OP0167 A low molecular weight baff signallinginhibitor, bik-13, ameliorates b cell activation in vitro and in vivo autoimmune models and consequently suppresses production of igg and cytokines
Authors: K. Yoshimoto, N. Seki, K. Suzuki, K. Sugahara, K. Chiba, T. Takeuchi
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> We reported that BAFF robustly increases IL-6 production by peripheral monocytes of patients with primary Sjögren's syndrome (pSS) and that the BAFF-induced IL-6 production and serum IgG levels of the patients were positively correlated with the expression level of a BAFF receptor (BR3) in pSS monocytes. Moreover, we found that IgG production by pSS B cells <i>in vitro</i> was significantly enhanced by BAFF-stimulated monocytes. These results collectively suggest that BAFF signalling via BR3 is involved in IgG overproduction and that is a possible therapeutic target to treat autoimmune diseases, such as pSS. We successfully discovered a pyrroloprymidine derivative, BIK-13, which inhibits BAFF binding to BR3 by our original high throughput screening. <h3>Objectives</h3> To explored the possibility of BIK-13 as a drug to treat autoimmune diseases. <h3>Methods</h3> Human PBMC were stimulated <i>in vitro</i> with a mixture of soluble BAFF (sBAFF), recombinant human IL-21, and anti-IgM and anti-CD40 antibodies ('multiple stimulation') to differentiate B cells into plasma blasts and/or plasma cells. BIK-13 was added to the culture and the differentiation of B cells was monitored by the expression levels of CD19/CD38/IgD and Activation-induced cytidine deaminase (AID) analysed by FACS and quantitative RT-PCR, respectively. The amounts of IL-6, IL-10 and IgG in the culture supernatants were measured by ELISA. BIK-13 was administered intraperitoneally to MRL/lpr mice and serum levels of an anti-dsDNA antibody, IL-6 and IL-10 were measured by ELISA. The proportion of B cells among splenic lymphocytes of the mice was analysed by FACS. Production of cytokines <i>in vitro</i> by stimulated splenic lymphocytes was measured by ELISA. Infiltration of lymphocytes into organs was analysed by immunohistochemistry. <h3>Results</h3> FACS analysis of multiple-stimulated human PBMC indicated that differentiation of B cells into plasma blasts and/or plasma cells was inhibited by BIK-13 in a dose dependent manner. Interestingly, increased IgG, IL-6 and IL-10 production by the stimulated PBMC were concomitantly and significantly suppressed by BIK-13. In addition, the expression level of AID in the cells was also suppressed by BIK-13, suggesting that an IgG class switching was impaired. Administration of BIK-13 to MRL/lpr mice for 16 weeks decreased the serum levels of an anti-dsDNA antibody, IL-6 and IL-10 as compared to the control. Notably, immunohistochemical analysis revealed that infiltration of B cells into salivary and lacrimal glands was remarkably suppressed in BIK-13-treated mice. Moreover, the proportion of B cells among splenic lymphocytes was also decreased in BIK-13-treated mice as compared to the control. In addition, production of IL-6 and IL-10 by activated splenic lymphocytes of the BIK-13-treated mice was also remarkably suppressed as compared to control mice. <h3>Conclusions</h3> Our data collectively suggest that BIK-13, a low molecular weight BAFF-signalling inhibitor, suppresses B cell activation/differentiation <i>in vitro</i> and consequently inhibits production of IgG and cytokines, such as IL-6 and IL-10, by the cells. The compound inhibited infiltration of B cells into organs of model mice of autoimmune diseases. These data suggest that the compound is a promising drug candidate to treat autoimmune diseases, such as pSS. <h3>Disclosure of Interest</h3> K. Yoshimoto: None declared, N. Seki Employee of: Mitsubishi Tanabe Pharma Corporation, K. Suzuki: None declared, K. Sugahara Employee of: Mitsubishi Tanabe Pharma Corporation, K. Chiba Employee of: Mitsubishi Tanabe Pharma Corporation, T. Takeuchi Grant/research support from: Mitsubishi Tanabe Pharma Corporation