The study was registered at http://trialregister.nl. Identifier: NTR1909.).

Inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease, are disabling conditions characterised by chronic, relapsing inflammation of the gastrointestinal tract. Current treatments are not universally effective or, in the case of therapeutic antibodies, are hampered by immune responses. Janus kinase inhibitors are orally delivered small molecules that target cytokine signalling by preventing phosphorylation of Janus kinases associated with the cytokine receptor. Subsequently, phosphorylation of signal transducers and activators of transcription that relay Janus kinase signalling and transcription of cytokines in the nucleus will be diminished. Key cytokines in the pathogenesis of inflammatory bowel diseases are targeted by Janus kinase inhibitors. Several Janus kinase inhibitors are in development for the treatment of inflammatory bowel diseases. Tofacitinib, inhibiting signalling via all Janus kinase family members, was effective in phase 2 and 3 trials in moderate-severe ulcerative colitis. GSK2586184, a Janus kinase 1 selective inhibitor, induced clinical and endoscopic response in ulcerative colitis; however, the study was discontinued at an early stage due to liver toxicity observed in systemic lupus patients receiving the drug. Filgotinib, a Janus kinase 1 selective inhibitor investigated in treatment of Crohn’s disease, was superior to placebo. As adverse events associated with the broad immunological effect of these agents have been reported, the future application of these drugs is potentially limited. We will discuss the treatment efficacy of Janus kinase inhibition in inflammatory bowel diseases, how current Janus kinase inhibitors available target immune responses relevant in inflammatory bowel disease, and whether more specific kinase inhibition could be effective.

Background Janus kinases (JAKs) mediate cytokine signaling involved in inflammatory bowel disease. The pan-JAK inhibitor tofacitinib has shown efficacy in the treatment of ulcerative colitis. However, concerns regarding adverse events due to their wide spectrum inhibition fueled efforts to develop selective JAK inhibitors. Given the crucial role of myeloid cells in intestinal immune homeostasis, we evaluated the effect of pan-JAK and selective JAK inhibitors on pro- and anti-inflammatory macrophage polarization and function (M1/M2) and in experimental colitis. Methods Murine bone marrow–derived macrophages or human monocytes were treated using JAK1 and JAK3 selective inhibitors (JAK1i;JAK3i) and tofacitinib and were evaluated by transcriptional, functional, and metabolic analyses. In vivo, oral administration of JAK1i and tofacitinib (10 or 30 mg/kg) was tested in both acute and acute rescue dextran sodium sulfate (DSS) colitis. Results Both tofacitinib and JAK1i but not JAK3i effectively inhibited STAT1 phosphorylation and interferon gamma–induced transcripts in M1 polarized macrophages. Strikingly, transcriptional profiling suggested a switch from M1 to M2 type macrophages, which was supported by increased protein expression of M2-associated markers. In addition, both inhibitors enhanced oxidative phosphorylation rates. In vivo, JAK1i and tofacitinib did not protect mice from acute DSS-induced colitis but ameliorated recovery from weight loss and disease activity during acute rescue DSS-induced colitis at the highest dose. Conclusion JAK1i and tofacitinib but not JAK3i induce phenotypical and functional characteristics of anti-inflammatory macrophages, suggesting JAK1 as the main effector pathway for tofacitinib in these cells. In vivo, JAK1i and tofacitinib modestly affect acute rescue DSS-induced colitis.

Background and Aims Tyrosine kinase 2 (TYK2) is required for signalling of key cytokines in the pathogenesis of inflammatory bowel disease (IBD). We assessed the efficacy of a novel selective TYK2 inhibitor (TYK2i) in experimental colitis using pharmacological and genetic tools. Methods At onset of T-cell transfer colitis RAG1 -/- mice received vehicle or TYK2i daily by oral gavage. T-cells lacking TYK2 kinase activity (TYK2 KE) were used to confirm selectivity of the inhibitor. To this end RAG1 -/- or RAG1 -/-TYK2 KE animals were transferred with either wild type (WT) or TYK2 KE-CD45RB high colitogenic T-cells. Loss of bodyweight, endoscopic disease, the disease activity index (DAI) and histopathology scores were recorded. Tissues were analysed ex vivo for lymphocyte populations by flow cytometry. The impact of TYK2 inhibition on human DC-T-cell interactions were studied using autologous Revaxis specific T-cell assays. Results TYK2i (70 mg/kg) prevented weight loss and limited endoscopic activity during T-cell transfer colitis. TYK2i (70 mg/kg) decreased DAI. While transfer of WT T-cells into RAG -/-TYK2 KE hosts induced colitis, TYK2 KE T-cells transferred into RAG1 -/-TYK2 KErecipients failed to do so. Ex vivo analysis showed a decrease in colon tissue Th1 cells and an increase in Th17 cells upon transfer of TYK2 KE-CD45RB high cells. In human antigen triggered T-cells, TYK2i displayed reduced Th1 differentiation similar to murine Th1 cells. Conclusion Oral administration of TYK2i, as well as transfer of T-cells lacking TYK2 activity, reduced human Th1 differentiation and ameliorated the course of murine T-cell transfer colitis. We conclude that TYK2 is a promising drug target for the treatment of IBD.

Tofacitinib, a non-selective Janus kinase (JAK) inhibitor, is effective in inducing clinical and endoscopic remission in patients with active ulcerative colitis (UC). Tofacitinib inhibits cytokine signalling through blockade of JAK1, JAK2, JAK3 and tyrosine kinase 2 (TYK2). Adverse events including neutropenia and anaemia resulting from JAK2 inhibition have been observed in actively treated patients. By selectively targeting JAK1, such adverse events could be expected to be avoided. This open label study was designed to enrol 15 patients with UC, however the trial was discontinued after two inclusions due to safety concerns with the agent in a parallel trial for systemic lupus erythematosus. GSK2586184 was administered in two patients with moderate-to-severe UC. The JAK1 selective inhibitor GSK2586184 was well tolerated and induced clinical and endoscopic response in two patients with moderate-to-severe UC. In addition, treatment with GSK2586184 decreased histology scores and faecal calprotectin levels at early withdrawal.