JAK-Inhibitors for the Treatment of Rheumatoid Arthritis: A Focus on the Present and an Outlook on the Future

Abstract

Janus kinase inhibitors (JAKi) belong to a new class of oral targeted disease-modifying drugs which have recently revolutionized the therapeutic panorama of rheumatoid arthritis (RA) and other immune-mediated diseases, placing alongside or even replacing conventional and biological drugs. JAKi are characterized by a novel mechanism of action, consisting of the intracellular interruption of the JAK-STAT pathway crucially involved in the immune response. The aim of this narrative review is to globally report the most relevant pharmacological features and clinical outcomes of the developed and incoming JAKi for RA, based on the available preclinical and clinical evidence. A total of 219 papers, including narrative and systematic reviews, randomized controlled trials (RCTs), observational studies, case reports, guidelines, and drug factsheets, were selected. The efficacy and safety profile of both the first generation JAKi (baricitinib and tofacitinib) and the second generation JAKi (upadacitinib, filgotinib, peficitinib, decernotinib and itacitinib) were compared and discussed. Results from RCTs and real-life data are encouraging and outline a rapid onset of the pharmacologic effects, which are maintained during the time. Their efficacy and safety profile are comparable or superior to those of biologic agents and JAKi proved to be efficacious when given as monotherapy. Finally, the manufacturing of JAKi is relatively easier and cheaper than that of biologics, thus increasing the number of compounds being formulated and tested for clinical use.

Keywords: Janus kinase-inhibitors; Janus kinases; rheumatoid arthritis; small molecules.

Figure 1

Literature selection process for this article (JAKi, JAK-inhibitors; RCTs, randomized controlled trials).

Figure 2

The JAK-STAT canonical signaling pathway. The specific cytokine binds to the transmembrane receptors type I o II. This binding causes the auto-phosphorylation of the receptor itself which summons cytosolic monomeric JAK proteins (1). Once recruited, JAKs phosphorylate the receptor (2), allowing, in turn, a second phosphorylation of STAT monomers (3,4). STATs dimerize (5) and translocate into the nucleus (6), activating the transcription of pro-inflammatory genes (7). (JAK: Janus kinase; STAT: JAK signal transducer and activator of transcription; IL: interleukin; G-CSF: granulocyte-colony-stimulating factor; TYK: tyrosine kinase; GH: growth hormone; EPO: erythropoietin; TPO: thrombopoietin; IFN: interferon).

Figure 3

Molecular structure of first and second generation JAKi compared.