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C Humblet

Publications and source records attributed to C Humblet.

At least 55 records · Page 3Linked to original sources
PubMed1993

Multiple binding modes for the receptor-bound conformations of cyclic AII agonists.

Angiotensin II, Asp-Arg-Val-Tyr-His-Pro-Phe, binds its receptor with a postulated turn centered at residue four. Analogs of angiotensin II which contain a disulfide bridge between the side chains of residues 3 and 5 retain significant activity consistent with this hypothesis. Incorporation of 4-mercaptoproline residues, a hybrid, or chimeric amino acid which combines the properties of proline and homocysteine, into either of these positions with analogous disulfide bridges allows retention of high affinity for the receptor. These more highly constrained bicyclic systems give new insight into the details of molecular recognition of residues 3-5 of angiotensin by the receptor. Retention of activity by the antiparallel dimer of [Sar1,Cys3,5]-AII in which the peptide backbone is held in an extended conformation was unexpected. Analysis of the conformational constraints imposed in these active analogs suggests that AII agonists bind to their receptor with different backbone conformations in the region of the central tyrosine residue.

Amino Acid Sequence↗
PubMed1992

X-ray crystallographic analysis of inhibition of endothiapepsin by cyclohexyl renin inhibitors.

The crystal structures of endothiapepsin, a fungal aspartic proteinase (EC 3.4.23.6), cocrystallized with two oligopeptide renin inhibitors, PD125967 and PD125754, have been determined at 2.0-A resolution and refined to R-factors of 0.143 and 0.153, respectively. These inhibitors, which are of the hydroxyethylene and statine types, respectively, possess a cyclohexylalanine side chain at P1 and have interesting functionalities at the P3 position which, until now, have not been subjected to crystallographic analysis. PD125967 has a bis(1-naphthylmethyl)acetyl residue at P3, and PD125754 possesses a hydroxyethylene analogue of the P3-P2 peptide bond for proteolytic stability. The structures reveal that the S3 pocket accommodates one naphthyl ring with conformational changes of the Asp 77 and Asp 114 side chains, the other naphthyl group residing in the S4 region. The P3-P2 hydroxyethylene analogue of PD125754 forms a hydrogen bond with the NH of Thr 219, thereby making the same interaction with the enzyme as the equivalent peptide groups of all inhibitors studied so far. The absence of side chains at the P2 and P1' positions of this inhibitor allows water molecules to occupy the respective pockets in the complex. The relative potencies of PD125967 and PD125754 for endothiapepsin are consistent with the changes in solvent-accessible area which take place on inhibitor binding.

Amino Acid Sequence↗
PubMed1992

Generation of N-methyl-D-aspartate agonist and competitive antagonist pharmacophore models. Design and synthesis of phosphonoalkyl-substituted tetrahydroisoquinolines as novel antagonists.

The preparation and binding affinity of a series of tetrahydroisoquinoline carboxylic acids at the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor is described, together with a molecular modeling analysis of NMDA agonists and antagonists. Using published NMDA ligands, the active analogue mapping approach was employed in the generation of an agonist pharmacophore model. Although known competitive antagonists such as CPP (1) could be superimposed onto the agonist model, to overcome the assumption that they bind to the same receptor site, an independent modeling approach was used to derive a separate pharmacophore model. Development of a competitive antagonist model involved a stepwise approach that included the definition of a preferred geometry for PO3H2-receptor interactions, multiple conformational searches, and the determination of volume and electronic tolerances. This model, which is described in detail, is consistent with observed affinities of potent NMDA antagonists and has provided an explanation for the observed periodicity in affinities for the known antagonists AP5, AP6, and AP7. The features of the agonist and antagonist models are compared, and hypotheses advanced about the nature of the receptor interactions for these two classes of compounds. The pharmacophore models reported herein are consistent with a single recognition site at the NMDA receptor that can accommodate both agonist and antagonist ligands. To assist in first defining and later exploring the predictive power of the competitive antagonist model, a series of conformationally constrained NMDA antagonist (phosphonoalkyl)tetrahydroisoquinoline-1- and 3-carboxylates was prepared. From this work, 1,2,3,4-tetrahydro-5-(2-phosphonoethyl)-3- isoquinolinecarboxylic acid (89) was identified as the most active lead structure, with an IC50 of 270 nM in [3H]CPP binding. The synthesis and structure-activity relationships of these novel antagonists are described.

Binding, Competitive↗
PubMed1992

Renin inhibitors containing alpha-heteroatom amino acids as P2 residues.

A series of renin inhibitors having alpha-heteroatom amino acids as P2 substitutions has been prepared. Examples where the heteroatom is oxygen, sulfur, or nitrogen are described. Many of the compounds exhibit subnanomolar potency when tested in vitro against monkey renin. When selected compounds were tested orally in conscious, salt-depleted, normotensive, Cynomolgus monkeys, low to moderate blood pressure lowering was observed. At an oral dose of 30 mg/kg, compound 53a lowered blood pressure by a maximum of 18 mmHg at 2.5 h post-dose.

Amino Acids↗
PubMed1992

Modeling rhodopsin, a member of G-protein coupled receptors, by computer graphics. Interpretation of chemical shifts of fluorinated rhodopsins.

An attempt has been made to construct a 3-D model of rhodopsin, a member of G-protein coupled receptors. Sequence homology of rhodopsin with the latter was a factor considered in the modeling procedure. The constructed model has been used to compare currently available specific protein/substrate interaction information, the shape of the binding cavity derived from shape of binding retinal isomers and analogs and challenged to explain recently available results from a series of fluorinated rhodopsins.

Amino Acid Sequence↗
PubMed1992

Analysis by in situ hybridization of cells expressing mRNA for tumor-necrosis factor in the developing thymus of mice.

We have used in situ hybridization to investigate the expression of TNF-alpha genes by thymic cells during fetal development in mice. In 14-day-old fetal thymuses, very scarce cells produce TNF-alpha mRNA. A second phase of cytokine gene expression starts on day 16. The density of positive cells progressively increases up to day 20. Thymuses at 15 days of gestation and after birth do not express detectable cytokine mRNA. In an attempt to identify the nature of the TNF-alpha mRNA-producing cells, acid phosphatase activity, which is characteristic of the macrophage lineage, was studied in the same thymuses. Acid phosphatase-positive cells only appear on day 15. Their frequency increases up to birth. However, no correlation can be established between acid phosphatase--and TNF alpha mRNA--positive cells. The results indicate that a small subset of thymic cells is responsible for TNF-alpha mRNA production during ontogeny: These cells are not yet identified. The possible role of TNF-alpha in thymic ontogeny is discussed.

Acid Phosphatase↗
PubMed1991

An investigation of Chromatium vinosum high-potential iron-sulfur protein by EPR and Mossbauer spectroscopy; evidence for a freezing-induced dimerization in NaCl solutions.

The high-potential iron-sulfur protein (HiPIP) from Chromatium vinosum contains a cubane prosthetic group that shuttles between the [4Fe-4S]3+,2+ states. We find that the EPR spectra from this protein can be explained as a sum of two components, a major one with g = 2.02; 2.04; 2.12, and a minor one with g = 2.04; 2.07; approximately 2.13. In the presence of 0.1-2.0 M NaCl, freezing induces polymerization of the protein (presumably dimers), which is detected as intercluster spin-spin interaction in the EPR. The observed spin-spin interactions are interpreted as being due to two very similar dimeric structures in an approx. 1:2 ratio. Computer simulation of the X- and Q-band EPR spectra shows that the z-components of the g-tensors in each dimer pair must be co-linear, with center-to-center distances between the clusters of approximately 13 A and approximately 16 A. Inspection of possible dimeric structures of C. vinosum HiPIP by standard molecular graphics procedures revealed that the Fe/S cluster is exposed toward a flattened surface and is accessible to solvent. Moreover, the Fe/S clusters in two HiPIP molecules can easily achieve a center-to-center distance of approximately 14 A when approaching along a common 3-fold axis that extends through the S4 sulfur atom of the cubane; the z-component of the EPR g-tensor is co-linear with this symmetry axis.

Chromatium↗
PubMed1991

Highly selective kappa opioid analgesics. 4. Synthesis of some conformationally restricted naphthalene derivatives with high receptor affinity and selectivity.

This paper describes the synthesis and kappa and mu opioid receptor binding affinity of some conformationally restrained derivatives of the arylacetamide group in the selective kappa opioid receptor agonist (+/-)-trans-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzo [b]thiophene-4-acetamide monohydrochloride (1,PD117302), which is an analogue of U-50, 488. The methyl-substituted derivatives (+/-)-trans-N, alpha-dimethyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzo-[b] thiophene-4-acetamide monohydrochloride (6a,b) possess significantly weaker affinity than 1 for the kappa opioid receptor (Ki = 172 and 3.7 nM, respectively). It is proposed that this is due to the conformational restriction imposed by the methyl group of 6. In order to test this proposal the acenaphthene derivative and the 4,5-dihydro-3H-naphtho [1,8-bc]thiophene derivative were prepared. The acenaphthene derivative (+)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro [4.5]dec-8-yl]acenaphthenecarboxamide monohydrochloride (9) was found to have high kappa opioid receptor affinity and selectivity (kappa Ki = 0.37 +/- 0.05 nM, mu/kappa = 659, delta/kappa = 1562) and is 100 times more potent than morphine as an analgesic in the rat paw pressure test for analgesia after intravenous administration (MPE50 = 0.014 and 1.4 mg/kg, respectively). The 4,5-dihydro-3H-naphtho[1,8-bc]thiophene derivative (-)-4,5-dihydro-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro [4.5]dec-8-yl]-3H-naphthol[1,8-bc]thiophene-5-carboxamide p-toluenesulfonate (17) also has high kappa opioid receptor affinity and selectivity (kappa Ki = 4.65 nM, mu/kappa = 109).

Analgesics↗
PubMed1990

Effect of interferon-gamma and tumor necrosis factor-alpha on lymphoepithelial interactions within thymic nurse cells.

Isolated thymic nurse cells (TNC) represent a specialized microenvironment in vivo where thymocytes interact specifically with subcapsular epithelial cells. They are thought to play a critical role in the process of T cell differentiation. We demonstrate that recombinant murine interferon-gamma and recombinant human tumor necrosis factor-alpha can act on these interactions: they stimulate TNC-derived epithelial cells to establish interactions with thymocytes in vitro and to form new lymphoepithelial complexes. This phenomenon is partially inhibited by anti-Ia monoclonal antibodies. Implications of these findings for normal intrathymic differentiation are discussed.

Animals↗
PubMed1990

Cellular events in radiation-induced lymphomagenesis.

Fractionated whole-body irradiation induces thymic lymphomas in most of treated C57Bl/Ka mice. The cellular events occurring during the latency period consist of the emergence of preleukaemic cells and of marked alterations to the T-cell lineage and the microenvironment within the thymus. The proportions of the various thymocyte subsets are modified, suggesting a blockage in the normal differentiation process. Thymic epithelial cells are functionally modified, leading to decreased interactions with immature thymocytes. Interestingly, bone marrow grafting early after irradiation, which inhibits the development of lymphomas, induces the disappearance of preleukaemic cells from the thymus, whereas thymocyte subpopulations and thymic epithelium are restored. Interferon gamma and tumor necrosis factor alpha also prevent the onset of lymphomas. Studies on the effect of bone marrow transplantation and cytokine inoculation in split-dose irradiated mice should allow characterization of the factors that modulate the progression of preleukaemic cells towards the neoplastic state.

Animals↗
PubMed1990

Abnormal thymocyte subpopulations in split dose irradiated C57BL/Ka mice before the onset of lymphomas. Effects of bone marrow grafting.

Fractionated whole-body X irradiation (4 x 1.75 Gy at weekly intervals) induces a high percentage of thymic lymphomas in C57BL/Ka mice. The present work reports the phenotypic alterations of thymocyte subpopulations during the preleukemic period: there were a decrease of CD4+ CD8+ cells and an increase of CD4- CD8- and CD4- CD8+ cells. Marrow grafting early after irradiation that prevents lymphoma development restores the thymocyte subpopulations. In many instances, transplantation of 'preleukemic thymocyte inoculate' gives rise to an active and long lasting repopulation of recipient thymuses. However in all cases, donor lymphomas can develop after inoculation of 'preleukemic thymocyte inoculate'.

Animals↗
PubMed1989

Tumor necrosis factor and interferon gamma inhibit the development of radiation-induced thymic lymphomas in C57BL/Ka mice.

Recombinant tumor necrosis factor and/or gamma-interferon were injected into C57BL/Ka mice after completion of a whole body split dose irradiation, which usually induces thymic lymphomas in more than 90% of the animals. The survival and the incidence of thymic lymphomas were significantly reduced in the cytokine-injected irradiated mice. The protective effect was similar to that obtained by grafting normal bone marrow cells after irradiation. The mechanisms of lymphoma inhibition by TNF or IFN-gamma are discussed.

Animals↗
PubMed1989

Control of lymphoepithelial interactions within thymic nurse cells by gamma-interferon and tumor necrosis factor alpha. Possible role in the modulation of intrathymic education?

The role of cytokines in the process of intrathymic differentiation is not yet clearly established. The results presented in this paper demonstrate that interferon-gamma and tumor necrosis factor-alpha regulate 'in vivo' and 'in vitro' the interactions between epithelial cells and thymocytes within thymic nurse cells. The mechanism of action of these cytokines and their possible physiologic role 'in vivo' are discussed.

Animals↗
PubMed1989

Further studies on the mechanism of radiation induced thymic lymphoma prevention by bone marrow transplantation in C57BL mice.

Whole body fractionated irradiation induces thymic lymphomas in C57BL/Ka mice after a latent period during which intrathymic lymphopoiesis is modified; thymocyte numbers are subnormal and the epithelial component of thymic nurse cells (TNCs) is altered as estimated by the number of TNCs in vivo and by its ability to interact with immature thymocytes in vitro. A graft of normal bone marrow cells immediately after the last irradiation prevents the development of lymphomas; but when such a graft is performed 1 month later, it does not inhibit the emergence of tumors. In both cases the grafted precursors home and repopulate the thymus. However, the delayed graft does not exert any effect upon the altered epithelial component of TNCs, whereas the early one restores the numbers of TNCs and the function of their epithelial component. The results thus demonstrate that lymphoid thymic repopulation by a bone marrow graft is not sufficient to prevent the development of lymphomas and that there is an intimate relationship between tumor development and alterations of nurse cells microenvironment.

Animals↗