SUMMARY Type-1 interferon (IFN) is a key mediator of organismal responses to pathogens, eliciting prototypical “Interferon Signature Genes” which 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 1398 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.

Animal models of rheumatoid arthritis (RA) are widely used for testing potential new therapies for RA. However, the question of which animal model is most predictive of therapeutic efficacy in human RA commonly arises in data evaluation. A retrospective review of the animal models used to evaluate approved, pending RA therapies, and compounds that were discontinued during phase II or III clinical trials found that the three most commonly used models were adjuvant-induced arthritis (AIA) in rats and collagen-induced arthritis (CIA) in rats and mice. Limited data were found for more recently developed genetically modified animal models. Examination of the efficacy of various compounds in these animal models revealed that a compound's therapeutic efficacy, rather than prophylactic efficacy, in AIA and CIA models was more predictive of clinical efficacy in human RA than data from either model alone.

Objective. Interleukin-21 (IL-21) is a T cellderived cytokine that modulates T cell, B cell, and natural killer cell responses. In this study, the effects of blocking IL-21 were examined in 2 rodent models of rheumatoid arthritis (RA) to determine whether IL-21 contributes to their pathologic processes.Methods. DBA/1 mice were immunized with bovine type II collagen and then treated with murine IL-21 receptor Fc fusion protein (IL-21R.Fc), which was initiated after the onset of arthritis symptoms in 10% of the cohort. The mice were assessed 3 times per week for signs of disease, including histologic features as well as serum cytokine, Ig, and cytokine messenger RNA (mRNA) levels in the paws. In a separate experiment, Lewis rats were immunized with Freund's complete adjuvant followed by administration of IL-21R.Fc at the peak of inflammation in the joints. Rats were assessed daily for histologic features and for scoring of arthritis severity. In addition, the effects of IL-21R.Fc on the production of interferon-␥ (IFN␥) by T cells were examined.Results Conclusion. These findings demonstrate a pathogenic role for IL-21 in animal models of RA, and support consideration of IL-21 as a therapeutic target in human RA.

PF-06651600, a newly discovered potent JAK3-selective inhibitor, is highly efficacious at inhibiting γc cytokine signaling, which is dependent on both JAK1 and JAK3. PF-06651600 allowed the comparison of JAK3-selective inhibition to pan-JAK or JAK1-selective inhibition, in relevant immune cells to a level that could not be achieved previously without such potency and selectivity. In vitro, PF-06651600 inhibits Th1 and Th17 cell differentiation and function, and in vivo it reduces disease pathology in rat adjuvant-induced arthritis as well as in mouse experimental autoimmune encephalomyelitis models. Importantly, by sparing JAK1 function, PF-06651600 selectively targets γc cytokine pathways while preserving JAK1-dependent anti-inflammatory signaling such as the IL-10 suppressive functions following LPS treatment in macrophages and the suppression of TNFα and IL-1β production in IL-27-primed macrophages. Thus, JAK3-selective inhibition differentiates from pan-JAK or JAK1 inhibition in various immune cellular responses, which could potentially translate to advantageous clinical outcomes in inflammatory and autoimmune diseases.

Pathogenic mechanisms relevant to rheumatoid arthritis occur in the mouse model of collagen-induced arthritis (CIA). Cytosolic phospholipase A2α (cPLA2α) releases arachidonic acid from cell membranes to initiate the production of prostaglandins and leukotrienes. These inflammatory mediators have been implicated in the development of CIA. To test the hypothesis that cPLA2α plays a key role in the development of CIA, we backcrossed cPLA2α-deficient mice on the DBA/1LacJ background that is susceptible to CIA. The disease severity scores and the incidence of disease were markedly reduced in cPLA2α-deficient mice compared with wild-type littermates. At completion of the study, >90% of the wild-type mice had developed disease whereas none of the cPLA2α-deficient mice had more than one digit inflamed. Furthermore, visual disease scores correlated with severity of disease determined histologically. Pannus formation, articular fibrillation, and ankylosis were all dramatically reduced in the cPLA2α-deficient mice. Although the disease scores differed significantly between cPLA2α mutant and wild-type mice, anti-collagen antibody levels were similar in the wild-type mice and mutant littermates. These data demonstrate the critical role of cPLA2α in the pathogenesis of CIA.

Through fragment-based drug design focused on engaging the active site of IRAK4 and leveraging three-dimensional topology in a ligand-efficient manner, a micromolar hit identified from a screen of a Pfizer fragment library was optimized to afford IRAK4 inhibitors with nanomolar potency in cellular assays. The medicinal chemistry effort featured the judicious placement of lipophilicity, informed by co-crystal structures with IRAK4 and optimization of ADME properties to deliver clinical candidate PF-06650833 (compound 40). This compound displays a 5-unit increase in lipophilic efficiency from the fragment hit, excellent kinase selectivity, and pharmacokinetic properties suitable for oral administration.

TNF-α is a pleiotropic cytokine considered a primary mediator of immune regulation and inflammatory response and has been shown to play a central role in rheumatoid arthritis (RA). MAPKAP kinase 2 (MK2) is a serine/threonine kinase that is regulated through direct phosphorylation by p38 MAPK, and has been shown to be an essential component in the inflammatory response that regulates the biosynthesis of TNF-α at a posttranscriptional level. The murine model of collagen-induced arthritis (CIA) is an established disease model to study pathogenic mechanisms relevant to RA. In this study, we report that deletion of the MK2 gene in DBA/1LacJ mice confers protection against CIA. Interestingly, the MK2 heterozygous mutants display an intermediate level of protection when compared with homozygous mutant and wild-type littermates. We show that MK2−/− and MK2+/− mice exhibit decreased disease incidence and severity in the CIA disease model and reduced TNF-α and IL-6 serum levels following LPS/d-Gal treatment compared with wild-type mice. Additionally, we show that levels of IL-6 mRNA in paws of mice with CIA correlate with the disease status. These findings suggest that an MK2 inhibitor could be of great therapeutic value to treat inflammatory diseases like RA.

Cytokine signaling is an important characteristic of autoimmune diseases. Many pro-inflammatory cytokines signal through the Janus kinase (JAK)/Signal transducer and activator of transcription (STAT) pathway. JAK1 is important for the γ-common chain cytokines, interleukin (IL)-6, and type-I interferon (IFN) family, while TYK2 in addition to type-I IFN signaling also plays a role in IL-23 and IL-12 signaling. Intervention with monoclonal antibodies (mAbs) or JAK1 inhibitors has demonstrated efficacy in Phase III psoriasis, psoriatic arthritis, inflammatory bowel disease, and rheumatoid arthritis studies, leading to multiple drug approvals. We hypothesized that a dual JAK1/TYK2 inhibitor will provide additional efficacy, while managing risk by optimizing selectivity against JAK2 driven hematopoietic changes. Our program began with a conformationally constrained piperazinyl-pyrimidine Type 1 ATP site inhibitor, subsequent work led to the discovery of PF-06700841 (compound 23), which is in Phase II clinical development (NCT02969018, NCT02958865, NCT03395184, and NCT02974868).