Ternatin and improved synthetic variants kill cancer cells by targeting the elongation factor-1A ternary complex.

Jordan D Carelli,Steven G Sethofer,Nathan T Ross,Jillian L Simard,Jack Taunton,Rishi K Jain,William C Merrick,Geoffrey A Smith,Howard R Miller

doi:10.7554/elife.10222

Abstract

Cyclic peptide natural products have evolved to exploit diverse protein targets, many of which control essential cellular processes. Inspired by a series of cyclic peptides with partially elucidated structures, we designed synthetic variants of ternatin, a cytotoxic and anti-adipogenic natural product whose molecular mode of action was unknown. The new ternatin variants are cytotoxic toward cancer cells, with up to 500-fold greater potency than ternatin itself. Using a ternatin photo-affinity probe, we identify the translation elongation factor-1A ternary complex (eEF1A·GTP·aminoacyl-tRNA) as a specific target and demonstrate competitive binding by the unrelated natural products, didemnin and cytotrienin. Mutations in domain III of eEF1A prevent ternatin binding and confer resistance to its cytotoxic effects, implicating the adjacent hydrophobic surface as a functional hot spot for eEF1A modulation. We conclude that the eukaryotic elongation factor-1A and its ternary complex with GTP and aminoacyl-tRNA are common targets for the evolution of cytotoxic natural products.

Highlights

Macrocyclic natural products are a rich source of biologically active compounds, and identification of their targets can open up new opportunities for therapeutic intervention (Driggers et al, 2008; Villar et al, 2014)
Synthesis of 3 and 4 proceeded uneventfully according to a route previously established for ternatin (Shimokawa et al, 2007)
Using the ternary complex assembled from eukaryotic elongation factor-1A (eEF1A), GTP, and PhetRNA, we found that didemnin and ansatrienin could compete with photo-ternatin 5 (Figure 4d)

Summary

Introduction

Macrocyclic natural products are a rich source of biologically active compounds, and identification of their targets can open up new opportunities for therapeutic intervention (Driggers et al, 2008; Villar et al, 2014). Examples of cyclic peptides with well characterized cellular targets include cyclosporin (Liu et al, 1991), trapoxin and romidepsin (Taunton et al, 1996; Nakajima et al, 1998), and cotransin/CAM741 and decatransin (Besemer et al, 2005; Garrison et al, 2005; Junne et al, 2015). These macrocyclic compounds target conserved eukaryotic proteins that play essential roles in calcium-mediated signaling (cyclophilin/calcineurin), epigenetic regulation (histone deacetylases), and secretory protein biogenesis (Sec translocon), respectively.

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Results

Conclusion