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PubMed2005

Studies towards the synthesis of epothilone A via organoboranes.

Studies towards the synthesis of epothilone A via organoboranes have been described. A modified procedure for the large-scale preparation of B-gamma,gamma-dimethylallyldiisopinocampheylborane from prenyl alcohol has been developed. This reagent, upon reaction with various aldehydes, provides the corresponding alpha,alpha-dimethylhomoallylic alcohols in high enantioselectivities. The application of this reagent for the synthesis of the C1-C6 subunit of epothilone has been demonstrated. Alternatively, inter- and intramolecular asymmetric reduction protocols have also been utilized for the synthesis of the C1-C6 subunit of epothilone A. The synthesis of the C7-C21 fragment of epothilone A involving asymmetric alkoxyallyl- and crotylboration using alpha-pinene-derived reagents has also been described.

Boranes↗

PubMed2000

Cloning and heterologous expression of the epothilone gene cluster.

The polyketide epothilone is a potential anticancer agent that stabilizes microtubules in a similar manner to Taxol. The gene cluster responsible for epothilone biosynthesis in the myxobacterium Sorangium cellulosum was cloned and completely sequenced. It encodes six multifunctional proteins composed of a loading module, one nonribosomal peptide synthetase module, eight polyketide synthase modules, and a P450 epoxidase that converts desoxyepothilone into epothilone. Concomitant expression of these genes in the actinomycete Streptomyces coelicolor produced epothilones A and B. Streptomyces coelicolor is more amenable to strain improvement and grows about 10-fold as rapidly as the natural producer, so this heterologous expression system portends a plentiful supply of this important agent.

Bacterial Proteins↗

PubMed2006

Epothilones in the treatment of cancer.

Epothilones are cytotoxic macrolides with a similar mechanism of action to paclitaxel but with the potential advantage of activity in taxane-resistant settings in preclinical models. The epothilones ixabepilone, patupilone, BMS-310705, KOS-862 and ZK-EPO are in early clinical trials for cancer treatment. Phase I studies have shown that dose-limiting toxicities of epothilones are generally neurotoxicity and neutropoenia although initial studies with patupilone indicated that diarrhoea was dose limiting. Neuropathy induced by ixabepilone may be schedule dependent. Over 20 Phase II studies of epothilones in cancer treatment have been reported, and significant activity in taxane-sensitive tumour types (such as breast, lung and prostate cancers) has been noted. Response rates in taxane-refractory metastatic breast cancer are relatively modest, but ixabepilone and patupilone have shown promising efficacy in hormone-refractory metastatic prostate cancer and in taxane-refractory ovarian cancer.

Animals↗

PubMed2003

Generation of novel epothilone analogs with cytotoxic activity by biotransformation.

The epothilones represent a new class of bacterial natural products with broad spectrum of antiproliferative activity against various types of human tumors and tumor cell lines. The attractive preclinical profile of epothilones has made them promising lead compounds for novel anticancer agents and has spurred a strong interest in obtaining different derivatives to fully evaluate their therapeutic potentials. We have generated a number of novel epothilone D and 10,11-dehydroepothilone D (Epo490) analogs via biotransformation using Amycolata autotrophica to alter the oxidation state of the parental compounds. The bioconverted compounds displayed different degrees of potency in cytotoxicity assays against a panel of human tumor cell lines, with 11-hydroxyepothilone D, 14-hydroxyepothilone D, and 21-hydroxyepothilone D showing comparable activity to that of epothilone D, and 21-hydroxy Epo490 being comparable to Epo490. The addition of hydroxyl group(s) seems to cause a decrease in cytotoxic activity against multiple drug resistant cell lines (with overexpressed P-glycoprotein). The compounds generated by biotransformation exert differential effects on tubulin polymerization, which correlate with their biological activities.

Actinomycetales↗

PubMed2002

Late activation of apoptotic pathways plays a negligible role in mediating the cytotoxic effects of discodermolide and epothilone B in non-small cell lung cancer cells.

Discodermolide and epothilone B are promising novel chemotherapeutic agentsthat induce cell death through potent stabilization of microtubules. In this study, we investigated the cellular and molecular events underlying the cytotoxicity of these drugs in non-small cell lung carcinoma (NSCLC) cell lines, focusing on apoptotic characteristics. IC80 concentrations of either drug effectively disrupted the microtubule cytoskeleton of H460 cells and induced cell cycle disturbances with early accumulation in the G2-M phase and development of a hypodiploid cell population in both H460 and SW1573 cells. These events were followed by abnormal chromosome segregation during mitosis and subsequent appearance of multinucleated cells. At later time points, the cells displayed several apoptotic features, such as nuclear condensation and fragmentation as well as Annexin V staining, cleavage of poly(ADP-ribose) polymerase and the activation of caspases. To examine the contribution of apoptotic pathways to the cytotoxic effects of these agents, the involvement of the mitochondria and death receptor routes was studied. At 48 h after treatment, both agents disrupted mitochondria of H460 cells, as indicated by cytochrome c release. Nonetheless, H460 cells stably overexpressing antiapoptotic Bcl-2 or Bcl-xL did not show any protective effect from cell death induced by either drug. Possible death receptor dependency was investigated in H460 cells stably overexpressing dominant-negative FADD, which failed to reduce the cytotoxic effects of discodermolide and epothilone B. To study the role of caspases more directly, the effect of stable overexpression of the caspase-8 inhibitor cytokine response modifier A was studied in H460 cells. Furthermore, the effect of the pancaspase inhibitor z-Val-Ala-Asp-fluoromethyl ketone was investigated in a panel of lung carcinoma cell lines. Interestingly, caspase inhibition did not rescue cells from discodermolide or epothilone B-induced cell death. In conclusion, these results demonstrate that despite several apoptotic features detected at relatively late time points after drug exposure, apoptosis is not the dominant mode of cell death and induced low but efficacious concentrations of discodermolide and epothilone B.

Alkanes↗

PubMed2003

Naturally mosaic operons for secondary metabolite biosynthesis: variability and putative horizontal transfer of discrete catalytic domains of the epothilone polyketide synthase locus.

A putative instance of horizontal gene transfer (HGT) involving adjacent, discrete beta-ketoacyl synthase (KS), acyl carrier protein (ACP) and nonribosomal peptide synthase (NRPS) domains of the epothilone Type I polyketide biosynthetic gene cluster from the myxobacterium Sorangium cellulosom was identified using molecular phylogenetics and sequence analyses. The specific KS domain of the module EPO B fails to cluster phylogenetically with other epothilone KS sequences present at this locus, in contrast to what is typically observed in many other Type I polyketide synthase (PKS) biosynthetic loci. Furthermore, the GC content of the epoB KS, epoA ACP and NRPS domains differs significantly from the base composition of other epothilone domain sequences. In addition, the putatively transferred epothilone loci are located near previously identified transposon-like sequences. Lastly, comparison with other KS loci revealed another possible case of horizontal transfer of secondary metabolite genes in the genus Pseudomonas. This study emphasizes the use of several lines of concordant evidence (phylogenetics, base composition, transposon sequences) to infer the evolutionary history of particular gene and enzyme sequences, and the results support the idea that genes coding for adaptive traits, e.g. defensive natural products, may be prone to transposition between divergent prokaryotic taxa and genomes.

Catalytic Domain↗

PubMed2000

Studies on the biosynthesis of epothilones: the biosynthetic origin of the carbon skeleton.

The biosynthetic origin of the epothilone skeleton was studied by the incorporation of 13C and radioactively labeled precursors by Sorangium cellulosum So ce90. The carbon atoms are derived from acetate, propionate, the methyl group of S-adenosyl-methionine, and cysteine which also introduces the sulfur and nitrogen atoms. Epothilone biosynthesis starts with the formation of the thiazole part from acetate and cysteine. The incorporation of acetate or propionate units results in the formation of epothilones A and B, respectively. To introduce the epoxide function of epothilones A and B molecular oxygen is used.

Carbon↗

PubMed2002

[New taxanes and epothilone derivatives in clinical trials].

This review describes the experimental and clinical properties of new taxanes and epothilones. Six new taxanes are currently in clinical trials: BMS 184476, BMS 188797, BMS 275183, IDN 5109/BAY 598862, RPR 109881A et RPR 116258 All these derivatives share the same feature which is a decreased recognition by Pgp-170, the product of the MDR1 gene. This confers innovative properties such as in vitro and in vivo activities on tumors expressing the Pgp-170, activity by the oral route. Identification of other families of molecules bearing the same mechanism of action as taxol has been a goal pursued by many groups. The discovery of epothilones led to the pharmaceutical development of two molecules: EPO 906 (which corresponds to the natural compound epothilone B) and BMS 247550. Phase I clinical trials have established that all these investigational drugs (taxanes and epothilones) can be safely administered in patients, the limiting toxicity being most of the time febrile neutropenia. Many tumor responses have been noted.

Animals↗

PubMed2004

Synthesis of furano-epothilone D.

The total synthesis of furano-epothilone D by a convergent route is reported. The key fragments are available on a large scale to provide sufficient material for biological evaluation. The approach involves a palladium-catalyzed coupling that generates a highly functionalized aldehyde which is connected in a stereoselective aldol reaction to yield the framework of furano-epothilone D. Finally, a macrolactonization provides furano-epothilone D.

Epothilones↗

PubMed2006

A retrospective evaluation of second-line chemotherapy response in hormone-refractory prostate carcinoma: second line taxane-based therapy after first-line epothilone-B analog ixabepilone (BMS-247550) therapy.

BACKGROUND: Epothilones and taxanes interfere with microtubule function. Ixabepilone, which is an epothilone-B analog, has activity against taxane-resistant cell lines and as first-line therapy for men with hormone-refractory prostate carcinoma (HRPC). Clinical cross-resistance of ixabepilone and taxanes in HRPC is unknown. METHODS: Records were evaluated retrospectively from patients with HRPC who were treated on a randomized Phase II trial of ixabepilone with or without estramustine and who subsequently received taxane chemotherapy. Posttherapy declines in prostate-specific antigen (PSA) levels and time to PSA progression were defined by consensus criteria. The median survival was evaluated by using the Kaplan-Meier method. RESULTS: Forty-nine patients who received ixabepilone with estramustine (28 patients) or without estramustine (21 patients) subsequently received second-line taxane therapy. Second-line PSA declines > or = 50% were achieved by 51% of patients (95% confidence interval [95% CI], 33-66%). Second-line PSA declines > or = 50% were achieved by 61% of patients (95% CI, 42-78%) who achieved a first-line PSA decline > or = 50% with ixabepilone, compared with 33% of patients (95% CI, 13-59%) who did not (P = 0.08). Patients who discontinued first-line ixabepilone treatment for disease progression were less likely to achieve a PSA decline > or = 50% in response to second-line, taxane-based therapy compared with patients who discontinued for toxicity or patient preference (36% vs. 71%; P = 0.01). CONCLUSIONS: Second-line taxane chemotherapy after ixabepilone resulted in a substantial frequency of PSA declines. Although patients with ixabepilone-refractory disease were less likely to respond to second-line taxane chemotherapy, 36% did achieve a PSA response. These findings were consistent with incomplete clinical cross-resistance between the taxanes and the epothilones.

Aged↗

PubMed2000

Synthesis and biological evaluation of highly potent analogues of epothilones B and D.

A series of new epothilone B and D analogues incorporating fused hetero-aromatic side chains have been prepared. The synthetic strategy is based on olefin 3 as the common intermediate and allows variation of the side-chain structure in a highly convergent and stereoselective manner. Epothilone analogues 1a-d and 2a-d are more potent inhibitors of cancer cell proliferation than the corresponding parent epothilones B or D.

Antineoplastic Agents↗

PubMed1998

Oxidative and reductive transformations of epothilone A.

The C7 hydroxy group of cytotoxic epothilone A was selectively oxidized using PDC. A selective oxidation of the C3 hydroxy group was accomplished with Me2S/(PhCO2)2 after in situ protection of C7-OH. Reduction of epothilone A or of a C5, C7 dioxo derivative with NaBH4 proceeded at the C5 carbonyl group. Oxidation and hydrogenation of the C16-C17 double bond proved to be difficult but it was easily cleaved with ozone and the resulting keto derivative was transformed to epothilone analogs with different side chains.

Antineoplastic Agents↗

PubMed1998

Derivatization of the C12-C13 functional groups of epothilones A, B and C.

Epothilone A reacted with hydrohalic acids to C12-C13 halohydrin regioisomers (ratios: 2:1-4:1), whereas epothilone B gave under the same conditions the isomerically pure C12 halo C13 hydroxy derivative. With non-nucleophilic Brønstedt acids and with Lewis acids a highly solvent dependent product distribution and some unexpected rearrangement products were observed. Epothilone C bearing a double bond between C12 and C13 was regioselectively dihydroxylated or hydrogenated at that position.

Antineoplastic Agents↗

PubMed1999

Total synthesis of epothilone E and related side-chain modified analogues via a Stille coupling based strategy.

A Stille coupling strategy has been utilized to complete a total synthesis of epothilone E from vinyl iodide 7 and thiazole-stannane 8h. The central core fragment 7 and its trans-isomer 11 were prepared from triene 15 using ring-closing metathesis (RCM), and were subsequently coupled to a variety of alternative stannanes to provide a library of epothilone analogues 18a-o and 19a-o. The Stille coupling approach was then used to prepare epothilone B analogues from the key macrolactone intermediate 24 which was itself synthesized by a macrolactonization based strategy.

Chromatography, Thin Layer↗

PubMed2000

Synthesis, structure proof, and biological activity of epothilone cyclopropanes.

[structure--see text] A semisynthetic route to epothilone cyclopropanes from epothilones A and B is described. Of significance, the deoxygenation of the 12, 13-epoxide to give the corresponding olefin was achieved with high efficiency. The title compounds (8, 9) were active in both tubulin polymerization and cytotoxicity assays, which is in direct contrast to a previously published report. These results provide further evidence that the role of the 12,13-epoxide of epothilones is largely conformational and argue against some of the current pharmacophore models.

Antineoplastic Agents↗

PubMed2002

SAR and pH stability of cyano-substituted epothilones.

[formula: see text] 3-Cyano epothilones 15-18 are the only examples of non-hydroxy C-3-substituted analogues. Their tubulin binding affinity and cytotoxicity provide meaningful structure-activity relationship information on the dependence of C-1/C-3 conformation upon activity. 12-Cyano epothilone 24 has improved pH stability over epothilone B, and its activity further supports the hypothesis that C-12 stereochemistry is not critical for tubulin affinity.

Antineoplastic Agents↗

PubMed1998

Desoxyepothilone B: an efficacious microtubule-targeted antitumor agent with a promising in vivo profile relative to epothilone B.

A new class of 16-membered macrolides, the epothilones (Epos), has been synthesized and evaluated for antitumor potential in vitro and in vivo. Recent studies in these and other laboratories showed that epothilones and paclitaxel (paclitaxel) share similar mechanisms of action in stabilizing microtubule arrays as indicated by binding-displacement studies, substitution for paclitaxel in paclitaxel-dependent cell growth, and electron microscopic examinations. The present study examined cell growth-inhibitory effects in two rodent and three human tumor cell lines and their drug-resistant sublines. Although paclitaxel showed as much as 1, 970-fold cross-resistance to the sublines resistant to paclitaxel, adriamycin, vinblastine, or actinomycin D, most epothilones exhibit little or no cross-resistance. In multidrug-resistant CCRF-CEM/VBL100 cells, IC50 values for EpoA (1), EpoB (2), desoxyEpoA (3) (dEpoA), desoxyEpoB (4) (dEpoB), and paclitaxel were 0.02, 0.002, 0.012, 0.017, and 4.14 microM, respectively. In vivo studies, using i.p. administration, indicated that the parent, EpoB, was highly toxic to mice and showed little therapeutic effect when compared with a lead compound, dEpoB. More significantly, dEpoB (25-40 mg/kg, Q2Dx5, i.p.) showed far superior therapeutic effects and lower toxicity than paclitaxel, doxorubicin, camptothecin, or vinblastine (at maximal tolerated doses) in parallel experiments. For mammary adenocarcinoma xenografts resistant to adriamycin, MCF-7/Adr, superior therapeutic effects were obtained with dEpoB compared with paclitaxel when i.p. regimens were used. For ovarian adenocarcinoma xenografts, SK-OV-3, dEpoB (i.p.), and paclitaxel (i. v.) gave similar therapeutic effects. In nude mice bearing a human mammary carcinoma xenograft (MX-1), marked tumor regression and cures were obtained with dEpoB.

Animals↗

PubMed2005

In vivo evaluation of ixabepilone (BMS247550), a novel epothilone B derivative, against pediatric cancer models.

PURPOSE: Vinca alkaloids, agents that cause depolymerization of microtubules, are highly active in treatment of many pediatric cancers. In contrast, taxanes, agents that stabilize microtubules, are far less effective against the same cancer types. The purpose of the current study was to evaluate the antitumor activity of ixabepilone, an epothilone B derivative representing a new class of microtubule-stabilizing antimitotic agent in a wide variety of pediatric solid tumor models. EXPERIMENTAL DESIGN: Ixabepilone was administered i.v. every 4 days for three doses to scid mice bearing s.c. human rhabdomyosarcoma (three lines), neuroblastoma (four), Wilms' tumors (six), osteosarcoma (four), or brain tumors (seven). Tumor diameters were measured weekly, and tumor growth or regressions were determined. Pharmacokinetic studies were done following a single administration of drug at the maximum tolerated dose (MTD) level (10 mg/kg). RESULTS: At the MTD (10 mg/kg), ixabepilone induced objective responses (all tumors in a group achieved > or = 50% volume regression) in three of three rhabdomyosarcoma lines, three of five neuroblastomas, six of seven Wilms' tumor models, two of six osteosarcoma, and four of eight brain tumor models. However, the dose-response curve was steep with only 2 of 19 tumors models regressing (> or = 50%) at 4.4 mg/kg. In comparison, paclitaxel administered at the MTD on the same schedule failed to induce objective regressions of three tumor lines that were highly sensitive to treatment with ixabepilone. Pharmacokinetics following single i.v. administration of ixabepilone at its MTD (10 mg/kg) were biexponential with C(max) of 12.5 micromol/L, elimination half-life of 19.2 hours, and total area under the curve of 5.8 micromol/L-h. The achieved drug exposure of ixabepilone at this efficacious MTD dose level in mice is similar to those achieved in patients given the recommended phase II dose of 40 mg/m2 by either 1- or 3-hour infusion every 3 weeks, a regimen that has shown significant anticancer activity in phase II clinical trials in adult patients. CONCLUSIONS: Administered at doses ranging from 66% to 100% of its MTD in mice, the epothilone B derivative ixabepilone shows broad spectrum activity against a panel of pediatric tumor xenograft models. Pharmacokinetic analysis indicates that the systemic ixabepilone exposure achieved in mice at its MTD is similar to that achieved in patients at the recommended phase II dose of 40 mg/m2 administered every 3 weeks. Importantly, the present results showed a clear distinction in sensitivity of pediatric solid tumors to this epothilone derivative compared with paclitaxel.

Animals↗