Assessing the Essentiality of Leishmania donovani Nitroreductase and Its Role in Nitro Drug Activation

Abstract

The nitroimidazole fexinidazole has potential as a safe and effective oral drug therapy for the treatment of visceral leishmaniasis. To date, nitroheterocyclics have not been used in the treatment of leishmaniasis, and relatively little is known about their mechanism of action. In African trypanosomes, nitro drugs are reductively activated by a type I nitroreductase (NTR), absent in mammalian cells. Modulation of nitroreductase levels in Trypanosoma brucei directly affected sensitivity to nitro compounds, with reduced concentrations of the enzyme leading to moderate nitro drug resistance. In view of the progression of fexinidazole into clinical development for visceral leishmaniasis, here we assess the essentiality of the nitroreductase in Leishmania donovani and the effect of modulating nitroreductase levels on susceptibility to fexinidazole. The failure to directly replace both endogenous copies of the NTR gene, except in the presence of an ectopic copy of the gene, suggests that the NTR gene is essential for the growth and survival of L. donovani promastigotes. Loss of a single chromosomal copy of the L. donovani NTR gene resulted in parasites that were mildly resistant (<2-fold) to the predominant in vivo metabolite of fexinidazole, while parasites overexpressing NTR were 18-fold more susceptible. These data confirm that Leishmania NTR plays a pivotal role in fexinidazole activation. Reliance on a single enzyme for prodrug activation may leave fexinidazole vulnerable to the emergence of drug resistance. However, the essentiality of the NTR in L. donovani promastigotes, combined with the limited resistance shown by NTR single knockout cells, suggests that the potential for the spread of NTR-based resistance to fexinidazole may be limited.

Activation of Bicyclic Nitro-drugs by a Novel Nitroreductase (NTR2) in Leishmania

“…This has made researchers wary of developing further nitro-compounds for the treatment of the trypanosomatid diseases. In this study we have confirmed that several bicyclic nitro-drugs, either in preclinical development or demonstrating promising anti-leishmanial activity, are not activated via NTR1, known to activate monocyclic nitro-compounds nifurtimox, benznidazole and fexinidazole [7,10,12,22]. Importantly, resistance to bicyclic nitro-compounds in Leishmania promastigotes does not result in striking levels of cross-resistance to NTR1-activated compounds.…”

“…In-macrophage infectivity assays were carried out using starch-elicited mouse peritoneal macrophages harvested from BALB/c mice [7] and metacyclic promastigotes, as previously described [12]. …”

Antitrypanosomatid Pharmacomodulation at Position 3 of the 8‐Nitroquinolin‐2(1H)‐one Scaffold Using Palladium‐Catalysed Cross‐Coupling Reactions

“…[26] This result was then improvedb yr eplacing Na 2 CO 3 with K 2 CO 3 ,w hich afforded ay ield of 84 %. The nature of the catalystw as then studied ( Table 1, entries [13][14][15], but noneo f these reactions led to an improvement in the yield, and only a few percent conversionw as observed. Finally,t he best results were obtained by using Cs 2 CO 3 or CsF as ab ase ( Table 1, entries 16 and 17), which afforded efficient Suzuki-Miyaura crosscoupling reactions of this substrate.…”

Developing imidazole analogues as potential inhibitor forLeishmania donovanitrypanothione reductase: virtual screening, molecular docking, dynamics and ADMET approach

“…This compound has shown negligible toxicity along with inhibitory activity for human African trypanosomiasis and second stage gambience human African trypanosomiasis (Eperon et al, 2014). This drug has shown minimal side effect with antileishmanial activity in animal model, when it was administered orally (Wyllie, Patterson, & Fairlamb, 2013;Wyllie et al, 2012). interactions (Hazra et al, 2013;Verma et al, 2012) (Sahoo et al, 2014).…”