Leishmania donovani Parasites Are Inhibited by the Benzoxaborole AN2690 Targeting Leucyl-tRNA Synthetase.

Visceral leishmaniasis is an important public health threat in parts of India. It is caused by a protozoan parasite, Currently available drugs manifest severe side effects. Hence, there is a need to identify new drug targets and drugs. Aminoacyl-tRNA synthetases, required for protein synthesis, are known drug targets for bacterial and fungal pathogens. The aim of the present study was to obtain essentiality data for leucyl-tRNA synthetase (LRS) by gene replacement. Gene replacement studies indicate that this enzyme plays an essential role in the viability of this pathogenic organism and appears to be indispensable for its survival The heterozygous mutant parasites demonstrated a growth deficit and reduced infectivity in mouse macrophages compared to the wild-type cells. We also report that recombinant LRS displayed aminoacylation activity and that the protein localized to both the cytosol and the mitochondrion. A broad-spectrum antifungal, 5-fluoro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2690), was found to inhibit parasite growth in both the promastigote and amastigote stages as well as in BALB/c mice. This compound exhibited low toxicity to mammalian cells. AN2690 was effective in inhibiting the aminoacylation activity of the recombinant LRS. We provide preliminary chemical validation of LRS as a drug target by showing that AN2690 is an inhibitor both of LRS and of cell growth.