Peptidomimetic-based identification of FDA-approved compounds inhibiting IRE1 activity.

Dimitrios Doultsinos,Eric Chevet,Chetan Chintha,Adrienne W Paton,Leif A Eriksson,Antonio Carlesso,Afshin Samali,James C Paton

doi:10.1111/febs.15372

Abstract

Inositol-requiring enzyme 1 (IRE1) is a bifunctional serine/threonine kinase and endoribonuclease that is a major mediator of the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress. Tumour cells experience ER stress due to adverse environmental cues such as hypoxia or nutrient shortage and high metabolic/protein-folding demand. To cope with those stresses, cancer cells utilise IRE1 signalling as an adaptive mechanism. Here, we report the discovery of the FDA-approved compounds methotrexate, cefoperazone, folinic acid and fludarabine phosphate as IRE1 inhibitors. These were identified through a structural exploration of the IRE1 kinase domain using IRE1 peptide fragment docking and further optimisation and pharmacophore development. The inhibitors were verified to have an impact on IRE1 activity invitro and were tested for their ability to sensitise human cell models of glioblastoma multiforme (GBM) to chemotherapy. We show that all molecules identified sensitise glioblastoma cells to the standard-of-care chemotherapy temozolomide (TMZ).

Highlights

The unfolded protein response (UPR) is a homeostatic mechanism designed to alleviate endoplasmic reticulum (ER) stress caused by the accumulation of misfolded proteins
We demonstrate that they have an impact on Inositol-requiring enzyme 1 (IRE1) activity in vitro and in human cell models of glioblastoma multiforme (GBM) whilst at the same time addressing the clinical relevance of IRE1 inhibition in oncology by demonstrating that the administration of these compounds sensitises human cancer cells to chemotherapy
The peptides preferentially occupied this active site. At this point, having explored potential docking of the peptide library on the entire kinase domain it was evident that small peptides derived from the IRE1 kinase structure would preferentially dock onto the adenosine triphosphate (ATP)-binding pocket

Summary

Introduction

The unfolded protein response (UPR) is a homeostatic mechanism designed to alleviate endoplasmic reticulum (ER) stress caused by the accumulation of misfolded proteins. It has been shown that IRE1 in particular plays a decisive role in tumorigenesis and tumour aggressiveness, as well as post-therapy response in, for example, cancers of the breast, pancreas, prostate and brain [3,4,5,6] This pertains to the possibility that targeting IRE1 activity could lead to sensitisation of tumours to current therapies as cancer cells would exhibit reduced capacity to cope with the hostile environment. Such studies have been performed in triple-negative breast cancer (TNBC) showing that the inhibition of IRE1 RNase activity with salicylaldehyde MKC8866 increased paclitaxel-dependent attenuation of TNBC development in mouse xenograft models [7] or in glioblastoma multiforme (GBM) models [8]. This covalent inhibitor is currently tested on other types of cancers

Methods

Results

Conclusion