Nanotechnology and malaria: Evaluation of efficacy and toxicity of green nanoparticles and future perspectives.

Malaria is a global health problem that causes 1.5-2.7 million deaths worldwide each year. Resistance to antimalarial drugs in malaria parasites and to insecticides in vectors is one of the most serious issues in the fight against this disease. Moreover, the lack of an effective vaccine against malaria is still a major problem. Recent developments in nanotechnology have resulted in new prospects for the fight against malaria, especially by obtaining metal nanoparticles (NPs) that are less toxic, highly biocompatible, environmentally friendly, and less expensive. Numerous studies have been conducted on the synthesis of green NPs using plants and microorganisms (bacteria, fungi, algae, actinomycetes, and viruses). To our knowledge, there is no literature review that compares toxicities and antimalarial effects of some of the existing metallic nanoparticles, revealing their advantages and disadvantages. Hence, the purpose of this work is to assess metal NPs obtained through various green synthesis processes, to display the worth of future malaria research and determine future strategies. Results revealed that there are very few studies on green NPs covering all stages of malaria parasites. Additionally, green metal nanoparticles have yet to be studied for their possible toxic effects on infected as well as healthy erythrocytes. Morever, the toxicities of green metal NPs obtained from various sources differed according to concentration, size, shape, synthesis method, and surface charge, indicating the necessity of optimizing the methods to be used in future studies. It was concluded that studies on the toxic properties of green nanoparticles would be very important for the future.

CHLOROQUINE INDUCED LESIONS IN LIVER OF ALBINO MICE.

A study was carried out to demonstrate the effects of chloroquine on liver of developing albino rats. In this study, 20 white albino mice were used, and distributed in 2 groups. They were kept in the animal house of the College of Veterinary Medicine, their ages ranged between (4-3) months and they were in good health. The first group (G1) was considered a control group, this group included 10 mice who were given regular food in addition to sterilized water daily for a period of (30) days, the second group (G2) included 10 mice, they were given food and water with chloroquine after mixing it in 1ml of distilled water at a dose of 1.2 mg/kg/day for each animal orally for a period of 30 days, it was found that chloroquine induced toxicity in liver tissue of albino mice which were exposed to chloroquine drug for longer during their life. Histological sections of stomach revealed that degenerative cases were present in the mucosa of it and the gastric glands also demonstrated sloughing of its mucus cells, and histological sections of small intestine indicated that the degenerative changes were present in the mucosa and submucosa reflected by sloughing of certain villi and the intestinal glands were also affected, lymphocytic infiltration was present in between the intestinal glands with plasma cells. The present study indicated that the liver tissue was affected by drug used via effect on the histological structure, as there was hypertrophy and degeneration of liver cells, hypertrophy of Kupffer cells in the blood sinusoids.

An innovative study design with intermittent dosing to generate a GLP-regulatory package in preclinical species for long lasting molecule M5717, inhibitor of Plasmodium eukaryotic translation elongation factor 2.

M5717 is a novel drug inhibiting synthesis of elongation factor 2 (PeEF2) in Plasmodium species, showing potent anti-malarial activity in preclinical studies. Traditional daily-dosing animal experiments estimating maximum safe starting dose for a first-in-human study ('no observed adverse effect level'; NOAEL) were unsuccessful due to the long pharmacokinetic half-life of M5717, causing significant drug accumulation and high exposure. This study describes an innovative strategy to produce a GLP-certified toxicology package and estimate NOAEL for long-lasting molecules like M5717. Simulated pharmacokinetic/toxicokinetic profiles were used to design the dosing schedule for preclinical safety studies and to determine the 14-day total exposure. Animals (rats/dogs) were administered various doses of M5717 using an intermittent dosing schedule allowing partial drug elimination and alleviation of toxicity during off-treatment days to maintain a minimal parasitical concentration (MPC) of 10 ng/mL; subsequently animals were monitored for toxicity and mortality. Results showed good correlation to the modelled data used to design the dosing regimen and required MPC was reached for M5717 in study animals and could be used to calculate NOAEL. This fit-for-purpose study design allowed for maintaining clinically relevant exposure to M5717, whilst minimizing toxicity-causing compound accumulation, an aspect unaddressed by traditional NOAEL-estimating experiments. This is the first time that a compound-specific, species-specific, kinetic model-based approach to preclinical study design for regulatory toxicology studies has been described and applied to an antimalarial drug candidate with long pharmacokinetic half-life. It has potential for application to other drugs with long half-lives, supporting their clinical development.

Structure- and function-based design of Plasmodium-selective proteasome inhibitors.

The proteasome is a multi-component protease complex responsible for regulating key processes such as the cell cycle and antigen presentation. Compounds that target the proteasome are potentially valuable tools for the treatment of pathogens that depend on proteasome function for survival and replication. In particular, proteasome inhibitors have been shown to be toxic for the malaria parasite Plasmodium falciparum at all stages of its life cycle. Most compounds that have been tested against the parasite also inhibit the mammalian proteasome, resulting in toxicity that precludes their use as therapeutic agents. Therefore, better definition of the substrate specificity and structural properties of the Plasmodium proteasome could enable the development of compounds with sufficient selectivity to allow their use as anti-malarial agents. To accomplish this goal, here we use a substrate profiling method to uncover differences in the specificities of the human and P. falciparum proteasome. We design inhibitors based on amino-acid preferences specific to the parasite proteasome, and find that they preferentially inhibit the ß2-subunit. We determine the structure of the P. falciparum 20S proteasome bound to the inhibitor using cryo-electron microscopy and single-particle analysis, to a resolution of 3.6 Å. These data reveal the unusually open P. falciparum ß2 active site and provide valuable information about active-site architecture that can be used to further refine inhibitor design. Furthermore, consistent with the recent finding that the proteasome is important for stress pathways associated with resistance of artemisinin family anti-malarials, we observe growth inhibition synergism with low doses of this ß2-selective inhibitor in artemisinin-sensitive and -resistant parasites. Finally, we demonstrate that a parasite-selective inhibitor could be used to attenuate parasite growth in vivo without appreciable toxicity to the host. Thus, the Plasmodium proteasome is a chemically tractable target that could be exploited by next-generation anti-malarial agents.

Antiplasmodial activity of alkaloids from Croton linearis leaves.

Croton linearis is a shrub that grows in Caribbean regions, which is rich in metabolites such as alkaloids. The main aim of this study was to evaluate the antiplasmodial effect of alkaloids from this species. Three isoquinoline alkaloids, i.e. reticuline (1), laudanidine (2) and 8,14-dihydrosalutaridine (3), were isolated from the leaves of C. linearis by flash chromatography and semi-preparative HPLC-DAD-MS. Their structures were elucidated by spectroscopic techniques. Antiplasmodial activity against the chloroquine-resistant strain Plasmodium falciparum K1 and cytotoxicity against MRC-5 cells (human fetal lung fibroblast cells) were assessed in vitro. Reticuline, laudanidine and 8,14-dihydrosalutaridine showed moderate antiplasmodial activity with IC50 values of 46.8 ± 0.6, 17.7 ± 0.6 and 16.0 ± 0.5 µM, respectively, but no cytotoxicity was observed in a concentration up to 64.0 µM. This is the first report on the antiplasmodial activity of laudanidine and 8,14-dihydrosalutaridine.

Acute and subacute oral toxicity of artemisinin-hydroxychloroquine sulfate tablets in rats.

Artemisinin-hydroxychloroquine sulfate tablets (AH) are considered a relatively inexpensive and novel combination therapy for treating all forms of malaria, especially aminoquinoline drugs-resistant strains of P.falciparum. We aim to carry out acute and subacute oral toxicity studies in rats to acquire preclinical data on the safety of AH. Acute toxicity was evaluated in Sprague-Dawley (SD) rats at a single dose of 1980, 2970, 4450, 6670, and 10000 mg/kg. A 14-days subacute toxicity was assessed in SD rats at doses of 0, 146, 219, 328, and 429 mg/kg. The median lethal dose (LD50) of acute oral administration of AH in rats is found to be 3119 mg/kg, and toxic symptoms include decreased spontaneous activity, dyspnea, bristling, soft feces, spasticity, and convulsion. Repeated doses of AH have toxic effects on the nervous system, skin, blood system, liver, kidney, and spleen in rats. The main toxic reactions include epilation, emaciation, mental irritability, decreased body weight gain and food consumption, changes in the hematological and biochemical parameters, especially pathological lesions in the liver, kidney, and spleen. The no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) of AH are considered to be 219 mg/kg and 328 mg/kg, respectively.

Review of the mechanism underlying mefloquine-induced neurotoxicity.

Mefloquine, a potent blood schizontocide, is effective against drug-resistant Plasmodium falciparum. This property, along with its unique pharmacokinetic profile, makes mefloquine a widely prescribed antimalarial drug. However, several epidemiological studies have raised concerns on the safety of mefloquine as prophylaxis for malaria. Well-documented side-effects of mefloquine include abnormal dreams, insomnia, anxiety, and depressed mood, as well as nausea and dizziness (the last two most frequent effects). The mechanisms that underlie the neurological/psychiatric complications of mefloquine are poorly understood. The aim of this study was to review the literature on the neurotoxic mechanisms of action of mefloquine to better understand its potential toxicity in the central nervous system, highlighting the mechanisms that lead to its psychiatric disorders. Experimental studies on the neurotoxic effects of mefloquine discussed herein include brain transporters of mefloquine, alteration in neurotransmitters, disruption on calcium (Ca2+) homeostasis and neuroinflammation, generation of oxidative stress response in neurons (involving glutathione, increased F2-isoprostanes, accumulation of cytosolic lipid globules), and alteration of voltage-dependent channels, as well as gap junction intercellular communications. Although several hypotheses have been proposed for the mechanisms that mediate mefloquine-induced brain damage, they are not fully understood, necessitating additional studies in the future.

Preclinical evaluation of strasseriolides A-D, potent antiplasmodial macrolides isolated from Strasseria geniculata CF-247,251.

BACKGROUND: Malaria is a global health problem for which novel therapeutic compounds are needed. To this end, a recently published novel family of antiplasmodial macrolides, strasseriolides A-D, was herein subjected to in vivo efficacy studies and preclinical evaluation in order to identify the most promising candidate(s) for further development. METHODS: Preclinical evaluation of strasseriolides A-D was performed by MTT-based cytotoxicity assay in THLE-2 (CRL-2706) liver cells, cardiotoxicity screening using the FluxOR™ potassium assay in hERG expressed HEK cells, LC-MS-based analysis of drug-drug interaction involving CYP3A4, CYP2D6 and CYP2C9 isoforms inhibition and metabolic stability assays in human liver microsomes. Mice in vivo toxicity studies were also accomplished by i.v. administration of the compounds (vehicle: 0.5% HPMC, 0.5% Tween 80, 0.5% Benzyl alcohol) in mice at 25 mg/kg dosage. Plasma were prepared from mice blood samples obtained at different time points (over a 24-h period), and analysed by LC-MS to quantify compounds. The most promising compounds, strasseriolides C and D, were subjected to a preliminary in vivo efficacy study in which transgenic GFP-luciferase expressing Plasmodium berghei strain ANKA-infected Swiss Webster female mice (n = 4-5) were treated 48 h post-infection with an i.p. dosage of strasseriolide C at 50 mg/kg and strasseriolide D at 22 mg/kg for four days after which luciferase activity was quantified on day 5 in an IVIS® Lumina II imager. RESULTS: Strasseriolides A-D showed no cytotoxicity, no carditoxicity and no drug-drug interaction problems in vitro with varying intrinsic clearance (CLint). Only strasseriolide B was highly toxic to mice in vivo (even at 1 mg/kg i.v. dosage) and, therefore, discontinued in further in vivo studies. Strasseriolide D showed statistically significant activity in vivo giving rise to lower parasitaemia levels (70% lower) compared to the controls treated with vehicle. CONCLUSIONS: Animal efficacy and preclinical evaluation of the recently discovered potent antiplasmodial macrolides, strasseriolides A-D, led to the identification of strasseriolide D as the most promising compound for further development. Future studies dealing on structure optimization, formulation and establishment of optimal in vivo dosage explorations of this novel compound class could enhance their clinical potency and allow for progress to later stages of the developmental pipeline.

Antiplasmodial, antimalarial activities and toxicity of African medicinal plants: a systematic review of literature.

BACKGROUND: Malaria still constitutes a major public health menace, especially in tropical and subtropical countries. Close to half a million people mainly children in Africa, die every year from the disease. With the rising resistance to frontline drugs (artemisinin-based combinations), there is a need to accelerate the discovery and development of newer anti-malarial drugs. A systematic review was conducted to identify the African medicinal plants with significant antiplasmodial and/or anti-malarial activity, toxicity, as wells as assessing the variation in their activity between study designs (in vitro and in vivo). METHODS: Key health-related databases including Google Scholar, PubMed, PubMed Central, and Science Direct were searched for relevant literature on the antiplasmodial and anti-malarial activities of African medicinal plants. RESULTS: In total, 200 research articles were identified, a majority of which were studies conducted in Nigeria. The selected research articles constituted 722 independent experiments evaluating 502 plant species. Of the 722 studies, 81.9%, 12.4%, and 5.5% were in vitro, in vivo, and combined in vitro and in vivo, respectively. The most frequently investigated plant species were Azadirachta indica, Zanthoxylum chalybeum, Picrilima nitida, and Nauclea latifolia meanwhile Fabaceae, Euphorbiaceae, Annonaceae, Rubiaceae, Rutaceae, Meliaceae, and Lamiaceae were the most frequently investigated plant families. Overall, 248 (34.3%), 241 (33.4%), and 233 (32.3%) of the studies reported very good, good, and moderate activity, respectively. Alchornea cordifolia, Flueggea virosa, Cryptolepis sanguinolenta, Zanthoxylum chalybeum, and Maytenus senegalensis gave consistently very good activity across the different studies. In all, only 31 (4.3%) of studies involved pure compounds and these had significantly (p = 0.044) higher antiplasmodial activity relative to crude extracts. Out of the 198 plant species tested for toxicity, 52 (26.3%) demonstrated some degree of toxicity, with toxicity most frequently reported with Azadirachta indica and Vernonia amygdalina. These species were equally the most frequently inactive plants reported. The leaves were the most frequently reported toxic part of plants used. Furthermore, toxicity was observed to decrease with increasing antiplasmodial activity. CONCLUSIONS: Although there are many indigenous plants with considerable antiplasmodial and anti-malarial activity, the progress in the development of new anti-malarial drugs from African medicinal plants is still slothful, with only one clinical trial with Cochlospermum planchonii (Bixaceae) conducted to date. There is, therefore, the need to scale up anti-malarial drug discovery in the African region.

Selecting an anti-malarial clinical candidate from two potent dihydroisoquinolones.

BACKGROUND: The ongoing global malaria eradication campaign requires development of potent, safe, and cost-effective drugs lacking cross-resistance with existing chemotherapies. One critical step in drug development is selecting a suitable clinical candidate from late leads. The process used to select the clinical candidate SJ733 from two potent dihydroisoquinolone (DHIQ) late leads, SJ733 and SJ311, based on their physicochemical, pharmacokinetic (PK), and toxicity profiles is described. METHODS: The compounds were tested to define their physicochemical properties including kinetic and thermodynamic solubility, partition coefficient, permeability, ionization constant, and binding to plasma proteins. Metabolic stability was assessed in both microsomes and hepatocytes derived from mice, rats, dogs, and humans. Cytochrome P450 inhibition was assessed using recombinant human cytochrome enzymes. The pharmacokinetic profiles of single intravenous or oral doses were investigated in mice, rats, and dogs. RESULTS: Although both compounds displayed similar physicochemical properties, SJ733 was more permeable but metabolically less stable than SJ311 in vitro. Single dose PK studies of SJ733 in mice, rats, and dogs demonstrated appreciable oral bioavailability (60-100%), whereas SJ311 had lower oral bioavailability (mice 23%, rats 40%) and higher renal clearance (10-30 fold higher than SJ733 in rats and dogs), suggesting less favorable exposure in humans. SJ311 also displayed a narrower range of dose-proportional exposure, with plasma exposure flattening at doses above 200 mg/kg. CONCLUSION: SJ733 was chosen as the candidate based on a more favorable dose proportionality of exposure and stronger expectation of the ability to justify a strong therapeutic index to regulators.

A new look at 9-substituted acridines with various biological activities.

Heterocycles have long been the focus of intensive study in attempts to develop novel therapeutic compounds, and acridine, a polynuclear nitrogen molecule containing a heterocycle, has attracted a considerable amount of scientific attention. Acridine derivatives have been studied in detail and have been found to possess multitarget properties, which inhibit topoisomerase enzymes that regulate topological changes in DNA and interfere with the essential biological function of DNA. This article describes some recent advancements in the field of new 9-substituted acridine heterocyclic agents and describes both the structure and the structure-activity relationship of the most promising molecules. The article will also present the IC50 values of the novel derivatives against various human cancer cell lines. The mini review also investigates the topoisomerase inhibition and antibacterial and antimalarial activity of these polycyclic aromatic derivatives.

Safety assessment of MEFAS: an innovative hybrid salt of mefloquine and artesunate for malaria treatment.

Malaria is a global public health problem that causes approximately 445 000 deaths annually worldwide, especially in underdeveloped countries. Because of the high prevalence and mortality of the disease, new and less toxic therapeutic agents need to be developed, such as MEFAS, a low-cost hybrid salt that consists of artesunate and mefloquine. However, the efficacy of MEFAS has been systematically demonstrated, its safety requires further investigation. This study investigated the acute toxicity of MEFAS and its precursors, artesunate, and mefloquine. A total of 42 female Swiss mice were divided into seven groups (n = 6/group) that were treated orally by gavage with vehicle (filtered water, negative control), MEFAS (50, 500, and 1000 mg/kg), and 1:1 concentrations of artesunate + mefloquine (50, 500, and 1000 mg/kg). Clinical signs of toxicity were observed for 14 d after treatment. On day 15, the animals were weighed, deeply anesthetized with isoflurane, and euthanized for subsequent collection of the liver, spleen, and kidneys. The relative organ weights were determined, followed by histopathological analysis. Artesunate + mefloquine produced toxic effects compared with the negative control group, reflected by changes in clinical signs, relative organ weights, and histopathological alterations. In MEFAS-treated animals, no changes were observed compared with the negative control group. These findings demonstrate that MEFAS is safer than artesunate + mefloquine after acute administration in mice.

Chemotherapeutic and prophylactic antimalarial drugs induce cell death through mitochondrial-mediated apoptosis in murine models.

Malaria is a parasitic disease that has defied many treatment plans. This study was carried out to investigate the host mitochondrial response to malarial infection and selected antimalarial chemotherapy using murine models. The effects of artesunate (ART) and proguanil (PRG) on mitochondrial Permeability Transition (mPT), mitochondrial ATPase (mATPase), level of malondialdehyde (MDA) and activities of antioxidant enzymes; catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), Xanthine oxidase (XO), glutathione S-transferase (GST) and reduced glutathione (GSH) were estimated in Plasmodium berghei-infected mice treated with ART and PRG. Besides, apoptotic markers, such as caspases 3, 9 and DNA fragmentation were estimated. Unparasitised (NORMAL) and parasitized but untreated (PU) animals were used as controls. The mPT pore opening fold of 9 (ART), 3 (PRG), and 4 (PU) were observed relative to calcium (23) for in vivo study. In vitro, graded concentrations (20, 40, 80 and 160 µg/mL) of ART gave mPT induction folds of 1, 21, 23 and 25, respectively, relative to calcium (9) while PRG did not have effect in the absence of calcium. In vivo, ART significantly (p < 0.001) enhanced mATPase activity than PRG. The PRG and ART increased the MDA levels in vivo. Oral administration of ART and PRG altered antioxidant enzymes status, Caspases 3 and 9 were significantly activated in PRG-treated groups; there was significant increase in DNA fragmentation in PU and PRG groups compared with the normal control. The results obtained showed that malaria parasite and antimalarial drugs cause mitochondrial-mediated apoptosis.

Identification of 3,4-Dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine Derivatives as Novel Selective Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase.

Plasmodium falciparum's resistance to available antimalarial drugs highlights the need for the development of novel drugs. Pyrimidine de novo biosynthesis is a validated drug target for the prevention and treatment of malaria infection. P. falciparum dihydroorotate dehydrogenase (PfDHODH) catalyzes the oxidation of dihydroorotate to orotate and utilize ubiquinone as an electron acceptor in the fourth step of pyrimidine de novo biosynthesis. PfDHODH is targeted by the inhibitor DSM265, which binds to a hydrophobic pocket located at the N-terminus where ubiquinone binds, which is known to be structurally divergent from the mammalian orthologue. In this study, we screened 40,400 compounds from the Kyoto University chemical library against recombinant PfDHODH. These studies led to the identification of 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine and its derivatives as a new class of PfDHODH inhibitor. Moreover, the hit compounds identified in this study are selective for PfDHODH without inhibition of the human enzymes. Finally, this new scaffold of PfDHODH inhibitors showed growth inhibition activity against P. falciparum 3D7 with low toxicity to three human cell lines, providing a new starting point for antimalarial drug development.

Systematic review of artemisinin embryotoxicity in animals: Implications for malaria control in human pregnancy.

Pregnant women are one of the most susceptible and vulnerable groups to malaria, the most important parasitic disease worldwide. Artemisinin-based combination therapies (ACTs) are recommended for the treatment of uncomplicated malaria in all population groups including pregnant women. However, due to the embryotoxicity observed in animal studies, ACTs have long been contraindicated during the first trimester in pregnant women. Despite the safety concerns raised in pre-clinical studies, recent findings on ACTs's use in pregnant women appear to be reassuring regarding safety and have prompted a revision of malaria treatment guidelines for first trimester of pregnancy. To contribute to the risk-benefit assessment of ACTs, we conducted a systematic literature review of animal studies published between 2007 and 2019, which evaluated the embryotoxic effects of artemisinin and its derivatives among pregnant mammals. Eighteen experimental studies fitted the inclusion criteria. These studies confirmed and further characterized the severe embryolethal and embryotoxic dose-dependent effects of artemisinin and its derivatives when administered during the organogenesis period in rats, rabbits and monkeys. Timing of administration and dosage of the drug were found to be key factors in the appearance of embryo damage. Overall, the translation of the findings of artemisinin derivatives use in animal studies to pregnant women remains disturbing. Thus, a policy change in the use of ACTs during the first trimester in pregnant women for the treatment of uncomplicated malaria does not seem pertinent and if implemented, it should be accompanied by solid pharmacovigilance systems, which are challenging to establish in malaria endemic countries.

In silico and in vivo anti-malarial investigation on 1-(heteroaryl)-2-((5-nitroheteroaryl)methylene) hydrazine derivatives.

BACKGROUND: Resistance of Plasmodium falciparum against common anti-malarial drugs emphasizes the need of alternative and more effective drugs. Synthetic derivatives of 1-(heteroaryl)-2-((5-nitroheteroaryl)methylene) hydrazine have showed in vitro anti-plasmodial activities. The present study aimed to evaluate the molecular binding and anti-plasmodial activity of synthetic compounds in vivo. METHODS: The molecular docking was used to study the binding of compounds to haem and Plasmodium falciparum lactate dehydrogenase (PfLDH). Acute toxicity of the synthetic compounds was evaluated based on the modified up & down method. The anti-plasmodial activity of the compounds was conducted by the two standard tests of Peters' and of Rane, using chloroquine-sensitive Plasmodium berghei in mice. Also, the toxicity to the internal organs of mice was evaluated on the seventh day after the treatment in addition to the histopathology of their liver. Compound 3 that showed high activity in the lowest dose was selected for further pharmacodynamic studies. RESULTS: According to the docking studies, the active site of PfLDH had at least four common residues, including Ala98, Ile54, Gly29, and Tyr97 to bind the compounds with the affinity, ranging from - 8.0 to - 8.4 kcal/mol. The binding mode of ligands to haem revealed an effective binding affinity, ranging from - 5.1 to - 5.5 kcal/mol. Compound 2 showed the highest  % suppression of parasitaemia (99.09%) at the dose of 125 mg/kg/day in Peters' test. Compound 3, with 79.42% suppression, was the best in Rane's test at the lowest dose (31 mg/kg/day). Compound 3 was confirmed by the pharmacodynamic study to have faster initial parasite elimination in the lowest concentration. The histopathology of the livers of mice did not reveal any focal necrosis of hepatocytes in the studied compounds. CONCLUSIONS: The docking studies verified Pf LDH inhibition and the inhibitory effect on the haemozoin formation for the studied compounds. Accordingly, some compounds may provide new avenues for the development of anti-malarial drugs without liver toxicity, although further studies are required to optimize their anti-plasmodial activity.

Assessment of in vitro and in vivo antimalarial efficacy and GC-fingerprints of selected medicinal plant extracts.

A hallmark of mortality and morbidity, malaria is affecting nearly half of the world's population. Emergence of drug-resistant strains of malarial parasite prompts identification and evaluation of medicinal plants and their constituents that may hold the key to a new and effective anti-malarial drug. In this context, nineteen methanolic extracts from seventeen medicinal plants were evaluated for anti-plasmodial potential against Plasmodium falciparum strain 3D7 (Chloroquine (CQ) sensitive) and INDO (CQ resistant) using fluorescence based SYBR-Green assay and for cytotoxic effects against mammalian cell lines. Leaf extract of two plants showed promising in vitro anti-malarial activity (Pf3D7 IC50 ≤ 10 µg/ml); one plant extract showed good activity (Pf3D7 IC50 = 10.1-20 µg/ml); seven were moderately active (IC50 = 20.1-50 µg/ml), four plant extracts showed poor activity (PfD7 IC50 = 50.1-100 µg/ml) and five extracts showed no activity up to IC50 = 100 µg/ml. Further, six extracts were found equipotent to PfINDO (resistance index ranging 0.4-2) and relatively nontoxic to mammalian cell lines HEK293 (cytotoxicity index ranging 1.4-12.5). Based on good resistance and selectivity indices, three extracts were evaluated for in vivo activity in Plasmodium berghei ANKA infected mice at a dose of 500 mg/kg and they showed significant suppression of P. berghei parasitemia. Further, these active plant extracts were fractionated using silica-gel chromatography and their fractions were evaluated for anti-plasmodial action. Obtained fractions showed enrichment in antimalarial activity. Active fractions were analyzed by gas chromatography and mass-spectrometery. Results suggests that the three active plant extracts could serve as potent source of anti-malarial agent and therefore require further analysis.

Antiplasmodial potential of Thalictrum foliolosum (Ranunculaceae) against lethal murine malaria.

BACKGROUND AND OBJECTIVES: The emergence of multi-drug resistant (MDR) strains of Plasmodium falciparum highlights the need to develop novel antimalarial drugs. Present study explores the in vivo antiplasmodial activity of ethanol leaf extract of Thalictrum foliolosum (ELETF) against lethal murine malaria. METHODS: The acute toxicity of the extract was assessed by Limit test of Lorke. The suppressive activity of the extract was evaluated by Peter's 4 day test. In vivo preventive and curative activity of ELETF was assessed by Peter's method and Ryley and Peter's method respectively. Biochemical assays were carried out using standard methods. RESULTS: ELETF (1000 mg/kg) exhibited considerable in vivo schizontocidal activity with 67.11% chemosuppression on Day 5. The ED50 of the extract was 579.56 mg/kg. ELETF also showed significant repository activity with 87.70% chemosuppression at 750 mg/kg, which was greater than pyrimethamine (78.78%). ELETF exhibited dose dependent chemosuppression in the curative test with maximum 70.06% chemosuppression (750 mg/kg). Maximum Mean Survival Time (MST) was 19.2±4.60 and 22.66±4.41 days respectively in the suppressive and curative test, which was extremely statistically significant (p<0.0005) in comparison to untreated control which died by Day 9 post inoculation. Biochemical analysis revealed the safety of ELETF to the hepatic and renal functions of the rodent host. INTERPRETATION & CONCLUSION: The study reports the antiplasmodial potential of Thalictrum foliolosum (ELETF) against Plasmodium berghei infection. The extract can be developed as a phytomedicine against malaria. Alternatively, the active components can be isolated as new lead compounds against the disease.

In vitro and in vivo characterization of anti-malarial acylphenoxazine derivatives prepared from basic blue 3.

BACKGROUND: Basic blue 3 is a promising anti-malarial lead compound based on the π-delocalized lipophilic cation hypothesis. Its derivatives with nitrogen atoms bonded to carbon atoms at the 3- and 7-positions on the phenoxazine ring were previously shown to exert potent antiprotozoal activity against Plasmodium falciparum, Trypanosoma cruzi, Trypanosoma brucei rhodesiense, and Leishmania donovani parasites in vitro. However, compounds with nitrogen modification at the 10-position on the phenoxazine ring were not evaluated. METHODS: Six acylphenoxazine derivatives (ITT-001 to 006) with nitrogen modification at the 10-position on the phenoxazine ring, which were synthesized from basic blue 3, were characterized and evaluated for anti-malarial activity in vitro with an automated haematology analyzer (XN-30) and light microscopy. Intensity of self-fluorescence was measured using a fluorometer. Localization of basic blue 3 was observed by fluorescence microscopy. Cytotoxicity was evaluated using human cell lines, HEK293T and HepG2 cells. Finally, anti-malarial activity was evaluated in a rodent malaria model. RESULTS: All the six derivatives showed anti-malarial efficacy even against chloroquine-, pyrimethamine-, and artemisinin-resistant field isolates similar to the sensitive strains and isolates in vitro. The efficacy of basic blue 3 was the strongest, followed by that of ITT-001 to 004 and 006, while that of ITT-005 was the weakest. Basic blue 3 showed strong self-fluorescence, whereas ITT derivatives had five- to tenfold lower intensity than that of basic blue 3, which was shown by fluorescence microscopy to be selectively accumulated in the plasmodial cytoplasm. In contrast, ITT-003, 004, and 006 exhibited the lowest cytotoxicity in HEK293T and HepG2 cells in vitro and the highest selectivity between anti-malarial activity and cytotoxicity. The in vivo anti-malarial assay indicated that oral administration of ITT-004 was the most effective against the rodent malaria parasite, Plasmodium berghei NK65 strain. CONCLUSIONS: The six ITT derivatives were effective against chloroquine- and pyrimethamine-resistant strains and artemisinin-resistant field isolates as well as the sensitive ones. Among them, ITT-004, which had high anti-malarial activity and low cytotoxicity in vitro and in vivo, is a promising anti-malarial lead compound.

Antiplasmodial profile of selected compounds from Malaria Box: in vitro evaluation, speed of action and drug combination studies.

BACKGROUND: Artemisinin-based combination therapy (ACT) is used as the first-line treatment of uncomplicated malaria caused by the Plasmodium falciparum parasite and chloroquine-resistant Plasmodium vivax parasites. Evidence of resistance to ACT has been reported in Cambodia, and without new and effective anti-malarial agents, malaria burden and mortality will rise. METHODS: The used MolPrint 2D fingerprints and the Tanimoto similarity index were used to perform a structural similarity search within the Malaria Box collection to select diverse molecular scaffolds that are different from artesunate. Next, the inhibitory potency against the P. falciparum 3D7 strain (SYBR Green I inhibition assay) and the cytotoxicity against HepG2 cells (MTT and neutral red assays) were evaluated. Then, the speed of action, the combination profile of selected inhibitors with artesunate, and the P. berghei in vivo activity of the best compounds were assessed. RESULTS: A set of 11 structurally diverse compounds from the Malaria Box with a similarity threshold of less than 0.05 was selected and compared with artesunate. The in vitro inhibitory activity of each compound confirmed the reported potencies (IC50 values ranging from 0.005 to 1 µM). The cytotoxicity of each selected compound was evaluated and used to calculate the selectivity index (SI values ranging from 15.1 to 6100). Next, both the speed of action and the combination profile of each compound with artesunate was assessed. Acridine, thiazolopyrimidine, quinoxaline, benzimidazole, thiophene, benzodiazepine, isoxazole and pyrimidoindole derivatives showed fast in vitro inhibitory activity of parasite growth, whereas hydrazinobenzimidazole, indenopyridazinone and naphthalenone derivatives were slow-acting in vitro inhibitors. Combinatory profile evaluation indicated that thiazolopyrimidinone and benzodiazepine derivatives have an additive profile, suggesting that the combination of these inhibitors with artesunate is favourable for in vitro inhibitory activity. The remaining compounds showed an antagonistic combinatory profile with artesunate. The collected data indicated that the indenopyridazinone derivative, a bc1 complex inhibitor, had a similar association profile in combination with proguanil when compared to atovaquone combined with proguanil, thereby corroborating the correlation between the molecular target and the combination profile. Lastly, the in vivo activity of the thiazolopyrimidinone and benzodiazepine derivatives were assessed. Both compounds showed oral efficacy at 50 mg/kg in a mouse model of Plasmodium berghei malaria (64% and 40% reduction in parasitaemia on day 5 post-infection, respectively). CONCLUSIONS: The findings in this paper shed light on the relationship among the speed of action, molecular target and combinatory profile and identified new hits with in vivo activity as candidates for anti-malarial combination therapy.