Signal transducer and activator of transcription (STAT) 3 is a key signalling protein engaged by a multitude of growth factors and cytokines to elicit diverse biological outcomes including cellular growth, differentiation, and survival[3].Ochromycinone ((Rac)-STA-21) is a natural antibiotic and a STAT3 inhibitor. Ochromycinone can inhibits STAT3 DNA binding activity, STAT3 dimerization. Ochromycinone has anticancer and antimicrobial activity[4].STA-21 inhibits STAT3 DNA binding activity, STAT3 dimerization, and STAT3-dependent luciferase activity. Moreover, STA-21 reduces the survival of breast carcinoma cells with constitutive STAT3 signaling but has minimal effect on the cells in which constitutive STAT3 signaling is absent[5]. STA-21 enhanced the clinical course of arthritis in CAIA mice and decreased CD8+RORγt+ and CD8+IL-21+ cells while inducing the production of CD8+Foxp3+ cells. Furthermore, STA-21 prevented the production of TNF-α and IL-6 in peripheral blood and increased IL-27 production by CD14+ cells. Moreover, STA-21 not only regulates Th1/Th2 serum cytokine levels but also the mRNA and protein expression of key factors including NF-κB p65, RORγt, T-bet, IL-4, GATA-3, JAK1, Stat3, and IL-21[6].STA-21 suppressed inflammatory arthritis in IL-1Ra-KO mice. The proportion of Th17 cells was decreased and the proportion of Treg cells expressing FoxP3 was markedly increased in the spleens of STA-21-treated mice. Adoptive transfer of CD4+CD25+ T cells obtained from STA-21-treated IL-1Ra-KO mice markedly suppressed inflammatory arthritis. In vitro treatment with STA-21 induced the expression of FoxP3 and repressed IL-17 expression in both mouse and human CD4+ T cells. Moreover, STA-21 prevented both mouse BMM cells and human monocytes from differentiating into osteoclasts in vitro[7].
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