Polyamidoamine Dendrimers as Universal Pore-Blocking Binary Toxin Inhibitors

Abstract

Attaching multiple functional groups onto an inert scaffold is very beneficial for drug design objectives. These multi-ligand compounds often possess an additive or cooperative affinity towards multiple binding sites which is significantly higher than that of a single functional group interacting with a single binding site. Here we explore a new group of potential multivalent pore-blocking antitoxins - dendrimers, which are the repeatedly branched polymers with all bonds emanating from a central core. Dendrimers are unique highly branched macromolecules with numerous groundbreaking biomedical applications under development. In this study, we identified polyamidoamine (PAMAM) dendrimers as novel blockers for the pore-forming B components of the binary anthrax toxin (PA63) and Clostridium botulinum C2 toxin (C2IIa). These pores are essential for delivery of the enzymatic A components of the internalized toxins from endosomes into the cytosol of target cells. We demonstrate that at low µM concentrations, cationic PAMAM dendrimers block PA63 and C2IIa to inhibit channel mediated transport of the A components, thereby protecting HeLa and Vero cells from intoxication. By channel reconstitution and high-resolution current recording, we show that the PAMAM dendrimers obstruct transmembrane PA63 and C2IIa pores in planar lipid bilayers at nM concentrations. These findings suggest a new potential role for the PAMAM dendrimers as effective polyvalent channel-blocking inhibitors, which can protect human target cells from intoxication with binary toxins from pathogenic bacteria.