Human glioblastoma U87MG cells transduced with a dominant negative p53 (TP53) adenovirus construct undergo radiation-induced mitotic catastrophe

The FOXO1 inhibitor AS1842856 triggers apoptosis in glioblastoma multiforme and basal-like breast cancer cells

Basal-like breast cancer (BBC) and glioblastoma multiforme (GBM) are poor-prognosis cancers that lack effective targeted therapies and harbor embryonic stem gene expression signatures. Recently, our group and others found that forkhead box transcription factor FOXO1 promotes stem gene expression in BBC and GBM cell lines. Given the critical role of cancer stem cells in promoting cancer progression, we examined the impact of FOXO1 inhibition with AS1842856 (a cell-permeable small molecule that directly binds to unphosphorylated FOXO1 protein to block transcriptional regulation) on BBC and GBM cell viability. We treated a set of BBC and GBM cancer cell lines with increasing concentrations of AS1842856 and found reduced colony formation. Treatment of BBC and GBM cancer cells with AS1842856 led to increases in FAS (FAS cell surface death receptor) and BIM (BCL2L11) gene expression, as well as increased positivity for markers for apoptosis such as annexin V and propidium iodide. Treatment with another FOXO1 inhibitor AS1708727 or FOXO1 RNAi also led to FAS induction. This work is the first to show that targeting BBC and GBM with FOXO1 inhibition leads to apoptosis. These novel findings may ultimately expand the repertoire of therapies for poor-prognosis cancers.

Biology of Glioblastoma Multiforme-Exploration of Mitotic Catastrophe as a Potential Treatment Modality

Glioblastoma multiforme (GBM) represents approximately 60% of all brain tumors in adults. This malignancy shows a high biological and genetic heterogeneity associated with exceptional aggressiveness, leading to a poor survival of patients. This review provides a summary of the basic biology of GBM cells with emphasis on cell cycle and cytoskeletal apparatus of these cells, in particular microtubules. Their involvement in the important oncosuppressive process called mitotic catastrophe will next be discussed along with select examples of microtubule-targeting agents, which are currently explored in this respect such as benzimidazole carbamate compounds. Select microtubule-targeting agents, in particular benzimidazole carbamates, induce G₂/M cell cycle arrest and mitotic catastrophe in tumor cells including GBM, resulting in phenotypically variable cell fates such as mitotic death or mitotic slippage with subsequent cell demise or permanent arrest leading to senescence. Their effect is coupled with low toxicity in normal cells and not developed chemoresistance. Given the lack of efficient cytostatics or modern molecular target-specific compounds in the treatment of GBM, drugs inducing mitotic catastrophe might offer a new, efficient alternative to the existing clinical management of this at present incurable malignancy.

Radiation-Induced Mitotic Catastrophe Enhanced by Gold Nanoparticles: Assessment with a Specific Automated Image Processing Workflow

In recent years, the use of gold-based nanoparticles in radiotherapy has been extensively studied, and the associated radiosensitization mechanism has been evaluated in a variety of in vitro studies. Given that mitotic catastrophe is widely involved in radiation-induced cell death, we evaluated the effect of gold nanoparticles on this key event. Most of the methods currently used to visualize and quantify morphological changes and multinucleation are manual. To circumvent this time-consuming step, we developed and optimized an image processing workflow (based on freely accessible software and plugins) for the automated quantification of mitotic catastrophes. We validated this approach in three cell lines by comparing the number of radiation-induced mitotic catastrophes detected using the automated and manual methods in the presence and absence of nanoparticles. With the Bland-Altman analysis, the automated and manual counting methods were found to be fully interchangeable. The ultimate goal of this work was to determine whether mitotic catastrophe was critically involved in radiationinduced cell death after prior exposure to gold nanoparticles. In the radioresistant U87 cell line, exposure to gold nanoparticles was associated with a shorter time course for the events related to mitotic catastrophe, which peaked at 96 h postirradiation. Mitotic catastrophe was dose-dependent in both the presence and absence of gold nanoparticles. These results demonstrate that cell exposure to gold nanoparticles led to an increase in mitotic catastrophe events, and confirm the marked radiosensitizing effect observed in clonogenic assays.

Resveratrol abrogates the temozolomide-induced G2 arrest leading to mitotic catastrophe and reinforces the temozolomide-induced senescence in glioma cells

Background

Temozolomide (TMZ) is the most widely used drug to treat glioblastoma (GBM), which is the most common and aggressive primary tumor of the Central Nervous System and one of the hardest challenges in oncotherapy. TMZ is an alkylating agent that induces autophagy, apoptosis and senescence in GBM cells. However, therapy with TMZ increases survival after diagnosis only from 12 to 14.4 months, making the development of combined therapies to treat GBM fundamental. One candidate for GBM therapy is Resveratrol (Rsv), which has additive toxicity with TMZ in several glioma cells in vitro and in vivo. However, the mechanism of Rsv and TMZ additive toxicity, which is the aim of the present work, is not clear, especially concerning cell cycle dynamics and long term effects.

Methods

Glioma cell lines were treated with Rsv and TMZ, alone or in combinations, and the induction and the role of autophagy, apoptosis, cell cycle dynamics, protein expression and phosphorylation status were measured. We further evaluated the long term senescence induction and clonogenic capacity.

Results

As expected, temozolomide caused a G2 cell cycle arrest and extensive DNA damage response. Rsv did not reduced this response, even increasing pATM, pChk2 and gammaH2Ax levels, but abrogated the temozolomide-induced G2 arrest, increasing levels of cyclin B and pRb(S807/811) and reducing levels of pWee1(S642) and pCdk1(Y15). This suggests a cellular state of forced passage through G2 checkpoint despite large DNA damage, a scenario that may produce mitotic catastrophe. Indeed, the proportion of cells with high nuclear irregularity increased from 6 to 26% in 48 h after cotreatment. At a long term, a reduction in clonogenic capacity was observed, accompanied by a large induction of senescence.

Conclusion

The presence of Rsv forces cells treated with TMZ through mitosis leading to mitotic catastrophe and senescence, reducing the clonogenic capacity of glioma cells and increasing the chronic effects of temozolomide.

Near-infrared exposure changes cellular responses to ionizing radiation

Near infrared (NIR) and X-rays are radiations from different sides of the wavelength spectrum but both are used during medical treatments, as they have severe impacts on cellular processes, including metabolism, gene expression, proliferation and survival. However, both radiations differ strictly in their consequences for exposed patients: NIR effects are generally supposed to be positive, mostly ascribed to a stimulation of metabolism, whereas X-ray leads to genetic instability, an increase of reactive oxygen species (ROS) and DNA damages and finally to cellular death by apoptosis in tumor cells. Since genomic stability after X-irradiation depends on the mitochondrial metabolism, which is well known to be regulated by NIR, we analyzed the impact of NIR on cellular responses of fibroblasts, retinal progenitor cells and keratinocytes to X-radiation. Our data show that previous exposure to naturally occurring doses of nonthermal NIR combined with clinically relevant X-ray doses leads to (1) increased genomic instability, indicated by elevated ratios of mitotic catastrophes, (2) increased ROS, (3) higher amounts of X-irradiated cells entering S-phase and (4) impaired DNA double-strand break repair. Taken together, our data show tremendous effects of NIR on cellular responses to X-rays, probably affecting the results of radiotherapy after NIR exposure during cancer treatment.

Morphological analysis of CDC2 and glycogen synthase kinase 3β phosphorylation as markers of g2 → m transition in glioma

G2 → M transition is a strategic target for glioma chemotherapy. Key players in G2 → M transition include CDC2 and glycogen synthase kinase 3β (GSK3β), which are highly regulated by posttranslational phosphorylation. This report is a morphological analysis of CDC2 and GSK3β phosphorylation using immunohistochemistry in gliomas with different biological properties. GBM showed a 2.8-fold and 5.6-fold increase in number of cells positive for pThr161CDC2 and a 4.2- and 6.9-fold increase in number of cells positive for pTyr15CDC2 relative to oligodendroglioma and ependymoma, respectively. Elevated labeling for inhibited phospho-CDC2 (pTyr15CDC) correlates with elevated levels of phosphorylated glycogen synthase kinase 3β (GSK3β). 71% of the GBM cases showed intermediate to high intensity staining for pSer9SGK3β 53% of oligodendroglioma, and 73% of ependymoma showed low intensity staining. CDC2 gene amplification correlates with increased survival in glioblastoma multiforme (GBM) and astrocytoma WHO grades II-III, but not in oligodendroglioma WHO grades II-III.

DNA repair and resistance of gliomas to chemotherapy and radiotherapy

The importance of DNA repair as a resistance mechanism in gliomas, the most aggressive form of brain tumor, is a clinically relevant topic. Recent studies show that not all cells are equally malignant in gliomas. Certain subpopulations are particularly prone to drive tumor progression and resist chemo- and radiotherapy. Those cells have been variably named cancer stem cells or cancer-initiating cells or tumor-propagating cells, owing to their possible (but still uncertain) origin from normal stem cells. Although DNA repair reduces the efficacy of chemotherapeutics and ionizing radiation toward bulk gliomas, its contribution to resistance of the rare glioma stem cell subpopulations is less clear. Mechanisms other than DNA repair (in particular low proliferation and activation of the DNA damage checkpoint response) are likely main players of resistance in glioma stem cells and their targeting might yield significant therapeutic gains.

Doublecortin induces mitotic microtubule catastrophe and inhibits glioma cell invasion

Doublecortin (DCX) is a microtubule (MT) binding protein that induces growth arrest at the G2-M phase of cell cycle in glioma and suppresses tumor xenograft in immunocompromised hosts. DCX expression was found in neuronal cells, but lacking in glioma cells. We tested the hypothesis that DCX inhibits glioma U87 cell mitosis and invasion. Our data showed that DCX synthesizing U87 cells underwent mitotic MT spindle catastrophe in a neurabin II dependent pathway. Synthesis of both DCX and neurabin II were required to induce apoptosis in U87 and human embryonic kidney 293T cells. In DCX expressing U87 cells, association of phosphorylated DCX with protein phosphatase-1 (PP1) in the cytosol disrupted the interaction between kinesin-13 and PP1 in the nucleus and yielded spontaneously active kinesin-13. The activated kinesin-13 caused mitotic MT catastrophe in spindle checkpoint. Phosphorylated-DCX induced depolymerization of actin filaments in U87 cells, down-regulated matrix metalloproteinases-2 and -9, and inhibited glioma U87 cell invasion in a neurabin II dependent pathway. Thus, localization of the DCX-neurabin II-PP1 complex in the cytosol of U87 tumor cells inhibited PP1 phosphatase activities leading to anti-glioma effects via (1) mitotic MT spindle catastrophe that blocks mitosis and (2) depolymerization of actin that inhibits glioma cell invasion.

Activation of meiosis-specific genes is associated with depolyploidization of human tumor cells following radiation-induced mitotic catastrophe

Cancer is frequently characterized histologically by the appearance of large cells that are either aneuploid or polyploid. Aneuploidy and polyploidy are hallmarks of radiation-induced mitotic catastrophe (MC), a common phenomenon occurring in tumor cells with impaired p53 function following exposure to various cytotoxic and genotoxic agents. MC is characterized by altered expression of mitotic regulators, untimely and abnormal cell division, delayed DNA damage, and changes in morphology. We report here that cells undergoing radiation-induced MC are more plastic with regards to ploidy and that this plasticity allows them to reorganize their genetic material through reduction division to produce smaller cells which are morphologically indistinguishable from control cells. Experiments conducted with the large-scale digital cell analysis system are discussed and show that a small fraction of polyploid cancer cells formed via radiation-induced MC can survive and start a process of depolyploidization that yields various outcomes. Although most multipolar divisions failed and cell fusion occurred, some of these divisions were successful and originated a variety of cell progeny characterized by different ploidy. Among these ploidy phenotypes, a progeny of small mononucleated cells, indistinguishable from the untreated control cells, is often seen. We report here evidence that meiosis-specific genes are expressed in the polyploid cells during depolyploidization. Tumor cells might take advantage of the temporary change from a promitotic to a promeiotic division regimen to facilitate depolyploidization and restore the proliferative state of the tumor cell population. These events might be mechanisms by which tumor progression and resistance to treatment occur in vivo.

Regulation of the leucocyte chemoattractant receptor FPR in glioblastoma cells by cell differentiation

The G protein-coupled formylpeptide receptor (FPR), known to mediate phagocytic leucocyte chemotaxis in response to bacterial- and host-derived agonists, was expressed by tumor cells in specimens of surgically removed more highly malignant human gliomas. In human glioblastoma cell lines, FPR activation increased cell motility, tumorigenicity and production of angiogenic factors. In studies of the mechanistic basis for the selective expression of FPR in more highly malignant gliomas, we found that the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (Aza), while promoting the differentiation of human glioblastoma cells, downregulated FPR expression. Aza also reduced the global methylation levels in glioblastoma cells and activated the pathway of p53 tumor suppressor. Methylation-specific polymerase chain reaction revealed that Aza treatment of tumor cells reduced the methylation of p53 promoter, which was accompanied by increased expression of p53 gene and protein. In addition, overexpression of p53 in glioblastoma cells mimicked the effect of Aza treatment as shown by increased cell differentiation but reduction in FPR expression, the capacity of tumor sphere formation in soft agar and tumorigenesis in nude mice. Furthermore, Aza treatment or overexpression of the wild-type p53 in glioblastoma cells increased the binding of p53 to FPR promoter region shown by chromatin immunoprecipitation. These results indicate that increased methylation of p53 gene retains human glioblastoma cells at a more poorly differentiated phase associated with the aberrant expression of FPR as a tumor-promoting cell surface receptor.

Death through a tragedy: mitotic catastrophe

Mitotic catastrophe (MC) has long been considered as a mode of cell death that results from premature or inappropriate entry of cells into mitosis and can be caused by chemical or physical stresses. Whereas it initially was depicted as the main form of cell death induced by ionizing radiation, it is today known to be triggered also by treatment with agents influencing the stability of microtubule, various anticancer drugs and mitotic failure caused by defective cell cycle checkpoints. Although various descriptions explaining MC exist, there is still no general accepted definition of this phenomenon. Here, we present evidences indicating that death-associated MC is not a separate mode of cell death, rather a process ('prestage') preceding cell death, which can occur through necrosis or apoptosis. The final outcome of MC depends on the molecular profile of the cell.