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Robinson JA. Beta-hairpin peptidomimetics: design, structures and biological activities. Acc Chem Res 2008; 41:1278-88. [PMID: 18412373 DOI: 10.1021/ar700259k] [Citation(s) in RCA: 264] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The folded 3D structures of peptides and proteins provide excellent starting points for the design of synthetic molecules that mimic key epitopes (or surface patches) involved in protein-protein and protein-nucleic acid interactions. Protein epitope mimetics (PEMs) may recapitulate not only the structural and conformational properties of the target epitope but also their biological activities. By transferring the epitope from a recombinant to a synthetic scaffold that can be produced by parallel combinatorial methods, it is possible to optimize properties through iterative cycles of library synthesis and screening, and even to evolve new biological activities. One very interesting scaffold is found in beta-hairpin motifs, which are used by many proteins to mediate molecular recognition events. This motif is readily amenable to PEM design, for example, by transplanting hairpin loop sequences from folded proteins onto hairpin-stabilizing templates, such as the dipeptide D-Pro-L-Pro. In addition, beta-hairpin peptidomimetics can also be exploited to mimic other types of epitopes, such as those based on alpha-helical secondary structures. The size and shape of beta-hairpin PEMs appear well suited for the design of inhibitors of both protein-protein and protein-nucleic acid interactions, endeavors that have so far proven difficult using small "drug-like" molecules. In recent work, it was shown that beta-hairpin PEMs can be designed that mimic the canonical conformations of antibody hypervariable loops, suggesting that novel small-molecule antibody mimics may be feasible. Using naturally occurring peptides as starting points, beta-hairpin mimetics have been discovered that possess antimicrobial activity, while others are potent inhibitors of the chemokine receptor CXCR4. Beta-hairpin PEMs have also been designed and optimized that mimic an alpha-helical epitope in p53 and so block its interaction with HDM2. A crystal structure of one HDM2-mimetic complex revealed how the surface of the protein had adapted to the shape of the hairpin, thereby enhancing inhibitor affinity. Small folded RNA motifs also make interesting targets for inhibitor design. For example, beta-hairpin mimetics have been designed and optimized that bind with high affinity and good selectivity to the TAR and RRE RNA motifs from HIV-1. Solution structures of the mimetics both free and bound to the RNA target provided some surprises, as well as an improved understanding of the mechanisms of binding. These mimetics represent still a relatively new family of RNA-binding molecules, but clearly one with potential for development into novel antiviral agents.
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Affiliation(s)
- John A. Robinson
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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Robinson JA, Demarco S, Gombert F, Moehle K, Obrecht D. The design, structures and therapeutic potential of protein epitope mimetics. Drug Discov Today 2008; 13:944-51. [PMID: 18725320 DOI: 10.1016/j.drudis.2008.07.008] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 07/21/2008] [Accepted: 07/22/2008] [Indexed: 10/21/2022]
Abstract
Using a biologically relevant peptide or protein structure as a starting point for lead identification represents one of the most powerful approaches in modern drug discovery. Here, we focus on the protein epitope mimetic (PEM) approach, where folded 3D structures of peptides and proteins are taken as starting points for the design of synthetic molecules that mimic key epitopes involved in protein-protein and protein-nucleic acid interactions. By transferring the epitope from a recombinant to a synthetic scaffold that can be produced by parallel combinatorial methods, it is possible to optimize target affinity and specificity as well as other drug-like ADMET properties. The PEM technology is a powerful tool for target validation, and for the development of novel PEM-based drugs.
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Affiliation(s)
- John A Robinson
- Organic Chemistry Institute, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
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53
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Strimpakos AS, Sharma RA. Curcumin: preventive and therapeutic properties in laboratory studies and clinical trials. Antioxid Redox Signal 2008; 10:511-45. [PMID: 18370854 DOI: 10.1089/ars.2007.1769] [Citation(s) in RCA: 420] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Curcumin is a natural polyphenol used in ancient Asian medicine. Since the first article referring to the use of curcumin to treat human disease was published in The Lancet in 1937, >2,600 research studies using curcumin or turmeric have been published in English language journals. The mechanisms implicated in the inhibition of tumorigenesis by curcumin are diverse and appear to involve a combination of antiinflammatory, antioxidant, immunomodulatory, proapoptotic, and antiangiogenic properties via pleiotropic effects on genes and cell-signaling pathways at multiple levels. The potentially adverse sequelae of curcumin's effects on proapoptotic genes, particularly p53, represent a cause for current debate. When curcumin is combined with some cytotoxic drugs or certain other diet-derived polyphenols, synergistic effects have been demonstrated. Although curcumin's low systemic bioavailability after oral dosing may limit access of sufficient concentrations for pharmacologic effects in tissues outside the gastrointestinal tract, chemical analogues and novel delivery methods are in preclinical development to overcome this barrier. This article provides an overview of the extensive published literature on the use of curcumin as a therapy for malignant and inflammatory diseases and its potential use in the treatment of degenerative neurologic diseases, cystic fibrosis, and cardiovascular diseases. Despite the breadth of the coverage, particular emphasis is placed on the prevention and treatment of human cancers.
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Leão JC, Gomes VB, Porter S. Ulcerative lesions of the mouth: an update for the general medical practitioner. Clinics (Sao Paulo) 2007; 62:769-80. [PMID: 18209920 DOI: 10.1590/s1807-59322007000600018] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Accepted: 08/27/2007] [Indexed: 11/22/2022] Open
Abstract
Oral ulceration is a common complaint of patients attending out-patient clinics. Because of the diversity in causes of oral ulceration, patients presenting with oral mucosal disease can be challenging to diagnose and manage. Patients with signs or symptoms of oral ulcers are sometimes referred to gastroenterology clinics; however, in most instances the ulcers do not result from gastrointestinal disease. The aim of the present article is to review aspects of the etiology, diagnosis and management of common ulcerative disorders of the oral mucosa. A search in the National Library of Medicine computerized bibliographic database MEDLINE was performed. Selection of publications, extraction of data, and validity assessment were then performed by the authors. Based upon the searched literature, it is concluded that there are several systemic disorders that can present with similar clinical signs and symptoms, and knowledge of each disease is necessary for the clinician to provide proper management.
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Affiliation(s)
- Jair Carneiro Leão
- Departamento de Clínica e Odontologia Preventiva, Universidade Federal de Pernambuco, Recife, PE, Brazil.
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Srinivas N, Moehle K, Abou-Hadeed K, Obrecht D, Robinson JA. Biaryl amino acid templates in place of D-Pro-L-Pro in cyclic beta-hairpin cationic antimicrobial peptidomimetics. Org Biomol Chem 2007; 5:3100-5. [PMID: 17878968 DOI: 10.1039/b706370a] [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: 11/21/2022]
Abstract
The turn-forming D-Pro-L-Pro template has been frequently used to promote regular beta-hairpin conformations in cyclic protein epitope mimetics. Here the use of three isomeric biaryl templates has been studied as alternatives to D-Pro-L-Pro in the preparation of beta-hairpin peptidomimetics. The o,o'- o,m'- and m,m'-isomers of carboxymethyl- and aminomethyl-substituted biaryl templates have been incorporated into novel macrocyclic mimics of the naturally occurring cationic antimicrobial peptide protegrin I. The presence of the o-carboxymethyl-o'-aminomethyl-biaryl template within the macrocyclic peptide resulted in the appearance of slowly interconverting atropisomers. Although none of the resulting mimetics adopted stable beta-hairpin structures in aqueous solution, they all nevertheless retained a significant antimicrobial activity against Gram positive and Gram negative bacteria. These mimetics provide interesting starting points for an optimization program in the search for potent and novel antimicrobial compounds.
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Affiliation(s)
- Nityakalyani Srinivas
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
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Aggarwal BB, Sundaram C, Malani N, Ichikawa H. CURCUMIN: THE INDIAN SOLID GOLD. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 595:1-75. [PMID: 17569205 DOI: 10.1007/978-0-387-46401-5_1] [Citation(s) in RCA: 842] [Impact Index Per Article: 49.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Turmeric, derived from the plant Curcuma longa, is a gold-colored spice commonly used in the Indian subcontinent, not only for health care but also for the preservation of food and as a yellow dye for textiles. Curcumin, which gives the yellow color to turmeric, was first isolated almost two centuries ago, and its structure as diferuloylmethane was determined in 1910. Since the time of Ayurveda (1900 Bc) numerous therapeutic activities have been assigned to turmeric for a wide variety of diseases and conditions, including those of the skin, pulmonary, and gastrointestinal systems, aches, pains, wounds, sprains, and liver disorders. Extensive research within the last half century has proven that most of these activities, once associated with turmeric, are due to curcumin. Curcumin has been shown to exhibit antioxidant, anti-inflammatory, antiviral, antibacterial, antifungal, and anticancer activities and thus has a potential against various malignant diseases, diabetes, allergies, arthritis, Alzheimer's disease, and other chronic illnesses. These effects are mediated through the regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases, and other enzymes. Curcumin exhibits activities similar to recently discovered tumor necrosis factor blockers (e.g., HUMIRA, REMICADE, and ENBREL), a vascular endothelial cell growth factor blocker (e.g., AVASTIN), human epidermal growth factor receptor blockers (e.g., ERBITUX, ERLOTINIB, and GEFTINIB), and a HER2 blocker (e.g., HERCEPTIN). Considering the recent scientific bandwagon that multitargeted therapy is better than monotargeted therapy for most diseases, curcumin can be considered an ideal "Spice for Life".
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MESH Headings
- Animals
- Anti-Bacterial Agents/chemistry
- Anti-Bacterial Agents/pharmacology
- Anti-Bacterial Agents/therapeutic use
- Anti-Inflammatory Agents, Non-Steroidal/chemistry
- Anti-Inflammatory Agents, Non-Steroidal/pharmacology
- Anti-Inflammatory Agents, Non-Steroidal/therapeutic use
- Antifungal Agents/chemistry
- Antifungal Agents/pharmacology
- Antifungal Agents/therapeutic use
- Antineoplastic Agents, Phytogenic/chemistry
- Antineoplastic Agents, Phytogenic/pharmacology
- Antineoplastic Agents, Phytogenic/therapeutic use
- Antioxidants/chemistry
- Antioxidants/pharmacology
- Antioxidants/therapeutic use
- Antiviral Agents/chemistry
- Antiviral Agents/pharmacology
- Antiviral Agents/therapeutic use
- Arthritis, Rheumatoid/drug therapy
- Curcuma/chemistry
- Curcumin/analogs & derivatives
- Curcumin/chemistry
- Curcumin/metabolism
- Curcumin/pharmacology
- Curcumin/therapeutic use
- Humans
- India
- Medicine, Ayurvedic
- Models, Biological
- Molecular Structure
- Neoplasms/drug therapy
- Phytotherapy
- Plants, Medicinal
- Spices
- Structure-Activity Relationship
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Affiliation(s)
- Bharat B Aggarwal
- Department of Experimental Therapeutics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
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Fernández M, Caballero J. Analysis of protegrin structure–activity relationships: the structural characteristics important for antimicrobial activity using smoothed amino acid sequence descriptors. MOLECULAR SIMULATION 2007. [DOI: 10.1080/08927020701236771] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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59
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Hancock REW, Sahl HG. Antimicrobial and host-defense peptides as new anti-infective therapeutic strategies. Nat Biotechnol 2007; 24:1551-7. [PMID: 17160061 DOI: 10.1038/nbt1267] [Citation(s) in RCA: 2950] [Impact Index Per Article: 173.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Short cationic amphiphilic peptides with antimicrobial and/or immunomodulatory activities are present in virtually every life form, as an important component of (innate) immune defenses. These host-defense peptides provide a template for two separate classes of antimicrobial drugs. Direct-acting antimicrobial host-defense peptides can be rapid-acting and potent, and possess an unusually broad spectrum of activity; consequently, they have prospects as new antibiotics, although clinical trials to date have shown efficacy only as topical agents. But for these compounds to fulfill their therapeutic promise and overcome clinical setbacks, further work is needed to understand their mechanisms of action and reduce the potential for unwanted toxicity, to make them more resistant to protease degradation and improve serum half-life, as well as to devise means of manufacturing them on a large scale in a consistent and cost-effective manner. In contrast, the role of cationic host-defense peptides in modulating the innate immune response and boosting infection-resolving immunity while dampening potentially harmful pro-inflammatory (septic) responses gives these peptides the potential to become an entirely new therapeutic approach against bacterial infections.
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Affiliation(s)
- Robert E W Hancock
- Centre for Microbial Diseases and Immunity Research, Room 232, 2259 Lower Mall Research Station, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4.
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61
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DeMarco SJ, Henze H, Lederer A, Moehle K, Mukherjee R, Romagnoli B, Robinson JA, Brianza F, Gombert FO, Lociuro S, Ludin C, Vrijbloed JW, Zumbrunn J, Obrecht JP, Obrecht D, Brondani V, Hamy F, Klimkait T. Discovery of novel, highly potent and selective beta-hairpin mimetic CXCR4 inhibitors with excellent anti-HIV activity and pharmacokinetic profiles. Bioorg Med Chem 2006; 14:8396-404. [PMID: 17010618 DOI: 10.1016/j.bmc.2006.09.003] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 08/26/2006] [Accepted: 09/06/2006] [Indexed: 11/25/2022]
Abstract
Novel highly potent CXCR4 inhibitors with good pharmacokinetic properties were designed and optimized starting from the naturally occurring beta-hairpin peptide polyphemusin II. The design involved incorporating important residues from polyphemusin II into a macrocyclic template-bound beta-hairpin mimetic. Using a parallel synthesis approach, the potency and ADME properties of the mimetics were optimized in iterative cycles, resulting in the CXCR4 inhibitors POL2438 and POL3026. The inhibitory potencies of these compounds were confirmed in a series of HIV-1 invasion assays in vitro. POL3026 showed excellent plasma stability, high selectivity for CXCR4, favorable pharmacokinetic properties in the dog, and thus has the potential to become a therapeutic compound for application in the treatment of HIV infections (as an entry inhibitor), cancer (for angiogenesis suppression and inhibition of metastasis), inflammation, and in stem cell transplant therapy.
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MESH Headings
- Animals
- Anti-HIV Agents/chemistry
- Anti-HIV Agents/pharmacokinetics
- Anti-HIV Agents/pharmacology
- Antimicrobial Cationic Peptides/chemistry
- Calcium/metabolism
- Chemokine CXCL12
- Chemokines, CXC/metabolism
- Chemokines, CXC/pharmacology
- Chemotaxis/drug effects
- Dogs
- Drug Design
- HIV-1/drug effects
- HIV-1/physiology
- Humans
- Leukemia/pathology
- Microsomes/drug effects
- Molecular Mimicry
- Oligopeptides/chemistry
- Oligopeptides/pharmacokinetics
- Oligopeptides/pharmacology
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/pharmacokinetics
- Peptides, Cyclic/pharmacology
- Protein Binding
- Protein Structure, Secondary
- Rats
- Rats, Sprague-Dawley
- Rats, Wistar
- Receptors, CXCR4/antagonists & inhibitors
- Tumor Cells, Cultured
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Affiliation(s)
- Steven J DeMarco
- Chemistry Department, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
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62
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Fasan R, Dias RLA, Moehle K, Zerbe O, Obrecht D, Mittl PRE, Grütter MG, Robinson JA. Structure-activity studies in a family of beta-hairpin protein epitope mimetic inhibitors of the p53-HDM2 protein-protein interaction. Chembiochem 2006; 7:515-26. [PMID: 16511824 DOI: 10.1002/cbic.200500452] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Inhibitors of the interaction between the p53 tumor-suppressor protein and its natural human inhibitor HDM2 are attractive as potential anticancer agents. In earlier work we explored designing beta-hairpin peptidomimetics of the alpha-helical epitope on p53 that would bind tightly to the p53-binding site on HDM2. The beta-hairpin is used as a scaffold to display energetically hot residues in an optimal array for interaction with HDM2. The initial lead beta-hairpin mimetic, with a weak inhibitory activity (IC(50)=125 microM), was optimized to afford cyclo-(L-Pro-Phe-Glu-6ClTrp-Leu-Asp-Trp-Glu-Phe-D-Pro) (where 6ClTrp=L-6-chlorotryptophan), which has an affinity almost 1,000 times higher (IC(50)=140 nM). In this work, insights into the origins of this affinity maturation based on structure-activity studies and an X-ray crystal structure of the inhibitor/HDM2(residues 17-125) complex at 1.4 A resolution are described. The crystal structure confirms the beta-hairpin conformation of the bound ligand, and also reveals that a significant component of the affinity increase arises through new aromatic/aromatic stacking interactions between side chains around the hairpin and groups on the surface of HDM2.
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Affiliation(s)
- Rudi Fasan
- Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
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Frecer V. QSAR analysis of antimicrobial and haemolytic effects of cyclic cationic antimicrobial peptides derived from protegrin-1. Bioorg Med Chem 2006; 14:6065-74. [PMID: 16714114 DOI: 10.1016/j.bmc.2006.05.005] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2006] [Revised: 04/12/2006] [Accepted: 05/03/2006] [Indexed: 11/25/2022]
Abstract
In this paper we quantitatively analyse antimicrobial and haemolytic activities of porcine protegrin-1 (PG-1) mimetics-cyclic cationic peptides with beta-hairpin fold synthesised by Robinson et al. [Bioorg. Med. Chem.2005, 13, 2055]. The presented QSAR models, which use molecular properties related to possible mechanisms of cell membrane disruption that can be easily calculated from available data on amino acids, rationalize the relationships between sequences and antimicrobial and haemolytic potencies of the cyclic peptides. The best models obtained by application of genetic function approximation algorithm correlate antimicrobial potencies to the peptide's charge and amphipathicity index, while the haemolytic effect correlates well with the lipophilicity of residues forming the nonpolar face of the beta-hairpin. The models permit selection of site-directed residue substitutions leading to simultaneous optimization of antimicrobial and haemolytic potencies. Examples of such residue substitutions in the nonpolar face of a symmetric cyclic beta-hairpin PG-1 analogue with an ideal amphipathic structure are given.
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Affiliation(s)
- Vladimir Frecer
- Cancer Research Institute, Slovak Academy of Sciences, Bratislava SK-83391, Slovakia.
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Fischer PM. Peptide, Peptidomimetic, and Small-molecule Antagonists of the p53-HDM2 Protein-Protein Interaction. Int J Pept Res Ther 2006; 12:3-19. [PMID: 19617922 PMCID: PMC2710987 DOI: 10.1007/s10989-006-9016-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/27/2005] [Indexed: 12/19/2022]
Abstract
Modulation of intracellular protein-protein interactions has been - and remains - a challenging goal for the discovery and development of small-molecule therapeutic agents. Progress in the pharmacological targeting and understanding at the molecular level of one such interaction that is relevant to cancer drug research, viz. that between the tumour suppressor protein p53 and its negative regulator HDM2, is reviewed here. The first X-ray crystal structure of a complex between a small peptide from the trans-activation domain of p53 and the N-terminal domain of HDM2 was reported almost 10 years ago. The nature of this interaction, which involves just three residue side chains in the p53 peptide ligand and a compact hydrophobic binding pocket in the HDM2 receptor, together with the attractive concept of reactivating the anti-proliferative functions of p53 in tumour cells, has spurned a great deal of effort aimed at finding drug-like antagonists of this interaction. A variety of approaches, including both structure-guided peptidomimetic and de novo design, as well as high through-put screening campaigns, have provided a wealth of leads that might be turned into actual drugs. There is still some way to go as far as optimisation and preclinical development of such leads is concerned, but it is clear already now that antagonists of the p53-HDM2 protein-protein interaction have a good chance of ultimately being successful in providing a new anti-cancer therapy modality, both in monotherapy and to potentiate the effectiveness of existing chemotherapies.
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Affiliation(s)
- Peter M. Fischer
- Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, NG7 2RD Nottingham, UK
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65
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Rai R, Raghothama S, Balaram P. Design of a Peptide Hairpin Containing a Central Three-Residue Loop. J Am Chem Soc 2006; 128:2675-81. [PMID: 16492054 DOI: 10.1021/ja056861v] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The construction of a designed beta-hairpin structure, containing a central three-residue loop has been successfully achieved in the synthetic nonapeptide Boc-Leu-Phe-Val-(D)Pro-(L)Pro-(D)Ala-Leu-Phe-Val-OMe (2). The design is based on expanding the two-residue loop established in the peptide beta-hairpin Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe (1). Characterization of the registered beta-hairpins in peptides 1 and 2 is based on the observation of key nuclear Overhauser effects (NOEs) in CDCl(3) and CD(3)OH. Solvent titration and temperature dependence of NH chemical shifts establish the identity of NH groups involved in interstrand hydrogen bonding. In peptide 2, the antiparallel registry is maintained, with the formation of a (D)Pro-(L)Pro-(D)Ala loop, stabilized by a 5-->1 hydrogen bond between Val3 CO and Leu7 NH groups (C(13), alpha-turn) and a 3-->1 hydrogen bond between (D)Pro4 CO and (d)Ala6 NH groups (C(7), gamma-turn). NMR derived structures suggest that in peptide 2, (d)Ala(6) adopts an alpha(L) conformation. In peptide 1, the (D)Pro-(L)Pro segment adopts a type II' beta-turn. Replacement of (D)Ala (6) in peptide 2 by (L)Ala in peptide 3 yields a beta-hairpin conformation, with a central (D)Pro-(L)Pro two-residue loop. Strand slippage at the C-terminus results in altered registry of the antiparallel strands.
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Affiliation(s)
- Rajkishor Rai
- Molecular Biophysics Unit and NMR Research Center, Indian Institute of Science, Bangalore
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