Malaria control and elimination are threatened by the emergence and spread of resistance to artemisinin-based combination therapies (ACTs). Experimental evidence suggests that when an artemisinin (ART)-sensitive (K13 wild-type) Plasmodium falciparum strain is exposed to ART derivatives such as dihydroartemisinin (DHA), a small population of the early ring-stage parasites can survive drug treatment by entering cell cycle arrest or dormancy. After drug removal, these parasites can resume growth. Dormancy has been hypothesized to be an adaptive physiological mechanism that has been linked to recrudescence of parasites after monotherapy with ART and, possibly contributes to ART resistance. Here, we evaluate the in vitro drug sensitivity profile of normally-developing P. falciparum ring stages and DHA-pretreated dormant rings (DP-rings) using a panel of antimalarial drugs, including the Plasmodium phosphatidylinositol-4-OH kinase (PI4K)-specific inhibitor KDU691. We report that while KDU691 shows no activity against rings, it is highly inhibitory against DP-rings; a drug effect opposite to that of ART. Moreover, we provide evidence that KDU691 also kills DP-rings of P. falciparum ART-resistant strains expressing mutant K13.
A series of 5-aryl-2-amino-
i
midazo
t
hia
d
iazole (ITD) derivatives
were identified by a phenotype-based high-throughput screening using
a blood stage
Plasmodium falciparum
(
Pf
) growth inhibition assay. A lead optimization program focused on
improving antiplasmodium potency, selectivity against human kinases,
and absorption, distribution, metabolism, excretion, and toxicity
properties and extended pharmacological profiles culminated in the
identification of
INE963
(
1
), which demonstrates
potent cellular activity against
Pf
3D7 (EC
50
= 0.006 μM) and achieves “artemisinin-like”
kill kinetics
in vitro
with a parasite clearance
time of <24 h. A single dose of 30 mg/kg is fully curative in the
Pf
-humanized severe combined immunodeficient mouse model.
INE963
(
1
) also exhibits a high barrier to resistance
in drug selection studies and a long half-life (
T
1/2
) across species. These properties suggest the significant
potential for
INE963
(
1
) to provide a curative
therapy for uncomplicated malaria with short dosing regimens. For
these reasons,
INE963
(
1
) was progressed
through GLP toxicology studies and is now undergoing Ph1 clinical
trials.
Artemisinin (ART) resistance has spread through Southeast Asia, posing a serious threat to the control and elimination of malaria. ART resistance has been associated with mutations in the Plasmodium falciparum kelch-13 (Pfk13) propeller domain. Phenotypically, ART resistance is defined as delayed parasite clearance in patients due to the reduced susceptibility of early ring-stage parasites to the active metabolite of ART dihydroartemisinin (DHA). Early rings can enter a state of quiescence upon DHA exposure and resume growth in its absence. These quiescent rings are referred to as dormant rings or DHA-pretreated rings (here called dormant rings). The imidazolopiperazines (IPZ) are a novel class of antimalarial drugs that have demonstrated efficacy in early clinical trials. Here, we characterized the stage of action of the IPZ GNF179 and evaluated its activity against rings and dormant rings in wild-type and ART-resistant parasites. Unlike DHA, GNF179 does not induce dormancy. We show that GNF179 is more rapidly cidal against schizonts than against ring and trophozoite stages. However, with 12 h of exposure, the compound effectively kills rings and dormant rings of both susceptible and ART-resistant parasites within 72 h. We further demonstrate that in combination with ART, GNF179 effectively prevents recrudescence of dormant rings, including those bearing pfk13 propeller mutations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.