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Pain is the major symptom of osteoarthritis (OA) and is an important factor in strategies to manage this disease. However, the current standard of care does not provide satisfactory pain relief for many patients. The pathophysiology of OA is complex, and its presentation as a clinical syndrome is associated with pathologies of multiple joint tissues. Inflammation is associated with both OA pain and disease outcome and is therefore a major treatment target for OA and OA pain. Unlike TNF inhibitors and IL-1 inhibitors, established drugs such as glucocorticoids and methotrexate can reduce OA pain. Although central nociceptive pathways contribute to OA pain, crosstalk between the immune system and nociceptive neurons is central to inflammatory pain; therefore, new therapies might target this crosstalk. Newly identified drug targets, including neurotrophins and the granulocyte–macrophage colony-stimulating factor (GM-CSF)–CC-chemokine ligand 17 (CCL17) chemokine axis, offer the hope of better results but require clinical validation.Pain management is presently the focus of osteoarthritis (OA) therapy, but traditional pain-relieving drugs such as NSAIDs and glucocorticoids have limited utility. In this Review, the next generation of OA analgesics and their potential mechanisms of action are discussed.

Key Points Colony-stimulating factors (CSFs) are pleiotropic, but each has its own unique biological role. All CSFs control myeloid cell numbers, but each has a level of specificity in regard to its target cells and effects. Preclinical and/or clinical data suggest that targeting granulocyte–macrophage CSF (GM-CSF), CSF1, granulocyte CSF (G-CSF) or IL-3 could be useful in the treatment of numerous autoimmune and/or inflammatory pathologies, including rheumatoid arthritis and multiple sclerosis. Further investigation of the potential of targeting CSFs in other pathologies is warranted. CSF targeting, as well as associated patient stratification, should be based on the specific CSF biology. There is not necessarily an inverse relationship between the effects of CSF blockade and administration of the protein itself on a particular pathology. The colony-stimulating factors (CSFs) have roles in inflammation and immunity, and are potential targets for diseases caused by aberrant immune activation, including rheumatoid arthritis and multiple sclerosis. Hamilton et al . describe how distinguishing attributes could be used to target individual CSFs for therapeutic use in immune and inflammatory conditions and the progress that has been made towards that goal. They also clarify misconceptions about targeting this class of molecules. Granulocyte–macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF; also known as CSF1), granulocyte colony-stimulating factor (G-CSF) and interleukin-3 (IL-3) can each play a part in the host response to injury and infection, and there is burgeoning interest in targeting these CSFs in inflammatory and autoimmune disorders, as well as in cancer. For success in clinical medicine, therapeutic targeting will need to be delineated from current strategies. The individual CSFs have unique biological roles, suggesting that they could be used to target specific conditions. This Review compares the CSFs, with a focus on how they could be targeted, discusses the relevant clinical trial data and summarizes the potential clinical applications of targeting each CSF. Importantly, we discuss the novelty of CSF biology and attempt to clarify some of the surrounding misconceptions and issues that can affect therapeutic decisions.

Rheumatoid arthritis (RA) is a heterogeneous, prevalent, chronic autoimmune disease characterized by painful swollen joints and significant disabilities. Symptomatic relief can be achieved in up to 50% of patients using biological agents that inhibit tumor necrosis factor (TNF) or other mechanisms of action, but there are no universally effective therapies. Recent advances in basic and preclinical science reveal that reflex neural circuits inhibit the production of cytokines and inflammation in animal models. One well-characterized cytokine-inhibiting mechanism, termed the “inflammatory reflex,” is dependent upon vagus nerve signals that inhibit cytokine production and attenuate experimental arthritis severity in mice and rats. It previously was unknown whether directly stimulating the inflammatory reflex in humans inhibits TNF production. Here we show that an implantable vagus nerve-stimulating device in epilepsy patients inhibits peripheral blood production of TNF, IL-1β, and IL-6. Vagus nerve stimulation (up to four times daily) in RA patients significantly inhibited TNF production for up to 84 d. Moreover, RA disease severity, as measured by standardized clinical composite scores, improved significantly. Together, these results establish that vagus nerve stimulation targeting the inflammatory reflex modulates TNF production and reduces inflammation in humans. These findings suggest that it is possible to use mechanism-based neuromodulating devices in the experimental therapy of RA and possibly other autoimmune and autoinflammatory diseases.

ObjectivesWe explored the effects of B-cell directed therapy in subjects at risk of developing autoantibodypositive rheumatoid arthritis (RA), who never experienced inflammatory arthritis before, and explored biomarkers predictive of arthritis development.MethodsIndividuals positive for both anti-citrullinated peptide antibodies and rheumatoid factor but without arthritis were included in a randomised, double-blind, placebo-controlled study to receive a single infusion of 1000 mg rituximab or placebo.ResultsEighty-one individuals received treatment and were followed up for a mean of 29.0 (0–54) months, during which 30/81 (37%) individuals developed arthritis. The observed risk of developing arthritis in the placebo-treated group was 40%, which was decreased by 55% (HR 0.45, 95% CI 0.154 to 1.322) in the rituximab-treated group at 12 months. Rituximab treatment caused a delay in arthritis development of 12 months compared with placebo treatment at the point when 25% of the subjects had developed arthritis (p<0.0001). Erythrocyte sedimentation rate and the presence of anti-citrullinated α-enolase peptide 1 at baseline were significant predictors of arthritis development.ConclusionsA single infusion of 1000 mg rituximab significantly delays the development of arthritis in subjects at risk of developing RA, providing evidence for the pathogenetic role of B cells in the earliest, prearthritis stage of autoantibody positive RA.

Sirukumab, a human monoclonal antibody that selectively binds to the interleukin-6 cytokine with high affinity, is under development for the treatment of rheumatoid arthritis and other diseases. We aimed to assess the efficacy and safety of sirukumab for rheumatoid arthritis in a phase 3 study (SIRROUND-T). We did a randomised, double-blind, placebo-controlled, parallel-group, multicentre study at 183 hospitals and private rheumatology clinics in 20 countries (Argentina, Australia, Austria, Belgium, Canada, France, Germany, Italy, Japan, Lithuania, Mexico, Netherlands, Poland, Portugal, Russia, South Korea, Spain, Taiwan, UK, and USA). Eligible participants were patients with active rheumatoid arthritis aged at least 18 years, with four or more of 68 tender joints and four or more of 66 swollen joints, who were refractory or intolerant to previous treatment with at least one anti-TNF drug. We randomly assigned patients (1:1:1) via a central interactive voice or web response system to either placebo every 2 weeks, 50 mg sirukumab every 4 weeks, or 100 mg sirukumab every 2 weeks, all given for 52 weeks or less. We allowed participants to continue using any concomitant disease-modifying antirheumatic drugs (DMARDs). We based the randomisation on a computer-generated, permuted-block schedule stratified by use of methotrexate at baseline (0, >0 to <12·5 mg/week, or ≥12·5 mg/week). Masking was achieved with the use of multipart labels on the study drug containers which contained directions for use and other information, but not the drug's identity. Treatments were administered by subcutaneous injection; patients assigned to 50 mg sirukumab given every 4 weeks also received a placebo injection every 2 weeks to maintain masking. At week 18, placebo-treated patients meeting early escape criteria (<20% improvement in swollen and tender joint counts) were randomly reassigned to either 50 mg or 100 mg of sirukumab. All remaining placebo-treated patients were subsequently randomly reassigned at week 24 to either sirukumab dose (crossover). The primary outcome was the proportion of patients who achieved a response of at least 20% improvement at week 16 according to American College of Rheumatology criteria (ACR20) in the intention-to-treat population (all randomly assigned participants). Safety analyses included all participants who received at least one dose (partial or complete) of study drug. This study is registered at EudraCT (number: 2010-022243-38) and ClinicalTrials.gov (number: NCT01606761). Between July 25, 2012, and Jan 12, 2016, we randomly assigned 878 patients to treatment: 294 to placebo, 292 to 50 mg sirukumab every 4 weeks, and 292 to 100 mg sirukumab every 2 weeks. 523 (60%) of 878 patients had previously received two or more biological treatments including non-TNF drugs, and 166 (19%) of 878 were not taking a DMARD at baseline. The proportions of patients who achieved an ACR20 response at week 16 were 117 (40%) of 292 with 50 mg sirukumab every 4 weeks, and 132 (45%) of 292 with 100 mg sirukumab every 2 weeks versus 71 (24%) of 294 with placebo; differences compared with placebo were 0·16 (95% CI 0·09–0·23) for 50 mg sirukumab every 4 weeks and 0·21 (0·14–0·29) for 100 mg sirukumab every 2 weeks (both p<0·0001). Adverse event incidences in the 24-week placebo-controlled period were similar across groups (at least one event occurred for 182 patients assigned to placebo [62%, including early escape patients switched to sirukumab at week 18] of 294; 194 [66%] of 292 with 50 mg sirukumab every 4 weeks; and 207 [71%] of 292 with 100 mg sirukumab every 2 weeks). The most common adverse events in this period were injection-site erythema (four [1%] with placebo, 22 [8%] with 50 mg sirukumab every 4 weeks, and 41 [14%] with 100 mg sirukumab every 2 weeks). At week 52, of all patients receiving sirukumab including those reassigned from placebo, the most common adverse events were again injection-site erythema (33 [8%] of 416 with 50 mg sirukumab every 4 weeks and 66 [16%] of 418 with 100 mg sirukumab every 2 weeks). In patients with active rheumatoid arthritis who were refractory or intolerant to anti-TNF drugs and other biological treatments, both dosing regimens of sirukumab were well tolerated and significantly improved signs and symptoms of the disease, compared with placebo, in this difficult-to-treat population. Janssen Research & Development, LLC, and GlaxoSmithKline.

Background Histone deacetylase inhibitors (HDACi) display potent therapeutic efficacy in animal models of arthritis and suppress inflammatory cytokine production in rheumatoid arthritis (RA) synovial macrophages and tissue. Objectives To determine the molecular mechanisms contributing to the suppressive effects of HDACi on RA synovial cell activation, using interleukin 6 (IL-6) regulation as a model. Methods RA fibroblast-like synoviocytes (FLS) and healthy donor macrophages were treated with IL-1β, tumour necrosis factor (TNF)α, lipopolysaccharide or polyinosinic:polycytidylic acid (poly(I:C)) in the absence or presence of the HDACi trichostatin A (TSA) or ITF2357 (givinostat). IL-6 production and mRNA expression was measured by ELISA and quantitative PCR (qPCR), respectively. Protein acetylation and the activation of intracellular signalling pathways were assessed by immunoblotting. The DNA-binding activity of nuclear factor κB (NFκB) and activator protein 1 (AP-1) components was measured by ELISA-based assays. Results HDACi (0.25–1.0 μM) suppressed RA FLS IL-6 production induced by IL-1β, TNFα and Toll-like receptor ligands. Phosphorylation of mitogen-activated protein kinases and inhibitor of κBα (IκBα) following IL-1β stimulation were unaffected by HDACi, as were AP-1 composition and binding activity, and c-Jun induction. TSA induced a significant reduction in nuclear retention of NFκB in FLS 24 h after IL-1β stimulation, but this did not reduce NFκB transcriptional activity or correlate temporally with reductions in IL-6 mRNA accumulation. HDACi significantly reduced the stability of IL-6 mRNA in FLS and macrophages. Conclusions Our study identifies a novel, shared molecular mechanism by which HDACi can disrupt inflammatory cytokine production in RA synovial cells, namely the promotion of mRNA decay, and suggests that targeting HDAC activity may be clinically useful in suppressing inflammation in RA.

ObjectivesInterleukin-6 (IL-6) is implicated in rheumatoid arthritis (RA) pathophysiology. Unlike IL-6 receptor inhibitors, sirukumab is a human monoclonal antibody that selectively binds to the IL-6 cytokine. The phase III, multicentre, randomised, double-blind, placebo-controlled, parallel-group SIRROUND-D study (ClinicalTrials.gov identifier NCT01604343) evaluated the efficacy and safety of sirukumab in patients with active RA refractory to disease-modifying antirheumatic drugs.MethodsPatients were randomised 1:1:1 to treatment with sirukumab 100 mg every 2 weeks, 50 mg every 4 weeks or placebo every 2 weeks subcutaneously. Results through week 52 are reported.ResultsOf 1670 randomised patients, significantly more patients achieved American College of Rheumatology 20% (ACR20) response at week 16 (coprimary endpoint) with sirukumab 100 mg every 2 weeks (53.5%) or 50 mg every 4 weeks (54.8%) versus placebo (26.4%; both p<0.001). Mean (SD) change from baseline in modified Sharp/van der Heijde score at week 52 (coprimary endpoint) was significantly lower with sirukumab (100 mg every 2 weeks: 0.46 (3.26); 50 mg every 4 weeks: 0.50 (2.96)) versus placebo (3.69 (9.25); both p<0.001). All major secondary endpoints (week 24 Health Assessment Questionnaire–Disability Index change from baseline, ACR50 response, 28-joint Disease Activity Score based on C reactive protein and major clinical response (ACR70 for six continuous months by week 52)) were met. The most common adverse events with sirukumab were elevated liver enzymes, upper respiratory tract infection, injection site erythema and nasopharyngitis.ConclusionsSirukumab 100 mg every 2 weeks and 50 mg every 4 weeks led to significant reductions in RA symptoms, inhibition of structural damage progression and physical function and quality of life improvements, with an expected safety profile.Trial registration numberNCT01604343; Results.

ObjectiveTo investigate the effects of BET bromodomain protein inhibition on inflammatory activation and functional properties of rheumatoid arthritis synovial fibroblasts (RASF).MethodsThe expression of the BET bromodomain proteins BRD2, BRD3 and BRD4 was analysed in synovial tissue by immunohistochemistry. RASF were stimulated with tumour necrosis factor (TNF)-α, interleukin (IL)-1β and toll-like receptor (TLR) ligands (Pam3, pIC and lipopolysaccharide (LPS)) in the presence or absence of the BET inhibitor I-BET151, or siRNA targeting BRD2, BRD3 and BRD4. RASF expression of inflammatory mediators, including MMP1, MMP3, IL-6 and IL-8, was measured by q-PCR, q-PCR array and ELISA. Cellular viability, apoptosis, proliferation and chemoattractive properties of RASF were investigated using MTT, cell apoptosis ELISA, BrdU-based proliferation and transwell migration assays.ResultsBRD2, BRD3 and BRD4 proteins were detected in rheumatoid arthritis (RA) synovial tissue, expressed in both RASF and macrophages. I-BET151 suppressed cytokine and TLR ligand-induced secretion of MMP1, MMP3, IL-6 and IL-8, and mRNA expression of more than 70% of genes induced by TNF-α and IL-1β. Combined silencing of BRD2, BRD3 and BRD4 significantly reduced cytokine and TLR ligand-induced expression of a subset of gene products targeted by I-BET151, including MMP1, CXCL10 and CXCL11. I-BET151 treatment of RASF reduced RASF proliferation, and the chemotactic potential for peripheral blood leucocytes of RASF conditioned medium.ConclusionsInhibition of BET family proteins suppresses the inflammatory, matrix-degrading, proliferative and chemoattractive properties of RASF and suggests a therapeutic potential in the targeting of epigenetic reader proteins in RA.

Background Studies examining the relationship between serological status (rheumatoid factor and/or anticitrullinated antibody) and rituximab treatment outcome in rheumatoid arthritis (RA) have been hampered by limited numbers of seronegative patients. Objective To carry out a meta-analysis of trials from the rituximab RA clinical programme to investigate this relationship further. Methods This was a meta-analysis of four placebo-controlled, phase II or III clinical trials. The efficacy end point in all analyses was change from baseline in Disease Activity Score in 28 joints-erythrocyte sedimentation rate (DAS28-ESR) at 24 weeks. Assay of serotype and missing data imputation methods were consistent across all studies. Results The population analysed comprised 2177 patients (rituximab, n=1416; placebo, n=761). Demographics and baseline disease characteristics were well balanced. When a fixed-effects meta-analysis approach was used, the overall-effect model indicated evidence of additional treatment benefit with rituximab in seropositive patients: reduction in DAS28-ESR at week 24 was on average 0.35 units (95% CI 0.12 to 0.84; n=1394) greater than in seronegative patients; this effect was not seen in placebo patients. Heterogeneity indices indicated significant uncertainty in the overall-effect model (Q=8.8, I=0.77; p=0.03 (χ2 test)). Baseline Health Assessment Questionnaire score, pain visual analogue scale, swollen joint counts of 28 joints and race were significant contributors to this heterogeneity, with additional analysis indicating that these effects may predominate in early RA (methotrexate-naïve) populations. A dominant effect was seen in patients for whom one or more tumour necrosis factor inhibitors had failed. Conclusion Although the difference was modest, the overall-effect model indicates that seropositive patients respond better to rituximab than seronegative patients.

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects females three times more frequently than males. A potential role for hormones, such as prolactin (PRL), may in part explain this phenomenon. The risk of developing RA is increased in women who are lactating after the first pregnancy, which might be related to breastfeeding and the release of PRL. Other studies found a protective effect of PRL on RA development. Some studies have reported that hyperprolactinemia is more common in RA and serum PRL levels are correlated with several disease parameters, although others could not confirm these findings. Overall the plasma PRL levels are on average not elevated in RA. Previously, a small number of open-label clinical trials using bromocriptine, which indirectly decreases PRL levels, were performed in RA patients and showed clinical benefit, although others found the opposite effect. Locally produced PRL at the site of inflammation may have a crucial role in RA as well, as it has been shown that PRL can be produced by synovial macrophages. Locally produced PRL has both pro-inflammatory and anti-inflammatory effects in arthritis. Psoriatic arthritis (PsA) is also an autoinflammatory disease, in which the prolactin receptor is also expressed in macrophages. The aim of this review is to provide an overview of the potential role of PRL signaling in inflammatory joint diseases (RA and PsA) and its potential as a therapeutic target.