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Newly Designed Quinolinol Inhibitors Mitigate the Effects of Botulinum Neurotoxin A in Enzymatic, Cell-Based, and ex Vivo Assays

Bremer, PT;Adler, M;Phung, CH;Singh, AK;Janda, KD;

Botulinum neurotoxin A (BoNT/A) is one of the most deadly toxins and is the etiological agent of the potentially fatal condition, botulism. Herein, we investigated 8-hydroxyquinoline (quinolin-8-ol) as a potential inhibitor scaffold for preventing the deadly neurochemical effects of the toxin. Quinolinols are known chelators that can disrupt the BoNT/A metalloprotease zinc-containing active site, thus impeding its proteolysis of the endogenous protein substrate, synaptosomal-associated protein 25 (SNAP-25). By use of this information, the structure-activity relationship (SAR) of the quinolinol-5-sulfonamide scaffold was explored through preparation of a crude sulfonamide library and evaluation of the library in a BoNT/A LC enzymatic assay. Potency optimization of the sulfonamide hit compounds was undertaken as informed by docking studies, granting a lead compound with a submicromolar Ki. These quinolinol analogues demonstrated inhibitory activity in a cell-based model for SNAP-25 cleavage and an ex vivo assay for BoNT/A-mediated muscle paralysis.