Tracking JAKs in spondyloarthritis: rationale and expectations

Purine metabolites promote ectopic new bone formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease that mainly affects the axial skeleton, whose typical features are inflammatory back pain, bone structural damage and pathological new bone formation. The pathology of ectopic new bone formation is still little known. In this study, we found increased purine metabolites in plasma of patients with AS. Similarly, metabolome analysis indicated increased purine metabolites in both serum of CD4-Cre; Ptpn11^fl/fl and SHP2-deficient chondrocytes. SHP2-deficient chondrocytes promoted the growth of wild type chondrocytes and differentiation of osteoblasts in CD4-Cre; Ptpn11^fl/fl mice, which spontaneously developed AS-like bone disease. Purine metabolites, along with PTHrP derived from SHP2-deficient chondrocytes, accelerated the growth of chondrocytes and ectopic new bone formation through PKA/CREB signaling. Moreover, Suramin, a purinergic receptor antagonist, suppressed pathological new bone formation in AS-like bone disease. Overall, these results highlight the potential role of targeting purinergic signaling in retarding ectopic new bone formation in AS.

Novel therapies in axial spondyloarthritis

Over the past two decades, advancements in understanding the pathogenesis of axial spondyloarthritis have led to discoveries of new therapeutic targets, particularly the interleukin-17, tumor necrosis factor axis, and Janus kinase-signal transducer and activator of transcription pathway. While many of the available agents have proven to be efficacious and safe for the treatment of axial spondyloarthritis, a remarkable percentage of patients either fail or cannot tolerate these medications. This has prompted researchers to look for new targets that would maximize efficacy and minimize toxicity. In this article, we review novel agents that were recently approved, in trials, and possible future targets or mechanisms. We also discuss their role as it pertains to the prevention of radiographic progression and the management of extra-musculoskeletal manifestations.

The Use of Janus Kinase Inhibitors in Axial Spondyloarthritis: Current Insights

Current pharmacological treatments of axial spondyloarthritis (axSpA) are limited to non-steroidal anti-inflammatory drugs (NSAIDs) and biological agents, including TNFα inhibitors and IL-17 inhibitors. Despite the availability of these agents, many patients either fail to respond adequately, lose their initial therapeutic response over time, or develop undesirable side effects, thus highlighting the need for new treatment options. Janus kinase (JAK) and signal transducers and activators of transcription (STAT) are a group of intracellular kinases that play a role in the signaling pathway induced by cytokines and certain growth factors associated with the inflammatory process of axSpA. There are several lines of evidence implicating the JAK–STAT pathway in the pathophysiological process of axSpA, including genetic data, the use of certain JAK in the intracellular signal of specific cytokines involved in axSpA (IL-23, IL-22, and IL-6), and data from experimental models of SpA. This provides a rationale for the assessment of JAK inhibitors (JAKi) in clinical trials with patients with axSpA. In this review, we examine the role of JAK–STAT signaling in the pathogenesis of axSpA and summarize the results from recent clinical trials of JAKi (tofacitinib, upadacitinib, and filgotinib) in patients with axSpA.

Long-term Safety of Oral Systemic Therapies for Psoriasis: A Comprehensive Review of the Literature

Oral systemic therapies are important treatment options for patients with moderate-to-severe psoriasis, either as monotherapy or in therapy-recalcitrant cases as combination therapy with phototherapy, other oral systemics or biologics. Long-term treatment is needed to maintain sufficient disease control in psoriasis, but continuous use of systemic treatments is limited by adverse events (AEs) and cumulative toxicity risks. The primary aim of this comprehensive literature review was to examine the long-term safety profiles of oral agents commonly used in the treatment of adults with psoriasis. Searches were conducted in EMBASE and PubMed up to November 2018, and 157 relevant publications were included. Long-term treatment with acitretin could be associated with skeletal toxicity and hepatotoxicity, although evidence for skeletal toxicity is mixed and hepatotoxicity is rare, particularly at low doses. Other safety issues include hyperlipidaemia and potential for teratogenicity up to 2-3 years after discontinuation of treatment. There is a paucity of data on long-term treatment with apremilast. Continued exposure to apremilast does not seem to increase the incidence of common AEs, such as gastrointestinal (GI) AEs, upper respiratory tract infections and headache, while the long-term risks for depression, suicidal thoughts and weight loss are unknown. Long-term ciclosporin treatment is associated with renal toxicity, hypertension, non-melanoma skin cancer, neurological AEs and GI AEs. Long-term methotrexate treatment is associated with hepatotoxicity, GI AEs, haematological toxicity, renal toxicity and alopecia. Finally, long-term treatment with fumaric acid esters (FAE) is associated with GI AEs, flushing, lymphocytopenia, proteinuria and elevated liver enzymes. Median drug survival estimates varied considerably: ~  2.9-9.7 months for apremilast; ~ 5.4 months for ciclosporin; ~ 8.6 months for acitretin; ~ 12.1-21.6 months for methotrexate; and ~  54.8 months for FAE. These long-term safety profiles may help to guide clinicians to select the optimal oral systemic treatment for the long-term treatment of psoriasis in adults.