Abstract 4507: Discovery of a smart molecular glue: A small-molecular compound selectively degrades Nrf2 in KEAP1-mutated tumor cells, by restoring the broken KEAP1 mutant/Nrf2 interaction
Authors: Tian Xiaohong , Aboulkassim Tahar , Liu Qiang , Hancock Mark , Wu Jian Hui , Batist Gerald 
Published: March 2024

Overcoming therapeutic resistance without incurring prohibitive normal tissue toxicity is a great challenge in anticancer therapies. Transcription factor NRF2 is a master regulator of cellular protective response, which provides protective effects in normal tissues. KEAP1, the endogenous NRF2 inhibitor, binds NRF2 and redirect it towards proteasome-dependent degradation. KEAP1/NRF2 interaction is therefore critical for maintaining NRF2 at a basal level. Accumulated studies revealed cancer cells could hijack NRF2 pathway to confer drug resistance. A number of clinically-relevant KEAP1 mutations were shown to disrupt the KEAP1/NRF2 interaction, leading to elevated NRF2 level and confer drug resistance. Here, by structure-based drug design approach, we discovered a small-molecule NRF2 inhibitor, R16, which selectively binds KEAP1 mutants and restores their NRF2-inhibitory function in tumor cells. We performed in silico screening against the NCI-open database. Top-ranking candidates were initially evaluated by ARE-luc reporter assays, leading to discovery of R16. Effect of R16 in restoring interaction between KEAP1 mutants and NRF2 were evaluated by BRET2 assays. Among 14 KEAP1 mutations that result in disruption of KEAP1/NRF2 interaction, R16 is active against 11 of them. A variety of assays, including tryptophan quenching, cellular target engagement, BRET2 and GST-pull down assays, indicated that R16 selectively engage KEAP1 mutants and restore their interaction with NRF2, leading to NRF2 degradation. R16 at 0.5 uM substantially sensitizes KEAP1-mutated tumor cells to cisplatin and gefitinib, with no obvious effect in wild-type KEAP1 cells. Importantly, R16 showed significant in-vivo efficacy in sensitizing A549 xenograft bearing KEAP1 G333C mutation to cisplatin, while it has no effect on xenograft with wild-type KEAP1. KEAP1-mutated tumors are emerging as a sub-group with severe resistance to currently available therapies. Here, we have identified a KEAP1 mutant-selective NRF2 inhibitor, which potently sensitizes KEAP1-mutated cells/tumors to anticancer agents, with little effects on the WT-KEAP1. Our work demonstrated it is feasible to restore the NRF2-inhibitory function of KEAP1 mutants, by targeting the mutants with compounds to repair the disrupted KEAP1 mutant/NRF2 interactions. The KEAP1 mutant-selectivity is critical, as NRF2 is a master regulator of cellular defense response in WT-KEAP1 normal tissues.

Citation Format: Xiaohong Tian, Tahar Aboulkassim, Qiang Liu, Mark Hancock, Jian Hui Wu, Gerald Batist. Discovery of a smart molecular glue: A small-molecular compound selectively degrades Nrf2 in KEAP1-mutated tumor cells, by restoring the broken KEAP1 mutant/Nrf2 interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4507.