Biomedical subjects

Chris M Ireland

Publications and source records attributed to Chris M Ireland.

At least 37 records · Page 2Linked to original sources

PubMed2004

Dictyosphaeric acids A and B: new decalactones from an undescribed Penicillium sp. obtained from the alga Dictyosphaeria versluyii.

Fungal isolate F01V25 was obtained from the alga Dictyosphaeria versluyii collected near Dravuni, Fiji, in 2001 and represented a previously undescribed Penicillium sp. Fermentation of isolate F01V25 resulted in the production of two new polyketides, dictyosphaeric acids A and B, along with the known anthraquinone carviolin. The relative stereochemistry of dictyosphaeric acids A and B was determined using the J-based configuration analysis method in conjunction with ROE and NOE correlations.

Eukaryota↗

PubMed2004

Cytotoxic isoquinoline quinones from sponges of the genus Petrosia.

Bioassay-guided fractionation of two Philippine sponges of the genus Petrosia has resulted in the isolation of the novel natural product cribrostatin 7 (1) and the known compounds renierone (2) and O-demethylrenierone (3). The structures of these isoquinoline quinones were determined by interpretation of spectroscopic data. Compounds 1, 2 and 3 were cytotoxic against the HCT 116 human colon carcinoma cell line with IC50 values of 45, 24 and 34 microg/mL, respectively.

Animals↗

PubMed2003

A new cytotoxic and tubulin-interactive milnamide derivative from a marine sponge Cymbastela sp.

[structure: see text] The crude methanol extract of a marine sponge Cymbastela sp. collected in Papua New Guinea was selected for chemical investigation due to its significant cytotoxicity. Fractionation of the extract led to the isolation of jaspamide (1), hemiasterlin (2), milnamide A (3), and a new metabolite, milnamide D (4). The structure was solved by interpretation of NMR and mass spectra data. The cytotoxic and antitubulin activities of milnamide D (4) were evaluated.

Animals↗

PubMed2003

The anti-neoplastic and novel topoisomerase II-mediated cytotoxicity of neoamphimedine, a marine pyridoacridine.

Topoisomerase IIalpha (top2) is a target of some of the most useful anticancer drugs. All clinically approved top2 drugs act to stabilize a drug-enzyme-DNA cleavable complex. Here we report the novel top2 activity of neoamphimedine, an isomer of the marine pyridoacridine amphimedine. Neoamphimedine was cytotoxic in yeast and mammalian cell lines. Neoamphimedine exhibited enhanced toxicity in top2 over-expressing yeast cells and was toxic in every mammalian cell line tested. However, neoamphimedine did not possess enhanced toxicity in a mammalian cell line sensitive to stabilized cleavable complexes. Therefore, we hypothesized that neoamphimedine is a top2-dependent drug, whose primary mechanism of action is not the stabilization of cleavable complexes. Top2-directed activity was determined in purified enzyme systems. Neoamphimedine-induced catenation of plasmid DNA only in the presence of active top2. This catenation correlated with the ability of neoamphimedine to aggregate DNA. Catenation was also observed using a filter-binding assay and transmission electron microscopy. Catenation was confirmed when only restriction enzyme digestion could resolve the catenated plasmid complex to monomer length plasmid DNA. Neoamphimedine also showed potent anti-neoplastic activity in human xenograft tumors in athymic mice. Neoamphimedine was as effective as etoposide in mice bearing KB tumors and as effective as 9-aminocamptothecin in mice bearing HCT-116 tumors. Amphimedine did not induce DNA aggregation or catenation in vitro, nor did it display any significant anti-neoplastic activity. These results suggest that neoamphimedine has a novel top2-mediated mechanism of cytotoxicity and anticancer potential.

Acridines↗

PubMed2003

An improved solution structure for psi-conotoxin PiiiE.

A revised, high-resolution structure of psi-conotoxin Piiie (psi-Piiie), a noncompetitive inhibitor of the nicotinic acetylcholine receptor (nAChR), produced through the use of NMR and molecular modeling calculations is presented. The original structures of psi-Piiie had a relatively high degree of disorder, particularly in the conformation of the disulfide bridges. Our studies utilized (13)C-labeling of selected cysteine residues allowing the resolution of all problems of resonance overlap for the cysteine residues. The improved data were used to produce a new set of structures by a molecular modeling process incorporating relaxation matrix methods for the determination of interproton distance restraints and a combination of distance geometry and simulated annealing for structure generation. The structures produced are very well converged with the RMSD of backbone atom positions of the main body of the peptide improving from 0.73 to 0.13 A. Other indicators of correlation with the experimental data and quality of covalent geometry showed significant improvement in the new structures. The overall conformation of the peptide backbone is similar between the two determinations with the exception of the N-terminus. This difference leads to a significant effect on the predicted distribution of positive charge within psi-Piiie, a property likely to influence interpretation of future mutational studies.

Algorithms↗

PubMed2003

Characterization and three-dimensional structure determination of psi-conotoxin Piiif, a novel noncompetitive antagonist of nicotinic acetylcholine receptors.

A novel inhibitor of nicotinic acetylcholine receptors (nAChRs), psi-conotoxin Piiif, was isolated from the venom of Conus purpurascens and found to have the sequence GOOCCLYGSCROFOGCYNALCCRK-NH2. The sequence is highly homologous to that of psi-conotoxin Piiie, a previously identified noncompetitive inhibitor of Torpedo electroplax nAChR, also isolated from C. purpurascens. Both psi-conotoxins block Torpedo and mouse nicotinic acetylcholine receptors (nAChRs), but psi-Piiif is less potent by a factor of 10(1)-10(2). A high-resolution structure of psi-Piiif was determined by NMR and molecular modeling calculations. Psi-Piiif analogues containing [(13)C]-labeled cysteine at selected positions were synthesized to resolve spectral overlap of Cys side chain proton signals. The structures are well-converged, with backbone atom position RMSDs of 0.21 A for the main body of the peptide between residues 4 and 22 and 0.47 A for all residues. The overall backbone conformation is closely similar to psi-Piiie, the main difference being in the degree of conformational disorder at the two termini. Psi-Piiie and psi-Piiif have similar locations of positive charge density, although psi-Piiif has a lower overall charge. One disulfide bridge of psi-Piiif appears to undergo dynamic conformational fluctuations based on both the model and on experimental observation. Chimeras in which the three intercysteine loops were swapped between psi-Piiie and psi-Piiif were tested for inhibitory activity against Torpedo nAChRs. The third loop, which contains no charged residues in either peptide, is the prime determinant of potency in these psi-conotoxins.

Amino Acid Sequence↗

PubMed2003

Brocaenols A-C: novel polyketides from a marine derived Penicillium brocae.

Chemical investigation of a Penicillium brocae, obtained from a tissue sample of a Fijian Zyzyya sp. sponge, yielded two known diketopiperazines and three novel cytotoxic polyketides, brocaenols A-C. The brocaenols contain an unusual enolized oxepine lactone ring system that to the best of our knowledge is unprecedented in the literature. The structures were elucidated by using 2D-NMR methods including an INADEQUATE experiment. The absolute stereochemistry of brocaenol A was established by using a modified Mosher method. The taxonomy of the producing fungus was elucidated by using both morphological and rDNA sequence analysis.

Animals↗

PubMed2003

Naamidine A intensifies the phosphotransferase activity of extracellular signal-regulated kinases causing A-431 cells to arrest in G1.

The binding of epidermal growth factor to its receptor activates the mitogen-activated protein kinase pathway. This pathway has been identified as a vital link between membrane-bound Ras and nuclear events and, therefore, is a potential target for chemotherapeutic drugs. We reported previously that naamidine A (NA), an alkaloid from the calcareous sponge Leucetta chagosensis, potently inhibited epidermal growth factor-stimulated DNA synthesis. In this current study, we demonstrate that in addition to its antimitogenic effects (complete inhibition of DNA synthesis at 0.78 micro M in A-431 cells after 30 h), NA at 1.56 micro M caused cells to arrest in the G(1) phase of the cell cycle. In vitro kinase, in-gel kinase, and Western blotting experiments demonstrate that extracellular signal-regulated kinase (ERK) 1 and ERK2 are primary molecular targets for NA in A-431 cells. Treatment with NA at concentrations between 0.78 and 3.13 micro M produces changes in the phosphorylation states of the ERKs, and strongly induces the phosphotransferase activity of the ERK enzymes. Our data indicate that treatment with NA generates a robust ERK signal. NA is the first small molecule reported to cause this effect on the ERK kinases and consequent G(1) cell cycle arrest.

Blotting, Western↗

PubMed2002

Isolation, structure determination, and biological activity of a novel alkaloid, perophoramidine, from the Philippine ascidian Perophora namei.

Chemical investigation of the Philippine ascidian Perophora namei has resulted in the isolation of a novel polycyclic alkaloid, perophoramidine (1). The structure of 1 was determined by the interpretation of 1D/2D NMR and MS data. Dehalogenation of perophoramidine (1) by ammonium formate catalyzed transfer hydrogenation confirmed the type and number of halogen atoms present in 1.

Alkaloids↗

PubMed2002

Sebastianines A and B, novel biologically active pyridoacridine alkaloids from the Brazilian ascidian Cystodytes dellechiajei.

Fractionation of the crude methanol extract of the ascidian Cystodytes dellechiajei collected in Brazil yielded two novel alkaloids, sebastianine A (1) and sebastianine B (2). The structures of both 1 and 2 were established by analysis of spectroscopic data, indicating an unprecedented ring system for both compounds, comprising a pyridoacridine system fused with a pyrrole unit in sebastianine A (1) and a pyridoacridine system fused with a pyrrolidine system condensed with alpha-hydroxyisovaleric acid in sebastianine B (2). Both alkaloids displayed a cytotoxic profile against a panel of HCT-116 colon carcinoma cells indicative of a p53 dependent mechanism.

Acridines↗

PubMed2002

Inhibition of tubulin polymerization by vitilevuamide, a bicyclic marine peptide, at a site distinct from colchicine, the vinca alkaloids, and dolastatin 10.

Vitilevuamide, a bicyclic 13 amino acid peptide, was isolated from two marine ascidians, Didemnum cuculiferum and Polysyncranton lithostrotum. Vitilevuamide was cytotoxic in several human tumor cell lines, with LC(50) values ranging from 6 to 311nM, and analysis in a 25-cell line panel revealed a weak correlation with several taxol analogs. Vitilevuamide was strongly positive in a cell-based screen for inhibitors of tubulin polymerization. Vitilevuamide at 9 microg/mL (5.6 microM) had an effect equivalent to the maximal effect of colchicine at 25 microg/mL (62.5 microM). Vitilevuamide was active in vivo against P388 lymphocytic leukemia, increasing the lifespan of leukemic mice 70% at 30 microg/kg. We hypothesized that at least part of the cytotoxic mechanism of vitilevuamide was due to its inhibition of tubulin polymerization. Vitilevuamide was found to inhibit polymerization of purified tubulin in vitro, with an IC(50) value of approximately 2 microM. Cell cycle analysis showed that vitilevuamide arrested cells in the G(2)/M phase with 78% of treated cells tetraploid after 16hr. Therefore, vitilevuamide was tested for its ability to inhibit binding of known tubulin ligands. Vitilevuamide exhibited non-competitive inhibition of vinblastine binding to tubulin. Colchicine binding to tubulin was stabilized in the presence of vitilevuamide in a fashion similar to vinblastine. Dolastatin 10 binding was unaffected by vitilevuamide at low concentrations, but inhibited at higher ones. GTP binding was also found to be weakly affected by the presence of vitilevuamide. These results suggest the possibility that vitilevuamide inhibits tubulin polymerization via an interaction at a unique site.

Animals↗

PubMed2002

Aldisine alkaloids from the Philippine sponge Stylissa massa are potent inhibitors of mitogen-activated protein kinase kinase-1 (MEK-1).

Raf/MEK-1/MAPK cascade inhibitor activity-directed fractionation of the sponge Stylissa massa afforded eight known alkaloids: aldisine (1), 2-bromoaldisine (2), 10Z-debromohymenialdisine (3), 10E-hymenialdisine (4), 10Z-hymenialdisine (5), hymenin (6), oroidin (7), and 4,5-dibromopyrrole-2-carbonamide (8). Both 4 and 5 showed significant enzyme inhibitory activity (IC(50) 3 and 6 nM, respectively). Secondary assays identified these compounds as potent MEK-1 inhibitors. Compounds 4 and 5 also inhibited the growth of human tumor LoVo cells.

Animals↗

PubMed2002

p-Sulfooxyphenylpyruvic acid from the red macro alga Ceratodictyon spongiosum and its sponge symbiont Haliclona cymaeformis.

Investigation of a Philippine specimen of the red alga Ceratodictyon spongiosum and its sponge symbiont Haliclona cymaeformis led to the isolation of p-sulfooxyphenylpyruvic acid, whose structure was elucidated using spectroscopic methods, with the Z-enol geometry determined through analysis of (3)J(C,H) coupling constants. The metabolite was tested for tyrosine kinase inhibition using a (3)H-thymidine incorporation assay, but was found inactive.

Animals↗

PubMed2002

Bioactive isomalabaricane triterpenes from the marine sponge Rhabdastrella globostellata.

Two new isomalabaricane triterpenes, stellettin H (1) and stellettin I (2), have been isolated from the marine sponge Rhabdastrella globostellata, collected from the Philippines. Stellettins A-D (3-6), (-)-stellettin E (7), and rhabdastrellic acid-A (8) were also isolated and characterized. Stellettin B (4) and (-)-stellettin E (7) showed selective cytotoxicity toward p21(WAF1/Cip1)-deficient human colon tumor (HCT-116) cells with IC(50) values of 0.043 and 0.039 microM, respectively.

Animals↗

PubMed2002

Iridoid glycosides from Globularia davisiana.

From the ethanolic extract of the aerial parts of Globularia davisiana, a new iridoid glycoside, davisioside (1), was isolated. Davisioside (1) comprises a rare iridoid aglycone structure with a saturated double bond between C-3 and C-4. Nine known iridoid glycosides, asperuloside (2), alpinoside (3), geniposide (4), globularin (5), globularicisin (6), 10-O-benzoylcatalpol (7), lytanthosalin (8), melampyroside (9), agnuside (10), and three known phenylethanoid glycosides, verbascoside, isoacteoside and leucosceptoside A were also isolated and characterized. The structures of the isolates were established by spectroscopic methods (one-dimensional (1D)- and two-dimensional (2D)-NMR, MS).

Biphenyl Compounds↗

PubMed2002

Lucidin type anthraquinone glycosides from Putoria calabrica.

Two new lucidin type anthraquinone glycosides, putorinoside A (1) and putorinoside B (2) were isolated from Putoria calabrica, in addition to two known anthraquinone glycosides, lucidin 3-O-beta-glucopyranoside (3) and lucidin 3-O-primeveroside (4). Based on spectroscopic data, putorinosides A and B were identified as 2-hydroxymethyl-1-methoxy-3,5,6-trihydroxyanthraquinone 3-O-beta-glucopyranoside and 2-hydroxymethyl-1-methoxy-3,6-dihydroxyanthraquinone 3-O-beta-glucopyranoside, respectively.

Anthraquinones↗

PubMedDate not supplied

Platelet aggregation inhibitors from Philippine marine invertebrate samples screened in a new microplate assay.

A new microplate assay for Ca(2+)-induced platelet aggregation as detected by Giemsa dye was used to screen marine invertebrate samples from the Philippines for inhibitors of human platelet aggregation. Out of 261 crude methanol extracts of marine sponges and tunicates, 25 inhibited aggregation at 2 mg/ml. Inhibition of agonist-induced aggregation in an aggregometer was used to confirm results of the microplate assay and to determine the specific mode of inhibition of 2 samples. The marine sponge Xestospongia sp. yielded a xestospongin/araguspongine-type molecule that inhibited collagen-induced aggregation by 87% at 2 micro g/ml, and epinephrine-induced aggregation by 78% at 20 micro g/ml, while the marine sponge Aplysina sp. yielded 5,6-dibromotryptamine, which inhibited epinephrine-induced aggregation by 51% at 20 micro g/ml. In this study we have found that the microplate assay is a simple, inexpensive, yet useful preliminary tool to qualitatively screen a large number of marine samples for antiplatelet aggregation activity.

Adenosine Diphosphate↗

PubMedDate not supplied

Neolignan glucosides from Phlomis chimerae Boiss.

From the aerial parts of the plant Phlomis chimerae, a new neolignan glucoside, (-)-4-O-methyldihydrodehydrodiconiferyl alcohol-9'-O-beta-D-glucopyranoside (1) was characterized along with the known neolignan glucosides, (-)-4-O-methyldehydrodiconiferyl alcohol-9'-O-beta-D-glucopyranoside (= longifloroside A) (2) and (-)-dihydrodehydrodiconiferyl alcohol-9-O-beta-D-glucopyranoside (3). The structure of the new compound was established on the basis of spectroscopic evidence.

Asteraceae↗