The incretin system: glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in type 2 diabetes

▪ Abstract The prostaglandin endoperoxide H synthases-1 and 2 (PGHS-1 and PGHS-2; also cyclooxygenases-1 and 2, COX-1 and COX-2) catalyze the committed step in prostaglandin synthesis. PGHS-1 and 2 are of particular interest because they are the major targets of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen, and the new COX-2 inhibitors. Inhibition of the PGHSs with NSAIDs acutely reduces inflammation, pain, and fever, and long-term use of these drugs reduces fatal thrombotic events, as well as the development of colon cancer and Alzheimer's disease. In this review, we examine how the structures of these enzymes relate mechanistically to cyclooxygenase and peroxidase catalysis, and how differences in the structure of PGHS-2 confer on this isozyme differential sensitivity to COX-2 inhibitors. We further examine the evidence for independent signaling by PGHS-1 and PGHS-2, and the complex mechanisms for regulation of PGHS-2 gene expression.

Cyclooxygenases: Structural, cellular, and molecular biology

For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

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Structural and Functional Aspects of Metal Sites in Biology

Heme-Containing Oxygenases

The role of fluorine in drug design and development is expanding rapidly as we learn more about the unique properties associated with this unusual element and how to deploy it with greater sophistication. The judicious introduction of fluorine into a molecule can productively influence conformation, pKa, intrinsic potency, membrane permeability, metabolic pathways, and pharmacokinetic properties. In addition, 18F has been established as a useful positron emitting isotope for use with in vivo imaging technology that potentially has extensive application in drug discovery and development, often limited only by convenient synthetic accessibility to labeled compounds. The wide ranging applications of fluorine in drug design are providing a strong stimulus for the development of new synthetic methodologies that allow more facile access to a wide range of fluorinated compounds. In this review, we provide an update on the effects of the strategic incorporation of fluorine in drug molecules and applications in po...

Applications of Fluorine in Medicinal Chemistry

The present invention relates to novel inhibitors of serine type peptidases in general and of serine type dipeptidyl peptidases in particular. The present invention further relates to the use of the dipeptidyl peptidase inhibitors for selective inhibition of dipeptidyl peptidases. The present invention also relates to pharmaceutical compositions comprising these novel dipeptidyl peptidase inhibitors. The present invention further relates to the use of the novel inhibitors in therapy, diagnosis and research.

Dipeptidyl peptidase inhibitors

For the first time elementary reactions involving chloroperoxidase compounds I and II have been investigated. A multi-mixing stopped-flow apparatus was used to study the kinetics of the reactions of compounds I and II with ascorbic acid, ferrocyanide and p-phenolsulfonic acid. The second-order rate constants of the reactions of both compounds with all three substrates were determined between pH 3 and pH 7. In all cases the rate constants decrease with increasing pH. The reactions of p-phenolsulfonic acid are influenced by a catalytically important group on both compounds I and II with a pKa of 3.7 +/- 0.2. With ascorbic acid and ferrocyanide as substrates, a decrease in rate was observed upon ionization of the substrate. Comparisons with horseradish peroxidase show that chloroperoxidase is a much less efficient peroxidatic enzyme. The kinetic data were used to calculate the percentage composition of the mixture of chloroperoxidase species which contribute to the spectra measured during the turnover with ascorbate as substrate.

Kinetics of the oxidation of ascorbic acid, ferrocyanide and p-phenolsulfonic acid by chloroperoxidase compounds I and II.

Prolyl oligopeptidase (PO) interacts with α-syncline in vitro. It is a weak interaction that induces a nucleation prone conformation of α-synuclein. PO accelerates aggregation and fibril formation of α-syncline in a process that can be reversed by specific inhibitors and is also influenced by an impairing mutation in the PO active site. There is evidence that PO and α-synuclein also interact intracellularly, especially in conditions where the expression of α-synuclein is high. Specific PO inhibitors reduce the number of cells with α-synuclein inclusions in a cellular model of Parkinson's disease. If these interactions also exist in the human brain, PO may be a target for the treatment of Parkinson's disease and other synucleinopathies. Whether PO also contributes to the normal physiological functions of α-syncline remains an open question, but there are some intriguing parallels between the proposed functions of both proteins that deserve further investigation.

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Interaction of Prolyl Oligopeptidase with α-Synuclein

DPP IV has been attributed a large array of functions, some of which are mediated by its exopeptidase activity. Although it only removes two amino acid residues at the N-terminus of the peptide, this cleavage can inactivate or modify the activity of regulatory peptides, peptide hormones, chemokines and neuropeptides. Several excellent DPP IV substrates with high specificity constants were identified by the in vitro kinetic study of the truncation of bioactive peptides by DPP IV. In vivo studies e.g. with DPP IV negative animals and in vivo inhibition experiments could enlighten us on the physiological relevance of these truncations. The DPP IV mediated truncation of bioactive peptides has been reviewed on several occasions (Mentlein et al 1999, Lambeir et al 2003, DeMeester et al 2000 and 2003). Here we want (1) to present some data on a novel DPP IV substrate, (2) to review some of the recent literature on known substrates and (3) to discuss the possible truncation of known DPP IV substrates by related dipeptidyl peptidases.

Peptide substrates of dipeptidyl peptidases.

Urokinase plasminogen activator (uPA) is a biomarker and therapeutic target for several cancer types. Its inhibition is regarded as a promising, noncytotoxic approach in cancer therapy by blocking growth and/or metastasis of solid tumors. Earlier, we reported the modified substrate activity screening (MSAS) approach and applied it for the identification of fragments with affinity for uPA’s S1 pocket. Here, these fragments are transformed into a novel class of uPA inhibitors with an imidazo[1,2-a]pyridine scaffold. The SAR for uPA inhibition around this scaffold is explored, and the best compounds in the series have nanomolar uPA affinity and selectivity with respect to the related trypsin-like serine proteases (thrombin, tPA, FXa, plasmin, plasma kallikrein, trypsin, FVIIa). Finally, the approach followed for translating fragments into small molecules with a decorated scaffold architecture is conceptually straightforward and can be expected to be broadly applicable in fragment-based drug design.

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Anne-Marie Lambeir

Papers

Dipeptidyl peptidase inhibitors

Kinetics of the oxidation of ascorbic acid, ferrocyanide and p-phenolsulfonic acid by chloroperoxidase compounds I and II.

Interaction of Prolyl Oligopeptidase with α-Synuclein

Peptide substrates of dipeptidyl peptidases.

Discovery and SAR of Novel and Selective Inhibitors of Urokinase Plasminogen Activator (uPA) with an Imidazo[1,2-a]pyridine Scaffold.