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Identification of 3,4-Dihydro-2 H,6 H-pyrimido[1,2- c][1,3]benzothiazin-6-imine Derivatives as Novel Selective Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase. Int J Mol Sci 2021; 22:ijms22137236. [PMID: 34281290 PMCID: PMC8268581 DOI: 10.3390/ijms22137236] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 06/30/2021] [Accepted: 07/02/2021] [Indexed: 12/12/2022] Open
Abstract
Plasmodium falciparum's resistance to available antimalarial drugs highlights the need for the development of novel drugs. Pyrimidine de novo biosynthesis is a validated drug target for the prevention and treatment of malaria infection. P. falciparum dihydroorotate dehydrogenase (PfDHODH) catalyzes the oxidation of dihydroorotate to orotate and utilize ubiquinone as an electron acceptor in the fourth step of pyrimidine de novo biosynthesis. PfDHODH is targeted by the inhibitor DSM265, which binds to a hydrophobic pocket located at the N-terminus where ubiquinone binds, which is known to be structurally divergent from the mammalian orthologue. In this study, we screened 40,400 compounds from the Kyoto University chemical library against recombinant PfDHODH. These studies led to the identification of 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine and its derivatives as a new class of PfDHODH inhibitor. Moreover, the hit compounds identified in this study are selective for PfDHODH without inhibition of the human enzymes. Finally, this new scaffold of PfDHODH inhibitors showed growth inhibition activity against P. falciparum 3D7 with low toxicity to three human cell lines, providing a new starting point for antimalarial drug development.
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Deng H, Lei Q, Wu Y, He Y, Li W. Activity-based protein profiling: Recent advances in medicinal chemistry. Eur J Med Chem 2020; 191:112151. [PMID: 32109778 DOI: 10.1016/j.ejmech.2020.112151] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 02/04/2020] [Accepted: 02/13/2020] [Indexed: 02/05/2023]
Abstract
Activity-based protein profiling (ABPP) has become an emerging chemical proteomic approach to illustrate the interaction mechanisms between compounds and proteins. This approach has combined organic synthesis, biochemistry, cell biology, biophysics and bioinformatics to accelerate the process of drug discovery in target identification and validation, as well as in the stage of lead discovery and optimization. This review will summarize new developments and applications of ABPP in medicinal chemistry. Here, we mainly described the design principles of activity-base probes (ABPs) and general workflows of ABPP approach. Moreover, we discussed various basic and advanced ABPP strategies and their applications in medicinal chemistry, including competitive and comparative ABPP, two-step ABPP, fluorescence polarization ABPP (FluoPol-ABPP) and ABPs for visualization. In conclusion, this review will give a general overview of the applications of ABPP as a powerful and efficient technique in medicinal chemistry.
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Affiliation(s)
- Hui Deng
- Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Targeted Tracer Research and Development Laboratory, Precision Medicine Key Laboratory of Sichuan Province & Precision Medicine Center, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China.
| | - Qian Lei
- Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Targeted Tracer Research and Development Laboratory, Precision Medicine Key Laboratory of Sichuan Province & Precision Medicine Center, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China
| | - Yangping Wu
- Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Targeted Tracer Research and Development Laboratory, Precision Medicine Key Laboratory of Sichuan Province & Precision Medicine Center, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China
| | - Yang He
- Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Targeted Tracer Research and Development Laboratory, Precision Medicine Key Laboratory of Sichuan Province & Precision Medicine Center, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China
| | - Weimin Li
- Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Targeted Tracer Research and Development Laboratory, Precision Medicine Key Laboratory of Sichuan Province & Precision Medicine Center, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China
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3
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Guo X, Wang L, Hu J, Zhang M. CuI nanoparticle-catalyzed synthesis of tetracyclic benzo[ e]benzo[4,5]imidazo[1,2- c][1,3]thiazin-6-imine heterocycles by S NAr-type C-S, C-N bond formation from isothiocyanatobenzenes and benzimidazoles. RSC Adv 2018; 8:22259-22267. [PMID: 35541714 PMCID: PMC9081286 DOI: 10.1039/c8ra02552e] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Accepted: 06/04/2018] [Indexed: 11/21/2022] Open
Abstract
In this paper, a simple and practical synthesis of benzo[e]benzo[4,5]imidazo[1,2-c][1,3]thiazin-6-imine tetracyclic heterocycles via a CuI nanoparticle-catalyzed intramolecular C(sp2)-S coupling reaction is presented. This strategy provides a straightforward method for synthesizing analogs of the anti-HIV drug 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182). The reaction rate and yield were increased by employing CuI nanoparticles.
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Affiliation(s)
- Xiaolong Guo
- Department of Chemistry, Capital Normal University Beijing 100048 China
| | - Luyao Wang
- Department of Chemistry, Capital Normal University Beijing 100048 China
| | - Jing Hu
- Department of Chemistry, Capital Normal University Beijing 100048 China
| | - Mengmeng Zhang
- Department of Chemistry, Capital Normal University Beijing 100048 China
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Dormán G, Nakamura H, Pulsipher A, Prestwich GD. The Life of Pi Star: Exploring the Exciting and Forbidden Worlds of the Benzophenone Photophore. Chem Rev 2016; 116:15284-15398. [PMID: 27983805 DOI: 10.1021/acs.chemrev.6b00342] [Citation(s) in RCA: 133] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The widespread applications of benzophenone (BP) photochemistry in biological chemistry, bioorganic chemistry, and material science have been prominent in both academic and industrial research. BP photophores have unique photochemical properties: upon n-π* excitation at 365 nm, a biradicaloid triplet state is formed reversibly, which can abstract a hydrogen atom from accessible C-H bonds; the radicals subsequently recombine, creating a stable covalent C-C bond. This light-directed covalent attachment process is exploited in many different ways: (i) binding/contact site mapping of ligand (or protein)-protein interactions; (ii) identification of molecular targets and interactome mapping; (iii) proteome profiling; (iv) bioconjugation and site-directed modification of biopolymers; (v) surface grafting and immobilization. BP photochemistry also has many practical advantages, including low reactivity toward water, stability in ambient light, and the convenient excitation at 365 nm. In addition, several BP-containing building blocks and reagents are commercially available. In this review, we explore the "forbidden" (transitions) and excitation-activated world of photoinduced covalent attachment of BP photophores by touring a colorful palette of recent examples. In this exploration, we will see the pros and cons of using BP photophores, and we hope that both novice and expert photolabelers will enjoy and be inspired by the breadth and depth of possibilities.
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Affiliation(s)
- György Dormán
- Targetex llc , Dunakeszi H-2120, Hungary.,Faculty of Pharmacy, University of Szeged , Szeged H-6720, Hungary
| | - Hiroyuki Nakamura
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology , Yokohama 226-8503, Japan
| | - Abigail Pulsipher
- GlycoMira Therapeutics, Inc. , Salt Lake City, Utah 84108, United States.,Division of Head and Neck Surgery, Rhinology - Sinus and Skull Base Surgery, Department of Surgery, University of Utah School of Medicine , Salt Lake City, Utah 84108, United States
| | - Glenn D Prestwich
- Division of Head and Neck Surgery, Rhinology - Sinus and Skull Base Surgery, Department of Surgery, University of Utah School of Medicine , Salt Lake City, Utah 84108, United States
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5
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Strmiskova M, Desrochers GF, Shaw TA, Powdrill MH, Lafreniere MA, Pezacki JP. Chemical Methods for Probing Virus-Host Proteomic Interactions. ACS Infect Dis 2016; 2:773-786. [PMID: 27933785 DOI: 10.1021/acsinfecdis.6b00084] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Interactions between host and pathogen proteins constitute an important aspect of both infectivity and the host immune response. Different viruses have evolved complex mechanisms to hijack host-cell machinery and metabolic pathways to redirect resources and energy flow toward viral propagation. These interactions are often critical to the virus, and thus understanding these interactions at a molecular level gives rise to opportunities to develop novel antiviral strategies for therapeutic intervention. This review summarizes current advances in chemoproteomic methods for studying these molecular altercations between different viruses and their hosts.
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Affiliation(s)
- Miroslava Strmiskova
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
| | - Geneviève F. Desrochers
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
| | - Tyler A. Shaw
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
| | - Megan H. Powdrill
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
| | - Matthew A. Lafreniere
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
| | - John Paul Pezacki
- Department of Chemistry and Biomolecular Sciences, Centre
for Chemical and Synthetic Biology, University of Ottawa, 10 Marie-Curie Private, Ottawa, Ontario, Canada K1N 6N5
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Morel E, Poyer F, Vaslin L, Bombard S, Teulade-Fichou MP. Photoactivatable platinum(II) terpyridine derivatives for G-quadruplex DNA double anchoring. Inorganica Chim Acta 2016. [DOI: 10.1016/j.ica.2016.02.033] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Lee B, Sun W, Lee H, Basavarajappa H, Sulaiman RS, Sishtla K, Fei X, Corson TW, Seo SY. Design, synthesis and biological evaluation of photoaffinity probes of antiangiogenic homoisoflavonoids. Bioorg Med Chem Lett 2016; 26:4277-81. [PMID: 27481561 DOI: 10.1016/j.bmcl.2016.07.043] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Revised: 07/16/2016] [Accepted: 07/20/2016] [Indexed: 12/26/2022]
Abstract
A naturally occurring homoisoflavonoid, cremastranone (1) inhibited angiogenesis in vitro and in vivo. We developed an analogue SH-11037 (2) which is more potent than cremastranone in human retinal microvascular endothelial cells (HRECs) and blocks neovascularization in animal models. Despite their efficacy, the mechanism of these compounds is not yet fully known. In the course of building on a strong foundation of SAR and creating a novel chemical tool for target identification of homoisoflavonoid-binding proteins, various types of photoaffinity probes were designed and synthesized in which benzophenone and biotin were attached to homoisoflavanonoids using PEG linkers on either the C-3' or C-7 position. Notably, the photoaffinity probes linking on the phenol group of the C-3' position retain excellent activity of inhibiting retinal endothelial cell proliferation with up to 72nM of GI50.
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Affiliation(s)
- Bit Lee
- College of Pharmacy and Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon 21936, South Korea
| | - Wei Sun
- College of Pharmacy and Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon 21936, South Korea
| | - Hyungjun Lee
- College of Pharmacy and Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon 21936, South Korea
| | - Halesha Basavarajappa
- Eugene and Marilyn Glick Eye Institute, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, United States
| | - Rania S Sulaiman
- Eugene and Marilyn Glick Eye Institute, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Biochemistry, Faculty of Pharmacy, Cairo University, Cairo, Egypt
| | - Kamakshi Sishtla
- Eugene and Marilyn Glick Eye Institute, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, IN 46202, United States
| | - Xiang Fei
- College of Pharmacy and Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon 21936, South Korea
| | - Timothy W Corson
- Eugene and Marilyn Glick Eye Institute, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, United States
| | - Seung-Yong Seo
- College of Pharmacy and Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon 21936, South Korea.
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8
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Lee H, Lee JW. Target identification for biologically active small molecules using chemical biology approaches. Arch Pharm Res 2016; 39:1193-201. [DOI: 10.1007/s12272-016-0791-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 07/01/2016] [Indexed: 11/28/2022]
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9
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Recent developments and applications of clickable photoprobes in medicinal chemistry and chemical biology. Future Med Chem 2015; 7:2143-71. [DOI: 10.4155/fmc.15.136] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Photoaffinity labeling is a well-known biochemical technique that has grown significantly since the turn of the century, principally due to its combination with bioorthogonal/click chemistry reactions. This review highlights new developments and applications of clickable photoprobes in medicinal chemistry and chemical biology. In particular, recent examples of clickable photoprobes for target identification, activity- or affinity-based protein profiling (ABPP or AfBPP), characterization of sterol– or lipid–protein interactions and characterization of ligand-binding sites are presented.
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10
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Okazaki S, Oishi S, Mizuhara T, Shimura K, Murayama H, Ohno H, Matsuoka M, Fujii N. Investigations of possible prodrug structures for 2-(2-mercaptophenyl)tetrahydropyrimidines: reductive conversion from anti-HIV agents with pyrimidobenzothiazine and isothiazolopyrimidine scaffolds. Org Biomol Chem 2015; 13:4706-13. [PMID: 25800792 DOI: 10.1039/c5ob00301f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
3,4-Dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182) and 3,4-dihydro-2H-benzo[4,5]isothiazolo[2,3-a]pyrimidine are the heterocyclic antiretroviral agents against human immunodeficiency virus type 1 (HIV-1) infection. On the basis of similar structure-activity relationships of anti-HIV activities toward the early-stage of viral infection between these unique scaffolds, the transformations under the bioassay conditions were investigated. The distinctive S-N bond in the isothiazolopyrimidine scaffold was immediately cleaved under reductive conditions in the presence of GSH to generate a thiophenol derivative. A similar rapid conversion of PD 404182 into the same thiophenol derivative was observed, suggesting that pyrimidobenzothiazine and isothiazolopyrimidine scaffolds may work as prodrug forms of the common bioactive thiophenol derivatives.
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Affiliation(s)
- Shiho Okazaki
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
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11
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Okazaki S, Mizuhara T, Shimura K, Murayama H, Ohno H, Oishi S, Matsuoka M, Fujii N. Identification of anti-HIV agents with a novel benzo[4,5]isothiazolo[2,3-a]pyrimidine scaffold. Bioorg Med Chem 2015; 23:1447-52. [PMID: 25744188 DOI: 10.1016/j.bmc.2015.02.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 02/06/2015] [Accepted: 02/10/2015] [Indexed: 12/29/2022]
Abstract
3,4-Dihydro-2H-benzo[4,5]isothiazolo[2,3-a]pyrimidine is a newly identified antiviral agent against human immunodeficiency virus type 1 (HIV-1) infection, derived from 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182). The introduction of the hydrophobic 8-aryl substituent on the benzene substructure improved its anti-HIV activity, resulting in the identification of 6-fold more potent analogs. In addition, it was demonstrated that these isothiazolopyrimidine derivatives exert anti-HIV effects at an early stage of viral infection.
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Affiliation(s)
- Shiho Okazaki
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Tsukasa Mizuhara
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Kazuya Shimura
- Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hiroto Murayama
- Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hiroaki Ohno
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Shinya Oishi
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
| | - Masao Matsuoka
- Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Nobutaka Fujii
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
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12
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Ghebremariam YT, Erlanson DA, Cooke JP. A novel and potent inhibitor of dimethylarginine dimethylaminohydrolase: a modulator of cardiovascular nitric oxide. J Pharmacol Exp Ther 2013; 348:69-76. [PMID: 24135074 DOI: 10.1124/jpet.113.206847] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
PD 404182 [6H-6-imino-(2,3,4,5-tetrahydropyrimido)[1,2-c]-[1,3]benzothiazine], a heterocyclic iminobenzothiazine derivative, is a member of the Library of Pharmacologically Active Compounds (LOPAC) that is reported to possess antimicrobial and anti-inflammatory properties. In this study, we used biochemical assays to screen LOPAC against human dimethylarginine dimethylaminohydrolase isoform 1 (DDAH1), an enzyme that physiologically metabolizes asymmetric dimethylarginine (ADMA), an endogenous and competitive inhibitor of nitric oxide (NO) synthase. We discovered that PD 404182 directly and dose-dependently inhibits DDAH. Moreover, PD 404182 significantly increased intracellular levels of ADMA in cultured primary human vascular endothelial cells (ECs) and reduced lipopolysaccharide-induced NO production in these cells, suggesting its therapeutic potential in septic shock-induced vascular collapse. In addition, PD 404182 abrogated the formation of tube-like structures by ECs in an in vitro angiogenesis assay, indicating its antiangiogenic potential in diseases characterized by pathologically excessive angiogenesis. Furthermore, we investigated the potential mechanism of inhibition of DDAH by this small molecule and found that PD 404182, which has striking structural similarity to ADMA, could be competed by a DDAH substrate, suggesting that it is a competitive inhibitor. Finally, our enzyme kinetics assay showed time-dependent inhibition, and our inhibitor dilution assay showed that the enzymatic activity of DDAH did not recover significantly after dilution, suggesting that PD 404182 might be a tightly bound, covalent, or an irreversible inhibitor of human DDAH1. This proposal is supported by mass spectrometry studies with PD 404182 and glutathione.
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Affiliation(s)
- Yohannes T Ghebremariam
- Department of Cardiovascular Sciences, Houston Methodist Research Institute, Houston, Texas (Y.T.G., J.P.C.); and SPARK Translational Research Program, Stanford University, School of Medicine, Stanford, California (D.A.E.)
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Recent advances in target characterization and identification by photoaffinity probes. Molecules 2013; 18:10425-51. [PMID: 23994969 PMCID: PMC6270116 DOI: 10.3390/molecules180910425] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 08/23/2013] [Accepted: 08/23/2013] [Indexed: 11/17/2022] Open
Abstract
Target identification of biologically active molecules such as natural products, synthetic small molecules, peptides, and oligonucleotides mainly relies on affinity chromatography, activity-based probes, or photoaffinity labeling (PAL). Amongst them, activity-based probes and PAL have offered great advantages in target identification technology due to their ability to form covalent bonds with the corresponding targets. Activity-based probe technology mainly relies on the chemical reactivity of the target proteins, thereby limiting the majority of the biological targets to enzymes or proteins which display reactive residues at the probe-binding site. In general, the probes should bear a reactive moiety such as an epoxide, a Michael acceptor, or a reactive alkyl halide in their structures. On the other hand, photoaffinity probes (PAPs) are composed of a target-specific ligand and a photoactivatable functional group. When bound to the corresponding target proteins and activated with wavelength-specific light, PAPs generate highly reactive chemical species that covalently cross-link proximal amino acid residues. This process is better known as PAL and is widely employed to identify cellular targets of biologically active molecules. This review highlights recent advances in target identification by PAL, with a focus on the structure and chemistry of the photoaffinity probes developed in the recent decade, coupled to the target proteins identified using these probes.
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