PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Epothilones”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2000

Total synthesis of 16-desmethylepothilone B, epothilone B10, epothilone F, and related side chain modified epothilone B analogues.

The macrolactonization-based strategy for the total synthesis of epothilones has been streamlined and improved to a high level of efficiency and stereoselectivity. This strategy has been applied to the construction of vinyl iodide 19 which served as a common intermediate for the synthesis of a series of natural and designed epothilones including an epothilone B10 (3), epothilone F (5), 16-desmethylepothilone B (14), pyridine epothilones 57a-57g, dimeric epothilones 59 and 61, and benzenoid epothilones 63a-63g.

Antineoplastic Agents↗
PubMed2003

Crystal structures of epothilone D-bound, epothilone B-bound, and substrate-free forms of cytochrome P450epoK.

Epothilones are potential anticancer drugs that stabilize microtubules by binding to tubulin in a manner similar to paclitaxel. Cytochrome P450epoK (P450epoK), a heme containing monooxygenase involved in epothilone biosynthesis in the myxobacterium Sorangium cellulosum, catalyzes the epoxidation of epothilones C and D into epothilones A and B, respectively. The 2.10-, 1.93-, and 2.65-A crystal structures reported here for the epothilone D-bound, epothilone B-bound, and substrate-free forms, respectively, are the first crystal structures of an epothilone-binding protein. Although the substrate for P450epoK is the largest of a P450 whose x-ray structure is known, the structural changes along with substrate binding or product release are very minor and the overall fold is similar to other P450s. The epothilones are positioned with the macrolide ring roughly perpendicular to the heme plane and I helix, and the thiazole moiety provides key interactions that very likely are critical in determining substrate specificity. Interestingly, there are strong parallels between the epothilone/P450epoK and paclitaxel/tubulin interactions. Based on structural similarities, a plausible epothilone tubulin-binding mode is proposed.

Binding Sites↗
PubMed2003

Epothilone C macrolactonization and hydrolysis are catalyzed by the isolated thioesterase domain of epothilone polyketide synthase.

Epothilone C is produced by the combined action of one nonribosomal peptide synthetase (NRPS) and nine polyketide synthase (PKS) modules in a multienzyme system. The final step in the biosynthesis is the thioesterase (TE)-catalyzed cyclorelease of epothilone from the EpoF protein. It has been unclear whether isolated PKS TE domains could exhibit macrolactonization activity. Here we demonstrate that the excised epothilone TE domain can catalyze the efficient cyclization of the N-acetylcysteamine thioester of seco-epothilone C to generate epothilone C (kcat/KM = 0.41 +/- 0.03 min-1 mM-1). The TE domain also catalyzes the hydrolysis of both the N-acetylcysteamine thioester of seco-epothilone C (kcat = 0.087 +/- 0.005 min-1, KM = 291 +/- 53 muM) and that of the epothilone C (kcat = 0.67 +/- 0.01 min-1, KM = 117 +/- 5 muM) to form seco-epothilone C.

Catalysis↗
PubMed2006

Cloning and expression of a cytochrome P450 hydroxylase gene from Amycolatopsis orientalis: hydroxylation of epothilone B for the production of epothilone F.

Degenerate PCR primers were used to amplify cytochrome P450 gene fragments from the high-GC gram-negative bacteria Amycolatopsis orientalis, which catalyzes the hydroxylation of epothilone B to produce epothilone F. The amplified fragments were used as hybridization probes to identify and clone two intact cytochrome P450 genes. The expression of one of the cloned genes in a Streptomyces lividans transformant resulted in the biotransformation of epothilone B to epothilone F. The conversion of epothilone B to epothilone F by the S. lividans transformant was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy.

Actinomycetales↗
PubMed2001

Total synthesis of epothilone B, epothilone D, and cis- and trans-9,10-dehydroepothilone D.

The phosphonium salt 35, representing one of the two principal subunits of the epothilones, was prepared from propargyl alcohol via heptenone 22. A Wittig reaction of the phosphorane from 35 with aldehyde 33, obtained from aldol condensation of ketone 27 with aldehyde 28, afforded 37. Seco acid 42 derived from 37 underwent lactonization to give cis-9,10-dehydroepothilone D (43) which was selectively reduced with diimide to yield epothilone D (4) and, after epoxidation, epothilone B (2). An alternative route to epothilone D employed alkyne 39, obtained from 33, in a Castro-Stephens reaction with allylic bromide 34 to furnish enyne 40. The latter was semi-hydrogenated to provide 37. Alkyne 46, prepared from alcohol 45, was converted to trans-vinylstannane 47 which, in a Stille coupling with allylic chloride 50, gave 51. Seco acid 52 derived from 51 underwent lactonization to give trans-9,10-dehydroepothilone D (54). Bioassay data comparing the antiproliferative activity and tubulin polymerization of 43 and 54 with epothilone B (2), epothilone D (4), and paclitaxel (7) showed that the synthetic analogues were less potent than their natural counterparts, although both retain full antiproliferative activity against a paclitaxel-resistant cell line. No significant difference in potency was noted between cis analogue 43 and its trans isomer 54.

Animals↗
PubMed2002

Highly concise routes to epothilones: the total synthesis and evaluation of epothilone 490.

A concise modular laboratory construction of the epothilone class of promising antitumor agents has been accomplished. For the first time in the epothilone area, the new synthesis exploits the power of ring-closing olefin metathesis (RCM) in a stereospecific way. Previous attempts at applying RCM to epothilone syntheses have been repeatedly plagued by complete lack of stereocontrol in the generation of the desired 12,13-olefin geometry in the products. The isolation of epothilone 490 (3) prompted us to reevaluate the utility of the RCM procedure for fashioning the 10,11-olefin, with the Z-12,13-olefin geometry already in place. Olefin metathesis of the triene substrate 12 afforded the product diene macrolide in stereoselective fashion. For purposes of greater synthetic convergency, the C3-(S)-alcohol was fashioned late in the synthesis, using chiral titanium-mediated aldol conditions with the entire O-alkyl fragment as a C15 acetate as the enolate component. Examination of the effects of protecting groups on the RCM process showed that deprotection of the C7 alcohol has a beneficial effect on the reaction yield. Performing the RCM as the last synthetic step in the sequence afforded a 64% yield of only the desired E-olefin. Selective diimide reduction of the new 10,11-olefin yielded 12,13-desoxyepothilone B, our current clinical candidate, demonstrating the utility of this new RCM-reduction protocol in efficiently generating the epothilone framework. Furthermore, the new olefin was selectively funtionalized to demonstrate the advantage conferred by this route for the construction of new analogues for SAR studies, in cytoxicity and microtubule affinity screens. Also described is the surprisingly poor in vivo performance of epothilone 490 in xenografts in the light of very promising in vitro data. This disappointing outcome was traced to unfavorable pharmacokinetic features of the drug in murine plasma. By the pharmacokinetic criteria, the prognosis for the effectiveness of 3 in humans is, in principle, much more promising.

Animals↗
PubMed1998

Synthesis and biological properties of C12,13-cyclopropyl-epothilone A and related epothilones.

BACKGROUND: The epothilones are natural substances that are potently cytotoxic, having an almost identical mode of action to Taxoltrade mark as tubulin-polymerization and microtubule-stabilizing agents. The development of detailed structure-activity relationships for these compounds and the further elucidation of their mechanism of action is of high priority. RESULTS: The chemical synthesis of the C12,13-cyclopropyl analog of epothilone A and its C12,13-trans-diastereoisomer has been accomplished. These compounds and several other epothilone analogs have been screened for their ability to induce tubulin polymerization and death of a number of tumor cells. Several interesting structure-activity trends within this family of compounds were identified. CONCLUSIONS: The results of the biological tests conducted in this study have demonstrated that, although a number of positions on the epothilone skeleton are amenable to modification without significant loss of biological activity, the replacement of the epoxide moiety of epothilone A with a cyclopropyl group leads to total loss of activity.

Animals↗
PubMed2001

Synthesis of epothilone analogues by antibody-catalyzed resolution of thiazole aldol synthons on a multigram scale. Biological consequences of C-13 alkylation of epothilones.

Three monoclonal aldolase antibodies (84G3, 85H6, and 93F3), generated against a beta-diketone hapten (II) by the reactive immunization technique, catalyzed highly enantioselective retro-aldol reactions of the racemic thiazole aldols 13-20. Antibody 84G3 (0.0004-0.005 mol%) was used to resolve (+/-)-13-(+/-)-18 to afford compounds 13-18 in multigram quantities. Multiple 13-alkyl analogues of epothilone (7-12) and their trans isomers ((E)-7-(E)-12) were synthesized starting from thiazole aldols 13-18. Construction of the trisubstituted olefin moiety in compounds 7-12 and (E)-7-(E)-12 was catalyzed by Grubbs' catalyst (X). Initial biological testing with compounds 7-10 and their trans isomers showed that compounds 9, 10, and (E)-10 have appreciable tubulin polymerization and antiproliferative activities that approached those of epothilone C. The most active compound, (E)-9, even displayed potencies comparable to those observed for epothilones A and D. Interestingly, all trans analogues were more potent than their corresponding cis isomers. While introduction of an alkyl group at C-13 in the cis series led to an overall reduction in biological activity (compared to epothilone C), appropriate modification of the thiazole moiety (replacement of the 2-methyl substituent by a 2-methylthio group) was able to compensate for this loss. These results are encouraging in view of the expectation that epoxidations of these compounds should further increase their cellular activities. Thus, compounds 9, 10, and (E)-9 and (E)-10 represent highly promising candidates for further studies.

Aldehyde-Lyases↗
PubMed2001

Studies on the biosynthesis of epothilones: the PKS and Epothilone C/D monooxygenase.

Nonproducer mutants support the assumption that epothilones A and B are synthesized by the same polyketide synthase (PKS). The endproducts of the PKS, epothilones C and D, compete for the active site of a constitutively synthesized monooxygenase which is regulated by product inhibition. The postulated C-13 hydroxy-epothilones as direct precursors of epothilones C and D were not detected.

Binding Sites↗
PubMed2002

Studies on the biosynthesis of epothilones: hydroxylation of Epo A and B to epothilones E and F.

When Sorangium cellulosum So ce90 is grown without XAD adsorber resin there is a steady state of epothilone A and B biosynthesis and hydroxylation of these products to epothilones E and F. This biotransformation at position C-21 of the thiazole ring is not restricted to producers of epothilones. It is carried out by a substrate induced monooxygenase. Epothilones E and F are further degraded by opening of the lactone ring by an esterase. Steps of degradation of different strains of S. cellulosum are compared.

Antineoplastic Agents↗
PubMed2001

In vivo metabolism of epothilone B in tumor-bearing nude mice: identification of three new epothilone B metabolites by capillary high-pressure liquid chromatography/mass spectrometry/tandem mass spectrometry.

Epothilone B is a 16-membered macrolide produced by the myxobacterium Sorangium cellulosum and is currently under clinical investigation. Experimentally, epothilone B demonstrates potent antiproliferative activity at the nanomolar level in vitro, and potent regression-producing antitumor activity in vivo, similar to paclitaxel (Taxol). In order to foster the design of improved derivatives, the potential biotransformation products of epothilone B formed in liver of tumor-bearing mice after intravenous administration of 10 mg/kg were characterized in an early stage of compound development. Solely on the basis of capillary high-performance liquid chromatography, combined either with electrospray tandem mass spectrometry (in precursor and product ion scan mode) and single analyzing time-of-flight mass spectrometry (H/D exchange and accurate mass measurement), three main metabolites could be detected. The three metabolites, formed by the liver, have in common that the epoxide ring was hydrolyzed and that the macrocyclic lactone ring was opened to the acid. In two cases it is assumed that open-chain intermediates re-cycled either to a lactone or, after conjugation with taurine, to the respective lactam. The proposed structures were additionally supported by the determination of the number of the exchangeable hydrogen atoms and by confirmation of the proposed elemental composition by exact mass measurement.

Animals↗
PubMed2001

Catalytic antibody route to the naturally occurring epothilones: total synthesis of epothilones A-F.

Naturally occurring epothilones have been synthesized starting from enantiomerically pure aldol compounds 9-11, which were obtained by antibody catalysis. Aldolase antibody 38C2 catalyzed the resolution of (+/-)-9 by enantioselective retro-aldol reaction to afford 9 in 90% ee at 50 % conversion. Compounds 10 and 11 were obtained in more than 99% ee at 50% conversion by resolution of their racemic mixtures using newly developed aldolase antibodies 84G3, 85H6 or 93F3. Compounds 9, 10 and 11 were resolved in multigram quantities and then converted to the epothilones by metathesis processes, which were catalyzed by Grubbs' catalysts.

Anti-Bacterial Agents↗
PubMed2002

Total synthesis of epothilone a through stereospecific epoxidation of the p-methoxybenzyl ether of epothilone C.

The total synthesis of epothilone A is described by the coupling four segments 4-7 a. Three of the segments, 4, 5 and 7 a, have only one chiral center; all other chiral centers were introduced by simple asymmetric catalytic reactions. The key steps are the ring opening of epoxide 5 with acetylide 8 for the construction of the C12-C13 cis double bond and a practical hydrolytic kinetic resolution (HKR) developed by Jacobsen group for the introduction the chiral center at C3. Especially, the stereospecific epoxidation of 3-O-PMB epothilone C 3 b through long-range effect of 3-O-PMB protecting group gave high yields of the C12-C13 alpha-epoxide for the synthesis of target molecule.

Antineoplastic Agents↗
PubMed2000

A common pharmacophore for epothilone and taxanes: molecular basis for drug resistance conferred by tubulin mutations in human cancer cells.

The epothilones are naturally occurring antimitotic drugs that share with the taxanes a similar mechanism of action without apparent structural similarity. Although photoaffinity labeling and electron crystallographic studies have identified the taxane-binding site on beta-tubulin, similar data are not available for epothilones. To identify tubulin residues important for epothilone binding, we have isolated two epothilone-resistant human ovarian carcinoma sublines derived in a single-step selection with epothilone A or B. These epothilone-resistant sublines exhibit impaired epothilone- and taxane-driven tubulin polymerization caused by acquired beta-tubulin mutations (beta274(Thr-->Ile) and beta282(Arg-->Gln)) located in the atomic model of alphabeta-tubulin near the taxane-binding site. Using molecular modeling, we investigated the conformational behavior of epothilone, which led to the identification of a common pharmacophore shared by taxanes and epothilones. Although two binding modes for the epothilones were predicted, one mode was identified as the preferred epothilone conformation as indicated by the activity of a potent pyridine-epothilone analogue. In addition, the structure-activity relationships of multiple taxanes and epothilones in the tubulin mutant cells can be fully explained by the model presented here, verifying its predictive value. Finally, these pharmacophore and activity data from mutant cells were used to model the tubulin binding of sarcodictyins, a distinct class of microtubule stabilizers, which in contrast to taxanes and the epothilones interact preferentially with the mutant tubulins. The unification of taxane, epothilone, and sarcodictyin chemistries in a single pharmacophore provides a framework to study drug-tubulin interactions that should assist in the rational design of agents targeting tubulin.

Alkaloids↗
PubMed2001

New natural epothilones from Sorangium cellulosum, strains So ce90/B2 and So ce90/D13: isolation, structure elucidation, and SAR studies.

In addition to epothilones A (1) and B (2), 37 natural epothilone variants and epothilone-related compounds were isolated from the culture broth of a 700 L fermentation of Sorangium cellulosum, strain So ce90/B2. Of these, only the 12,13-desoxyepothilones, epothilone C (14) and D (15), were produced in significant amounts (3-6 mg/L); the 21-hydroxy derivatives and epothilones E (3) and F (4), in low and variable amounts due to further degradation by the producing organism. Most of the other epothilone variants were produced only in 1-100 microg/L amounts. The new compounds are very similar in structure to the parent compounds 1, 2 and 14, 15 and are presumably the result of the imperfect selectivity of the biosynthetic enzymes for acetate and propionate. Further, epothilones containing an oxazole moiety (10-13) in the side chain instead of a thiazole as well as ring-expanded 18-membered macrolides, epothilones I (30-35), and a ring contracted 14-membered macrolide, epothilone K (36), were found as very minor metabolites. The mutant strain, So ce90/D13, instead of macrolactones, produced short-chain carboxylic acids 40, 41, and 42 bearing the characteristic thiazole side chain. The structures of the new epothilones were elucidated on the basis of comprehensive NMR and MS data. The new epothilone variants were tested in a cytotoxicity assay with mouse fibroblasts (cell line L929), and structure-activity relationships were established. Several new natural epothilones showed activity comparable to 1 and 2, but in no case exceeded that of 2.

Animals↗
PubMed2002

Epothilones: a novel class of non-taxane microtubule-stabilizing agents.

The epothilones are a novel class of non-taxane microtubule-stabilizing agents obtained from the fermentation of the cellulose degrading myxobacteria, Sorangium cellulosum. Preclinical studies have shown that the epothilones are more potent than the taxanes and active in some taxane-resistant models. Similar to paclitaxel and other taxanes, the epothilones block cells in mitosis, resulting in cell death. The chief components of the fermentation process are epothilones A and B, with epothilones C and D found in smaller amounts. Trace amounts of other epothilones have also been detected. Pre-clinical studies have shown that epothilone B is the most active form, exhibiting significantly higher antitumor activity than paclitaxel and docetaxel. Several phase I and phase II clinical trials are ongoing with epothilone B and BMS 247550, an epothilone B analog. Preliminary reports indicate these agents are active against human cancers in heavily pre-treated patients. The epothilones appear to be well tolerated, with a side effect profile that is similar to that reported with the taxanes. This article will review some basic aspects of epothilone chemistry and biology, and pre-clinical and preliminary clinical experience with epothilone B and its analog, BMS 247550.

Antineoplastic Agents↗
PubMed2005

Recent developments in the chemical biology of epothilones.

Epothilones A and B are naturally occurring microtubule-stabilizers, which inhibit the growth of human cancer cells in vitro at nM or even sub-nM concentrations. In contrast to paclitaxel (Taxol) epothilones are also active against different types of multidrug-resistant cancer cell lines in vitro and against multidrug-resistant tumors in vivo (epothilone B). Their attractive preclinical profile has made epothilones important lead structures in the search for improved cytotoxic anticancer drugs and epothilone B is currently undergoing phase II clinical trials. Numerous synthetic and semi-synthetic analogs have been prepared since the absolute stereochemistry of epothilone B was first disclosed in mid-1996 and their in vitro biological activity has been determined. Apart from generating a wealth of SAR information, these efforts have led to the identification of at least four compounds (in addition to epothilone B), which are currently at various stages of clinical evaluation in humans. This review is first intended to provide a summary of the basic features of the in vitro biological profile of epothilone B, with particular emphasis on recent developments in this area. A second part will outline the most relevant aspects of the epothilone SAR with regard to effects on tubulin polymerization, in vitro antiproliferative activity, and in vivo antitumor activity. This will include a brief discussion of research directed at the determination of the bioactive conformation of epothilones. In a final section, the preclinical profile of those epothilone analogs currently in clinical development will be discussed in greater detail.

Antineoplastic Agents↗