Development Of New Antimalarial Drugs Research Articles

Pyrimidine Azepine Targets the Plasmodium bc 1 Complex and Displays Multistage Antimalarial Activity.

Malaria control and elimination efforts would benefit from the identification and validation of new malaria chemotherapeutics. Recently, a transgenic Plasmodium berghei line was used to perform a series of high-throughput in vitro screens for new antimalarials acting against the parasite sexual stages. The screens identified pyrimidine azepine chemotypes with potent activity. Here, we validate the activity of PyAz90, the most potent pyrimidine azepine chemotype identified, against P. falciparum and P. vivax in the asexual and sexual stages. PyAz90 blocked parasite transmission to the mosquito vector at nanomolar concentrations and inhibited in vitro asexual parasite multiplication with a fast-action profile. Through the generation of P. falciparum PyAz90-resistant parasites and in vitro assays of mitochondrial activity, we identified cytochrome b as a molecular target of PyAz90. This work characterizes a promising chemotype that can be explored for the future development of new antimalarials targeting the Plasmodium cytochrome bc 1 complex.

Exploration and characterization of the antimalarial activity of cyclopropyl carboxamides that target the mitochondrial protein, cytochrome b

Drug resistance against antimalarials is rendering them increasingly ineffective and so there is a need for the development of new antimalarials. To discover new antimalarial chemotypes a phenotypic screen of the Janssen Jumpstarter library against the P. falciparum asexual stage was undertaken, uncovering the cyclopropyl carboxamide structural hit class. Structure-activity analysis revealed that each structural moiety was largely resistant to change, although small changes led to the frontrunner compound, WJM280, which has potent asexual stage activity (EC50 40 nM) and no human cell cytotoxicity. Forward genetics uncovered that cyclopropyl carboxamide resistant parasites have mutations and an amplification in the cytochrome b gene. Cytochrome b was then verified as the target with profiling against cytochrome b drug-resistant parasites and a mitochondrial oxygen consumption assay. Accordingly, the cyclopropyl carboxamide class was shown to have slow-acting asexual stage activity and activity against male gametes and exoerythrocytic forms. Enhancing metabolic stability to attain efficacy in malaria mouse models remains a challenge in the future development of this antimalarial chemotype.

Antimalarial Mechanisms and Resistance Status of Artemisinin and Its Derivatives.

Artemisinin is an endoperoxide sesquiterpene lactone isolated from Artemisia annua and is often used to treat malaria. Artemisinin's peroxide bridge is the key structure behind its antimalarial action. Scientists have created dihydroartemisinin, artemether, artesunate, and other derivatives preserving artemisinin's peroxide bridge to increase its clinical utility value. Artemisinin compounds exhibit excellent efficacy, quick action, and minimal toxicity in malaria treatment and have greatly contributed to malaria control. With the wide and unreasonable application of artemisinin-based medicines, malaria parasites have developed artemisinin resistance, making malaria prevention and control increasingly challenging. Artemisinin-resistant Plasmodium strains have been found in many countries and regions. The mechanisms of antimalarials and artemisinin resistance are not well understood, making malaria prevention and control a serious challenge. Understanding the antimalarial and resistance mechanisms of artemisinin drugs helps develop novel antimalarials and guides the rational application of antimalarials to avoid the spread of resistance, which is conducive to malaria control and elimination efforts. This review will discuss the antimalarial mechanisms and resistance status of artemisinin and its derivatives, which will provide a reference for avoiding drug resistance and the research and development of new antimalarial drugs.

Disruption of Plasmodium falciparum kinetochore proteins destabilises the nexus between the centrosome equivalent and the mitotic apparatus

Plasmodium falciparum is the causative agent of malaria and remains a pathogen of global importance. Asexual blood stage replication, via a process called schizogony, is an important target for the development of new antimalarials. Here we use ultrastructure-expansion microscopy to probe the organisation of the chromosome-capturing kinetochores in relation to the mitotic spindle, the centriolar plaque, the centromeres and the apical organelles during schizont development. Conditional disruption of the kinetochore components, PfNDC80 and PfNuf2, is associated with aberrant mitotic spindle organisation, disruption of the centromere marker, CENH3 and impaired karyokinesis. Surprisingly, kinetochore disruption also leads to disengagement of the centrosome equivalent from the nuclear envelope. Severing the connection between the nucleus and the apical complex leads to the formation of merozoites lacking nuclei. Here, we show that correct assembly of the kinetochore/spindle complex plays a previously unrecognised role in positioning the nascent apical complex in developing P. falciparum merozoites.

Feasibility Study on the Development of New Antimalarial Drugs Using Halofuginone and its Derivatives

Feasibility Study on the Development of New Antimalarial Drugs Using Halofuginone and its Derivatives

Amodiaquine Nonspecifically Binds Double Stranded and Three-Way Junction DNA Structures.

The 4-aminoquinoline class of compounds includes the important antimalarial compounds amodiaquine and chloroquine. Despite their medicinal importance, the mode of action of these compounds is poorly understood. In a previous study we observed these compounds, as well as quinine and mefloquine, tightly bind the DNA cocaine-binding aptamer. Here, we further explore the range of nucleic acid structures bound by these compounds. To gauge a wide range of binding affinities, we used isothermal titration calorimetry to explore high affinity binding (nM to tens of μM) and NMR spectroscopy to assay weak binding biding in the hundreds of micromolar range. We find that amodiaquine tightly binds all double stranded DNA structures explored. Mefloquine binds double stranded DNA duplex molecules tightly and weakly associates with a three-way junction DNA construct. Quinine and chloroquine only weakly bind duplex DNA but do not tightly bind any of the DNA constructs explored. A simulation of the free energy of binding of these ligands to the Dickerson-Drew dodecamer resulted in an excellent agreement between the simulated and experimental free energy. These results provide new insight into the DNA binding of clinically important antimalarial compounds and may play a role in future development of new antimalarials.

Efficacy of Albizia malacophylla (A.Rich.) Walp. (Leguminosae) methanol (80%) leaf extract and solvent fractions against Plasmodium berghei-induced malaria in mice model

Ethnopharmacological relevanceNovel drugs are needed to address the issue of malarial infection resistance; natural items can be a different source of these medications. Albizia malacophylla (A. Rich.) Walp. (Leguminosae) is listed as one of the antimalarial medicinal plants in Ethiopian folk medicine. However, there are no reports regarding the biological activity or phytochemistry of the plant. Aim of the studyThus, this study aimed to evaluate the A. malacophylla crude extract and solvent fractions' in vivo antimalarial activity utilizing 4-day suppressive, preventative, and curative tests in mice infected with P. berghei. Materials and methodsThe parasite Plasmodium berghei, which causes rodent malaria, was used to infect healthy male Swiss Albino mice, weighing 23–28 g and aged 6–8 weeks. Solvent fractions such as methanol, water, and chloroform were given in addition to an 80% methanolic extract at 100, 200, and 400 mg/kg doses. A Conventional test such as parasitemia, survival time, body weight, temperature, and packed cell capacity were employed to ascertain factors such as the suppressive, curative, and preventive tests. ResultsEvery test substance dramatically reduced the number of parasites in every experiment. Crude extract (with the highest percentage suppression of 67.78%) performs better antimalarial effect than the methanol fraction, which is the most efficient solvent fraction with a percentage suppression of 55.74%. With a suppression value of 64.83% parasitemia level, the therapeutic effects of 80% methanolic crude extract were greater than its curative and preventative effects in a four-day suppressive test. The survival period (17 days) was longer with the hydroalcoholic crude extract dose of 400 mg/kg than with other doses of the materials under investigation. ConclusionsThe results of this investigation validate the antimalarial characteristics of A. malacophylla leaf extract. The crude extract prevented weight loss, a decline in temperature, and a reduction in PCV. The results demonstrate that the plant has a promising antimalarial effect against P. berghei, hence supporting the traditional use of the plant. Therefore, it could serve as a foundation for the development of new antimalarial drugs.

In Vitro Analysis of Antimalarial Activity of Achillea fragrantissima (Forssk.) Sch.Bip Extracts Based on Beta-Hematin Formation

Introduction: The use of medicinal plants from traditional knowledge systems has increased in recent years. Achillea fragrantissima-infused water has a historical use in relieving gastrointestinal complaints and treating skin inflammations. With the rising resistance to antimalarial drugs, finding safe and affordable new drugs is crucial. Exploring medicinal plants shows promise for drug development in the fight against malaria. Methods: The objective of this research is to examine the in vitro antimalarial activity of A. fragrantissima-infused water, as well as water-ethanol extracts of its leaves, flowers, and stems based on β-hematin formation. Colorimetric semiquantitative assessments based on β-hematin inhibition and evaluation of optical density at 405 nm were employed. Results: The results demonstrated promising antimalarial activity of the different plant parts. The aqueous flower extract exhibited strong activity, comparable to that of the positive control. The leaves extract also showed strong antimalarial activity. The stem's aqueous and ethanolic extracts exhibited lower inhibitory activity compared to flowers and leaves. Synergistic antimalarial activity was observed when mixing the stem and leaves water extracts, as well as when mixing each of the stem and leaves extracts with the flower extract. The highest synergistic effect was observed when all three parts of the plant were mixed, resulting in activity comparable to the positive control. The high-performance liquid chromatography photodiode array (HPLC-PDA) chromatographic method confirmed the presence of rutin in the leaves extract. Conclusion: The findings of this study highlight the potential antimalarial activity of A. fragrantissima. The aqueous flower extract and leaves extract exhibited strong antimalarial activity, while the stem extracts showed relatively lower activity. Furthermore, synergistic effects were observed when combining different parts of the plant. These results suggest that A. fragrantissima holds promise as a potential source for the development of new antimalarial drugs. The confirmation of rutin presence in the leaves extract through HPLC-PDA analysis provides additional insights into the plant's chemical composition.

In silico prediction and in vitro assessment of novel heterocyclics with antimalarial activity

The development of new antimalarials is paramount to keep the goals on reduction of malaria cases in endemic regions. The search for quality hits has been challenging as many inhibitory molecules may not progress to the next development stage. The aim of this work was to screen an in-house library of heterocyclic compounds (HCUV) for antimalarial activity combining computational predictions and phenotypic techniques to find quality hits. The physicochemical determinants, pharmacokinetic properties (ADME), and drug-likeness of HCUV were evaluated in silico, and compounds were selected for structure-based virtual screening and in vitro analysis. Seven Plasmodium target proteins were selected from the DrugBank Database, and ligands and receptors were processed using UCSF Chimera and Open Babel before being subjected to docking using Autodock Vina and Autodock 4. Growth inhibition of P. falciparum (3D7) cultures was tested by SYBR Green assays, and toxicity was assessed using hemolytic activity tests and the Galleria mellonella in vivo model. From a total of 792 compounds, 341 with good ADME properties, drug-likeness, and no interference structures were subjected to in vitro analysis. Eight compounds showed IC50 ranging from 0.175 to 0.990 µM, and active compounds included pyridyl-diaminopyrimido-diazepines, pyridyl-N-acetyl- and pyridyl-N-phenyl-pyrazoline derivatives. The most potent compound (UV802, IC50 0.178 µM) showed no toxicophoric and was predicted to interact with P. falciparum 1-cysperoxidredoxin (PfPrx1). For the remaining 7 hits (IC50 < 1 μM), 3 showed in silico binding to PfPrx1, one was predicted to bind the haloacid dehalogenase-like hydrolase and plasmepsin II, and one interacted with the plasmodial heat shock protein 90.

In vitro antiplasmodial activity, LC-MS analysis, and molecular docking studies of bioactive compounds from Tetrapleura tetraptera (Fabaceae) fruits

Malaria continues to be a major public health concern, particularly for children and pregnant women in areas where the disease is endemic. Developing safe and efficient antimalarial therapies to fight the disease is essential. Medicinal plants represent a potential source for the development of new antimalarial drugs. Tetrapleura tetraptera is a plant native to West Africa and traditionally used to treat several diseases including Malaria. Here, we investigated the antiplasmodial activities of T. tetraptera fruit extracts against the chloroquine-sensitive (Pf3D7) and chloroquine-resistant (PfDD2) strains of Plasmodium falciparum in vitro using SYBR green assay. In addition, the antioxidant potential of the fruit extracts was also determined. LC-MS analysis was carried out to identify the bioactive compounds in the extracts. Molecular docking studies provide significant prima facie evidence of inhibition hence, to evaluate the potential inhibition of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH), a validated malaria drug target, the identified compounds were docked against PfDHODH. Strong antiplasmodial activities were demonstrated by the ethyl acetate and ethanolic extracts of T. tetraptera fruit, with IC50 values of 16.12 ± 0.04 µg/mL and 2.06 ± 0.02 µg/mL against the Pf3D7 strain, respectively. In the DPPH radical scavenging experiment, the ethanolic extract revealed considerable antioxidant activity with an EC50 value of 0.21 ± 0.82 mg/mL. Seven bioactive compounds were identified in the extract using LC-MS analysis. N-Methyl-1H-indole-3-propanamide (I), Tazolol (II), and Isopentyl salicylate (III) were identified as potential inhibitors of PfDHODH with high binding affinities ranging from -32.08 to -30.69 kcal/mol. The potential lead compounds also interacted with Gly181, Leu531, and Arg265, which are critical amino acid residues in the catalytic activity of PfDHODH. These findings support the traditional use of T. tetraptera fruit extracts for the treatment of malaria and as promising avenues for antimalarial drug development.

Terpenoids from Euphorbiaceae as a source of antimalarial medicines: A literature review

Background: Malaria is an infectious disease caused by the Plasmodium parasite and transmitted by the Anopheles mosquito. Plasmodium falciparum is a parasite that causes the most deaths. Currently, there is resistance to various antimalarial drugs. For this reason, it is necessary to search for new antimalarial agents. Medicinal plants have been shown to play an important role in treating malaria for thousands of years. Some of Euphorbiaceae family plants contains terpenoid compounds, which are compounds with antimalarial activity. Objective: The present review aims to provide an overview of the terpenoid compounds from Euphorbiaceae family as an antimalarial. Method: Comprehensive information on Euphorbiaceae family from 2002-2022 was searched for literature relevant to major science-based data, including Scopus, Science, ScienceDirect, Pubmed, and SciFinder, using appropriate keyword combinations. Result: A total of 15 papers were included in this review. The terpenoids isolated from 14 species of Euphorbiaceae family and reported to possess antimalarial activity are presented. Conclusion: Terpenoids are found in almost all parts of Euphorbiaceae family plants and are reported to have moderate to high antimalarial activity. Screening of antimalarial terpenoid activity in Ephorbiaceae family plants can be a key step in the source and development of new antimalarial drugs.

Leveraging off higher plant phylogenetic insights for antiplasmodial drug discovery

The antimalarial drug-resistance conundrum which threatens to reverse the great strides taken to curb the malaria scourge warrants an urgent need to find novel chemical scaffolds to serve as templates for the development of new antimalarial drugs. Plants represent a viable alternative source for the discovery of unique potential antiplasmodial chemical scaffolds. To expedite the discovery of new antiplasmodial compounds from plants, the aim of this study was to use phylogenetic analysis to identify higher plant orders and families that can be rationally prioritised for antimalarial drug discovery. We queried the PubMed database for publications documenting antiplasmodial properties of natural compounds isolated from higher plants. Thereafter, we manually collated compounds reported along with plant species of origin and relevant pharmacological data. We systematically assigned antiplasmodial-associated plant species into recognised families and orders, and then computed the resistance index, selectivity index and physicochemical properties of the compounds from each taxonomic group. Correlating the generated phylogenetic trees and the biological data of each clade allowed for the identification of 3 ‘hot’ plant orders and families. The top 3 ranked plant orders were the (i) Caryophyllales, (ii) Buxales, and (iii) Chloranthales. The top 3 ranked plant families were the (i) Ancistrocladaceae, (ii) Simaroubaceae, and (iii) Buxaceae. The highly active natural compounds (IC50 ≤ 1 µM) isolated from these plant orders and families are structurally unique to the ‘legacy’ antimalarial drugs. Our study was able to identify the most prolific taxa at order and family rank that we propose be prioritised in the search for potent, safe and drug-like antimalarial molecules.

Steroids from Toona sureni-derived Endophytic Fungi Stemphylium sp. MAFF 241962 and Their Heme Polymerization Inhibition Activity

Abstract Antimalarial drug resistance is a major cause of the increasing incidence of malaria worldwide, necessitating an urgent demand for the development of new antimalarial drugs. However, the availability of bioactive natural compounds derived from plants is often limited. To address this issue, continuous exploration of bioactive secondary metabolites from endophytic fungi derived from medicinal plants has been recognized as a viable alternative. Therefore, this research aimed to isolate and characterize three ergosteroids, namely isocyathisterol (1), ergosterol-5,8-peroxide (3), cerevisterol (4), and a phytosterol, β-sitosterol (2), from the rice cultures of endophytic fungus Stemphylium sp. MAFF 241962, derived from Toona sureni. Endophytic fungi species were determined using molecular analysis of the internal transcribed region (ITS) of the ribosomal DNA. After comparing the sequence data to the NCBI database using BLAST, endophytic fungi were identified as Stemphylium sp. 241962 with 100% similarity. The chemical structures were elucidated using spectroscopic methods, including 1D and 2D NMR. Antimalarial activities of compounds 1-4 were evaluated using heme polymerization inhibition activity (HPIA) method. The results showed moderate inhibition activities with IC50 values of 7.70 ± 0.11, 9.48 ± 0.09, 7.88 ± 0.10, and 8.36 ± 0.56 mg/mL, respectively, compared to positive control chloroquine diphosphate with IC50 values of 1.59 ± 0.03 mg/mL. Keywords: Steroid, Stemphylium sp., Toona sureni, Antimalarial activity, Heme polymerization inhibition

Novel Therapeutics for Malaria.

Malaria is a potentially fatal disease caused by protozoan parasites of the genus Plasmodium. It is responsible for significant morbidity and mortality in endemic countries of the tropical and subtropical world, particularly in Africa, Southeast Asia, and South America. It is estimated that 247 million malaria cases and 619,000 deaths occurred in 2021 alone. The World Health Organization's (WHO) global initiative aims to reduce the burden of disease but has been massively challenged by the emergence of parasitic strains resistant to traditional and emerging antimalarial therapy. Therefore, development of new antimalarial drugs with novel mechanisms of action that overcome resistance in a safe and efficacious manner is urgently needed. Based on the evolving understanding of the physiology of Plasmodium, identification of potential targets for drug intervention has been made in recent years, resulting in more than 10 unique potential anti-malaria drugs added to the pipeline for clinical development. This review article will focus on current therapies as well as novel targets and therapeutics against malaria.

Ganaplacide plus lumefantrine solid dispersion formulation: considerations for development and rollout

Due to reliance on antimalarials for clinical case management, drug resistance is a recurrent challenge for malaria control and elimination that requires relentless discovery and development of novel medicines with new modes of action. 1 Feachem RGA Chen I Akbari O et al. Malaria eradication within a generation: ambitious, achievable, and necessary. Lancet. 2019; 394: 1056-1112 Summary Full Text Full Text PDF PubMed Scopus (167) Google Scholar Since the widespread use of chloroquine in the 1950s, resistance has compromised the efficacy of all major classes of antimalarial drugs that are widely used to treat Plasmodium falciparum. These drugs include sulfadoxine–pyrimethamine and since 2007, 2 Fairhurst RM Dondorp AM Artemisinin-resistant Plasmodium falciparum malaria. Microbiol Spectr. 2016; 4 (10.1128/microbiolspec.EI10-0013-2016.) Crossref PubMed Scopus (174) Google Scholar artemisinin-class medicines and partner drugs, which have been crucial for preventing deaths from malaria in the past two decades. 1 Feachem RGA Chen I Akbari O et al. Malaria eradication within a generation: ambitious, achievable, and necessary. Lancet. 2019; 394: 1056-1112 Summary Full Text Full Text PDF PubMed Scopus (167) Google Scholar , 3 Ishengoma DS Saidi Q Sibley CH Roper C Alifrangis M Deployment and utilization of next-generation sequencing of Plasmodium falciparum to guide anti-malarial drug policy decisions in sub-Saharan Africa: opportunities and challenges. Malar J. 2019; 18: 267 Crossref PubMed Scopus (15) Google Scholar Partial resistance to artemisinin-based combinations threatens their efficacy throughout southeast Asia, and is now emerging rapidly in sub-Saharan Africa. 4 Rosenthal PJ Has artemisinin resistance emerged in Africa?. Lancet Infect Dis. 2021; 21: 1056-1057 Summary Full Text Full Text PDF PubMed Scopus (0) Google Scholar Although complete resistance has not yet been documented, this risk would be disastrous, necessitating urgent development of new antimalarial drugs that are effective against artemisinin-resistant parasites. Ganaplacide (KAF156) plus lumefantrine solid dispersion formulation combination for uncomplicated Plasmodium falciparum malaria: an open-label, multicentre, parallel-group, randomised, controlled, phase 2 trialGanaplacide plus lumefantrine-SDF was effective and well tolerated in patients, especially adults and adolescents, with uncomplicated P falciparum malaria. Ganaplacide 400 mg plus lumefantrine-SDF 960 mg once daily for 3 days was identified as the optimal treatment regimen for adults, adolescents, and children. This combination is being evaluated further in a phase 2 trial ( NCT04546633 ). Full-Text PDF

In silico screening, synthesis, and antimalarial evaluation of PABA substituted 1,3,5-triazine derivatives as Pf-DHFR inhibitors

ObjectivesDrug resistance in malaria parasites necessitates the development of new antimalarial drugs with unique mechanisms of action. In the present research work, the PABA conjugated 1,3,5-triazine derivatives were designed as an antimalarial agent. MethodsIn this present work, a library of two hundred-seven compounds was prepared in twelve different series such as [4A (1-23), 4B(1-22), 4C(1-21), 4D(1-20), 4E(1-19), 4F(1-18), 4G(1-17), 4H(1-16), 4I(1-15), 4J(1-13), 4K(1-12) and 4L(1-11) ] respectively using different primary and secondary aliphatic and aromatic amines. Ten compounds were ultimately selected through in silico screening. They were synthesized by conventional and microwave-assisted methods followed by in vitro antimalarial evaluations performed in chloroquine-sensitive (3D7) and resistant (DD2) strains of P. falciparum. ResultsThe docking results showed that compound 4C(11) had good binding interaction with Phe116, Met55 (−464.70 kcal/mol) and Phe116, Ser111 (−432.60 kcal/mol) against wild (1J3I) and quadruple mutant (1J3K) type of Pf-DHFR. Furthermore, in vitro, antimalarial activity results indicated that compound 4C(11) showed potent antimalarial activity against chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2) strain of P. falciparum along with IC50 (14.90 μg mL−1) and (8.30 μg mL−1). ConclusionThese PABA-substituted 1,3,5-triazine compounds could be exploited to develop a new class of Pf-DHFR inhibitors as a lead candidate.

Susceptibility of Ugandan Plasmodium falciparum Isolates to the Antimalarial Drug Pipeline.

Malaria, especially Plasmodium falciparum infection, remains an enormous problem, and its treatment and control are seriously challenged by drug resistance. New antimalarial drugs are needed. To characterize the Medicines for Malaria Venture pipeline of antimalarials under development, we assessed the ex vivo drug susceptibilities to 19 compounds targeting or potentially impacted by mutations in P. falciparum ABC transporter I family member 1, acetyl-CoA synthetase, cytochrome b, dihydroorotate dehydrogenase, elongation factor 2, lysyl-tRNA synthetase, phenylalanyl-tRNA synthetase, plasmepsin X, prodrug activation and resistance esterase, and V-type H+ ATPase of 998 fresh P. falciparum clinical isolates collected in eastern Uganda from 2015 to 2022. Drug susceptibilities were assessed by 72-h growth inhibition (half-maximum inhibitory concentration [IC50]) assays using SYBR green. Field isolates were highly susceptible to lead antimalarials, with low- to midnanomolar median IC50s, near values previously reported for laboratory strains, for all tested compounds. However, outliers with decreased susceptibilities were identified. Positive correlations between IC50 results were seen for compounds with shared targets. We sequenced genes encoding presumed targets to characterize sequence diversity, search for polymorphisms previously selected with in vitro drug pressure, and determine genotype-phenotype associations. We identified many polymorphisms in target genes, generally in <10% of isolates, but none were those previously selected in vitro with drug pressure, and none were associated with significantly decreased ex vivo drug susceptibility. Overall, Ugandan P. falciparum isolates were highly susceptible to 19 compounds under development as next-generation antimalarials, consistent with a lack of preexisting or novel resistance-conferring mutations in circulating Ugandan parasites. IMPORTANCE Drug resistance necessitates the development of new antimalarial drugs. It is important to assess the activities of compounds under development against parasites now causing disease in Africa, where most malaria cases occur, and to determine if mutations in these parasites may limit the efficacies of new agents. We found that African isolates were generally highly susceptible to the 19 studied lead antimalarials. Sequencing of the presumed drug targets identified multiple mutations in these genes, but these mutations were generally not associated with decreased antimalarial activity. These results offer confidence that the activities of the tested antimalarial compounds now under development will not be limited by preexisting resistance-mediating mutations in African malaria parasites.

In silico screening of phytochemicals from Dissotis rotundifolia against Plasmodium falciparum Dihydrofolate Reductase

BackgroundMalaria remains a major health concern in developing countries with high morbidity and mortality, especially in pregnant women and infants. A major obstacle to the treatment of malaria is a low effectiveness and an increase resistance of the parasite to antimalarial drugs. As a result, there is an ongoing demand for new and potent antimalarial drugs. Medicinal plants remain a potential source for the development of new antimalarial drugs. Amongst them is Dissotis rotundifolia is an ethnomedical important plant used in West Africa to treat malaria. PurposeThis study aimed at identifying new potential antifolates by virtually screening phytochemicals characterized from the whole plant methanolic extract of D. rotundifolia against Plasmodium falciparum Dihydrofolate Reductase (PfDHFR). MethodsLC-ESI-Q-TOF-MS analysis was employed to identify the phytochemicals present in the whole plant methanolic extract of D. rotundifolia. These phytochemicals were docked against the catalytic site of PfDHFR. The docking protocol was evaluated using the Area Under the Curve (AUC) of a Receiver Operating Characteristic (ROC) curve. The binding mechanisms and the drug-likeness of the phytochemicals were characterized. A 100 ns Molecular Dynamics (MD) simulation and Molecular Mechanics-Poisson Boltzmann Surface Area (MM-PBSA) calculations were utilized to analyze the stability, the energy decomposition per residue and the binding free energy of the potential leads. ResultsTwenty nine phytochemicals were characterized and docked against PfDHFR. Dimethylmatairesinol, flavodic acid, sakuranetin, and sesartemin were identified as potential leads with binding affinities of -8.4, -8.9, -8.6, and -8.9 kcal/mol respectively, greater than a stringent threshold of -8.0 kcal/mol. The potential leads also interacted hydrophobically with critical residue Phe58. A novel critical residue, Leu46 was identified to be crucial in the catalytic activity of PfDHFR. The potential leads were also predicted to be anti-protozoal with a probability of active (Pa) value ranging from 0.319 to 0.537. ConclusionThis study elucidates the potential inhibition of PfDHFR by dimethylmatairesinol, flavodic acid, sakuranetin and sesartemin present in D. rotundifolia. These compounds are druglike, do not violate Lipinski's rule of five, have a high binding affinity to PfDHFR, and interact with crucial residues involved in the catalytic activity PfDHFR. Dimethylmatairesinol, flavodic acid, sakuranetin and sesartemin could therefore be further investigated and developed as new antifolate drugs for malaria.

Novel Transmission-Blocking Antimalarials Identified by High-Throughput Screening of Plasmodium berghei Ookluc.

Safe and effective malaria transmission-blocking chemotherapeutics would allow a community-level approach to malaria control and eradication efforts by targeting the mosquito sexual stage of the parasite life cycle. However, only a single drug, primaquine, is currently approved for use in reducing transmission, and drug toxicity limits its widespread implementation. To address this limitation in antimalarial chemotherapeutics, we used a recently developed transgenic Plasmodium berghei line, Ookluc, to perform a series of high-throughput in vitro screens for compounds that inhibit parasite fertilization, the initial step of parasite development within the mosquito. Screens of antimalarial compounds, approved drug collections, and drug-like molecule libraries identified 185 compounds that inhibit parasite maturation to the zygote form. Seven compounds were further characterized to block gametocyte activation or to be cytotoxic to formed zygotes. These were further validated in mosquito membrane-feeding assays using Plasmodium falciparum and P. vivax. This work demonstrates that high-throughput screens using the Ookluc line can identify compounds that are active against the two most relevant human Plasmodium species and provides a list of compounds that can be explored for the development of new antimalarials to block transmission.

7-N-Substituted-3-oxadiazole Quinolones with Potent Antimalarial Activity Target the Cytochrome bc1 Complex.

The development of new antimalarials is required because of the threat of resistance to current antimalarial therapies. To discover new antimalarial chemotypes, we screened the Janssen Jumpstarter library against the P. falciparum asexual parasite and identified the 7-N-substituted-3-oxadiazole quinolone hit class. We established the structure-activity relationship and optimized the antimalarial potency. The optimized analog WJM228 (17) showed robust metabolic stability in vitro, although the aqueous solubility was limited. Forward genetic resistance studies uncovered that WJM228 targets the Qo site of cytochrome b (cyt b), an important component of the mitochondrial electron transport chain (ETC) that is essential for pyrimidine biosynthesis and an established antimalarial target. Profiling against drug-resistant parasites confirmed that WJM228 confers resistance to the Qo site but not Qi site mutations, and in a biosensor assay, it was shown to impact the ETC via inhibition of cyt b. Consistent with other cyt b targeted antimalarials, WJM228 prevented pre-erythrocytic parasite and male gamete development and reduced asexual parasitemia in a P. berghei mouse model of malaria. Correcting the limited aqueous solubility and the high susceptibility to cyt b Qo site resistant parasites found in the clinic will be major obstacles in the future development of the 3-oxadiazole quinolone antimalarial class.