LAUSR

Background With the approval of the Janus kinase inhibitors (JAKi) Tofacitinib and Baricitinib for the treatment of rheumatoid arthritis (RA) in the European Union (EU), the opportunities for a successful therapy were extended by a new substance class. Other JAKi like Peficitinib and Filgotinib are currently examined in clinical trials. Peficitinib is a pan-JAKi, whereas the other substances differ clearly in the capability to block the four members of the Janus kinase family. It is unclear, if the new substances offer an additional benefit in RA treatment in comparison to the approved JAKi. Objectives This study characterised the effect of the different JAKi on inflammatory response of activated fibroblast-like synoviocytes from patients with RA (RA-FLS). Methods RA-FLS were isolated from synovial tissue of patients with RA undergoing joint replacement surgery. The cells were pretreated for 2 hour 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 and MMP-3 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 To detect the most effective JAKi in blocking the inflammatory response induced by IL1-β, RA-FLS were first pretreated with different JAKi for 2 hour with concentrations of 1 µM and 10 µM and then additionally stimulated with IL1-β (20 ng/ml) for 18 hour. Even at the highest concentration of 10 µM Tofacitinib and Baricitinib did not change the IL-6 levels, whereas Peficitinib and Filgotinib reduced the IL-6 release at 10 µM. Tofacitinib and Baricitinib reduced the cytokine release if the RA-FLS were stimulated with OSM, a factor directly inducing the JAK-dependent IL-6-pathway (n=3). To obtain a dose-response curve for the clinically relevant range of concentrations between 0.01 µM and 5 µM, RA-FLS were pretreated with Filgotinib and Peficitinib for 2 hour and then stimulated with IL1-β (10 ng/ml) for 17 hour. In contrast to Filgotinib, Peficitinib at 5 µM caused a reduction of IL-6 levels of 66% compared to control with IL1-β (p<0.01, n=5). The MMP-3 release was decreased by both substances at 5 µM: In comparison to the control with IL1-β, Peficitinib caused a reduction of 92% (p<0.0001, n=5) whereas Filgotinib only reduced the levels by 43% (p<0.05, n=3). Furthermore, Peficitinib at 1 µM decreased the MMP-3 release by 46% (p<0.01). The treatment with Peficitinib did not affect the viability, cytotoxicity or apoptosis of RA-FLS (n=3). Therefore, the effects of Peficitinib on the inflammatory response were not caused by cell death. Conclusions Peficitinib reduced the release of proinflammatory cytokines and of matrix metalloproteinases after activation of RA-FLS with IL1-β and appeared to be superior to Tofacitinib and Baricitinib in targeting the pro-inflammatory and matrix destructive properties of RA-FLS. Disclosure of Interest None declared