Chloroquine-resistant Strains Of Plasmodium Falciparum Research Articles

Terpurinflavone: An antiplasmodial flavone from the stem of Tephrosia Purpurea

The stem extract of Tephrosia purpurea showed antiplasmodial activity against the D6 (chloroquine-sensitive) and W2 (chloroquine-resistant) strains of Plasmodium falciparum with IC 50 values of 10.47 ± 2.22 μg/ml and 12.06 ± 2.54 μg/ml, respectively. A new prenylated flavone, named terpurinflavone, along with the known compounds lanceolatin A, (−)-semiglabrin and lanceolatin B have been isolated from this extract. The new compound, terpurinflavone, showed the highest antiplasmodial activity with IC 50 values of 3.12 ± 0.28 μM (D6) and 6.26 ± 2.66 μM (W2). The structures were determined on the basis of spectroscopic evidence.

Novel thiolactone–isatin hybrids as potential antimalarial and antitubercular agents

The synthesis of a novel series of thiolactone-isatin hybrids led to the discovery of tetracyclic by-products which displayed superior antiplasmodial activity. The tetracycles thus formed the basis of a more focused SAR study. Identified from this series is a compound with an IC(50) of 6.92 μM against the chloroquine-resistant (W2) strain of Plasmodium falciparum. Useful antimalarial SARs delineated include the need for substitution at C-5 of the isatin scaffold and the enhancement of activity by increasing the linker length. In contrast to their antimalarial activity, the tetracycles were devoid of antitubercular activity whereas the advanced intermediates displayed growth inhibitory activity against the H(37)Rv strain of Mycobacterium tuberculosis as revealed by BACTEC, MABA and LORA assays.

Incorporation of Basic Side Chains into Cryptolepine Scaffold: Structure−Antimalarial Activity Relationships and Mechanistic Studies

The synthesis of cryptolepine derivatives containing basic side-chains at the C-11 position and their evaluations for antiplasmodial and cytotoxicity properties are reported. Propyl, butyl, and cycloalkyl diamine side chains significantly increased activity against chloroquine-resistant Plasmodium falciparum strains while reducing cytotoxicity when compared with the parent compound. Localization studies inside parasite blood stages by fluorescence microscopy showed that these derivatives accumulate inside the nucleus, indicating that the incorporation of a basic side chain is not sufficient enough to promote selective accumulation in the acidic digestive vacuole of the parasite. Most of the compounds within this series showed the ability to bind to a double-stranded DNA duplex as well to monomeric hematin, suggesting that these are possible targets associated with the observed antimalarial activity. Overall, these novel cryptolepine analogues with substantially improved antiplasmodial activity and selectivity index provide a promising starting point for development of potent and highly selective agents against drug-resistant malaria parasites.

In vitro antiplasmodial activity and cytotoxicity of nine plants traditionally used in Gabon

As part of a project to identify new compounds active on malarial parasites, we tested the in vitro antiplasmodial activity of nine plants traditionally used to treat malaria symptoms in Haut-Ogooué Province, South-East Gabon. Dichloromethane and methanolic extracts of each plant were tested for their antiplasmodial activity on two chloroquine-resistant strains of Plasmodium falciparum (FCB and W2), based on lactate dehydrogenase activity. Cytotoxicity was assessed with the MTT test on MRC-5 human diploid embryonic lung cells. The methanolic extract of Staudtia gabonensis and the dichloromethane extract of Adhatoda latibracteata showed high antiplasmodial activity (IC₅₀<1 μg/ml) and low cytotoxicity, with selectivity indexes of about 58.25 and 16.43, respectively. The methanolic extract of Monodora myristica and the dichloromethane extract of Afromomum giganteum also showed promising activity (1<IC₅₀<10 μg/ml) and low cytotoxicity, with selectivity indexes about 15.70 and 12.48, respectively. Dichloromethane extracts of Monodora myristica and Leonotis Africana showed moderate activity (10<IC₅₀<40 μg/ml), with selectivity indexes about 6.07 and 28.89, respectively. Both extracts of Culcasia lancifolia had IC₅₀ values of 10-40 μg/ml but high cytotoxicity (selectivity indexes <2.77). The methanolic extract of Dorstenia klaineana had moderate antiplasmodial activity (IC₅₀ around 17 μg/ml) but strong cytotoxicity (0.43 μg/ml), giving a selectivity index of about 0.03. Most extracts of nine selected plants traditionally used to treat malaria in Gabon had interesting antiplasmodial activity in vitro. This supports continued investigations of traditional medicines in the search for new antimalarial agents. The compounds responsible for the observed antiplasmodial effects are under investigation.

Cryptolepine and development of new antimalarial agents

Natural product-derived drugs exemplified by quinine, isolated from South American Cinchona species and artemisinin discovered in China are of immense importance for the treatment of malaria. Although malaria parasites resistant to artemisinin have not yet been found in malaria patients, the need for new antimalarial agents remains. The burden of malaria is heaviest in Africa where over a million children die of the disease each year, but although many medicinal plants are used in African traditional medicines for the treatment of malaria, none has yet yielded and effective antimalarial compound. Cryptolepis sanguinolenta (Periplocaceae), is a West African climbing shrub used traditionally for the treatment of malaria. Cryptolepine, an indoloquinoline alkaloid is the major constituent of the roots of C. sanguinolenta and has potent activity against malaria parasites in vitro, but it is cytotoxic on account of its abilities to inhibit topoisomerase II and to intercalate into DNA and it is also toxic to mice in vivo. However, the antimalarial mode of action of cryptolepine appears to involve a quinine-like mechanism (inhibition of ?-haematin formation) that is independent of interactions with DNA. This opens up the possibility that it may be feasible to prepare analogues of cryptolepine that do not interact with DNA (and hence may be less cytotoxic) but that retain or have enhanced antiplasmodial activities. Using various synthetic routes, a number of substituted cryptolepine analogues have been made and evaluated for their potential as leads to new antimalarial agents. Compounds were assessed for in-vitro activities against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and for cytotoxic activities. Some compounds have been assessed for their abilities to interact with DNA and a number of compounds has also been assessed for antimalarial activity against P. berghei in mice. Several cryptolepine analogues were found to have potent antiplasmodial activities (IC50 < 0.1 µM) against chloroquine-resistant P. falciparum (IC50 for chloroquine = 0.44 µM), but they are generally of similar cytotoxicity to cryptolepine. However, while cryptolepine is toxic to mice, a number of analogues have been shown to have promising antimalarial activities in the mouse-malaria model with no apparent toxicity. In view of this, derivatives of cryptolepine appear to be worthy of further investigation as potential antimalarial agents. In this lecture, the current status of antimalarial cryptolepine research will be reviewed and the potential of cryptolepine as a lead to new antimalarial agents will be discussed.

Karavilagenin C derivatives as antimalarials

Karavilagenin C (1), a cucurbitane-type triterpenoid, previously isolated from the aerial parts of Momordica balsamina, was acylated with different alkanoyl, aroyl and cinnamoyl chlorides/anydrides, yielding ten new mono or diesters, karavoates F (7) and H-P (8-16). Furthermore, the new compound cucurbalsaminol C (17) was isolated from the same plant. Their structures were assigned by spectroscopic methods, including 2D NMR experiments. Compounds 1 and 17 and the acyl derivatives 8-16 along with other five esters (2-6, karavoates A-E), previously prepared from 1, were evaluated for their in vitro antimalarial activity against the chloroquine-sensitive (3D7) and the chloroquine-resistant (Dd2) strains of Plasmodium falciparum. Compound 1 exhibited a moderate activity and 17 was inactive. However, a remarkable antiplasmodial activity was observed for most of karavilagenin C alkanoyl and monoaroyl/cynamoyl derivatives. Karavoates B, D, E, I, and M were the most active, displaying IC(50) values similar to those found for chloroquine, particularly against the resistant strain (IC(50) <0.6μM). Structure-activity relationships (SAR) are discussed. Moreover, the preliminary toxicity toward human cells of compounds 1-17 was also evaluated in breast cancer cell line (MCF-7). Most of the esters showed no toxicity, displaying, in general, much higher selectivity index values than those obtained for the parent compound.

Antiplasmodial activity of three bisbenzylisoquinoline alkaloids from the tuber of Stephania rotunda

Three bisbenzylisoquinoline alkaloids were isolated for the first time from Stephania rotunda tuber. Their structures were elucidated by spectroscopic methods and their antiplasmodial activity was investigated in vitro on chloroquine resistant Plasmodium falciparum strain W2. These alkaloids were identified as 2-norcepharanthine (1), cepharanoline (2) and fangchinoline (3). In vitro, they displayed significant antiplasmodial activity with inhibitory concentration 50 values of 0.3, 0.2 and 0.3 µM.

Plants used by native Amazonian groups from the Nanay River (Peru) for the treatment of malaria

In order to evaluate the antimalarial potential of traditional remedies used in Peru, Indigenous and Mestizo populations from the river Nanay in Loreto were interviewed about traditional medication for the treatment of malaria. The survey took place on six villages and led to the collection of 59 plants. 35 hydro-alcoholic extractions were performed on the 21 most cited plants. The extracts were then tested for antiplasmodial activity in vitro on Plasmodium falciparum chloroquine resistant strain (FCR-3), and ferriprotoporphyrin inhibition test was also performed in order to assume pharmacological properties. Extracts from 9 plants on twenty-one tested (Abuta rufescens, Ayapana lanceolata, Capsiandra angustifolia, Citrus limon, Citrus paradise, Minquartia guianensis, Potalia resinífera, Scoparia dulcis, and Physalis angulata) displayed an interesting antiplasmodial activity (IC(50)<10 μg/ml) and 16 remedies were active on the ferriprotoporphyrin inhibition test. The results give scientific validation to the traditional medical knowledge of the Amerindian and Mestizo populations from Loreto and exhibit a source of potentially active plants.

Falcipain 2 inhibitors and antiplasmodial compounds from a bio-guided fractionation of the fruits of Sorindeia juglandifolia A. Rich. (Anacardiaceae) growing in Cameroon

Materials and methods Fresh fruits were collected by an ethnobotanist in Yaounde area in May 2009. The plant was dried at Room Temperature during 7 days, powdered and extracted using organic solvents. The extract was fractionated by flash chromatography over silica gel (70-230 mesh, Merck, 7 x 42 cm), eluting with gradients of hexane-ethyl acetate mixtures, and resulted in 35 fractions, which were pooled on the basis of thin layer chromatography patterns. Resulting fractions were tested in vitro against the Plasmodium falciparum chloroquine-resistant strain W2, and the recombinant cysteine protease Falcipain 2 (F2) [1]. Two fractions showed the best potency and were selected for phytochemical investigation guided by biological activity.

A New Xanthone from the Bark Extract of Rheedia acuminata and Antiplasmodial Activity of Its Major Compounds

Bioassay-guided fractionation of the ethyl acetate bark extract of Rheedia acuminata led to the isolation of the new compound 1,5,6-trihydroxy-3-methoxy-7-geranyl-xanthone (1), together with four known compounds 2-5. These compounds were tested in vitro for their antiplasmodial activity on a chloroquine-resistant strain of Plasmodium falciparum (FcB1) and for their cytotoxicity against the human diploid embryonic lung cell line MRC-5.

Antiplasmodial Constituents from the Fruit Pericarp ofPentadesma butyracea

Bioassay-guided fractionation of the fruit pericarp of Pentadesma butyracea, using the antiplasmodial test, led to the isolation of a new xanthone, named pentadexanthone (1), together with six known compounds: cratoxylone (2), α-mangostin (3), 1,3,5-trihydroxy-2-methoxyxanthone (4), garcinone E (5), (-)-epicathechin (6), and lupeol (7). The structure of 1 was elucidated by spectroscopic data analysis. An antiplasmodial assay was performed with the isolates, in which compounds 1- 3 and 5 exhibited potent activity in vitro against Plasmodium falciparum chloroquine-resistant strain W2, with IC₅₀ values below 3 µM.

Chemometric modelling of antimalarial activity of aryltriazolylhydroxamates

We have performed quantitative structure–activity relationship (QSAR) and quantitative activity–activity relationship (QAAR) studies for aryltriazolylhydroxamates having antimalarial activity data against both chloroquine-sensitive (D6 clone) and chloroquine-resistant (W2 clone) strains of Plasmodium falciparum to understand the relationships between the biological activity and molecular properties for the design of new compounds. The QSAR studies were performed using 35 compounds among which 26 molecules were taken using k-means clustering technique in the training set for the derivation of the QSAR models and nine molecules were kept as the test-set compounds to evaluate the predictive ability of the derived models. The chemometric tool used for the analysis was the genetic function approximation. The developed models were analysed in terms of their predictive ability, and comparable results were obtained for cross-validated predictive variance (Q 2) and externally predicted variance (R 2 pred) values (0.761 and 0.829, respectively, for the D6 model, 0.708 and 0.748, respectively, for the W2 model and 0.984 and 0.982, respectively for the QAAR model). The QSAR models suggest that the number of methylene groups (between the triazolyl and hydroxamate moieties) and partially negatively charged surface areas of the molecules are important parameters for the antimalarial activity.

Pharmacological interactions of essential oil constituents on the in vitro growth of Plasmodium falciparum

The pharmacological properties of essential oils have been widely studied. However the interaction and contribution of the individual constituents assayed singularly and in combination remains relatively unexplored. To investigate these possible interactions, various essential oil constituents (EOC's) were combined and the interactions on their antimalarial and toxicity properties determined using the tritiated hypoxanthine incorporation and the tetrazolium-based cellular viability assays, respectively. In combination, two inactive EOC's (IC50 values greater than 1 mM), ρ-cymene and carvacrol interacted in a synergistic manner (∑ FIC = 0.02) against a chloroquine-resistant strain of Plasmodium falciparum. This interaction was comparable to that between the potent E- and Z-(±)-nerolidol (IC50 value: 0.9 ± 0.3 μM) and the standard antimalarial, quinine (IC50 value: 0.13 ± 0.04 μM) (∑ FIC = 0.01). However, this latter combination also potentiated the toxicity (∑ FIC = 0.001) of each molecule. A similar increase in toxicity was noted between ρ-cymene and γ-terpinene, as well as E- and Z-(±)-nerolidol and (−)-pulegone. These results show that the pharmacological activities of individual EOC's can vary greatly when used in combination, and show potential as adjuvants in the elimination of malaria infections.

Evaluation of Diarylureas for Activity Against Plasmodium falciparum

A library of diarylurea IGFR inhibitors was screened for activity against chloroquine-sensitive (3D7) and chloroquine-resistant (K1) strains of Plasmodium falciparum. The 4-aminoquinaldine-derived diarylureas displayed promising antimalarial potency. Further exploration of the B ring of 4-aminoquinaldinyl ureas allowed identification of several quinaldin-4-yl ureas 4{13, 39} and 4{13, 58} sufficiently potent against both 3D7 and K1 strains to qualify as bone fide leads.

Quassinoid constituents of Quassia amara L. (Simaroubaceae) leaf herbal tea. Impact on its antimalarial activity and cytotoxicity.

French Guiana records high malaria incidence rates. The traditional antimalarial remedy most widespread and still very much in use there is a tea made out from Quassia amara mature leaves. The antimalarial activity of this preparation was assessed [1] and in order to optimize the in vitro activity, different types of preparation have been realized and tested. The most active in vitro preparation is an infusion of fresh young leaves. It demonstrated a very good activity, in vitro as well as in vivo [2]. A known quassinoid, simalikalactone D (SkD), was identified as the active compound, with an IC50 value of 10 nM against FcB1 Plasmodium falciparum chloroquine resistant strain in vitro [3]. Our next objective was to assess whether it could be contemplated to recommend this young leaves tea for treatment against malaria, since it seemed from literature precedent that SkD was also cytotoxic to a number of cellular lineages [4,5]. We then characterized and quantified the antiparasitic and cytotoxic activities of all the constituents. Several quassinoids were isolated and characterized in the tea: SkD, quassin, neoquassin, and picrasins B, H, I (new) and J (new), SkD being responsible of both antiplasmodial activity and cytotoxicity. In addition, in the context of an antimalarial treatment, it appeared that the dose necessary for obtaining a curative antimalarial effect is close to the toxic dose of an SkD analogue, bruceantin. Prior to emitting a definitive conclusion, a clinical study in humans similar to the one done with bruceantin [6] should be performed.

Treatment of malaria in Iranian traditional medicine

The declining efficacy of classical medication in relation to the rapid extension of Plasmodium falciparum chloroquine-resistant strains has led to a need for new efficient anti malarial drugs. It is a real necessity to search for new efficient anti malarial compounds and make them accessible to most of the people. An ethnobotanical study was conducted to find plants traditionally used against malaria in Iran. In this study 35 plants were found on the basis of ethnobotanical investigation and searching in Iranian ancient traditional physician's books (1–4). At the same time the anopheles mosquito has developed resistance to many insecticides. There are some plants in Iran that are traditionally used as insect repellent (1–4). Also matching the old medicinal plant names with scientific terminology was done (5–8). First ethnobotanical studies on these plants were carried out at theTraditional Medicine and Materia Medica Research Center (TMRC). Further assessments are in process.

Antiprotozoal activities of some constituents ofMarkhamiatomentosa(Bignoniaceae)

Phytochemical investigation of an ethyl-acetate extract of the stem bark of Markhamia tomentosa (Bignoniaceae), which had good antimalarial activity in vitro, resulted in the isolation of eight known compounds: 2-acetylnaphtho[2,3-b]furan-4,9-dione (1), 2-acetyl-6-methoxynaphtho[2,3-b]furan-4,9-dione (2), oleanolic acid (3), pomolic acid (4), 3-acetylpomolic acid (5), tormentic acid (6), beta-sitosterol (7) and beta-sitosterol-3-O-beta-D-glucopyranoside (8). The structures of these compounds were established by spectroscopic methods. Each of compounds 1, 2, 4 and 5 was evaluated in vitro for its antiprotozoal activities against the ring stages of two chloroquine-resistant strains of Plasmodium falciparum (K1 and W2), the amastigotes of Leishmania donovani, and the bloodstream trypomastigotes of Trypanosoma brucei rhodesiense (the species responsible for human malaria, visceral leishmaniasis and African trypanosomiasis, respectively). Although compounds 1 and 2 exhibited potent antiprotozoal activities, they also showed high toxicity against a mammalian (L-6) cell line.

Two new anti-plasmodial flavonoid glycosides from Duranta repens

The CHCl3-soluble fraction of the whole plant of Duranta repens showed anti-plasmodial activity against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum, with IC50 values of 8.5 ± 0.9 and 10.2 ± 1.5 μg/mL, respectively. From this fraction, two new flavonoid glycosides, 7-O-α-d-glucopyranosyl-3,4′-dihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6-dimethoxyflavone (1) and 7-O-α-d-glucopyranosyl(6′′′-p-hydroxcinnamoyl)-3,4′-dihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6-dimethoxyflavone (2), along with five known flavonoids, 3,7,4′-trihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6-dimethoxyflavone (3), 3,7-dihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6,4′-trimethoxyflavone (4), 5,7-dihydroxy-3′-(2-hydroxy-3-methyl-3-butenyl)-3,6,4′-trimethoxyflavone (5), 3,7-dihydroxy-3′-(2-hydroxy-3-methyl-3-buten-yl)-5,6,4′-trimethoxyflavone (6), and 7-O-α-d-glucopyranosyl-3,5-dihydroxy-3′-(4′′-acetoxy-3′′-methylbutyl)-6,4′-dimethoxyflavone (7), have been isolated as anti-plasmodial principles. Their structures were deduced by spectroscopic analysis including 1D and 2D NMR techniques. The compounds (1–7) showed potent anti-plasmodial activities against D6 and W2 strains of Plasmodium falciparum, with IC50 values in the range of 5.2–13.5 μM and 5.9–13.1 μM, respectively.

Investigation of plant extracts in traditional medicine of the Brazilian Cerrado against protozoans and yeasts

Aim of the study To investigate the activities of the 217 plant extracts in traditional medicine of the Brazilian Cerrado against protozoans and yeasts. Materials and methods Plant extracts were prepared by the method of maceration using solvents of different polarities. The growth inhibition of chloroquine-resistant Plasmodium falciparum strain (FcB1) was determined by measuring the radioactivity of the tritiated hypoxanthine incorporated. Activity against Leishmania ( Leishmania) chagasi and Trypanosoma cruzi was measured by the MTT colorimetric assay. The antifungal tests were carried out by using the CLSI method. The active extracts were tested also by cytotoxicity assay using NIH-3T3 cells of mammalian fibroblasts. Results Two hundred and seventeen extracts of plants were tested against Plasmodium falciparum. The eleven active extracts, belonging to eight plant species were evaluated against L. (L.) chagasi, Trypanosoma cruzi, yeasts and in NIH-3T3 cells. The results found in these biological models are consistent with the ethnopharmacological data of these plants. The ethyl acetate extract of Diospyros hispida root showed IC 50 values of 1 μg/mL against Plasmodium falciparum. This extract demonstrated no toxicity against mammalian cells, resulting in a significant selectivity index (SI) of 435.8. The dichloromethane extract of Calophyllum brasiliense root wood was active against Cryptococcus gattii LMGO 01 with MIC of 1.95 μg/mL; and Candida albicans ATCC 10231 and Candida krusei LMGO 174, both with MIC of 7.81 μg/mL. The same extract was also active against Plasmodium falciparum and L. (L.) chagasi with IC 50 of 6.7 and 27.6 μg/mL respectively. The ethyl acetate extract of Spiranthera odoratissima leaves was active against Cryptococcus gattii LMGO 01 with MIC of 31.25 μg/mL, and against Plasmodium falciparum with IC 50 of 9.2 μg/mL and Trypanosoma cruzi with IC 50 of 56.3 μg/mL. Conclusion The active extracts for protozoans and human pathogenic yeasts are considered promising to continue the search for the identification and development of leading compounds.

1-Azaaurones derived from the naturally occurring aurones as potential antimalarial drugs

We report the synthesis and in vitro antiplasmodial activity of 35 compounds, designed as analogues of the naturally occurring aurones. Several of these analogues showed submicromolar antimalarial activity against a chloroquine-resistant strain of Plasmodium falciparum (FcB1-Columbia strain) cultured on human erythrocytes. Substitution of the intracyclic oxygen in aurones by a nitrogen atom and systematic variation of the substituent at the B-ring revealed promising leads showing good activity on the CQ-resistant strain. In particular, 4,6-dimethoxy-4′-ethylazaaurone 22 showed antiplasmodial potency without noticeable toxicity. The easy synthesis of this family of compounds and the relevant antiplasmodial activity are in favor of promising candidates for further development.