title: Identification of new classes of ricin toxin inhibitors by virtual screening.
abstract: We used two virtual screening programs, ICM and GOLD, to dock nearly 50,000 compounds into each of two conformations of the target protein ricin A chain (RTA). A limited control set suggests that candidates scored highly by two programs may have a higher probability of being ligands than those in a list from a single program. Based on the virtual screens, we purchased 306 compounds that were subjected to a kinetic assay. Six compounds were found to give modest, but significant, inhibition of RTA. They also tended to inhibit Shiga toxin A chain, with roughly the same IC(50). The compounds generally represent novel chemical platforms that do not resemble RTA substrates, as currently known inhibitors do. These six were also tested in a cell-based assay for their ability to protect cells from intact ricin. Two compounds were effective in this regard, showing modest to strong ricin inhibition, but also showing some cytotoxicity. RTA, with its large, polar active site is a difficult drug design target which is expected to bind small molecules only weakly. The ability of the method to find these novel platforms is encouraging and suggests virtual screening can contribute to the search for ricin and Shiga toxin inhibitors.
authors.affiliation: Institute of Cellular and Molecular Biology, Department of Chemistry and Biochemistry, 1 University Station A5300, University of Texas, Austin, TX 78712, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Bai
authors.forename: Beth
authors.initials: B
authors.lastname: Watt
authors.forename: Paul G
authors.initials: PG
authors.lastname: Wahome
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Mantis
authors.forename: Jon D
authors.initials: JD
authors.lastname: Robertus
mesh_terms: D000465:Algorithms; D000818:Animals; D001665:Binding Sites; D002522:Chlorocebus aethiops; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D007700:Kinetics; D046609:Libraries, Digital; D008024:Ligands; D008968:Molecular Conformation; D012276:Ricin / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000494:pharmacology; D022621:Shiga Toxin / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology; D054852:Small Molecule Libraries; D012984:Software; D014709:Vero Cells
chemical_list: D004791:Enzyme Inhibitors; D008024:Ligands; C493898:Shiga toxin subunit A; D054852:Small Molecule Libraries; D022621:Shiga Toxin; D012276:Ricin