Background: Biologically active natural products continue to be useful in the exploration and control of intracellular signaling processes. For example, the sesquiterpene lactone parthenolide from the anti-inflammatory medicinal herb Feverfew (Tanacetum parthenium) appears to inhibit the pro-inflammatory signaling pathway. Parthenolide's direct molecular target, however, remains unknown. We set out to identify the molecular mechanisms of parthenolide's anti-inflammatory activity.
Results: A parthenolide affinity reagent was synthesized and shown to bind directly to and inhibit IkappaB kinase beta (IKKbeta), the kinase subunit known to play a critical role in cytokine-mediated signaling. Mutation of cysteine 179 in the activation loop of IKKbeta abolished sensitivity towards parthenolide. Moreover, we showed that parthenolide's in vitro and in vivo anti-inflammatory activity is mediated through the alpha-methylene gamma-lactone moiety shared by other sesquiterpene lactones.
Conclusions: In recent years, the multi-subunit IKK complex has been shown to be responsible for cytokine-mediated stimulation of genes involved in inflammation and as such represents an attractive target for pharmaceutical intervention. Our finding that parthenolide targets this kinase complex provides a possible molecular basis for the anti-inflammatory properties of parthenolide. In addition, these results may be useful in the development of additional anti-inflammatory agents.