NF-κB inhibitor is a synthetic peptide corresponding to the nuclear localization sequence of NF-κB p105 subunit (also known as p50) appended to a hydrophobic sequence to facilitate import into living cells. It blocks the nuclear import of p105 in cells treated with activators of NF-κB signaling, including LPS and TNF-α. In this way, NF-κB inhibitor blocks gene expression that is regulated by NF-κB. This peptide is commonly used to evaluate the role of NF-κB signaling in cellular responses.