Introduction In 2017, the Janus kinase inhibitors (JAKi) Tofacitinib and Baricitinib were approved for the treatment of Rheumatoid arthritis (RA) in the European Union (EU) by the European Medicines Agency (EMA). Other JAKi like Peficitinib, Filgotinib and Upadacitinib are currently examined in clinical trials. The effect of these substances is mainly based on blocking the IL-6 pathway in immune cells.¹ However the effect of the different JAKi on activated fibroblast-like synoviocytes from patients with RA (RA-FLS) is not well characterised.

Objectives This study compared the effect of different JAKi on the pro-inflammatory response of activated RA-FLS.

Methods RA-FLS were isolated from synovial tissue of patients with known RA undergoing joint replacement surgery. The cells were pretreated with different concentrations of JAKi or vehicle control and then stimulated with IL1-β (10 or 20 ng/ml) or Oncostatin M (OSM, 100 ng/ml). After the indicated time (17–24 hour), the supernatants were collected and the concentrations of IL-6 were measured by ELISA. An assay combining the measurement of cell viability, cytotoxicity and apoptosis was performed to exclude effects of JAKi caused by cell toxicity.

Results In a pretest-setting, RA-FLS were pretreated with JAKi for 2 hour with concentrations of 1 µM and 10 µM and then stimulated with IL1-β (20 ng/ml) for 18 hour. At the concentration of 10 µM, Peficitinib, Filgotinib and Upadacitinib reduced the IL-6 release by RA-FLS, whereas Tofacitinib and Baricitinib did not change the IL-6-levels. Tofacitinib and Baricitinib at 1 and 5 µM only reduced the cytokine release if the IL-6 pathway was activated selectively with OSM (n=3). In further analyses, RA-FLS were again pretreated with Filgotinib and Peficitinib for 2 hour with clinically relevant concentrations (range between 0.01 µM and 5 µM) and then stimulated with IL1-β (10 ng/ml) for 17 hour. At the concentration of 5 µM, Peficitinib caused a reduction of IL-6 levels of 66% compared to control with IL1-β (p<0.01, n=5). However, a reduction of only 24% (p=0.12, n=5) could be observed at 1 µM. Filgotinib did not decrease IL-6 levels. Peficitinib did not change the viability, cytotoxicity or apoptosis (n=2), confirming that the observed effects were JAKi dependent.

Conclusions Peficitinib reduced the inflammatory response of RA-FLS after activation with IL1-β and appeared to be superior to Tofacitinib and Baricitinib in targeting RA-FLS. The lack of effect of Tofacitinib and Baricitinib on RA-FLS activated by IL1-β could explain the treatment failure in some patients.

Reference

1. . Schwartz, et al. Type I/II cytokines, JAKs, and new strategies for treating autoimmune diseases. Nat Rev Rheumatol2016January;12(1):25–36.

Disclosure of interest None declared