Oxadiazole 2-oxides are toxic to the human hookworm, Ancylostoma ceylanicum, however glutathione reductase is not the primary target

Abstract

Hookworm disease, characterized by severe anemia and cognitive and growth delays, currently affects an estimated 740million people worldwide. Despite the prevalence of this parasitic disease, few effective drug therapies are in use today, and the heavy reliance upon benzimidazoles highlights the need for the development of novel chemotherapies. Recent work with the trematode parasite Schistosoma mansoni has identified oxadiazole 2-oxides as effective antischistosomal compounds that function by targeting and inhibiting the antioxidant enzyme, thioredoxin glutathione reductase. In this study, a related enzyme, glutathione reductase, from the human hookworm Ancylostoma ceylanicum was identified and characterized, and its in vitro activity in the presence of the oxadiazole 2-oxides was analyzed. Ex vivo worm killing assays were also conducted to establish the relationship between a given compound’s effect upon worm survival and inhibition of recombinant glutathione reductase (rAceGR). Finally, the in vivo anthelminthic efficacy of furoxan (Fx) was assessed in the hamster model of hookworm infection. The predicted amino acid sequence of AceGR contained a prototypical glutathione reductase active site sequence, but no thioredoxin reductase consensus sequences, suggesting that the glutathione and thioredoxin pathways of A. ceylanicum are distinct. Although 10 of the 42 oxadiazole 2-oxides tested inhibited rAceGR activity by at least 50%, and 15 compounds were toxic to parasites ex vivo, little overlap existed between these two results. We therefore suggest that AceGR is not the primary target of the oxadiazole 2-oxides in effecting parasite death. Lastly, oral treatment of A. ceylanicum infected hamsters with furoxan resulted in significantly improved weight gains and reduced intestinal worm burdens compared to vehicle treated controls, supporting continued development of this molecule as a novel anthelminthic.