betadex and Anthrax

Cellular adaptation to different stresses related to survival and function has been demonstrated in several cell types. Anthrax lethal toxin (LeTx) induces rapid cell death, termed "pyroptosis," by activating NLRP1b/caspase-1 in murine macrophages. We and others (S. D. Ha et al., J. Biol. Chem. 282:26275-26283, 2007; I. I. Salles et al., Proc. Natl. Acad. Sci. U. S. A. 100:12426 -12431, 2003) have shown that RAW264.7 cells preexposed to sublethal doses of LeTx become resistant to subsequent high cytolytic doses of LeTx, termed toxin-induced resistance (TIR). To date, the cellular mechanisms of pyroptosis and TIR are largely unknown. We found that LeTx caused NLRP1b/caspase-1-dependent mitochondrial dysfunction, including hyperpolarization and generation of reactive oxygen species, which was distinct from that induced by stimuli such as NLRP3-activating ATP. In TIR cells, these mitochondrial events were not detected, although caspase-1 was activated, in response to LeTx. We identified that downregulation of the late endosomal cholesterol-transferring protein MLN64 in TIR cells was involved in TIR. The downregulation of MLN64 in TIR cells was at least in part due to DNA methyltransferase 1-mediated DNA methylation. In wild-type RAW264.7 cells and primary bone marrow-derived macrophages, LeTx caused NLRP1b/caspase-1-dependent mitochondrial translocation of MLN64, resulting in cholesterol enrichment, membrane hyperpolarization, reactive oxygen species (ROS) generation, and depletion of free glutathione (GSH). This study demonstrates for the first time that MLN64 plays a key role in LeTx/caspase-1-induced mitochondrial dysfunction.

Topics: Animals; Anthrax; Antigens, Bacterial; Bacillus anthracis; Bacterial Toxins; beta-Cyclodextrins; Caspase 1; Cell Death; Cell Line; Cells, Cultured; Cholesterol; DNA Methylation; Down-Regulation; Glutathione; Macrophages; Membrane Potential, Mitochondrial; Mice; Mitochondria; Phosphoproteins; Reactive Oxygen Species

Three new series of potential anthrax toxin inhibitors based on the β-cyclodextrin (βCD) scaffold were developed by exploiting face-selective Cu(I)-catalyzed azide-alkyne 1,3-cycloadditions, amine-isothiocyanate coupling, and allyl group hydroboration-oxidation/hydroxy → amine replacement reactions. The molecular design follows the "symmetry-complementarity" concept between homogeneously functionalized polycationic βCD derivatives and protective antigen (PA), a component of anthrax toxin known to form C₇-symmetric pores on the cell membrane used by lethal and edema factors to gain access to the cytosol. The synthesis and antitoxin activity of a collection of βCD derivatives differing in the number, arrangement, and face location of the cationic elements are reported herein. These results set the basis for a structure-activity relationship development program of new candidates to combat the anthrax threat.

Topics: Animals; Anthrax; Antigens, Bacterial; Bacillus anthracis; Bacterial Toxins; beta-Cyclodextrins; Cell Line; Chemistry, Pharmaceutical; Cluster Analysis; Computer-Aided Design; Mice; Models, Molecular; Polyamines; Polyelectrolytes; Structure-Activity Relationship

Topics: Anthrax; beta-Cyclodextrins; Biomarkers; Chelating Agents; Europium; Humans; Microscopy, Fluorescence; Picolinic Acids

We evaluated the in vivo efficacy of three beta-cyclodextrin derivatives that block the anthrax protective antigen pore. These compounds were at least 15-fold more potent than previously described beta-cyclodextrins in protecting against anthrax lethal toxin in a rat model. One of the drugs was shown to protect mice from bacterial infection.

Topics: Animals; Anthrax; Antigens, Bacterial; Bacillus anthracis; Bacterial Toxins; beta-Cyclodextrins; Disease Models, Animal; Mice; Treatment Outcome

Bacillus anthracis secretes three polypeptides: protective antigen (PA), lethal factor (LF), and edema factor (EF), which interact at the surface of mammalian cells to form toxic complexes. LF and EF are enzymes that target substrates within the cytosol; PA provides a heptameric pore to facilitate LF and EF transport into the cytosol. Other than administration of antibiotics shortly after exposure, there is currently no approved effective treatment for inhalational anthrax. Here we demonstrate an approach to disabling the toxin: high-affinity blockage of the PA pore by a rationally designed low-molecular weight compound that prevents LF and EF entry into cells. Guided by the sevenfold symmetry and predominantly negative charge of the PA pore, we synthesized small cyclic molecules of sevenfold symmetry, beta-cyclodextrins chemically modified to add seven positive charges. By channel reconstitution and high-resolution conductance recording, we show that per-6-(3-aminopropylthio)-beta-cyclodextrin interacts strongly with the PA pore lumen, blocking PA-induced transport at subnanomolar concentrations (in 0.1 M KCl). The compound protected RAW 264.7 mouse macrophages from cytotoxicity of anthrax lethal toxin (= PA + LF). More importantly, it completely protected the highly susceptible Fischer F344 rats from lethal toxin. We anticipate that this approach will serve as the basis for a structure-directed drug discovery program to find new and effective treatments for anthrax.

Topics: Animals; Anthrax; Antigens, Bacterial; Bacillus anthracis; Bacterial Toxins; beta-Cyclodextrins; Cell Line; Dose-Response Relationship, Drug; Drug Design; Electrophysiology; Humans; Macrophages; Male; Mice; Microbial Sensitivity Tests; Models, Molecular; Molecular Structure; Protein Conformation; Rats; Rats, Inbred F344