Advances in developing noncovalent small molecules targeting Keap1

Expanding the ligand spaces for E3 ligases for the design of protein degraders

Targeted protein degradation (TPD) has recently emerged as an exciting new drug modality. However, the strategy of developing small molecule-based protein degraders has evolved over the past two decades and has now established molecular tags that are already in clinical use, as well as chimeric molecules, PROteolysis TArgeting Chimeras (PROTACs), based mainly on ligand systems developed for the two E3 ligases CRBN and VHL. The large size of the human E3 ligase family suggests that PROTACs can be developed by targeting a large diversity of E3 ligases, some of which have restricted expression patterns with the potential to design disease- or tissue-specific degraders. Indeed, many new E3 ligands have been published recently, confirming the druggability of E3 ligases. This review summarises recent data on E3 ligases and highlights the challenges in developing these molecules into efficient PROTACs rivalling the established degrader systems.

Specific targeting of the NRF2/β-TrCP axis promotes beneficial effects in NASH

Non-alcoholic steatohepatitis (NASH) is a common chronic liver disease that compromises liver function, for which there is not a specifically approved medicine. Recent research has identified transcription factor NRF2 as a potential therapeutic target. However, current NRF2 activators, designed to inhibit its repressor KEAP1, exhibit unwanted side effects. Alternatively, we previously introduced PHAR, a protein-protein interaction inhibitor of NRF2/β-TrCP, which induces a mild NRF2 activation and selectively activates NRF2 in the liver, close to normal physiological levels. Herein, we assessed the effect of PHAR in protection against NASH and its progression to fibrosis. We conducted experiments to demonstrate that PHAR effectively activated NRF2 in hepatocytes, Kupffer cells, and stellate cells. Then, we used the STAM mouse model of NASH, based on partial damage of endocrine pancreas and insulin secretion impairment, followed by a high fat diet. Non-invasive analysis using MRI revealed that PHAR protects against liver fat accumulation. Moreover, PHAR attenuated key markers of NASH progression, including liver steatosis, hepatocellular ballooning, inflammation, and fibrosis. Notably, transcriptomic data indicate that PHAR led to upregulation of 3 anti-fibrotic genes (Plg, Serpina1a, and Bmp7) and downregulation of 6 pro-fibrotic (including Acta2 and Col3a1), 11 extracellular matrix remodeling, and 8 inflammatory genes. Overall, our study suggests that the mild activation of NRF2 via the protein-protein interaction inhibitor PHAR holds promise as a strategy for addressing NASH and its progression to liver fibrosis.