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

Leflunomide is a novel immunosuppressive and antiinflammatory agent currently being tested for treatment of autoimmune diseases and transplant rejection. NF-κB is a transcription factor activated in response to a wide variety of inflammatory stimuli, including TNF, but whether leflunomide blocks NF-κB 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-κB activation in a dose- and time-dependent manner, with maximum inhibition at 5–10 μM. Inhibition was not restricted to TNF-induced activation, because leflunomide also inhibited NF-κB activation induced by other inflammatory agents, including phorbol ester, LPS, H 2 O 2 , okadaic acid, and ceramide. Leflunomide blocked the degradation of IκBα and subsequent nuclear translocation of the p65 subunit, steps essential for NF-κB activation. This correlated with inhibition of dual specificity-mitogen-activated protein kinase kinase as well as an Src protein tyrosine kinase, p56 lck , by leflunomide. Reducing agents did not reverse the effect of leflunomide. Leflunomide also suppressed the TNF-activated NF-κB-dependent reporter gene expression. Our results thus indicate that leflunomide is a potent inhibitor of NF-κB activation induced by a wide variety of inflammatory stimuli, and this provides the molecular basis for its anti-inflammatory and immunosuppressive effects.