A tiger behind many doors: multiple genetic pathways to malignant glioma

EPIDERMAL GROWTH FACTOR RECEPTOR ANTAGONISTS: NOVEL THERAPY FOR THE TREATMENT OF HIGH-GRADE GLIOMAS

Overactivation of epidermal growth factor receptor (EGFR) signaling has been recognized as an important step in the pathogenesis and progression of multiple forms of cancer of epithelial origin. This knowledge has led to a surge of interest in novel anticancer therapies targeting key constituents of the EGFR signal transduction pathway. Several molecular strategies have been developed recently to modulate either EGFR or the downstream signal beyond the cell surface receptor. The important role of aberrant EGFR signaling in the progression of malignant gliomas makes EGFR-targeted therapies of particular interest in this form of cancer. The use of anti-EGFR therapies against malignant brain tumors, although in its infancy, promises to yield exciting results as these new drugs probably will enhance the usefulness of existing therapies.

High expression of Aurora-B/Aurora and Ipll-like midbody-associated protein (AIM-1) in astrocytomas

OBJECTIVE

Impaired regulation of Aurora-B/AIM-1 expression in human cells causes chromosomal abnormality and instability, and recent observations of high expression but not mutation of Aurora-B/AIM-1 in human cancers imply that Aurora-B/AIM-1 might be a candidate molecule for cancer progression. We analyzed the effects of modification of Aurora-B/AIM-1 expression on the growth of a human glioma cell line and the expression of Aurora-B/AIM-1 in astrocytomas.

METHODS

A glioma cell line, U251MG was transfected with wild type (WT) of Aurora-B/AIM-1 or kinase-inactive mutant of Aurora-B/AIM-1 in order to test the effects of overexpression of WT or kinase-inactive Aurora-B/AIM-1 on cell morphology and cell growth. Brain tissue samples were obtained during surgery and processed for reverse transcription-polymerase chain reaction, immunofluorescence in order to analyze the expression of Aurora-B/AIM-1 mRNA and protein.

RESULTS

Exogenous overexpression of WT of Aurora-B/AIM-1 in cultured cells of U251MG produced multinuclearity and increased ploidy, and inhibited the growth of tumor cells. Exogenous overexpression of kinase-inactive Aurora-B/AIM-1 in a human glioma cell line also suppressed the tumor cell growth without affecting ploidy. Aurora-B/AIM-1 was highly expressed in astrocytomas and U251MG, and mRNA and protein levels of Aurora-B/AIM-1 in tumor tissues well correlated with their histological malignancy (World Health Organization grading). Survival time also negatively correlated with the levels of Aurora-B/AIM-1 mRNA in tumor samples.

CONCLUSION

Aurora-B/AIM-1 was highly expressed in high-grade gliomas and its expression was well correlated with histological malignancy and clinical outcomes. The modification of the level of Aurora-B/AIM-1 expression might be a new target for glioma therapy.

Inverse correlation between genetic aberrations and malignancy grade in ependymal tumors: a paradox?

OBJECTIVE

The goal of our study was to investigate the inverse correlation between number of genetic aberrations and malignancy grade in ependymal tumors at the ploidy level.

METHODS

we examined seven myxopapillary ependymomas (mpEs) (WHO grade I), 28 spinal and cerebral ependymomas (Es) (WHO grade II), and 18 cerebral anaplastic ependymomas (aEs) (WHO grade III) using image DNA cytometry. The ploidy status was correlated with clinicopathological characteristics and with the results obtained by comparative genomic hybridization (CGH) analysis that we performed in about half of these tumors.

RESULTS

mpEs were exclusively located in the spinal cord and aEs in the cerebrum only, whereas Es were located in both the spinal cord and brain. We found aneuploidy or tetraploidy to be common in the group of mpEs (6 out of 7) and much less frequent in Es (6 out of 28) and aEs (4 out of 18). Three-year postoperative survival was 100% for mpEs, 100% for spinal Es, 92% for cerebral Es, and 33% for aEs. Our CGH results in a selection of these tumors revealed the highest number of genetic aberrations in the mpEs (average 16; n = 2), a lower number in Es (average 12; n = 11) and the lowest number in aEs (average 5; n = 6). Interestingly, in the group of Es and aEs, a high number of genetic aberrations as detected by CGH was not correlated with aneuploidy or tetraploidy. Three patients, all with mpEs had local seeding.

CONCLUSION

These results underline that mpEs are distinctly different from Es and aEs at the genetic level and that extensive genomic alterations and aneuploidy in ependymal tumors are not in itself an indicator of malignant behavior.

EGF-R and PDGF-R, but not bcl-2, overexpression predict overall survival in patients with low-grade astrocytomas

BACKGROUND AND OBJECTIVES

Therapy of malignant glioma tumors is based on histology and clinical factors. However, comparable lesions may correspond with important prognostic differences. Our purpose was to analyze retrospectively the prognostic input of platelet-derived growth factor receptor (PDGF-R), epidermal growth factor (EGF-R), and bcl-2 expression in 103 malignant gliomas from uniformly treated patients.

METHODS

The expression of the antigens was analyzed by immunohistochemistry (IHC). Prognostic evaluation was performed with the multivariate proportional hazards model. The follow-up period lasted 19 (5-122) months for survivors.

RESULTS

We observed that almost 50% of gliomas showed high expression of PDGF-R, while a lower expression of EGF-R and bcl-2 was found. No association between the main prognostic factors in malignant glioma (sex, age, histological grade, and Karnofsky score) and the labeling index (LI) of these antigens was observed. We found that only PDGF-R and EGF-R overexpression were associated with a shorter survival in patients with World Health Organization (WHO) II astrocytomas, being both associations independent of known prognostic factors, as shown by Cox model. Besides, we confirmed other authors' results that high histological grade and low performance score were associated with worse prognosis.

CONCLUSIONS

PDGF-R and EGF-R expression could be relevant in determining the prognosis of low-grade astrocytomas (LGAs) and in providing a more objective mechanism for their classification.

Progressive paralysis associated with diffuse astrocyte anaplasia in Delta202 mice homozygous for a transgene encoding the SV40 T antigen*

A convenient transgenic astrocytoma model in delta202 mice, homozygous for a construct encoding the early region of the SV40 virus genome, is described. In the offspring of crosses between delta202 mice heterozygous for the transgene nearly 60% were transgenic; one third of these developed progressive paralysis starting in the hindlimbs at approximately 35 days of age and died at 90 +/- 30 days of age. In affected mice proliferating-non-neuronal cells immunostained with antibodies to the GFAP, an astrocyte marker, whose number increased with age were found in the white matter of the brain, cerebellum and spinal cord, and progressive degeneration and necrosis of spinal motoneurons was observed that-may explain the paralysis. The early onset and reproducible time course of the neurological disease suggest that homozygous delta202 mice, whose proliferating astrocytes appear to damage spinal motoneurons, are a useful model to study astrocyte differentiation, function and tumorigenesis.

Characterization of the 1p/19q Chromosomal Loss in Oligodendrogliomas Using Comparative Genomic Hybridization Arrays (CGHa)

Loss of genetic material from the short arm of chromosome 1 and the long arm of chromosome 19 in anaplastic oligodendrogliomas has been shown to predict responsiveness to chemotherapy. Currently, the most common approach used to detect this loss of 1p/19q material employs microsatellite/FISH analysis using markers along the length of these chromosome arms. This analysis is highly focused and carried out on a locus-by-locus basis and gives no indication of the extent of other genetic changes occurring in the tumor cells, which may be important in future studies to explore genetic heterogeneity in the response to treatment. We have investigated the use of comparative genomic hybridization arrays (CGHa) of bacterial artificial chromosomes (BACs) in the identification of tumor samples that carry loss of the 1p/19q chromosome arms. These BAC arrays carry approximately 6,000 BAC clones and provide an average inter-BAC resolution of 500 Kb. Using this approach we have clearly shown that 1p/19q loss in these cases, when compared with microsatellite-mediated detection of loss of heterozygosity, is due to physical hemizygous deletion of the whole chromosome arms in all cases. Furthermore, CGHa allows the simultaneous definition of the other genetic changes that are occurring in the tumors. From our survey of 14 tumors consisting of low-grade oligodendrogliomas (n = 6), anaplastic oligodendrogliomas (n = 5), or mixed oligoastrocytoma (n = 3). we were able to demonstrate the presence of additional genetic markers that were characteristic of the various grades of tumors as well as novel changes that had occurred. Thus, CGHa provides a robust, high throughput, genome-wide analysis of genetic changes of oligodendroglial tumors that can be used not only to predict chemo-responsiveness but also place these genetic changes in the context of other abnormalities in the same experiment without the need for extensive chromosome or LOH analysis.

Genetic analysis of human glioblastomas using a genomic microarray system

Genomic microarray systems can simultaneously provide substantial genetic and chromosomal information in a relatively short time. We have analyzed genomic DNA from frozen sections of 30 cases of primary glioblastomas by GenoSensor Array 300 in order to characterize gene amplifications, gene deletions, and chromosomal information in the whole genome. Genes that were frequently amplified included RFC2/CYLN2 (63.3%), EGFR (53.3%), IL6 (53.3%), ABCB1 (MDR1) (36.7%), and PDGFRA (26.7%). Genes that were frequently deleted included (56.7%), FGFR2 (66.7%), MTAP (60.0%), DMBT1 CDKN2A (p16)/MTAP (50.0%), PIK3CA (43.3%), and EGR2 (43.3%), but deletion of RB1 or TP53 was rarely detected. Chromosomal gains were observed frequently for 7q (33.3%), 7p (20.0%), and 17q (13.3%). Loss of the 10q was frequently detected in 13 of 30 cases (46.7%). Loss of the entire chromosome 10 was seen in 9 of 30 cases (30.0%), and was often accompanied by EGFR amplification (7 cases, 77.8%). The GenoSensor Array 300 proved to be useful for identification of genome-wide molecular changes in glioblastomas. The obtained microarray profile can also yield valuable insight into the molecular events underlying carcinogenesis of brain tumors and may provide clues about clinical correlations, including response to treatment.

Frequent LOH at chromosome 12q22-23 and Apaf-1 inactivation in glioblastoma

Glioblastoma (GB) often has loss of heterozygosity on the chromosomes, 1p, 10p, 10q, 11p, 17p, 19q, 22q, and several others. In the case of chromosome 12q, however, it remains to be seen whether LOH occurs. Apaf-1, the apoptotic protease activating factor-1, located at chromosome 12q22-23, is a major effecter of the p53 mediated apoptosis pathway, and Apaf-1 inactivation due to chromosome 12q22-23 LOH and hypermethylation may be involved in some of the neoplasms in malignancy. However, little is known about the frequency of the 12q22-23 LOH or the state of Apaf-1 in GB. To elucidate their involvement in GB, we analyzed a series of 33 GBs for chromosome 12q22-23 LOH, Apaf-1 mRNA expression, and Apaf-1 protein expression, using microsatellite analysis, reverse transcription (RT)-PCR analysis, and immunohistochemical (IHC) analysis, respectively. We also evaluated if and how the 12q22-23 LOH correlated with the p53 gene mutation and EGFR gene amplification. Chromosome 12q22-23 LOH was detected in 14 (42%) of 33 cases. Among the examined cases with LOH at 12q22-23, a low expression of Apaf-1 mRNA was detected in 9 (69%) of 13 cases, and a low expression of Apaf-1 protein was detected in 12 (86%) of 14 cases. The 12q22-23 LOH was significantly correlated with low expression of mRNA and protein (p<0.05, p<0.001 respectively). The p53 gene mutation and EGFR gene amplification were found in 13 cases (39%) and 8 cases (24%), respectively, and these gene alterations were inversely correlated. However, 12q22-23 LOH had no correlations with the p53 gene mutation or EGFR gene amplification. Six of 9 GBs (67%) with neither p53 gene mutation nor EGFR gene amplification tested positive for 12q22-23 LOH. These GBs are likely to belong to another subset independent from the 2 common genetic subsets in GB (one with p53 gene mutation and without EGFR gene amplification, and the other with EGFR gene amplification and without p53 gene mutation). Twenty-three (70%) out of the 33 GBs with the 12q22-23 LOH also tested positive for Apaf-1 inactivation or p53 gene mutation. This high frequency of alterations in the apoptosis-associated factors prompts a speculation that abrogation of the Apaf-1 and p53 mediated apoptosis pathway may play an important role in the tumorigenesis of GB.

Classification of glioblastoma multiforme in adults by molecular genetics

Recent advances in cytogenetic and molecular methodologies have elucidated certain principal characteristics of oncogenesis in glioblastoma multiforme. The earliest clues implicate gene sequence alterations, such as gene amplification and numerical gain or loss of function in specific chromosomes. Genetic classification and expression patterns have thus been constructed, conferring the likelihood of two types of glioblastoma, primary (de novo) as opposed to secondary (evolving from a pre-existing low-grade glioma). The former group of tumors exhibits more frequent occurrences of EGFR gene amplification, whereas the latter group relies strongly on TP53 gene inactivation. Many other tumor suppressor genes and oncogenes have been discovered. Most gene alterations induce cell cycle dysfunction on a complex molecular level. Further insight into tumor genesis by means of genomic assays may aid in predicting the clinical behavior of glioblastoma and in providing individualized potential targets for therapeutic agents.

Prognostic value of loss of heterozygosity around three candidate tumor suppressor genes on chromosome 10q in astrocytomas

We thoroughly examined loss of heterozygosity (LOH) around three candidate tumor suppressor genes on chromosome 10q to determine whether LOH of each tumor suppressor gene is associated with the previously defined clinical prognostic indices. We also examined whether LOH can help predict prognostic variables in astrocytomas. We selected samples from 40 astrocytomas (grades 2-4), performed Ki-67 immunostaining, and counted positive cells. Using DNA from aliquots of tumor blocks and leukocytes, we investigated LOH around the PTEN, NEURL, and DMBTI genes (10q23.3-26.1) with the silver staining procedure. We then statistically evaluated the relationship among histological features, regional LOH on chromosome 10q, and survival. The mean survival period for patients with LOH around PTEN was 7.2 months after surgery, while that for patients without LOH around PTEN was 21.4 months. Thus, LOH around PTEN was closely associated with a reduced overall survival (p = 0.0020) but LOH at NEURL or DMBTI was not (p > 0.05). The combined features of an increase in histological grading and Ki-67-positive cells and the presence of LOH around PTEN significantly correlated with poor prognosis. These factors may be useful predictors of survival, and LOH analysis of tumor suppressor genes on chromosome 10q can contribute greatly to the treatment of patients with astrocytoma.

Genome-wide survey for chromosomal imbalances in ganglioglioma using comparative genomic hybridization

Ganglioglioma is a mixed neuronal and glial tumor first described by Perkin in 1926. Because of its rare occurrence in the central nervous system, the pathogenesis of this neoplasm is still largely unknown. Previous studies of ganglioglioma mainly focused on histologic features, immunohistochemical analysis, clinical treatment, and patient outcome. Very few cytogenetic and molecular genetic studies have been reported on this neoplasm. To better understand the mechanism underlying the development of ganglioglioma, we performed comparative genomic hybridization analysis to investigate chromosomal imbalances across the entire genome in five cases of gangliogliomas. Loss of genetic material on the short arm of chromosome 9 was a common genetic alteration found in three of five cases. Overrepresentation of partial or the whole chromosome 7 was another recurrent chromosomal imbalance, confirmed by fluorescence in situ hybridization. Immunohistochemical analysis was performed; all five cases revealed no reaction or low expression for epidermal growth factor receptor antibody. Our study highlights chromosomal regions for further fine mapping and investigation of candidate tumor suppressor genes involved in the pathogenesis of ganglioglioma.

Multiplexed analysis of post-PCR fluorescence-labeled microsatellite alleles and statistical evaluation of their imbalance in brain tumors

Detection of the loss of chromosomal regions in cancerous tissues has diagnostic and prognostic relevance, and the development of a reliable and cost-effective technique for this is clinically important. Here we present an efficient technique for quantitative detection of microsatellite alleles, using a post-PCR fluorescence-labeling procedure and multiplexed analysis. We also present a new statistical method for the interpretation of the data that permits reliable and sensitive evaluation of the allelic status of sampled DNA. A high-resolution analysis of allelic imbalance on chromosomes 1p, 10 and 19q in 28 glioma samples of various types using this method revealed that allelic imbalances are more frequent than have been reported, suggesting the diagnostic value of this method in examining the genetic profiles of gliomas.

Genetic imbalances in pleomorphic xanthoastrocytoma detected by comparative genomic hybridization and literature review

Pleomorphic xanthoastrocytoma (PXA) is a rare, low-grade astrocytic tumor found in the central nervous system. Histologically, the tumor is characterized by markedly pleomorphic and lipidized cells. Although most of the patients have a favorable prognosis, a small number of cases undergoing recurrence or progression to anaplastic astrocytoma were reported. Very few genetic studies have been performed on PXA because of its rarity and the pathogenesis of this neoplasm is largely unknown. In order to provide an overview of genetic alterations in PXA, we performed comparative genomic hybridization to identify chromosomal imbalances (DNA gains and losses) in three cases of PXA. Genetic imbalance was detected on at least one chromosome for each case. One case, which revealed multiple genetic alterations, showed a poor prognosis. DNA gain on chromosome 7 and loss on 8p were demonstrated in two of three cases, suggesting that the candidate gene(s) located on these regions may play a role in the development of PXA. Further studies are needed to identify the residing candidate genes that are involved in the tumorigenesis of PXA. In addition, the histopathological features and previous genetic studies on PXA are reviewed.

Underediting of glutamate receptor GluR-B mRNA in malignant gliomas

In mammals, RNA editing by site-selective adenosine deamination regulates key functional properties of neurotransmitter receptors in the central nervous system. Glutamate receptor subunit B is nearly 100% edited at one position (the Q/R-site), which is essential for normal receptor function. Its significance is apparent from mouse models in which a slightly reduced rate of Q/R-site editing is associated with early onset epilepsy and premature death. Here we report that in tissues from malignant human brain tumors, this editing position of glutamate receptor subunit B is substantially underedited compared with control tissues. We also observe alterations in editing and alternative splicing of serotonin receptor 5-HT(2C) transcripts. These changes correlate with a decrease in enzymatic activity of the editing enzyme adenosine deaminase acting on RNA (ADAR) 2, as deduced from analysis of ADAR2 self-editing. Our results suggest a role for RNA editing in tumor progression and may provide a molecular model explaining the occurrence of epileptic seizures in association with malignant gliomas.

Histamine H1 receptor activation stimulates mitogenesis in human astrocytoma U373 MG cells

In human astrocytoma U373 MG cells that express histamine H1 receptors (180 +/- 6 fmol/mg protein) but not H2 or H3 receptors, histamine stimulated mitogenesis as assessed by [3H]-thymidine incorporation (173 +/- 2% of basal; EC50, 2.5 +/- 0.4 microM). The effect of 100 microM histamine was fully blocked by the selective H1 antagonist mepyramine (1 microM) and was markedly reduced (93 +/- 4% inhibition) by the phospholipase C inhibitor U73122 (10 microM). The activator of protein kinase C (PKC) phorbol 12-tetradecanoyl-13-acetate (TPA, 100nM) stimulated [3H]-thymidine incorporation (270 +/- 8% of basal), and this response was not additive with that to 100 microM histamine. The incorporation of [3H]-thymidine induced by 100 microM histamine was partially reduced by the PKC inhibitor Ro 31-8220 (57 +/- 7% inhibition at 300 nM) and by the compound PD 098,059 (30 microM, 62 +/- 14% inhibition), an inhibitor of the mitogen-activated kinase (MAPK) kinases MEK1/MEK2. These results show that histamine H1 receptor activation stimulates the proliferation of human astrocytoma U373 MG cells. The action of histamine appears to be partially mediated by PKC stimulation and MAPK activation.

Loss of DCC expression in astrocytomas: relation to p53 abnormalities, cell kinetics, and survival

AIMS

Although frequent reduction or loss of DCC (deleted in colorectal carcinomas) has been demonstrated in gliomas, the association with cell kinetics and survival is still unclear.

METHODS

A total of 119 astrocytomas, comprising 39 grade IV, 36 grade III, and 44 low grade tumours, were immunohistochemically investigated, along with 26 normal adult brain samples and two fetal brains. The results were compared with p53 abnormalities, Ki-67 labelling index (LI), mitotic index (MI), apoptotic index (AI), and survival.

RESULTS

In normal adult and fetal brain tissues, DCC expression was detected in mature and terminally differentiated neuronal cells but not glial elements. In astrocytomas, whereas DCC expression was still clearly shown with low grade malignancy, DCC scores were significantly decreased in high histological grade malignancy, along with an increase in cell kinetics determined by AI, MI, and Ki-67 LI values. In addition, p53 LI values were significantly increased, although a direct link between DCC scores and p53 LI values was not evident. Univariate analysis revealed that high DCC scores and low p53 LI values were closely related to a favourable outcome for astrocytoma, although only the AI was an independent prognostic factor.

CONCLUSIONS

The loss of DCC expression may be closely related to changes in cell kinetics and tumour phenotype in astrocytomas, independent of p53 abnormalities.

Analysis of loss of heterozygosity on chromosome 10 in patients with malignant astrocytic tumors: correlation with patient age and survival

OBJECT

The most frequent genetic abnormality in human malignant gliomas is loss of heterozygosity (LOH) on chromosome 10. Candidate genes on chromosome 10 that are associated with the prognosis of patients with anaplastic astrocytoma (AA) and glioblastoma (GBM) were evaluated.

METHODS

The authors used 12 fluorescent microsatellite markers on both arms of chromosome 10 to study LOH in 108 primary astrocytic tumors. The LOH on chromosome 10 was observed in 11 (32%) of 34 AAs and 34 (56%) of 61 GBMs. No LOH was detected in 13 low-grade gliomas. Loss of heterozygosity was not detected in any AA in the seven patients younger than 35 years, but it was discovered in 41% of the patients older than 35 years. The prognostic significance of LOH at each locus was evaluated in 89 patients older than 15 years; 33 (37%) had supratentorial AAs and 56 (63%) had supratentorial GBMs. The Cox proportional hazards model, adjusted for patient age at surgery, the preoperative Karnofsky Performance Scale score, and the extent of surgical resection revealed that LOH on marker D10S209 near the FGFR2 and DMBT1 genes was significantly associated with shorter survival in patients with AA. The LOH on markers D10S215 and D10S541, which contain the PTEN/MMAC1 gene between them, was significantly associated with shorter survival in patients with GBM.

CONCLUSIONS

In the present study it is found that LOH on chromosome 10 is an age-dependent event for patients with AAs and that LOH on marker D10S209 near the FGFR2 and DMBT1 loci is a significantly unfavorable prognostic factor. It is also reported that LOH on the PTEN/MMAC1 gene is a significantly unfavorable prognostic factor in patients with GBM.

A novel member of the WD-repeat gene family, WDR11, maps to the 10q26 region and is disrupted by a chromosome translocation in human glioblastoma cells

Allelic deletions of 10q25-26 and 19q13.3-13.4 are the most common genetic alterations in glial tumors. We have identified a balanced t(10;19) reciprocal translocation in the A172 glioblastoma cell line which involves both critical regions on chromosomes 10 and 19. In addition, loss of an entire copy of chromosome 10 has occurred in this cell line suggesting that the translocation event may provide a highly specific critical inactivating event in a gene responsible for tumorigenesis. Positional cloning of this translocation breakpoint resulted in the identification of a novel chromosome 10 gene, WDR11, which is a member of the WD-repeat gene family. The WDR11 gene is ubiquitously expressed, including normal brain and glial tumors. WDR11 is composed of 29 exons distributed over 58 kilobases and oriented towards the telomere. The translocation resulted in deletion of exon 5 and consequently fusion of intron 4 of WDR11 to the 3' untranslated region of a novel member, ZNF320, of the Krüppel-like zinc finger gene family. Since ZNF320 is oriented toward the centromere of chromosome 19, both genes appeared on the same derivative chromosome der(10). The chimeric transcript encodes the WDR11 polypeptide, which is truncated after the second of six WD-repeats. ZNF320 is also expressed in A172 cells, although it is not clear if the translocation affects the expression of the altered gene because of the presence of another unrearranged gene on chromosome 19. We suggest that, because of its localization in a region frequently showing LOH and the observation of inactivation of this gene in glioblastoma cells, WDR11 is a candidate gene for the frequently proposed tumor suppressor gene in 10q25-26 which is involved in tumorigenesis of glial and other tumors showing frequent alterations in the distal 10q region.

PTEN is a target of chromosome 10q loss in anaplastic oligodendrogliomas and PTEN alterations are associated with poor prognosis

Allelic loss of 10q is a common genetic event in malignant gliomas, with three 10q tumor suppressor genes, ERCC6, PTEN, and DMBT1, putatively implicated in the most common type of malignant glioma, glioblastoma. Anaplastic oligodendroglioma, another type of malignant glioma, provides a unique opportunity to study the relevance of particular genetic alterations to chemosensitivity and survival. We therefore analyzed these three genes in 72 anaplastic oligodendrogliomas. Deletion mapping demonstrated 10q loss in 14 of 67 informative cases, with the PTEN and DMBT1 regions involved in all deletions but with the ERCC6 locus spared in two cases. Seven tumors had PTEN gene alterations; two had homozygous DMBT1 deletions, but at least one reflected unmasking of a germline DMBT1 deletion. No mutations were found in ERCC6 exon 2. Chemotherapeutic response occurred in two of the seven tumors with PTEN alterations, but with unexpected short survival times. PTEN gene alterations were not associated with poor therapeutic response in multivariate analysis, but were independently predictive of poor prognosis even after multivariate adjustment for both 10q and 1p loss. In anaplastic oligodendroglioma, therefore, PTEN is a target of 10q loss, and PTEN alterations are associated with poor prognosis, even in chemosensitive cases.

Alterations of the p53 and pRB pathways in human astrocytoma

Human astrocytomas are characterized by a number of molecular changes affecting two critical tumor suppressor pathways: the pRB and the p53 pathways. Genetic alterations functionally eliminate pRB and p53 themselves or upstream and/or downstream molecules such as products of the Ink4a/ARF locus, p16Ink4a and p14ARF. As a result, malignant cells are defective in critical cell cycle and apoptosis regulatory elements contributing to unrelenting tumour growth and invasion. Current research aims to discover effective means of reconstituting p53 and pRB pathway components in an effort to attenuate the aggressive phenotype of astrocytoma.

TP53 deleted cells in de novo glioblastomas using fluorescence in situ hybridization

Glioblastoma (GBM) has been known to have two distinct genetic pathways of tumorigenesis. Secondary GBM shows frequent TP53 mutation, but de novo (primary) GBM is usually independent of TP53 alteration. However, the subpopulation of TP53 altered cells in the latter tumor is obscure. In order to assess TP53 deleted cells in de novo GBM quantitatively, we performed dual color fluorescence in situ hybridization (FISH) for TP53 and centromere 17 in nine cases of de novo GBM with frozen surgical materials. Single TP53 signal cells indicating TP53 deletion were recognized in 8.7-35.6% (mean, 21.3%) among the nine cases. In addition, immunohistochemistry was performed for the Ki-67 antigen (MIB-1) and p53 protein in all nine cases. Labeling indices (LI) of MIB-1 ranged from 2.8 to 46.9% (mean, 20.8%). Between the group with the more dense subpopulation of TP53 deleted cells (15% or more) by FISH and the group with less subpopulation than the former, these LI of MIB-1 demonstrated statistically significant difference (respective means, 28.2% and 6.1%; P < 0.05). Conversely, LI of p53 protein shown to be 0-50.9% (mean, 24.9%) had no correlation with the subpopulation of TP53 deleted cells by FISH. Four cases who had higher LI of p53 protein (mean, 39.7%) than the subpopulation of TP53 deleted cells (mean, 12.7%), respectively, indicated the presence of many p53 protein immunoreactive cells without TP53 deletion. These results suggest that: (i) de novo GBM also has subpopulation of TP53 deleted cells; (ii) TP53 alteration, which may not be a major event, participates in cell proliferation of de novo GBM; and (iii) de novo GBM tends to have accumulation of wild-type p53 protein.

Tumour suppressor activity of human imprinted gene PEG3 in a glioma cell line

BACKGROUND

Mouse imprinted gene Peg3 encodes a large C2H2 type zinc finger protein with unique characteristics. Peg3 knockout mice were found to show an impairment in maternal behaviour of the adult female. Mouse Peg3 is located on the proximal region of chromosome 7 which is syntenic to the long arm of human chromosome 19. It has been reported that a loss of heterozygosity (LOH) of chromosome 19q occurs frequently in several glioma types.

RESULTS

We isolated human PEG3 cDNA. Both human and mouse PEG3 were strongly expressed in the adult brain and the Peg3 protein was localized in the nuclei of both neurones and glial cells. A significant decrease in PEG3 expression was more commonly observed in glioma cell lines as compared with that in primary cultures of astrocytes. Transfection of PEG3 cDNA in a glioma cell line resulted in a loss of tumorigenicity in nude mice.

CONCLUSIONS

The human PEG3 gene is a paternally expressed imprinted gene. Introduction of PEG3 cDNA into the glioma cells suggests that human PEG3 protein functions as a tumour suppressor. Human PEG3 is located on 19q13.4 and is one of the candidates for tumour suppressor genes that are predicted to be sited in gliomas.

Segregation analysis of cancer in families of glioma patients

A small proportion of brain tumors are attributed to a genetic predisposition; however, the hereditary proportion is undetermined. This study evaluates the degree of familial aggregation of cancer in a large series of brain tumor patients. Our study included 5,088 relatives of 639 probands (3,810 first- and 1,278 second-degree), diagnosed with a glioma between June 1992 and June 1995 at The University of Texas M. D. Anderson Cancer Center, Houston, Texas, with diagnosis under age 65 years, and residents of the United States or Canada. We conducted an in-person or telephone interview with patients and/or their next-of-kin, and obtained family histories for the probands' first-degree (parents, siblings, offspring) and selected second-degree relatives (aunts, uncles, grandparents) using a sequential sampling strategy. Reported cancers were documented by medical records and/or death certificates (if the relative was deceased and medical records were unavailable). We conducted segregation analysis using the Pedigree Analysis Program (PAP). The analyses were divided into two categories: (1) all 639 families, and (2) a subset of families whose gliomas stained positive on p53 immunohistochemistry analysis. We demonstrated that a multifactorial Mendelian model was favored, while a model postulating a purely environmental cause of brain cancer was rejected. This study indicates that familial cancer in relatives of glioma patients are probably a result of multigenic action, and familial clustering of cancer among relatives of glioma patients may involve unknown environmental exposures.

The relationship between genetic aberrations as detected by comparative genomic hybridization and vascularization in glioblastoma xenografts

Angiogenesis is of vital importance for the growth of solid tumors and constitutes a target for anti-cancer therapy. Glioblastomas (GBMs) are histologically characterized by striking microvascular proliferation. The identification of the mechanism of angiogenesis is of major importance for the further development of anti-angiogenic therapy. Tumor angiogenesis might be the result of a combination of local tissue conditions (especially hypoxia) and specific genetic alterations acquired during oncogenesis. In order to investigate the relationship between genetic aberrations and tumor angiogenesis in GBM xenograft lines, the genetic alterations were examined by Comparative Genomic Hybridization (CGH). Two vascular phenotypes of GBM xenografts could be identified: a well vascularized and a poorly vascularized type. In this model, the poorly vascularized type had a larger number of genetic alterations. However, there was no unequivocal correlation between angiogenesis, growth rate and patterns of genetic alterations as detected by CGH.

Chromosome imbalances in familial gliomas detected by comparative genomic hybridization

Familial occurrence of gliomas, in the absence of well-defined hereditary multisystem disorders, is reported occasionally. We describe 17 families that have been afflicted with two or more gliomas but do not raise suspicion of other inheritable syndromes. The families were identified among 369 consecutive glioma patients operated at the Tampere University Hospital during 1983-1994. We applied comparative genomic hybridization (CGH) analysis on 21 gliomas occurring in these 17 families. The most frequent genetic alterations, detected in over 20% of the tumors, were losses of 6q, 10, 4q, 9p and gains of 7, 19, 20q, 1p. We compared the chromosomal alterations detected in the familial gliomas to those reported previously on 209 sporadic gliomas in nine different CGH studies. In this comparison, the familial gliomas more often showed losses of chromosome arms 4q and 6q and gains of 1p and 22q. The most frequent losses (9/21 tumors) in the familial gliomas resided on chromosome arm 6q (P = 0.005, Fisher's exact test; with Bonferroni correction, P = 0.04). The loss of 6q was also the most common intrafamilial aberration, present in four separate gliomas belonging to two families. The minimal common area of loss on this chromosome resided at 6q14-16. In conclusion, we have found several characteristic aberrations by CGH in the familial gliomas and we present new chromosomal regions possibly involved in the familial predisposition to gliomas.

Molecular genetics of radiographically defined de novo glioblastoma multiforme

Glioblastoma multiforme (GBM) represents the final endpoint of anaplastic progression in astrocytomas. GBM which arise without clinical evidence of a prior low-grade astrocytoma (LGA) have been designated de novo GBM, and are thought to develop rapidly from initial tumour formation. However, a purely clinical definition of de novo GBM does not exclude a long-standing, asymptomatic low-grade tumour. This study therefore sought to determine the genetic features of a unique group of cases in which GBMs were documented to have arisen radiographically in defined period of time (radiographically defined de novo GBM). Clinical and genetic features were examined in a group of 11 patients with a histological diagnosis of high-grade astrocytoma at first biopsy and radiographically defined de novo GBM. The mean age of the patients at tumour diagnosis was 62 years (range 32-87). Six of 11 tumours arose in the temporal lobes. Eight of 11 tumours had epidermal growth factor receptor (EGFR) overexpression, and EGFR gene amplification was found in five of the six analysed cases. Overexpression of p53 was observed in only one tumour, and a TP53 mutation was present in this case. p16 immunostaining was undetectable in 10 cases, and homozygous deletion of CDKN2A was observed in four of the six studied tumours. pRb expression was lost in four tumours. Mutations in the PTEN gene were detected in two of six cases. The results in this unique group of cases confirms the prior hypothesis that the profile of genetic alterations in de novo GBM is distinct from that of GBM arising from a known LGA, and that these specific genetic pathways promote the rapid development of GBM.

What role(s) for TGFalpha in the central nervous system?

Transforming growth factor alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR or erbB1). Identified since 1985 in the central nervous system (CNS), its functions in this organ have started to be determined during the past decade although numerous questions remain unanswered. TGFalpha is widely distributed in the nervous system, both glial and neuronal cells contributing to its synthesis. Although astrocytes appear as its main targets, mediating in part TGFalpha effects on different neuronal populations, results from different studies have raised the possibility for a direct action of this growth factor on neurons. A large array of experimental data have thus pointed to TGFalpha as a multifunctional factor in the CNS. This review is an attempt to present, in a comprehensive manner, the very diverse works performed in vitro and in vivo which have provided evidences for (i) an intervention of TGFalpha in the control of developmental events such as neural progenitors proliferation/cell fate choice, neuronal survival/differentiation, and neuronal control of female puberty onset, (ii) its role as a potent regulator of astroglial metabolism including astrocytic reactivity, (iii) its neuroprotective potential, and (iv) its participation to neuropathological processes as exemplified by astroglial neoplasia. In addition, informations regarding the complex modes of TGFalpha action at the molecular level are provided, and its place within the large EGF family is precised with regard to the potential interactions and substitutions which may take place between TGFalpha and its kindred.

Systemic metastasis in glioblastoma may represent the emergence of neoplastic subclones

Glioblastomas only rarely metastasize to sites outside the central nervous system, for reasons that are poorly understood. We report the clinicopathological and molecular genetic findings in 6 patients with metastatic glioblastoma. Four patients were under the age of 32 and all but 1 patient died within 2 yr of diagnosis. The number of metastases ranged from 1 to 3. At the time of death, 3 patients had apparent tumor control at their primary site. We evaluated DNA from both primary and metastatic glioblastomas for genetic alterations commonly found in glioblastomas: TP53 mutations, CDKN2A/p16 deletions, EGFR amplification, and allelic loss of chromosomes 1p, 10q and 19q. Four of 6 cases had TP53 mutations and only single cases had EGFR amplification, CDKN2A/p16 deletions, or allelic loss of 1p, 10q and 19q; 2 cases had no detectable genetic alterations. In 2 cases, the primary and metastatic tumors had identical genotypes. Remarkably, however, 2 cases had different TP53 alterations in the primary and metastatic lesions, or among the metastatic tumors, which suggests that some metastatic deposits may represent emergence of subclones that were not necessarily dominant in the primary tumor. The present observations and a review of the recent literature demonstrate that metastatic glioblastomas tend to occur in younger adults who do not follow long clinical courses, and may be characterized by TP53 mutations and differential clonal selection.

Radiotherapy for brain tumors

Over the last 2 years, several advances have been made in the field of radiotherapy for brain tumors. Key advances are summarized in this review. Crucial technologic advances, such as radiosurgery, fractionated stereotactic radiotherapy, and intensity-modulated radiotherapy, are discussed. Better understanding of the interaction between the processes of angiogenesis, apoptosis, cell-cycle regulation, and signal transduction and the effects of ionizing radiation has made it clear that many of these "new agents" are, in fact, valuable modulators of the radiation response. Another exciting molecular discovery is the recognition of radiation-induced promoters that can be exploited to cause spatially and temporally configured expression of selected genes; this approach may represent the ideal application of conformal radiation techniques in the future, yielding well-defined genetic changes in specifically targeted tissues. The final "frontier" covered in this review is the newer categories of radiosensitizers, ranging from topoisomerase-I inhibitors, to expanded metalloporphyrins, to oxygen- dissociating agents.

Long survival and therapeutic responses in patients with histologically disparate high-grade gliomas demonstrating chromosome 1p loss

OBJECT

Allelic loss of chromosome 1p is a powerful predictor of tumor chemosensitivity and prolonged survival in patients with anaplastic oligodendrogliomas. Chromosome 1p loss also occurs in astrocytic and oligoastrocytic gliomas, although less commonly than in pure oligodendroglial tumors. This observation raises the possibility investigated in this study that chromosome 1p loss might also provide prognostic information for patients with high-grade gliomas with astrocytic components.

METHODS

The authors report on seven patients with high-grade gliomas composed of either pure astrocytic or mixed astrocytic-oligodendroglial phenotypes, who had remarkable neuroradiological responses to therapy or unexpectedly long survivals. All of the tumors from these seven patients demonstrated chromosome 1p loss, whereas other genetic alterations characteristic of high-grade gliomas (p53 gene mutations, EGFR gene amplification, chromosome 10 loss, chromosome 19q loss, or CDKN2A/p16 deletions) were only found in occasional cases. The authors also assessed the frequency of chromosome 1p loss in a series of anonymous high-grade astrocytoma samples obtained from a tumor bank and demonstrate that this genetic change is uncommon, occurring in only 10% of cases.

CONCLUSIONS

Although any prognostic importance of chromosome 1p loss in astrocytic or mixed astrocytic-oligodendroglial gliomas can only be determined in larger and prospective series, these findings raise the possibility that some high-grade gliomas with chromosome 1p loss, in addition to pure anaplastic oligodendrogliomas, may follow a more favorable clinical course.

Clinical evidence of distinct subgroups of astrocytic tumors defined by comparative genomic hybridization

In astrocytic tumors, the relationship between genetic pathways and patients' prognoses has not been fully investigated. In our studies of astrocytic tumors using comparative genomic hybridization, the presence of 8q gain was mutually exclusive of 7p gain or amplification. In this study, 45 cases of astrocytic tumor were divided into 3 groups: those with 7p gain, cases with 8q gain, or those with neither; and their clinical course, p53, and epidermal growth factor receptor (EGFR) expressions and proliferative activity were then compared. Of the cases examined, 17 (12 glioblastomas and 5 anaplastic astrocytomas) showed 7p gain. Eleven cases (5 glioblastomas, 2 anaplastic, and 4 low-grade astrocytomas) showed 8q gain. p53 accumulation was observed more frequently in cases with 8q gain than in those with 7p gain. Astrocytic tumors with 8q gain occurred more frequently in younger patients than those with 7p gain. Kaplan-Meier survival rate analysis showed higher survival rates in patients with 8q gain than in those with 7p gain. This tendency also was observed when only patients with malignant glioma were included in the survival analysis. Our results provide evidence for distinct clinical manifestations in astrocytic tumors with 8q and 7p gain.

A review of astrocytoma models

Despite tremendous technical improvements in neuroimaging and neurosurgery, the prognosis for patients with malignant astrocytoma remains devastating because of the underlying biology and growth characteristics of the tumor. However, our understanding of the molecular bases of these tumors has greatly increased due to study findings involving operative specimens, astrocytoma predisposing human syndromes, teratogen-induced animal and established human astrocytoma cell lines, and more recently transgenic mouse models. Appropriate small-animal models of spontaneously occurring astrocytomas, which replicate the growth and molecular characteristics found in human tumors, are essential to test the relevance and interactions of these molecular aberrations. In addition, it is hoped that relevant molecular targets will eventually be therapeutically exploited to improve patient outcomes. Appropriate animal models are also essential for testing these novel biological therapies, before they are brought to the clinic, requiring a large investment of time and money. In this paper, various astrocytoma models are discussed, with emphasis on transgenic mouse models that are of great interest to laboratory investigators.

Anti-tumoral action of cannabinoids: involvement of sustained ceramide accumulation and extracellular signal-regulated kinase activation

Delta9-Tetrahydrocannabinol, the main active component of marijuana, induces apoptosis of transformed neural cells in culture. Here, we show that intratumoral administration of Delta9-tetrahydrocannabinol and the synthetic cannabinoid agonist WIN-55,212-2 induced a considerable regression of malignant gliomas in Wistar rats and in mice deficient in recombination activating gene 2. Cannabinoid treatment did not produce any substantial neurotoxic effect in the conditions used. Experiments with two subclones of C6 glioma cells in culture showed that cannabinoids signal apoptosis by a pathway involving cannabinoid receptors, sustained ceramide accumulation and Raf1/extracellular signal-regulated kinase activation. These results may provide the basis for a new therapeutic approach for the treatment of malignant gliomas.

Alterations of chromosome arms 1p and 19q as predictors of survival in oligodendrogliomas, astrocytomas, and mixed oligoastrocytomas

PURPOSE

A recent report suggests that alterations of chromosome arms 1p and 19q are associated with chemotherapeutic response and overall survival in anaplastic oligodendroglioma patients treated with procarbazine, lomustine, and vincristine chemotherapy. We set out to further clarify the diagnostic and prognostic implications of these alterations in a broader set of diffuse gliomas, including astrocytic neoplasms and low-grade oligodendrogliomas.

PATIENTS AND METHODS

Fluorescence in situ hybridization (FISH) signals from DNA probes mapping to 1p and 19q common deletion regions were enumerated in 162 diffuse gliomas (79 astrocytomas, 52 oligodendrogliomas, and 31 mixed oligoastrocytomas), collected as part of an ongoing prospective investigation of CNS tumors.

RESULTS

The oligodendroglial phenotype was highly associated with loss of 1p (P =.0002), loss of 19q (P <.0001), and combined loss of 1p and 19q (P <.0001). Combined loss of 1p and 19q was identified as a univariate predictor of prolonged overall survival among patients with pure oligodendroglioma (log-rank, P =.03) and remained a significant predictor after adjusting for the effects of patient age and tumor grade (P <.01). This favorable association was not evident in patients with astrocytoma or mixed oligoastrocytoma.

CONCLUSION

Combined loss of 1p and 19q is a statistically significant predictor of prolonged survival in patients with pure oligodendroglioma, independent of tumor grade. Given the lack of this association in patients with astrocytic neoplasms and the previously demonstrated chemosensitivity of oligodendrogliomas, a combined approach of histologic and genotypic assessment could potentially improve existing strategies for patient stratification and management.

Phenotype vs genotype in the evolution of astrocytic brain tumors

Astrocytic brain tumors are the most frequent human gliomas and they include a wide range of neoplasms with distinct clinical, histopathologic, and genetic features. Diffuse astrocytomas are predominantly located in the cerebral hemispheres of adults and have an inherent tendency to progress to anaplastic astrocytoma and (secondary) glioblastoma. The majority of glioblastomas develop de novo (primary glioblastomas), without an identifiable less-malignant precursor lesion. These subtypes of glioblastoma evolve through different genetic pathways, affect patients at different ages, and are likely to differ in their responses to therapy. Primary glioblastomas occur in older patients and typically show epidermal growth factor receptor (EGFR) overexpression, PTEN mutations, p16 deletions, and, less frequently, MDM2 amplification. Secondary glioblastomas develop in younger patients and often contain TP53 mutations as their earliest detectable alteration. Morphologic variants of glioblastoma were shown to have intermediate clinical and genetic profiles. The giant cell glioblastoma clinically and genetically occupies a hybrid position between primary (de novo) and secondary glioblastomas. Gliosarcomas show identical gene mutations in the gliomatous and sarcomatous tumor components, which strongly supports the concept that there is a monoclonal origin for gliosarcomas and an evolution of the sarcomatous component due to aberrant mesenchymal differentiation in a highly malignant astrocytic neoplasm.

Accumulation of mutant p53(V143A) modulates the growth, clonogenicity, and radiochemosensitivity of malignant glioma cells independent of endogenous p53 status

Alterations of the p53 gene have been attributed a major role in the development and resistance to therapy of several human cancers. Accumulation of p53 in tumor cells may result from mutations associated with prolonged half-life or from stabilization of wild-type p53 by different mechanisms. To address the role of p53 accumulation in the response of malignant glioma cells to radiochemotherapy, we expressed the p53 mutant p53(V143A) in five human malignant glioma cell lines with different genetic and functional p53 status. Accumulation of p53(V143A) modulated proliferation in three and clonogenicity in four of five cell lines without a clear pattern with regard to their endogenous p53 status. p53(V143A) inhibited the camptothecin-induced accumulation of p21(WAF1/CIP1) in cell lines with p53 functional wild-type activity, but not in cell lines lacking p53 activity, consistent with a transdominant-negative effect of p53(V143A). Irradiation induced a moderate G2/M arrest in all cell lines, irrespective of the p53 status, that was unaffected by p53(V143A). Radiosensitivity as well as sensitivity to BCNU, teniposide (VM26), topotecan, vincristine, Taxol, and cisplatin both in cytotoxic cell death and in clonogenic cell death was unchanged in p53(V143A)-transfected cells with few exceptions. These data do not support the hypothesis that accumulation of mutant p53 is a major determinant of the response to adjuvant radiochemotherapy in human malignant glioma cells.

Expression of activated epidermal growth factor receptors, Ras-guanosine triphosphate, and mitogen-activated protein kinase in human glioblastoma multiforme specimens

OBJECTIVE

Amplification of the epidermal growth factor receptor (EGFR) is a common event in the molecular pathogenesis of high-grade astrocytic tumors, occurring in 50% of glioblastoma multiforme (GBM) cases. A subset of GBMs also express a constitutively phosphorylated truncated receptor (EGFRvIII). Expression of transfected EGFRvIII in cells has been reported to activate the Ras-mitogen-activated protein kinase pathway and to provide a growth advantage. Novel therapeutic agents targeting signal transduction pathways are entering early clinical trials; determination of which GBMs express EGFRvIII might help identify patients who might benefit from these biological agents.

METHODS

A cohort of 15 flash-frozen surgical specimens (12 GBMs, 2 gliosarcomas, and 1 adult low-grade glioma) were evaluated for EGFR and EGFRvIII expression and for EGFR activation status using immunohistochemical (IHC) analysis, Western blotting, and reverse transcription-polymerase chain reaction assays. Levels of activated Ras-guanosine triphosphate were measured using a nonradioactive luciferase-based technique. Mitogen-activated protein kinase activation was determined using a myelin basic protein assay. IHC analysis was performed on paraffin-embedded, formalin-fixed, pathological specimens. Normal control samples included white matter specimens distal to tumors (n = 5), a sample obtained during a lobectomy for treatment of epilepsy (n = 1), and cultured fetal human astrocytes (n = 1).

RESULTS

We demonstrated higher levels of activated Ras and mitogen-activated protein kinase in GBM specimens, compared with normal brain tissue or the low-grade glioma. There was a very good correlation between results obtained using specialized molecular techniques and those obtained using routine IHC techniques. Screening for EGFRvIII expression may be of prognostic importance, because patients with EGFRvIII-positive tumors exhibited shorter life expectancies (mean survival time for patients with EGFRvIII-positive tumors, 4.5 +/- 0.6 mo; mean survival time for patients with EGFRvIII-negative tumors, 11.2 +/- 0.9 mo).

CONCLUSION

We demonstrated that routine IHC techniques using commercially available antibodies are capable of identifying which GBM specimens express EGFRvIII and whether the EGFRs are activated. Such a molecular classification of GBMs might allow us to determine which patients might benefit from biologically targeted therapies. In addition, characterization of specimens with respect to their EGFRvIII status seems to be of prognostic value.

Loss of chromosome 10 is an independent prognostic factor in high-grade gliomas

Loss of heterozygosity (LOH) for chromosome 10 is the most frequent genetic abnormality observed in high-grade gliomas. We have used fluorescent microsatellite markers to examine a series of 83 patients, 34 with anaplastic astrocytoma (grade 3) and 49 with glioblastoma multiforme (grade 4), for LOH of chromosome 10. Genotype analysis revealed LOH for all informative chromosome 10 markers in 12 (35%) of patients with grade 3 and 29 (59%) grade 4 tumours respectively, while partial LOH was found in a further eight (24%) grade 3 and ten (20%) grade 4 tumours. Partial LOH, was confined to the long arm (10q) in six and the short arm (10p) in three cases, while alleles from both arms were lost in four cases. Five tumours (one grade 3 and four grade 4) showed heterogeneity with respect to loss at different loci. There was a correlation between any chromosome 10 loss and poorer performance status at presentation (chi2 P = 0.005) and with increasing age at diagnosis (Mann-Whitney U-test P = 0.034) but not with tumour grade (chi2 p= 0.051). A Cox multivariate model for survival duration identified age (proportional hazards (PH), P= 0.004), grade (PH, P= 0.012) and any loss of chromosome 10 (PH, P= 0.009) as the only independent prognostic variables. Specifically, LOH for chromosome 10 was able to identify a subgroup of patients with grade 3 tumours who had a significantly shorter survival time. We conclude that LOH for chromosome 10 is an independent, adverse prognostic variable in high-grade glioma.

Mutational spectra of PTEN/MMAC1 gene: a tumor suppressor with lipid phosphatase activity

PTEN/MMAC1 (phosphatase, tensin homologue/mutated in multiple advanced cancers) is a tumor suppressor protein that has sequence homology with dual-specificity phosphatases, which are capable of dephosphorylating both tyrosine phosphate and serine/threonine phosphate residues on proteins. The in vivo function of PTEN/MMAC1 appears to be dephosphorylation of phosphotidylinositol 3,4, 5-triphosphate. The PTEN/MMAC1 gene is mutated in the germline of patients with rare autosomal dominant cancer syndromes and in subsets of specific cancers. Here we review the mutational spectra of the PTEN/MMAC1 gene in tumors from various tissues, especially endometrium, brain, prostate, and ovary, in which the gene is inactivated very frequently. Germline and somatic mutations in the PTEN/MMAC1 gene occur mostly in the protein coding region and involve the phosphatase domain and poly(A)(6) stretches. Compared with germline alterations found in the PTEN/MMAC1 gene, there is a substantially increased frequency of frameshift mutations in tumors. Glioblastomas and endometrial carcinomas appear to have distinct mutational spectra, probably reflecting differences in the underlying mechanisms of inactivation of the PTEN/MMAC1 gene in the two tissue types. Also, depending on the tissue type, the gene appears to be involved in the initiation or the progression of cancers. Further understanding of PTEN/MMAC1 gene mutations in different tumors and the physiologic consequences of these mutations is likely to open up new therapeutic opportunities for targeting this critical gene.

The genomic structure of the DMBT1 gene: evidence for a region with susceptibility to genomic instability

Increasing evidence has accumulated for an involvement of the inactivation of tumour suppressor genes at chromosome 10q in the carcinogenesis of brain tumours, melanomas, and carcinomas of the lung, the prostate, the pancreas, and the endometrium. The gene DMBT1 (Deleted in Malignant Brain Tumours 1) is located at chromosome 10q25.3-q26.1, within one of the putative intervals for tumour suppressor genes. DMBT1 is a member of the scavenger-receptor cysteine-rich (SRCR) superfamily and displays homozygous deletions or lack of expression in glioblastoma multiforme, medulloblastoma, and in gastrointestinal and lung cancers. Based on these properties, DMBT1 has been proposed to be a candidate tumour suppressor gene. We have determined the genomic sequence of DMBT1 to allow analyses of mutations. The gene has at least 54 exons that span a genomic region of about 80 kb. We have identified a putative exon with coding potential for a transmembrane domain. Our data further suggest that alternative splicing gives rise to isoforms of DMBT1 with a differential utilization of SRCR domains and SRCR interspersed domains. The major part of the gene harbours locus specific repeats. These repeats may point to the DMBT1 locus as a region susceptible to chromosomal instability.

PTEN gene and integrin signaling in cancer

Integrins are major adhesion- and signaling-receptor proteins that mediate cell migration and invasion. They also trigger a variety of signal transduction pathways and regulate cytoskeletal organization, specific gene expression, growth control, and apoptosis (programmed cell death). Consequently, integrins are thought to play important roles in embryonic development and in the biology of cancers. The functions of integrins can be negatively regulated by the recently discovered tumor suppressor PTEN, a protein with homology to protein tyrosine phosphatases and tensin. The PTEN gene is mutated in a wide range of human cancers. PTEN inhibits cell migration and invasion by directly dephosphorylating two key tyrosine-phosphorylated proteins, thereby antagonizing interactions of integrins with the extracellular matrix and integrin-triggered signaling pathways. Other studies demonstrate important roles for PTEN in dephosphorylating a key signal transduction lipid. In the absence of PTEN, this lipid signal transduction pathway can protect tumor cells from apoptosis. Thus, PTEN appears to be a unique tumor suppressor-with both lipid phosphatase and protein tyrosine phosphatase activities-that negatively regulates cell interactions with the extracellular matrix and that maintains cell sensitivity to apoptosis, e.g., after loss of cell contact with the extracellular matrix. The complex signal transduction pathways regulated by PTEN are described in this review. PTEN and the signaling pathways it regulates may provide novel targets for potential therapy.

Allele-specific losses of heterozygosity on chromosomes 1 and 17 revealed by whole genome scan of ethylnitrosourea-induced BDIX x BDIV hybrid rat gliomas

The induction of neural tumors by N-ethyl-N-nitrosourea (EtNU) in inbred strains of rats has evolved as a valuable model system of developmental stage- and cell type-dependent oncogenesis. Tumor yield and latency times are strongly influenced by genetic background. Compared with BDIX rats, BDIV rats are relatively resistant to the induction of brain tumors by EtNU, with a lower tumor incidence and latency periods prolonged by a factor of 3. To characterize genetic abnormalities associated with impaired tumor suppressor gene function in neuro-oncogenesis, losses of heterozygosity (LOHs) and microsatellite instability (MI) were investigated in brain tumors induced by EtNU in (BDIV x BDIX) F(1) and F(2) rats. The polymerase chain reaction was used to amplify 55 polymorphic microsatellite markers spanning the entire rat genome. The tumors displayed different histologies and grades of malignancy, corresponding to part of the spectrum of human gliomas. MI was not observed in any of the tumors. LOH of rat chromosome 1q was predominantly detected in oligodendrogliomas and mixed gliomas, with a 30% incidence in informative cases. 11p15.5, the human genome region syntenic to the consensus region of LOHs observed on rat chromosome 1, has been shown to be involved in the formation of gliomas in humans. Furthermore, rat brain tumors of different histologies often showed allelic imbalances on chromosome 17p. In both cases of LOH, there was a clear bias in favor of the parental BDIV allele, suggesting the involvement of tumor suppressor genes functionally polymorphic between the two rat strains.

Isolation and characterization of glioblastoma-associated homozygously deleted DNA fragments from chromosomal region 9p21 suggests involvement of multiple tumour suppressor genes

Representational difference analysis (RDA) of a human glioblastoma xenograft resulted in the isolation of five tumour-associated homozygously deleted DNA fragments, all originating from chromosome 9, region p21. Subsequent analysis of a series of ten glioblastomas using the newly isolated RDA fragments in conjunction with a series of known 9p21 DNA markers revealed homozygous deletions in nine of the ten (90 per cent) tumours. These deletions encompass the p15/p16 complex and two additional putative tumour suppressor loci. The RDA fragments correspond to the latter two loci. Taken together, these results suggest the involvement of multiple tumour suppressor genes from the 9p21 region in glioblastoma tumourigenesis. The novel RDA fragments will be instrumental in the isolation of the relevant genes.

Loss of chromosome 10 in glioblastoma: relation to proliferation and angiogenesis

Loss of chromosome 10 was assessed in 17 specimens of glioblastoma (GBM) by fluorescence in situ hybridization (FISH) technique using the centromere probe for chromosome 10. Cytospinned smear specimens were prepared from paraffin-embedded specimens. The percentage of nuclei containing a single fluorescent signal ranged from 19.2 to 88. 0% (mean, 49.3%). Thirteen tumors (76.5%) were designated as monosomy 10 because the proportion of single-signal nuclei exceeded the cut-off value (31.5%: mean of five control materials +3 standard deviations). The results confirmed the importance of the loss of chromosome 10 for the development of GBM, although no significant correlation was demonstrated between the loss of chromosome 10 and survival. In addition, proliferation potential and angiogenesis of GBM were immunohistochemically analyzed using antibodies against Ki-67 antigen (MIB-1), factor VIII-related antigen (FVIII R/Ag) and vascular endothelial growth factor (VEGF), respectively. The labeling indices of MIB-1 (1.5-57.8%) and the number of blood vessels immunoreactive for FVIII R/Ag (18-279/10 high-power fields) were not significantly related to the loss of chromosome 10. Vascular endothelial growth factor immunoreactivity in areas microvessels were counted was seen in 12 cases. However, neither the loss of chromosome 10 nor number of vessels was not correlated with VEGF expression. Other genetic abnormalities as well as loss of chromosome 10 may be involved in the cell proliferation and angiogenesis of GBM.

Localization of common deletion regions on 1p and 19q in human gliomas and their association with histological subtype

Allelic alterations of chromosomes 1 and 19 are frequent events in human diffuse gliomas and have recently proven to be strong predictors of chemotherapeutic response and prolonged survival in oligodendrogliomas (Cairncross et al., 1998; Smith et al., submitted). Using 115 human diffuse gliomas, we localized regions of common allelic loss on chromosomes 1 and 19 and assessed the association of these deletion intervals with glioma histological subtypes. Further, we evaluated the capacity of multiple modalities to detect these alterations, including loss of heterozygosity (LOH), fluorescence in situ hybridization (FISH), and comparative genomic hybridization (CGH). The correlation coefficients for detection of 1p and 19q alterations, respectively, between modalities were: 0.98 and 0.87 for LOH and FISH, 0.79 and 0.60 for LOH and CGH, and 0.79 and 0.53 for FISH and CGH. Minimal deletion regions were defined on 19q13.3 (D19S412-D19S596) and 1p (D1S468-D1S1612). Loss of the 1p36 region was found in 18% of astrocytomas (10/55) and in 73% (24/33) of oligodendrogliomas (P < 0.0001), and loss of the 19q13.3 region was found in 38% (21/55) of astrocytomas and 73% (24/33) of oligodendrogliomas (P = 0.0017). Loss of both regions was found in 11% (6/55) of astrocytomas and in 64% (21/33) of oligodendrogliomas (P < 0.0001). All gliomas with LOH on either 1p or 19q demonstrated loss of the corresponding FISH probe, 1p36 or 19q13.3, suggesting not only locations of putative tumor suppressor genes, but also a simple assay for assessment of 1p and 19q alterations as diagnostic and prognostic markers.

Molecular genetic alterations in radiation-induced astrocytomas

Astrocytic tumors occasionally arise in the central nervous system following radiotherapy. It is not clear if these gliomas represent a unique molecular genetic subset. We identified nine cases in which an astrocytoma arose within ports of previous radiation therapy, with total doses ranging from 2400 to 5500 cGy. Irradiated primary lesions included craniopharyngioma, pituitary adenoma, Hodgkin's lymphoma, ependymoma, pineal neoplasm, rhabdomyosarcoma, and three cases of lymphoblastic malignancies. Patients ranged from 9 to 60 years of age and developed secondary tumors 5 to 23 years after radiotherapy. The 9 postradiation neoplasms presented as either anaplastic astrocytoma (3 cases) or glioblastoma multiforme (6 cases). Two of the latter contained malignant mesenchymal components. We performed DNA sequence analysis, differential polymerase chain reaction (PCR), and quantitative PCR on DNA from formalin-fixed, paraffin-embedded tumors to evaluate possible alterations of p53, PTEN, K-ras, EGFR, MTAP, and p16 (MTS1/CDKN2) genes. By quantitative PCR, we found EGFR gene amplification in 2 of 8 tumors. One of these demonstrated strong immunoreactivity for EGFR. Quantitative PCR showed chromosome 9p deletions including p16 tumor suppressor gene (2 of 7 tumors) and MTAP gene (3 of 7). Five of 9 tumors demonstrated diffuse nuclear immunoreactivity for p53 protein. Sequencing of the p53 gene in these 9 cases revealed a mutation in only one of these cases, a G-to-A substitution in codon 285 (exon 8). Somewhat unexpectedly, no mutations were identified in PTEN, a commonly altered tumor suppressor gene in de novo glioblastoma multiformes. Unlike some radiation-induced tumors, no activating point mutations of the K-ras proto-oncogene or base pair deletions of tumor suppressor genes were noted. These radiation-induced tumors are distinctive in their high histological grade at clinical presentation. The spectrum of molecular genetic alterations appears to be similar to that described in spontaneous high grade astrocytomas, especially those of the de novo type.