JAK inhibitors, Psoriatic Arthritis, and Axial Spondyloarthritis: a Critical Review of Clinical Trials.

Introduction Psoriatic arthritis (PsA) and spondyloarthritis (SpA) are inflammatory arthritides associated with progressive damage, deformity and morbidity. Janus kinase (JAK) inhibitors block JAKs, cytoplasmic protein tyrosine kinases important in signal transduction and immune processes that are currently being studied as synthetic disease modifying anti-rheumatic drugs (tsDMARDs) in psoriatic arthritis and spondyloarthritis. Areas covered This review evaluates published phase 2 and 3 clinical trial data for JAK kinase inhibitors for psoriatic arthritis and spondyloarthritis. A literature search using PubMed was conducted using the following keywords: "psoriatic arthritis", "ankylosing spondylitis", "axial spondyloarthritis", "non-radiographic axial spondyloarthritis", "tofacitinib", "baricitinib", "filgotinib" and "upadacitinib". Mechanism of action, phase 2 and 3 clinical trial data including efficacy and safety are discussed. Expert opinion JAK kinase inhibitors are important orally administered agents conferring different degrees of selectivity towards JAK1, JAK2, and JAK3 which may have implications on efficacy and safety in PsA and SpA. Phase 2 and 3 clinical trials in PsA for tofacitinib and upadacitinib and phase 2 for filgotinib confirmed efficacy comparable to biologic DMARDs. In SpA, phase 2 and 2/3 studies confirmed significant efficacy of tofacitinib, filgotinib and upadacitinib compared to placebo. Safety was comparable to clinical trial, long-term extension and registry data for rheumatoid arthritis.