Assessment of the Induction of Dormant Ring Stages in Plasmodium falciparum Parasites by Artemisone and Artemisone Entrapped in Pheroid Vesicles In Vitro

Abstract

cThe in vitro antimalarial activities of artemisone and artemisone entrapped in Pheroid vesicles were compared, as was their ability to induce dormancy in Plasmodium falciparum. There was no increase in the activity of artemisone entrapped in Pheroid vesicles against multidrug-resistant P. falciparum lines. Artemisone induced the formation of dormant ring stages similar to dihydroartemisinin. Thus, the Pheroid delivery system neither improved the activity of artemisone nor prevented the induction of dormant rings. Since 2006, artemisinin-based combination treatment (ACT) has been the cornerstone of malaria chemotherapy (1). However, high treatment failure rates with artesunate-mefloquine (AS-MQ) (2) and dihydroartemisinin (DHA)-piperaquine (3) in western Cambodia highlight the urgent need for effective ACTs until more potent replacement drugs can be developed.Although artemisinin and its derivatives are the most potent and rapidly acting drugs for the treatment of Plasmodium falciparum malaria (4), this drug class is associated with high recrudescence. Artemisone (AMS), a new derivative, has potent antiplasmodial activity, good oral bioavailability, and metabolic stability (5) and is well tolerated in humans (6), with an effective curative dose approximately one-third that of artesunate (7). However, use of artemisone alone, as with the other artemisinins, also leads to recrudescence in nonhuman primates (8). A plausible explanation for recrudescence is drug-induced quiescence or dormancy that protects ring-stage parasites against artemisinin exposure (9, 10). The artemisinin-treated ring stages of P. falciparum thereby enter a temporary growth arrest (11, 12), wherein they survive drug treatment, resuming normal growth once drug pressure is removed (13-15).Formulations involving liposomes and self-emulsifying drug delivery systems enhance the efficacy of anti-infective agents, including antimalarial drugs, such as artemisinins (16)(17)(18)(19). A Pheroid delivery system has been shown to increase the in vitro antimalarial activities of azithromycin, mefloquine, and quinine significantly (20,21). Entrapment of artemisone in Pheroid vesicles also has been shown to enhance blood artemisone concentrations in mice (22) and primates (23). We investigated the effect of a Pheroid formulation on the antimalarial activity of artemisone and on dormancy in vitro. If this formulation prevents the induction of dormancy in vitro, it may circumvent recrudescences occurring following artemisinin treatment.Chloroquine diphosphate (CQ) and MQ (Sigma-Aldrich, St. Louis, MO), atovaquone (ATQ) (GlaxoSmithKline, Middlesex, United Kingdom), DHA, and AS (DK Pharma, Hanoi, Vietnam) were used. Artemisone and its metabolite M1 were obtained from the Hong Kong University of Science and Technology. The active M1 metabolite is formed via dehydrogenation in the thiomorpholine-dioxide moiety of artemisone (5, 6). The artemisone-entrapped Pheroid vesicles (AMS-Phe) were prepared by adding 30 mM artemisone to a pro-Pheroid formulation (i.e., oil...

Inhibiting the Plasmodium eIF2α Kinase PK4 Prevents Artemisinin-Induced Latency

“…ARTs induce PK4 activation in the ER of ring stages, resulting in the phosphorylation of eIF2α that promotes latency associated with recrudescent infection (Cheng et al, 2012; Codd et al, 2011; LaCrue et al, 2011; Teuscher et al, 2012; Teuscher et al, 2010). Ring stage parasites respond to ARTs by phosphorylating eIF2α (Figure 2), which is concordant with previous reports describing the induction of latent rings by ARTs (Grobler et al, 2014; LaCrue et al, 2011; O’Brien et al, 2011; Teuscher et al, 2012; Teuscher et al, 2010; Tucker et al, 2012; Witkowski et al, 2010). …”

“…Consequently, longer courses of therapy or twice-a-day dosing intervals are recommended to efficiently clear the infection (Dogovski et al, 2015). Recent studies also indicate that ARTs induce transition of a subset of parasites into latent rings that are responsible for recrudescence (Codd et al, 2011; Grobler et al, 2014; LaCrue et al, 2011; Teuscher et al, 2012; Teuscher et al, 2010). Despite its clinical importance, the molecular mechanism of ART-induced parasite latency remains unknown.…”

The Spiroindolone KAE609 Does Not Induce Dormant Ring Stages in Plasmodium falciparum Parasites

“…Both DHA (700 nM) and ART (500 nM) produced dormant ring stages at 24 to 48 h after the start of treatment, with parasites recovering 3 to 5 days after drug exposure. This finding is in accord with the class effect of the artemisinin derivatives resulting in the induction of dormant rings reported elsewhere (38,39), even though the time to recovery of the parasites was shorter than that reported previously (17,39,40). A plausible explanation for the difference is that in the present study, magnetic columns were not used on days 1, 2, and 3 after the start of the experiment to remove growing parasites (late stages) not killed by DHA treatment as well as those emerging from dormant parasites with the short duration of dormancy (24 to 48 h).…”

Do hypnozoites cause relapse in malaria?

“…To clarify, ring-stage P. falciparum parasites in erythrocytes can become temporarily quiescent when exposed in vitro to artemisinin derivatives [57][58][59][60][61]. One of these derivatives is dihydroartemisinin, which is widely used for treating P. falciparum malaria.…”