A small bioactive glycoside inhibits epsilon toxin and prevents cell death

• Published in: Disease models & mechanisms 2019-10, Vol.12 (10)
• Main Authors: Shivappagowdar, Abhishek, Pati, Soumya, Narayana, Chintam, Ayana, Rajagopal, Kaushik, Himani, Sah, Raj, Garg, Swati, Khanna, Ashish, Kumari, Jyoti, Garg, Lalit, Sagar, Ram, Singh, Shailja
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Bacterial Toxins - chemistry; Bacterial Toxins - toxicity; Calcium - metabolism; Cell death; Cell Death - drug effects; Crystal structure; Cytotoxicity; Dogs; Glucose; glycoside-4; Glycosides; Glycosides - biosynthesis; Glycosides - chemistry; Glycosides - pharmacology; Green Chemistry Technology; Homeostasis - drug effects; Kidneys; Ligands; Liposomes - ultrastructure; Madin Darby Canine Kidney Cells; Mice, Inbred C57BL; micelle formation; Molecular Docking Simulation; Molecular Dynamics Simulation; NMR; Nuclear magnetic resonance; oligomerization; Proteins; Simulation; structure-activity relationship; Toxicity; β-pft
• ISSN: 1754-8403; 1754-8411
• DOI: 10.1242/dmm.040410

epsilon toxin (Etx) is categorized as the third most lethal bioterrorism agent by the Centers for Disease Control and Prevention (CDC), with no therapeutic counter measures available for humans. Here, we have developed a high-affinity inhibitory compound by synthesizing and evaluating the structure activity relationship (SAR) of a library of diverse glycosides (numbered 1-12). SAR of glycoside-Etx heptamers revealed exceptionally strong H-bond interactions of glycoside-4 with a druggable pocket in the oligomerization and β-hairpin region of Etx. Analysis of its structure suggested that glycoside-4 might self-aggregate to form a robust micelle-like supra-molecular complex due to its linear side-chain architecture, which was authenticated by fluorescence spectroscopy. Further, this micelle hinders the Etx monomer-monomer interaction required for oligomerization, validated by both surface plasmon resonance (SPR) and immunoblotting. This phenomenon in turn leads to blockage of pore formation. Downstream evaluation revealed that glycoside-4 effectively blocked cell death of Etx-treated cultured primary cells and maintained cellular homeostasis via disrupting oligomerization, blocking pore formation, restoring calcium homeostasis, stabilizing the mitochondrial membrane and impairing high mobility group box 1 (HMGB1) translocation from nucleus to cytoplasm. Furthermore, a single dosage of glycoside-4 protected the Etx-challenged mice and restored normal function to multiple organs. This work reports for the first time a potent, nontoxic glycoside with strong ability to occlude toxin lethality, representing it as a bio-arm therapeutic against Etx-based biological threat.