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Abstract Background Artemisinin-based combination therapy (ACT) has been a mainstay for malaria prevention and treatment. However, emergence of drug resistance has incentivised development of new drugs. Defining the kinetics with which circulating parasitized red blood cells (pRBC) are lost after drug treatment, referred to as the “parasite clearance curve”, has been critical for assessing drug efficacy; yet underlying mechanisms remain partly unresolved. The clearance curve may be shaped both by the rate at which drugs kill parasites, and the rate at which drug-affected parasites are removed from circulation. Methods In this context, two anti-malarials, SJ733, and an ACT partner drug, pyronaridine were compared against sodium artesunate in mice infected with Plasmodium berghei (strain ANKA). To measure each compound’s capacity for pRBC removal in vivo, flow cytometric monitoring of a single cohort of fluorescently-labelled pRBC was employed, and combined with ex vivo parasite culture to assess parasite maturation and replication. Results These three compounds were found to be similarly efficacious in controlling established infection by reducing overall parasitaemia. While sodium artesunate acted relatively consistently across the life-stages, single-dose SJ733 elicited a biphasic effect, triggering rapid, partly phagocyte-dependent removal of trophozoites and schizonts, followed by arrest of residual ring-stages. In contrast, pyronaridine abrogated maturation of younger parasites, with less pronounced effects on mature parasites, while modestly increasing pRBC removal. Conclusions Anti-malarials SJ733 and pyronaridine, though similarly efficacious in reducing overall parasitaemia in mice, differed markedly in their capacity to arrest replication and remove pRBC from circulation. Thus, similar parasite clearance curves can result for anti-malarials with distinct capacities to inhibit, kill and clear parasites.

Summary: Background: SJ733, a newly developed inhibitor of P. falciparum ATP4, has a favorable safety profile and rapid antiparasitic effect but insufficient duration to deliver a single-dose cure of malaria. We investigated the safety, tolerability, and pharmacokinetics of a multidose SJ733 regimen and a single-dose pharmacoboost approach using cobicistat to inhibit CYP3A4, thereby increasing exposure. Methods: Two multidose unboosted cohorts (n = 9) (SJ733, 300 mg and 600 mg daily for 3 days) followed by three single-dose boosted cohorts combining SJ733 (n = 18) (75-, 300-, or 600-mg single dose) with cobicistat (150-mg single dose) as a pharmacokinetic booster were evaluated in healthy volunteers (ClinicalTrials.gov: NCT02661373). Findings: All participants tolerated SJ733 well, with no serious adverse events (AEs), dose-limiting toxicity, or clinically significant electrocardiogram or laboratory test findings. All reported AEs were Grade 1, clinically insignificant, and considered unlikely or unrelated to SJ733. Compared to unboosted cohorts, the SJ733/cobicistat-boosted cohorts showed a median increase in area under the curve and maximum concentration of 3·9 × and 2·6 ×, respectively, and a median decrease in the ratio of the major CYP3A-produced metabolite SJ506 to parent drug of 4·6 × . Incorporating these data in a model of parasite dynamics indicated that a 3-day regimen of SJ733/cobicistat (600 mg/150 mg daily) relative to a single 600-mg dose ± cobicistat would increase parasite clearance from 106 to 1012 parasites/µL. Interpretation: The multidose and pharmacoboosted approaches to delivering SJ733 were well-tolerated and significantly increased drug exposure and prediction of cure. This study supports the further development of SJ733 and demonstrates an innovative pharmacoboost approach for an antimalarial. Funding: Global Health Innovative Technology Fund, Medicines for Malaria Venture, National Institutes of Health, and American Lebanese Syrian Associated Charities.

Background: Artemisinin-based combination therapy (ACT) has been a mainstay for malaria prevention and treatment. However, emergence of drug resistance has incentivised development of new drugs. Defining the kinetics with which circulating parasitized red blood cells (pRBC) are lost after drug treatment, referred to as the "parasite clearance curve", has been critical for assessing drug efficacy; yet underlying mechanisms remain partly unresolved. The clearance curve may be shaped both by the rate at which drugs kill parasites, and the rate at which drug-affected parasites are removed from circulation. Methods: In this context, two anti-malarials, SJ733, and an ACT partner drug, pyronaridine were compared against sodium artesunate in mice infected with Plasmodium berghei (strain ANKA). To measure each compound's capacity for pRBC removal in vivo, flow cytometric monitoring of a single cohort of fluorescently-labelled pRBC was employed, and combined with ex vivo parasite culture to assess parasite maturation and replication. Results: These three compounds were found to be similarly efficacious in controlling established infection by reducing overall parasitaemia. While sodium artesunate acted relatively consistently across the life-stages, single-dose SJ733 elicited a biphasic effect, triggering rapid, partly phagocyte-dependent removal of trophozoites and schizonts, followed by arrest of residual ring-stages. In contrast, pyronaridine abrogated maturation of younger parasites, with less pronounced effects on mature parasites, while modestly increasing pRBC removal. Conclusions: Anti-malarials SJ733 and pyronaridine, though similarly efficacious in reducing overall parasitaemia in mice, differed markedly in their capacity to arrest replication and remove pRBC from circulation. Thus, similar parasite clearance curves can result for anti-malarials with distinct capacities to inhibit, kill and clear parasites. [ABSTRACT FROM AUTHOR]

Background: SJ733, a newly developed inhibitor of P. falciparum ATP4, has a favorable safety profile and rapid antiparasitic effect but insufficient duration to deliver a single-dose cure of malaria. We investigated the safety, tolerability, and pharmacokinetics of a multidose SJ733 regimen and a single-dose pharmacoboost approach using cobicistat to inhibit CYP3A4, thereby increasing exposure., Methods: Two multidose unboosted cohorts (n = 9) (SJ733, 300 mg and 600 mg daily for 3 days) followed by three single-dose boosted cohorts combining SJ733 (n = 18) (75-, 300-, or 600-mg single dose) with cobicistat (150-mg single dose) as a pharmacokinetic booster were evaluated in healthy volunteers (ClinicalTrials.gov: NCT02661373)., Findings: All participants tolerated SJ733 well, with no serious adverse events (AEs), dose-limiting toxicity, or clinically significant electrocardiogram or laboratory test findings. All reported AEs were Grade 1, clinically insignificant, and considered unlikely or unrelated to SJ733. Compared to unboosted cohorts, the SJ733/cobicistat-boosted cohorts showed a median increase in area under the curve and maximum concentration of 3·9 × and 2·6 ×, respectively, and a median decrease in the ratio of the major CYP3A-produced metabolite SJ506 to parent drug of 4·6 × . Incorporating these data in a model of parasite dynamics indicated that a 3-day regimen of SJ733/cobicistat (600 mg/150 mg daily) relative to a single 600-mg dose ± cobicistat would increase parasite clearance from 10 6 to 10 12 parasites/µL., Interpretation: The multidose and pharmacoboosted approaches to delivering SJ733 were well-tolerated and significantly increased drug exposure and prediction of cure. This study supports the further development of SJ733 and demonstrates an innovative pharmacoboost approach for an antimalarial., Funding: Global Health Innovative Technology Fund, Medicines for Malaria Venture, National Institutes of Health, and American Lebanese Syrian Associated Charities., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Among novel compounds under recent investigation as potential new antimalarial drugs are three independently developed inhibitors of the Plasmodium falciparum P-type ATPase (PfATP4): KAE609 (cipargamin), PA92, and SJ733. We assessed ex vivo susceptibilities to these compounds of 374 fresh P. falciparum isolates collected in Tororo and Busia districts, Uganda, from 2016 to 2019. Median IC 50 s were 65 nM for SJ733, 9.1 nM for PA92, and 0.5 nM for KAE609. Sequencing of pfatp4 for 218 of these isolates demonstrated many nonsynonymous single nucleotide polymorphisms; the most frequent mutations were G1128R (69% of isolates mixed or mutant), Q1081K/R (68%), G223S (25%), N1045K (16%), and D1116G/N/Y (16%). The G223S mutation was associated with decreased susceptibility to SJ733, PA92, and KAE609. The D1116G/N/Y mutations were associated with decreased susceptibility to SJ733, and the presence of mutations at both codons 223 and 1116 was associated with decreased susceptibility to PA92 and SJ733. In all of these cases, absolute differences in susceptibilities of wild-type (WT) and mutant parasites were modest. Analysis of clones separated from mixed field isolates consistently identified mutant clones as less susceptible than WT. Analysis of isolates from other sites demonstrated the presence of the G223S and D1116G/N/Y mutations across Uganda. Our results indicate that malaria parasites circulating in Uganda have a number of polymorphisms in PfATP4 and that modestly decreased susceptibility to PfATP4 inhibitors is associated with some mutations now present in Ugandan parasites.