Artemisinin-resistant Plasmodium Falciparum Research Articles

Artemisinin-resistant Plasmodium falciparum Kelch13 mutant proteins display reduced heme-binding affinity and decreased artemisinin activation.

The potency of frontline antimalarial drug artemisinin (ART) derivatives is triggered by heme-induced cleavage of the endoperoxide bond to form reactive heme-ART alkoxy radicals and covalent heme-ART adducts, which are highly toxic to the parasite. ART-resistant (ART-R) parasites with mutations in the Plasmodium falciparum Kelch-containing protein Kelch13 (PfKekch13) exhibit impaired hemoglobin uptake, reduced yield of hemoglobin-derived heme, and thus decreased ART activation. However, any direct involvement of PfKelch13 in heme-mediated ART activation has not been reported. Here, we show that the purified recombinant PfKelch13 wild-type (WT) protein displays measurable binding affinity for iron and heme, the main effectors for ART activation. The heme-binding property is also exhibited by the native PfKelch13 protein from parasite culture. The two ART-R recombinant PfKelch13 mutants (C580Y and R539T) display weaker heme binding affinities compared to the ART-sensitive WT and A578S mutant proteins, which further translates into reduced yield of heme-ART derivatives when ART is incubated with the heme molecules bound to the mutant PfKelch13 proteins. In conclusion, this study provides the first evidence for ART activation via the heme-binding propensity of PfKelch13. This mechanism may contribute to the modulation of ART-R levels in malaria parasites through a novel function of PfKelch13.

Enhanced cell stress response and protein degradation capacity underlie artemisinin resistance in Plasmodium falciparum.

Malaria remains a global health burden, killing over half a million people each year. Decreased therapeutic efficacy to artemisinin, the most efficacious antimalarial, has been detected in sub-Saharan Africa, a worrying fact given that over 90% of deaths occur on this continent. Mutations in Kelch13 are the most well-established molecular marker for artemisinin resistance, but these do not explain all artemisinin-resistant isolates. Understanding the biological underpinnings of drug resistance is key to curbing the emergence and spread of artemisinin resistance. Artemisinin-mediated non-specific alkylation leads to the accumulation of misfolded and damaged proteins and activation of the parasite unfolded protein response (UPR). In addition, the parasite proteasome is vital to artemisinin resistance, as we have previously shown that chemical inhibition of the proteasome or mutations in the β2 proteasome subunit increase parasite susceptibility to dihydroartemisinin (DHA), the active metabolite of artemisinins. Here, we investigate parasites with mutations at the Kelch13 and/or 19S and 20S proteasome subunits with regard to UPR regulation and proteasome activity in the context of artemisinin resistance. Our data show that perturbing parasite proteostasis kills parasites, early parasite UPR signaling dictates DHA survival outcomes, and DHA susceptibility correlates with impairment of proteasome-mediated protein degradation. Importantly, we show that functional proteasomes are required for artemisinin resistance in a Kelch13-independent manner, and compound-selective proteasome inhibition demonstrates why artemisinin-resistant Kelch13 mutants remain susceptible to the related antimalarial peroxide OZ439. These data provide further evidence for targeting the parasite proteasome and UPR to overcome existing artemisinin resistance.IMPORTANCEDecreased therapeutic efficacy represents a major barrier to malaria treatment control strategies. The malaria proteasome and accompanying unfolded protein response are crucial to artemisinin resistance, revealing novel antimalarial therapeutic strategies.

Artemisinin-resistant malaria.

SUMMARYThe artemisinin antimalarials are the cornerstone of current malaria treatment. The development of artemisinin resistance in Plasmodium falciparum poses a major threat to malaria control and elimination. Recognized first in the Greater Mekong subregion of Southeast Asia nearly 20 years ago, artemisinin resistance has now been documented in Guyana, South America, in Papua New Guinea, and most recently, it has emerged de novo in East Africa (Rwanda, Uganda, South Sudan, Tanzania, Ethiopia, Eritrea, and eastern DRC) where it has now become firmly established. Artemisinin resistance is associated with mutations in the propeller region of the PfKelch gene, which play a causal role, although the parasites' genetic background also makes an important contribution to the phenotype. Clinically, artemisinin resistance manifests as reduced parasiticidal activity and slower parasite clearance and thus an increased risk of treatment failure following artemisinin-based combination therapy (ACT). This results from the loss of artemisinin activity against the younger circulating ring stage parasites. This loss of activity is likely to diminish the life-saving advantage of artesunate in the treatment of severe falciparum malaria. Gametocytocidal and thus transmission blocking activities are also reduced. At current levels of resistance, artemisinin-resistant parasites still remain susceptible at the trophozoite stage of asexual development, and so, artemisinin still contributes to the therapeutic response. As ACTs are the most widely used antimalarial drugs in the world, it is essential from a malaria control perspective that ACT cure rates remain high. Better methods of identifying uncomplicated hyperparasitemia, the main cause of ACT treatment failure, are required so that longer courses of treatment can be given to these high-risk patients. Reducing the use of artemisinin monotherapies will reduce the continued selection pressure which could lead potentially to higher levels of artemisinin resistance. Triple artemisinin combination therapies should be deployed as soon as possible to protect the ACT partner drugs and thereby delay the emergence of higher levels of resistance. As new affordable antimalarial drugs are still several years away, the control of artemisinin resistance must depend on the better use of available tools.

In artemisinin-resistant falciparum malaria parasites, mitochondrial metabolic pathways are essential for survival but not those of apicoplast

Emergence and spread of parasite resistance to artemisinins, the first-line antimalarial therapy, threaten the malaria eradication policy. To identify therapeutic targets to eliminate artemisinin-resistant parasites, the functioning of the apicoplast and the mitochondrion was studied, focusing on the fatty acid synthesis type II (FASII) pathway in the apicoplast and the electron transfer chain in the mitochondrion. A significant enrichment of the FASII pathway among the up-regulated genes in artemisinin-resistant parasites under dihydroartemisinin treatment was found, in agreement with published transcriptomic data. However, using GC-MS analyzes of fatty acids, we demonstrated for the first time that the FASII pathway is non-functional, ruling out the use of FASII inhibitors to target artemisinin-resistant parasites. Conversely, by assessing the modulation of the oxygen consumption rate, we evidenced that mitochondrial respiration remains functional and flexible in artemisinin-resistant parasites and even at the quiescent stage. Two novel compounds targeting electron transport chain (ELQ300, ELQ400) efficiently killed quiescent artemisinin-resistant parasites. Therefore, mitochondrial respiration represents a key target for the elimination of artemisinin-resistant persistent Plasmodium falciparum parasites.

Mutations in Plasmodium falciparum Kelch13 (PfK13) dysregulates PI3K/AKT signalling pathway in artemisinin resistance

BackgroundPfK13 protein mutations are associated with the emergence of artemisinin resistance in Plasmodium falciparum. PfK13 protein is essential for mediating ubiquitination and controlling the PI3K/AKT pathway. Mutant PfK13 variations can interfere with substrate binding, especially with PfPI3K, which raises PfPI3K levels. MethodsDUET, DynaMut2, mCSM, iStable 2.0, I-Mutant 2.0, and MuPro were utilized to study the protein stability and protein-substrate binding was studied using HADDOCK 2.4 docking algorithm between Wild-type and mutant PfK13 with the helical and catalytic domain of PfPI3K. Resultsi-Stable server analysis predicted that seven, out of the nine mutations associated with artemisinin resistance (F446I, Y493H, R539T, I543T, P553L, R561H, C580Y) reduced the protein stability. HADDOCK scores of the catalytic domain underscores the significant impact of the reported mutations on the binding affinity of the PfK13 protein. Further validation through the MM_GBSA technique, the binding free energy (DDG) between the wild-type and the mutant PfK13 protein analysis revealed a loss of interactions resulting from mutations in PfK13. ConclusionThe study finding suggest that mutations in the PfK13 cause destabilization in the protein structure and affects the binding of PfPI3K. Although the findings remain preliminary and require further validation, it provides the basis for further research considering the importance of the interaction of PfK13 and PfPI3K to overcome the impact of artemisinin resistance.

Synthesis, molecular modelling studies of artemisinin-chalcone derivatives and their antimalarial activity evaluation

Twenty-two monomers and dimers of artemisinin having chalcone as a linker were synthesised, and their antimalarial activity against Plasmodium falciparum was determined, and a quantitative structure-activity relationship (QSAR) was developed. Artemisinin is a frontline antimalarial drug known worldwide but is threatened because of the rapidly emerging artemisinin-resistant strain Plasmodium falciparum. In vitro, antimalarial IC50 (half-maximal inhibitory concentration) activity of a molecule against malaria parasites provides a good first screen for identifying the antimalarial potential of a particular molecule. The most active compound was artemisinin dimer dimethoxy chalcone as a linker (22) with IC50 of 4.34 nM. The molecular mechanism was explored through in silico docking & ADMET studies for the active compounds.

Prefoldins are novel regulators of the unfolded protein response in artemisinin resistant Plasmodium falciparum malaria

Emerging Artemisinin (ART) resistance in Plasmodium falciparum (Pf) poses challenges for the discovery of novel drugs to tackle ART-resistant parasites. Concentrated efforts toward the ART resistance mechanism indicated a strong molecular link of ART resistance with upregulated expression of unfolded protein response pathways involving Prefoldins (PFDs). However, a complete characterization of PFDs as molecular players taking part in ART resistance mechanism, and discovery of small molecule inhibitors to block this process have not been identified to date. Here, we functionally characterized all Pf Prefoldin subunits (PFD1-6) and established a causative role played by PFDs in ART resistance by demonstrating their expression in intra-erythrocytic parasites along with their interactions with Kelch13 protein through immunoprecipitation coupled MS/MS analysis. Systematic biophysical interaction analysis between all subunits of PFDs revealed their potential to form a complex. The role of PFDs in ART resistance was confirmed in orthologous yeast PFD6 mutants, where PfPFD6 expression in yeast mutants reverted phenotype to ART resistance. We identified an FDA-approved drug "Biperiden" that restricts the formation of Prefoldin complex and inhibits its interaction with its key parasite protein substrates, MSP-1 and α-tubulin-I. Moreover, Biperiden treatment inhibits the parasite growth in ART-sensitive Pf3D7 and resistant Pf3D7k13R539T strains. Ring survival assays that are clinically relevant to analyze ART resistance in Pf3D7k13R539T parasites demonstrate the potency of BPD to inhibit the growth of survivor parasites. Overall, our study provides the first evidence of the role of PfPFDs in ART resistance mechanisms and opens new avenues for the management of resistant parasites.

Molecular Surveillance of Artemisinin-Resistant Plasmodium falciparum Parasites in Mining Areas of the Roraima Indigenous Territory in Brazil.

Multidrug- and artemisinin-resistant (ART-R) Plasmodium falciparum (Pf) parasites represent a challenge for malaria elimination worldwide. Molecular monitoring in the Kelch domain region (pfk13) gene allows tracking mutations in parasite resistance to artemisinin. The increase in illegal miners in the Roraima Yanomami indigenous land (YIL) could favor ART-R parasites. Thus, this study aimed to investigate ART-R in patients from illegal gold mining areas in the YIL of Roraima, Brazil. A questionnaire was conducted, and blood was collected from 48 patients diagnosed with P. falciparum or mixed malaria (Pf + P. vivax). The DNA was extracted and the pfk13 gene was amplified by PCR. The amplicons were subjected to DNA-Sanger-sequencing and the entire amplified fragment was analyzed. Among the patients, 96% (46) were from illegal mining areas of the YIL. All parasite samples carried the wild-type genotypes/ART-sensitive phenotypes. These data reinforce the continued use of artemisinin-based combination therapies (ACTs) in Roraima, as well as the maintenance of systematic monitoring for early detection of parasite populations resistant to ART, mainly in regions with an intense flow of individuals from mining areas, such as the YIL. This is especially true when the achievement of falciparum malaria elimination in Brazil is planned and expected by 2030.

Delving into artemisinin’s shadow: Insights from a unique case of artesunate – resistant complicated falciparum malaria

The emergence of drug-resistant malaria poses a formidable health challenge in emerging nations such as India. The ineffectiveness of the medicine artemisinin, which is essential for treating malaria, will quickly undermine the treatment and outlook for malaria patients. If, following a complete course of therapy with Artesunate Combination Therapy and without any instances of vomiting or diarrhoea, there is no clinical or parasitological improvement in the patient within 72 hours, resistance may be considered. Reports of artemisinin-resistant Plasmodium falciparum malaria are rare in the southern regions of India. This article details a case of rare Artesunate-resistant complex falciparum malaria.

Detection of drug-resistant malaria in resource-limited settings: efficient and high-throughput surveillance of artemisinin and partner drug resistance.

Artemisinin-resistant Plasmodium falciparum malaria is currently spreading globally, including in Africa. Artemisinin resistance also leads to resistance to partner drugs used in artemisinin-based combination therapies. Sequencing of kelch13, which is associated with artemisinin resistance, culture-based partner drug susceptibility tests, and ELISA-based growth measurement are conventionally used to monitor resistance; however, their application is challenging in resource-limited settings. An experimental package for field studies with minimum human/material requirements was developed. First, qPCR-based SNP assay was applied in artemisinin resistance screening, which can detect mutations within 1 h and facilitate sample selection for subsequent processes. It had 100% sensitivity and specificity compared with DNA sequencing in the detection of the two common artemisinin resistance mutations in Uganda, C469Y and A675V. Moreover, in the partner drug susceptibility test, the cultured samples were dry-preserved on a 96-well filter paper plate and shipped to the central laboratory. Parasite growth was measured by ELISA using redissolved samples. It well reproduced the results of direct ELISA, reducing significant workload in the field (Pearson correlation coefficient: 0.984; 95% CI: 0.975-0.990). Large-scale and sustainable monitoring is required urgently to track rapidly spreading drug-resistant malaria. In malaria-endemic areas, where research resources are often limited, simplicity and feasibility of the procedure is especially important. Our approach combines a qPCR-based rapid test, which is also applicable to point-of-care diagnosis of artemisinin resistance and centralized analysis of ex vivo culture. The approach could improve efficiency of field experiments and accelerate global drug resistance surveillance.

Potential role of CI-679 against artemisinin-resistant <i>Plasmodium falciparum</i>

Purpose: To investigate the role of nitroquine (CI-679) against artemisinin-resistant Plasmodium falciparum (P. falciparum) C580Y strain.
 Methods: Antimalarial activity of CI-679 against blood stages in Plasmodium yoelii (P. yoelii) - infected BALB/c mice model was first identified. Thereafter, in vitro assays were performed to investigate the inhibitory activity against blood stages of artemisinin-sensitive P. falciparum 3D7 strain. Finally, the potential effect of CI-679 was also investigated on artemisinin-resistant P. falciparum, which was constructed by introducing C580Y mutation in K13 of the 3D7 using the CRISPR-CAS9 technology.
 Results: CI-679 significantly suppressed the growth of rodent malaria parasite, P. yoelii BY265, in a dose-dependent manner, and also inhibited the development of the parasites in mice (p < 0.05). Furthermore, CI-679 efficiently inhibited the growth of artemisinin-sensitive P. falciparum 3D7 in vitro, with more sensitivity against late phase of blood stages (p < 0.05). Also, CI-679 suppressed the development of artemisinin-resistant P. falciparum C580Y strain, and the inhibitory effect was comparable to that of artemisinin-sensitive 3D7 strain.
 Conclusion: CI-679 exhibits potent antimalarial activity against blood stages of P. yoelii BY265 in vivo, and both artemisinin-sensitive P. falciparum 3D7 and artemisinin-resistant P. falciparum C580Y in vitro. Further pharmacokinetic properties, tolerability and safety of the compound need to be investigated to support this claim.

Screening for K13-Propeller Mutations Associated with Artemisinin Resistance in Plasmodium falciparum in Yambio County (Western Equatoria State, South Sudan).

Artemisinin-combined treatments are the recommended first-line treatment of Plasmodium falciparum malaria, but they are being threatened by emerging artemisinin resistance. Mutations in pfk13 are the principal molecular marker for artemisinin resistance. This study characterizes the presence of mutations in pfk13 in P. falciparum in Western Equatoria State, South Sudan. We analyzed 468 samples from patients with symptomatic malaria and found 15 mutations (8 nonsynonymous and 7 synonymous). Each mutation appeared only once, and none were validated or candidate markers of artemisinin resistance. However, some mutations were in the same or following position of validated and candidate resistance markers, suggesting instability of the gene that could lead to resistance. The R561L nonsynonymous mutation was found in the same position as the R561H validated mutation. Moreover, the A578S mutation, which is widespread in Africa, was also reported in this study. We found a high diversity of other pfk13 mutations in low frequency. Therefore, routine molecular surveillance of resistance markers is highly recommended to promptly detect the emergence of resistance-related mutations and to limit their spread.

Molecular insights into artemisinin resistance in Plasmodium falciparum: An updated review.

Malaria still poses a major burden on human health around the world, especially in endemic areas. Plasmodium resistance to several antimalarial drugs has been one of the major hindrances in control of malaria. Thus, the World Health Organization recommended artemisinin-based combination therapy (ACT) as a front-line treatment for malaria. The emergence of parasites resistant to artemisinin, along with resistant to ACT partner drugs, has led to ACT treatment failure. The artemisinin resistance is mostly related to the mutations in the propeller domain of the kelch13 (k13) gene that encodes protein Kelch13 (K13). The K13 protein has an important role in parasite reaction to oxidative stress. The most widely spread mutation in K13, with the highest degree of resistance, is a C580Y mutation. Other mutations, which are already identified as markers of artemisinin resistance, are R539T, I543T, and Y493H. The objective of this review is to provide current molecular insights into artemisinin resistance in Plasmodium falciparum. The trending use of artemisinin beyond its antimalarial effect is described. Immediate challenges and future research directions are discussed. Better understanding of the molecular mechanisms underlying artemisinin resistance will accelerate implementation of scientific findings to solve problems with malarial infection.

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

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

Examining the Early Distribution of the Artemisinin-Resistant Plasmodium falciparum kelch13 R561H Mutation in Areas of Higher Transmission in Rwanda.

Artemisinin resistance mutations in Plasmodium falciparum kelch13 (Pfk13) have begun to emerge in Africa, with Pfk13-R561H being the first reported in Rwanda in 2014, but limited sampling left questions about its early distribution and origin. We genotyped P. falciparum positive dried blood spot (DBS) samples from a nationally representative 2014-2015 Rwanda Demographic Health Surveys (DHS) HIV study. DBS were subsampled from DHS sampling clusters with >15% P. falciparum prevalence, as determined by rapid testing or microscopy done during the DHS study (n clusters = 67, n samples = 1873). We detected 476 parasitemias among 1873 residual blood spots from a 2014-2015 Rwanda Demographic Health Survey. We sequenced 351 samples: 341/351 were wild-type (97.03% weighted), and 4 samples (1.34% weighted) harbored R561H that were significantly spatially clustered. Other nonsynonymous mutations found were V555A (3), C532W (1), and G533A (1). Our study better defines the early distribution of R561H in Rwanda. Previous studies only observed the mutation in Masaka as of 2014, but our study indicates its presence in higher-transmission regions in the southeast of the country at that time.

The Parasite Reduction Ratio (PRR) Assay Version 2: Standardized Assessment of Plasmodium falciparum Viability after Antimalarial Treatment In Vitro

With artemisinin-resistant Plasmodium falciparum parasites emerging in Africa, the need for new antimalarial chemotypes is persistently high. The ideal pharmacodynamic parameters of a candidate drug are a rapid onset of action and a fast rate of parasite killing or clearance. To determine these parameters, it is essential to discriminate viable from nonviable parasites, which is complicated by the fact that viable parasites can be metabolically inactive, whilst dying parasites can still be metabolically active and morphologically unaffected. Standard growth inhibition assays, read out via microscopy or [3H] hypoxanthine incorporation, cannot reliably discriminate between viable and nonviable parasites. Conversely, the in vitro parasite reduction ratio (PRR) assay is able to measure viable parasites with high sensitivity. It provides valuable pharmacodynamic parameters, such as PRR, 99.9% parasite clearance time (PCT99.9%) and lag phase. Here we report the development of the PRR assay version 2 (V2), which comes with a shorter assay duration, optimized quality controls and an objective, automated analysis pipeline that systematically estimates PRR, PCT99.9% and lag time and returns meaningful secondary parameters such as the maximal killing rate of a drug (Emax) at the assayed concentration. These parameters can be fed directly into pharmacokinetic/pharmacodynamic models, hence aiding and standardizing lead selection, optimization, and dose prediction.

Dinuclear and mononuclear metal(II) polypyridyl complexes against drug-sensitive and drug-resistant Plasmodium falciparum and their mode of action

BackgroundMalaria remains one of the most virulent and deadliest parasitic disease in the world, particularly in Africa and Southeast Asia. Widespread occurrence of artemisinin-resistant Plasmodium falciparum strains from the Greater Mekong Subregion is alarming. This hinders the national economies, as well as being a major drawback in the effective control and elimination of malaria worldwide. Clearly, an effective anti-malarial drug is urgently needed.MethodsThe dinuclear and mononuclear copper(II) and zinc(II) complexes were synthesized in ethanolic solution and characterized by various physical measurements (FTIR, CHN elemental analysis, solubility, ESI-MS, UV-Visible, conductivity and magnetic moment, and NMR). X-ray crystal structure of the dicopper(II) complex was determined. The in vitro haemolytic activities of these metal complexes were evaluated spectroscopically on B+ blood while the anti-malarial potency was performed in vitro on blood stage drug-sensitive Plasmodium falciparum 3D7 (Pf3D7) and artemisinin-resistant Plasmodium falciparum IPC5202 (Pf5202) with fluorescence dye. Mode of action of metal complexes were conducted to determine the formation of reactive oxygen species using PNDA and DCFH-DA dyes, JC-1 depolarization of mitochondrial membrane potential, malarial 20S proteasome inhibition with parasite lysate, and morphological studies using Giemsa and Hoechst stains.ResultsCopper(II) complexes showed anti-malarial potency against both Pf3D7 and Pf5202 in sub-micromolar to micromolar range. The zinc(II) complexes were effective against Pf3D7 with excellent therapeutic index but encountered total resistance against Pf5202. Among the four, the dinuclear copper(II) complex was the most potent against both strains. The zinc(II) complexes caused no haemolysis of RBC while copper(II) complexes induced increased haemolysis with increasing concentration. Further mechanistic studies of both copper(II) complexes on both Pf3D7 and Pf5202 strains showed induction of ROS, 20S malarial proteasome inhibition, loss of mitochondrial membrane potential and morphological features indicative of apoptosis.ConclusionThe dinuclear [Cu(phen)-4,4′-bipy-Cu(phen)](NO3)4 is highly potent and can overcome the total drug-resistance of Pf5202 towards chloroquine and artemisinin. The other three copper(II) and zinc(II) complexes were only effective towards the drug-sensitive Pf3D7, with the latter causing no haemolysis of RBC. Their mode of action involves multiple targets.Graphical

Bibliometric analysis of publications pertaining to artemisinin resistance in Plasmodium falciparum based on Web of Science from 2011 to 2022

To analyze the global literature output and citation of publications pertaining to artemisinin (ART) resistance in Plasmodium falciparum from 2011 to 2021, so as to provide insights into researches on resistance of P. falciparum to ART. The publications pertaining to ART resistance in P. falciparum were retrieved from the Science Citation Index Expanded (SCIE) database in Web of Science during the period from January 2011 through May 2022. The subject, journal, country, affiliation and author distributions and citations of publications were descriptively analyzed. A total of 1 640 publications pertaining to ART resistance in P. falciparum were retrieved in the SCIE database during the period from January 2011 through May 2022, and the number of publications appeared an overall tendency towards a rise during the study period. These articles were published in 343 journals, and the three most productive journals included Malaria Journal (341 publications, 20.79%), Antimicrobial Agents and Chemotherapy (141 publications, 8.60%), American Journal of Aropical Medicine and Hygiene (68 publications, 4.15%), with infectious diseases (565 publications, 34.45%), parasitology (531 publications, 32.38%), and tropical medicine (517 publications, 31.54%) as the predominant subject. The three most productive countries included the United States of America (627 publications, 38.23%), United Kingdom (395 publications, 24.08%), and Thailand (294 publications, 17.94%), with total citations of 25 280, 18 622 and 15 474, respectively, and the most productive countries included Mahidol University (Thailand), Oxford University (England) and London University (England), with 234, 220 publications and 142 publications and 15 058, 15 421 citations and 6 191 citations, respectively. The three most productive authors were all from Mahidol University, with 85, 77 and 63 publications, respectively; and among the three most cited authors, two were from Mahidol University, Thailand, with 8 623 and 7 961 total citations, and one from National Institutes of Health, the United States of America, with 6 267 total citations. A total of 138 articles were published by Chinese scientists, with 3 434 total citations, and National Institute of Parasitic Diseases of Chinese Center for the Diseases Control and Prevention was the most productive Chinese institution, with 35 publications, 1 165 total citations and 33.29 citations per publication. The literature output of ART resistance in P. falciparum was relatively high in the United States of America, Europe, and Southeast Asian countries during the period from 2011 to 2021, with a relatively high academic impact. Publications in Malaria Journal and Antimicrobial Agents and Chemotherapy are recommended to be paid much attention by Chinese scientists to understand the latest advances and extend the research interests.

Targeting malaria parasites with novel derivatives of azithromycin.

The spread of artemisinin resistant Plasmodium falciparum parasites is of global concern and highlights the need to identify new antimalarials for future treatments. Azithromycin, a macrolide antibiotic used clinically against malaria, kills parasites via two mechanisms: 'delayed death' by inhibiting the bacterium-like ribosomes of the apicoplast, and 'quick-killing' that kills rapidly across the entire blood stage development. Here, 22 azithromycin analogues were explored for delayed death and quick-killing activities against P. falciparum (the most virulent human malaria) and P. knowlesi (a monkey parasite that frequently infects humans). Seventeen analogues showed improved quick-killing against both Plasmodium species, with up to 38 to 20-fold higher potency over azithromycin after less than 48 or 28 hours of treatment for P. falciparum and P. knowlesi, respectively. Quick-killing analogues maintained activity throughout the blood stage lifecycle, including ring stages of P. falciparum parasites (<12 hrs treatment) and were >5-fold more selective against P. falciparum than human cells. Isopentenyl pyrophosphate supplemented parasites that lacked an apicoplast were equally sensitive to quick-killing analogues, confirming that the quick killing activity of these drugs was not directed at the apicoplast. Further, activity against the related apicoplast containing parasite Toxoplasma gondii and the gram-positive bacterium Streptococcus pneumoniae did not show improvement over azithromycin, highlighting the specific improvement in antimalarial quick-killing activity. Metabolomic profiling of parasites subjected to the most potent compound showed a build-up of non-haemoglobin derived peptides that was similar to chloroquine, while also exhibiting accumulation of haemoglobin-derived peptides that was absent for chloroquine treatment. The azithromycin analogues characterised in this study expand the structural diversity over previously reported quick-killing compounds and provide new starting points to develop azithromycin analogues with quick-killing antimalarial activity.

Keystone Malaria Symposium 2022: a vibrant discussion of progress made and challenges ahead from drug discovery to treatment

Keystone Malaria Symposium 2022: a vibrant discussion of progress made and challenges ahead from drug discovery to treatment