Small-Molecule Quinolinol Inhibitor Identified Provides Protection against BoNT/A in Mice

Abstract

Botulinum neurotoxins (BoNTs), etiological agents of the life threatening neuroparalytic disease botulism, are the most toxic substances currently known. The potential for the use as bioweapon makes the development of small-molecule inhibitor against these deadly toxins is a top priority. Currently, there are no approved pharmacological treatments for BoNT intoxication. Although an effective vaccine/immunotherapy is available for immuno-prophylaxis but this cannot reverse the effects of toxin inside neurons. A small-molecule pharmacological intervention, especially one that would be effective against the light chain protease, would be highly desirable. Similarity search was carried out from ChemBridge and NSC libraries to the hit (7-(phenyl(8-quinolinylamino)methyl)-8-quinolinol; NSC 84096) to mine its analogs. Several hits obtained were screened for in silico inhibition using AutoDock 4.1 and 19 new molecules selected based on binding energy and Ki. Among these, eleven quinolinol derivatives potently inhibited in vitro endopeptidase activity of botulinum neurotoxin type A light chain (rBoNT/A-LC) on synaptosomes isolated from rat brain which simulate the in vivo system. Five of these inhibitor molecules exhibited IC50 values ranging from 3.0 nM to 10.0 µM. NSC 84087 is the most potent inhibitor reported so far, found to be a promising lead for therapeutic development, as it exhibits no toxicity, and is able to protect animals from pre and post challenge of botulinum neurotoxin type A (BoNT/A).

A Rabbit Model for the Evaluation of Drugs for Treating the Chronic Phase of Botulism

“…To date, only a few publications have shown beneficial treatment of botulism with experimental INABDs [21,[27][28][29][30][31][32][33][34]. Due to the absence of approved INABDs, the proof of concept of our model, in terms of measuring the beneficial effects of potential anti-BoNT/A compounds, was assessed by pharmaceutical antitoxin.…”

High-Throughput Screening Uncovers Novel Botulinum Neurotoxin Inhibitor Chemotypes

“…These IC 50 values are consistent with previous studies that reported lowmicromolar IC 50 values. 26,35,38 Using these compounds as a starting point, this series has been expanded and detailed structure−activity and ADME studies have been performed. 37 Next, we determined the potency of 27 spiro(indolthiadiazole) compounds (1 hit and 26 additional structures) available from the ChemBridge small molecule repository.…”

“…Several small molecule HTS campaigns with recombinant LC/A (rLC/A) have been described, although the majority of inhibitory compounds initially identified possess poor (i.e., micromolar) inhibitory constants ( K i ). − More recently, inhibitory compounds with submicromolar K i values have been reported, including a betulin-derived triterpenoid with a K i of 800 nM, a quinolinol inhibitor with an estimated IC 50 of 40 nM in a rat synaptosomal model, and a “hybrid” small molecule with a K i of 600 nM . Several potent hydroxamate inhibitors have been reported, including 2,4-dichlorocinnamic hydroxamate ( K i = 300 nM), a related benzothiophene hydroxamic acid ( K i = 77 nM), and a recently reported adamantine hydroxamate ( K i = 27 nM) .…”

Substrate-based inhibitors exhibiting excellent protective and therapeutic effects against Botulinum Neurotoxin A intoxication

“…In order to further test the inhibitory effect of the most promising peptide inhibitors, a mouse model test was performed as previously reported 44 . Six-week-old female BALB/c mice were used in all the assays.…”