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Abrocitinib is an oral once-daily Janus kinase 1 selective inhibitor being developed for the treatment of moderate-to-severe atopic dermatitis. This study examined the disposition of abrocitinib in male participants following oral and intravenous administration using accelerator mass spectroscopy methodology to estimate pharmacokinetic parameters and characterize metabolite (M) profiles. The results indicated abrocitinib had a systemic clearance of 64.2 L/h, a steady-state volume of distribution of 100 L, extent of absorption90%, time to maximum plasma concentration of ∼0.5 hours, and absolute oral bioavailability of 60%. The half-life of both abrocitinib and total radioactivity was similar, with no indication of metabolite accumulation. Abrocitinib was the main circulating drug species in plasma (∼26%), with 3 major monohydroxylated metabolites (M1, M2, and M4) at10%. Oxidative metabolism was the primary route of elimination for abrocitinib, with the greatest disposition of radioactivity shown in the urine (∼85%). In vitro phenotyping indicated abrocitinib cytochrome P450 fraction of metabolism assignments of 0.53 for CYP2C19, 0.30 for CYP2C9, 0.11 for CYP3A4, and ∼0.06 for CYP2B6. The principal systemic metabolites M1, M2, and M4 were primarily cleared renally. Abrocitinib, M1, and M2 showed pharmacology with similar Janus kinase 1 selectivity, whereas M4 was inactive. SIGNIFICANCE STATEMENT: This study provides a detailed understanding of the disposition and metabolism of abrocitinib, a Janus kinase inhibitor for atopic dermatitis, in humans, as well as characterization of clearance pathways and pharmacokinetics of abrocitinib and its metabolites.

This article reviews therapeutic drug monitoring (TDM) use for current inflammatory bowel disease (IBD) treatments. IBD comprises Crohn's disease and ulcerative colitis-chronic gastrointestinal inflammatory disorders. Treatment options for moderate to severe IBD include thiopurines; methotrexate; biologic agents targeting tumor necrosis factor, α4β7 integrin or interleukins 12 and 23; and Janus kinase inhibitors. TDM is recommended to guide treatment decisions for some of these agents. Published literature concerning TDM for IBD treatments was reviewed. S.D.L., R.S., and E.V.L. drew on their clinical experiences. Polymorphisms resulting in altered enzymatic activity inactivating thiopurine metabolites can lead to myelotoxicity and hepatotoxicity. Increased elimination of biologic agents can result from immunogenicity or higher disease activity, leading to low drug concentration and consequent nonresponse or loss of response. TDM may aid treatment and dose decisions for individual patients, based on monitoring metabolite levels for thiopurines, or serum drug trough concentration and antidrug antibody levels for biologic agents. Challenges remain around TDM implementation in IBD, including the lack of uniform assay methods and guidance for interpreting results. The Janus kinase inhibitor tofacitinib is not impacted by enzyme polymorphisms or disease activity, and is not expected to stimulate the formation of neutralizing antidrug antibodies. TDM is associated with implementation challenges, despite the recommendation of its use for guiding many IBD treatments. Newer small molecules with less susceptibility to patient variability factors may fulfill the unmet need of treatment options that do not require TDM, although further study is required to confirm this.

The pathogenesis of SpA is multifactorial and involves a range of immune cell types and cytokines, many of which utilize Janus kinase (JAK) pathways for signaling. In this review, we summarize the animal and pre-clinical data that have demonstrated the effects of JAK blockade on the underlying molecular mechanisms of SpA and provide a rationale for JAK inhibition for the treatment of SpA. We also review the available clinical trial data evaluating JAK inhibitors tofacitinib, baricitinib, peficitinib, filgotinib and upadacitinib in PsA, AS and related inflammatory diseases, which have demonstrated the efficacy of these agents across a range of SpA-associated disease manifestations. The available clinical trial data, supported by pre-clinical animal model studies demonstrate that JAK inhibition is a promising therapeutic strategy for the treatment of SpA and may offer the potential for improvements in multiple articular and extra-articular disease manifestations of PsA and AS.

The inflammatory diseases ulcerative colitis and Crohn's disease constitute the two main forms of inflammatory bowel disease (IBD). They are characterized by chronic, relapsing inflammation of the gastrointestinal tract, significantly impacting on patient quality of life and often requiring prolonged treatment. Existing therapies for IBD are not effective for all patients, and an unmet need exists for additional therapies to induce and maintain remission. Here we describe the mechanism of action of the Janus kinase (JAK) inhibitor, tofacitinib, for the treatment of IBD and the effect of JAK inhibition on the chronic cycle of inflammation that is characteristic of the disease. The pathogenesis of IBD involves a dysfunctional response from the innate and adaptive immune system, resulting in overexpression of multiple inflammatory cytokines, many of which signal through JAKs. Thus JAK inhibition allows multiple cytokine signaling pathways to be targeted and is expected to modulate the innate and adaptive immune response in IBD, thereby interrupting the cycle of inflammation. Tofacitinib is an oral, small molecule JAK inhibitor that is being investigated as a targeted immunomodulator for IBD. Clinical development of tofacitinib and other JAK inhibitors is ongoing, with the aspiration of providing new treatment options for IBD that have the potential to deliver prolonged efficacy and clinically meaningful patient benefits.

Type 1 interferon (IFN) is a key mediator of organismal responses to pathogens, eliciting prototypical “interferon signature genes” that encode antiviral and inflammatory mediators. For a global view of IFN signatures and regulatory pathways, we performed gene expression and chromatin analyses of the IFN-induced response across a range of immunocyte lineages. These distinguished ISGs by cell-type specificity, kinetics, and sensitivity to tonic IFN and revealed underlying changes in chromatin configuration. We combined 1,398 human and mouse datasets to computationally infer ISG modules and their regulators, validated by genetic analysis in both species. Some ISGs are controlled by Stat1/2 and Irf9 and the ISRE DNA motif, but others appeared dependent on non-canonical factors. This regulatory framework helped to interpret JAK1 blockade pharmacology, different clusters being affected under tonic or IFN-stimulated conditions, and the IFN signatures previously associated with human diseases, revealing unrecognized subtleties in disease footprints, as affected by human ancestry., Pfizer Inc.

Loss-of-function mutations in the tyrosine kinase JAK3 cause autosomal recessive severe combined immunodeficiency (SCID). Defects in this form of SCID are restricted to the immune system, which led to the development of immunosuppressive JAK inhibitors. We find that the B6.Cg-Nr1d1tm1Ven/LazJ mouse line purchased from Jackson Laboratories harbors a spontaneous mutation in Jak3, generating a SCID phenotype and an inability to generate antigen-independent professional cytokine-producing innate lymphoid cells (ILCs). Mechanistically, Jak3 deficiency blocks ILC differentiation in the bone marrow at the ILC precursor and the pre-NK cell progenitor. We further demonstrate that the pan-JAK inhibitor tofacitinib and the specific JAK3 inhibitor PF-06651600 impair the ability of human intraepithelial ILC1 (iILC1) to produce IFN-γ, without affecting ILC3 production of IL-22. Both inhibitors impaired the proliferation of iILC1 and ILC3 and differentiation of human ILC in vitro. Tofacitinib is currently approved for the treatment of moderate-to-severely active rheumatoid arthritis. Both tofacitinib and PF-06651600 are currently in clinical trials for several other immune-mediated conditions. Our data suggest that therapeutic inhibition of JAK may also impact ILCs and, to some extent, underlie clinical efficacy.

Immediate early gene (IEG) expression is coordinated by multiple MAP kinase signaling pathways in a signal specific manner. Stress-activated p38α MAP kinase is implicated in transcriptional regulation of IEGs via MSK-mediated CREB phosphorylation. The protein kinases downstream to p38, MAPKAP kinase (MK) 2 and MK3 have been identified to regulate gene expression at the posttranscriptional levels of mRNA stability and translation. Here, we analyzed stress-induced IEG expression in MK2/3-deficient cells. Ablation of MKs causes a decrease of p38α level and p38-dependent IEG expression. Unexpectedly, restoration of p38α does not rescue the full-range IEG response. Instead, the catalytic activity of MKs is necessary for the major transcriptional activation of IEGs. By transcriptomics, we identified MK2-regulated genes and recognized the serum response element (SRE) as a common promoter element. We show that stress-induced phosphorylation of serum response factor (SRF) at serine residue 103 is significantly reduced and that induction of SRE-dependent reporter activity is impaired and can only be rescued by catalytically active MK2 in MK2/3-deficient cells. Hence, a new function of MKs in transcriptional activation of IEGs via the p38α-MK2/3-SRF-axis is proposed which probably cooperates with MKs’ role in posttranscriptional gene expression in inflammation and stress response.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterised by infiltration of immune cells into the affected synovium, release of inflammatory cytokines and degradative mediators, and subsequent joint damage. Both innate and adaptive arms of the immune response play a role, with activation of immune cells leading to dysregulated expression of inflammatory cytokines. Cytokines work within a complex regulatory network in RA, signalling through different intracellular kinase pathways to modulate recruitment, activation and function of immune cells and other leukocytes. As our understanding of RA has advanced, intracellular signalling pathways such as Janus kinase (JAK) pathways have emerged as key hubs in the cytokine network and, therefore, important as therapeutic targets. Tofacitinib is an oral JAK inhibitor for the treatment of RA. Tofacitinib is a targeted small molecule, and an innovative advance in RA therapy, which modulates cytokines critical to the progression of immune and inflammatory responses. Herein we describe the mechanism of action of tofacitinib and the impact of JAK inhibition on the immune and inflammatory responses in RA.

MAP KAP kinase 2 (MK2), a Ser/Thr kinase, plays a crucial role in the inflammatory process. We have determined the crystal structures of a catalytically active C-terminal deletion form of human MK2, residues 41–364, in complex with staurosporine at 2.7 Å and with ADP at 3.2 Å, revealing overall structural similarity with other Ser/Thr kinases. Kinetic analysis reveals that the Km for ATP is very similar for MK2 41–364 and p38-activated MK2 41–400. Conversely, the catalytic rate and binding for peptide substrate are dramatically reduced in MK2 41–364. However, phosphorylation of MK2 41–364 by p38 restores the Vmax and Km for peptide substrate to values comparable to those seen in p38-activated MK2 41–400, suggesting a mechanism for regulation of enzyme activity.

Mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2) is activated upon stress by p38 MAPK alpha and -beta, which bind to a basic docking motif in the C terminus of MK2 and which subsequently phosphorylate its regulatory sites. As a result of activation MK2 is exported from the nucleus to the cytoplasm and cotransports active p38 MAPK to this compartment. Here we show that the amount of p38 MAPK is significantly reduced in cells and tissues lacking MK2, indicating a stabilizing effect of MK2 for p38. Using a murine knockout model, we have previously shown that elimination of MK2 leads to a dramatic reduction of tumor necrosis factor (TNF) production in response to lipopolysaccharide. To further elucidate the role of MK2 in p38 MAPK stabilization and in TNF biosynthesis, we analyzed the ability of two MK2 isoforms and several MK2 mutants to restore both p38 MAPK protein levels and TNF biosynthesis in macrophages. We show that MK2 stabilizes p38 MAPK through its C terminus and that MK2 catalytic activity does not contribute to this stabilization. Importantly, we demonstrate that stabilizing p38 MAPK does not restore TNF biosynthesis. TNF biosynthesis is only restored with MK2 catalytic activity. We further show that, in MK2-deficient macrophages, formation of filopodia in response to extracellular stimuli is reduced. In addition, migration of MK2-deficient mouse embryonic fibroblasts (MEFs) and smooth muscle cells on fibronectin is dramatically reduced. Interestingly, reintroducing catalytic MK2 activity into MEFs alone is not sufficient to revert the migratory phenotype of these cells. In addition to catalytic activity, the proline-rich N-terminal region is necessary for rescuing the migratory phenotype. These data indicate that catalytic activity of MK2 is required for both cytokine production and cell migration. However, the proline-rich MK2 N terminus provides a distinct role restricted to cell migration.

TRADD is a multifunctional signaling adaptor protein that is recruited to TNFR1 upon ligand binding. The C-terminal of TRADD comprises the "death domain" that is responsible for association of TNFR1 and other death domain-containing proteins such as FADD and RIP. The N-terminal domain (N-TRADD) promotes the recruitment of TRAF2 to TNFR1 by binding to the C-terminal of TRAF2, leading to the activation of JNK/AP1 and NF-kappa B. The solution structure of N-TRADD was determined, revealing a novel protein fold. A combination of NMR, BIAcore, and mutagenesis experiments was used to help identify the site of interaction of N-TRADD with C-TRAF2, providing a framework for future attempts to selectively inhibit the TNF signaling pathways.

Engagement of the tumor necrosis factor-alpha (TNF-alpha) receptors by the TNF-alpha ligand results in the rapid induction of TNF-alpha gene expression. The study presented here shows that autoregulation of TNF-alpha gene transcription by selective signaling through tumor necrosis factor receptor 1 (TNFR1) requires p38 mitogen-activated protein (MAP) kinase activity and the binding of the transcription factors ATF-2 and Jun to the TNF-alpha cAMP-response element (CRE) promoter element. Consistent with these findings, TNFR1 engagement results in increased p38 MAP kinase activity and p38-dependent phosphorylation of ATF-2. Furthermore, overexpression of MADD (MAP kinase-activating death domain protein), an adapter protein that binds to the death domain of TNFR1 and activates MAP kinase cascades, results in CRE-dependent induction of TNF-alpha gene expression. Thus, the TNF-alpha CRE site is the target of TNFR1 stimulation and mediates the autoregulation of TNF-alpha gene transcription.

The ets-1 proto-oncogene codes for a transcription factor. In order to understand how ets-1 is regulated, we have cloned its promoter. We show that the promoter is inducible by serum and expression of c-Fos and c-Jun, and it is positively auto-regulated by its gene product. A 50 base-pair sequence is sufficient to confer c-Fos + c-Jun and c-Ets-1 responsiveness to a heterologous promoter. This element contains two AP1 and one Ets-1 like motifs. Striking, AP-1 and Ets-1 motifs are found in oncogene responsive units (ORU's) of other promoters, suggesting that combining these motifs is a common mechanism for generating mitogen responsive transcription elements.

Tumor necrosis factor alpha (TNFalpha) is a pro-inflammatory cytokine that controls the initiation and progression of inflammatory diseases such as rheumatoid arthritis. Tpl2 is a MAPKKK in the MAPK (i.e. ERK) pathway, and the Tpl2-MEK-ERK signaling pathway is activated by the pro-inflammatory mediators TNFalpha, interleukin (IL)-1beta, and bacterial endotoxin (lipopolysaccharide (LPS)). Moreover, Tpl2 is required for TNFalpha expression. Thus, pharmacologic inhibition of Tpl2 should be a valid approach to therapeutic intervention in the pathogenesis of rheumatoid arthritis and other inflammatory diseases in humans. We have developed a series of highly selective and potent Tpl2 inhibitors, and in the present study we have used these inhibitors to demonstrate that the catalytic activity of Tpl2 is required for the LPS-induced activation of MEK and ERK in primary human monocytes. These inhibitors selectively target Tpl2 in these cells, and they block LPS- and IL-1beta-induced TNFalpha production in both primary human monocytes and human blood. In rheumatoid arthritis fibroblast-like synoviocytes these inhibitors block ERK activation, cyclooxygenase-2 expression, and the production of IL-6, IL-8, and prostaglandin E(2), and the matrix metalloproteinases MMP-1 and MMP-3. Taken together, our results show that inhibition of Tpl2 in primary human cell types can decrease the production of TNFalpha and other pro-inflammatory mediators during inflammatory events, and they further support the notion that Tpl2 is an appropriate therapeutic target for rheumatoid arthritis and other human inflammatory diseases.

MK2 and MK3 represent protein kinases downstream of p38 mitogen-activated protein kinase (MAPK). Deletion of the MK2 gene in mice resulted in an impaired inflammatory response although MK3, which displays extensive structural similarities and identical functional properties in vitro, is still present. Here, we analyze tumor necrosis factor (TNF) production and expression of p38 MAPK and tristetraprolin (TTP) in MK3-deficient mice and demonstrate that there are no significant differences with wild-type animals. We show that in vivo MK2 and MK3 are expressed and activated in parallel. However, the level of activity of MK2 is always significantly higher than that of MK3. Accordingly, we hypothesized that MK3 could have significant effects only in an MK2-free background and generated MK2/MK3 double-knockout mice. Unexpectedly, these mice are viable and show no obvious defects due to loss of compensation between MK2 and MK3. However, there is a further reduction of TNF production and expression of p38 and TTP in double-knockout mice compared to MK2-deficient mice. This finding, together with the observation that ectopically expressed MK3 can rescue MK2 deficiency similarly to MK2, indicates that both kinases share the same physiological function in vivo but are expressed to different levels.

We have recently shown that the neuronal exchange factor p140 Ras-GRF becomes activated in vivo in response to elevated calcium levels [C. L. Farnsworth, N. W. Freshney, L. B. Rosen, A. Ghosh, M. E. Greenberg, and L. A. Feig, Nature (London) 376:524-527, 1995]. Activation is mediated by calcium-induced calmodulin binding to an IQ domain near the N terminus of Ras-GRF. Here we show that the adjacent N-terminal pleckstrin homology (PH), coiled-coil, and IQ domains function cooperatively to allow Ras-GRF activation. Deletion of the N-terminal PH domain redistributes a large percentage of Ras-GRF from the particulate to the cytosolic fraction of cells and renders the protein insensitive to calcium stimulation. A similar cellular distribution and biological activity are observed when only the core catalytic domain is expressed. Although the PH domain is necessary for particulate association of Ras-GRF, it is not sufficient for targeting the core catalytic domain to this cellular location. This requires the PH domain and the adjacent coiled-coil and IQ sequences. Remarkably, this form of Ras-GRF is constitutively activated. The PH and coiled-coil domains must also perform an additional function, since targeting to the particulate fraction of cells is not sufficient to allow Ras-GRF activation by calcium. A Ras-GRF mutant containing the PH domain from Ras-GTPase-activating protein in place of its own N-terminal PH domain localizes to the particulate fraction of cells but does not respond to calcium. Similar phenotypes are seen with mutant Ras-GRFs containing point mutations in either the PH or coiled-coil domain. These findings argue that the N-terminal PH, coiled-coil, and IQ domains of Ras-GRF function together to connect Ras-GRF to multiple components in the particulate fractions of cells that are required for responsiveness of the protein to calcium signaling.