Multidrug-resistant Strains Of Plasmodium Falciparum Research Articles

Investigation of the anti-salmonellal and antiplasmodial properties of leaf extracts of Rourea coccinea Beninese medicinal plant

Rourea coccinea, also called Byrsocarpus coccineus is a medicinal plant widely used in primary health care in West Africa and in this case in Benin. In the present study, the hydroethanolic extract of these leaves was investigated for its anti-salmonella and antiplasmodial properties. The evaluation of anti-salmonella activity was carried out by the micro dilution method associated with resazurine while that of antiplasmodial activity by method described by Syber Green. Minimum inhibitory concentrations (MICs) of the hydroethanolic extract against Salmonella strains were higher than 2000 μg/mL. This extract was active against multidrug-resistant Plasmodium falciparum strains (PfDd2) with an inhibitory concentration (IC50) of 32.26 μg/mL. These works on Rourea coccinea justify that the plant has a clearly remarkable antiplasmodial activity rather than anti-salmonella one and its use in traditional medicine to treat malaria in Benin.

Combating multi-drug resistant malaria parasite by inhibiting falcipain-2 and heme-polymerization: Artemisinin-peptidyl vinyl phosphonate hybrid molecules as new antimalarials.

Artemisinin-based combination therapies (ACTs) have been able to reduce the clinical and pathological malaria cases in endemic areas around the globe. However, recent reports have shown a progressive decline in malaria parasite clearance in South-east Asia after ACT treatment, thus envisaging a need for new artemisinin (ART) derivatives and combinations. To address the emergence of drug resistance to current antimalarials, here we report the synthesis of artemisinin-peptidyl vinyl phosphonate hybrid molecules that show superior efficacy than artemisinin alone against chloroquine-resistant as well as multidrug-resistant Plasmodium falciparum strains with EC50 in pico-molar ranges. Further, the compounds effectively inhibited the survival of ring-stage parasite for laboratory-adapted artemisinin-resistant parasite lines as compared to artemisinin. These hybrid molecules showed complete parasite clearance invivo using P.berghei mouse malaria model in comparison to artemisinin alone. Studies on the mode of action of hybrid molecules suggested that these artemisinin-peptidyl vinyl phosphonate hybrid molecules possessed dual activities: inhibited falcipain-2 (FP-2) activity, a P.falciparum cysteine protease involved in hemoglobin degradation, and also blocked the hemozoin formation in the food-vacuole, a step earlier shown to be blocked by artemisinin. Since these hybrid molecules blocked multiple steps of a pathway and showed synergistic efficacies, we believe that these lead compounds can be developed as effective antimalarials to prevent the spread of resistance to current antimalarials.

Redesigned TetR-Aptamer System To Control Gene Expression in Plasmodium falciparum.

One of the most powerful approaches to understanding gene function involves turning genes on and off at will and measuring the impact at the cellular or organismal level. This particularly applies to the cohort of essential genes where traditional gene knockouts are inviable. In Plasmodium falciparum, conditional control of gene expression has been achieved by using multicomponent systems in which individual modules interact with each other to regulate DNA recombination, transcription, or posttranscriptional processes. The recently devised TetR-DOZI aptamer system relies on the ligand-regulatable interaction of a protein module with synthetic RNA aptamers to control the translation of a target gene. This technique has been successfully employed to study essential genes in P. falciparum and involves the insertion of several aptamer copies into the 3' untranslated regions (UTRs), which provide control over mRNA fate. However, aptamer repeats are prone to recombination and one or more copies can be lost from the system, resulting in a loss of control over target gene expression. We rectified this issue by redesigning the aptamer array to minimize recombination while preserving the control elements. As proof of concept, we compared the original and modified arrays for their ability to knock down the levels of a putative essential apicoplast protein (PF3D7_0815700) and demonstrated that the modified array is highly stable and efficient. This redesign will enhance the utility of a tool that is quickly becoming a favored strategy for genetic studies in P. falciparumIMPORTANCE Malaria elimination efforts have been repeatedly hindered by the evolution and spread of multidrug-resistant strains of Plasmodium falciparum The absence of a commercially available vaccine emphasizes the need for a better understanding of Plasmodium biology in order to further translational research. This has been partly facilitated by targeted gene deletion strategies for the functional analysis of parasite genes. However, genes that are essential for parasite replication in erythrocytes are refractory to such methods, and require conditional knockdown or knockout approaches to dissect their function. One such approach is the TetR-DOZI system that employs multiple synthetic aptamers in the untranslated regions of target genes to control their expression in a tetracycline-dependent manner. Maintaining modified parasites with intact aptamer copies has been challenging since these repeats can be lost by recombination. By interspacing the aptamers with unique sequences, we created a stable genetic system that remains effective at controlling target gene expression.

Oral Ingestion of Cannabis sativa: Risks, Benefits, and Effects on Malaria-Infected Hosts.

Background: The emergence of a multidrug-resistant strain of Plasmodium falciparum (Pf Pailin) raises concern about malaria control strategies. Unfortunately, the role(s) of natural plants/remedies in curtailing malaria catastrophe remains uncertain. The claims of potential antimalarial activity of Cannabis sativa in vivo have not been well established nor the consequences defined. This study was, therefore, designed to evaluate the effects of whole cannabis consumption on malaria-infected host.Methods: Thirty mice were inoculated with dose of 1×107 chloroquine-resistant Plasmodium berghei ANKA-infected erythrocyte and divided into six treatment groups. Cannabis diet formulations were prepared based on weighted percentages of dried cannabis and standard mice diet and the study animals were fed ad libitum. Chemosuppression of parasitemia, survival rates, parasite clearance, and recrudescence time were evaluated. Histopathological studies were performed on the prefrontal cortex (PFC) and hippocampus of the animals after 14 days' consumption of cannabis diet formulation by naive mice.Results: There was a significant difference (p<0.05) in the day-4 chemosuppression of parasitemia between the animals that were fed C. sativa and chloroquine relative to the untreated controls. There was also a significant difference in the survival rate (p<0.05) of animals fed C. sativa diet (40%, 20%, 10%, and 1%) in contrast to control animals on standard mice diet. A parasite clearance time of 2.18±0.4 was recorded in the chloroquine treatment group, whereas recrudescence in chloroquine group occurred on day 7. There were slight histomorphological changes in the PFC and cell densities of the dentate gyrus of the hippocampus of animals that were fed C. sativa.Conclusions: C. sativa displayed mild antimalarial activity in vivo. There was evident reduction in symptomatic manifestation of malaria disease, though unrelated to levels of parasitemia. This disease tolerance status may be beneficial, but may also constitute a transmission burden through asymptomatic carriage of parasites by habitual cannabis users.

Efficacy and safety evaluation of a novel trioxaquine in the management of cerebral malaria in a mouse model

BackgroundThe emergence of multidrug-resistant strains of Plasmodium falciparum poses a great threat of increased fatalities in cases of cerebral and other forms of severe malaria infections in which parenteral artesunate monotherapy is the current drug of choice. The study aimed to investigate in a mouse model of human cerebral malaria whether a trioxaquine chemically synthesized by covalent linking of a 4,7-dichloroquinoline pharmacophore to artesunate through a recent drug development approach termed ‘covalent bitherapy’ could improve the curative outcomes in cerebral malaria infections.MethodsHuman cerebral malaria rodent model, the C57BL/6 male mice were infected intraperitoneally (ip) with Plasmodium berghei ANKA and intravenously (iv) treated with the trioxaquine from day 8 post-infection (pi) at 12.5 and 25 mg/kg, respectively, twice a day for 3 days. Treatments with the trioxaquine precursors (artesunate and 4,7-dichloroquine), and quinine were also included as controls. In vivo safety evaluation for the trioxaquine was done according to Organization for Economic Co-operation and Development (OECD) guidelines 423, where female Swiss albino mice were orally administered with either 300 or 2000 mg/kg of the trioxaquine and monitored for signs of severity, and or mortality for 14 days post-treatment.ResultsThe trioxaquine showed a potent and a rapid antiplasmodial activity with 80% parasite clearance in the first 24 h for the two dosages used. Long-term parasitaemia monitoring showed a total parasite clearance as the treated mice survived beyond 60 days post-treatment, with no recrudescence observed. Artesunate treated mice showed recrudescence 8 days post-treatment, with all mice in this group succumbing to the infection. Also, 4,7-dichloroquinoline and quinine did not show any significant parasitaemia suppression in the first 24 h post-treatment, with the animals succumbing to the infection.ConclusionCovalent bitherapy proves to be a viable source of urgently needed new anti-malarials for management of cerebral malaria, and this polypharmacology approach could be a potential strategy to protect artesunate from parasite resistance and in potentially improving clinical outcomes in severe forms of malaria infections.

Evolution of Fitness Cost-Neutral Mutant PfCRT Conferring P. falciparum 4-Aminoquinoline Drug Resistance Is Accompanied by Altered Parasite Metabolism and Digestive Vacuole Physiology.

Southeast Asia is an epicenter of multidrug-resistant Plasmodium falciparum strains. Selective pressures on the subcontinent have recurrently produced several allelic variants of parasite drug resistance genes, including the P. falciparum chloroquine resistance transporter (pfcrt). Despite significant reductions in the deployment of the 4-aminoquinoline drug chloroquine (CQ), which selected for the mutant pfcrt alleles that halted CQ efficacy decades ago, the parasite pfcrt locus is continuously evolving. This is highlighted by the presence of a highly mutated allele, Cam734 pfcrt, which has acquired the singular ability to confer parasite CQ resistance without an associated fitness cost. Here, we used pfcrt-specific zinc-finger nucleases to genetically dissect this allele in the pathogenic setting of asexual blood-stage infection. Comparative analysis of drug resistance and growth profiles of recombinant parasites that express Cam734 or variants thereof, Dd2 (the most common Southeast Asian variant), or wild-type pfcrt, revealed previously unknown roles for PfCRT mutations in modulating parasite susceptibility to multiple antimalarial agents. These results were generated in the GC03 strain, used in multiple earlier pfcrt studies, and might differ in natural isolates harboring this allele. Results presented herein show that Cam734-mediated CQ resistance is dependent on the rare A144F mutation that has not been observed beyond Southeast Asia, and reveal distinct impacts of this and other Cam734-specific mutations on CQ resistance and parasite growth rates. Biochemical assays revealed a broad impact of mutant PfCRT isoforms on parasite metabolism, including nucleoside triphosphate levels, hemoglobin catabolism and disposition of heme, as well as digestive vacuole volume and pH. Results from our study provide new insights into the complex molecular basis and physiological impact of PfCRT-mediated antimalarial drug resistance, and inform ongoing efforts to characterize novel pfcrt alleles that can undermine the efficacy of first-line antimalarial drug regimens.

Endoperoxide antimalarials: development, structural diversity and pharmacodynamic aspects with reference to 1,2,4-trioxane-based structural scaffold.

Malaria disease continues to be a major health problem worldwide due to the emergence of multidrug-resistant strains of Plasmodium falciparum. In recent days, artemisinin (ART)-based drugs and combination therapies remain the drugs of choice for resistant P. falciparum malaria. However, resistance to ART-based drugs has begun to appear in some parts of the world. Endoperoxide compounds (natural/semisynthetic/synthetic) representing a huge number of antimalarial agents possess a wide structural diversity with a desired antimalarial effectiveness against resistant P. falciparum malaria. The 1,2,4-trioxane ring system lacking the lactone ring that constitutes the most important endoperoxide structural scaffold is believed to be the key pharmacophoric moiety and is primarily responsible for the pharmacodynamic potential of endoperoxide-based antimalarials. Due to this reason, research into endoperoxide, particularly 1,2,4-trioxane-, 1,2,4-trioxolane- and 1,2,4,5-teraoxane-based scaffolds, has gained significant interest in recent years for developing antimalarial drugs against resistant malaria. In this paper, a comprehensive effort has been made to review the development of endoperoxide antimalarials from traditional antimalarial leads (natural/semisynthetic) and structural diversity of endoperoxide molecules derived from 1,2,4-trioxane-, 1,2,4-trioxolane- and 1,2,4,5-teraoxane-based structural scaffolds, including their chimeric (hybrid) molecules, which are newer and potent antimalarial agents.

Expression of β-glucosidase increases trichome density and artemisinin content in transgenic Artemisia annua plants.

Artemisinin is highly effective against multidrug-resistant strains of Plasmodium falciparum, the aetiological agent of the most severe form of malaria. However, a low level of accumulation of artemisinin in Artemisia annua is a major limitation for its production and delivery to malaria endemic areas of the world. While several strategies to enhance artemisinin have been extensively explored, enhancing storage capacity in trichome has not yet been considered. Therefore, trichome density was increased with the expression of β-glucosidase (bgl1) gene in A.annua through Agrobacterium-mediated transformation. Transgene (bgl1) integration and transcript were confirmed by molecular analysis. Trichome density increased up to 20% in leaves and 66% in flowers of BGL1 transgenic plants than Artemisia control plants. High-performance liquid chromatography, time of flight mass spectrometer data showed that artemisinin content increased up to 1.4% in leaf and 2.56% in flowers (per g DW), similar to the highest yields achieved so far through metabolic engineering. Artemisinin was enhanced up to five-fold in BGL1 transgenic flowers. This study opens the possibility of increasing artemisinin content by manipulating trichomes' density, which is a major reservoir of artemisinin. Combining biosynthetic pathway engineering with enhancing trichome density may further increase artemisinin yield in A.annua. Because oral feeding of Artemisia plant cells reduced parasitemia more efficiently than the purified drug, reduced drug resistance and cost of prohibitively expensive purification process, enhanced expression should play a key role in making this valuable drug affordable to treat malaria in a large global population that disproportionally impacts low-socioeconomic areas and underprivileged children.

Apollon, a new Artemisia annua variety with high artemisinin content

Artemisinin, a sesquiterpene lactone endoperoxide isolated from the herb Artemisia annua L. (Asteraceae), is a highly potent antimalarial compound, which is efficient againt multidrug-resistant strains of Plasmodium falciparum. The promotion of artemisinin-based combination therapies (ACTs) by the WHO during the past years lead to a strong pressure on the world market of artemisinin. The artemisinin world market is volatile and therefore efforts to improve performance of this culture are often limited. The use of varieties with high artemisinin content is a key factor for the development of such cultures. This should secure the supply of artemisinin, lower its cost of production and improve the competitiveness of this new culture with other commercial crops. After the variety Artemis, Mediplant launches a new variety called Apollon with about 20% yield increase. Performances of this new hybrid, with artemisinin content nearing 1.6%, are being presented.

Optimizing nitrogen levels combined with gibberellic acid for enhanced yield, photosynthetic attributes, enzyme activities, and artemisinin content of Artemisia annua

Artemisia annua L. is an aromatic-antibacterial herb that destroys malarial parasites, lowers fever, and checks bleeding, and from which the secondary compound of interest is artemisinin. It has become increasingly popular as an effective and safe alternative therapy against malaria, and its derivatives are effective against multidrug resistant Plasmodium falciparum strains. Nitrogen is required by the plants in the largest quantity and is most limiting where biomass production is desired. On the other hand, gibberellic acid plays an important role in flowering, growth, and development and also in other physiological and biochemical processes. The feasibility of foliar GA3 (75 mg·L−1) alone or with varying levels of soil applied nitrogen (40, 80, and 120 mg·kg−1 soil) was tested on A. annua in the present study. The application of GA3 proved effective in alleviating the growth, photosynthesis, and enzyme activities of A. annua. However, N levels combined with GA3 showed better responses, and further improvement in these parameters was observed. Furthermore, the most important task we were interested in was to increase the artemisinin content and its yield on a per plant basis. The N combination (80 mg·kg−1 soil) together with GA3 augmented the content (21.8% more) and yield (55.8% more); this is true for both the treated plants, which were more than the control.

Inhibitors of the Mitochondrial Electron Transport Chain and de novo Pyrimidine Biosynthesis as Antimalarials: The Present Status

Malaria is a major worldwide public health threat with worrying social and economic burdens due to the rapid emergence of multidrug-resistant Plasmodium falciparum strains. As a result, there is an urgent need to find novel drugs that might overcome clinical resistance to marketed antimalarials. In recent years, the mitochondrial electron transport chain (mtETC) has been explored for the development of new antimalarials. Type II NADH:quinone oxidoreductase (PfNDH2), succinate dehydrogenase (SDH) and cytochrome bc1 have become a major focus of those efforts, leading to several studies of its biochemistry and the design of potent inhibitors. Furthermore, de novo pyrimidine biosynthesis in malaria parasites, particularly dihydroorotate dehydrogenase (PfDHODH), is also receiving increasing attention. The enzymes involved in the mtETC are valuable targets in malaria chemotherapy, not only because they play a critical role in metabolic pathways of P. falciparum, but also because they differ significantly from the analogous mammalian system. Inhibition of such enzymes results in the shutdown of mitochondrial electron flow, leading to the arrest of pyrimidine biosynthesis and consequent parasite death. In this review, we aim to outline recent advances in the inhibition of mitochondrial metabolic pathways, highlighting the major classes of known inhibitors and those that are currently being developed.

Liquid chromatographic analysis of halofantrine from dosage form and its metal interaction studies

Abstract The reversed-phase high-performance liquidchromatographic method has been developed for thedetermination of halofantrine from dosage form in pres-ence of losartan potassium as an internal standard. Sepa-ration was performed on a Chrompack hypersil C 18 (150 9 4.6 mm) analytical reversed-phase column. Mobilephase consisted of methanol–water (70:30, v/v) pH wasadjusted to 3.2 with 85% orthophosphoric acid. Mobilephase was pumped at a flow rate of 0.5 mL min -1 and UVdetection was performed at 248 nm. The method wasvalidated for linearity, precision, accuracy and specificity.The linearity was observed in the concentration range1.0–50 lgmL -1 with correlation coefficient (r 2 ) of 0.9998.Accuracy was ranged 98–100% with precision less than1%. The limits of detection (LOD) and (LOQ) were 0.01and 0.03 lgmL -1 , respectively. This method was appliedto study the drug–metal (calcium, magnesium, manganese,cobalt, ferrous, ferric chromium, zinc, nickel, cadmium,iron and copper) interaction studies which were carried outat 37 C. These studies were beneficial to determine thedrug in therapeutic concentrations inside human body aswell as its complexation with metal ions. The proposedmethod is rapid, accurate, economical and selectivebecause of its sensitivity and reproducibility.Keywords Halofantrine HPLC MetalsIntroductionHalofantrine, 1-(1,3-dichloro-6-trifluoromethylphenanthyl)-3-N,N-dibutylaminopropan-1-ol, is an effective drug for thetreatment of malaria (Yetunde et al., 2006)causedbychloroquine-resistant and multidrug-resistant strains ofPlasmodium falciparum (ter Kuile et al., 1993; Tracy andWebster, 1996).Various methods have been employed for the analysis ofhalofantrine by titrimetry, spectrophotometry (Koladeet al., 2006; Ahmad and Hridaya, 2002) and halofantrinewith its metabolite in biological fluids (Onyeji and Aid-eloje, 1997; Humberstone et al., 1995; Gaillard et al.,1995; Mberu et al., 1992; Gimenez et al., 1992; Kee-ratithakul et al., 1991; Milton et al., 1988; Gawienowskiet al., 1988; Hines et al., 1985) by high-performance liquidchromatography.All these methods were expensive, complex in natureand make a column more susceptible to damage. In thesemethods, mobile phases used were mostly different buffers,which are very much hazardous for the column life andefficiency (theoretical plates). Consequently, there was stilla need to develop a simple, less time consuming andeconomical HPLC method for the determination of halo-fantrine in dosage form and employed in halofantrine–metal interaction studies.The systemic availability of halofantrine was signifi-cantly increased in the presence of food (Milton et al.,1989) but there is no information in the literature on theeffect of metals on the availability of halofantrine. There-fore, the purpose of this study was to determine whetherhalofantrine interacts with metals in vitro.

PERFORMANCE OF ARTEMISIA ANNUA L. CULTIVARS IN DIFFERENT LOCATIONS IN ARGENTINA

Artemisinin, a sesquiterpene lactone endoperoxide isolated from the herb Artemisia annua L. (Asteraceae), is a highly potent antimalarial compound, which is efficient against multidrug-resistant strains of Plasmodium falciparum. The promotion of artemisinin-based combination therapies (ACTs) by the WHO during the past years lead to strong pressure on the world market of artemisinin. In order to assess the potential of this new culture in Argentina, the 'Artemis' cultivar was grown in 2007 and 2008 in four different locations. On one of the sites, 2 new hybrids were tested to assess their potential. The following parameters were recorded during the growing period: plant height, phenology, biomass production, percentage of dry leaves and artemisinin content. The results obtained with the cultivar 'Artemis' showed that the highest yield of biomass reached at the time of harvest was 2.5 t/ha dry leaves. At the harvesting stage, artemisinin contents ranged from 0.77% to 1.12% depending on the location. The two new hybrids tested showed a similar production of leaves, but a significantly higher level of artemisinin than those observed for 'Artemis'. Future trials are planned to optimise the cultivation of annual wormwood in Argentina.

Drug interaction studies of H2-receptor antagonists with mefloquine, pyrimethamine and sulfadoxine

Fansimef is a new antimalarial schizontocide that contains mefloquine, pyrimethamine, and sulfadoxine with a weight ratio of 1:20:10. This antimalarial combination is highly active against multidrug-resistant strains of Plasmodium falciparum. H2-receptor antagonists (cimetidine, famotidine, and ranitidine) are reversible competitive blockers of histamine at H2-receptor and do not affect the H1-receptor. These are potent inhibitors of all phases of gastric acid secretion. They do so by binding to H2-receptors on the parietal cells of stomach. The effect of various dissolution mediums with respect to pH on these drug–drug interactions and in vitro availability reveals that availability of antimalarial drugs increased to a smaller extent in the presence of H2-receptors. The influence of temperatures on these interactions has been examined to elucidate the mechanism of these interactions. Antimalarial drugs could be administrated concurrently with H2-receptor antagonist (cimetidine and famotidine); however, ranitidine should not be given because availability was almost suppressed in the presence of antimalarial drugs.

Quantification of artemisinin in Artemisia annua extracts by 1H‐NMR

Artemisinin is a polycyclic sesquiterpene lactone that is highly effective against multidrug-resistant strains of Plasmodium falciparum, the etiological agent of the most severe form of malaria. Determination of artemisinin in the source plant, Artemisia annua, is a challenging problem since the compound is present in very low concentrations, is thermolabile and unstable, and lacks chromophoric or fluorophoric groups. The ain of this study was to develop a simple protocol for the quantification of artemisinin in a plant extract using an (1)H-NMR method. Samples were prepared by extraction of leaf material with acetone, treatment with activated charcoal to remove chlorophylls and removal of solvent. (1)H-NMR spectra were measured on samples dissolved in deuterochloroform with tert-butanol as internal standard. Quantification was carried out using the using the delta 5.864 signal of artemisinin and the delta 1.276 signal of tert-butanol. The method was optimised and fully validated against a reference standard of artemisinin. The results were compared with those obtained from the same samples quantified using an HPLC-refractive index (RI) method. The (1)H-NMR method gave a linear response for artemisinin within the range 9.85-97.99 mm (r(2) = 0.9968). Using the described method, yields of artemisinin in the range 0.77-1.06% were obtained from leaves of the A. annua hybrid CPQBA x POP, and these values were in agreement with those obtained using an HPLC-RI.

NEW ARTEMISIA ANNUA HYBRIDS WITH HIGH ARTEMISININ CONTENT

NEW ARTEMISIA ANNUA HYBRIDS WITH HIGH ARTEMISININ CONTENT

Antimalarial quinolones: Synthesis, potency, and mechanistic studies

In the present article we examine the antiplasmodial activities of novel quinolone derivatives bearing extended alkyl or alkoxy side chains terminated by a trifluoromethyl group. In the series under investigation, the IC 50 values ranged from 1.2 to ≈30 nM against chloroquine-sensitive and multidrug-resistant Plasmodium falciparum strains. Modest to significant cross-resistance was noted in evaluation of these haloalkyl- and haloalkoxyquinolones for activity against the atovaquone-resistant clinical isolate Tm90-C2B, indicating that a primary target for some of these compounds is the parasite cytochrome bc 1 complex. Additional evidence to support this biochemical mechanism includes the use of oxygen biosensor plate technology to show that the quinolone derivatives block oxygen consumption by parasitized red blood cells in a fashion similar to atovaquone in side-by-side experiments. Atovaquone is extremely potent and is the only drug in clinical use that targets the Plasmodium bc 1 complex, but rapid emergence of resistance to it in both mono- and combination therapy is evident and therefore additional drugs are needed to target the cytochrome bc 1 complex which are active against atovaquone-resistant parasites. Our study of a number of halogenated alkyl and alkoxy 4(1 H)-quinolones highlights the potential for development of “endochin-like quinolones” (ELQ), bearing an extended trifluoroalkyl moiety at the 3-position, that exhibit selective antiplasmodial effects in the low nanomolar range and inhibitory activity against chloroquine and atovaquone-resistant parasites. Further studies of halogenated alkyl- and alkoxy-quinolones may lead to the development of safe and effective therapeutics for use in treatment or prevention of malaria and other parasitic diseases.

Tetraoxane Antimalarials and Their Reaction with Fe(II)

Mixed tetraoxanes 5a and 13 synthesized from cholic acid and 4-oxocyclohexanecarboxylic acid were as active as artemisinin against chloroquine-susceptible, chloroquine-resistant, and multidrug-resistant Plasmodium falciparum strains (IC50, IC90). Most active 13 is metabolically stable in in vitro metabolism studies. In vivo studies on tetraoxanes with a C(4' ') methyl group afforded compound 15, which cured 4/5 mice at 600 and 200 mg.kg-1.day-1, and 2/5 mice at 50 mg.kg-1.day-1, showing no toxic effects. Tetraoxane 19 was an extremely active antiproliferative with LC50 of 17 nM and maximum tolerated dose of 400 mg/kg. In Fe(II)-induced scission of tetraoxane antimalarials only RO* radicals were detected by EPR experiments. This finding and the indication of Fe(IV)=O species led us to propose that RO* radicals are probably capable of inducing the parasite's death. Our results suggest that C radicals are possibly not the only lethal species derived from peroxide prodrug antimalarials, as currently believed.

In vitro antimalarial activity of flavonoid derivatives dehydrosilybin and 8-(1;1)-DMA-kaempferide

Multidrug-resistant Plasmodium falciparum strains are an increasing problem in endemic areas and are partly responsible for the worsening malaria situation around the world. New cheap and effective compounds active in combination with available drug in the field are urgently needed. The aim of this work was to explore the potential antiplasmodial effect of flavonoid derivatives on parasites growth in vitro. In vitro antiplasmodial activity of dehydrosilybin and 8-(1;1)-DMA-kaempferide has been evaluated by real time PCR for five P. falciparum strains. Both revealed significative antimalarial activity against the different strains. Since this drug family has been largely used and well-tolerated in humans, flavonoid derivatives could be in the near future associated with already available drugs in order to delay the spread of P. falciparum resistance.

Antimalarial and antileishmanial activities of aroyl-pyrrolyl-hydroxyamides, a new class of histone deacetylase inhibitors.

Members of the genus Leishmania are parasitic protozoans that infect about two million people per annum (5), and they are emerging as serious opportunistic infective agents in human immunodeficiency virus-infected patients (4). Malaria parasites are responsible for 1.5 to 2.7 million deaths annually, primarily in Africa (10). The effort to find new antimalarial agents is still a high priority given the increasing malaria emergency largely due to multidrug-resistant Plasmodium falciparum strains. The histones of P. falciparum have recently been proposed as targets for drug treatment of blood stage parasites (6). They also play an important role in chromatin remodeling in trypanosomatids, which include Leishmania species and trypanosomes (3).