title: Aryl ureas represent a new class of anti-trypanosomal agents.
abstract: BACKGROUND
  The trypanosomal diseases including Chagas' disease, African sleeping sickness and Nagana have a substantial impact on human and animal health worldwide. Classes of effective therapeutics are needed owing to the emergence of drug resistance as well as the toxicity of existing agents. The cysteine proteases of two trypanosomes, Trypanosoma cruzi (cruzain) and Trypanosoma brucei (rhodesain), have been targeted for a structure-based drug design program as mechanistic inhibitors that target these enzymes are effective in cell-based and animal models of trypanosomal infection.
  
  
  RESULTS
  We have used computational methods to identify new lead scaffolds for non-covalent inhibitors of cruzain and rhodesain, have demonstrated the efficacy of these compounds in cell-based and animal assays, and have synthesized analogs to explore structure activity relationships. Nine compounds with varied scaffolds identified by DOCK4.0.1 were found to be active at concentrations below 10 microM against cruzain and rhodesain in enzymatic studies. All hits were calculated to have substantial hydrophobic interactions with cruzain. Two of the scaffolds, the urea scaffold and the aroyl thiourea scaffold, exhibited activity against T. cruzi in vivo and both enzymes in vitro. They also have predicted pharmacokinetic properties that meet Lipinski's 'rule of 5'. These scaffolds are synthetically tractable and lend themselves to combinatorial chemistry efforts. One of the compounds, 5'(1-methyl-3-trifluoromethylpyrazol-5-yl)-thiophene 3'-trifluoromethylphenyl urea (D16) showed a 3.1 microM IC(50) against cruzain and a 3 microM IC(50) against rhodesain. Infected cells treated with D16 survived 22 days in culture compared with 6 days for their untreated counterparts. The mechanism of the inhibitors of these two scaffolds is confirmed to be competitive and reversible.
  
  
  CONCLUSIONS
  The urea scaffold and the thiourea scaffold are promising leads for the development of new effective chemotherapy for trypanosomal diseases. Libraries of compounds of both scaffolds need to be synthesized and screened against a series of homologous parasitic cysteine proteases to optimize the potency of the initial leads.
authors.affiliation: Department of Cellular and Molecular Pharmacology and Medicine, University of California, San Francisco 94143-0450, USA.
authors.forename: X
authors.initials: X
authors.lastname: Du
authors.forename: E
authors.initials: E
authors.lastname: Hansell
authors.forename: J C
authors.initials: JC
authors.lastname: Engel
authors.forename: C R
authors.initials: CR
authors.lastname: Caffrey
authors.forename: F E
authors.initials: FE
authors.lastname: Cohen
authors.forename: J H
authors.initials: JH
authors.lastname: McKerrow
mesh_terms: D000818:Animals; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000737:chemistry; D013890:Thiourea / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D014344:Trypanocidal Agents / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000187:drug effects / Q000201:enzymology; D014349:Trypanosoma cruzi / Q000187:drug effects / Q000201:enzymology
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; D015800:Protozoan Proteins; D013449:Sulfonamides; D014344:Trypanocidal Agents; D003546:Cysteine Endopeptidases; C074032:cruzain, Trypanosoma cruzi; D013890:Thiourea