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Abstract
The discovery, development and optimal utilization of pharmaceuticals can be greatly enhanced by knowledge of their modes of action. However, many drugs currently on the market act by unknown mechanisms. Untargeted metabolomics offers the potential to discover modes of action for drugs that perturb cellular metabolism. Development of high resolution LC-MS methods and improved data analysis software now allows rapid detection of drug-induced changes to cellular metabolism in an untargeted manner. Several studies have demonstrated the ability of untargeted metabolomics to provide unbiased target discovery for antimicrobial drugs, in particular for antiprotozoal agents. Furthermore, the utilization of targeted metabolomics techniques has enabled validation of existing hypotheses regarding antiprotozoal drug mechanisms. Metabolomics approaches are likely to assist with optimization of new drug candidates by identification of drug targets, and by allowing detailed characterization of modes of action and resistance of existing and novel antiprotozoal drugs.
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102
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Induced resistance to methionyl-tRNA synthetase inhibitors in Trypanosoma brucei is due to overexpression of the target. Antimicrob Agents Chemother 2013; 57:3021-8. [PMID: 23587950 DOI: 10.1128/aac.02578-12] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
New classes of antiparasitic drugs active against Trypanosoma brucei are needed to combat human African trypanosomiasis. Inhibitors of methionyl-tRNA synthetase (MetRS) have excellent potential to be developed for this purpose (S. Shibata, J. R. Gillespie, A. M. Kelley, A. J. Napuli, Z. Zhang, K. V. Kovzun, R. M. Pefley, J. Lam, F. H. Zucker, W. C. Van Voorhis, E. A. Merritt, W. G. Hol, C. L. Verlinde, E. Fan, and F. S. Buckner, Antimicrob. Agents Chemother. 55:1982-1989, 2011). In order to assess the potential for resistance to develop against this new class of inhibitors, T. brucei cultures were grown in the presence of MetRS inhibitors or comparison drugs. Resistance up to ∼50 times the baseline 50% inhibitory concentration (IC50) was induced against a MetRS inhibitor after ∼120 days. A similar level of resistance to the clinical drug eflornithine was induced after ∼50 days and for pentamidine after ∼80 days. Thus, resistance was induced more slowly against MetRS inhibitors than against clinically used drugs. The parasites resistant to the MetRS inhibitor were shown to overexpress MetRS mRNA by a factor of 35 over the parental strain. Southern analysis indicated that the MetRS gene was amplified in the genome by nearly 8-fold. When injected into mice, the MetRS inhibitor-resistant parasites caused a reduced level of infection, indicating that the changes associated with resistance attenuated their virulence. This finding and the fact that resistance to MetRS inhibitors developed relatively slowly are encouraging for further development of this class of compounds. Published studies on other antitrypanosomal drugs have primarily shown that alterations in membrane transporters were the mechanisms responsible for resistance. This is the first published report of induced drug resistance in the African trypanosome due to overexpression of the target enzyme.
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103
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High-throughput decoding of drug targets and drug resistance mechanisms in African trypanosomes. Parasitology 2013; 141:77-82. [DOI: 10.1017/s0031182013000243] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SUMMARYThe availability of genome sequence data has facilitated the development of high-throughput genetic screening approaches in microbial pathogens. In the African trypanosome, Trypanosoma brucei, genome-scale RNA interference screens have proven particularly effective in this regard. These genetic screens allow for identification of the genes that contribute to a particular pathway or mechanisms of interest. The approach has been used to assess loss-of-fitness, revealing the genes and proteins required for parasite viability and growth. The outputs from these screens predict essential and dispensable genes and facilitate drug target prioritization efforts. The approach has also been used to assess resistance to anti-trypanosomal drugs, revealing the genes and proteins that facilitate drug uptake and action. These outputs also highlight likely mechanisms underlying clinically relevant drug resistance. I first review these findings in the context of what we know about current drugs. I then describe potential contributions that these high-throughput approaches could make to the development and implementation of new drugs.
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104
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Abstract
The trypanosomes cause two neglected tropical diseases, Chagas disease in the Americas and African trypanosomiasis in sub-Saharan Africa. Over recent years a raft of molecular tools have been developed enabling the genetic dissection of many aspects of trypanosome biology, including the mechanisms underlying resistance to some of the current clinical and veterinary drugs. This has led to the identification and characterization of key resistance determinants, including transporters for the anti-Trypanosoma brucei drugs, melarsoprol, pentamidine and eflornithine, and the activator of nifurtimox-benznidazole, the anti-Trypanosoma cruzi drugs. More recently, advances in sequencing technology, combined with the development of RNA interference libraries in the clinically relevant bloodstream form of T. brucei have led to an exponential increase in the number of proteins known to interact either directly or indirectly with the anti-trypanosomal drugs. In this review, we discuss these findings and the technological developments that are set to further revolutionise our understanding of drug-trypanosome interactions. The new knowledge gained should inform the development of novel interventions against the devastating diseases caused by these parasites.
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105
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Jones AJ, Avery VM. Whole-organism high-throughput screening against Trypanosoma brucei brucei. Expert Opin Drug Discov 2013; 8:495-507. [PMID: 23540598 DOI: 10.1517/17460441.2013.783816] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION Human African trypanosomiasis (HAT) occurs as a result of infection with the protozoan parasites Trypanosoma brucei gambiense and T.b. rhodesiense and is nearly always fatal without treatment. However, current therapeutic options are severely limited and there is a desperate need for new compounds to treat the disease. Whole-cell high-throughput screening (HTS) is a technique frequently used to identify compounds with trypanocidal activity. AREAS COVERED The authors examine the development of whole-organism HTS assays for T.b. brucei. The authors describe the successes achieved through HTS and discuss the advantages and disadvantages of whole-organism HTS. EXPERT OPINION Despite hundreds of trypanocidal molecules being identified by whole-organism HTS, very few have progressed into preclinical development. The failure of molecules identified by HTS to progress along the drug development pathway is due to a multitude of factors including undrug-like molecules and molecules having poor pharmacodynamics/kinetic properties. Future studies should focus on screening libraries that contain drug-like molecules that possess some of the properties required in the final compound.
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Affiliation(s)
- Amy J Jones
- Discovery Biology, Eskitis Institute (N27), Griffith University, Brisbane, 4111, Australia
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106
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A versatile proline/alanine transporter in the unicellular pathogen Leishmania donovani regulates amino acid homoeostasis and osmotic stress responses. Biochem J 2013; 449:555-66. [PMID: 22994895 DOI: 10.1042/bj20121262] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Unlike all other organisms, parasitic protozoa of the family Trypanosomatidae maintain a large cellular pool of proline that, together with the alanine pool, serve as alternative carbon sources as well as reservoirs of organic osmolytes. These reflect adaptation to their insect vectors whose haemolymphs are exceptionally rich in the two amino acids. In the present study we identify and characterize a new neutral amino acid transporter, LdAAP24, that translocates proline and alanine across the Leishmania donovani plasma membrane. This transporter fulfils multiple functions: it is the sole supplier for the intracellular pool of proline and contributes to the alanine pool; it is essential for cell volume regulation after osmotic stress; and it regulates the transport and homoeostasis of glutamate and arginine, none of which are its substrates. Notably, we provide evidence that proline and alanine exhibit different roles in the parasitic response to hypotonic shock; alanine affects swelling, whereas proline influences the rate of volume recovery. On the basis of our data we suggest that LdAAP24 plays a key role in parasite adaptation to its varying environments in host and vector, a phenomenon essential for successful parasitism.
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107
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Baker N, de Koning HP, Mäser P, Horn D. Drug resistance in African trypanosomiasis: the melarsoprol and pentamidine story. Trends Parasitol 2013; 29:110-8. [PMID: 23375541 PMCID: PMC3831158 DOI: 10.1016/j.pt.2012.12.005] [Citation(s) in RCA: 170] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 12/16/2012] [Accepted: 12/17/2012] [Indexed: 01/07/2023]
Abstract
Melarsoprol and pentamidine represent the two main classes of drugs, the arsenicals and diamidines, historically used to treat the diseases caused by African trypanosomes: sleeping sickness in humans and Nagana in livestock. Cross-resistance to these drugs was first observed over 60 years ago and remains the only example of cross-resistance among sleeping sickness therapies. A Trypanosoma brucei adenosine transporter is well known for its role in the uptake of both drugs. More recently, aquaglyceroporin 2 (AQP2) loss of function was linked to melarsoprol-pentamidine cross-resistance. AQP2, a channel that appears to facilitate drug accumulation, may also be linked to clinical cases of resistance. Here, we review these findings and consider some new questions as well as future prospects for tackling the devastating diseases caused by these parasites.
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Affiliation(s)
- Nicola Baker
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
| | - Harry P. de Koning
- University of Glasgow, Institute of Infection, Immunity and Inflammation, Sir Graeme Davies Building, 120 University Place, Glasgow, G12 8TA, Scotland
| | - Pascal Mäser
- Swiss Tropical and Public Health Institute, Socinstr. 57, 4051 Basel, Switzerland
- University of Basel, Petersplatz 1, 4003 Basel, Switzerland
| | - David Horn
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
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108
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Schröder J, Klinger A, Oellien F, Marhöfer RJ, Duszenko M, Selzer PM. Docking-based virtual screening of covalently binding ligands: an orthogonal lead discovery approach. J Med Chem 2013; 56:1478-90. [PMID: 23350811 DOI: 10.1021/jm3013932] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In pharmaceutical industry, lead discovery strategies and screening collections have been predominantly tailored to discover compounds that modulate target proteins through noncovalent interactions. Conversely, covalent linkage formation is an important mechanism for a quantity of successful drugs in the market, which are discovered in most cases by hindsight instead of systematical design. In this article, the implementation of a docking-based virtual screening workflow for the retrieval of covalent binders is presented considering human cathepsin K as a test case. By use of the docking conditions that led to the best enrichment of known actives, 44 candidate compounds with unknown activity on cathepsin K were finally selected for experimental evaluation. The most potent inhibitor, 4-(N-phenylanilino)-6-pyrrolidin-1-yl-1,3,5-triazine-2-carbonitrile (CP243522), showed a K(i) of 21 nM and was confirmed to have a covalent reversible mechanism of inhibition. The presented approach will have great potential in cases where covalent inhibition is the desired drug discovery strategy.
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Affiliation(s)
- Jörg Schröder
- MSD Animal Health Innovation GmbH, Zur Propstei, D-55270 Schwabenheim, Germany
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109
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Kennedy PG. Clinical features, diagnosis, and treatment of human African trypanosomiasis (sleeping sickness). Lancet Neurol 2012; 12:186-94. [PMID: 23260189 DOI: 10.1016/s1474-4422(12)70296-x] [Citation(s) in RCA: 276] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Human African trypanosomiasis, or sleeping sickness, is caused by infection with parasites of the genus Trypanosoma, transmitted by the tsetse fly. The disease has two forms, Trypanosoma brucei (T b) rhodesiense and T b gambiense; and is almost always fatal if untreated. Despite a recent reduction in the number of reported cases, patients with African trypanosomiasis continue to present major challenges to clinicians. Because treatment for CNS-stage disease can be very toxic, diagnostic staging to distinguish early-stage from late-stage disease when the CNS in invaded is crucial but remains problematic. Melarsoprol is the only available treatment for late-stage T b rhodesiense infection, but can be lethal to 5% of patients owing to post-treatment reactive encephalopathy. Eflornithine combined with nifurtimox is the first-line treatment for late-stage T b gambiense. New drugs are in the pipeline for treatment of CNS human African trypanosomiasis, giving rise to cautious optimism.
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Affiliation(s)
- Peter Ge Kennedy
- Department of Neurology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Institute of Neurological Sciences, Southern General Hospital, Glasgow, UK.
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110
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Yang Y, Voak A, Wilkinson SR, Hu L. Design, synthesis, and evaluation of potential prodrugs of DFMO for reductive activation. Bioorg Med Chem Lett 2012; 22:6583-6. [PMID: 23031595 DOI: 10.1016/j.bmcl.2012.09.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Revised: 08/31/2012] [Accepted: 09/04/2012] [Indexed: 01/28/2023]
Abstract
A series of potential DFMO prodrugs was designed through the incorporation of 4-nitrobenzyl ester or carbamate groups for potential activation by trypanosomal nitroreductase. It was found that only modification of N(ε)-amino group of DFMO by 4-nitro-2-fluorobenzyloxycarbonyl resulted in significant trypanocidal activity and could serve as a lead for further investigation.
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Affiliation(s)
- Yanhui Yang
- Department of Medicinal Chemistry, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
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111
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Kennedy PG. An alternative form of melarsoprol in sleeping sickness. Trends Parasitol 2012; 28:307-10. [DOI: 10.1016/j.pt.2012.05.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 05/18/2012] [Accepted: 05/21/2012] [Indexed: 10/28/2022]
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112
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Friedman AJ, Durrant JD, Pierce LCT, McCorvie TJ, Timson DJ, McCammon JA. The molecular dynamics of Trypanosoma brucei UDP-galactose 4'-epimerase: a drug target for African sleeping sickness. Chem Biol Drug Des 2012; 80:173-81. [PMID: 22487100 PMCID: PMC3399956 DOI: 10.1111/j.1747-0285.2012.01392.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 03/07/2012] [Accepted: 04/01/2012] [Indexed: 02/03/2023]
Abstract
During the past century, several epidemics of human African trypanosomiasis, a deadly disease caused by the protist Trypanosoma brucei, have afflicted sub-Saharan Africa. Over 10 000 new victims are reported each year, with hundreds of thousands more at risk. As current drug treatments are either highly toxic or ineffective, novel trypanocides are urgently needed. The T. brucei galactose synthesis pathway is one potential therapeutic target. Although galactose is essential for T. brucei survival, the parasite lacks the transporters required to intake galactose from the environment. UDP-galactose 4'-epimerase (TbGalE) is responsible for the epimerization of UDP-glucose to UDP-galactose and is therefore of great interest to medicinal chemists. Using molecular dynamics simulations, we investigate the atomistic motions of TbGalE in both the apo and holo states. The sampled conformations and protein dynamics depend not only on the presence of a UDP-sugar ligand, but also on the chirality of the UDP-sugar C4 atom. This dependence provides important insights into TbGalE function and may help guide future computer-aided drug discovery efforts targeting this protein.
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Affiliation(s)
- Aaron J Friedman
- Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, CA 92093-0365, USA.
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113
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Vincent IM, Creek DJ, Burgess K, Woods DJ, Burchmore RJS, Barrett MP. Untargeted metabolomics reveals a lack of synergy between nifurtimox and eflornithine against Trypanosoma brucei. PLoS Negl Trop Dis 2012; 6:e1618. [PMID: 22563508 PMCID: PMC3341325 DOI: 10.1371/journal.pntd.0001618] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2012] [Accepted: 03/05/2012] [Indexed: 01/08/2023] Open
Abstract
A non-targeted metabolomics-based approach is presented that enables the study of pathways in response to drug action with the aim of defining the mode of action of trypanocides. Eflornithine, a polyamine pathway inhibitor, and nifurtimox, whose mode of action involves its metabolic activation, are currently used in combination as first line treatment against stage 2, CNS-involved, human African trypanosomiasis (HAT). Drug action was assessed using an LC-MS based non-targeted metabolomics approach. Eflornithine revealed the expected changes to the polyamine pathway as well as several unexpected changes that point to pathways and metabolites not previously described in bloodstream form trypanosomes, including a lack of arginase activity and N-acetylated ornithine and putrescine. Nifurtimox was shown to be converted to a trinitrile metabolite indicative of metabolic activation, as well as inducing changes in levels of metabolites involved in carbohydrate and nucleotide metabolism. However, eflornithine and nifurtimox failed to synergise anti-trypanosomal activity in vitro, and the metabolomic changes associated with the combination are the sum of those found in each monotherapy with no indication of additional effects. The study reveals how untargeted metabolomics can yield rapid information on drug targets that could be adapted to any pharmacological situation.
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Affiliation(s)
- Isabel M. Vincent
- The Wellcome Trust Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Darren J. Creek
- The Wellcome Trust Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Glasgow Polyomics Facility, University of Glasgow, Glasgow, United Kingdom
| | - Karl Burgess
- The Wellcome Trust Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Glasgow Polyomics Facility, University of Glasgow, Glasgow, United Kingdom
| | - Debra J. Woods
- Pfizer Animal Health, Pfizer Inc, Kalamazoo, Michigan, United States of America
| | - Richard J. S. Burchmore
- The Wellcome Trust Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Glasgow Polyomics Facility, University of Glasgow, Glasgow, United Kingdom
| | - Michael P. Barrett
- The Wellcome Trust Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Glasgow Polyomics Facility, University of Glasgow, Glasgow, United Kingdom
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114
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Update on field use of the available drugs for the chemotherapy of human African trypanosomiasis. Parasitology 2012; 139:842-6. [PMID: 22309684 DOI: 10.1017/s0031182012000169] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Despite the fact that eflornithine was considered as the safer drug to treat human African trypanosomiasis (HAT) and has been freely available since 2001, the difficulties in logistics and cost burden associated with this drug meant that the toxic melarsoprol remained the drug of choice. The World Health Organization responded to the situation by designing a medical kit containing all the materials needed to use eflornithine, and by implementing a training and drugs distribution programme which has allowed a transition to this much safer treatment. The introduction of the combination of nifurtimox and eflornithine (NECT) has accelerated the shift from melarsoprol to the best treatment available, due to reduced dosage and treatment time for eflornithine that has significantly lessened the cost and improved the burden of logistics encountered during treatment and distribution. The decrease in the use of more dangerous but cheaper melarsoprol has meant a rise in the per patient cost of treating HAT. Although NECT is cheaper than eflornithine monotherapy, an unexpected consequence has been a continuing rise in the per patient cost of treating HAT. The ethical decision of shifting to the best available treatment imposes a financial burden on HAT control programmes that might render long-term application unsustainable. These factors call for continuing research to provide new safer and more effective drugs that are simple to administer and cheaper when compared to current drugs.
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115
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Alsford S, Eckert S, Baker N, Glover L, Sanchez-Flores A, Leung KF, Turner DJ, Field MC, Berriman M, Horn D. High-throughput decoding of antitrypanosomal drug efficacy and resistance. Nature 2012; 482:232-6. [PMID: 22278056 PMCID: PMC3303116 DOI: 10.1038/nature10771] [Citation(s) in RCA: 241] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Accepted: 12/07/2011] [Indexed: 01/24/2023]
Abstract
The concept of disease-specific chemotherapy was developed a century ago. Dyes and arsenical compounds that displayed selectivity against trypanosomes were central to this work, and the drugs that emerged remain in use for treating human African trypanosomiasis (HAT). The importance of understanding the mechanisms underlying selective drug action and resistance for the development of improved HAT therapies has been recognized, but these mechanisms have remained largely unknown. Here we use all five current HAT drugs for genome-scale RNA interference target sequencing (RIT-seq) screens in Trypanosoma brucei, revealing the transporters, organelles, enzymes and metabolic pathways that function to facilitate antitrypanosomal drug action. RIT-seq profiling identifies both known drug importers and the only known pro-drug activator, and links more than fifty additional genes to drug action. A bloodstream stage-specific invariant surface glycoprotein (ISG75) family mediates suramin uptake, and the AP1 adaptin complex, lysosomal proteases and major lysosomal transmembrane protein, as well as spermidine and N-acetylglucosamine biosynthesis, all contribute to suramin action. Further screens link ubiquinone availability to nitro-drug action, plasma membrane P-type H(+)-ATPases to pentamidine action, and trypanothione and several putative kinases to melarsoprol action. We also demonstrate a major role for aquaglyceroporins in pentamidine and melarsoprol cross-resistance. These advances in our understanding of mechanisms of antitrypanosomal drug efficacy and resistance will aid the rational design of new therapies and help to combat drug resistance, and provide unprecedented molecular insight into the mode of action of antitrypanosomal drugs.
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Affiliation(s)
- Sam Alsford
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
| | - Sabine Eckert
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK
| | - Nicola Baker
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
| | - Lucy Glover
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
| | | | - Ka Fai Leung
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Daniel J. Turner
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK
| | - Mark C. Field
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Matthew Berriman
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK
| | - David Horn
- London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
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116
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Abstract
BACKGROUND The current treatments for human African trypanosomiasis (HAT), Chagas disease and leishmaniasis (collectively referred to as the kinetoplastid diseases) are far from ideal but, for some, there has been significant recent progress. For HAT the only advances in treatment over the past two decades have been the introduction of an eflornithine/nifurtimox co-administration and a shorter regime of the old standard melarsoprol. SOURCES OF DATA PubMed. AREAS OF AGREEMENT There is a need for new safe, oral drugs for cost-effective treatment of patients and use in control programmes for all the trypanosomatid diseases. AREAS OF CONTROVERSY Cutaneous leishmaniasis is not on the agenda and treatments are lagging behind. GROWING POINTS There are three compounds in development for the treatment of the CNS stage of HAT: fexinidazole, currently due to entry into phase II clinical studies, a benzoxaborole (SCYX-7158) in phase I trials and a diamidine derivative (CPD-0802), in advanced pre-clinical development. For Chagas disease, two anti-fungal triazoles are now in clinical trial. In addition, clinical studies with benznidazole, a drug previously recommended only for acute stage treatment, are close to completion to determine the effectiveness in the treatment of early chronic and indeterminate Chagas disease. For visceral leishmaniasis new formulations, therapeutic switching, in particular AmBisome, and the potential for combinations of established drugs have significantly improved the opportunities for the treatment in the Indian subcontinent, but not in East Africa. AREAS TIMELY FOR DEVELOPING RESEARCH Improved diagnostic tools are needed to support treatment, for test of cure in clinical trials and for monitoring/surveillance of populations in control programmes.
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Affiliation(s)
- Michael P Barrett
- Wellcome Trust Centre of Molecular Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, UK
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117
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Willert E, Phillips MA. Regulation and function of polyamines in African trypanosomes. Trends Parasitol 2011; 28:66-72. [PMID: 22192816 DOI: 10.1016/j.pt.2011.11.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 10/31/2011] [Accepted: 11/01/2011] [Indexed: 02/03/2023]
Abstract
The polyamine biosynthetic pathway is an important drug target for the treatment of human African trypanosomiasis (HAT), raising interest in understanding polyamine function and their mechanism of regulation. Polyamine levels are tightly controlled in mammalian cells, but similar regulatory mechanisms appear absent in trypanosomes. Instead trypanosomatid S-adenosylmethionine decarboxylase (AdoMetDC), which catalyzes a key step in the biosynthesis of the polyamine spermidine, is activated by dimerization with an inducible protein termed prozyme. Prozyme is an inactive paralog of the active AdoMetDC enzyme that evolved by gene duplication and is found only in the trypanosomatids. In Trypanosoma brucei, AdoMetDC activity appears to be controlled by regulation of prozyme protein levels, potentially at the translational level.
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Affiliation(s)
- Erin Willert
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Road, Dallas, TX 75390-9041, USA
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118
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Penuliar GM, Furukawa A, Nakada-Tsukui K, Husain A, Sato D, Nozaki T. Transcriptional and functional analysis of trifluoromethionine resistance in Entamoeba histolytica. J Antimicrob Chemother 2011; 67:375-86. [PMID: 22110087 DOI: 10.1093/jac/dkr484] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
OBJECTIVES Drug resistance in parasitic protozoa is an obstacle to successful chemotherapy. Understanding how pathogens respond to drugs is crucial in preventing resistance. Previously, we have shown that in Entamoeba histolytica, methionine γ-lyase (EhMGL) downregulation results in trifluoromethionine resistance. The transcriptional response, however, of this parasite to the drug is not known. In this study, we used microarray analysis to determine whether additional genes are involved. METHODS The expression profiles of 9230 genes in wild-type and trifluoromethionine-resistant strains were compared. Episomal overexpression of EhBspA1 was performed to verify its role in trifluoromethionine resistance. The transcriptomes of a trifluoromethionine-resistant strain cultured with or without trifluoromethionine, an EhMGL gene-silenced strain, a strain with reduced susceptibility to metronidazole and a wild-type strain under cysteine-deprived conditions were compared to determine the specificity of the changes observed in the trifluoromethionine-resistant strain. RESULTS The expression of 35 genes differed at least 3-fold between trifluoromethionine-resistant and wild-type strains. Some of the genes play roles in metabolism, the stress response and gene regulation. EhMGL and EhBspA1 were found to be highly downregulated and upregulated, respectively. Overexpression of EhBspA1 conferred partial resistance to trifluoromethionine. Comparative transcriptome analysis showed that genes modulated in trifluoromethionine-resistant strains were specific. CONCLUSIONS E. histolytica has few known resistance mechanisms against drugs. In this study, we showed that aside from EhMGL downregulation, induction of EhBspA1 plays a role in trifluoromethionine resistance. We also showed a unique set of induced genes that could represent the signature profile of trifluoromethionine resistance in E. histolytica.
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Affiliation(s)
- Gil M Penuliar
- Department of Parasitology, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan
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Creek DJ, Anderson J, McConville MJ, Barrett MP. Metabolomic analysis of trypanosomatid protozoa. Mol Biochem Parasitol 2011; 181:73-84. [PMID: 22027026 DOI: 10.1016/j.molbiopara.2011.10.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Revised: 10/04/2011] [Accepted: 10/06/2011] [Indexed: 01/05/2023]
Abstract
Metabolomics aims to measure all low molecular weight chemicals within a given system in a manner analogous to transcriptomics, proteomics and genomics. In this review we highlight metabolomics approaches that are currently being applied to the kinetoplastid parasites, Trypanosoma brucei and Leishmania spp. The use of untargeted metabolomics approaches, made possible through advances in mass spectrometry and informatics, and stable isotope labelling has increased our understanding of the metabolism in these organisms beyond the views established using classical biochemical approaches. Set within the context of metabolic networks, predicted using genome-wide reconstructions of metabolism, new hypotheses on how to target aspects of metabolism to design new drugs against these protozoa are emerging.
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Affiliation(s)
- Darren J Creek
- Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, United Kingdom
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120
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Barrett MP, Vincent IM, Burchmore RJS, Kazibwe AJN, Matovu E. Drug resistance in human African trypanosomiasis. Future Microbiol 2011; 6:1037-47. [DOI: 10.2217/fmb.11.88] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Human African trypanosomiasis or ‘sleeping sickness’ is a neglected tropical disease caused by the parasite Trypanosoma brucei. A decade of intense international cooperation has brought the incidence to fewer than 10,000 reported cases per annum with anti-trypanosomal drugs, particularly against stage 2 disease where the CNS is involved, being central to control. Treatment failures with melarsoprol started to appear in the 1990s and their incidence has risen sharply in many foci. Loss of plasma membrane transporters involved in drug uptake, particularly the P2 aminopurine transporter and also a transporter termed the high affinity pentamidine transporter, relate to melarsoprol resistance selected in the laboratory. The same two transporters are also responsible for the uptake of the stage 1 drug pentamidine and, to varying extents, other diamidines. However, reports of treatment failures with pentamidine have been rare from the field. Eflornithine (difluoromethylornithine) has replaced melarsoprol as first-line treatment in many regions. However, a need for protracted and complicated drug dosing regimens slowed widespread implementation of eflornithine monotherapy. A combination of eflornithine with nifurtimox substantially decreases the required dose and duration of eflornithine administration and this nifurtimox-eflornithine combination therapy has enjoyed rapid implementation. Unfortunately, selection of resistance to eflornithine in the laboratory is relatively easy (through loss of an amino acid transporter believed to be involved in its uptake), as is selection of resistance to nifurtimox. The first anecdotal reports of treatment failures with eflornithine monotherapy are emerging from some foci. The possibility that parasites resistant to melarsoprol on the one hand, and eflornithine on the other, are present in the field indicates that genes capable of conferring drug resistance to both drugs are in circulation. If new drugs, that act in ways that will not render them susceptible to resistance mechanisms already in circulation do not appear soon, there is also a risk that the current downward trend in Human African trypanosomiasis prevalence will be reversed and, as has happened in the past, the disease will become resurgent, only this time in a form that resists available drugs.
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Affiliation(s)
| | - Isabel M Vincent
- Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity & Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, Scotland
| | - Richard JS Burchmore
- Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity & Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, Scotland
| | - Anne JN Kazibwe
- Makerere University School of Veterinary Medicine, Kampala, Uganda
| | - Enock Matovu
- Makerere University School of Veterinary Medicine, Kampala, Uganda
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121
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Brun R, Don R, Jacobs RT, Wang MZ, Barrett MP. Development of novel drugs for human African trypanosomiasis. Future Microbiol 2011; 6:677-91. [DOI: 10.2217/fmb.11.44] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Human African trypanosomiasis (HAT) or ‘sleeping sickness’ is a neglected tropical disease caused by the parasite Trypanosoma brucei. Novel models for funding pharmaceutical development against HAT are beginning to yield results. The Drugs for Neglected Diseases initiative (DNDi) rediscovered a nitroimidazole, fexinidazole, which is currently in Phase I clinical trials. Novel benzoxaboroles, discovered by Anacor, Scynexis and DNDi, have good pharmacokinetic properties in plasma and in the brain and are curative in a murine model of stage two HAT with brain infection. The Consortium for Parasitic Drug Development (CPDD) has identified a series of dicationic compounds that can cure a monkey model of stage two HAT. With other screening programs yielding hits, the pipeline for new HAT drugs might finally begin to fill.
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Affiliation(s)
- Reto Brun
- Department Medical Parasitology & Infection Biology, Swiss Tropical & Public Health Institute, and, University of Basel, CH-4002 Basel, Switzerland
| | - Robert Don
- Drugs for Neglected Diseases initiative, Geneva, Switzerland
| | - Robert T Jacobs
- Department of Chemistry, SCYNEXIS, Inc., PO Box 12878, Research Triangle Park, NC, 27709-2878, USA
| | - Michael Zhuo Wang
- Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC, USA
| | - Michael P Barrett
- Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, Scotland
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Trypanocidal furamidine analogues: influence of pyridine nitrogens on trypanocidal activity, transport kinetics, and resistance patterns. Antimicrob Agents Chemother 2011; 55:2352-61. [PMID: 21402852 DOI: 10.1128/aac.01551-10] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Current therapies for human African trypanosomiasis (HAT) are unsatisfactory and under threat from emerging drug resistance linked to the loss of transporters, e.g., the P2 aminopurine transporter (TbAT1). Here we compare the uptake and trypanocidal properties of furamidine (DB75), recently evaluated in clinical trials against stage 1 (haemolymphatic) HAT, and two aza analogues, DB820 and CPD0801 (DB829), which are candidate compounds for treatment of stage 2 (neurological) disease. Values of 50% inhibitory concentrations (IC50s) determined in vitro against both wild-type and transporter mutant parasites were submicromolar, with DB75 trypanotoxicity shown to be better than and DB820 trypanotoxicity similar to that of the widely used veterinary trypanocide diminazene, while CPD0801 was less active. Activity correlated with uptake and with the minimum drug exposure time necessary to kill trypanosomes: DB75 accumulated at double and 10-fold the rates of DB820 and CPD0801, respectively. All three compounds inhibited P2-mediated adenosine transport with similar Ki values, indicating affinity values for this permease in the low to submicromolar range. Uptake of DB75, DB820, and CPD0801 was significantly reduced in tbat1-/- parasites and was sensitive to inhibition by adenine, showing that all three compounds are substrates for the P2 transporter. Uptake in vitro was significantly less than that seen with parasites freshly isolated from infected rats, correlating with a downregulation of P2 activity in vitro. We conclude that DB75, DB820, and CPD0801 are actively accumulated by Trypanosoma brucei brucei, with P2 as the main transport route. The aza analogues of DB75 accumulate more slowly than furamidine itself and reveal less trypanocidal activity in standard in vitro drug sensitivity assays.
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Baker N, Alsford S, Horn D. Genome-wide RNAi screens in African trypanosomes identify the nifurtimox activator NTR and the eflornithine transporter AAT6. Mol Biochem Parasitol 2010; 176:55-7. [PMID: 21093499 PMCID: PMC3032052 DOI: 10.1016/j.molbiopara.2010.11.010] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 11/08/2010] [Accepted: 11/12/2010] [Indexed: 11/17/2022]
Abstract
To be effective, therapeutic compounds must typically enter target cells and, in some cases, must be concentrated or modified. Thus, uptake and activation mechanisms often form the basis of selectivity against infectious agents. Loss-of-function screens can be used to identify proteins involved in drug uptake and metabolism and may also identify clinically relevant potential resistance mechanisms. We used a genome-scale RNA interference (RNAi) library to identify loss-of-function resistance mechanisms in bloodstream-form Trypanosoma brucei. Nifurtimox-Eflornithine Combination Therapy (NECT) was recently introduced for Human African Trypanosomiasis and we focus on these drugs here. Screens for resistance to nifurtimox and a related drug, benznidazole, identified loss of nitroreductase (NTR) pro-drug activator function. A screen for resistance to the amino-acid analogue, eflornithine, identified loss of amino-acid transporter (AAT6) function. Our results confirm recent findings and suggest that NTR or AAT6 loss-of-function represent major potential mechanisms of resistance to these drugs. Thus, bloodstream-form T. brucei RNAi libraries present a versatile tool for selective genetic screening and for the rapid identification of drug-activation, uptake and potential resistance mechanisms.
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Affiliation(s)
- Nicola Baker
- London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
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