Peptide and small molecule inhibitors of the Keap1-Nrf2 protein-protein interaction.

The transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2) up-regulates the expression of a range of cytoprotective enzymes with antioxidant response elements in their promoter regions and thus can protect cells against oxidative damage. Increasing Nrf2 activity has been proposed as a therapeutic intervention in a range of chronic neurodegenerative conditions and cancer chemoprevention. One of the main mechanisms by which Nrf2 is negatively regulated involves an interaction with the ubiquitination facilitator protein, Kelch-like ECH-associated protein 1 (Keap1) that facilitates degradation of Nrf2. Inhibition of this process underlies the mode of action of a broad group of compounds that increase Nrf2 activity. A number of natural products, including the isothiocyanate sulforaphane, up-regulate Nrf2 by interacting with Keap1 in a covalent manner to stall its activity. Recently, a number of peptide and small molecule inhibitors of the protein-protein interaction (PPI) between Keap1 and Nrf2 have been described. These classes of compound have contrasting modes of action at the molecular level and there is emerging evidence that their biological activities have similarities and differences. This review describes the various classes of PPI inhibitor that have been described in the literature and the biological evaluations that have been performed.