Utidelone plus capecitabine versus capecitabine alone for heavily pretreated metastatic breast cancer refractory to anthracyclines and taxanes: a multicentre, open-label, superiority, phase 3, randomised controlled trial.

BACKGROUND: Utidelone, a genetically engineered epothilone analogue, has shown promise as a potential treatment for breast cancer in phase 1 and 2 trials. The aim of this phase 3 trial was to compare the efficacy and safety of utidelone plus capecitabine versus capecitabine alone in patients with metastatic breast cancer. METHODS: We did a multicentre, open-label, superiority, phase 3, randomised controlled trial in 26 hospitals in China. Eligible participants were female patients with metastatic breast cancer refractory to anthracycline and taxane chemotherapy regimens. We randomly assigned participants (2:1) using computer based randomisation and block sizes of 6 to a 21-day cycle of either utidelone (30 mg/m2 intravenously once per day on days 1-5) plus capecitabine (1000 mg/m2 orally twice per day on days 1-14), or capecitabine alone (1250 mg/m2 orally twice per day on days 1-14), until disease progression or unacceptable toxicity occurred. Patients, physicians, and assessors were not masked to treatment allocation; however, an independent radiology review committee used to additionally assess response was masked to allocation. The primary endpoint was centrally assessed (by an independent radiology review committee) progression-free survival, and analysed using the Kaplan-Meier product-limit method in the intention-to-treat population. Safety was assessed in all participants who received at least one dose of study drug. Follow-up is ongoing. This study is registered at ClinicalTrials.gov, number NCT02253459. FINDINGS: Between Aug 8, 2014, and Dec 14, 2015, we enrolled and randomly assigned 270 patients to treatment with utidelone plus capecitabine, and 135 to capecitabine alone. Median follow-up for progression-free survival was 6·77 months (IQR 3·81-10·32) for the utidelone plus capecitabine group and 4·55 months (2·55-9·39) for the capecitabine alone group. Median progression-free survival by central review in the utidelone plus capecitabine group was 8·44 months (95% CI 7·95-9·92) compared with 4·27 months (3·22-5·68) in the capecitabine alone group; hazard ratio 0·46, 95% CI 0·36-0·59; p<0·0001. Peripheral neuropathy was the most common grade 3 adverse event in the utidelone plus capecitabine group (58 [22%] of 267 patients vs 1 [<1%] of 130 patients in the capecitabine alone group). Palmar-plantar erythrodysaesthesia was the most prominent grade 3 adverse event in the capacitabine alone group (in 10 [8%] of 130 patients) and was the next most frequent grade 3 event in the utidelone plus capecitabine group (in 18 [7%] of 267 patients). 16 serious adverse events were reported in the combination therapy group (diarrhoea was the most common, in three [1%] patients) and 14 serious adverse events were reported in the monotherapy group (the most common were diarrhoea, increased blood bilirubin, and anaemia, in two [2%] patients for each event). 155 patients died (99 in the combination therapy arm, 56 in the monotherapy arm). All deaths were related to disease progression except for one in each group (attributed to pericardial effusion in the combination therapy group and dyspnoea in the monotherapy group) that were considered possibly or probably treatment-related. INTERPRETATION: Despite disease progression with previous chemotherapies, utidelone plus capecitabine was more efficacious compared with capecitabine alone for the outcome of progression-free survival, with mild toxicity except for peripheral sensory neuropathy, which was manageable. The findings from this study support the use of utidelone plus capecitabine as an effective option for patients with metastatic breast cancer. FUNDING: Beijing Biostar Technologies, Beijing, China.

Phase II trial of utidelone as monotherapy or in combination with capecitabine in heavily pretreated metastatic breast cancer patients.

BACKGROUND: The treatment of metastatic breast cancer (MBC) remains a great clinical challenge as drug resistance frequently develops. Alternative agents that can overcome drug resistance would offer new therapeutic options. The primary aim of this phase II study was to evaluate the efficacy and safety of utidelone as a monotherapy or in combination with capecitabine in metastatic breast cancer patients previously treated with and resistant to anthracyclines and taxanes. METHODS: In two open-label, noncomparative clinical studies, patients with metastatic breast cancer who previously received anthracycline- and/or taxane-containing regimens were given (1) 25 to 35 mg/m(2)/day intravenously infused utidelone, once daily for 5 days, in combination with 14 days of 2000 mg/m(2) capecitabine, divided in two equal daily oral doses or (2) 40 mg/m(2)/day intravenously infused utidelone, once daily for 5 days. These regimens were administered per each 21-day treatment cycle, and the maximum of treatment cycles allowed per protocol is 6. Objective response rate (ORR), progression-free survival (PFS), and tolerability were evaluated. RESULTS: In the combination study, 33 patients completed a median of 6 cycles of therapy, which was the highest cycles a trial patient could receive under the criteria of the study protocol. Efficacy was evaluated (n = 32) with an ORR of 42.4 % (FAS, 95 % CI, 26.6, 60.9) and a median PFS of 7.9 (FAS, 95 % CI, 6.1, 9.8) months. The monotherapy study (n = 63) resulted in an ORR of 28.57 % (FAS, 95 % CI, 18.4, 40.6) and a median PFS of 5.4 (FAS, 95 % CI, 2.9, 9.8) months. In both studies, common toxicities associated with utidelone administration included peripheral neuropathy, fatigue, myalgia, and arthralgia, but the toxicities were limited and manageable. Notably, very mild myelosuppression, low liver and renal toxicities, and very limited gastrointestinal toxic effect were observed, in contrast to other agents in the same class. CONCLUSIONS: Utidelone showed promising efficacy, tolerability, and advantageous safety profiles in the treatment of patients with advanced anthracycline/taxane-refractory metastatic breast cancer and may offer new treatment options to overcome drug resistance. TRIAL REGISTRATION: CHiCTR-TRC-13004205 , registered on August 15, 2013.

Concentration-dependent differential effects of an epothilone analog on cell cycle and p53 signaling.

The tumor-suppressor protein p53 is considered to be one of the most important transport hubs of cell signal transduction, playing critical roles in the control of cell cycle arrest, apoptosis and many other processes as a nuclear transcription factor. p53 also acts in the cytoplasm to trigger apoptosis. Paclitaxel and other microtubule inhibitors can inhibit the growth of different types of cancer cells and induce apoptosis which is believed to be p53-independent. In the present study, we demonstrated that UTD1, a genetically engineered epothilone analog and a new microtubule inhibitor, activated p53 as a transcription factor at low concentrations demonstrated by its enhanced transcriptional activity and accumulation of p21, which led to cell cycle arrest. However, at high concentrations of UTD1, p53 was accumulated in the cytoplasm which contributed to induction of apoptosis. These observations indicate that the epothilone analog has differential effects on intracellular signaling and implies that p53 plays different roles in cells exposed to different concentrations of the anticancer agent.

Construction of the co-expression plasmids of fostriecin polyketide synthases and heterologous expression in Streptomyces.

CONTEXT: Polyketides are bioactive natural products with diverse bioactivities, and heterologous production of polyketides in easily engineered microbial hosts is preferred for the production of structurally diverse and the therapeutically active polyketides. OBJECTIVE: In this study, heterologous expression of the biosynthetic genes encoding type I polyketide synthases (PKS) involved in biosynthesis of fostriecin, a unique phosphate monoester polyketide antibiotic, was attempted. MATERIALS AND METHODS: Fostriecin PKS (Fos-PKS) biosynthetic gene cluster in a total of 48.4 kb were cloned downstream of the act I promoter in two compatible Streptomyces vectors using Red/ET recombination. The co-expression plasmids were sequentially transferred into Streptomyces lividans and Streptomyces coelicolor. Active transcription of the polyketide genes was confirmed by reverse transcription PCR (RT-PCR) analysis, and the metabolites were detected using high-performance liquid chromatography (HPLC). RESULTS: The recombinant strains S. lividans TK24/p6-fosAB-p4-fosCDEF and S. coelicolor M512/p6-fosAB-p4-fosCDEF were obtained for heterologous expression in Streptomyces. Pigmentation was observed in the recombinant strains, whereas the control strain with empty vector displayed no change in pigment production. Active transcription of the polyketide genes was confirmed by RT-PCR analysis and subsequent sequencing. CONCLUSION: The present study is the first attempt to overexpress Fos-PKS biosynthetic gene cluster in Streptomyces. More studies on heterologous expression of the fostriecin biosynthetic gene cluster would be beneficial for further understanding the mechanisms of its structural as well as the potential pharmaceutically effect.

Seamless stitching of biosynthetic gene cluster containing type I polyketide synthases using Red/ET mediated recombination for construction of stably co-existing plasmids.

Type I polyketides are natural products with diverse functions that are important for medical and agricultural applications. Manipulation of large biosynthetic gene clusters containing type I polyketide synthases (PKS) for heterologous expression is difficult due to the existence of conservative sequences of PKS in multiple modules. Red/ET mediated recombination has permitted rapid manipulation of large fragments; however, it requires insertion of antibiotic selection marker in the cassette, raising the problem of interference of expression by leaving "scar" sequence. Here, we report a method for precise seamless stitching of large polyketide biosynthetic gene cluster using a 48.4kb fragment containing type I PKS involved in fostriecin biosynthesis as an example. rpsL counter-selection was used to assist seamless stitching of large fragments, where we have overcome both the size limitations and the restriction on endonuclease sites during the Red/ET recombination. The compatibility and stability of the co-existing vectors (p184 and pMT) which respectively accommodate 16kb and 32.4kb inserted fragments were demonstrated. The procedure described here is efficient for manipulation of large DNA fragments for heterologous expression.

Multiple Effects of a Novel Epothilone Analog on Cellular Processes and Signaling Pathways Regulated by Rac1 GTPase in the Human Breast Cancer Cells.

The epothilones are a class of microtubule inhibitors that exhibit a strong antitumor activity. UTD2 is a novel epothilone analog generated by genetic manipulation of the polyketide biosynthetic gene cluster. This study investigated the effects of UTD2 on the actin cytoskeleton and its critical regulators, and the signaling pathways which are essential for cell motility, growth and survival in MCF-7 breast cancer cells. Results showed that UTD2 inhibited the cellular functions of actin cytoskeleton, such as wound-closure, migration and invasion, as well as adhesion. Our study further demonstrated that UTD2 suppressed Rac1 GTPase activation and reduced the activity of PAK1, which is a downstream effector of Rac1, while the activity of Cdc42 was not affected. Additionally, the phosphorylation of p38 and ERK were significantly inhibited, but the phosphorylation of JNK remained the same after UTD2 treatment. Moreover, UTD2 inhibited the activity and mRNA expression of MMP-2, which plays a key role in cell motility. UTD2 also reduced the phosphorylation of Akt, which is an important signaling kinase regulating the cell survival through Rac1. Furthermore, UTD2 interrupted the synergy between Rac1 and Raf in focus formation assays. Taken together, these results indicated that UTD2 exerted multiple effects on the actin cytoskeleton and signaling pathways associated with Rac1. This study provided novel insights into the molecular mechanism of the antineoplastic and antimetastatic activities of epothilones. Our findings also suggest that the signaling pathways regulated by Rac1 may be evaluated as biomarkers for the response to therapy in clinical trials of epothilones.

Identification of the post-polyketide synthase modification enzymes for fostriecin biosynthesis in Streptomyces pulveraceus.

Fostriecin (FST, 1) is a natural product with promising antitumor activity produced by Streptomyces pulveraceus. Its antitumor activity is associated with the selective inhibition of protein phosphatase activities. The biosynthetic gene cluster for FST has recently been cloned and sequenced. To better understand the post-polyketide synthase (PKS) modification steps in the biosynthetic pathway of FST, we constructed and characterized three post-PKS modification gene mutants of fosG, fosK, and fosM by knockout inactivation in S. pulveraceus. As a result, we determined that a fosK-encoded cytochrome P450 monooxygenase is responsible for C-18 hydroxylation, formation of an unsaturated lactone is dependent upon FosM, and the fosG gene product is involved in hydroxylation at C-4 after the action of FosM to yield PD 113,271 from FST. The accumulated analogues from the ΔfosK and ΔfosM mutant strains possessed a malonyl ester moiety that suggested that all the post-PKS modification steps in FST biosynthesis occur with the polyketide chain bearing a malonyl ester at the C-3 position, with formation of the unsaturated six-membered lactone as the last step in FST biosynthesis.

Elucidation of the biosynthetic gene cluster and the post-PKS modification mechanism for fostriecin in Streptomyces pulveraceus.

Fostriecin is a unique phosphate monoester antibiotic that was isolated from Streptomyces pulveraceus as a protein phosphatase 2A (PP2A) and PP4A selective inhibitor. However, its biosynthetic mechanism remains to be elucidated. In this study, a 73 kb gene cluster encoding a six modular Type I polyketide synthases (PKS) and seven tailoring enzymes was identified by cosmid sequencing from the producer. The functions of two tailoring enzymes were characterized by gene disruption and an in vitro enzyme activity assay. Remarkably, the isolation of three malonylated fostriecin analogs from post-PKS gene knockout mutants indicated malonylated-polyketide formation could be a normal biosynthetic process in the formation of the unsaturated six-membered lactone in fostriecin. Based on this study, a comprehensive post-PKS modification mechanism for fostriecin biosynthesis was proposed.

Tautomycetin induces apoptosis by inactivating Akt through a PP1-independent signaling pathway in human breast cancer cells.

Tautomycetin (TMC), originally isolated from Streptomyces griseochromogenes, has been suggested as a potential drug retaining specificity toward colorectal cancer. However, we found that TMC exhibited inhibitory effects on cell proliferation of many cancer cell lines including adriamycin-resistant human breast adenocarcinoma. We investigated its anti-tumor activity and mechanisms in human breast cancer cells for the first time. In this study, we showed that TMC effectively inhibited breast cancer cell proliferation, migration, and invasion. TMC also induced apoptosis in MCF-7 cells. This apoptotic response was in part mediated by Bcl-2 cleavage, leading to the release of cytochrome c, which facilitates binding of Apaf-1 to caspase-9 in its presence and subsequent activation of caspase-7 in apoptosis induction signaling pathways. Furthermore, we identified that TMC induced apoptosis by suppressing Akt signaling pathway activation, which is independent of protein phosphatase PP1 inhibition. The levels of downstream targets of Akt, including phospho-forkhead transcription factor and Bad, were also reduced after TMC treatment. Overall, our results indicate that TMC could be used as a potential drug candidate for breast cancer therapy. More importantly, our study provides new mechanisms for the anticancer effects of TMC.

Functional characterization of the genes tauO, tauK, and tauI in the biosynthesis of tautomycetin.

Tautomycetin is a specific protein phosphatase I inhibitor. In an effort to elucidate the biosynthetic mechanism of tautomycetin, we inactivated genes of the tautomycetin biosynthetic gene cluster, tauI, tauO, and tauK, which encode for putative P450 oxidase, citryl-CoA lyase, and esterase enzymes, respectively. The mutant STQ0606 (ΔtauO) did not produce any detectable amount of tautomycetin intermediates but could convert dialkylmaleic anhydride to tautomycetin, strongly indicating that TauO was involved in dialkylmaleic anhydride biosynthesis. STQ1211 (ΔtauK) accumulated dialkylmaleic anhydride, whereas the cofermentation of STQ1211 (ΔtauK) and STQ0606 (ΔtauO) restored the production of tautomycetin. Together, these results suggest that TauK was responsible for the conjugation of dialkylmaleic anhydride and the polyketide moiety in tautomycetin biosynthesis. The disruption of tauI resulted in the accumulation of 5-des-keto-tautomycetin, revealing that TauI was responsible for the oxidation at C5 as the last step. Although the shunt pathways were involved in the biosynthesis of tautomycetin, the main post-polyketide synthase tailoring steps were dehydration, decarboxylation and oxidation, taking place consecutively. This study allowed us to predict the biosynthesis of tautomycetin more accurately and provided novel insights into the mechanism of the biosynthesis of tautomycetin.

Differential effects of tautomycetin and its derivatives on protein phosphatase inhibition, immunosuppressive function and antitumor activity.

In the present work, we studied the structure-activity relationship (SAR) of tautomycetin (TMC) and its derivatives. Further, we demonstrated the correlation between the immunosuppressive fuction, anticancer activity and protein phosphatase type 1 (PP1) inhibition of TMC and its derivatives. We have prepared some TMC derivatives via combinatorial biosynthesis, isolation from fermentation broth or chemical degradation of TMC. We found that the immunosuppressive activity was correlated with anticancer activity for TMC and its analog compounds, indicating that TMC may home at the same targets for its immunosuppressive and anticancer activities. Interestingly, TMC-F1, TMC-D1 and TMC-D2 all retained significant, albeit reduced PP1 inhibitory activity compared to TMC. However, only TMC-D2 showed immunosuppressive and anticancer activities in studies carried out in cell lines. Moreover, TMC-Chain did not show any significant inhibitory activity towards PP1 but showed strong growth inhibitory effect. This observation implicates that the maleic anhydride moiety of TMC is critical for its phosphatase inhibitory activity whereas the C1-C18 moiety of TMC is essential for the inhibition of tumor cell proliferation. Furthermore, we measured in vivo phosphatase activities of PP1 in MCF-7 cell extracts treated with TMC and its related compounds, and the results indicate that the cytotoxicity of TMC doesn't correlate with its in vivo PP1 inhibition activity. Taken together, our study suggests that the immunosuppressive and anticancer activities of TMC are not due to the inhibition of PP1. Our results provide a novel insight for the elucidation of the underlying molecular mechanisms of TMC's important biological functions.

Phase I clinical and pharmacokinetic study of UTD1, a genetically engineered epothilone analog in patients with advanced solid tumors.

PURPOSE: The epothilones are a novel class of microtubule-stabilizing agents. UTD1 is an epothilone analog generated by genetic manipulation of the polyketide biosynthetic gene cluster. This phase I study was designed to evaluate the safety and pharmacokinetic(PK) profiles of UTD1 in patients with advanced solid tumors. PATIENTS AND METHODS: This was an open-label, single-arm, one site, phase I, dose-escalation study. Patients were treated with escalating doses of UTD1 as a 3-h intravenous infusion every 3 weeks. RESULTS: Twenty-one patients were enrolled and received UTD1 at six dose levels ranging from 25 to 225 mg/m(2). Dose-limiting toxicity (DLT) was ataxia, and other frequent non-haematological toxicities were peripheral neuropathy, gastrointestinal disorders, fatigue, and myalgia/arthralgia. Myelosuppression was rare, with no grade 3 and 4 neutropenia, in contrast to paclitaxel and ixabepilone. The maximum-tolerated dose was established as 170 mg/m(2). Preliminary results showed linear pharmacokinetics along the range of doses tested. Prolonged disease stabilization was observed in patients with breast cancer, non-small lung cancer, and other cancers. CONCLUSIONS: The recommended phase II dose of UTD1 is 170 mg/m(2) as a 3-h infusion every 3 weeks. Ataxia was the DLT. UTD1 showed advantages over paclitaxel and Ixapebilone in relation to safety profile, especially myelosuppression. The acceptable tolerability warrants further phase II study.

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.

A new cytotoxic epothilone from modified polyketide synthases heterologously expressed in Myxococcus xanthus.

A new epothilone, 10,11-didehydroepothilone D (5), was isolated from a strain of the heterologous host Myxococcus xanthus genetically engineered to produce epothilone D (4). The structure of 5 was determined from NMR and MS data. The epothilone polyketide synthase was further modified in a recombinant M. xanthus strain to produce 5 as the major epothilone-related metabolite. The cytotoxicity of 5 against a panel of tumor cell lines, including several with multidrug resistance, and its effect on tubulin polymerization were comparable to epothilone D (4).