51
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Mukai T, Taketomi M, Tashiro M, Yamamoto F, Maeda M. 6-[(2-Iminopyrrolidinyl)methyl]-5-[125I]iodouracil as a potential thymidine phosphorylase-targeted radiopharmaceutical: synthesis and preliminary biological evaluation. J Labelled Comp Radiopharm 2009. [DOI: 10.1002/jlcr.1581] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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52
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Edwards PN. A kinetic, modeling and mechanistic re-analysis of thymidine phosphorylase and some related enzymes. J Enzyme Inhib Med Chem 2008; 21:483-99. [PMID: 17194017 DOI: 10.1080/14756360600721075] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Thymidine phosphorylase (TP) is an important target enzyme for cancer chemotherapy but currently available inhibitors lack in vivo potency. Related enzymes also are therapeutic targets. A greater understanding of enzyme structure and mechanism may help in the design of improved drugs and this work assists in that regard. Also important is the correct identification of the ionization states and tautomeric forms of substrates and products when bound to the enzyme and during the course of the reaction. Approximate methods for estimating some deltapK(a)s between aqueous and protein-bound substrates are exemplified for nucleobases and nucleosides. The estimates demonstrate that carbonyl-protonated thymidine and hydroxy tautomers of thymine are not involved in TP's actions. Other estimates indicate that purine nucleoside phosphorylase binds inosine and guanosine as zwitterionic tautomers and that phosphorolysis proceeds through these forms. Extensive molecular modeling based on an X-ray structure of human TP indicates that TP is likely to be mechanistically similar to all other natural members of the class in proceeding through a alpha-oxacarbenium-like transition state or states.
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Affiliation(s)
- Philip N Edwards
- School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
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53
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Gbaj A, Edwards PN, Reigan P, Freeman S, Jaffar M, Douglas KT. Thymidine phosphorylase fromEscherichia coli: Tight-binding inhibitors as enzyme active-site titrants. J Enzyme Inhib Med Chem 2008; 21:69-73. [PMID: 16570508 DOI: 10.1080/14756360500424010] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Thymidine phosphorylase (EC 2.4.2.4) catalyses the reversible phosphorolysis of pyrimidine 2'-deoxynucleosides, forming 2-deoxyribose-1-phosphate and pyrimidine. 5-Chloro-6-(2-imino-pyrrolidin-1-yl)methyl-uracil hydrochloride (TPI, 1) and its 5-bromo analogue (2), 6-(2-amino-imidazol-1-yl)methyl-5-bromo-uracil (3) and its 5-chloro analogue (4) act as tight-binding stoichiometric inhibitors of recombinant E. coli thymidine phosphorylase, and thus can be used as the first active-site titrants for it using either thymidine or 5-nitro-2'-deoxyuridine as substrate.
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Affiliation(s)
- Abdul Gbaj
- Wolfson Centre for Rational Structure-Based Design of Molecular Diagnostics, School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester M13 9PL, UK
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54
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Schwab T, Skegro D, Mayans O, Sterner R. A Rationally Designed Monomeric Variant of Anthranilate Phosphoribosyltransferase from Sulfolobus solfataricus is as Active as the Dimeric Wild-type Enzyme but Less Thermostable. J Mol Biol 2008; 376:506-16. [DOI: 10.1016/j.jmb.2007.11.078] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2007] [Revised: 11/14/2007] [Accepted: 11/23/2007] [Indexed: 11/28/2022]
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55
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Syntheses of N3-substituted thymine acyclic nucleoside phosphonates and a comparison of their inhibitory effect towards thymidine phosphorylase. Bioorg Med Chem Lett 2008; 18:1364-7. [DOI: 10.1016/j.bmcl.2008.01.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2007] [Revised: 01/02/2008] [Accepted: 01/03/2008] [Indexed: 11/20/2022]
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56
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Nencka R, Votruba I, Hřebabecký H, Jansa P, Tloušt'ová E, Horská K, Masojídková M, Holý A. Discovery of 5-Substituted-6-chlorouracils as Efficient Inhibitors of Human Thymidine Phosphorylase. J Med Chem 2007; 50:6016-23. [DOI: 10.1021/jm070644i] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Radim Nencka
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Ivan Votruba
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Hubert Hřebabecký
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Petr Jansa
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Eva Tloušt'ová
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Květa Horská
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Milena Masojídková
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
| | - Antonín Holý
- Gilead Sciences & IOCB Research Centre, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Centre for New Antivirals and Antineoplastics (IOCB), Flemingovo nám. 2, CZ-166 10, Prague 6, Czech Republic
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57
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Schramm VL. Binding isotope effects: boon and bane. Curr Opin Chem Biol 2007; 11:529-36. [PMID: 17869163 PMCID: PMC2066183 DOI: 10.1016/j.cbpa.2007.07.013] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 07/23/2007] [Accepted: 07/27/2007] [Indexed: 11/19/2022]
Abstract
Kinetic isotope effects are increasingly applied to investigate enzyme reactions and have been used to understand transition state structure, reaction mechanisms, quantum mechanical hydride ion tunneling and to design transition state analogue inhibitors. Binding isotope effects are an inherent part of most isotope effect measurements but are usually assumed to be negligible. More detailed studies have established surprisingly large binding isotope effects with lactate dehydrogenase, hexokinase, thymidine phosphorylase, and purine nucleoside phosphorylase. Binding reactants into catalytic sites immobilizes conformationally flexible groups, polarizes bonds, and distorts bond angle geometry, all of which generate binding isotope effects. Binding isotope effects are easily measured and provide high-resolution and detailed information on the atomic changes resulting from ligand-macromolecular interactions. Although binding isotope effects complicate kinetic isotope effect analysis, they also provide a powerful tool for finding atomic distortion in molecular interactions.
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Affiliation(s)
- Vern L Schramm
- Department of Biochemistry, Albert Einstein College of Medicine of Yeshiva University, 1300 Morris Park Avenue, Bronx, NY 10461, United States.
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58
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Reigan P, Gbaj A, Stratford IJ, Bryce RA, Freeman S. Xanthine oxidase-activated prodrugs of thymidine phosphorylase inhibitors. Eur J Med Chem 2007; 43:1248-60. [PMID: 17870212 DOI: 10.1016/j.ejmech.2007.07.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Accepted: 07/13/2007] [Indexed: 11/15/2022]
Abstract
Thymidine phosphorylase (TP) is over-expressed in various tumour types and plays an important role in tumour angiogenesis, growth, invasion and metastasis. The enzymatic activity of TP is required for the angiogenic effect of TP, therefore, inhibitors of TP are of significant interest in cancer chemotherapy. A series of xanthine oxidase (XO) activated prodrugs of known inhibitors of TP have been designed and synthesized with the ultimate intent of improving tumour selectivity and pharmacokinetic characteristics. These prodrugs were not inhibitors of TP, but were selectively oxidized by XO at C-2 and/or C-4 of the uracil ring moiety to generate the desired TP inhibitor. Molecular modelling of both the TP inhibitors and XO-activated prodrugs rationalized their binding in the active site of the human TP crystal structure.
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Affiliation(s)
- Philip Reigan
- School of Pharmacy and Pharmaceutical Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
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59
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Liekens S, Bronckaers A, Pérez-Pérez MJ, Balzarini J. Targeting platelet-derived endothelial cell growth factor/thymidine phosphorylase for cancer therapy. Biochem Pharmacol 2007; 74:1555-67. [PMID: 17572389 DOI: 10.1016/j.bcp.2007.05.008] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Accepted: 05/08/2007] [Indexed: 11/18/2022]
Abstract
Thymidine phosphorylase (TP) is a key enzyme in the pyrimidine nucleoside salvage pathway, but it also recognizes and inactivates various anti-cancer chemotherapeutic agents. Moreover, TP is identical to platelet-derived endothelial cell growth factor (PD-ECGF), an angiogenic factor with anti-apoptotic properties. Increased expression of PD-ECGF/TP is found in many tumor and stromal cells, and elevated TP levels are associated with aggressive disease and/or poor prognosis. Thus, progression and metastasis of TP-expressing tumors might be abrogated by TP inhibitors that are used as single agents or in combination with (TP-sensitive) nucleoside analogues. On the other hand, increased TP activity in tumors may be exploited for the tumor-specific activation of fluoropyrimidine prodrugs, such as capecitabine. This review will focus on the different biological activities of PD-ECGF/TP and their implications for cancer progression and treatment.
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Affiliation(s)
- Sandra Liekens
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, K.U. Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium.
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60
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Hartshorn MJ, Verdonk ML, Chessari G, Brewerton SC, Mooij WTM, Mortenson PN, Murray CW. Diverse, high-quality test set for the validation of protein-ligand docking performance. J Med Chem 2007; 50:726-41. [PMID: 17300160 DOI: 10.1021/jm061277y] [Citation(s) in RCA: 447] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A procedure for analyzing and classifying publicly available crystal structures has been developed. It has been used to identify high-resolution protein-ligand complexes that can be assessed by reconstructing the electron density for the ligand using the deposited structure factors. The complexes have been clustered according to the protein sequences, and clusters have been discarded if they do not represent proteins thought to be of direct interest to the pharmaceutical or agrochemical industry. Rules have been used to exclude complexes containing non-drug-like ligands. One complex from each cluster has been selected where a structure of sufficient quality was available. The final Astex diverse set contains 85 diverse, relevant protein-ligand complexes, which have been prepared in a format suitable for docking and are to be made freely available to the entire research community (http://www.ccdc.cam.ac.uk). The performance of the docking program GOLD against the new set is assessed using a variety of protocols. Relatively unbiased protocols give success rates of approximately 80% for redocking into native structures, but it is possible to get success rates of over 90% with some protocols.
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Affiliation(s)
- Michael J Hartshorn
- Astex Therapeutics, Ltd., 436 Cambridge Science Park, Milton Road, Cambridge CB4 0QA, United Kingdom
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61
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Millen AL, Archibald LAB, Hunter KC, Wetmore SD. A kinetic and thermodynamic study of the glycosidic bond cleavage in deoxyuridine. J Phys Chem B 2007; 111:3800-12. [PMID: 17388517 DOI: 10.1021/jp063841m] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Density functional theory was used to study the thermodynamics and kinetics for the glycosidic bond cleavage in deoxyuridine. Two reaction pathways were characterized for the unimolecular decomposition in vacuo. However, these processes are associated with large reaction barriers and highly endothermic reaction energies, which is in agreement with experiments that suggest a (water) nucleophile is required for the nonenzymatic glycosidic bond cleavage. Two (S(N)1 and S(N)2) reaction pathways were characterized for direct hydrolysis of the glycosidic bond by a single water molecule; however, both pathways also involve very large barriers. Activation of the water nucleophile via partial proton abstraction steadily decreases the barrier and leads to a more exothermic reaction energy as the proton affinity of the molecule interacting with water increases. Indeed, our data suggests that the barrier heights and reaction energies range from that for hydrolysis by water to that for hydrolysis by the hydroxyl anion, which represents the extreme of (full) water activation (deprotonation). Hydrogen bonds between small molecules (hydrogen fluoride, water, or ammonia) and the nucleobase were found to further decrease the barrier and overall reaction energy but not to the extent that the same hydrogen-bonding interactions increase the acidity of the nucleobase. Our results suggest that the nature of the nucleophile plays a more important role in reducing the barrier to glycosidic bond cleavage than the nature of the small molecule bound, and models with more than one hydrogen fluoride molecule interacting with the nucleobase provide further support for this conclusion. Our results lead to a greater fundamental understanding of the effects of the nucleophile, activation of the nucleophile, and interactions with the nucleobase for this important biological reaction.
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Affiliation(s)
- Andrea L Millen
- Department of Chemistry, Mount Allison University, 63C York Street, Sackville, New Brunswick E4L 1G8, Canada
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62
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Affiliation(s)
- Lionel Ginsberg
- University Department of Clinical Neurosciences, Hampstead Campus, Royal Free and University College Medical School, University College London, UK.
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63
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Omari K, Bronckaers A, Liekens S, Pérez-Pérez MJ, Balzarini J, Stammers D. Structural basis for non-competitive product inhibition in human thymidine phosphorylase: implications for drug design. Biochem J 2006; 399:199-204. [PMID: 16803458 PMCID: PMC1609907 DOI: 10.1042/bj20060513] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
HTP (human thymidine phosphorylase), also known as PD-ECGF (platelet-derived endothelial cell growth factor) or gliostatin, has an important role in nucleoside metabolism. HTP is implicated in angiogenesis and apoptosis and therefore is a prime target for drug design, including antitumour therapies. An HTP structure in a closed conformation complexed with an inhibitor has previously been solved. Earlier kinetic studies revealed an ordered release of thymine followed by ribose phosphate and product inhibition by both ligands. We have determined the structure of HTP from crystals grown in the presence of thymidine, which, surprisingly, resulted in bound thymine with HTP in a closed dead-end complex. Thus thymine appears to be able to reassociate with HTP after its initial ordered release before ribose phosphate and induces the closed conformation, hence explaining the mechanism of non-competitive product inhibition. In the active site in one of the four HTP molecules within the crystal asymmetric unit, additional electron density is present. This density has not been previously seen in any pyrimidine nucleoside phosphorylase and it defines a subsite that may be exploitable in drug design. Finally, because our crystals did not require proteolysed HTP to grow, the structure reveals a loop (residues 406-415), disordered in the previous HTP structure. This loop extends across the active-site cleft and appears to stabilize the dimer interface and the closed conformation by hydrogen-bonding. The present study will assist in the design of HTP inhibitors that could lead to drugs for anti-angiogenesis as well as for the potentiation of other nucleoside drugs.
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Affiliation(s)
- Kamel EL Omari
- *Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, U.K
| | | | - Sandra Liekens
- †Rega Institute for Medical Research, K.U.Leuven, B-3000 Leuven, Belgium
| | | | - Jan Balzarini
- †Rega Institute for Medical Research, K.U.Leuven, B-3000 Leuven, Belgium
| | - David K. Stammers
- *Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, U.K
- To whom correspondence should be addressed (email )
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64
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Marino M, Deuss M, Svergun DI, Konarev PV, Sterner R, Mayans O. Structural and mutational analysis of substrate complexation by anthranilate phosphoribosyltransferase from Sulfolobus solfataricus. J Biol Chem 2006; 281:21410-21421. [PMID: 16714288 DOI: 10.1074/jbc.m601403200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The metabolic synthesis and degradation of essential nucleotide compounds are primarily carried out by phosphoribosyltransferases (PRT) and nucleoside phosphorylases (NP), respectively. Despite the resemblance of their reactions, five classes of PRTs and NPs exist, where anthranilate PRT (AnPRT) constitutes the only evolutionary link between synthesis and degradation processes. We have characterized the active site of dimeric AnPRT from Sulfolobus solfataricus by elucidating crystal structures of the wild-type enzyme complexed to its two natural substrates anthranilate and 5-phosphoribosyl-1-pyrophosphate/Mg(2+). These bind into two different domains within each protomer and are brought together during catalysis by rotational domain motions as shown by small angle x-ray scattering data. Steady-state kinetics of mutated AnPRT variants address the role of active site residues in binding and catalysis. Results allow the comparative analysis of PRT and pyrimidine NP families and expose related structural motifs involved in nucleotide/nucleoside recognition by these enzyme families.
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Affiliation(s)
- Marco Marino
- Division of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Miriam Deuss
- Institut für Biophysik und physikalische Biochemie, Universität Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany; Institut für Biochemie, Universität zu Köln, Otto-Fischer-Strasse 12-14, D-50674 Köln, Germany
| | - Dmitri I Svergun
- European Molecular Biology Laboratory, Hamburg Outstation, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany; Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, 117333 Moscow, Russia
| | - Petr V Konarev
- European Molecular Biology Laboratory, Hamburg Outstation, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany; Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, 117333 Moscow, Russia
| | - Reinhard Sterner
- Institut für Biophysik und physikalische Biochemie, Universität Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany; Institut für Biochemie, Universität zu Köln, Otto-Fischer-Strasse 12-14, D-50674 Köln, Germany
| | - Olga Mayans
- Division of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
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65
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Berti PJ, McCann JAB. Toward a detailed understanding of base excision repair enzymes: transition state and mechanistic analyses of N-glycoside hydrolysis and N-glycoside transfer. Chem Rev 2006; 106:506-55. [PMID: 16464017 DOI: 10.1021/cr040461t] [Citation(s) in RCA: 211] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Paul J Berti
- Department of Chemistry, McMaster University, Hamilton, Ontario, Canada.
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66
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Nencka R, Votruba I, Hrebabecký H, Tloust'ová E, Horská K, Masojídková M, Holý A. Design and synthesis of novel 5,6-disubstituted uracil derivatives as potent inhibitors of thymidine phosphorylase. Bioorg Med Chem Lett 2006; 16:1335-7. [PMID: 16337119 DOI: 10.1016/j.bmcl.2005.11.050] [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: 10/24/2005] [Revised: 11/14/2005] [Accepted: 11/14/2005] [Indexed: 11/17/2022]
Abstract
We report on a series of novel 5,6-disubstituted uracils with significant inhibitory activity against human and Escherichia coli thymidine phosphorylases. Bis-uracil conjugates were identified as the most potent inhibitors of TPs in this study.
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Affiliation(s)
- Radim Nencka
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 166 10 Prague 6, Czech Republic.
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67
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Hatano A, Harano A, Kirihara M. Importance of 3′-Hydroxyl Group of the Nucleosides for the Reactivity of Thymidine Phosphorylase fromEscherichia coli. CHEM LETT 2006. [DOI: 10.1246/cl.2006.232] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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68
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Kalman TI, Lai L. 6-substituted 5-fluorouracil derivatives as transition state analogue inhibitors of thymidine phosphorylase. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2005; 24:367-73. [PMID: 16247953 DOI: 10.1081/ncn-200059790] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
A combination of mechanism-based and structure-based design strategies led to the synthesis of a series of 5- and 6-substituted uracil derivatives as potential inhibitors of thymidine phosphorlase/platelet derived endothelial cell growth factor (TP/PD-ECGF). Among those tested, 6-imidazolylmethyl-5-fluorouracil was found to be the most potent inhibitor with a Ki-value of 51 nM, representing a new class of 5-fluoropyrimidines with a novel mechanism of action.
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Affiliation(s)
- Thomas I Kalman
- Department of Chemistry, University at Buffalo, Amherst, NY 14260, USA.
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69
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Landowski CP, Song X, Lorenzi PL, Hilfinger JM, Amidon GL. Floxuridine Amino Acid Ester Prodrugs: Enhancing Caco-2 Permeability and Resistance to Glycosidic Bond Metabolism. Pharm Res 2005; 22:1510-8. [PMID: 16132363 DOI: 10.1007/s11095-005-6156-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Accepted: 05/26/2005] [Indexed: 10/25/2022]
Abstract
PURPOSE The aim of this study was to synthesize amino acid ester prodrugs of 5-fluoro-2'-deoxyuridine (floxuridine) to enhance intestinal absorption and resistance to glycosidic bond metabolism. METHODS Amino acid ester prodrugs were synthesized and examined for their hydrolytic stability in human plasma, in Caco-2 cell homogenates, and in the presence of thymidine phosphorylase. Glycyl-L: -sarcosine uptake inhibition and direct uptake studies with HeLa/PEPT1 cells [HeLa cells overexpressing oligopeptide transporter (PEPT1)] were conducted to determine PEPT1-mediated transport and compared with permeability of the prodrugs across Caco-2 monolayers. RESULTS Isoleucyl prodrugs exhibited the highest chemical and enzymatic stability. The prodrugs enhanced the stability of the glycosidic bond of floxuridine. Thymidine phosphorylase rapidly cleaved floxuridine to 5-fluorouracil, whereas with the prodrugs no detectable glycosidic bond cleavage was observed. The 5'-L: -isoleucyl and 5'-L: -valyl monoester prodrugs exhibited 8- and 19-fold PEPT1-mediated uptake enhancement in HeLa/PEPT1 cells, respectively. Uptake enhancement in HeLa/PEPT1 cells correlated highly with Caco-2 permeability for all prodrugs tested. Caco-2 permeability of 5'-L: -isoleucyl and 5'-L: -valyl prodrugs was 8- to 11-fold greater compared with floxuridine. CONCLUSIONS Amino acid ester prodrugs such as isoleucyl floxuridine that exhibit enhanced Caco-2 transport and slower rate of enzymatic activation to parent, and that are highly resistant to metabolism by thymidine phosphorylase may improve oral delivery and therapeutic index of floxuridine.
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Affiliation(s)
- Christopher P Landowski
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA
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70
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Reigan P, Edwards PN, Gbaj A, Cole C, Barry ST, Page KM, Ashton SE, Luke RWA, Douglas KT, Stratford IJ, Jaffar M, Bryce RA, Freeman S. Aminoimidazolylmethyluracil Analogues as Potent Inhibitors of Thymidine Phosphorylase and Their Bioreductive Nitroimidazolyl Prodrugs. J Med Chem 2005; 48:392-402. [PMID: 15658853 DOI: 10.1021/jm049494r] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thymidine phosphorylase (TP) is an important target enzyme for cancer chemotherapy because it is expressed at high levels in the hypoxic regions of many tumors and inhibitors of TP have been shown in animal model studies to inhibit angiogenesis and metastasis, and to promote tumor cell apoptosis. The 5-halo-6-[(2'-aminoimidazol-1'-yl)methyl]uracils (3, X = Cl, Br) are very potent inhibitors of E. coli and human TP with IC(50) values of approximately 20 nM when the enzyme concentration is approximately 40 nM. Their 4'-aminoimidazol-1'-yl analogues (4, X = Cl, Br) are >350-fold less active with IC(50) values of approximately 7 microM. The 5-unsubstituted analogues (3 and 4, X = H) were both less active than their 5-halo derivatives. Determination of pK(a) values and molecular modeling studies of these compounds in the active site of human TP was used to rationalize their activities. The finding that 3, X = Br has a poor pharmacokinetic (PK) profile in mice, coupled with the desire for tumor selectivity, led us to design prodrugs. The corresponding 2'-nitroimidazol-1'-ylmethyluracils (5, X = Cl, Br) are >1000-fold less active (IC(50) 22-24 microM) than their 2'-amino analogues and are reduced to the 2'-amino inhibitors (3, X = Cl, Br) by xanthine oxidase (XO). As XO is also highly expressed in many tumors, the 2'-nitro prodrugs have the potential to selectively deliver the potent 2'-aminoimidazol-1'-yl TP inhibitors into hypoxic solid tumors.
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Affiliation(s)
- Philip Reigan
- School of Pharmacy & Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Akiyama SI, Furukawa T, Sumizawa T, Takebayashi Y, Nakajima Y, Shimaoka S, Haraguchi M. The role of thymidine phosphorylase, an angiogenic enzyme, in tumor progression. Cancer Sci 2004; 95:851-7. [PMID: 15546501 PMCID: PMC11159696 DOI: 10.1111/j.1349-7006.2004.tb02193.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Revised: 08/27/2004] [Accepted: 08/27/2004] [Indexed: 01/23/2023] Open
Abstract
Thymidine phosphorylase (TP), an enzyme involved in pyrimidine metabolism, is identical with an angiogenic factor, platelet-derived endothelial cell growth factor (PD-ECGF). TP is overexpressed in various tumors and plays an important role in angiogenesis, tumor growth, invasion and metastasis. The enzymatic activity of TP is required for the angiogenic effect of TP. A novel, specific TP inhibitor, TPI, inhibits angiogenesis induced by overexpression of TP in KB/TP cells (human KB epidermoid carcinoma cells transfected with TP cDNA), as well as the growth and metastasis of KB/TP cells in vivo. 2-deoxy-D-ribose, the degradation product of thymidine generated by TP activity, has both angiogenic and chemotactic activity. Both 2-deoxy-D-ribose and TP inhibit a hypoxia-induced apoptotic pathway. These findings suggest that 2-deoxy-D-ribose is a downstream mediator of TP function. 2-deoxy-L-ribose, a stereoisomer of 2-deoxy-D-ribose, inhibits the promotion of angiogenesis, tumor growth and metastasis by TP. Although the mechanism of the action of 2-deoxy-D-ribose is still unknown, 2-deoxy-L-ribose may inhibit the physiological activities of 2-deoxy-D-ribose, and consequently those of TP. Inhibition of TP activity and function appears to be a promising approach for the chemotherapy of various tumors.
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Affiliation(s)
- Shin-ichi Akiyama
- Department of Molecular Oncology, Course of Advanced Therapeutics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima 890-8544.
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Birck MR, Schramm VL. Binding Causes the Remote [5‘-3H]Thymidine Kinetic Isotope Effect in Human Thymidine Phosphorylase. J Am Chem Soc 2004; 126:6882-3. [PMID: 15174854 DOI: 10.1021/ja0492642] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The remote 5'-3H V/K kinetic isotope effect (KIE) observed in human thymidine phosphorylase (6.1%) is significantly larger than can be explained by the reaction chemistry. One hypothesis connects the 5'-3H KIE in purine nucleoside phosphorylase to that enzyme's SN1 transition state. The transition state of thymidine phosphorylase, however, is an SN2 nucleophilic displacement. Here we report equilibrium binding isotope effects sufficiently large to explain the presence of this substantial KIE in thymidine phosphorylase.
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Affiliation(s)
- Matthew R Birck
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA
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Liekens S, Hernández AI, Ribatti D, De Clercq E, Camarasa MJ, Pérez-Pérez MJ, Balzarini J. The nucleoside derivative 5'-O-trityl-inosine (KIN59) suppresses thymidine phosphorylase-triggered angiogenesis via a noncompetitive mechanism of action. J Biol Chem 2004; 279:29598-605. [PMID: 15123637 DOI: 10.1074/jbc.m402602200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thymidine phosphorylase (TPase) catalyzes the reversible phosphorolysis of pyrimidine deoxynucleosides to 2-deoxy-d-ribose-1-phosphate and their respective pyrimidine bases. The enzymatic activity of TPase was found to be essential for its angiogenesis-stimulating properties. All of the previously described TPase inhibitors are either pyrimidine analogues that interact with the nucleoside-binding site of the enzyme or modified purine derivatives that mimic the pyrimidine structure and either compete with thymidine or act as a multisubstrate (competitive) inhibitor. We now describe the inhibitory activity of the purine riboside derivative KIN59 (5'-O-tritylinosine) against human and bacterial recombinant TPase and TPase-induced angiogenesis. In contrast to previously described TPase inhibitors, KIN59 does not compete with the pyrimidine nucleoside or the phosphate-binding site of the enzyme but noncompetitively inhibits TPase when thymidine or phosphate is used as the variable substrate. In addition, KIN59 was far more active than other TPase inhibitors, previously tested by us, against TPase-induced angiogenesis in the chorioallantoic membrane assay. The observed anti-angiogenic effect of KIN59 was not accompanied by inflammation or any visible toxicity. Inosine did not inhibit the enzymatic or angiogenic activity of the enzyme, indicating that the 5'-O-trityl group in KIN59 is essential for the observed effects. In contrast with current concepts, our data indicate that the angiogenic activity of TPase is not solely directed through its functional nucleoside and phosphate-binding sites. Other regulatory (allosteric) site(s) in TPase may play an important role in the mechanism of TPase-triggered angiogenesis stimulation and apoptosis inhibition. Identification of these site(s) is important to obtain a better insight into the molecular role of TPase in the progression of cancer and angiogenic diseases.
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Affiliation(s)
- Sandra Liekens
- Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
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