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Aldfer MM, Hulpia F, van Calenbergh S, De Koning HP. Mapping the transporter-substrate interactions of the Trypanosoma cruzi NB1 nucleobase transporter reveals the basis for its high affinity and selectivity for hypoxanthine and guanine and lack of nucleoside uptake. Mol Biochem Parasitol 2024; 258:111616. [PMID: 38401850 DOI: 10.1016/j.molbiopara.2024.111616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 02/19/2024] [Accepted: 02/20/2024] [Indexed: 02/26/2024]
Abstract
Trypanosoma cruzi is a protozoan parasite and the etiological agent of Chagas disease, a debilitating and sometimes fatal disease that continues to spread to new areas. Yet, Chagas disease is still only treated with two related nitro compounds that are insufficiently effective and cause severe side effects. Nucleotide metabolism is one of the known vulnerabilities of T. cruzi, as they are auxotrophic for purines, and nucleoside analogues have been shown to have genuine promise against this parasite in vitro and in vivo. Since purine antimetabolites require efficient uptake through transporters, we here report a detailed characterisation of the T. cruzi NB1 nucleobase transporter with the aim of elucidating the interactions between TcrNB1 and its substrates and finding the positions that can be altered in the design of novel antimetabolites without losing transportability. Systematically determining the inhibition constants (Ki) of purine analogues for TcrNB1 yielded their Gibbs free energy of interaction, ΔG0. Pairwise comparisons of substrate (hypoxanthine, guanine, adenine) and analogues allowed us to determine that optimal binding affinity by TcrNB1 requires interactions with all four nitrogen residues of the purine ring, with N1 and N9, in protonation state, functioning as presumed hydrogen bond donors and unprotonated N3 and N7 as hydrogen bond acceptors. This is the same interaction pattern as we previously described for the main nucleobase transporters of Trypanosoma brucei spp. and Leishmania major and makes it the first of the ENT-family genes that is functionally as well as genetically conserved between the three main kinetoplast pathogens.
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Affiliation(s)
- Mustafa M Aldfer
- School of Infection and Immunity, Sir Graeme Davies Building, 120 University Place, University of Glasgow, GlasgowG12 8TA, UK
| | - Fabian Hulpia
- Laboratory for Medicinal Chemistry (Campus Heymans), Ghent University, Ottergemsesteenweg 460, 9000 Gent, Belgium
| | - Serge van Calenbergh
- Laboratory for Medicinal Chemistry (Campus Heymans), Ghent University, Ottergemsesteenweg 460, 9000 Gent, Belgium
| | - Harry P De Koning
- School of Infection and Immunity, Sir Graeme Davies Building, 120 University Place, University of Glasgow, GlasgowG12 8TA, UK.
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2
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Chen W, Zou R, Mei Y, Li J, Xuan Y, Cui B, Zou J, Wang J, Lin S, Zhang Z, Wang C. Structural insights into drug transport by an aquaglyceroporin. Nat Commun 2024; 15:3985. [PMID: 38734677 PMCID: PMC11088622 DOI: 10.1038/s41467-024-48445-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Accepted: 04/29/2024] [Indexed: 05/13/2024] Open
Abstract
Pentamidine and melarsoprol are primary drugs used to treat the lethal human sleeping sickness caused by the parasite Trypanosoma brucei. Cross-resistance to these two drugs has recently been linked to aquaglyceroporin 2 of the trypanosome (TbAQP2). TbAQP2 is the first member of the aquaporin family described as capable of drug transport; however, the underlying mechanism remains unclear. Here, we present cryo-electron microscopy structures of TbAQP2 bound to pentamidine or melarsoprol. Our structural studies, together with the molecular dynamic simulations, reveal the mechanisms shaping substrate specificity and drug permeation. Multiple amino acids in TbAQP2, near the extracellular entrance and inside the pore, create an expanded conducting tunnel, sterically and energetically allowing the permeation of pentamidine and melarsoprol. Our study elucidates the mechanism of drug transport by TbAQP2, providing valuable insights to inform the design of drugs against trypanosomiasis.
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Affiliation(s)
- Wanbiao Chen
- Center for Human Tissues and Organs Degeneration, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 581055, China
| | - Rongfeng Zou
- Shenzhen Jingtai Technology Co., Ltd. (XtalPi), Shenzhen, 518000, China
| | - Yi Mei
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China
| | - Jiawei Li
- Center for Human Tissues and Organs Degeneration, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 581055, China
- Department of Geriatric Medicine, Shenzhen Longhua District Central Hospital, Shenzhen, 518110, China
| | - Yumi Xuan
- Center for Human Tissues and Organs Degeneration, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 581055, China
| | - Bing Cui
- Center for Human Tissues and Organs Degeneration, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 581055, China
- School of Basic Medicine and Clinical Pharmacy, and State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
| | - Junjie Zou
- Shenzhen Jingtai Technology Co., Ltd. (XtalPi), Shenzhen, 518000, China
| | - Juncheng Wang
- Advanced Medical Research Institute, Shandong University, Jinan, China
| | - Shaoquan Lin
- Centre for Polymers in Medicine, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, 581055, China
| | - Zhe Zhang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China.
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China.
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou, Jiangsu Province, 221004, China.
| | - Chongyuan Wang
- Center for Human Tissues and Organs Degeneration, Faculty of Pharmaceutical Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 581055, China.
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Nucleoside Transport and Nucleobase Uptake Null Mutants in Leishmania mexicana for the Routine Expression and Characterization of Purine and Pyrimidine Transporters. Int J Mol Sci 2022; 23:ijms23158139. [PMID: 35897714 PMCID: PMC9331716 DOI: 10.3390/ijms23158139] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 07/05/2022] [Accepted: 07/20/2022] [Indexed: 12/02/2022] Open
Abstract
The study of transporters is highly challenging, as they cannot be isolated or studied in suspension, requiring a cellular or vesicular system, and, when mediated by more than one carrier, difficult to interpret. Nucleoside analogues are important drug candidates, and all protozoan pathogens express multiple equilibrative nucleoside transporter (ENT) genes. We have therefore developed a system for the routine expression of nucleoside transporters, using CRISPR/cas9 to delete both copies of all three nucleoside transporters from Leishmania mexicana (ΔNT1.1/1.2/2 (SUPKO)). SUPKO grew at the same rate as the parental strain and displayed no apparent deficiencies, owing to the cells’ ability to synthesize pyrimidines, and the expression of the LmexNT3 purine nucleobase transporter. Nucleoside transport was barely measurable in SUPKO, but reintroduction of L. mexicana NT1.1, NT1.2, and NT2 restored uptake. Thus, SUPKO provides an ideal null background for the expression and characterization of single ENT transporter genes in isolation. Similarly, an LmexNT3-KO strain provides a null background for transport of purine nucleobases and was used for the functional characterization of T. cruzi NB2, which was determined to be adenine-specific. A 5-fluorouracil-resistant strain (Lmex5FURes) displayed null transport for uracil and 5FU, and was used to express the Aspergillus nidulans uracil transporter FurD.
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4
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Natto MJ, Miyamoto Y, Munday JC, AlSiari TA, Al-Salabi MI, Quashie NB, Eze AA, Eckmann L, De Koning HP. Comprehensive characterization of purine and pyrimidine transport activities in Trichomonas vaginalis and functional cloning of a trichomonad nucleoside transporter. Mol Microbiol 2021; 116:1489-1511. [PMID: 34738285 PMCID: PMC8688338 DOI: 10.1111/mmi.14840] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Revised: 10/30/2021] [Accepted: 10/30/2021] [Indexed: 11/30/2022]
Abstract
Trichomoniasis is a common and widespread sexually-transmitted infection, caused by the protozoan parasite Trichomonas vaginalis. T. vaginalis lacks the biosynthetic pathways for purines and pyrimidines, making nucleoside metabolism a drug target. Here we report the first comprehensive investigation into purine and pyrimidine uptake by T. vaginalis. Multiple carriers were identified and characterized with regard to substrate selectivity and affinity. For nucleobases, a high-affinity adenine transporter, a possible guanine transporter and a low affinity uracil transporter were found. Nucleoside transporters included two high affinity adenosine/guanosine/uridine/cytidine transporters distinguished by different affinities to inosine, a lower affinity adenosine transporter, and a thymidine transporter. Nine Equilibrative Nucleoside Transporter (ENT) genes were identified in the T. vaginalis genome. All were expressed equally in metronidazole-resistant and -sensitive strains. Only TvagENT2 was significantly upregulated in the presence of extracellular purines; expression was not affected by co-culture with human cervical epithelial cells. All TvagENTs were cloned and separately expressed in Trypanosoma brucei. We identified the main broad specificity nucleoside carrier, with high affinity for uridine and cytidine as well as purine nucleosides including inosine, as TvagENT3. The in-depth characterization of purine and pyrimidine transporters provides a critical foundation for the development of new anti-trichomonal nucleoside analogues.
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Affiliation(s)
- Manal J. Natto
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Yukiko Miyamoto
- Department of Medicine, University of California, San Diego, La Jolla, California 92093, United States
| | - Jane C. Munday
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Tahani A. AlSiari
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Mohammed I. Al-Salabi
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Neils B. Quashie
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
- Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, University of Ghana
| | - Anthonius A. Eze
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
- Current affiliation: Department of Medical Biochemistry, Faculty of Basic Medical Sciences, College of Medicine, University of Nigeria, Enugu Campus, Enugu, Nigeria
| | - Lars Eckmann
- Department of Medicine, University of California, San Diego, La Jolla, California 92093, United States
| | - Harry P. De Koning
- Institute of Infection, Immunity and Inflammation, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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5
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Alghamdi AH, Munday JC, Campagnaro GD, Gurvic D, Svensson F, Okpara CE, Kumar A, Quintana J, Martin Abril ME, Milić P, Watson L, Paape D, Settimo L, Dimitriou A, Wielinska J, Smart G, Anderson LF, Woodley CM, Kelly SPY, Ibrahim HM, Hulpia F, Al-Salabi MI, Eze AA, Sprenger T, Teka IA, Gudin S, Weyand S, Field M, Dardonville C, Tidwell RR, Carrington M, O'Neill P, Boykin DW, Zachariae U, De Koning HP. Positively selected modifications in the pore of TbAQP2 allow pentamidine to enter Trypanosoma brucei. eLife 2020; 9:56416. [PMID: 32762841 PMCID: PMC7473772 DOI: 10.7554/elife.56416] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 08/06/2020] [Indexed: 11/25/2022] Open
Abstract
Mutations in the Trypanosoma brucei aquaporin AQP2 are associated with resistance to pentamidine and melarsoprol. We show that TbAQP2 but not TbAQP3 was positively selected for increased pore size from a common ancestor aquaporin. We demonstrate that TbAQP2’s unique architecture permits pentamidine permeation through its central pore and show how specific mutations in highly conserved motifs affect drug permeation. Introduction of key TbAQP2 amino acids into TbAQP3 renders the latter permeable to pentamidine. Molecular dynamics demonstrates that permeation by dicationic pentamidine is energetically favourable in TbAQP2, driven by the membrane potential, although aquaporins are normally strictly impermeable for ionic species. We also identify the structural determinants that make pentamidine a permeant although most other diamidine drugs are excluded. Our results have wide-ranging implications for optimising antitrypanosomal drugs and averting cross-resistance. Moreover, these new insights in aquaporin permeation may allow the pharmacological exploitation of other members of this ubiquitous gene family. African sleeping sickness is a potentially deadly illness caused by the parasite Trypanosoma brucei. The disease is treatable, but many of the current treatments are old and are becoming increasingly ineffective. For instance, resistance is growing against pentamidine, a drug used in the early stages in the disease, as well as against melarsoprol, which is deployed when the infection has progressed to the brain. Usually, cases resistant to pentamidine are also resistant to melarsoprol, but it is still unclear why, as the drugs are chemically unrelated. Studies have shown that changes in a water channel called aquaglyceroporin 2 (TbAQP2) contribute to drug resistance in African sleeping sickness; this suggests that it plays a role in allowing drugs to kill the parasite. This molecular ‘drain pipe’ extends through the surface of T. brucei, and should allow only water and a molecule called glycerol in and out of the cell. In particular, the channel should be too narrow to allow pentamidine or melarsoprol to pass through. One possibility is that, in T. brucei, the TbAQP2 channel is abnormally wide compared to other members of its family. Alternatively, pentamidine and melarsoprol may only bind to TbAQP2, and then ‘hitch a ride’ when the protein is taken into the parasite as part of the natural cycle of surface protein replacement. Alghamdi et al. aimed to tease out these hypotheses. Computer models of the structure of the protein were paired with engineered changes in the key areas of the channel to show that, in T. brucei, TbAQP2 provides a much broader gateway into the cell than observed for similar proteins. In addition, genetic analysis showed that this version of TbAQP2 has been actively selected for during the evolution process of T. brucei. This suggests that the parasite somehow benefits from this wider aquaglyceroporin variant. This is a new resistance mechanism, and it is possible that aquaglyceroporins are also larger than expected in other infectious microbes. The work by Alghamdi et al. therefore provides insight into how other germs may become resistant to drugs.
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Affiliation(s)
- Ali H Alghamdi
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Jane C Munday
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | | | - Dominik Gurvic
- Computational Biology Centre for Translational and Interdisciplinary Research, University of Dundee, Dundee, United Kingdom
| | - Fredrik Svensson
- IOTA Pharmaceuticals Ltd, St Johns Innovation Centre, Cambridge, United Kingdom
| | - Chinyere E Okpara
- Department of Chemistry, University of Liverpool, Liverpool, United Kingdom
| | - Arvind Kumar
- Chemistry Department, Georgia State University, Atlanta, United States
| | - Juan Quintana
- School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | | | - Patrik Milić
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Laura Watson
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Daniel Paape
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Luca Settimo
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Anna Dimitriou
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Joanna Wielinska
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Graeme Smart
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Laura F Anderson
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | | | - Siu Pui Ying Kelly
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Hasan Ms Ibrahim
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Fabian Hulpia
- Laboratory for Medicinal Chemistry, University of Ghent, Ghent, Belgium
| | - Mohammed I Al-Salabi
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Anthonius A Eze
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Teresa Sprenger
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Ibrahim A Teka
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Simon Gudin
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Simone Weyand
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Mark Field
- School of Life Sciences, University of Dundee, Dundee, United Kingdom.,Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Ceske Budejovice, Czech Republic
| | | | - Richard R Tidwell
- Department of Pathology and Lab Medicine, University of North Carolina at Chapel Hill, Chapel Hill, United States
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Paul O'Neill
- Department of Chemistry, University of Liverpool, Liverpool, United Kingdom
| | - David W Boykin
- Chemistry Department, Georgia State University, Atlanta, United States
| | - Ulrich Zachariae
- Computational Biology Centre for Translational and Interdisciplinary Research, University of Dundee, Dundee, United Kingdom
| | - Harry P De Koning
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
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6
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Campagnaro GD, de Koning HP. Purine and pyrimidine transporters of pathogenic protozoa - conduits for therapeutic agents. Med Res Rev 2020; 40:1679-1714. [PMID: 32144812 DOI: 10.1002/med.21667] [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: 11/11/2019] [Revised: 02/12/2020] [Accepted: 02/18/2020] [Indexed: 02/06/2023]
Abstract
Purines and pyrimidines are essential nutrients for any cell. Most organisms are able to synthesize their own purines and pyrimidines, but this ability was lost in protozoans that adapted to parasitism, leading to a great diversification in transporter activities in these organisms, especially for the acquisition of amino acids and nucleosides from their hosts throughout their life cycles. Many of these transporters have been shown to have sufficiently different substrate affinities from mammalian transporters, making them good carriers for therapeutic agents. In this review, we summarize the knowledge obtained on purine and pyrimidine activities identified in protozoan parasites to date and discuss their importance for the survival of these parasites and as drug carriers, as well as the perspectives of developments in the field.
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Affiliation(s)
- Gustavo D Campagnaro
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, 120 University Place, Glasgow, UK
| | - Harry P de Koning
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, 120 University Place, Glasgow, UK
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7
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Hulpia F, Mabille D, Campagnaro GD, Schumann G, Maes L, Roditi I, Hofer A, de Koning HP, Caljon G, Van Calenbergh S. Combining tubercidin and cordycepin scaffolds results in highly active candidates to treat late-stage sleeping sickness. Nat Commun 2019; 10:5564. [PMID: 31804484 PMCID: PMC6895180 DOI: 10.1038/s41467-019-13522-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Accepted: 11/13/2019] [Indexed: 12/29/2022] Open
Abstract
African trypanosomiasis is a disease caused by Trypanosoma brucei parasites with limited treatment options. Trypanosoma is unable to synthesize purines de novo and relies solely on their uptake and interconversion from the host, constituting purine nucleoside analogues a potential source of antitrypanosomal agents. Here we combine structural elements from known trypanocidal nucleoside analogues to develop a series of 3’-deoxy-7-deazaadenosine nucleosides, and investigate their effects against African trypanosomes. 3’-Deoxytubercidin is a highly potent trypanocide in vitro and displays curative activity in animal models of acute and CNS-stage disease, even at low doses and oral administration. Whole-genome RNAi screening reveals that the P2 nucleoside transporter and adenosine kinase are involved in the uptake and activation, respectively, of this analogue. This is confirmed by P1 and P2 transporter assays and nucleotide pool analysis. 3’-Deoxytubercidin is a promising lead to treat late-stage sleeping sickness. Trypanosoma brucei relies on uptake and conversion of purines from the host, which constitutes a potential drug target. Here, Hulpia et al. combine structural elements from known trypanocidal nucleoside analogues and develop a potent trypanocide with curative activity in animal models of acute and late stage sleeping sickness.
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Affiliation(s)
- Fabian Hulpia
- Laboratory for Medicinal Chemistry (Campus Heymans), Ghent University, Ottergemsesteenweg 460, 9000, Gent, Belgium
| | - Dorien Mabille
- Laboratory of Microbiology, Parasitology and Hygiene (LMPH), University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium
| | - Gustavo D Campagnaro
- College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, G12 8TA, UK
| | - Gabriela Schumann
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Louis Maes
- Laboratory of Microbiology, Parasitology and Hygiene (LMPH), University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium
| | - Isabel Roditi
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Anders Hofer
- Department of Medical Biochemistry and Biophysics, Umeå University, 901 87, Umeå, Sweden
| | - Harry P de Koning
- College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, G12 8TA, UK
| | - Guy Caljon
- Laboratory of Microbiology, Parasitology and Hygiene (LMPH), University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium
| | - Serge Van Calenbergh
- Laboratory for Medicinal Chemistry (Campus Heymans), Ghent University, Ottergemsesteenweg 460, 9000, Gent, Belgium.
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8
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Campagnaro GD, de Freitas Nascimento J, Girard RB, Silber AM, de Koning HP. Cloning and characterisation of the Equilibrative Nucleoside Transporter family of Trypanosoma cruzi: ultra-high affinity and selectivity to survive in the intracellular niche. Biochim Biophys Acta Gen Subj 2018; 1862:2750-2763. [DOI: 10.1016/j.bbagen.2018.08.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 08/22/2018] [Accepted: 08/23/2018] [Indexed: 12/27/2022]
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9
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Campagnaro GD, Alzahrani KJ, Munday JC, De Koning HP. Trypanosoma brucei bloodstream forms express highly specific and separate transporters for adenine and hypoxanthine; evidence for a new protozoan purine transporter family? Mol Biochem Parasitol 2018; 220:46-56. [DOI: 10.1016/j.molbiopara.2018.01.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 01/10/2018] [Accepted: 01/19/2018] [Indexed: 10/18/2022]
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10
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El Kouni MH. Pyrimidine metabolism in schistosomes: A comparison with other parasites and the search for potential chemotherapeutic targets. Comp Biochem Physiol B Biochem Mol Biol 2017; 213:55-80. [PMID: 28735972 PMCID: PMC5593796 DOI: 10.1016/j.cbpb.2017.07.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 06/29/2017] [Accepted: 07/03/2017] [Indexed: 12/18/2022]
Abstract
Schistosomes are responsible for the parasitic disease schistosomiasis, an acute and chronic parasitic ailment that affects >240 million people in 70 countries worldwide. It is the second most devastating parasitic disease after malaria. At least 200,000 deaths per year are associated with the disease. In the absence of the availability of vaccines, chemotherapy is the main stay for combating schistosomiasis. The antischistosomal arsenal is currently limited to a single drug, Praziquantel, which is quite effective with a single-day treatment and virtually no host-toxicity. Recently, however, the question of reduced activity of Praziquantel has been raised. Therefore, the search for alternative antischistosomal drugs merits the study of new approaches of chemotherapy. The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Pyrimidine metabolism is an excellent target for such studies. Schistosomes, unlike most of the host tissues, require a very active pyrimidine metabolism for the synthesis of DNA and RNA. This is essential for the production of the enormous numbers of eggs deposited daily by the parasite to which the granulomas response precipitates the pathogenesis of schistosomiasis. Furthermore, there are sufficient differences between corresponding enzymes of pyrimidine metabolism from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Specificities of pyrimidine transport also diverge significantly between parasites and their mammalian host. This review deals with studies on pyrimidine metabolism in schistosomes and highlights the unique characteristic of this metabolism that could constitute excellent potential targets for the design of safe and effective antischistosomal drugs. In addition, pyrimidine metabolism in schistosomes is compared with that in other parasites where studies on pyrimidine metabolism have been more elaborate, in the hope of providing leads on how to identify likely chemotherapeutic targets which have not been looked at in schistosomes.
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Affiliation(s)
- Mahmoud H El Kouni
- Department of Pharmacology and Toxicology, Center for AIDS Research, Comprehensive Cancer Center, General Clinical Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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9-(2'-Deoxy-2'-Fluoro-β-d-Arabinofuranosyl) Adenine Is a Potent Antitrypanosomal Adenosine Analogue That Circumvents Transport-Related Drug Resistance. Antimicrob Agents Chemother 2017; 61:AAC.02719-16. [PMID: 28373184 PMCID: PMC5444181 DOI: 10.1128/aac.02719-16] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 03/27/2017] [Indexed: 01/25/2023] Open
Abstract
Current chemotherapy against African sleeping sickness, a disease caused by the protozoan parasite Trypanosoma brucei, is limited by toxicity, inefficacy, and drug resistance. Nucleoside analogues have been successfully used to cure T. brucei-infected mice, but they have the limitation of mainly being taken up by the P2 nucleoside transporter, which, when mutated, is a common cause of multidrug resistance in T. brucei We report here that adenine arabinoside (Ara-A) and the newly tested drug 9-(2'-deoxy-2'-fluoro-β-d-arabinofuranosyl) adenine (FANA-A) are instead taken up by the P1 nucleoside transporter, which is not associated with drug resistance. Like Ara-A, FANA-A was found to be resistant to cleavage by methylthioadenosine phosphorylase, an enzyme that protects T. brucei against the antitrypanosomal effects of deoxyadenosine. Another important factor behind the selectivity of nucleoside analogues is how well they are phosphorylated within the cell. We found that the T. brucei adenosine kinase had a higher catalytic efficiency with FANA-A than the mammalian enzyme, and T. brucei cells treated with FANA-A accumulated high levels of FANA-A triphosphate, which even surpassed the level of ATP and led to cell cycle arrest, inhibition of DNA synthesis, and the accumulation of DNA breaks. FANA-A inhibited nucleic acid biosynthesis and parasite proliferation with 50% effective concentrations (EC50s) in the low nanomolar range, whereas mammalian cell proliferation was inhibited in the micromolar range. Both Ara-A and FANA-A, in combination with deoxycoformycin, cured T. brucei-infected mice, but FANA-A did so at a dose 100 times lower than that of Ara-A.
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Targeting the parasite's DNA with methyltriazenyl purine analogs is a safe, selective, and efficacious antitrypanosomal strategy. Antimicrob Agents Chemother 2015; 59:6708-16. [PMID: 26282430 PMCID: PMC4604408 DOI: 10.1128/aac.00596-15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 07/22/2015] [Indexed: 12/04/2022] Open
Abstract
The human and veterinary disease complex known as African trypanosomiasis continues to inflict significant global morbidity, mortality, and economic hardship. Drug resistance and toxic side effects of old drugs call for novel and unorthodox strategies for new and safe treatment options. We designed methyltriazenyl purine prodrugs to be rapidly and selectively internalized by the parasite, after which they disintegrate into a nontoxic and naturally occurring purine nucleobase, a simple triazene-stabilizing group, and the active toxin: a methyldiazonium cation capable of damaging DNA by alkylation. We identified 2-(3-acetyl-3-methyltriazen-1-yl)-6-hydroxypurine (compound 1) as a new lead compound, which showed submicromolar potency against Trypanosoma brucei, with a selectivity index of >500, and it demonstrated a curative effect in animal models of acute trypanosomiasis. We investigated the mechanism of action of this lead compound and showed that this molecule has significantly higher affinity for parasites over mammalian nucleobase transporters, and it does not show cross-resistance with current first-line drugs. Once selectively accumulated inside the parasite, the prodrug releases a DNA-damaging methyldiazonium cation. We propose that ensuing futile cycles of attempted mismatch repair then lead to G2/M phase arrest and eventually cell death, as evidenced by the reduced efficacy of this purine analog against a mismatch repair-deficient (MSH2−/−) trypanosome cell line. The observed absence of genotoxicity, hepatotoxicity, and cytotoxicity against mammalian cells revitalizes the idea of pursuing parasite-selective DNA alkylators as a safe chemotherapeutic option for the treatment of human and animal trypanosomiasis.
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Li Q, Leija C, Rijo-Ferreira F, Chen J, Cestari I, Stuart K, Tu BP, Phillips MA. GMP synthase is essential for viability and infectivity of Trypanosoma brucei despite a redundant purine salvage pathway. Mol Microbiol 2015; 97:1006-20. [PMID: 26043892 DOI: 10.1111/mmi.13083] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/04/2015] [Indexed: 12/28/2022]
Abstract
The causative agent of human African trypanosomiasis, Trypanosoma brucei, lacks de novo purine biosynthesis and depends on purine salvage from the host. The purine salvage pathway is redundant and contains two routes to guanosine-5'-monophosphate (GMP) formation: conversion from xanthosine-5'-monophosphate (XMP) by GMP synthase (GMPS) or direct salvage of guanine by hypoxanthine-guanine phosphoribosyltransferase (HGPRT). We show recombinant T. brucei GMPS efficiently catalyzes GMP formation. Genetic knockout of GMPS in bloodstream parasites led to depletion of guanine nucleotide pools and was lethal. Growth of gmps null cells was only rescued by supraphysiological guanine concentrations (100 μM) or by expression of an extrachromosomal copy of GMPS. Hypoxanthine was a competitive inhibitor of guanine rescue, consistent with a common uptake/metabolic conversion mechanism. In mice, gmps null parasites were unable to establish an infection demonstrating that GMPS is essential for virulence and that plasma guanine is insufficient to support parasite purine requirements. These data validate GMPS as a potential therapeutic target for treatment of human African trypanosomiasis. The ability to strategically inhibit key metabolic enzymes in the purine pathway unexpectedly bypasses its functional redundancy by exploiting both the nature of pathway flux and the limited nutrient environment of the parasite's extracellular niche.
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Affiliation(s)
- Qiong Li
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA
| | - Christopher Leija
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA
| | - Filipa Rijo-Ferreira
- Department of Neuroscience, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.,Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.,Graduate Program in Areas of Basic and Applied Biology, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
| | - Jun Chen
- Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA
| | - Igor Cestari
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA, 98109-5219, USA
| | - Kenneth Stuart
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA, 98109-5219, USA
| | - Benjamin P Tu
- Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA
| | - Margaret A Phillips
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA
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Munday JC, Tagoe DNA, Eze AA, Krezdorn JAM, Rojas López KE, Alkhaldi AAM, McDonald F, Still J, Alzahrani KJ, Settimo L, De Koning HP. Functional analysis of drug resistance-associated mutations in the Trypanosoma brucei adenosine transporter 1 (TbAT1) and the proposal of a structural model for the protein. Mol Microbiol 2015; 96:887-900. [PMID: 25708978 PMCID: PMC4755147 DOI: 10.1111/mmi.12979] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/21/2015] [Indexed: 02/01/2023]
Abstract
The Trypanosoma brucei aminopurine transporter P2/TbAT1 has long been implicated in the transport of, and resistance to, the diamidine and melaminophenyl arsenical classes of drugs that form the backbone of the pharmacopoeia against African trypanosomiasis. Genetic alterations including deletions and single nucleotide polymorphisms (SNPs) have been observed in numerous strains and clinical isolates. Here, we systematically investigate each reported mutation and assess their effects on transporter function after expression in a tbat1(-/-) T. brucei line. Out of a set of six reported SNPs from a reported 'resistance allele', none significantly impaired sensitivity to pentamidine, diminazene or melarsoprol, relative to the TbAT1-WT allele, although several combinations, and the deletion of the codon for residue F316, resulted in highly significant impairment. These combinations of SNPs, and ΔF316, also strongly impaired the uptake of [(3)H]-adenosine and [(3)H]-diminazene, identical to the tbat1(-/-) control. The TbAT1 protein model predicted that residues F19, D140 and F316 interact with the substrate of the transporter. Mutation of D140 to alanine resulted in an inactive transporter, whereas the mutation F19A produced a transporter with a slightly increased affinity for [(3)H]-diminazene but reduced the uptake rate. The results presented here validate earlier hypotheses of drug binding motifs for TbAT1.
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Affiliation(s)
- Jane C Munday
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, UK
| | - Daniel N A Tagoe
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Department of Laboratory Technology, University of Cape Coast, Cape Coast, Ghana
| | - Anthonius A Eze
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Department of Medical Biochemistry, College of Medicine, University of Nigeria, Enugu Campus, Enugu, Nigeria
| | - Jessica A M Krezdorn
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
| | - Karla E Rojas López
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
| | - Abdulsalam A M Alkhaldi
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Department of Biology, College of Science, Aljouf University, Sakaka, Saudi Arabia
| | - Fiona McDonald
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
| | - Jennifer Still
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
| | - Khalid J Alzahrani
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Faculty of Medical Sciences, Taif University, Taif, Saudi Arabia
| | - Luca Settimo
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
- Department of Chemistry and Chemical Biology, 417 Egan Research Center, Northeastern University, 360 Huntington Avenue, Boston, MA, 02115, USA
| | - Harry P De Koning
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8TA, UK
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15
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Alkhaldi AAM, Creek DJ, Ibrahim H, Kim DH, Quashie NB, Burgess KE, Changtam C, Barrett MP, Suksamrarn A, de Koning HP. Potent trypanocidal curcumin analogs bearing a monoenone linker motif act on trypanosoma brucei by forming an adduct with trypanothione. Mol Pharmacol 2014; 87:451-64. [PMID: 25527638 DOI: 10.1124/mol.114.096016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
We have previously reported that curcumin analogs with a C7 linker bearing a C4-C5 olefinic linker with a single keto group at C3 (enone linker) display midnanomolar activity against the bloodstream form of Trypanosoma brucei. However, no clear indication of their mechanism of action or superior antiparasitic activity relative to analogs with the original di-ketone curcumin linker was apparent. To further investigate their utility as antiparasitic agents, we compare the cellular effects of curcumin and the enone linker lead compound 1,7-bis(4-hydroxy-3-methoxyphenyl)hept-4-en-3-one (AS-HK014) here. An AS-HK014-resitant line, trypanosomes adapted to AS-HK014 (TA014), was developed by in vitro exposure to the drug. Metabolomic analysis revealed that exposure to AS-HK014, but not curcumin, rapidly depleted glutathione and trypanothione in the wild-type line, although almost all other metabolites were unchanged relative to control. In TA014 cells, thiol levels were similar to untreated wild-type cells and not significantly depleted by AS-HK014. Adducts of AS-HK014 with both glutathione and trypanothione were identified in AS-HK014-exposed wild-type cells and reproduced by chemical reaction. However, adduct accumulation in sensitive cells was much lower than in resistant cells. TA014 cells did not exhibit any changes in sequence or protein levels of glutathione synthetase and γ-glutamylcysteine synthetase relative to wild-type cells. We conclude that monoenone curcuminoids have a different mode of action than curcumin, rapidly and specifically depleting thiol levels in trypanosomes by forming an adduct. This adduct may ultimately be responsible for the highly potent trypanocidal and antiparasitic activity of the monoenone curcuminoids.
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Affiliation(s)
- Abdulsalam A M Alkhaldi
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Darren J Creek
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Hasan Ibrahim
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Dong-Hyun Kim
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Neils B Quashie
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Karl E Burgess
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Chatchawan Changtam
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Michael P Barrett
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Apichart Suksamrarn
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
| | - Harry P de Koning
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom (A.A.M.A, D.J.C., H.I., D.-H.K., N.B.Q., K.E.B., M.P.B., H.P.K.); Department of Biology, College of Science, Aljouf University, Skaka, Kingdom of Saudi Arabia (A.A.M.A); Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Australia (D.J.C.); Faculty of Science, Department of Zoology, Sebha University, Libya (H.I.); Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham, United Kingdom (D.-H.K.); Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, Accra, Ghana (N.B.Q.); Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (C.C.); Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom (M.P.B.); and Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok, Thailand (A.S.)
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Lüscher A, Lamprea-Burgunder E, Graf FE, de Koning HP, Mäser P. Trypanosoma brucei adenine-phosphoribosyltransferases mediate adenine salvage and aminopurinol susceptibility but not adenine toxicity. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2013; 4:55-63. [PMID: 24596669 PMCID: PMC3940079 DOI: 10.1016/j.ijpddr.2013.12.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Revised: 11/30/2013] [Accepted: 12/03/2013] [Indexed: 11/30/2022]
Abstract
African trypanosomes possess two distinct adenine phosphoribosyltransferases. Trypanosoma brucei TbAPRT1 is cytosolic, TbAPRT2 localizes to the glycosome. Aprt1,2 null mutants are viable but do not incorporate adenine into nucleotides. Aprt1,2 null mutants are resistant to aminopurinol but still sensitive to adenine. Aminopurinol is a trypanocide with submicromolar activity against T. brucei.
African trypanosomes, like all obligate parasitic protozoa, cannot synthesize purines de novo and import purines from their hosts to build nucleic acids. The purine salvage pathways of Trypanosoma brucei being redundant, none of the involved enzymes is likely to be essential. Nevertheless they can be of pharmacological interest due to their role in activation of purine nucleobase or nucleoside analogues, which only become toxic when converted to nucleotides. Aminopurine antimetabolites, in particular, are potent trypanocides and even adenine itself is toxic to trypanosomes at elevated concentrations. Here we report on the T. brucei adenine phosphoribosyltransferases TbAPRT1 and TbAPRT2, encoded by the two genes Tb927.7.1780 and Tb927.7.1790, located in tandem on chromosome seven. The duplication is syntenic in all available Trypanosoma genomes but not in Leishmania. While TbAPRT1 is cytosolic, TbAPRT2 possesses a glycosomal targeting signal and co-localizes with the glycosomal marker aldolase. Interestingly, the distribution of glycosomal targeting signals among trypanosomatid adenine phosphoribosyltransferases is not consistent with their phylogeny, indicating that the acquisition of adenine salvage to the glycosome happened after the radiation of Trypanosoma. Double null mutant T. brucei Δtbaprt1,2 exhibited no growth phenotype but no longer incorporated exogenous adenine into the nucleotide pool. This, however, did not reduce their sensitivity to adenine. The Δtbaprt1,2 trypanosomes were resistant to the adenine isomer aminopurinol, indicating that it is activated by phosphoribosyl transfer. Aminopurinol was about 1000-fold more toxic to bloodstream-form T. brucei than the corresponding hypoxanthine isomer allopurinol. Aminopurinol uptake was not dependent on the aminopurine permease P2 that has been implicated in drug resistance.
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Affiliation(s)
- Alexandra Lüscher
- Institute of Cell Biology, University of Bern, 3012 Bern, Switzerland
| | | | - Fabrice E Graf
- Swiss Tropical and Public Health Institute, 4051 Basel, Switzerland ; University of Basel, 4000 Basel, Switzerland
| | - Harry P de Koning
- Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow G12 8RA, UK
| | - Pascal Mäser
- Swiss Tropical and Public Health Institute, 4051 Basel, Switzerland ; University of Basel, 4000 Basel, Switzerland
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17
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Ali JAM, Tagoe DNA, Munday JC, Donachie A, Morrison LJ, de Koning HP. Pyrimidine biosynthesis is not an essential function for Trypanosoma brucei bloodstream forms. PLoS One 2013; 8:e58034. [PMID: 23505454 PMCID: PMC3591441 DOI: 10.1371/journal.pone.0058034] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Accepted: 01/29/2013] [Indexed: 11/18/2022] Open
Abstract
Background African trypanosomes are capable of both pyrimidine biosynthesis and salvage of preformed pyrimidines from the host, but it is unknown whether either process is essential to the parasite. Methodology/Principal Findings Pyrimidine requirements for growth were investigated using strictly pyrimidine-free media, with or without single added pyrimidine sources. Growth rates of wild-type bloodstream form Trypanosoma brucei brucei were unchanged in pyrimidine-free medium. The essentiality of the de novo pyrimidine biosynthesis pathway was studied by knocking out the PYR6-5 locus that produces a fusion product of orotate phosphoribosyltransferase (OPRT) and Orotidine Monophosphate Decarboxylase (OMPDCase). The pyrimidine auxotroph was dependent on a suitable extracellular pyrimidine source. Pyrimidine starvation was rapidly lethal and non-reversible, causing incomplete DNA content in new cells. The phenotype could be rescued by addition of uracil; supplementation with uridine, 2′deoxyuridine, and cytidine allowed a diminished growth rate and density. PYR6-5−/− trypanosomes were more sensitive to pyrimidine antimetabolites and displayed increased uracil transport rates and uridine phosphorylase activity. Pyrimidine auxotrophs were able to infect mice although the infection developed much more slowly than infection with the parental, prototrophic trypanosome line. Conclusions/Significance Pyrimidine salvage was not an essential function for bloodstream T. b. brucei. However, trypanosomes lacking de novo pyrimidine biosynthesis are completely dependent on an extracellular pyrimidine source, strongly preferring uracil, and display reduced infectivity. As T. brucei are able to salvage sufficient pyrimidines from the host environment, the pyrimidine biosynthesis pathway is not a viable drug target, although any interruption of pyrimidine supply was lethal.
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Affiliation(s)
- Juma A. M. Ali
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Faculty of Science, Department of Zoology, Al Jabal Al Gharbi University, Gharyan, Libya
| | - Daniel N. A. Tagoe
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Jane C. Munday
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom
| | - Anne Donachie
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Liam J. Morrison
- Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow, United Kingdom
- Roslin Institute, University of Edinburgh, Easter Bush, United Kingdom
| | - Harry P. de Koning
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- * E-mail:
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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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19
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Ibrahim HMS, Al-Salabi MI, El Sabbagh N, Quashie NB, Alkhaldi AAM, Escale R, Smith TK, Vial HJ, de Koning HP. Symmetrical choline-derived dications display strong anti-kinetoplastid activity. J Antimicrob Chemother 2010; 66:111-25. [PMID: 21078603 DOI: 10.1093/jac/dkq401] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
OBJECTIVES to investigate the anti-kinetoplastid activity of choline-derived analogues with previously reported antimalarial efficacy. METHODS from an existing choline analogue library, seven antimalarial compounds, representative of the first-, second- and third-generation analogues previously developed, were assessed for activity against Trypanosoma and Leishmania spp. Using a variety of techniques, the effects of choline analogue exposure on the parasites were documented and a preliminary investigation of their mode of action was performed. RESULTS the activities of choline-derived compounds against Trypanosoma brucei and Leishmania mexicana were determined. The compounds displayed promising anti-kinetoplastid activity, particularly against T. brucei, to which 4/7 displayed submicromolar EC(50) values for the wild-type strain. Low micromolar concentrations of most compounds cleared trypanosome cultures within 24-48 h. The compounds inhibit a choline transporter in Leishmania, but their entry may not depend only on this carrier; T. b. brucei lacks a choline carrier and the mode of uptake remains unclear. The compounds had no effect on the overall lipid composition of the cells, cell cycle progression or cyclic adenosine monophosphate production or short-term effects on intracellular calcium levels. However, several of the compounds, displayed pronounced effects on the mitochondrial membrane potential; this action was not associated with production of reactive oxygen species but rather with a slow rise of intracellular calcium levels and DNA fragmentation. CONCLUSIONS the choline analogues displayed strong activity against kinetoplastid parasites, particularly against T. b. brucei. In contrast to their antimalarial activity, they did not act on trypanosomes by disrupting choline salvage or phospholipid metabolism, instead disrupting mitochondrial function, leading to chromosomal fragmentation.
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Affiliation(s)
- Hasan M S Ibrahim
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, UK
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20
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Evaluation of nucleoside hydrolase inhibitors for treatment of African trypanosomiasis. Antimicrob Agents Chemother 2010; 54:1900-8. [PMID: 20194690 DOI: 10.1128/aac.01787-09] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this paper, we present the biochemical and biological evaluation of N-arylmethyl-substituted iminoribitol derivatives as potential chemotherapeutic agents against trypanosomiasis. Previously, a library of 52 compounds was designed and synthesized as potent and selective inhibitors of Trypanosoma vivax inosine-adenosine-guanosine nucleoside hydrolase (IAG-NH). However, when the compounds were tested against bloodstream-form Trypanosoma brucei brucei, only one inhibitor, N-(9-deaza-adenin-9-yl)methyl-1,4-dideoxy-1,4-imino-d-ribitol (UAMC-00363), displayed significant activity (mean 50% inhibitory concentration [IC(50)] +/- standard error, 0.49 +/- 0.31 microM). Validation in an in vivo model of African trypanosomiasis showed promising results for this compound. Several experiments were performed to investigate why only UAMC-00363 showed antiparasitic activity. First, the compound library was screened against T. b. brucei IAG-NH and inosine-guanosine nucleoside hydrolase (IG-NH) to confirm the previously demonstrated inhibitory effects of the compounds on T. vivax IAG-NH. Second, to verify the uptake of these compounds by T. b. brucei, their affinities for the nucleoside P1 and nucleoside/nucleobase P2 transporters of T. b. brucei were tested. Only UAMC-00363 displayed significant affinity for the P2 transporter. It was also shown that UAMC-00363 is concentrated in the cell via at least one additional transporter, since P2 knockout mutants of T. b. brucei displayed no resistance to the compound. Consequently, no cross-resistance to the diamidine or the melaminophenyl arsenical classes of trypanocides is expected. Third, three enzymes of the purine salvage pathway of procyclic T. b. brucei (IAG-NH, IG-NH, and methylthioadenosine phosphorylase [MTAP]) were investigated using RNA interference. The findings from all these studies showed that it is probably not sufficient to target only the nucleoside hydrolase activity to block the purine salvage pathway of T. b. brucei and that, therefore, it is possible that UAMC-00363 acts on an additional target.
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21
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A comprehensive model of purine uptake by the malaria parasite Plasmodium falciparum: identification of four purine transport activities in intraerythrocytic parasites. Biochem J 2008; 411:287-95. [PMID: 18215139 DOI: 10.1042/bj20071460] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Plasmodium falciparum is incapable of de novo purine biosynthesis, and is absolutely dependent on transporters to salvage purines from the environment. Only one low-affinity adenosine transporter has been characterized to date. In the present study we report a comprehensive study of purine nucleobase and nucleoside transport by intraerythrocytic P. falciparum parasites. Isolated trophozoites expressed (i) a high-affinity hypoxanthine transporter with a secondary capacity for purine nucleosides, (ii) a separate high-affinity transporter for adenine, (iii) a low-affinity adenosine transporter, and (iv) a low-affinity/high-capacity adenine carrier. Hypoxanthine was taken up with 12-fold higher efficiency than adenosine. Using a parasite clone with a disrupted PfNT1 (P. falciparum nucleoside transporter 1) gene we found that the high-affinity hypoxanthine/nucleoside transport activity was completely abolished, whereas the low-affinity adenosine transport activity was unchanged. Adenine transport was increased, presumably to partly compensate for the loss of the high-affinity hypoxanthine transporter. We thus propose a model for purine salvage in P. falciparum, based on the highly efficient uptake of hypoxanthine by PfNT1 and a high capacity for purine nucleoside uptake by a lower affinity carrier.
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22
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Papageorgiou I, De Koning HP, Soteriadou K, Diallinas G. Kinetic and mutational analysis of the Trypanosoma brucei NBT1 nucleobase transporter expressed in Saccharomyces cerevisiae reveals structural similarities between ENT and MFS transporters. Int J Parasitol 2007; 38:641-53. [PMID: 18036529 DOI: 10.1016/j.ijpara.2007.10.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Revised: 10/04/2007] [Accepted: 10/08/2007] [Indexed: 02/04/2023]
Abstract
Parasitic protozoa are unable to synthesise purines de novo and thus depend on the uptake of nucleosides and nucleobases across their plasma membrane through specific transporters. A number of nucleoside and nucleobase transporters from Trypanosoma brucei brucei and Leishmania major have recently been characterised and shown to belong to the equilibrative nucleoside transporter (ENT) family. A number of studies have demonstrated the functional importance of particular transmembrane segments (TMS) in nucleoside-specific ENT proteins. TbNBT1, one of only three bona fide nucleobase-selective members of the ENT family, has previously been shown to be a high-affinity transporter for purine nucleobases and guanosine. In this study, we use the Saccharomyces cerevisiae expression system to build a biochemical model of how TbNBT1 recognises nucleobases. We next performed random in vitro and site-directed mutagenesis to identify residues critical for TbNBT1 function. The identification of residues likely to contribute to permeant binding, when combined with a structural model of TbNBT1 obtained by homology threading, yield a tentative three-dimensional model of the transporter binding site that is consistent with the binding model emerging from the biochemical data. The model strongly suggests the involvement of TMS5, TMS7 and TMS8 in TbNBT1 function. This situation is very similar to that concerning transporters of the major facilitator superfamily (MFS), one of which was used as a template for the threading. This point raises the possibility that ENT and MFS carriers, despite being considered evolutionarily distinct, might in fact share similar topologies and substrate translocations pathways.
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Affiliation(s)
- I Papageorgiou
- Department of Botany, University of Athens, Panepistimioupolis, Athens 15781, Greece
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23
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Bridges DJ, Gould MK, Nerima B, Mäser P, Burchmore RJS, de Koning HP. Loss of the high-affinity pentamidine transporter is responsible for high levels of cross-resistance between arsenical and diamidine drugs in African trypanosomes. Mol Pharmacol 2007; 71:1098-108. [PMID: 17234896 DOI: 10.1124/mol.106.031351] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Treatment of many infectious diseases is under threat from drug resistance. Understanding the mechanisms of resistance is as high a priority as the development of new drugs. We have investigated the basis for cross-resistance between the diamidine and melaminophenyl arsenical classes of drugs in African trypanosomes. We induced high levels of pentamidine resistance in a line without the tbat1 gene that encodes the P2 transporter previously implicated in drug uptake. We isolated independent clones that displayed very considerable cross-resistance with melarsen oxide but not phenylarsine oxide and reduced uptake of [(3)H]pentamidine. In particular, the high-affinity pentamidine transport (HAPT1) activity was absent in the pentamidine-adapted lines, whereas the low affinity pentamidine transport (LAPT1) activity was unchanged. The parental tbat1(-/-) line was sensitive to lysis by melarsen oxide, and this process was inhibited by low concentrations of pentamidine, indicating the involvement of HAPT1. This pentamidine-inhibitable lysis was absent in the adapted line KO-B48. Likewise, uptake of the fluorescent diamidine 4',6-diamidino-2-phenylindole dihydrochloride was much delayed in live KO-B48 cells and insensitive to competition with up to 10 muM pentamidine. No overexpression of the Trypanosoma brucei brucei ATP-binding cassette transporter TbMRPA could be detected in KO-B48. We also show that a laboratory line of Trypanosoma brucei gambiense, adapted to high levels of resistance for the melaminophenyl arsenical drug melarsamine hydrochloride (Cymelarsan), had similarly lost TbAT1 and HAPT1 activity while retaining LAPT1 activity. It seems therefore that selection for resistance to either pentamidine or arsenical drugs can result in a similar phenotype of reduced drug accumulation, explaining the occurrence of cross-resistance.
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Affiliation(s)
- Daniel J Bridges
- Institute of Biomedical and Life Sciences, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, United Kingdom
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24
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Al-Salabi MI, Wallace LJM, Lüscher A, Mäser P, Candlish D, Rodenko B, Gould MK, Jabeen I, Ajith SN, de Koning HP. Molecular interactions underlying the unusually high adenosine affinity of a novel Trypanosoma brucei nucleoside transporter. Mol Pharmacol 2006; 71:921-9. [PMID: 17185380 DOI: 10.1124/mol.106.031559] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Trypanosoma brucei encodes a relatively high number of genes of the equilibrative nucleoside transporter (ENT) family. We report here the cloning and in-depth characterization of one T. brucei brucei ENT member, TbNT9/AT-D. This transporter was expressed in Saccharomyces cerevisiae and displayed a uniquely high affinity for adenosine (Km = 0.068 +/- 0.013 microM), as well as broader selectivity for other purine nucleosides in the low micromolar range, but was not inhibited by nucleobases or pyrimidines. This selectivity profile is consistent with the P1 transport activity observed previously in procyclic and long-slender bloodstream T. brucei, apart from the 40-fold higher affinity for adenosine than for inosine. We found that, like the previously investigated P1 activity of long/slender bloodstream trypanosomes, the 3'-hydroxy, 5'-hydroxy, N3, and N7 functional groups contribute to transporter binding. In addition, we show that the 6-position amine group of adenosine, but not the inosine 6-keto group, makes a major contribution to binding (DeltaG0 = 12 kJ/mol), explaining the different Km values of the purine nucleosides. We further found that P1 activity in procyclic and long-slender trypanosomes is pharmacologically distinct, and we identified the main gene encoding this activity in procyclic cells as NT10/AT-B. The presence of multiple P1-type nucleoside transport activities in T. brucei brucei facilitates the development of nucleoside-based treatments for African trypanosomiasis and would delay the onset of uptake-related drug resistance to such therapy. We show that both TbNT9/AT-D and NT10/AT-B transport a range of potentially therapeutic nucleoside analogs.
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Affiliation(s)
- Mohammed I Al-Salabi
- Institute of Biomedical and Life Sciences, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, United Kingdom
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25
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Gudin S, Quashie NB, Candlish D, Al-Salabi MI, Jarvis SM, Ranford-Cartwright LC, de Koning HP. Trypanosoma brucei: a survey of pyrimidine transport activities. Exp Parasitol 2006; 114:118-25. [PMID: 16620810 DOI: 10.1016/j.exppara.2006.02.018] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2005] [Revised: 02/23/2006] [Accepted: 02/24/2006] [Indexed: 11/24/2022]
Abstract
Purine uptake has been studied in many protozoan parasites in the last few years, and several of the purine transporters have been cloned. In contrast, very little is known about the salvage of preformed pyrimidines by protozoa, and no pyrimidine transporters have been cloned, yet chemotherapy based on pyrimidine nucleobases and nucleosides has been as effective as purine antimetabolites in the treatment of infectious and neoplastic disease. Here, we surveyed the presence of pyrimidine transporters in Trypanosoma brucei brucei. We could not detect any mediated uptake of thymine, thymidine or cytidine, but identified a very high-affinity transporter for cytosine, designated C1, with a K(m) value of 0.048+/-0.009 microM. We also confirmed the presence of the previously reported U1 uracil transporter and found it capable of mediating uridine uptake as well, with a K(m) of 33+/-5 microM. A higher-affinity U2 uridine transporter (K(m)=4.1+/-2.1 microM) was also identified, but efficiency of the C1 and U2-mediated transport was low. Pyrimidine antimetabolites were tested as potential trypanocidal agents and only 5-fluorouracil was found to be effective. This drug was efficiently taken up by bloodstream forms of T. b. brucei.
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Affiliation(s)
- Simon Gudin
- Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Biomedical Research Center, Glasgow G12 8TA, UK
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26
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Stoffel SA, Rodenko B, Schweingruber AM, Mäser P, de Koning HP, Schweingruber ME. Biosynthesis and uptake of thiamine (vitamin B1) in bloodstream form Trypanosoma brucei brucei and interference of the vitamin with melarsen oxide activity. Int J Parasitol 2005; 36:229-36. [PMID: 16375907 DOI: 10.1016/j.ijpara.2005.10.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2005] [Revised: 10/11/2005] [Accepted: 10/24/2005] [Indexed: 11/29/2022]
Abstract
Bloodstream forms of Trypanosoma brucei brucei were cultivated in the presence and absence of thiamine (vitamin B1) and pyridoxine (vitamin B6). The vitamins do not change growth behaviour, indicating that Trypanosoma brucei is prototrophic for the two vitamins even though in silico no bona-fide thiamine-biosynthetic genes could be identified in the T. brucei genome. Intracellularly, thiamine is mainly present in its diphosphate form. We were unable to detect significant uptake of [3H]thiamine and structural thiamine analogues such as pyrithiamine, oxithiamine and amprolium were not toxic for the bloodstream forms of T. brucei, indicating that the organism does not have an efficient uptake system for thiamine and its analogues. We have previously shown that, in the fission yeast Saccharomyces pombe, the toxicity of melarsen oxide, the pharmacologically active derivative of the frontline sleeping sickness drug melarsoprol, is abolished by thiamine and the drug is taken up by a thiamine-regulated membrane protein which is responsible for the utilization of thiamine. We show here that thiamine also has weak effects on melarsen oxide-induced growth inhibition and lysis in T. brucei. These effects were consistent with a low affinity of thiamine for the P2 adenosine transporter that is responsible for uptake of melaminophenyl arsenicals in African trypanosomes.
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Affiliation(s)
- Sabine A Stoffel
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
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27
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de Koning HP, Bridges DJ, Burchmore RJS. Purine and pyrimidine transport in pathogenic protozoa: From biology to therapy. FEMS Microbiol Rev 2005; 29:987-1020. [PMID: 16040150 DOI: 10.1016/j.femsre.2005.03.004] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2004] [Revised: 03/22/2005] [Accepted: 03/24/2005] [Indexed: 01/10/2023] Open
Abstract
Purine salvage is an essential function for all obligate parasitic protozoa studied to date and most are also capable of efficient uptake of preformed pyrimidines. Much progress has been made in the identification and characterisation of protozoan purine and pyrimidine transporters. While the genes encoding protozoan or metazoan pyrimidine transporters have yet to be identified, numerous purine transporters have now been cloned. All protozoan purine transporter-encoding genes characterised to date have been of the Equilibrative Nucleoside Transporter family conserved in a great variety of eukaryote organisms. However, these protozoan transporters have been shown to be sufficiently different from mammalian transporters to mediate selective uptake of therapeutic agents. Recent studies are increasingly addressing the structure and substrate recognition mechanisms of these vital transport proteins.
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Affiliation(s)
- Harry P de Koning
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK.
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28
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Geiser F, Lüscher A, de Koning HP, Seebeck T, Mäser P. Molecular pharmacology of adenosine transport in Trypanosoma brucei: P1/P2 revisited. Mol Pharmacol 2005; 68:589-95. [PMID: 15933219 DOI: 10.1124/mol.104.010298] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Trypanosoma brucei are unicellular parasites that cause sleeping sickness in humans and nagana in livestock. Trypanosomes salvage purines from their hosts through a variety of transporters, of which adenosine permeases deserve particular attention because of their role in drug sensitivity. T. brucei possess two distinct adenosine transport systems, P1 and P2, the latter of which also mediates cellular uptake of the drugs melarsoprol and pentamidine. Loss or mutation of P2 has been associated with drug resistance and sleeping sickness treatment failures. However, genetic disruption in Trypanosoma brucei brucei of the gene encoding P2, TbAT1, reduced the susceptibility to melarsoprol and pentamidine by only a factor of approximately 2. In this study, we show stronger phenotypes of the tbat1 null mutant with respect to its sensitivity toward toxic adenosine analogs. Compared with parental TbAT1+/+ trypanosomes, the tbat1-/- mutant is 77-fold less sensitive to tubercidin and 14-fold less sensitive to cordycepin. Resistance is further increased by the addition of inosine but is reverted by adenine. It is surprising that the tbat1-/- mutant grows faster than TbAT1+/+ trypanosomes and that it overexpresses genes of the TbNT cluster encoding P1-type transporters. These unexpected phenotypes show that there are conditions other than drug pressure under which loss of P2 may confer a selective advantage to bloodstream-form trypanosomes. Overexpression of P1 by trypanosomes after loss of P2 indicates that combinatorial chemotherapy with trypanocidal P1 and P2 substrates may be a promising strategy to prevent drug resistance in sleeping sickness.
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Affiliation(s)
- Federico Geiser
- Institute of Cell Biology, Baltzerstrasse 4, CH-3012 Bern, Switzerland
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29
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Wallace LJM, Candlish D, Hagos A, Seley KL, de Koning HP. Selective transport of a new class of purine antimetabolites by the protozoan parasite Trypanosoma brucei. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2005; 23:1441-4. [PMID: 15571273 DOI: 10.1081/ncn-200027660] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Purine antimetabolites have been very successful therapeutic agents against a host of infectious diseases and malignancies. Success of the treatment relies as much on the efficient accumulation by the target cell or organism as it does on selective action on a vital biochemical pathway of the target cell. Here we compare the ability of a new class of tricyclic purine antimetabolites to interact with transporters from human erythrocytes or Trypanosoma brucei. We show that these compounds display a remarkable selectivity for the parasite's transporters. The adenine analogue showed greater trypanocidal activity than the hypoxanthine or guanine analogues in vitro.
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Affiliation(s)
- L J M Wallace
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, University of Glasgow, Glasgow, UK
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30
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Natto MJ, Wallace LJM, Candlish D, Al-Salabi MI, Coutts SE, de Koning HP. Trypanosoma brucei: expression of multiple purine transporters prevents the development of allopurinol resistance. Exp Parasitol 2005; 109:80-6. [PMID: 15687014 DOI: 10.1016/j.exppara.2004.11.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2004] [Revised: 11/03/2004] [Accepted: 11/18/2004] [Indexed: 11/26/2022]
Abstract
Allopurinol is a hypoxanthine analogue used to treat Leishmania infections that also displays activity against the related parasite Trypanosoma brucei. We have investigated the ease by which resistance to this drug is established in Trypanosoma brucei brucei and correlated this to the mechanisms by which it is accumulated by the parasite. Long-term exposure of procyclic T. b. brucei to 3mM allopurinol did not induce resistance. This appears to be related to the fact that allopurinol was taken up through two distinct nucleobase transporters, H1 and H4, both with high affinity for the drug. The apparent Km for [3H]allopurinol transport by H4 (2.1+/-0.4 microM) was determined by expressing the encoding gene in Saccharomyces cerevisiae. Long-term allopurinol exposure did not change Km (hypoxanthine), Ki (allopurinol), or Vmax values of either H1 or H4 transporters and the cells retained their ability to proliferate with hypoxanthine as sole purine source. This study shows that transport-related resistance to purine antimetabolites is not easily induced in Trypanosoma spp. as long as uptake is mediated by multiple transporters.
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Affiliation(s)
- Manal J Natto
- Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, UK
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Landfear SM, Ullman B, Carter NS, Sanchez MA. Nucleoside and nucleobase transporters in parasitic protozoa. EUKARYOTIC CELL 2004; 3:245-54. [PMID: 15075255 PMCID: PMC387651 DOI: 10.1128/ec.3.2.245-254.2004] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Scott M Landfear
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
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32
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Sanchez MA, Tryon R, Pierce S, Vasudevan G, Landfear SM. Functional expression and characterization of a purine nucleobase transporter gene from Leishmania major. Mol Membr Biol 2004; 21:11-8. [PMID: 14668134 DOI: 10.1080/0968768031000140845] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Leishmania major, like all the other kinetoplastid protozoa, are unable to synthesize purines and rely on purine nucleobase and nucleoside acquisition across the parasite plasma membrane by specific permeases. Although, several genes have been cloned that encode nucleoside transporters in Leishmania and Trypanosoma brucei, much less progress has been made on nucleobase transporters, especially at the molecular level. The studies reported here have cloned and expressed the first gene for a L. major nucleobase transporter, designated LmaNT3. The LmaNT3 permease shows 33% identity to L. donovani nucleoside transporter 1.1 (LdNT1.1) and is, thus, a member of the equilibrative nucleoside transporter (ENT) family. ENT family members identified to date are nucleoside transporters, some of which also transport one or several nucleobases. Functional expression studies in Xenopus laevis oocytes revealed that LmaNT3 mediates high levels of uptake of hypoxanthine, xanthine, adenine and guanine. Moreover, LmaNT3 is an high affinity transporter with K(m) values for hypoxanthine, xanthine, adenine and guanine of 16.5 +/- 1.5, 8.5 +/- 0.6, 8.5 +/- 1.1, and 8.8 +/- 4.0 microM, respectively. LmaNT3 is, thus, the first member of the ENT family identified in any organism that functions as a nucleobase rather than nucleoside or nucleoside/nucleobase transporter.
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Affiliation(s)
- Marco A Sanchez
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR 97201, USA.
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33
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Matovu E, Stewart ML, Geiser F, Brun R, Mäser P, Wallace LJM, Burchmore RJ, Enyaru JCK, Barrett MP, Kaminsky R, Seebeck T, de Koning HP. Mechanisms of arsenical and diamidine uptake and resistance in Trypanosoma brucei. EUKARYOTIC CELL 2004; 2:1003-8. [PMID: 14555482 PMCID: PMC219364 DOI: 10.1128/ec.2.5.1003-1008.2003] [Citation(s) in RCA: 166] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Sleeping sickness, caused by Trypanosoma brucei spp., has become resurgent in sub-Saharan Africa. Moreover, there is an alarming increase in treatment failures with melarsoprol, the principal agent used against late-stage sleeping sickness. In T. brucei, the uptake of melarsoprol as well as diamidines is thought to be mediated by the P2 aminopurine transporter, and loss of P2 function has been implicated in resistance to these agents. The trypanosomal gene TbAT1 has been found to encode a P2-type transporter when expressed in yeast. Here we investigate the role of TbAT1 in drug uptake and drug resistance in T. brucei by genetic knockout of TbAT1. Tbat1-null trypanosomes were deficient in P2-type adenosine transport and lacked adenosine-sensitive transport of pentamidine and melaminophenyl arsenicals. However, the null mutants were only slightly resistant to melaminophenyl arsenicals and pentamidine, while resistance to other diamidines such as diminazene was more pronounced. Nevertheless, the reduction in drug sensitivity might be of clinical significance, since mice infected with tbat1-null trypanosomes could not be cured with 2 mg of melarsoprol/kg of body weight for four consecutive days, whereas mice infected with the parental line were all cured by using this protocol. Two additional pentamidine transporters, HAPT1 and LAPT1, were still present in the null mutant, and evidence is presented that HAPT1 may be responsible for the residual uptake of melaminophenyl arsenicals. High-level arsenical resistance therefore appears to involve the loss of more than one transporter.
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Affiliation(s)
- Enock Matovu
- Institute of Cell Biology, CH-3012 Bern, Switzerland
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34
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Abstract
Drug resistance in African trypanosomes has been studied for almost a hundred years. Beginning with Paul Ehrlich's work that led to the chemoreceptor hypothesis, reduction of net drug uptake has emerged as the most frequent cause of resistance. This review, therefore, focuses on trypanosomal drug transporter genes. TbAT1 encodes purine permease P2, which mediates influx of melarsoprol and diamidines. Disruption of TbAT1 in Trypanosoma brucei reduced sensitivity to these trypanocides. TbMRPA encodes a putative trypanothione-conjugate efflux pump, and overexpression of TbMRPA in T. brucei causes melarsoprol resistance. It will be important to determine the role of TbAT1 and TbMRPA in sleeping sickness treatment failures.
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Affiliation(s)
- Pascal Mäser
- Institute of Cell Biology, University of Bern, Bern, Switzerland
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35
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Abstract
Parasites are responsible for a wide variety of infectious diseases in human as well as in domestic and wild animals, causing an enormous health and economical blight. Current containment strategies are not entirely successful and parasitic infections are on the rise. In the absence of availability of antiparasitic vaccines, chemotherapy remains the mainstay for the treatment of most parasitic diseases. However, there is an urgent need for new drugs to prevent or combat some major parasitic infections because of lack of a single effective approach for controlling the parasites (e.g., trypanosomiasis) or because some serious parasitic infections developed resistance to presently available drugs (e.g., malaria). The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Some of the most striking differences between parasites and their mammalian host are found in purine metabolism. Purine nucleotides can be synthesized by the de novo and/or the so-called "salvage" pathways. Unlike their mammalian host, most parasites studied lack the pathways for de novo purine biosynthesis and rely on the salvage pathways to meet their purine demands. Moreover, because of the great phylogenic separation between the host and the parasite, there are in some cases sufficient distinctions between corresponding enzymes of the purine salvage from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Furthermore, the specificities of purine transport, the first step in purine salvage, diverge significantly between parasites and their mammalian host. This review highlights the unique transporters and enzymes responsible for the salvage of purines in parasites that could constitute excellent potential targets for the design of safe and effective antiparasitic drugs.
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Affiliation(s)
- Mahmoud H el Kouni
- Department of Pharmacology and Toxicology, Center for AIDS Research, Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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36
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Henriques C, Sanchez MA, Tryon R, Landfear SM. Molecular and functional characterization of the first nucleobase transporter gene from African trypanosomes. Mol Biochem Parasitol 2003; 130:101-10. [PMID: 12946846 DOI: 10.1016/s0166-6851(03)00167-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
African trypanosomes are unable to synthesize purines and depend upon purine nucleoside and nucleobase transporters to salvage these compounds from their hosts. To understand the crucial role of purine salvage in the survival of these parasites, a central objective is to identify and characterize all of the purine permeases that mediate uptake of these essential nutrients. We have cloned and functionally expressed in a purine nucleobase transport deficient strain of Saccharomyces cerevisiae a novel nucleobase transporter gene, TbNT8.1, from Trypanosoma brucei. The permease encoded by this gene mediates the uptake of hypoxanthine, adenine, guanine, and xanthine with Kms in the low micromolar range. The TbNT8.1 protein is a member of the equilibrative nucleoside transporter (ENT) family of permeases that occur in organisms as diverse as protozoa and mammals. TbNT8.1 is distinct from other ENT permeases that have been identified in trypanosomes in utilizing multiple purine nucleobases, rather than purine nucleosides, as substrates and is hence the first bona fide nucleobase permease identified in these parasites. Furthermore, unlike the mRNAs for other purine transporters, TbNT8.1 mRNA is significantly more abundant in insect stage procyclic forms than in mammalian stage bloodstream forms, and the TbNT8.1 permease thus may represent a major route for purine nucleobase uptake in procyclic trypanosomes.
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Affiliation(s)
- Cristina Henriques
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201, USA
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37
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De Koning HP, Al-Salabi MI, Cohen AM, Coombs GH, Wastling JM. Identification and characterisation of high affinity nucleoside and nucleobase transporters in Toxoplasma gondii. Int J Parasitol 2003; 33:821-31. [PMID: 12865082 DOI: 10.1016/s0020-7519(03)00091-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The protozoan parasite Toxoplasma gondii depends upon salvaging the purines that it requires. We have re-analysed purine transport in T. gondii and identified novel nucleoside and nucleobase transporters. The latter transports hypoxanthine (TgNBT1; K(m)=0.91+/-0.19 microM) and is inhibited by guanine and xanthine: it is the first high affinity nucleobase transporter to be identified in an apicomplexan parasite. The previously reported nucleoside transporter, TgAT1, is low affinity with K(m) values of 105 and 134 microM for adenosine and inosine, respectively. We have now identified a second nucleoside transporter, TgAT2, which is high affinity and inhibited by adenosine, inosine, guanosine, uridine and thymidine (K(m) values 0.28-1.5 microM) as well as cytidine (K(i)=32 microM). TgAT2 also recognises several nucleoside analogues with therapeutic potential. We have investigated the basis for the broad specificity of TgAT2 and found that hydrogen bonds are formed with the 3' and 5' hydroxyl groups and that the base groups are bound through H-bonds with either N3 of the purine ring or N(3)H of the pyrimidine ring, and most probably pi-pi-stacking as well. The identification of these high affinity purine nucleobase and nucleoside transporters reconciles for the first time the low abundance of free nucleosides and nucleobases in the intracellular environment with the efficient purine salvage carried out by T. gondii.
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Affiliation(s)
- Harry P De Koning
- Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, UK.
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38
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Burchmore RJS, Wallace LJM, Candlish D, Al-Salabi MI, Beal PR, Barrett MP, Baldwin SA, de Koning HP. Cloning, heterologous expression, and in situ characterization of the first high affinity nucleobase transporter from a protozoan. J Biol Chem 2003; 278:23502-7. [PMID: 12707261 DOI: 10.1074/jbc.m301252200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
While multiple nucleoside transporters, some of which can also transport nucleobases, have been cloned in recent years from many different organisms, no sequence information is available for the high affinity, nucleobase-selective transporters of metazoa, parazoa, or protozoa. We have identified a gene, TbNBT1, from Trypanosoma brucei brucei that encodes a 435-residue protein of the equilibrative nucleoside transporter superfamily. The gene was expressed in both the procyclic and bloodstream forms of the organism. Expression of TbNBT1 in a Saccharomyces cerevisiae strain lacking an endogenous purine transporter allowed growth on adenine as sole purine source and introduced a high affinity transport activity for adenine and hypoxanthine, with Km values of 2.1 +/- 0.6 and 0.66 +/- 0.22 microm, respectively, as well as high affinity for xanthine, guanine, guanosine, and allopurinol and moderate affinity for inosine. A transporter with an indistinguishable kinetic profile was identified in T. b. brucei procyclics and designated H4. RNA interference of TbNBT1 in procyclics reduced cognate mRNA levels by approximately 80% and H4 transport activity by approximately 90%. Expression of TbNBT1 in Xenopus oocytes further confirmed that this gene encodes the first high affinity nucleobase transporter from protozoa or animals to be identified at the molecular level.
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Affiliation(s)
- Richard J S Burchmore
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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39
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Al-Salabi MI, Wallace LJM, De Koning HP. A Leishmania major nucleobase transporter responsible for allopurinol uptake is a functional homolog of the Trypanosoma brucei H2 transporter. Mol Pharmacol 2003; 63:814-20. [PMID: 12644582 DOI: 10.1124/mol.63.4.814] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nucleobase transporters play an important role in the physiology of protozoan parasites, because these organisms are purine auxotrophs and rely entirely on salvage of these vital compounds. Purine transporters have also been shown to mediate the uptake of important antiparasitic drugs. In the current study, we investigated the uptake of [(3)H]adenine, [(3)H]hypoxanthine, and [(3)H]allopurinol, an antileishmanial hypoxanthine analog, by Leishmania major. These compounds were all taken up by a single high-affinity transporter, LmNBT1, with K(m) values of 4.6 +/- 0.9, 0.71 +/- 0.07, and 54 +/- 3 microM, respectively. Guanine and xanthine fully inhibited [(3)H]adenine transport, with K(i) values of 2.8 +/- 0.7 and 23 +/- 8 microM. Using purine analogs, an inhibitor profile for LmNBT1 was obtained, which allowed the construction of a quantitative model for the interactions between the transporter binding site and the permeant. The model predicts that hypoxanthine was bound through hydrogen bonds to N(1)H, N3, N7, and N(9)H of the purine ring, with a total Gibbs free energy of -39.5 kJ/mol. The interactions with adenine were similar, except for a weak hydrogen bond to N1 (unprotonated in adenine). The predicted mode of substrate binding for LmNBT1 was almost identical to that for the Trypanosoma brucei H2 (TbH2) transporter. It is proposed that the architecture of their respective binding sites is very similar and that LmNBT1 can be named a functional homolog of TbH2.
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Affiliation(s)
- Mohammed I Al-Salabi
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Joseph Black Building, University of Glasgow, Glasgow, United Kingdom
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40
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Wallace LJM, Candlish D, De Koning HP. Different substrate recognition motifs of human and trypanosome nucleobase transporters. Selective uptake of purine antimetabolites. J Biol Chem 2002; 277:26149-56. [PMID: 12004061 DOI: 10.1074/jbc.m202835200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The therapeutic index of antimetabolites such as purine analogues is in large part determined by the extent to which it is selectively accumulated by the target cell. In the current study we have compared the transport of purine nucleobase analogues by the H2 transporter of bloodstream form Trypanosoma brucei brucei and the equilibrative nucleobase transporter of human erythrocytes. The H2 transporter forms hydrogen bonds with hypoxanthine at positions N3, N7, N(1)H, and N(9)H of the purine ring, with apparent Delta G(0) of 7.7-12.6 kJ/mol. The transporter also appears to H-bond with the amine group of adenine. The human transporter forms hydrogen bonds that form to (6)NH(2) and N1 of adenine. An H-bond is also formed with N3 and the 6-keto and amine groups of guanine but not with the protonated N1, thus explaining the low affinity for hypoxanthine. N7 and N9 do not directly interact with the human transporter in the form of H-bonds, and it is proposed that pi-pi stacking interactions contribute significantly to permeant binding. The potential for selective uptake of antimetabolites by the parasite transporter was demonstrated.
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Affiliation(s)
- Lynsey J M Wallace
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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41
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Sanchez MA, Tryon R, Green J, Boor I, Landfear SM. Six related nucleoside/nucleobase transporters from Trypanosoma brucei exhibit distinct biochemical functions. J Biol Chem 2002; 277:21499-504. [PMID: 11937511 DOI: 10.1074/jbc.m202319200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Purine nucleoside and nucleobase transporters are of fundamental importance for Trypanosoma brucei and related kinetoplastid parasites because these protozoa are not able to synthesize purines de novo and must salvage the compounds from their hosts. In the studies reported here, we have identified a family of six clustered genes in T. brucei that encode nucleoside/nucleobase transporters. These genes, TbNT2/927, TbNT3, TbNT4, TbNT5, TbNT6, and TbNT7, have predicted amino acid sequences that show high identity to each other and to TbNT2, a P1 type nucleoside transporter recently identified in our laboratory. Expression in Xenopus laevis oocytes revealed that TbNT2/927, TbNT5, TbNT6, and TbNT7 are high affinity adenosine/inosine transporters with K(m) values of <5 microm. In addition, TbNT5, and to a limited degree TbNT6 and TbNT7, also mediate the uptake of the nucleobase hypoxanthine. Ribonuclease protection assays showed that mRNA from all of the six members of this gene family are expressed in the bloodstream stage of the T. brucei life cycle but that TbNT2/927 and TbNT5 mRNAs are also expressed in the insect stage of the life cycle. These results demonstrate that T. brucei expresses multiple purine transporters with distinct substrate specificities and different patterns of expression during the parasite life cycle.
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Affiliation(s)
- Marco A Sanchez
- Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon 97201, USA.
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42
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de Koning HP, Jarvis SM. Uptake of pentamidine in Trypanosoma brucei brucei is mediated by the P2 adenosine transporter and at least one novel, unrelated transporter. Acta Trop 2001; 80:245-50. [PMID: 11700182 DOI: 10.1016/s0001-706x(01)00177-2] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Diamidine drugs such as pentamidine and berenil (diminazene aceturate) are vital drugs for the treatment of early stage human African trypanosomiasis and the corresponding veterinary condition, respectively. The action of diamidines on trypanosomes is critically dependent on their efficient uptake by the parasite. We have therefore investigated the mode of uptake of pentamidine by Trypanosoma brucei brucei, using [(125)I]iodopentamidine as a permeant. [(125)I]Iodopentamidine uptake was linear for up to 15 min and inhibited by adenosine with a K(i) value of 0.64+/-0.03 microM to a maximum of 50-70%. The adenosine-sensitive flux was also inhibited by adenine with a K(i) value of 0.44+/-0.04 microM. Iodopentamidine uptake was saturable, with the adenosine-insensitive flux displaying a K(m) of 22+/-2 microM and a V(max) of 2.2+/-0.9 pmol(10(7) cells)(-1)s(-1), whereas the adenosine-sensitive flux was inhibited by much lower iodopentamidine concentrations. These results clearly demonstrate that iodopentamidine is taken up by at least two different T. b. brucei transporters, an adenosine-sensitive pentamidine transporter (ASPT1) and a low-affinity pentamidine transporter (LAPT1). The identity of these transporters was investigated, and their significance for drug uptake and resistance in African trypanosomes is discussed.
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Affiliation(s)
- H P de Koning
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, University of Glasgow, Glasgow G12 8QQ, UK.
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43
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Seed JR, Black SJ. The classic paper of Tobie, von Brand, and Mehlman (1950) revisited. J Parasitol 2001; 87:718-20. [PMID: 11534631 DOI: 10.1645/0022-3395(2001)087[0718:tcpotv]2.0.co;2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- J R Seed
- Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill 27599-7400, USA
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44
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Abstract
Nucleoside transporters play central roles in the biochemistry of parasitic protozoa such as Leishmania and African trypanosomes, because these parasites cannot synthesize purines de novo and are absolutely reliant upon purine salvage from their hosts. Furthermore, nucleoside transporters are important to the pharmacology of these significant human pathogens, because they mediate the uptake of purine analogs, as well as some non-purine drugs, that are selectively cytotoxic to the parasites. Recent advances in molecular biology and genomics have allowed the cloning and functional expression of several nucleoside transporter genes from Leishmania donovani and Trypanosoma brucei, providing molecular reagents for a detailed functional examination of these permeases and their role in the delivery of nutrients and drugs to the parasites. Furthermore, the molecular basis of drug-resistant mutants that are deficient in nucleoside transport functions can now be fathomed.
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Affiliation(s)
- S M Landfear
- Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201, USA.
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45
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Abstract
Sleeping sickness is an increasing problem in many parts of sub-Saharan Africa. The problems are compounded by the lack of new medication, and the increasing resistance against traditional drugs such as melarsoprol, berenil and isometamidium. Over the last few years, much progress has been made in understanding how drug action, and the development of resistance, is related to the mechanisms by which the parasite ingests the drugs. In some cases novel transporters have been identified. In other cases, transporters do not appear to be involved in drug uptake, and selectivity must lie with other parasite features, such as a specific target or activation of the drug. Lessons learned from studying the uptake of drugs currently in use may assist the design of a much needed new generation of trypanocides.
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Affiliation(s)
- H P de Koning
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Joseph Black Building, University of Glasgow, G12 8QQ, Glasgow, UK.
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46
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Abstract
The malaria parasite is a unicellular eukaryotic organism which, during the course of its complex life cycle, invades the red blood cells of its vertebrate host. As it grows and multiplies within its host blood cell, the parasite modifies the membrane permeability and cytosolic composition of the host cell. The intracellular parasite is enclosed within a so-called parasitophorous vacuolar membrane, tubular extensions of which radiate out into the host cell compartment. Like all eukaryote cells, the parasite has at its surface a plasma membrane, as well as having a variety of internal membrane-bound organelles that perform a range of functions. This review focuses on the transport properties of the different membranes of the malaria-infected erythrocyte, as well as on the role played by the various membrane transport systems in the uptake of solutes from the extracellular medium, the disposal of metabolic wastes, and the origin and maintenance of electrochemical ion gradients. Such systems are of considerable interest from the point of view of antimalarial chemotherapy, both as drug targets in their own right and as routes for targeting cytotoxic agents into the intracellular parasite.
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Affiliation(s)
- K Kirk
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australian Capital Territory, Australia.
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47
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Abstract
African trypanosomes live free in the bloodstream and central nervous system of mammalian hosts and also within the midgut of the tsetse fly vectors which transmit them. The parasite plasma membrane represents the interface between both hosts and parasite, and trypanosomes accumulate many essential metabolites via specific transport processes. L-Methionine uptake by procyclic and bloodstream forms of Trypanosoma brucei has been measured and shown to be mediated by a transporter presenting similar characteristics in both forms of the parasite. The carrier shows, in both forms, a relatively high affinity for methionine (Km ca. 30 microM). The effect of inhibitors of ion gradients across the membrane indicated that the uptake process is likely to be dependent upon a proton motive force. Various methionine analogues were tested against the transporter and these have demonstrated that the recognition depends on the motif common to all amino acids, and an electronegative group at the position of the sulphur atom separated from the alpha-carbon atom by a two carbon spacer.
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Affiliation(s)
- M P Hasne
- IBLS, Division of Infection and Immunity, University of Glasgow, UK
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48
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Abstract
Purines and pyrimidines play a key role in nucleic acid and nucleotide metabolism of all cells. In addition, they can be used as nitrogen sources in plants and many microorganisms. Transport of nucleobases across biological membranes is mediated by specific transmembrane transport proteins. Nucleobase transporters have been identified genetically and/or physiologically in bacteria, fungi, protozoa, algae, plants and mammals. A limited number of bacterial and fungal transporter genes have been cloned and analysed in great detail at the molecular level. Very recently, nucleobase transporters have been identified in plants. In other systems, with less accessible genetics, such as vertebrates and protozoa, no nucleobase transporter genes have been identified, and the transporters have been characterized and classified by physiological and biochemical approaches instead. In this review, it is shown that nucleobase transporters and similar sequences of unknown function present in databases constitute three basic families, which will be designated NAT, PRT and PUP. The first includes members from archea, eubacteria, fungi, plants and metazoa, the second is restricted to prokaryotes and fungi, and the last one is only found in plants. Interestingly, mammalian ascorbate transporters are homologous to NAT sequences. The function of different nucleobase transporters is also described, as is how their expression is regulated and what is currently known about their structure-function relationships. Common features emerging from these studies are expected to prove critical in understanding what governs nucleobase transporter specificity and in selecting proper model microbial systems for cloning and studying plant, protozoan and mammalian nucleobase transporters of agricultural, pharmacological and medical importance.
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Affiliation(s)
- H de Koning
- Institute of Biomedical and Life Sciences, University of Glasgow, UK
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49
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de Koning HP, MacLeod A, Barrett MP, Cover B, Jarvis SM. Further evidence for a link between melarsoprol resistance and P2 transporter function in African trypanosomes. Mol Biochem Parasitol 2000; 106:181-5. [PMID: 10743623 DOI: 10.1016/s0166-6851(99)00206-6] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- H P de Koning
- Research School of Biosciences, University of Kent, Canterbury, UK
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50
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de Koning HP, Watson CJ, Sutcliffe L, Jarvis SM. Differential regulation of nucleoside and nucleobase transporters in Crithidia fasciculata and Trypanosoma brucei brucei. Mol Biochem Parasitol 2000; 106:93-107. [PMID: 10743614 DOI: 10.1016/s0166-6851(99)00203-0] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The regulation of the activity of purine transporters in two protozoan species, Crithidia fasciculata and Trypanosoma brucei brucei, was investigated in relation to purine availability and growth cycle. In C. fasciculata, two high-affinity purine nucleoside transporters were identified. The first, designated CfNT1, displayed a K(m) of 9.4 +/- 2.8 microM for adenosine and was inhibited by pyrimidine nucleosides as well as adenosine analogues; a second C. fasciculata nucleoside transporter (CfNT2) recognized inosine (K(m) = 0.38 +/- 0.06 microM) and guanosine but not adenosine. The activity of both transporters increased in cells at mid-logarithmic growth, as compared to cells in the stationary phase, and was also stimulated 5-15-fold following growth in purine-depleted medium. These increased rates were due to increased Vmax values (K(m) remained unchanged) and inhibited by cycloheximide (10 microM). In the procyclic forms of T. b. brucei, adenosine transport by the P1 transporter was upregulated by purine starvation but only after 48 h, whereas hypoxanthine transport was maximally increased after 24 h. The latter effect was due to the expression of an additional hypoxanthine transporter, H2, that is normally absent from procyclic forms of T. b. brucei and was characterised by its high affinity for hypoxanthine (K(m) approximately 0.2 microM) and its sensitivity to inhibition by guanosine. The activity of the H1 hypoxanthine transporter (K(m) approximately 10 microM) was unchanged. These results show that regulation of the capacity of the purine transporters is common in different protozoa, and that, in T. b. brucei, various purine transporters are under differential control.
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Affiliation(s)
- H P de Koning
- Research School of Biosciences, University of Kent at Canterbury, UK.
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