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

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.