The Keap1-Nrf2-ARE ((Kelch-like ECH-Associating protein 1) nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway is one of the most important defense mechanisms against oxidative and/or electrophilic stresses, and it is closely associated with inflammatory diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and aging. In recent years, progress has been made in strategies aimed at modulating the Keap1-Nrf2-ARE pathway. The Nrf2 activator DMF (Dimethylfumarates) has been approved by the FDA as a new first-line oral drug to treat patients with relapsing forms of multiple sclerosis, while a phase 3 study of another promising candidate, CDDO-Me, was terminated for safety reasons. Directly inhibiting Keap1-Nrf2 protein-protein interactions as a novel Nrf2-modulating strategy has many advantages over using electrophilic Nrf2 activators. The development of Keap1-Nrf2 protein-protein interaction inhibitors has become a topic of intense research, and potent inhibitors of this target have been identified. In addition, inhibiting Nrf2 activity has attracted an increasing amount of attention because it may provide an alternative cancer therapy. This review summarizes the molecular mechanisms and biological functions of the Keap1-Nrf2-ARE system. The main focus of this review is on recent progress in studies of agents that target the Keap1-Nrf2-ARE pathway and the therapeutic applications of such agents.
Keap1 is known to mediate the ubiquitination of Nrf2, a master regulator of the antioxidant response. Directly interrupting the Keap1-Nrf2 interaction has been emerged as a promising strategy to develop novel class of antioxidant, antiinflammatory, and anticancer agents. On the basis of the molecular binding determinants analysis of Keap1, we successfully designed and characterized the most potent protein-protein interaction (PPI) inhibitor of Keap1-Nrf2, compound 2, with K(D) value of 3.59 nM binding to Keap1 for the first time to single-digit nanomolar. Compound 2 can effectively disrupt the Nrf2-Keap1 interaction with an EC50 of 28.6 nM in the fluorescence polarization assay. It can also activate the Nrf2 transcription activity in the cell-based ARE-luciferase reporter assay in a dose-dependent manner. The qRT-PCR results of Nrf2 transcription targets gave the consistent results. These results confirm direct and highly efficient interruption of the Keap1-Nrf2 PPI can be fully achieved by small molecules.
Hsp90 is one of the
most important chaperones involved in regulating
the maturation of more than 300 client proteins, many of which are
closely associated with refractory diseases, including cancer, neurodegenerative
diseases, and viral infections. Clinical Hsp90 inhibitors bind to
the ATP pocket in the N-terminal domain of Hsp90 and subsequently
suppress the ATPase activity of Hsp90. Recently, with the increased
understanding of the discrepancies in the isoforms of Hsp90 and the
modes of Hsp90-co-chaperone-client complex interactions, some new
strategies for Hsp90 inhibition have emerged. Novel Hsp90 inhibitors
that offer selective suppression of Hsp90 isoforms or specific disruption
of Hsp90-co-chaperone protein–protein interactions are expected
to show with satisfactory efficacy and safety profiles. This review
summarizes the recent progress in Hsp90 inhibitors. Additionally,
Hsp90 inhibitory strategies are emphasized in this review.
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