Antimalarial Candidates Research Articles

A novel class of fast-acting antimalarial agents: Substituted 15-membered azalides.

Background and PurposeEfficacy of current antimalarial treatments is declining as a result of increasing antimalarial drug resistance, so new and potent antimalarial drugs are urgently needed. Azithromycin, an azalide antibiotic, was found useful in malaria therapy, but its efficacy in humans is low.Experimental ApproachFour compounds belonging to structurally different azalide classes were tested and their activities compared to azithromycin and chloroquine. in vitro evaluation included testing against sensitive and resistant Plasmodium falciparum , cytotoxicity against HepG2 cells, accumulation and retention in human erythrocytes, antibacterial activity, and mode of action studies (delayed death phenotype and haem polymerization). in vivo assessment enabled determination of pharmacokinetic profiles in mice, rats, dogs, and monkeys and in vivo efficacy in a humanized mouse model.Key ResultsNovel fast‐acting azalides were highly active in vitro against P. falciparum strains exhibiting various resistance patterns, including chloroquine‐resistant strains. Excellent antimalarial activity was confirmed in a P. falciparum murine model by strong inhibition of haemozoin‐containing trophozoites and quick clearance of parasites from the blood. Pharmacokinetic analysis revealed that compounds are metabolically stable and have moderate oral bioavailability, long half‐lives, low clearance, and substantial exposures, with blood cells as the preferred compartment, especially infected erythrocytes. Fast anti‐plasmodial action is achieved by the high accumulation into infected erythrocytes and interference with parasite haem polymerization, a mode of action different from slow‐acting azithromycin.Conclusion and ImplicationsThe hybrid derivatives described here represent excellent antimalarial drug candidates with the potential for clinical use in malaria therapy.

Methnaridine is an orally bioavailable, fast-killing and long-acting antimalarial agent that cures Plasmodium infections in mice.

Malaria is one of the deadliest diseases in the world. Novel chemotherapeutic agents are urgently required to combat the widespread Plasmodium resistance to frontline drugs. Here, we report the discovery of a novel benzonaphthyridine antimalarial, methnaridine, which was identified using a structural optimization strategy. An integrated pharmacological approach was used to evaluate the antimalarial profile of methnaridine. The pharmacokinetic properties of methnaridine were investigated along with the associated safety profile. Host immune response patterns were also analysed. Methnaridine exhibited potent antimalarial activity against P. falciparum (3D7: IC50 = 0.0066 μM; Dd2: IC50 = 0.0056 μM). In P. berghei-infected mice, oral administration effectively suppressed parasitemia (ED50 = 0.52 mg·kg-1 ·day-1 ) and cured the established infection (CD50 = 10.13 mg·kg-1 ·day-1 ). These results are equivalent to or better than those of other antimalarial agents in clinical use. Notably, a four-dose oral regimen at a dosage of 25 mg·kg-1 achieved a complete cure of P. berghei infection in mice. Methnaridine exhibited a rapid parasiticidal profile (PCT99 = 36.0 h) and showed no cross-resistance to chloroquine. Pharmacokinetic studies revealed that methnaridine is readily absorbed, long-lasting and slowly cleared. The safety profile of methnaridine is also satisfactory (maximum tolerated dose = 1,125 mg·kg-1 ). In addition, following methnaridine treatment, infection-induced Th1 immune response was almost fully alleviated in mice. Methnaridine is an orally bioavailable, fast-acting and long-lasting agent with excellent antimalarial properties. Our study highlights the potential of methnaridine for clinical development as a promising antimalarial candidate.

Regioisomerization of Antimalarial Drug WR99210 Explains the Inactivity of a Commercial Stock.

WR99210, a former antimalarial drug candidate now widely used for the selection of Plasmodium transfectants, selectively targets the parasite's dihydrofolate reductase thymidine synthase bifunctional enzyme (DHFR-TS) but not human DHFR, which is not fused with TS. Accordingly, WR99210 and plasmids expressing the human dhfr gene have become valued tools for the genetic modification of parasites in the laboratory. Concerns over the ineffectiveness of WR99210 from some sources encouraged us to investigate the biological and chemical differences of supplies from two different companies (compounds 1 and 2). Compound 1 proved effective at low nanomolar concentrations against Plasmodium falciparum parasites, whereas compound 2 was ineffective, even at micromolar concentrations. Intact and fragmented mass spectra indicated identical molecular formulae of the unprotonated (free base) structures of compounds 1 and 2; however, the compounds displayed differences by thin-layer chromatography, reverse-phase high-performance liquid chromatography, and UV-visible spectroscopy, indicating important isomeric differences. Structural evaluations by 1H, 13C, and 15N nuclear magnetic resonance spectroscopy confirmed compound 1 as WR99210 and compound 2 as a dihydrotriazine regioisomer. Induced fit computational docking models showed that compound 1 binds tightly and specifically in the P. falciparum DHFR active site, whereas compound 2 fits poorly to the active site in loose and varied orientations. Stocks and concentrates of WR99210 should be monitored for the presence of regioisomer 2, particularly when they are not supplied as the hydrochloride salt or are exposed to basic conditions that may promote rearrangement. Absorption spectroscopy can serve for assays of the unrearranged and rearranged triazines.

Synthesis, Molecular Docking and Pharmacological Investigation of Some 4-Methylphenylsulphamoyl Carboxylic Acid Analogs

Compounds bearing and amino acid moieties are considered the basis for sulfa drug development. The synthesis of 4-methylphenylsulphamoyl acids and the evaluation of their pharmacological activities are reported. The synthesis of these compounds was accomplished by the reaction of various acids and 4-methyl chloride in basic aqueous solution. Structures were confirmed by FTIR, 1HNMR, 13CNMR spectra and elemental analytical data. Molecular docking interactions of the analogues were determined using PyRx. In the in antimicrobial activity analysis, compounds 1, 3, 5and 7 had antimicrobial inhibitory concentration range of 0.5-1.0mg/ml comparable with 0.1-2.0mg/ml of and . In the in anti-oxidant activity study compounds 1, 2and 6displayed half-maximal inhibitory concentrations (IC50) of 1.104±0.001 /ml, 1.159±0.002µg/ml and1.240±0.001µg/ml respectively comparable with 0.999±0.002µg/ml of acid. In the molecular docking study, compound 4 had a strong 2D binding interaction with II amino acid residue and compounds 1, 3, 4, 5, 6 and 7 had in antimicrobial, anti-oxidant, and antimalarial properties similar to their standard drugs. Considering the outstanding pharmacological properties and their strict compliance with Lipinski’s rule, the synthesized 4-methylphenylsulphamoyl analogues could be considered as antimicrobial, antimalarial, and anti-oxidant drug candidates.

Probing the B- & C-rings of the antimalarial tetrahydro-β-carboline MMV008138 for steric and conformational constraints

The antimalarial candidate MMV008138 (1a) is of particular interest because its target enzyme (IspD) is absent in human. To achieve higher potency, and to probe for steric demand, a series of analogs of 1a were prepared that featured methyl-substitution of the B- and C-rings, as well as ring-chain transformations. X-ray crystallography, NMR spectroscopy and calculation were used to study the effects of these modifications on the conformation of the C-ring and orientation of the D-ring. Unfortunately, all the B- and C-ring analogs explored lost in vitro antimalarial activity. The possible role of steric effects and conformational changes on target engagement are discussed.

Computational Chemogenomics Drug Repositioning Strategy Enables the Discovery of Epirubicin as a New Repurposed Hit for Plasmodium falciparum and P. vivax.

Widespread resistance against antimalarial drugs thwarts current efforts for controlling the disease and urges the discovery of new effective treatments. Drug repositioning is increasingly becoming an attractive strategy since it can reduce costs, risks, and time-to-market. Herein, we have used this strategy to identify novel antimalarial hits. We used a comparative in silico chemogenomics approach to select Plasmodium falciparum and Plasmodium vivax proteins as potential drug targets and analyzed them using a computer-assisted drug repositioning pipeline to identify approved drugs with potential antimalarial activity. Among the seven drugs identified as promising antimalarial candidates, the anthracycline epirubicin was selected for further experimental validation. Epirubicin was shown to be potent in vitro against sensitive and multidrug-resistant P. falciparum strains and P. vivax field isolates in the nanomolar range, as well as being effective against an in vivo murine model of Plasmodium yoelii Transmission-blocking activity was observed for epirubicin in vitro and in vivo Finally, using yeast-based haploinsufficiency chemical genomic profiling, we aimed to get insights into the mechanism of action of epirubicin. Beyond the target predicted in silico (a DNA gyrase in the apicoplast), functional assays suggested a GlcNac-1-P-transferase (GPT) enzyme as a potential target. Docking calculations predicted the binding mode of epirubicin with DNA gyrase and GPT proteins. Epirubicin is originally an antitumoral agent and presents associated toxicity. However, its antiplasmodial activity against not only P. falciparum but also P. vivax in different stages of the parasite life cycle supports the use of this drug as a scaffold for hit-to-lead optimization in malaria drug discovery.

A review of antimalarial activity of two or three nitrogen atoms containing heterocyclic compounds

Malaria, a nocuous disease, which has become a major challenge for the health resulting in deaths of millions of people around the globe. Malaria is a parasitic disease propagated by mosquitoes and infects the human beings. Several species of Plasmodium are responsible for this life-threatening disease and Plasmodium falciparum being the most virulent. In order to eradicate the malarial parasite, the researchers are making consistent efforts in synthesizing new antimalarial drug candidates by paying attention to the various drug targets. In this manuscript, the main focus is on the antimalarial activity of numerous heterocyclic compounds reported by the researchers since 2010 against the different strains of Plasmodium. Antimalarial activities of the two and three nitrogen-containing heterocycles along with their structure–activity relationship are described.

Antimalarial activity of goat bile against Plasmodium berghei ANKA infection in BALB/c mice

Abstract Goat bile has been used by some Indonesian people to treat malaria and increase their stamina. This study aimed to prove whether goat bile toxic or not in BALB/c mice and to verify the antimalarial activity of goat bile at various concentrations in mice infected with Plasmodium berghei ANKA. Acute toxicity test was performed using twenty male BALB/c mice with an average body weight of 25 grams, which were divided into four groups. Mice were given 25%, 50%, and 100% goat bile, respectively, while negative control was given distilled water. Any change in weight, odor, color, agitation, appearance, color of urine and feces, coma, and death, were recorded. A different set of mice were infected with P. berghei ANKA. This study conducted using the posttest only control group design with four treatments and five replications. A four day-treatment of goat bile was given by oral gavage to find out its effect on parasitemia level. Infected mice were divided randomly into 4 groups, where the GBNeg group as negative control was given only distilled water. The GB25, GB50, and GB100 groups were treated with 25%, 50%, and 100% goat bile, respectively. The parasitemia was observed daily on Giemsa-stained tail blood smears of each mice. No death or other sign of toxicity was found in goat bile-treated mice. Goat bile showed anti-malarial activity. The parasitemia in all goat bile treated groups was lower compared with the negative control group. The ED50 of goat bile against the growth of parasite was 48,55 %. Goat bile is a potential source of new antimalarial therapies. Further investigations are recommended to yield new anti-malarial drug candidates. Keywords : Goat bile, parasitemia, Plasmodium berghei ANKA, ED50Correspondence : heny-a@fk.unair.ac.id

Pre-Erythrocytic Vaccines against Malaria.

Malaria, caused by the protozoan Plasmodium, is a devastating disease with over 200 million new cases reported globally every year. Although immunization is arguably the best strategy to eliminate malaria, despite decades of research in this area we do not have an effective, clinically approved antimalarial vaccine. The current impetus in the field is to develop vaccines directed at the pre-erythrocytic developmental stages of Plasmodium, utilizing novel vaccination platforms. We here review the most promising pre-erythrocytic stage antimalarial vaccine candidates.

β-Carboline Derivatives Tackling Malaria: Biological Evaluation and Docking Analysis.

Increasing resistance to presently available antimalarial drugs urges the need to look for new promising compounds. The β-carboline moiety, present in several biologically active natural products and drugs, is an important scaffold for antimalarial drug discovery. The present study explores the antimalarial activity of a β-carboline derivative (1R,3S)-methyl 1-(benzo[d][1,3]dioxol-5-yl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylate (9a) alone in vitro against Plasmodium falciparum and in vivo in combination therapy with the standard drug artesunate against Plasmodium berghei. Compound 9a inhibited both 3D7 and RKL-9 strains of P. falciparum with half-maximal inhibitory concentration (IC50) < 1 μg/mL, respectively. The compound was nontoxic (50% cytotoxic concentration (CC50) > 640 μg/mL) to normal dermal fibroblasts. Selectivity index was >10 against both the strains. The compound exhibited considerable in vivo antimalarial activity (median effective dose (ED50) = 27.74 mg/kg) in monotherapy. The combination of 9a (100 mg/kg) and artesunate (50 mg/kg) resulted in 99.69% chemosuppression on day 5 along with a mean survival time of 25.8 ± 4.91 days with complete parasite clearance. Biochemical studies indicated the safety of the HIT compound to hepatic and renal functions of mice. Molecular docking also highlighted the suitability of 9a as a potential antimalarial candidate.

Morin, quercetin, catechin and quercitrin as novel natural antimalarial candidates

Morin, quercetin, catechin and quercitrin as novel natural antimalarial candidates

In vitro and in vivo evaluation of the antimalarial MMV665831 and structural analogs

Antimalarial candidates possessing novel mechanisms of action are needed to control drug resistant Plasmodium falciparum. We were drawn to Malaria Box compound 1 (MMV665831) by virtue of its excellent in vitro potency, and twelve analogs were prepared to probe its structure–activity relationship. Modulation of the diethyl amino group was fruitful, producing compound 25, which was twice as potent as 1 against cultured parasites. Efforts were made to modify the phenolic Mannich base functionality of 1, to prevent formation of a reactive quinone methide. Homologated analog 28 had reduced potency relative to 1, but still inhibited growth with EC50 ≤ 200 nM. Thus, the antimalarial activity of 1 does not derive from quinone methide formation. Chemical stability studies on dimethyl analog 2 showed remarkable hydrolytic stability of both the phenolic Mannich base and ethyl ester moieties, and 1 was evaluated for in vivo efficacy in P. berghei-infected mice (40 mg/kg, oral). Unfortunately, no reduction in parasitemia was seen relative to control. These results are discussed in the context of measured plasma and hepatocyte stabilities, with reference to structurally-related, orally-efficacious antimalarials.

Lipid Compositions in Infant Formulas Affect the Solubilization of Antimalarial Drugs Artefenomel (OZ439) and Ferroquine during Digestion.

Recent studies have shown that the solubilization of two antimalarial drug candidates, artefenomel (OZ439) and ferroquine (FQ), designed to provide a single-dose combination therapy for uncomplicated malaria can be enhanced using milk as a lipid-based formulation. However, milk as an excipient faces significant quality and regulatory hurdles. We therefore have investigated infant formula as a potential alternative formulation approach. The significance of the lipid species present in a formula with different lipid compositions upon the solubilization of OZ439 and FQ during digestion has been investigated. Synchrotron small-angle X-ray scattering was used to measure the diffraction from a dispersed drug during digestion and thereby determine the extent of drug solubilization. High-performance liquid chromatography was used to quantify the amount of drug partitioned into the digested lipid phases. Our results show that both the lipid species and the amount of lipids administered were key determinants for the solubilization of OZ439, while the solubilization of FQ was independent of the lipid composition. Infant formulas could therefore be designed and used as milk substitutes to tailor the desired level of drug solubilization while circumventing the variability of components in naturally derived milk. The enhanced solubilization of OZ439 was achieved during the digestion of medium-chain triacylglycerols (MCT), indicating the potential applicability of MCT-fortified infant formula powder as a lipid-based formulation for the oral delivery of OZ439 and FQ.

Heterologous Expression, Purification, and Functional Analysis of the Plasmodium falciparum Phosphatidylinositol 4-Kinase IIIβ.

Recently, we heterologously expressed, purified, and analyzed the function of the sole Plasmodium falciparum phosphatidylinositol 3-kinase (PI3K), found that the enzyme is a "class III" or "Vps34" PI3K, and found that it is irreversibly inhibited by Fe2+-mediated covalent, nonspecific interactions with the leading antimalarial drug, dihydroartemisinin [Hassett, M. R., et al. (2017) Biochemistry 56, 4335-4345]. One of several P. falciparum phosphatidylinositol 4-kinases [putative IIIβ isoform (PfPI4KIIIβ)] has generated similar interest as a druggable target; however, no validation of the mechanism of action for putative PfPI4K inhibitors has yet been possible due to the lack of purified PfPI4KIIIβ. We therefore codon optimized the pfpi4kIIIβ gene, successfully expressed the protein in yeast, and purified an N-lobe catalytic domain PfPI4KIIIβ protein. Using an enzyme-linked immunosorbent assay strategy previously perfected for analysis of PfPI3K (PfVps34), we measured the apparent initial rate, Km,app(ATP), and other enzyme characteristics and found full activity for the construct and that PfPI4KIIIβ activity is most consistent with the class IIIβ designation. Because several novel antimalarial drug candidates with different chemical scaffolds have been proposed to target PfPI4KIIIβ, we titrated enzyme inhibition for these candidates versus purified PfPI4KIIIβ and PfVps34. We also analyzed the activity versus purified PfPI4KIIIβ mutants previously expressed in P. falciparum selected for resistance to these drugs. Interestingly, we found that a putative PfPI4KIIIβ inhibitor currently in advanced trials (MMV390048; MMV '0048) is a potent inhibitor of both PfVps34 and PfPI4KIIIβ. These data are helpful for further preclinical optimization of an exciting new class of P. falciparum PI kinase inhibitor ("PfPIKi") antimalarial drugs.

Cytokine modulation during malaria infections by some medicinal plants

BackgroundMedicinal plants displaying both antimalarial and immunomodulatory mechanisms of action are better candidates for antimalarial drug development. The effects of aqueous leaf and stem bark extracts of Nauclea latifolia and Morinda lucida, and leaf extracts of Lawsonia inermis, Chromolaena odorataandTithonia diversifoliaon malaria immune responses and Plasmodium parasite were studied. MethodsInbred balb/c mice were treated with all extracts individually at 100 mg/kg. Initial cytokines measurements were determined from plasma samples of mice before exposure to plant extracts. Mice were treated for 3 days, and then infected with Plasmodium chabaudi chabaudi. Plasma samples were further collected on 3, 5, and 7 days post-infection and pro-inflammatory cytokines (IL-6, IFN-ɤ, IL-12p70 and TNF-α), Chemokine (MCP-1) and anti-inflammatory cytokine (IL-10) were quantified using flow cytometry. Extracts Percentage Chemoprophylaxis was determined. ResultsAfter treatment, M. lucida stem bark extract significantly stimulated both pro-inflammatory and anti-inflammatory cytokines, with percentage immunomodulatory activity of 69.6%, 87.2%, 38.3%, 81.4% and 45.0% for IL-6, MCP-1, IL-10, IL-12p70 and TNF-α respectively. On day 3 post-infection, N.latifolia stem bark extract significantly produced higher pro-inflammatory (IL-6, IL-12 and TNF-α) and anti-inflammatory (IL-10) cytokines when compared to control. M. lucida stem bark extract group further displayed lower values of IL-6, MCP-1, IFN-ɤ and TFN-α when compared to control at 3-day post-infection. T. diversifolia and L. inermis displayed delayed inflammatory responses. All extracts suppressed parasitaemia, and the highest percentage chemoprophylaxis of 71.9% and 70.5% was observed in N. latifolia and M. lucida stem barks treated groups. ConclusionThese suggest that the plants have immunomodulatory and antiplasmodial potentials and a few of them can be exploited as antimalarial drug candidates and adjuvants.

Nanoemulsion composed of 10-(4,5-dihydrothiazol-2-yl)thio)decan-1-ol), a synthetic analog of 3-alkylpiridine marine alkaloid: development, characterization, and antimalarial activity

Malaria treatment is based on a reduced number of antimalarial drugs, and drug resistance has emerged, leading to the search for new antimalarial drugs incorporated into pharmaceutical formulations. In this study, 10-(4,5-dihydrothiazol-2-yl)thio)decan-1-ol) (thiazoline), a synthetic analog of 3-alkylpiridine marine alkaloid, and a potent antimalarial substance, was incorporated into O/W nanoemulsion. This formulation was prepared by a 23 factorial design. It was characterized by globule diameter, polydispersity index, zeta potential, encapsulation efficiency, in vitro thiazoline release at pH 2 and 6.86, and accelerated stability. In vitro and in vivo antimalarial activity was determined against P. falciparum and P. berghei, respectively. Thiazoline nanoemulsion showed 248.8 nm of globule diameter, 0.236 of polydispersity index, -38.5 mV of zeta potential, 96.92% encapsulation efficiency, and it was stable for 6 months. Thiazoline release profiles differed in acidic and neutral media, but in both cases, the nanoemulsion controlled and prolonged the thiazoline delivery. Thiazoline nanoemulsion exerted in vitro antimalarial activity against the parasite (IC50 = 1.32 µM), and it significantly reduced the in vivo parasitemia for 8 days without increasing the survival time of animals. Therefore, the thiazoline nanoemulsion represents a strategy to treat malaria combining an antimalarial candidate and a new nanocarrier.

In silico, in vitro and in vivo evaluation of natural Bignoniaceous naphthoquinones in comparison with atovaquone targeting the selection of potential antimalarial candidates

The natural naphthoquinones lapachol, α- and β-lapachone are found in Bignoniaceous Brazilian plant species of the Tabebuia genus (synonym Handroanthus) and are recognized for diverse bioactivities, including as antimalarial. The aim of the present work was to perform in silico, in vitro and in vivo studies to evaluating the antimalarial potential of these three naphthoquinones in comparison with atovaquone, a synthetic antimalarial. The ADMET properties of these compounds were predicted in silico by the preADMET program. The in vitro toxicity assays were experimentally determined in immortalized and tumoral cells from different organs. In vivo acute oral toxicity was also evaluated for lapachol. Several favorable pharmacokinetics data were predicted although, as expected, high cytotoxicity was experimentally determined for β-lapachone. Lapachol was not cytotoxic or showed low cytotoxicity to all of the cells assayed (HepG2, A549, Neuro 2A, LLC-PK1, MRC-5), it was nontoxic in the acute oral test and disclosed the best parasite selectivity index in the in vitro assays against chloroquine resistant Plasmodium falciparum W2 strain. On the other hand, α- and β-lapachone were more potent than lapachol in the antiplasmodial assays but with low parasite selectivity due to their cytotoxicity. The diversity of data here reported disclosed lapachol as a promising candidate to antimalarial drug development.

Naphthylisoquinoline alkaloids, validated as hit multistage antiplasmodial natural products

The discovery and development of multistage antimalarial drugs targeting intra-erythrocytic asexual and sexual Plasmodium falciparum parasites is of utmost importance to achieve the ambitious goal of malaria elimination. Here, we report the validation of naphthylisoquinoline (NIQ) alkaloids and their synthetic analogues as multistage active antimalarial drug candidates. A total of 30 compounds were tested, of which 17 exhibited IC50 values <1 μM against drug-sensitive P. falciparum parasites (NF54 strain); 15 of these retained activity against a panel of drug-resistant strains. These compounds showed low in vitro cytotoxicity against HepG2 cells, with selectivity indices of >10. The tested compounds showed activity in vitro against both early- and late-stage P. falciparum gametocytes while blocking male gamete formation (>70% inhibition of exflagellation at 2 μM). Additionally, five selected compounds were found to have good solubility (≥170 μM in PBS at pH 6.5), while metabolic stability towards human, mouse, and rat microsomes ranged from >90% to >7% after 30 min. Dioncophylline C (2a) emerged as a front runner from the study, displaying activity against both asexual parasites and gametocytes, a lack of cross-resistance to chloroquine, good solubility, and microsomal stability. Overall, this is the first report on the multistage activity of NIQs and their synthetic analogues including gametocytocidal and gametocidal effects induced by this class of compounds.

In silico studies of 2,5-disubstituted furans as active antimalarial drug candidates

BackgrondIn silico studies are essential techniques in the modern medicinal chemistry. QSAR modeling and molecular docking are important techniques in both drug discovery and development and have been successfully deployed in the field of medicinal chemistry for the discovery, design, and development of many drug candidates. These techniques were used in this work to come up with a model that relate 2,5-disubstituted furans with their antiplasmodium activities for the development of more active antimalarial drugs.ResultsPredictive and robust QSAR model was generated using Genetic Function Algorithm. The model was statistically validated to have internal and external squared correlation coefficient, R2 of 0.982 and 0.735 respectively; predictive squared correlation coefficient, R2pred of 0.599; adjusted squared correlation coefficient, Radj of 0.974; and leave-one-out cross-validation coefficient, Q2cv of 0.966. It was found out that the antiplasmodium activities of 2,5-disubstituted furans relied on the parameters: GATS5c, minsCl RDF130m, RDF75p, and RDF115s descriptors. All the descriptors except minsCl influenced the antiplasmodium activities of the compounds negatively. That is, their increase decreases the activities of the furans and vice versa. The docking study revealed that most of the furans bind more tightly to Plasmodium falciparum lactate dehydrogenase (pfLDH) than chloroquine, but the enzyme may not be their major target.ConclusionInsight into the relationship between 2,5-disubstituted furans and their antiplasmodium activities has been revealed from the results of this work. Therefore, this could serve as a model for designing novel 2,5-disubstituted furans as potential antimalarial drugs with better activities.

Whole-Cell Phenotypic Screening of Medicines for Malaria Venture Pathogen Box Identifies Specific Inhibitors of Plasmodium falciparum Late-Stage Development and Egress.

We report a systematic, cellular phenotype-based antimalarial screening of the Medicines for Malaria Venture Pathogen Box collection, which facilitated the identification of specific blockers of late-stage intraerythrocytic development of Plasmodium falciparum First, from standard growth inhibition assays, we identified 173 molecules with antimalarial activity (50% effective concentration [EC50] ≤ 10 μM), which included 62 additional molecules over previously known antimalarial candidates from the Pathogen Box. We identified 90 molecules with EC50 of ≤1 μM, which had significant effect on the ring-trophozoite transition, while 9 molecules inhibited the trophozoite-schizont transition and 21 molecules inhibited the schizont-ring transition (with ≥50% parasites failing to proceed to the next stage) at 1 μM. We therefore rescreened all 173 molecules and validated hits in microscopy to prioritize 12 hits as selective blockers of the schizont-ring transition. Seven of these molecules inhibited the calcium ionophore-induced egress of Toxoplasma gondii, a related apicomplexan parasite, suggesting that the inhibitors may be acting via a conserved mechanism which could be further exploited for target identification studies. We demonstrate that two molecules, MMV020670 and MMV026356, identified as schizont inhibitors in our screens, induce the fragmentation of DNA in merozoites, thereby impairing their ability to egress and invade. Further mechanistic studies would facilitate the therapeutic exploitation of these molecules as broadly active inhibitors targeting late-stage development and egress of apicomplexan parasites relevant to human health.