Analog Docetaxel Research Articles

Preparation and evaluation of paclitaxel-imprinted polymers with a rosin-based crosslinker as the stationary phase in high-performance liquid chromatography

In this study, molecularly imprinted polymer (MIP) microspheres for paclitaxel (PTX) were prepared by microsuspension polymerization and used as a stationary phase in high-performance liquid chromatography (HPLC) for the separation of PTX and its structural analog docetaxel (DOC). For MIP synthesis, ethylene glycol maleic rosinate acrylate and 2-vinylpyridine were used as the cross-linker and functional monomer, respectively. MIP microspheres were characterized by scanning electron microscopy, laser granulometry, nitrogen sorption porosimetry, and thermogravimetric analysis. Results indicated the formation of regular MIPs with an even pore size distribution; furthermore, these MIPs exhibited excellent thermal stability. These MIP microspheres were packed into a stainless steel column for the selective separation of PTX and DOC. Under optimum chromatographic conditions, a separation factor of 2.54 and an imprinting factor of 2.37 were obtained. In addition, thermodynamic data obtained from van’t Hoff plots revealed enthalpy-driven separation and higher contribution from functional group interactions as compared with that from steric complementary interactions. Microcalorimetry was employed to investigate the binding mechanisms of the analytes on the MIP surface.

Novel therapeutic potential in targeting microtubules by nanoparticle albumin-bound paclitaxel in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) shows low response to most conventional chemotherapies. To facilitate target identification for novel therapeutic development, we deployed gene expression profiling on 43 paired HCC tumors and adjacent non-tumoral liver, which is also considered as the pre-malignant liver lesion. In conjunction with ontology analysis, a major functional process found to play a role in the malignant transformation of HCC was microtubule-related cellular assembly. We further examined the potential use of microtubule targeting taxane drugs, including paclitaxel and docetaxel, and compared with findings to results from doxorubicin, a common chemotherapeutic agent used in HCC. Recent studies showed that drug delivery by nanoparticles have enhanced efficacy with reduced side effects. In this regard, the nanoparticle albumin-bound (nab)-paclitaxel was also examined. In a panel of HCC cell lines studied, a high sensitivity towards taxane drugs was generally found, although the effect from nab-paclitaxel was most profound. The nab-paclitaxel showed an effective IC50 dose at 15-fold lower than paclitaxel alone or the derivative analogue docetaxel, and ~450-fold less compared to doxorubicin. Flow cytometric analysis confirmed a cell cycle blockade at the G2/M phase and increased apoptosis following nab-paclitaxel treatment. In vivo animal studies also showed that nab-paclitaxel readily inhibited xenograft growth with less toxicity to host cells compared to other anti-microtubule drugs and doxorubicin. Gene silencing of the microtubule regulatory gene STMN1 by RNAi suggested a distinct synergistic effect in the combined treatment with nab-paclitaxel. Our findings in this study highly suggest that the microtubule assembly represents a promising therapeutic target development in HCC.

Targeting Apoptosis Pathway with Natural Terpenoids: Implications for Treatment of Breast and Prostate Cancer

Terpenoids represent a large and diverse class of naturally occurring compounds found in a variety of fruits, vegetables and medicinal plants. Structurally some of the terpenoids are similar to human hormones. A diet rich in terpenoids is inversely related with the risk of chronic diseases including cancers. Breast and prostate cancers are hormone-related diseases and the second leading cause of female and male cancer mortality. Diterpenoid paclitaxel, and its semi-synthetic analogue docetaxel, have entered clinical use against established breast and prostate cancers. Here we reviewed potential molecular targets and biological properties of natural terpenoids, including monoterpenoids, diterpenoids, triterpenoids and tetraterpenoids, and their applications in treatment of human breast and prostate cancers. These terpenoids are able to inhibit tumor cell proliferation and induce tumor cell death by inhibiting multiple cancer-specific targets including the proteasome, NF-kappaB, and antiapoptotic protein Bcl-2. The efficacy of these terpenoids against breast or prostate cancer cells, as demonstrated in pre-clinical studies support clinical application of these naturally occurring terpenoids in treatment of hormone-related human cancers.

Abstract 4423: Novel therapeutic potential in targeting the microtubules by nanoparticle albumin-bound paclitaxel in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) shows low responses to most conventional chemotherapies. To facilitate target identifications for novel therapeutic developments, we deployed gene expression profiling on 43 paired HCC tumors and adjacent non-tumoral liver. Coupled with ontology analysis, the major functional process suggested in the malignant transformation of HCC was microtubule-related cellular assembly. We further examined the potential use of microtubule targeting Taxane drugs, including Paclitaxel and Docetaxel, and compared findings to the results obtained from Doxorubicin, a common chemotherapeutic agent used in the treatment of a number of neoplasms. Recent studies showed that drug delivery by nanoparticles have enhanced efficacy with reduced side effects. In this regard, the nanoparticle albumin-bound (nab)-Paclitaxel was also examined. In a panel of HCC cell lines studied, a high sensitivity towards Taxane drugs was generally found, although the effect from nab-Paclitaxel was most profound. The nab-Paclitaxel showed an effective IC50 dose at 15-fold lower than Paclitaxel alone or the derivative analogue Docetaxel, and approx.450-fold less compared to Doxorubicin. Flow cytometric analysis confirmed a cell cycle blockade at the G2/M phase and increased apoptosis following treatment with nab-Paclitaxel. In-vivo animal study also showed that nab-Paclitaxel readily inhibited xenograft growth with less toxicity compared to other anti-microtubule drugs and Doxorubicin. Silencing of a major microtubule regulatory gene STMN1 suggested a distinct synergistic effect in the combined treatment with nab-Paclitaxel. Our findings in this study would suggest the microtubule organizations to represent a promising target for treatment developments in HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4423.

Inhibition of the Androgen Receptor as a Novel Mechanism of Taxol Chemotherapy in Prostate Cancer

Taxol chemotherapy is one of the few therapeutic options for men with castration-resistant prostate cancer (CRPC). However, the working mechanisms for Taxol are not fully understood. Here, we showed that treatment of 22Rv1, a PTEN-positive CRPC cell line, with paclitaxel and its semisynthetic analogue docetaxel decreases expression of the androgen receptor (AR)-activated genes prostate-specific antigen (PSA) and Nkx3.1 but increases expression of the AR repression gene maspin, suggesting that Taxol treatment inhibits AR activity. This was further supported by the observation that the activity of AR luciferase reporter genes was inhibited by paclitaxel. In contrast, paclitaxel treatment failed to inhibit AR activity in the PTEN-null CRPC cell line C4-2. However, pretreatment of C4-2 cells with the phosphoinositide 3-kinase inhibitor LY294002 restored paclitaxel inhibition of the AR. Treatment of 22Rv1 xenografts in mice with docetaxel induced mitotic arrest and a decrease in PSA expression in tumor cells adjacent to vascular vessels. We further showed that paclitaxel induces nuclear accumulation of FOXO1, a known AR suppressive nuclear factor, and increases the association of FOXO1 with AR proteins in the nucleus. FOXO1 knockdown with small interfering RNA attenuated the inhibitory effect of paclitaxel on AR transcriptional activity, expression of PSA and Nkx3.1, and cell survival. These data reveal a previously uncharacterized, FOXO1-mediated, AR-inhibitory effect of Taxol in CRPC cells that may play an important role in Taxol-mediated inhibition of CRPC growth.

Differences in Paclitaxel and Docetaxel Interactions with Tubulin Detected by Mutagenesis of Yeast Tubulin

Differences in Paclitaxel and Docetaxel Interactions with Tubulin Detected by Mutagenesis of Yeast Tubulin

Bcl-2 Expression as a Predictive Marker of Hormone-Refractory Prostate Cancer Treated with Taxane-Based Chemotherapy

Bcl-2 inhibits apoptosis, and its overexpression is associated with hormone refractory prostate cancer (HRPC). Bak and Bax are in the Bcl-2 family and counteract the antiapoptotic function of Bcl-2. Taxane-induced (paclitaxel and its analogue docetaxel) phosphorylation of Bcl-2 abolishes the potential antiapoptotic effect of Bcl-2. We hypothesized that (a) survival benefit in HRPC patients treated with taxanes is determined by the presence of Bcl-2 protein and (b) altered expression of Bak and Bax protein caused by genetic mutation is associated with biological aggressiveness of prostate cancer. Forty localized prostate cancer and 30 HRPC cases were used in this study. Surgical specimens of localized prostate cancer and biopsy specimens of HRPC were used for immunostaining of Bcl-2, Bak, and Bax as well as DNA extraction. Mutations in the Bak and Bax genes were screened by single-strand conformational polymorphism, and confirmed by direct DNA sequencing. Bcl-2-positive HRPC showed longer cause-specific survival in comparison with the counterparts. Multivariate analysis revealed that the level of Bcl-2 expression before treatment with taxane-based chemotherapy was an independent predictor for cause-specific survival (P < 0.01) and baseline prostate-specific antigen level was an independent predictor for progression-free survival (P < 0.01). Bax gene mutation was found in only one HRPC specimen. Bcl-2 expression in addition to prostate-specific antigen measurement before treatment could identify HRPC patients who may benefit from taxane-based chemotherapy. Mutation of the Bak and Bax genes is a rare event in prostate cancer.

Docetaxel

The taxoid analogue docetaxel is a potent inhibitor of microtubular depolymerisation and, in hormone-refractory metastatic prostate cancer, it also counters the effects of the anti-apoptotic protein Bcl-2. Overall survival was significantly increased in patients with hormone-refractory metastatic prostate cancer receiving intravenous docetaxel every 3 weeks plus oral prednisone or estramustine, compared with patients receiving intravenous mitoxantrone every 3 weeks plus prednisone in two large phase III trials (TAX 327 and SWOG [Southwest Oncology Group] 9916). In the TAX 327 study, patients receiving docetaxel 75 mg/m(2) every 3 weeks plus prednisone had a median overall survival duration of 18.9 months; in the SWOG 9916 study, median overall survival duration was 17.5 months with docetaxel 60 mg/m(2) every 3 weeks plus estramustine 280 mg three times daily on days 1-5. The median overall survival duration for the control arm of mitoxantrone 12 mg/m(2) every 3 weeks plus prednisone was 16-17 months. Compared with mitoxantrone plus prednisone, docetaxel plus prednisone improved prostate specific antigen response rate, pain and health-related quality of life, and docetaxel plus estramustine increased progression-free survival. Adverse events were more common with docetaxel- than mitoxantrone-based treatment regimens, but most events associated with docetaxel were mild-to-moderate in severity.

Evading Search and Destroy

PHARMACOLOGY Anticancer agents such as taxol often encounter two barriers to their effectiveness: metabolism by the cytochrome P450 family of enzymes (CYPs) and clearance from cells by the P-glycoprotein efflux pump (MDR1). Synold et al. demonstrate that taxol elicits both mechanisms in human hepatocytes and intestinal epithelial cells by activating the steroid and xenobiotic nuclear receptor (SXR), which detects a broad spectrum of drugs. Taxol reversed SXR interaction with nuclear corepressors, thereby allowing the expression of genes such as CYPs and MDR1 . The inability of the taxol analog docetaxel to displace SXR corepressors may explain why it is a relatively effective antineoplastic agent, and the development of more “SXR-transparent” compounds such as docetaxel could improve the retention and duration of anticancer drugs. — LDC Nature Med. 7 , 584 (2001).

Cell cycle status and apoptosis of hematopoietic progenitor cells released into the peripheral blood after taxanes and granulocyte colony-stimulating factor in breast cancer patients.

Paclitaxel and its analogue docetaxel show a significant antitumor activity, particularly evident in breast cancer. Paclitaxel has also been proved to be effective as a peripheral blood progenitor cell (CPC) mobilizing agent. To optimize the use of active, disease-specific drugs as CPC priming, we have evaluated the effects of either paclitaxel or docetaxel both at standard dosages and followed by granulocyte colony-stimulating factor (G-CSF), on circulating CPC release and function in 18 patients with advanced breast cancer who had failed previous anthracycline-based regimens. The reported differences in biological behaviour between bone marrow and blood-derived hematopoietic progenitor cells and the ability of both paclitaxel and docetaxel to induce apoptosis, prompted us to simultaneously evaluate the cell cycle perturbations induced on CD34+ cells. Median CD34+ peaks were 24 microl (range: 10-58) in the paclitaxel-treated patients and 39 microl (range: 17-91), respectively, in the patients who received docetaxel. After paclitaxel, the percentage of CD34+ cells in S-phase was low (bromodeoxyuridine, BrdU, labelling index = 3.4+/-2%) with a concomitant presence of early apoptotic cells (8.1+/-3%). On the contrary, after docetaxel, the percentage of CD34+ cells in S-phase was higher (BrdU labelling index = 14.5+/-4%, p<0.05 vs. paclitaxel), while early apoptotic cells were detected at a similar rate (8. 6+/-3%, p = n.s. vs. paclitaxel). In conclusion, when used at standard dosages, with respect to paclitaxel + G-CSF, docetaxel + G-CSF is a more satisfactory tool to mobilize CPC and to induce them into the cell cycle. These data should be taken into account when combinations of docetaxel with other agents are explored as CPC mobilizing regimens for autografting.

Changes in Microtubule Protofilament Number Induced by Taxol Binding to an Easily Accessible Site: INTERNAL MICROTUBULE DYNAMICS

We have investigated the accessibility of the Taxol-binding site and the effects of Taxol binding on the structures of assembled microtubules. Taxol and docetaxel readily bind to and dissociate from microtubules, reaching 95% ligand exchange equilibrium in less than 3 min under our solution conditions (microtubules were previously assembled from GTP-tubulin, GTP-tubulin and microtubule-associated proteins, or GDP-tubulin and taxoid). Microtubules assembled from purified tubulin with Taxol are known to have typically one protofilament less than with the analogue docetaxel and control microtubules. Surprisingly, Taxol binding and exchange induce changes in the structure of preformed microtubules in a relatively short time scale. Cryoelectron microscopy shows changes toward the protofilament number distribution characteristic of Taxol or docetaxel, with a half-time of approximately 0.5 min, employing GDP-tubulin-taxoid microtubules. Correspondingly, synchrotron x-ray solution scattering shows a reduction in the mean microtubule diameter upon Taxol binding to microtubules assembled from GTP-tubulin in glycerol-containing buffer, with a structural relaxation half-time of approximately 1 min. These results imply that microtubules can exchange protofilaments upon Taxol binding, due to internal dynamics along the microtubule wall. The simplest interpretation of the relatively fast taxoid exchange observed and labeling of cellular microtubules with fluorescent taxoids, is that the Taxol-binding site is at the outer microtubule surface. On the contrary, if Taxol binds at the microtubule lumen in agreement with the electron crystallographic structure of tubulin dimers, our results suggest that the inside of microtubules is easily accessible from the outer solution. Large pores or moving lattice defects in microtubules might facilitate the binding of taxoids, as well as of possible endogenous cellular ligands of the inner microtubule wall.

New microtubular agents in pediatric oncology.

The taxanes are a new group of anticancer agents with a novel mechanism of action. They promote microtubule assembly and stabilize the microtubules. Paclitaxel (Taxol), the first agent in this group in clinical trials was isolated from the Pacific yew, Taxus brevifolia in 1971. Both in preclinical and clinical studies, paclitaxel and its semisynthetic analog docetaxel exhibit significant antitumor activity. This review will provide an overview of the clinical experience with the group of anti-microtubular agents, the taxanes in pediatric oncology.

Taxanes: a new class of antitumor agents.

Taxanes belong to a new group of antineoplastic agents with a novel mechanism of action for a cytotoxic drug. They promote microtubule assembly and stabilize the microtubules. Paclitaxel, the first agent in this group to become available, was isolated from the Pacific yew, Taxus brevifolia, in 1971. In preclinical and clinical studies, paclitaxel and its semisynthetic analog docetaxel exhibit significant antitumor activity. This review deals with the physicochemical properties, pharmacology, and results of preclinical and clinical trials of the taxanes.