Aryl ureas represent a new class of anti-trypanosomal agents

Background: The trypanosomal diseases including Chagas' disease, African sl eeping sickness and Nagana have a substantial impact on human and animal he alth worldwide. Classes of effective therapeutics are needed owing to the e mergence of drug resistance as well as the toxicity of existing agents. The cysteine proteases of two trypanosomes, Trypanosoma cruzi (cruzain) and Tr ypanosoma brucei (rhodesain), have been targeted for a structure-based drug design program as mechanistic inhibitors that target these enzymes are eff ective 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 synt hesized analogs to explore structure activity relationships. Nine compounds with varied scaffolds identified by DOCK4.0.1 were found to be active at c oncentrations below 10 mu M against cruzain and rhodesain in enzymatic stud ies. All hits were calculated to have substantial hydrophobic interactions with cruzain. Two of the scaffolds, the urea scaffold and the aroyl thioure a scaffold, exhibited activity against T. cruzi in vivo and both enzymes in vitro. They also have predicted pharmacokinetic properties that meet Lipin ski's 'rule of 5'. These scaffolds are synthetically tractable and lend the mselves to combinatorial chemistry efforts. One of the compounds, 5'(1-meth yl-3-triiluoromethylpyrazol-5-yl)-thiophene 3'-trifluoromethylphenyl urea ( D16) showed a 3.1 mu M IC50 against cruzain and a 3 mu M IC50 against rhode sain. Infected cells treated with D16 survived 22 days in culture compared with 6 days for their untreated counterparts. The mechanism of the inhibito rs of these two scaffolds is confirmed to be competitive and reversible.