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Biomedical subjects

E Hamel

Publications and source records attributed to E Hamel.

At least 73 records · Page 4Linked to original sources
PubMed1999

Functional calcitonin gene-related peptide type 1 and adrenomedullin receptors in human trigeminal ganglia, brain vessels, and cerebromicrovascular or astroglial cells in culture.

Calcitonin gene-related peptide (CGRP) and adrenomedullin (ADM) are potent dilators of human brain arteries, and they have been implicated in the neurogenic inflammation underlying migraine headache and in the evolution of stroke, respectively. However, little is known about the presynaptic and postsynaptic distribution of their respective receptors in the human cerebrovascular bed and trigeminovascular system. In the current study, the expression of mRNA for ADM and the two cloned human CGRP1 receptors (identified here as A-CGRP1 receptors [Aiyar et al., 1996] and K-CGRP1 receptors) [Kapas and Clark, 1995] were evaluated in human brain vessels and trigeminal ganglia. Further, the ability of CGRP and ADM to activate adenylate cyclase in cerebromicrovascular and astroglial cell cultures was determined, and the receptors involved were characterized pharmacologically. Isolated human pial vessels, intracortical microvessels, and capillaries, as well as cultures of brain endothelial (EC), smooth muscle (SMC), and astroglial (AST) cells, all expressed mRNA for the two cloned CGRP1 receptors; however, message for the K-CGRP1 receptor was barely detectable in microvascular tissues and cells. In contrast, only isolated capillaries and cultured AST exhibited message for the ADM receptor. In human trigeminal ganglia, mRNA for ADM and the two CGRP1 receptors was systematically present. The CGRP dose-dependently increased (up to 50-fold) cAMP formation in cell cultures, an effect significantly blocked by 0.1 to 10 micromol/L of the CGRP1 receptor antagonist CGRP8-37. The ADM receptor agonist, ADM13-52 (1 micromol/L), similarly increased cAMP production in all cell types, and this response was virtually abolished by 1 micromol/L CGRP8-37. Low concentrations (1 to 10 micromol/L) of the ADM receptor antagonist ADM22-52 blocked the ADM13-52-induced cAMP formation in AST (26% at 10 micromol/L, P < 0.05), whereas they potentiated this response in brain EC and SMC (40% and 100%, P < 0.001, respectively). Even at a higher dose (50 micromol/L), ADM22-52 inhibited the ADM13-52 effect in vascular cells (45%) much less effectively than in AST (95%). These results indicate that both CGRP and ADM can affect human brain vessels through a CGRP1 receptor, and they further suggest the presence of functional ADM receptors in human astroglial cells.

Astrocytes↗
PubMed1999

Current concepts of migraine pathophysiology.

Although the exact cascade of events that culminate into a migraine attack remains elusive, the mechanisms that underlie the manifestation of migraine pain have been better studied, and results obtained in animal models provide insight into the human situation. In this respect, primary headaches such as migraine and cluster headaches are best described as "the manifestation of a hereditary or predisposed sensitivity of neurovascular reactions to certain stimuli or to cyclic changes in the central nervous system". Evidence indicates that a migraine originates in the brain and, in its process and evolution, affects the meningeal blood vessels and leads to the development of head pain. This manifestation has been related to the activation of the trigeminovascular sensory nerves, which release neuropeptides that mediate vasodilation, and the proinflammatory reaction thought to be involved in pain generation and transmission. Such a concept underscores the fact that the relationship between the nerves and the blood vessels is of paramount importance in the manifestation of the disease's symptoms. Multiple characteristics in migraine sufferers, including recently identified genetic factors, may determine their thresholds to various neuronal and/or vascular stimuli and as such may form the basis for the future understanding of migraine pathogenesis.

Animals↗
PubMed1998

Synthesis and biological evaluation of 2-acyl analogues of paclitaxel (Taxol).

The anticancer drug paclitaxel (Taxol) has been converted to a large number of 2-debenzoyl-2-aroyl derivatives by three different methods. The bioactivities of the resulting analogues were determined in both tubulin polymerization and cytotoxicity assays, and several analogues with enhanced activity as compared with paclitaxel were discovered. Correlation of cytotoxicity in three cell lines with tubulin polymerization activity showed reasonable agreement. Among the cell lines examined, the closest correlation with antitubulin activity was observed with a human ovarian carcinoma cell line.

Antineoplastic Agents, Phytogenic↗
PubMed1998

Structure-activity requirements for flavone cytotoxicity and binding to tubulin.

A series of 79 flavones related to centaureidin (3,6,4'-trimethoxy-5, 7,3'-trihydroxyflavone, 1) was screened for cytotoxicity in the NCI in vitro 60-cell line human tumor screen. The resulting cytotoxicity profiles of these flavones were compared for degree of similarity to the profile of 1. Selected compounds were further evaluated with in vitro assays of tubulin polymerization and [3H]colchicine binding to tubulin. Maximum potencies for tubulin interaction and production of differential cytotoxicity profiles characteristic of 1 were observed only with compounds containing hydroxyl substituents at C-3' and C-5 and methoxyl groups at C-3 and C-4'.

Antineoplastic Agents, Phytogenic↗
PubMed1998

Antitumor agents. 185. Synthesis and biological evaluation of tridemethylthiocolchicine analogues as novel topoisomerase II inhibitors.

Several 1,2,3-tridemethyldeacetylthiocolchicine derivatives have been synthesized and evaluated for cytotoxic activity against various human tumor cell lines and for their inhibitory effects on DNA topoisomerases in vitro. Exhaustive demethylation of thiocolchicine analogues completely changes their biological profiles. Instead of displaying antitubulin activity, most target compounds inhibited topoisomerase II activity. Only compounds with a larger side chain, such as 15a, 23a, and 24a, did not interfere with topoisomerase II enzymatic functions. The cytotoxicity of target compounds was reduced by 3 orders of magnitude compared to that of colchicine in most cell lines. The hydrophilicity of phenolic compounds might prevent drug passage through the cell plasma membrane and, thus, be responsible for the relatively weak cytotoxicity. To test this hypothesis, 27-30 were prepared from 16a by protecting all hydroxy groups with esters with an aim to facilitate drug transportation. In vitro cytotoxicity assays indicated that 27 was more potent than its parent compound in all tested tumor cell lines and showed tissue selective cytotoxicity with a significant inhibitory effect against KB cells (IC50 = 2.7 microg/mL). Therefore, we propose that 27 acts as a prodrug, liberating 16a to exert its antitopoisomerase activity and, finally, to cause cell death.

Antineoplastic Agents↗
PubMed1998

Antineoplastic agents. 379. Synthesis of phenstatin phosphate.

A structure-activity relationship (SAR) study of the South African willow tree (Combretum caffrum) antineoplastic constituent combretastatin A-4 (1b) directed at maintaining the (Z)-stilbene relationship of the olefin diphenyl substituents led to synthesis of a potent cancer cell growth inhibitor designated phenstatin (3b). Initially phenstatin silyl ether (3a) was unexpectedly obtained by Jacobsen oxidation of combretastatin A-4 silyl ether (1c --> 3a), and the parent phenstatin (3b) was later synthesized (6a --> 3a --> 3b) in quantity. Phenstatin was converted to the sodium phosphate prodrug (3d) by a dibenzyl phosphite phosphorylation and subsequent hydrogenolysis sequence (3b --> 3c --> 3d). Phenstatin (3b) inhibited growth of the pathogenic bacterium Neisseriagonorrhoeae and was a potent inhibitor of tubulin polymerization and the binding of colchicine to tubulin comparable to combretastatin A-4 (1b). Interestingly, the prodrugs were found to have reduced activity in these biochemical assays. While no significant tubulin activity was observed with the phosphorylated derivative of combretastatin A-4 (1d), phosphate 3d retained detectable inhibitory effects in both assays.

Animals↗
PubMed1998

Direct photoaffinity labeling of cysteine-295 of alpha-tubulin by guanosine 5'-triphosphate bound in the nonexchangeable site.

The alphabeta-tubulin heterodimer has two high affinity guanosine 5'-triphosphate binding sites, so that purified tubulin usually contains two molecules of bound guanosine nucleotide. Half this nucleotide is freely exchangeable with exogenous guanine nucleotide, and its binding site has been readily localized to the beta-subunit. The remaining nonexchangeable guanosine 5'-triphosphate can only be released from tubulin by denaturing the protein. We replaced the exchangeable site nucleotide of tubulin with 2'-deoxyguanosine 5'-diphosphate, exposed the resulting tubulin to ultraviolet light, degraded the protein, and isolated ribose-containing peptide derived from the nonexchangeable site. A large cyanogen bromide peptide was recovered, and its further degradation with endoproteinase Glu-C established that cysteine-295 of alpha-tubulin was the major reactive amino acid cross-linked to guanosine by ultraviolet irradiation.

Affinity Labels↗
PubMed1998

Antitumor agents. 181. Synthesis and biological evaluation of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl-4-quinolones as a new class of antimitotic antitumor agents.

A novel series of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl- 4-quinolones were synthesized and evaluated for interactions with tubulin and for cytotoxic activity against a panel of human tumor cell lines, including ileocecal carcinoma (HCT-8), breast cancer (MCF-7), lung carcinoma (A-549), epidermoid carcinoma of the nasopharynx (KB), renal cancer (CAKI-1), and melanoma cancer (SKMEL-2). Most compounds (18, 20, 22-27) showed potent cytotoxic and antitubulin effects. The most active compounds (23, 26, 27) demonstrated strong cytotoxic effects with ED50 values in the nanomolar or subnanomolar range in almost all tumor cell lines. Three active racemates (20, 22, 25) were separated into the enantiomers, and generally, the optically pure (-)-isomers (20a, 22a, 25a) exhibited greater biological activity than the racemates or (+)-isomers. Cytotoxicity and antitubulin activity were closely correlated, with the most active compounds (23, 26, 27) having effects comparable to those of colchicine, podophyllotoxin, and combretastatin A-4.

Antibiotics, Antineoplastic↗
PubMed1998

Curacin D, an antimitotic agent from the marine cyanobacterium Lyngbya majuscula.

Curacin D is a novel brine shrimp toxic metabolite isolated from a Virgin Islands collection of the marine cyanobacterium Lyngbya majuscula. Structure elucidation of curacin D was accomplished through multidimensional NMR, GC/MS, and comparisons with curacin A. Curacin D provides new insights into structure-activity relationships in this natural product class as well as some aspects of the likely biosynthetic pathway of the curacins.

Cyanobacteria↗
PubMed1998

Endothelial expression of the 5-hydroxytryptamine1B antimigraine drug receptor in rat and human brain microvessels.

In addition to triggering vasoconstriction of peripheral blood vessels, which led to its discovery as a circulating neurohormone 50 years ago, serotonin (5-hydroxytryptamine) acts as a neurotransmitter/ modulator in the central nervous system and regulates local cerebral blood flow and vascular permeability through direct and indirect effects on intraparenchymal microvessels. Among the various 5-hydroxytryptamine receptors which mediate these effects, particular attention has been paid to the 5-hydroxytryptamine1B and 5-hydroxytryptamine1D subtypes, as the preferred targets of modern antimigraine agents. Immunoelectron microscopic labeling of the 5-hydroxytryptamine1B receptor in rat brain parenchyma has revealed a distinct localization to the endothelium of microvessels, which was predominantly cytoplasmic as opposed to membrane-bound, contrary to that on preterminal unmyelinated axons [Riad et al. (1997) Soc. Neurosci. Abstr. 23, 1214]. Similar observations have now been made in human cortical tissue, in which the expected localization of the vascular 5-hydroxytryptamine1B receptor to periarteriolar myocytes was also confirmed. Such a dual localization in human brain microvessels suggests that the 5-hydroxytryptamine1B receptor might mediate opposite effects, vasodilatory and contractile, depending upon its activation by circulating or centrally released 5-hydroxytryptamine. It raises new possibilities as regards 5-hydroxytryptamine effects on human brain microvessels in health and disease, and notably the triggering of migraine headache.

Animals↗
PubMed1998

Antitumor agents. Part 186: Synthesis and biological evaluation of demethylcolchiceinamide analogues as cytotoxic DNA topoisomerase II inhibitors.

Demethylation of colchiceinamide (2) and its analogues (3-10) afforded a novel class of mammalian DNA topoisomerase II inhibitors (2a-10a) without displaying tubulin inhibitory activity. All target compounds inhibited the catalytic activity of topoisomerase II at drug concentrations at 100 microM. An in vitro cytotoxicity assay indicated that compounds 3a and 8a were strong and tissue-selective cytotoxic agents against the MCF-7 breast cancer cell line (IC50 = 0.36 and 0.48 microgram/mL, respectively) and the CAKI-1 renal cancer cell line (IC50 = 0.72 and 0.96 microgram/mL, respectively).

Antineoplastic Agents↗
PubMed1998

Assessment of the peripheral benzodiazepine receptors in human gliomas by two methods.

This study was designed to evaluate the density of peripheral benzodiazepine receptor (PBR) sites as a function of tumor malignancy in human gliomas, and to compare the results obtained with autoradiographic and liquid scintillation measurements performed on the same tissue specimens. In vitro binding of [3H]PK-11195[1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoguinol ine carboxamide] to human gliomas in radioligand binding studies revealed a significantly higher level (about 3 fold) of PBR binding sites in both low grade and high grade gliomas as compared to normal cortex. The Bmax (mean +/- SD) of high and low grade gliomas, when entire tissue sections were measured by autoradiography, was 5.5 +/- 0.3 pmol/mg-tissue (n = 5) and 1.8 +/- 0.9 pmol/mg-tissue (n = 6), respectively, although it was evident that there was area of hot spots in the high grade tumors. This difference was significant (p < 0.05; two-tailed t-test). Similarly, the KD values (dissociation constant; nM) between the high (KD = 20.4 +/- 1.3 nM) and low (KD = 14.3 +/- 2.1 nM) grade gliomas were significantly different. A significant difference in binding site density (Bmax) between the two types of gliomas was also obtained in liquid scintillation measurements. The hot spot areas which showed the most intense binding of [3H]PK-11195 had KD of 24.5 +/- 1.0 nM and Bmax of 6.2 +/- 0.42 pmol/mg-tissue, values significantly higher (p < 0.05, two-tailed t-test) than those obtained when the entire tissue section was measured. The data on the Bmax/KD ratios presented here suggest that it might be possible to differentiate high from low grade gliomas in human by in vivo imaging with 11C-labelled PK-11195.

Astrocytoma↗
PubMed1998

Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurons and cloning of the rat Y2 receptor.

1 Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time. 2 More than 70% of the hippocampal neurones were endowed with [125I]-[Leu31,Pro34]PYY Y1-like receptor silver grain accumulations and Y1 receptor immunostaining. These radio- and immuno-labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal-like neuronal cells, as confirmed by neurone-specific enolase and MAP-2 staining. 3 Competition binding profiles revealed that specific [125I]-[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub-type with [Leu31,Pro34]substituted NPY/PYY analogues >> C-terminal fragments = pancreatic polypeptides, with the non-peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]-[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors. 4 The expression of the genuine Y1 receptor was confirmed by RT-PCR in hippocampal cultures. In contrast, negligible levels of Y2-like/[125I]-PYY3-36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT-PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero. 5 Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

Amino Acid Sequence↗
PubMed1998

Structure-activity analysis of the interaction of curacin A, the potent colchicine site antimitotic agent, with tubulin and effects of analogs on the growth of MCF-7 breast cancer cells.

Originally purified as a major lipid component of a strain of the cyanobacterium Lyngbya majuscula isolated in Curaçao, curacin A is a potent inhibitor of cell growth and mitosis, binding rapidly and tightly at the colchicine site of tubulin. Because its molecular structure differs so greatly from that of colchicine and other colchicine site inhibitors, we prepared a series of curacin A analogs to determine the important structural features of the molecule. These modifications include reduction and E-to-Z transitions of the olefinic bonds in the 14-carbon side chain of the molecule; disruption of and configurational changes in the cyclopropyl moiety; disruption, oxidation, and configurational reversal in the thiazoline moiety; configurational reversal and substituent modifications at C13; and demethylation at C10. Inhibitory effects on tubulin assembly, the binding of colchicine to tubulin, and the growth of MCF-7 human breast carcinoma cells were examined. The most important portions of curacin A required for its interaction with tubulin seem to be the thiazoline ring and the side chain at least through C4, the portion of the side chain including the C9-C10 olefinic bond, and the C10 methyl group. Only two modifications totally eliminated the tubulin-drug interaction. The inactive compounds were a segment containing most of the side chain, including its two substituents, and analogs in which the methyl group at the C13 oxygen atom was replaced by a benzoate residue. Antiproliferative activity comparable with that observed with curacin A was only reproduced in compounds that were potent inhibitors of the binding of colchicine to tubulin. Molecular modeling and quantitative structure-activity relationship studies demonstrated that most active analogs overlapped extensively with curacin A but failed to provide an explanation for the apparent structural analogy between curacin A and colchicine.

Animals↗
PubMed1998

Antineoplastic agents 393. Synthesis of the trans-isomer of combretastatin A-4 prodrug.

The (E)-stilbene isomer (2a) of the (Z)-combretastatin A-4 prodrug (1b) was efficiently prepared from (E)-combretastatin A-4 by a reaction sequence employing phosphorylation (dibenzyl chlorophosphite), cleavage (trimethyliodosilane) of the benzyl ester and reaction of the resulting phosphoric acid with sodium methoxide. The sodium phosphate product (2c) was also found to be an important side-product, presumably from iodine-catalyzed isomerization, when the analogous synthetic route was used to obtain the combretastatin A-4 prodrug (1b). The phosphoric acid precursor of prodrug 1b derived from (Z)-combretastatin A-4 (1a) was converted into a series of metal cation and ammonium cation salts to evaluate effects on human cancer cell growth, antimicrobial activities and solubility behavior.

Animals↗
PubMed1998

Antineoplastic agents 360. Synthesis and cancer cell growth inhibitory studies of dolastatin 15 structural modifications.

Dolastatin 15 (1), a potent antineoplastic constituent of the Indian Ocean shell-less mollusk Dolabella auricularia, was utilized as the lead substance for a series of structure-activity studies. The synthetic methods, in vitro evaluations against a variety of murine and human cancer cell lines, as well as a selection of bacteria and fungi, and inhibition of tubulin polymerization are described. Remarkably, all of the compounds studied, in which the C-terminal (S)-dolapyrrolidinone unit (Dpy) was replaced with a series of structurally diverse and more readily available amides, showed cancer cell growth inhibition activities generally quite comparable to those of the parent molecule (1). All analogues, however, were less potent than 1 as inhibitors of tubulin polymerization. The structurally modified peptides, like the parent compound, caused mitotic arrest in cultured cells, consistent with tubulin being the primary cellular target. The ability of dolastatin 15 and eight modifications or precursors thereof to inhibit the growth of a Gram-negative bacterium suggests that these compounds have an additional target distinct from tubulin.

Animals↗
PubMed1998

Antineoplastic agents 365. Dolastatin 10 SAR probes.

The remarkable anticancer drug dolastatin 10 (1a) from the Indian Ocean sea hare Dolabella auricularia is currently undergoing phase I clinical trials. Thirty-eight new structural modifications of this unusual peptide have been synthesized and evaluated against a variety of human and murine cancer cell lines, and for their ability to inhibit tubulin polymerization and vinblastine and GTP binding to tubulin. Dolastatin 10 and one structural modification was found to have antifungal activity, while one other structural modification of the parent compound exhibited antibacterial activity. Some of the new peptides approximated the antineoplastic potency of dolastatin 10, especially those based on replacement of the Doe unit with Met, Phe or an appropriately substituted phenylethylamide.

Animals↗