The synthetic triterpenoid, CDDO-Imidazolide blocks nuclear factor-κB activation through direct inhibition of IκB kinase-beta.

A94

Signaling cascades emanating from nuclear factor-kappaB (NF-κB) activation have been shown to play pivotal roles in the processes of tumor initiation, promotion, and progression. Inhibition of this pathway is in an attractive target for chemopreventive and chemotherapeutic agents. The synthetic triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im) is a multifunctional agent with potent anti-inflammatory, anti-proliferative, cytoprotective, and apoptotic activities, whose molecular targets are unknown. Using both cell-free and cellular assays we show that CDDO-Im, at mid to high nM concentrations is a direct inhibitor of IκB kinase-beta (IKKβ), and that it thereby inhibits binding of nuclear factor-κB (NF-κB) to DNA and subsequent transcriptional activation. Pretreatment of cells with CDDO-Im prevents IκB alpha (IκBα) phosphorylation and degradation in response to tumor necrosis factor alpha (TNFα). The kinetics of this inhibition by CDDO-Im are rapid and occur with 15 minutes. A biotinylated analog of CDDO-Im showed that CDDO-Im binds to the IKK signalsome. Furthermore, we show that cysteine 179 on IKK is a target for CDDO-Im. This is the first report to demonstrate that this novel synthetic triterpenoid binds to and inhibits IKKβ directly. Due to the critical role played by NF-κB in tumor initiation, promotion, and progression, inhibition of IKKβ by this novel triterpenoid may play an important pharmacological role in its chemopreventive and chemotherapeutic capabilities. CDDO-Im is currently being evaluated as a chemopreventive agent in a number of preclinical disease models.