The chemical diversification of natural products provides a robust and general method for the creation of stereochemically rich and structurally diverse small molecules. The resulting compounds have physicochemical traits different from those in most screening collections, and as such are an excellent source for biological discovery. Herein, we subject the diterpene natural product pleuromutilin to reaction sequences focused on creating ring system diversity in few synthetic steps. This effort resulted in a collection of compounds with previously unreported ring systems, providing a novel set of structurally diverse and highly complex compounds suitable for screening in a variety of different settings. Biological evaluation identified the novel compound ferroptocide, a small molecule that rapidly and robustly induces ferroptotic death of cancer cells. Target identification efforts and CRISPR knockout studies reveal that ferroptocide is an inhibitor of thioredoxin, a key component of the antioxidant system in the cell. Ferroptocide positively modulates the immune system in a murine model of breast cancer and will be a useful tool to study the utility of pro-ferroptotic agents for treatment of cancer.
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The data supporting the findings of this study are available within the paper and Supplementary Information and are available from the corresponding author upon request. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD012805 (www.ebi.ac.uk/pride/archive/projects/PXD012805). The RNA sequencing data have been deposited to the GEO repository with accession number GSE126868 (www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE126868). The X-ray crystallography data have been deposited in the Cambridge Crystallographic Data Centre (CCDC) using the following identifiers (www. ccdc.cam.ac.uk/structures/): 1851845 (compound P1) and 1849494 (Ferroptocide).
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The authors acknowledge support from the University of Illinois and Cancer Scholars for Translational and Applied Research (C*STAR) programme and thank the NIH (R01GM118575) for support of some of the synthetic studies. The authors thank W. Woods and P. Perez Pinera for assistance with CRISPR–Cas9 studies, D. Gray and T. Woods for X-ray analysis of compounds, L. Dirikolu for calculation of pharmacokinetic (PK) parameters, B. Drown for chemoinformatic analysis of compounds, M.E. Vinyard and A. Sowers for synthetic assistance and S. Tasker for many helpful discussions.
The University of Illinois has filed patents on some compounds described in this manuscript.
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The Supplementary Information contains Supplementary Figs. 1–15, methods, chemical schemes, and NMR data
Crystallographic data for compound P1. CCDC reference 1851845
Structure factors file for compound P1. CCDC reference 1851845
Crystallographic data for Ferroptocide. CCDC reference 1849494
Structure factors file for Ferroptocide. CCDC reference 1849494
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Llabani, E., Hicklin, R.W., Lee, H.Y. et al. Diverse compounds from pleuromutilin lead to a thioredoxin inhibitor and inducer of ferroptosis. Nat. Chem. 11, 521–532 (2019). https://doi.org/10.1038/s41557-019-0261-6
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