Artemisinins: their growing importance in medicine

Activation of aqueous hydrogen peroxide for non-catalyzed dihydroperoxidation of ketones by azeotropic removal of water

Cyclic and acyclic ketones were selectively converted to gem-dihydroperoxides in 72–99% yield with 30% aq. hydrogen peroxide by azeotropic distillation of water from the reaction mixture without any catalyst.

Sesquiterpene Lactones from Artemisia Genus: Biological Activities and Methods of Analysis

Sesquiterpene lactones are a large group of natural compounds, found primarily in plants of Asteraceae family, with over 5000 structures reported to date. Within this family, genus Artemisia is very well represented, having approximately 500 species characterized by the presence of eudesmanolides and guaianolides, especially highly oxygenated ones, and rarely of germacranolides. Sesquiterpene lactones exhibit a wide range of biological activities, such as antitumor, anti-inflammatory, analgesic, antiulcer, antibacterial, antifungal, antiviral, antiparasitic, and insect deterrent. Many of the biological activities are attributed to the α-methylene-γ-lactone group in their molecule which reacts through a Michael-addition with free sulfhydryl or amino groups in proteins and alkylates them. Due to the fact that most sesquiterpene lactones are thermolabile, less volatile compounds, they present no specific chromophores in the molecule and are sensitive to acidic and basic mediums, and their identification and quantification represent a difficult task for the analyst. Another problematic aspect is represented by the complexity of vegetal samples, which may contain compounds that can interfere with the analysis. Therefore, this paper proposes an overview of the methods used for the identification and quantification of sesquiterpene lactones found in Artemisia genus, as well as the optimal conditions for their extraction and separation.

A Randomised, Double Blind, Placebo-Controlled Pilot Study of Oral Artesunate Therapy for Colorectal Cancer

BACKGROUND

Artesunate is an antimalarial agent with broad anti-cancer activity in in vitro and animal experiments and case reports. Artesunate has not been studied in rigorous clinical trials for anticancer effects.

AIM

To determine the anticancer effect and tolerability of oral artesunate in colorectal cancer (CRC).

METHODS

This was a single centre, randomised, double-blind, placebo-controlled trial. Patients planned for curative resection of biopsy confirmed single primary site CRC were randomised (n = 23) by computer-generated code supplied in opaque envelopes to receive preoperatively either 14 daily doses of oral artesunate (200 mg; n = 12) or placebo (n = 11). The primary outcome measure was the proportion of tumour cells undergoing apoptosis (significant if > 7% showed Tunel staining). Secondary immunohistochemical outcomes assessed these tumour markers: VEGF, EGFR, c-MYC, CD31, Ki67 and p53, and clinical responses.

FINDINGS

20 patients (artesunate = 9, placebo = 11) completed the trial per protocol. Randomization groups were comparable clinically and for tumour characteristics. Apoptosis in > 7% of cells was seen in 67% and 55% of patients in artesunate and placebo groups, respectively. Using Bayesian analysis, the probabilities of an artesunate treatment effect reducing Ki67 and increasing CD31 expression were 0.89 and 0.79, respectively. During a median follow up of 42 months 1 patient in the artesunate and 6 patients in the placebo group developed recurrent CRC.

INTERPRETATION

Artesunate has anti-proliferative properties in CRC and is generally well tolerated.

Anti-malarial drug artesunate protects against cigarette smoke-induced lung injury in mice

Cigarette smoking is the primary cause of chronic obstructive pulmonary disease (COPD), which is mediated by lung infiltration with inflammatory cells, enhanced oxidative stress, and tissue destruction. Anti-malarial drug artesunate has been shown to possess anti-inflammatory and anti-oxidative actions in mouse asthma models. We hypothesized that artesunate can protect against cigarette smoke-induced acute lung injury via its anti-inflammatory and anti-oxidative properties. Artesunate was given by oral gavage to BALB/c mice daily 2h before 4% cigarette smoke exposure for 1h over five consecutive days. Bronchoalveolar lavage (BAL) fluid and lungs were collected for analyses of cytokines, oxidative damage and antioxidant activities. Bronchial epithelial cell BEAS-2B was exposed to cigarette smoke extract (CSE) and used to study the mechanisms of action of artesunate. Artesunate suppressed cigarette smoke-induced increases in BAL fluid total and differential cell counts; levels of IL-1β, MCP-1, IP-10 and KC; and levels of oxidative biomarkers 8-isoprostane, 8-OHdG and 3-nitrotyrosine in a dose-dependent manner. Artesunate promoted anti-oxidant catalase activity and reduced NADPH oxidase 2 (NOX2) protein level in the lungs from cigarette smoke-exposed mice. In BEAS-2B cells, artesunate suppressed pro-inflammatory PI3K/Akt and p44/42 MAPK signaling pathways, and increased nuclear Nrf2 accumulation in response to CSE. Artesunate possesses anti-inflammatory and anti-oxidative properties against cigarette smoke-induced lung injury, probably via inhibition of PI3K and p42/22 MAPK signaling pathways, augmentation of Nrf2 and catalase activities, and reduction of NOX2 level. Our data suggest that artesunate may have therapeutic potential for treating COPD.

In vitro efficacy of ethanolic extract of Artemisia absinthium (Asteraceae) against Leishmania major L. using cell sensitivity and flow cytometry assays

Leishmaniasis is one of the most neglected human diseases with an estimated global burden ranking second in mortality and fourth in morbidity among the tropical infections. Chemotherapy involving the use of drugs like glucantime is the mainstay treatment in endemic areas of Iran. Drug resistance is increasingly prevalent, so search for alternative therapy is gathering pace. Medicinal herbs, like wormwood Artemisia, have chemical compounds effective against a number of pathogens. In this study, the efficacy of ethanol extract from Artemisia absinthium (Asteraceae) against Leishmania major L. was investigated in vitro. The outcome of different effective doses (1-40 mg/ml) of ethanol extracts from this medicinal herb, A. absinthium, on a standard Iranian parasite strain of L. major was examined. The L. major promastigote cell sensitivity and mortality or viability effects due to the addition of herbal extract were measured using the MTT assay and the flow cytometry technique, respectively. There was complete agreement between the two assays. The lethal concentration (LC50) was measured as 101 mg/ml. Some contrasting relationships between the medicinal herb concentrations and the viability of parasites were observed; so that there was an increased multiplication of the parasite at low concentrations of the drug, but an anti-parasitic apoptotic effect was seen at high concentrations of A. absinthium. It was concluded that there might be one or more chemical constituents within the herbal extract of wormwood which at high concentration controlled cell division and affected the relevant activity within the only one giant mitochondrion in this flagellate parasite. At low doses, however, it showed the opposite effect of leading to mitotic cell divisions.

Present-day anthelmintics and perspectives on future new targets

In absence of vaccines for the majority of helminths, chemotherapy is still the mainstay for controlling human helminthiases. However, a limited number of drugs are available in the market to combat parasitic helminths in human. Besides, the development and spread of drug resistance have declined the use of most currently available anthelmintics. Clearly, availability of new anthelmintic agents will be essential in the next few years. More research into the mechanisms of drug actions and their targets are eminent for the discovery and development of novel anthelmintic agents. Recent drug discovery techniques mostly rely on mechanism-based screening of compounds on heterologously expressed targets in bacterial, mammalian or yeast cells. Although this is usually a successful approach, it is money- and time-consuming; meanwhile, pharmaceutical companies prefer the tested target that is chosen based on basic research. The nervous system is the site of action of several chemotherapeutics including pesticides and antinematode drugs; accordingly, the nervous system continues to be a promising target. Recent advances in exploring helminths' nervous system, neurotransmitters and receptors have paved the way for the development of potential agents targeting the nervous system and its components.

The antimalarial drug artesunate inhibits primary human cultured airway smooth muscle cell proliferation

Airway smooth muscle (ASM) cell hyperplasia contributes to airway wall remodeling (AWR) in asthma. Glucocorticoids, which are used as first-line therapy for the treatment of inflammation in asthma, have limited impact on AWR, and protracted usage of high doses of glucocorticoids is associated with an increased risk of side effects. Moreover, patients with severe asthma often show reduced sensitivity to glucocorticoids. Artesunate, a semisynthetic artemisinin derivative used to treat malaria with minimal toxicity, attenuates allergic airway inflammation in mice, but its impact on AWR is not known. We examined the effects of artesunate on ASM proliferation in vitro and in vivo. Primary human ASM cells derived from nonasthmatic donors were treated with artesunate before mitogen stimulation. Artesunate reduced mitogen-stimulated increases in cell number and cyclin D1 protein abundance but had no significant effect on ERK1/2 phosphorylation. Artesunate, but not dexamethasone, inhibited phospho-Akt and phospho-p70(S6K) protein abundance. Artesunate, but not dexamethasone, inhibited mitogen-stimulated increases in cell number, cyclin D1, and phospho-Akt protein abundance on ASM cells derived from asthmatic donors. In a murine model of allergic asthma, artesunate reduced the area of α-smooth muscle actin-positive cells and decreased cyclin D1 protein abundance. Our study provides a basis for the future development of artesunate as a novel anti-AWR agent that targets ASM hyperplasia via the PI3K/Akt/p70(S6K) pathway and suggests that artesunate may be used as combination therapy with glucocorticoids.

Subchronic toxicological study of two artemisinin derivatives in dogs

The objective of our study was to profile and compare the systematic changes between orally administered artesunate and intramuscularly injected artemether at a low dose over a 3-month period (92 consecutive days) in dogs. Intramuscular administration of 6 mg kg-1 artemether induced a decreased red blood cell (RBC) count (anemia), concurrent extramedullary hematopoiesis in the spleen and inhibition of erythropoiesis in the bone marrow. We also observed a prolonged QT interval and neuropathic changes in the central nervous system, which demonstrated the cortex and motor neuron vulnerability, but no behavioral changes. Following treatment with artesunate, we observed a decreased heart rate, which was most likely due to cardiac conduction system damage, as well as a deceased RBC count, extramedullary hematopoiesis in the spleen and inhibition of erythropoiesis in the bone marrow. However, in contrast to treatment with artemether, neurotoxicity was not observed following treatment with artesunate. In addition, ultra-structural examination by transmission electron microscopy showed mitochondrial damage following treatment with artesunate. These findings demonstrated the spectrum of toxic changes that result upon treatment with artesunate and artemether and show that the prolonged administration of low doses of these derivatives result in diverse toxicity profiles.

Drug repurposing and human parasitic protozoan diseases

Parasitic diseases have an enormous health, social and economic impact and are a particular problem in tropical regions of the world. Diseases caused by protozoa and helminths, such as malaria and schistosomiasis, are the cause of most parasite related morbidity and mortality, with an estimated 1.1 million combined deaths annually. The global burden of these diseases is exacerbated by the lack of licensed vaccines, making safe and effective drugs vital to their prevention and treatment. Unfortunately, where drugs are available, their usefulness is being increasingly threatened by parasite drug resistance. The need for new drugs drives antiparasitic drug discovery research globally and requires a range of innovative strategies to ensure a sustainable pipeline of lead compounds. In this review we discuss one of these approaches, drug repurposing or repositioning, with a focus on major human parasitic protozoan diseases such as malaria, trypanosomiasis, toxoplasmosis, cryptosporidiosis and leishmaniasis.

Effects of sesquiterpene, flavonoid and coumarin types of compounds from Artemisia annua L. on production of mediators of angiogenesis

BACKGROUND

In addition to recognized antimalarial effects, Artemisia annua L. (Qinghao) possesses anticancer properties. The underlying mechanisms of this activity are unknown. The aim of our experiments was to investigate the effects of distinct types of compounds isolated from A. annua on the immune-activated production of major mediators of angiogenesis playing a crucial role in growth of tumors and formation of metastasis.

METHODS

Included in the study were the sesquiterpene lactones artemisinin and its biogenetic precursors arteannuin B and artemisinic acid. The semi-synthetic analogue dihydroartemisinin was used for comparative purposes. The flavonoids were represented by casticin and chrysosplenol D, the coumarin type of compounds by 4-methylesculetin. Their effects on the lipopolysaccharide (LPS)-induced in vitro production of nitric oxide (NO) were analyzed in rat peritoneal cells using Griess reagent. The LPS-activated production of prostaglandin E2 (PGE2) and cytokines (VEGF, IL-1β, IL-6 and TNF-α) was determined in both rat peritoneal cells and human peripheral blood mononuclear cells using ELISA.

RESULTS

All sesquiterpenes (artemisinin, dihydroartemisinin, artemisinic acid, arteannuin B) significantly reduced production of PGE2. Arteannuin B also inhibited production of NO and secretion of cytokines. All NO, PGE2 and cytokines were suppressed by flavonoids casticin and chrysosplenol D. The coumarin derivative, 4-methylesculetin, was ineffective to change the production of any of these factors.

CONCLUSIONS

The inhibition of immune mediators of angiogenesis by sesquiterpene lactones and flavonoids may be one of the mechanisms of anticancer activity of Artemisia annua L.

Anticancer properties of distinct antimalarial drug classes

We have tested five distinct classes of established and experimental antimalarial drugs for their anticancer potential, using a panel of 91 human cancer lines. Three classes of drugs: artemisinins, synthetic peroxides and DHFR (dihydrofolate reductase) inhibitors effected potent inhibition of proliferation with IC50s in the nM- low µM range, whereas a DHODH (dihydroorotate dehydrogenase) and a putative kinase inhibitor displayed no activity. Furthermore, significant synergies were identified with erlotinib, imatinib, cisplatin, dasatinib and vincristine. Cluster analysis of the antimalarials based on their differential inhibition of the various cancer lines clearly segregated the synthetic peroxides OZ277 and OZ439 from the artemisinin cluster that included artesunate, dihydroartemisinin and artemisone, and from the DHFR inhibitors pyrimethamine and P218 (a parasite DHFR inhibitor), emphasizing their shared mode of action. In order to further understand the basis of the selectivity of these compounds against different cancers, microarray-based gene expression data for 85 of the used cell lines were generated. For each compound, distinct sets of genes were identified whose expression significantly correlated with compound sensitivity. Several of the antimalarials tested in this study have well-established and excellent safety profiles with a plasma exposure, when conservatively used in malaria, that is well above the IC50s that we identified in this study. Given their unique mode of action and potential for unique synergies with established anticancer drugs, our results provide a strong basis to further explore the potential application of these compounds in cancer in pre-clinical or and clinical settings.

Advances in nanomedicines for malaria treatment

Malaria is an infectious disease that mainly affects children and pregnant women from tropical countries. The mortality rate of people infected with malaria per year is enormous and became a public health concern. The main factor that has contributed to the success of malaria proliferation is the increased number of drug resistant parasites. To counteract this trend, research has been done in nanotechnology and nanomedicine, for the development of new biocompatible systems capable of incorporating drugs, lowering the resistance progress, contributing for diagnosis, control and treatment of malaria by target delivery. In this review, we discussed the main problems associated with the spread of malaria and the most recent developments in nanomedicine for anti-malarial drug delivery.

Artesunate possesses anti-leukemia properties that can be enhanced by arsenic trioxide

Artesunate (ART), an effective and safe anti-malaria drug, also exhibits anticancer activity. We studied the effects of ART on proliferation and apoptosis of human K562 and U937 leukemia cell lines. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay demonstrated that ART inhibits cell growth in a dose- and time-dependent manner. Based on the findings obtained from light, fluorescence and transmission electron microscopy and propidium iodide staining, the effect of ART was shown to be mediated through apoptosis. In parallel, ART treatment increased Fas expression, while it decreased the c-Fos level in K562 cells. Furthermore, co-treatment with arsenic trioxide (ATO) significantly facilitated ART-induced K562 cell apoptosis. These findings demonstrated that ART had an antitumor activity against K562 and U937 leukemia cells, largely due to inhibition of proliferation and induction of apoptosis via the intrinsic pathway; and this tumoricidal function could be enhanced by ATO.

In vivo study of effects of artesunate nanoliposomes on human hepatocellular carcinoma xenografts in nude mice

To investigate the effect of artesunate nanoliposomes on cultured cells in vitro and hepatocellular carcinoma xenografts in BALB/c-nu mice. Fluorescence polarization was applied for measurement of mitochondrial membrane fluidities; inhibition test of tumor cell proliferation in vitro was performed and nude mice xenograft model from human hepatocellular carcinoma (HCC) was established. Cytotoxicity of these compounds was evaluated by MTT assay on hepatocellular carcinoma xenografts in nude mice. Anisotropy (r-value) of blank nanoliposomes didn't change, it had no statistically significance between the blank nanoliposomes group and the control group, it indicated that artesunate had no obvious effect on L-O2 human normal liver cells. IC₅₀ values of artesunate nanoliposomes and artesunate API (active pharmaceutical ingredient) against HepG-2 cells were 15.997 and 19.706 μg/ml; IC₅₀ values of the same drugs against L-O2 normal human liver cells were 100.23 and 105.54 μg/ml, respectively. Tumor growth inhibitory effect of artesunate nanoliposomes was 32.7%, and artesunate API was 20.5%, respectively. HepG-2 cells treated with artesunate nanoliposomes showed dose-dependent apoptosis. The antitumor effect of artesunate nanoliposomes on human hepatoma HepG2 cells were stronger than that of artesunate API at the same concentration.

Anti-allergic action of anti-malarial drug artesunate in experimental mast cell-mediated anaphylactic models

BACKGROUND

Allergy is an acquired hypersensitivity reaction of the immune system mediated by cross-linking of allergen-specific IgE-bound high-affinity IgE receptors, leading to immediate mast cell degranulation. Artesunate is a semi-synthetic derivative of artemisinin, an active component of the medicinal plant Artemisia annua. Artesunate is a clinically effective anti-malarial drug and has recently been shown to attenuate allergic asthma in mouse models. This study investigated potential anti-allergic effects of artesunate in animal models of IgE-dependent anaphylaxis.

METHODS

Anti-allergic actions of artesunate were evaluated in passive cutaneous anaphylaxis and passive systemic anaphylaxis mouse models, and in ovalbumin-induced contraction of bronchial rings isolated from sensitized guinea pigs. Direct mast cell-stabilizing effect of artesunate was examined in RBL-2H3 mast cell line and in mature human cultured mast cells. Anti-allergic signaling mechanisms of action of artesunate in mast cells were also investigated.

RESULTS

Artesunate prevented IgE-mediated cutaneous vascular hyperpermeability, hypothermia, elevation in plasma histamine level, and tracheal tissue mast cell degranulation in mice in a dose-dependent manner. In addition, artesunate suppressed ovalbumin-mediated guinea pig bronchial smooth muscle contraction. Furthermore, artesunate concentration-dependently blocked IgE-mediated degranulation of RBL-2H3 mast cells and human culture mast cells. Artesunate was found to inhibit IgE-induced Syk and PLCγ1 phosphorylation, production of IP(3) , and rise in cytosolic Ca(+2) level in mast cells.

CONCLUSIONS

We report here for the first time that artesunate possesses anti-allergic activity by blocking IgE-induced mast cell degranulation, providing a foundation for developing artesunate for the treatment of allergic asthma and other mast cell-mediated allergic disorders.

Small molecule anti-malarial patents: a review (January 2010-June 2011)

INTRODUCTION

Malaria causes a huge humanitarian and economic burden. Parasite resistance to established and recently launched anti-malarials is a major issue which, when combined with a malaria eradication agenda, means there is a considerable need for new small molecule anti-malarials. Catalyzed by a recent surge in funding for malaria drug discovery and development, there is an increasing number of compounds in the malaria pipeline.

AREAS COVERED

This review covers patents published in English between January 2010 and June 2011, which feature small molecules for the treatment of malaria. Approximately 50 series of compounds are described. Patents covering clinical applications, diagnosis kits or vaccines are not included, nor patents where the principle disease focus is not malaria.

EXPERT OPINION

There is considerable activity in the field of small molecules for malaria which is likely to continue. The ultimate goal is to identify novel drugs to support the malaria eradication agenda. This requires safe and efficacious compounds, from novel chemotypes, which rapidly kill parasites and which are readily synthesized from cheap starting materials. In addition, compounds which have activity in the liver stages or in transmission blocking may be prioritized for development over analogs related to established anti-malarial series targeting the asexual blood stages of the parasite.

Pharmacodynamics of antimalarial chemotherapy

Malaria chemotherapy is under constant threat from the emergence and spread of multidrug resistance of Plasmodium falciparum. Resistance has been observed to almost all currently used antimalarials. Some drugs are also limited by toxicity. A fundamental component of the strategy for malaria chemotherapy is based on prompt, effective and safe antimalarial drugs. To counter the threat of resistance of P. falciparum to existing monotherapeutic regimens, current malaria treatment is based principally on the artemisinin group of compounds, either as monotherapy or artemisinin-based combination therapies for treatment of both uncomplicated and severe falciparum malaria. Key advantages of artemisinins over the conventional antimalarials include their rapid and potent action, with good tolerability profiles. Their action also covers transmissible gametocytes, resulting in decreased disease transmission. Up to now there has been no prominent report of drug resistance to this group of compounds. Treatment of malaria in pregnant women requires special attention in light of limited treatment options caused by potential teratogenicity coupled with a paucity of safety data for the mother and fetus. Treatment of other malaria species is less problematic and chloroquine is still the drug of choice, although resistance of P. vivax to chloroquine has been reported. Multiple approaches to the identification of new antimalarial targets and promising antimalarial drugs are being pursued in order to cope with drug resistance.

Artemether resistance in vitro is linked to mutations in PfATP6 that also interact with mutations in PfMDR1 in travellers returning with Plasmodium falciparum infections

Background

Monitoring resistance phenotypes for Plasmodium falciparum, using in vitro growth assays, and relating findings to parasite genotype has proved particularly challenging for the study of resistance to artemisinins.

Methods

Plasmodium falciparum isolates cultured from 28 returning travellers diagnosed with malaria were assessed for sensitivity to artemisinin, artemether, dihydroartemisinin and artesunate and findings related to mutations in pfatp6 and pfmdr1.

Results

Resistance to artemether in vitro was significantly associated with a pfatp6 haplotype encoding two amino acid substitutions (pfatp6 A623E and S769N; (mean IC₅₀ (95% CI) values of 8.2 (5.7 – 10.7) for A623/S769 versus 623E/769 N 13.5 (9.8 – 17.3) nM with a mean increase of 65%; p = 0.012). Increased copy number of pfmdr1 was not itself associated with increased IC₅₀ values for artemether, but when interactions between the pfatp6 haplotype and increased copy number of pfmdr1 were examined together, a highly significant association was noted with IC₅₀ values for artemether (mean IC₅₀ (95% CI) values of 8.7 (5.9 – 11.6) versus 16.3 (10.7 – 21.8) nM with a mean increase of 87%; p = 0.0068). Previously described SNPs in pfmdr1 are also associated with differences in sensitivity to some artemisinins.

Conclusions

These findings were further explored in molecular modelling experiments that suggest mutations in pfatp6 are unlikely to affect differential binding of artemisinins at their proposed site, whereas there may be differences in such binding associated with mutations in pfmdr1. Implications for a hypothesis that artemisinin resistance may be exacerbated by interactions between PfATP6 and PfMDR1 and for epidemiological studies to monitor emerging resistance are discussed.

Phytochemical analysis of a herbal tea from Artemisia annua L

Strategies to control diffusion of malaria needs to account for the increase of resistance of the parasite to the conventional antimalarial drugs. It has been proposed that a traditional aqueous preparation from Artemisia annua, with a low content of the active compound, artemisinin, may reduce the risk of resistance of the protozoa and be relatively more effective in the treatment of the disease. The solubility properties of the molecule have been the matter of concern about the therapeutic usefulness of herbal teas from A. annua. The present study aimed at analysing the chemical profile of a tea infusion from A. annua. Tea from A. annua was prepared through infusion of the plant aerial parts in water for 1, 24 and 48 h. Content of artemisinin was determined by HPLC-ELSD. Overall chemical characterization of the extracts was carried out by a combination of metabolomic techniques. The artemisinin content varied only slightly in the three different extracts (about 0.12%). A series of mono-caffeoyl- and mono-feruloyl-quinic acids, di-caffeoyl- and di-feruloyl-quinic acids was identified as main components of the tea infusion, together with some flavonoids. Reconstitution of the same extracts in less polar or apolar solvents resulted in a different composition with no phenolics and a much lower concentration of artemisinin.

Semisynthetic Artemisinin and Synthetic Peroxide Antimalarials

Since the discovery of the endoperoxide sesquiterpene lactone artemisinin, numerous second-generation semisynthetic artemisinins and synthetic peroxides have been prepared and tested for their antimalarial properties. Using a case-study approach, we describe the discovery of the investigational semisynthetic artemisinins artelinic acid (8) and artemisone (9), and the structurally diverse synthetic peroxides arteflene (10), fenozan B07 (11), arterolane (12), PA1103/SAR116242 (13), and RKA182 (14).

The Plasmodium falciparum Ca(2+)-ATPase PfATP6: insensitive to artemisinin, but a potential drug target

The disease malaria, caused by the parasite Plasmodium falciparum, remains one of the most important causes of morbidity and mortality in sub-Saharan Africa. In the absence of an efficient vaccine, the medical treatment of malaria is dependent on the use of drugs. Since artemisinin is a powerful anti-malarial drug which has been proposed to target a particular Ca2+-ATPase (PfATP6) in the parasite, it has been important to characterize the molecular properties of this enzyme. PfATP6 is a 139 kDa protein composed of 1228 amino acids with a 39% overall identity with rabbit SERCA1a (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 1a). PfATP6 conserves all sequences and motifs that are important for the function and/or structure of a SERCA, such as two high-affinity Ca2+-binding sites, a nucleotide-binding site and a phosphorylation site. We have been successful in isolating PfATP6 after heterologous expression in yeast and affinity chromatography in a pure, active and stable detergent-solubilized form. With this preparation, we have characterized and compared with the eukaryotic SERCA1a isoform the substrate (Ca2+ and ATP) -dependency for PfATP6 activity as well as the specific inhibition/interaction of the protein with drugs. Our data fully confirm that PfATP6 is a SERCA, but with a distinct pharmacological profile: compared with SERCA1a, it has a lower affinity for thapsigargin and much higher affinity for cyclopiazonic acid. On the other hand, we were not able to demonstrate any inhibition by artemisinin and were also not able to monitor any binding of the drug to the isolated enzyme. Thus it is unlikely that PfATP6 plays an important role as a target for artemisinin in the parasite P. falciparum.

From innovation to application: social-ecological context, diagnostics, drugs and integrated control of schistosomiasis

Compared to malaria, tuberculosis and HIV/AIDS, schistosomiasis remains a truly neglected tropical disease. Schistosomiasis, perhaps more than any other disease, is entrenched in prevailing social-ecological systems, since transmission is governed by human behaviour (e.g. open defecation and patterns of unprotected surface water contacts) and ecological features (e.g. living in close proximity to suitable freshwater bodies in which intermediate host snails proliferate). Moreover, schistosomiasis is intimately linked with poverty and the disease has spread to previously non-endemic areas as a result of demographic, ecological and engineering transformations. Importantly though, thanks to increased advocacy there is growing awareness, financial and technical support to control and eventually eliminate schistosomiasis as a public health problem at local, regional and global scales. The purpose of this review is to highlight recent progress made in innovation, validation and application of new tools and strategies for research and integrated control of schistosomiasis. First, we explain that schistosomiasis is deeply embedded in social-ecological systems and explore linkages with poverty. We then summarize and challenge global statistics, risk maps and burden estimates of human schistosomiasis. Discovery and development research pertaining to novel diagnostics and drugs forms the centrepiece of our review. We discuss unresolved issues and emerging opportunities for integrated and sustainable control of schistosomiasis and conclude with a series of research needs.

Artesunate potentiates antibiotics by inactivating heme-harbouring bacterial nitric oxide synthase and catalase

Background

A current challenge of coping with bacterial infection is that bacterial pathogens are becoming less susceptible to or more tolerant of commonly used antibiotics. It is urgent to work out a practical solution to combat the multidrug resistant bacterial pathogens.

Findings

Oxidative stress-acclimatized bacteria thrive in rifampicin by generating antibiotic-detoxifying nitric oxide (NO), which can be repressed by artesunate or an inhibitor of nitric oxide synthase (NOS). Suppressed bacterial proliferation correlates with mitigated NO production upon the combined treatment of bacteria by artesunate with antibiotics. Detection of the heme-artesunate conjugate and accordingly declined activities of heme-harbouring bacterial NOS and catalase indicates that artesunate renders bacteria susceptible to antibiotics by alkylating the prosthetic heme group of hemo-enzymes.

Conclusions

By compromising NO-mediated protection from antibiotics and triggering harmful hydrogen peroxide burst, artesunate may serve as a promising antibiotic synergist for killing the multidrug resistant pathogenic bacteria.

Plasmodial sugar transporters as anti-malarial drug targets and comparisons with other protozoa

Glucose is the primary source of energy and a key substrate for most cells. Inhibition of cellular glucose uptake (the first step in its utilization) has, therefore, received attention as a potential therapeutic strategy to treat various unrelated diseases including malaria and cancers. For malaria, blood forms of parasites rely almost entirely on glycolysis for energy production and, without energy stores, they are dependent on the constant uptake of glucose. Plasmodium falciparum is the most dangerous human malarial parasite and its hexose transporter has been identified as being the major glucose transporter. In this review, recent progress regarding the validation and development of the P. falciparum hexose transporter as a drug target is described, highlighting the importance of robust target validation through both chemical and genetic methods. Therapeutic targeting potential of hexose transporters of other protozoan pathogens is also reviewed and discussed.

Anti-malarial drug artesunate attenuates experimental allergic asthma via inhibition of the phosphoinositide 3-kinase/Akt pathway

BACKGROUND

Phosphoinositide 3-kinase (PI3K)/Akt pathway is linked to the development of asthma. Anti-malarial drug artesunate is a semi-synthetic derivative of artemisinin, the principal active component of a medicinal plant Artemisia annua, and has been shown to inhibit PI3K/Akt activity. We hypothesized that artesunate may attenuate allergic asthma via inhibition of the PI3K/Akt signaling pathway.

METHODOLOGY/PRINCIPAL FINDINGS

Female BALB/c mice sensitized and challenged with ovalbumin (OVA) developed airway inflammation. Bronchoalveolar lavage fluid was assessed for total and differential cell counts, and cytokine and chemokine levels. Lung tissues were examined for cell infiltration and mucus hypersecretion, and the expression of inflammatory biomarkers. Airway hyperresponsiveness was monitored by direct airway resistance analysis. Artesunate dose-dependently inhibited OVA-induced increases in total and eosinophil counts, IL-4, IL-5, IL-13 and eotaxin levels in bronchoalveolar lavage fluid. It attenuated OVA-induced lung tissue eosinophilia and airway mucus production, mRNA expression of E-selectin, IL-17, IL-33 and Muc5ac in lung tissues, and airway hyperresponsiveness to methacholine. In normal human bronchial epithelial cells, artesunate blocked epidermal growth factor-induced phosphorylation of Akt and its downstream substrates tuberin, p70S6 kinase and 4E-binding protein 1, and transactivation of NF-κB. Similarly, artesunate blocked the phosphorylation of Akt and its downstream substrates in lung tissues from OVA-challenged mice. Anti-inflammatory effect of artesunate was further confirmed in a house dust mite mouse asthma model.

CONCLUSION/SIGNIFICANCE

Artesunate ameliorates experimental allergic airway inflammation probably via negative regulation of PI3K/Akt pathway and the downstream NF-κB activity. These findings provide a novel therapeutic value for artesunate in the treatment of allergic asthma.

Artemisia annua extracts, artemisinin and 1,8-cineole, prevent fruit infestation by a major, cosmopolitan pest of apples

CONTEXT

Extracts of Artemisia annua (L.) (Asteraceae) and artemisinins are used for treatment of malaria, parasitic infections and have potent anticancer properties in cell lines. Eucalyptus oil and 1,8-cineole have antimicrobial, immune-stimulatory, anti-inflammatory, antioxidant, analgesic, and spasmolytic effects. Codling moth, Cydia pomonella, (L.) (Tortricidae), is a major cosmopolitan pest of the apple, potentially causing damage translating to 40 billion US dollars per year, globally. Currently used control measures are either hazardous to agricultural workers and harmful to environment, or ineffective. The potential of plant-derived semiochemicals for codling moth control is heavily understudied.

OBJECTIVE

This study evaluated the potential of A. annua extracts, and two chemicals that this plant contains, artemisinin and 1,8-cineole, for preventing apple feeding and infestation by neonate Cydia pomonella larvae.

METHODS

We studied effects of A. annua extracts, artemisinin and 1,8-cineole on apple infestation by neonate codling moth larvae using fruit choice assay in laboratory experiments. Preference of fruit treated with test solutions versus fruit treated with solvent was recorded and analyzed.

RESULTS

Crude A. annua extracts prevented fruit feeding at 1, 3, and 10 mg/ml. Artemisinin had feeding deterrent effects at 10 and 30 mg/ml, and 1,8-cineole at 100 and 300 mg/ml.

DISCUSSION AND CONCLUSIONS

A. annua contains chemicals that prevent apple infestation by codling moth neonates. Artemisinin and 1,8-cineole are among them, but there are other, polar constituents of A. annua, which have similar effects. There is a potential of using our findings in codling moth control and production of codling moth-resistant apples.

Artesunate tolerance in transgenic Plasmodium falciparum parasites overexpressing a tryptophan-rich protein

Due to their rapid, potent action on young and mature intraerythrocytic stages, artemisinin derivatives are central to drug combination therapies for Plasmodium falciparum malaria. However, the evidence for emerging parasite resistance/tolerance to artemisinins in southeast Asia is of great concern. A better understanding of artemisinin-related drug activity and resistance mechanisms is urgently needed. A recent transcriptome study of parasites exposed to artesunate led us to identify a series of genes with modified levels of expression in the presence of the drug. The gene presenting the largest mRNA level increase, Pf10_0026 (PArt), encoding a hypothetical protein of unknown function, was chosen for further study. Immunodetection with PArt-specific sera showed that artesunate induced a dose-dependent increase of the protein level. Bioinformatic analysis showed that PArt belongs to a Plasmodium-specific gene family characterized by the presence of a tryptophan-rich domain with a novel hidden Markov model (HMM) profile. Gene disruption could not be achieved, suggesting an essential function. Transgenic parasites overexpressing PArt protein were generated and exhibited tolerance to a spike exposure to high doses of artesunate, with increased survival and reduced growth retardation compared to that of wild-type-treated controls. These data indicate the involvement of PArt in parasite defense mechanisms against artesunate. This is the first report of genetically manipulated parasites displaying a stable and reproducible decreased susceptibility to artesunate, providing new possibilities to investigate the parasite response to artemisinins.

Antiplasmodial and antitumor activity of dihydroartemisinin analogs derived via the aza-Michael addition reaction

A series of dihydroartemisinin derivatives were synthesized via an aza-Michael addition reaction to a dihydroartemisinin-based acrylate and were evaluated for antiplasmodial and antitumor activity. The target compounds showed excellent antiplasmodial activity, with dihydroartemisinin derivatives 5, 7, 9 and 13 exhibiting IC(50) values of ≤10 nM against both D10 and Dd2 strains of Plasmodium falciparum. Derivative 4d was the most active against the HeLa cancer cell line, with an IC(50) of 0.37 μM and the highest tumor specificity.

Artesunate mitigates proliferation of tumor cells by alkylating heme-harboring nitric oxide synthase

Artesunate (ART), a semi-synthetic derivative of antimalarial artemisinin, kills cancer cells with uncertain mechanisms. Here, we report for the first time that ART may exert the anti-tumor activity by conjugating the prosthetic heme of hemoproteins in a hepatoma cell line, HepG2, which was evident by monitoring the shift of absorbance from heme (A₄₁₅) to the ART-heme adduct (A₄₇₆). Accordingly, a transient elevation of A₄₁₅ was observed with a synchronous burst of nitric oxide (NO) and a high rate of survival following incubation of HepG2 with 50 μM ART. In contrast, ART at above 100 μM led to an abrogation of NO generation and a decline of the survival rate in HepG2. These data implied that heme-containing nitric oxide synthase (NOS) may represent a major cellular target of ART in killing tumor cells.

Artemisone uptake in Plasmodium falciparum-infected erythrocytes

Artemisone is one of the most promising artemisinin derivatives in clinical trials. Previous studies with radiolabeled artemisinin and dihydroartemisinin have measured uptake in Plasmodium falciparum-infected erythrocytes. Uptake is much greater in infected than in uninfected erythrocytes, but the relative contributions of transport, binding, and metabolism to this process still await definition. In this study, we characterized mechanisms by which [(14)C]artemisone is taken up into uninfected and P. falciparum-infected human erythrocytes in vitro. Radiolabeled artemisone rapidly enters uninfected erythrocytes without much exceeding extracellular concentrations. Unlabeled artemisone does not compete in this process. Radiolabeled artemisone is concentrated greatly by a time- and temperature-dependent mechanism in infected erythrocytes. This uptake is abrogated by unlabeled artemisone. In addition, the uptake of artemisone into three subcellular fractions, and its distribution into these fractions, is examined as a function of parasite maturation. These data are relevant to an understanding of the mechanisms of action of this important class of drugs.

Facile oxidation of leucomethylene blue and dihydroflavins by artemisinins: relationship with flavoenzyme function and antimalarial mechanism of action

The antimalarial drug methylene blue (MB) affects the redox behaviour of parasite flavin-dependent disulfide reductases such as glutathione reductase (GR) that control oxidative stress in the malaria parasite. The reduced flavin adenine dinucleotide cofactor FADH(2) initiates reduction to leucomethylene blue (LMB), which is oxidised by oxygen to generate reactive oxygen species (ROS) and MB. MB then acts as a subversive substrate for NADPH normally required to regenerate FADH(2) for enzyme function. The synergism between MB and the peroxidic antimalarial artemisinin derivative artesunate suggests that artemisinins have a complementary mode of action. We find that artemisinins are transformed by LMB generated from MB and ascorbic acid (AA) or N-benzyldihydronicotinamide (BNAH) in situ in aqueous buffer at physiological pH into single electron transfer (SET) rearrangement products or two-electron reduction products, the latter of which dominates with BNAH. Neither AA nor BNAH alone affects the artemisinins. The AA-MB SET reactions are enhanced under aerobic conditions, and the major products obtained here are structurally closely related to one such product already reported to form in an intracellular medium. A ketyl arising via SET with the artemisinin is invoked to explain their formation. Dihydroflavins generated from riboflavin (RF) and FAD by pretreatment with sodium dithionite are rapidly oxidised by artemisinin to the parent flavins. When catalytic amounts of RF, FAD, and other flavins are reduced in situ by excess BNAH or NAD(P)H in the presence of the artemisinins in the aqueous buffer, they are rapidly oxidised to the parent flavins with concomitant formation of two-electron reduction products from the artemisinins; regeneration of the reduced flavin by excess reductant maintains a catalytic cycle until the artemisinin is consumed. In preliminary experiments, we show that NADPH consumption in yeast GR with redox behaviour similar to that of parasite GR is enhanced by artemisinins, especially under aerobic conditions. Recombinant human GR is not affected. Artemisinins thus may act as antimalarial drugs by perturbing the redox balance within the malaria parasite, both by oxidising FADH(2) in parasite GR or other parasite flavoenzymes, and by initiating autoxidation of the dihydroflavin by oxygen with generation of ROS. Reduction of the artemisinin is proposed to occur via hydride transfer from LMB or the dihydroflavin to O1 of the peroxide. This hitherto unrecorded reactivity profile conforms with known structure-activity relationships of artemisinins, is consistent with their known ability to generate ROS in vivo, and explains the synergism between artemisinins and redox-active antimalarial drugs such as MB and doxorubicin. As the artemisinins appear to be relatively inert towards human GR, a putative model that accounts for the selective potency of artemisinins towards the malaria parasite also becomes apparent. Decisively, ferrous iron or carbon-centered free radicals cannot be involved, and the reactivity described herein reconciles disparate observations that are incompatible with the ferrous iron-carbon radical hypothesis for antimalarial mechanism of action. Finally, the urgent enquiry into the emerging resistance of the malaria parasite to artemisinins may now in one part address the possibilities either of structural changes taking place in parasite flavoenzymes that render the flavin cofactor less accessible to artemisinins or of an enhancement in the ability to use intra-erythrocytic human disulfide reductases required for maintenance of parasite redox balance.

Investigations into the role of the Plasmodium falciparum SERCA (PfATP6) L263E mutation in artemisinin action and resistance

Artemisinin-based combination therapies (ACTs) are highly effective for the treatment of Plasmodium falciparum malaria, yet their sustained efficacy is threatened by the potential spread of parasite resistance. Recent studies have provided evidence that artemisinins can inhibit the function of PfATP6, the P. falciparum ortholog of the ER calcium pump SERCA, when expressed in Xenopus laevis oocytes. Inhibition was significantly reduced in an L263E variant, which introduced the mammalian residue into a putative drug-binding pocket. To test the hypothesis that this single mutation could decrease P. falciparum susceptibility to artemisinins, we implemented an allelic-exchange strategy to replace the wild-type pfatp6 allele by a variant allele encoding L263E. Transfected P. falciparum clones were screened by PCR analysis for disruption of the endogenous locus and introduction of the mutant L263E allele under the transcriptional control of a calmodulin promoter. Expression of the mutant allele was demonstrated by reverse transcriptase (RT) PCR and verified by sequence analysis. Parasite clones expressing wild-type or L263E variant PfATP6 showed no significant difference in 50% inhibitory concentrations (IC(50)s) for artemisinin or its derivatives dihydroartemisinin and artesunate. Nonetheless, hierarchical clustering analysis revealed a trend toward reduced susceptibility that neared significance (artemisinin, P approximately = 0.1; dihydroartemisinin, P = 0.053 and P = 0.085; and artesunate, P = 0.082 and P = 0.162 for the D10 and 7G8 lines, respectively). Notable differences in the distribution of normalized IC(50)s provided evidence of decreased responsiveness to artemisinin and dihydroartemisinin (P = 0.02 for the D10 and 7G8 lines), but not to artesunate in parasites expressing mutant PfATP6.