Geldanamycin-Derived HSP90 Inhibitors Are Synthetic Lethal with NRF2

Abstract

Activating mutations in KEAP1-NRF2 are frequently found in tumours of the lung, oesophageous and liver, where they are associated with aggressive growth, resistance to cancer therapies, and low overall survival. Despite the fact that NRF2 is a validated driver of tumorigenesis and chemotherapeutic resistance, there are currently no approved drugs which can inhibit its activity. Therefore, there is an urgent clinical need to identify NRF2-selective cancer therapies. To this end, we developed a novel synthetic lethal assay, based on fluorescently labelled isogenic wild-type and Keap1 knockout cell lines, in order to screen for compounds which selectively kill cells in an NRF2-dependent manner. Through this approach, we identified three compounds based on the geldanamycin scaffold which display synthetic lethality with NRF2. Mechanistically, we show that NRF2 target genes metabolize the quinone-containing geldanamycin compounds into more potent HSP90 inhibitors, which enhances their cytotoxicity while simultaneously restricting the synthetic lethal effect to cells with aberrant NRF2 activity. As all three of the geldanamycin-derived compounds have been used in clinical trials, they represent ideal candidates for drug repositioning to target the currently untreatable NRF2 activity in cancer.

The diverse functionality of NQO1 and its roles in redox control

“…Nrf2 is activated in many tumor types and such tumors often exhibit resistance to existing therapies resulting in poor patient outcomes [ 141 ]. This has led to the development of Keap1 knockout cell line screens for the identification of compounds that exhibit synthetic lethality with Nrf2 overexpression [ 142 , 143 ]. Compounds such as mitomycin C and quinone based Hsp90 inhibitors which are activated by NQO1 have been identified in screens for agents that induce selective toxicity to tumors with activated Nrf2 [ 142 , 143 ].…”

“…This has led to the development of Keap1 knockout cell line screens for the identification of compounds that exhibit synthetic lethality with Nrf2 overexpression [ 142 , 143 ]. Compounds such as mitomycin C and quinone based Hsp90 inhibitors which are activated by NQO1 have been identified in screens for agents that induce selective toxicity to tumors with activated Nrf2 [ 142 , 143 ]. Nrf2 activation would increase tumor NQO1 levels leading to activation of either mitomycin C to reactive quinone methide metabolites capable of alkylating DNA and the generation of hydroquinone derivatives of geldanamycin quinones which are more active Hsp90 inhibitors [ 22 , 24 ].…”

“…However, additional molecules such as the aurora kinase inhibitor AT9283 have also been identified in these screens for selective killing of tumor cells with elevated Nrf2 levels [ 147 ] which do not have obvious links to NQO1-mediated bioreductive activation, although NQO1 has been reported to bind directly to aurora A [ 148 ]. A more complete analysis of compounds activated in cells with activated Nrf2 is detailed in the original references [ 142 , 143 , 147 ] and in a comprehensive recent review by Hayes and colleagues [ 141 ].…”

Heat Shock Proteins in Oxidative Stress and Ischemia/Reperfusion Injury and Benefits from Physical Exercises: A Review to the Current Knowledge

“…Baird et al showed that Nrf2 target genes metabolize the quinone-containing geldanamycin compounds into more potent HSP90 inhibitors. They can enhance their cytotoxicity while simultaneously restricting the lethal effect on cells with aberrant Nrf2 activity, resulting in cell death [ 34 ]. This is a different approach to understanding the interaction network between HSP and OS.…”

The KEAP1–NRF2 System as a Molecular Target of Cancer Treatment

“…NRF2-addicted cancers show constitutively upregulation of NRF2 target genes. A cell culture system was established in which KEAP1-deleted cells and KEAP1-expressing normal cells were cocultured, and their proliferation was monitored by the distinct colors of fluorescence [ 91 ]. Drug screenings that aim to identify synthetic lethal chemical compounds that specifically kill cancer cells with intrinsically high NRF2 activity have been identified.…”