Artemisone and Artemiside Are Potent Panreactive Antimalarial Agents That Also Synergize Redox Imbalance in Plasmodium falciparum Transmissible Gametocyte Stages

Abstract

The emergence of resistance toward artemisinin combination therapies (ACTs) by the malaria parasite has the potential to severely compromise malaria control. Therefore, the development of new artemisinins in combination with new drugs that impart activities toward both intraerythrocytic proliferative asexual and transmissible gametocyte stages, in particular, those of resistant parasites, is urgently required. We define artemisinins as oxidant drugs through their ability to oxidize reduced flavin cofactors of flavin disulfide reductases critical for maintaining redox homeostasis in the malaria parasite. Here we compare the activities of 10-amino artemisinin derivatives toward the asexual and gametocyte stages of parasites. Of these, artemisone and artemiside inhibited asexual and gametocyte stages, particularly stage V gametocytes, in the low-nanomolar range. Further, treatment of both early and late gametocyte stages with artemisone or artemiside combined with the pro-oxidant redox partner methylene blue displayed notable synergism. These data suggest that modulation of redox homeostasis is likely an important druggable process, particularly in gametocytes, and this finding thereby enhances the prospect of using combinations of oxidant and redox drugs for malaria control.

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“…[6][7][8][9] Modulation of redox homeostasis and the synergism between pro-and antioxidants is also an important factor in the formation of gametocytes. 10 This confirms many statements and claims I have made in my publications. Plasmodium falciparum is not killed by the supposedly high antioxidant properties of Artemisia but because this herb is poor in antioxidants.…”

Optimal 10-Aminoartemisinins With Potent Transmission-Blocking Capabilities for New Artemisinin Combination Therapies–Activities Against Blood Stage P. falciparum Including PfKI3 C580Y Mutants and Liver Stage P. berghei Parasites

“…The accepted thesis for induction of artemisinin resistance holds that DHA 2, used as a clinical artemisinin in its own right, or as the principal metabolite of the clinical artemisinins artemether 3 and artesunate 4, competitively binds to Pf PI3K which prevents the kinase binding to Pf K13, thereby inhibiting ubiquitinylation and proteasome degradation and leading to cell-cycle arrest and quiescence (Mbengue et al, 2015;Van Hook, 2015). However, the "DHAbinding" thesis is open to question (Coertzen et al, 2018). The notable lability of DHA under physiological conditions wherein DHA rearranges irreversibly via ring-opening and closure to the peroxyhemiacetal 5 (Figure 1) (Haynes et al, 2007;Jansen, 2010;Parapini et al, 2015) precludes binding of the intact molecule to Pf KI3.…”

“…Overall, artemisinin resistance more likely reflects modulation of redox-sensitive signal transduction pathways according to other closely-related systems (Kim et al, 2005;Liu et al, 2012;Okoh et al, 2013). Thus, the inhibition equates with an enhanced response to the oxidative stress induced by the artemisinin via generation of reactive oxygen species (ROS) (Haynes et al, 2011(Haynes et al, , 2012Coertzen et al, 2018). The origins of the stress response are in accord with one of the conceptual models for mechanism of action of artemisinins: this posits enhancement of oxidative stress brought about by the facile oxidation by artemisinins of reduced flavin cofactors of flavin disulfide reductases important for maintaining redox homeostasis in the malaria parasite (Haynes et al, 2011(Haynes et al, , 2012.…”

“…Thus, in addition to the new artemisinin component, we need to examine with particular care the combination partners, and if these are likely to affect quiescent ring stage parasites so as to "protect" the artemisinin. We proposed use of the new artemisinin, which we term an oxidant drug by virtue of its ability to irreversibly oxidize reduced flavin cofactors, in combination with a redox (or "pro-oxidant") drug such as a phenothiazine, e.g., methylene blue (MB), phenoxazine, naphthoquinone (Sidorov et al, 2016), quinone-imine, redox metal chelating agent (Parkinson et al, 2019), or other (Kubota and Gorton, 1999;Dharmaraja, 2017), with a third drug with a different mode of action (Coertzen et al, 2018). MB oxidizes reduced flavin cofactors of flavin disulfide reductases just as does the artemisinin (Haynes et al, 2011(Haynes et al, , 2012.…”

“…Naphthoquinones are likely to act in the same way as these oxidize reduced flavin cofactors of other flavoenzymes (Sollner and Macheroux, 2009). The benefit of combining the oxidant artemisinin with the redox drug accrues through the artemisinin abruptly inducing oxidative stress that is then maintained or enhanced by redox cycling of the MB or other redox active drug (Coertzen et al, 2018). The specific benefits bestowed by MB are potent activity against early asexual ring stage parasites (Akoachere et al, 2005) and against transmissible blood stage gametocytes (Adjalley et al, 2011).…”