Falciparum Chloroquine Resistance Research Articles

Design, synthesis and mechanistic insights into triclosan derived dimers as potential anti-plasmodials.

In pursuit of novel anti-plasmodial agents, a library of triclosan-based dimers both with and without a 1H-1,2,3 triazole core were designed and synthesized in order to achieve a multitargeted approach. In vitro assessment against chloroquine-susceptible (3D7) and resistant (W2) P. falciparum strains identified that two of the synthesized dimers containing triazole were the most potent in the series. The most potent of the synthesized compounds exhibited IC50 values of 9.27 and 12.09 μM against the CQ-resistant (W2) and CQ-susceptible (3D7) strains of P. falciparum, with an RI of 0.77, suggesting little or no cross-resistance with CQ. Heme binding and molecular modelling studies revealed the most promising scaffold as a dual inhibitor for hemozoin formation and a P. falciparum chloroquine resistance transporter (PfCRT), respectively. In silico studies of the most potent compound revealed that it shows better binding affinity with PfACP and PfCRT compared to TCS. To the best of our knowledge, this is the first report of triclosan-based compounds demonstrating promising heme-inhibition behaviour, with binding values comparable to those of chloroquine (CQ).

Genetic surveillance shows spread of ACT resistance during period of malaria decline in Vietnam (2018-2020).

Vietnam's goal to eliminate malaria by 2030 is challenged by the further spread of drug-resistant Plasmodium falciparum malaria to key antimalarials, particularly dihydroartemisinin-piperaquine (DHA-PPQ). The custom targeted NGS amplicon sequencing assay, AmpliSeq Pf Vietnam v2, targeting drug resistance, population genetic- and other markers, was applied to detect genetic diversity and resistance profiles in samples from 8 provinces in Vietnam (n = 354), in a period of steep decline of incidence (2018-2020). Variants in 14 putative resistance genes, including P. falciparum Kelch 13 (PfK13) and P. falciparum chloroquine resistance transporter (Pfcrt), were analyzed and within-country parasite diversity was evaluated. Other targets included KEL1-lineage markers and diagnostic markers of Pfhrp2/3. A concerning level of DHA-PPQ resistance was detected. The C580Y mutation in PfK13 was found in nearly 80% of recent samples, a significant rise from previous data. Vietnam has experienced a significant challenge with the spread of DHA-PPQ resistant malaria parasites, particularly in the provinces of Binh Phuoc and Gia Lai. Resistance spread to high levels in Binh Thuan prior to the country-wide treatment policy change from DHA-PPQ to pyronadine-artesunate (PA). A complex picture of PPQ-resistance dynamics was observed, with an increase of PPQ-resistance associated Pfcrt mutations, indicating an evolutionary response to antimalarial pressure. Additionally, the compensatory mutation C258W in Pfcrt, which increases chloroquine (CQ) resistance while reversing PPQ resistance, is emerging in Gia Lai following the adoption of PA as the first-line treatment. This study found high levels of multidrug resistance, with over 70% of parasites in 6 out of 8 provinces showing significant sulfadoxine-pyrimethamine (SP) resistance and widespread chloroquine-resistant Pfcrt haplotypes. We also report an absence of P. falciparum histidine rich protein 2 and 3 (Pfhrp2/3) gene deletions, ensuring the continued reliability of HRP2/3-based rapid diagnostic tests. P. falciparum populations in Vietnam are becoming more isolated, with clonal populations showing high geographical clustering by province. The central highlands, particularly Gia Lai province, have the highest residual malaria burden but exhibit low diversity and clonal populations, likely due to the pressures from the antimalarial drugs and targeted national malaria control program (NMCP) efforts. In conclusion, examining a broad panel of full-length resistance genes and SNPs provided high-resolution insights into genetic diversity and resistance evolution in Vietnam, offering valuable information to inform local treatment and intervention strategies.

Design, synthesis and mechanistic exploration of anti-plasmodial Indolo[2,3-b]quinoxaline-7-chloroquinoline hybrids.

Aim: The aim of this study is to synthesize indolo[2,3-b]quinoxaline-4-aminoquinoline-based hybrids and evaluate their effectiveness against chloroquine-susceptible (3D7) and resistant (W2) Plasmodium falciparum strains, with expected inhibition of P. falciparum chloroquine resistance transporter (PfCRT) and heme.Methods: The hybrids were synthesized and in vitro evaluated against both susceptible and resistant strains. Molecular docking and studies were conducted to assess the binding affinities for the PfCRT protein. Additionally, heme-inhibition studies using hemin chloride provided valuable insights into the interaction between the ligand and heme. The binding constant (logK) was calculated, providing quantitative details about the strength of this interaction.Conclusion: The synthesized hybrids showed reasonable potency against both P. falciparum strains. The most potent hybrid 10d, with fluorine-substitution exhibited good activity. Molecular docking studies indicated strong binding affinities for the PfCRT protein. Heme inhibition studies further supported the potential of 10d as an effective anti-plasmodial agent.

Frequency of chloroquine-resistant haplotype of Plasmodium falciparum (CVIET) in Ibadan, Southwest Nigeria 17 years post-chloroquine withdrawal

The replacement of chloroquine with artemisinin-based combination therapies (ACTs) for over a decade has had varying impacts on the ability of the malaria parasite to sustain its chloroquine resistance prowess in different malaria-endemic regions. We evaluated the frequency of Plasmodium falciparum chloroquine resistance transporter (PfCRT) mutations in Ibadan, Nigeria 17 years after the replacement of chloroquine with ACTs for malaria treatment. Fragments of PfCRT gene from genomic DNA of microscopically confirmed P. falciparum-infected patients were amplified and sequenced. There were 19% CVIET mutant and 81% CVMNK wild-type haplotypes on residues 72–76. A220S change were found in 16.7% of samples occurring concurrently with the CVIET haplotype, while a Q271E mutation occurred in a PfCRT wild-type isolate. The reduced prevalence of the PfCRT mutant alleles in this study compared to previous reports suggests a gradual disappearance of chloroquine-resistant malaria parasites following reduced drug pressure. It may also be a result of fitness demand on the parasites in attempts to evolve resistance against the current first-line regimen. However, evaluating the prevalence of other chloroquine resistance markers such as Plasmodium falciparum multidrug resistance 1 gene mutations in this population, and a more robust sample size will help to consolidate these findings.

High frequency of artemisinin partial resistance mutations in the Great Lakes region revealed through rapid pooled deep sequencing.

In Africa, the first Plasmodium falciparum artemisinin partial resistance mutation, was Kelch13 (K13) 561H - detected and validated at appreciable frequency in Rwanda in 2014. Surveillance to better define the extent of the emergence in Rwanda and neighboring countries is critical. We used novel liquid blood drop preservation combined with pooled sequencing to provide cost-effective rapid assessment of resistance mutation frequencies at multiple collection sites across Rwanda and neighboring regions in Uganda, Tanzania, and the Democratic Republic of the Congo (DRC). Malaria-positive samples (n=5,465) from 39 health facilities collected between May 2022 and March 2023 were sequenced in 199 pools. In Rwanda, K13 561H and 675V were detected in 90% and 65% of sites with an average frequency of 19.0% (0-54.5%) and 5.0% (0-35.5%), respectively. In Tanzania, 561H had high frequency in multiple sites. 561H appeared at 1.6% in Uganda. 561H was absent from the DRC, although 675V was seen at low frequency. Concerningly candidate mutations were observed: 441L, 449A, and 469F co-occurred with validated mutations suggesting they are arising under the same pressures. Other markers for decreased susceptibility to artemether-lumefantrine are common: P. falciparum multidrug resistance protein 1 N86 at 98.0% (63.3-100%) and 184F at 47.0% (0-94.3%) and P. falciparum chloroquine resistance transporter 76T at 14.7% (0-58.6%). Additionally, sulfadoxine-pyrimethamine-associated mutations show high frequencies. K13 mutations are rapidly expanding in the region further endangering control efforts with the potential of engendering partner drug resistance.

Assessment of Saliva and Urine Performance for Antimalarial Drug Resistance Molecular Markers Study

<i>Background</i>: The malaria diagnostic tools developed to date require blood to be taken. However, certain groups in the population are reluctant to take blood samples because of their cultural habits (blood taboo), or because of the fear associated with the trauma of the injection, especially when the sample is taken repeatedly. Saliva and urine, which are not very invasive to collect, have not been widely used for malaria diagnosis. The aim of this study is to assess the performance of saliva and urine in detecting molecular markers of <i>Plasmodium falciparum </i>resistance to antimalarial drugs. <i>Methodology</i>: Blood, urine and saliva samples were collected in three different localities from 94 patients over 2 years of age with microscopically confirmed <i>Plasmodium falciparum </i>uncomplicated malaria. <i>P. falciparum </i>genomic DNA (Deoxyribonucleic acid) was then extracted and amplified using primers specific for the <i>Pfcrt (Plasmodium falciparum Chloroquine Resistance Transporter), Pfdhfr (Plasmodium falciparum dihydrofolate reductase) </i>and <i>PfK13 propeller (Plasmodium falciparum Kelch13 propeller) </i>genes. The amplification products were processed by electrophoresis and analyzed against blood, saliva and urine samples. A multivariate statistical analysis in R programming environment was performed aiming to assess the performance of blood, saliva and urine samples in detecting molecular markers of <i>P. falciparum </i>resistance. <i>Results</i>: Agarose gel electrophoresis of the amplification products of each gene detected the <i>Pfcrt </i>genes at 80.85% (76/94), <i>Pfdhfr </i>at 95.74% (90/94) and <i>PfK13 Propeller </i>at 98.93% (93/94) in blood. In saliva, gene detection levels were 50% (47/94), 69.14% (65/94) and 4.26% (4/94) respectively for the <I>K13</I> propeller, <i>Pfdhfr</i> and <i>Pfcrt</i> genes. Unlike the <i>Pfcrt </i>gene, which was not detected, 45.74% (43/94) and 38.30% (36/94) of <i>PfK13</i> Propeller and <i>pfdhfr</i> genes respectively were detected in urine. Taking blood as the reference biological sample, statistical analysis showed that unlike urine, saliva exhibited a detection performance for molecular markers of antimalarial drug resistance (<i>pfcrt,</i> <i>pfdhfr</i>, <i>pfK13</i> propeller) close to that of blood (p < 0.05). The performance of saliva and urine was also assessed on the basis of the detection of the molecular markers <i>pfdhfr</i>, <i>pfcrt </i>and <i>pfK13 </i>using ROC (<i>receiver operational characteristic</i>) analysis. The data revealed a high sensitivity of saliva compared with urine in the detection of the <i>pfdhfr</i>, <i>pfcrt </i>and <i>pfK13 propeller </i>genes. <i>Conclusion</i>: The levels of detection of molecular markers of antimalarial drug resistance studied in saliva are close to those in blood. Saliva is a high-performance biological product that could potentially be used as an alternative non-invasive sample for the study of molecular markers of Plasmodium falciparum resistance to antimalarial drugs.

The Role of the Plasmodium falciparum Chloroquine Resistance Transporter Gene in Malaria Drug Resistance and its implication on malaria control in Africa

The Role of the Plasmodium falciparum Chloroquine Resistance Transporter Gene in Malaria Drug Resistance and its implication on malaria control in Africa

A Plasmodium falciparum genetic cross reveals the contributions of pfcrt and plasmepsin II/III to piperaquine drug resistance.

Piperaquine (PPQ) is widely used in combination with dihydroartemisinin as a first-line treatment against malaria. Multiple genetic drivers of PPQ resistance have been reported, including mutations in the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and increased copies of plasmepsin II/III (pm2/3). We generated a cross between a Cambodia-derived multidrug-resistant KEL1/PLA1 lineage isolate (KH004) and a drug-susceptible Malawian parasite (Mal31). Mal31 harbors a wild-type (3D7-like) pfcrt allele and a single copy of pm2/3, while KH004 has a chloroquine-resistant (Dd2-like) pfcrt allele with an additional G367C substitution and multiple copies of pm2/3. We recovered 104 unique recombinant parasites and examined a targeted set of progeny representing all possible combinations of variants at pfcrt and pm2/3. We performed a detailed analysis of competitive fitness and a range of PPQ susceptibility phenotypes with these progenies, including PPQ survival assay, area under the dose response curve, and a limited point IC50. We find that inheritance of the KH004 pfcrt allele is required for reduced PPQ sensitivity, whereas copy number variation in pm2/3 further decreases susceptibility but does not confer resistance in the absence of additional mutations in pfcrt. A deep investigation of genotype-phenotype relationships demonstrates that progeny clones from experimental crosses can be used to understand the relative contributions of pfcrt, pm2/3, and parasite genetic background to a range of PPQ-related traits. Additionally, we find that the resistance phenotype associated with parasites inheriting the G367C substitution in pfcrt is consistent with previously validated PPQ resistance mutations in this transporter.IMPORTANCEResistance to piperaquine, used in combination with dihydroartemisinin, has emerged in Cambodia and threatens to spread to other malaria-endemic regions. Understanding the causal mutations of drug resistance and their impact on parasite fitness is critical for surveillance and intervention and can also reveal new avenues to limiting the evolution and spread of drug resistance. An experimental genetic cross is a powerful tool for pinpointing the genetic determinants of key drug resistance and fitness phenotypes and has the distinct advantage of quantifying the effects of naturally evolved genetic variation. Our study was strengthened since the full range of copies of KH004 pm2/3 was inherited among the progeny clones, allowing us to directly test the role of the pm2/3 copy number on resistance-related phenotypes in the context of a unique pfcrt allele. Our multigene model suggests an important role for both loci in the evolution of this multidrug-resistant parasite lineage.

Distribution patterns of molecular markers of antimalarial drug resistance in Plasmodium falciparum isolates on the Thai-Myanmar border during the periods of 1993–1998 and 2002–2008

BackgroundPolymorphisms of Plasmodium falciparum chloroquine resistance transporter (pfcrt), Plasmodium falciparum multi-drug resistance 1 (pfmdr1) and Plasmodium falciparum kelch 13-propeller (pfk13) genes are accepted as valid molecular markers of quinoline antimalarials and artemisinins. This study investigated the distribution patterns of these genes in P. falciparum isolates from the areas along the Thai-Myanmar border during the two different periods of antimalarial usage in Thailand.ResultsPolymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) were used to detect pfcrt mutations at codons 76, 220, 271, 326, 356, and 371 as well as pfmdr1 mutation at codon 86. The prevalence of pfcrt mutations was markedly high (96.4–99.7%) in samples collected during both periods. The proportions of mutant genotypes (number of mutant/total isolate) at codons 76, 220, 271, 326, 356 and 371 in the isolates collected during 1993–1998 (period 1) compared with 2002–2008 (period 2) were 97.9% (137/140) vs. 97.1% (401/413), 97.9% (140/143) vs. 98.8% (171/173), 97.2% (139/143) vs. 97.1% (333/343), 98.6% (140/142) vs. 99.7% (385/386), 96.4% (134/139) vs. 98.2% (378/385) and 97.8% (136/139) vs. 98.9% (375/379), respectively. Most isolates carried pfmdr1 wild-type at codon 86, with a significant difference in proportions genotypes (number of wild type/total sample) in samples collected during period 1 [92.9% (130/140)] compared with period 2 [96.9% (379/391)]. Investigation of pfmdr1 copy number was performed by real-time PCR. The proportions of isolates carried 1, 2, 3 and 4 or more than 4 copies of pfmdr1 (number of isolates carried correspondent copy number/total isolate) were significantly different between the two sample collecting periods (65.7% (90/137) vs. 87.8% (390/444), 18.2% (25/137) vs. 6.3%(28/444), 5.1% (7/137) vs. 1.4% (6/444) and 11.0% (15/137) vs. 4.5% (20/444), for period 1 vs. period 2, respectively). No pfk13 mutation was detected by nested PCR and nucleotide sequencing in all samples with successful analysis (n = 68).ConclusionsThe persistence of pfcrt mutations and pfmdr1 wild-types at codon 86, along with gene amplification in P. falciparum, contributes to the continued resistance of chloroquine and mefloquine in P. falciparum isolates in the study area. Regular surveillance of antimalarial drug resistance in P. falciparum, incorporating relevant molecular markers and treatment efficacy assessments, should be conducted.

Prevalence of polymorphisms in marker genes associated with antimalarial drug resistance in Plasmodium falciparum following 10 years of artemisinin-based combination therapy implementation in urban Kolkata.

Resistance to antimalarial drugs is one of the major challenges for malaria elimination. In India, artemisinin combination therapy (artesunate-sulfadoxin pyrimethamine) was introduced in place of chloroquine (CQ) for the treatment of uncomplicated falciparum malaria in 2010. Periodical monitoring of polymorphisms in antimalarial drug resistance marker genes will be useful for assessing drug pressure, mapping and monitoring of drug resistance status; and will be helpful for searching alternative treatments. This study was conducted to study the polymorphisms in antimalarial drug resistance marker genes among clinical Plasmodium falciparum isolates collected from Kolkata after 10 years of artemisinin-based combination therapie (ACT) implementation. Blood samples were collected from P. falciparum mono-infected patients and polymorphisms in P. falciparum CQ resistance transporter (pfcrt), P. falciparum multidrug resistance (pfmdr-1), P. falciparum dihydrofolate reductase (pfdhfr), P. falciparum dihydropteroate synthetase (pfdhps), pfATPase6 and pfK-13 propeller genes were analysed by polymerase chain reaction and DNA sequencing. In pfcrt gene, C72S, and K76T mutation was recorded in 100% isolates and no mutations was detected in any of the targeted codons of pfmdr-1 gene. A double mutant pfcrt haplotype SVMNT and wildtype haplotype NYD in pfmdr-1 were prevalent in 100% of study isolates. Triple mutant pfdhfr-pfdhps haplotype ANRNI-SGKAA was recorded. No polymorphism in pfK13 gene was documented in any of the isolates. Observed wild codon N86 along with Y184 and D1246 of pfmdr-1 gene might be an indication of the reappearance of CQ sensitivity. The absence of quadruple and quintuple haplotypes in pfdhfr-pfdhps gene along with the wild haplotype of pfK13 is evidence of ACT effectivity. Hence, similar studies with large sample size are highly suggested for monitoring the drug resistance status of P. falciparum.

Designing hybrid CRISPR-Cas12 and LAMP detection systems for treatment-resistant Plasmodium falciparum with in silico method.

Genes associated with drug resistance of first line drugs for Plasmodium falciparum have been identified and characterized of which three genes most commonly associated with drug resistance are P. falciparum chloroquine resistance transporter gene (PfCRT), P. falciparum multidrug drug resistance gene 1 (PfMDR1), and P. falciparum Kelch protein K13 gene (PfKelch13). Polymorphism in these genes could be used as molecular markers for identifying drug resistant strains. Nucleic acid amplification test (NAAT) along with DNA sequencing is a powerful diagnostic tool that could identify these polymorphisms. However, current NAAT and DNA sequencing technologies require specific instruments which might limit its application in rural areas. More recently, a combination of isothermal amplification and CRISPR detection system showed promising results in detecting mutations at a nucleic acid level. Moreover, the Loop-mediated isothermal amplification (LAMP)-CRISPR systems offer robust and straightforward detection, enabling it to be deployed in rural and remote areas. The aim of this study was to develop a novel diagnostic method, based on LAMP of targeted genes, that would enable the identification of drug-resistant P. falciparum strains. The methods were centered on sequence analysis of P. falciparum genome, LAMP primers design, and CRISPR target prediction. Our designed primers are satisfactory for identifying polymorphism associated with drug resistant in PfCRT, PfMDR1, and PfKelch13. Overall, the developed system is promising to be used as a detection method for P. falciparum treatment-resistant strains. However, optimization and further validation the developed CRISPR-LAMP assay are needed to ensure its accuracy, reliability, and feasibility.

Genomic analysis of Plasmodium vivax describes patterns of connectivity and putative drivers of adaptation in Ethiopia

Ethiopia has the greatest burden of Plasmodium vivax in Africa, but little is known about the epidemiological landscape of parasites across the country. We analysed the genomic diversity of 137 P. vivax isolates collected nine Ethiopian districts from 2012 to 2016. Signatures of selection were detected by cross-country comparisons with isolates from Thailand (n = 104) and Indonesia (n = 111), representing regions with low and high chloroquine resistance respectively. 26% (35/137) of Ethiopian infections were polyclonal, and 48.5% (17/35) of these comprised highly related clones (within-host identity-by-descent > 25%), indicating frequent co-transmission and superinfection. Parasite gene flow between districts could not be explained entirely by geographic distance, with economic and cultural factors hypothesised to have an impact on connectivity. Amplification of the duffy binding protein gene (pvdbp1) was prevalent across all districts (16–75%). Cross-population haplotype homozygosity revealed positive selection in a region proximal to the putative chloroquine resistance transporter gene (pvcrt-o). An S25P variant in amino acid transporter 1 (pvaat1), whose homologue has recently been implicated in P. falciparum chloroquine resistance evolution, was prevalent in Ethiopia (96%) but not Thailand or Indonesia (35–53%). The genomic architecture in Ethiopia highlights circulating variants of potential public health concern in an endemic setting with evidence of stable transmission.

Impact of piperaquine resistance in Plasmodium falciparum on malaria treatment effectiveness in The Guianas: a descriptive epidemiological study

Plasmodium falciparum is an apicomplexan parasite responsible for lethal cases of malaria. According to WHO recommendations, P falciparum cases are treated with artemisinin-based combination therapy including dihydroartemisinin-piperaquine. However, the emergence of resistant parasites against dihydroartemisinin-piperaquine was reported in southeast Asia in 2008 and, a few years later, suspected in South America. To characterise resistance emergence, a treatment efficacy study was performed on the reported patients infected with P falciparum and treated with dihydroartemisinin-piperaquine in French Guiana (n=6, 2016-18). Contemporary isolates collected in French Guiana were genotyped for P falciparum chloroquine resistance transporter (pfCRT; n=845) and pfpm2 and pfpm3 copy number (n=231), phenotyped using the in vitro piperaquine survival assay (n=86), and analysed through genomic studies (n=50). Additional samples from five Amazonian countries and one outside the region were genotyped (n=1440). In field isolates, 40 (47%) of 86 (95% CI 35·9-57·1) were resistant to piperaquine in vitro; these phenotypes were more associated with pfCRTC350R (ie, Cys350Arg) and pfpm2 and pfpm3 amplifications (Dunn test, p<0·001). Those markers were also associated with dihydroartemisinin-piperaquine treatment failure (n=3 [50%] of 6). A high prevalence of piperaquine resistance markers was observed in Suriname in 19 (83%) of 35 isolates and in Guyana in 579 (73%) of 791 isolates. The pfCRTC350R mutation emerged before pfpm2 and pfpm3 amplification in a temporal sequence different from southeast Asia, and in the absence of artemisinin partial resistance, suggesting a geographically distinctive epistatic relationship between these genetic markers. The high prevalence of piperaquine resistance markers in parasite populations of the Guianas, and the risk of associated therapeutic failures calls for caution on dihydroartemisinin-piperaquine use in the region. Furthermore, greater attention should be given to potential differences in genotype to phenotype mapping across genetically distinct parasite populations from different continents. Pan American Health Organization and WHO, French Ministry for Research, European Commission, Santé publique France, Agence Nationale de la Recherche, Fundação de Amparo à Pesquisa do Estado do Amazonas, Ministry of Health of Brazil, Oswaldo Cruz Foundation, and National Institutes of Health. For the French and Portuguese translations of the abstract see Supplementary Materials section.

In vitro and in silico anti-malarial activity and cytotoxicity of n-hexyl 1-O-rutinoside (a glycoside) isolated from Annickia polycarpa (DC.) Setten and Maas ex I.M. Turner (Annonaceae)

Ethnopharmacological relevanceAnnickia polycarpa leaf is an effective anti-malarial agent. However, its chemical constituents have not been isolated and assayed against any pathogen. Aim of the studyTo isolate and characterize anti-malarial compound(s) from the leaf of A. polycarpa. Materials and methodsBioassay-guided fractionation was employed to isolated the compound (AL1) from the chloroform fraction (ALCF) of the basified ethanol extract of A. polycarpa leaf (ALE). AL1 was characterized by LC-MS, 1D and 2D NMR spectroscopic analysis. Anti-malarial activity was evaluated against drug resistance Dd2 and drug sensitive 3D7 Plasmodium falciparum strains using the SYBR green assay. Cytotoxicity and mechanistic studies were determined using tetrazolium-based colorimetric assay and molecular docking respectively. ResultsAL1 was characterized as n-hexyl 1-O-rutinoside. The IC50 values of ALE and ALCF against 3D7 and Dd2 P. falciparum strains ranges from 3.441 (0.3389) - 4.255 (0.2246) μg/mL. The IC50s obtained for n-hexyl 1-O-rutinoside and Artesunate (standard drug) were 7.71 (0.5473) and 0.001 (0.00008) nM against the 3D7 parasite strain respectively. Also, the efficacy of n-hexyl 1-O-rutinoside increased by 24.40% against the chloroquine resistance Dd2 P. falciparum strain whiles that of Artesunate decreased by 98.96%. Furthermore, ALE, ALCF and n-hexyl 1-O-rutinoside were weakly cytotoxic to human RBCs with high selectivity indices. N-hexyl 1-O-rutinoside inhibits P. falciparum chloroquine resistance transporter (PfCRT) and dihydrofolate reductase-thymidylate synthase (PfDHFR-TS) better than chloroquine and pyrimethamine respectively. But, produced similar inhibition of P. falciparum 2-trans-enoyl -ACP-reductase (PfERN) as triclosan. ConclusionThese results show that A. polycarpa leaf and n-hexyl 1-O-rutinoside possessed profound anti-malarial activity and are not cytotoxic. N-hexyl 1-O-rutinoside could therefore, be developed into a new anti-malarial medicine. This is the first study to report the anti-malarial activity of n-hexyl 1-O-rutinoside and its isolation from the genus Annickia.

Rebound of multiple infections and prevalence of anti-malarial resistance associated markers following malaria upsurges in Dielmo village, Senegal, West Africa

BackgroundThanks to the scale up of malaria control interventions, the malaria burden in Senegal has decreased substantially to the point that the National Malaria Control Programme plans to achieve malaria elimination by 2030. To guide such efforts, measuring and monitoring parasite population evolution and anti-malarial drugs resistance is extremely important. Information on the prevalence of parasite mutations related to drug resistance can provide a first signal of emergence, introduction and selection that can help with refining drug interventions. The aim of this study was to analyse the prevalence of anti-malarial drug resistance-associated markers before and after the implementation of artemisinin-based combination therapy (ACT) from 2005 to 2014 in Dielmo, a model site for malaria intervention studies in Senegal.MethodsSamples from both malaria patients and Plasmodium falciparum asymptomatic carriers were analysed with high resolution melting (HRM) technique to genotype P. falciparum chloroquine resistance transporter (Pfcrt) gene haplotypes and multidrug-resistant protein 1 (Pfmdr1) gene at codons N86 and Y184.ResultsAmong the 539 samples analysed, 474, 486, and 511 were successfully genotyped for Pfmdr1 N86, Y184, and Pfcrt, respectively. The prevalence of drug resistance markers was high, particularly during the malaria upsurges. Following the scale-up in bed net distribution, only the mutant (86F-like) variant of Pfmdr1 86 was present while during the malaria upsurges the predominance of two types 86Y-86N (43%) and 86F-like (56%) were observed. Most infections (87%) carried the wild type Y-allele at Pfmdr1 184 during the period of nets scale-up while during the malaria upsurges only 16% of infections had wild type and 79% of infections had mixed (mutant/wild) type. The frequency of the mixed genotypes SVMNT-like_CVMNK and SVMNT-like_CVIET within Pfcrt gene was particularly low during bednet scale up. Their frequency increased significantly (P < 0.001) during the malaria upsurges.ConclusionThis data demonstrated the effect of multiple interventions on the dynamics of drug resistance-associated mutations in the main malaria parasite P. falciparum in an endemic village in Senegal. Monitoring drug resistance markers should be conducted periodically to detect threats of emergence or resurgence that could compromise the efficacy of anti-malarial drugs.

Epitope specific antibodies to N- and C cytoplasmic domains of the Plasmodium falciparum chloroquine resistance transporter (PfCRT) differentiate native and post-translationally modified variant

Polymorphisms in Plasmodium falciparum chloroquine resistance transporter (or PfCRT) were shown to be causative of decreased sensitivity to diverse quinoline-based antimalarials. In this report we describe the identification of a post-translational variant of PfCRT using highly characterized antibodies raised against its N- and C-terminal cytoplasmic domains (e.g., 58 and 26 amino acids, respectively). Western blot analyses of P. falciparum protein extracts with anti N-PfCRT antiserum revealed two polypeptides with apparent molecular masses of 52 kDa and 42 kDa, relative to the calculated molecular mass of PfCRT of 48.7 kDa. The 52 kDa polypeptide was detectable with anti C-PfCRT antiserum, only after alkaline phosphatase treatment of P. falciparum extracts. Detailed epitope mapping of anti N- and C-PfCRT antisera revealed epitopes covering two previously identified phosphorylation sites, Ser411 and Thr416, whereby substitution of these residues with Asp amino acid, to mimic phosphorylated residues, dramatically inhibited anti C-PfCRT binding. Consistently, alkaline phosphatase treatment of P. falciparum extract unmasked the binding of anti C-PfCRT to the 52 kDa polypeptide, suggesting that the 52 kDa but not 42 kDa polypeptide is phosphorylated at its C-terminal Ser411 and Thr416. Interestingly, Pfcrt expressed in HEK-293F human kidney cells showed the same reactive polypeptides with anti N- and C-PfCRT antisera, consistent with PfCRT origin of the two polypeptides (e.g., 42 kDa and 52 kDa), but lacking PfCRT phosphorylation at its C-terminal. Immunohistochemical staining of late trophozoite-infected erythrocytes with anti N-or C-PfCRT antisera showed both polypeptides are localized to the parasite's digestive vacuole. Moreover, both polypeptides are detected in chloroquine-susceptible and -resistant strains of P. falciparum. This is the first report describing a post-translationally modified variant of PfCRT. The physiologic role of the 52 kDa phosphorylated PfCRT in P. falciparum remains to be determined.

IFNγ, TNFα polymorphisms and IFNγ serum levels are associated with the clearance of drug-resistant P. falciparum in Malian children.

Host immunity has been suggested to clear drug-resistant parasites in malaria-endemic settings. However, the immunogenetic mechanisms involved in parasite clearance are poorly understood. Characterizing the host's immunity and genes involved in controlling the parasitic infection can inform the development of blood-stage malaria vaccines. This study investigates host regulatory cytokines and immunogenomic factors associated with the clearance of Plasmodium falciparum carrying a chloroquine resistance genotype. Biological samples from participants of previous drug efficacy trials conducted in two Malian localities were retrieved. The P. falciparum chloroquine resistance transporter (Pfcrt) gene was genotyped using parasite DNA. Children carrying parasites with the mutant allele (Pfcrt-76T) were classified based on their ability to clear their parasites. The levels of the different cytokines were measured in serum. The polymorphisms of specific human genes involved in malaria susceptibility were genotyped using human DNA. The prevalence of the Pfcrt-76T was significantly higher in Kolle than in Bandiagara (81.6% vs 38.6%, p<10-6). The prevalence of children who cleared their mutant parasites was significantly higher in Bandiagara than in Kolle (82.2% vs 67.4%, p<0.05). The genotyping of host genes revealed that IFN-γ -874T and TNF-α -308A alleles were positively associated with parasite clearance. Cytokine profiling revealed that IFN-γ level was positively associated with parasite clearance (p=0.04). This study highlights the role of host's immunity and immunogenetic factors to clear resistant parasites, suggesting further characterization of these polymorphisms may help to develop novel approaches to antiparasitic treatment strategies.

Monitoring antimalarial drug-resistance markers in Somalia.

The use of an effective antimalarial drug is the cornerstone of malaria control. However, the development and spread of resistant Plasmodium falciparum strains have placed the global eradication of malaria in serious jeopardy. Molecular marker analysis constitutes the hallmark of the monitoring of Plasmodium drug-resistance. This study included 96 P. falciparum PCR-positive samples from southern Somalia. The P. falciparum chloroquine resistance transporter gene had high frequencies of K76T, A220S, Q271E, N326S, and R371I point mutations. The N86Y and Y184F mutant alleles of the P. falciparum multidrug resistance 1 gene were present in 84.7 and 62.4% of the isolates, respectively. No mutation was found in the P. falciparum Kelch-13 gene. This study revealed that chloroquine resistance markers are present at high frequencies, while the parasite remains sensitive to artemisinin (ART). The continuous monitoring of ART-resistant markers and in vitro susceptibility testing are strongly recommended to track resistant strains in real time.

Structures of Plasmodium falciparum Chloroquine Resistance Transporter (PfCRT) Isoforms and Their Interactions with Chloroquine.

Using a recently elucidated atomic-resolution cryogenic electron microscopy (cryo-EM) structure for the Plasmodium falciparum chloroquine resistance transporter (PfCRT) protein 7G8 isoform as template [Kim, J.; Nature 2019, 576, 315-320], we use Monte Carlo molecular dynamics (MC/MD) simulations of PfCRT embedded in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane to solve energy-minimized structures for 7G8 PfCRT and two additional PfCRT isoforms that harbor 5 or 7 amino acid substitutions relative to 7G8 PfCRT. Guided by drug binding previously defined using chloroquine (CQ) photoaffinity probe labeling, we also use MC/MD energy minimization to elucidate likely CQ binding geometries for the three membrane-embedded isoforms. We inventory salt bridges and hydrogen bonds in these structures and summarize how the limited changes in primary sequence subtly perturb local PfCRT isoform structure. In addition, we use the "AlphaFold" artificial intelligence AlphaFold2 (AF2) algorithm to solve for domain structure that was not resolved in the previously reported 7G8 PfCRT cryo-EM structure, and perform MC/MD energy minimization for the membrane-embedded AF2 structures of all three PfCRT isoforms. We compare energy-minimized structures generated using cryo-EM vs AF2 templates. The results suggest how amino acid substitutions in drug resistance-associated isoforms of PfCRT influence PfCRT structure and CQ transport.

Residues involved in proton-coupled transport of antimalarial drugs by PfCRT.

A major setback in the fight against malaria has been the emergence of P. falciparum parasites resistant to chloroquine (CQ), the primary antimalarial drug. Neutral CQ enters the parasite's digestive vacuole (DV) and obtains two protons preventing its passive efflux through the membrane. The trapped CQ2+ kills the parasite by disrupting the detoxification process of heme released from proteolyzed host hemoglobin. CQ-resistant parasites show mutations in a DV membrane transporter, P. falciparum CQ resistance transporter (PfCRT), that enables active, proton-coupled efflux of CQ2+. While biochemical measurements established the coupling of PfCRT's transport function to the DV membrane proton gradient, the proton-coupled transport mechanism has remained elusive. Particularly it is still unclear what the proton binding site(s) is(are). Recently, the cryo-EM structure of PfCRT from a CQ-resistant variant was determined with a bound Fab fragment occupying its binding pocket. Using us-long all-atom molecular dynamics (MD) simulations we examined the stability of the transporter in the DV-open conformation in the absence of bound Fab fragments, discovering surprising protein stability upon removal of Fab. Next, utilizing constant pH (cpHMD) simulations at 7 different pH values, and considering Galvani potential offset corrections, we determined the pKa of the four titratable residues (H97, D137, D326, and D329) lining the binding pocket. These simulations allowed unambiguous determination of the primary site responding to DV's acidic environment. Finally, with protonation states compatible with the acidic pH of the DV for the aforementioned residues, we studied binding of CQ2+ to the transporter via a series of driven MD simulations. We then repeated the cpHMD simulations and determined the proton binding site in the presence of the bound CQ2+. Our results shed light on PfCRT's transport mechanism and open new possibilities to design new effective drugs against malaria.