Subsets of glioblastoma multiforme defined by molecular genetic analysis

Molecular abnormalities and correlations with tumor response and outcome in glioma patients

Molecular analysis approaches hold promise to refine the management of patients with malignant gliomas. An important step in the application of these techniques to guide clinical decision-making involves transitioning these approaches from the research setting into the clinical diagnostic arena, using methods that can be performed rapidly and reliably on surgically obtained tumor specimens. Many centers have begun this process for the detection of chromosome 1p and 19q deletions in oligodendroglial neoplasms. It is likely that the current limited portfolio of prognostic markers will be increased substantially during the next several years as innovative techniques for tumor genotyping and gene expression profiling help to identify additional correlates of tumor prognosis. An associated challenge involves demonstrating that biological stratification can support therapeutic stratification that will influence, rather than merely predict, the outcome of patients with brain tumors. The realization of this long-range goal will require the identification of novel therapeutic strategies that hold promise for improving the outcome of molecularly defined subsets of high-grade gliomas, which as a group remain largely resistant to conventional therapies.

Genetic alterations associated with adult diffuse astrocytic tumors

Astrocytic tumors make up a wide range of neoplasms that differ in their location in the central nervous system, morphologic features, progressive and invasive behaviors, and the age and gender of people they affect. This report reviews the cytogenetic, molecular cytogenetic, and molecular genetic abnormalities associated with diffuse infiltrating astrocytomas in adults. This group of tumors is subdivided into low-grade astrocytomas (WHO grade II), anaplastic astrocytomas (WHO grade III), and glioblastoma multiforme (WHO grade IV).

Gliomatosis cerebri: molecular pathology and clinical course

Gliomatosis cerebri is a rare, diffusely growing neuroepithelial tumor characterized by extensive brain infiltration involving more than two cerebral lobes. Among 13 patients with gliomatosis cerebri (median age, 46 years), biopsies showed features of diffuse astrocytoma (n = 4), oligoastrocytoma (n = 1), anaplastic astrocytoma (n = 5), anaplastic oligoastrocytoma (n = 1), or glioblastoma (n = 2). Molecular genetic investigation showed TP53 mutations in three of seven tumors and both PTEN mutation and epidermal growth factor receptor overexpression in one tumor. Amplification of CDK4 or MDM2 or homozygous deletion of CDKN2A was not detected. Three of 10 patients receiving radiotherapy showed a partial response (one patient) or had stable disease (two patients) lasting for more than 1 year. Four of six patients treated with procarbazine, carmustine, vincristine chemotherapy demonstrated partial remission (one patient), minor response (two patients), or stable disease (one patient). Median survival time from diagnosis was 14 months (range, 4-91+ months). Infratentorial involvement was associated with shorter survival. We conclude that (1) the molecular genetic alterations in gliomatosis cerebri resemble those in diffuse astrocytomas; (2) the prognosis of gliomatosis cerebri is variable but for at least 50% of patients as poor as for glioblastoma; and (3) some patients respond to radiotherapy and/or procarbazine, carmustine, vincristine chemotherapy.

The molecular and genetic basis of neurological tumours

There are no effective therapies for many tumours of the nervous system. This is, in part, a consequence of their location within relatively inaccessible tissues. It is also likely, however, that the unique characteristics of the cells that give rise to these tumours create a set of conditions that facilitate tumour development. Here, we consider recent advances in molecular genetics, the development of mouse models and developmental neurobiology as they relate to tumours of neuroectodermal origin. It is likely that these advances will provide insight into underlying mechanisms and provide a rational framework for the development of effective interventions.

Immunohistochemical markers for prognosis of cerebral glioblastomas

Glioblastoma is the commonest neuroectodermal tumor and the most malignant in the range of cerebral astrocytic gliomas. The prognostic utility of various biological markers for glioblastomas has been broadly tested but the results obtained are regarded as controversial. In the present study, 302 glioblastoma specimens were studied to evaluate a possible association between clinical outcome and expression of some immunohistochemical variables. Furthermore, tumors examined were subdivided on the three cytological subsets--small-cell (SGB), pleomorphic-cell (PGB) and gemistocytic (GGB). Immunohistochemical variables differed between various subsets: the number of p53-positive tumors was found to be prevailed among the PGB, whereas the number of tumors with EGFR and mdm2 positivity was significantly greater in SGB. GGB contained significantly lowest mean proliferating cell nuclear antigen (PCNA) labeling index (LI), greater number of p21ras positive cases, and higher mean apoptotic index (AI). Survival time in patients with SGB, EGFR and mdm2-positivity and PCNA LI >40% was found to be significantly shorter, whereas presence of p21ras and AI >0.5% were associated with prolonged survival. Multivariate analysis revealed that survival time is associated with SGB, EGFR-positivity, and AI (p = 0.0023, p = 0.0035 and p = 0.0029 respectively). We conclude that although some immunohistochemical variables were found to be significant for glioblastoma outcome, they appear to be closely related to biology of single cytological subsets. Furthermore, these variables exhibited no prognostic value when they were analyzed within each cytological subset separately. Therefore, the glioblastoma subdivision on three cytological subsets proposed by us is carrying some element of rationality but, undoubtedly, requires further prospective studies.

Molecular markers of prognosis in astrocytic tumors

BACKGROUND

Astrocytoma is a primary brain tumor that affects 20,000 Americans each year. To date, only age and histologic grade stand out as independent predictors of survival. There is now increased interest in the use of molecular markers as objective standards against which to establish diagnosis and grade.

METHODS

The study evaluated human glioma tumor suppressor genes and associated loci in fresh snap-frozen gliomas from 63 males and 37 females, with a median age of 42 years, including 19 low-grade astrocytomas. The tumor samples were selected so that about equal numbers of glioblastomas from younger and older patients were represented in the series. Methods for suppressor gene and genetic loci evaluation included loss of heterozygosity (LOH) analysis, multiplex polymerase chain reaction analysis, and gene sequencing.

RESULTS

Low-grade astrocytomas had the least number of molecular abnormalities. LOH on 9p and/or CDKN2A deletion occurred more often in glioblastomas (P < 0.001), LOH on 17p/TP53 mutations occurred more frequently in anaplastic astrocytomas (AAs; P = 0.112), and LOH on 10q/PTEN mutation frequency was similar in glioblastomas and AAs (P < 0.001). Poorer survival was associated significantly with the occurrence of either deletion of p16 (P = 0.031), LOH on 9p (P = 0.016), or LOH on 10q (P = 0.0007). The absence of LOH on 17p and the presence of PTEN mutation were associated marginally with survival. Even though TP53 mutations were more frequent among younger patients with glioblastoma, they had no statistically significant effect on survival after adjustment for age (P = 0.62). In all multivariate models, age and grade were the only significant predictors of survival or were nearly significant predictors of survival.

CONCLUSIONS

The results suggest that LOH on 9p and p16 deletions may prove to be objective standards for the diagnosis of patients with high-grade gliomas, although the absence of these abnormalities is nonprognostic.

Impact of genotype and morphology on the prognosis of glioblastoma

The recognition of molecular subsets among glioblastomas has raised the question whether distinct mutations in glioblastoma-associated genes may serve as prognostic markers. The present study on glioblastomas (GBM) from 97 consecutively sampled adult patients is based on a clinical, histopathological, immunohistochemical, and molecular genetic analysis. Parameters assessed were age at diagnosis, survival, cell type, proliferation, necrosis, microvascular proliferation, sarcomatous growth, lymphocytic infiltration, thromboses, calcifications, GFAP expression, MIB-1 index, loss of heterozygosity (LOH) of the chromosomal arms 1p, 10p, 10q, 17p, 19q and structural alterations in the TP53, EGFR and PTEN genes. As in previous studies, younger age was significantly associated with better survival. Among the molecular parameters, TP53 mutations and LOH10q emerged as favorable and poor prognostic factors, respectively. TP53 mutations were a favorable prognostic factor independent of whether glioblastomas were primary or secondary. LOH1p or 19q, lesions suspected to be over-represented in long term survivors with malignant glioma, were not associated with better survival. However, the combination of LOH1p and LOH19q defined GBM patients with a significantly better survival. Notably, these patients did not exhibit morphological features reminiscent of oligodendroglioma. These findings indicate that genotyping of glioblastoma may provide clinical information of prognostic importance.

Evaluation of molecular markers in low-grade diffuse astrocytomas: loss of p16 and retinoblastoma protein expression is associated with short survival

Diffuse astrocytomas have a median survival of 6-8 years. However, in a minority of cases that are histologically low grade, progression is rapid, leading to death within 2 years. Loss of p16, retinoblastoma protein, and deleted-in-colon-carcinoma protein expression, and monosomy of chromosome 10 have been shown to occur in malignant astrocytic tumors. We have investigated the prognostic value of expression of these markers, using techniques applicable in many histopathology laboratories, in diffuse astrocytomas that are histologically low grade. Paraffin sections from 71 diffuse, supratentorial, low-grade astrocytomas, from patients with at least 8-year survival data, were immunostained with antibodies to p16, deleted-in-colon-carcinoma protein, p53, Ki67, and retinoblastoma protein. In situ hybridization with a digoxigenin-labeled probe to chromosome 10 was used to assess chromosomal loss. In most cases there was immunostaining of virtually all tumor cell nuclei with antibodies to p16 and retinoblastoma protein. Three of the 68 tumors in which assessment of p16 was possible included discrete foci with lack of detectable immunoreactivity in tumor cells. The three patients concerned had a significantly shortened median survival (1.1 years vs 4.4 years in those without loss of p16; p <0.01). In six of the 61 cases where assessment of retinoblastoma protein was possible, <70% of tumor cell nuclei showed immunoreactivity. These six patients had a shorter survival (4.0 years) than had the remaining patients (5.4 years), although this difference was not statistically significant. The tumor from one of these patients included areas where only 36% of tumor cells showed retinoblastoma protein immunoreactivity, and this patient survived only 1.5 years. Tumors showing loss of both p16 and retinoblastoma were not seen. p53 and deleted-in-colon-carcinoma protein expression was highly variable and did not correlate with survival. Tumors with monosomy for chromosome 10 were not identified. Both polyploidy and the Ki67 labeling index were significantly associated with the p53 labeling index but not with survival. Focal loss of p16 or retinoblastoma protein is demonstrable in approximately 5% and 10% of diffuse low-grade diffuse astrocytomas, respectively. Tumors with focal loss of immunoreactivity for these proteins are associated with shorter survival than those without, suggesting that immunohistochemistry for p16 and retinoblastoma protein may be a useful adjunct to other methods for assessing the prognosis of astrocytomas.

The WHO classification of tumors of the nervous system

The new World Health Organization (WHO) classification of nervous system tumors, published in 2000, emerged from a 1999 international consensus conference of neuropathologists. New entities include chordoid glioma of the third ventricle, cerebellar liponeurocytoma, atypical teratoid/rhabdoid tumor, and perineurioma. Several histological variants were added, including tanycytic ependymoma, large cell medulloblastoma, and rhabdoid meningioma. The WHO grading scheme was updated and, for meningiomas, extensively revised. In recognition of the emerging role of molecular diagnostic approaches to tumor classification, genetic profiles have been emphasized, as in the distinct subtypes of glioblastoma and the already clinically useful 1p and 19q markers for oligodendroglioma and 22q/INI1 for atypical teratoid/rhabdoid tumors. In accord with the new WHO Blue Book series, the actual classification is accompanied by extensive descriptions and illustrations of clinicopathological characteristics of each tumor type, including molecular genetic features, predictive factors, and separate chapters on inherited tumor syndromes. The 2000 WHO classification of nervous system tumors aims at being used and implemented by the neuro-oncology and biomedical research communities worldwide.

Expression of p53 and prognosis in children with malignant gliomas

BACKGROUND

The prognosis of children with high-grade gliomas is uncertain, even when clinical and histologic findings are considered. We investigated whether mutations in the TP53 gene or the degree of expression of p53 protein in high-grade gliomas is associated with progression-free survival in children with these tumors.

METHODS

Paraffin-embedded specimens of malignant gliomas from children treated in the Children's Cancer Group study CCG-945 were assessed by mutational analysis of TP53 (121 specimens) and immunohistochemical analysis of p53 (115 specimens). For mutational studies, areas of tissue that contained malignant glioma were isolated by microdissection, and the DNA was subjected to polymerase-chain-reaction-based amplification and sequencing of TP53 exons 5, 6, 7, and 8. Immunohistochemical analysis was performed with the use of a microwave-enhanced antigen retrieval and an antibody that bound both wild-type and mutant p53.

RESULTS

We found a significant association between overexpression of p53 and outcome; this association was independent of histologic features, age, sex, the extent of resection, and tumor location. The rate ( +/- SE) of progression-free survival at five years was 44 +/- 6 percent in the group of 74 patients whose tumors had low levels of expression of p53 and 17 +/- 6 percent in the group of 41 patients whose tumors had overexpression of p53 (P<0.001). A nonsignificant association was observed between mutations in TP53 and outcome.

CONCLUSIONS

Overexpression of p53 in malignant gliomas during childhood is strongly associated with an adverse outcome, independently of clinical prognostic factors and histologic findings.

Preradiation chemotherapy for pediatric patients with high-grade glioma

BACKGROUND

To evaluate the feasibility and efficacy of intensive chemotherapy given prior to irradiation in pediatric patients with malignant glioma, the Society of Pediatric Oncology in Germany started a randomized trial in 1991. The high-grade glioma strata had to be closed because of insufficient patient accrual. The follow-up data from these patients are reported.

METHODS

Fifty-two patients with World Health Organization (WHO) Grade 4 malignant glioma (n = 27 patients) or with WHO Grade 3 anaplastic astrocytoma (n = 25 patients) between the ages of 3 years and 17 years were available for analysis. The tumor locations were supratentorial in 42 patients, the cerebellum in 8 patients, and the spinal cord in 2 patients (the brainstem was excluded). Tumor surgeries were biopsy in 10 patients, partial resection in 5 patients, subtotal resection in 10 patients, and macroscopic total resection in 21 patients. Patients received either 54 grays of irradiation (n = 22 patients) followed by chemotherapy with lomustine, vincristine, and cisplatin (maintenance chemotherapy) or sandwich chemotherapy (n = 30 patients), which consisted of ifosfamide, etoposide, methotrexate, cisplatin, and cytosine arabinoside followed by irradiation.

RESULTS

The extent of resection was the most important prognostic factor. The median survival was 5.2 years for patients who underwent tumor resection of > or = 90% compared with 1.3 years for patients who underwent less than complete resection (P < 0.0005). After undergoing macroscopic total resection, sandwich chemotherapy (n = 15 patients) resulted in better overall survival (median, 5.2 years) compared with the maintenance protocol (n = 16 patients; median survival, 1.9 years; P = 0.015). A Cox multivariate regression analysis showed better survival for female patients (P = 0.025), WHO Grade 3 disease (P = 0.016), tumor resection of > or = 90% (P = 0.003), irradiation with > or = 54 grays (P = 0.003), and sandwich chemotherapy (P = 0.006).

CONCLUSIONS

These data suggest that early, intensive chemotherapy increases survival rates in patients with malignant glioma who undergo complete resection.

Genetic and biologic progression in astrocytomas and their relation to angiogenic dysregulation

Infiltrative astrocytic neoplasms are the most common malignancies of the central nervous system. They remain clinically problematic because of their involvement of brain structures critical to proper cognitive, behavioral, and motor function; their widely invasive properties, which make them difficult to resect totally; and their nearly inevitable biologic progression in spite of adjuvant therapy. Glioblastoma multiforme (GBM, World Health Organization grade IV), the most malignant form of infiltrating astrocytoma, can present as a high-grade lesion from the outset (so-called de novo GBM) or can evolve from a lower grade precursor lesion (secondary GBM). Molecular genetic investigations suggest that GBM is best regarded as a clinicopathologic entity composed of multiple molecular genetic subsets. Molecular alterations associated with progression to GBM and that define genetic subsets include epidermal growth factor receptor amplifications, p53 mutations, retinoblastoma pathway alterations [most commonly, p16(CDKN2A) losses], and chromosome 10 alterations, including PTEN mutations. Despite the wide range of genetic events that ultimately lead to GBM, the vascular changes that evolve are remarkably similar. Microvascular hyperplasia is spatially and temporally associated with pseudopalisading necrosis in GBM and is believed to be driven by hypoxia-induced expression of proangiogenic cytokines such vascular endothelial growth factor. In addition, genetic alterations in GBM are thought to contribute directly or indirectly to angiogenic dysregulation. Both p53 mutations and genetic losses on chromosome 10 may tip the balance toward an angiogenic phenotype through upregulation of proangiogenic factors and/or downregulation of angiogenesis inhibitors. Understanding genetic events and their relation to angiogenic regulation in astrocytic neoplasms may eventually lead to therapies that are specifically directed at molecularly defined subsets of these diseases.

Genetics of nervous system tumors

Genetic aberrations are being defined for the various glial tumors. Astrocytic tumors can evolve by two different pathways. The genetic aberrations now being defined for these two pathways are different and can be associated with the grade of malignancy. In oligodendrogliomas, the genetic lesions differ from the astrocytic tumors, and several markers have been linked to chemosensitivity response and survival. Genetic aberrations in ependymomas also differ from the astrocytic tumors or oligodendrogliomas. Although additional cases are needed to study the genetic aberrations, the abnormalities identified suggest that spinal cord tumors carry different markers than intracranial tumors and that the markers within the cranium may be different based on their location.

Diagnosis and management of astrocytomas, oligodendrogliomas and mixed gliomas: a review

Low-grade gliomas are a diverse group of neoplasms which, as the name implies, are thought to arise from glial cells. Common among this group are astrocytomas (low-grade astrocytoma; LGA), oligodendrogliomas and mixed gliomas. Among these, LGA is the commonest low-grade glioma and, occasionally, although incorrectly, the terms are used interchangeably. Advances in imaging technology have improved the accuracy of preoperative diagnosis. The management of low-grade gliomas is controversial. Recent evidence suggests that previously considered standard therapy (i.e. surgery plus radiotherapy) may not be in the patient's best interests. A review of the available published research concerning low-grade gliomas is therefore timely.

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.

Malignant transformation of a gangliocytoma/ganglioglioma into a glioblastoma multiforme: a molecular genetic analysis. Case report

A gangliocytoma/ganglioglioma with no atypical or malignant features was subtotally resected from the right temporal lobe of a 16-year-old woman. A second resection was performed 8 years later to treat a locally recurrent lesion with increased cellularity that was diagnosed as a World Health Organization Grade II ganglioglioma on the basis of neuropathological examination. Molecular analysis of the recurrent tumor revealed a TP53 gene mutation, but no amplification of the epidermal growth factor receptor (EGFR) gene. Radiotherapy (60 Gy) was administered after the second resection. The patient returned 1 year later with a second focal recurrence. The specimen obtained during the third resection of tumor exhibited exclusively astrocytic differentiation, cellular pleomorphism with multinucleated cells, high mitotic activity, and endothelial proliferation. Therefore, the tumor was diagnosed to be a glioblastoma multiforme (GBM). Molecular analysis of tumor DNA from the second recurrent tumor demonstrated the presence of the TP53 mutation, which previously had been observed in the first recurrent tumor, but again no evidence of EGFR amplification. Findings demonstrate that the presence of TP53 mutation in progressed gangliogliomas should be interpreted as a progression-associated mutation rather than a consequence of treatment. This is the first report to indicate that the molecular pathways of gangliocytomas/gangliogliomas progressing to become GBMs may parallel those of diffuse astrocytomas progressing to become GBMs.

Biological mechanisms of glioma invasion and potential therapeutic targets

The current understanding of glioma biology reveals targets for anti-invasive therapy which include manipulations of extracellular matrix and receptors, growth factors and cytokines, proteases, cytoskeletal components, oncogenes and tumor suppressor genes. A better understanding of the complex regulation and the signalling molecules involved in glioma invasion is still needed in order to design new and effective treatment modalities towards invasive tumor cells. Representative and valid in vitro experimental systems and animal models of gliomas are necessary for the characterization of the invasive phenotype and further development of anti-invasive therapy. In the future, it will probably be important to move from comparative genomic modelling through protein characterization based on advanced proteomic techniques to analyse tissue samples, where the aim for gliomas should be to compare invaded and non-invaded tissue. This will hopefully render promising new therapeutic targets for gliomas.

Genetically engineered mouse models of astrocytoma: GEMs in the rough?

Astrocytomas are the most common form of brain cancer and are essentially incurable due to their diffusely infiltrative nature. Mouse models of astrocytoma provide a useful system for understanding tumorigenesis of astrocytomas and for designing and testing new therapies. Although molecular genetic alterations have been characterized in human astrocytomas, many of the mice engineered with these mutations do not develop astrocytomas. Recently, successful modeling of astrocytoma in the mouse has suggested that the combination of molecular alterations, the cell type in which the alterations take place, and the strain background all play a role in generating a model of astrocytoma.

Genetics of brain neoplasms

Transformation of a normal cell into a malignant cell involves a series of events that damage the genome. Gliomas are the most common adult neoplasm of the central nervous system. To develop new therapeutic strategies requires an understanding of the specific lesions that occur and contribute to this malignant process. Initially, data reported from the analyses of human gliomas were quite variable. This has recently changed as more data have become available and the selection of tissue analyzed is coupled with clinical criteria. Specific genetic lesions are now defining different glioma pathways, and some aberrations may be indicative of therapeutic response. This review focuses on the specific genetic aberrations associated with astrocytic and oligodenroglial tumors.

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.

Prognostic value of the expression of tumor suppressor genes p53, p21, p16 and prb, and Ki-67 labelling in high grade astrocytomas treated with radiotherapy

Cumulative inactivation of tumor suppressor genes and/or amplification of oncogenes lead to progressively more malignant astrocytic tumors. We have analyzed the significance of tumor suppressor genes p53, p21, p16 and retinoblastoma protein (pRb) and proliferative activity for survival in 77 high grade astrocytic tumors. After operation, the patients--25 anaplastic astrocytomas (AA) and 52 glioblastomas (GBs)--were treated with similar radiotherapy. The expression of the suppressor genes and the proliferative activity were analyzed immunohistochemically. p53 immunopositivity was found in 44% of AAs and 46% of GBs. Tumors with aberrant p53 expression had lower proliferation indices than p53 immunonegative tumors. Neither p53 expression nor p21 immunonegativity (52% of AAs and 48% of GBs) correlated with survival. p16 immunostaining was negative in 16% of AAs and in 44% of GBs, and it correlated inversely with survival in both uni- and multivariate analyses. pRb immunostaining was negative only in 8% of both AAs and GBs and the absence of p16 and pRb were mutually exclusive. Ki-67 labelling index (LI) was significantly higher in GBs (26.8%) than in AAs (20.3%), and in multivariate analysis it was an independent prognostic factor for survival. In 48% of AAs Ki-67 LI exceeded 20% and this subset of AAs had similar prognosis as GB. In high grade astrocytic tumors p16 immunonegativity was an independent indicator of poor prognosis in addition to the previously established patient's age, histopathology and Ki-67 LI. Furthermore, there was a subset of AAs with a high proliferation rate (> 20%) in which the histopathological hallmarks of GB were lacking, but which had similarly dismal prognosis as GB.

Gliomagenesis: genetic alterations and mouse models

Glioblastoma multiforme is the most malignant of the primary brain tumours and is almost always fatal. The treatment strategies for this disease have not changed appreciably for many years and most are based on a limited understanding of the biology of the disease. However, in the past decade, characteristic genetic alterations have been identified in gliomas that might underlie the initiation or progression of the disease. Recent modelling experiments in mice are helping to delineate the molecular aetiology of this disease and are providing systems to identify and test novel and rational therapeutic strategies.

Animal models of cell cycle dysregulation and the pathogenesis of gliomas

Mutations in gliomas, for the most part, fall into two main categories. The first category of mutations affects genes that produce proteins which activate signal transduction pathways downstream of tyrosine kinase receptors; the second category disrupts the pathways leading to cell cycle arrest. Cell cycle arrest pathways normally maintain cells in the G1 phase of the cell cycle, preventing inappropriate proliferation. The role of disregulation of these pathways in tumor formation is currently the focus of many investigations. Studies carried out with astrocytes and other cell types indicate that these pathways may also function in maintenance of appropriate chromosome number and differentiated phenotype, and in acquisition of senescence. Genetically defined mouse models of gliomagenesis have been helpful in increasing our understanding of how cell cycle arrest pathways cooperate with alterations in signal transduction pathways to provoke tumor formation in many cell types, including glial cells. Various strategies for experimental cell cycle arrest disruption show minimal or no formation of gliomas. In contrast, gliomas are generated with a number of strategies that enhance signal transduction downstream of tyrosine kinase receptors. Experimental disruption of the cell cycle arrest pathways is required for gliomagenesis in some of these models, but not in others. Furthermore in some cases, although not required for gliomagenesis, disruption of the cell cycle arrest pathways appears to enhance glioma formation. The results of these mouse model experiments imply a potentially complex role for cell cycle arrest disruption in human gliomagenesis.

Genotype-phenotype correlation in gemistocytic astrocytomas

OBJECTIVE

Gemistocytic astrocytomas often behave aggressively and carry the least favorable prognosis among diffuse astrocytomas. The frequency of p53 mutations has been reported to be significantly higher in the gemistocytic variant as compared with other astrocytomas.

METHODS

Between 1985 and 1998, we selected 25 tumor samples from among 201 samples from patients with gemistocytic astrocytomas operated on at the Mayo Clinic. Exons 5 to 8 of the p53 gene were sequenced using an automated deoxyribonucleic acid sequencer. Morphometric characterization of individual gemistocytes was performed using an image analysis program.

RESULTS

Of 25 tissue samples analyzed, 16 were found to carry a p53 missense mutation (three in exon 5, three in exon 6, one in exon 7, and nine in exon 8), and one sequence variant was synonymous. Mutations were clustered at codons 151 (2 of 17 mutations), 193 (3 of 17 mutations), and 273 (5 of 17 mutations) of the p53 gene. Patients whose tumors carried a p53 mutation were significantly younger than other patients, and their tumors tended to accumulate more p53 protein than those of other patients. Phenotype analysis of gemistocytes revealed that the sizes of tumor cell nuclei and of entire tumor cells in the same tissue area were positively correlated. Smaller tumor cell nuclei tended to be less circular or more atypical. In addition, more atypical gemistocytes were found in tumors lacking a wild-type p53 allele as well as in tissue from patients whose postoperative survival was shorter.

CONCLUSION

Our data confirm that the frequency of p53 mutations is significantly higher (approximately twofold) in gemistocytic astrocytomas as compared with other astrocytoma subtypes. Whether the high frequency of p53 mutations contributes to the more aggressive behavior of gemistocytic astrocytomas, however, remains unclear.

Promoter hypermethylation of the RB1 gene in glioblastomas

Loss of expression of the retinoblastoma gene (RB1) has been shown to occur in up to 25% of glioblastomas (WHO Grade IV). To elucidate the underlying mechanism, we assessed RB1 promoter hypermethylation using methylation-specific polymerase chain reaction and RB1 expression by immunohistochemistry in 35 primary (de novo) glioblastomas and in 21 secondary glioblastomas that had progressed from low-grade diffuse astrocytoma (WHO Grade II) or anaplastic astrocytoma (WHO Grade III). Promoter hypermethylation was significantly more frequent in secondary (9 of 21, 43%) than in primary glioblastomas (5 of 35, 14%; p = 0.0258). There was a clear correlation between loss of RB1 expression and promoter hypermethylation. In the majority of glioblastomas with loss of RB1 expression, there was promoter hypermethylation (11 of 13, 85%), whereas 93% of tumors with RB1 expression had a normal RB1 gene status (p < 0.0001). In three glioblastomas, areas with and without RB1 expression were microdissected; promoter hypermethylation was detected only in areas lacking RB1 expression. In patients with multiple biopsies, methylation of the RB1 promoter was not detectable in the less malignant precursor lesions, ie, low-grade diffuse and anaplastic astrocytoma. These results indicate that promoter hypermethylation is a late event during astrocytoma progression and is the major mechanism underlying loss of RB1 expression in glioblastomas.

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.

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.

Low grade astrocytomas: controversies in management

Low grade astrocytomas are common brain neoplasms that primarily affect young adults. Although these patients often have a reasonably long survival, most will ultimately succumb to their tumours. Often the tumours progress to higher grade astrocytomas. The optimal management plan for these tumours is controversial and ranges from observation to macroscopic excision, radiotherapy and chemotherapy. The evidence for each of these approaches is presented in this review and a management algorithm is presented.

The Akt/protein kinase B-dependent anti-apoptotic pathway and the mitogen-activated protein kinase cascade are alternatively activated in human glioblastoma multiforme

We investigated the activation of two important signal transduction pathways in human glioblastoma cells and found a constitutive phosphorylation of either Akt or mitogen-activated protein kinase (MAPK) under serum free conditions. In all but one cell line Wortmannin-sensitive activation of Akt could be attributed to the loss of functional PTEN protein. All cell lines with Akt activation exhibited only weak phosphorylation of the MAPK signal pathway, whereas those without constitutive Akt activation demonstrated high levels of phosphorylated MAPK under serum free conditions. Our data might indicate the presence of two functional subtypes of glioblastoma multiforme, since Akt and MAPK are involved in cellular survival and proliferation signalling, respectively.

Chromosomal instability and p53 inactivation are required for genesis of glioblastoma but not for colorectal cancer in patients with germline mismatch repair gene mutation

We have previously reported high-frequency microsatellite instability (MSI-H) and germ-line mismatch repair gene mutation in patients with unusually young onset of high-grade glioma. Some of these patients developed metachronous MSI-H colorectal cancer and conformed to the diagnosis of Turcot's syndrome. Frameshift mutation of TGFbetaRII was present in all the colorectal carcinomas but not in brain tumours. We further characterized the genetic pathways of tumour evolution in these metachronous gliomas and colorectal carcinomas. All MSI-H glioblastomas had inactivation of both alleles of the p53 gene and showed over-expression of the p53 protein while none of the colorectal carcinomas had p53 mutation or protein over-expression. Flow cytometry and comparative genomic hybridization revealed that all glioblastomas were chromosomal unstable with aneuploid DNA content, and with a variable number of chromosomal arm aberrations. In contrast, the colorectal carcinomas had diploid or near-diploid DNA content with few chromosomal arm aberrations. The pattern of chromosomal aberrations in the two organs was different. Loss of 9p was consistently observed in all glioblastomas but not in colorectal carcinomas. Epidermal growth factor receptor amplification was absent in all glioblastomas and colorectal carcinomas. Our results suggest that both the frequency of p53 mutation and its effects differ greatly in the two organs. Following loss of mismatch repair function, p53 inactivation and chromosomal instability are not necessary for development of colorectal carcinoma, but are required for genesis of glioblastoma. Oncogene (2000) 19, 4079 - 4083.

Comprehensive allelotype and genetic anaysis of 466 human nervous system tumors

Brain tumors pose a particular challenge to molecular oncology. Many different tumor entities develop in the nervous system and some of them appear to follow distinct pathogenic routes. Molecular genetic alterations have increasingly been reported in nervous system neoplasms. However, a considerable number of affected genes remain to be identified. We present here a comprehensive allelotype analysis of 466 nervous system tumors based on loss of heterozygosity (LOH) studies with 129 microsatellite markers that span the genome. Specific alterations of the EGFR, CDK4, CDKN2A, TP53, DMBT1, NF2, and PTEN genes were analyzed in addition. Our data point to several novel genetic loci associated with brain tumor development, demonstrate relationships between molecular changes and histopathological features, and further expand the concept of molecular tumor variants in neuro-oncology. This catalogue may provide a valuable framework for future studies to delineate molecular pathways in many types of human central nervous system tumors.

Loss of heterozygosity on chromosome 19 in secondary glioblastomas

Glioblastomas develop rapidly de novo (primary glioblastomas) or slowly through progression from low-grade or anaplastic astrocytoma (secondary glioblastomas). Recent studies have shown that these glioblastoma subtypes develop through different genetic pathways. Primary glioblastomas are characterized by EGFR amplification/overexpression, PTEN mutation, homozygous p16 deletion, and loss of heterozygosity (LOH) on entire chromosome 10, whereas secondary glioblastomas frequently contain p53 mutations and show LOH on chromosome 10q. In this study, we analyzed LOH on chromosomes 19q, 1p, and 13q, using polymorphic microsatellite markers in 17 primary glioblastomas and in 13 secondary glioblastomas that progressed from low-grade astrocytomas. LOH on chromosome 19q was frequently found in secondary glioblastomas (7 of 13, 54%) but rarely detected in primary glioblastomas (1 of 17, 6%, p = 0.0094). The common deletion was 19q13.3 (between D19S219 and D19S902). These results suggest that tumor suppressor gene(s) located on chromosome 19q are frequently involved in the progression from low-grade astrocytoma to secondary glioblastoma, but do not play a major role in the evolution of primary glioblastomas. LOH on chromosome 1p was detected in 12% of primary and 15% of secondary glioblastomas. LOH on 13q was detected in 12% of primary and in 38% of secondary glioblastomas and typically included the RB locus. Except for 1 case, LOH 13q and 19q were mutually exclusive.

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.

Genetic reflection of glioblastoma biopsy material in xenografts: characterization of 11 glioblastoma xenograft lines by comparative genomic hybridization

OBJECT

Human tumors implanted as subcutaneous xenografts in nude mice are widely used for the study of tumor biology and therapy. Validation of these models requires knowledge of the genetic makeup of the xenografts. The aim of this study was to establish whether chromosomal imbalances in 11 xenograft lines derived from human glioblastomas multiforme (x-GBMs) are similar to those found in GBM biopsy samples. The authors also studied genetic stability during serial passaging of three xenograft lines.

METHODS

Chromosomal imbalances in x-GBMs were detected using comparative genomic hybridization (CGH). The authors compared the CGH results in x-GBMs with those in the original GBMs (o-GBMs) that were used to establish three of the xenograft lines and with the GBM biopsy results reported in the literature (1-GBMs). In three xenograft lines two different passages were analyzed.

CONCLUSIONS

The results show that the chromosomal imbalances in x-GBMs are similar to those in o-GBMs and 1-GBMs, indicating that the GBM xenograft lines used were valid models from a genetic point of view. The CGH analysis of two different passages of three xenograft lines indicates that x-GBMs (like 1-GBMs) show intratumoral genetic heterogeneity and do not acquire chromosomal imbalances as a result of serial passaging.

Genetic profile of gliosarcomas

There are distinct genetic pathways leading to the glioblastoma, the most malignant astrocytic brain tumor. Primary (de novo) glioblastomas develop in older patients and are characterized by epidermal growth factor (EGF) receptor amplification/overexpression, p16 deletion, and PTEN mutations, whereas secondary glioblastomas that progressed from low-grade or anaplastic astrocytoma develop in younger patients and frequently contain p53 mutations. In this study, we assessed the genetic profile of gliosarcoma, a rare glioblastoma variant characterized by a biphasic tissue pattern with alternating areas displaying glial and mesenchymal differentiation. Single-strand conformation polymorphism followed by direct DNA sequencing revealed p53 mutations in five of 19 gliosarcomas (26%) and PTEN mutations in seven cases (37%). Homozygous p16 deletion was detected by differential polymerase chain reaction in seven (37%) gliosarcomas. The overall incidence of alterations in the Rb pathway (p16 deletion, CDK4 amplification, or loss of pRb immunoreactivity) was 53%, and these changes were mutually exclusive. Coamplification of CDK4 and MDM2 was detected in one gliosarcoma. None of the gliosarcomas showed amplification or overexpression of the EGF receptor. Thus gliosarcomas exhibit a genetic profile similar to that of primary (de novo) glioblastomas, except for the absence of EGFR amplification/overexpression. Identical PTEN mutations in the gliomatous and sarcomatous tumor components were found in two cases. Other biopsies contained p16 deletions, an identical p53 mutation, or coamplification of MDM2 and CDK4 in both tumor areas. This strongly supports the concept of a monoclonal origin of gliosarcomas and an evolution of the sarcomatous component due to aberrant mesenchymal differentiation in a highly malignant astrocytic neoplasm.

A mouse model for glioma: biology, pathology, and therapeutic opportunities

The epidermal growth factor receptor (EGFR) gene is amplified or mutated in 30-50% of human glioblastoma multiforme. These mutations are usually associated with deletions of the INK4a-ARF locus, which encodes 2 gene products (p16INK4a and p19ARF) involved in cell cycle arrest and apoptosis. We have investigated the role of EGFR mutation in gliomagenesis using avian retroviral vectors to transfer a mutant EGFR gene to glial precursors and astrocytes in transgenic mice. These mice express tv-a, a gene encoding the retrovirus receptor TVA, which is under the control of brain cell type-specific promoters. We demonstrate that expression of a constitutively active, mutant form of EGFR in cells in the glial lineage can induce lesions with many similarities to human gliomas, including increased cell density, vascular proliferation, and immunohistochemical staining for glial fibrillary acidic protein (GFAP) and nestin. We also demonstrate that primary astrocytes cultured from transgenic mice expressing tv-a from the GFAP promoter are efficiently infected in culture, and such genetically modified cell cultures can be tumorigenic in nude mice. The combinations of genetic lesions (eg, mutated EGFR, INK4a-/-) leading to tumor formation in these 2 mouse systems are similar to those found in human gliomas. These genetically defined animal models for gliomas will allow for the testing of therapies that are targeted specifically at the gene products involved in the pathogenesis of gliomas.

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.

Adenovirus-mediated p53 gene therapy for human gliomas

OBJECTIVE

The rationale and current evidence for using p53 gene replacement as a potential treatment for human gliomas are reviewed. The possible benefits of and obstacles to this approach are delineated.

METHODS

One approach to overcoming the poor outcomes associated with conventional glioma therapies involves the replacement of tumor suppressor genes that are fundamental to glioma development. The p53 gene is one of the most frequently mutated genes in human gliomas, and loss of p53 function is critical to the development of glial neoplasms. Consequently, replacement of the p53 gene using viral vectors may be a potential treatment for human gliomas.

RESULTS

In vitro studies demonstrate that adenovirus-mediated p53 gene transfer into gliomas with mutant p53 results in massive apoptosis. Similarly, transfer of p53 inhibits tumor growth in vivo. In contrast to mutant p53 gliomas, wild-type p53 glioma cells are resistant to the apoptotic effects of p53 transfer, but this resistance can be overcome by the addition of deoxyribonucleic acid-damaging agents such as ionizing radiation or chemotherapy. The main obstacle to p53 gene therapy involves the limitations associated with current modes of delivery.

CONCLUSION

Preclinical data strongly support the use of p53 gene transfer as a potential treatment for human gliomas.

Genetic alterations in pediatric high-grade astrocytomas

High-grade astrocytomas are tumors that are uncommon in children. Relatively few studies have been performed on their molecular properties and so it is not certain whether they follow different genetic pathways from those described in adult diffuse astrocytomas. In this study, we evaluated 24 pediatric high-grade astrocytomas (11 anaplastic astrocytomas and 13 glioblastomas) all of which were sporadic and primary. We studied mutations of p53, phosphatase and tensin homolog (PTEN), loss of heterozygosity (LOH) of chromosomes 17p13, 9p21 and 10q23-25, amplification of epidermal growth factor receptor (EGFR), and overexpression of EGFR and p53 protein. In addition, we searched for microsatellite instability (MSI) by using MSI sensitive and specific microsatellite markers. p53 mutations were found in 38% (9/24) of the high-grade astrocytomas and all brain stem tumors except 2 (71%, 5/7) had p53 mutations. PTEN mutations were found in 8% (2/24) of high-grade astrocytomas. However, no EGFR amplification was found in any of them. LOH was found at 17p13.1 in 50% (3/6 informative tumors), 9p21 in 83% (5/6 informative tumors), and 10q23-25 in 78% (7/9 informative tumors). Four tumors showed MSI, and 2 of them that showed widespread MSI were regarded as tumors with replication error (RER+) phenotype. All 4 tumors with MSI showed concurrent LOH of 9p21 and 10q23-25. Combining gene alterations, LOH, MSI, and gene mutations, inactivation of both alleles of PTEN and p53 was found in 57% (4/7 informative tumors) and 50% (3/6 informative tumors) of the cases respectively. We conclude that development of pediatric high-grade astrocytomas may follow pathways different from the primary or secondary paradigm of adult glioblastomas. In a subset of these tumors, genomic instability was also implicated.

Gene therapy for gliomas: molecular targets, adenoviral vectors, and oncolytic adenoviruses

Currently, most of the approved clinical gene therapy protocols involve cancer patients and several of the therapies are designed to treat brain tumors. Two factors promoting the use of gene therapy for gliomas are the failure and toxicity of conventional therapies and the identification of the genetic abnormalities that contribute to the malignancy of gliomas. During the malignant progression of astrocitic tumors several tumor suppressor genes are inactivated, and numerous growth factors and oncogenes are overexpressed progressively. Thus, theoretically, brain tumors could be treated by targeting their fundamental molecular defects, provided the gene-drug can be delivered to a sufficient number of malignant cells. However, gene therapy strategies have not been abundantly successful clinically, in part because the delivery systems are still imperfect. In the first part of this brief review we will discuss the most common targets for gene therapy in brain tumors. In the second part, we will review the evolution of adenoviruses as gene vehicles. In addition, we will examine the role of recombinant mutant oncolytic adenoviruses as anticancer tools. From the results to date it is clear that gene therapy strategies for brain tumors are quite promising but more critical research is required, mainly in the vector field, if the strategies are to achieve their true potential in ameliorating patients with gliomas.

Clinicopathologic study of 85 similarly treated patients with anaplastic astrocytic tumors. An analysis of DNA content (ploidy), cellular proliferation, and p53 expression

BACKGROUND

The biologic behavior of anaplastic (World Health Organization Grade III) astrocytomas and oligoastrocytomas is highly variable, ranging from rapid progression to prolonged survival. It is difficult to predict the outcome of an individual patient based on morphology alone.

METHODS

To determine the prognostic value of commonly used clinicopathologic markers, we reviewed our experience with 85 similarly treated patients enrolled in 3 North Central Cancer Treatment Group high grade glioma protocols. The pathology was comprised exclusively of primary anaplastic astrocytic tumors (66 astrocytomas and 19 oligoastrocytomas). Variables examined included patient age, morphologic type, preoperative performance score, extent of surgery, solitary versus multiple mitoses, DNA flow cytometric and image morphometric parameters, and expression of proliferating cell nuclear antigen, MIB-1, and p53 expression.

RESULTS

The study was comprised of 48 men and 37 women ranging in age from 14-79 years (median age, 47 years). Overall survival ranged from <1 month to >12 years (median, 21.6 months). Statistical analyses revealed that age accounted for the majority of this extensive variability in survival. The median survival times were 65. 5 months, 22.1 months, and 4.4 months, respectively, for the groups <40 years, 40-59 years, and >/=60 years, respectively (P < 0.0001). On univariate analyses, aneuploidy by flow cytometry and a low performance score also predicted a better survival (P values of 0.04 and 0.009, respectively). Statistical trends predicting a better survival were observed for patients with a solitary mitosis and p53 immunopositivity. However, only patient age remained significant in multivariate models.

CONCLUSIONS

In a small but relatively uniformly treated cohort of patients with anaplastic astrocytomas and oligoastrocytomas, patient age was associated strongly and inversely with overall survival. Once patient age was taken into account, the clinical and pathologic markers tested appeared to be of limited prognostic value.

Molecular genetic analysis of ependymal tumors. NF2 mutations and chromosome 22q loss occur preferentially in intramedullary spinal ependymomas

Ependymal tumors are heterogeneous with regard to morphology, localization, age at first clinical manifestation, and prognosis. Several molecular alterations have been reported in these tumors, including allelic losses on chromosomes 10, 17, and 22 and mutations in the NF2 gene. However, in contrast to astrocytic gliomas, no consistent molecular alterations have been associated with distinct types of ependymal tumors. To evaluate whether morphological subsets of ependymomas are characterized by specific genetic lesions, we analyzed a series of 62 ependymal tumors, including myxopapillary ependymomas, subependymomas, ependymomas, and anaplastic ependymomas, for allelic losses on chromosome arms 10q and 22q and mutations in the PTEN and NF2 genes. Allelic losses on 10q and 22q were detected in 5 of 56 and 12 of 54 tumors, respectively. Six ependymomas carried somatic NF2 mutations, whereas no mutations were detected in the PTEN gene. All six of the NF2 mutations occurred in ependymomas of WHO grade II and were exclusively observed in tumors with a spinal localization (P = 0.0063). These findings suggest that a considerable fraction of spinal ependymomas are associated with molecular events involving chromosome 22 and that mutations in the NF2 gene may be of primary importance for their genesis. Furthermore, our data suggest that the more favorable clinical course of spinal ependymomas may relate to a distinct pattern of genetic alterations different from that of intracerebral ependymomas.