Bibliometric analysis of antimalarial drug resistance

Background

Malaria has always been a serious infectious disease prevalent in the world. Antimalarial drugs such as chloroquine and artemisinin have been the main compounds used to treat malaria. However, the massive use of this type of drugs accelerates the evolution and spread of malaria parasites, leading to the development of resistance. A large number of related data have been published by researchers in recent years. CiteSpace software has gained popularity among us researchers in recent years, because of its ability to help us obtain the core information we want in a mass of articles. In order to analyze the hotspots and develop trends in this field through visual analysis, this study used CiteSpace software to summarize the available data in the literature to provide insights.

Method

Relevant literature was collected from the Web of Science Core Collection (WOSCC) from 1 January 2015 to 29 March 2023. CiteSpace software and Microsoft Excel were used to analyze and present the data, respectively.

Results

A total of 2,561 literatures were retrieved and 2,559 literatures were included in the analysis after the removal of duplicates. An irrefutable witness of the ever-growing interest in the topic of antimalarial drug resistance could be expressed by the exponentially increased number of publications and related citations from 2015 to 2022, and its sustained growth trend by 2023. During the past 7 years, USA, Oxford University, and David A Fidock are the country, institution, and author with the most publications in this field of research, respectively. We focused on the references and keywords from literature and found that the research and development of new drugs is the newest hotspot in this field. A growing number of scientists are devoted to finding new antimalarial drugs.

Conclusion

This study is the first visual metrological analysis of antimalarial drug resistance, using bibliometric methods. As a baseline information, it is important to analyze research output published globally on antimalarial drug resistance. In order to better understand the current research situation and future research plan agenda, such baseline data are needed accordingly.

Progression and expansion of quinoline as bioactive moiety: a patent review

Quinoline inhibitors are appealing medicinal products for a range of illnesses and problems. It is bicyclic heterocyclic scaffold has been intensively employed in pharmacological research and is well known for its wide range of biological purposes. Biological activities exhibited by quinoline derivatives, such as anti-inflammatory properties, antioxidant, antimicrobial, anti-tubercular, antidiabetic, anti-malarial and others are covered in detail in this review. The IC50 of patented inhibitors might range from nm to μM range, based on the experiments used. It presents an outline of patents file between 2002 and 2023 concerning to biological activities by quinoline derivatives. As a result, it is critical to develop additional chemical quinoline core alterations for novel chemical compounds and enhanced pharmacological impacts.

Synthesis, Antimicrobial and Antioxidant Activity of some New Pyrazolines Containing Azo Linkages

Background Pyrazolines and azo-pyrazolines are influential groups of heterocyclic compounds with two nitrogen atoms inside the five-membered ring. They play an important role in a wide range of biological processes, such as antifungal, antioxidant, antimalarial and other antimicrobial activities. Objective The main objective of this study is to synthesize some new heterocyclic compounds with antioxidant and antimicrobial activity. Methods One-pot three components and traditional synthesis of new azo-pyrazoline compounds were achieved in this work. The preparation process has been started by diazotizing 4-(6-methylbenzothiazol-2-yl) benzamine and its coupling reaction with 4-hydroxy acetophenone producing azo-acetophenone, followed by benzylation with benzyl chloride to form the starting material, azo-benzyloxy acetophenone. A series of substituted benzaldehydes were reacted with the latter compound via one pot and classical methods, forming new chalcones containing azo linkages and benzyloxy moieties, which were then converted into new target azo-pyrazoline derivatives. Results The structures of the synthesized compounds were confirmed by spectroscopic techniques using FT-IR, 1H-NMR, 13C-NMR, and 13C- DEPT- 135 spectra. Finally, the synthesized compounds were screened for their antioxidant and antimicrobial activities against Staphylococcus aureus and Escherichia coli. Conclusion Overall, the one-pot three-component synthesis of pyrazoline compounds generally provides advantages in terms of efficiency, simplicity, and time-consumption compared to classical synthesis methods. Hence, the study advocates the one-pot method because it eliminates the tedious process of making chalcones, which takes time, materials, and unnecessary effort. Therefore, this is the most convenient and effective approach to green chemistry.

Synthetic Approaches and Pharmacological Attributes of Benzosuberone Skeleton

BACKGROUND

Benzocycloheptanone is the main structural feature of numerous famous natural pharmacophores such as Colchicine and Theaflavins. It has gained popularity in the field of medicinal chemistry, attributing to its broad-spectrum effect.

OBJECTIVE

Numerous research publications addressing the derivatization of the benzosuberone molecule have been published, and their biological and pharmacological features have been extensively addressed. Numerous derivatives have been discovered as lead compounds for the development of novel medications. Thus, the goal of this article is to summarize and analyze all published findings on the synthesis and biological assessment of the benzosuberone skeleton.

METHODS

All main databases including SciFinder, PubMed and google scholar were used with appropriate keywords to select related reported literature, and further bibliography in related literature was also used to find linked reports.

RESULTS

Synthetic routes to benzosuberone-based ring systems were identified from the literature and explained stepwise and after this, pharmacological activities of all benzosuberone derivatives are listed target-wise and a detailed structure-activity relationship is developed.

CONCLUSION

The current review discusses numerous synthetic approaches for the synthesis of benzosuberone skeleton and its applications in many domains of medical chemistry. Compounds possessing the benzosuberone skeleton play an important role in the drug development process due to their wide range of biological actions such as anti-cancer, antibacterial, antifungal, antiinflammatory, and so on. The results of antibacterial screening and Structure-Activity Relationship (SAR) revealed that the compounds containing this skeleton with the piperazine and morpholine rings have antimicrobial potential when compared to the commercial antibiotic Norfloxacin. Despite extensive study to date, there is still room for the development of novel and efficient pharmacophores using the structure-based drug design technique.

Chloroquine-Induced Psychosis: A Case Report

The use of antimalarial drugs for prophylaxis is a widespread practice while traveling to underdeveloped nations, particularly those with a high malaria prevalence. Chloroquine is still one of the most commonly recommended antimalarials, either alone or in combination with others, for prophylaxis. However, its increased use over the past few decades has been associated with many adverse effects, including headaches, dizziness, vomiting, and diarrhea, as well as neuropsychiatric symptoms such as psychosis. Here, we discuss the case of a 30-year-old Asian man who, after starting a 500-milligram (mg) prophylactic dosage of chloroquine per week, developed psychotic symptoms. This case highlights the need to use chloroquine and other antimalarials with care, especially when beginning as a prophylactic measure with the lowest suggested dosage.

Genus Zanthoxylum as Sources of Drugs for Treatment of Tropical Parasitic Diseases

The tropical parasitic infections account to more than 2 billion infections and cause substantial morbidity and mortality, and accounts to several million deaths every year. Majorly parasitic infections in humans and animals are caused by protozoa and helminths. Chronic infections in host can cause retardation, impairment of cognitive skills, development in young children and weaken the immune system. The burden is felt to a greater extent in developing countries due to poverty, inaccessibility to medicines and resistance observed to drugs. Thus, human health continues to be severely harmed by parasitic infections. Medicinal plants have received much attention as alternative sources of drugs. Zanthoxylum genus has been used ethnobotanically as an antiparasitic agent and the phytoconstituents in Zanthoxylum, show wide variety of chemical substances with proven pharmacological actions such as alkaloids (isoquinolines and quinolines responsible for antitumor activity, antimalarial, antioxidant and antimicrobial actions), lignans, coumarins (antibacterial, antitumour, vasodilatory and anticoagulant activities), alkamide (strong insecticidal properties, anthelminthic, antitussive and analgesic anti antimalarial property). Therefore, this article is an attempt to review the existing literature that emphasizes on potential of genus Zanthoxylum as source of lead compounds for treatment of parasitic diseases.

Identification of first-in-class plasmodium OTU inhibitors with potent anti-malarial activity

OTU proteases antagonize the cellular defense in the host cells and involve in pathogenesis. Intriguingly, P. falciparum, P. vivax, and P. yoelii have an uncharacterized and highly conserved viral OTU-like proteins. However, their structure, function or inhibitors have not been previously reported. To this end, we have performed structural modeling, small molecule screening, deconjugation assays to characterize and develop first-in-class inhibitors of P. falciparum, P. vivax, and P. yoelii OTU-like proteins. These Plasmodium OTU-like proteins have highly conserved residues in the catalytic and inhibition pockets similar to viral OTU proteins. Plasmodium OTU proteins demonstrated Ubiquitin and ISG15 deconjugation activities as evident by intracellular ubiquitinated protein content analyzed by western blot and flow cytometry. We screened a library of small molecules to determine plasmodium OTU inhibitors with potent anti-malarial activity. Enrichment and correlation studies identified structurally similar molecules. We have identified two small molecules that inhibit P. falciparum, P. vivax, and P. yoelii OTU proteins (IC50 values as low as 30 nM) with potent anti-malarial activity (IC50 of 4.1-6.5 µM). We also established enzyme kinetics, druglikeness, ADME, and QSAR model. MD simulations allowed us to resolve how inhibitors interacted with plasmodium OTU proteins. These findings suggest that targeting malarial OTU-like proteases is a plausible strategy to develop new anti-malarial therapies.

Investigation of Andrographolide Effect on Non-Infected Red Blood Cells Using the 1H-NMR-Based Metabolomics Approach

Andrographolide (AG) has been shown to have several medicinal and pharmaceutical effects, such as antimicrobial, anti-inflammatory, antioxidant, anti-diabetic, and anti-malarial activities. Moreover, studies to assess the pharmacological effect of AG on the metabolic changes of uninfected red blood cells (uRBCs) have not yet been investigated. This study aims to evaluate the pharmacological effects of AG compared to chloroquine (CQ) on the metabolic variations of uRBCs in vitro using a proton nuclear magnetic resonance (¹H-NMR)-based metabolomics approach coupled with multivariate data analysis (MVDA). Forty-one metabolites were successfully identified by ¹H-NMR. The results of the unsupervised data analysis principal component analysis (PCA) showed ideal differentiation between AG and CQ. PC1 and PC2 accounted for 71.4% and 17.7% of the explained variation, respectively, with a total variance of 89.10%. Based on S-plot and VIP values, a total of 28 and 32 metabolites were identified as biomarkers in uRBCs-AG and uRBCs-CQ, respectively. In uRBCs treated with AG, ten metabolic pathways were determined to be disturbed, including riboflavin metabolism, d-glutamate and d-glutamine metabolism, phenylalanine metabolism, glutathione metabolism, proline and arginine metabolism, arginine biosynthesis, citrate cycle, glycolysis/gluconeogenesis, and pyruvate metabolism as well as alanine, aspartate, and glutamate metabolism. In contrast, in CQ-treated uRBCs, nine affected metabolic pathways were determined, which involved the same metabolic pathways for uRBCs-AG, except for glutathione metabolism. These findings suggest an evident relationship between AG and CQ associated with metabolic changes in intact RBCs after being exposed to the treatment. The metabolomics results could allow useful comprehensive insights into the underlying mechanism of the action of AG and CQ on red blood cells. Consequently, the ¹H-NMR-based metabolomics approach was successfully utilized to identify the pharmacological effects of AG and CQ on the metabolic variations of uRBCs.

Phytochemistry, Traditional Use and Pharmacological Activity of Picrasma quassioides: A Critical Reviews

Picrasma quassioides is a member of the Simaroubaceae family commonly grown in the regions of Asia, the Himalayas, and India and has been used as a traditional herbal medicine to treat various illnesses such as fever, gastric discomfort, and pediculosis. This study aims to critically review the presence of phytochemicals in P. quassioides and correlate their pharmacological activities with the significance of its use as traditional medicine. Data were collected by reviewing numerous scientific articles from several journal databases on the pharmacological activities of P. quassioides using certain keywords. As a result, approximately 94 phytochemicals extracted from P. quassioides were found to be associated with quassinoids, β-carbolines and canthinones. These molecules exhibited various pharmacological benefits such as anti-inflammatory, antioxidant, anti-cancer, anti-microbial, and anti-parasitic activities which help to treat different diseases. However, P. quassioides were also found to have several toxicity effects in high doses, although the evidence regarding these effects is limited in proving its safe use and efficacy as herbal medicine. Accordingly, while it can be concluded that P. quassioides may have many potential pharmacological benefits with more phytochemistry discoveries, further research is required to determine its real value in terms of quality, safety, and efficacy of use.

Structure-Activity Relationship of Anti-malarial Allylpyrocatechol Isolated from Piper betle

Malaria disease remains a serious worldwide health problem. In South-East Asia, one of the malaria infection "hot-spots," medicinal plants such as Piper betle have traditionally been used for the treatment of malaria, and allylpyrocatechol (1), a constituent of P. betle, has been shown to exhibit anti-malarial activities. In this study, we verified that 1 showed in vivo anti-malarial activity through not only intraperitoneal (i.p.) but also peroral (p.o.) administration. Additionally, some analogs of 1 were synthesized and the structure-activity relationship was analyzed to disclose the crucial sub-structures for the potent activity.

Alkaloids from the root of Indonesian Annona muricata L

Annona muricata L. has been used traditionally in Indonesia to treat disease. Phytochemical studies on the alkaloid fractions from the root of Annona muricata L. from Malang-Indonesia resulted in the isolation of an unreported benzylisoquinoline alkaloid (+)-xylopine 5 as well as four known alkaloids (1-4). The crude methanol extract and alkaloid fractions were tested against Plasmodium falciparum K1 and against bacteria (Escherichia coli, Klebsiella pneumonia, Acinetobacter buamanii, Pseudomonas aeruginosa, Methicillin-resistant Staphylococcus aureus) with insignificant activities (MIC > 32 µg/mL). Individual alkaloids were tested against a human suspension cancer cell line (HL-60 leukemia cells) and two human fibroblastic cancer cell lines (A549 lung cancer cells and HepG2 liver cancer cells) in which compound 5 was the most toxic alkaloid with IC₅₀ values ranging from 20 to 80 µM.

Anti-Trypanosomal and Antimalarial Properties of Tetralone Derivatives and Structurally Related Benzocycloalkanones

Background and objectives: Sleeping sickness and malaria alike are insect-borne protozoan diseases that share overlapping endemic areas in sub-Saharan Africa. The causative agent for malaria has developed resistance against all currently deployed anti-malarial agents. In the case of sleeping sickness, the currently deployed therapeutic options are limited in efficacy and activity spectra, and there are very few drug candidates in the development pipeline. Thus, there is a need to search for new drug molecules with a novel mode of actions. Materials and Methods: In the current study, an in vitro screening of a library of tetralone derivatives and related benzocycloalkanones was effected against T. b. brucei and P. falciparum. Results: Several hits with low micromolar activity (0.4–8 µM) against T. b. brucei were identified. Conclusions: The identified hits have a low molecular weight (<280 Da), a low total polar surface area (<50 Ų), and a defined structure activity relationship, which all make them potential starting points for further hit optimization studies.

Hydroxyenone Derivatives: In vitro Anti-malarial and Docking Studies against P. falciparum

METHODS

A series of 1-{2-(prop-2-ynyloxy)aryl}-3-hydroxy-3-(4'-trifluoromethylphenyl) prop-2-en-1-ones obtained by photo-irradiation of 2-{2-(prop-2-ynyloxy)benzoyl}-3-(4- trifluorome-thyl-phenyl)oxiranes (that were characterized by spectral studies: FT-IR, 1H NMR, 13C NMR and Mass analysis) was screened for the anti-malarial activity by evaluating against chloroquine-sensitive P. falciparum (CD7). The molecular docking studies using AutoDock Vina were also performed to further ascertain the efficacy of these compounds with PDB:4ORM.

RESULTS

Among these, the hydroxyenone derivatives 2b, 2c and 2a exhibited very potent antimalarial activity that was clearly evinced by the results of molecular docking. Binding energies of hydroxyenone compounds were calculated and found in the range of -10.4 to -9.0 kcal/mol.

CONCLUSION

Compound 2b had the strongest binding affinity with docking score of -10.4 kcal/mol.

Fusaripeptide A: new antifungal and anti-malarial cyclodepsipeptide from the endophytic fungus Fusarium sp

From the culture of the endophytic fungus Fusarium sp. isolated from the roots of Mentha longifolia L. (Labiatae) growing in Saudi Arabia, a new cyclodepsipeptide, namely fusaripeptide A (1), along with three known compounds adenosine (2), 2[(2-hydroxypropionyl)amino]benzamide (3), and cyclopentanol (4), have been isolated. Their structures were determined, using extensive 1D and 2D NMR and HRESI and GC mass spectral data. That is the first report for the isolation of compound 4 from natural source. In addition, compounds 2 and 3 are reported here for the first time from Fusarium sp. The absolute configuration of the amino acid residues of 1 was assigned by chiral GCMS and Marfey's analysis after acid hydrolysis. Fusaripeptide A differs from the reported ones from Fusarium sp. in the length of fatty acidic alkyl chain. Compound 1 was evaluated for its antifungal, anti-malarial, and cytotoxic activities. It exhibited potent antifungal activity toward C. albicans, C. glabrata, C. krusei, and A. fumigates with IC₅₀ values of 0.11, 0.24, 0.19, and 0.14 μM, respectively. Furthermore, it had significant anti-malarial activity toward P. falciparum (D6 clone) with IC₅₀ value of 0.34 μM. However, it showed cytotoxic activity toward the tested cell lines.

Effect of immunosuppressive therapies on survival of systemic lupus erythematosus: a propensity score analysis of a longitudinal cohort

Objectives The aim of this study was to study the relationship between immunosuppressive drug treatment and survival in patients with systemic lupus erythematosus (SLE). Methods Patients who fulfilled four or more American College of Rheumatology criteria for SLE were followed longitudinally. Clinical characteristics, use of immunosuppressive agents and mortality were reviewed. Cox regression was used to study the relationship between immunosuppressive treatment and survival, adjusted for age, sex, vascular risk factors, organ damage, the anti-phospholipid antibodies and a propensity score for the indication of individual immunosuppressive agent derived from separate regression models. Results A total of 803 SLE patients were studied (92% women; age of SLE onset 33.2±14 years; follow-up time 10.8±7.7 years). The frequencies of ever use of immunosuppressive agents were: high-dose prednisolone (≥0.6 mg/kg/day for ≥4 weeks) (85%), azathioprine (63%), cyclophosphamide (25%), mycophenolate mofetil (27%), the calcineurin inhibitors (23%) and hydroxychloroquine (69%). Ninety-seven patients (12%) died and 56 (7%) patients were lost to follow-up. The causes of death were infection (44%), cerebrovascular events (12%), cardiovascular events (10%) and malignancy (8.2%). Cox regression revealed that the ever use of high-dose prednisolone, mycophenolate mofetil, calcineurin inhibitors or cyclophosphamide was not significantly associated with improved survival. However, the ever use of hydroxychloroquine (hazard ratio 0.59 (0.37-0.93); P=0.02) and azathioprine (hazard ratio 0.46 (0.28-0.75); P=0.002) was significantly associated with reduced mortality (41% and 54%, respectively) after adjustment for the propensity score and other confounding factors. A similar beneficial effect of hydroxychloroquine and azathioprine on survival was also observed in patients with lupus nephritis. Conclusions In this longitudinal cohort of Chinese SLE patients, the ever use of hydroxychloroquine and azathioprine was significantly associated with a probability of better survival. Treatment with high-dose prednisolone, cyclophosphamide, mycophenolate mofetil or the calcineurin inhibitors was not associated with long-term survival benefit.

Antiplasmodial Compounds from Leaves of Dodonaea angustifolia

Background:

Dodonaea angustifolia is used in Ethiopian traditional medicine to treat malaria. The objective of this work was to conduct bioassay guided fractionation of the leaves of D. angustifolia using Plasmodium berghei infected mice.

Method:

The antiplasmodial activity of the extracts and pure compounds was evaluated using the standard Peter’s four-day suppressive method. The structures of isolated compounds were elucidated using chemi-cal and spectroscopic methods.

Results:

In this study, the ethyl acetate soluble portion of the 80% aqueous MeOH extract of the leaves significantly suppressed parasitaemia in Plasmodium berghei infected mice (80.28% at 150 mg/kg). Three active compounds which exhibited significant percent suppression of parasitaemia by 81% at 40 mg/kg, 80% at 50 mg/kg and 70% at 40 mg/kg, respectively were identified. These are the flavanone pinocembrin (1), the flavanol santin (2) and the clerodane diterpene 2-hydroxy-15,16-epoxyceloda-3,13(16),14-trien-18-oic acid (3). Under similar conditions, chloroquine suppressed parasitaemia by 100% at 25 mg/kg. Chemical study of the ethanol extract of the leaves yielded 5,7,4'-trihydroxy-3,6-dimethoxyflavone (4), ent-16-hydroxy-labdan-3α,8β-dihydroxy,13(14)-en-15,16-olide (5) and 5,6,7-trihydroxy-3,4'-dimethoxyflavone (6). Compound 6 has not been reported before as a natural product.

Conclusion:

From the leaves of D. angustifolia, three compounds with significant antiplasmodial activi-ties were isolated and characterized, with pinocembrin as the most active compound.

Docking Based 3D-QSAR Study of Tricyclic Guanidine Analogues of Batzelladine K As Anti-Malarial Agents

The Plasmodium falciparum Lactate Dehydrogenase enzyme (PfLDH) catalyzes inter-conversion of pyruvate to lactate during glycolysis producing the energy required for parasitic growth. The PfLDH has been studied as a potential molecular target for development of anti-malarial agents. In an attempt to find the potent inhibitor of PfLDH, we have used Discovery studio to perform molecular docking in the active binding pocket of PfLDH by CDOCKER, followed by three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of tricyclic guanidine batzelladine compounds, which were previously synthesized in our laboratory. Docking studies showed that there is a very strong correlation between in silico and in vitro results. Based on docking results, a highly predictive 3D-QSAR model was developed with q² of 0.516. The model has predicted r² of 0.91 showing that predicted IC₅₀ values are in good agreement with experimental IC₅₀ values. The results obtained from this study revealed the developed model can be used to design new anti-malarial compounds based on tricyclic guanidine derivatives and to predict activities of new inhibitors.

M1 aminopeptidases as drug targets: broad applications or therapeutic niche?

M1 aminopeptidase enzymes are a diverse family of metalloenzymes characterized by conserved structure and reaction specificity. Excluding viruses, M1 aminopeptidases are distributed throughout all phyla, and have been implicated in a wide range of functions including cell maintenance, growth and development, and defense. The structure and catalytic mechanism of M1 aminopeptidases are well understood, and make them ideal candidates for the design of small‐molecule inhibitors. As a result, many research groups have assessed their utility as therapeutic targets for both infectious and chronic diseases of humans, and many inhibitors with a range of target specificities and potential therapeutic applications have been developed. Herein, we have aimed to address these studies, to determine whether the family of M1 aminopeptidases does in fact present a universal target for the treatment of a diverse range of human diseases. Our analysis indicates that early validation of M1 aminopeptidases as therapeutic targets is often overlooked, which prevents the enzymes from being confirmed as drug targets. This validation cannot be neglected, and needs to include a thorough characterization of enzymes’ specific roles within complex physiological pathways. Furthermore, any chemical probes used in target validation must be carefully designed to ensure that specificity over the closely related enzymes has been achieved. While many drug discovery programs that target M1 aminopeptidases remain in their infancy, certain inhibitors have shown promise for the treatment of a range of conditions including malaria, hypertension, and cancer.

Therapeutic Assessment of Primaquine for Radical Cure of Plasmodium vivax Malaria at Primary and Tertiary Care Centres in Southwestern India

Acquaintance is scanty on primaquine (PQ) efficacy and Plasmodium vivax recurrence in Udupi district, Karnataka, India. We assessed the efficacy of 14 days PQ regimen (0.25 mg/kg/day) to prevent P. vivax recurrence. Microscopically, aparasitemic adults (≥18 years) after acute vivax malaria on day 28 were re-enrolled into 15 months’ long follow-up study. A peripheral blood smear examination was performed with participants at every 1–2 month interval. A nested PCR test was performed to confirm the mono-infection with P. vivax. Of 114 participants, 28 (24.6%) recurred subsequently. The median (IQR) duration of the first recurrence was 3.1 (2.2–5.8) months which ranged from 1.2 to 15.1 months, including initial 28 days. Participants with history of vivax malaria had significantly higher risk of recurrence, with hazard ratio (HR) (95% CI) of 2.62 (1.24–5.54) (P=0.012). Severity of disease (11.4%, 13/114) was not associated (P=1.00) with recurrence. Of 28 recurrence cases, the nPCR proved that P. vivax mono-infection recurrence rate was at least 72.7% (16/22) at first recurrence. In Udupi district, PQ dose of 0.25 mg/kg/day over 14 days seems inadequate to prevent recurrence in substantial proportion of vivax malaria. Patients with a history of vivax malaria are at high risk of recurrences.

New Insight into Isoprenoids Biosynthesis Process and Future Prospects for Drug Designing in Plasmodium

The MEP (Methyl Erythritol Phosphate) isoprenoids biosynthesis pathway is an attractive drug target to combat malaria, due to its uniqueness and indispensability for the parasite. It is functional in the apicoplast of Plasmodium and its products get transported to the cytoplasm, where they participate in glycoprotein synthesis, electron transport chain, tRNA modification and several other biological processes. Several compounds have been tested against the enzymes involved in this pathway and amongst them Fosmidomycin, targeted against IspC (DXP reductoisomerase) enzyme and MMV008138 targeted against IspD enzyme have shown good anti-malarial activity in parasite cultures. Fosmidomycin is now-a-days prescribed clinically, however, less absorption, shorter half-life, and toxicity at higher doses, limits its use as an anti-malarial. The potential of other enzymes of the pathway as candidate drug targets has also been determined. This review details the various drug molecules tested against these targets with special emphasis to Plasmodium. We corroborate that MEP pathway functional within the apicoplast of Plasmodium is a major drug target, especially during erythrocytic stages. However, the major bottlenecks, bioavailability and toxicity of the new molecules needs to be addressed, before considering any new molecule as a potent antimalarial.

Combinatorial pathway engineering for optimized production of the anti-malarial FR900098

As resistance to current anti-malarial therapeutics spreads, new compounds to treat malaria are increasingly needed. One promising compound is FR900098, a naturally occurring phosphonate. Due to limitations in both chemical synthesis and biosynthetic methods for FR900098 production, this potential therapeutic has yet to see widespread implementation. Here we applied a combinatorial pathway engineering strategy to improve the production of FR900098 in Escherichia coli by modulating each of the pathway's nine genes with four promoters of different strengths. Due to the large size of the library and the low screening throughput, it was necessary to develop a novel screening strategy that significantly reduced the sample size needed to find an optimal strain. This was done by using biased libraries that localize searching around top hits and home in on high-producing strains. By incorporating this strategy, a significantly improved strain was found after screening less than 3% of the entire library. When coupled with culturing optimization, a strain was found to produce 96 mg/L, a 16-fold improvement over the original strain. We believe the enriched library method developed here can be used on other large pathways that may be difficult to engineer by combinatorial methods due to low screening throughput.

The challenge to avoid anti-malarial medicine stock-outs in an era of funding partners: the case of Tanzania

BACKGROUND

Between 2007 and 2013, the Tanzanian public sector received 93.1 million doses of first-line anti-malarial artemisinin-based combination therapy (ACT) in the form of artemether-lumefantrine entirely supplied by funding partners. The introduction of a health facility ACT stock monitoring system using SMS technology by the National Malaria Control Programme in mid 2011 revealed a high frequency of stock-outs of ACT in primary care public health facilities. The objective of this study was to determine the pattern of availability of ACT and possible causes of observed stock-outs across public health facilities in Tanzania since mid-2011.

METHODS

Data were collected weekly by the mobile phone reporting tool SMS for Life on ACT availability from over 5,000 public health facilities in Tanzania starting from September 2011 to December 2012. Stock data for all four age-dose levels of ACT across health facilities were summarized and supply of ACT at the national level was also documented.

RESULTS

Over the period of 15 months, on average 29% of health facilities in Tanzania were completely stocked out of all four-age dose levels of the first-line anti-malarial with a median duration of total stock-out of six weeks. Patterns of total stock-out by region ranged from a low of 9% to a high of 52%. The ACT stock-outs were most likely caused by: a) insufficient ACT supplies entering Tanzania (e.g. in 2012 Tanzania received 10.9 million ACT doses compared with a forecast demand of 14.4 million doses); and b) irregular pattern of ACT supply (several months with no ACT stock).

CONCLUSION

The reduced ACT availability and irregular pattern of supply were due to cumbersome bureaucratic processes and delays both within the country and from the main donor, the Global Fund to Fight AIDS, Tuberculosis and Malaria. Tanzania should invest in strengthening both the supply system and the health information system using mHealth solutions such as SMS for Life. This will continue to assist in tracking ACT availability across the country where all partners work towards more streamlined, demand driven and accountable procurement and supply chain systems.

[Delayed diagnosis of Plasmodium falciparum in a soldier in Uganda: false-positive rapid diagnostic test associated with reduced repeats in pfhrp2]

Rapid diagnostic tests (RDTs) are the best alternative for malaria diagnosis where a microscopic examination cannot be performed. We report here the first case of P. falciparum (false-negative) misdiagnosis in a soldier stationed in Uganda, associated with a reduced number of repeats in the P. falciparum histidine-rich protein 2 gene (pfhrp2). This gene was subsequently sequenced to determine the reason for the discordance between the RDT results and the later microscopic examination. Ten repeats of the type 2 motif AHHAHHAAD and four repeats of the type 7 motif AHHAAD were found. This isolate belongs to the group of non-sensitive parasites (<43 repeats) that are not detected by HRP2 RDTs. This inappropriate case management could have been fatal for the patient. This case confirms the problem of negative RDT results in isolated situations and of basing a therapeutic strategy on these negative results. Investigations should be conducted in Uganda and other areas of Africa to determine the presence and the geographical spread of parasites with pfhrp2 gene deletion to ensure the best performance of RDTs.

Tafenoquine at therapeutic concentrations does not prolong Fridericia-corrected QT interval in healthy subjects

Tafenoquine is being developed for relapse prevention in Plasmodium vivax malaria. This Phase I, single-blind, randomized, placebo- and active-controlled parallel group study investigated whether tafenoquine at supratherapeutic and therapeutic concentrations prolonged cardiac repolarization in healthy volunteers. Subjects aged 18-65 years were randomized to one of five treatment groups (n = 52 per group) to receive placebo, tafenoquine 300, 600, or 1200 mg, or moxifloxacin 400 mg (positive control). Lack of effect was demonstrated if the upper 90% CI of the change from baseline in QTcF following supratherapeutic tafenoquine 1200 mg versus placebo (ΔΔQTcF) was <10 milliseconds for all pre-defined time points. The maximum ΔΔQTcF with tafenoquine 1200 mg (n = 50) was 6.39 milliseconds (90% CI 2.85, 9.94) at 72 hours post-final dose; that is, lack of effect for prolongation of cardiac depolarization was demonstrated. Tafenoquine 300 mg (n = 48) or 600 mg (n = 52) had no effect on ΔΔQTcF. Pharmacokinetic/pharmacodynamic modeling of the tafenoquine-QTcF concentration-effect relationship demonstrated a shallow slope (0.5 ms/μg mL(-1) ) over a wide concentration range. For moxifloxacin (n = 51), maximum ΔΔQTcF was 8.52 milliseconds (90% CI 5.00, 12.04), demonstrating assay sensitivity. In this thorough QT/QTc study, tafenoquine did not have a clinically meaningful effect on cardiac repolarization.

In vitro studies on the sensitivity pattern of Plasmodium falciparum to anti-malarial drugs and local herbal extracts

BACKGROUND

The resistance of human malaria parasites to anti-malarial compounds has become considerable concern, particularly in view of the shortage of novel classes of anti-malarial drugs. One way to prevent resistance is by using new compounds that are not based on existing synthetic antimicrobial agents.

RESULTS

Sensitivity of 100 Plasmodium falciparum isolates to chloroquine, quinine, amodiaquine, mefloquine, sulphadoxine/pyrimethamine, artemisinin, Momordica charantia ('Ejirin') Diospyros monbuttensis ('Egun eja') and Morinda lucida ('Oruwo') was determined using the in vitro microtest (Mark III) technique to determine the IC50 of the drugs. All the isolates tested were sensitive to quinine, mefloquine and artesunate. Fifty-one percent of the isolates were resistant to chloroquine, 13% to amodiaquine and 5% to sulphadoxine/pyrimethamine. Highest resistance to chloroquine (68.9%) was recorded among isolates from Yewa zone while highest resistance to amodiaquine (30%) was observed in Ijebu zone. Highest resistance to sulphadoxine/pyrimethamine was recorded in Yewa and Egba zones, respectively. A positive correlation was observed between the responses to artemisinin and mefloquine (P<0.05), artemisinin and quinine (P<0.05) and quinine and mefloquine (P<0.05). A negative correlation was observed between the responses to chloroquine and mefloquine (P>0.05). Highest anti-plasmodial activity was obtained with the ethanolic extract of D. monbuttensis (IC50 = 3.2 nM) while the lowest was obtained from M. lucida (IC50 = 25 nM).

CONCLUSIONS

Natural products isolated from plants used in traditional medicine, which have potent anti-plasmodial action in vitro, represent potential sources of new anti-malarial drugs.

Two series of new semisynthetic triterpene derivatives: differences in anti-malarial activity, cytotoxicity and mechanism of action

BACKGROUND

The discovery and development of anti-malarial compounds of plant origin and semisynthetic derivatives thereof, such as quinine (QN) and chloroquine (CQ), has highlighted the importance of these compounds in the treatment of malaria. Ursolic acid analogues bearing an acetyl group at C-3 have demonstrated significant anti-malarial activity. With this in mind, two new series of betulinic acid (BA) and ursolic acid (UA) derivatives with ester groups at C-3 were synthesized in an attempt to improve anti-malarial activity, reduce cytotoxicity, and search for new targets. In vitro activity against CQ-sensitive Plasmodium falciparum 3D7 and an evaluation of cytotoxicity in a mammalian cell line (HEK293T) are reported. Furthermore, two possible mechanisms of action of anti-malarial compounds have been evaluated: effects on mitochondrial membrane potential (ΔΨm) and inhibition of β-haematin formation.

RESULTS

Among the 18 derivatives synthesized, those having shorter side chains were most effective against CQ-sensitive P. falciparum 3D7, and were non-cytotoxic. These derivatives were three to five times more active than BA and UA. A DiOC(6)(3) ΔΨm assay showed that mitochondria are not involved in their mechanism of action. Inhibition of β-haematin formation by the active derivatives was weaker than with CQ. Compounds of the BA series were generally more active against P. falciparum 3D7 than those of the UA series.

CONCLUSIONS

Three new anti-malarial prototypes were obtained from natural sources through an easy and relatively inexpensive synthesis. They represent an alternative for new lead compounds for anti-malarial chemotherapy.