Biomedical subjects

E Hamel

Publications and source records attributed to E Hamel.

At least 91 records · Page 5Linked to original sources

PubMed1998

[Comparative efficacy and risks of low molecular weight heparins and thrombolysis in massive pulmonary embolism without cardiogenic shock].

The aim of this retrospective study was to assess pulmonary reperfusion by scintigraphy, the risks of recurrent embolism and of bleeding complications at the 7th day and 3rd month in 2 groups of patients admitted to hospital for massive pulmonary embolism without cardiogenic shock treated by intravenous thrombolysis (Group I) and by subcutaneous low molecular weight heparin (Group II) paired by Miller's index. The basal characteristics of the two groups, each comprising 31 patients, were comparable with respect to the severity of the pulmonary embolism with an average global scintigraphic defect of 40.6 +/- 13.5% in Group I and 39 +/- 13.7% in Group II. The scintigraphic changes at the 7th day were comparable with a relative improvement of 55 and 51% respectively and at 3 months of 74% in both groups. There was no significant difference in terms of recurrence of embolism (3 versus 0% at the 7th day and 3% in each group at 3 months) or of bleeding complications (13 and 10% at the 7th day and 10 and 6% at 3 months respectively). Low molecular weight heparin seems to be as effective as intravenous thrombolysis for the treatment of massive pulmonary embolism without shock. This result requires confirmation by a large scale prospective randomised trial.

Aged↗

PubMed1997

Associations between neuropeptide Y nerve terminals and intraparenchymal microvessels in rat and human cerebral cortex.

Neuropeptide Y (NPY) can influence local brain perfusion, possibly via direct relationships with the microvascular bed. To evaluate this possibility, the authors quantitatively analyzed by light and electron microscopy the morphological associations between immunostained NPY neuronal elements and intraparenchymal microvessels in the rat and human cerebral cortex. At the light microscopic level in the rat frontoparietal cortex, about 16% of NPY neurons and large proximal processes as well as a subset of nerve terminals not affected by double sympathectomy were associated with penetrating arterioles and local microvessels. In human temporal cortex, a dense network of NPY nerve fibers was observed, many of which approached and/or contacted intracortical vessels. At the ultrastructural level, 14% of NPY axonal varicosities in the rat cerebral cortex were considered perivascular and associated with capillaries (approximately 70%) or microarterioles (approximately 30%). They were particularly enriched in the immediate vicinity (< 0.25 micron) of the microvessels, where the perivascular astrocytic leaflets represented a frequent target. In human cerebral cortex, NPY varicosities were observed in proximity to microvessels corresponding primarily to capillaries. Perivascular NPY varicosities never established synaptic junctions with vascular or astroglial elements. The results show that central NPY nerve terminals associate with microvessels and perivascular astroglial cells in the rat and human cerebral cortex. Thus, NPY released from these nerves could possibly influence (via a parasynaptic mode of action) vascular and/or astrocytic functions depending on the distribution of NPY receptors in these cellular compartments. These results provide morphological support for the effects of NPY on brain perfusion and homeostasis.

Adult↗

PubMed1997

The selectivity of MDL 74,721 in models of neurogenic versus vascular components of migraine.

MDL 74,721 (R)-2-(N1,N1-dipropylamino)-8-methylaminosulfonylmethyl-1,2,3,4-te trahydronaphthalene, a sulfonamidotetralin, has been found to exhibit a 10,000-fold greater potency in neurogenic versus vascular models of migraine. Sumatriptan, a relatively pure 5-HT1D/5-HT1B receptor agonist, also showed higher potency versus neurogenic inflammation. However, for sumatriptan the potency difference (100-fold) in the two pathophysiological models was less pronounced than seen for MDL 74,721. The affinity profile of MDL 74,721 at 5-HT1 receptor subtypes may in part explain its ability to differentiate these two physiological responses. MDL 74,721 demonstrated nanomolar affinity for 5-HT1A (12.7 +/- 0.3 nM) and 5-HT1D (41.3 +/- 10.9 nM) but considerably lower affinity for 5-HT1B receptors (> 1000 nM). Serotonin-like activity was seen in in vitro functional assays including inhibition of forskolin-stimulated cAMP accumulation in human 5-HT1D receptor-transfected fibroblasts or eliciting vasoconstriction in isolated human pial arteries. The intrinsic activity (relative to 5 - HT[E(Amax)]) and affinity (pD2) for the human cerebrovascular 5-HT receptors were: 5-HT (100%, 7.51 +/- 0.09), sumatriptan (94%, 6.85 +/- 0.1) and MDL 74,721 (66%, 5.70 +/- 0.23). In anaesthetised cats, treatment with MDL 74,721 resulted in a dose-related reduction in the percentage of carotid flow going through the arteriovenous anastomoses to the lungs, with an ED50 of 0.3 mg/kg i.v., the same as sumatriptan. However, in the guinea-pig neurogenic model, MDL 74,721 inhibited plasma protein extravasation with an ED50 of 0.023 microg/kg compared to 2.5 microg/kg for sumatriptan. MDL 74,721 was also effective in this model (in rats) after oral administration. In conclusion, MDL 74,721 demonstrates a preclinical profile consistent with anti-migraine efficacy. Its marked preference for inhibiting neurogenic inflammation makes this compound a useful tool for assessing the relative contribution of this pathophysiological mechanism to the human disease state.

Animals↗

PubMed1997

Antitumor agents. 178. Synthesis and biological evaluation of substituted 2-aryl-1,8-naphthyridin-4(1H)-ones as antitumor agents that inhibit tubulin polymerization.

As part of our continuing search for potential anticancer drug candidates in the 2-aryl-1,8-naphthyridin-4(1H)-one series, we have synthesized two series of 3'-substituted 2-phenyl-1,8-naphthyridin-4(1H)-ones and 2-naphthyl-1,8-naphthyridin-4(1H)-ones. All compounds showed significant cytotoxic effects (log GI50 < -4.0; log molar drug concentration required to cause 50% growth inhibition) against a variety of human tumor cell lines of the National Cancer Institute's in vitro screen, including cells derived from solid tumors such as non-small cell lung, colon, central nervous system, melanoma, ovarian, prostate, and breast cancers. All 3'-substituted compounds demonstrated strong cytotoxic effects in almost all tumor cell lines. Introduction of an aromatic ring at the 2'- and 3'-positions also generated compounds with potent antitumor activity. Incorporation of an aromatic ring at the 3'- and 4'-positions produced compounds with reduced activity. Interestingly, introduction of a halogen at the 3'-position yielded compounds with different selectivity for the tumor cell lines tested. All 3'-halogenated compounds (29-36) and compounds 38 and 42-44 were potent inhibitors of tubulin polymerization with activities nearly comparable to those of the potent antimitotic natural products colchicine, podophyllotoxin, and combretastatin A-4. Active agents also inhibited the binding of [3H]colchicine to tubulin.

Antineoplastic Agents↗

PubMed1997

Regulation of ornithine decarboxylase induction by deguelin, a natural product cancer chemopreventive agent.

Deguelin, a plant-derived rotenoid, mediates potent chemopreventive responses through transcriptional regulation of phorbol ester-induced ornithine decarboxylase (ODC) activity. To explore the mechanism of this effect, the activity of this compound was evaluated with a number of model systems. Using cultured mouse epidermal 308 cells, the steady-state levels of both 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ODC mRNA and c-fos were decreased by treatment with deguelin. ODC activity was also inhibited by bullatacin and various antimitotic agents (podophyllotoxin, vinblastine, and colchicine), but only deguelin and bullatacin were active as inhibitors of ODC levels in a TPA-independent c-Myc-mediated induction system using cultured BALB/c c-MycER cells. These results suggest that antimicrotubule effects, as mediated by rotenone, for example, are not responsible for inhibitory activity facilitated by deguelin. This was confirmed by use of an in vitro model of tubulin polymerization in which deguelin and a variety of other rotenoids were investigated and found to be inactive. As anticipated, however, NADH dehydrogenase was inhibited by these rotenoids. Moreover, inhibition of this enzyme correlated with a rapid depletion of ATP levels and potential to inhibit either TPA- or c-Myc-induced ODC activity. It therefore seems that deguelin-mediated interference with transient requirements for elevated energy can inhibit the induction of ODC activity and thereby yield a cancer chemopreventive response.

3T3 Cells↗

PubMed1997

Synthesis of analogs of 2-methoxyestradiol with enhanced inhibitory effects on tubulin polymerization and cancer cell growth.

A new series of estradiol analogs was synthesized in an attempt to improve on the anticancer activity of 2-methoxyestradiol, a naturally occurring mammalian tubulin polymerization inhibitor. The compounds were evaluated as inhibitors of tubulin polymerization and the binding of [3H]colchicine to tubulin, as well as for in vitro cytotoxicity in human cancer cell cultures. Overall, the most potent of the new compounds were 2-(2',2',2'-trifluoroethoxy)-6-oximinoestradiol, 2-ethoxy-6-oximinoestradiol, and 2-ethoxy-6-methoximinoestradiol. These agents lacked significant affinity for the estrogen receptor. The cytotoxicities of the compounds correlated in general with their abilities to inhibit tubulin polymerization, thus supporting inhibition of tubulin polymerization as the primary mechanism causing inhibition of cell growth.

2-Methoxyestradiol↗

PubMed1997

Antitumor agents. 174. 2',3',4',5,6,7-Substituted 2-phenyl-1,8-naphthyridin-4-ones: their synthesis, cytotoxicity, and inhibition of tubulin polymerization.

Two series of 2',3',4',5,6,7-substituted 2-phenyl-1,8-naphthyridin-4-ones and 2-phenylpyrido[1,2-alpha]pyrimidin-4-ones have been synthesized and evaluated as cytotoxic compounds and as inhibitors of tubulin polymerization. Most 2-phenyl-1,8-naphthyridin-4-ones showed potent cytotoxic and antitubulin activities, whereas 2-phenylpyrido[1,2-alpha]pyrimidin-4-ones showed no activity in either assay. In general, a good correlation was found between cytotoxicity and inhibition of tubulin polymerization in the 2-phenyl-1,8-naphthyridin-4-one series. The 2-phenyl-1,8-naphthyridin-4-ones (44-49) with a methoxy group at the 3'-position showed potent cytotoxicity against most tumor cell lines with GI50 values in the low micromolar to nanomolar concentration range in the National Cancer Institute's 60 human tumor cell line in vitro screen. Introduction of substituents (e.g. F, Cl, CH3, and OCH3) at the 4'-position led to compounds with reduced or little activity and substitution at the 2'-position resulted in inactive compounds. The effects of various A-ring substitutions on activity depend on the substitution in ring C. Compounds 44-50 were potent inhibitors of tubulin polymerization, with activity nearly comparable to that of the potent antimitotic natural products colchicine, podophyllotoxin, and combretastatin A-4. Compounds 44-49 also inhibited the binding of radiolabeled colchicine to tubulin, but the inhibition was less potent than that obtained with the natural products. Further investigation is underway to determine if substitution at the 3'-position and multisubstitutions in ring C will result in compounds with increased activity.

Animals↗

PubMed1997

Synthesis of epothilones A and B in solid and solution phase.

Epothilones A and B, two compounds that have been recently isolated from myxobacterium Sorangium cellulosum strain 90, have generated intense interest among chemists, biologists and clinicians owing to the structural complexity, unusual mechanism of interaction with microtubules and anticancer potential of these molecules. Like taxol, they exhibit cytotoxicity against tumour cells by inducing microtubule assembly and stabilization, even in taxol-resistant cell lines. Following the structural elucidation of these molecules by X-ray crystallography in 1996, several syntheses of epothilones A and B have been reported, indicative of the potential importance of these molecules in the cancer field. Here we report the first solid-phase synthesis of epothilone A, the total synthesis of epothilone B, and the generation of a small epothilone library. The solid-phase synthesis applied here to epothilone A could open up new possibilities in natural-product synthesis and, together with solution-phase synthesis of other epothilones, paves the way for the generation of large combinatorial libraries of these important molecules for biological screening.

Antineoplastic Agents↗

PubMed1997

Antitumor agents. 172. Synthesis and biological evaluation of novel deacetamidothiocolchicin-7-ols and ester analogs as antitubulin agents.

A series of novel 7-O-substituted deacetamidothiocolchicine derivatives has been synthesized and evaluated for their inhibitory activity against tubulin polymerization, the binding of [3H]-colchicine to tubulin, and the growth of human Burkitt lymphoma cells. Of these new derivatives, thiocolchicone (8), wherein an acetamido group in thiocolchicine is replaced by a carbonyl oxygen at C(7), was obtained from deacetythiocolchicine (6) by Schiffs base equilibration and acid hydrolysis. Reduction of thiocolchiocone with sodium borohydride yielded the racemic alcohol 9, the structure of which was verified by X-ray crystallographic analysis. Optically pure alcohols 9a,b were obtained by treatment of 9 with the optically pure reagent (1S)-(-)-camphanic chloride followed by chromatographic separation of the camphanate esters and hydrolysis of the diastereomers. X-ray crystallographic analysis established the aS,7S-configuration of 9a. Racemic and optically active esters 11-15, 11a,b, 12a, 14a, and 15a were obtained by esterification of the corresponding alcohols. The compounds showing activity equivalent to or greater than (-)-thiocolchicione (2a) in all the biological assays were three (-)-aS,7S optically pure enantiomers: the alcohol 9a, the acetate 11a (an oxygen isostere of thiocolchicine), and the isonicotinoate 15a. In addition, the ketone 8 and two (-)-aS,7S enantiomers (12a, 14a) had high activity in the biochemical assays with tubulin but reduced antiproliferative activity. In all cases, optically pure isomers with the (-)-aS,7S configuration exhibited greater biological activity than racemic mixtures or isomers or isomers with the (+)-aR,7R configuration.

Antineoplastic Agents↗

PubMed1997

Activities of the microtubule-stabilizing agents epothilones A and B with purified tubulin and in cells resistant to paclitaxel (Taxol(R)).

Epothilones A and B, natural products with minimal structural analogy to taxoids, have effects similar to those of paclitaxel (Taxol(R)) in cultured cells and on microtubule protein, but differ from paclitaxel in retaining activity in multidrug-resistant cells. We examined interactions of the epothilones with purified tubulin and additional cell lines, including a paclitaxel-resistant ovarian carcinoma line with an altered beta-tubulin. The epothilones, like paclitaxel, induced tubulin to form microtubules at low temperatures and without GTP and/or microtubule-associated proteins. The epothilones are competitive inhibitors of the binding of [3H]paclitaxel to tubulin polymers. The apparent Ki values for epothilones A and B were 1.4 and 0.7 microM by Hanes analysis and 0.6 and 0.4 microM by Dixon analysis. In the paclitaxel-sensitive human cell lines we examined, epothilone B had greater antiproliferative activity than epothilone A or paclitaxel, while epothilone A was usually less active than paclitaxel. A multidrug-resistant colon carcinoma line and the paclitaxel-resistant ovarian line retained sensitivity to the epothilones. With Potorous tridactylis kidney epithelial (PtK2) cells examined by indirect immunofluorescence, microtubule bundles appeared more rapidly following epothilone B treatment, and there were different proportions of various mitotic aberrations following treatment with different drugs.

Drug Resistance, Multiple↗

PubMed1997

Inhibition of angiogenesis and breast cancer in mice by the microtubule inhibitors 2-methoxyestradiol and taxol.

2-Methoxyestradiol (2-ME), an endogenous estrogen metabolite which disrupts microtubule function, has been shown to inhibit proliferating cells in vitro and suppress certain murine tumors in vivo. In vitro screening has determined that breast cancer cell lines are most sensitive to inhibition by 2-ME. Additionally, 2-ME has been shown to inhibit angiogenesis in vitro. We tested whether 2-ME suppresses cytokine-induced angiogenesis in vivo and inhibits growth of a human breast carcinoma in severe combined immunodeficient mice. A model of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF)-induced corneal neovascularization in C57BL/6 mice was used to evaluate the antiangiogenic effects of 2-ME and other microtubule inhibitors such as Taxol, vincristine, and colchicine. 2-ME (150 mg/kg p.o., n = 20) inhibited bFGF and VEGF-induced neovascularization by 39% and 54%, respectively. Taxol (6 mg/kg i.p., n = 17) inhibited bFGF and VEGF-induced neovascularization by 45% and 37%, respectively. Vincristine (0.2 mg/kg i.p., n = 8) and colchicine (0.25 mg/kg i.p., n = 8) had no effect. Treatment with 2-ME (75 mg/kg p.o., n = 9) for 1 month suppressed the growth of a human breast carcinoma in mice by 60% without toxicity. Recognition of the antiangiogenic and antitumor properties of 2-ME and Taxol may be crucial in planning clinical applications to angiogenesis-dependent diseases.

2-Methoxyestradiol↗

PubMed1997

Cholinergic basal forebrain projections to nitric oxide synthase-containing neurons in the rat cerebral cortex.

Stimulation of basal forebrain neurons elicits regional cerebral blood flow increases which are reportedly mediated by acetylcholine and nitric oxide. However, the modality of interaction between these two mediators remains unclear. Particularly, little is known about the source, i.e. endothelial, glial and/or neuronal, of the potent gaseous vasodilator nitric oxide. In the present study, we examined, by double immunocytochemical labelling of nitric oxide synthase and choline acteyltransferase at the light and electron microscopic level, the existence of morphological relationships between cortical nitric oxide synthase-containing neurons and cholinergic cells or nerve fibres. Using anterograde tract tracing and selective basal forebrain lesions, we further investigated the origin of the cholinergic input to cortical nitric oxide synthase neurons. The results confirm that cortical nitric oxide synthase-immunoreactive neurons are often associated with the local microvascular bed, show that intracortical neurons immunostained for nitric oxide synthase and choline acetyltransferase belong to two distinct neuronal populations and, further, that a subset of nitric oxide synthase-containing cell bodies and their proximal dendrites receive a cholinergic input which originates primarily from basalocortical projections. Altogether, these findings suggest that cholinergic basal forebrain neurons could increase cortical blood flow partly via a local nitric oxide relay neuron whereby the freely diffusing gas would be the direct smooth muscle vasodilator agent. It is concluded that this interaction might contribute to the complex relationships between the basal forebrain and the cortical microcirculation, interactions which result in fine regulation of cortical perfusion.

Animals↗

PubMed1997

Synthesis and biological evaluation of 1,1-dichloro-2,3-diarylcyclopropanes as antitubulin and anti-breast cancer agents.

Z-1,1-Dichloro-2,3-diphenylcyclopropane (1) is an effective anti-breast cancer agent in rodents and in cell culture. We recently determined that 1 inhibits tubulin assembly in vitro and causes microtubule loss in breast cancer cells, leading to accumulation in the G2/M portion of the cell cycle. Aryl ring-halogenated, methoxylated and benzyloxylated derivatives of 1, as well as its E-isomer and the dichlorocyclopropyl derivative of diethylstilbestrol (DES), were synthesized and tested for their ability to inhibit, the assembly of tubulin into microtubules. Including 1, 17 cyclopropyl compounds were tested. One (Z-1,1-dichloro-2-(4-methoxyphenyl)-3-phenylcyclopropane (12)) was found to be more active than 1. In addition, E-1,1-dichlorocyclopropylDES (17) was more potent than DES. The E-isomer of 1 (16) was inactive. The cytostatic activities of the compounds against MCF-7 and MDA-MB231 human breast cancer cells, and their abilities to perturb microtubules in MCF-7 cells were also evaluated. Z-Dichloro-2-(4-fluorophenyl)-3-phenylcyclopropane (5), Z-1,1-dichloro-2-(4-fluorophenyl)-3-(4-methoxyphenyl)cyclopropane (11), and Z-1,1-dichloro-2-(4-methoxyphenyl)-3-phenylcyclopropane (12) were more potent than 1 against the breast cancer cells.

Animals↗

PubMed1997

Synthesis and biological activity of A-nor-paclitaxel analogues.

A number of paclitaxel analogues with a 5-membered A-ring (A-nor-paclitaxels, or (15-->1)-abeo-paclitaxels) have been prepared in order to determine whether analogues of this class might have improved bioactivity as compared with paclitaxel. Most of the compounds synthesized were less active than paclitaxel, but one analogue was equivalent to paclitaxel in a tubulin-assembly assay, and another analogue was more cytotoxic than paclitaxel in two different cell lines of the NCI screen.

Antineoplastic Agents, Phytogenic↗

PubMed1997

Antitumor agents--CLXXV. Anti-tubulin action of (+)-thiocolchicine prepared by partial synthesis.

(+)-Thiocolchicine (2b) was prepared from (+/-)-colchicine (1) in a five-step reaction sequence that included chromatographic separation of appropriate camphanylated diastereomers. Acid hydrolysis of the (+)-diastereomer, followed by acetylation, yielded the desired product 2b. (+)-Thiocolchicine has 15-fold lower inhibitory activity against tubulin polymerization than (-)-thiocolchicine, and is 29-fold less potent for inhibiting growth of human Burkitt lymphoma cells. The enantiomer 2a, prepared from the (-)-camphanylated diastereomer, had potent activity in all assays comparable to that of (-)-thiocolchicine prepared by other methods. These results support the hypothesis that the proper configuration of colchicine-related compounds is an important requirement for their anti-tubulin action.

Antineoplastic Agents↗

PubMed1997

Astroglial and vascular interactions of noradrenaline terminals in the rat cerebral cortex.

Noradrenaline (NA) has been shown to influence astrocytic and vascular functions related to brain homeostasis, metabolism, local blood flow, and blood-brain barrier permeability. In the current study, we investigate the possible associations that exist between NA-immunoreactive nerve terminals and astrocytes and intraparenchymal blood vessels in the rat frontoparietal cortex, both at the light and electron microscopic levels. As a second step, we sought to determine whether the NA innervation around intracortical microvessels arises from peripheral or central structures by means of injections of N-(2-chloroethyl-N-ethyl-2-bromobenzylamine) (DSP-4), a neurotoxin that specifically destroys NA neurons from the locus ceruleus. At the light microscopic level, 6.8% of all NA-immunoreactive nerve terminals in the frontoparietal cortex were associated with vascular walls, and this perivascular noradrenergic input, together with that of the cerebral cortex, almost completely disappeared after DSP-4 administration. When analyzed at the ultrastructural level in control rats, NA terminals in the neuropil had a mean surface area of 0.53 +/- 0.03 micron2 and were rarely junctional (synaptic incidence close to 7%). Perivascular terminals (located within a 3-micron perimeter from the vessel basal lamina) counted at the electron microscopic level represented 8.8% of the total NA terminals in the cortical tissue. They were smaller (0.29 +/- 0.01 micron2, P < 0.05) than their neuronal counterparts and were located, on average, 1.34 +/- 0.08 microns away from intracortical blood vessels, which consisted mostly of capillaries (65%). None of the perivascular NA terminals engaged in junctional contacts with surrounding neuronal or vascular elements. The primary targets of both neuronal and perivascular NA nerve terminals consisted of dendrites, nerve terminals, astrocytes, and axons, whereas in the immediate vicinity (0.25 micron or less) of the microvessels, astrocytic processes represented the major target. The results of the current study show that penetrating arteries and intracortical microvessels receive a central NA input, albeit parasynaptic in its interaction, originating from the locus ceruleus. Particularly, they point to frequent appositions between both neuronal and perivascular NA terminals and astroglial cells and their processes. Such NA neuronal-glial and neuronal-glial-vascular associations could be of significance in the regulation of local metabolic and vascular functions under normal and pathologic situations.

Animals↗

PubMed1997

The microtubule-stabilizing agent discodermolide competitively inhibits the binding of paclitaxel (Taxol) to tubulin polymers, enhances tubulin nucleation reactions more potently than paclitaxel, and inhibits the growth of paclitaxel-resistant cells.

The lactone-bearing polyhydroxylated alkatetraene (+)-discodermolide, which was isolated from the sponge Discodermia dissoluta, induces the polymerization of purified tubulin with and without microtubule-associated proteins or GTP, and the polymers formed are stable to cold and calcium. These effects are similar to those of paclitaxel (Taxol), but discodermolide is more potent. We confirmed that these properties represent hypernucleation phenomena; we obtained lower tubulin critical concentrations and shorter polymers with discodermolide than paclitaxel under a variety of reaction conditions. Furthermore, we demonstrated that discodermolide is a competitive inhibitor with [3H]paclitaxel in binding to tubulin polymer, with an apparent Ki value of 0.4 microM. Multidrug-resistant human colon and ovarian carcinoma cells overexpressing P-glycoprotein, which are 900- and 2800-fold resistant to paclitaxel, respectively, relative to the parental lines, retained significant sensitivity to discodermolide (25- and 89-fold more resistant relative to the parental lines). Ovarian carcinoma cells that are 20-30-fold more resistant to paclitaxel than the parental line on the basis of expression of altered beta-tubulin polypeptides retained nearly complete sensitivity to discodermolide. The effects of discodermolide on the reorganization of the microtubules of Potorous tridactylis kidney epithelial cells were examined at different times. Intracellular microtubules were reorganized into bundles in interphase cells much more rapidly after discodermolide treatment compared with paclitaxel treatment. A variety of spindle aberrations were observed after treatment with both drugs. The proportions of the different types of aberration were different for the two drugs and changed with the length of drug treatment.

Alkanes↗

PubMed1996

Characterization of the interaction of cryptophycin 1 with tubulin: binding in the Vinca domain, competitive inhibition of dolastatin 10 binding, and an unusual aggregation reaction.

The antimitotic depsipeptide cryptophycin 1 (CP1) was compared to the antimitotic peptide dolastatin 10 (D10) as an antiproliferative agent and in its interactions with purified tubulin. The potent activity of CP1 as an inhibitor of cell growth was confirmed. The agent had an IC50 of 20 pM against L1210 murine leukemia cells versus 0.5 nM for D10. Both drugs were comparable as inhibitors of the glutamate-induced assembly of purified tubulin, with D10 being slightly more potent. CP1, like D10, was a noncompetitive inhibitor of the binding of [3H]vinblastine to tubulin (apparent Ki, 3.9 microM); and the depsipeptide was a competitive inhibitor of the binding of [3H]D10 to tubulin (apparent Ki, 2.1 microM). CP1 was less potent than D10 as an inhibitor of nucleotide exchange on tubulin, but the two drugs were equivalent in stabilizing the colchicine binding activity of tubulin. CP1, like D10, caused the formation of extensive structured aggregates of tubulin when present in stoichiometric amounts relative to the protein. Whereas at lower concentrations the drugs were equivalent in causing formation of small oligomers detected by gel permeation high-performance liquid chromatography, there were notable differences in the aggregation reactions induced by the two drugs. The electron micrographic appearance of the D10-induced aggregate differed substantially from that of the CP1-induced aggregate. With D10, but not CP1, aggregate morphology was greatly altered in the presence of microtubule-associated proteins. Finally, although CP1 caused the formation of massive aggregates, as did D10, there was little turbidity change with the depsipeptide as opposed to the peptide.

Antifungal Agents↗