Rheumatoid arthritis (RA) is a representative autoimmune disease characterized by chronic inflammation and joint destruction. Although biological inhibitors such as TNF-α and IL-6 antibodies have achieved success in clinical therapy, small molecule inhibitors against the Janus kinases (JAKs) involved in the signaling pathways of various cytokine receptors have gained more attraction as safe and efficacious options. In this study, we identified CS12192 as a novel selective JAK3/JAK1/TBK1 inhibitor and investigated its pharmacological effects on the experimental arthritis models in rat and mouse. We found that CS12192 showed a more selective inhibitory activity on JAK3, and to a less extent on JAK1 and TBK1, that were verified by decreased activation of p-STATs and p-IRF3 as well as down-regulation of IFN gene expression in the cultured cells with relevant stimuli. Furthermore, oral treatment with CS12192 dose-dependently ameliorated the disease severity, hind paw swelling, body weight loss, and bone destruction in rat models of adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA). In a mouse CIA model, CS12192 also attenuated the disease severity, which was correlated with the suppressed CD4+ T cell activation and Th17 function, as well as the reduced cytokine levels in sera and pro-inflammatory cytokine and chemokine gene expression in joint tissue. Corroboratively, RANKL-induced osteoclast formation was inhibited by CS12192. Thus, these results suggest that CS12192 as a novel selective JAK inhibitor has therapeutic potential for the treatment of RA and may provide a new strategy for the control of autoimmune diseases.
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