Chloroquine-sensitive 3D7 Research Articles

In vitro antiplasmodial activity of plants used in Benin in traditional medicine to treat malaria

Aim of the study The aim of the study was to evaluate the in vitro antiplasmodial activity of crude extracts of 12 plant species traditionally used in Benin for the treatment of malaria in order to validate their use. Materials and methods For each species, dichloromethane, methanol and total aqueous extracts were tested. The antiplasmodial activity of extracts was evaluated using the measurement of the plasmodial lactate dehydrogenase activity on chloroquine-sensitive (3D7) and resistant (W2) strains of Plasmodium falciparum. The selectivity of the different extracts was evaluated using the MTT test on J774 macrophage-like murine cells and WI38 human normal fibroblasts. Results The best growth inhibition of both strains of Plasmodium falciparum was observed with the dichloromethane extracts of Acanthospermum hispidum DC. (Asteraceae) (IC 50 = 7.5 μg/ml on 3D7 and 4.8 μg/ml on W2), Keetia leucantha (K. Krause) Bridson (syn. Plectronia leucantha Krause) (Rubiaceae) leaves and twigs (IC 50 = 13.8 and 11.3 μg/ml on 3D7 and IC 50 = 26.5 and 15.8 μg/ml on W2, respectively), Carpolobia lutea G.Don. (Polygalaceae) (IC 50 = 19.4 μg/ml on 3D7 and 8.1 μg/ml on W2) and Strychnos spinosa Lam. (Loganiaceae) leaves (IC 50 = 15.6 μg/ml on 3D7 and 8.9 μg/ml on W2). All these extracts had a low cytotoxicity. Conclusion Our study gives some justifications for the traditional uses of some investigated plants.

Semi-synthetic and synthetic 1,2,4-trioxaquines and 1,2,4-trioxolaquines: synthesis, preliminary SAR and comparison with acridine endoperoxide conjugates

A novel series of semi-synthetic trioxaquines and synthetic trioxolaquines were prepared, in moderate to good yields. Antimalarial activity was evaluated against both the chloroquine-sensitive 3D7 and resistant K1 strain of Plasmodium falciparum and both series of compounds were shown to be active in the low nanomolar range. For comparison the corresponding 9-amino acridine analogues were also prepared and shown to have low nanomolar activity like their quinoline counterparts.

Structural Determinants of Antimicrobial and Antiplasmodial Activity and Selectivity in Histidine-rich Amphipathic Cationic Peptides

Designed histidine-rich amphipathic cationic peptides, such as LAH4, have enhanced membrane disruption and antibiotic properties when the peptide adopts an alignment parallel to the membrane surface. Although this was previously achieved by lowering the pH, here we have designed a new generation of histidine-rich peptides that adopt a surface alignment at neutral pH. In vitro, this new generation of peptides are powerful antibiotics in terms of the concentrations required for antibiotic activity; the spectrum of target bacteria, fungi, and parasites; and the speed with which they kill. Further modifications to the peptides, including the addition of more hydrophobic residues at the N terminus, the inclusion of a helix-breaking proline residue or using D-amino acids as building blocks, modulated the biophysical properties of the peptides and led to substantial changes in toxicity to human and parasite cells but had only a minimal effect on the antibacterial and antifungal activity. Using a range of biophysical methods, in particular solid-state NMR, we show that the peptides are highly efficient at disrupting the anionic lipid component of model membranes. However, we also show that effective pore formation in such model membranes may be related to, but is not essential for, high antimicrobial activity by cationic amphipathic helical peptides. The information in this study comprises a new layer of detail in the understanding of the action of cationic helical antimicrobial peptides and shows that rational design is capable of producing potentially therapeutic membrane active peptides with properties tailored to their function.

Phytochemical licochalcone A enhances antimalarial activity of artemisinin in vitro

Resistance to synthetic first-line antimalarial drugs is considered to be a major cause of increased malaria morbidity and mortality. Use of artemisinin-based combination therapies (ACTs) is being encouraged to reduce the malaria mortality in areas of falciparum resistance. Artemisinin is a natural product at times in short supply. With projected rise in demand of artemisinin there is an unmet need for alternate ACTs. Novel compounds that reduce dependance on artemisinin are required. In vitro cultures of Plasmodium falciparum provide a screen system for identifying and evaluating new drug combinations. Interactions of two phytochemicals, artemisinin and licochalcone A, has been studied against synchronized erythrocytic stages of chloroquine-sensitive 3D7 and chloroquine-resistant RKL 303 strains of P. falciparum. These two compounds in combination show synergistic antiplasmodial activity in vitro on these strains. Artemisinin but not licochalcone A interferes with hemozoin formation. Neither of the phytochemicals alone or in combination obstructs sorbitol-induced hemolysis.

Synthesis, Antimalarial Activity, and Intracellular Targets of MEFAS, a New Hybrid Compound Derived from Mefloquine and Artesunate

A new synthetic antimalarial drug, a salt derived from two antimalarial molecules, mefloquine (MQ) and artesunate (AS), here named MEFAS, has been tested for its pharmacological activity. Combinations of AS plus MQ hydrochloride are currently being used in areas with drug-resistant Plasmodium falciparum parasites; although AS clears parasitemia in shorter time periods than any other antimalarial drug, it does not cure infected patients; in addition, MQ causes side effects and is rather expensive, important problems considering that malaria affects mostly populations in poor countries. Here, we show that MEFAS is more effective than the combination of AS and MQ, tested in parallel at different mass proportions, against P. falciparum (chloroquine-resistant clone W2 and chloroquine-sensitive clone 3D7) in vitro and in mice infected with Plasmodium berghei, promoting cure of this infection. MEFAS tested against HepG2 hepatoma cells exhibited lower toxicity than the antimalarials AS and MQ alone or combined. Possible targets of MEFAS have been studied by confocal microscopy using fluorescent probes (Fluo-4 AM and BCECF-AM) in P. falciparum synchronous culture of W2-infected red blood cells. Dynamic images show that MEFAS exhibited intracellular action increasing cytoplasmic Ca(2+) at 1.0 ng/ml. This effect was also observed in the presence of tapsigargin, an inhibitor of SERCA, suggesting an intracellular target distinct from the endoplasmic reticulum. Trophozoites loaded with BCECF-AM, when treated with MEFAS, were still able to mobilize protons from the digestive vacuole (DV), altering the pH gradient. However, in the presence of bafilomycin A1, an inhibitor of the H(+) pump from acidic compartments of eukaryotic cells, MEFAS had no action on the DV. In conclusion, the endoplasmic reticulum and DV are intracellular targets for MEFAS in Plasmodium sp., suggesting two modes of action of this new salt. Our data support MEFAS as a candidate for treating human malaria.

Antimalarial activity of natural product extracts from Papua New Guinean and Australian plants against Plasmodium falciparum

In the search for new antimalarial compounds, a subset of a natural product extract library prepared from plant samples collected from Papua New Guinea and Australia was screened for in vitro activity against the chloroquine-sensitive 3D7 and chloroquine-resistant Dd2 strains of Plasmodium falciparum. Using the incorporation of ((3)H)-hypoxanthine into parasite nucleic acid as a marker of growth, 93 of the 794 extracts screened displayed >40% inhibition against 3D7 infected erythrocytes at 312 microge/mL. Antimalarial activity was confirmed in 48 of these extracts against both 3D7 and Dd2 infected erythrocytes at concentrations between 78 and 390 microge/mL, 14 of which caused >90% growth inhibition of 3D7 at the lowest concentration screened. Extracts were also tested for mammalian cell cytotoxicity to evaluate selectivity of action.

Structural insights into the Plasmodium falciparum histone deacetylase 1 ( PfHDAC-1): A novel target for the development of antimalarial therapy

The histone deacetylase (HDAC) enzyme from Plasmodium falciparum has been identified as a novel target for the development of antimalarial therapy. A ligand-refined homology model of PfHDAC-1 was generated from the crystal structures of human HDAC8 and HDLP using a restraint guided optimization procedure involving the OPLS/GBSA potential setup. The model was extensively validated using protein structure checking tools. A predictive docking study was carried out using a set of known human HDAC inhibitors, which were shown to have in vitro antimalarial activity against the chloroquine sensitive D6 and resistant W2 strains of P. falciparum. Pose validation and score-based active/inactive separation studies provided independent validation of the geometric accuracy and the predictive ability of the generated model. Comparative analysis was carried out with the human HDACs to identify differences in the binding site topology and interacting residues, which might be utilized to develop selective PfHDAC-1 inhibitors.

Common dietary flavonoids inhibit the growth of the intraerythrocytic malaria parasite

BackgroundFlavonoids are abundant plant phenolic compounds. More than 6000 have been identified to date, and some have been shown to possess antiparasitic activity. Here we investigate the effects of a range of common dietary flavonoids on the growth of two strains of the human malaria parasite Plasmodium falciparum.FindingsA chloroquine-sensitive (3D7) and a chloroquine-resistant (7G8) strain of P. falciparum were tested for in vitro susceptibility to a range of individual dietary flavonoids and flavonoid combinations. Parasite susceptibility was measured in 96-well plates over 96 h using a previously described [3H]hypoxanthine incorporation assay. Of the eleven flavonoids tested, eight showed antiplasmodial activity against the 3D7 strain (with IC50 values between 11 and 66 μM), and all showed activity against the 7G8 strain (with IC50 values between 12 and 76 μM). The most active compound against both strains was luteolin, with IC50 values of 11 ± 1 μM and 12 ± 1 μM for 3D7 and 7G8, respectively. Luteolin was found to prevent the progression of parasite growth beyond the young trophozoite stage, and did not affect parasite susceptibility to the antimalarial drugs chloroquine or artemisinin. Combining low concentrations of flavonoids was found to produce an apparent additive antiplasmodial effect.ConclusionCertain common dietary flavonoids inhibit the intraerythrocytic growth of the 3D7 and 7G8 strains of P. falciparum. Flavonoid combinations warrant further investigation as antiplasmodial agents.

Ayurveda and eCAM: A Closer Connection

Ayurveda and <i>eCAM</i>: A Closer Connection

γ‐Substituted Bis(pivaloyloxymethyl)ester Analogues of Fosmidomycin and FR900098

The synthesis and in-vitro antimalarial activity of gamma-substituted bis(pivaloyloxymethyl)ester analogues of the drug candidate fosmidomycin have been investigated. In contrast to the high antimalarial activity of alpha-aryl substituted fosmidomycin analogues like alpha-phenylfosmidomycin, gamma-substituted derivatives display only weak to moderate activity against the chloroquine-sensitive strain 3D7 of Plasmodium falciparum.

Pharmacophore-based predictive model generation for potent antimalarials targeting haem detoxification pathway

Pharmacophore hypotheses were developed for molecules having antimalarial activities targeting the haem detoxification pathway of the malaria parasite. A training set consisting of 23 compounds was selected to generate these hypotheses, and their activities were evaluated for haem polymerization inhibition and against chloroquine-sensitive (3D7) as well as chloroquine-resistant (K1) strains of p. falciparum. The models were cross-validated by Fischer’s randomization test at a 95% confidence level. The model developed against chloroquine-resistant malaria parasites was found to yield the best predictions among the three models.

Multiple antibiotics exert delayed effects against the Plasmodium falciparum apicoplast.

Several classes of antibiotics exert antimalarial activity. The mechanisms of action of antibiotics against malaria parasites have been unclear, and prior studies have led to conflicting results, in part because they studied antibiotics at suprapharmacological concentrations. We examined the antimalarial effects of azithromycin, ciprofloxacin, clindamycin, doxycycline, and rifampin against chloroquine-resistant (W2) and chloroquine-sensitive (3D7) Plasmodium falciparum strains. At clinically relevant concentrations, rifampin killed parasites quickly, preventing them from initiating cell division. In contrast, pharmacological concentrations of azithromycin, ciprofloxacin, clindamycin, and doxycycline were relatively inactive against parasites initially but exerted a delayed death effect, in which the progeny of treated parasites failed to complete erythrocytic development. The drugs that caused delayed death did not alter the distribution of apicoplasts into developing progeny. However, the apicoplasts inherited by the progeny of treated parasites were abnormal. The loss of apicoplast function became apparent as the progeny of antibiotic-treated parasites initiated cell division, with the failure of schizonts to fully mature or for erythrocyte rupture to take place. These findings explain the slow antimalarial action of multiple antibiotics.

Conformationally Restrained Aromatic Analogues of Fosmidomycin and FR900098

The synthesis and in-vitro antimalarial activity of conformationally restrained bis(pivaloyloxymethyl) ester analogues of the natural product fosmidomycin is presented. In contrast to alpha-aryl-substituted analogues, conformationally restrained aromatic analogues exhibit only moderate in-vitro antimalarial activity against the chloroquine-sensitive strain 3D7 of Plasmodium falciparum. The most active derivative displays an IC(50) value of 47 microM.

Low antiplasmodial activity of alkaloids and amides from the stem bark ofZanthoxylum rubescens(Rutaceae)

The stem bark of Zanthoxylum rubescens (syn. Fagara rubescens) is used for treating fevers associated with malaria in the Ivory Coast. Three alkaloids: N-nornitidine, 7,9-dimethoxy-2,3-methylenedioxybenzophenanthridine, and bis[6-5,6-dihydrochelerythrinyl)] ether; and two amides: zanthomamide and lemairamide, were isolated from the stem bark of this plant. These compounds were screened in vitro against the chloroquine-sensitive 3D7 strain and the chloroquine-resistant FCM29 strain of P. falciparum. N-nornitidine was found to be inactive. 7,9-dimethoxy-2,3-methylenedioxybenzophenanthridine, lemairamide and zanthomamide showed weak activity with average IC50 values ranging from 45.6 microM to 149.9 microM. Bis[6-15,6-dihydrochelerythrinyl)] ether was the most active of the tested compounds with mean IC50s of 14.9 +/- 1.4 microM in FCM29 strain and 15.3 +/- 3.4 microM in 3D7 strain (approximately 58 to approximately 1130 times less active than chloroquine respectively). The anti-Plasmodium activities of the tested alkaloids of Z. rubescens were low; and do not encourage the use of this plant as antimalarial.

Investigation of Indian Diospyros Species for Antiplasmodial Properties

Despite decades of intense research, malaria remains a deadly disease worldwide and new antimalarials are urgently needed due to increasing drug resistance of Plasmodium falciparum to existing drugs. This article reports the evaluation of four Indian Diospyros species viz., Diospyros melanoxylon, D. peregrina, D. sylvatica, D. tomentosa for antiplasmodial activities against chloroquine-sensitive (3D7) and chloroquine-resistant (K1) strains of P. falciparum. Six of eight methanolic extracts were found to have significant activity, (IC50 = 16.5–92.9 µg ml−1), against strain 3D7 and five of these showed similar activities against strain K1 (IC50 = 20.5–121.6 µg ml−1). Diospyros sylvatica was found to be the most active species (IC50 = 16.5–29.4 µg ml−1) and is worthy of further investigation.

α-Phenylethyl Substituted Bis(pivaloyloxymethyl) Ester Analogues of Fosmidomycin and FR900098

α-Phenylethyl substituted bis(pivaloyloxymethyl) ester analogues of the natural products Fosmidomycin and FR900098 have been synthesized, and their in vitro antimalarial activity determined. The α-phenylethyl substituted Fosmidomycin analogue displays moderate in vitro antimalarial activity against the chloroquine-sensitive strain 3D7 of Plasmodium falciparum.

Lupeol Long-Chain Fatty Acid Esters with Antimalarial Activity from Holarrhena floribunda

An ethnopharmacological investigation was conducted among the Baka pygmies of Dja biosphere reserve (Cameroon) to collect information on the antimalarial plants used in their daily life. Holarrhena floribunda is one of those plants. Extracts of the stem barks of H. floribunda showed remarkable inhibitory activity against drug-resistant strains of Plasmodium falciparum at doses of 1.02-18.53 microg/mL when tested in vitro against two parasite clones designated as Indochina (W-2) and Sierra Leone (D-6). The aqueous extract was the most active against Indochina (W-2), with IC50 values of 1.02 microg/mL, while the ethanolic extract appeared to be the most active against Sierra Leone (D-6), with an IC50 of 4.33 microg/mL. The bioassay-guided fractionation of the neutral fraction of the crude extract led to the isolation of lupeol (1) and its three new long-chain fatty acid ester derivatives, namely, 3-O-(3'-hydroxyeicosanoyl)lupeol (2), 3-O-[(2'-(tetracosyloxy)acetyl]lupeol (3), and 3-O-[(1' '-hydroxyoctadecyloxy)-2'-hydroxypropanoyl]lupeol (4). These new compounds displayed some in vitro inhibition activity against the chloroquine-resistant strain FCR-3 isolated from Gambia and the chloroquine-sensitive standard strain 3D7. The hydroxy group of the fatty acid side chain appears to decrease the observed activity.

Biomimetic synthesis, antimicrobial, antileishmanial and antimalarial activities of euglobals and their analogues

In the present communication, naturally occurring phloroglucinol–monoterpene adducts, euglobals G1–G4 ( 3b/ a and 4a/ b) and 16 new analogues ( 13a/ b– 18a/ b and 19– 22) were synthesized by biomimetic approach. These synthetic compounds differ from natural euglobals in the nature of monoterpene and acyl functionality. All of these compounds were evaluated for their antibacterial, antifungal, antileishmanial and antimalarial activities. Analogue 17b possessed good antibacterial activity against methicillin-resistant Staphylococcus aureus, while analogues 19– 22 possessed potent antifungal activity against Candida glabrata with IC 50s ranging from 1.5 to 2.5 μg/mL. Euglobals along with all synthesized analogues exhibited antileishmanial activity. Amongst these, euglobal G2 ( 3a), G3 ( 4a) and analogues 13a and 14a showed potent antileishmanial activity with IC 50s ranging from 2.8 to 3.9 μg/mL. Analogue 16a possessed antimalarial activity against chloroquine sensitive D6 clone of Plasmodium falciparum. None of the compounds showed toxicity against mammalian kidney fibroblasts (vero cells) upto the concentration of 4.76 μg/ml.

In vitro interactions of Aspilia africana (Pers.) C.D. Adams, a traditional antimalarial medicinal plant, with artemisinin against Plasmodium falciparum

Traditional antimalarial medicinal preparations are widely used concurrently with antimalarial drugs in malaria endemic areas. The plant Aspilia africana (Pers.) C.D. Adams is commonly used for traditional treatment of malaria symptoms in East and Central Africa. An in vitro study of interactions between an extract from this plant with artemisinin against two strains of Plasmodium falciparum showed an antagonist relationship against both the chloroquine-sensitive D10 and the chloroquine- and sulphonamide-resistant K1 strains of Plasmodium falciparum. The extract reduced accumulation of radiolabelled dihydroartemisinin ( 3H-DHA) by erythrocytes infected with the chloroquine- and sulphonamide-resistant K1 strain of Plasmodium falciparum while it increased its accumulation by erythrocytes infected with the chloroquine-sensitive D10 strain. These results suggest complex interactions between the antimalarial medicinal plant and artemisinin. This study also proposes an in vitro approach to investigating interactions between antimalarial drugs and traditional medicines.

Synthesis and antimalarial activities of some furoxan sulfones and related furazans

Furoxan derivatives bearing a sulfone moiety at position 3 or 4 were synthesized and tested for their antimalarial action on the chloroquine-sensitive D10 and the chloroquine-resistent W2 strains of Plasmodium falciparum. The furazan analogues were considered for comparison. The most active compounds were the products in which the –SO 2R groups are at the 3-position of the furoxan system. These latter substances displayed an antimalarial activity in the μM range, possibly related in part to their ability to release NO.