Paclitaxel

The barks of Taxus yunnanensis

Paclitaxel is a novel antineoplastic agent, which was discovered in a screen of extracts of thousands of plants and natural products for antineoplastic activity by a National Cancer Institute program. Alought it functions as a mitotic inhibitor like vinca alkaloids, paclitaxel promotes the polymerization of tubulin instead of inducing the disassembly of microtubules, which inhibits the microtubules disassembly and promotes the formation of excessively stable, dysfunctional microtubules. Paclitaxel has exhibited antitumor activity against a broad spectrum of human cancers, including ovarian, breast, head and neck, and lung cancer, in a large number of studies.

Reference

Ross C. Donehower. The clinical development of paclitaxel: a successful collaboration of academia, industry and the National cancer Institute. STEM CELLS 1996;14:25-28

Investigation of protective role of curcumin against paclitaxel-induced inner ear damage in rats.[Pubmed:25583134]

Laryngoscope. 2015 May;125(5):1175-82.

OBJECTIVES/HYPOTHESIS: The aim of this study was to investigate the potential protective effect of curcumin on Paclitaxel-induced ototoxicity in rats by means of immunohistochemical and histopathological analysis and distortion product otoacoustic emissions (DPOAEs). STUDY DESIGN: Animal study. METHODS: Forty Sprague-Dawley rats were randomized into five groups. Group 1 was administered no Paclitaxel and curcumin during the study. Groups 2, 3, 4 and 5 were administered 5 mg/kg Paclitaxel; 200 mg/kg curcumin; 5 mg/kg Paclitaxel, followed by 200 mg/kg curcumin; 200 mg/kg curcumin and a day later 5 mg/kg Paclitaxel followed intraperitoneally by 200 mg/kg curcumin once a week for 4 consecutive weeks, respectively. After the final DPOAEs test, the animals were sacrificed and their cochlea were prepared for hematoxylin and eosin and caspase-3 staining. RESULTS: The DPOAEs thresholds and histopathological and immunohistochemical findings were substantially correlated in all groups. The histopathologic findings in the cochlea of the Paclitaxel-treated animals showed not only changes in the organ of Corti, but also damage to the stria vascularis and spiral limbus, including nuclear degeneration, cytoplasmic vacuolization, and atrophy of intermediate cells. Additionally, cochlear changes in group 2, such as intense apoptosis, were confirmed by caspase-3 immunohistochemical staining. In group 4, coreceiving curcumin could not sufficiently prevent Paclitaxel-induced ototoxicity, and the results in group 5 were similar to the control group. CONCLUSIONS: In our study, we have concluded that pre- and coreceiving curcumin can significantly protect the cochlear morphology and functions on Paclitaxel-induced ototoxicity in rats. Curcumin might be considered as a potential natural product that, used as a dietary supplement, could be easily given to patients undergoing Paclitaxel chemotherapy. LEVEL OF EVIDENCE: NA

Antitumor activity of paclitaxel is significantly enhanced by a novel proapoptotic agent in non-small cell lung cancer.[Pubmed:25498514]

J Surg Res. 2015 Apr;194(2):622-30.

BACKGROUND: Newer targeted agents are increasingly used in combination chemotherapy regimens with enhanced survival and improved toxicity profile. Taxols, such as Paclitaxel, independently potentiate tumor destruction via apoptosis and are used as first line therapy in patients with advanced non-small cell lung cancer (NSCLC). Procaspase-3-activating compound-1 (PAC-1) is a novel proapoptotic agent that directly activates procaspase-3 (PC-3) to caspase-3, leading to apoptosis in human lung adenocarcinoma cells. Hence, we sought to evaluate the antitumor effects of Paclitaxel in combination with PAC-1. METHODS: Human NSCLC cell lines (A-549 and H-322m) were incubated in the presence of PAC-1 and Paclitaxel. Tumor cell viability was determined by a tetrazolium-based colorimetric assay (MTT assay). Western blot and flow cytometric analysis were performed to evaluate expression of PC-3 and the proportion of apoptotic cells, respectively. A xenograft murine model of NSCLC was used to study the in vivo antitumor effects of PAC-1. RESULTS: PAC-1 significantly reduced the inhibitory concentration 50% of Paclitaxel from 35.3 to 0.33 nM in A-549 and 8.2 to 1.16 nM in H-322m cell lines. Similarly, the apoptotic activity significantly increased to 85.38% and 70.36% in A-549 and H322m, respectively. Significantly enhanced conversion of PC-3 to caspase-3 was observed with PAC-1 Paclitaxel combination (P < 0.05). Mice treated with a drug combination demonstrated 60% reduced tumor growth rate compared with those of controls (P < 0.05). CONCLUSIONS: PAC-1 significantly enhances the antitumor activity of Paclitaxel against NSCLC. The activation of PC-3 and thus the apoptotic pathway is a potential strategy in the treatment of human lung cancer.

A randomized Phase III trial of weekly or 3-weekly doses of nab-paclitaxel versus weekly doses of Cremophor-based paclitaxel in patients with previously treated advanced gastric cancer (ABSOLUTE Trial).[Pubmed:25516635]

Jpn J Clin Oncol. 2015 Mar;45(3):303-6.

Paclitaxel is an agent widely used in second-line chemotherapy for advanced gastric cancer. The aim of this trial is to evaluate the efficacy and safety of 3-weekly or weekly doses of nanoparticle albumin-bound-Paclitaxel compared with weekly doses of Cremophor-based Paclitaxel in patients with unresectable or recurrent gastric cancer refractory to first-line chemotherapy comprising fluoropyrimidines. A total of 730 patients will be enrolled from 72 institutions. The primary endpoint is the overall survival, and the secondary endpoints are progression-free survival, time to treatment failure, overall response rate, disease control rate, quality of life (by using the EQ-5D system) and safety.

Taxol induces caspase-10-dependent apoptosis.[Pubmed:15452117]

J Biol Chem. 2004 Dec 3;279(49):51057-67.

Taxol (Paclitaxel) is known to inhibit cell growth and trigger significant apoptosis in various cancer cells. Although taxol induces apoptosis of cancer cells, its exact mechanism of action is not yet known. In this study we investigated death receptors, FAS-associated death domain protein (FADD), the activation of caspases-10 and -8 as well as the downstream caspases, and reactive oxygen species (ROS) in taxol-induced apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line. Pretreating the cells with neutralizing antibodies to Fas, tumor necrosis factor (TNF)-alpha receptor 1, or TNF-related apoptosis-inducing ligand receptors (DR4 and DR5) did not affect taxol-induced apoptosis, but transfection of the cells with a dominant negative FADD plasmid resulted in inhibition of taxol-induced apoptosis, revealing that taxol induces apoptosis independently of these death receptors but dependently on FADD. Furthermore, the drug induced activation of caspases-10, -8, -6, and -3, cleaved Bcl-2, Bid, poly(ADP-ribose) polymerase, and lamin B, and down-regulated cellular levels of FLICE-like inhibitory protein (FLIP) and X-chromosome-linked inhibitor of apoptosis protein (XIAP). However, despite the release of cytochrome c from the mitochondria in taxol-treated cells, caspase-9 was not activated. Inhibitors of caspases-8, -6, or -3 partially inhibited taxol-induced apoptosis, whereas the caspase-10 inhibitor totally abrogated this process. Taxol-induced apoptosis was also associated with decreased mitochondrial membrane potential (Deltapsim) and a significant increase in ROS generation. However, increased ROS production was not directly involved in taxol-triggered apoptosis. Therefore, these results demonstrate for the first time that taxol induces FADD-dependent apoptosis primarily through activation of caspase-10 but independently of death receptors.

Characterization of the Taxol binding site on the microtubule. Identification of Arg(282) in beta-tubulin as the site of photoincorporation of a 7-benzophenone analogue of Taxol.[Pubmed:10608867]

J Biol Chem. 1999 Dec 31;274(53):37990-4.

Photoaffinity labeling methods have allowed a definition of the sites of interaction between Taxol and its cellular target, the microtubule, specifically beta-tubulin. Our previous studies have indicated that [(3)H]3'-(p-azidobenzamido)Taxol photolabels the N-terminal 31 amino acids of beta-tubulin (Rao, S., Krauss, N. E., Heerding, J. M., Swindell, C. S., Ringel, I., Orr, G. A., and Horwitz, S. B. (1994) J. Biol. Chem. 269, 3132-3134) and [(3)H]2-(m-azidobenzoyl)Taxol photolabels a peptide containing amino acid residues 217-233 of beta-tubulin (Rao, S., Orr, G. A., Chaudhary, A. G., Kingston, D. G. I., and Horwitz, S. B. (1995) J. Biol. Chem. 270, 20235-20238). The site of photoincorporation of a third photoaffinity analogue of Taxol, [(3)H]7-(benzoyldihydrocinnamoyl) Taxol, has been determined. This analogue stabilizes microtubules polymerized in the presence of GTP, but in contrast to Taxol, does not by itself enhance the polymerization of tubulin to its polymer form. CNBr digestion of [(3)H]7-(benzoyldihydrocinnamoyl)Taxol-labeled tubulin, with further arginine-specific cleavage by clostripain resulted in the isolation of a peptide containing amino acid residues 277-293. Amino acid sequence analysis indicated that the photoaffinity analogue cross-links to Arg(282) in beta-tubulin. Advances made by electron crystallography in understanding the structure of the tubulin dimer have allowed us to visualize the three sites of photoincorporation by molecular modeling. There is good agreement between the binding site of Taxol in beta-tubulin as determined by photoaffinity labeling and electron crystallography.

Taxol: a novel investigational antimicrotubule agent.[Pubmed:1973737]

J Natl Cancer Inst. 1990 Aug 1;82(15):1247-59.

Microtubules are among the most strategic subcellular targets of anticancer chemotherapeutics. Despite this fact, new antimicrotubule agents that possess unique mechanisms of cytotoxic action and have broader antineoplastic spectra than the vinca alkaloids have not been introduced over the last several decades--until the recent development of taxol. Unlike classical antimicrotubule agents like colchicine and the vinca alkaloids, which induce depolymerization of microtubules, taxol induces tubulin polymerization and forms extremely stable and nonfunctional microtubules. Taxol has demonstrated broad activity in preclinical screening studies, and antineoplastic activity has been observed in several classically refractory tumors. These tumors include cisplatin-resistant ovarian carcinoma in phase II trials and malignant melanoma and non-small cell lung carcinoma in phase I studies. Taxol's structural complexity has hampered the development of feasible processes for synthesis, and its extreme scarcity has limited the use of a conventional, broad-scale screening approach for evaluation of clinical antitumor activity. However, taxol's unique mechanism of action, its spectrum of preclinical antitumor activity, and tumor responses in early clinical trials have generated renewed interest in pursuing its development.

Taxol: a unique antineoplastic agent with significant activity in advanced ovarian epithelial neoplasms.[Pubmed:2569287]

Ann Intern Med. 1989 Aug 15;111(4):273-9.

STUDY OBJECTIVE: To assess the activity of taxol in patients with advanced, progressive, and drug-refractory ovarian cancer and to delineate more clearly the toxicity of taxol in this patient population. DESIGN: Nonrandomized, prospective phase II trial. PATIENTS: Forty-seven patients with drug-refractory epithelial ovarian cancer who had one or more lesions measurable in perpendicular diameters. Of these patients, 45 were evaluable for toxicity and 40 were evaluable for response. INTERVENTIONS: PATIENTS were treated every 22 days with varying doses of taxol (110 to 250 mg/m2 body surface) given as a 24-hour infusion with subsequent doses based on adverse effects. A premedication regimen was used to avoid acute hypersensitivity reactions. MEASUREMENTS AND MAIN RESULTS: Twelve patients (30%; CI, 16% to 44%) responded to taxol for periods lasting from 3 to 15 months. The dose-limiting toxicity was myelosuppression with leukocytes affected more severely and commonly than thrombocytes or reticulocytes. Leukopenia was usually brief in duration but was associated with sepsis in 3 cases (2 fatal). Other adverse effects included myalgias, arthralgias, alopecia, diarrhea, nausea, vomiting, mucositis, and peripheral neuropathy. Rare cases of cardiac and central neurotoxicity were also noted. CONCLUSIONS: Taxol is an active agent in drug-refractory ovarian cancer and deserves further study in combination with other active drugs in previously untreated patients with advanced ovarian cancer.

Paclitaxel is a naturally occurring antineoplastic agent and stabilizes tubulin polymerization. Paclitaxel can cause both mitotic arrest and apoptotic cell death. Paclitaxel also induces autophagy.

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