title: Small-molecule inhibitor leads of ribosome-inactivating proteins developed using the doorstop approach.
abstract: Ribosome-inactivating proteins (RIPs) are toxic because they bind to 28S rRNA and depurinate a specific adenine residue from the α-sarcin/ricin loop (SRL), thereby inhibiting protein synthesis. Shiga-like toxins (Stx1 and Stx2), produced by Escherichia coli, are RIPs that cause outbreaks of foodborne diseases with significant morbidity and mortality. Ricin, produced by the castor bean plant, is another RIP lethal to mammals. Currently, no US Food and Drug Administration-approved vaccines nor therapeutics exist to protect against ricin, Shiga-like toxins, or other RIPs. Development of effective small-molecule RIP inhibitors as therapeutics is challenging because strong electrostatic interactions at the RIP•SRL interface make drug-like molecules ineffective in competing with the rRNA for binding to RIPs. Herein, we report small molecules that show up to 20% cell protection against ricin or Stx2 at a drug concentration of 300 nM. These molecules were discovered using the doorstop approach, a new approach to protein•polynucleotide inhibitors that identifies small molecules as doorstops to prevent an active-site residue of an RIP (e.g., Tyr80 of ricin or Tyr77 of Stx2) from adopting an active conformation thereby blocking the function of the protein rather than contenders in the competition for binding to the RIP. This work offers promising leads for developing RIP therapeutics. The results suggest that the doorstop approach might also be applicable in the development of other protein•polynucleotide inhibitors as antiviral agents such as inhibitors of the Z-DNA binding proteins in poxviruses. This work also calls for careful chemical and biological characterization of drug leads obtained from chemical screens to avoid the identification of irrelevant chemical structures and to avoid the interference caused by direct interactions between the chemicals being screened and the luciferase reporter used in screening assays.
authors: Computer-Aided Molecular Design Laboratory, Mayo Clinic, Rochester, Minnesota, United States of America. pang@mayo.edu
authors: Yuan-Ping
authors: YP
authors: Pang
authors: Jewn Giew
authors: JG
authors: Park
authors: Shaohua
authors: S
authors: Wang
authors: Anuradha
authors: A
authors: Vummenthala
authors: Rajesh K
authors: RK
authors: Mishra
authors: John E
authors: JE
authors: McLaughlin
authors: Rong
authors: R
authors: Di
authors: Jennifer Nielsen
authors: JN
authors: Kahn
authors: Nilgun E
authors: NE
authors: Tumer
authors: Laszlo
authors: L
authors: Janosi
authors: Jon
authors: J
authors: Davis
authors: Charles B
authors: CB
authors: Millard
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D051379:Mice; D015394:Molecular Structure; D011119:Polynucleotides / Q000737:chemistry / Q000494:pharmacology*; D054788:Ribosome Inactivating Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D012276:Ricin / Q000737:chemistry; D022641:Shiga Toxin 2 / Q000737:chemistry
chemical_list: D011119:Polynucleotides; D022641:Shiga Toxin 2; D012276:Ricin; D054788:Ribosome Inactivating Proteins