Background/Purpose: We reported that the expression level of a BAFF receptor (BR3) was upregulated in peripheral monocytes of patients with primary Sjogren’s syndrome (pSS) and that the level was correlated with clinical parameters of pSS. Moreover, we found that IgG production by pSS B cells was significantly enhanced in vitro as compared to healthy controls when the cells were co-cultured with autologous BAFF-stimulated monocytes. Our data strongly suggest that the BAFF-BR3 axis plays an important role in activation of monocytes and B cells in pSS. In our different study, we discovered a pyrroloprymidine derivative, BIK-13, which inhibits BAFF binding to BR3 by our original high throughput screening for drug candidates for autoimmune diseases, such as pSS. We also discovered a structural analogue of BIK-13, BIK387, which has a stronger efficacy in suppression of B cell/monocyte functions in vitro. In this study, we demonstrate the effects of oral administration of BIK387 on differentiation of B cells and production of autoantibody in MRL/lpr mice.

Methods: BIK387 was administered orally to model mice for autoimmune diseases, MRL/lpr, of 9 weeks of age 5 times a week at a dose of 0,03, 0.1, 0.3, 1 mg/kg for 20 weeks. Serum level of an anti-dsDNA antibody was measured by ELISA. The proportion of CD138⁺ subset among B220⁺CD19⁺CD3^– B cells in spleen was analyzed by FACS after 20 weeks of administration. Splenocytes were stimulated with a combination of an anti-IgM antibody, CD40 Ligand, BAFF and IL-21(multiple B cell stimulants) for 7 days and the amounts of IgG and anti-dsDNA antibody in the culture supernatants were measured by ELISA. The expression levels of IRF4 and Blimp1 in splenocytes were analyzed by qPCR.

Results: The titer of serum anti-dsDNA antibody in MRL/lpr mice orally received BIK387 was significantly suppressed in a dose dependent manner as compared to the control mice. The proportion of B220⁺CD19⁺CD3^– cells (total B cells) to total lymphocytes was significantly lower in BIK387-treated mice at the dose of 1 mg/kg than control (p = 0.04). Notably, the population of CD138⁺ plasma cells was also reduced among total B cells (p = 0.04). In addition, the production of total IgG and anti-dsDNA antibody by stimulated B cells and the expression levels of IRF4 and Blimp1in splenocytes were significantly decreased in BIK387-treated mice.

Conclusion: Our data suggest that oral administration of BIK387 suppresses B cell activation and differentiation into plasma cells in vivo, and shows the therapeutic possibility of the compound to treat autoimmune diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/oral-administration-of-a-novel-pyrrolopyrimidine-derivative-that-inhibits-baff-signaling-suppresses-b-cell-differentiation-and-production-of-autoantibody-in-autoimmune-model-mice/