Impact of Janus Kinase Inhibition on the Treatment of Axial Spondyloarthropathies

Many immune cells and effector molecules (e.g. cytokines, Interferons, growth factors) utilize different combinations of Janus kinase (JAK) and signal transducer and activator of transcription (STAT) molecules to transduce signals from the cell surface to the nucleus, where they regulate transcription. This pathway is basically involved in almost all inflammatory diseases and also in the interleukin (IL)-23/IL-17 cascade, which is an essential part of the pathogenesis of spondyloarthropathies (SpA). Upon evidence from in vitro and in vivo experiments indicating disease-modifying effects of JAK inhibition in inflammatory joint disease, numerous inhibitors of the JAK/STAT pathway (= JAKinibs) with different selectivity against the four members of the JAK family [JAK1, JAK2, JAK3, and tyrosine kinase 2 (TYK2)] were developed. Trials in rheumatoid arthritis were successful with respect to efficacy and safety, and currently, three JAKinibs are approved for the treatment of rheumatoid arthritis in the European Union. Although new treatment options (anti-IL-23, anti-IL-17, and phosphodiesterase 4 inhibitors) have become available for spondyloarthritis and especially psoriatic arthritis (PsA) within the last years, most of them are biologics and do not address all disease manifestations equally. Therefore, multiple trials were initiated to evaluate JAKinibs in PsA and axial spondyloarthritis (axSpA). A trial of Tofacitinib (OPAL) was successful in PsA and has led to the inclusion of JAKinibs into the treatment algorithm. Currently many trials with JAKinibs are ongoing for PsA and axSpA, with one phase III trial of upadacitinib (selective JAK1 inhibitor) showing good therapeutic response in active radiographic axSpA.