Iguratimod as a New Drug for Rheumatoid Arthritis: Current Landscape

Iguratimod, a novel disease-modifying antirheumatic drug, which is now used in clinics in China and Japan, has been confirmed as a highly efficacious and safe drug for rheumatoid arthritis therapy. The antiarthritic mechanism of iguratimod, especially compared with that of the classical disease-modifying antirheumatic drugs, has not been elucidated. In this study, we conducted a comparative analysis of the antiarthritic effects of iguratimod and two reference drugs, methotrexate and leflunomide. We found that iguratimod dose dependently and potently inhibited arthritic inflammation of the synovium in collagen-induced arthritis and predominantly targeted IL-17 signaling. Consistent with its effects in vivo, iguratimod significantly suppressed the expression of various proinflammatory factors triggered by IL-17 in the cultured fibroblast-like synoviocytes. The inhibition of IL-17 signaling by iguratimod was further linked to a decrease in the mRNA stability of related genes and a reduction in phosphorylation of MAPKs. Iguratimod mainly targets Act1 to disrupt the interaction between Act1 and TRAF5 and IKKi in the IL-17 pathway of synoviocytes. Together, our results suggest that iguratimod yields a strong improvement in arthritis via its unique suppression of IL-17 signaling in fibroblast-like synoviocytes. This feature of iguratimod is different from those of methotrexate and leflunomide. This study may be helpful for further understanding the unique antiarthritic mechanism of iguratimod in patients with rheumatoid arthritis.

To clarify the pharmacological action of an anti-rheumatic agent T-614, we investigated its effects on immunoglobulin (Ig) production by cultured B cells and Ig secretion from synovial tissues of patients with rheumatoid arthritis (RA) using SCID mice engrafted with human RA tissue (SCID-HuRAg). Murine B cells were prepared from mouse spleen by a T-cell depletion method. The cells were cultured with lipopolysaccharide (LPS) and/or interleukin 4 (IL-4) in the absence or presence of T-614. Human B cells were isolated from peripheral blood of healthy donors and the Ig production was induced by co-culture with autologous T cells and anti-CD3 antibody. SCID-HuRAg was prepared according to our previous method. T-614 was orally administered to the mice once daily for 4 weeks starting on the fourth week after the implantation. Then, peripheral blood was obtained and the implanted tissues were removed. Igs in the culture media or the sera were determined by enzyme-linked immunosorbent assay (ELISA). In murine B-cell cultures, T-614 significantly decreased not only the IgM production stimulated with LPS but IgG1 production induced by LPS and IL-4. Regarding human B cells stimulated with T cells, it also inhibited IgM and IgG production. In SCID-HuRAg mice, high concentrations of polyclonal human IgG were detectable in the sera of all mice. A significant decrease in the IgG level was observed in the T-614-treated group compared with the control group. We showed that T-614 inhibited Ig production by the cultured B cells and also decreased the high level of human IgG observed in SCID-HuRAg mice. These results may support its effect on plasma Ig in RA patients and provide insights into the mechanisms of its anti-rheumatic effect.

To assess the efficacy and safety of T-614 versus methotrexate (MTX) in patients with active rheumatoid arthritis (RA). In this multicenter, double-blind trial, 489 patients randomly received either T-614 25 mg/day for the first 4 weeks and 50 mg/day for the subsequent 20 weeks (group 1, n = 163), T-614 50 mg/day for 24 weeks (group 2, n = 163), or MTX 10 mg/week for the first 4 weeks and 15 mg/week for the subsequent 20 weeks (n = 163). Clinical and laboratory parameters were analyzed at baseline and at 4, 10, 17, and 24 weeks. After 24 weeks of treatment, the American College of Rheumatology 20% improvement criteria response rate for patients in T-614 group 2 (63.8%) was not statistically significantly different from that for patients receiving MTX treatment (62.0%), and was superior to that for patients in T-614 group 1 (50.9%). The result of the noninferiority analysis indicated that the efficacy of T-614 (50 mg/day) was not lower than that of MTX by <10%. Rheumatoid factor and IgA, IgG, and IgM demonstrated a statistically significant decrease in all groups. Frequently reported adverse events included hematologic disorder, skin reactions, gastrointestinal symptoms, and transient liver enzyme elevations in the T-614 therapy groups. Side effects in the T-614 groups were generally fewer and milder than in the MTX group, except for skin reactions. There were no prominent cardiovascular adverse events and gastrointestinal ulcers found in the T-614 groups. Results indicate that T-614 therapy 50 mg/day is effective and well tolerated, and represents a new option for the treatment of patients with active RA.