Inhibition of Inflammatory Cytokine Production from Rheumatoid Synovial Fibroblasts by a Novel IκB Kinase Inhibitor

Nuclear factor-κB (NF-κB) is involved in the pathophysiology of rheumatoid arthritis (RA) and is considered to be a feasible molecular target in treating patients. In the RA joint tissues, activation of NF-κB is often observed together with high amounts of the proinflammatory cytokines tumor necrosis factor (TNF)α and interleukin (IL)-1β. TNFα and IL-1β are known to stimulate NF-κB signaling and are produced as the effect of NF-κB signaling, thus forming a vicious cycle leading to a self-perpetuating nature of rheumatoid inflammation and expansion of such inflammatory response to other joints. Because a kinase called IκB kinase complex (IKK) is involved in the NF-κB activation cascade, we examined the effect of a novel IKK inhibitor, (7-[2-(cyclopropyl-methoxy)-6-hydroxyphenyl]-5-[(3S)-3-piperidinyl]-1,4-dihydro-2H-pyrido[2,3-d][1,3]oxazin-2-one hydrochloride; CHPD), on the production of inflammatory cytokines from rheumatoid synovial fibroblasts (RSF). TNFα stimulation induced production of inflammatory cytokines such as IL-6 and IL-8 in RSF, and the extent of IL-6 and IL-8 induction was dramatically reduced by CHPD under noncytotoxic concentrations. Likewise, expression of il-6 and il-8 genes was significantly reduced by CHPD. In addition, chromatin immunoprecipitation assays revealed that the DNA binding of NF-κB (p65) to il-8 promoter in RSF was induced after TNFα stimulation and that, upon CHPD treatment to RSF for 1 h, the NF-κB binding to il-8 promoter was significantly decreased. Here, we have demonstrated that an IKKβ inhibitor, CHPD, acts as an effective inhibitor for the production of inflammatory cytokines in response to proinflammatory cytokines. These findings indicate that such a IKKβ inhibitor could be a feasible candidate for an antirheumatic drug.