Immunosuppressive leflunomide metabolite (A77 1726) blocks TNF-dependent nuclear factor-kappa B activation and gene expression

Leflunomide is a novel immunosuppressive and antiinflammatory agent current ly being tested for treatment of autoimmune diseases and transplant rejecti on. NF-kappa B is a transcription factor activated in response to a wide va riety of inflammatory stimuli, including TNF, but whether leflunomide block s NF-kappa B activation is not known. In the present report we demonstrate that treatment of a human T cell line (Jurkat) with leflunomide blocks TNF- mediated NF-kappa B activation in a dose- and time-dependent manner, with m aximum inhibition at 5-10 mu M. Inhibition was not restricted to TNF-induce d activation, because leflunomide also inhibited NF-kappa B activation indu ced by other inflammatory agents, including phorbol ester, LPS, H2O2, okada ic acid, End ceramide, Leflunomide blocked the degradation of I kappa B alp ha and subsequent nuclear translocation of the p65 subunit, steps essential for NF-kappa B activation. This correlated with inhibition of dual specifi city-mitogen-activated protein kinase kinase as well as an Src protein tyro sine kinase, p56(lck), by leflunomide, Reducing agents did not reverse the effect of leflunomide. Leflunomide also suppressed the TNF-activated NF-kap pa B-dependent reporter gene expression. Our results thus indicate that lef lunomide is a potent inhibitor of NF-kappa B activation induced by a wide v ariety of inflammatory stimuli, and this provides the molecular basis for i ts anti-inflammatory and immunosuppressive effects.