Drug-resistant Strains Of Plasmodium Falciparum Research Articles

Investigating the impact of solvation on p-Phenylenediamine - 2-Amino pyrimidine - Formaldehyde Terpolymer (P2APF) ligand's reactivity and drug suitability for malaria treatment: Insights from experimental and quantum calculations

This study aims at investigating the drug potential of p-Phenylenediamine – 2-Amino Pyrimidine – Formaldehyde terpolymer (P2APF) ligand against drug resistant Plasmodium falciparum. Plasmodium falciparum, an embodiment of cunning among malaria parasites, thrives in regions plagued by rampant mosquito transmission, subpar vector control, and limited access to effective treatments. To this end, this study explored the structural properties of the p-Phenylenediamine – 2-Amino Pyrimidine – Formaldehyde terpolymer (P2APF) ligand, (comprising p-Phenylenediamine, 2-Aminopyrimidine, and Formaldehyde) as a drug potent ligand against the common proteins coding for malaria infection. Various spectroscopic techniques such as FT-IR, UV–visible, and NMR (1H & 13C) spectroscopy were employed both experimentally and theoretically. Additionally, the ligand's surface morphology was investigated using scanning electron microscopy. To comprehend the influence of solvation, theoretical investigations utilizing density functional theory (DFT) at the B3LYPD(BJ)/6-311G++G (2d,2p) level were conducted in DMSO, water, and methanol solvents. The results from the frontier molecular orbital (FMO) analysis provided valuable insights into the electronic properties and solvation effects of P2APF. Specifically, the calculated energy gap of 3.671 eV for P2APF_methanol and 3.672 eV for P2APF_DMSO suggested these solvents as promising environments for reactivity and interactions. Molecular docking studies unveiled the most notable binding affinity between P2APF and the 5UMB chaperone protein receptor, exhibiting a binding affinity of -7.3 kcal/mol on serine and aspartic acid residues, with an average bond distance of 2.25 Å. This robust protein-ligand interaction signifies the promising potential of the P2APF ligand in targeting this specific receptor, thereby combating drug-resistant strains of Plasmodium falciparum for the present and the future.

Structure-Activity Relationship Analysis of Novel Compounds Against Drug-Resistant Plasmodium Falciparum Strains

The escalating issue of drug-resistant Plasmodium falciparum strains poses a significant challenge to malaria treatment. This research paper presents a comprehensive analysis of the Structure-Activity Relationship (SAR) of innovative compounds designed to combat drug-resistant malaria. Through systematic examination of the chemical structures and their biological activity, we aim to identify potential drug candidates that can effectively address this global health concern. Our study contributes to the ongoing efforts in antimalarial drug development, offering insights into the design of novel compounds that may prove instrumental in countering drug resistance among Plasmodium falciparum strains and improving the efficacy of malaria treatment strategies. Keywords: Plasmodium falciparum, Antimalarial Compounds, Drug Resistance, Chemical Structure Analysis, Novel Compounds

Structure-based virtual screening approach reveals natural multi-target compounds for the development of antimalarial drugs to combat drug resistance

Compared to the previous year, there has been an increase of nearly 2 million malaria cases in 2021. The emergence of drug-resistant strains of Plasmodium falciparum, the most deadly malaria parasite, has led to a decline in the effectiveness of existing antimalarial drugs. To address this problem, the present study aimed to identify natural compounds with the potential to inhibit multiple validated antimalarial drug targets. The natural compounds from the Natural Product Activity and Species Source (NPASS) database were screened against ten validated drug targets of Plasmodium falciparum using a structure-based molecular docking method. Twenty compounds, with targets ranging from three to five, were determined as the top hits. The molecular dynamics simulations of the top six complexes (NPC246162 in complex with PfAdSS, PfGDH, and PfNMT; NPC271270 in complex with PfCK, PfGDH, and PfdUTPase) confirmed their stable binding affinity in the dynamic environment. The Tanimoto coefficient and distance matrix score analysis show the structural divergence of all the hit compounds from known antimalarials, indicating minimum chances of cross-resistance. Thus, we propose further investigating these compounds in biochemical and parasite inhibition studies to reveal the real therapeutic potential. If found successful, these compounds may be a new avenue for future drug discovery efforts to combat existing antimalarial drug resistance. Communicated by Ramaswamy H. Sarma

Marmesin isolated from Celtis durandii Engl. root bioactive fraction inhibits β-hematin formation and contributes to antiplasmodial activity

Ethnopharmacological relevanceMalaria is a leading cause of death in many developing countries, especially in sub-Saharan Africa. Nigeria is endowed with an abundance of medicinal plants, many of which are used to treat malaria. Celtis durandii Engl. is one such plant used as a traditional antimalarial remedy in southeast Nigeria. However, its antiplasmodial potential is poorly explored. Aim of the studyThe study aimed at identifying the antiplasmodial components of C. durandii root extract through antiplasmodial activity-guided fractionation. Materials and methodsDichloromethane/methanol mixture extract (1:1 v/v) of C. durandii root was prepared and partitioned against water to obtain the organic phase, which was further separated by column chromatography into nine (C1 – C9) fractions. The antiplasmodial activity was evaluated by in vitro screening of the different fractions against drug-sensitive and drug-resistant Plasmodium falciparum strains. Further purification of the active column fractions resulted in a potent anti-Plasmodial compound that was subsequently investigated for its effect on β-hematin formation. Additionally, the isolated compound was characterized and identified as marmesin using mass spectrometry and nuclear magnetic resonance spectroscopy. ResultsCeltis durandii root extract exhibited promising antiplasmodial activity {IC50 (μg/ml) 5.92, 6.04, and 6.92} against PfW2mef, PfINDO, and Pf3D7 respectively. Pooled fractions with good antiplasmodial activity {IC50 (μg/ml) Pf3D7: 3.99; PfINDO: 2.24} and selectivity for the parasites (SI: 21) yielded a compound that was fourteen-fold potent in antiplasmodial activity against Pf3D7(IC50: 0.28 μg/ml). It also inhibited β-hematin formation with an IC50 = 150 μM. Further studies using spectral data, literature, and chemical databases identified the purified compound as marmesin. ConclusionThis work has demonstrated that Celtis durandii root extract has good antiplasmodial activity against drug-sensitive and drug-resistant P. falciparum. The inhibition of β-hematin formation by marmesin accounts in part for this activity.

Development of diphenylmethylpiperazine hybrids of chloroquinoline and triazolopyrimidine using Petasis reaction as new cysteine proteases inhibitors for malaria therapeutics

Malaria is a widespread infectious disease, causing nearly 247 million cases in 2021. The absence of a broadly effective vaccine and rapidly decreasing effectiveness of most of the currently used antimalarials are the major challenges to malaria eradication efforts. To design and develop novel antimalarials, we synthesized a series of 4,7-dichloroquinoline and methyltriazolopyrimidine analogues using a multi-component Petasis reaction. The synthesized molecules (11–31) were screened for in-vitro antimalarial activity against drug-sensitive and drug-resistant strains of Plasmodium falciparum with an IC50 value of 0.53 μM. The selected compounds were screened to evaluate in-vitro and in-silico enzyme inhibition efficacy against two cysteine proteases, PfFP2 and PfFP3. The compounds 15 and 17 inhibited PfFP2 with an IC50 = 3.5 and 4.8 μM, respectively and PfFP3 with an IC50 = 4.9 and 4.7 μM, respectively. Compounds 15 and 17 were found equipotent against the Pf3D7 strain with an IC50 value of 0.74 μM, whereas both were displayed IC50 values of 1.05 μM and 1.24 μM for the PfW2 strain, respectively. Investigation of effect of compounds on parasite development demonstrated that compounds were able to arrest the growth of the parasites at trophozoite stage. The selected compounds were screened for in-vitro cytotoxicity against mammalian lines and human red-blood-cell (RBC), which demonstrated no significant cytotoxicity associated with the molecules. In addition, in silico ADME prediction and physiochemical properties supported the drug-likeness of the synthesized molecules. Thus, the results highlighted the diphenylmethylpiperazine group cast on 4,7-dichloroquinoline and methyltriazolopyrimidine using Petasis reaction may serve as models for the development of new antimalarial agents.

Activity-based Crosslinking to Identify Substrates of Thioredoxin-domain Proteinsin Malaria Parasites.

Malaria remains a major public health issue, infecting nearly 220 million people every year. The spread of drug-resistant strains of Plasmodium falciparum around the world threatens the progress made against this disease. Therefore, identifying druggable and essential pathways in P. falciparum parasites remains a major area of research. One poorly understood area of parasite biology is the formation of disulfide bonds, which is an essential requirement for the folding of numerous proteins. Specialized chaperones with thioredoxin (Trx) domains catalyze the redox functions necessary for breaking incorrect and forming correct disulfide bonds in proteins. Defining the substrates of these redox chaperones is difficult and immunoprecipitation based assays cannot distinguish between substrates and interacting partners. Further, the substrate or client interactions with the redox chaperones are usually transient in nature. Activity based crosslinkers that rely on the nucleophilic cysteines on Trx domains and the disulfide bond forming cysteines on clients provide an easily scalable method to trap and identify the substrates of Trx-domain containing chaperones. The cell permeable crosslinker divinyl sulfone (DVSF) is active only in the presence of nucleophilic cysteines in proteins and, therefore, traps Trx domains with their substrates, as they form mixed disulfide bonds during the course of their catalytic activity. This allows the identification of substrates that rely on Trx activity for their folding, as well as discovering small molecules that interfere with Trx domain activity. Graphic abstract: Identification of thioredoxin domain substrates via divinylsulfone crosslinking and immunoprecipitation-mass spectrometry.

Design and synthesis of novel hydroxamic acid derivatives based on quisinostat as promising antimalarial agents with improved safety

In our previous work, the clinical phase II HDAC inhibitor quisinostat was identified as a promising antimalarial agent through a drug repurposing strategy, but its safety was a matter of concern. Herein, further medicinal chemistry methods were used to identify new chemical entities with greater effectiveness and safety than quisinostat. In total, 38 novel hydroxamic acid derivatives were designed and synthesized, and their in vitro antimalarial activities were systematically investigated. These compounds at nanomolar concentrations showed inhibitory effects on wild-type and drug-resistant Plasmodium falciparum strains in the erythrocyte stage. Among them, compound 30, after oral administration, resulted in complete elimination of parasites in mice infected with Plasmodium yoelii, and also exhibited better safety and metabolic properties than observed in our previous work. Mechanistically, compound 30 upregulated plasmodium histone acetylation, according to western blotting, thus suggesting that it exerts antimalarial effects through inhibition of Plasmodium falciparum HDAC enzymes.

Rolling out the radical cure for vivax malaria in Asia: a qualitative study among policy makers and stakeholders

BackgroundWide-spread implementation of treatment regimens for the radical cure of vivax malaria is hindered by a range of factors. This has resulted in an increase in the relative proportion of vivax malaria and is an important obstacle in the achievement of global malaria elimination by 2030. The main objective of this study was to explore the current policies guiding the treatment plans on vivax malaria, and the factors affecting the implementation of radical cure in South/South East Asian and Asian Pacific countries.MethodsThis was a qualitative study among respondents who represented national malaria control programmes (NMCPs) or had a role and influence in the national malaria policies. 33 respondents from 17 countries in South/South East Asia and Asia Pacific participated in interviews between October 15 and December 15, 2020. Semi-structured interviews were conducted virtually except for two face to face interviews and audio-recorded. Transcribed audio-records underwent thematic analysis using QSR NVivo.ResultsPolicies against vivax malaria were underprioritized, compared with the focus on falciparum malaria and, in particular, drug resistant Plasmodium falciparum strains. Despite the familiarity with primaquine (PQ) as the essential treatment to achieve the radical cure, the respondents contested the need for G6PD testing. Optional G6PD testing was reported to have poor adherence. The fear of adverse events led health workers to hesitate prescribing PQ. In countries where G6PD was mandatory, respondents experienced frequent stockouts of G6PD rapid diagnostic kits in peripheral health facilities, which was compounded by a short shelf life of these tests. These challenges were echoed across participating countries to various degrees. Most respondents agreed that a shorter treatment regimen, such as single dose tafenoquine could resolve these problems but mandatory G6PD testing will be needed. The recommendation of shorter regimens including tafenoquine or high dose PQ requires operational evidence demonstrating the robust performance of point of care G6PD tests (biosensors).ConclusionThere was sparse implementation and low adherence to the radical cure in South/South East Asian and Asian pacific countries. Shorter treatment regimens with appropriate point of care quantitative G6PD tests may resolve the current challenges. Operational evidence on point of care quantitative G6PD tests that includes the feasibility of integrating such tests into the radical cure regimen are critical to ensure its implementation.

Design, molecular docking, drug-likeness, and molecular dynamics studies of 1,2,4-trioxane derivatives as novel Plasmodium falciparum falcipain-2 (FP-2) inhibitors.

Despite significant progress made in drug discovery and development over the past few decades, malaria remains a life-threatening infectious disease across the globe. Because of the widespread emergence of drug-resistant strains of Plasmodium falciparum, the clinical utility of existing drug therapies including Artemisinin-based Combination Therapies (ACTs) in the treatment of malaria has been increasingly limited. It has become a serious health concern which, therefore, necessitates the development of novel drug molecules and/or alternative therapies to combat, particularly resistant P. falciparum. The objective of the present study was to develop 1,2,4-trioxane derivatives as novel antimalarial agents that would be effective against resistant P. falciparum. In our study, 15 new trioxane derivatives were designed by molecular modification of the 1,2,4-trioxane scaffold as possible antimalarial agents. Molecular modeling studies of trioxane derivatives were performed based on the CADD approach using Biovia Discovery Studio (DS) 2018 software. The protein-ligand docking study was performed against P. falciparum falcipain 2 (FP-2) using the simulation-based docking protocol LibDock by the flexible docking method. The assessment of drug-likeness, ADMET properties, and toxicity was also performed. Furthermore, the compounds CC3 and CC7, which showed the best binding affinity against the target P. falciparum FP-2, were investigated by molecular dynamics (MD) simulation studies followed by the calculation of MM-PBSA binding free energy of protein-ligand complexes using DS 2020. Results of the docking study showed that among the 15 compounds, three trioxane derivatives were found to possess promising binding affinity with LibDock scores ranging from 117.16 to 116.90. Drug-likeness, ADMET, and toxicity properties were found to be satisfactory for all the compounds. Among the 15 compounds, two compounds, namely CC3 and CC7, showed the highest binding affinity against FP-2 with LibDock score of 117.166 and 117.200, respectively. The Libdock score of the co-crystal inhibitor was 114.474. MD studies along with MM-PBSA calculations of binding energies further confirmed the antimalarial potential of the compounds CC3 and CC7, with the formation of well-defined and stable receptor-ligand interactions against the P. falciparum FP-2 enzyme. Additionally, the selectivity of trioxane hits identified as potential inhibitors of P. falciparum cysteine protease FP-2 was determined on human cysteine proteases such as cathepsins (Cat K and Cat L), which are host homologous. Finally, it was concluded that the newly designed 1,2,4-trioxane derivatives can be further studied for in vitro and in vivo antimalarial activities for their possible development as potent antimalarial agents effective against resistant P. falciparum.

Interaction between the Antimalarial Drug Dispiro-Tetraoxanes and Human Serum Albumin: A Combined Study with Spectroscopic Methods and Computational Studies.

Dispiro-tetraoxanes, a class of fully synthetic peroxides which can be used as an antiplasmodial remedy for multiple drug-resistant strains of Plasmodium falciparum, were selected for the interaction study with human serum albumin (HSA). The insight into the interaction of the two chemically synthesized, most potent antimalarial tetraoxane analogues (TO1 and TO2) and HSA has been scrutinized using distinct spectroscopic techniques such as. UV–visible absorption, fluorescence, time-resolved fluorescence, and circular dichroism (CD). Fluorescence quenching experiments divulged the static mode of quenching and binding constants obtained (∼104) indicated the moderate affinity of the analogues to HSA. CD confirmed the conformational changes in the serum albumin upon interaction with these analogues. Molecular docking validated the empirical results as these two analogues bind through hydrophobic interactions and hydrogen bonding with HSA. Present work first defined the binding mechanism of dispiro-tetraoxanes with HSA and thus provides a fresh insight into the drug transportation and metabolism. The present study could direct toward designing more potent tetraoxane analogues for their use in the biomedical field.

An Overview of Available Antimalarials: Discovery, Mode of Action and Drug Resistance.

Malaria is one of the three most deadly infectious diseases in the world and seriously endangers human health and life. To reduce the public health burden of this disease, scientists have focused on the discovery and development of effective antimalarial drugs, from quinine and chloroquine to antifolates and artemisinin and its derivatives, which all play a profound role in the treatment of malaria. However, drugresistant strains of Plasmodium falciparum have emerged due to frequent use of antimalarials and have become increasingly resistant to existing antimalarial drugs, causing disastrous consequences in the world. In particular, artemisinin resistance is of greatest concern which was reported in 2008. Resistance to artenisinins has been a major obstacle for malaria control, and current efforts to curb artemisinin resistance have not been successful. Based on the current situation, it is urgent to develop more effective new antimalarials with distinct targets from conventional antimalarials in the world, which could facilitate to minimize the phenomenon of drug resistance. This review aims to summarize different kinds of antimalarial therapeutic efficacy, mechanisms of action and resistance, and proposes new solutions aiming towards further improvement of malaria elimination.

In Vitro Antiplasmodium and Chloroquine Resistance Reversal Effects of Andrographolide.

The emergence of drug-resistant strains of Plasmodium falciparum is the worst catastrophe that has ever confronted the dedicated efforts to eradicate malaria. This urged for searching other alternatives or sensitizers that reverse chloroquine resistance. In this experiment, the potential of andrographolide to inhibit plasmodial growth and reverse CQ resistance was tested in vitro using the SYBRE green-1-based drug sensitivity assay and isobologram technique, respectively. Its safety level toward mammalian cells was screened as well against Vero cells and RBCs using MTT-based drug sensitivity and RBC hemolysis assays, respectively. Its effect against hemozoin formation was screened using β-hematin formation and heme fractionation assays. Its molecular characters were determined using the conventional tests for the antioxidant effect measurement and the in silico molecular characterization using the online free chemi-informatic Molinspiration software. Results showed that andrographolide has a moderate antiplasmodium effect that does not entitle it to be a substituent for chloroquine. Furthermore, andrographolide ameliorated the sensitivity of the parasite to chloroquine. Besides, it showed an indirect inhibitory effect against hemozoin formation within the parasite and augmented the chloroquine-induced inhibition of hemozoin formation. The study suggests that its chloroquine resistance reversal effect may be due to inhibition of chloroquine accumulation or due to its impact on the biological activity of the parasite. Overall, this in vitro study is a clue for the reliability of andrographolide to be added with chloroquine for reversal of chloroquine resistance and tolerance, but further in vivo studies are recommended to confirm this notion. In spite of its prominent and safe in vitro and in vivo growth inhibitory effect and its in vitro chloroquine resistance reversing effect, it is inapplicable to implement it in malaria chemotherapy to substitute chloroquine or to reverse its resistance.

Hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant Plasmodium falciparum.

Malaria is a tropical disease, leading to around half a million deaths annually. Antimalarials such as quinolines are crucial to fight against malaria, but malaria control is extremely challenged by the limited pipeline of effective pharmaceuticals against drug-resistant strains of Plasmodium falciparum which are resistant toward almost all currently accessible antimalarials. To tackle the growing resistance, new antimalarial drugs are needed urgently. Hybrid molecules which contain two or more pharmacophores have the potential to overcome the drug resistance, and hybridization of quinoline privileged antimalarial building block with other antimalarial pharmacophores may provide novel molecules with enhanced in vitro and in vivo activity against drug-resistant (including multidrug-resistant) P falciparum. In recent years, numerous of quinoline hybrids were developed, and their activities against a panel of drug-resistant P falciparum strains were screened. Some of quinoline hybrids were found to possess promising in vitro and in vivo potency. This review emphasized quinoline hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant P falciparum, covering articles published between 2010 and 2019.

Erratum: Leaf Decoction of Carica papaya Combined with Artesunate Prevents Recrudescence in Plasmodium berghei-Infected Mice.

Malaria treatment and control have become increasingly difficult because of the spread of drug-resistant strains of Plasmodium falciparum and Plasmodium vivax. Thus, there is a continuous need to develop new combination therapies such as artemisinin-based combination therapies (ACTs) to contrast the emergence of resistant Plasmodium strains. Despite ACT has been recommended by the World Health Organization since 2001, its overall deployment in poor endemic areas is very slow, principally due to its high cost. In the malaria endemic areas, plant remedies are still widely used mostly without assurance of their efficacy and/or safety. A variety of widespread herbal drugs or natural products were already reported for their possible plasmodicidal activities, but the studies concerning their activity in combination with artemisinins are very scarce. The antimalarial activity of papaya is mostly anecdotal, and the present study is aimed at investigating the antiplasmodial activity of a decoction obtained by traditional recipe from the mature leaves of Carica papaya. The decoction was analyzed by HPLC-DAD-MS (high performance liquid chromatography coupled with diodoarray detector and mass spectrometry) showing the presence of caffeoyl derivatives and di- and triglycosides of flavonols. The extract was found to be active against P. falciparum 3D7 strains with a synergism in the presence of artemisinin. In vivo activity against the murine malaria model of Plasmodium berghei was disclosed both for the dried extract alone (250, 500, and 750 mg/kg/d) and for its combination with artesunate (250 mg/kg/d papaya plus 10 mg/kg/d artesunate). This combination displayed the greatest antimalarial activity in terms of reduction of parasitemia and prevention of recrudescence in animals recovered from the infection.

Leaf Decoction of Carica papaya Combined with Artesunate Prevents Recrudescence in Plasmodium berghei-Infected Mice.

Malaria treatment and control have become increasingly difficult because of the spread of drug-resistant strains of Plasmodium falciparum and Plasmodium vivax. Thus, there is a continuous need to develop new combination therapies such as artemisinin-based combination therapies (ACTs) to contrast the emergence of resistant Plasmodium strains. Despite ACT has been recommended by the World Health Organization since 2001, its overall deployment in poor endemic areas is very slow, principally due to its high cost. In the malaria endemic areas, plant remedies are still widely used mostly without assurance of their efficacy and/or safety. A variety of widespread herbal drugs or natural products were already reported for their possible plasmodicidal activities, but the studies concerning their activity in combination with artemisinins are very scarce. The antimalarial activity of papaya is mostly anecdotal, and the present study is aimed at investigating the antiplasmodial activity of a decoction obtained by traditional recipe from the mature leaves of Carica papaya. The decoction was analyzed by HPLC-DAD-MS (high performance liquid chromatography coupled with diodoarray detector and mass spectrometry) showing the presence of caffeoyl derivatives and di- and triglycosides of flavonols. The extract was found to be active against P. falciparum 3D7 strains with a synergism in the presence of artemisinin. In vivo activity against the murine malaria model of Plasmodium berghei was disclosed both for the dried extract alone (250, 500, and 750 mg/kg/d) and for its combination with artesunate (250 mg/kg/d papaya plus 10 mg/kg/d artesunate). This combination displayed the greatest antimalarial activity in terms of reduction of parasitemia and prevention of recrudescence in animals recovered from the infection.

In vitro Antiplasmodial Activity of Methanol Stem Extract of Costus afer Ker Gawl. (Costaceae) and its Residual Aqueous Fraction Against Some Drug-sensitive and Drug-resistant Plasmodium falciparum Strains

In vitro Antiplasmodial Activity of Methanol Stem Extract of Costus afer Ker Gawl. (Costaceae) and its Residual Aqueous Fraction Against Some Drug-sensitive and Drug-resistant Plasmodium falciparum Strains

Chemosuppressive activities in in vivo studies of Plasmodium falciparum-infected mice using isolated oil of Stigmaphyllon ovatum (Amazon vine) Cav.

Abstract Problem: In sub-Saharan Africa, malaria remains one of the leading health problems. This situation has been aggravated by the increasing spread of drug-resistant Plasmodium falciparum strains. The study was conducted to determine the chemosuppressive activities in in vivo studies of Plasmodium falciparum-infected mice with isolated oil of Stigmaphyllon ovatum leaves used in the traditional treatment of malaria in Nigeria. Methodology: The plant leaves were collected, dried, pulverized and extracted in Soxhlet extractor with hexane solvent. The crude extract was concentrated using a rotary evaporator and phytochemical screening performed using standard methods. Isolation of oil from hexane extract was done using vacuum liquid chromatography while characterization was done by gas chromatography-mass spectrometry (GC-MS). Chemosuppressive activities were conducted along with quinine to determine the antimalarial potency in Plasmodium falciparum- infected BALB/c albino mice. Findings: Glycosides, saponins, phenolics, and alkaloids among others were present. Components detected from the isolated yellow oil of S. ovatum were 9-octadecenoic acid (oleic acid) (Rt:20.0, 19.37%), an unsaturated fatty acid, squalene (Rt:25.6, 4.58%), a terpene; 7-tetradecenal (Rt:22.6, 2.40%), an aldehyde and alicyclic compounds like bicycle (3,10) hexan-3-one (Rt:16.7, 0.22%). Quinine-treated mice exhibited the lowest parasite counts of 0.27±0.01 (83.82% mean chemosuppression) at day 4 of therapy while the lowest parasite counts for the isolated oil was 0.95±0.05 (42.92% mean chemosuppression) at day 4 of therapy. Conclusion: The chemosuppressive activities revealed that the isolated oil exhibit significant suppression (P<0.05) of Plasmodium falciparum when compared with the standard, quinine which was evident by the photomicrograph results. This work corroborates the local use of the plants for the treatment of malaria in Southern Nigeria.

Evidence of a Mild Mutator Phenotype in Cambodian Plasmodium falciparum Malaria Parasites.

Malaria control efforts have been continuously stymied by drug-resistant strains of Plasmodium falciparum, which typically originate in Southeast Asia prior to spreading into high-transmission settings in Africa. One earlier proposed explanation for Southeast Asia being a hotbed of resistance has been the hypermutability or “Accelerated Resistance to Multiple Drugs” (ARMD) phenotype, whereby multidrug-resistant Southeast Asian parasites were reported to exhibit 1,000-fold higher rates of resistance to unrelated antimalarial agents when compared to drug-sensitive parasites. However, three recent studies do not recapitulate this hypermutability phenotype. Intriguingly, genome sequencing of recently derived multidrug-resistant Cambodian isolates has identified a high proportion of DNA repair gene mutations in multidrug-resistant parasites, suggesting their potential role in shaping local parasite evolution. By adapting fluctuation assays for use in P. falciparum, we have examined the in vitro mutation rates of five recent Cambodian isolates and three reference laboratory strains. For these studies we also generated a knockout parasite line lacking the DNA repair factor Exonuclease I. In these assays, parasites were typed for their ability to acquire resistance to KAE609, currently in advanced clinical trials, yielding 13 novel mutations in the Na+/H+-ATPase PfATP4, the primary resistance determinant. We observed no evidence of hypermutability. Instead, we found evidence of a mild mutator (up to a 3.4-fold increase in mutation rate) phenotype in two artemisinin-resistant Cambodian isolates, which carry DNA repair gene mutations. We observed that one such mutation in the Mismatch Repair protein Mlh1 contributes to the mild mutator phenotype when modeled in yeast (scmlh1-P157S). Compared to basal rates of mutation, a mild mutator phenotype may provide a greater overall benefit for parasites in Southeast Asia in terms of generating drug resistance without incurring detrimental fitness costs.

In vitro sensitivity of Plasmodium falciparum clinical isolates to 4-aminoquinolines in Northeast Nigeria.

Widespread dr ug-resistant Plasmodium falciparum strains have challenged the pivotal role played by 4-aminoquinolines, including chloroquine (CQ), which has been delisted for the treatment of malaria in most parts of the world. This study assessed the in vitro sensitivity of P. falciparum clinical isolates (PfCIs) to amodiaquine (AQ) and CQ in Northeast Nigeria. PfCIs were collected from subjects with uncomplicated P. falciparum malaria in Azare, Bauchi State and Maiduguri, Borno State following an informed consent. The in vitro sensitivity was assessed by micro-test (MarkIII) method and the IC50 of AQ and CQ was determined using HN-NonLin Version VI.1 software. The reference standard cut-off values for in vitro AQ and CQ resistance of 80 and 160 nmol/l, respectively, were used. Isolates that were inhibited by lower AQ and CQ concentrations were referred to as sensitive. Valid in vitro assay r esults were obtained for 88.9% (80/90) of the PfCIs; Azare had 93.3% (28/30) and Maiduguri had 86.7% (52/60) [χ2 = 0.35; df = 1; p = 0.486]. The geometric mean (GM) IC50 of AQ and CQ were 24.2 nmol/l (95% CI, 10.5 - 49.6 nmol/l) and 39.5 nmol/l (95% CI, 34.5 - 49.6 nmol/l), respectively. The AQ (p = 0.922) and CQ (p = 0.085) GM IC50 were similar between Azare and Maiduguri PfCIs. Only one isolate showed in vitro resistance to AQ giving a sensitivity of 98.8% (79/80) while 17 PfCIs showed in vitro resistance to CQ giving a sensitivity of 78.8% (63/80). The CQ sensitivity was similar between Azare (67.9%; 19/28) and Maiduguri (84.6%; 44/52) PfCIs (χ2 = 3.05; df = 1; p = 0.081). The findings may suggest that the AQ in vitro sensitivity remains high and the isolates in Northeast Nigeria may appear more sensitive to CQ than isolates from other parts. These findings may affect malaria treatment and control policy in Nigeria.

In vitro efficacy of 2,N-bisarylated 2-ethoxyacetamides against Plasmodium falciparum.

Investigation of a series of 2,N-bisarylated 2-ethoxyacetamides resulted in the identification of four inhibitors 5, 20, 24, 29 with single-digit micromolar in vitro efficacy against two drug-resistant Plasmodium falciparum strains. These compounds are analogs of structurally-related 1,3-bisaryl-2-propen-1-ones (chalcones), the latter showing efficacy in vitro but not in a malaria-infected mouse. The 2,N-bisarylated 2-ethoxyacetamides (e.g., 2, 5, 20) were shown to possess significantly greater stability in the presence of metabolizing enzymes than the corresponding 1,3-bisaryl-2-propen-1-ones (e.g., 1, 3, 18).