Biomedical subjects

David G I Kingston

Publications and source records attributed to David G I Kingston.

At least 19 recordsLinked to original sources

PubMed2007

Rotational-echo double-resonance NMR distance measurements for the tubulin-bound Paclitaxel conformation.

The important anticancer drug Taxol (paclitaxel, PTX) owes its unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. The conformation of the microtubule-bound drug has been the focus of numerous research efforts, since the inability of polymerized tubulin to form crystals precludes structure proof by X-ray crystallography. Likewise, although the alpha,beta-tubulin dimer structure has been solved by electron crystallography, the 3.7 A resolution is too low to permit direct determination of either ligand conformation or binding pose. In this article, we present experimental results from 2H{19F} REDOR NMR that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.

Animals↗

PubMed2006

The shape of things to come: structural and synthetic studies of taxol and related compounds.

The history of the development of Taxol (paclitaxel) as an anticancer drug is reviewed, and some aspects of the phytochemistry of Taxus species and of the medicinal chemistry of taxol are discussed. The nature of the taxol-tubulin interaction is then described, with an emphasis on studies that led to the discovery and experimental proof of the T-taxol conformation as the tubulin-binding conformation of taxol. The implications of this conformation for future drug development are also briefly covered.

Animals↗

PubMed2006

Antiplasmodial activity of compounds from Sloanea rhodantha (Baker) Capuron var. rhodantha from the Madagascar rain forest.

Bioassay-directed separation of the butanol-soluble portion of an extract of Sloanea rhodantha (Baker) Capuron var. Rhodantha (Elaeocarpaceae) active against the drug-sensitive HB3 strain of Plasmodium falciparum led to the isolation of seven phenolic compounds, gallic acid (1), 3,5-di-O-galloylquinic acid (2), 1,6-di-O-galloyl glucopyranoside (3), 3,4,5-tri-O-galloylquinic acid (4), 1-O-eudesmoylquinic acid (5), 1,2,3,6-tetra-O-galloyl glucopyranoside (6), and 3,4,5-trimethoxyphenyl-(6'-O-galloyl)-O-b-D-glucopyranoside (7). The structure of the new compound 5 was established on the basis of interpretation of its 1D and 2D NMR spectroscopic data. Compounds 2, 3, 4, 6, and 7 showed weak inhibitory activity against the drug-sensitive HB3 and the drug-resistant FCM29 strains of P. falciparum, with IC (50) values ranging from 8.0 - 43.0 and 16.1 - 93.0 microg/mL, respectively.

Animals↗

PubMed2006

Promotion of tubulin assembly by poorly soluble taxol analogs.

Promotion or inhibition of tubulin assembly into microtubules is the standard in vitro assay for evaluating potential antimicrotubule agents. Many agents to be tested are poorly soluble in aqueous solution and require a cosolvent such as dimethyl sulfoxide (DMSO). However, DMSO itself can promote tubulin assembly, and its inclusion in assays for compounds that induce tubulin assembly complicates interpretation of the results. Substituting GDP for GTP in the exchangeable nucleotide binding site of tubulin produces a less active form of the protein, tubulin-GDP. Here it is shown that tubulin-GDP can be assembled into normal microtubules in DMSO concentrations up to 15% (v/v), and polymerization assays performed under these conditions can be compared with assays run under more standard conditions. Assays for measuring the effective concentration of a ligand for promotion of tubulin assembly (EC(50)), measuring the concentration for inhibition of tubulin assembly (IC(50)) by a colchicine site ligand, and measuring tubulin critical concentrations in the presence of poorly soluble taxol derivatives are illustrated.

Biopolymers↗

PubMed2006

Bridging converts a noncytotoxic nor-paclitaxel derivative to a cytotoxic analogue by constraining it to the T-Taxol conformation.

The synthesis of the bridged A-nor-paclitaxel 4 has been achieved from paclitaxel in a key test of the T-Taxol conformational hypothesis. Although the unbridged A-nor-paclitaxel 3 is essentially noncytotoxic, the bridged analogue 4 is strongly cytotoxic. This result provides strong evidence for the T-Taxol conformation as the bioactive tubulin-binding conformation of paclitaxel.

Animals↗

PubMed2006

Cytotoxic diterpenoids from Podocarpus madagascariensis from the Madagascar rainforest.

Bioassay-directed fractionation of an extract of the root and bark of Podocarpus madagascariensis resulted in the isolation of a new totarol diterpenoid (1) in addition to the three known cytotoxic diterpenoids 19-hydroxytotarol (2), totaradiol (3), and 4beta-carboxy-19-nor-totarol (4). The structure of the new compound 1 was established as methyl-13-hydroxy-14-isopropyl-9(11),12,14(8)-podocarpatriene-19-oate on the basis of 1D and 2D NMR spectroscopic interpretation and methylation of 4. All the compounds exhibited cytotoxic activity against the A2780 ovarian cancer cell line.

Antineoplastic Agents, Phytogenic↗

PubMed2006

Design, synthesis, and bioactivity of simplified paclitaxel analogs based on the T-Taxol bioactive conformation.

A strategy for the design and synthesis of simplified paclitaxel analogs based on the T-Taxol conformation is presented. The resulting compounds have both cytotoxic and tubulin polymerization activities, although less so than those of paclitaxel itself.

Antineoplastic Agents, Phytogenic↗

PubMed2006

Synthesis and biological evaluation of N-(arylsulfanyl)carbonyl analogues of paclitaxel (taxol).

Four new N-(arylsufanyl)carbonyl paclitaxel analogues (2a-d) were prepared from 7-(triethylsilyl)-protected baccatin III (5). Their cytotoxicities against human ovarian (A2780) and prostate cancer (PC3) cell lines, as well as their tubulin-assembly activities, were determined. In these assays, the new compounds showed rather weak activities, one two orders of magnitude below those of paclitaxel (taxol; 1). The known 3'-N-[(thiophen-2-yl)carbonyl] paclitaxel analogue 3 was also prepared. As previously reported, 3 exhibited strongly improved cytotoxicities and tubulin-assembly activities as compared to paclitaxel (1).

Antineoplastic Agents, Phytogenic↗

PubMed2006

Cytotoxic and other compounds from Didymochlaena truncatula from the Madagascar rain forest.

Bioassay-guided fractionation of the EtOH extracts obtained from a plant identified as Didymochlaena truncatula led to the isolation of two cytotoxic alkaloids, camptothecin and 9-methoxycamptothecin. A second plant collection yielded three lignan derivatives, didymochlaenone A (1), didymochlaenone B (2), and (-)-wikstromol, one stilbene, (E)-3-methoxy-5-hydroxystilbene, and two stigmasterol derivatives, stigmast-4-en-3beta-ol and stigmast-4-en-3-one, but no camptothecins, and it is probable that a coding error led to a mistaken identification of the original extract. The structures of the new compounds 1 and 2 were established on the basis of extensive interpretation of one- and two-dimensional NMR spectroscopic data.

Antineoplastic Agents, Phytogenic↗

PubMed2006

Cytotoxic diterpenes from Cassipourea madagascariensis from the Madagascar rainforest.

Bioassay-directed fractionation of ethanol extracts of the roots and leaves of the plant Cassipourea madagascariensis resulted in the isolation of the two new terpenoids cassipourol (1) and cassipouryl acetate (2) in addition to the three known compounds, 3beta,30-dihydroxylup-20(29)-ene (3), 30-hydroxylup-20(29)-en-3-one (4), and combretol (5). The structures of the two new compounds were established on the basis of 1D and 2D NMR spectroscopic data and chemical conversion. All the isolated compounds were tested against the A2780 human ovarian cancer cell line; the two diterpenes (1 and 2) showed moderate cytotoxic activity, while the three known compounds (3-5) were weakly active.

Antineoplastic Agents, Phytogenic↗

PubMed2006

Bioactive isomalabaricane triterpenoids from Rhabdastrella globostellata that stabilize the binding of DNA polymerase beta to DNA.

Four isomalabaricane triterpenoids were isolated from an extract of the sponge Rhabdastrella globostellata that was active in an assay measuring stabilization of the binding of DNA with DNA polymerase beta. The known compounds stelliferin riboside (1) and 3-epi-29-acetoxystelliferin E (2) were shown to induce 29% and 23% binding, respectively, at 28 microg/mL, while the new compound stellettin J (3) induced 5% binding at 28 microg/mL. The new compound stellettin K (4) had no activity in the binding assay. The compounds were characterized by spectroscopic methods. These compounds displayed varying levels of activity toward the A2780 ovarian cancer cell line, revealing structure-based effects on both the level of cytotoxicity and DNA-polymerase beta binding. This is the first report of natural products with the ability to promote stabilization of the DNA-polymerase beta covalent binary complex.

Animals↗

PubMed2006

Two new isoflavone derivatives from the roots of an Egyptian collection of Lotus polyphyllos.

Investigation of the roots of Lotus polyphyllos Clarke resulted in the isolation of two new isoflavone derivatives; 4'-O-methylerythrinin C (3) and 4'-O-methyl-2''-hydroxydihydroalpinumisoflavone (4). In addition, the three known isoflavone derivatives 4'-O-methylalpinumisoflavone (1) lupinalbin F (5), 4',7-dimethoxy-5-hydroxyisoflavone (6), and the phenylpropanoid ester tetracosyl p-coumarate (2) were also identified. The structures were determined from spectroscopic data.

Egypt↗

PubMed2006

Cytotoxic compounds of Physena madagascariensis from the Madagascar rain forest paragraph sign.

Two new flavanones, remangiflavanones D and E (1 and 2), were isolated from an extract of the twigs, leaves, and flowers of Physena madagascariensis together with three known flavanones, remangiflavanones A-C (3-5), and (E)-N-feruloyltyramine (6). The structures of the new compounds 1 and 2 were established on the basis of one-dimensional and two-dimensional NMR spectroscopic data interpretation. All compounds were evaluated for their cytotoxicity in the A2780 human ovarian cancer cell line. Compound 5 was the most active with an IC50 value of 2.5 microg mL-1.

Antineoplastic Agents, Phytogenic↗

PubMed2005

Cytotoxic diterpenoids from two lianas from the Suriname rainforest.

Bioassay-guided fractionation of the MeOH and EtOAc fractions of extracts of two lianas collected in Suriname has led to the isolation of five new diterpenoids, humirianthone 1, 1-hydroxy-humirianthone 2, 15R-humirianthol 3, patagonol 4, and patagonal 5, and the five known diterpenoids, humirianthol 7, annonalide 8, acrenol 9, icacinol 10, and the oxidized annonalide 11. All 10 diterpenoids showed cytotoxic activity against the A2780 human ovarian cancer cell line, and compounds 1, 3, 8, and 9 also showed activity against phytopathogenic fungi.

Antifungal Agents↗

PubMed2005

Four diterpenoid inhibitors of Cdc25B phosphatase from a marine anemone.

Three new diterpenoids and one known diterpenoid have been isolated from a sea anemone of the order Actiniara, and the structures of the new compounds, actiniarins A-C (1-3) were established on the basis of extensive 1D and 2D NMR spectroscopic data interpretation. Compound 1 has a six-membered ring hemiacetal ring, and the equilibrium of this ring is discussed. All the isolates were evaluated for their inhibition of Cdc25B and for cytotoxicity against the A2780 ovarian cancer cell line.

Anemone↗

PubMed2005

Sesterterpenoids and an alkaloid from a Thorectandra sp. as inhibitors of the phosphatase Cdc25B.

Bioassay-directed separation of an extract of a Thorectandra sp. sponge led to the isolation of three new sesterterpenoids, 16-oxoluffariellolide (1), 16-hydroxyluffariellolide (2) and (2E,6E,10E)-3-formyl-7,11-dimethyl-13-(2,6,6-trimethylcyclohex-1-enyl)trideca-2,6,10-trienoic acid (3); two known sesterterpenoids, luffariellolide (4) and dehydroluffariellolide diacid (5); and one known alkaloid, fascaplysin (6). The structures of the new compounds 1-3 were established on the basis of extensive 1D and 2D NMR spectroscopic data interpretation. Compound 6 showed inhibitory activity in the Cdc25B assay, with an IC50 value of 1.0 microg/mL.

Alkaloids↗

PubMed2005

The taxol pharmacophore and the T-taxol bridging principle.

Different approaches to developing an accurate model of the binding conformation of paclitaxel (Taxol, PTX) on beta-tubulin are discussed. Electron crystallography, molecular modeling, NMR and synthetic studies all point to the T-Taxol conformation as the bioactive form. The range of molecular designs represented by synthetic taxoids prepared to test the latter, with an emphasis on internally bridged analogs, is summarized. Key implications and conclusions derived from the retrospective are presented.

Animals↗

PubMed2005

Halenaquinone and xestoquinone derivatives, inhibitors of Cdc25B phosphatase from a Xestospongia sp.

Separation of an extract of a Xestospongia sp., guided by bioassay against Cdc25B, led to the isolation of nine compounds, halenaquinone (1), xestoquinone (2), adociaquinones A (3) and B (4), 3-ketoadociaquinones A (5) and B (6), tetrahydrohalenaquinones A (7) and B (8), and 13-O-methyl xestoquinol sulfate (9). The structures of the new natural products 6 and 9 were established on the basis of extensive one- and two-dimensional NMR studies. Compounds 1, 4, and 6 inhibited recombinant human Cdc25B in vitro with IC50 values of 0.7, 0.07, and 0.2 microM, respectively, and were 19- to 150-fold less active against two related protein phosphatases. Compound 4 blocked cell cycle progression through mitosis.

Animals↗