Targeting NF-κB p65 with a Helenalin Inspired Bis-electrophile

The canonical NF-κB
signaling pathway is a mediator of the
cellular inflammatory response and a target for developing therapeutics
for multiple human diseases. The furthest downstream proteins in the
pathway, the p50/p65 transcription factor heterodimer, have been recalcitrant
toward small molecule inhibition despite the substantial number of
compounds known to inhibit upstream proteins in the activation pathway.
Given the roles of many of these upstream proteins in multiple biochemical
pathways, targeting the p50/p65 heterodimer offers an opportunity
for enhanced on-target specificity. Toward this end, the p65 protein
presents two nondisulfide cysteines, Cys38 and Cys120, at its DNA-binding
interface that are amenable to targeting by covalent molecules. The
natural product helenalin, a sesquiterpene lactone, has been previously
shown to target Cys38 on p65 and ablate its DNA-binding ability. Using
helenalin as inspiration, simplified helenalin analogues were designed,
synthesized, and shown to inhibit induced canonical NF-κB signaling
in cell culture. Moreover, two simplified helenalin probes were proficient
at forming covalent protein adducts, binding to Cys38 on recombinant
p65, and targeting p65 in HeLa cells without engaging canonical NF-κB
signaling proteins IκBα, p50, and IKKα/β.
These studies further support that targeting the p65 transcription
factor–DNA interface with covalent small molecule inhibitors
is a viable approach toward regulating canonical NF-κB signaling.