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

Abstract

Visceral leishmaniasis is an important public health threat in parts of India. It is caused by a protozoan parasite, <i>Leishmania donovani</i> 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 <i>Leishmania donovani</i> leucyl-tRNA synthetase (<i>Ld</i>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 <i>in vitro</i> The heterozygous mutant parasites demonstrated a growth deficit and reduced infectivity in mouse macrophages compared to the wild-type cells. We also report that <i>Leishmania donovani</i> 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 <i>in vitro</i> as well as <i>in vivo</i> in BALB/c mice. This compound exhibited low toxicity to mammalian cells. AN2690 was effective in inhibiting the aminoacylation activity of the recombinant <i>Ld</i>LRS. We provide preliminary chemical validation of <i>Ld</i>LRS as a drug target by showing that AN2690 is an inhibitor both of <i>L. donovani</i> LRS and of <i>L. donovani</i> cell growth.