Progress in the research of artemisinin-related antimalarials: an update

Artemisinin: a novel chiral electrochemiluminescence luminophore-assisted enantiospecific recognition and mechanism identification

Exploring novel electrochemiluminescence (ECL) molecules with high efficiency and good stability in aqueous solutions is crucial for achieving highly sensitive detection of analytes. However, developing chiral luminophores with efficient ECL performance is still a challenge. Herein, we first uncover that artemisinin (ART), a well-known chiral antimalarial drug, features a strong ECL emission at 726 nm with the assistance of a co-reactant potassium persulfate (K2S2O8), and an ECL efficiency of 195.3%, compared to that of standard Ru(bpy)3Cl2/K2S2O8. Mechanistic studies indicate that the strong ECL signal of ART is generated when the excited state formed by the reduction of ART peroxide bonds and combination with persulfate returns to the ground state. Significantly, we found that the ECL sensor based on chiral ART could efficiently identify and detect chiral cysteine (Cys) through ECL signals, with a lower limit of detection of 3.7 nM for l-Cys. Density functional theory calculations and scanning electrochemical microscopy technology further confirm that the disparity in the ECL signals is attributed to the different affinity between chiral ART and d/l-Cys, resulting in distinct electron transfer rates. The study demonstrates a new role of ART in ECL investigation and for the first time, achieves the development of ART for the enantioselective recognition and sensitive detection of chiral substances. This will be of vital significance for ECL and chirality research.

Antimalarial chemotherapy: orally curative artemisinin-derived trioxane dimer esters

Eight new artemisinin-derived trioxane dimer esters 5 have been prepared and tested for antimalarial efficacy in malaria-infected mice. At a single oral dose of only 6mg/kg combined with 18mg/kg of mefloquine, each of the dimer esters 5 outperformed the antimalarial drug artemether (2). The most efficacious dimer, dichlorobenzoate ester 5h, prolonged mouse survival past day 30 of infection with three of the four mice in this group having no detectable parasitemia and appearing and acting healthy on day 30.

Reprint of "Pharmacokinetic modelling of the anti-malarial drug artesunate and its active metabolite dihydroartemisinin"

A four compartment mechanistic mathematical model is developed for the pharmacokinetics of the commonly used anti-malarial drug artesunate and its principle metabolite dihydroartemisinin following oral administration of artesunate. The model is structurally unidentifiable unless additional constraints are imposed. Combinations of mechanistically derived constraints are considered to assess their effects on structural identifiability and on model fits. Certain combinations of the constraints give rise to locally or globally identifiable model structures. Initial validation of the model under various combinations of the constraints leading to identifiable model structures was performed against a dataset of artesunate and dihydroartemisinin concentration-time profiles of 19 malaria patients. When all the discussed constraints were imposed on the model, the resulting globally identifiable model structure was found to fit reasonably well to those patients with normal drug absorption profiles. However, there is wide variability in the fitted parameters and further investigation is warranted.

Pharmacokinetic modelling of the anti-malarial drug artesunate and its active metabolite dihydroartemisinin

A four compartment mechanistic mathematical model is developed for the pharmacokinetics of the commonly used anti-malarial drug artesunate and its principle metabolite dihydroartemisinin following oral administration of artesunate. The model is structurally unidentifiable unless additional constraints are imposed. Combinations of mechanistically derived constraints are considered to assess their effects on structural identifiability and on model fits. Certain combinations of the constraints give rise to locally or globally identifiable model structures. Initial validation of the model under various combinations of the constraints leading to identifiable model structures was performed against a dataset of artesunate and dihydroartemisinin concentration-time profiles of 19 malaria patients. When all the discussed constraints were imposed on the model, the resulting globally identifiable model structure was found to fit reasonably well to those patients with normal drug absorption profiles. However, there is wide variability in the fitted parameters and further investigation is warranted.

Dihydroartemisinin enhances Apo2L/TRAIL-mediated apoptosis in pancreatic cancer cells via ROS-mediated up-regulation of death receptor 5

BACKGROUND

Dihydroartemisinin (DHA), a semi-synthetic derivative of artemisinin, has recently shown antitumor activity in various cancer cells. Apo2 ligand or tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is regarded as a promising anticancer agent, but chemoresistance affects its efficacy as a treatment strategy. Apoptosis induced by the combination of DHA and Apo2L/TRAIL has not been well documented, and the mechanisms involved remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report that DHA enhances the efficacy of Apo2L/TRAIL for the treatment of pancreatic cancer. We found that combined therapy using DHA and Apo2L/TRAIL significantly enhanced apoptosis in BxPC-3 and PANC-1 cells compared with single-agent treatment in vitro. The effect of DHA was mediated through the generation of reactive oxygen species, the induction of death receptor 5 (DR5) and the modulation of apoptosis-related proteins. However, N-acetyl cysteine significantly reduced the enhanced apoptosis observed with the combination of DHA and Apo2L/TRAIL. In addition, knockdown of DR5 by small interfering RNA also significantly reduced the amount of apoptosis induced by DHA and Apo2L/TRAIL.

CONCLUSIONS/SIGNIFICANCE

These results suggest that DHA enhances Apo2L/TRAIL-mediated apoptosis in human pancreatic cancer cells through reactive oxygen species-mediated up-regulation of DR5.

Artesunate inhibiting angiogenesis induced by human myeloma RPMI8226 cells

Multiple myeloma (MM) remains an incurable plasma cell disorder to date; therefore, new biologically target-based therapies are in urgent demand. Our previous studies showed that the antimalarial artesunate (ART) possessed anti-myeloma effect by inhibiting proliferation and inducing apoptosis of myeloma cells. The present study evaluated the effect of ART on human myeloma cell-induced angiogenesis and elucidated its mechanism. The human umbilical vein endothelial cells (HUVECs) migration test, aortic sprouting in fibrin gel in vitro and chicken chorioallantoic membrane (CAM) neovascularization in vivo model were used to examine the effect of ART on angiogenesis induced by human myeloma cells. The results showed that ART could inhibit HUVECs migration, even at a lower concentration (3 μmol/l, P < 0.01, compared with the result of control group), and suppress efficiently the angiogenic ability of myeloma RPMI8226 cells in a dose-dependent pattern (3-12 μmol/l, P < 0.05). The levels of VEGF and Ang-1 in the conditioned medium (CM) were quantified by enzyme-linked immunosorbent assay (ELISA). The results confirmed that 3 μmol/l ART could significantly decrease VEGF and Ang-1 secretion by RPMI8226 cells (P < 0.05), which correlated well with the reduction of angiogenesis induced by myeloma RPMI8226 cells. The present study also showed that ART downregulated the expression of VEGF and Ang-1 in RPMI8226 cells and reduced the activation of extracellular signal-regulated kinase 1 (ERK1) as well. Therefore, ART can block ERK1/2 activation, downregulate VEGF and Ang-1 expression and inhibit angiogenesis induced by human multiple myeloma RPMI8226 cells. Combined with our previous published data, results from the present study indicate that ART possesses potential anti-myeloma effect.

A glandular trichome-specific monoterpene alcohol dehydrogenase from Artemisia annua

The major components of the isoprenoid-rich essential oil of Artemisia annua L. accumulate in the subcuticular sac of glandular secretory trichomes. As part of an effort to understand isoprenoid biosynthesis in A. annua, an expressed sequence tag (EST) collection was investigated for evidence of genes encoding trichome-specific enzymes. This analysis established that a gene denoted Adh2, encodes an alcohol dehydrogenase and shows a high expression level in glandular trichomes relative to other tissues. The gene product, ADH2, has up to 61% amino acid identity to members of the short chain alcohol dehydrogenase/reductase (SDR) superfamily, including Forsythia x intermedia secoisolariciresinol dehydrogenase (49.8% identity). Through in vitro biochemical analysis, ADH2 was found to show a strong preference for monoterpenoid secondary alcohols including carveol, borneol and artemisia alcohol. These results indicate a role for ADH2 in monoterpenoid ketone biosynthesis in A. annua glandular trichomes.

Dihydroartemisinin accelerates c-MYC oncoprotein degradation and induces apoptosis in c-MYC-overexpressing tumor cells

Artemisinin and its derivatives (ARTs) are effective antimalarial drugs and also possess profound anticancer activity. However, the mechanism accounted for its distinctive activity in tumor cells remains unelucidated. We computed Pair wise Pearson correlation coefficients to identify genes that show significant correlation with ARTs activity in NCI-55 cell lines using data obtained from studies with HG-U133A Affymetrix chip. We found c-myc is one of the genes that showed the highest positive correlation coefficients among the probe sets analyzed (r=0.585, P<0.001). Dihydroartemisinin (DHA), the main active metabolite of ARTs, induced significant apoptosis in HL-60 and HCT116 cells that express high levels of c-MYC. Stable knockdown of c-myc abrogated DHA-induced apoptosis in HCT116 cells. Conversely, forced expression of c-myc in NIH3T3 cells sensitized these cells to DHA-induced apoptosis. Interestingly, DHA irreversibly down-regulated the protein level of c-MYC in DHA-sensitive HCT116 cells, which is consistent to persistent G1 phase arrest induced by DHA. Further studies demonstrated that DHA accelerated the degradation of c-MYC protein and this process was blocked by pretreatment with the proteasome inhibitor MG-132 or GSK 3beta inhibitor LiCl in HCT116 cells. Taken together, ARTs might be useful in the treatment of c-MYC-overexpressing tumors. We also suggest that c-MYC may potentially be a biomarker candidate for prediction of the antitumor efficacies of ARTs.

Synthesis and phytotoxic activity of ozonides

The [4 + 3] cycloaddition of the proper furans with the oxyallyl cation, generated in situ from 2,4-dibromopentan-3-one, produced a series of 8-oxabicyclo [3.2.1]oct-6-en-3-ones. Exposure of the oxabicycles to ozone afforded the corresponding 8,9,10,11-tetraoxatricyclo[5.2.1.1 (2,6)]undecan-4-ones in variable yields (7-100%). The phytotoxic properties of these ozonides (or 1,2,4-trioxolanes) and their oxabicycle precursors were evaluated as the ability to interfere with the growth of Sorghum bicolor and Cucumis sativus seedlings. Among oxabicycles, the highest inhibitory activity was shown by compounds possessing a alpha,beta-unsaturated carbonyl moiety. A differential sensitivity of the two crops was evident with ozonides. The most active compounds were also tested against the weed species Ipomoea grandifolia and Brachiaria decumbens. To the best of our knowledge, this is the first article describing ozonides as potential herbicides.

Artesunate inhibits angiogenesis and downregulates vascular endothelial growth factor expression in chronic myeloid leukemia K562 cells

Artesunate (ART), a semi-synthetic derivative of artemisinin extracted from the Chinese herb Artemisia annua, is a safe and effective antimalarial drug. In the present investigation, we analyzed the inhibitory effects of ART on angiogenesis and on VEGF production in chronic myeloid leukemia (CML) K562 cells in vitro and in vivo. In order to analyze the effect of ART on VEGF secretion in K562 cells, we examined the level of VEGF secreted in conditioned media (CM) by ELISA assay. The result showed that ART could decrease the VEGF level in CM of K562 cells, even at a lower concentration (2 micromol/l, P<0.01). The inhibitory effect of in vitro angiogenesis was tested on aortic sprouting in fibrin gel. ART could effectively suppress the stimulating angiogenic ability of CM by pretreated with K562 cells for 48 h in a time-dependent manner (days 3-14). The antiangiogenic effect of ART was further evaluated in vivo in chicken chorioallantoic membrane (CAM) neovascularization model. The result indicated that the stimulating angiogenic activity was decreased in response to the K562 cells treated with ART or the CM from K562 cells pretreated with ART in a dose-dependent manner (3-12 micromol/l). Furthermore, we analyzed the level of VEGF expression by western blot and detected the form of VEGF mRNA by RT-PCR in K562 cells. The experiments showed that ART could inhibit the VEGF expression, correlated well with the level of VEGF secreted in CM. These findings suggest that ART might present potential antileukemia effect as a treatment for CML therapy, or as an adjunct to standard chemotherapeutic regimens.

Allelopathy--a natural alternative for weed control

Allelopathy studies the interactions among plants, fungi, algae and bacteria with the organisms living in a certain ecosystem, interactions that are mediated by the secondary metabolites produced and exuded into the environment. Consequently, allelopathy is a multidisciplinary science where ecologists, chemists, soil scientists, agronomists, biologists, plant physiologists and molecular biologists offer their skills to give an overall view of the complex interactions occurring in a certain ecosystem. As a result of these studies, applications in weed and pest management are expected in such different fields as development of new agrochemicals, cultural methods, developing of allelopathic crops with increased weed resistance, etc. The present paper will focus on the chemical aspects of allelopathy, pointing out the most recent advances in the chemicals disclosed, their mode of action and their fate in the ecosystem. Also, attention will be paid to achievements in genomics and proteomics, two emerging fields in allelopathy. Rather than being exhaustive, this paper is intended to reflect a critical vision of the current state of allelopathy and to point to future lines of research where in the authors' opinion the main advances and applications could and should be expected.

Targeted treatment of cancer with artemisinin and artemisinin-tagged iron-carrying compounds

Artemisinin is a chemical compound that reacts with iron to form free radicals which can kill cells. Cancer cells require and uptake a large amount of iron to proliferate. They are more susceptible to the cytotoxic effect of artemisinin than normal cells. Cancer cells express a large concentration of cell surface transferrin receptors that facilitate uptake of the plasma iron-carrying protein transferrin via endocytosis. By covalently tagging artemisinin to transferrin, artemisinin could be selectively picked up and concentrated by cancer cells. Futhermore, both artemisinin and iron would be transported into the cell in one package. Once an artemisinin-tagged transferrin molecule is endocytosed, iron is released and reacts with artemisinin moieties tagged to transferrin. Formation of free radicals kills the cancer cell. The authors have found that artemisinin-tagged transferrin is highly selective and potent in killing cancer cells. Thus, artemisinin and artemisinin-tagged iron-carrying compounds could be developed into powerful anticancer drugs.

Dihydroartemisinin inhibits angiogenesis induced by multiple myeloma RPMI8226 cells under hypoxic conditions via downregulation of vascular endothelial growth factor expression and suppression of vascular endothelial growth factor secretion

Multiple myeloma remains incurable to date; therefore, new biologically target-based therapies are urgently needed. Our previous studies have showed that the antimalarial dihydroartemisinin possessed antiangiogenic activity in solid tumors. The present study evaluated the effect of dihydroartemisinin on human multiple myeloma-induced angiogenesis under hypoxia and elucidated its mechanism of action. An in-vivo chicken chorioallantoic membrane model was used to examine the effect of dihydroartemisinin on multiple myeloma-induced angiogenesis. Compared with conditioned medium of control, conditioned medium from human multiple myeloma RPMI8226 cells pretreated with 3 micromol/l dihydroartemisinin in hypoxia was observed to reduce microvessel growth on chicken chorioallantoic membranes by approximately 28.6% (P<0.05). The level of vascular endothelial growth factor in conditioned medium was determined by enzyme-linked immunosorbent assay. The results confirmed that 3 micromol/l dihydroartemisinin could significantly decrease vascular endothelial growth factor secretion by RPMI8226 cells (P<0.05), which correlated well with the reduction of multiple myeloma-induced angiogenesis on chicken chorioallantoic membranes. Western blot and reverse transcription-polymerase chain reaction results revealed that dihydroartemisinin downregulated the expression of vascular endothelial growth factor in RPMI8226 cells in hypoxia. In addition, we demonstrated that dihydroartemisinin reduced extracellular signal-regulated kinase 1/2 activation and inhibited growth of RPMI8226 cells under hypoxic conditions. Therefore, we concluded that dihydroartemisinin, which is already used to treat malaria and is well tolerated, possesses potential as an antiangiogenic drug in multiple myeloma therapy and thereby may improve patient outcome.

Determination of artemisinin in Artemisia sieberi and anticoccidial effects of the plant extract in broiler chickens

Artemisinin has received much attention in the treatment of malaria in recent years, and it is now considered as a potential candidate to reduce coccidial infection in chickens. It is a sesquiterpene compound which has been isolated from Aretemisia annua for the first time. The present study aimed to investigate the occurrence of artemisinin in A. sieberi (AS) and to test the anticoccidial effects of plant extract in broiler chickens. The aerial parts of the plant were collected during different seasons from Yazd Province, in the centre of Iran. The artemisinin content of the AS was extracted with petrol ether and analysed by high-performance liquid chromatography using UV detection. Anticoccidial effects of the plant extract were tested on chicks challenged with various species of Eimeria. The infected chickens were treated with doses of 1 or 2.5 mg/kg per day artemisinin via oral administration of plant extract. The analytical results showed that the level of artemisinin in AS was 0.2% and 0.14% of dried weight (DW) of plant materials in summer and autumn, respectively. Treatment of experimentally infected chickens with AS extracts showed that artemisinin was able to reduce the severity of coccidial infection induced by Eimeria tenella and E. acervulina, but not E. maxima. The anticoccidial effects of artemisinin were shown by significant decrease in output of number of oocysts per gram of faeces in chickens challenged with different species of Eimeria. This study showed that the levels of artemisinin in AS were comparable with those in other species including A. annua, and that the extract of this plant can reduce coccidial infection in broiler chickens.

Dihydroartemisinin downregulates vascular endothelial growth factor expression and induces apoptosis in chronic myeloid leukemia K562 cells

Dihydroartemisinin (DHA), a more water-soluble active metabolite of artemisinin derivatives, is safe and the most effective antimalarial analog of artemisinin. In the present investigation, we assessed the effect of DHA on vascular endothelial growth factor (VEGF) expression and apoptosis in chronic myeloid leukemia (CML) K562 cells. The results demonstrated that in addition to its antiproliferation effect on CML cells, DHA was also found to induce K562 cells apoptosis. The percentage of apoptotic cells was increased to 6.9 and 15.8% after being treated with 5 and 10 micromol/l DHA for 48 h, respectively (P<0.001). In order to analyze the effect of DHA on VEGF expression in K562 cells, we assessed the level of VEGF expression by western blot; detected the form of VEGF mRNA by RT-PCR and examined the level of VEGF secreted in conditioned media (CM) by ELISA assay. All these experiments suggested that DHA could inhibit the VEGF expression and secretion effectively in K562 cells, even at a lower concentration (2 micromol/l, P<0.05). Moreover, we further assessed the stimulating angiogenic activity of CM from K562 cells on CAM model. The angiogenic activity was decreased in response to the CM from K562 cells pretreated with DHA in a dose-dependent manner. Taken together, these results from our study together with its known low toxicity make it possible that DHA might present potential antileukemia effect as a treatment for CML therapy, or as an adjunct to standard chemotherapeutic regimens.

Artesunate reduces chicken chorioallantoic membrane neovascularisation and exhibits antiangiogenic and apoptotic activity on human microvascular dermal endothelial cell

Artesunate (ART), a semi-synthetic derivative of artemisinin extracted from the Chinese herb Artemisia annua, is a safe and effective antimalarial drug. ART has now been analyzed for its anti-angiogenic activity in vivo and in vitro. The anti-angiogenic effect in vivo was evaluated on chicken chorioallantoic membrane (CAM) neovascularisation model. ART started to significantly inhibit CAM angiogenesis at a low concentration of 10 nm/100 microl/egg, and completely inhibited the angiogenesis at 80 nm/100 microl/egg. The inhibitory effect of in vitro angiogenesis was tested on the models of proliferation and differentiation of human microvascular dermal endothelial cell line, an important representive of endothelial cells, as well as immunocytochemistry assay for two major VEGF receptors (Flt-1 and KDR/flk-1) expressions. The results showed that ART could remarkably inhibit proliferation and differentiation of endothelial cells in a dose-dependent form in a range of 12.5-100 microM. ART also could reduce Flt-1 and KDR/flk-1 expressions in a range of 0.1-0.5 microM. Furthermore, we examined the apoptosis of human microvascular dermal endothelial cell line induced by ART. The apoptosis was detected by morphological assay of ethidium bromide (EB)/acridine orange (AO) dual staining as well as DNA fragmentation assay of TUNEL labeling and quantified by flowcytometric PI assay. Our results suggest that the antiangiogenic effect induced by ART might occur by the induction of cellular apoptosis. These findings and the known low toxicity indicated ART might be a promising candidate for angiogenesis inhibitors.

In vitro and in vivo evaluation of betulinic acid as an antimalarial

The lupane-type triterpene betulinic acid was isolated from an ethanol extract of the root bark of the Tanzanian tree Uapaca nitida Müll-Arg. (Euphorbiaceae). The in vitro antiplasmodial IC50 values of betulinic acid against chloroquine resistant (K1) and sensitive (T9-96) Plasmodium falciparum were found to be 19.6 micrograms/mL and 25.9 micrograms/mL, respectively. The in vitro activities of several related triterpenes were also evaluated. Betulin was found to be inactive at 500 micrograms/mL for both K1 and T9-96. Ursolic acid exhibited IC50 values of 36.5 micrograms/mL and 28 micrograms/mL, and oleanolic acid exhibited IC50 values of 88.8 micrograms/mL and 70.6 micrograms/mL against K1 and T9-96, respectively. When betulinic acid was tested for in vivo activity in a murine malaria model (P. berghei) the top dosage employed of 250 mg/kg/day was ineffective at reducing parasitaemia and exhibited some toxicity. Betulinic acid has not previously been evaluated for in vivo activity. This is believed to be the first compound to be isolated from U. nitida.

Stability of artemisinin in aqueous environments: impact on its cytotoxic action to Ehrlich ascites tumour cells

We have recently shown artemisinin to be cytotoxic against Ehrlich ascites tumour cells. The aim of this study was to investigate the stability of this compound in the aqueous environment of the in-vitro Ehrlich ascites tumour cell system (RPMI 1640 cell culture medium supplemented with 10% foetal bovine serum (RPMI/FBS) with reference to its cytotoxic action. Literature data show that artemisinin can react with Fe2+ yielding reactive intermediates leaving artemisinin G as a major end-product. The current study showed that only excess addition of Fe2+ to artemisinin in distilled water, phosphate-buffered saline (PBS) and RPMI/FBS and incubation for 24 h led to degradation of artemisinin and yielded artemisinin G. If Fe2+ was not added results from HPLC analysis were indicative of complete recovery of artemisinin from distilled water and RPMI/FBS, with or without cells, at 37 degrees C for at least 24 h. In addition, incubation of artemisinin in RPMI/FBS with or without cells at 37 degrees C for 24 h before cytotoxicity assay did not change its cytotoxic action. On the basis of these results, we suggest that cytotoxicity to tumour cells was caused by unchanged artemisinin. This is not so for the antimalarial activity of artemisinin and derivatives, for which the presence of a pool of (haem) Fe2+ is a prerequisite resulting in free radicals or electrophilic intermediates or both.

The role of plant-derived drugs and herbal medicines in healthcare

Many of our present medicines are derived directly or indirectly from higher plants. While several classic plant drugs have lost much ground to synthetic competitors, others have gained a new investigational or therapeutical status in recent years. In addition, a number of novel plant-derived substances have entered into Western drug markets. Clinical plant-based research has made particularly rewarding progress in the important fields of anticancer (e.g. taxoids and camptothecins) and antimalarial (e.g. artemisinin compounds) therapies. In addition to purified plant-derived drugs, there is an enormous market for crude herbal medicines. Natural product research can often be guided by ethnopharmacological knowledge, and it can make substantial contributions to drug innovation by providing novel chemical structures and/or mechanisms of action. In the end, however, both plant-derived drugs and crude herbal medicines have to take the same pharmacoeconomic hurdle that has become important for new synthetic pharmaceuticals.

Bioavailability of different artemisinin tablet formulations in rabbit plasma--correlation with results obtained by an in vitro dissolution method

The demonstration of a good overall correlation with in vivo data is the ultimate proof of qualification for any dissolution-rate test. For artemisinin, a very hydrophobic compound at a high content in oral solid dosage forms, all official dissolution apparatus were estimated unsuitable. A modified two phase partition-dissolution method was applied to solve this problem. This study reports on the bioavalability of three different formulations of artemisinin tablets in rabbit plasma. Artemisinin concentrations in plasma were determined by liquid chromatography. A linear correlation between results obtained by the partition-dissolution method described and the obtained in vivo data confirmed the validity of the dissolution method.

Stereochemistry-dependent cytotoxicity of some artemisinin derivatives

We determined the cytotoxicity of some artemisinin derivatives against EN2 tumor cells using the MTT assay. Artemisinin (1) was clearly more cytotoxic than deoxyartemisinin (2), which lacks the endoperoxide bridge. Ether-linked dimers of dihydroartemisinin with defined stereochemistry were found to differ in the extent of cytotoxic effect on EN2 cells. The nonsymmetrical dimer (3) was more cytotoxic than the symmetrical dimer (4). The nonsymmetrical dimer of dihydrodeoxyartemisinin (5) lacking the endoperoxide bridges was also effective in the MTT assay, although less cytotoxic than 3 and 4. Similarly, the symmetrical dimer (6) was less effective than 5. Epoxides of artemisitene also showed that stereochemistry was an important factor for cytotoxicity. The results suggested that the endoperoxide bridge was not crucial for cytotoxicity to the tumor cells, but contributed to the cytotoxic effect apparently exerted by the ether linkage of the dimers. Flow cytometry data indicated that the dimers 3 and 4 caused an accumulation of the cells in the G1-phase of the cell cycle. In contrast, artemisinin (1) caused a slight increase of S-phase cells.

Design and evaluation of two-phase partition-dissolution method and its use in evaluating artemisinin tablets

A method is described for the assessment of the dissolution behavior of solid dosage forms with a high content of a very water insoluble drug. In this method the dissolved drug is continuously extracted from the aqueous dissolution medium into an organic phase. The reported data on the dissolution of artemisinin show that this method guarantees sink conditions in the aqueous dissolution medium during the total duration of the experiment.

Transport of artemisinin and sodium artesunate in Caco-2 intestinal epithelial cells

Artemisinin and its derivatives are becoming interesting alternatives to the commonly used antimalarial drugs because they are efficient in treating severe and multidrug resistant forms of Plasmodium falciparum malaria. A major drawback is the occurrence of recrudescence some time after treatment. Moderate oral bioavailability has been suggested as a possible cause. As one of the factors that might limit absorption after oral administration, we studied the intestinal permeability using an in vitro system of the intestinal mucosa, Caco-2. Concentrations of artemisinin were determined by UV after alkaline degradation, while for sodium artesunate, a capillary electrophoresis method was developed. Artemisinin easily crossed the epithelial cells by passive diffusion (Papp = 30.4 +/- 1.7 x 10(-6) cm s-1, pH 7.4). Permeability of the hemisuccinate analogue, sodium artesunate, was 8-fold lower (Papp = 4.0 +/- 0.4 x 10(-6) cm s-1 at pH 7.4) and strongly dependent on pH, which might result in site dependent resorption in an in vivo situation. Enzyme catalyzed ester hydrolysis of sodium artesunate in Caco-2 monolayers to the biologically active metabolite, dihydroartemisinin, was moderate. The results indicate that the transepithelial permeability is probably not a limiting factor in the overall absorption process after oral administration of artemisinin or sodium artesunate. Solubility, dissolution rate, stability, and first-pass metabolism are suggested as alternative limiting factors.

Artemisinin and the antimalarial endoperoxides: from herbal remedy to targeted chemotherapy

Artemisinin and its derivatives are endoperoxide-containing compounds which represent a promising new class of antimalarial drugs. In the presence of intraparasitic iron, these drugs are converted into free radicals and other electrophilic intermediates which then alkylate specific malaria target proteins. Combinations of available derivatives and other antimalarial agents show promise both as first-line agents and in the treatment of severe disease.

The mode of action of the antimalarial artemisinin and its derivatives

1. Atremisinin (qinghaosu) is a sesquiterpene endoperoxide derived from a plant which was used in Chinese herbal medicine for thousands of years. 2. Artemisinin and its derivatives have potent antimalarial activity, and are now being used clinically in much of the world. 3. The artemisinin derivatives have an unusual mode of action involving the iron-catalyzed generation of a carbon-centered free radical followed by the alkylation of malaria-specific proteins.

Traditional Chinese herbal medicine

Herbal medicine, acupuncture and moxibustion, and massage are the three major constituent parts of traditional Chinese medicine. Although acupuncture is well known in many Western countries, Chinese herbal medicine, the most important part of traditional Chinese medicine, is less well known in the West. This article gives a brief introduction to the written history, theory, and teaching of Chinese herbal medicine in China. It also describes modern scientific research into and the quality control of Chinese herbal medicines in China. Some examples of how new drugs derived from Chinese herbs have been developed on the basis of traditional therapeutic experience are presented. Finally, the situation of Chinese herbal medicine in the West is discussed.