Securinine induced apoptosis in human leukemia HL-60 cells.
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AIM: To study whether securinine might induce apoptosis in human leukemia HL-60 cells. METHODS: Inhibition of proliferation was measured using MTT assay. The amount of apoptotic cells was measured by flow cytometry. DNA fragmentation was visualized by DNA agarose gel electrophoresis and the cellular changes were observed by electron microscope. RESULTS: Securinine 5-80 mg.L-1 elicited typical apoptosis morphological changes and DNA fragmentation in a concentration-dependent manner in HL-60 cells. Securinine inhibited HL-60 cell proliferation in a time- and concentration-dependent manner. The IC50 and 95% confidence limits were 27 (15-47) mg.L-1 after 12-h treatment with securinine. CONCLUSION: Securinine induced apoptosis in HL-60 cells. (+info)
Cluster organization and pore structure of ion channels formed by beticolin 3, a nonpeptidic fungal toxin.
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Beticolin 3 (B3) belongs to a family of nonpeptidic phytotoxins produced by the fungus Cercospora beticola, which present a broad spectrum of cytotoxic effects. We report here that, at cytotoxic concentration (10 microM), B3 formed voltage-independent, weakly selective ion channels with multiple conductance levels in planar lipid bilayers. In symmetrical standard solutions, conductance values of the first levels were, respectively, 16 +/- 1 pS, 32 +/- 2 pS, and 57 +/- 2 pS (n = 4) and so on, any conductance level being roughly twice the lower one. Whether a cluster organization of elementary channels or different channel structures underlies this particular property was addressed by investigating the ionic selectivity and the pore size corresponding to the first three conductance levels. Both selectivity and pore size were found to be almost independent of the conductance level. This indicated that multiple conductance behavior resulted from a cluster organization of "B3 elementary channels." According to the estimated pore size and analyses of x-ray diffraction of B3 microcrystals, a structural model for "B3 elementary channels" is proposed. The ability to form channels is likely to be involved in the biological activity of beticolins. (+info)
Huprine X is a novel high-affinity inhibitor of acetylcholinesterase that is of interest for treatment of Alzheimer's disease.
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Inhibitors of the enzyme acetylcholinesterase (AChE) slow and sometimes reverse the cognitive decline experienced by individuals with Alzheimer's disease. Huperzine A, a natural product used in traditional Chinese herbal medicine, and tacrine (Cognex) are among the potent AChE inhibitors used in this treatment, but the search for more selective inhibitors continues. We report herein the synthesis and characterization of (-)-12-amino-3-chloro-9-ethyl-6,7, 10,11-tetrahydro-7,11-methanocycloocta[b]quinoline hydrochloride (huprine X), a hybrid that combines the carbobicyclic substructure of huperzine A with the 4-aminoquinoline substructure of tacrine. Huprine X inhibited human AChE with an inhibition constant K(I) of 26 pM, indicating that it binds to this enzyme with one of the highest affinities yet reported. Under equivalent assay conditions, this affinity was 180 times that of huperzine A, 1200 times that of tacrine, and 40 times that of E2020 (donepezil, Aricept), the most selective AChE inhibitor currently approved for therapeutic use. The association and dissociation rate constants for huprine X with AChE were determined, and the location of its binding site on the enzyme was probed in competition studies with the peripheral site inhibitor propidium and the acylation site inhibitor edrophonium. Huprine X showed no detectable affinity for the edrophonium-AChE complex. In contrast, huprine X did form a ternary complex with propidium and AChE, although its affinity for the free enzyme was found to be 17 times its affinity for the propidium-AChE complex. These data indicated that huprine X binds to the enzyme acylation site in the active site gorge but interferes slightly with the binding of peripheral site ligands. (+info)
Memnobotrins and memnoconols: novel metabolites from Memnoniella echinata.
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Four novel metabolites have been isolated from a rice culture of Memnoniella echinata (JS6308) by solvent extraction and radial silica chromatography. The structures were elucidated by spectroscopic techniques, and the absolute stereochemistry of memnobotrin A determined by X-ray crystallography. (+info)
In vitro and in vivo anticancer activities of synthetic macrocyclic ketone analogues of halichondrin B.
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Halichondrin B is a highly potent anticancer agent originally found in marine sponges. Although scarcity of the natural product has hampered efforts to develop halichondrin B as a new anticancer drug, the existence of a complete synthetic route has allowed synthesis of structurally simpler analogues that retain the remarkable potency of the parent compound. In this study, we show that two macrocyclic ketone analogues of halichondrir B, ER-076349 and ER-086526, have sub-nM growth inhibitory activities in vitro against numerous human cancer cell lines as well as marked in vivo activities at 0.1-1 mg/kg against four human xenografts: MDA-MB-435 breast cancer, COLO 205 colon cancer, LOX melanoma, and NIH: OVCAR-3 ovarian cancer. ER-076349 and ER-086526 induce G2-M cell cycle arrest and disruption of mitotic spindles, consistent with the tubulin-based antimitotic mechanism of halichondrin B. This is supported further by direct binding of the biotinylated analogue ER-040798 to tubulin and inhibition of tubulin polymerization in vitro by ER-076349 and ER-086526. Retention of the extraordinary in vitro and in vivo activity off halichondrin B in structurally simplified, fully synthetic analogues establishes the feasibility of developing halichondrin B-based agents as highly effective, novel anticancer drugs. (+info)
Caffeoyl, coumaroyl, galloyl, and hexahydroxydiphenoyl glucoses from Balanophora japonica.
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Eighteen new and sixteen known acyl glucoses having caffeoyl, coumaroyl, galloyl, and hexahydroxydiphenoyl groups were isolated from a medicinal parasitic plant, Balanophora japonica. Their structures were determined by spectroscopic and chemical methods. Caffeoyl ellagitannins, which have been rarely found in nature, were major phenolic constituents of this plant, and this is the first report of the isolation of ellagitannins from Balanophoraceae. (+info)
Effects of 12 beticolins, Cercospora beticola toxins, on proliferation of ras-transformed adrenocortical cell.
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AIM: To explore different effects of 12 beticolins, Cercospora beticola toxins, on ras-transformed adrenocortical cell growth inhibition and their functional mechanism. METHODS: Beticolin-induced inhibition was measured with survival cell number determined by an automated photocolorimetric method. The penetration of beticolin was examined by confocal microscopy. Ras protein determined by Lowry method were separated by 14 % SDS-PAGE and electroblotted to Immobilon-P transfer membrane and detected with pan-Ras (Ab-3) monoclonal antibody. The Ca2+ chelation by beticolin was investigated using a calcium ionophore. RESULTS: Cell growth inhibition was found dose- and time-dependently at submicromolar level for beticolin-1, -2, and -13 (IC50 +info)
The new anti-actin agent dihydrohalichondramide reveals fenestrae-forming centers in hepatic endothelial cells.
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BACKGROUND: Liver sinusoidal endothelial cells (LSECs) react to different anti-actin agents by increasing their number of fenestrae. A new structure related to fenestrae formation could be observed when LSECs were treated with misakinolide. In this study, we investigated the effects of two new actin-binding agents on fenestrae dynamics. High-resolution microscopy, including immunocytochemistry and a combination of fluorescence- and scanning electron microscopy was applied. RESULTS: Halichondramide and dihydrohalichondramide disrupt microfilaments within 10 minutes and double the number of fenestrae in 30 minutes. Dihydrohalichondramide induces fenestrae-forming centers, whereas halichondramide only revealed fenestrae-forming centers without attached rows of fenestrae with increasing diameter. Correlative microscopy showed the absence of actin filaments (F-actin) in sieve plates and fenestrae-forming centers. Comparable experiments on umbilical vein endothelial cells and bone marrow sinusoidal endothelial cells revealed cell contraction without the appearance of fenestrae or fenestrae-forming centers. CONCLUSION: (I) A comparison of all anti-actin agents tested so far, revealed that the only activity that misakinolide and dihydrohalichondramide have in common is their barbed end capping activity; (II) this activity seems to slow down the process of fenestrae formation to such extent that it becomes possible to resolve fenestrae-forming centers; (III) fenestrae formation resulting from microfilament disruption is probably unique to LSECs. (+info)