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 37 records · Page 2Linked to original sources

PubMed2004

Epothilone induced cytotoxicity is dependent on p53 status in prostate cells.

BACKGROUND: Epothilones are a promising class of drugs in clinical trials of prostate cancer that target the microtubules, similar to taxanes, and induce apoptosis in taxane resistant tumors. The tumor suppressor p53 is one important molecular mechanism of chemotherapy resistance that in some studies predicted tumor sensitivity to paclitaxel. We hypothesized that epothilone induced cytotoxicity would be influenced by the status of p53 in prostate cells. METHODS: LNCaP, DU145, and a transformed rat prostate (RP) epithelial cell line with a temperature sensitive mutant p53 (val 135) were studied for the effect of epothilone on cell viability, cell cycle, and cell cycle checkpoint proteins. RESULTS: Epothilone had greater cytotoxicity in p53 mutant cancer cells compared to wild type cells. We confirmed our findings by creating a transformed RP epithelial cell line with a temperature sensitive mutant p53 (val 135). Using a tetrazolium (MTT) assay we found that epothilone (100 nM) decreased cell viability in RP cells by 90% with mutant p53 compared to 45% with wild type p53 (P < 0.01). Epothilone induced G2/M arrest in 50% of cells with mutant p53 compared to 25% with wild type p53 (P < 0.01). To begin to understand mechanism of epothilone induced G2/M arrest, we assessed cell cycle checkpoint proteins. We found that the effect to enhance G2/M cell cycle arrest was associated with dephosphorylation of cdc2 in both p53 wild type and p53 mutant RP cells. CONCLUSIONS: These results demonstrate that epothilone is more active against transformed prostate epithelial cells with mutant compared to wild type p53. Epothilone is capable of dephosphorylation of cdc2 in both p53 wild type and mutant cells, which is associated with G2/M cell cycle arrest. These data provide a basis for further study of p53, and the phosphorylation status of cdc-2, as markers for epothilone sensitivity in clinical studies.

Animals↗

PubMed1997

Activities of the microtubule-stabilizing agents epothilones A and B with purified tubulin and in cells resistant to paclitaxel (Taxol(R)).

Epothilones A and B, natural products with minimal structural analogy to taxoids, have effects similar to those of paclitaxel (Taxol(R)) in cultured cells and on microtubule protein, but differ from paclitaxel in retaining activity in multidrug-resistant cells. We examined interactions of the epothilones with purified tubulin and additional cell lines, including a paclitaxel-resistant ovarian carcinoma line with an altered beta-tubulin. The epothilones, like paclitaxel, induced tubulin to form microtubules at low temperatures and without GTP and/or microtubule-associated proteins. The epothilones are competitive inhibitors of the binding of [3H]paclitaxel to tubulin polymers. The apparent Ki values for epothilones A and B were 1.4 and 0.7 microM by Hanes analysis and 0.6 and 0.4 microM by Dixon analysis. In the paclitaxel-sensitive human cell lines we examined, epothilone B had greater antiproliferative activity than epothilone A or paclitaxel, while epothilone A was usually less active than paclitaxel. A multidrug-resistant colon carcinoma line and the paclitaxel-resistant ovarian line retained sensitivity to the epothilones. With Potorous tridactylis kidney epithelial (PtK2) cells examined by indirect immunofluorescence, microtubule bundles appeared more rapidly following epothilone B treatment, and there were different proportions of various mitotic aberrations following treatment with different drugs.

Drug Resistance, Multiple↗

PubMed2002

Gene expression profiling of epothilone A-resistant cells.

In the current study, we isolated sublines of the human breast adenocarcinoma cell line MDA 435 that exhibited increasing resistance to epothilone A, a microtubule-stabilizing cytotoxic agent. The resistant cells did not express P glycoprotein or multidrug resistance-associated protein (MRP) which are known mediators of multidrug resistance (MDR). Two groups of epothilone A-resistant cells were selected: cells which exhibited low resistance to both epothilone A and Taxol, and cells which exhibit low resistance to Taxol but high resistance to epothilone A. cDNA microarrays of epothilone A-resistant and Taxol-resistant cells were utilized to further characterize epothilone A resistance. Hierarchical clustering of genes according to their levels of expression indicated that the majority of genes which were highly expressed in epothilone A-resistant cells but not in taxol-resistant MDR cells encode known interferon-inducible proteins. Genes whose expression increased with increasing epothilone A resistance include microtubule-associated GTPases, cytoskeletal proteins, cell signalling proteins and a drug metabolising enzyme. The majority of the genes that were repressed in both epothilone A- and Taxol-resistant cells encode proteins regulating cellular growth signalling mechanisms.

Adenocarcinoma↗

PubMed2000

The biosynthetic gene cluster for the microtubule-stabilizing agents epothilones A and B from Sorangium cellulosum So ce90.

BACKGROUND: Epothilones are produced by the myxobacterium Sorangium cellulosum So ce90, and, like paclitaxel (Taxol((R))), they inhibit microtubule depolymerisation and arrest the cell cycle at the G2-M phase. They are effective against P-glycoprotein-expressing multiple-drug-resistant tumor cell lines and are more water soluble than paclitaxel. The total synthesis of epothilones has been achieved, but has not provided an economically viable alternative to fermentation. We set out to clone, sequence and analyze the gene cluster responsible for the biosynthesis of the epothilones in S. cellulosum So ce90. RESULTS: A cluster of 22 open reading frames spanning 68,750 base pairs of the S. cellulosum So ce90 genome has been sequenced and found to encode nine modules of a polyketide synthase (PKS), one module of a nonribosomal peptide synthetase (NRPS), a cytochrome P450, and two putative antibiotic transport proteins. Disruptions in the genes encoding the PKS abolished epothilone production. The first PKS module and the NRPS module are proposed to co-operate in forming the thiazole heterocycle of epothilone from an acetate and a cysteine by condensation, cyclodehydration and subsequent dehydrogenation. The remaining eight PKS modules are responsible for the elaboration of the rest of the epothilone carbon skeleton. CONCLUSIONS: The overall architecture of the gene cluster responsible for epothilone biosynthesis has been determined. The availability of the cluster should facilitate the generation of designer epothilones by combinatorial biosynthesis approaches, and the heterologous expression of epothilones in surrogate microbial hosts.

Anti-Bacterial Agents↗

PubMed2002

The biology and medicinal chemistry of epothilones.

Epothilones are naturally occurring 16-membered macrolides with the ability to promote tubulin polymerization in vitro and to stabilize preformed microtubules against Ca(2+)- or cold-induced depolymerization. At the cellular level, interference with microtubule functionality results in potent inhibition of cancer cell proliferation at nM to even sub-nM concentrations. Most significantly, epothilones, unlike paclitaxel (Taxol), are equally active against drug-sensitive and multidrug-resistant cell lines in vitro and epothilone B has also shown potent in vivo antitumor activity in Taxol-resistant human tumor models. Epothilone B is currently undergoing Novartis-sponsored Phase II clinical trials. In addition to naturally occurring epothilones, 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. These studies have generated a wealth of SAR data in a remarkably short period of time, given the complexity of the synthetic targets pursued. One of these analogs, BMS-247550, is presently in Phase II clinical trials by Bristol-Myers Squibb. In a first part this review is intended to provide a summary of the basic features of the in vitro biological profile of epothilones A and B, including emerging data on potential cellular epothilone resistance mechanisms. The second and third part will feature a comprehensive discussion of the epothilone SAR as it has emerged from the work of various (industrial and academic) laboratories across the world, including our own, with regard to effects on tubulin polymerization, in vitro antiproliferative activity, and in vivo antitumor activity.

Antineoplastic Agents↗

PubMed2003

Suppression of microtubule dynamics by epothilone B is associated with mitotic arrest.

The epothilones are a group of novel microtubule-targeted, antimitotic compounds that have a paclitaxel-like, assembly enhancing effect on tubulin in vitro as well as in cultured cells. We hypothesize that epothilones induce mitotic arrest by suppressing microtubule dynamics. To test this hypothesis, we used MCF7 cells stably transfected with GFP-alpha-tubulin to analyze microtubule dynamics at three concentrations of epothilone B, one that induced no mitotic arrest (0.2 nM, 20 h), one that induced one-third maximal mitotic arrest (IC(33,) 2 nM, 20 h), and one that induced half-maximal mitotic arrest (IC(50,) 3.5 nM, 20 h). We found that epothilone B suppressed microtubule dynamics in a concentration-dependent manner coincident with mitotic block. At 0.2 nM epothilone B, dynamics were not significantly altered. At 2 nM epothilone B (IC(33)), the mean growth and shortening rates were decreased by 38 and 27%, respectively. Dynamicity was decreased by 47%. At the IC(50), 80% of the cells had nearly complete stabilization of microtubule dynamics, and no anaphase or telophase figures were observed. Comparison of the effects of epothilone B on microtubule dynamics with those of paclitaxel indicated that both drugs alter the same microtubule dynamic parameters to a similar extent. At the IC(50) for mitotic arrest, dynamicity was reduced by 54% by paclitaxel compared with 62% for epothilone B. In 65% of the cells treated with paclitaxel, the microtubules were completely stabilized. Thus, the effects of epothilone B on microtubule dynamics are remarkably similar to those of paclitaxel, suggesting that both drugs induce mitotic block by a similar mechanism.

Anaphase↗

PubMed2006

Heterologous production of epothilone C and D in Escherichia coli.

The epothilones are a family of polyketide natural products that show a high potential as anticancer drugs. They are synthesized by the action of a hybrid nonribosomal peptide synthetase/polyketide synthase in the myxobacterium Sorangium cellulosum. In this work, the genes encoding the entire cluster,epoA, epoB, epoC, epoD, epoE, and epoF, were redesigned and synthesized to allow for expression in Escherichia coli. The expression of the largest of the proteins, EpoD, also required the protein be separated into two polypeptides with compatible module linkers. Using a combination of lowered temperature, chaperone coexpression, and alternative promoters, we succeeded in producing a soluble protein from all genes in the epothilone cluster. The entire synthetic epothilone cluster was then expressed in a strain of E. coli modified to enable polyketide biosynthesis, resulting in the production of epothilones C and D. Furthermore, feeding a thioester of the normal substrate for EpoD to cells expressing the epoD, epoE, and epoF genes also led to the production of epothilones C and D. The design of the synthetic epothilone genes together with E. coli expression provides the ideal platform for both the biochemical investigation of the epothilone PKS and the generation of novel biosynthetic epothilone analogues.

Catalysis↗

PubMed2002

Utilization of alternate substrates by the first three modules of the epothilone synthetase assembly line.

The epothilones, a family of macrolactone natural products produced by the myxobacterial species Sorangium cellulosum, are of current clinical interest as antitumor agents. Inspection of the structure of the epothilones suggests a hybrid polyketide/nonribosomal peptide biosynthetic origin, and the recent sequencing of the epothilone biosynthetic gene cluster has validated this proposal. Here we have examined unnatural substrates with the first two enzymes of the biosynthetic pathway, EpoA and EpoB, to investigate the enzymatic construction of alternate heterocyclic structures and the subsequent elongation of these products by the third enzyme of the pathway, EpoC. The epothilone biosynthetic machinery can utilize serine to install an oxazole in place of a thiazole in the epothilone structure and will tolerate functionalized donor groups from the EpoA-ACP domain to produce epothilone fragments modified at the C21 position. These studies with the early enzymes of the epothilone biosynthesis cluster suggest that combinatorial biosynthesis may be a viable means for producing a variety of epothilone analogues that incorporate diversity into the heterocycle starter unit.

Epothilones↗

PubMed2002

Heterologous expression of epothilone biosynthetic genes in Myxococcus xanthus.

Epothilones are potential anticancer drugs that stabilize microtubules in a manner similar to paclitaxel (Taxol). Epothilones are produced from the myxobacterium Sorangium cellulosum, which has a 16-h doubling time and produces only milligram-per-liter amounts of epothilone A and epothilone B. Furthermore, genetic manipulation of S. cellulosum is difficult. To produce epothilones in a more genetically amenable and rapidly growing host, we chose the closely related and best-characterized myxobacteria Myxococcus xanthus. We inserted 65.4 kb of S. cellulosum DNA that encompassed the entire epothilone gene cluster into the chromosome of M. xanthus by a series of homologous recombination events. The resulting strain produced epothilones A and B. Construction of a strain that contained a mutation in epoK, the P450 epoxidase, resulted in production of epothilones C and D.

Bacterial Proteins↗

PubMed2003

Epothilone B and its analogs - a new family of anticancer agents.

Epothilones are naturally occurring 16-membered macrolides with the ability to promote tubulin polymerization in vitro and to stabilize preformed microtubules against Ca(2+)- or cold-induced depolymerization. In contrast to paclitaxel (Taxol((R))) epothilones are also active in vitro against multidrug-resistant cancer cell lines as well as cell lines whose paclitaxel-resistance is derived from specific beta-tubulin mutations. Based on their attractive in vitro biological profile epothilones have turned into important lead structures in anticancer drug discovery and hundreds of analogs and derivatives of epothilone A and B have been prepared and biologically characterized over the past four years. A number of compounds, including natural epothilone B, deoxyepothilone B, and epothilone B lactam (BMS-247550) have also been reported to exhibit profound in vivo antitumor activity in animal models. Apart from providing a brief summary of the SAR that has emerged from the above in vitro studies, this minireview will largely focus on the biology and chemistry of those analogs for which in vivo antitumor activity has been reported in the literature. Two of these compounds, natural epothilone B and epothilone B lactam (BMS-247550) have advanced to clinical studies in humans.

Antineoplastic Agents↗

PubMed1997

Epothilone B stabilizes microtubuli of macrophages like taxol without showing taxol-like endotoxin activity.

Epothilones are a new class of potential antitumor compounds that were isolated from the myxobacterium Sorangium cellulosum. Epothilones have effects on the cytoskeleton similar to those of the antineoplastic drug Taxol. Both compounds inhibit cell proliferation by stabilizing microtubuli, and they compete for the same binding site. In addition, Taxol displays endotoxin-like properties in that it activates macrophages to synthesize proinflammatory cytokines and nitric oxide. We measured nitric oxide release by IFN-gamma-treated murine macrophages as an indicator of macrophage activation by epothilone B. Although epothilone B showed the expected effects on the microtubuli, there was no indication of macrophage stimulatory activity by epothilone B, nor did epothilone B inhibit lipopolysaccharide-mediated nitric oxide release. We conclude that, unlike Taxol, epothilone-mediated microtubuli stabilization does not trigger endotoxin-signaling pathways. Moreover, because the endotoxin-like activity of Taxol may be the cause of some nonhematological clinical side effects, it is to be expected that such effects may not occur with epothilones.

Animals↗

PubMed2001

Comparative molecular field analysis (coMFA) study of epothilones-tubulin depolymerization inhibitors: pharmacophore development using 3D QSAR methods.

A three-dimensional quantitative structure-activity relationship (3D QSAR) study has been carried out on epothilones based on comparative molecular field analyses (CoMFA) using a large data set of epothilone analogs, which are potent inhibitors of tubulin depolymerization. Microtubules, which are polymers of the a/beta-tubulin heterodimer, need to dissociate in order to form the mitotic spindle, a structure required for cell division. A rational pharmacophore searching method using 3D QSAR procedures was carried out and the results for the epothilones are described herein. One-hundred and sixty-six epothilone analogs and their depolymerization inhibition properties with tubulin were used as a training set. Over a thousand molecular field energies were generated and applied to generate the descriptors of QSAR equations. Using a genetic function algorithm (GFA) method, combined with a least square approach, multiple QSAR models were considered during the search for pharmacophore elements. Each GFA run resulted in 100 QSAR models, which were ranked according to their lack of fit (LOF) scores, with a total of 40 GFA runs having been performed. The 40 best QSAR equations from each run had adequate fitted correlation coefficients (R from 0.813 to 0.863) and were of sufficient statistical significance (F value from 7.2 to 10.9). The pharmacophore elements for epothilones were studied by investigating the hit frequency of descriptors (i.e. the sampling probabilities of grid points from the GFA studies) from the set of the 4,000 top scoring QSAR equations. By comparing the frequency with which each grid point appeared in the QSAR equations, three candidate regions in the epothilones were proposed to be pharmacophore elements. Two of them are completely compatible with the recent model proposed by Ojima et al. [Proc. Natl. Acad. Sci. USA, 96 (1999) 4256], however, one is quite different and is necessary to accurately predict the activities of all 166 epothilone molecules used in our training set. Finally, by visualizing the 35 most probable grid points, it was found that changes related to the C6, C7, C8, C 12, S20, and C21 atoms of the epothilones were highly correlated to their activity.

Algorithms↗

PubMed2003

Polyketide-nonribosomal peptide epothilone antitumor agents: the EpoA, B, C subunits.

The epothilones are a family of macrolactone natural products from the myxobacterial species Sorangium cellulosum. Similar to taxol, they are of current clinical interest as anticancer agents. Sequence analysis of the epothilone gene cluster allowed the identification of polyketide synthase and nonribosomal peptide synthetase modules involved in catalyzing epothilone biosynthesis. Given this information, it has been possible to test the predicted functions of several modules to date. EpoA ACP, EpoB, and EpoC have been overproduced in Escherichia coli, allowing in vitro reconstitution of the EpoA/B/C interface and production of the expected epothilone precursor. Further experiments probed the tolerance of EpoB and EpoC for unnatural substrates. These studies of the first three modules of the epothilone biosynthetic cluster suggest that combinatorial biosynthesis may lead to the production of a variety of epothilone analogs that incorporate diversity into the heterocycle starter unit. Additional efforts with the remaining modules, coupled with increased understanding of the macrocyclizing thioesterase domain, may lead to the production of epothilone variants with improved clinical properties.

Antineoplastic Agents↗

PubMed1997

Synthesis of epothilones A and B in solid and solution phase.

Epothilones A and B, two compounds that have been recently isolated from myxobacterium Sorangium cellulosum strain 90, have generated intense interest among chemists, biologists and clinicians owing to the structural complexity, unusual mechanism of interaction with microtubules and anticancer potential of these molecules. Like taxol, they exhibit cytotoxicity against tumour cells by inducing microtubule assembly and stabilization, even in taxol-resistant cell lines. Following the structural elucidation of these molecules by X-ray crystallography in 1996, several syntheses of epothilones A and B have been reported, indicative of the potential importance of these molecules in the cancer field. Here we report the first solid-phase synthesis of epothilone A, the total synthesis of epothilone B, and the generation of a small epothilone library. The solid-phase synthesis applied here to epothilone A could open up new possibilities in natural-product synthesis and, together with solution-phase synthesis of other epothilones, paves the way for the generation of large combinatorial libraries of these important molecules for biological screening.

Antineoplastic Agents↗

PubMed2003

[The PKS/NRPS hetero-gene cluster of epothilones].

Novel macrolides epothilones, produced by cellulolytic myxobacterium Sorangium cellulosum, have the activity to promote microtubule assembly, and are considered to be a potential successor to the famous antitumor drug taxol. The biosynthetic genes leading to the epothilones are clustered into a large operon. The multi-enzyme complex is a hetero-gene cluster of polyketide synthase (PKS) and non-ribosomal peptide synthetases (NRPS) and contains several functional modules, i.e. a loading module, one NRPS module, eight PKS modules, and a P450 epoxidase. The former ten modules biosynthesize desoxyepothilone (epothilones C and D), which is then epoxidized at C12 and C13 and converted into epothilones (epothilones A and B) by the P450 epoxidase. The NRPS module is responsible for the formation of the thiazole side chain from cysteine. The biosynthesis procedure of epothilones can be divided into 5 stages, i.e. formation of holo-ACP/PCP, chain initiation and thiazole ring formation, chain elongation, termination and epoxidation, and post-modification. The analysis of the gene cluster and the biosynthetic pathway reveals that novel epothilone analogs could not only be produced by chemical synthesis/modification, tranditional microbial technologies, but also can be genetically manipulated through combinatiorial biosynthesis approaches.

Bacterial Proteins↗

PubMed2002

Epothilone and paclitaxel: unexpected differences in promoting the assembly and stabilization of yeast microtubules.

Paclitaxel (Taxol) and the epothilones are antimitotic agents that promote the assembly of mammalian tubulin and stabilization of microtubules. The epothilones competitively inhibit the binding of paclitaxel to mammalian brain tubulin, suggesting that the two types of compounds share a common binding site in tubulin, despite the lack of structural similarities. It is known that paclitaxel does not stabilize microtubules formed in vitro from Saccharomyces cerevisiae tubulin; thus, it would be expected that the epothilones would not affect yeast microtubules. However, we found that epothilone A and B do stimulate the formation of microtubules from purified yeast tubulin. In addition, epothilone B severely dampens the dynamics of yeast microtubules in vitro in a manner similar to the effect of paclitaxel on mammalian microtubules. We used current models describing paclitaxel and epothilone binding to mammalian beta-tubulin to explain why paclitaxel apparently fails to bind to yeast tubulin. We propose that three amino acid substitutions in the N-terminal region and at position 227 in yeast beta-tubulin weaken the interaction of the 3'-benzamido group of paclitaxel with the protein. These results also indicate that mutagenesis of yeast tubulin could help define the sites of interaction with paclitaxel and the epothilones.

Animals↗

PubMed1999

The microtubule-stabilizing agents epothilones A and B and their desoxy-derivatives induce mitotic arrest and apoptosis in human prostate cancer cells.

Epothilones are a new class of natural products that bind to tubulin and prevent the depolymerization of microtubules, although they have no structural similarity to paclitaxel. Taxanes are only marginally effective in the treatment of disseminated prostate cancer, although they may have useful activity when administered in combination with estramustine. Unlike paclitaxel, epothilones are not substrates for P-glycoprotein and are active in multidrug resistant cells. Epothilones A and B (EA, EB) have recently been synthesized in toto. In this report, we examine the effects of synthetic epothilones and their desoxy derivatives, as well as paclitaxel, on prostate cancer cell lines. EB was the most active of these compounds in tissue culture (IC(50): 50-75 pM), four to ten-fold more potent than paclitaxel. EA and the desoxyderivatives of EA and EB (dEA, dEB) were also active, but less potent than EB. Each of these compounds causes mitotic block followed by apoptotic cell death. The relative potencies for cell cycle arrest and cytotoxicity directly correlate with the ability of the drugs to bind microtubules, stabilize mitotic spindles and induce the formation of interphase microtubule bundles. Therefore, synthetic epothilones are potent inhibitors of prostate cancer cell lines and work in a fashion similar to paclitaxel. Recently, we showed that farnesyl transferase inhibitors sensitize tumor cells to paclitaxel-induced mitotic arrest. We now have extended these observations to show that paclitaxel and the epothilones synergize with FTI to arrest the growth of prostate cancer cells. Moreover, this occurs in DU145, a cell line that is not particularly sensitive to the FTI. The combination of FTI and epothilone represent a new potential clinical strategy for the treatment of advanced prostatic cancer.

Journal Article↗

PubMed2002

Modulation of epothilone analog production through media design.

Recently, the epothilone polyketide synthase (PKS) was successfully introduced into a heterologous production host for the large-scale production of epothilone D. We have found that at least three other epothilones can also be produced as the major fermentation product of this recombinant strain by supplementation of specific substrates to the production media. Addition of acetate or propionate to the media results in modulation of the epothilone D:C ratio, whereas addition of L-serine with either acetate or propionate yields epothilone H(1) or H(2) as the major product. This strategy permits production of at least four novel epothilones by culturing a single host with a genetically modified epothilone PKS in various media.

Acetates↗