Synthesis and antiproliferative activity of a cyclic analog of dolastatin 10.

A cyclic analog of the natural antiproliferative compound dolastatin 10 was synthesized by introducing an ester link between the N- and C-terminal residues which were modified accordingly. The final macrolactonization was performed by using isopropenyl chloroformate and DMAP as reagents. This analog exhibits submicromolar antiproliferative activity against the L1210 and HT29 cell lines and inhibits in vitro tubulin polymerization (IC50, 39 microM).

Fluorescent and biotinylated analogues of docetaxel: synthesis and biological evaluation.

Six novel docetaxel analogues that possess a N-(7-nitrobenz-2-oxa-1,3-diazo-4-yl)amido-6-caproyl chain in position 7 or 3' (11 and 16a), a N-(7-nitrobenz-2-oxa-1,3-diazo-4-yl)amido-3-propanoyl group at 3' (16b) and a 5'-biotinyl amido-6-caproyl chain in position 7, 10 or 3', respectively, have been synthesized. These compounds exhibit activity against microtubule disassembly similar to that of docetaxel but show discrepant activities on living cells. Although addition of microtubules to 11, 16a and b enhance their fluorescence, no shift of the emission maxima was observed. The fluorescent docetaxel derivatives show a specific labeling of microtubules in living cells, demonstrating that the microtubule cytoskeleton constitutes their main subcellular localization.

Psycholeine, a natural alkaloid extracted from Psychotria oleoides, acts as a weak antagonist of somatostatin.

The effects of psycholeine, a plant alkaloid, were investigated on binding of radiolabelled somatostatin ([125I]N-Tyr-SRIF) and on somatostatin (SRIF)-induced inhibition of adenylate cyclase activity and growth hormone (GH) secretion by rat anterior pituitary cells. Psycholeine was shown to displace specific binding of [125I]N-Tyr-SRIF to pituitary membrane preparations, with an IC50 of 10(-5) M. At this concentration, psycholeine was also effective in significantly reducing the SRIF-induced inhibition of adenylate cyclase activity previously stimulated by growth hormone releasing factor (GRF). In parallel, it reduced the SRIF-induced inhibition of GH release stimulated by GRF in primary pituitary cell cultures in a dose-dependent manner. At a moderate concentration, the alkaloid affected neither adenylate cyclase activity nor GH release when applied in the absence of SRIF. These data suggest that psycholeine has antagonistic properties at the SRIF receptor. Quadrigemine C, a precursor of psycholeine, has a similar action.

Antimitotic and cytotoxic flavonols from Zieridium pseudobtusifolium and Acronychia porteri.

Bioassay-guided fractionation of the extracts of Zieridium pseudobtusifolium and Acronychia porteri led to the isolation of 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone [1], which showed activity against (KB) human nasopharyngeal carcinoma cells (IC50 0.04 micrograms/ml) and inhibited tubulin assembly into microtubules (IC50 12 microM). Two other known flavonols, digicitrin [2] and 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone [5], were also isolated together with three new ones, 3-O-demethyldigicitrin [3], 3,5,3'-trihydroxy-6,7,8,4'-tetramethoxyflavone [4], and 3,5-dihydroxy-6,7,8,3',4'-pentamethoxyflavone [6]. All of these flavonols showed cytotoxic activity against KB cells.

[Chemical and biological studies on Taxol (Paclitaxel) and Taxotere (Docetaxel), new antineoplastic agents]. / Recherches chimique et biologique autour du Taxol (Paclitaxel) et du Taxotère (Docetaxel), nouveaux agents antitumoraux.

Since the discovery of Taxol and of its antitumor activity a number of chemical, pharmacological and clinical studies have been performed on this natural diterpene isolated from the genus Taxus. Because the extraction of Taxol from the bark is expensive, difficult and damaging to the Taxus species, alternative sources have been studied. To date, one of the most promising alternatives is the semisynthesis of Taxol from 10-deacetylbaccatin III, a renewable precursor found in the needles of the European yew tree, Taxus baccata. From this natural compound, a number of new active compounds bearing different substituents at carbons 2, 4, 5, 7, 10, 13, 2' and 3' have been prepared. Among the new substances, Taxotere (N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyltaxol) was found to be one of the most potent in its interaction to the cellular target of antitumor taxoids: tubulin. The chemistry and structure-activity relationships of the antitumor taxoids are presented.

Taxoids, a new class of antitumour agents of plant origin: recent results.

The taxoids are natural products isolated from the yew tree (Taxaceae). Certain compounds of this family possess interesting antitumour properties. The discovery of one such compound, taxol and the development of an even more active derivative, Taxotere, are described. Taxotere represents a major progress in the domain of cancer chemotherapy.

[Taxotere: from yew's needles to clinical practice]. / Le taxotère: des aiguilles d'if à la clinique.

Taxotere [N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl taxol] is a new chemical entity obtained by semisynthesis from 10-deacetylbaccatin III, a non cytotoxic precursor extracted from the needles of the European yew Taxus baccata. Taxotere retains the unique mechanism of action of taxol and inhibits the depolymerisation of microtubules into tubulin. In vitro, Taxotere is cytotoxic against murine and human tumor cells with IC50 values ranging from 4 to 35 ng/ml. Taxotere inhibits the clonogenic properties of fresh human tumor cells at clinically relevant concentrations. Taxotere is highly active in vivo against several experimental models: it is 2.7-fold more active than taxol on a log cell kill basis against B16 melanoma; ten out of the twelve models of grafted murine tumors tested respond to Taxotere; it is active with 80% complete regressions against advanced C38 colon adenocarcinoma and PO3 pancreatic ductal adenocarcinoma. Finally, Taxotere is active against several human xenografts implanted in nude mice. Safety studies were performed in dogs and mice according to NCI guidelines. Toxicological effects are observed mostly is tissues with high cell turnover (bone marrow in mice and dogs, gastrointestinal tract in dogs only) or in those where microtubules play an important role (peripheral nerves in mice only). Because of its availability, due to an efficient process using a renewable source of natural precursor, its preclinical profile (higher antitumoral activity than taxol with a comparable toxicological profile) and its unique mechanism of action, Taxotere has entered Phase I clinical trials in Europe, United States and Japan. The dose limiting toxicity is a neutropenia. Evidence of clinical activity has been noted (breast, ovarian, lung). Taxotere is now in Phase II clinical trials.

Hepatic metabolism and biliary excretion of Taxol in rats and humans.

To date there have been limited studies of the metabolism and disposition of Taxol in animals and humans. Renal disposition of unmetabolized Taxol has been documented to account for a maximum of 5% to 10% of an administered dose of Taxol in humans, but the principal processes involved in drug disposition, particularly the roles of biliary excretion and drug metabolism, have not been evaluated. Therefore, the biliary excretion of Taxol has been studied in rats and in a human patient receiving Taxol in a phase I trial. Of the total doses administered to rats and the patient, 40% and 20%, respectively, were excreted in the bile in the forms of unmetabolized Taxol and Taxol metabolites until 24 hours posttreatment. Although the biliary excretion of unmetabolized Taxol accounted for 10% and 3% of total drug disposition in the rats and in the patient, respectively, the remaining portion consisted of several metabolites. Nine metabolites were detected in rat bile, and five metabolites were detected in human bile. The chemical structures of four of the rat metabolites and three of the human metabolites have been identified thus far. With the exception of baccatin III, a minor metabolite found only in rat bile that lacks the side chain at C-13 position of the taxane ring, the other metabolites were monohydroxylated or dihydroxylated and had intact taxane rings and side chains at taxane ring positions C-2 and C-13. The taxane ring and both the C-2 and C-13 side chains were susceptible to hydroxylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity relationships of Taxol and Taxotere analogues.

From Taxol, Taxotere, and 10-deacetyl baccatin III, a number of compounds have been prepared. Their biological activity was evaluated on microtubule disassembly at 0 degrees C. The conformation of these Taxol and Taxotere analogues was determined by molecular modeling experiments and nuclear magnetic resonance spectroscopy and compared with the structure of Taxotere in the crystal, obtained by an x-ray analysis. The results of these studies given information on the crucial parts of the active molecules involved in the binding to tubulin.

Alkaloids from Psychotria oleoides with activity on growth hormone release.

Bioactivity-guided purification of a crude alkaloid extract of Psychotria oleoides has afforded a new alkaloid, psycholeine [1], together with quadrigemine C [2], a tetrameric pyrrolidinoindoline compound of unknown stereochemistry. A comparison study of nmr and cd spectra of quadrigemine C and hodgkinsine [3], a trimeric pyrrolidinoindoline substance, led us to suggest the stereochemistry of quadrigemine C. The structure and configuration of psycholeine was determined by spectroscopic means and chemical correlation with quadrigemine C. Psycholeine interacts with somatostatin receptors and exhibits a somatostatin antagonistic activity on GH secretion by pituitary cells in primary culture.

[Anticancer substances of vegetable origin. Spindle poisons: vincaleukoblastine, leurocristine and navelbine; taxol and taxotere]. / Substances anticancéreuses d'origine végétale. Les poisons du fuseau: vincaleucoblastine, leurocristine et Navelbine; taxol et Taxotère.

The biological activity of spindle poisons can easily be measured using an in vitro assay based on the interaction of these substances with their cellular "receptor": tubulin. The use of this assay led us to select Navelbine and Taxotere as antimitotic substances. These compounds, as well as their natural parents: vincaleucoblastine, leurocristine and taxol respectively, have been obtained by semi-synthesis using relatively abundant natural precursors as starting materials. This paper summarizes the preparation of these important anticancer drugs.

Experimental antitumor activity of taxotere (RP 56976, NSC 628503), a taxol analogue.

Taxotere (RP 56976; NSC 628503; N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl taxol) is a new microtubule stabilizing agent. It is obtained by semisynthesis from a noncytotoxic precursor extracted from the needles of the tree, Taxus baccata L. Taxotere was evaluated for antitumor activity against a variety of transplantable tumors of mice. Taxotere had no marked schedule dependency and was found active by the i.v. and the i.p. routes. Upon i.v. administration, 9 of 11 tumor models tested responded to Taxotere. B16 melanoma was found highly sensitive to Taxotere, with a tumor growth inhibition of 0% and a 3.0 log10 tumor cell kill at the maximum tolerated dose. In the same trial, taxol produced only a 1.1 log10 tumor cell kill at the maximum tolerated dose. Taxotere cured early stage pancreatic ductal adenocarcinoma 03 (6 of 6 cures) and colon adenocarcinoma 38 (7 of 7 cures). It also effected greater than 80% complete regressions of advanced stage disease with both tumors. Taxotere was active against early and advanced stage colon adenocarcinoma 51, with 2.3 and 1.7 log10 cell kill, respectively. Four other tumors responded to a lesser extent: Lewis lung (5.5% tumor growth inhibition), Glasgow osteogenic sarcoma (27.2% tumor growth inhibition), L1210 and P388 leukemias (70 and 54% increase in life span, respectively). Because of its good preclinical activity and its unique mechanism of action, Taxotere has entered Phase I clinical trials.

Relationships between the structure of taxol analogues and their antimitotic activity.

A variety of synthetic analogues of taxol, a naturally occurring antitumor diterpene, were examined for their potency to inhibit microtubule disassembly. For some of the compounds, the in vitro cytotoxic properties showed a good correlation with the tubulin assay. This structure-activity relationship study shows that inhibition of microtubule disassembly is quite sensitive to the configuration at C-2' and C-3'. A correlation between the conformation of the side chain at C-13 and the activity is suggested. Of all the compounds examined, one of the most potent in inhibiting microtubule disassembly and in inhibiting murine P388 leukemic cells, N-debenzoyl-N-tert-(butoxycarbonyl)-10-deacetyltaxol, named taxotere, was selected for evaluation as a potential anticancer agent.

Taxol metabolism. Isolation and identification of three major metabolites of taxol in rat bile.

The elimination of nonradioactive taxol in bile and urine was investigated in the rat after administration via the caudal vein (10 mg/kg). As in humans, no metabolites of taxol were detected by HPLC in rat urine, and only 10% of the injected taxol was recovered in urine over a 24-hr period. In contrast, 11.5% and 29% of the injected taxol was recovered in rat bile as unchanged taxol and metabolites, respectively. Among the nine taxol metabolites detected by HPLC, the side chain at C13, which is required for pharmacological activity, had been removed in only one minor metabolite, baccatin III. The chemical structures of the two major hydroxylated metabolites were determined by mass spectrometry (fast atom bombardment and desorption chemical ionization) and 1H-NMR spectroscopy. One was a taxol derivative hydroxylated on the phenyl group at C3' of the side chain at C13, while the other corresponded to a taxol derivative hydroxylated in the m-position on the benzoate of the side chain at C2. Although these two major taxol metabolites were as active as taxol in preventing cold microtubule disassembly, they were, respectively, 9 and 39 times less cytotoxic as taxol on in vitro L1210 leukemia growth. These results show for the first time that there is a significant hepatic metabolism of taxol.

Interaction of 7-acetyltaxol with different tubulin assemblies.

Equilibrium microdialysis of [3H]acetyltaxol against different tubulin assemblies showed that: (i) the binding capacity of tubulin does not depend on the temperature; (ii) two classes of 'polymers' exist, with respect to Ac-taxol binding. Some of them (plaques, complex cylinders induced with some polycations and spirals made with rhazinilam) bound Ac-taxol, as do normal microtubules. In contrast, spirals formed with vinblastine and griseofulvin, rings made with polycations and complex cylinders induced with spermine do not bind Ac-taxol as is the case with free tubulin.

Absence of 7-acetyl taxol binding to unassembled brain tubulin.

The effect of taxol on microtubule proteins at 0 degrees C is controversial. In order to determine if taxol is unable to bind to unassembled tubulin, as has been hypothesized, the binding of [3H]acetyl taxol has been studied using equilibrium microdialysis. Ac-taxol bound to microtubules at 37 degrees C and the binding remained stable when the temperature was lowered to 0 degrees C. Ac-taxol bound also at 0 degrees C to microtubules stabilized with rhazinilam. In contrast, there was no binding of Ac-taxol to unassembled tubulin, either free tubulin at 0 degrees C or tubulin, complexed with several microtubule poisons, at 0 and 37 degrees C.

Isolation and characterization of 9-hydroxy-10-trans,12-cis-octadecadienoic acid, a novel regulator of platelet adenylate cyclase from Glechoma hederacea L. Labiatae.

We have identified and characterized a fatty acid, (9S,10E,12Z)-9-hydroxy-10,12-octadecadienoic acid (9-HODE) as a regulator of adenylate cyclase activity of human platelet membranes. This fatty acid was isolated from a methanolic extract of the plant Glechoma hederacea L. Labiatae (commonly known as 'lierre terrestre', 'ground ivy' or 'creeping Charlie'; it was identified by nuclear magnetic resonance and mass spectroscopy. This compound increased basal adenylate cyclase activity in platelet membranes about threefold and had an EC50 of 10-20 microM. This increase in adenylate cyclase activity occurred without a temporal lag, was reversible, and represented an increase in Vmax without a substantial change in Km for ATP, Mg2+ or Mn2+. In addition, 9-HODE additively or synergistically increased platelet adenylate cyclase activity in response to guanosine 5'-[beta,gamma-imido]triphosphate and forskolin, but the fatty acid failed to alter inhibition of adenylate cyclase activity mediated by epinephrine (alpha 2-adrenergic receptor). Studies of the interaction of 9-HODE with activation of platelet adenylate cyclase activity mediated by prostaglandin E1 (PGE1) and prostaglandin D2 (PGD2) indicated that this fatty acid produced a parallel shift in the concentration/response curve of PGE1 and PGD2 without altering maximal response, which was substantially greater than that observed with 9-HODE alone. From these results, we conclude that 9-HODE appears to be a partial agonist at PGE1 and PGD2 receptors on human platelets. We believe that this is a novel example of a plant-derived fatty acid which acts on cells to regulate adenylate cyclase via prostaglandin receptors.

Taxol and derivatives: a biogenetic hypothesis.

Based on the structural differences of compounds isolated from various species of Taxus, this brief review suggests a biogenetic approach to taxol. This hypothesis could be of some help in the synthesis of this complex molecule exhibiting significant antitumor properties.