Authors

Discussion

Methionyl tRNA synthetase (MetRS) has been chemically validated as a drug target in the kinetoplastid parasite Trypanosoma brucei. In the present study we investigate the validity of this target in the related trypanosomatid Leishmania donovani. Following development of a robust high-throughput compatible biochemical assay, a compound screen identified DDD806905 as a highly potent inhibitor of LdMetRS (K_i 18 nM). Crystallography revealed this compound binds to the methionine pocket of MetRS with enzymatic studies confirming DDD806905 displays competitive inhibition with respect to methionine and mixed inhibition with respect to ATP binding. DDD806905 showed activity, albeit with different levels of potency, in various Leishmania cell-based viability assays, with on-target activity observed in both Leishmania promastigote cell assays and a Leishmania tarentolae in vitro translation assay. Unfortunately this compound failed to show efficacy in an animal model of leishmaniasis, with high levels of plasma protein binding and sequestration of this dibasic compound into acidic cellular compartments providing possible explanations for this failure to translate. Although DDD806905 is not a developable anti-leishmanial compound, MetRS remains an attractive anti-leishmanial drug target.