Blocking anthrax lethal toxin at the protective antigen channel by using structure-inspired drug design

Area of Science:

• Biochemistry
• Toxicology
• Drug Discovery

Background:

• Bacillus anthracis secretes toxins (protective antigen, lethal factor, edema factor) that form lethal complexes.
• Protective antigen (PA) creates a pore for lethal factor (LF) and edema factor (EF) entry into host cells.
• Current treatments for inhalational anthrax are limited, especially post-exposure.

Purpose of the Study:

• To develop a novel therapeutic approach by blocking the PA pore to prevent anthrax toxin entry.
• To design and synthesize small molecules targeting the PA pore's structure and charge.

Main Methods:

• Rational drug design based on PA pore symmetry and charge.
• Chemical modification of beta-cyclodextrins to create positively charged molecules.
• Channel reconstitution and high-resolution conductance recording to assess pore blockage.
• In vitro cytotoxicity assays and in vivo animal studies (mice and rats).

Main Results:

• A modified beta-cyclodextrin derivative, per-6-(3-aminopropylthio)-beta-cyclodextrin, effectively blocked the PA pore at subnanomolar concentrations.
• The compound demonstrated significant protection against anthrax lethal toxin-induced cytotoxicity in mouse macrophages.
• Complete protection was observed in Fischer F344 rats challenged with anthrax lethal toxin.

Conclusions:

• High-affinity blockage of the PA pore by a rationally designed small molecule is a viable strategy against anthrax toxin.
• This approach holds potential for developing new, structure-directed treatments for anthrax.
• Further drug discovery efforts can build upon this method for effective anthrax therapies.