. Because all potency measurements have underlying uncertainty, understanding error propagation is essential to interpreting selectivity data. Assay noise introduces ambiguity in the statistical significance of selectivity ratios, particularly at low replicate numbers when compounds are often prioritized for subsequent testing. The ability to differentiate potency results for any pair of compounds in one assay is evaluated using a metric called minimum significant ratio (MSR). Potency results of one compound tested in a pair of assays can be differentiated by the minimum significant selectivity ratio (MSSR). To differentiate selectivity ratios for any pair of compounds, we extend this concept by proposing two new parameters called the minimum significant ratio of selectivity ratios (MSRSR) and confidence in ratio of selectivity ratios (CRSR). Importantly, these tools can be used after a single selectivity measurement. We describe these methods and illustrate their usefulness using structure-activity relationship data from a Janus kinase inhibitor project, in which these tools informed a cogent retesting strategy and enabled rapid and objective decision making.

Inflammation and bone destruction in arthritis: synergistic activity of immune and mesenchymal cells in joints

Rheumatoid arthritis (RA) is an immune-mediated disease of the joints that is characterized by chronic inflammation and synovial hyperplasia that eventually lead to cartilage and bone destruction. Synovial fibroblasts are mesenchymal cells recognized as a key cell population in RA due to their hyperproliferative and hypersensitive properties in the inflammatory milieu and hyperproduction of both inflammatory cytokines and matrix-degrading enzymes. On the immune cell side, a wealth of evidence has shown that CD4⁺T-cells, especially IL-17 producing helper T (Th17) cells, play a prominent role, particularly in the initiation of systemic immune response in RA. However, it is still unclear how the local chronic inflammation in the joint is elicited by a systemic immune response. Recent studies have shed light on the importance of the interaction between immune and mesenchymal cells in joints including synovial fibroblasts. In particular, mesenchymal cells contribute to the Th17-mediated chronic inflammation in RA by promoting the migration of Th17 cells to the inflamed site and then the homeostatic proliferation and concomitant increase in IL-17 production. In addition, recent progress in osteoimmunology has provided new insight into the pathogenesis of the bone destruction which takes place in RA. Th17-related cytokines have been shown to enhance osteoclastogenesis, mainly via synovial fibroblasts. Thus, mesenchymal cells are a determinant of the development of RA that links the systemic immune response and the local disorder in the joints. In addition, the interaction of immune and mesenchymal cells plays a key role in both the chronic inflammation and bone destruction seen in RA. Elucidation of the precise events involved in this interaction will lead to a better understanding of the mechanisms by which chronic inflammation and bone destruction in joint results from a systemic immune response, and also will help provide a molecular basis for novel therapeutic strategies to treat RA.

Risk of tuberculosis reactivation with tofacitinib (CP-690550)

Individuals with latent tuberculosis infection (LTBI) live with a risk of reactivation, and several treatments for chronic inflammatory conditions are highly associated with such reactivation. A new Janus kinase inhibitor, tofacitinib (CP-690550), has shown promising results for treatment of inflammatory disorders, thus raising concerns of risk of active tuberculosis. Our goal was to characterize the impact of tofacitinib on LTBI using a mouse model of contained tuberculosis. Our data indicate that tofacitinib reduces host containment of Mycobacterium tuberculosis and promotes bacterial replication in the lungs, suggesting tuberculosis reactivation. Tofacitinib may carry a significant risk for LTBI reactivation in humans.

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.

Current landscape for T-cell targeting in autoimmunity and transplantation

In recent years, substantial advances in T-cell immunosuppressive strategies and their translation to routine clinical practice have revolutionized management and outcomes in autoimmune disease and solid organ transplantation. More than 80 diseases have been considered to have an autoimmune etiology, such that autoimmune-associated morbidity and mortality rank as third highest in developed countries, after cardiovascular diseases and cancer. Solid organ transplantation has become the therapy of choice for many end-stage organ diseases. Short-term outcomes such as patient and allograft survival at 1 year, acute rejection rates, as well as time course of disease progression and symptom control have steadily improved. However, despite the use of newer immunosuppressive drug combinations, improvements in long-term allograft survival and complete resolution of autoimmunity remain elusive. In addition, the chronic use of nonspecifically targeted immunosuppressive drugs is associated with significant adverse effects and increased morbidity and mortality. In this article, we discuss the current clinical tools for immune suppression and attempts to induce long-term T-cell tolerance induction as well as much-needed future approaches to produce more short-acting, antigen-specific agents, which may optimize outcomes in the clinic.

Treatment of systemic lupus erythematosus: new advances in targeted therapy

Treatment for systemic lupus erythematosus (SLE) has traditionally been restricted to broad-based immunosuppression, with glucocorticoids being central to care. Recent insights into lupus pathogenesis promise new, selective therapies with more favorable side effect profiles. The best example of this is belimumab, which targets the B cell cytokine BLyS and has now received Food and Drug Administration (FDA) approval for its use in SLE. Strategies targeting other cytokines, such as interleukin 6 (IL-6) and interferon (IFN)-α, are also on the horizon. Blockade of costimulatory interactions between immune cells offers another opportunity for therapeutic intervention, as do small molecule inhibitors that interfere with cell signaling pathways. We review here the current strategies for SLE treatment, with particular focus on therapies now in active pharmaceutical development. We will also discuss new understandings in lupus pathogenesis that may lead to future advances in therapy.

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.

Low dose CP-690,550 (tofacitinib), a pan-JAK inhibitor, accelerates the onset of experimental autoimmune encephalomyelitis by potentiating Th17 differentiation

Th17 cells, which have been implicated in autoimmune diseases, require STAT3 signaling activated by IL-6 or IL-23 for their development. Other Th1 and Th2 cytokines such as IL-2, IFN-γ and IL-4 strongly suppress Th17 development. Recently, CP-690,550 (tofacitinib), originally developed as a JAK3 inhibitor, has been shown to be effective in phase III clinical trials of rheumatoid arthritis and collagen-induced arthritis (CIA) models, but the precise mechanism of the effect, especially with respect to Th17 cells, is poorly understood. To our surprise, a low dose CP-690,550 was found to accelerate the onset of experimental autoimmune encephalomyelitis (EAE) at a concentration that suppressed CIA. At an early stage after immunization, more IL-17 production was observed in 15mg/kg body weight CP-690,550-treated mice than in untreated mice. In vitro, CP-690,550 inhibited both Th1 and Th2 development, while promoting Th17 differentiation at 10-50nM concentrations. Enhancement of Th17 by CP-690,550 is probably due to suppression of IL-2 signaling, because anti-IL-2 antibodies cancel the Th17-promoting effect of CP-690,550. CP-690,550 selectively inhibited IFN--induced STAT1, IL-4-induced STAT6 and IL-2-induced STAT5 at 3-30nM, while suppression of IL-6-induced STAT3 phosphorylation required a concentration greater than 100nM. In HEK293T cells, CP-690,550 less effectively suppressed JAK1-mediated STAT3 phosphorylation compared with JAK3. These results suggest that CP-690,550 has a different effects among JAKs and STATs, thereby affecting helper T cell differentiation, and murine autoimmune disease models.

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.

Characterization of BMS-911543, a functionally selective small-molecule inhibitor of JAK2

We report the characterization of BMS-911543, a potent and selective small-molecule inhibitor of the Janus kinase (JAK) family member, JAK2. Functionally, BMS-911543 displayed potent anti-proliferative and pharmacodynamic (PD) effects in cell lines dependent upon JAK2 signaling, and had little activity in cell types dependent upon other pathways, such as JAK1 and JAK3. BMS-911543 also displayed anti-proliferative responses in colony growth assays using primary progenitor cells isolated from patients with JAK2(V617F)-positive myeloproliferative neoplasms (MPNs). Similar to these in vitro observations, BMS-911543 was also highly active in in vivo models of JAK2 signaling, with sustained pathway suppression being observed after a single oral dose. At low dose levels active in JAK2-dependent PD models, no effects were observed in an in vivo model of immunosuppression monitoring antigen-induced IgG and IgM production. Expression profiling of JAK2(V617F)-expressing cells treated with diverse JAK2 inhibitors revealed a shared set of transcriptional changes underlying pharmacological effects of JAK2 inhibition, including many STAT1-regulated genes and STAT1 itself. Collectively, our results highlight BMS-911543 as a functionally selective JAK2 inhibitor and support the therapeutic rationale for its further characterization in patients with MPN or in other disorders characterized by constitutively active JAK2 signaling.

IL-1β and TNFα-initiated IL-6-STAT3 pathway is critical in mediating inflammatory cytokines and RANKL expression in inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease that causes irreversible joint damage and significant disability. However, the fundamental mechanisms underlying how inflammation and joint destruction in RA develop and are sustained chronically remain largely unknown. Here, we show that signal transducer and activator of transcription 3 (STAT3) is the key mediator of both chronic inflammation and joint destruction in RA. We found that inflammatory cytokines highly expressed in RA patients, such as IL-1β, tumor necrosis factor alpha and IL-6, activated STAT3 either directly or indirectly and in turn induced expression of IL-6 family cytokines, further activating STAT3 in murine osteoblastic and fibroblastic cells. STAT3 activation also induced expression of receptor activator of nuclear factor kappa B ligand (RANKL), a cytokine essential for osteoclastogenesis, and STAT3 deficiency or pharmacological inhibition promoted significant reduction in expression of both IL-6 family cytokines and RANKL in vitro. STAT3 inhibition was also effective in treating an RA model, collagen-induced arthritis, in vivo through significant reduction in expression of IL-6 family cytokines and RANKL, inhibiting both inflammation and joint destruction. Leukemia inhibitory factor expression and STAT3 activation by IL-1β were mainly promoted by IL-6 but still induced in IL-6-deficient cells. Thus, our data provide new insight into RA pathogenesis and provide evidence that inflammatory cytokines trigger a cytokine amplification loop via IL-6-STAT3 that promotes sustained inflammation and joint destruction.