Induction of Multidrug Tolerance in Plasmodium falciparum by Extended Artemisinin Pressure

Plasmodium falciparum resistance to artemisinin derivatives in Southeast Asia threatens global malaria control strategies. Whether delayed parasite clearance, which exposes larger parasite numbers to artemisinins for longer times, selects higher-grade resistance remains unexplored. We investigated whether long-lasting artemisinin pressure selects a novel multidrug-tolerance profile. Although 50% inhibitory concentrations for 10 antimalarial drugs tested were unchanged, drug-tolerant parasites showed higher recrudescence rates for endoperoxides, quinolones, and an antifolate, including partner drugs of recommended combination therapies, but remained susceptible to atovaquone. Moreover, the age range of intraerythrocytic stages able to resist artemisinin was extended to older ring forms and trophozoites. Multidrug tolerance results from drug-induced quiescence, which enables parasites to survive exposure to unrelated antimalarial drugs that inhibit a variety of metabolic pathways. This novel resistance pattern should be urgently monitored in the field because this pattern is not detected by current assays and represents a major threat to antimalarial drug policy.     

Holotransferrin enhances selective anticancer activity of artemisinin against human hepatocellular carcinoma cells

Artemisinin, also termed qinghaosu, is extracted from the traditional Chinese medicine ar- temesia annua L. （the blue-green herb） in the early 1970s, which has been confirmed for effectively treating malaria, Additionally, emerging data prove that artemisinin exhibits anti-cancer effects against many types of cancers such as leukemia, melanoma, etc. Artemisinin becomes cytotoxic in the presence of ferrous iron. Since iron influx is high in cancer cells, artemisinin and its analogs selectively kill can- cer cells with increased intracellular iron concentrations. This study is aimed to investigate the selective inhibitory effects of artemisinin on SMMC-7721 cells in vitro and determine the effect of holotransfer- fin, which increases the concentration of ferrous iron in cancer cells, combined with artemisinin on the anticancer activity. MTT assay was used for assessing the proliferation of SMMC-7721 cells treated with artemisinin. The induction of apoptosis and inhibition of colony formation in SMMC-7721 cells treated with artemisinin were determined by TdT-mediated dUTP nick end labeling （TUNEL） and col- ony formation assay, respectively. The results showed that artemisinin at various concentrations signifi- cantly inhibited growth, colony formation and cell viability of SMMC-7721 cells （P〈0.05）, likely due to induction of apoptosis of SMMC-7721 cells. Of interest, it was found that incubation of artemisinin combined with holotransferrin sensitized the growth inhibitory effect of artemisinin on SMMC-7721 cells （P〈0.01）. Our data suggest that treatment with artemisinin leads to inhibition of viability and pro- liferation, and apoptosis of SMMC-7721 ceils. Furthermore, we observed that holotransferrin signifi- cantly enhanced the anti-cancer activity of artemisinin. This study may provide a potential therapeutic choice for liver cancer.     

More insights into the pharmacological effects of artemisinin

Artemisinin is one of the most widely prescribed drugs against malaria and has recently received increased attention because of its other potential biological effects. The aim of this review is to summarize recent discoveries of the pharmaceutical effects of artemisinin in basic science along with its mechanistic action, as well as the intriguing results of recent clinical studies, with a focus on its antitumor activity. Scientific evidence indicates that artemisinin exerts its biological activity by generating reactive oxygen species that damage the DNA, mitochondrial depolarization, and cell death. In the present article review, scientific evidence suggests that artemisinin is a potential therapeutic agent for various diseases. Thus, this review is expected to encourage interested scientists to conduct further preclinical and clinical studies to evaluate these biological activities.     

青蒿素脂质体的制备及质量评价

目的通过对青蒿素脂质体的处方和制备工艺研究,研制高包封率和稳定的脂质体。方法采用乙醇注入法制备脂质体,以正交实验优化处方。测定了脂质体中药物的包封率;并初步考察了脂质体的稳定性。结果优化处方与工艺所得脂质体形态均匀,包封率〉85％,载药量达27．22％,粒径约为90nm,Zeta电位约为一68．4mV,具有良好的稳定性。结论乙醇注入法制备脂质体工艺简便,包封率高,制备的脂质体稳定性好。     

Artemisinin activity-based probes identify multiple molecular targets within the asexual stage of the malaria parasites Plasmodium falciparum 3D7

The artemisinin (ART)-based antimalarials have contributed significantly to reducing global malaria deaths over the past decade, but we still do not know how they kill parasites. To gain greater insight into the potential mechanisms of ART drug action, we developed a suite of ART activity-based protein profiling probes to identify parasite protein drug targets in situ. Probes were designed to retain biological activity and alkylate the molecular target(s) of Plasmodium falciparum 3D7 parasites in situ. Proteins tagged with the ART probe can then be isolated using click chemistry before identification by liquid chromatography–MS/MS. Using these probes, we define an ART proteome that shows alkylated targets in the glycolytic, hemoglobin degradation, antioxidant defense, and protein synthesis pathways, processes essential for parasite survival. This work reveals the pleiotropic nature of the biological functions targeted by this important class of antimalarial drugs.Malaria is a global health problem with 214 million new cases of malaria and 438,000 deaths reported in 2015, mostly in sub-Saharan Africa (1). The endoperoxide class of antimalarial drugs, such as artemisinin (ART), is the first line of defense against malaria infection against a backdrop of multidrug-resistant parasites (2) and lack of effective vaccines (3, 4). Given the effectiveness of the ART class, the question arises: how do these drugs kill parasites? A suggested mechanism of action involves the cleavage of the endoperoxide bridge by a source of Fe²⁺ or heme. This cleavage results in the formation of oxyradicals that rearrange into primary or secondary carbon-centered radicals. These radicals have been proposed to alkylate parasite proteins that somehow result in the death of the parasite (5). However, this proposal remains a subject of intense debate (6, 7), while these alkylated proteins are yet to be formally identified. So far, the proposed targets of ART action include a PfATP6 enzyme, the Plasmodium falciparum ortholog of mammalian sarcoendoplasmic reticulum Ca²¹-ATPases (SERCAs) (5), translational controlled tumor protein, and heme (5). Additionally, Haynes et al. (8) proposed that ART may act by impairing parasite redox homeostasis as a consequence of an interaction between the drug and flavin adenine dinucleotide (FADH) and/or other parasite flavoenzymes in the parasite, leading to the generation of reactive oxygen species (ROS). New approaches are required for definitive identification of ART molecular targets. This insight into the drug activation-dependent mechanism of action will be invaluable in the target-led development of more potent drugs with the potential to circumvent the emergence of resistance to current first-line ART-based therapies. The goal of this study was to identify ART-targeted proteins and their interacting partners in P. falciparum. We recently adopted a proteomic approach developed by Speers and Cravatt (9) to synthesize a suite of pyrethroid activity-based protein profiling probes (ABPPs) (10). Using alkyne/azide-coupling partners through “click chemistry,” we identified several cytochrome P450 enzymes that metabolized deltamethrin in rat liver microsomes (10). More recently, a chemical proteomic approach was developed to identify parasite proteins targeted by an albitiazolium antimalarial drug candidate in situ using a photoactivation cross-linking approach (11). However, this generic approach can introduce significant promiscuity in the proteins tagged based on the intracompartmental distribution of drug independent of actual mechanisms.Here, we introduced the design and synthesis of click chemistry-compatible activity-based probes incorporating the endoperoxide scaffold of ART as a warhead to alkylate and identified the ART molecular target(s) in asexual stages of the malaria parasite (Fig. 1). A major advantage of this strategy is that the reporter tags are introduced under “click” reaction conditions performed after the drug has achieved its biological effects, enabling purification, identification, and quantification of alkylated parasite’s proteins and their interacting partners as shown in Fig. 1B. To avoid nonspecific probe-dependent tagging, a common limitation of these approaches, we generated the respective “control” nonperoxide partners to improve the specificity and biological relevance of our resultant tagged protein list.Open in a separate windowFig. 1.Rational design of the ART-ABPPs. (A) Conversion of ART to ART-ABPPs involves the addition of a clickable handle (i.e., an alkyne or azide to the ART drug pharmacophore by the peptide-coupling method illustrated in SI Text). The structures of the alkyne (P1) and azide (P2) probes and respective inactive deoxy controls CP1 and CP2 with in vitro IC₅₀ values are presented. (B) General workflow of copper-catalyzed and copper-free click chemistry approaches used in the identification of alkylated proteins after in situ treatment of P. falciparum parasite with alkyne and azide ART-ABPPs. The azide- and alkyne-modified proteins are tagged with biotin azide and biotin dibenzocyclooctyne (Biotin-DIBO), respectively, via click reactions followed by affinity purification tandem with LC-MS/MS for protein identification.     

Multifunctional mesoporous nanoparticles as pH-responsive Fe reservoirs and artemisinin vehicles for synergistic inhibition of tumor growth

Artemisinin (ART) is an iron-dependent anti-cancer drug. However, simultaneous delivery of hydrophobic ART and Fe²⁺ ions into cancer cells remains a major challenge. Herein, we reported Fe₃O₄@C/Ag@mSiO₂ (FCA@mSiO₂) multifunctional nanocarriers which can load ART as high as 484 mg/g. Moreover, FCA@mSiO₂ nanoparticles demonstrated pH-responsive Fe²⁺ release, the concentration of Fe²⁺ ions can reach 2.765 nmol/L in HeLa cells cultured with FCA@mSiO₂ nanoparticles. The antitumor efficacy of ART-loaded FCA@mSiO₂ nanoparticles measured by MTT assay was significantly enhanced compared with free ART. It was suggested that the ART-loaded FCA@mSiO₂ nanoparticles are internalized by HeLa cells and located at the acidic compartments of endosomes and lysosomes, releasing Fe²⁺ ions to non-enzymatically convert ART to toxic products for killing cancer cells. This result provides a way for using promising natural drugs in anti-cancer therapeutics.     

Parasitaemia and gametocytaemia after treatment with chloroquine, pyrimethamine/sulfadoxine, and pyrimethamine/sulfadoxine combined with artesunate in young Gambians with uncomplicated malaria

As part of a study to assess the infectivity of gametocytes after treatment with four antimalarial regimens, the efficacy of each treatment was also determined. From September to December 1998, 598 children with uncomplicated malaria were treated; 135 received chloroquine (CQ) alone, 276 received pyrimethamine/sulfadoxine (Fansidar, PSD) alone, 113 received PSD with a single dose of artesunate (PSD + 1ART) and 74 received PSD combined with three doses of artesunate (PSD + 3ART). On day 28 19/63 (30.2%; 95% C.I. 19.2% to 43.1%) of children treated with CQ alone, 5/134 (3.7%; 95% C.I. 1.2% to 8.5%) treated with PSD alone, 1/71 (1.4%, 95% C.I. 0.0% to 7.9%) treated with PSD + 1ART and 0/45 (0.0%; 95% C.I. 0.0% to 7.9%) treated with PSD + 3ART were parasitaemic. The proportion of children with gametocytes on day 7 after treatment with CQ alone was 16/89 (18.0%; 95% C.I. 10.6% to 27.6%), 98/174 (56.3%; 95% C.I. 48.6% to 63.8%) after treatment with PSD alone, 8/70 (11.4%; 95% C.I. 5.1% to 21.3%) after treatment with PSD + 1ART and 4/46 (8.7%; 95% C.I., 2.4% to 20.8%) after treatment with PSD + 3ART. CQ thus has a lower efficacy than PSD or either of the PSD and artesunate combinations. Use of PSD alone as an alternative first line treatment results in a very high post-treatment gametocyte prevalence that is likely to enhance transmission. There would be greater and more sustainable benefits from using PSD and artesunate combinations.     

Low efficacy of the combination artesunate plus amodiaquine for uncomplicated falciparum malaria among children under 5 years in Kailahun, Sierra Leone

OBJECTIVE: In 2004, Sierra Leone adopted artesunate plus amodiaquine as first-line antimalarial treatment. We evaluated the efficacy of this combination in Kailahun, where a previous study had shown 70.2% efficacy of amodiaquine in monotherapy. METHODS: Method and outcome classification of the study complied with WHO guidelines. Children 6-59 months with uncomplicated malaria were followed-up for 28 days. PCR genotyping was used to distinguish recrudescence from reinfection. Reinfections were reclassified as cured. RESULTS: Of 172 children who were referred to the study clinic, 126 satisfied inclusion criteria and were enrolled. No early treatment failures were reported. The day 14, efficacy was 98.2% (95% CI: 93.8-99.8). Of 65 recurrent parasitaemias analysed by PCR, 17 were recrudescences. The PCR-adjusted day 28 efficacy was 84.5% (95% CI: 76.4-90.7). All true failures occurred in the last 8 days of follow-up. Of 110 children who completed the 28-day follow-up, 54 (49.1%) experienced a novel infection. CONCLUSION: The efficacy of this combination was disappointing. The high reinfection rate suggested little prophylactic effect. In Kailahun a more efficacious combination might be necessary in the future. The efficacy of AS + AQ needs to be monitored in Kailahun and in the other regions of Sierra Leone.