Urea-Based Inhibitors of Trypanosoma brucei Methionyl-tRNA Synthetase: Selectivity and in Vivo Characterization

Abstract

Urea-based methionyl-tRNA synthetase inhibitors were designed, synthesized and evaluated for their potential towards treating human African trypanosomiasis (HAT). With the aid of a homology model and a structure-activity-relationship approach, low nM inhibitors were discovered that show high selectivity towards the parasite enzyme over the closest human homolog. These compounds inhibit parasite growth with EC50 values as low as 0.15 μM while having low toxicity to mammalian cells. Two compounds (2 and 26) showed excellent membrane permeation in the MDR1-MDCKII model, and encouraging oral pharmacokinetic properties in mice. Compound 2 was confirmed to enter the CNS in mice. Compound 26 had modest suppressive activity against T. brucei rhodesiense in the mouse model, suggesting that more potent analogs or compounds with higher exposures need to be developed. The urea-based inhibitors are thus a promising starting point for further optimization towards the discovery of orally available and CNS active drugs to treat HAT.

Induced Resistance to Methionyl-tRNA Synthetase Inhibitors in Trypanosoma brucei Is Due to Overexpression of the Target

“…The synthesis methods of 1312 and 1433 were previously described (6,10). Eflornithine and pentamidine were purchased from Sigma-Aldrich.…”

“…(ii) Growth inhibition assays. Three clones from each group and the population were tested in the T. brucei growth inhibition assay as previously described (10). Cross-resistance was also tested for each clone by assaying the clone with the other compounds (1433, 1312, eflornithine, and/or pentamidine) that the clone was not cultured in.…”

“…Two classes of MetRS inhibitors have been discovered with selective activity on T. brucei over mammalian cells (6,10). A class of aminoquinolones (Fig.…”

Inhibition of Protein Synthesis and Malaria Parasite Development by Drug Targeting of Methionyl-tRNA Synthetases

“…Inhibitors that target MRSs are already under development against bacterial infections (24). Derivatives of diarylamines, quinolones, urea, and various other lead compounds with potent activities against MRSs have been tested (25)(26)(27). Therefore, we decided to explore various attributes of malarial MRSs with the aim of probing their potential for drug targeting.…”

Genetic Validation of Aminoacyl-tRNA Synthetases as Drug Targets in Trypanosoma brucei

“…Several T. brucei aaRS genes have been reported to be essential in parasites in either the insect stage (procyclic) or the mammalian stage (21,(25)(26)(27)(28)(29)(30). Several groups have also reported the identification of MetRS, IleRS, and LeuRS inhibitors with antitrypanosome activity (30)(31)(32)(33)(34)(35). Crystal structures have been solved for many of the aaRSs across several species (15), including the structures of HisRS (36) and TrpRS (37) from T. brucei, which will aid in understanding how to target these enzymes for HAT drug discovery.…”