JAK inhibition in the treatment of inflammatory rheumatic diseases.

The most common immune-mediated inflammatory rheumatic diseases, rheumatoid arthritis, psoriatic arthritis and axial spondyloarthritis and have reached significant advances in recent years with the introduction of biological therapies against cytokines and immune cells, but also against intracellular enzymes, specifically Janus kinases (JAKs). Intracellular JAK signalling is activated by binding of various cytokines or growth factors to the respective cellular receptors, allowing the activation of STAT (Signal Transducers and Activators of Transcription) transcription factors and ultimately the transcription of genes with important roles during the innate and adaptive immune response. Four Janus kinases have been described: JAK1, JAK2, JAK3 and tyrosine kinase-2 (TYK2). Four JAK inhibitors (tofacitinib, baricitinib, upadacitinib and filgotinib) are currently approved for the treatment of rheumatoid arthritis, and some for the treatment of psoriatic arthritis and axial spondyloarthritis. JAK inhibitors have varying selectivity against individual kinases. Some JAK inhibitors are being tested in other rarer systemic connective tissue diseases. The general advantages of JAK inhibitors are oral administration, rapid onset of action, and efficacy in monotherapy. The safety profile of JAK inhibitors compared with biologic therapy appears to be comparable, with a higher incidence of herpes zoster, and an increased incidence of major cardiovascular disease, thromboembolic complications, and cancer in at-risk patients is discussed. The aim of this paper will be to summarize the latest findings on JAK inhibitors in approved indications for the most common rheumatic diseases.