Impact of Extended Duration of Artesunate Treatment on Parasitological Outcome in a Cytocidal Murine Malaria Model

Abstract

Artemisinin-based combination therapies are a key pillar in global malaria control and are recommended as a first-line Plasmodium falciparum treatment. They rely upon a rapid 4-log-unit reduction in parasitemia by artemisinin compounds with a short half-life and the killing of remaining parasites by a partner compound with a longer half-life. Current treatment guidelines stipulate giving three 24-h-interval doses or six 12-h-interval doses over a 3-day period. Due to the short half-life of artesunate and artemether, almost all of the resulting cytocidal activity is confined within a single 48-h asexual P. falciparum cycle. Here, we utilized a luciferase reporter, Plasmodium berghei ANKA, in a cytocidal model in which treatment was initiated at high parasitemia, allowing us to monitor a greater than 3-log-unit reduction in parasite density, as well as 30-day survival. In this study, we demonstrated that increasing the artesunate duration from spanning one asexual cycle to spanning three asexual cycles while keeping the total dose constant results in enhanced cytocidal activity. Single daily artesunate doses at 50 mg/kg of body weight over 7 days were the minimum necessary for curative monotherapy. In combination with a single sub-human-equivalent dose of the partner drug amodiaquine or piperaquine, the three-asexual-cycle artesunate duration was able to cure 75% and 100% of mice, respectively, whereas 0% and 33% cures were achieved with the single-asexual-cycle artesunate duration. In summary, cytocidal activity of the artemisinin compounds, such as artesunate, can be improved solely by altering the dosing duration.KEYWORDS antimalarial agents, artemisinin, pharmacodynamics I nfection with the malaria parasite resulted in approximately 438,000 deaths in 2015, with 99% of the cases attributable to the most lethal species, Plasmodium falciparum (1). As there is no available vaccine, antimalarial drugs remain the primary defense against this deadly disease. Current guidelines from the World Health Organization recommend the use of artemisinin-based combination therapy (ACT) for cases of uncomplicated malaria caused by P. falciparum (2). Naturally occurring artemisinin is not used clinically; rather, it has been replaced by its semisynthetic derivatives artesunate and artemether or by the metabolite of the semisynthetic derivatives, dihydroartemisinin (DHA) (3). Dihydroartemisinin is activated by iron and or heme to cause radical damage to surrounding proteins, resulting in reduction of the total parasite burden more rapidly than other antimalarials (4). However, both dihydroartemisinin and the parent drugs have a short plasma half-life of less than a few hours, necessitating a partner drug with a longer plasma half-life to clear residual parasites (5,6). Over the past decade, the adoption of ACT as a first-line treatment has been integral in a promising 30% decrease in malaria-associated mortality rates (1).

Experimentally Engineered Mutations in a Ubiquitin Hydrolase, UBP-1, Modulate In Vivo Susceptibility to Artemisinin and Chloroquine in Plasmodium berghei

“…S2D), suggesting that despite being principally enriched by ART, the V2721F mutation also modulates some resistance to CQ. Meanwhile, when we challenged the G1807 line (V2752F single mutation) with CQ at higher doses (20,30, and 50 mg/kg), a recrudescent population was observed on day 10 with CQ 30 mg/kg (Fig. 1D).…”

Efficacy and resistance of different artemisinin-based combination therapies: a systematic review and network meta-analysis

“…The overall NMA showed that artemisinin monotherapy has a high risk of recrudescence. We believe that this may be a result of its rapid mode of action and a short half-life leading to its inability to clear all the malaria parasites in the body [8]. The same is observed for chlorproguanil-dapsone in which rapid elimination from the body is believed to be the reason for treatment failure [32].…”

“…This necessitated the need of a new antimalarial drug and it was not until 1972 when artemisinin was discovered by Youyou Tu [6]. Artemisinin is a fast acting drug that targets blood-stage Plasmodium falciparum [7] but its efficacy when used as monotherapy is limited by its short half-life [8]. Artemisinin Combination Therapy (ACT) was therefore subsequently introduced in 2001 [9].…”

Superior Pyronaridine Single-Dose Pharmacodynamics Compared to Artesunate, Chloroquine, and Amodiaquine in a Murine Malaria Luciferase Model

“…Luciferase assay and analysis. A dilution series was performed using P. berghei-infected blood to establish a standard curve for the translation of the luciferase signal (total flux) into the number of parasites per well (27). Five microliters of blood was drawn from 24 mice with parasitemias ranging from approximately 6 to 12% and added to 45 l of lysis buffer.…”

“…Data are represented as the mean Ϯ standard error of the mean (SEM). The luciferase raw data log 10 total flux (number of photons per second ϭ y) was transformed to the number of parasites per microliter (Y) using the equation Y ϭ (10 {[log(y) Ϫ 0.55]/0.05} ) • 2 (27). All data were normalized to the geometric mean parasitemia of 5 million parasites per l at the time of drug treatment.…”