Abstract
Nitroaromatic prodrugs are used to treat a range of microbial infections with selectivity achieved by specific activation reactions. For trypanosomatid parasites this is mediated by type I nitroreductases (NTRs). Here, we demonstrate that the causative agent of leishmaniasis, Leishmania major, expresses a FMN-containing NTR (LmNTR) that metabolises a wide range of substrates and based on electron donor and acceptor preferences may function as a NADH:quinone oxidoreductase. Using gene deletion approaches, we demonstrate that this activity is essential to L. major promastigotes, the parasite forms found in the insect vector. Intriguingly, although LmNTR+/- heterozygote promastigote parasites could differentiate into infectious form metacyclic cells, these were unable to establish infections in cultured mammalian cells and cause delayed pathology in mice. Further, we exploit the LmNTR activity evaluating a library of nitrobenzylphosphoramide mustards using biochemical and phenotypic screens. We identify a subset of compounds that display significant growth inhibitory properties against the intracellular parasite form found in the mammalian host. The leishmanicidal activity was shown to be LmNTR specific as the LmNTR+/- heterozygote promastigotes displayed resistance to the most potent mustards. We conclude that LmNTR can be targeted for drug development by exploiting its prodrug activating property or by designing specific inhibitors to block its endogenous function.