Drug-resistant Plasmodium Research Articles

Breaking the cycle of malaria treatment failure.

Treatment of symptomatic malaria became a routine component of the clinical and public health response to malaria after the second world war. However, all antimalarial drugs deployed against malaria eventually generated enough drug resistance that they had to be removed from use. Chloroquine, sulfadoxine-pyrimethamine, and mefloquine are well known examples of antimalarial drugs to which resistance did and still does ready evolve. Artemisinin-based combination therapies (ACTs) are currently facing the same challenge as artemisinin resistance is widespread in Southeast Asia and emerging in Africa. Here, I review some aspects of drug-resistance management in malaria that influence the strength of selective pressure on drug-resistant malaria parasites, as well as an approach we can take in the future to avoid repeating the common mistake of deploying a new drug and waiting for drug resistance and treatment failure to arrive. A desirable goal of drug-resistance management is to reduce selection pressure without reducing the overall percentage of patients that are treated. This can be achieved by distributing multiple first-line therapies (MFT) simultaneously in the population for the treatment of uncomplicated falciparum malaria, thereby keeping treatment levels high but the overall selection pressure exerted by each individual therapy low. I review the primary reasons that make MFT a preferred resistance management option in many malaria-endemic settings, and I describe two exceptions where caution and additional analyses may be warranted before deploying MFT. MFT has shown to be feasible in practice in many endemic settings. The continual improvement and increased coverage of genomic surveillance in malaria may allow countries to implement custom MFT strategies based on their current drug-resistance profiles.

On the genetics of malaria parasites, a memoir: Part II, the diversity and phylogeny of the rodent malaria parasites.

In this abbreviated extract of his memoirs of a life in malaria research, Richard Carter (1945-2021) describes the expansion and genetic characterisation of the rodent malaria parasite collection in Edinburgh, culminating in the description of four species, Plasmodium yoelii, Plasmodium berghei, Plasmodium chabaudi and Plasmodium vinckei, and the separation of these into multiple sub-species. The origins of the use of P. chabaudi for the investigation of the genetic determinants of drug resistance in malaria parasites is discussed.

Quinoline-based heterocyclic hydrazones: Design, synthesis, anti-plasmodial assessment, and mechanistic insights.

A library of quinoline-based hydrazones bearing 1H-1,2,3-triazole core was designed, synthesized, and evaluated for their antiplasmodial activity against the drug-resistant Plasmodium falciparum W2 strain. The inclusion of pyrazine-2-carboxylic acid with a flexible propyl spacer afforded the most active scaffold with an IC50 value of 0.26 μM. Mechanistically, the compound inhibited heme to hemozoin formation, as demonstrated by UV-vis and mass spectral studies.

Population genomics reveal distinct and diverging populations of An. minimus in Cambodia

Anopheles minimus is an important malaria vector throughout its wide geographic range across Southeast Asia. Genome sequencing could provide important insights into the unique malaria transmission dynamics in this region, where many vector species feed and rest outdoors. We describe results from a study using Illumina deep whole-genome sequencing of 302 wild-caught An. minimus collected from three Cambodian provinces over several years (2010, 2014, 2016) and seasons to examine the level of population structure and genetic diversity within this species. These specimens cluster into four distinct populations of An. minimus s.s., with two populations overlapping geographically. We describe the underlying genetic diversity and divergence of these populations and investigated the genetic variation in genes known to be involved in insecticide resistance. We found strong signals of selection within these An. minimus populations, most of which were present in the two Northeastern Cambodian populations and differ from those previously described in African malaria vectors. Cambodia is the focus of the emergence and spread of drug-resistant malaria parasites, so understanding the underlying genetic diversity and resilience of the vectors of these parasites is key to implementing effective malaria control and elimination strategies. These data are publicly available as part of the MalariaGEN Vector Observatory, an open access resource of genome sequence data.

Molecular Survey of Plasmodium falciparum Drug Resistant Genes Among Pregnant Women Attending ANC at Maryam Abacha Women and Children Hospital (MAWCH) Sokoto, Nigeria

Research was conducted on the molecular survey of drug resistant Plasmodium falciparum malaria among pregnant women attending ante natal care (ANC) at Maryam Abacha Women and Children Hospital (MAWCH) Sokoto, Nigeria from February, 2020 to May, 2020. Blood samples of 200 pregnant women who came for ANC in the Hospital were collected and Questionnaire administered. Thin and thick blood film microscopy and Plasmodium falciparum mono clonal antibody specific RDT kit were used to detect Plasmodium falciparum. P. falciparum positive dried blood samples were investigated for the presence of Pfmdr1 and Pfcrt genes using PCR protocol. Results for the investigation of Pfcrt and Pfmdr1 genes revealed 26.30% and 89.50% prevalence respectively, while 4 samples were positive for both genes representing 21.05% prevalence. Prevalence of Pfcrt and Pfmdr1 genes do not associate (p>0.05) with any of the parameters tested. Spread of the mutant genes observed in this study may be attributed to the continuous use of antimalarial drugs that the parasite developed resistant to. Pregnant women should be attending early ante-natal care booking and attend clinic regularly, malaria control programs should be carried out in the state.

Molecular Profiles of Multiple Antimalarial Drug Resistance Markers in Plasmodium falciparum and Plasmodium vivax in the Mandalay Region, Myanmar.

Emergence and spreading of antimalarial drug resistant malaria parasites are great hurdles to combating malaria. Although approaches to investigate antimalarial drug resistance status in Myanmar malaria parasites have been made, more expanded studies are necessary to understand the nationwide aspect of antimalarial drug resistance. In the present study, molecular epidemiological analysis for antimalarial drug resistance genes in Plasmodium falciparum and P. vivax from the Mandalay region of Myanmar was performed. Blood samples were collected from patients infected with P. falciparum and P. vivax in four townships around the Mandalay region, Myanmar in 2015. Partial regions flanking major mutations in 11 antimalarial drug resistance genes, including seven genes (pfdhfr, pfdhps, pfmdr-1, pfcrt, pfk13, pfubp-1, and pfcytb) of P. falciparum and four genes (pvdhfr, pvdhps, pvmdr-1, and pvk12) of P. vivax were amplified, sequenced, and overall mutation patterns in these genes were analyzed. Substantial levels of mutations conferring antimalarial drug resistance were detected in both P. falciparum and P. vivax isolated in Mandalay region of Myanmar. Mutations associated with sulfadoxine-pyrimethamine resistance were found in pfdhfr, pfdhps, pvdhfr, and pvdhps of Myanmar P. falciparum and P. vivax with very high frequencies up to 90%. High or moderate levels of mutations were detected in genes such as pfmdr-1, pfcrt, and pvmdr-1 associated with chloroquine resistance. Meanwhile, low frequency mutations or none were found in pfk13, pfubp-1, pfcytb, and pvk12 of the parasites. Overall molecular profiles for antimalarial drug resistance genes in malaria parasites in the Mandalay region suggest that parasite populations in the region have substantial levels of mutations conferring antimalarial drug resistance. Continuous monitoring of mutations linked with antimalarial drug resistance is necessary to provide useful information for policymakers to plan for proper antimalarial drug regimens to control and eliminate malaria in the country.

Malaria Surveillance - United States, 2018.

Malaria Surveillance - United States, 2018.

Developing Molecular Surveillance Capacity for Asymptomatic and Drug-Resistant Malaria in a Resource-Limited Setting-Experiences and Lessons Learned.

The COVID-19 pandemic has highlighted the important role molecular surveillance plays in public health. Such capacity however is either weak or nonexistent in many low-income countries. This article outlines a 2-year effort to establish two high-throughput molecular surveillance laboratories in Myanmar for tracking asymptomatic and drug resistant Plasmodium falciparum malaria. The lessons learned from this endeavor may prove useful for others seeking to establish similar molecular surveillance capacity in other resource-limited settings.

Ellagic Acid Induces in vitro Alkalinisation of the Digestive Vacuole in Drug-Sensitive Plasmodium falciparum Strain.

BackgroundMalaria is one of the leading causes of death worldwide caused by parasites of the genus Plasmodium. The reduced efficacy of the mainstay antimalarial drugs due to the widespread of drug-resistant Plasmodium falciparum (P. falciparum) necessitates an effort to develop novel antimalarial drugs with new targets. The effects of a phenolic compound, ellagic acid, against the malaria parasite have previously been reported. This present study aimed to evaluate the effect of ellagic acid on pH of the P. falciparum digestive vacuole.MethodsThe antimalarial potential of ellagic acid against the chloroquine-sensitive strain (3D7) of P. falciparum was assessed by using a malarial SYBR Green 1 fluorescence-based (MSF) assay. The effect of different concentrations of ellagic acid on the pH of the parasite’s digestive vacuole at mid-trophozoite stage was examined by using a ratiometric pH indicator, fluorescein isothiocyanate (FITC)-dextran on the flow cytometry.ResultsThe result of the MSF assay showed that ellagic acid has an antimalarial activity (half-maximal inhibitory concentration [IC50] = 1.85 ± 4.57 nM) at par with a standard drug, artemisinin (IC50 = 1.91 ± 5.41 nM). The pH of the digestive vacuole of ellagic acid-treated parasites was significantly changed (pH values ranged from 6.11 to 6.74) in a concentration-dependent manner as compared to untreated parasites (P < 0.001). A similar effect was shown by the parasites treated with a standard proton pump inhibitor, concanamycin A.ConclusionThese findings suggest that ellagic acid might have altered the digestive vacuole pH through the inhibition of proton pumps that regulate the acidification of this organelle. Overall, this study provides a valuable insight into the potential of ellagic acid as a promising antimalarial candidate with a novel mechanism of action.

The influence of biological, epidemiological, and treatment factors on the establishment and spread of drug-resistant Plasmodium falciparum.

The effectiveness of artemisinin-based combination therapies (ACTs) to treat Plasmodium falciparum malaria is threatened by resistance. The complex interplay between sources of selective pressure-treatment properties, biological factors, transmission intensity, and access to treatment-obscures understanding how, when, and why resistance establishes and spreads across different locations. We developed a disease modelling approach with emulator-based global sensitivity analysis to systematically quantify which of these factors drive establishment and spread of drug resistance. Drug resistance was more likely to evolve in low transmission settings due to the lower levels of (i) immunity and (ii) within-host competition between genotypes. Spread of parasites resistant to artemisinin partner drugs depended on the period of low drug concentration (known as the selection window). Spread of partial artemisinin resistance was slowed with prolonged parasite exposure to artemisinin derivatives and accelerated when the parasite was also resistant to the partner drug. Thus, to slow the spread of partial artemisinin resistance, molecular surveillance should be supported to detect resistance to partner drugs and to change ACTs accordingly. Furthermore, implementing more sustainable artemisinin-based therapies will require extending parasite exposure to artemisinin derivatives, and mitigating the selection windows of partner drugs, which could be achieved by including an additional long-acting drug.

Evaluation of the Effect of Gene Duplication by Genome Editing on Drug Resistance in Plasmodium falciparum.

The emergence and spread of drug-resistant Plasmodium falciparum have compromised antimalarial efficacy and threatened the global malaria elimination campaign using artemisinin combination therapies. The impacts of amino acid substitutions in antimalarial drug resistance-associated genes on drug susceptibility have been investigated; however, the effects of amplification of those genes remain unexplored due to the lack of robust genetic approaches. Here, we generated transgenic P. falciparum parasites with an additional copy of a drug resistance-associated gene using the highly efficient CRISPR/Cas9 system and investigated their drug response. Insertion of a drug resistance-associated gene expression cassette in the genome resulted in a roughly twofold increase of mRNA levels of the target gene mdr1, which encodes multidrug resistance protein 1. The gene duplication event contributed to resistance to mefloquine, lumefantrine, and dihydroartemisinin, while the duplication of a genomic region encoding plasmepsin 2 and plasmepsin 3 did not affect resistance to antimalarial drugs, including piperaquine. We further demonstrated that mdr1 mRNA expression levels are strongly associated with mefloquine resistance in several field-derived P. falciparum lines with various genetic backgrounds. This study provides compelling evidence that mdr1 could serve as a molecular marker for the surveillance of mefloquine-resistant parasites. Long DNA integration into parasite genomes using the CRISPR/Cas9 system provides a useful tool for the evaluation of the effect of copy number variation on drug response.

BIOORGANOMETALLIC FERROQUINE AND RELATED COMPOUNDS AS ANTIMALARIAL CHEMOTHERAPEUTIC AGENTS: A SHORT REVIEW

Drug resistant Plasmodium falciparum is a major threat to global health. Eradicating the parasite in endemic regions, especially sub-Saharan Africa is daunting. Milestones and a general target of 2030 have been set for this. However, funding and disruptions due to Ebola virus disease epidemic and COVID-19 pandemic are some of the cog in the wheel of the malaria eradication program. The recent WHO approval of the first malaria vaccine is a hope raiser and is expected to merely catalyze the eradication effort. Chemoprevention is a key malaria eradication strategy. Ferroquine, an organometallic chloroquine-ferrocene conjugate with effective antimalarial properties is capable of overcoming resistant strains and restoring chloroquine antimalarial properties. It has a novel mechanism of action. Like chloroquine, it forms complex with Fe(III)PPIX, strongly inhibit ß-hematin formation and drug accumulation in the acidic digestive vacuole. ferroquine is more lipophilic at cytosolic pH and cannot be pumped out of digestive vacuole thereby evading the chloroquine resistance mechanism. Clinical trials showed the drug candidate to be safe and tolerable. The ferroquine molecule can be conveniently synthesized via a reductive amination reaction involving a condensation of 7-chloroquinolin-4-amine and amino ferrocenyl aldehyde in a single stage procedure. It is well characterized. Studies revealed that covalently bonded chloroquine-ferrocene is responsible for the molecule's efficacy against P. falciparum. The pure chloroquine or ferrocene moieties are less active. Structural adjustments in amino group side chain, changes in position of the ferrocenyl organometallic group, substituting the Fe with other bioactive metals (Ru, Rh, Os) and substituting chloroquine for other organic molecules with antimalarial properties, all resulted in analogues with potent antimalarial properties similar to or better than chloroquine but not as effective as ferroquine.

Drug resistance in plasmodium, future malaria management strategies and importance of medicinal plants

Malaria, the most common and destructive parasite disease in humans, take the lives of 1-2 million people every year. With the exception of artemisinin, resistance to most of the existing antimalarial agent classes has arisen, resulting in a new spike in malaria-related mortality, particularly in Africa. Southeast Asia has been a focal point for the development of drug resistance in Plasmodium falciparum since the late 1950s, when the first example of chloroquine resistance was discovered along the Thai-Combodian border. Despite the fact that the first incidence of quinine resistance had been documented far earlier in South America, the emergence of chloroquine resistance in Southeast Asia signalled the beginning of a new era in malaria history. Following the development of chloroquine resistance, Thailand and African countries shifted to a sulphadoxine-pyrimethamine combination as their first-line medication (SP). SP was subsequently superseded by mefloquine. Because of the quick development of resistance to this new medicine, artemisinin was introduced as a combination drug in the mid-1990s. Artimisinin resistance has been identified in several parts of the world, and if it continues, malaria control initiatives could be jeopardised, as there is now no substitute antimalarial medicine available. The purpose of this review is to summarise the current state of knowledge about drug-resistant malaria and to sketch out the evolving trends of resistance to antibiotics, such as its causal factors, current situation in various geographical areas, molecular markers, consequences for preventing the emergence and spread of drugresistant malaria, and the role of medicinal plants in the discovery of novel antimalarials.

Designing and development of phthalimides as potent anti-tubulin hybrid molecules against malaria

Constant emergence of drug-resistant Plasmodium falciparum warrants urgent need for effective and inexpensive drugs. Herein, phthalimide (Pht) analogs possessing the bioactive scaffolds, benzimidazole and 1,2,3-triazole, were evaluated for in vitro and in vivo anti-plasmodial activity without any apparent hemolysis, or cytotoxicity. Analogs 4(a-e) inhibited the growth of 3D7 and RKL-9 strains at submicromolar concentrations. Defects were observed during parasite egress from or invasion of the red blood cells. Mitochondrial membrane depolarization was measured as one of the causes of cell death. Phts 4(a-e) in combination with artemisinin exhibited two-to three-fold increased efficacy. Biophysical and biochemical analysis suggest that Pht analogs mediate plasmodial growth inhibition by interacting with tubulin protein of the parasite. Lastly, Phts 4(a-e) significantly decreased parasitemia and extended host survival in murine model Plasmodium berghei ANKA infection. Combined, the data indicate that Pht analogs should be further explored, which could offer novel value to the antimalarial drug development pipeline.

Antimalarial drug resistance—is it time to re-evaluate Plasmodium falciparum orthologous genes?

Antimalarial drug resistance—is it time to re-evaluate Plasmodium falciparum orthologous genes?

An overview of the Plasmodium falciparum hexose transporter and its therapeutic interventions.

Despite intense elimination efforts, human malaria, caused by the infection of five Plasmodium species, remains the deadliest parasitic disease in the world. Even worse, with the emergence and spreading of the first-line drug-resistant Plasmodium parasites, therapeutic interventions based on novel plasmodial drug targets are more necessary than ever. Given that the blood-stage parasites primarily rely on glycolysis for their energy supply, blocking glucose uptake, the rate-limiting step of ATP generation, was considered a promising approach to kill these parasites. To achieve this goal, characterization of the plasmodial hexose transporter and development of selective inhibitors have been pursued for decades. Here, we review the identification and characterization of the Plasmodium falciparum hexose transporter (PfHT1) and summarize current advances in its inhibitor development.

In-Silico Structural Modeling and Prediction of Conformational B-Cell Epitopes of Potential Vaccine Candidate Pre-Binding Protein

Malaria is a life threatening infectious disease causes by Plasmodium species, wherein Plasmodium falciparum being the most lethal causes severe malaria. Plasmodium parasites have a complex life cycle and employed several immunity evading mechanism that enable the parasite to multiply and survive avoiding the host immunity. The rise in drug-resistant Plasmodium parasites and the unavailability of an effective vaccine lead to major challenges in controlling the parasite. Therefore, it is of utmost important to identify novel potential targets that can be directed for therapeutic intervention. In the present study, conservancy, localization, and the antigenicity of PREBP was determined by using different bioinformatics tools. The 3D structure of PREBP was modeled and conformational B-cell epitopes of the protein were predicted using Ellipro. The resulted epitopes might be of great importance as a vaccine sub-unit in the development of an effective malaria vaccine and the generated 3D structure of the protein can be further used for other structural analysis.

Pediatric Participant Retention Rates in a Longitudinal Malaria Immunology Study.

ABSTRACT.The resurgence of drug-resistant Plasmodium falciparum parasites continues to motivate the development of a safe and efficacious malaria vaccine. Immuno-epidemiologic studies of naturally acquired immunity (NAI) have been a useful strategy to identify new malaria vaccine targets. However, retention of pediatric participants throughout longitudinal studies is essential for gathering comprehensive exposure and outcome data. Within the context of a 3-year cohort (N = 400) study involving monthly finger prick and bi-annual venous blood sample collections, we conducted qualitative surveys to assess factors impacting participant retention. Phase 1 was conducted 3 months after enrollment in July 2018 and phase 2, 12 months later. In phase 1, 236 parents/guardians participated in focus groups and three withdrawn participants and 10 community health volunteers (CHVs) in key informant interviews. Qualitative analysis indicated overall satisfaction with the study, with 61.8% (136/220 respondents) reporting no concerns. Focus group discussants associated attendance with benefits such as improved access to comprehensive healthcare services. Community health volunteers reported concerns over village rumors of inappropriate use of blood samples and dangers associated with venous blood draws. Phase 2 involved 205 parents/guardians and revealed continued satisfaction, with 46.3% (95/205) identifying no concerns, but expressed increasing worries regarding the amount of venous blood sample. This concern was reflected in an uptick of missed visits when venous blood samples were scheduled. Future studies will address parental concerns to determine whether community engagement and education measures increase study retention until completion.

In vivo antimalarial efficacy of Psidium guajava leaf crude extract and fractions in Plasmodium berghei infected mice

Background: Malaria is a life-threatening disease caused by the protozoan parasite, Plasmodium. The emergence of drug-resistant Plasmodium species to currently available antimalarials has necessitated the search for more effective drugs. This study evaluated the antimalarial potential of the crude extract and fractions of Psidium guajava leaf in Plasmodium berghei infected mice. Method: Mice infected with Plasmodium berghei (P. berghei) were administered orally with the crude extract and fractions at doses ranging from 100-500 and 50-200mg/kg/day respectively, for five consecutive days. Results: The crude extract significantly (p&lt;0.05) inhibited parasite growth as well as prevented body weight loss and packed cell volume reduction dose-dependently. Among the fractions, aqueous fraction was the most active with 54.26% inhibition of parasite growth at 200mg/kg. Remarkable inhibition of parasite growth by the crude extract and aqueous fraction was evident in the prolongation of mice survival relative to the control (27.33±1.76, 24.67±0.67, 28.0±1.16 and 8.33±0.67 for crude extract (500mg/kg), aqueous fraction (200mg/kg), chloroquine and negative control groups respectively). Phytochemical screening of the crude extract revealed the presence of phenol, alkaloids, flavonoids, and terpenoids. Conclusion: The results indicate that crude extract and aqueous fraction of P. guajava leaf are potent antimalarial agent that can be employed in the development of antimalarial drugs.

Iloneoside, an antimalarial pregnane glycoside isolated from Gongronema latifolium leaf, potentiates the activity of chloroquine against multidrug resistant Plasmodium falciparum

The rapid spread of drug resistant malaria parasites has necessitated the search for novel antimalarials and chemosensitizers capable of reversing drug resistance in the parasites. A number of studies have revealed the resistance reversal activities of pregnane glycosides and the antimalarial activity of a pregnane glycoside obtained from Gongronema species. However, the pregnane (2) and pregnane glycosides (1, 3–4) isolated from Gongronema latifolium leaf have not been evaluated for these activities. This study was therefore carried out to evaluate the antiplasmodial and chloroquine resistance reversal activities of a pregnane and three pregnane glycosides isolated from G. latifolium leaf in vitro. The compounds were evaluated for their inhibitory activities against P. falciparum 3D7 (a chloroquine-sensitive strain) and P. falciparum W2 (a chloroquine-resistant clone) in vitro. The activities of chloroquine in separate combination with each of the compounds against P. falciparum W2 were also evaluated. Moreover, the interaction of the active compounds (1 and 4) with selected P. falciparum proteins (PfProteins) were evaluated in silico. The results revealed that only 1 and 4 were active against P. falciparum 3D7 and P. falciparum W2. Also, 2 and 3 did not exhibit chloroquine resistance reversal activity. Activity of chloroquine against P. falciparum W2 was potentiated by 1 by 3200% at concentrations higher than 0.625 µg/mL. Also, 1 and 4 demonstrated similar binding patterns and higher binding tendencies to the selected PfProteins compared to chloroquine. Thus, 1 (iloneoside) is an antimalarial pregnane glycoside which can potentiate the activity of chloroquine against multidrug resistant P. falciparum.