Peptide and small molecule inhibitors of the Keap1–Nrf2 protein–protein interaction

Abstract

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.

The Keap1/Nrf2 pathway in health and disease: from the bench to the clinic

“…In addition, small molecules that can directly disrupt the Keap 1-Nrf2 protein-protein interaction are in early development and have not yet made pre-clinical trials. These include peptides and other small molecules such as tetrahydrosioquinolines and naphthalene sulfonamides, which are demonstrating potential as lead compounds for new Nrf2 activator drugs [15]. Keap-1-independent Nrf2-activators have also been identified, including nordihydroguaiaretic acid, 4U8C and LS-102.…”

Nrf2 Is an Attractive Therapeutic Target for Retinal Diseases

“…Higher concentrations of these compounds interact with other cysteine-rich proteins with lower binding affinities, leading to activation of caspases and induction of apoptosis [46]. To overcome this issue, peptide and small molecule inhibitors of the Keap1-Nrf2 protein-protein interaction (PPI) have been investigated [57, 58]. The Keap1 homodimer binds to Nrf2 through a “hinge and latch” mechanism, in which the ETGE and DLG motifs of Nrf2 interact with Keap1-DC domains (the double glycine repeat domain [DGR] plus the C-terminal region of Keap1) [59].…”

The pharmacological regulation of cellular mitophagy

“…We recently reported the identification of a small molecule that activates Nrf2 by disrupting its regulatory proteinprotein interaction (PPI) with Keap1 (Kelch-Like ECH-Associated Protein 1), 85 a redoxsensitive protein that acts as an adaptor for the Cullin 3/Rbx1 ubiquitin ligase complex, facilitating the ubiquitination of Nrf2 and its subsequent proteasomal degradation (Figure 4). 86 This compound, which we named p62/SQSTM1-mediated mitophagy inducer (PMI), increases the expression of p62/SQSTM1 and drives mitochondria into autophagy without disrupting the ΔΨm (Figure 5a). Moreover, PMI does not alter mitochondrial morphology and in contrast to common mitophagy inducers, the activation of mitophagy is not accompanied by mitochondrial swelling or fragmentation.…”

“…89 However, the vast majority of these compounds are capable of reacting with a range of cysteine-containing redox sensitive proteins, giving rise to a host of off-target effects. 86 The activation of general autophagy by sulforaphane is an example of great relevance as it occurs via a ROS-dependent mechanism and independently of its effects on Nrf2. 90 On the other hand, PMI promotes a targeted autophagic degradation of mitochondria without affecting general autophagy.…”