Paclitaxel resistance in non-small-cell lung cancer associated with beta-tubulin gene mutations

Molecular aspects of cancer cell resistance to chemotherapy

Cancer cell resistance to chemotherapy is still a heavy burden that impairs treatment of cancer patients. Both intrinsic and acquired resistance results from the numerous genetic and epigenetic changes occurring in cancer cells. Most of the hallmarks of cancer cells provide general mechanisms to sustain stresses such as the ones induced by chemotherapeutic drugs. Moreover, specific changes in the target bring resistance to specific drugs like modification in nucleotide synthesis enzymes upon anti-metabolite exposure, in microtubule composition upon spindle poison treatment, in topoisomerase activity upon topoisomerase inhibitor incubation or in intracellular signaling pathways when targeting tyrosine kinase receptors. Finally, the stemness properties of a few cancer cells as well as components of the tumor stroma, like fibroblasts and tumor-associated macrophages but also hypoxia, also help tumor to resist to anticancer agents. These processes provide an additional level of complexity to the understanding of the tumor resistance phenomenon. This review aims to describe the different general mechanisms as well as some examples of specific on target modifications inducing cancer cell resistance to chemotherapy at the molecular level. Perspectives to develop more efficient treatment, using genomic signature or more specific biomarkers to characterize putative resistance mechanisms in patients before choosing the more appropriate treatment, will also be discussed.

Intratumoral injection of taxol in vivo suppresses A549 tumor showing cytoplasmic vacuolization

Based on our recent in vitro studies, this report was designed to explore the mechanism by which high concentration of taxol (70 µM) induced paraptosis-like cell death in human lung carcinoma (A549) cells, and to evaluate the therapeutic efficacy of taxol using A549 tumor-bearing mice in vivo. Exposure of cells to taxol induced time-dependent cytotoxicity and cytoplasmic vacuolization without the involvement of Bax, Bak, Mcl-1, Bcl-XL, and caspase-3. Although taxol treatment induced activating transcription factor 6 (ATF6) cleavage indicative of endoplasmic reticulum (ER) stress, silencing ATF6 by shATF6 did not prevent taxol-induced both cytotoxcity and cytoplasmic vacuolization, suggesting that taxol-induced cytoplasmic vacuolization and cell death were not due to ER stress. Moreover, taxol-treated cells did not show DNA fragmentation and loss of mitochondrial membrane potential, the typical characteristics of apoptosis. In addition, taxol-induced cytoplasmic vacuolization did not show the cellular lysis, the characteristics of oncosis, and positive of β-galactosidase, the characteristic of senescence, indicating that taxol induced paraptosis-like cell death is neither oncosis nor senescence. Moreover, our in vivo data showed that intratumoral injection of taxol (50 mg/kg) in A549 tumor xenograft mice on day 1 and day 19 potently suppressed tumor growth showing significant ER vacuolization without toxicity. In conclusion, high concentration of taxol exhibits a significant anticancer activity by inducing paraptosis-like cell death in vitro and in vivo, without significant toxicity, suggesting a promising therapeutic strategy for apoptosis-resistance cancer by inducing ER vacuolization.

Understanding the basis of drug resistance of the mutants of αβ-tubulin dimer via molecular dynamics simulations

The vital role of tubulin dimer in cell division makes it an attractive drug target. Drugs that target tubulin showed significant clinical success in treating various cancers. However, the efficacy of these drugs is attenuated by the emergence of tubulin mutants that are unsusceptible to several classes of tubulin binding drugs. The molecular basis of drug resistance of the tubulin mutants is yet to be unraveled. Here, we employ molecular dynamics simulations, protein-ligand docking, and MMPB(GB)SA analyses to examine the binding of anticancer drugs, taxol and epothilone to the reported point mutants of tubulin--T274I, R282Q, and Q292E. Results suggest that the mutations significantly alter the tubulin structure and dynamics, thereby weaken the interactions and binding of the drugs, primarily by modifying the M loop conformation and enlarging the pocket volume. Interestingly, these mutations also affect the tubulin distal sites that are associated with microtubule building processes.

Parallel evolution under chemotherapy pressure in 29 breast cancer cell lines results in dissimilar mechanisms of resistance

Background

Developing chemotherapy resistant cell lines can help to identify markers of resistance. Instead of using a panel of highly heterogeneous cell lines, we assumed that truly robust and convergent pattern of resistance can be identified in multiple parallel engineered derivatives of only a few parental cell lines.

Methods

Parallel cell populations were initiated for two breast cancer cell lines (MDA-MB-231 and MCF-7) and these were treated independently for 18 months with doxorubicin or paclitaxel. IC50 values against 4 chemotherapy agents were determined to measure cross-resistance. Chromosomal instability and karyotypic changes were determined by cytogenetics. TaqMan RT-PCR measurements were performed for resistance-candidate genes. Pgp activity was measured by FACS.

Results

All together 16 doxorubicin- and 13 paclitaxel-treated cell lines were developed showing 2–46 fold and 3–28 fold increase in resistance, respectively. The RT-PCR and FACS analyses confirmed changes in tubulin isofom composition, TOP2A and MVP expression and activity of transport pumps (ABCB1, ABCG2). Cytogenetics showed less chromosomes but more structural aberrations in the resistant cells.

Conclusion

We surpassed previous studies by parallel developing a massive number of cell lines to investigate chemoresistance. While the heterogeneity caused evolution of multiple resistant clones with different resistance characteristics, the activation of only a few mechanisms were sufficient in one cell line to achieve resistance.

Exploring biomarkers in head and neck cancer

Personalized medicine based on predictive markers linked to drug response, it is hoped, will lead to improvements in outcomes and avoidance of unnecessary treatment in squamous cell carcinoma of the head and neck (SCCHN). Recent research has shown that expression of ERCC1 may predict resistance to treatment with platinum agents. Future testing for this marker may help select the optimal type of chemotherapy. Infection with human papillomavirus (HPV) is associated with less aggressive disease and better prognosis in locally advanced SCCHN treated with chemoradiation or radiation alone; HPV-positive patients may ultimately benefit from less intensive, less toxic therapy. K-RAS mutations, occurring in about 40% of colorectal cancers and associated with lack of benefit from epidermal growth factor receptor (EGFR) antibodies in this disease, are found in <5% of SCCHN patients, making routine testing for K-RAS mutations unwarranted at this time. Virtually all head and neck tumors overexpress EGFR, which limits the usefulness of EGFR expression as a marker for treatment selection. Although the incidence of EGFR tyrosine kinase domain mutations is very rare, a better understanding of the role of EGFR mutations, expression, amplification, and downstream effects in SCCHN may help define the role of EGFR in this setting. These observations caution against extrapolating results obtained with biomarkers in other types of cancer to SCCHN. Validation of each biomarker in the context of SCCHN clinical trials will be required before a specific marker can be incorporated into daily practice.

Alterations in tumor necrosis factor signaling pathways are associated with cytotoxicity and resistance to taxanes: a study in isogenic resistant tumor cells

INTRODUCTION

The taxanes paclitaxel and docetaxel are widely used in the treatment of breast, ovarian, and other cancers. Although their cytotoxicity has been attributed to cell-cycle arrest through stabilization of microtubules, the mechanisms by which tumor cells die remains unclear. Paclitaxel has been shown to induce soluble tumor necrosis factor alpha (sTNF-α) production in macrophages, but the involvement of TNF production in taxane cytotoxicity or resistance in tumor cells has not been established. Our study aimed to correlate alterations in the TNF pathway with taxane cytotoxicity and the acquisition of taxane resistance.

METHODS

MCF-7 cells or isogenic drug-resistant variants (developed by selection for surviving cells in increasing concentrations of paclitaxel or docetaxel) were assessed for sTNF-α production in the absence or presence of taxanes by enzyme-linked immunosorbent assay (ELISA) and for sensitivity to docetaxel or sTNF-α by using a clonogenic assay (in the absence or presence of TNFR1 or TNFR2 neutralizing antibodies). Nuclear factor (NF)-κB activity was also measured with ELISA, whereas gene-expression changes associated with docetaxel resistance in MCF-7 and A2780 cells were determined with microarray analysis and quantitative reverse transcription polymerase chain reaction (RTqPCR).

RESULTS

MCF-7 and A2780 cells increased production of sTNF-α in the presence of taxanes, whereas docetaxel-resistant variants of MCF-7 produced high levels of sTNF-α, although only within a particular drug-concentration threshold (between 3 and 45 nM). Increased production of sTNF-α was NF-κB dependent and correlated with decreased sensitivity to sTNF-α, decreased levels of TNFR1, and increased survival through TNFR2 and NF-κB activation. The NF-κB inhibitor SN-50 reestablished sensitivity to docetaxel in docetaxel-resistant MCF-7 cells. Gene-expression analysis of wild-type and docetaxel-resistant MCF-7, MDA-MB-231, and A2780 cells identified changes in the expression of TNF-α-related genes consistent with reduced TNF-induced cytotoxicity and activation of NF-κB survival pathways.

CONCLUSIONS

We report for the first time that taxanes can promote dose-dependent sTNF-α production in tumor cells at clinically relevant concentrations, which can contribute to their cytotoxicity. Defects in the TNF cytotoxicity pathway or activation of TNF-dependent NF-κB survival genes may, in contrast, contribute to taxane resistance in tumor cells. These findings may be of strong clinical significance.

Drug resistance to paclitaxel is not only associated with ABCB1 mRNA expression but also with drug accumulation in intracellular compartments in human lung cancer cell lines

In order to clarify the mechanisms of resistance to paclitaxel in lung cancer, three human lung cancer cell lines which exhibit different sensitivity to paclitaxel were investigated from the following viewpoints: overexpression of ATP-binding cassette, sub-family B, member 1 (ABCB1), mutations on paclitaxel binding site of β-tubulin genes, quantity of polymerized tubulin and the intracellular localization of paclitaxel. ABCB1 expression was evaluated by real-time RT-PCR. No correlations were noted between the ABCB1 expression in the sensitive and resistant cell lines at the mRNA level. No mutations on the paclitaxel binding site of the β-tubulin genes were detected in either the resistant or sensitive cells. Live cell images obtained by confocal laser microscopy revealed that the resistant cell line, RERF-LC-KJ, had more accumulation of Oregon Green^® 488 conjugated paclitaxel in the lysosomal and extra-lysosomal compartments of cytoplasm than other cell lines. The results obtained in this study indicated that the changes in the subcellular localization could contribute to the production of paclitaxel resistance in lung cancer cell lines. Further studies should be conducted to elucidate the molecular mechanisms that differentiate the intracellular localization of paclitaxel.

Inhibition of α Folate Receptor Resulting in a Reversal of Taxol Resistance in Nasopharyngeal Carcinoma

Objective. To further determine the role of FOLR1 in taxol resistance of nasopharyngeal carcinoma (NPC) and whether inhibition of FOLR1 expression reverses the taxol-resistant phenotype.

Study Design. Correlation study between gene expression and cancer cell survival.

Setting. University hospital.

Subjects and Methods. Three taxol-resistant sub–cell lines with a different resistant index were established from the parental CNE-1 NPC cell line. The correlation between FOLR1 expression and taxol sensitivity was statistically analyzed. Inhibition of FOLR1 expression was carried out by RNA interference and by a FOLR1-specific monoclonal antibody, and taxol sensitivity was examined by colony formation assays. FOLR1 expression was also examined in 72 NPC patient specimens by immunohistochemistry.

Results. The levels of FOLR1 expression were positively and significantly correlated with a taxol resistance phenotype ( P < .05). Inhibition of FOLR1 expression resulted in a significantly increased sensitivity of taxol to taxol-resistant NPC cells ( P < .05). An increase of FOLR1 expression by gene transfection caused a taxol-resistant phenotype in parental NPC cells. The level of FOLR1 expression was found to be related to clinical stage in NPC tissue samples.

Conclusion. These results suggest that FOLR1 plays an important role in taxol resistance of NPC cells.

Analysis of Beta-Tubulin Gene Exon 4 Mutations in Advanced Stage III or IV Gastric Cancer

The mechanisms that cause chemoresistance of gastric cancer have yet to be elucidated. Taxanes and promising agents that were recently approved for treatment of advanced or recurrent gastric cancer. Mutations of beta-tubulin, which is a target of taxianes, have been shown to confer chemoresistance against these agents. The aim of the present study is to investigate the presence of mutations of the beta-tubulin in gastric cancer tissues. Sixty-six patients with advanced stage III or IV gastric cancer patients enrolled in this study. Paired samples of gastric cancer tissue and normal mucosa were obtained by endoscopy. The guanosine 5'-triphosphate (GTP)-binding site in exon 4 of the beta-tubulin gene was examined by polymerase chain reaction single-strand conformational polymorphism (PCR-SSCP) analysis, followed by sequencing of the products with abnormally shifted bands. SSCP analysis showed abnormal bands upstream of the GTP-binding site in 7 of the 66 patients, but sequence analysis found no nucleotide substitutions in these patients. Three variant bands were also detected down stream of the the GTP-binding site, but the sequences of the 3 products corresponded to those of two independent pseudogenes. Thus, none of the tumor samples showed mutation of the beta-tubulin exon 4 GTP-binding site. In conclusion, these findings suggest that mutations of the beta-tubulin gene are rare and are unlikely to be an important cause of taxane resistance to taxians.

Design, synthesis, and SAR studies of 4-substituted methoxylbenzoyl-aryl-thiazoles analogues as potent and orally bioavailable anticancer agents

In a continued effort to improve upon the previously published 4-substituted methoxybenzoyl-aryl-thiazole (SMART) template, we explored chemodiverse "B" rings and "B" to "C" ring linkage. Further, to overcome the poor aqueous solubility of this series of agents, we introduced polar and ionizable hydrophilic groups to obtain water-soluble compounds. For instance, based on in vivo pharmacokinetic (PK) studies, an orally bioavailable phenyl-amino-thiazole (PAT) template was designed and synthesized in which an amino linkage was inserted between "A" and "B" rings of compound 1. The PAT template maintained nanomolar (nM) range potency against cancer cell lines via inhibiting tubulin polymerization and was not susceptible to P-glycoprotein mediated multidrug resistance in vitro, and markedly improved solubility and bioavailability compared with the SMART template (45a-c (PAT) vs 1 (SMART)).

Thymidine Phosphorylase/β-tubulin III expressions predict the response in Chinese advanced gastric cancer patients receiving first-line capecitabine plus paclitaxel

BACKGROUND

To assess the role of Thymidine Phosphorylase and β-tubulin III in clinical outcome of Chinese advanced gastric cancer patients receiving first-line capecitabine plus paclitaxel.

METHODS

The clinical data and tumor biopsies prior treatment from 33 advanced gastric cancer patients receiving capecitabine plus paclitaxel (cohort 1, experimental group) and 18 patients receiving capecitabine plus cisplatin (cohort 2, control group) in Beijing Cancer Hospital from July 2003 to December 2008 were retrospectively collected and analyzed for Thymidine Phosphorylase and β-tubulin III expressions by immunohistochemistry. The relationships between expressions of biomarkers and response or survival were determined by statistical analysis.

RESULTS

The median age of 51 patients was 57 years (range, 27-75) with male 34 and female 17, and the response rate, median progression-free survival and overall survival were 43.1%, 120d and 265d. Among cohort 1, the response rate, median progression-free survival and overall survival in β-tubulin III positive (n = 22) and negative patients (n = 11) were 36.4%/72.7% (positive vs negative, P = 0.049), 86d/237d (P = 0.046) and 201d/388d (P = 0.029), respectively; the response rate (87.5% vs 14.3%, P = 0.01) and median progression-free survival (251d vs 84d, P = 0.003) in Thymidine Phosphorylase positive & β-tubulin III negative patients (n = 8) were also significantly higher than those in Thymidine Phosphorylase negative & β-tubulin III positive patients (n = 7). There was no correlation between β-tubulin III expression and response or survival among cohort 2 (n = 18).

CONCLUSIONS

In Chinese advanced gastric cancer, Thymidine Phosphorylase positive & β-tubulin III negative might predict response and prognosis to capecitabine plus paclitaxel chemotherapy. Further prospective evaluation in large samples should be performed to confirm these preliminary findings.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

Biological activity of 4-substituted methoxybenzoyl-aryl-thiazole: an active microtubule inhibitor

Formation of microtubules is a dynamic process that involves polymerization and depolymerization of αβ-tubulin heterodimers. Drugs that enhance or inhibit tubulin polymerization can destroy this dynamic process, arresting cells in the G(2)/M phase of the cell cycle. Although drugs that target tubulin generally demonstrate cytotoxic potency in the subnanomolar range, resistance due to drug efflux is a common phenomenon among the antitubulin agents. We recently reported a class of 4-substituted methoxybenzoyl-aryl-thiazoles (SMART) that exhibited great in vitro potency and broad spectrum cellular cytotoxicity. Evaluation of the in vitro and in vivo anticancer activities of 3 SMART compounds, SMART-H (H), SMART-F (F), and SMART-OH (OH), with varying substituents at the 4-position of aryl ring, demonstrated that they bind potently to the colchicine-binding site in tubulin, inhibit tubulin polymerization, arrest cancer cells in G(2)/M phase of the cell cycle, and induce their apoptosis. The SMART compounds also equipotently inhibit the growth of parental and MDR-overexpressing cells in vitro, indicating that they can overcome multidrug resistance. In vivo antitumor efficacy studies in human prostate (PC-3) and melanoma (A375) cancer xenograft models demonstrated that SMART-H and SMART-F treatments resulted in %T/C values ranging from 4% to 30%. In addition, in vivo SMART-H treatment for 21 days at the higher dose (15 mg/kg) failed to produce any apparent neurotoxicity. These studies provide the first in vivo evidence and proof-of-concept that SMART compounds are similarly efficacious to currently FDA approved antitubulin drugs for cancer treatment, but they can circumvent P-glycoprotein-mediated drug resistance.

Parameters for individualizing systemic therapy in non-small cell lung cancer

Rational drug design based on molecular targets is starting to revolutionize cancer care. To maximize its potential for patients, a concomitant leveraging of molecular knowledge for selection of patients to future and current therapeutic options is paramount. The terms "individualized", "personalized", or "precision therapy" are currently used to describe these efforts. Here, we summarize current knowledge for selection of systemic targeted and cytotoxic therapy for patients with non-small-cell lung cancer. Based on this knowledge, we present a potential decision algorithm to best select patients for currently available therapies, which include the treatment options single-agent erlotinib or gefitinib, the ALK inhibitor crizotinib, double agent gemcitabine and platinum, double agent platinum and pemetrexed, and as a default option a taxane combined with a non-platinum drug, for instance a vinca alkaloid. The addition of bevacizumab to double-agent chemotherapy is also discussed. Currently available data on predictive biomarkers are largely based on subgroup or companion biomarker analyses of patient cohorts or clinical trials. Current and emerging markers must be incorporated prospectively into the design of clinical trials that test novel and established agents to better understand their clinical utility and to refine selection parameters and marker interactions. Future development will lead to increasing complexity in clinical decision making with substantial anticipated benefits to patients including increased therapeutic efficacy, reduced toxicity, and better quality of life.

Ixabepilone, a new treatment option for metastatic breast cancer

Patients with metastatic breast cancer (MBC) who develop resistance to anthracyclines and taxanes have limited therapeutic options. There is an unmet need for agents that can overcome tumor resistance and are effective in treating drug-resistant disease. The novel epothilone B analog, ixabepilone, binds to β-tubulin and stabilizes microtubules, leading to growth inhibition and apoptosis. Ixabepilone is able to overcome common mechanisms of resistance that limit the efficacy of many chemotherapeutic agents such as anthracyclines, taxanes, and capecitabine. Single-agent ixabepilone has clinical activity and a manageable safety profile against several different solid tumors including MBC, nonsmall cell lung cancer (NSCLC), and prostate cancer. Several phase II and III trials have demonstrated that ixabepilone-as monotherapy and in combination with capecitabine-is active in patients with pretreated or resistant MBC. Ixabepilone is the first epothilone approved for use as monotherapy or in combination with capecitabine in the treatment of metastatic or locally advanced breast cancer that is resistant or refractory to anthracyclines, taxanes, and/or capecitabine. Further clinical studies are evaluating the combination of ixabepilone with targeted agents such as trastuzumab or bevacizumab to further define the role of this novel agent in the treatment of MBC.

Endometrial carcinoma: a review of chemotherapy, drug resistance, and the search for new agents

The article examines current treatment options in patients with endometrial carcinoma, the role of drug resistance, and the rationale for the use of epothilones in treating this disease.

Adenocarcinoma of the endometrium represents the most common gynecologic malignancy in developed countries. Although early-stage cancers are effectively treated surgically, commonly without adjuvant therapy, the treatment of high-risk and advanced disease is more complex. Chemotherapy has evolved into an important modality in high-risk early-stage and advanced-stage disease, and in recurrent endometrial cancer. Taxane-based therapy consistently demonstrates the highest response rates in the first-line and salvage settings of endometrial cancer. Unfortunately, response to chemotherapy is modest and strategies are needed to predict chemotherapy-responsive and chemotherapy-resistant populations. Chemotherapy resistance mediated by overexpression of drug efflux pump proteins and mutations in β-tubulin isoforms in both primary and recurrent disease represent unique treatment challenges and highlight the need for new agents that are less susceptible to these known resistance pathways. Epothilone B analogs are novel cytotoxic agents with activity in solid tumors, including advanced/recurrent endometrial carcinoma, and may have unique properties that can overcome resistance in some settings. These agents alone and in combination represent a new therapeutic opportunity in endometrial carcinoma.

Microtubule-binding agents: a dynamic field of cancer therapeutics

Microtubules are dynamic filamentous cytoskeletal proteins composed of tubulin and are an important therapeutic target in tumour cells. Agents that bind to microtubules have been part of the pharmacopoeia of anticancer therapy for decades and until the advent of targeted therapy, microtubules were the only alternative to DNA as a therapeutic target in cancer. The screening of a range of botanical species and marine organisms has yielded promising new antitubulin agents with novel properties. In the current search for novel microtubule-binding agents, enhanced tumour specificity, reduced neurotoxicity and insensitivity to chemoresistance mechanisms are the three main objectives.

Pharmacogenomics of paclitaxel

The microtubule-stabilizing drug paclitaxel is a cytotoxic agent widely used for the treatment of a variety of tumor types. Since its introduction to the clinic, modifications to the administration schedule and treatments for hypersensitivity reactions and neutropenia have significantly improved paclitaxel therapy. On the other hand, severe neurotoxicity and lack of response are still clinical challenges. During the last decade a deeper knowledge of paclitaxel pharmacokinetics and pharmacodynamics has been achieved, together with an in-depth characterization of genes involved in its elimination and therapeutic response. Pharmacogenetic studies aimed at the identification of paclitaxel outcome biomarkers have been performed, however, further efforts will be required to successfully integrate these and future results to provide the basis for personalized paclitaxel therapy.

Human mutations that confer paclitaxel resistance

The involvement of tubulin mutations as a cause of clinical drug resistance has been intensely debated in recent years. In the studies described here, we used transfection to test whether beta1-tubulin mutations and polymorphisms found in cancer patients are able to confer resistance to drugs that target microtubules. Three of four mutations (A185T, A248V, R306C, but not G437S) that we tested caused paclitaxel resistance, as indicated by the following observations: (a) essentially 100% of cells selected in paclitaxel contained transfected mutant tubulin; (b) paclitaxel resistance could be turned off using tetracycline to turn off transgene expression; (c) paclitaxel resistance increased as mutant tubulin production increased. All the paclitaxel resistance mutations disrupted microtubule assembly, conferred increased sensitivity to microtubule-disruptive drugs, and produced defects in mitosis. The results are consistent with a mechanism in which tubulin mutations alter microtubule stability in a way that counteracts drug action. These studies show that human tumor cells can acquire spontaneous mutations in beta1-tubulin that cause resistance to paclitaxel, and suggest that patients with some polymorphisms in beta1-tubulin may require higher drug concentrations for effective therapy.

Differences in the expression profiles of excision repair crosscomplementation group 1, x-ray repair crosscomplementation group 1, and betaIII-tubulin between primary non-small cell lung cancer and metastatic lymph nodes and the significance in mid-term survival

INTRODUCTION

This study aimed to compare the expression profiles of excision repair crosscomplementation group 1 (ERCC1), x-ray repair crosscomplementation group 1 (XRCC1), and betaIII-tubulin between patients with primary non-small cell lung cancer (NSCLC) and those with metastatic lymph nodes and to identify the prognostic significance of each chemotherapy resistance protein.

MATERIALS

Those who met the inclusion criteria were patients (1) with NSCLC, (2) with metastatic lymph nodes (N1 or N2), and (3) who underwent surgical resection followed by platinum-based adjuvant chemotherapy. A total of 82 patients were included in the study. The expression profile of each protein was evaluated by immunohistochemistry and compared according to tumor location.

RESULTS

The mean age of the patients was 57.5 +/- 8.4 years. There were 30 N1 and 52 N2 patients. ERCC1 expression was upregulated in 55% and downregulated in 8% of metastatic lymph nodes, when compared with primary tumors (p < 0.05). XRCC1 was also upregulated in 56% and downregulated in 6% (p < 0.05). However, betaIII-tubulin was upregulated in 12% and downregulated in 45% of patients (p < 0.05). betaIII-tubulin expression in metastatic lymph nodes was greater in patients with adenocarcinoma than other cell types. Upregulation of ERCC1 in metastatic lymph nodes was a poor prognostic factor in N1 patients but not in N2 patients.

CONCLUSIONS

Significant changes in the expression profile of each protein were observed in metastatic lymph nodes. The resistance protein-guided treatment should be performed after integrative interpretation of expression profiles of each protein in both primary and metastatic sites.

Pharmacogenomics of taxane/platinum therapy in ovarian cancer

OBJECTIVES

Taxane (paclitaxel or docetaxel) and platinum (cisplatin or carboplatin) chemotherapy is commonly used in the treatment of ovarian cancer. Despite an initial high response to therapy, the 5-year survival rate remains low. The identification of pharmacogenomic markers to identify patients unlikely to respond or at risk for severe toxicity will assist in the goal of individualizing ovarian cancer treatment.

MATERIALS AND METHODS

Most studies have assessed single nucleotide polymorphisms from genes involved in the pharmacokinetics and pharmacodynamics of the drugs.

RESULTS

Unfortunately, most markers identified have not been replicated in subsequent studies.

CONCLUSIONS

Other mechanisms of variability, including epigenetic control of gene expression and copy number variation, may play important roles. In addition, nongenetic influences such as concurrent medications, and physiological and environmental factors could also affect individual responses to taxane and platinum therapy.

The role of betaIII tubulin in predicting chemoresistance in non-small cell lung cancer

Lung cancer is a leading cause of death among adults. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancer cases. For more than half of all patients diagnosis does not occur until the disease has metastasised. At this advanced stage, the 5-year survival rate is just 15%. Platinum-based chemotherapy forms the backbone of treatment for patients with advanced NSCLC and forms an important component of the therapeutic regimen for many patients with earlier stage disease. However, although a number of agents are available to partner the platinum-based compounds, treatment selection is largely empiric, and chemoresistance is a considerable barrier to improving outcomes. The identification of biologic and other markers to guide treatment selection, thus ensuring patients receive the most effective regimen for their individual tumour and avoid exposure to toxic agents from which they are unlikely to benefit, will be critical to improve outcomes for patients with NSCLC. The development of alternative agents for those patients who express predictors of a negative clinical response is of vital importance. A variety of biomarkers are emerging, including expression of DNA repair enzymes, ribonucleotide subunits and betaIII tubulin. Treatment algorithms based on elucidation of such markers to guide treatment selection can already be envisaged. For example, those patients with high betaIII tubulin expression should be considered for epothilone therapy as an alternative to taxane-based regimens. The epothilones may be preferred option as the evidence suggests that these agents retain activity versus taxane-resistant cancers. This paper reviews the evidence base for betaIII tubulin expression as a prognostic and predictive biomarker in NSCLC and briefly explores the implications for clinical decision making of this and other emerging biomarkers.

Paclitaxel chemotherapy for the treatment of gastric cancer

A comprehensive review of phase I and phase II clinical trials of paclitaxel and paclitaxel-containing chemotherapy regimens for advanced gastric cancer was performed. Response rates, median progression-free survivals, and median overall survivals were examined, together with the treatment regimens and the numbers of patients registered in each trial. Although paclitaxel monotherapy produced considerable improvement in tumor response and prognosis, combination doublet or triplet chemotherapy with fluoropyrimidines and/or platinum compounds showed better results than the paclitaxel monotherapy. With regard to the schedule of paclitaxel administration, weekly injection seemed to show less toxicity and better results than administration every 3 weeks. Adjuvant therapies, chemoradiation therapies, and paclitaxel treatment for gastric ascites were also investigated and are discussed.

Identification and characterization of an intermediate taxol binding site within microtubule nanopores and a mechanism for tubulin isotype binding selectivity

Tubulin, the primary subunit of microtubules, is remarkable for the variety of small molecules to which it binds. Many of these are very useful or promising agents in cancer chemotherapy. One of the most useful of these is paclitaxel. The tubulin molecule is itself an alpha/beta heterodimer, both alpha- and beta-tubulin monomers existing as multiple isotypes. Despite the success of paclitaxel as an anticancer drug, resistance often occurs in cancer cells and has been associated with variations in tubulin isotype expression, most notably with the increased expression of betaIII-tubulin. Paclitaxel is thought to reach its binding site on beta-tubulin by diffusion through nanopores in the microtubule wall. It has been suggested that a transitional step in this process may be the binding of paclitaxel to an intermediate site within a nanopore, from which it moves directly to its binding site in the microtubule interior facing the lumen. To test this hypothesis, we have computationally docked paclitaxel within a microtubule nanopore and simulated its passage to the intermediate binding site. Targeted molecular dynamics was then used to test the hypothesis that paclitaxel utilizes the H6/H7 loop as a hinge to move directly from this intermediate binding site to its final position in the luminal binding site. We observed that this motion appears to be stabilized by the formation of a hydrogen bond involving serine 275 in beta-tubulin isotypes I, IIa, IIb, IVa, IVb, V, VII, and VIII. Interestingly, this residue is replaced by alanine in the betaIII and VI isotypes. This observation raises the possibility that the observed isotype difference in paclitaxel binding may be a kinetic effect arising from the isotype difference at this residue. We are now able to suggest derivatives of paclitaxel that may reverse the isotype-specificity or lead to an alternate stabilizing hydrogen-bond interaction with tubulin, thus increasing the rate of passage to the luminal binding site and hopefully offering a therapeutic advantage in paclitaxel resistant cases.

Pharmacogenomics in non-small-cell lung cancer chemotherapy

The disappointing results in long-term survival of patients who have a resectable non-small cell lung cancer (NSCLC) may reflect the lack of knowledge on the way by which molecular abnormalities in neoplastic cells affect responsiveness to adjuvant therapy. This issue deserves intensive investigation to select methodological approaches for a new generation of chemotherapeutic strategies. Remarkable advances in the understanding of NSCLC biology have been made, including the discovery of critical mutations in oncogenes (i.e. K-Ras and c-myc), as well as the loss of tumor-suppressor genes, such as TP53, p16(INK4) or Rb. Other studies demonstrated the role of mutations or deregulation of the expression of several molecular determinants involved in cell cycle control such as epidermal growth factor receptor (EGFR). All these characteristics, as well as alterations in gene products directly related to drug activity, might contribute to the aggressive behaviour of NSCLC. The future challenge of chemotherapy of NSCLC relies on the identification of molecular markers that are predictive of drug sensitivity and are helpful in the selection of chemotherapeutic agents best suited to the individual patient. Other intriguing issues will be the identification of the optimal drug sequence in combination regimens and the pharmacogenetics of severe toxicities. Moreover, due to the developments of novel technologies to decipher genetic alterations involved in tumor progression, new agents are gaining momentum, including inhibitors of intracellular signal transduction, and a large body of research, using prospective clinical trials, should be devoted to this area.

Tumoral expression of TXR1 and TSP1 predicts overall survival of patients with lung adenocarcinoma treated with first-line docetaxel-gemcitabine regimen

PURPOSE

In vitro data suggest that down-regulation of thrombospondin 1 (TSP1) expression from TXR1 is associated with resistance to taxane-based chemotherapy. The prognostic and predictive value of tumoral expression of both genes was evaluated in patients with lung adenocarcinoma treated with first-line docetaxel and gemcitabine.

EXPERIMENTAL DESIGN

Tumor samples from 96 patients, with stage IIIB (with pleural effusion) or IV lung adenocarcinomas, were analyzed for TXR1 and TSP1 mRNA levels by quantitative real-time PCR, from microdissected cells derived from patients' primary tumors.

RESULTS

The mRNA levels of the two genes were inversely correlated (Spearman's test = -0.49; P < 0.0001). Patients with low TXR1 mRNA levels experienced a longer median time to tumor progression (TTP; P < 0.0001) and median overall survival (mOS; P = 0.001) when compared with patients with high TXR1 expression. Patients with high TSP1 expression presented longer TTP (P = 0.002) and mOS (P < 0.0001) when compared with patients with low TSP1 expression. Moreover, patients with high TSP1 and low TXR1 expression (n = 36) presented higher prolonged TTP (P = 0.009) and mOS (P < 0.0001) compared with patients with high TXR1 and low TSP1 expression. Multivariate analysis showed that high TXR1/low TSP1 expression was an independent prognostic factor for decreased TTP (hazard ratio, 1.7; 95% confidence interval, 1.1-3.27; P = 0.016) and mOS (hazard ratio, 2.55; 95% confidence interval, 1.57-4.15; P < 0.0001).

CONCLUSION

These data confirm the in vitro model of TSP1 and TXR1 effect on taxane resistance in lung adenocarcinomas and merit further evaluation.

Ixabepilone: targeting betaIII-tubulin expression in taxane-resistant malignancies

Microtubule-targeting agents, such as taxanes and epothilones, block mitosis and cell proliferation by targeting the dynamics of the cytoskeleton. The taxanes are widely used for treatment of various malignancies, but primary and acquired resistance to chemotherapy remains a significant clinical concern. Class I, II, III, IV, and V beta-tubulin isotypes are expressed in human tumors. Overexpression of the betaIII-tubulin isotype is one mechanism that can render tumor cells resistant to taxanes. The relative expression of betaIII-tubulin correlates with clinical outcomes in several tumor types, including breast cancer, non-small cell lung cancer, and ovarian cancer. A novel analogue of epothilone B, ixabepilone, has recently been approved in combination with capecitabine for the treatment of patients with anthracycline- and taxane-resistant locally advanced or metastatic breast cancer and as monotherapy in patients whose tumors are resistant or refractory to an anthracycline, a taxane, and capecitabine. The significant antitumor activity of ixabepilone in taxane-resistant tumors may be related to its preferential suppression of the dynamic instability of alpha/betaIII-microtubules in cells expressing high levels of betaIII-tubulin.

Novel microtubule-targeting agents - the epothilones

Epothilones are a new class of antimicrotubule agents currently in clinical trials. Their chemical structures are distinct from taxanes and are more amenable to synthetic modification. Six epothilones have been studied in preclinical and clinical trials: patupilone (epothilone B), ixabepilone (BMS247550), BMS 310705, sagopilone (ZK-EPO), KOS-862 (epothilone D), and KOS-1584. In vitro data have shown increased potency in taxane-sensitive and taxane-resistant cancer cell lines. This enhanced cytotoxic effect has been attributed to epothilone being a poor substrate for p-glycoprotein drug resistance protein and having high affinity to the various beta tubulin isoforms. Phase I clinical data have shown different dose-limiting toxicities for each of the epothilones. These effects are drug specific, dose specific, and schedule of administration specific. While diarrhea and myelosuppression are the dose-limiting toxicities for patupilone and BMS 310705, respectively, neurologic toxicity, as seen with taxanes, is the dose-limiting toxicity of ixabepilone, sagopilone, and KOS-862. In an effort to decrease neurologic toxicity, investigators have modified dosing schedules with limited success. Ixabepilone has the most mature clinical results with published phase II and III data, and regulatory approval for clinical use in the treatment of breast cancer. Ixabepilone has also been combined with other anticancer agents and has regulatory approval in combination with capecitabine for heavily treated breast cancer.

Gemcitabine plus UFT combination chemotherapy as second- or third-line therapy in non-small cell lung cancer: a pilot study

BACKGROUND

Gemcitabine plus UFT combination chemotherapy are highly effective and less toxic in the first line setting in patients with non-small cell lung cancer (NSCLC). The purpose of the study is to confirm the feasibility of this regimen as second- or third-line therapy in NSCLC.

METHODS

Fifteen patients with performance status of 0-1 were enrolled. UFT (tegafur 250 mg/m(2)/day) was administered orally twice a day from days 1-14, and gemcitabine of 900 mg/m(2) was administered intravenously on days 8 and 15 every three weeks on an outpatient setting. The treatment was repeated for at least 3 cycles and continued unless the disease progressed.

RESULTS

The response rate and the disease control rate were 6.7% and 66.7%, respectively. Grade 3-4 toxicities included neutropenia in one patient and elevation of transaminases in one patient. The mean relative dose intensity of gemcitabine and UFT were 0.93 and 0.97, respectively.

CONCLUSION

High disease control rate and less toxicity suggested the potential of gemcitabine and UFT combination chemotherapy as second- or third-line therapy in NSCLC.

Secondary mutations correct fitness defects in Toxoplasma gondii with dinitroaniline resistance mutations

Dinitroanilines (oryzalin, trifluralin, ethafluralin) disrupt microtubules in protozoa but not in vertebrate cells, causing selective death of intracellular Toxoplasma gondii parasites without affecting host cells. Parasites containing alpha1-tubulin point mutations are dinitroaniline resistant but show increased rates of aberrant replication relative to wild-type parasites. T. gondii parasites bearing the F52Y mutation were previously demonstrated to spontaneously acquire two intragenic mutations that decrease both resistance levels and replication defects. Parasites bearing the G142S mutation are largely dependent on oryzalin for viable growth in culture. We isolated 46 T. gondii lines that have suppressed microtubule defects associated with the G142S or the F52Y mutations by acquiring secondary mutations. These compensatory mutations were alpha1-tubulin pseudorevertants or extragenic suppressors (the majority alter the beta1-tubulin gene). Many secondary mutations were located in tubulin domains that suggest that they function by destabilizing microtubules. Most strikingly, we identified seven novel mutations that localize to an eight-amino-acid insert that stabilizes the alpha1-tubulin M loop, including one (P364R) that acts as a compensatory mutation in both F52Y and G142S lines. These lines have reduced dinitroaniline resistance but most perform better than parental lines in competition assays, indicating that there is a trade-off between resistance and replication fitness.

Paclitaxel and docetaxel resistance: molecular mechanisms and development of new generation taxanes

Taxanes represent one of the most promising classes of anticancer agents. Unfortunately, their clinical success has been limited by the insurgence of cellular resistance, mainly mediated by the expression of the MDR phenotype or by microtubule alterations. However, the remarkable relevance of paclitaxel and docetaxel in clinical oncology stimulated intensive efforts in the last decade to identify new derivatives endowed with improved activities towards resistant tumor cells, resulting in a huge number of novel natural and synthetic taxanes. Among them, several structurally different derivatives were found to exhibit a promising behavior against the MDR phenotype in terms of either MDR inhibiting properties, or enhanced cytotoxicity compared to parental drugs, or both. On the other hand, only in more recent years have the first taxanes retaining activity against resistant cancer cells bearing alterations of the tubulin/microtubule system emerged. This review describes the main molecular mechanisms of resistance to paclitaxel and docetaxel identified so far, focusing on the advances achieved in the development of new taxanes potentially useful for the treatment of resistant tumors.

Crystallization and preliminary X-ray diffraction analysis of the beta subunit Yke2 of the Gim complex from Saccharomyces cerevisiae

The Gim complex (GimC) from Saccharomyces cerevisiae is a heterohexameric protein complex, also known as prefoldin (PFD), which binds and stabilizes unfolded target polypeptides and subsequently delivers them to chaperonins for completion of folding. In this study, the crystallization and preliminary X-ray analysis of one of the beta subunits of the Gim complex (Yke2) from S. cerevisiae are described. The purified protein was crystallized by the vapour-diffusion method, producing two types of crystals that belonged to the orthorhombic space group C222 or the primitive monoclinic space group P2(1). The unit-cell parameters for the C-centred orthorhombic crystal were a = 48.2, b = 168.86, c = 131.81 A and the unit-cell parameters for the primitive monoclinic crystal were a = 47.83, b = 134.90, c = 81.50 A, beta = 100.71 degrees . The Yke2 crystals diffracted to 4.2 and 3.1 A resolution, respectively, on a rotating-anode generator under cryoconditions. This is the first report concerning the crystallization of a beta subunit of a eukaryotic prefoldin.

Cellular mechanisms of resistance to anthracyclines and taxanes in cancer: intrinsic and acquired

Taxanes and anthracyclines are two of the most potent and broadly effective classes of chemotherapeutic agents. However, resistance to these agents is common and significantly limits their potential. As such, there is a great need to understand the mechanisms underlying de novo and acquired resistance to these agents. Beyond the resistance barrier lies even greater potential to significantly alter the natural course of human cancer. This review discusses what we currently understand about the mechanisms of resistance to taxanes and anthracyclines. Preclinical models suggest a role for ATP-binding cassette transporters, tubulin isoforms, microtubule-associated proteins, tubulin gene mutations, and mitotic checkpoint signaling proteins in resistance to taxanes. Preclinical models also suggest that drug transport proteins, antioxidant defenses, apoptotic signaling, and topoisomerase modulation may mediate anthracycline resistance. Many of these hypotheses remain untested in appropriately designed clinical studies, but limited clinical evidence will be reviewed. Epothilones represent a novel class of non-taxane microtubule stabilizing agents with distinct drug-resistance profiles. Potential mechanisms behind these differences and their potential role in the treatment of both taxane- and anthracycline-refractory patients are discussed.

STX140 is efficacious in vitro and in vivo in taxane-resistant breast carcinoma cells

PURPOSE

The aim of these studies was to characterize the action of STX140 in a P-glycoprotein-overexpressing tumor cell line both in vitro and in vivo. In addition, its efficacy was determined against xenografts derived from patients who failed docetaxel therapy.

EXPERIMENTAL DESIGN

The effects of STX140, Taxol, and 2-methoxyestradiol (2-MeOE2) on cell proliferation, cell cycle, and apoptosis were assessed in vitro in drug-resistant cells (MCF-7(DOX)) and the parental cell line (MCF-7(WT)). Mice bearing an MCF-7(DOX) tumor on one flank and an MCF-7(WT) tumor on the other flank were used to assess the in vivo efficacy. Furthermore, the responses to STX140 of three xenografts, derived from drug-resistant patients, were assessed.

RESULTS

In this study, STX140 caused cell cycle arrest, cyclin B1 induction, and subsequent apoptosis of both MCF-7(DOX) and MCF-7(WT) cells. Taxol and 2-MeOE2 were only active in the MCF-7(WT) parental cell line. Although both STX140 and Taxol inhibited the growth of xenografts derived from MCF-7(WT) cells, only STX140 inhibited the growth of tumors derived from MCF-7(DOX) cells. 2-MeOE2 was ineffective at the dose tested against both tumor types. Two out of the three newly derived docetaxel-resistant xenografts, including a metastatic triple-negative tumor, responded to STX140 but not to docetaxel treatment.

CONCLUSIONS

STX140 shows excellent efficacy in both MCF-7(WT) and MCF-7(DOX) breast cancer xenograft models, in contrast to Taxol and 2-MeOE2. The clinical potential of STX140 was further highlighted by the efficacy seen in xenografts recently derived from patients who had failed on taxane therapy.

Is class III beta-tubulin a predictive factor in patients receiving tubulin-binding agents?

On the basis of preclinical studies that show overexpression of class III beta-tubulin is associated with resistance to tubulin-binding agents, several investigators have addressed the relation between class III beta-tubulin and outcome in patients treated with such agents. High expression of class III beta-tubulin has been found to be correlated either with low response rates in patients treated with regimens containing taxanes or vinorelbine or with reduced survival in patients with non-small-cell lung cancer, in breast, ovarian, and gastric cancers, and in cancers of unknown primary site. Two studies have shown patients with advanced non-small-cell lung cancer receiving paclitaxel whose tumours expressed high levels of class III beta-tubulin had a lower response to paclitaxel and shorter survival, whereas this variable was not found to be predictive in patients receiving regimens without tubulin-binding agents. Conversely, analysis of samples from patients in the JBR-10 trial, which compared adjuvant chemotherapy to no further therapy in operable non-small-cell lung cancer, showed that chemotherapy seemed to overcome the negative prognostic effect of high levels of expression of class III beta-tubulin and the greatest benefit from cisplatin/vinorelbine was seen in patients with high levels of expression of class III beta-tubulin. Further analyses in operable and advanced non-small-cell lung cancer showed a relation between high expression of class III beta-tubulin and baseline factors such as age under 60 years, adenocarcinoma and large-cell carcinoma histologies, and advanced stage of disease. These results suggest that class III beta-tubulin could be both a prognostic and a predictive factor. Large randomised studies are warranted to determine the prognostic or predictive value of class III beta-tubulin in different settings and tumours.

Biomarkers predictive for clinical efficacy of taxol-based chemotherapy in advanced breast cancer

BACKGROUND

Several studies looked for tumor biomarkers predictive for paclitaxel sensitivity but till now no reliable biomarkers are available. The aim of this study was to verify the potential predictive value of beta-tubulin III and IV, vascular endothelial growth factor-receptor (VEGFR-1), HER2/neu and microvessel density (mVD), in a group of 70 patients with advanced breast cancer (ABC) treated with paclitaxel-based chemotherapy.

PATIENTS AND METHODS

Immunohistochemical analysis (ICA) of HER2, VEGFR-1, mVd, beta-tubulin III and beta-tubulin IV expression were performed in a series of 72 advanced breast cancer. Furthermore apoptotic fraction with TUNEL analysis was evaluated.

RESULTS

beta-tubulin III ICA expression was predictive of progression after chemotherapy. In fact only 2% of the patients with low beta-tubulin III expression progressed after paclitaxel chemotherapy vs 38% of those with high beta-tubulin III tumor expression (P=0.000; by chi(2)). This evidence was confirmed by a logistic regression analysis (OR 28.789; 95% CI 3.212-258,072; P=0.004). There was not a significant association between other biomarkers' characteristics and clinical response to chemotherapy. A Cox multivariate analysis, with overall survival as a dependent variable, showed that only HER2 expression was independently associated (OR 2.39; 95% CI 1.09-5.23; P=0.03) with overall survival.

CONCLUSIONS

We suggest that class III beta-tubulin immunohistochemical expression analysis could be a potentially relevant tumor biomarker for paclitaxel resistance in advanced breast cancer patients.

Strategies for the development of novel Taxol-like agents

Taxol, the first microtubule stabilizer identified, is one of the most important new anticancer drugs to be brought to the clinic in the past 20 yr. The clinical success of TaxolTM led to the development of a second-generation taxane, docetaxel (Taxotere), and multiple third-generation taxane derivatives are under development. Non-taxane microtubule-stabilizers of diverse chemical structures, including the epothilones and discodermolide, show promising preclinical activities and several epothilones are progressing through clinical trials. One important advantage of the new stabilizers is their ability to circumvent drug resistance mechanisms. The clinical development of these new classes of agents suggests that microtubule stabilizers will continue to be important drugs for the treatment of cancer. This chapter provides a brief history of Taxol and the discovery and development status of other classes of microtubule stabilizers. Although all microtubule-stabilizers share similar mechanisms of action, interesting subtle differences among the stabilizers are being detected. This chapter also provides some strategies for identifying the differences among microtubule stabilizers that may help prioritize them for development and clinical use.

Pharmacology, pharmacokinetics and pharmacogenomics of paclitaxel

Paclitaxel is widely used in many cancers including ovarian, breast, lung, head and neck and primary unknown. Paclitaxel is extensively metabolized by cytochrome P450s and excreted in bile. The cytochromes involved include 2C8 and 3A4. This is a review of the pharmacokinetics, pharmacodynamics, drug interactions, metabolism and pharmacogenomics of paclitaxel.