Resistance has been recorded for every class of antimalarial, including artemisinin combination therapies (ACTs), the current first line. Drug resistant parasites have been reported to have an increased ability to manage oxidative stress and maintain redox homeostasis following drug treatment, possibly due to an enhanced antioxidant system. We hypothesised that disrupting this redox balance by targeting the parasites’ glutathione pathway will make parasites more susceptible to oxidative stress, and therefore re-sensitise them to existing antimalarials. This work aims to tackle resistance by identifying redox-modifying drugs that can be combined with artemisinin derivatives.
Growth inhibitory studies and ring-stage survival assays were used to determine the antimalarial activity of different redox compounds and to identify compounds that could be synergistic with artemisinin in vitro. Real time analysis of parasite intracellular glutathione was observed using P. falciparum NF54attB[hGrx1- roGFP2] parasite line and a plate reader based redox assay. Untargeted and targeted thiol metabolomic were carried out to identify metabolic changes in drug treated parasites.
We identified sulforaphane (SFN) to be a promising candidate, which alters parasite redox status and potentiates the activity of artemisinin. The combination of 15µM SFN with 700nM dihydroartemisin (DHA) in early ring-stage parasites resulted in a decrease in parasite survival compared to DHA alone (41% ± 7.3).15µM SFN resulted in an increased oxidative burden within parasites after 1 h incubation. Untargeted and targeted thiol metabolomics confirmed that SFN’s antimalarial activity is entirely redox mediated and not as a result of major metabolic changes within the parasite
The addition of SFN to existing antimalarial therapies would re-sensitise resistant parasites to existing antimalarials thereby extending their life span. Ongoing studies will elucidate the mechanism responsible for this synergistic activity and determine the safety and efficacy of this approach in drug-resistant in vivo models of malaria.