Multipolar Mitotic Spindles Research Articles

T0070907 inhibits repair of radiation-induced DNA damage by targeting RAD51

T0070907 (T007), a PPARγ inhibitor, can reduce α and β tubulin proteins in some cancer cell lines. Thus, T007 has been suggested as an antimicrotubule drug. We previously reported that T007 increased radiosensitivity by inducing mitotic catastrophe in cervical cancer cells. In this study, we investigated the underlying mechanisms of the T007-mediated increase in radiosensitivity. T007 pre-treatment attenuated RAD51 protein levels and ionising radiation (IR)-induced nuclear foci formation, resulting in more frequent centrosome amplification and multipolar mitotic spindle formation in cervical cancer cells. Furthermore, T007 pre-treatment delayed the clearance of IR-induced γ-H2AX and increased radiosensitivity in cervical cancer cells. In contrast, none of these changes were observed in normal cells. Our data demonstrate for the first time that T007 impairs the repair of IR-induced DNA double-strand breaks by inhibiting RAD51, a key protein in homologous recombination repair, increases IR-induced mitotic catastrophe, and leads to increased death of IR-treated cells. These findings support T007 as a potential RAD51 inhibitor to increase tumour response to radiation therapy.

Abstract 2296: An isoform of BARD1, associated with many types of cancer, is a driver of oncogenesis by inducing telomere aberrations in vitro and in vivo

Abstract BARD1 has tumor suppressor functions by binding to BRCA1 and to p53 via RING finger and ankyrin repeats, respectively. The BARD1-BRCA1 heterodimer has E3 ligase activity, and the BARD1-p53 interaction promotes apoptosis. The expression of N-terminally truncated RING-less BARD1 isoforms, however, was correlated with poor prognosis in various cancers. We performed overexpression experiments with various isoforms of BARD1 and found that BARD1δ, lacking RING and ANK regions, induces cell cycle arrest, multipolar mitotic spindles, genomic instability, and telomere aberrations. Co-localization studies and interaction assays in HeLa, MCF7, or HEK 293 cells, using tagged BARD1δ and full length (FL) BARD1, showed that the BRCT domains, present in BARD1δ and FL BARD1, interact with centrosome binding proteins and telomere binding proteins. BARD1δ overexpressing cells showed multipolar spindles and telomere alterations. Similar telomere alterations were observed in cells with reduced expression of FL BARD1 by siRNA. This is consistent with the observed distinct telomeric abnormalities in blood cells of patients with a BARD1 germline mutation that causes translation of a truncated protein lacking the BRCT domains. CRE-inducible BARD1δ transgenic mice showed dose-dependent growth arrest and tumor formation in various organs. These in vitro and in vivo observations suggest that BARD1δ plays a significant role in tumorigenesis by inducing genomic and telomere instability. Citation Format: Maxim Pilyugin, Pierre-Alain Andre, Magdalena Ratajska, Irmgard Irminger-Finger. An isoform of BARD1, associated with many types of cancer, is a driver of oncogenesis by inducing telomere aberrations in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2296. doi:10.1158/1538-7445.AM2015-2296

A novel family of katanin-like 2 protein isoforms (KATNAL2), interacting with nucleotide-binding proteins Nubp1 and Nubp2, are key regulators of different MT-based processes in mammalian cells.

Katanins are microtubule (MT)-severing AAA proteins with high phylogenetic conservation throughout the eukaryotes. They have been functionally implicated in processes requiring MT remodeling, such as spindle assembly in mitosis and meiosis, assembly/disassembly of flagella and cilia and neuronal morphogenesis. Here, we uncover a novel family of katanin-like 2 proteins (KATNAL2) in mouse, consisting of five alternatively spliced isoforms encoded by the Katnal2 genomic locus. We further demonstrate that in vivo these isoforms are able to interact with themselves, with each other and moreover directly and independently with MRP/MinD-type P-loop NTPases Nubp1 and Nubp2, which are integral components of centrioles, negative regulators of ciliogenesis and implicated in centriole duplication in mammalian cells. We find KATNAL2 localized on interphase MTs, centrioles, mitotic spindle, midbody and the axoneme and basal body of sensory cilia in cultured murine cells. shRNAi of Katnal2 results in inefficient cytokinesis and severe phenotypes of enlarged cells and nuclei, increased numbers of centrioles and the manifestation of aberrant multipolar mitotic spindles, mitotic defects, chromosome bridges, multinuclearity, increased MT acetylation and an altered cell cycle pattern. Silencing or stable overexpression of KATNAL2 isoforms drastically reduces ciliogenesis. In conclusion, KATNAL2s are multitasking enzymes involved in the same cell type in critically important processes affecting cytokinesis, MT dynamics, and ciliogenesis and are also implicated in cell cycle progression.

ATF5 Connects the Pericentriolar Materials to the Proximal End of the Mother Centriole

Although it is known that the centrioles play instructive roles in pericentriolar material (PCM) assembly and that the PCM is essential for proper centriole formation, the mechanism that governs centriole-PCM interaction is poorly understood. Here, we show that ATF5 forms a characteristic 9-fold symmetrical ring structure in the inner layer of the PCM outfitting the proximal end of the mother centriole. ATF5 controls the centriole-PCM interaction in a cell-cycle- and centriole-age-dependent manner. Interaction of ATF5 with polyglutamylated tubulin (PGT) on the mother centriole and with PCNT in the PCM renders ATF5 as a required molecule in mother centriole-directed PCM accumulation and in PCM-dependent centriole formation. ATF5 depletion blocks PCM accumulation at the centrosome and causes fragmentation of centrioles, leading to the formation of multi-polar mitotic spindles and genomic instability. These data show that ATF5 is an essential structural protein that is required for the interaction between the mother centriole and the PCM.

Triphenylphosphonium Cations of the Diterpenoid Isosteviol: Synthesis and Antimitotic Activity in a Sea Urchin Embryo Model.

A series of novel triphenylphosphonium (TPP) cations of the diterpenoid isosteviol (1, 16-oxo-ent-beyeran-19-oic acid) have been synthesized and evaluated in an in vivo phenotypic sea urchin embryo assay for antimitotic activity. The TPP moiety was applied as a carrier to provide selective accumulation of a connected compound into mitochondria. When applied to fertilized eggs, the targeted isosteviol TPP conjugates induced mitotic arrest with the formation of aberrant multipolar mitotic spindles, whereas both isosteviol and the methyltriphenylphosphonium cation were inactive. The structure-activity relationship study revealed the essential role of the TPP group for the realization of the isosteviol effect, while the chemical structure and the length of the linker only slightly influenced the antimitotic potency. The results obtained using the sea urchin embryo model suggested that TPP conjugates of isosteviol induced mitotic spindle defects and mitotic arrest presumably by affecting mitochondrial DNA. Since targeting mitochondria is considered as an encouraging strategy for cancer therapy, TPP-isosteviol conjugates may represent promising candidates for further design as anticancer agents.

α- and β-Santalols Directly Interact with Tubulin and Cause Mitotic Arrest and Cytotoxicity in Oral Cancer Cells.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with no major advancements in treatment over the past 40 years. The current study explores the biological effects of East Indian sandalwood oil (EISO) and its two major constituents, α- and β-santalol, against a variety of HNSCC lines. All three agents exhibited cytotoxic effects and caused accumulation of cells in the G2/M phases of the cell cycle. Additionally, treatment with these agents caused formation of multipolar mitotic spindles similar to those observed upon treatment of cells with compounds that affect microtubule polymerization. Indeed, the santalols, as well as EISO, inhibited the polymerization of purified tubulin, indicating for the first time that these compounds have the ability to directly bind to tubulin and affect microtubule formation. Modeling studies suggest that the santalols can weakly bind to the colchicine site on tubulin, and topical administration of EISO to a HNSCC xenograft inhibited tumor growth with no observed toxicities. Therefore, santalols can directly interact with tubulin to inhibit the polymerization of microtubules, similarly to established classes of chemotherapeutic agents, albeit with greatly reduced potency that is not associated with the classic toxicity associated with most other compounds that interact directly with tubulin.

Dis-organizing centrosomal clusters: specific cancer therapy for a generic spread?

Cancer is a leading cause of mortality and the annual incidence of new cancer cases is rising worldwide. Due to the frequent development of resistance and the side effects of established anti-cancer drugs, the quest for new drugs with improved therapeutic features goes on. In contrast to cytotoxic chemotherapy of the past, the concept of targeted chemotherapy attempts to increase specificity of therapy by attacking tumor-related mechanisms. A novel emerging treatment concept represents the inhibition of centrosomal clustering. The centrosome regulates mitotic spindle formation assuring uniform separation of chromosomes to daughter cells. Many tumors contain supernumerary centrosomes, which contribute to aneuploidy induction via multipolar mitotic spindle formation. As spindle multipolarity leads to cell death, tumor cells developed centrosomal clustering mechanism to prevent multipolar spindle formation by coalescence of multiple centrosomes into two functional spindle poles. Inhibition of centrosome clustering represents a novel strategy for drug development and leads to the formation of multipolar spindles and subsequent cell death. In the present review, we report advances in understanding the biology of centrosomal clustering as well as enlist compounds capable of inducing the formation of multipolar spindles such as indolquinolizines, integrin-linked kinase inhibitors (QLT-0267), noscapinoids (EM011), phthalamide derivatives (TC11), griseofulvin, phenanthridines (PJ-34), CCC1-01, CW069 GF-15, colcemid, nocodazole, paclitaxel, and vinblastine. We also present in silico result of compounds that bind to γ-tubulin under the ambit of centrosomal clustering inhibition. We observed maximum binding efficacy in GF-15, CW069, paclitaxel and larotaxel with GF-15 exhibiting least energy of -8.4 Kcal/mol and 0.7 μM Pki value.

Cucurbitacin-I inhibits Aurora kinase A, Aurora kinase B and survivin, induces defects in cell cycle progression and promotes ABT-737-induced cell death in a caspase-independent manner in malignant human glioma cells

Because STAT signaling is commonly activated in malignant gliomas as a result of constitutive EGFR activation, strategies for inhibiting the EGFR/JAK/STAT cascade are of significant interest. We, therefore, treated a panel of established glioma cell lines, including EGFR overexpressors, and primary cultures derived from patients diagnosed with glioblastoma with the JAK/STAT inhibitor cucurbitacin-I. Treatment with cucurbitacin-I depleted p-STAT3, p-STAT5, p-JAK1 and p-JAK2 levels, inhibited cell proliferation, and induced G2/M accumulation, DNA endoreduplication, and multipolar mitotic spindles. Longer exposure to cucurbitacin-I significantly reduced the number of viable cells and this decrease in viability was associated with cell death, as confirmed by an increase in the subG1 fraction. Our data also demonstrated that cucurbitacin-I strikingly downregulated Aurora kinase A, Aurora kinase B and survivin. We then searched for agents that exhibited a synergistic effect on cell death in combination with cucurbitacin-I. We found that cotreatment with cucurbitacin-I significantly increased Bcl-2/Bcl-xL family member antagonist ABT-737-induced cell death regardless of EGFR/PTEN/p53 status of malignant human glioma cell lines. Although >50% of the cucurbitacin-I plus ABT-737 treated cells were annexin V and propidium iodide positive, PARP cleavage or caspase activation was not observed. Pretreatment of z-VAD-fmk, a pan caspase inhibitor did not inhibit cell death, suggesting a caspase-independent mechanism of cell death. Genetic inhibition of Aurora kinase A or Aurora kinase B or survivin by RNA interference also sensitized glioma cells to ABT-737, suggesting a link between STAT activation and Aurora kinases in malignant gliomas.

A novel strategy for targeted killing of tumor cells: Induction of multipolar acentrosomal mitotic spindles with a quinazolinone derivative mdivi-1

Traditional antimitotic drugs for cancer chemotherapy often have undesired toxicities to healthy tissues, limiting their clinical application. Developing novel agents that specifically target tumor cell mitosis is needed to minimize the toxicity and improve the efficacy of this class of anticancer drugs. We discovered that mdivi-1 (mitochondrial division inhibitor-1), which was originally reported as an inhibitor of mitochondrial fission protein Drp1, specifically disrupts M phase cell cycle progression only in human tumor cells, but not in non-transformed fibroblasts or epithelial cells. The antimitotic effect of mdivi-1 is Drp1 independent, as mdivi-1 induces M phase abnormalities in both Drp1 wild-type and Drp1 knockout SV40-immortalized/transformed MEF cells. We also identified that the tumor transformation process required for the antimitotic effect of mdivi-1 is downstream of SV40 large T and small t antigens, but not hTERT-mediated immortalization. Mdivi-1 induces multipolar mitotic spindles in tumor cells regardless of their centrosome numbers. Acentrosomal spindle poles, which do not contain the bona-fide centrosome components γ-tubulin and centrin-2, were found to contribute to the spindle multipolarity induced by mdivi-1. Gene expression profiling revealed that the genes involved in oocyte meiosis and assembly of acentrosomal microtubules are highly expressed in tumor cells. We further identified that tumor cells have enhanced activity in the nucleation and assembly of acentrosomal kinetochore-attaching microtubules. Mdivi-1 inhibited the integration of acentrosomal microtubule-organizing centers into centrosomal asters, resulting in the development of acentrosomal mitotic spindles preferentially in tumor cells. The formation of multipolar acentrosomal spindles leads to gross genome instability and Bax/Bak-dependent apoptosis. Taken together, our studies indicate that inducing multipolar spindles composing of acentrosomal poles in mitosis could achieve tumor-specific antimitotic effect, and mdivi-1 thus represents a novel class of compounds as acentrosomal spindle inducers (ASI).

Abstract LB-116: Cep55, a master regulator of cytokinesis in breast cancer pathogenesis

Abstract Defects in the number, structure, and function of centrosomes can generate mono- or multipolar mitotic spindles and cytokinesis failure resulting in aneuploidy and chromosome instability, which are common characteristics of tumour cells. Centrosomal proteins thus play central roles in the execution of proper cell division. Cep55 is a centrosomal protein required for proper segregation of two daughter cells during cytokinesis. It often elevated in wide range of cancer types including breast cancer. To ascertain the functional role of Cep55 in breast cancer pathogenesis, we performed publically available data mining as well as IHC staining in a cohort of breast cancer patients and found that elevated levels of Cep55 is significantly associated with p53 mutation, basal like subtype, relapse free and distant-metastasis free survival. Immunoblot analysis of non-malignant and breast cancer cell lines revealed higher expression of Cep55 protein in basal like subtype. RNAi mediated Cep55 depletion in cultured human breast cancer cells resulted in decreased cell proliferation, induction of apoptosis in-vitro and failure to establish xenografts in-vivo. Moreover, these cells failed to establish lung colonisation due to less proliferative, migrative and invasive capacity in experimental metastasis models. In an initial effort to identify causal effective of Cep55 mediated breast cancer pathogenesis, we found that Cep55-depleted cells that survive following long term culture have restored their ploidy compared with aneuploid cells that have constitutively high levels of Cep55. Moreover, these non-tumorigenic cells also have defect in major signalling networks assessed by Kinexus proteomic array. In line with this finding, we found that constitutive overexpression of Cep55 in non-transformed mammary epithelial cells, MCF-10a induced ERK1/2 and STAT3 signalling possibly due to increase in chromosome instability. Taken together, these results indicate that Cep55 promotes breast cancer initiation, progression and lung colonisation through pleiotropic effect and genomic instability that likely contribute to aneuploidy state of breast cancer tumours Citation Format: Murugan Kalimutho, Jacinta Simmons, Winnie Fernando, Jodi Saunus, Kevin Spring, Sunil Lakhani, Fares Al-Ejeh, Kum Kum Khanna. Cep55, a master regulator of cytokinesis in breast cancer pathogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-116. doi:10.1158/1538-7445.AM2014-LB-116

Abstract 5085: Inducing multipolarity of acentrosomal mitotic spindles as a novel tumor-specific targeting strategy revealed by the antimitotic effect of mdivi-1

Abstract Traditional antimitotic drugs for cancer chemotherapy often have undesired toxicity to healthy tissue, limiting clinical application. Developing tumor-specific antimitotic strategies is necessary to improve the efficacy of drugs in the selective eradication of tumor cells. In this study, we discovered mdivi-1 (mitochondrial division inhibitor-1), which was originally reported as an inhibitor of mitochondrial fission protein dynamin-related protein 1 (Drp1), specifically disrupts M phase cell cycle progression only in human tumor cells and not in non-transformed fibroblasts and epithelial cells. The antimitotic effect of mdivi-1 is Drp1-independent, as M phase abnormality induced by mdivi-1 was observed in both Drp1 wild-type and Drp1 knockout MEF cells. We also identified that the tumor transformation process required for the antimitotic effect of mdivi-1 is downstream of SV40 large T and small t antigens - but not hTERT-mediated immortalization. Mdivi-1 induces multipolar mitotic spindles in tumor cells regardless of centrosome number. Acentrosomal spindle poles, which do not contain bona-fide centrosome components γ-tubulin and centrin-2, were found to contribute to the spindle multipolarity. The formation of such aberrant mitotic spindles leads to gross genome instability and apoptotic cell death through Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP). Gene expression profiling comparing non-transformed and transformed cells revealed that the genes involved in assembly of acentrosomal spindles are highly up-regulated in tumor cells, thus providing the mechanism underlying the preferential formation of acentrosomal multipolar spindles in tumor cells compared to normal cells after mdivi-1 treatment. Taken together, our studies imply that mdivi-1 represents a novel class of quinazolinone compounds that function as acentrosomal spindle inducers (ASI). We suggest that promoting the assembly of multipolar mitotic spindles composed of acentrosomal poles could serve as a novel strategy in achieving a tumor-specific antimitotic effect. (Work was supported by P30CA047904, GM087798, UPCI and PA Dept of Health CURE program) Note: This abstract was not presented at the meeting. Citation Format: Jingnan Wang, Wei Qian, Masahiro Shuda, Jianfeng Li, Lucas Santana-Santos, Robert W. Sobol, Bennett Van Houten. Inducing multipolarity of acentrosomal mitotic spindles as a novel tumor-specific targeting strategy revealed by the antimitotic effect of mdivi-1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5085. doi:10.1158/1538-7445.AM2014-5085

Radmis, a Novel Mitotic Spindle Protein that Functions in Cell Division of Neural Progenitors

Developmental dynamics of neural stem/progenitor cells (NSPCs) are crucial for embryonic and adult neurogenesis, but its regulatory factors are not fully understood. By differential subtractive screening with NSPCs versus their differentiated progenies, we identified the radmis (radial fiber and mitotic spindle)/ckap2l gene, a novel microtubule-associated protein (MAP) enriched in NSPCs. Radmis is a putative substrate for the E3-ubiquitin ligase, anaphase promoting complex/cyclosome (APC/C), and is degraded via the KEN box. Radmis was highly expressed in regions of active neurogenesis throughout life, and its distribution was dynamically regulated during NSPC division. In embryonic and perinatal brains, radmis localized to bipolar mitotic spindles and radial fibers (basal processes) of dividing NSPCs. As central nervous system development proceeded, radmis expression was lost in most brain regions, except for several neurogenic regions. In adult brain, radmis expression persisted in the mitotic spindles of both slowly-dividing stem cells and rapid amplifying progenitors. Overexpression of radmis in vitro induced hyper-stabilization of microtubules, severe defects in mitotic spindle formation, and mitotic arrest. In vivo gain-of-function using in utero electroporation revealed that radmis directed a reduction in NSPC proliferation and a concomitant increase in cell cycle exit, causing a reduction in the Tbr2-positive basal progenitor population and shrinkage of the embryonic subventricular zone. Besides, radmis loss-of-function by shRNAs induced the multipolar mitotic spindle structure, accompanied with the catastrophe of chromosome segregation including the long chromosome bridge between two separating daughter nuclei. These findings uncover the indispensable role of radmis in mitotic spindle formation and cell-cycle progression of NSPCs.

GSI promotes vincristine-induced apoptosis by enhancing multi-polar spindle formation

Gamma secretase inhibitors (GSI), cell-permeable small-molecule inhibitors of gamma secretase activity, had been originally developed for the treatment of Alzheimer disease. In recent years, it has been exploited in cancer research to inhibit Notch signaling that is aberrantly activated in various cancers. We previously found that GSI could synergize with anti-microtubule agent, vincristine (VCR) in a Notch-independent manner. Here, we delineate the underlying cell cycle-related mechanism using HeLa cells, which have strong mitotic checkpoints. GSI enhanced VCR-induced cell death, although GSI alone did not affect cell viability at all. GSI augmented VCR-induced mitotic arrest in a dose-dependent manner, which was preceded by apoptotic cell death, as shown by an increase in Annexin V-positive and caspase-positive cell population. Furthermore, GSI amplified multi-polar spindle formation triggered by VCR. Altogether, we show the evidence that GSI enhances VCR-induced apoptosis in HeLa cells via multi-polar mitotic spindle formation, independent of Notch signaling. These data suggest that one or more GS substrates, yet to be identified, in a post-GS processed form, may play a role in maintaining functional centrosomes/mitotic spindles. More significantly, the synergistic effect of GSI in combination with VCR could be exploited in clinical setting to improve the efficacy of VCR.

Abstract 1750: Clinically relevant paclitaxel concentrations cause chromosome missegregation rather than mitotic arrest.

Abstract Paclitaxel is a chemotherapeutic, microtubule-stabilizing drug used to treat a variety of cancers, including those of the breast. In the neoadjuvant setting, paclitaxel effects tumor shrinkage in up to half of patients. Identification of a biomarker to predict response to paclitaxel would reduce side effects and improve patient outcomes. It has long been known that micromolar concentrations of paclitaxel cause cells in culture to arrest in mitosis, which can lead to cell death. However, the concentration range found within patient tumors remains unclear, both because it has not been directly measured and because paclitaxel accumulates intracellularly up to 1000 fold. In a pilot clinical trial, we are directly measuring the intratumoral drug concentration in breast tumors following neoadjuvant paclitaxel treatment. Our preliminary data support the hypothesis that treatment of cultured cells with a low nanomolar concentration more accurately models the intratumoral drug levels in breast cancer patients. Unlike treatment with micromolar concentrations, treatment with low nanomolar paclitaxel does not cause a significant mitotic arrest. Rather, cells treated with low nanomolar paclitaxel frequently proceed through mitosis with multipolar mitotic spindles, resulting in chromosome missegregation and the production of two or more daughter cells. This alternative mechanism of action may explain why tumors treated with paclitaxel fail to show an increase in mitotic index. Previous studies have shown that low rates of chromosome missegregation are well tolerated, but high rates of chromosome missegregation cause cell death due to loss of both copies of one or more essential chromosomes. Therefore, the fidelity of chromosome segregation may be of use as a predictor of response to paclitaxel. In chromosomally stable breast cancer cells, exposure to paclitaxel for two days is sufficient to induce aneuploidy, and within three days there is an increase in cell death. However, a subset of cells are able to survive in low nM paclitaxel for over one week, and survival is higher than in cells which exhibit chromosomal instability (CIN), and have a preexisting rate of chromosome missegregation during division. In patients, chromosomal stability is of potential use as a predictive biomarker to select patients most likely to respond to paclitaxel treatment. Citation Format: Lauren M. Zasadil, Mark Burkard, Beth A. Weaver. Clinically relevant paclitaxel concentrations cause chromosome missegregation rather than mitotic arrest. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1750. doi:10.1158/1538-7445.AM2013-1750

Co-treatment with vorinostat synergistically enhances activity of Aurora kinase inhibitor against human breast cancer cells

Aurora kinases (AKs) regulate multiple components of mitotic cell division in eukaryotic cells. Aurora A is frequently amplified or overexpressed in breast cancer cells leading to aberrant chromosome segregation, genomic instability, and activation of oncogenic pathways. In the present studies, we determined the effects of treatment with the pan-AK inhibitor MK-0457 and/or the pan-histone deacetylase inhibitor vorinostat against human breast cancer cells that were either ER-, PR-, and HER2- (MDA-MB-468 and MDA-MB-231) or exhibited Aurora A amplification (BT-474 and MDA-MB-231 cells). Treatment with MK-0457 depleted p-AKs levels and their activity, as well as induced G2/M accumulation, DNA endoreduplication, multipolar mitotic spindles, and apoptosis of the breast cancer cells. Similar apoptotic effects were observed with treatment with the Aurora A-specific inhibitor, MLN8237. Treatment with vorinostat induced hsp90 acetylation and inhibited its chaperone association with AKs, leading to depletion of AKs and Survivin. Exposure of the siRNA to AK A also induced apoptosis, which was augmented by co-treatment with MK-0457 and vorinostat. Co-treatment with vorinostat enhanced MK-0457-mediated inhibition of the activities of Aurora A and Aurora B, leading to synergistic in vitro activity against human breast cancer cells. Co-treatment with MK-0457 and vorinostat also caused greater tumor growth inhibition and superior survival of mice bearing MDA-MB-231 xenografts. These pre-clinical findings indicate that combined treatment with a pan-AK inhibitor or an Aurora A-specific inhibitor and vorinostat represents a novel therapeutic strategy for the treatment of Aurora A-amplified and/or triple negative breast cancers.

Centrosome Amplification and Chromosomal Instability in Human and Animal Parthenogenetic Cell Lines

Parthenotes have been proposed as a source of embryonic stem cells but they lack the centriole which is inherited through the sperm in all mammalian species, except for rodents. We investigated the centrosome of parthenotes and parthenogenetic embryonic stem cells using parthenogenetic and biparental pig pre-implantation embryos, human and pig parthenogenetic and biparental embryonic stem cells, sheep fibroblasts derived from post implantation parthenogenetic and biparental embryos developed in vivo. We also determined the level of aneuploidy in parthenogenetic cells. Oocytes of all species were activated using ionomycin and 6-dimethylaminopurine (6-DMAP). Over 60% of parthenogenetic blastomeres were affected by an excessive number of centrioles. Centrosome amplification, was observed by microscopical and ultrastructural analysis also in parthenogenetic cell lines of all three species. Over expression of PLK2 and down regulation of CCNF, respectively involved in the stimulation and inhibition of centrosome duplication, were present in all species. We also detected down regulation of spindle assembly checkpoint components such as BUB1, CENPE and MAD2. Centrosome amplification was accompanied by multipolar mitotic spindles and all cell lines were affected by a high rate of aneuploidy. These observations indicate a link between centrosome amplification and the high incidence of aneuploidy and suggest that parthenogenetic stem cells may be a useful model to investigate how aneuploidy can be compatible with cell proliferation and differentiation.

Abstract 2030: Mechanisms of E2F-mediated centrosome amplification in HER2 positive breast cancer

Abstract Centrosome amplification associates with most human cancers and has been suggested to trigger tumor initiation and progression. Centrosomes are the major microtubule organizing centers in animal cells. They are duplicated once in each cell cycle and duplicated centrosomes establish mitotic spindle bipolarity. Centrosome duplication is tightly regulated because deregulated centrosome duplication leads to centrosome amplification, multipolar and pseudobipolar mitotic spindles that potentiate chromosome instability and may trigger tumorigenesis. One of the tumor types in which the relationship between centrosome amplification and tumorigenesis is well known are breast cancers, as most breast tumors exhibit centrosome amplification. Centrosome amplification arises through various mechanisms, such as deregulation of cell cycle regulators, oncogenes and tumor suppressor genes. Our laboratory discovered that HER2 positive breast cancer cells and K-RasG12D pre-malignant mouse mammary lesions displayed overexpressed E2F1-3 transcriptional activators. Although E2Fs are involved in various cellular processes, including the regulation of the cell and centrosome duplication cycles and differentiation, the role of E2Fs in centrosome amplification in breast tumors is unknown. To study the role of the E2F activators in centrosome amplification, we first assayed centrosome amplification in the E2F-overexpressing HER2 positive breast cancer cells, HCC1954, JIMT1 and SKBR3. There was increased centrosome amplification in the HER2 positive cell lines HCC1954, JIMT1 or SKBR3 relative to MCF10A control mammary epithelial cells. To find if centrosome amplification shown in HER2 positive cells overexpressing E2F1-3 was E2F-specific, the siRNA-mediated silencing technique was applied to transiently knock-down the E2F activators (E2F1-3a) and cells were assayed for centrosome amplification. In addition, to permanently knockdown E2Fs in HER2 positive cells, shRNA-mediated silencing technique will be applied. Western blots confirmed that E2Fs knockdown was efficient, followed by decreased centrosome amplification in HER2 positive cells downregulated for E2F1 and E2F3a; results for E2F2 are still awaiting. These data suggested that centrosome amplification detected in HER2 positive cells is specific to the E2F activators. Future experiments will involve the identification of E2F-dependent transcriptional targets mediating centrosome amplification in HER2 positive cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2030. doi:1538-7445.AM2012-2030

Hyperthermia induces cytoskeletal alterations and mitotic catastrophe in p53-deficient H1299 lung cancer cells

Hyperthermia is used in cancer therapy, however much remains to be discovered regarding its mechanisms of action at the cellular level. In this study, the effects of hyperthermia on cell death, survival, morphology and the cytoskeleton were investigated in a non-small cell lung cancer cell line, H1299. Despite the fact that this cell line is widely used in research, it has not yet been tested for heat shock sensitivity. Cells were given a 30-min heat shock at 43.5°C and 45°C and left to recover at 37°C for 24 and 48h. 24h after heat shock treatment, we monitored changes in the organization of the cytoskeleton using immunofluorescence microscopy. The number of actin stress fibers was significantly reduced, microtubules formed a looser meshwork, a portion of the cells possessed multipolar mitotic spindles, whereas vimentin filaments collapsed into perinuclear complexes. 48h following heat stress, most of the cells showed recovery of the cytoskeleton, however we observed a considerable number of giant cells that were multinucleated or contained one enlarged nucleus. The data obtained by MTT assay showed a dose-dependent decrease of cell viability, while flow cytometric analysis revealed an increase in the number of cells with externalized phosphatidylserine. The results suggest that one of the modes of heat-induced cell death in H1299 cells is mitotic catastrophe, which probably ends in apoptosis.

Patulin: Mechanism of genotoxicity

Patulin is a frequently found food contaminant mainly produced by the fungi Aspergillus and Penicillium. Patulin is suspected to be clastogenic, mutagenic, teratogenic and in higher concentrations cytotoxic. Here, we investigate the mechanism of the patulin-induced genotoxicity. Chromosomal damage was detected as micronucleus and nucleoplasmic bridge formation. Due to the activity of patulin on SH-groups, glutathione is a major compound in the cellular defense against patulin and the depletion of glutathione level with buthionine sulfoximine led to a strong increase in the genoxicity of patulin. A modified version of the alkaline comet assay was carried out to show the cross-linking properties of patulin. As a mechanistic hypothesis, we suspect patulin to cause structural DNA damage by cross-linking, yielding nucleoplasmic bridges and as a later consequence, micronucleus formation. The structural DNA damage may also lead to cell cycle delays, the consequence of which may be the observed centrosome amplification and formation of multipolar mitotic spindles.

Natural product–inspired cascade synthesis yields modulators of centrosome integrity

In biology-oriented synthesis, the scaffolds of biologically relevant compound classes inspire the synthesis of focused compound collections enriched in bioactivity. This criterion is, in particular, met by the scaffolds of natural products selected in evolution. The synthesis of natural product-inspired compound collections calls for efficient reaction sequences that preferably combine multiple individual transformations in one operation. Here we report the development of a one-pot, twelve-step cascade reaction sequence that includes nine different reactions and two opposing kinds of organocatalysis. The cascade sequence proceeds within 10-30 min and transforms readily available substrates into complex indoloquinolizines that resemble the core tetracyclic scaffold of numerous polycyclic indole alkaloids. Biological investigation of a corresponding focused compound collection revealed modulators of centrosome integrity, termed centrocountins, which caused fragmented and supernumerary centrosomes, chromosome congression defects, multipolar mitotic spindles, acentrosomal spindle poles and multipolar cell division by targeting the centrosome-associated proteins nucleophosmin and Crm1.