Formation Of Aneuploid Cells Research Articles

Empirical single-cell tracking and cell-fate simulation reveal dual roles of p53 in tumor suppression.

The tumor suppressor p53 regulates various stress responses via increasing its cellular levels. The lowest p53 levels occur in unstressed cells; however, the functions of these low levels remain unclear. To investigate the functions, we used empirical single-cell tracking of p53-expressing (Control) cells and cells in which p53 expression was silenced by RNA interference (p53 RNAi). Here, we show that p53 RNAi cells underwent more frequent cell death and cell fusion, which further induced multipolar cell division to generate aneuploid progeny. Those results suggest that the low levels of p53 in unstressed cells indeed have a role in suppressing the induction of cell death and the formation of aneuploid cells. We further investigated the impact of p53 silencing by developing an algorithm to simulate the fates of individual cells. Simulation of the fate of aneuploid cells revealed that these cells could propagate to create an aneuploid cell population. In addition, the simulation also revealed that more frequent induction of cell death in p53 RNAi cells under unstressed conditions conferred a disadvantage in terms of population expansion compared with Control cells, resulting in faster expansion of Control cells compared with p53 RNAi cells, leading to Control cells predominating in mixed cell populations. In contrast, the expansion of Control cells, but not p53 RNAi cells, was suppressed when the damage response was induced, allowing p53 RNAi cells to expand their population compared with the Control cells. These results suggest that, although p53 could suppress the formation of aneuploid cells, which could have a role in tumorigenesis, it could also allow the expansion of cells lacking p53 expression when the damage response is induced. p53 may thus play a role in both the suppression and the promotion of malignant cell formation during tumorigenesis.

Male meiosis in 18 species of 07 genera of the tribe Astereae (Asteraceae) from Western Himalaya

Meiotic studies in 18 species belonging to 7 genera of the tribe Astereae from various localities of Western Himalaya have been analyzed. The chromosome number has been reported for the first time in Aster albescens (n = 9) and A. indamellus (n = 9). Further, intraspecific variability has been reported for the first time in A. thomsonii (n = 27), Bellis perennis (n = 5) and Myriactis nepalensis (n = 18). In India, the chromosome numbers are reported for first time in Aster himalaicus (n = 9), Brachyactis roylei (n = 9), Erigeron bellidioides (n = 9) and E. borealis (n = 9). B-chromosomes have been reported for the first time in Erigeron acer (n = 9 + 1 − 2B). Besides, most of the populations show laggards, chromosome stickiness and cytomixis from early prophase to telophase-II, leading to the formation of aneuploid cells or meiocytes with doubled chromosome number. Such meiotic abnormalities produce unreduced pollen grains and adversely affect pollen viability.

Chromosome nondisjunction during bipolar mitoses of binucleated intermediates promote aneuploidy formation along with multipolar mitoses rather than chromosome loss in micronuclei induced by asbestos.

Asbestos is a well-known occupational carcinogen that can cause aneuploidy during the early stages of neoplastic development. To explore the origins of asbestos-induced aneuploidy, we performed long-term live-cell imaging followed by fluorescence in situ hybridization of chromosomes 8 and 12 in human bronchial epithelial (HBEC) and mesothelial (MeT5A) cells. We demonstrate that asbestos induces aneuploidy via binucleated intermediates resulting from cytokinesis failure. On the one hand, asbestos increases chromosome nondisjunction during bipolar divisions of binucleated intermediates and produces near-tetraploidy. On the other hand, asbestos increases multipolar divisions of binucleated intermediates to produce aneuploidy. Surprisingly, chromosomes in asbestos-induced micronucleated cells are not truly lost by the cells, and do not contribute to aneuploid cell formation in either cell type. These results clarify the cellular source of asbestos-induced aneuploidy. In particular, they show the asbestos-induced disruption of bipolar chromosomal segregation in tetraploid cells, thereby demonstrating the causality between binucleated intermediates and aneuploidy evolution, rather than chromosome loss in micronuclei.

Multipolar mitosis and aneuploidy after chrysotile treatment: a consequence of abscission failure and cytokinesis regression.

Chrysotile, like other types of asbestos, has been associated with mesothelioma, lung cancer and asbestosis. However, the cellular abnormalities induced by these fibers involved in cancer development have not been elucidated yet. Previous works show that chrysotile fibers induce features of cancer cells, such as aneuploidy, multinucleation and multipolar mitosis. In the present study, normal and cancer derived human cell lines were treated with chrysotile and the cellular and molecular mechanisms related to generation of aneuploid cells was elucidated. The first alteration observed was cytokinesis regression, the main cause of multinucleated cells formation and centrosome amplification. The multinucleated cells formed after cytokinesis regression were able to progress through cell cycle and generated aneuploid cells after abnormal mitosis. To understand the process of cytokinesis regression, localization of cytokinetic proteins was investigated. It was observed mislocalization of Anillin, Aurora B, Septin 9 and Alix in the intercellular bridge, and no determination of secondary constriction and abscission sites. Fiber treatment also led to overexpression of genes related to cancer, cytokinesis and cell cycle. The results show that chrysotile fibers induce cellular and molecular alterations in normal and tumor cells that have been related to cancer initiation and progression, and that tetraploidization and aneuploid cell formation are striking events after fiber internalization, which could generate a favorable context to cancer development.

Anomalous Chromosomal Behaviour and Chromosomal Data in Some Members of Subclass Gamopetalae from District Hamirpur (H. P.), India

The present study pertains to the cytomorphology of 19 species belonging to nine families of the subclass Gamopetalae from Hamirpur district (H. P.). Out of these, 5 species are new or varied chromosomes reports. Campanula benthamii (2n=2x=28) and Leucas hyssopifolia (2n=2x=22) are the first ever chromosome counts for the species. Spilanthes acmella (2n=6x=78) and Borreria articularis (2n=4x=52) are varied cytotypes. Meanwhile, the B chromosome is reported for the first time in Leucas lanata (2n=22+0-1B). Almost all of the accessions (with disparity in percentage) show laggards, chromosome stickiness and cytomixis from early prophase to telophase-II, leading to the formation of aneuploid cells or meiocytes with double the normal chromosome number. Such meiotic abnormalities produce unreduced pollen grains and reduce pollen viability.

Aurora B prevents chromosome arm separation defects by promoting telomere dispersion and disjunction.

The segregation of centromeres and telomeres at mitosis is coordinated at multiple levels to prevent the formation of aneuploid cells, a phenotype frequently observed in cancer. Mitotic instability arises from chromosome segregation defects, giving rise to chromatin bridges at anaphase. Most of these defects are corrected before anaphase onset by a mechanism involving Aurora B kinase, a key regulator of mitosis in a wide range of organisms. Here, we describe a new role for Aurora B in telomere dispersion and disjunction during fission yeast mitosis. Telomere dispersion initiates in metaphase, whereas disjunction takes place in anaphase. Dispersion is promoted by the dissociation of Swi6/HP1 and cohesin Rad21 from telomeres, whereas disjunction occurs at anaphase after the phosphorylation of condensin subunit Cnd2. Strikingly, we demonstrate that deletion of Ccq1, a telomeric shelterin component, rescued cell death after Aurora inhibition by promoting the loading of condensin on chromosome arms. Our findings reveal an essential role for telomeres in chromosome arm segregation.

Meiotic studies in some species of tribe Cichorieae (Asteraceae) from Western Himalayas.

The present paper deals with meiotic studies in 15 species belonging to 6 genera of the tribe Cichorieae from various localities of Western Himalayas. The chromosome number has been reported for the first time in Hieracium crocatum (2n = 10) and Lactuca lessertiana (2n = 2x = 16). Further, intraspecific variability has been reported for the first time in H. umbellatum (2n = 2x = 10 and 2n = 6x = 54), Tragopogon dubius (2n = 2x = 14 and 2n = 4x = 28), and T. gracilis (2n = 2x = 14). The chromosome report of 2n = 2x = 10 in Youngia tenuifolia is made for the first time in India. Maximum numbers of the populations show laggards, chromosome stickiness, and cytomixis from early prophase to telophase-II, leading to the formation of aneuploid cells or meiocytes with double chromosome number. Such meiotic abnormalities produce unreduced pollen grains and the reduced pollen viability.

C-terminus-deleted FoxM1 is expressed in cancer cell lines and induces chromosome instability

Forkhead Box M1 (FoxM1) protein is a transcription factor and regulates cell cycle. It is commonly upregulated in human cancer tissue and correlated with poor prognosis, suggesting that the overexpression of FoxM1 plays a critical role in carcinogenesis. In this study, we report the identification and characterization of a new variant of FoxM1, which was first isolated from our laboratory in hepatoma cell lines. Compared with wild-type FoxM1, the new variant lacks of C-terminus of FoxM1 (FoxM1ΔC), which is a transactivation domain. Reverse transcription-polymerase chain reaction and western blot analysis demonstrated that FoxM1ΔC was highly expressed in a variety of cancer cell lines such as HepG2, HeLa, A549, MB231, EJ, U2OS, Hep3B and MCF7, but not expressed in normal human dermal fibroblast (HDF). Immunoprecipitation assay revealed that FoxM1ΔC interacted with wild-type FoxM1. Furthermore, FoxM1ΔC bound to FoxM1 targeted gene promoter region and correlated with dysregulation of wild-type FoxM1. FoxM1ΔC delayed G2/M to G1 progression of cell cycle, decreased Aurora B(T232) phosphorylation and increased chromosome centromere interspace. Finally, FoxM1ΔC induced instability of chromosome and formation of aneuploid cells within 1 month when expressed in HDF. In conclusion, FoxM1ΔC is expressed in cancer cells and dysregulates normal cell cycle and induces chromosome instability.

P-1 Detection and quantitative evaluation of chromosome loss induced in Drosophila wing primordial cells

To detect and quantitatively characterize the abilities of environmental and genetic “agents” to induce chromosome loss in vivo we developed a simple, sensitive, inexpensive and rather fast genetic assay. It is based on the use of an engineered mwh+Y chromosome in Drosophila melanogaster. The mwh+ transgene in the mwh+Y chromosome completely rescues the mutant phenotype of mwh (multiple wing hairs), an outstanding recessive cell marker mutation. Loss of the mwh+Y chromosome in any cell of wing blade primordia leads to the formation of a cell without mwh+ gene function. (Importantly, the loss of the Y chromosome does not reduce cell viability.) Such a cell propagates its new trait during the subsequent rounds of mitoses along proliferation of the primordial cells. Its descending cells remain together and form an mwh mosaic spot (clone) on the developing wing blade, of course on mwh homozygous background. Strength of the studied environmental or genetic “agent” to induce chromosome loss is quantified based on the frequency and size of the mwh mosaic spots. Surveillance cellular mechanisms including spindle assembly checkpoint and mitotic catastrophe ensure the maintenance of chromosome/genome stability through the elimination of cells with e.g. unusual numbers of chromosomes. Reduced or depleted capacities of the surveillance mechanisms may lead to the formation of aneuploid cells. When surviving, such cells can subsequently be the source of mental retardation, miscarriage and cancer. Since components of the spindle assembly checkpoint and mitotic catastrophe appear to be evolutionary conserved, loss of the mwh+Y chromosome may well represent behavior of the chromosomes in general and thus the mwh+Y assay may be included some day in the battery of the so-called genetic toxicity testing procedures. In addition to a number of well known mutagens (X-rays, colchicine, ethyl methanesulfonate, formaldehyde, benzene), we characterized the effects of a parquet varnish and a synthetic thinner. These environmental components do induce chromosome losses, though with low efficiency. We also analyzed the chromosome destabilizing effects of gainand loss-of-function mutant lodestar Drosophila alleles that have been reported to induce chromosome instability. Lodestar, a member of the helicaserelated gene family, is a component of the mitotic catastrophe machinery and is engaged in placing the cohesin complex on the metaphase chromosomes. In Drosophila males, which carry the gain-of-function ldsHor-D mutant allele (that encodes the formation of sticky A777T-LDS molecules), (i) high frequencies of mostly equational nondisjunction occur during spermatogenesis and (ii) the chromosomes are rendered unstable such that they tend to be lost in the descending embryos. Loss of an unstable X chromosome, for example, leads to the formation of XX/X0, female/male mosaic (gynandromorph).

Establishment of Proliferative Tetraploid Cells from Normal Human Fibroblasts

The chromosomal instability of polyploid cells, which leads to the formation of aneuploid cells, is causally related to carcinogenesis in human tissues. However, the precise link between the chromosomal instability of polyploid cells and oncogenic transformation of them remains elusive. This is partly because we lack an experimental model in which non-transformed polyploid human cells can propagate in vitro. In a previous report, we demonstrated that proliferative tetraploid cells can be established from TIG-1 human fibroblasts by treatment with the spindle poison demecolcine (DC, colcemid) for 4 days. However, this procedure could not be applied to other human fibroblast strains because the resulting cells proliferated as a mixture of diploid and tetraploid populations. Here, we report a modified procedure to establish proliferative tetraploid cells from human fibroblasts of the BJ strain with minimum contamination by diploid cells. In the modified procedure, DC-arrested mitotic cells were collected by mitotic shake-off and treated with DC for an additional 3 days. DC-treated cells restarted proliferation as tetraploid cells after several days of growth arrest and showed similar growth to that of untreated diploid cells. The MDM2 antagonist Nutlin-3a activated p53 in established tetraploid cells and suppressed their growth, indicating that these cells have functional p53. These results contradicted the hypothesis that p53 functions as the tetraploidy checkpoint and prevents proliferation of tetraploid cells. Tetraploid cells established by our method could be a valuable model for the study of chromosomal instability and the oncogenic potential of polyploid cells.

Formation of bipolar spindles with two centrosomes in tetraploid cells established from normal human fibroblasts

Tetraploid cells with unstable chromosomes frequently arise as an early step in tumorigenesis and lead to the formation of aneuploid cells. The mechanisms responsible for the chromosome instability of polyploid cells are not fully understood, although the supernumerary centrosomes in polyploid cells have been considered the major cause of chromosomal instability. The aim of this study was to examine the integrity of mitotic spindles and centrosomes in proliferative polyploid cells established from normal human fibroblasts. TIG-1 human fibroblasts were treated with demecolcine (DC) for 4days to induce polyploidy, and the change in DNA content was monitored. Localization of centrosomes and mitotic spindles in polyploid mitotic cells was examined by immunohistochemistry and laser scanning cytometry. TIG-1 cells treated with DC became almost completely tetraploid at 2weeks after treatment and grew at the same rate as untreated diploid cells. Most mitotic cells with 8C DNA content had only two centrosomes with bipolar spindles in established tetraploid cells, although they had four or more centrosomes with multipolar spindles at 3days after DC treatment. The frequency of aneuploid cells increased as established tetraploid cells were propagated. These results indicate that tetraploid cells that form bipolar spindles with two centrosomes in mitosis can proliferate as diploid cells. These cells may serve as a useful model for studying the chromosome instability of polyploid cells.

Aurora Kinase B Expression in Breast Carcinoma: Cell Kinetic and Genetic Aspects

Background: Mitotic deregulations may contribute significantly to cell division errors and the development of aggressive tumor cells. The mitotic kinase Aurora B is essential for chromosome segregation. Its gene is located at 17p13 in close proximity to the TP53 gene. Although the frequent alteration of this locus is well known, the information about the AURKB status and protein expression is limited. Methods: 50 breast carcinoma cases were evaluated for 17p13 status and chromosome 17 ploidy by FISH and for Aurora B protein by immunohistochemistry. Results: Aurora B protein expression showed a strong correlation with cell proliferation (regression coefficient = 0.77). Therefore, the Aurora B/MIB-1 index was used as a measure of expression, which showed a wide range (1–35%, mean 0.32, SD ± 0.28). A gain in the 17p13 chromosome locus could not be shown while a deletion was stated in 10/50 cases including a subset with TP53 and AURKB codeletion in 6/10 cases. The loss of TP53/AURKB loci strongly correlated with aneusomy (p < 0.0001). Conclusion: Elevated Aurora B expression frequently occurs due to an increased cell proliferation rate in breast carcinoma. Codeletion of TP53 and AURKB at 17p13 indicates a concerted mechanism leading to the survival of cell clones with deficient mitotic kinase function which could contribute to the formation of aneuploid cells and an aggressive tumor phenotype.

The Fate of Chrysotile-Induced Multipolar Mitosis and Aneuploid Population in Cultured Lung Cancer Cells

Chrysotile is one of the six types of asbestos, and it is the only one that can still be commercialized in many countries. Exposure to other types of asbestos has been associated with serious diseases, such as lung carcinomas and pleural mesotheliomas. The association of chrysotile exposure with disease is controversial. However, in vitro studies show the mutagenic potential of chrysotile, which can induce DNA and cell damage. The present work aimed to analyze alterations in lung small cell carcinoma cultures after 48 h of chrysotile exposure, followed by 2, 4 and 8 days of recovery in fiber-free culture medium. Some alterations, such as aneuploid cell formation, increased number of cells in G2/M phase and cells in multipolar mitosis were observed even after 8 days of recovery. The presence of chrysotile fibers in the cell cultures was detected and cell morphology was observed by laser scanning confocal microscopy. After 4 and 8 days of recovery, only a few chrysotile fragments were present in some cells, and the cellular morphology was similar to that of control cells. Cells transfected with the GFP-tagged α-tubulin plasmid were treated with chrysotile for 24 or 48 h and cells in multipolar mitosis were observed by time-lapse microscopy. Fates of these cells were established: retention in metaphase, cell death, progression through M phase generating more than two daughter cells or cell fusion during telophase or cytokinesis. Some of them were related to the formation of aneuploid cells and cells with abnormal number of centrosomes.

Entosis: aneuploidy by invasion

Aneuploidy is one of the most prevalent phenotypes of human tumours, but the underlying cause of this phenomenon remains highly debated. Entosis, the invasion of a living cell into another cell's cytoplasm, is now shown to perturb cytokinesis and induce the formation of aneuploid cells.

A non-genetic route to aneuploidy in human cancers

Aneuploidy is common in human tumours and is often indicative of aggressive disease. Aneuploidy can result from cytokinesis failure, which produces binucleate cells that generate aneuploid offspring with subsequent divisions. In cancers, disruption of cytokinesis is known to result from genetic perturbations to mitotic pathways or checkpoints. Here we describe a non-genetic mechanism of cytokinesis failure that occurs as a direct result of cell-in-cell formation by entosis. Live cells internalized by entosis, which can persist through the cell cycle of host cells, disrupt formation of the contractile ring during host cell division. As a result, cytokinesis frequently fails, generating binucleate cells that produce aneuploid cell lineages. In human breast tumours, multinucleation is associated with cell-in-cell structures. These data define a previously unknown mechanism of cytokinesis failure and aneuploid cell formation that operates in human cancers.

Cytogenetic abnormalities caused by extremely low frequency electromagnetic fields in canola.

A meiotic study was performed on Brassica napus exposed to electromagnetic fields. Our investigation used plants grown from dry pretreated seeds with 10 mT for 4 h, wet pretreated seeds with 10 mT for 2 h, and a control line. A lower seed yield was produced in the plants grown from exposed grains. However, the weight of 1000 seeds were higher in the plants grown from exposed grains. The highest value of the weight of 1000 seeds occurred in the plants grown from pretreated dry seeds with 10 mT for 4 h. The size of yielding seeds of plants grown from dry pretreated seeds with 10 mT for 4 h were higher than that of the control seeds and they were of uniform size. A significant difference was observed for meiotic characters studied among genotypes. The mean value of total, terminal, and intercalary chiasmata seems to be reduced significantly in plants grown from exposed seeds, indicating that EM significantly reduces the mean value of the genetic recombination. Other meiotic characteristics including ring bivalent and quadrivalent formation were also reduced significantly in the plants grown from treated seeds. Cytological abnormalities observed are chromosome stickiness, laggards, and micronuclei formation which differed significantly among the genotypes indicating their genetic differences. Cytomixis occurred in treated plants, which led to the formation of aneuploid cells.

Chrysotile effects on human lung cell carcinoma in culture: 3-D reconstruction and DNA quantification by image analysis

BackgroundChrysotile is considered less harmful to human health than other types of asbestos fibers. Its clearance from the lung is faster and, in comparison to amphibole forms of asbestos, chrysotile asbestos fail to accumulate in the lung tissue due to a mechanism involving fibers fragmentation in short pieces. Short exposure to chrysotile has not been associated with any histopathological alteration of lung tissue.MethodsThe present work focuses on the association of small chrysotile fibers with interphasic and mitotic human lung cancer cells in culture, using for analyses confocal laser scanning microscopy and 3D reconstructions. The main goal was to perform the analysis of abnormalities in mitosis of fibers-containing cells as well as to quantify nuclear DNA content of treated cells during their recovery in fiber-free culture medium.ResultsHK2 cells treated with chrysotile for 48 h and recovered in additional periods of 24, 48 and 72 h in normal medium showed increased frequency of multinucleated and apoptotic cells. DNA ploidy of the cells submitted to the same chrysotile treatment schedules showed enhanced aneuploidy values. The results were consistent with the high frequency of multipolar spindles observed and with the presence of fibers in the intercellular bridge during cytokinesis.ConclusionThe present data show that 48 h chrysotile exposure can cause centrosome amplification, apoptosis and aneuploid cell formation even when long periods of recovery were provided. Internalized fibers seem to interact with the chromatin during mitosis, and they could also interfere in cytokinesis, leading to cytokinesis failure which forms aneuploid or multinucleated cells with centrosome amplification.

The Epigenetic Origin of Aneuploidy

Theodore Boveri, eminent German pathologist, observed aneuploidy in cancer cells more than a century ago and suggested that cancer cells derived from a single progenitor cell that acquires the potential for uncontrolled continuous proliferation. Currently, it is well known that aneuploidy is observed in virtually all cancers. Gain and loss of chromosomal material in neoplastic cells is considered to be a process of diversification that leads to survival of the fittest clones. According to Darwin’s theory of evolution, the environment determines the grounds upon which selection takes place and the genetic characteristics necessary for better adaptation. This concept can be applied to the carcinogenesis process, connecting the ability of cancer cells to adapt to different environments and to resist chemotherapy, genomic instability being the driving force of tumor development and progression. What causes this genome instability? Mutations have been recognized for a long time as the major source of genome instability in cancer cells. Nevertheless, an alternative hypothesis suggests that aneuploidy is a primary cause of genome instability rather than solely a simple consequence of the malignant transformation process. Whether genome instability results from mutations or from aneuploidy is not a matter of discussion in this review. It is most likely both phenomena are intimately related; however, we will focus on the mechanisms involved in aneuploidy formation and more specifically on the epigenetic origin of aneuploid cells. Epigenetic inheritance is defined as cellular information—other than the DNA sequence itself—that is heritable during cell division. DNA methylation and histone modifications comprise two of the main epigenetic modifications that are important for many physiological and pathological conditions, including cancer. Aberrant DNA methylation is the most common molecular cancer-cell lesion, even more frequent than gene mutations; tumor suppressor gene silencing by CpG island promoter hypermethylation is perhaps the most frequent epigenetic modification in cancer cells. Epigenetic characteristics of cells may be modified by several factors including environmental exposure, certain nutrient deficiencies, radiation, etc. Some of these alterations have been correlated with the formation of aneuploid cells in vivo. A growing body of evidence suggests that aneuploidy is produced and caused by chromosomal instability. We propose and support in this manuscript that not only genetics but also epigenetics, contribute in a major fashion to aneuploid cell formation.

Pericentromeric demethylation and chromosomal instability induced by chemicals

Background Chromosomal instability, aneuploidy in particular, plays an important role in the initiation, progression and aggressiveness of cancer cells. However, the mechanisms implicated in the formation of aneuploid cells are still not fully understood. DNA methylation is critical for condensation of chromatin and for determination of patterns of genetic expression in somatic cells. Pericentromeric heterochromatin form highly methylated chromosome regions, which sometimes are altered inducing different forms of chromosomal instability, including ruptures, centromere decondensation, formation of isochromosomes and other chromosomal aberrations. However, the role of pericentromeric heterochromatin methylation in the formation of aneuploid cells and the mechanisms implicated in this alteration are not known. In this work we evaluated the role of pericentromeric methylation in the formation of aneuploid cells induced by chemical substances.

Effects of Paclitaxel and Docetaxel on EGFR-Expressing Human Carcinoma Cells Under Normoxic Versus Hypoxic Conditions In Vitro

Human malignant tumors, such as non-small lung, breast, ovarian, head and neck, prostate, stomach and colorectal cancers express a number of growth factor receptors (e.g. EGFR or EGFR family members) that are regulated by tumor hypoxia and contribute to tumor growth and failure of cytotoxic therapy. Paclitaxel and docetaxel are indispensable substances in the treatment of these tumors. Despite the active clinical use of taxanes, little is known about their cytotoxic activity under hypoxia. The aim of the present work was to compare the cytotoxic effect of taxanes, paclitaxel and docetaxel on the EGFR-expressing carcinoma cell lines A431, MDA-MB-231 and NCI-H358 under normoxic and hypoxic conditions. The two taxanes caused different cell cycle distribution and varying aneuploid cell formation under hypoxia. EGFR-overexpressing carcinoma cells showed hypoxia to severely affect the cytotoxicity of paclitaxel, whereas docetaxel preserved its tumor cellkilling activity even at lowest concentrations (0.5 nM), as was observed for both taxanes under normoxia.