Abstract B133: Identification of elatol as a novel eIF4A inhibitor and stress response activator

Abstract

Abstract It is well established that protein translation can contribute the most adaptable regulation of protein-coding gene expression, is frequently hijacked during oncogenesis, and can be targeted therapeutically. Most regulation of protein translation occurs at the initiation step with formation and function of the eIF4F complex. Many different avenues, both direct and indirect, have been explored to inhibit eIF4F and thus protein translation initiation, in particular drugs targeting eIF4F’s core-enzymatic subunit, the DEAD-box RNA helicase eIF4A. Despite extensive preclinical evaluation and high antitumor activity of these compounds, none has progressed to evaluation in cancer patients, due to a variety of pharmacokinetic and pharmacodynamic issues. We designed a novel screen to identify eIF4A inhibitors by measuring ATP hydrolysis and screened a collection of ~1,200 natural compounds and purified extracts. The marine natural product elatol was the top hit in our screen, that not only showed selectivity for eIF4A over other dead box family helicases and a panel of 97 common kinases, but also induced apoptosis in a broad range of cancer cell lines from the NCI-60 cancer cell line and CCLE panels. Elatol is well tolerated in mice at a single dose of up to 65mg/kg and showed antitumor activity. Elatol treatment reduced global protein translation measured through polysome profiling and O-propargyl puromycin incorporation as well as cap-dependent translation measured by luciferase reporter and Western blotting. The effects of elatol are similar to the rocaglate silvestrol, which inhibits eIF4A although through a very different mechanism, but elatol requires higher concentrations to achieve these effects. Interestingly, elatol treatment causes strong immediate induction of the stress response transcription factor ATF4, though assessment in ATF4-deficient cells showed the toxicity of elatol is not dependent on ATF4. Unlike with silvestrol treatment, loss of translationally regulated proteins MYC and CYCLIN D3 following elatol treatment can be partially rescued by blocking the eIF2α-mediated stress response with ISRIB. Which eIF2α kinase may be mediating these effects is still under investigation. The novel mechanism of inhibition of ATP hydrolysis may be driving these unique observations compared to other eIF4A inhibitors. We believe this study provides a novel approach for identification of small molecules that have greater clinical promise for eIF4A inhibition. Citation Format: Tara L. Peters, Joseph Tillotson, Lingxiao Li, Eli Chapman, Jonathan H. Schatz. Identification of elatol as a novel eIF4A inhibitor and stress response activator [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B133.