Loss in expression of the retinoblastoma gene product in human gliomas is associated with advanced disease

AG488 as a therapy against gliomas

High-grade gliomas such as glioblastomas (GBM) present a deadly prognosis following diagnosis and very few effective treatment options. Here, we investigate if the small molecule AG488 can be an effective therapy against GBM with both anti-angiogenic as well as an anti-microtubule inhibiting modalities, using a human G55 glioma xenograft model in nude mice. From in vitro studies, we report that AG488 incubation reduced cell viability in G55 and HMEC-1 cells more so than TMZ treatment, and AG488 treatment also decreased cell viability in normal astrocytes, but not as much as for G55 cells (p<0.0001). In vivo investigations indicated that AG488 therapy helped reduce tumor volumes (p<0.0001), prolong survival (p<0.01), increase tumor perfusion (p<0.01), and decrease microvessel density (MVD) (p<0.05), compared to untreated mice or mice treated with non-specific IgG, in the G55 xenograft model. Additionally, AG488 did not induce apoptosis in normal mouse brain tissue. Animal survival and tumor volume changes for AG488 were comparable to TMZ or anti-VEGF therapies, however AG488 was found to be more effective in decreasing tumor-related vascularity (perfusion and MVD). AG488 is a potential novel therapy against high-grade gliomas.

Acidosis Acts through HSP90 in a PHD/VHL-Independent Manner to Promote HIF Function and Stem Cell Maintenance in Glioma

Hypoxia is a common feature of solid tumors, which controls multiple aspects of cancer progression. One important function of hypoxia and the hypoxia-inducible factors (HIF) is the maintenance of cancer stem-like cells (CSC), a population of tumor cells that possess stem cell-like properties and drives tumor growth. Among the changes promoted by hypoxia is a metabolic shift resulting in acidification of the tumor microenvironment. Here, we show that glioma hypoxia and acidosis functionally cooperate in inducing HIF transcription factors and CSC maintenance. We found that these effects did not involve the classical PHD/VHL pathway for HIF upregulation, but instead involved the stress-induced chaperone protein HSP90. Genetic or pharmacologic inactivation of HSP90 inhibited the increase in HIF levels and abolished the self-renewal and tumorigenic properties of CSCs induced by acidosis. In clinical specimens of glioma, HSP90 was upregulated in the hypoxic niche and was correlated with a CSC phenotype. Our findings highlight the role of tumor acidification within the hypoxic niche in the regulation of HIF and CSC function through HSP90, with implications for therapeutic strategies to target CSC in gliomas and other hypoxic tumors. Cancer Res; 76(19); 5845-56. ©2016 AACR.

Evaluation of RB Gene and Cyclin-Dependent Kinase Inhibitors P21 and P27 in Pleomorphic Xantoastrocytoma

Pleomorphic xantoastrocytoma (PXA) is a rare, circumscribed astrocytic tumor that usually occurs in the superficial cerebral hemispheres in children and young adults. Most patients have a favorable prognosis, but recurrence and malignant transformation have been reported. In diffuse gliomas, approximately one third demonstrate mutations of the RB gene. Low expression level and high activity of p27 are known to constitute an independent prognostic factor in patients with malignant gliomas, while p21 expressions have variable labeling ranges. The molecular and genetic basis for tumorigenesis and progression of PXA are still largely unknown. In this study, 13 PXAs were examined immunohistochemically for pRb, p21, and p27 expression. Nine PXAs expressed homogeneous pRb positivity in the most nuclei of the tumor cells. Four cases showed an abnormal pRb staining pattern. All PXAs were positive for nuclear expression of p21. Diffuse nuclear positivity of p27 was seen in 10 cases, focal in 2, and in 1 case was not present. The cases with focal and negative p27 nuclear expression had few pRb-positive nuclei. The majority of PXAs appear to have preserved pRb, p21, and p27 functions. Additional studies are necessary to investigate whether cases with altered pRb and p27 expressions are associated with increased risk of recurrence or malignant transformation.

Nerve growth factor: role in growth, differentiation and controlling cancer cell development

Recent progress in the Nerve Growth Factor (NGF) research has shown that this factor acts not only outside its classical domain of the peripheral and central nervous system, but also on non-neuronal and cancer cells. This latter observation has led to divergent hypothesis about the role of NGF, its specific distribution pattern within the tissues and its implication in induction as well as progression of carcinogenesis. Moreover, other recent studies have shown that NGF has direct clinical relevance in certain human brain neuron degeneration and a number of human ocular disorders. These studies, by suggesting that NGF is involved in a plethora of physiological function in health and disease, warrant further investigation regarding the true role of NGF in carcinogenesis. Based on our long-lasting experience in the physiopathology of NGF, we aimed to review previous and recent in vivo and in vitro NGF studies on tumor cell induction, progression and arrest. Overall, these studies indicate that the only presence of NGF is unable to generate cell carcinogenesis, both in normal neuronal and non-neuronal cells/tissues. However, it cannot be excluded the possibility that the co-expression of NGF and pro-carcinogenic molecules might open to different consequence. Whether NGF plays a direct or an indirect role in cell proliferation during carcinogenesis remains to demonstrate.

Sonic hedgehog signalling proteins are frequently expressed in retinoblastoma and are associated with aggressive clinicopathological features

AIMS

This study aimed to examine the expression of Sonic hedgehog (SHH) signalling proteins in retinoblastoma and to evaluate its clinical significance.

METHODS

Seventy-nine enucleated retinoblastoma tumours were investigated immunohistochemically using antibodies against SHH pathway proteins, such as SHH, glioma-associated oncogene homologue (GLI) 1, GLI2, GLI3 and ABC binding cassette G2 (ABCG2). Western blotting of SHH signalling proteins was performed in two retinoblastoma cell lines.

RESULTS

SHH was expressed in most retinoblastoma cases (78 of 79, 98.7%), with 21 cases (26.6%) showing strong expression. GLI1 and GLI2 were also frequently expressed: 67 of 78 cases (85.9%) and 71 of 77 cases (92.2%), respectively. GLI3, a transcriptional repressor, was expressed at low levels in 23 of the 78 cases (29.5%). High ABCG2 expression was found in 23 of the 78 cases (29.5%). High expression levels of these proteins in retinoblastoma cell lines were confirmed by western blotting. The expression of SHH was associated with advanced stages, local invasion and metastasis (all p<0.05).

CONCLUSIONS

SHH signalling molecules were frequently expressed in retinoblastoma tumour cells, and high SHH expression was closely related to an advanced disease status. Our results suggest that the SHH signalling pathway may play a role in the progression of retinoblastoma.

Gene therapy for malignant glioma

Glioblastoma multiforme (GBM) is the most frequent and devastating primary brain tumor in adults. Despite current treatment modalities, such as surgical resection followed by chemotherapy and radiotherapy, only modest improvements in median survival have been achieved. Frequent recurrence and invasiveness of GBM are likely due to the resistance of glioma stem cells to conventional treatments; therefore, novel alternative treatment strategies are desperately needed. Recent advancements in molecular biology and gene technology have provided attractive novel treatment possibilities for patients with GBM. Gene therapy is defined as a technology that aims to modify the genetic complement of cells to obtain therapeutic benefit. To date, gene therapy for the treatment of GBM has demonstrated anti-tumor efficacy in pre-clinical studies and promising safety profiles in clinical studies. However, while this approach is obviously promising, concerns still exist regarding issues associated with transduction efficiency, viral delivery, the pathologic response of the brain, and treatment efficacy. Tumor development and progression involve alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for GBM have been proposed. Improved viral vectors are being evaluated, and the potential use of gene therapy alone or in synergy with other treatments against GBM are being studied. In this review, we will discuss the most commonly studied gene therapy approaches for the treatment of GBM in preclinical and clinical studies including: prodrug/suicide gene therapy; oncolytic gene therapy; cytokine mediated gene therapy; and tumor suppressor gene therapy. In addition, we review the principles and mechanisms of current gene therapy strategies as well as advantages and disadvantages of each.

Immunobiology of malignant gliomas

The immune system of patients with malignant gliomas is profoundly suppressed. The suppression involves both the cellular and humoral immunity and it is mainly attributable to selective depletion and malfunction of helper T cells. Malignant glioma cells express potent immunosuppressive factors such as transforming growth factor-beta(2), inteleukin-10 and prostaglandin E(2). Malignant glioma cells also produce chemoattractants and immunostimulatory cytokines which may activate the immune cells. However, the production of these stimulatory cytokines is not self-destructive to glioma cells because of the immunosuppression. Rather, the tumour cells use them to gain a growth advantage. Indeed the cytokines may act as a growth stimulator of the tumour cells themselves (autocrine mechanism), they may act as angiogenic factors to endothelial cells (paracrine mechanism) or induce the attracted immune cells to secrete angiogenic factors. Some cytokines produced by malignant glioma cells are known to be growth inhibitory to normal astrocytes. Recent studies on tumour suppressor genes suggest a close link between the aberrant genes and the immunobiologic features of malignant glioma cells.

Oncolytic virus therapy for glioblastoma multiforme: concepts and candidates

Twenty years of oncolytic virus development have created a field that is driven by the potential promise of lasting impact on our cancer treatment repertoire. With the field constantly expanding-more than 20 viruses have been recognized as potential oncolytic viruses-new virus candidates continue to emerge even as established viruses reach clinical trials. They all share the defining commonalities of selective replication in tumors, subsequent tumor cell lysis, and dispersion within the tumor. Members from diverse virus classes with distinctly different biologies and host species have been identified. Of these viruses, 15 have been tested on human glioblastoma multiforme. So far, 20 clinical trials have been conducted or initiated using attenuated strains of 7 different oncolytic viruses against glioblastoma multiforme. In this review, we present an overview of viruses that have been developed or considered for glioblastoma multiforme treatment. We outline the principles of tumor targeting and selective viral replication, which include mechanisms of tumor-selective binding, and molecular elements usurping cellular biosynthetic machinery in transformed cells. Results from clinical trials have clearly established the proof of concept and have confirmed the general safety of oncolytic virus application in the brain. The moderate clinical efficacy has not yet matched the promising preclinical lab results; next-generation oncolytic viruses that are either "armed" with therapeutic genes or embedded in a multimodality treatment regimen should enhance the clinical results.

Phenotypic changes associated with exogenous expression of p16INK4a in human glioma cells

The tumor suppressor p16/CDKN2A/INK4a gene is frequently mutated, mostly by homozygous deletions in high-grade gliomas. Although the p16 protein suppresses cell proliferation primarily through inhibition of cell-cycle progression at the G1 phase, other phenotypic changes in glioma cells associated with p16INK4a alterations have not been fully described. To determine the roles of p16 alterations in glioma formation, we have established ecdysone-driven inducible p16 expression in the human glioblastoma cell line CL-4, which were derived from p16-null U87MG cells. Here we show that exogenous p16 expression in CL-4 cells results in morphological changes, with large and flattened cytoplasm, which are associated with increased formation of cytoplasmic actin-stress fibers and vinculin accumulation in the focal adhesion contacts. Adhesion of CL-4 cells to extracellular matrix proteins, such as laminin, fibronectin, and type IV collagen, significantly increased upon exogenous p16 expression, which correlated with increased expression of integrin alpha5 and alphav. Expression of a small GTP-binding protein, Rac, also decreased. Following epidermal growth factor stimulation, phosphorylation of MAP kinases ERK1 and 2 and induction of an early immediate gene product, c-Fos, were significantly reduced in CL-4 cells with p16 expression. These results suggest that the tumor suppressor p16 may exert its antitumor effects through modulation of multiple aspects of glioblastoma phenotypes, including proliferation, invasiveness, and responsiveness to extracellular growth stimuli.

Differential expression of novH and CTGF in human glioma cell lines

Aims-(1) To investigate the expression in human derived glioblastoma cell lines of two structurally related genes, novH (nephroblastoma overexpressed gene) and CTGF (connective tissue growth factor), which encode putative insulin-like growth factor binding proteins of a novel type. (2) To investigate whether the same transcription factors regulate CTGF and novH expression.Methods-Expression of novH and CTGF was analysed in 24 glioblastoma derived cell lines by northern blotting. The CTGF promoter region was characterised by nucleotide sequencing, RNase protection experiments, by transient transfections, and CAT assays.Results-CTGF and novH mRNA levels differed in the glioma cell lines studied. NovH and CTGF genes were not co-expressed in all cell lines. The CTGF promoter region was highly conserved compared with the corresponding region in the mouse (FISP12) and exhibited in vitro transcriptional activity.Conclusions-Although the coding regions of novH and CTGF are highly homologous, their promoter regions are substantially different, suggesting that these two genes may be regulated by different mechanisms. Considering that novH and CTGF are likely to be, respectively, negative and positive regulators of growth and that some glioma cell lines expressing novH are not tumorigenic, expression of these two genes might represent a key element in determining the stage of differentiation or the malignant potential, or both, of some tumour cell lines.

Activated BRAF induces gliomas in mice when combined with Ink4a/Arf loss or Akt activation

Mutations in receptor tyrosine kinase (RTK) growth factor receptors (epidermal growth factor receptor, platelet-derived growth factor receptor, MET and ERBB2), which result in downstream activation of the RAS/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway and PI(3)K/Akt pathway, are found in almost all high-grade gliomas and MAPK signaling is necessary for continued glioma maintenance. In addition, BRAF is mutated in the majority of low-grade gliomas and its expression and activity is significantly increased in the majority of high-grade gliomas. Although the importance of RTKs and RAS signaling in glioma development has been shown, the role of BRAF has yet to be characterized. We evaluated the effect of activated BRAF in glioma formation using the retroviral replication-competent avian leukosis virus long terminal repeat, splice acceptor (RCAS)/TVA system to transfer genes encoding activated forms of BRAF, KRas, Akt and Cre to nestin-expressing neural progenitor cells in Ink4a/Arf(lox/lox) mice in vivo. Although expression of activated BRAF alone is not sufficient for tumorigenesis, the combination of activated BRAF and Akt or BRAF with Ink4a/Arf loss is transforming. Interestingly, activated BRAF generates gliomas with characteristics similar to activated KRas in the context of Akt but not Ink4a/Arf loss. Our studies show a role for BRAF activation and signaling in glioma development and as potential target for glioma therapy.

Use of replication-competent retroviral vectors in an immunocompetent intracranial glioma model

OBJECT

The authors had previously reported on a replication-competent retrovirus (RCR) that has been demonstrated to be stable, capable of effective transduction, and able to prolong survival in an intracranial tumor model in nude mice. The purpose of this study was further investigation of this gene therapy option.

METHODS

The transduction efficiency of RCR in RG2, an immunocompetent intracranial tumor model, was tested in Fischer 344 rats. The immune response to the RCR vector was expressed by the quantification of CD4, CD8, and CD11/b in tumors. The pharmaceutical efficacy of the suicide gene CD in converting prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) was measured using fluorine-19 nuclear magnetic resonance (19F-NMR) spectroscopy. Animal survival data were plotted on Kaplan-Meier survival curves. Finally, the biodistribution of RCR was determined using quantitative real-time polymerase chain reaction (RT-PCR) for the detection of retroviral env gene. There was no evidence of viral transduction in normal brain cells. Neither severe inflammation nor immunoreaction occurred after intracranial injection of RCR-green fluorescent protein compared with phosphate-buffered saline (PBS). The 19F-NMR spectroscopy studies demonstrated that RCR-CD was able to convert 5-FC to 5-FU effectively in vitro. The infection of RG2 brain tumors with RCR-CD and their subsequent treatment with 5-FC significantly prolonged survival compared with that in animals with RG2 transduced tumors treated with PBS. In contrast to the nude mouse model, evidence of virus dissemination to the systemic organs after intracranial injection was not detected using RT-PCR.

CONCLUSIONS

The RCR-mediated suicide gene therapy described in this paper effectively transduced malignant gliomas in an immunocompetent in vivo rodent model, prolonging survival, without evidence of severe intracranial inflammation, and without local transduction of normal brain cells or systemic organs.

Conditionally replicative adenoviral vectors for malignant glioma

High-grade gliomas constitute an important challenge to modern medicine, and although great effort has been made to prolong patient survival, the prognosis for this disease remains poor. Due to recent discoveries in the molecular basis of gliomas, gene therapy is becoming a promising alternative. In this review, we discuss the use of conditionally replicative adenoviral vectors (CRAd) and their applications in neuro-oncology. Such vectors, when rendered conditionally replicative via transductional and transcriptional modifications, offer great promise for patients with malignant brain tumours. We review data from preclinical and clinical studies utilising such vectors and discuss the limitations and future perspectives of CRAd oncolytic therapy for malignant glioma.

A four-dimensional simulation model of tumour response to radiotherapy in vivo: parametric validation considering radiosensitivity, genetic profile and fractionation

The aim of this paper is to present the current state of a four-dimensional simulation model of solid tumour growth and response to radiotherapy developed by our group. The most prominent points of the algorithms describing the fundamental biological phenomena involved are outlined. A specific application of the model to a selected clinical case of glioblastoma multiforme is described and comparative studies are performed, using various exploratory values of the model parameters. Qualitative agreement with clinical observations has been achieved. Special emphasis is laid on the variability of radiosensitivity parameters throughout the cell cycle and on the influence of the genetic profile of the tumour on its radiosensitivity. The results of the simulation are three-dimensionally reconstructed. A valuable tool for getting insight into the biology of tumour growth and response to radiotherapy and at the same time an advanced patient specific decision support system is expected to emerge after the completion of the necessary extensive clinical evaluation.

Effect of HIV-1 Vpr on cell cycle regulators

Cell cycle is one of the most complex processes in the life of a dividing cell. It involves numerous regulatory proteins, which direct the cell through a specific sequence of events for the production of two daughter cells. Cyclin-dependent kinases (cdks), which complex with the cyclin proteins, are the main players in the cell cycle. They can regulate the progression of the cells through different stages regulated by several proteins including p53, p21(WAF1), p19, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRB and E2F. A cell cycle can be altered to the advantage of many viral agents, most notably polyomaviruses, papillomaviruses, adenoviruses, and retroviruses. In addition, viral protein R (Vpr) is a protein encoded by the human immunodeficiency virus type 1 (HIV-1). HIV-1, the causative agent of acquired immunodeficiency syndrome (AIDS), is a member of the lentivirus class of retroviruses. This accessory protein plays an important role in the regulation of the cell cycle by causing G(2) arrest and affecting cell cycle regulators. Vpr prevents infected cells from proliferating, and collaborates with the matrix protein (MA) to enable HIV-1 to enter the nucleus of nondividing cells. Studies from different labs including ours showed that Vpr affects the functions of cell cycle proteins, including p53 and p21(WAF1). Thus, the replication of HIV-1, and ultimately its pathogenesis, are intrinsically tied to cell-cycle control.

Proteases and the biology of glioma invasion

Despite optimal clinical treatment, the prognosis for malignant gliomas remains poor. One of the primary reasons for treatment failure is not diffuse dissemination, but local invasion. Recently, there has been an increase in information regarding specific molecules that determine the aggressiveness and invasion potential of high-grade astrocytic tumors. In particular, expression of matrix metalloproteases in high-grade gliomas appears to correlate with tissue invasiveness. It is the purpose of the present review to describe the connection between alterations in growth-related genes, protease activity, and tumor biology, and how these connections may suggest potential novel therapeutic targets.

Induction of medulloblastomas in p53-null mutant mice by somatic inactivation of Rb in the external granular layer cells of the cerebellum

Medulloblastomas are among the most common malignancies in childhood, and they are associated with substantial mortality and morbidity. The molecular pathogenesis as well as the ontogeny of these neoplasms is still poorly understood. We have generated a mouse model for medulloblastoma by Cre–LoxP-mediated inactivation ofRb and p53 tumor suppressor genes in the cerebellar external granular layer (EGL) cells. GFAP–Cre-mediated recombination was found both in astrocytes and in immature precursor cells of the EGL in the developing cerebellum.GFAP–Cre;RbLoxP/LoxP;p53−/−or LoxP/LoxP mice developed highly aggressive embryonal tumors of the cerebellum with typical features of medulloblastoma. These tumors were identified as early as 7 weeks of age on the outer surface of the molecular layer, corresponding to the location of the EGL cells during development. Our results demonstrate that loss of function of RB is essential for medulloblastoma development in the mouse and strongly support the hypothesis that medulloblastomas arise from multipotent precursor cells located in the EGL.

A mutant oncolytic adenovirus targeting the Rb pathway produces anti-glioma effect in vivo

Effective anti cancer strategies necessitate the use of agents that target tumor cells rather than normal tissues. In this study, we constructed a tumor-selective adenovirus, Delta24, that carries a 24-bp deletion in the E1A region responsible for binding Rb protein. Immunoprecipitation analyses verified that this deletion rendered Delta24 unable to bind the Rb protein. However, titration experiments in 293 cells demonstrated that the Delta24 adenovirus could replicate in and lyse cancer cells with great efficiency. Lysis of most human glioma cells was observed within 10 - 14 days after infection with Delta24 at 10 PFU/cell. In vivo, a single dose of the Delta24 virus induced a 66.3% inhibition (P<0.005) and multiple injections, an 83.8% inhibition (P<0.01) of tumor growth in nude mice. However, normal fibroblasts or cancer cells with restored Rb activity were resistant to the Delta24 adenovirus. These results suggest that the E1A-mutant Delta24 adenovirus may be clinically and therapeutically useful against gliomas and possibly other cancers with disrupted Rb pathway.

Simultaneous alterations of retinoblastoma and p53 protein expression in astrocytic tumors

The genetic alterations frequently involved in glial malignancies are in the tumor suppressor genes, Rb and p53. An altered Rb expression or p53 overexpression is thought to indicate defective tumor suppression and subsequently more aggressive tumors. Therefore, to assess the alterations in the conjoint expression of Rb and p53 proteins in formalin fixed paraffin embedded sections, 64 astrocytic tumors were studied (16 astrocytomas,7 gemistocytic astrocytomas, 19 anaplastic astrocytomas and 22 glioblastomas) using the avidin biotin immunoperoxidase technique. Fifty two cases (81.25%) were found to be positive for p53 protein. Seventeen of these showed aberrant heterogenous staining for pRb, of which 7 were glioblastomas. Only one case of astrocytoma showed aberrant expression of both p53 and Rb. Thus, of the 64 tumors, simultaneous aberrant expression of both p53 and Rb was seen in 21.9% of cases. This was more commonly observed among glioblastoma cases (7/22). No statistical difference was found between the survival rate of heterogenous pRb and p53 positivity in different grades of tumors. In glioblastomas, the survival rate appeared to be less in patients expressing heterogenous pRb, but this was not statistically significant. These results lead us to suspect that p53 and pRb pathways are inactivated, either through mutation or as part of the neoplastic process in astrocytic tumors.

A deletion polymorphism due to Alu-Alu recombination in intron 2 of the retinoblastoma gene: association with human gliomas

The retinoblastoma gene (RB) encodes a tumor suppressor that is inactivated in a number of different types of cancer. We searched for gross alterations of this gene in tumors of the central nervous system by using Southern blot hybridization. A common alteration was found in several tumors and was mapped to the region around exon 2. Nucleotide sequencing showed that the alteration was caused by a 799-bp deletion in intron 2 of the RB gene and was probably due to homologous recombination between two Alu repeats. Deletions of this type have not been found previously in the RB gene. The deletion turned out to be a polymorphism with an allele frequency estimated at 2.2% in 185 patients without cancer. The deletion was found in five of 48 patients with brain tumors (allele frequency of 5.2%). This difference is not statistically significant (P = 0.149, Fisher's exact test). Confining the analysis only to glioma brain tumors revealed a statistically significant difference compared with the cancer-free patient controls (P = 0.027, Fisher's exact test). Further study is needed to determine if the deletion is a weak brain cancer-predisposing mutation or a harmless polymorphism. Finding this mutation in a tumor and the germline DNA of a retinoblastoma patient could lead to incorrect estimation of the heritability of a tumor.

P16 deletion and mutation analysis in human brain tumors

We screened human primary and recurrent malignant glioma, juvenile pilocytic astrocytoma, medulloblastoma, and meningioma tissue specimens for alterations in p16 gene structure. Single strand conformation polymorphism (SSCP) analysis was used to screen for point mutations, and a quantitative polymerase chain reaction-based assay was used to screen for homozygous gene deletions. In malignant glioma specimens, homozygous p16 gene deletions were significantly more common in high-grade tumors than in low-grade gliomas. Point mutations causing alteration in predicted protein structure were not detected. Medulloblastomas showed rare homozygous deletions and no point mutations. No mutations were detected in meningiomas.

p53-dependent G1 arrest and p53-independent apoptosis influence the radiobiologic response of glioblastoma

PURPOSE

Loss of the p53 tumor suppressor gene has been associated with tumor progression, disease relapse, poor response to antineoplastic therapy, and poor prognosis in many malignancies. We have investigated the contribution of p53-mediated radiation-induced apoptosis and G1 arrest to the well described radiation resistance of glioblastoma multiforme (GM) cells.

METHODS AND MATERIALS

Radiation survival in vitro was quantitated using linear quadratic and repair-saturation mathematical models. Isogenic derivatives of glioblastoma cells differing only in their p53 status were generated using a retroviral vector expressing a dominant negative mutant of p53. Radiation-induced apoptosis was assayed by Fluorescence-activated cell sorter (FACS) analysis, terminal deoxynucleotide transferase labeling technique, and chromatin morphology. Cells were synchronized in early G1 phase and mitotic and labeling indices were measured.

RESULTS

Radiation-induced apoptosis of GM cells was independent of functional wild-type p53 (wt p53). Decreased susceptibility to radiation-induced apoptosis was associated with lower alpha values characterizing the shoulder of the clonogenic radiation survival curve. Using isogenic GM cells differing only in their p53 activity, we found that a p53-mediated function, radiation-induced G1 arrest, could also influence the value of alpha and clonogenic radiation resistance. Inactivation of wt p53 function by a dominant negative mutant of p53 resulted in a significantly diminished alpha value with no alteration in cellular susceptibility to radiation-induced apoptosis. The clonal derivative U87-LUX.8 expressing a functional wt p53 had an alpha (Gy-1) value of 0.609, whereas the isogenic clonal derivative U87-175.4 lacking wt p53 function had an alpha (Gy-1) value of 0.175.

CONCLUSION

We conclude that two distinct cellular responses to radiation, p53-independent apoptosis and p53-dependent G1-arrest, influence radiobiological parameters that characterize the radiation response of glioblastoma cells. Further understanding of the molecular basis of GM radiation resistance will lead to improvement in existing therapeutic modalities and to the development of novel treatment approaches.

Karyotype analyses of 20 human glioma cell lines

Human malignant gliomas are frequently associated with loss of gonosomes and chromosomes 13, 17, and 22. Their progression from anaplastic glioma to glioblastoma is marked by additional loss of chromosome 10. In addition, structural and numerical aberrations of chromosome 7 are frequently found. We report on the karyotypes of a series of 20 human gliomas of which 11 were analysed as established cell lines; 9 cases were investigated in early culture, 5 of which later also became established lines. In addition to the frequently reported overrepresentation of chromosome 7, four cell lines with polysomy for chromosome 22 were seen. A high incidence of structural chromosomal aberrations was present in early cultures as well as in cell lines after various in vitro passages. We found that the general characteristics of karyotypic aberrations found in early cultures or direct preparations of dispersed tumour material were reflected in the pattern of aberrations present in cell lines at much later time points. Thus it appears as if no systematic changes can be attributed to long-term cultures. Suspicious losses of chromosomes 14, 18, and 19 or gain of chromosome 22 indicate that individual cases may have originated due to other mechanisms than the ones already hypothesized, i.e., different suppressor genes or amplification of genes other than the EGF-R-gene. None of the established cell lines had a genomic rearrangement of c-erbB 1, c-erbB 2 or of the p 53 gene.