KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, is a novel compound to be effective on mouse systemic lupus erythematosus

B cell-activating factor (BAFF) is a key regulator of B lymphocyte development. Signals from BAFF are transmitted through binding to a specific BAFF receptor (BAFF-R). Here, we established screening method to find a specific inhibitor for the interference of BAFF–BAFF-R interactions. We screened oxazole-4-carbonylguanidine derivatives and selected KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, as a candidate to interfere BAFF–BAFF-R interactions. KR33426 inhibited BAFF-mediated anti-apoptotic effect on splenocytes as judged by hypodiploid cell formation. KR33426 also increased the degradation of procaspase-3 that was inhibited by BAFF protein. In addition, we examined whether KR33426 was effective on the treatment of systemic lupus erythematosus-like symptom in MRLlpr/lpr mouse. When 5 or 10 mg/kg KR33426 was intraperitoneally administered to MRLlpr/lpr mice for 4 weeks, histopathological changes were ameliorated in the narrowed space between renal glomerulus and glomerulus capsule. KR33426 reduced B220+ B cell population and B cell mitogen, lipopolysaccharide-stimulated lymphocyte proliferation in splenocytes. KR33426 attenuated an increase in CD43−IgM+ immature pro-B and a decrease in CD21+ IgM+ T2-B and IgD+ IgM−recirculating-B cells on B cell development. Data show that KR33426 inhibits BAFF–BAFF-R interactions and it is effective on the treatment of systemic lupus erythematosus-like symptom in MRLlpr/lpr mice. Thus, it suggests that KR33426 is a novel candidate to develop anti-autoimmune therapeutics by the interference of BAFF–BAFF-R interactions, specifically.