1
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Kumar S, Li X, McDew-White M, Reyes A, Delgado E, Sayeed A, Haile MT, Abatiyow BA, Kennedy SY, Camargo N, Checkley LA, Brenneman KV, Button-Simons KA, Duraisingh MT, Cheeseman IH, Kappe SHI, Nosten F, Ferdig MT, Vaughan AM, Anderson TJC. A Malaria Parasite Cross Reveals Genetic Determinants of Plasmodium falciparum Growth in Different Culture Media. Front Cell Infect Microbiol 2022; 12:878496. [PMID: 35711667 PMCID: PMC9197316 DOI: 10.3389/fcimb.2022.878496] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Accepted: 04/28/2022] [Indexed: 12/21/2022] Open
Abstract
What genes determine in vitro growth and nutrient utilization in asexual blood-stage malaria parasites? Competition experiments between NF54, clone 3D7, a lab-adapted African parasite, and a recently isolated Asian parasite (NHP4026) reveal contrasting outcomes in different media: 3D7 outcompetes NHP4026 in media containing human serum, while NHP4026 outcompetes 3D7 in media containing AlbuMAX, a commercial lipid-rich bovine serum formulation. To determine the basis for this polymorphism, we conducted parasite genetic crosses using humanized mice and compared genome-wide allele frequency changes in three independent progeny populations cultured in media containing human serum or AlbuMAX. This bulk segregant analysis detected three quantitative trait loci (QTL) regions [on chromosome (chr) 2 containing aspartate transaminase AST; chr 13 containing EBA-140; and chr 14 containing cysteine protease ATG4] linked with differential growth in serum or AlbuMAX in each of the three independent progeny pools. Selection driving differential growth was strong (s = 0.10 – 0.23 per 48-hour lifecycle). We conducted validation experiments for the strongest QTL on chr 13: competition experiments between ΔEBA-140 and 3D7 wildtype parasites showed fitness reversals in the two medium types as seen in the parental parasites, validating this locus as the causative gene. These results (i) demonstrate the effectiveness of bulk segregant analysis for dissecting fitness traits in P. falciparum genetic crosses, and (ii) reveal intimate links between red blood cell invasion and nutrient composition of growth media. Use of parasite crosses combined with bulk segregant analysis will allow systematic dissection of key nutrient acquisition/metabolism and red blood cell invasion pathways in P. falciparum.
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Affiliation(s)
- Sudhir Kumar
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Xue Li
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Marina McDew-White
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Ann Reyes
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Elizabeth Delgado
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Abeer Sayeed
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Meseret T. Haile
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Biley A. Abatiyow
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Spencer Y. Kennedy
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Nelly Camargo
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Lisa A. Checkley
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States
| | - Katelyn V. Brenneman
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States
| | - Katrina A. Button-Simons
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States
| | - Manoj T. Duraisingh
- Immunology and Infectious Diseases Department, Harvard T.H. Chan School of Public Health, Boston, MA, United States
| | - Ian H. Cheeseman
- Program in Host Pathogen Interactions, Texas Biomedical Research Institute, San Antonio, TX, United States
| | - Stefan H. I. Kappe
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
- Department of Pediatrics, University of Washington, Seattle, WA, United States
| | - François Nosten
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research building, University of Oxford, Oxford, United Kingdom
| | - Michael T. Ferdig
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States
| | - Ashley M. Vaughan
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
- Department of Pediatrics, University of Washington, Seattle, WA, United States
- *Correspondence: Ashley M. Vaughan, ; Tim J. C. Anderson,
| | - Tim J. C. Anderson
- Program in Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX, United States
- *Correspondence: Ashley M. Vaughan, ; Tim J. C. Anderson,
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2
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Plowe CV. Malaria chemoprevention and drug resistance: a review of the literature and policy implications. Malar J 2022; 21:104. [PMID: 35331231 PMCID: PMC8943514 DOI: 10.1186/s12936-022-04115-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 03/03/2022] [Indexed: 01/19/2023] Open
Abstract
Chemoprevention strategies reduce malaria disease and death, but the efficacy of anti-malarial drugs used for chemoprevention is perennially threatened by drug resistance. This review examines the current impact of chemoprevention on the emergence and spread of drug resistant malaria, and the impact of drug resistance on the efficacy of each of the chemoprevention strategies currently recommended by the World Health Organization, namely, intermittent preventive treatment in pregnancy (IPTp); intermittent preventive treatment in infants (IPTi); seasonal malaria chemoprevention (SMC); and mass drug administration (MDA) for the reduction of disease burden in emergency situations. While the use of drugs to prevent malaria often results in increased prevalence of genetic mutations associated with resistance, malaria chemoprevention interventions do not inevitably lead to meaningful increases in resistance, and even high rates of resistance do not necessarily impair chemoprevention efficacy. At the same time, it can reasonably be anticipated that, over time, as drugs are widely used, resistance will generally increase and efficacy will eventually be lost. Decisions about whether, where and when chemoprevention strategies should be deployed or changed will continue to need to be made on the basis of imperfect evidence, but practical considerations such as prevalence patterns of resistance markers can help guide policy recommendations.
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3
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Gil JP, Fançony C. Plasmodium falciparum Multidrug Resistance Proteins ( pfMRPs). Front Pharmacol 2021; 12:759422. [PMID: 34790129 PMCID: PMC8591188 DOI: 10.3389/fphar.2021.759422] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 10/05/2021] [Indexed: 12/19/2022] Open
Abstract
The capacity of the lethal Plasmodium falciparum parasite to develop resistance against anti-malarial drugs represents a central challenge in the global control and elimination of malaria. Historically, the action of drug transporters is known to play a pivotal role in the capacity of the parasite to evade drug action. MRPs (Multidrug Resistance Protein) are known in many phylogenetically diverse groups to be related to drug resistance by being able to handle a large range of substrates, including important endogenous substances as glutathione and its conjugates. P. falciparum MRPs are associated with in vivo and in vitro altered drug response, and might be important factors for the development of multi-drug resistance phenotypes, a latent possibility in the present, and future, combination therapy environment. Information on P. falciparum MRPs is scattered in the literature, with no specialized review available. We herein address this issue by reviewing the present state of knowledge.
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Affiliation(s)
- José Pedro Gil
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.,Faculty of Sciences, BioISI-Biosystems and Integrative Sciences Institute, University of Lisbon, Lisbon, Portugal.,Global Health and Tropical Medicine, Institute of Hygiene and Tropical Medicine, Nova University of Lisbon, Lisbon, Portugal
| | - Cláudia Fançony
- Centro de Investigação em Saúde de Angola (CISA)/Instituto Nacional de Investigação em Saúde (INIS), Caxito, Angola
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4
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Biguanides drugs: Past success stories and promising future for drug discovery. Eur J Med Chem 2021; 224:113726. [PMID: 34364161 DOI: 10.1016/j.ejmech.2021.113726] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 07/27/2021] [Accepted: 07/27/2021] [Indexed: 12/13/2022]
Abstract
Biguanides have attracted much attention a century ago and showed resurgent interest in recent years after a long period of dormancy. They constitute an important class of therapeutic agents suitable for the treatment of a wide spectrum of diseases. Therapeutic indications of biguanides include antidiabetic, antimalarial, antiviral, antiplaque, and bactericidal applications. This review presents an extensive overview of the biological activity of biguanides and different mechanisms of action of currently marketed biguanide-containing drugs, as well as their pharmacological properties when applicable. We highlight the recent developments in research on biguanide compounds, with a primary focus on studies on metformin in the field of oncology. We aim to provide a critical overview of all main bioactive biguanide compounds and discuss future perspectives for the design of new drugs based on the biguanide fragment.
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5
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Chitnumsub P, Jaruwat A, Talawanich Y, Noytanom K, Liwnaree B, Poen S, Yuthavong Y. The structure of Plasmodium falciparum hydroxymethyldihydropterin pyrophosphokinase-dihydropteroate synthase reveals the basis of sulfa resistance. FEBS J 2020; 287:3273-3297. [PMID: 31883412 DOI: 10.1111/febs.15196] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Revised: 12/04/2019] [Accepted: 12/27/2019] [Indexed: 11/28/2022]
Abstract
The clinical efficacy of sulfa drugs as antimalarials has declined owing to the evolution of resistance in Plasmodium falciparum (Pf) malaria parasites. In order to understand the basis of this resistance and to design more effective antimalarials, we have solved 13 structures of the bifunctional enzyme 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK)-dihydropteroate synthase (DHPS) from wild-type (WT) P. falciparum and sulfa-resistant mutants, both as apoenzyme and as complexes with pteroate (PTA) and sulfa derivatives. The structures of these complexes show that PTA, which effectively inhibits both the WT and mutants, stays in active sites without steric constraint. In contrast, parts of the sulfa compounds situated outside of the substrate envelope are in the vicinity of the resistance mutations. Steric conflict between compound and mutant residue along with increased flexibility of loop D2 in the mutants can account for the reduced compound binding affinity to the mutants. Kinetic data show that the mutants have enhanced enzyme activity compared with the WT. These PfDHPS structural insights are critical for the design of novel, substrate envelope-compliant DHPS inhibitors that are less vulnerable to resistance mutations. DATABASES: The data reported in this paper have been deposited in the Protein Data Bank, www.wwpdb.org. PDB ID codes: 6JWQ for apoWT; 6JWR, 6JWS, and 6JWT for PTA complexes of WT, A437G (3D7), and V1/S; 6JWU, 6JWV, and 6JWW for STZ-DHP complexes of WT, 3D7, and V1/S; 6JWX, 6JWY, and 6JWZ for SDX-DHP complexes of WT, 3D7, and W2; 6KCK, 6KCL, and 6KCM for Pterin/pHBA complexes of WT, TN1, and W2.
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Affiliation(s)
- Penchit Chitnumsub
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Aritsara Jaruwat
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Yuwadee Talawanich
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Krittikar Noytanom
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Benjamas Liwnaree
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Sinothai Poen
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
| | - Yongyuth Yuthavong
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Thailand
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6
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Counihan NA, Chisholm SA, Bullen HE, Srivastava A, Sanders PR, Jonsdottir TK, Weiss GE, Ghosh S, Crabb BS, Creek DJ, Gilson PR, de Koning-Ward TF. Plasmodium falciparum parasites deploy RhopH2 into the host erythrocyte to obtain nutrients, grow and replicate. eLife 2017; 6. [PMID: 28252383 PMCID: PMC5365316 DOI: 10.7554/elife.23217] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2016] [Accepted: 02/26/2017] [Indexed: 11/13/2022] Open
Abstract
Plasmodium falciparum parasites, the causative agents of malaria, modify their host erythrocyte to render them permeable to supplementary nutrient uptake from the plasma and for removal of toxic waste. Here we investigate the contribution of the rhoptry protein RhopH2, in the formation of new permeability pathways (NPPs) in Plasmodium-infected erythrocytes. We show RhopH2 interacts with RhopH1, RhopH3, the erythrocyte cytoskeleton and exported proteins involved in host cell remodeling. Knockdown of RhopH2 expression in cycle one leads to a depletion of essential vitamins and cofactors and decreased de novo synthesis of pyrimidines in cycle two. There is also a significant impact on parasite growth, replication and transition into cycle three. The uptake of solutes that use NPPs to enter erythrocytes is also reduced upon RhopH2 knockdown. These findings provide direct genetic support for the contribution of the RhopH complex in NPP activity and highlight the importance of NPPs to parasite survival.
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Affiliation(s)
| | | | | | - Anubhav Srivastava
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia
| | | | - Thorey K Jonsdottir
- Burnet Institute, Melbourne, Australia.,Department of Medicine, University of Melbourne, Parkville, Australia
| | | | - Sreejoyee Ghosh
- School of Medicine, Deakin University, Waurn Ponds, Australia
| | - Brendan S Crabb
- Burnet Institute, Melbourne, Australia.,Department of Medicine, University of Melbourne, Parkville, Australia.,Monash University, Melbourne, Australia
| | - Darren J Creek
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia
| | - Paul R Gilson
- Burnet Institute, Melbourne, Australia.,Monash University, Melbourne, Australia
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7
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Abstract
Folate is essential for DNA synthesis and the survival and growth of the malaria parasite. Folate sufficiency may be associated with an increased risk of malaria. Antifolate antimalarial drugs are of major importance in the prophylaxis and treatment of malaria. Folic acid reverses the inhibition by antifolate drugs of plasmodial growth or survival in vitro, and folic acid supplements given to children with malaria may increase the failure rate of treatment with antimalarials. There is no convincing evidence of a significant prevalence of folate deficiency in children in malarious areas, nor of a beneficial effect of folic acid supplementation on malarial anemia. In areas where Plasmodium falciparum malaria is holoendemic, universal supplementation of children with iron and folic acid may increase the incidence of severe morbidity and mortality. These regions should be excluded from the World Health Organization recommendation of universal folic acid supplementation of children in areas of high prevalence of anemia. This does not apply to supplementation of pregnant women with folic acid.
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8
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Odongo CO, Bisaso KR, Ntale M, Odia G, Ojara FW, Byamugisha J, Mukonzo JK, Obua C. Trimester-Specific Population Pharmacokinetics and Other Correlates of Variability in Sulphadoxine-Pyrimethamine Disposition Among Ugandan Pregnant Women. Drugs R D 2016; 15:351-62. [PMID: 26586482 PMCID: PMC4662941 DOI: 10.1007/s40268-015-0110-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Background Sulphadoxine–pyrimethamine (SP) is widely used as an intermittent preventive treatment for malaria in pregnancy (IPTp). However, pharmacokinetic studies in pregnancy show variable and often contradictory findings. We describe population and trimester-specific differences in SP pharmacokinetics among Ugandan women. Methods SP (three tablets) were administered to 34 nonpregnant and 87 pregnant women in the second trimester. Seventy-eight pregnant women were redosed in the third trimester. Blood was collected over time points ranging from 0.5 h to 42 days postdose. Data on the variables age, body weight, height, parity, gestational age, and serum creatinine, alanine transaminase and albumin levels were collected at baseline. Plasma drug assays were performed using high-performance liquid chromatography with ultraviolet detection. Population pharmacokinetic analysis was done using NONMEM software. Results A two-compartment model with first-order absorption and a lag time best described both the sulphadoxine and pyrimethamine data. Between trimesters, statistically significant differences in central volumes of distribution (V2) were observed for both drugs, while differences in the distribution half-life and the terminal elimination half-life were observed for pyrimethamine and sulphadoxine, respectively. Significant covariate relationships were identified on clearance (pregnancy status and serum albumin level) and V2 (gestational age) for sulphadoxine. For pyrimethamine, clearance (pregnancy status and age) and V2 (gestational age and body weight) were significant. Considering a 25 % threshold for clinical relevance, only differences in clearance of both drugs between pregnant and nonpregnant women were significant. Conclusion While clinically relevant differences in SP disposition between trimesters were not seen, increased clearance with pregnancy and the increasing volume of distribution in the central compartment with gestational age lend support to the revised World Health Organization guidelines advocating more frequent dosing of SP for IPTp.
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Affiliation(s)
- Charles O Odongo
- Department of Pharmacology and Therapeutics, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda.
- Department of Pharmacology and Therapeutics, Gulu University Faculty of Medicine, P.O. Box 166, Gulu, Uganda.
| | - Kuteesa R Bisaso
- Department of Pharmacology and Therapeutics, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda
- Breakthrough Analytics Ltd, Kampala, Uganda
| | - Muhammad Ntale
- Department of Chemistry, Makerere University College of Natural and Applied Sciences, P.O. Box 7062, Kampala, Uganda
| | - Gordon Odia
- Department of Pharmacology and Therapeutics, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda
| | - Francis W Ojara
- Department of Pharmacology and Therapeutics, Gulu University Faculty of Medicine, P.O. Box 166, Gulu, Uganda
| | - Josaphat Byamugisha
- Department of Obstetrics and Gynaecology, Makerere University College of Health Sciences, Mulago Hospital Complex, P.O. Box 7062, Kampala, Uganda
| | - Jackson K Mukonzo
- Department of Pharmacology and Therapeutics, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda
| | - Celestino Obua
- Mbarara University of Science and Technology, P.O. Box 1410, Mbarara, Uganda
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9
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Rijpma SR, van der Velden M, Bilos A, Jansen RS, Mahakena S, Russel FGM, Sauerwein RW, van de Wetering K, Koenderink JB. MRP1 mediates folate transport and antifolate sensitivity in Plasmodium falciparum. FEBS Lett 2016; 590:482-92. [PMID: 26900081 DOI: 10.1002/1873-3468.12079] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Revised: 01/12/2016] [Accepted: 01/18/2016] [Indexed: 11/05/2022]
Abstract
Multidrug resistance-associated proteins (MRP) of Plasmodium falciparum have been associated with altered drug sensitivity. Knowledge on MRP substrate specificity is indispensible for the characterization of resistance mechanisms and identifying its physiological roles. An untargeted metabolomics approach detected decreased folate concentrations in red blood cells infected with schizont stage parasites lacking expression of MRP1. Furthermore, a tenfold decrease in sensitivity toward the folate analog methotrexate was detected for parasites lacking MRP1. PfMRP1 is involved in the export of folate from parasites into red blood cells and is therefore a relevant factor for efficient malaria treatment through the folate pathway.
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Affiliation(s)
- Sanna R Rijpma
- Department of Pharmacology and Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Maarten van der Velden
- Department of Pharmacology and Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Albert Bilos
- Department of Pharmacology and Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Robert S Jansen
- Division of Molecular Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Sunny Mahakena
- Division of Molecular Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Frans G M Russel
- Department of Pharmacology and Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Robert W Sauerwein
- Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Koen van de Wetering
- Division of Molecular Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jan B Koenderink
- Department of Pharmacology and Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
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10
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Talawanich Y, Kamchonwongpaisan S, Sirawaraporn W, Yuthavong Y. Use of bacterial surrogates as a tool to explore antimalarial drug interaction: Synergism between inhibitors of malarial dihydrofolate reductase and dihydropteroate synthase. Acta Trop 2015; 149:64-9. [PMID: 25997881 DOI: 10.1016/j.actatropica.2015.05.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 03/31/2015] [Accepted: 05/13/2015] [Indexed: 11/17/2022]
Abstract
Interaction between antimalarial drugs is important in determining the outcome of chemotherapy using drug combinations. Inhibitors of dihydrofolate reductase (DHFR) such as pyrimethamine and of dihydropteroate synthase (DHPS) such as sulfa drugs are known to have synergistic interactions. However, studies of the synergism are complicated by the fact that the malaria parasite can also salvage exogenous folates, and the salvage may also be affected by the drugs. It is desirable to have a convenient system to study interaction of DHFR and DHPS inhibitors without such complications. Here, we describe the use of Escherichia coli transformed with malarial DHFR and DHPS, while its own corresponding genes have been inactivated by optimal concentration of trimethoprim and genetic knockout, respectively, to study the interaction of the inhibitors. Marked synergistic effects are observed for all combinations of pyrimethamine and sulfa inhibitors in the presence of trimethoprim. At 0.05μM trimethoprim, sum of fractional inhibitory concentrations, ΣFIC of pyrimethamine with sulfadoxine, pyrimethamine with sulfathiazole, pyrimethamine with sulfamethoxazole, and pyrimethamine with dapsone are in the range of 0.24-0.41. These results show synergism between inhibitors of the two enzymes even in the absence of folate transport and uptake. This bacterial surrogate system should be useful as a tool for assessing the interactions of drug combinations between the DHFR and DHPS inhibitors.
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Affiliation(s)
- Yuwadee Talawanich
- National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand
| | - Sumalee Kamchonwongpaisan
- National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand
| | - Worachart Sirawaraporn
- Department of Biochemistry, Faculty of Science, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand
| | - Yongyuth Yuthavong
- National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand.
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11
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Folate metabolism in human malaria parasites—75 years on. Mol Biochem Parasitol 2013; 188:63-77. [DOI: 10.1016/j.molbiopara.2013.02.008] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 02/15/2013] [Accepted: 02/19/2013] [Indexed: 12/21/2022]
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12
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Salcedo-Sora JE, Ward SA. The folate metabolic network of Falciparum malaria. Mol Biochem Parasitol 2013; 188:51-62. [PMID: 23454873 DOI: 10.1016/j.molbiopara.2013.02.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 02/04/2013] [Accepted: 02/11/2013] [Indexed: 01/07/2023]
Abstract
The targeting of key enzymes in the folate pathway continues to be an effective chemotherapeutic approach that has earned antifolate drugs a valuable position in the medical pharmacopoeia. The successful therapeutic use of antifolates as antimalarials has been a catalyst for ongoing research into the biochemistry of folate and pterin biosynthesis in malaria parasites. However, our understanding of the parasites folate metabolism remains partial and patchy, especially in relation to the shikimate pathway, the folate cycle, and folate salvage. A sizeable number of potential folate targets remain to be characterised. Recent reports on the parasite specific transport of folate precursors that would normally be present in the human host awaken previous hypotheses on the salvage of folate precursors or by-products. As the parasite progresses through its life-cycle it encounters very contrasting host cell environments that present radically different metabolic milieus and biochemical challenges. It would seem probable that as the parasite encounters differing environments it would need to modify its biochemistry. This would be reflected in the folate homeostasis in Plasmodium. Recent drug screening efforts and insights into folate membrane transport substantiate the argument that folate metabolism may still offer unexplored opportunities for therapeutic attack.
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Affiliation(s)
- J Enrique Salcedo-Sora
- Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.
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13
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Abdul-Ghani R, Farag HF, Allam AF. Sulfadoxine-pyrimethamine resistance in Plasmodium falciparum: a zoomed image at the molecular level within a geographic context. Acta Trop 2013; 125:163-90. [PMID: 23131424 DOI: 10.1016/j.actatropica.2012.10.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Revised: 10/25/2012] [Accepted: 10/26/2012] [Indexed: 10/27/2022]
Abstract
Antimalarial chemotherapy is one of the main pillars in the prevention and control of malaria. Following widespread resistance of Plasmodium falciparum to chloroquine, sulfadoxine-pyrimethamine came to the scene as an alternative to the cheap and well-tolerated chloroquine. However, widespread resistance to sulfadoxine-pyrimethamine has been documented. In vivo efficacy tests are the gold standard for assessing drug resistance and treatment failure. However, they have many disadvantages, such as influence of host immunity and drug pharmacokinetics. In vitro tests of antimalarial drug efficacy also have many technical difficulties. Molecular markers of resistance have emerged as epidemiologic tools to investigate antimalarial drug resistance even before becoming clinically evident. Mutations in P. falciparum dihydrofolate reductase and dihydrofolate synthase have been extensively studied as molecular markers for resistance to pyrimethamine and sulfadoxine, respectively. This review highlights the resistance of P. falciparum at the molecular level presenting both supporting and opposing studies on the utility of molecular markers.
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14
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Dantas G, Sommer MOA. Context matters - the complex interplay between resistome genotypes and resistance phenotypes. Curr Opin Microbiol 2012; 15:577-82. [PMID: 22954750 DOI: 10.1016/j.mib.2012.07.004] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2012] [Revised: 07/11/2012] [Accepted: 07/13/2012] [Indexed: 12/13/2022]
Abstract
Application of metagenomic functional selections to study antibiotic resistance genes is revealing a highly diverse and complex network of genetic exchange between bacterial pathogens and environmental reservoirs, which likely contributes significantly to increasing resistance levels in pathogens. In some cases, clinically relevant resistance genes have been acquired from organisms where their native function is not antibiotic resistance, and which may not even confer a resistance phenotype in their native context. In this review, we attempt to distinguish the resistance phenotype from the resistome genotype, and we highlight examples of genes and their hosts where this distinction becomes important in order to understand the relevance of environmental niches that contribute most to clinical problems associated with antibiotic resistance.
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Affiliation(s)
- Gautam Dantas
- Center for Genome Sciences & Systems Biology, Washington University School of Medicine, St Louis, MO, USA.
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15
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Salcedo-Sora JE, Ochong E, Beveridge S, Johnson D, Nzila A, Biagini GA, Stocks PA, O'Neill PM, Krishna S, Bray PG, Ward SA. The molecular basis of folate salvage in Plasmodium falciparum: characterization of two folate transporters. J Biol Chem 2011; 286:44659-68. [PMID: 21998306 PMCID: PMC3247980 DOI: 10.1074/jbc.m111.286054] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Tetrahydrofolates are essential cofactors for DNA synthesis and methionine metabolism. Malaria parasites are capable both of synthesizing tetrahydrofolates and precursors de novo and of salvaging them from the environment. The biosynthetic route has been studied in some detail over decades, whereas the molecular mechanisms that underpin the salvage pathway lag behind. Here we identify two functional folate transporters (named PfFT1 and PfFT2) and delineate unexpected substrate preferences of the folate salvage pathway in Plasmodium falciparum. Both proteins are localized in the plasma membrane and internal membranes of the parasite intra-erythrocytic stages. Transport substrates include folic acid, folinic acid, the folate precursor p-amino benzoic acid (pABA), and the human folate catabolite pABAGn. Intriguingly, the major circulating plasma folate, 5-methyltetrahydrofolate, was a poor substrate for transport via PfFT2 and was not transported by PfFT1. Transport of all folates studied was inhibited by probenecid and methotrexate. Growth rescue in Escherichia coli and antifolate antagonism experiments in P. falciparum indicate that functional salvage of 5-methyltetrahydrofolate is detectable but trivial. In fact pABA was the only effective salvage substrate at normal physiological levels. Because pABA is neither synthesized nor required by the human host, pABA metabolism may offer opportunities for chemotherapeutic intervention.
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Affiliation(s)
- J Enrique Salcedo-Sora
- Molecular and Biochemical Parasitology Group, Liverpool School of Tropical Medicine, Liverpool L3 5QA, United Kingdom
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16
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Chango A, Abdennebi-Najar L. Folate metabolism pathway and Plasmodium falciparum malaria infection in pregnancy. Nutr Rev 2011; 69:34-40. [PMID: 21198633 DOI: 10.1111/j.1753-4887.2010.00362.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Malaria induced by Plasmodium falciparum is a major cause of mortality. P. falciparum has the ability to use host plasma folate as its primary folate source. Folate is a cofactor needed for both malaria parasite growth and host erythrocyte production. This review examines the possible impairment of the folate-mediated one-carbon metabolism pathway as a result of P. falciparum malaria infection during pregnancy. Folate deficiency during malaria infection is presented, with an emphasis on the controversy regarding the decrease of plasma or erythrocyte folate secondary to malaria. Maternal folate deficiency increases the risk of adverse pregnancy outcomes. Functional folate deficiency and/or increased plasma homocysteine levels during pregnancy of infected women in areas endemic for malaria is a probable scenario accentuating the impairment of placenta function leading to the occurrence of neural tube defects, low birth weights, and intrauterine growth retardations. Potential questions that may be answered in future investigations using an appropriate protocol to study pregnant women with malaria are also addressed.
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Affiliation(s)
- Abalo Chango
- Department of Nutritional Sciences and Health, EGEAL Unit, Institut Polytechnique Lasalle Beauvais, Beauvais, France.
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17
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Stephens LL, Shonhai A, Blatch GL. Co-expression of the Plasmodium falciparum molecular chaperone, PfHsp70, improves the heterologous production of the antimalarial drug target GTP cyclohydrolase I, PfGCHI. Protein Expr Purif 2011; 77:159-65. [PMID: 21262365 DOI: 10.1016/j.pep.2011.01.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Revised: 01/17/2011] [Accepted: 01/18/2011] [Indexed: 11/19/2022]
Abstract
Molecular chaperones have been used for the improved expression of target proteins within heterologous systems; however, the chaperone and target protein have seldom been matched in terms of origin. We have developed a heterologous co-expression system that allows independent expression of the plasmodial chaperone, PfHsp70, and a plasmodial target protein. In this study, the target was Plasmodium falciparum GTP cyclohydrolase I (PfGCHI), the first enzyme in the plasmodial folate pathway. The sequential expression of the molecular chaperone followed by the target protein increased the expression of soluble functional PfGCHI. His-tagged PfGCHI was successfully purified using nickel affinity chromatography, and the specific activity was determined by high performance liquid chromatography with spectrofluorometeric detection to be 5.93nmol/h/mg. This is the first report of a heterologous co-expression system in which a plasmodial chaperone is harnessed for the improved production and purification of a plasmodial target protein.
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Affiliation(s)
- Linda L Stephens
- Department of Biochemistry, Microbiology and Biotechnology, Rhodes University, South Africa
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18
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Müller IB, Hyde JE. Antimalarial drugs: modes of action and mechanisms of parasite resistance. Future Microbiol 2010; 5:1857-73. [DOI: 10.2217/fmb.10.136] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Malaria represents one of the most serious threats to human health worldwide, and preventing and curing this parasitic disease still depends predominantly on the administration of a small number of drugs whose efficacy is continually threatened and eroded by the emergence of drug-resistant parasite populations. This has an enormous impact on the mortality and morbidity resulting from malaria infection, especially in sub-Saharan Africa, where the lethal human parasite species Plasmodium falciparum accounts for approximately 90% of deaths recorded globally. Successful treatment of uncomplicated malaria is now highly dependent on artemisinin-based combination therapies. However, the first cases of artemisinin-resistant field isolates have been reported recently and potential replacement antimalarials are only in the developmental stages. Here, we summarize recent progress in tackling the problem of parasite resistance and discuss the underlying molecular mechanisms that confer resistance to current antimalarial agents as far as they are known, understanding of which should assist in the rational development of new drugs and the more effective deployment of older ones.
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Affiliation(s)
- Ingrid B Müller
- Department of Biochemistry, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
| | - John E Hyde
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
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19
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Martinelli A, Henriques G, Cravo P, Hunt P. Whole genome re-sequencing identifies a mutation in an ABC transporter (mdr2) in a Plasmodium chabaudi clone with altered susceptibility to antifolate drugs. Int J Parasitol 2010; 41:165-71. [PMID: 20858498 PMCID: PMC3034870 DOI: 10.1016/j.ijpara.2010.08.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Revised: 07/27/2010] [Accepted: 08/13/2010] [Indexed: 12/16/2022]
Abstract
In malaria parasites, mutations in two genes of folate biosynthesis encoding dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) modify responses to antifolate therapies which target these enzymes. However, the involvement of other genes which modify the availability of exogenous folate, for example, has been proposed. Here, we used short-read whole-genome re-sequencing to determine the mutations in a clone of the rodent malaria parasite, Plasmodium chabaudi, which has altered susceptibility to both sulphadoxine and pyrimethamine. This clone bears a previously identified S106N mutation in dhfr and no mutation in dhps. Instead, three additional point mutations in genes on chromosomes 2, 13 and 14 were identified. The mutated gene on chromosome 13 (mdr2 K392Q) encodes an ABC transporter. Because Quantitative Trait Locus analysis previously indicated an association of genetic markers on chromosome 13 with responses to individual and combined antifolates, MDR2 is proposed to modulate antifolate responses, possibly mediated by the transport of folate intermediates.
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Affiliation(s)
- Axel Martinelli
- Centro de Malaria e Outras Doenças Tropicais/IHMT/UEI Biologia Molecular, Universidade Nova de Lisboa, Rua da Junqueira 96, 1349-008 Lisbon, Portugal.
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20
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Polymorphism in PfMRP1 (Plasmodium falciparum multidrug resistance protein 1) amino acid 1466 associated with resistance to sulfadoxine-pyrimethamine treatment. Antimicrob Agents Chemother 2009; 53:2553-6. [PMID: 19364873 DOI: 10.1128/aac.00091-09] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Sulfadoxine-pyrimethamine (SP) remains widely recommended for intermittent preventive treatment against Plasmodium falciparum malaria for pregnant women and infants in Africa. Resistance to SP is increasing and associated primarily with mutations in the P. falciparum dhfr (Pfdhfr) and Pfdhps genes. This study aimed to explore the hypothetical association of genetic alterations in the P. falciparum multidrug resistance protein gene (Pfmrp1) with the in vivo response to SP by detecting the selection of single nucleotide polymorphisms (SNPs) following standard single-dose treatment administered to children with acute uncomplicated P. falciparum malaria in Tanzania. We detected significant selection of parasites carrying the Pfmrp1 1466K allele in samples from children with recrudescent infections, with 12 (100%) of 12 such samples being positive for this allele, compared to 52 (67.5%) of 77 baseline samples (P = 0.017), in parallel with the selection of the Pfdhfr Pfdhps quintuple mutant haplotype in cases of recrudescence (P = 0.001). There was no association between the 1466K SNP and the Pfdhfr Pfdhps quintuple mutation, indicating independent selections. Our data point for the first time to a role for a P. falciparum multidrug resistance protein homologue in the antimalarial activity of SP. Moreover, they add to the growing evidence of the potential importance of Pfmrp1 in antimalarial drug resistance.
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21
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A 245kb mini-chromosome impacts on Leishmania braziliensis infection and survival. Biochem Biophys Res Commun 2009; 382:74-8. [PMID: 19254695 DOI: 10.1016/j.bbrc.2009.02.128] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Accepted: 02/24/2009] [Indexed: 11/20/2022]
Abstract
Leishmania (V.) braziliensis, the causative agent of mucocutaneous leishmaniasis in the New World, may present an LD1 type genomic amplification that appears as a small 245 kb linear chromosome, and is not clearly associated to the presence of a selection agent. A bt1 gene, codifying for a biopterin transporter protein, was identified in this small chromosome. Leishmania are auxotrophic for pterins and one of the proposed explanations for the appearance of this amplification is the improvement of biopterin capture by the parasite. We analyzed some biological aspects of two lineages of L. braziliensis strain M2903, with and without the small amplified chromosome. We showed differences in infectivity of these lineages, in macrophages and the insect vector Lutzomyia longipalpis, as well as in the uptake and metabolization of intermediates of the Leishmania biopterin salvage pathway. Our results suggest that the genomic amplification favors survival due to improved biopterin capture and at the same time hinders the infective capability, suggesting that within a population different parasites can perform different roles.
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22
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Dasgupta T, Chitnumsub P, Kamchonwongpaisan S, Maneeruttanarungroj C, Nichols SE, Lyons TM, Tirado-Rives J, Jorgensen WL, Yuthavong Y, Anderson KS. Exploiting structural analysis, in silico screening, and serendipity to identify novel inhibitors of drug-resistant falciparum malaria. ACS Chem Biol 2009; 4:29-40. [PMID: 19146480 DOI: 10.1021/cb8002804] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Plasmodium falciparum thymidylate synthase-dihydrofolate reductase (TS-DHFR) is an essential enzyme in folate biosynthesis and a major malarial drug target. This bifunctional enzyme thus presents different design approaches for developing novel inhibitors against drug-resistant mutants. We performed a high-throughput in silico screen of a database of diverse, drug-like molecules against a non-active-site pocket of TS-DHFR. The top compounds from this virtual screen were evaluated by in vitro enzymatic and cellular culture studies. Three compounds active to 20 microM IC(50)'s in both wildtype and antifolate-resistant P. falciparum parasites were identified; moreover, no inhibition of human DHFR enzyme was observed, indicating that the inhibitory effects appeared to be parasite-specific. Notably, all three compounds had a biguanide scaffold. However, relative free energy of binding calculations suggested that the compounds might preferentially interact with the active site over the screened non-active-site region. To resolve the two possible modes of binding, co-crystallization studies of the compounds complexed with TS-DHFR enzyme were performed. Surprisingly, the structural analysis revealed that these novel, biguanide compounds do indeed bind at the active site of DHFR and additionally revealed the molecular basis by which they overcome drug resistance. To our knowledge, these are the first co-crystal structures of novel, biguanide, non-WR99210 compounds that are active against folate-resistant malaria parasites in cell culture.
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Affiliation(s)
- Tina Dasgupta
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520
| | - Penchit Chitnumsub
- BIOTEC Central Research Unit, National Science and Technology Development Agency, Science Park, 113 Phaholyothin Road, Klong Luang, Pathumthani 12120, Thailand
| | - Sumalee Kamchonwongpaisan
- BIOTEC Central Research Unit, National Science and Technology Development Agency, Science Park, 113 Phaholyothin Road, Klong Luang, Pathumthani 12120, Thailand
| | - Cherdsak Maneeruttanarungroj
- BIOTEC Central Research Unit, National Science and Technology Development Agency, Science Park, 113 Phaholyothin Road, Klong Luang, Pathumthani 12120, Thailand
| | - Sara E. Nichols
- Interdepartmental Program in Computational Biology and Bioinformatics, Yale University, 300 George Street Suite 501, New Haven, Connecticut 06511
| | - Theresa M. Lyons
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
| | - Julian Tirado-Rives
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
| | - William L. Jorgensen
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
| | - Yongyuth Yuthavong
- BIOTEC Central Research Unit, National Science and Technology Development Agency, Science Park, 113 Phaholyothin Road, Klong Luang, Pathumthani 12120, Thailand
| | - Karen S. Anderson
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520
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23
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Hyde JE, Dittrich S, Wang P, Sims PFG, de Crécy-Lagard V, Hanson AD. Plasmodium falciparum: a paradigm for alternative folate biosynthesis in diverse microorganisms? Trends Parasitol 2008; 24:502-8. [PMID: 18805734 PMCID: PMC2720532 DOI: 10.1016/j.pt.2008.08.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 08/01/2008] [Accepted: 08/08/2008] [Indexed: 10/21/2022]
Abstract
Folates have a key role in metabolism, and the folate-dependent generation of DNA precursors in the form of deoxythymidine 5'-phosphate is particularly important for the replication of malaria parasites. Although Plasmodium falciparum can synthesize folate derivatives de novo, a long-standing mystery has been the apparent absence of a key enzyme, dihydroneopterin aldolase, in the classical folate biosynthetic pathway of this organism. The discovery that a different enzyme, pyruvoyltetrahydropterin synthase, can produce the necessary substrate for the subsequent step in folate synthesis raises the question of whether this solution is unique to P. falciparum. Bioinformatic analyses suggest otherwise and indicate that an alternative route to folate could be widespread among diverse microorganisms and could be a target for novel drugs.
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Affiliation(s)
- John E Hyde
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
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24
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Peters PJ, Thigpen MC, Parise ME, Newman RD. Safety and toxicity of sulfadoxine/pyrimethamine: implications for malaria prevention in pregnancy using intermittent preventive treatment. Drug Saf 2007; 30:481-501. [PMID: 17536875 DOI: 10.2165/00002018-200730060-00003] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Plasmodium falciparum infection during pregnancy is strongly associated with maternal anaemia and low birth weight, contributing to substantial morbidity and mortality in sub-Saharan Africa. Intermittent preventive treatment in pregnancy with sulfadoxine/pyrimethamine (IPTp-SP) has been one of the most effective approaches to reduce the burden of malaria during pregnancy in Africa. IPTp-SP is based on administering >or=2 treatment doses of sulfadoxine/pyrimethamine to pregnant women at predefined intervals after quickening (around 18-20 weeks). Randomised, controlled trials have demonstrated decreased rates of maternal anaemia and low birth weight with this approach. The WHO currently recommends IPTp-SP in malaria-endemic areas of sub-Saharan Africa. However, implementation has been suboptimal in part because of concerns of potential drug toxicities. This review evaluates the toxicity data of sulfadoxine/pyrimethamine, including severe cutaneous adverse reactions, teratogenicity and alterations in bilirubin metabolism. Weekly sulfadoxine/pyrimethamine prophylaxis is associated with rare but potentially fatal cutaneous reactions. Fortunately, sulfadoxine/pyrimethamine use in IPTp programmes in Africa, with 2-4 treatment doses over 6 months, has been well tolerated in multiple IPTp trials. However, sulfadoxine/pyrimethamine should not be administered concurrently with cotrimoxazole given their redundant mechanisms of action and synergistic worsening of adverse drug reactions. Therefore, HIV-infected pregnant women in malaria endemic areas who are already receiving cotrimoxazole prophylaxis should not also receive IPTp-SP. Although folate antagonist use in the first trimester is associated with neural tube defects, large case-control studies have demonstrated that sulfadoxine/pyrimethamine administered as IPTp (exclusively in the second and third trimesters and after organogenesis) does not result in an increased risk of teratogenesis. Folic acid supplementation is recommended for all pregnant women to reduce the rate of congenital anomalies but high doses of folic acid (5 mg/day) may interfere with the antimalarial efficacy of sulfadoxine/pyrimethamine. However, the recommended standard dose of folic acid supplementation (0.4 mg/day) does not affect antimalarial efficacy and may provide the optimal balance to prevent neural tube defects and maintain the effectiveness of IPTp-SP. No clinical association between sulfadoxine/pyrimethamine use and kernicterus has been reported despite the extensive use of sulfadoxine/pyrimethamine and related compounds to treat maternal malaria and congenital toxoplasmosis in near-term pregnant women and newborns. Although few drugs in pregnancy can be considered completely safe, sulfadoxine/pyrimethamine - when delivered as IPTp - has a favourable safety profile. Improved pharmacovigilance programmes throughout Africa are now needed to confirm its safety as access to IPTp-SP increases. Given the documented benefits of IPTp-SP in malaria endemic areas of Africa, access to this treatment for pregnant women should continue to expand.
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Affiliation(s)
- Philip J Peters
- Division of Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30303, USA.
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25
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Wang P, Wang Q, Sims PF, Hyde JE. Characterisation of exogenous folate transport in Plasmodium falciparum. Mol Biochem Parasitol 2007; 154:40-51. [PMID: 17509698 PMCID: PMC1906846 DOI: 10.1016/j.molbiopara.2007.04.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Revised: 04/03/2007] [Accepted: 04/03/2007] [Indexed: 12/02/2022]
Abstract
Folate salvage by Plasmodium falciparum is an important source of key cofactors, but little is known about the underlying mechanism. Using synchronised parasite cultures, we observed that uptake of this dianionic species against the negative-inward electrochemical gradient is highly dependent upon cell-cycle stage, temperature and pH, but not on mono- or divalent metal ions. Energy dependence was tested with different sugars; glucose was necessary for folate import, although fructose was also able to function in this role, unlike sugars that cannot be processed through the glycolytic pathway. Import into both infected erythrocytes and free parasites was strongly inhibited by the anion-channel blockers probenecid and furosemide, which are likely to be acting predominantly on specific folate transporters in both cases. Import was not affected by high concentrations of the antifolate drugs pyrimethamine and sulfadoxine, but was inhibited by the close folate analogue methotrexate. The pH optimum for folate uptake into infected erythrocytes was 6.5–7.0. Dinitrophenol and nigericin, which strongly facilitate the equilibration of H+ ions across biological membranes and thus abolish or substantially reduce the proton gradient, inhibited folate uptake profoundly. The ATPase inhibitor concanamycin A also greatly reduced folate uptake, further demonstrating a link to ATP-powered proton transport. These data strongly suggest that the principal folate uptake pathway in P. falciparum is specific, highly regulated, dependent upon the proton gradient across the parasite plasma membrane, and is likely to be mediated by one or more proton symporters.
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Affiliation(s)
| | | | | | - John E. Hyde
- Corresponding author. Tel.: +44 161 306 4185; fax: +44 161 306 5201.
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26
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Abstract
Synthesis de novo, acquisition by salvage and interconversion of purines and pyrimidines represent the fundamental requirements for their eventual assembly into nucleic acids as nucleotides and the deployment of their derivatives in other biochemical pathways. A small number of drugs targeted to nucleotide metabolism, by virtue of their effect on folate biosynthesis and recycling, have been successfully used against apicomplexan parasites such as Plasmodium and Toxoplasma for many years, although resistance is now a major problem in the prevention and treatment of malaria. Many targets not involving folate metabolism have also been explored at the experimental level. However, the unravelling of the genome sequences of these eukaryotic unicellular organisms, together with increasingly sophisticated molecular analyses, opens up possibilities of introducing new drugs that could interfere with these processes. This review examines the status of established drugs of this type and the potential for further exploiting the vulnerability of apicomplexan human pathogens to inhibition of this key area of metabolism.
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Affiliation(s)
- John E Hyde
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester M1 7ND, UK.
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27
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Kelly JX, Winter RW, Braun TP, Osei-Agyemang M, Hinrichs DJ, Riscoe MK. Selective killing of the human malaria parasite Plasmodium falciparum by a benzylthiazolium dye. Exp Parasitol 2006; 116:103-10. [PMID: 17266952 PMCID: PMC1965281 DOI: 10.1016/j.exppara.2006.12.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 11/30/2006] [Accepted: 12/06/2006] [Indexed: 11/25/2022]
Abstract
Malaria is an infectious disease caused by protozoan parasites of the genus Plasmodium. The most virulent form of the disease is caused by Plasmodium falciparum which infects hundreds of millions of people and is responsible for the deaths of 1-2 million individuals each year. An essential part of the parasitic process is the remodeling of the red blood cell membrane and its protein constituents to permit a higher flux of nutrients and waste products into or away from the intracellular parasite. Much of this increased permeability is due to a single type of broad specificity channel variously called the new permeation pathway (NPP), the nutrient channel, and the Plasmodial surface anion channel (PSAC). This channel is permeable to a range of low molecular weight solutes both charged and uncharged, with a strong preference for anions. Drugs such as furosemide that are known to block anion-selective channels inhibit PSAC. In this study, we have investigated a dye known as benzothiocarboxypurine, BCP, which had been studied as a possible diagnostic aid given its selective uptake by P. falciparum infected red cells. We found that the dye enters parasitized red cells via the furosemide-inhibitable PSAC, forms a brightly fluorescent complex with parasite nucleic acids, and is selectively toxic to infected cells. Our study describes an antimalarial agent that exploits the altered permeability of Plasmodium-infected red cells as a means to killing the parasite and highlights a chemical reagent that may prove useful in high throughput screening of compounds for inhibitors of the channel.
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Affiliation(s)
- Jane X. Kelly
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
| | - Rolf W. Winter
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
| | - Theodore P. Braun
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - Myralyn Osei-Agyemang
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - David J. Hinrichs
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - Michael K. Riscoe
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
- Mailing Address: *Michael Riscoe, Ph.D., Medical Research Service, RD-33, Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, Oregon 97239 Phone Number: 503-721-7885/Telefacsimile: 503-402-2817/e-mail:
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28
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Ouma P, Parise ME, Hamel MJ, ter Kuile FO, Otieno K, Ayisi JG, Kager PA, Steketee RW, Slutsker L, van Eijk AM. A randomized controlled trial of folate supplementation when treating malaria in pregnancy with sulfadoxine-pyrimethamine. PLOS CLINICAL TRIALS 2006; 1:e28. [PMID: 17053829 PMCID: PMC1617124 DOI: 10.1371/journal.pctr.0010028] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Accepted: 08/29/2006] [Indexed: 11/19/2022]
Abstract
OBJECTIVES Sulfadoxine-pyrimethamine (SP) is an antimalarial drug that acts on the folate metabolism of the malaria parasite. We investigated whether folate (FA) supplementation in a high or a low dose affects the efficacy of SP for the treatment of uncomplicated malaria in pregnant women. DESIGN This was a randomized, placebo-controlled, double-blind trial. SETTING The trial was carried out at three hospitals in western Kenya. PARTICIPANTS The participants were 488 pregnant women presenting at their first antenatal visit with uncomplicated malaria parasitaemia (density of >or= 500 parasites/microl), a haemoglobin level higher than 7 g/dl, a gestational age between 17 and 34 weeks, and no history of antimalarial or FA use, or sulfa allergy. A total of 415 women completed the study. INTERVENTIONS All participants received SP and iron supplementation. They were randomized to the following arms: FA 5 mg, FA 0.4 mg, or FA placebo. After 14 days, all participants continued with FA 5 mg daily as per national guidelines. Participants were followed at days 2, 3, 7, 14, 21, and 28 or until treatment failure. OUTCOME MEASURES The outcomes were SP failure rate and change in haemoglobin at day 14. RESULTS The proportion of treatment failure at day 14 was 13.9% (19/137) in the placebo group, 14.5% (20/138) in the FA 0.4 mg arm (adjusted hazard ratio [AHR], 1.07; 98.7% confidence interval [CI], 0.48 to 2.37; p = 0.8), and 27.1% (38/140) in the FA 5 mg arm (AHR, 2.19; 98.7% CI, 1.09 to 4.40; p = 0.005). The haemoglobin levels at day 14 were not different relative to placebo (mean difference for FA 5 mg, 0.17 g/dl; 98.7% CI, -0.19 to 0.52; and for FA 0.4 mg, 0.14 g/dl; 98.7% CI, -0.21 to 0.49). CONCLUSIONS Concomitant use of 5 mg FA supplementation compromises the efficacy of SP for the treatment of uncomplicated malaria in pregnant women. Countries that use SP for treatment or prevention of malaria in pregnancy need to evaluate their antenatal policy on timing or dose of FA supplementation.
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Affiliation(s)
- Peter Ouma
- Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - Monica E Parise
- Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
| | - Mary J Hamel
- Kenya Field Station, Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Feiko O. ter Kuile
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, United Kingdom
| | - Kephas Otieno
- Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - John G Ayisi
- Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - Piet A Kager
- Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
| | - Richard W Steketee
- Malaria Control and Evaluation Partnership in Africa, Program for Appropriate Technology in Health, Batiment Avant Centre, Ferney-Voltaire, France
| | - Laurence Slutsker
- Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
| | - Anna M van Eijk
- Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
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Kidgell C, Volkman SK, Daily J, Borevitz JO, Plouffe D, Zhou Y, Johnson JR, Le Roch KG, Sarr O, Ndir O, Mboup S, Batalov S, Wirth DF, Winzeler EA. A systematic map of genetic variation in Plasmodium falciparum. PLoS Pathog 2006; 2:e57. [PMID: 16789840 PMCID: PMC1480597 DOI: 10.1371/journal.ppat.0020057] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Accepted: 04/28/2006] [Indexed: 11/25/2022] Open
Abstract
Discovering novel genes involved in immune evasion and drug resistance in the human malaria parasite, Plasmodium falciparum, is of critical importance to global health. Such knowledge may assist in the development of new effective vaccines and in the appropriate use of antimalarial drugs. By performing a full-genome scan of allelic variability in 14 field and laboratory strains of P. falciparum, we comprehensively identified ≈500 genes evolving at higher than neutral rates. The majority of the most variable genes have paralogs within the P. falciparum genome and may be subject to a different evolutionary clock than those without. The group of 211 variable genes without paralogs contains most known immunogens and a few drug targets, consistent with the idea that the human immune system and drug use is driving parasite evolution. We also reveal gene-amplification events including one surrounding pfmdr1, the P. falciparum multidrug-resistance gene, and a previously uncharacterized amplification centered around the P. falciparum GTP cyclohydrolase gene, the first enzyme in the folate biosynthesis pathway. Although GTP cyclohydrolase is not the known target of any current drugs, downstream members of the pathway are targeted by several widely used antimalarials. We speculate that an amplification of the GTP cyclohydrolase enzyme in the folate biosynthesis pathway may increase flux through this pathway and facilitate parasite resistance to antifolate drugs. Variability in the genome of the human malaria parasite, Plasmodium falciparum, is key to the parasite's ability to cause disease and overcome therapeutic interventions such as drugs and vaccines. Elucidating the extent of genetic variation in the malaria parasite will therefore be central to decreasing the malaria disease burden. The authors performed a full-genome scan of variability in different strains of P. falciparum and observed a nonrandom distribution of variation. In particular, those genes that are predicted to have roles in evading the host immune response or antimalarial drugs show significantly higher levels of variation. In addition, the authors speculate that a previously unreported genome amplification in the folate biosynthesis pathway correlates with resistance to the antimalarial drug sulfadoxine. Such data enable hypotheses to be made about the function of many of the unknown elements in the parasite's genome, which may permit the identification of new targets that can be investigated for incorporation into a malaria vaccine and may aid in the understanding of how the parasite withstands drug pressure.
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Affiliation(s)
- Claire Kidgell
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Sarah K Volkman
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Johanna Daily
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Justin O Borevitz
- Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, California, United States of America
| | - David Plouffe
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
| | - Yingyao Zhou
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
| | - Jeffrey R Johnson
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Karine G. Le Roch
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
| | - Ousmane Sarr
- Faculty of Medicine and Pharmacy, Cheikh Anta Diop University, Dakar, Senegal
| | - Omar Ndir
- Faculty of Medicine and Pharmacy, Cheikh Anta Diop University, Dakar, Senegal
| | - Soulyemane Mboup
- Faculty of Medicine and Pharmacy, Cheikh Anta Diop University, Dakar, Senegal
| | - Serge Batalov
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
| | - Dyann F Wirth
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Elizabeth A Winzeler
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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Platteeuw JJ. Resistance to sulphadrug-based antifolate therapy in malaria: are we looking in the right place? Trop Med Int Health 2006; 11:804-8. [PMID: 16772001 DOI: 10.1111/j.1365-3156.2006.01646.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Sulphadrug treatment failure in malaria therapy cannot solely be ascribed to the build-up of genetic resistance within the parasitic genome. Although numerous in vitro studies have tried to determine the exact genetic markers that could predict treatment outcome in patients, this research has not been conclusive. Sulphadrugs work by competitive inhibition with pABA at one point of the pathway to de novo folate synthesis. However, evidence suggests that the malaria parasite is capable of overcoming this competitive inhibition by switching over to other metabolic pathways, like direct folate salvage from a person's bloodstream. In other words, increased folic acid administration, via diet or supplementation, may have reduced the effectiveness of sulphadrugs more than genetic mutations. Although in vitro studies are valuable for understanding disease mechanisms, we should not forget that the human being is infinitely more complex than any laboratory model.
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Yuthavong Y, Kamchonwongpaisan S, Leartsakulpanich U, Chitnumsub P. Folate metabolism as a source of molecular targets for antimalarials. Future Microbiol 2006; 1:113-25. [PMID: 17661690 DOI: 10.2217/17460913.1.1.113] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Folate metabolism of the malaria parasites provides two targets for current antimalarials: dihydrofolate reductase and dihydropteroate synthase. Dihydrofolate reductase inhibitors have been used as antimalarials over the past few decades, often in combination with dihydropteroate synthase inhibitors. Resistance to these antifolate drugs developed through mutations in both target enzymes. However, limited mutation possibilities gave opportunities for the development of new drugs. Furthermore, other enzymes in the folate and related pathways are potential new targets that remain to be exploited. These include thymidylate synthase, an enzyme fused with dihydrofolate reductase in the same protein chain, serine hydroxymethyltransferase, methylene tetrahydrofolate dehydrogenase, methionine synthase and enzymes in the glycine cleavage pathway.
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32
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Sazawal S, Black RE, Ramsan M, Chwaya HM, Stoltzfus RJ, Dutta A, Dhingra U, Kabole I, Deb S, Othman MK, Kabole FM. Effects of routine prophylactic supplementation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting: community-based, randomised, placebo-controlled trial. Lancet 2006; 367:133-43. [PMID: 16413877 DOI: 10.1016/s0140-6736(06)67962-2] [Citation(s) in RCA: 654] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Anaemia caused by iron deficiency is common in children younger than age 5 years in eastern Africa. However, there is concern that universal supplementation of children with iron and folic acid in areas of high malaria transmission might be harmful. METHODS We did a randomised, placebo-controlled trial, of children aged 1-35 months and living in Pemba, Zanzibar. We assigned children to daily oral supplementation with: iron (12.5 mg) and folic acid (50 mug; n=7950), iron, folic acid, and zinc (n=8120), or placebo (n=8006); children aged 1-11 months received half the dose. Our primary endpoints were all-cause mortality and admission to hospital. Analyses were by intention to treat. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN59549825. FINDINGS The iron and folic acid-containing groups of the trial were stopped early on Aug 19, 2003, on the recommendation of the data and safety monitoring board. To this date, 24 076 children contributed a follow-up of 25,524 child-years. Those who received iron and folic acid with or without zinc were 12% (95% CI 2-23, p=0.02) more likely to die or need treatment in hospital for an adverse event and 11% (1-23%, p=0.03) more likely to be admitted to hospital; there were also 15% (-7 to 41, p=0.19) more deaths in these groups. INTERPRETATION Routine supplementation with iron and folic acid in preschool children in a population with high rates of malaria can result in an increased risk of severe illness and death. In the presence of an active programme to detect and treat malaria and other infections, iron-deficient and anaemic children can benefit from supplementation. However, supplementation of those who are not iron deficient might be harmful. As such, current guidelines for universal supplementation with iron and folic acid should be revised.
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Affiliation(s)
- Sunil Sazawal
- Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205, USA
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Massimine KM, Doan LT, Atreya CA, Stedman TT, Anderson KS, Joiner KA, Coppens I. Toxoplasma gondii is capable of exogenous folate transport. A likely expansion of the BT1 family of transmembrane proteins. Mol Biochem Parasitol 2005; 144:44-54. [PMID: 16159678 DOI: 10.1016/j.molbiopara.2005.07.006] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Revised: 06/20/2005] [Accepted: 07/20/2005] [Indexed: 11/23/2022]
Abstract
Folates are key elements in eukaryotic biosynthetic processes. The protozoan parasite Toxoplasma gondii possesses the enzymes necessary for de novo folate synthesis and has been suggested to lack alternative mechanisms for folate acquisition. In this paper, we present a different view by providing evidence that Toxoplasma is capable of salvaging exogenous folates. By monitoring uptake of radiolabeled folates by parasites in axenic conditions, our studies revealed a common folate transporter that has a high affinity for folic acid. Transport of this compound across the parasite plasma membrane is rapid, biphasic, temperature dependent, bi-directional, concentration dependent and specific. In addition, morphological evidence demonstrates that fluorescent methotrexate, a folate analog, is internalized by Toxoplasma and shows localization reminiscent to the mitochondrion. The presence of putative folate transporter genes in the Toxoplasma genome, which are homologous to the BT1 family of proteins, suggests that Toxoplasma may encode proteins involved in folate transport. Interestingly, genome analysis suggests that the BT1 family of proteins exists not only in Toxoplasma, but in other Apicomplexan parasites as well. Altogether, our results not only have implications for current therapeutic regimens against T. gondii, but they also allude that the folate transport mechanism may represent a novel Apicomplexan target for the development of new drugs.
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Affiliation(s)
- Kristen M Massimine
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
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34
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Bell A. Antimalarial drug synergism and antagonism: mechanistic and clinical significance. FEMS Microbiol Lett 2005; 253:171-84. [PMID: 16243458 DOI: 10.1016/j.femsle.2005.09.035] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Revised: 09/22/2005] [Accepted: 09/22/2005] [Indexed: 11/18/2022] Open
Abstract
Interactions between antimicrobial agents provide clues as to their mechanisms of action and influence the combinations chosen for therapy of infectious diseases. In the treatment of malaria, combinations of drugs, in many cases acting synergistically, are increasingly important in view of the frequency of resistance to single agents. The study of antimalarial drug interactions is therefore of great significance to both treatment and research. It is therefore worrying that the analysis of drug-interaction data is often inadequate, leading in some cases to dubious conclusions about synergism or antagonism. Furthermore, making mechanistic deductions from drug-interaction data is not straightforward and of the many reported instances of antimalarial synergism or antagonism, few have been fully explained biochemically. This review discusses recent findings on antimalarial drug interactions and some pitfalls in their analysis and interpretation. The conclusions are likely to have relevance to other antimicrobial agents.
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Affiliation(s)
- Angus Bell
- Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin--Trinity College, Dublin 2, Ireland.
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35
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Arav-Boger R, Shapiro TA. MOLECULAR MECHANISMS OF RESISTANCE IN ANTIMALARIAL CHEMOTHERAPY: The Unmet Challenge. Annu Rev Pharmacol Toxicol 2005; 45:565-85. [PMID: 15822189 DOI: 10.1146/annurev.pharmtox.45.120403.095946] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
▪ Abstract The enormous public health problem posed by malaria has been substantially worsened in recent years by the emergence and worldwide spread of drug-resistant parasites. The utility of two major therapies, chloroquine and the synergistic combination of pyrimethamine/sulfadoxine, is now seriously compromised. Although several genetic mechanisms have been described, the major source of drug resistance appears to be point mutations in protein target genes. Clinically significant resistance to these agents requires the accumulation of multiple mutations, which genetic studies of parasite populations suggest arise focally and sweep through the population. Efforts to circumvent resistance range from the use of combination therapy with existing agents to laboratory studies directed toward discovering novel targets and therapies. The prevention and management of drug resistance are among the most important practical problems of tropical medicine and public health. Leonard J. Bruce-Chwatt, 1972
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Affiliation(s)
- Ravit Arav-Boger
- Division of Infectious Diseases, Department of Pediatrics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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36
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Wilson PE, Kazadi W, Alker AP, Meshnick SR. Rare Congolese Plasmodium falciparum DHFR alleles. Mol Biochem Parasitol 2005; 144:227-9. [PMID: 16183149 DOI: 10.1016/j.molbiopara.2005.08.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Revised: 08/11/2005] [Accepted: 08/12/2005] [Indexed: 11/16/2022]
Affiliation(s)
- Paul E Wilson
- Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
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37
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Nzila A, Ward SA, Marsh K, Sims PFG, Hyde JE. Comparative folate metabolism in humans and malaria parasites (part II): activities as yet untargeted or specific to Plasmodium. Trends Parasitol 2005; 21:334-9. [PMID: 15936248 PMCID: PMC2720531 DOI: 10.1016/j.pt.2005.05.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2004] [Revised: 02/10/2005] [Accepted: 05/10/2005] [Indexed: 01/26/2023]
Abstract
The folate pathway represents a powerful target for combating rapidly dividing systems such as cancer cells, bacteria and malaria parasites. Whereas folate metabolism in mammalian cells and bacteria has been studied extensively, it is understood less well in malaria parasites. In two articles, we attempt to reconstitute the malaria folate pathway based on available information from mammalian and microbial systems, in addition to Plasmodium-genome-sequencing projects. In part I, we focused on folate enzymes that are already used clinically as anticancer drug targets or that are under development in drug-discovery programs. In this article, we discuss mammalian folate enzymes that have not yet been exploited as potential drug targets, and enzymes that function in the de novo folate-synthesis pathway of the parasite--a particularly attractive area of attack because of its absence from the mammalian host.
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Affiliation(s)
- Alexis Nzila
- Kenya Medical Research Institute and Wellcome Trust Collaborative Research Program, Wellcome Trust Research Laboratories, PO Box 43640, Nairobi GPO 00100, Kenya.
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Abstract
As in centuries past, the main weapon against human malaria infections continues to be intervention with drugs, despite the widespread and increasing frequency of parasite populations that are resistant to one or more of the available compounds. This is a particular problem with the lethal species of parasite, Plasmodium falciparum, which claims some two million lives per year as well as causing enormous social and economic problems. Amongst the antimalarial drugs currently in clinical use, the antifolates have the best defined molecular targets, namely the enzymes dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS), which function in the folate metabolic pathway. The products of this pathway, reduced folate cofactors, are essential for DNA synthesis and the metabolism of certain amino acids. Moreover, their formation and interconversions involve a number of other enzymes that have not as yet been exploited as drug targets. Antifolates are of major importance as they currently represent the only inexpensive regime for combating chloroquine-resistant malaria, and are now first-line drugs in a number of African countries. Aspects of our understanding of this pathway and antifolate drug resistance are reviewed here, with a particular emphasis on approaches to analysing the details of, and balance between, folate biosynthesis by the parasite and salvage of pre-formed folate from exogenous sources.
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Affiliation(s)
- John E Hyde
- Faculty of life Sciences, University of Manchester, P.O. Box 88, Manchester M60 1QD, UK.
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Gregson A, Plowe CV. Mechanisms of resistance of malaria parasites to antifolates. Pharmacol Rev 2005; 57:117-45. [PMID: 15734729 DOI: 10.1124/pr.57.1.4] [Citation(s) in RCA: 309] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Antifolate antimalarial drugs interfere with folate metabolism, a pathway essential to malaria parasite survival. This class of drugs includes effective causal prophylactic and therapeutic agents, some of which act synergistically when used in combination. Unfortunately, the antifolates have proven susceptible to resistance in the malaria parasite. Resistance is caused by point mutations in dihydrofolate reductase and dihydropteroate synthase, the two key enzymes in the folate biosynthetic pathway that are targeted by the antifolates. Resistance to these drugs arises relatively rapidly in response to drug pressure and is now common worldwide. Nevertheless, antifolate drugs remain first-line agents in several sub-Saharan African countries where chloroquine resistance is widespread, at least partially because they remain the only affordable, effective alternative. New antifolate combinations that are more effective against resistant parasites are being developed and in one case, recently introduced into use. Combining these antifolates with drugs that act on different targets in the parasite should greatly enhance their effectiveness as well as deter the development of resistance. Molecular epidemiological techniques for monitoring parasite drug resistance may contribute to development of strategies for prolonging the useful therapeutic life of this important class of drugs.
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Affiliation(s)
- Aric Gregson
- Malaria Section, Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore Street, HSF1 Room 480, Baltimore, MD 21201, USA
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40
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Iliades P, Meshnick SR, Macreadie IG. Dihydropteroate synthase mutations in Pneumocystis jiroveci can affect sulfamethoxazole resistance in a Saccharomyces cerevisiae model. Antimicrob Agents Chemother 2004; 48:2617-23. [PMID: 15215118 PMCID: PMC434176 DOI: 10.1128/aac.48.7.2617-2623.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dihydropteroate synthase (DHPS) mutations in Pneumocystis jiroveci have been associated epidemiologically with resistance to sulfamethoxazole (SMX). Since P. jiroveci cannot be cultured, inherent drug resistance cannot be measured. This study explores the effects of these mutations in a tractable model organism, Saccharomyces cerevisiae. Based on the sequence conservation between the DHPS enzymes of P. jiroveci and S. cerevisiae, together with the structural conservation of the three known DHPS structures, DHPS substitutions commonly observed in P. jiroveci were reverse engineered into the S. cerevisiae DHPS. Those mutations, T(597)A and P(599)S, can occur singly but are most commonly found together and are associated with SMX treatment failure. Mutations encoding the corresponding changes in the S. cerevisiae dhps were made in a yeast centromere vector, p414FYC, which encodes the native yeast DHPS as part of a trifunctional protein that also includes the two enzymes upstream of DHPS in the folic acid synthesis pathway, dihydroneopterin aldolase and 2-amino-4-hydroxymethyl dihydropteridine pyrophosphokinase. A yeast strain with dhps deleted was employed as the host strain, and transformants having DHPS activity were recovered. Mutants having both T(597) and P(599) substitutions had a requirement for p-aminobenzoic acid (PABA), consistent with resistance being associated with altered substrate binding. These mutants could be adapted for growth in the absence of PABA, which coincided with increased sulfa drug resistance. Upregulated PABA synthesis was thus implicated as a mechanism for sulfa drug resistance for mutants having two DHPS substitutions.
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Affiliation(s)
- Peter Iliades
- CSIRO Health Sciences and Nutrition, 343 Royal Parade, Parkville, Victoria 3052, Australia.
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Wang P, Wang Q, Aspinall TV, Sims PFG, Hyde JE. Transfection studies to explore essential folate metabolism and antifolate drug synergy in the human malaria parasite Plasmodium falciparum. Mol Microbiol 2004; 51:1425-38. [PMID: 14982635 DOI: 10.1111/j.1365-2958.2003.03915.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Folate metabolism in Plasmodium falciparum is the target of important antimalarial agents. The biosynthetic pathway converts GTP to polyglutamated derivatives of tetrahydrofolate (THF), essential cofactors for DNA synthesis. Tetrahydrofolate can also be acquired by salvage mechanisms. Using a transfection system adapted to studying this pathway, we investigated modulation of dihydropteroate synthase (DHPS) activity on parasite phenotypes. Dihydropteroate synthase incorporates p-aminobenzoate (pABA) into dihydropteroate, the precursor of dihydrofolate. We were unable to obtain viable parasites where the dhps gene had been truncated. However, parasites where the protein was full-length but mutated at two key residues and having < 10% of normal activity were viable in folate-supplemented medium. Metabolic labelling showed that these parasites could still convert pABA to polyglutamated folates, albeit at a very low level, but they could not survive on pABA supplementation alone. This degree of disablement in DHPS also abolished the synergy of the antifolate combination pyrimethamine/sulfadoxine. These data indicate that DHPS activity above a low but critical level is essential regardless of the availability of salvageable folate and formally prove the role of this enzyme in antifolate drug synergy and folate biosynthesis in vivo. However, we found no evidence of a significant role for DHPS in folate salvage. Moreover, when biosynthesis was compromised by the absence of a fully functional DHPS, the parasite was able to compensate by increasing flux through the salvage pathway.
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Affiliation(s)
- Ping Wang
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 1QD, UK
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Gatton ML, Martin LB, Cheng Q. Evolution of resistance to sulfadoxine-pyrimethamine in Plasmodium falciparum. Antimicrob Agents Chemother 2004; 48:2116-23. [PMID: 15155209 PMCID: PMC415611 DOI: 10.1128/aac.48.6.2116-2123.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The development of resistance to sulfadoxine-pyrimethamine by Plasmodium parasites is a major problem for the effective treatment of malaria, especially P. falciparum malaria. Although the molecular basis for parasite resistance is known, the factors promoting the development and transmission of these resistant parasites are less clear. This paper reports the results of a quantitative comparison of factors previously hypothesized as important for the development of drug resistance, drug dosage, time of treatment, and drug elimination half-life, with an in-host dynamics model of P. falciparum malaria in a malaria-naïve host. The results indicate that the development of drug resistance can be categorized into three stages. The first is the selection of existing parasites with genetic mutations in the dihydrofolate reductase or dihydropteroate synthetase gene. This selection is driven by the long half-life of the sulfadoxine-pyrimethamine combination. The second stage involves the selection of parasites with allelic types of higher resistance within the host during an infection. The timing of treatment relative to initiation of a specific anti-P. falciparum EMP1 immune response is an important factor during this stage, as is the treatment dosage. During the third stage, clinical treatment failure becomes prevalent as the parasites develop sufficient resistance mutations to survive therapeutic doses of the drug combination. Therefore, the model output reaffirms the importance of correct treatment of confirmed malaria cases in slowing the development of parasite resistance to sulfadoxine-pyrimethamine.
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Affiliation(s)
- Michelle L Gatton
- Malaria and Scabies Group, Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Queensland 4029, Australia.
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Affiliation(s)
- Jürgen May
- Department of Molecular Medicine, Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Strasse 74, D-20359 Hamburg, Germany.
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Nzila A, Mberu E, Bray P, Kokwaro G, Winstanley P, Marsh K, Ward S. Chemosensitization of Plasmodium falciparum by probenecid in vitro. Antimicrob Agents Chemother 2003; 47:2108-12. [PMID: 12821454 PMCID: PMC161864 DOI: 10.1128/aac.47.7.2108-2112.2003] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Resistance to drugs can result from changes in drug transport, and this resistance can sometimes be overcome by a second drug that modifies the transport mechanisms of the cell. This strategy has been exploited to partly reverse resistance to chloroquine in Plasmodium falciparum. Studies with human tumor cells have shown that probenecid can reverse resistance to the antifolate methotrexate, but the potential for reversal of antifolate resistance has not been studied in P. falciparum. In the present study we tested the ability of probenecid to reverse antifolate resistance in P. falciparum in vitro. Probenecid, at concentrations that had no effect on parasite viability alone (50 microM), was shown to increase the sensitivity of a highly resistant parasite isolate to the antifolates pyrimethamine, sulfadoxine, chlorcycloguanil, and dapsone by seven-, five-, three-, and threefold, respectively. The equivalent effects against an antifolate-sensitive isolate were activity enhancements of approximately 3-, 6-, 1.2-, and 19-fold, respectively. Probenecid decreased the level of uptake of radiolabeled folic acid, suggesting a transport-based mechanism linked to folate salvage. When probenecid was tested with chloroquine, it chemosensitized the resistant isolate to chloroquine (i.e., enhanced the activity of chloroquine). This enhancement of activity was associated with increased levels of chloroquine accumulation. In conclusion, we have shown that probenecid can chemosensitize malaria parasites to antifolate compounds via a mechanism linked to reduced folate uptake. Notably, this effect is observed in both folate-sensitive and -resistant parasites. In contrast to the activities of antifolate compounds, the effect of probenecid on chloroquine sensitivity was selective for chloroquine-resistant parasites (patent P407595GB [W. P. Thompson & Co., Liverpool, United Kingdom] has been filed to protect this intellectual property).
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Affiliation(s)
- Alexis Nzila
- Kenya Medical Research Institute/Wellcome Trust Collaborative Research Program, Wellcome Trust Research Laboratories, Nairobi, Kenya.
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45
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Gil JP, Nogueira F, Strömberg-Nörklit J, Lindberg J, Carrolo M, Casimiro C, Lopes D, Arez AP, Cravo PV, Rosário VE. Detection of atovaquone and Malarone resistance conferring mutations in Plasmodium falciparum cytochrome b gene (cytb). Mol Cell Probes 2003; 17:85-9. [PMID: 12788029 DOI: 10.1016/s0890-8508(03)00006-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Clinical treatment failures of the hydroxynaphthoquinone atovaquone or its combination with proguanil (Malarone) in Plasmodium falciparum malaria has been recently documented. These events have been associated to single nucleotide polymorphisms (SNPs) in the parasite cytochrome b gene (cytb). In this report we describe a set of nest PCR-RFLP methods developed for the fast detection of all known cytb mutations associated to resistance to these drugs. The methods were successfully applied for the analysis of phenol-chloroform extracted DNA samples from patients not cured by Malarone, and from an established parasite clone. Further, the protocol for the detection of the A803C mutation was applied to 164 DNA field samples extracted through crude methanol-based protocols, originated from several malaria settings. The PCR-RFLP methods here presented can be used as a valuable for the clinical detection and study of Malarone and atovaquone P. falciparum resistance.
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Affiliation(s)
- J P Gil
- UEI Malária, Centro de Malária e outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Lisboa, Portugal.
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46
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Bwijo B, Kaneko A, Takechi M, Zungu IL, Moriyama Y, Lum JK, Tsukahara T, Mita T, Takahashi N, Bergqvist Y, Björkman A, Kobayakawa T. High prevalence of quintuple mutant dhps/dhfr genes in Plasmodium falciparum infections seven years after introduction of sulfadoxine and pyrimethamine as first line treatment in Malawi. Acta Trop 2003; 85:363-73. [PMID: 12659974 DOI: 10.1016/s0001-706x(02)00264-4] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Malawi changed its national policy for malaria treatment in 1993, becoming the first country in Africa to replace chloroquine by sulfadoxine and pyrimethamine combination (SP) as the first-line drug for uncomplicated malaria. Seven years after this change, we investigated the prevalence of dihydropteroate synthase (dhps) and dihydrofolate reductase (dhfr) mutations, known to be associated with decreased sensitivity to SP, in 173 asymptomatic Plasmodium falciparum infections from Salima, Malawi. A high prevalence rate (78%) of parasites with triple Asn-108/Ile-51/Arg-59 dhfr and double Gly-437/Glu-540 dhps mutations was found. This 'quintuple mutant' is considered as a molecular marker for clinical failure of SP treatment of P. falciparum malaria. A total of 11 different dhfr and dhps combinations were detected, 3 of which were not previously reported. Nineteen isolates contained the single Glu-540 mutant dhps, while no isolate contained the single Gly-437 mutant dhps, an unexpected finding since Gly-437 are mostly assumed to be one of the first mutations commonly selected under sulfadoxine pressure. Two isolates contained the dhps single or double mutant coupled with dhfr wild-type. The high prevalence rates of the three dhfr mutations in our study were consistent with a previous survey in 1995 in Karonga, Malawi, whereas the prevalences of dhps mutations had increased, most probably as a result of the wide use of SP. A total of 52 P. falciparum isolates were also investigated for pyrimethamine and sulfadoxine/pyrimethamine activity against parasite growth according to WHO in vitro standard protocol. A pyrimethamine resistant profile was found. When pyrimethamine was combined with sulfadoxine, the mean EC(50) value decreased to less than one tenth of the pyrimethamine alone level. This synergistic activity may be explained by sulfadoxine inhibition of dhps despite the double mutations in the dhps genes, which would interact with pyrimethamine acting to block the remaining folate despite dhfr mutations in the low p-aminobenzoic acid and low folic acid medium mixed with blood.
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Affiliation(s)
- B Bwijo
- Department of International Affairs and Tropical Medicine, Tokyo Women's Medical University, 8-1 Kawada-Cho, Shinjuku-Ku, Tokyo 162 8666, Japan
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47
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Mberu EK, Nzila AM, Nduati E, Ross A, Monks SM, Kokwaro GO, Watkins WM, Hopkins Sibley C. Plasmodium falciparum: in vitro activity of sulfadoxine and dapsone in field isolates from Kenya: point mutations in dihydropteroate synthase may not be the only determinants in sulfa resistance. Exp Parasitol 2002; 101:90-6. [PMID: 12427462 DOI: 10.1016/s0014-4894(02)00108-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have determined the relationship between point mutations in the gene that encodes the sulfa target, dihydropteroate synthase (DHPS) and the chemosensitivity profile to sulfadoxine and dapsone in 67 isolates from Kilifi, Kenya. We assessed the presence of mutations at codons 436, 437, 540, 581, and 613 of dhps. The results showed that the dhps genotype had a strong influence on the sensitivity to sulfadoxine and dapsone, but that the correlation was far from perfect. Eleven isolates carried a wild-type dhps allele, but were resistant to sulfadoxine (IC(50) values >10 microg/ml), and 4/28 isolates were classed as sensitive to sulfadoxine (IC(50) values <10 microg/ml), but carried a triple mutant (436/437/613) allele of dhps. These data show that in low folate medium in vitro, the dhps genotype alone did not account completely for sulfadoxine or dapsone resistance; other factors such as the utilisation of exogenous folate must also be considered.
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Affiliation(s)
- Edward K Mberu
- Kenya Medical Research Institute/Wellcome Trust Collaborative Research Program, CGMRC, P.O. Box 43640, Nairobi, Kenya
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48
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Meyer CG, May J, Arez AP, Gil JP, Do Rosario V. Genetic diversity of Plasmodium falciparum: asexual stages. Trop Med Int Health 2002; 7:395-408. [PMID: 12000649 DOI: 10.1046/j.1365-3156.2002.00875.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Christian G Meyer
- Department of Molecular Medicine, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
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49
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Abstract
Chemotherapy and chemoprophylaxis are the principal means of combating malaria parasite infections in the human host. In the last 75 years, since the introduction of synthetic antimalarials, only a small number of compounds have been found suitable for clinical usage, and this limited armoury is now greatly compromised by the spread of drug-resistant parasite strains. Our current knowledge of the molecular mechanisms underlying resistance in the lethal species Plasmodium falciparum is reviewed here.
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Affiliation(s)
- John E Hyde
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, P.O. Box 88, M60 1QD, Manchester, UK.
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50
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Abstract
Resistance to antifolates of the malaria parasite Plasmodium falciparum stems from stepwise mutations of the target enzyme dihydrofolate reductase (DHFR). New drugs can be developed against resistant parasites, which are assumed to have limited possibilities in mutations. Mechanisms of resistance other than reduced binding of inhibitors to mutant enzymes may be possible and need to be further explored. New synergistic combinations of drugs targeting DHFR and dihydropteroate synthase may be employed, with new provisions against development of resistance.
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Affiliation(s)
- Yongyuth Yuthavong
- National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Rama 6 Road, 10400, Bangkok, Thailand.
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