Subsets of glioblastoma multiforme defined by molecular genetic analysis

Molecular pathogenesis of pediatric astrocytic tumors

Astrocytomas are the most common pediatric brain tumors, accounting for 7%-8% of all childhood cancers. Relatively few studies have been performed on their molecular properties; therefore, classification of pediatric astrocytic tumors into genetic subtypes similar to that of adult tumors remains to be defined. Here, we report an extensive characterization of 44 pediatric astrocytomas--16 diffuse astrocytomas (WHO grade II), 10 anaplastic astrocytomas (WHO grade III), and 18 glioblastomas (WHO grade IV)--in terms of genetic alterations frequently observed in adult astrocytomas. Some form of p53 mutation was found in three diffuse astrocytomas, in three anaplastic astrocytomas, and in six glioblastomas examined; PTEN mutations were detected only in two glioblastomas. EGFR amplification was detected in only one anaplastic astrocytoma and two glioblastomas, but no amplification was observed for the PDGFR-alpha gene. Loss of heterozygosity (LOH) on 1p/19q and 10p/10q was less common in pediatric astrocytic tumors than in those seen in adults, but the frequency of LOH on 22q was comparable, occurring in 44% of diffuse astrocytomas, 40% of anaplastic astrocytomas, and 61% of glioblastomas. Interestingly, a higher frequency of p53 mutations and LOH on 19q and 22q in tumors from children six or more years of age at diagnosis was found, compared with those from younger children. Our results suggest some differences in children compared to adults in the genetic pathways leading to the formation of de novo astrocytic tumors. In addition, this study suggests potentially distinct developmental pathways in younger versus older children.

A changing paradigm of glioma biology

The past 30 years have witnessed a major paradigm shift in brain tumor research with the development of a wide variety of molecular biology techniques. These methods have permitted a better understanding of the pathogenesis of gliomas including the finding of neural stem cells that contribute to the establishment and continuous population of brain tumors. Molecular biology has contributed to our understanding of prognosis in these tumors with findings of genetic correlations to patient age, response to treatment, and outcome. Gene therapy has been made possible by molecular techniques that contribute to new treatment options. Nevertheless, if these advances are to make substantial clinical improvements, attention must be paid to issues of tumor evolution, local versus general pathogenesis, tumor heterogeneity, both general and regional, and the development of resistance to treatment. Appropriate clinical trials will be needed to test these new findings.

Ectopic doublecortin gene expression suppresses the malignant phenotype in glioblastoma cells

Doublecortin (DCX) is one of the three genes found from Affymetrix gene chip analysis related to glioma patient survival. Two other genes (e.g., osteonectin and semaphorin 3B) are well characterized as antioncogenic and tumor suppressor genes. However, there is no report about the involvement of DCX in cancer. Here, we show that gene transfer technology into DCX-deficient glioblastoma cell lines, such as A172, U87, U251N, RG2, and 9L, with DCX cDNA significantly suppressed growth of these glioma cells. U87 cells with ectopic expression of DCX exhibit a marked suppression of the transformed phenotype as growth arrested in the G(2) phase of the cell cycle progression, small colony formation in soft agar, and no tumor formation in nude rats. This transformed phenotype can be restored by knocking down DCX expression with DCX small interfering RNA. DCX was highly phosphorylated in glioma cells. Phosphorylation in the glioma cells was greater than in noncancer cells such as mouse NIH 3T3 and human embryonic kidney 293T cells. Coimmunoprecipitation of the phosphorylated DCX and spinophilin/neurabin II from DCX-synthesizing glioma cells indicated their interaction. This interaction would lead to a block of anchorage-independent growth as neurabin II is a synergistic inhibitor of anchorage-independent growth with p14ARF (ARF). Interaction between phosphorylated DCX and neurabin II may induce the association of the protein phosphatase 1 catalytic subunit (PP1) with neurabin II and inactivate PP1 and block mitosis during G(2) and M phases of the cell cycle progression. Thus, DCX seems to be a tumor suppressor of glioma.

O6-methylguanine-DNA methyltransferase expression strongly correlates with outcome in childhood malignant gliomas: results from the CCG-945 Cohort

PURPOSE

O6-methylguanine-DNA methyltransferase (MGMT) functions to counteract the cytotoxic effects of alkylating agents, such as nitrosoureas, which play a central role in the treatment of childhood malignant gliomas. Epigenetic silencing of MGMT has been associated with prolonged survival in adults with malignant gliomas, although the association between MGMT expression status and outcome in pediatric malignant gliomas has not been defined.

METHODS

We examined the association between MGMT expression and survival duration using tumor samples from the Children's Cancer Group 945 study, the largest randomized trial for childhood malignant gliomas completed to date. All patients received alkylator-based chemotherapy as a component of adjuvant therapy. Archival histopathologic material yielded tissue of sufficient quality for immunohistochemical assessment of MGMT expression status in 109 specimens.

RESULTS

Twelve of the 109 samples demonstrated overexpression of MGMT compared with normal brain. Five-year progression-free survival was 42.1% +/- 5% in the 97 patients whose tumors had low levels of MGMT expression versus 8.3% +/- 8% in the 12 patients whose tumors overexpressed MGMT (P = .017, exact log-rank test). The association between MGMT overexpression and adverse outcome remained significant after stratifying for institutional histologic diagnosis (eg, anaplastic astrocytoma or glioblastoma multiforme), as well as age, amount of residual tumor, and tumor location.

CONCLUSION

Overexpression of MGMT in childhood malignant gliomas is strongly associated with an adverse outcome in children treated with alkylator-based chemotherapy, independently of a variety of clinical prognostic factors.

Preferential inactivation of the p53 tumor suppressor pathway and lack of EGFR amplification distinguish de novo high grade pediatric astrocytomas from de novo adult astrocytomas

Classification of high grade astrocytomas of children into genetic subtypes similar to the adult remains to be defined. Here we report an extensive characterization of 29 high grade pediatric astrocytomas, 7 WHO grade III and 22 WHO grade IV, for genetic alterations frequently observed in high grade adult astrocytomas occurring in either the p53/MDM2/p14ARF or Rb/CDK4/p16INK4a tumor suppressor pathways. In addition, we have assessed the contribution of EGFR overexpression and amplification and LOH for chromosome 10, two genetic alterations commonly associated with the development of de novo adult glioblastoma for their roles in the development of de novo astrocytomas of childhood. Our results suggest two major differences in the genetic pathway(s) leading to the formation of de novo high grade astrocytomas in children compared with those of the adult. Our findings show preferential inactivation of the p53 tumor suppressor pathway in >95% of pediatric astrocytomas versus inactivation of the Rb tumor suppressor pathway in <25% of the same tumors. In addition, de novo high grade pediatric astrocytomas lack amplification of the EGFR gene compared with EGFR amplification in one-third of adult glioblastomas. Since drug treatments and gene therapy strategies exploit specific genetic alterations in tumor cells, our findings have important implications for the future development of treatments for high grade pediatric astrocytomas.

Frequent co-alterations of TP53, p16/CDKN2A, p14ARF, PTEN tumor suppressor genes in human glioma cell lines

In this study we established the simultaneous status of TP53, p16, p14ARF and PTEN tumor suppressor genes in 34 randomly chosen human glioma cell lines. Nine cell lines (26.4%) harbored mutations or deletions in all four tumor suppressor genes and 22 cell lines (64%) had alterations in at least three. Mutations/deletions were found at the following frequencies: TP53 (76.5%), p14ARF (64.7%), p16 (64.7%), PTEN (73.5%). Thus, there was a high incidence of alterations in the cellular pathways involving the p53 transcription factor (94.1%), the retinoblastoma protein (64.7%) and the PTEN phosphatase (73.5%) and 91% of cell lines carried mutations in two or more pathways. This provides the first clear genetic evidence that these tumor suppressors participate in biological pathways which are functioning separately/independently in glioma cells. The status of the gene alterations did not correlate with tumorigenicity in immunocompromized mice or any clinical parameters. Although the mutation rate was higher in glioma cell lines than that reported for glioma tissues, the alterations were molecularly representative of those found in adult de novo glioblastoma. This study highlights the importance of developing therapeutic approaches applicable to tumors with a broad range of genetic alterations and also provides an invaluable panel of glioma cell lines to make this possible.

p53 and brain tumors: from gene mutations to gene therapy

The p53 tumor suppressor gene (TP53) is the most frequently altered gene in human cancer and is also found mutated in several types of brain tumors. Loss of p53 function plays a central role in the development of cancer. The characterization of the biochemical pathways by which p53 alteration triggers tumorigenesis is the foundation for the design of novel therapeutic approaches. Investigations of the intracellular mechanisms at the origin of p53 tumor suppressive functions have shown that p53 is a transcription factor able to sense a variety of cellular insults and induce a dual response: cell growth arrest/senescence or apoptosis. Less well studied are p53's influences on extracellular events such as tumor angiogenesis, immunology and invasion. Here, we review these findings and specifically discuss their implications for brain tumor genesis, molecular diagnosis and prognosis. Of clinical importance are the findings that brain tumors with wild type (wt) or mutant p53 status may respond differently to radiation therapy and that novel therapeutic strategies using TP53 gene transfer or specifically targeting tumor cells with mutated p53 are being evaluated in clinical trials.

p14ARF deletion and methylation in genetic pathways to glioblastomas

The CDKN2A locus on chromosome 9p21 contains the p14ARF and p16INK4a genes, and is frequently deleted in human neoplasms, including brain tumors. In this study, we screened 34 primary (de novo) glioblastomas and 16 secondary glioblastomas that had progressed from low-grade diffuse astrocytomas for alterations of the p14ARF and p16INK4a genes, including homozygous deletion by differential PCR, promoter hypermethylation by methylation-specific PCR, and protein expression by immunohistochemistry. A total of 29 glioblastomas (58%) had a p14ARF homozygous deletion or methylation, and 17 (34%) showed p16INK4a homozygous deletion or methylation. Thirteen glioblastomas showed both p14ARF and p16INK4a homozygous deletion, while nine showed only a p14ARF deletion. Immunohistochemistry revealed loss of p14ARF expression in the majority of glioblastomas (38/50, 76%), and this correlated with the gene status, i.e. homozygous deletion or promoter hypermethylation. There was no significant difference in the overall frequency of p14ARF and p16INK4a alterations between primary and secondary glioblastomas. The analysis of multiple biopsies from the same patients revealed hypermethylation of p14ARF (5/15 cases) and p16INK4a (1/15 cases) already at the stage of low-grade diffuse astrocytoma but consistent absence of homozygous deletions. These results suggest that aberrant p14ARF expression due to homozygous deletion or promoter hypermethylation is associated with the evolution of both primary and secondary glioblastomas, and that p14ARF promoter methylation is an early event in subset of astrocytomas that undergo malignant progression to secondary glioblastoma.

Hans-Joachim Scherer (1906-1945), pioneer in glioma research

Hans-Joachim Scherer was among the most creative and productive neuropathologists of his time. Working as a political refugee in Antwerp (Belgium) during 1934-41, he published landmark papers on the morphology and biology of malignant gliomas, and was the first to clearly distinguish primary and secondary glioblastomas, and growth patterns reflecting the invasion of preexisting brain tissue (secondary structures). Scherer was a controversial personality, who at the end of World War II became entangled in the Nazi euthanasia programme.

Granular cell astrocytomas show a high frequency of allelic loss but are not a genetically defined subset

Granular cell astrocytomas (GCA) are an uncommon morphologic variant of infiltrative glioma that contains a prominent population of atypical granular cells. As a rule, they are biologically aggressive compared to similar tumors without granular features. We sought to determine whether GCAs possess distinct genotypic alterations that might reflect their unique morphology or clinical behavior. Eleven GCAs occurring in 7 men and 4 women ranging in age from 46 to 75 years were investigated for genetic alterations of known significance in glial tumorigenesis, including LOH at 1p, 9p, 10q, 17p, and 19q, point mutations of TP53, deletions of p16(CDKN2A) and p14ARF, as well as EGFR amplifications. Tumors included had an infiltrative growth pattern and consisted of large, round cells packed with eosinophilic, PAS-positive granules that varied in quantity, ranging from 30 to 100% of tumor cells. Three tumors were of WHO grade II, one was grade III, and 7 were grade IV lesions. Overall, the tumors showed higher frequencies of LOH at 1p, 9p, 10q, 17p, and 19q than typical infiltrating astrocytomas of similar grades. Losses on 9p and 10q occurred in nearly all cases, including low grade lesions. TP53 mutations were identified in 2 grade IV GCAs, while combined p14ARF and p16(CDKN2A) homozygous deletions were noted in only one grade IV lesion. None showed EGFR amplification. We found no genetic alterations specific for GCA. Instead, it appears that granular cell change occurs across genetic subsets. The high frequency of allelic loss, especially on 9p and 10q, may confer aggressive growth potential and be related to their rapid clinical progression.

Clonal analysis in glioblastoma with epithelial differentiation

Epithelial differentiation in glioblastomas (GBM) may be associated with circumscribed growth and focal keratin expression resembling carcinoma metastasis. Therefore these rare lesions can pose a diagnostic problem suggesting coincidental occurrence of two separate neoplasms. However molecular analysis should succeed in establishing a common origin of seemingly unrelated tumor samples. Five GBMs exhibiting epithelial differentiation were microdissected and analyzed for mutations in the TP53 gene. SSCP analysis of exons 5-8 was followed by direct sequencing of aberrantly migrating fragments. TP53 mutations were identified in tumors from two of five patients. A G-->T transversion in codon 176 was detected in a tumor, initially diagnosed as metastases of unknown origin, however, a later autopsy revealed GBM. In this lesion, the mutation was observed in both, areas of astrocytic differentiation and areas of epithelial differentiation. One tumor diagnosed as GBM with epithelial differentiation carried C-->T transition in codon 211 in both, areas of astrocytic and epithelial differentiation. Thus, molecular analysis proved clonality in two GBMs with epithelial differentiation, thereby excluding a collision tumor. The present data support the concept of clonal origin of these morphologically heterogeneous lesions.

Survival of patients with glioblastoma multiforme is not influenced by altered expression of p16, p53, EGFR, MDM2 or Bcl-2 genes

Deregulated expression of one or more growth control genes including p16, p53, EGF receptor (EGFR), MDM2 or Bcl-2 may contribute to the treatment resistance phenotype of GBM and generally poor patient survival. Clinically, GBM have been divided into two major groups defined by (1) histologic progression from a low grade tumor ("progressive" or "secondary" GBM) contrasted with (2) those which show initial clinical presentation without a prior history ("de novo" or "primary" GBM). Using molecular genetic analysis for p53 gene mutations together with immunophenotyping for overexpression of EGFR, up to four GBM variants can be distinguished, including the p53+/EGFR- progressive or the p53-/EGFR+ de novo variant. We examined the survival of 80 adult patients diagnosed with astrocytic GBM stratified by age category (>40, 41-60 or 61-80) to determine whether alterations in any one given growth control gene or whether different genetic variants of GBM (progressive versus de novo) were associated with different survival outcomes. Survival testing using Kaplan-Meier plots for GBM patients with or without altered expression of p16, p53, EGFR, MDM2 or Bcl-2 showed no significant differences by age group or by gene expression indicating a lack of prognostic value for GBM. Also the clinical outcome among patients with GBM showed no significant differences within each age category for any GBM variant including the progressive and de novo GBM variants indicating similar biologic behavior despite different genotypes. Using a pairwise comparison, one-third of the GBM with normal p16 expression showed accumulation of MDM2 protein and this association approached statistical significance (0.01 < P < 0.05) using the Bonferroni procedure. These GBM may represent a variant in which the p19ARF/MDM2/p53 pathway may be deregulated rather than the p16/cyclin D-CDK4/Rb pathway.

No complementation between TP53 or RB-1 and v-src in astrocytomas of GFAP-v-src transgenic mice

Human low-grade astrocytomas frequently recur and progress to states of higher malignancy. During tumor progression TP53 alterations are among the first genetic changes, while derangement of the p16/p14ARF/RB-1 system occurs later. To probe the pathogenetic significance of TP53 and RB-1 alterations, we introduced a v-src transgene driven by glial fibrillary acidic protein (GFAP) regulatory elements (which causes preneoplastic astrocytic lesions and stochastically astrocytomas of varying degrees of malignancy) into TP53+/- or RB-1+/- mice. Hemizygosity for TP53 or RB-1 did not increase the incidence or shorten the latency of astrocytic tumors in GFAP-v-src mice over a period of up to 76 weeks. Single strand conformation analysis of exons 5 to 8 of non-ablated TP53 alleles revealed altered migration patterns in only 3/16 tumors analyzed. Wild-type RB-1 alleles were retained in all RB-1+/-GFAP-v-src mice-derived astrocytic tumors analyzed, and pRb immunostaining revealed protein expression in all tumors. Conversely, the GFAP-v-src transgene did not influence the development of extraneural tumors related to TP53 or RB-1 hemizygosity. Therefore, the present study indicates that neither loss of RB-1 nor of TP53 confer a growth advantage in vivo to preneoplastic astrocytes expressing v-src, and suggests that RB-1 and TP53 belong to one single complementation group along with v-src in this transgenic model of astrocytoma development. The stochastic development of astrocytic tumors in GFAP-v-src, TP53+/- GFAP-v-src, and RB-1+/- GFAP-v-src transgenic mice indicates that additional hitherto unknown genetic lesions of astrocytes contribute to tumorigenesis, whose elucidation may prove important for our understanding of astrocytoma initiation and progression.

Targeted molecular therapy of GBM

Major advances in molecular biology, cellular biology and genomics have substantially improved our understanding of cancer. Now, these advances are being translated into therapy. Targeted therapy directed at specific molecular alterations is already creating a shift in the treatment of cancer patients. Glioblastoma (GBM), the most common brain cancer of adults, is highly suited for this new approach. GBMs commonly overexpress the oncogenes EGFR and PDGFR, and contain mutations and deletions of tumor suppressor genes PTEN and TP53. Some of these alterations lead to activation of the P13K/Akt and Ras/MAPK pathways, which provide targets for therapy. In this paper, we review the ways in which molecular therapies are being applied to GBM patients, and describe the tools of these approaches: pathway inhibitors, monoclonal antibodies and oncolytic viruses. We describe strategies to: i) target EGFR, its ligand-independent variant EGFRvIII, and PDGFR on the cell surface, ii) inhibit constitutively activate RAS/MAPK and PI3K/Akt signaling pathways, iii) target TP53 mutant tumors, and iv) block GBM angiogenesis and invasion. These new approaches are likely to revolutionize the treatment of GBM patients. They will also present new challenges and opportunities for neuropathology.

Recent advances in the molecular genetics of malignant gliomas disclose targets for antitumor agent perillyl alcohol

Tumors of glial origin such as glioblastoma multiforme (GBM) comprise the majority of human brain tumors. Despite advances in surgery, radiation, and chemotherapy, the prognosis for patients with malignant glioma has not improved, emphasizing the need for a search for new chemotherapeutic drugs. Deregulated p21-Ras function, as a result of mutation, overexpression, or growth factor-induced overactivation, contributes to the growth of GBM. The monoterpene perillyl alcohol (POH) has preventive and therapeutic effects in a wide variety of preclinical tumor models and is currently under phase I and phase II clinical trials. As inhibition of posttranslational isoprenylation of Ras, a family of proteins that are involved in signal transduction is among the drug-related activities observed in this compound; POH may be a potential chemotherapeutic agent for GBM. Intranasal delivery is a practical and noninvasive approach that allows therapeutic agents that do not cross the blood-brain barrier to enter the central nervous system, reducing unwanted systemic side effects. This article describes the effect of intranasal delivery of POH in a patient with relapsed GBM.

Distinct transcription profiles of primary and secondary glioblastoma subgroups

Glioblastomas are invasive and aggressive tumors of the brain, generally considered to arise from glial cells. A subset of these cancers develops from lower-grade gliomas and can thus be clinically classified as "secondary," whereas some glioblastomas occur with no prior evidence of a lower-grade tumor and can be clinically classified as "primary." Substantial genetic differences between these groups of glioblastomas have been identified previously. We used large-scale expression analyses to identify glioblastoma-associated genes (GAG) that are associated with a more malignant phenotype via comparison with lower-grade astrocytomas. We have further defined gene expression differences that distinguish primary and secondary glioblastomas. GAGs distinct to primary or secondary tumors provided information on the heterogeneous properties and apparently distinct oncogenic mechanisms of these tumors. Secondary GAGs primarily include mitotic cell cycle components, suggesting the loss of function in prominent cell cycle regulators, whereas primary GAGs highlight genes typical of a stromal response, suggesting the importance of extracellular signaling. Immunohistochemical staining of glioblastoma tissue arrays confirmed expression differences. These data highlight that the development of gene pathway-targeted therapies may need to be specifically tailored to each subtype of glioblastoma.

Patients with high-grade gliomas harboring deletions of chromosomes 9p and 10q benefit from temozolomide treatment

Surgical cure of glioblastomas is virtually impossible and their clinical course is mainly determined by the biologic behavior of the tumor cells and their response to radiation and chemotherapy. We investigated whether response to temozolomide (TMZ) chemotherapy differs in subsets of malignant glioblastomas defined by genetic lesions. Eighty patients with newly diagnosed glioblastoma were analyzed with comparative genomic hybridization and loss of heterozygosity. All patients underwent radical resection. Fifty patients received TMZ after radiotherapy (TMZ group) and 30 patients received radiotherapy alone (RT group). The most common aberrations detected were gains of parts of chromosome 7 and losses of 10q, 9p, or 13q. The spectrum of genetic aberrations did not differ between the TMZ and RT groups. Patients treated with TMZ showed significantly better survival than patients treated with radiotherapy alone (19.5 vs 9.3 months). Genomic deletions on chromosomes 9 and 10 are typical for glioblastoma and associated with poor prognosis. However, patients with these aberrations benefited significantly from TMZ in univariate analysis. In multivariate analysis, this effect was pronounced for 9p deletion and for elderly patients with 10q deletions, respectively. This study demonstrates that molecular genetic and cytogenetic analyses potentially predict responses to chemotherapy in patients with newly diagnosed glioblastomas.

Molecular genetic alterations in gliomatosis cerebri: what can we learn about the origin and course of the disease?

Gliomatosis cerebri (GC) is a neuroepithelial neoplasm with extensive infiltration of large parts of the brain. Recent data showing the involvement of TP53 mutation or nuclear protein accumulation in some cases have linked the astrocytic phenotype of the tumor cells to TP53 alterations frequently found in common astrocytomas. However, the frequency of these alterations is low, and other molecular genetic changes have been only rarely identified. Those found in common high-grade astrocytomas and glioblastomas are usually missing in GC. The distribution of TP53 point mutations, as well as non-coding polymorphic markers and some cytogenetic data, support a monoclonal origin in some cases, and are at least compatible with it in most cases, while no conclusive data suggesting a polyclonal origin have been reported. This raises the question of mechanisms responsible for the enhanced infiltrative potential of the tumor cells in this disease, which have not yet been identified.

Modeling prognosis for patients with malignant astrocytic gliomas: quantifying the expression of multiple genetic markers and clinical variables

The disparate lengths of survival among patients with malignant astrocytic gliomas (anaplastic astrocytomas [AAs] and glioblastoma multiforme [GBM]) cannot be adequately accounted for by clinical variables (patient age, histology, and recurrent status). Using real-time quantitative reverse transcription-polymerase chain reaction, we quantified the expression of four genes that were putative prognostic markers (CDK4, IGFBP2, MMP2, and RPS9) in a set of 43 AAs, 41 GBMs, and seven adjacent normal brain tissues. We previously explicated the expression and prognostic value of PAX6, PTEN, VEGF, and EGFR in these glioma tissues and established a comprehensive prognostic model (Zhou et al., 2003). This study attempts to improve that model by including four additional genetic markers, which exhibited a differential expression (P < 0.001) among tumor grades and between tumor and normal tissues. By including eight log-scaled gene expression variables, three clinical variables, and interaction terms among the eight genes, we established a prognostic model that accounted for two thirds of the variation (R2) in survival for this set of patients. To improve the R2 of the model without compromising its clinical utility, our data demonstrated that incorporating genes from different pathways markedly strengthens the model. Spearman rank correlation analysis of gene expression demonstrated a statistically significant positive correlation (P < 0.01) between the expression of IGFBP2-MMP2 and IGFBP2-VEGF in GBMs, but not in AAs. This finding suggests that the expression of IGFBP2 is associated with pathways activated specifically in GBMs that result in enhancing invasiveness and angiogenesis.

Molecular genetics of oligodendrogliomas: a model for improved clinical management in the field of neurooncology

Over the last several years, oligodendroglial tumors have become a model for the positive role of molecular genetics in improved treatment of patients with brain tumors. Oligodendrogliomas, in contrast to astrocytic gliomas, frequently respond to chemotherapy and have a better overall prognosis. Combined loss of chromosomes 1p and 19q has proven to be a powerful predictor of chemotherapeutic response and survival in oligodendrogliomas. In contrast, other genetic alterations, such as TP53 and PTEN mutations, EGFR amplification, and homozygous deletion of CDKN2A have been correlated with worse outcome in these tumors. Furthermore, 1p/19q loss has been shown to correlate with unequivocal oligodendroglial tumor histology, location and growth pattern of tumors within the brain, and magnetic resonance imaging characteristics. Although much is also known about the molecular pathological characteristics of astrocytic gliomas, the significance of this information to clinical management in patients with these tumors has not been as striking as has been the case for oligodendrogliomas; possible reasons for this are discussed. In this paper the author will summarize these advances, thus attempting to highlight the molecular genetic study of oligodendrogliomas as a model for improved clinical management in the field of neurooncology.

Frequent HRK inactivation associated with low apoptotic index in secondary glioblastomas

To detect and identify the genetic alterations and methylation status of the HRK gene in human glioblastomas, we analyzed a cohort of astrocytic tumors for hypermethylation, loss of heterozygosity on 12q13.1, and gene expression. Our study examined a series of 36 diffuse low-grade astrocytomas, 32 anaplastic astrocytomas, 64 primary glioblastomas, and 28 secondary glioblastomas that had evolved from either 24 low-grade diffuse astrocytomas or 4 anaplastic astrocytomas. The region around the HRK transcription start site was methylated in 19% of diffuse astrocytomas, in 22% of anaplastic astrocytomas, in 27% of primary glioblastomas, and in 43% of secondary glioblastomas. HRK expression was significantly reduced in 61% of secondary glioblastomas as compared to other types of tumors, and aberrant methylation was closely associated with loss of expression. Reverse transcription-PCR analysis also demonstrated a clear agreement between reduced HRK protein levels and low or absent HRK transcripts. Lack of HRK immunoreactivity was significantly correlated with a low apoptotic index, whereas a strong association between methylation status and apoptosis was found only in secondary glioblastomas. Abnormal methylation of HRK was detected in astrocytic tumors concurrent with methylation of multiple genes, including p16(INK4a) and p14(ARF). Interestingly, these epigenetic changes in secondary glioblastoma were further associated with wild-type p53. Our findings suggest that HRK is inactivated mainly by aberrant DNA methylation in astrocytic tumors and that reduced HRK expression contributes to the loss of apoptotic control in high-grade tumors. Reduced expression of HRK may serve as one important molecular mechanism in progression to secondary glioblastoma.

Oligodendroglioma: Impact of molecular biology on its definition, diagnosis and management

Molecular genetics and biology have been having significant influence on the practice of neuro-oncology in recent years, with oligodendrogliomas being the most prominent example. The majority of oligodendrogliomas show remarkable sensitivity to chemotherapy, and the finding that the loss of chromosome 1p was tightly associated with the response opened a new era in which the treatment can be tailored for each tumor patient based on molecular genetic diagnosis. It has been noticed that histological features, when closely examined, are also correlated with the molecular genetic data, such as losses of 1p/19q/10q and TP53 mutation. Furthermore, expression profiling using microarray technology showed that oligodendrogliomas with 1p loss express high levels of neuronal genes, suggesting that the progenitor of those tumors may be shared with neurons. Considering the rapid progress of the knowledge in neural developmental biology, it is possible that the classification, definition and diagnosis of gliomas will be rewritten based on such knowledge at the molecular level in the near future, if they reflect the biological features of each tumor better than the histological diagnosis based mostly on morphology.

YKL-40 expression is associated with poorer response to radiation and shorter overall survival in glioblastoma

PURPOSE

YKL-40 is a secreted protein that has been reported to be overexpressed in epithelial cancers and gliomas, although its function is unknown. Previous data in a smaller sample set suggested that YKL-40 was a marker associated with a poorer clinical outcome and a genetically defined subgroup of glioblastoma. Here we test these findings in a larger series of patients with glioblastoma, and in particular, determine if tumor YKL-40 expression is associated with radiation response.

EXPERIMENTAL DESIGN

Patients (n=147) with subtotal resections were studied for imaging-assessed changes in tumor size in serial studies following radiation therapy. An additional set (n=140) of glioblastoma patients who underwent a gross-total resection was tested to validate the survival association and extend them to patients with minimal residual disease.

RESULTS

In the subtotal resection group, higher YKL-40 expression was significantly associated with poorer radiation response, shorter time to progression and shorter overall survival. The association of higher YKL-40 expression with poorer survival was validated in the gross-total resection group. In multivariate analysis with both groups combined (n = 287), YKL-40 was an independent predictor of survival after adjusting for patient age, performance status, and extent of resection. YKL-40 expression was also compared with genetically defined subsets of glioblastoma by assessing epidermal growth factor receptor amplification and loss at chromosome 10q, two of the common recurring aberrations in these tumors, using fluorescent in situ hybridization. YKL-40 was significantly associated with 10q loss.

CONCLUSIONS

The findings implicate YKL-40 as an important marker of therapeutic response and genetic subtype in glioblastomas and suggest that it may play an oncogenic role in these tumors.

PAX6 suppresses growth of human glioblastoma cells

PURPOSE

Glioblastomas (GBMs) are the most common primary malignant brain tumors. Majority of GBMs has loss of heterozygosity of chromosome 10. The PAX6 encodes a transcription factor that involves in development of the brain, where its expression persists. We have reported that the expression of PAX6 was significantly reduced in GBMs and that a low level of PAX6 expression is a harbinger of an unfavorable prognosis for patients with malignant astrocytic glioma. Interestingly, PAX6 expression was increased in suppressed somatic cell hybrids derived from introducing a normal human chromosome 10 into U251 GBM cells. Thus it is interesting to determine if repression of PAX6 expression is involved in anti-tumor suppression function in GBM.

EXPERIMENTAL DESIGN

We overexpressed PAX6 in a GBM cell line U251HF via either stable transfection or infection with recombinant adenovirus, and examined cell growth in vitro and in vivo.

RESULT

Although we did not observe changes in the cell doubling time for PAX6-stable transfectants, significantly fewer numbers of PAX6-positive colonies grew in soft agar. Transient overexpression of PAX6 via adenovirus, however, suppressed cell growth by increasing the number of cells in G1 and by decreasing the number of cells in S-phase, and later on caused a dramatic level of cell death. Repeated subcutaneous and intracranial implantation experiments in nude mice using PAX6-stable transfectants provided solid evidence that PAX6 suppressed tumor growth in vivo and significantly extended mouse survival.

CONCLUSION

Our data demonstrate that PAX6exerts a tumor suppressor function that limits the growth of GBM cells.

Patient tumor EGFR and PDGFRA gene amplifications retained in an invasive intracranial xenograft model of glioblastoma multiforme

We have previously described a panel of serially transplantable glioblastoma multiforme xenograft lines established by direct subcutaneous injection of patient tumor tissue in the flanks of nude mice. Here we report the characterization of four of these lines with respect to their histopathologic, genetic, and growth properties following heterotopic-to-orthotopic (flank-to-intracranial) transfer. Cells from short-term cultures, established from excised flank xenografts, were harvested and injected into the brains of nude mice (10(6) cells per injection). The intracranial tumors generated from these injections were all highly mitotic as well as highly invasive, but they lacked necrotic features in most instances and failed to show endothelial cell proliferation in all instances. For mice receiving injections from a common explant culture, tumor intracranial growth rate was consistent, as indicated by relatively narrow ranges in survival time. In contrast to the loss of epidermal growth factor receptor gene (EGFR) amplification in cell culture, high-level amplification and overexpression of EGFR were retained in intracranial tumors established from two EGFR-amplified flank tumors. A third intracranial tumor retained patient tumor amplification and high-level expression of platelet-derived growth factor receptor alpha gene. Because the heterotopic-to-orthotopic transfer and propagation of glioblastoma multiforme preserves the receptor tyrosine kinase (RTK) gene amplification of patient tumors, this approach should facilitate investigations for determining the extent to which RTK amplification status influences tumor response to RTK-directed therapies. The fact that such studies were carried out by using an invasive tumor model in an anatomically appropriate context should ensure a rigorous preclinical assessment of agent efficacy.

Supratentorial glioblastoma in adults: identification of subsets and their clinical correlation

The concept of different genetic pathways leading to glioblastoma multiforme (GBM) has gained considerable acceptance, and two major groups are now described, primary or de novo GBM and secondary GBM. The present study was undertaken to elucidate whether additional pathways exist and to determine whether there is any correlation between these different variants and clinical parameters, such as age, duration of symptoms, and outcome. For this purpose, immunophenotyping was performed to study the simultaneous expression of p53 protein and epidermal growth factor receptor (EGFR) in 58 cases of adult supratentorial GBM. By this method, four variants of GBM could be distinguished: 34% were p53 positive only, 38% were EGFR positive only, 14% were double negative (p53 negative/EGFR negative), and 14% were double positive (p53 positive/EGFR positive). Interestingly, all nine cases of secondary GBM in which there was clinical and histological evidence of progression from a preexisting low-grade lesion were p53 positive. Differences were observed with regard to the age distribution of the four variants, in that the p53 negative/EGFR negative tumors occurred most frequently in the younger age group (21-40 years). In the elderly group (61-80 years), two-thirds of the tumors were p53 negative/EGFR positive primary GBMs, and no case of the double positive or double negative variant was encountered. The differences in duration of symptoms and symptom-free survival according to age group and genetic subset were not statistically significant. There were no differences in outcome within each age category for any GBM variant, although the longest mean symptom-free survival was noted among patients aged 41-60 years with the p53 positive/EGFR negative variant. This study therefore indicates that at least four subsets of GBM exist, but despite different genotypes, the biologic behavior remains similar. Other genetic alterations therefore need to be investigated to identify prognostic makers.

Frequent gene amplification and overexpression of decoy receptor 3 in glioblastoma

The decoy receptor 3 (DcR3) gene is amplified at high frequency in human lung, colon, and liver cancers. DcR3 has been demonstrated to produce a secreted member of the tumor necrosis factor receptor superfamily that negatively regulates Fas-mediated apoptosis. In this study we examined DcR3 gene amplification, DcR3 mRNA expression, and DcR3 protein expression in 46 human astrocytic brain tumors by quantitative genomic PCR, quantitative reverse transcription-PCR, and immunohistochemistry, respectively. The DcR3 gene amplification was detected in none of 6 (0%) low-grade astrocytomas, 1 of 16 (6%) anaplastic astrocytomas, and 6 of 24 ( 25%) glioblastomas. Six of 7 (86%) cases with gene amplification exhibited both mRNA overexpression and/or protein overexpression, suggesting that DcR3 mRNA and protein were expressed more abundantly in the cases with gene amplification. We thus concluded that high DcR3 mRNA expression and protein expression may be positively related to the gene amplification in astrocytic brain tumors, especially glioblastomas. Further, we speculated that the DcR3 gene amplification with overexpression may be responsible for malignant features in glioblastomas.

Frequent LOH on 22q12.3 and TIMP-3 inactivation occur in the progression to secondary glioblastomas

Frequent allelic losses on the long arm of chromosome 22 (22q) in gliomas indicate the presence of tumor suppressor gene (TSG) at this location. However, the target gene(s) residing in this chromosome are still unknown and their putative roles in the development of astrocytic tumors, especially in secondary glioblastoma, have not yet been defined. To compile a precise physical map for the region of common deletions in astrocytic tumors, we performed a high-density loss of heterozygosity (LOH) analysis using 31 polymorphic microsatellite markers spanning 22q in a series of grade II diffuse astrocytomas, anaplastic astrocytomas, primary glioblastomas, and secondary glioblastomas that had evolved from lower grade astrocytomas. LOH was found at one or more loci in 33% (12/36) of grade II diffuse astrocytomas, in 40% (4/10) of anaplastic astrocytomas, in 41% (26/64) of primary glioblastomas, and in 82% (23/28) of secondary glioblastomas. Characterization of the 22q deletions in primary glioblastomas identified two sites of minimally deleted regions at 22q12.3-13.2 and 22q13.31. Interestingly, 22 of 23 secondary glioblastomas affected shared a deletion in the same small (957 kb) region of 22q12.3, a region in which the human tissue inhibitor of metalloproteinases-3 (TIMP-3) is located. Investigation of the promoter methylation and expression of this gene indicated that frequent hypermethylation correlated with loss of TIMP-3 expression in secondary glioblastoma. This epigenetic change was significantly correlated to poor survival in eight patients with grade II diffuse astrocytoma. Our results suggest that a 957 kb locus, located at 22q12.3, may contain the putative TSG, TIMP-3, that appears to be relevant to progression to secondary glioblastoma and subsequently to the prognosis of grade II diffuse astrocytoma. In addition, the possibility of other putative TSGs on 22q12.3-13.2 and 22q13.31 that may also be involved in the development of primary glioblastomas cannot be ruled out.

Gene expression profiling of gliomas strongly predicts survival

In current clinical practice, histology-based grading of diffuse infiltrative gliomas is the best predictor of patient survival time. Yet histology provides little insight into the underlying biology of gliomas and is limited in its ability to identify and guide new molecularly targeted therapies. We have performed large-scale gene expression analysis using the Affymetrix HG U133 oligonucleotide arrays on 85 diffuse infiltrating gliomas of all histologic types to assess whether a gene expression-based, histology-independent classifier is predictive of survival and to determine whether gene expression signatures provide insight into the biology of gliomas. We found that gene expression-based grouping of tumors is a more powerful survival predictor than histologic grade or age. The poor prognosis samples could be grouped into three different poor prognosis groups, each with distinct molecular signatures. We further describe a list of 44 genes whose expression patterns reliably classify gliomas into previously unrecognized biological and prognostic groups: these genes are outstanding candidates for use in histology-independent classification of high-grade gliomas. The ability of the large scale and 44 gene set expression signatures to group tumors into strong survival groups was validated with an additional external and independent data set from another institution composed of 50 additional gliomas. This demonstrates that large-scale gene expression analysis and subset analysis of gliomas reveals unrecognized heterogeneity of tumors and is efficient at selecting prognosis-related gene expression differences which are able to be applied across institutions.

Molecular pathogenesis of astrocytic tumours

Our current knowledge of the molecular pathogenesis of the diffuse adult astrocytic tumours is vast if compared to 20 years ago, yet we are far from understanding the details of this process at the molecular level and using such an understanding to logically and specifically treat patients' tumours. In other astrocytic tumours we have little or no knowledge of the molecular processes. This article will attempt to summarise the histological classification criteria and genetic data for all the astrocytic tumours. The current World Health Organisation classification lists six entities, some with subgroups. Common problems associated with the diagnosis of these tumours are outlined. While the molecular findings are not as yet used clinically, we are approaching a time when the histological investigation will have to be supplemented with molecular data to ensure the best choice of treatment for the patient and as an accurate indicator of prognosis.

Low-level microsatellite instability phenotype in sporadic glioblastoma multiforme

PURPOSE

Genetic instability is a hallmark of glioblastoma multiforme (GBM). Microsatellite instability (MSI) is a significant event in the tumorigenesis of many sporadic malignancies. The aim of our investigation was to study microsatellite instability in newly diagnosed glioblastomas.

METHODS

MSI was investigated in 109 GBMs with 15 microsatellite markers. Immunohistochemistry was performed for the mismatch repair (MMR) proteins hMLH1, hMSH2, hPMS2, and hMSH6 in cases showing MSI. Sequence and promoter methylation status of hMLH1 were analyzed in the case of a decreased hMLH1 protein expression as well. To further investigate MSI(+) GBMs we carried out studies of LOH at selected chromosome regions, EGFR amplification, and sequence of p53 and PTEN.

RESULTS

MSI was observed in six GBMs (5.5%) and it was more frequent in GBMs with a previous lower grade astrocytoma (18.8% vs. 3.2%). MMR protein staining was positive in all MSI(+) GBMs except in one case, which showed an aberrant expression of hMLH1 and hPMS2 without hMLH1 inactivation. Among MSI(+) GBMs, one tumor corresponded to the GBM molecular type 1 (p53 mutation, no EGFR amplification), another tumor to type 2 (wild-type p53, EGFR amplification), and four tumors to neither type (wild-type p53, no EGFR amplification). None of the six tumors carried a PTEN mutation.

CONCLUSIONS

MSI in GBM might be caused by inactivation of minor MMR genes rather than by a deficiency of hMLH1 or hMSH2 and it appears not to play a decisive role in the pathogenesis of these tumors. MSI(+) GBMs predominantly showed a profile which included wild-type of p53 and PTEN and absence of EGFR amplification but MSI occurred in all GBM molecular subtypes.

Molecular genetic analysis of deep-seated glioblastomas

Glioblastoma can be divided into genetic subsets. The most prominent criterion for dividing glioblastomas into subsets is the dichotomy between TP53 mutation and EGFR amplification, two genetic alterations that almost never coincide in the same tumor. Approximately one third of glioblastomas have TP53 mutations, one third have EGFR amplification, and one third have neither. When viewed in terms of tumor progression, secondary glioblastomas have a much higher incidence of TP53 mutations than do primary glioblastomas. When viewed in terms of the age of tumor onset, glioblastomas in young adults are likely to have TP53 mutations. However, no correlations have yet been found between the tumor locations and the genetic subsets. In this study, we evaluated the associations between the glioblastoma sites and the genetic subsets defined by the presence of the TP53 mutation or EGFR amplification in nine deep-seated glioblastomas of the thalamus and basal ganglia. All nine tumors were clinically defined as primary glioblastomas. Our investigation revealed that all tumors had TP53 mutations and none had EGFR amplifications. These findings suggest that glioblastomas deep-seated in the thalamus and basal ganglia can be grouped into a subset of glioblastomas with TP53 mutations, akin to the subsets of secondary and younger adult glioblastomas. The locations where the glioblastomas originate may be associated with the genetic features.

Age-dependent prognostic effects of genetic alterations in glioblastoma

PURPOSE

Although the genetic alterations in glioblastoma have been well characterized, reports regarding their prognostic effects have been inconsistent.

EXPERIMENTAL DESIGN

In this series of 140 consecutive cases of glioblastoma treated at a single center, we analyzed the frequency, age dependency and prognostic effects of TP53 mutation, CDKN2A/p16 deletion, EGFR amplification, as well as loss of chromosome 1p, chromosome 10q, and chromosome 19q. The complete set of genetic alterations was available on 60 of 140 patients.

RESULTS

In this cohort of glioblastoma cases, TP53 mutation was significantly associated with patient age. The prognostic effects of TP53 mutation, EGFR amplification, CDKN2A/p16 alterations, and loss of chromosome 1p were dependent on the age of the patient.

CONCLUSIONS

This is the first observation that the prognostic effects of TP53, 1p, and CDKN2A/p16 alterations are dependent on patient age. These observations concerning the interactions of age and genetic changes in glioblastoma suggest that tumorigenic pathways to glioblastoma vary with the age of the patient and that future molecular marker studies should carefully evaluate the potential age-dependent prognostic effects of these biological variables. The inconsistent or negative prognostic effects of molecular markers reported in prior studies of glioblastoma may be because different effects at different ages may have resulted in a cancellation of an overall effect in the entire cohort.

Prognostic value of Mdm2, p53 and p16 in patients with astrocytomas

Surgical cure of gliomas infiltrating into the brain is practically impossible and their clinical course is primarily determined by the biological behavior of the tumor cell. The purpose of this study was to analyze retrospectively prognostic input of p53, Mouse double minute-2 (Mdm2) and p16 in 103 uniformly treated patients with astrocytic tumors. The expression of these molecules was measured by immunohistochemical procedure. Prognostic evaluation was performed with the multivariate proportional hazards model. The follow-up period lasted 19 (5-122) months for the survivors. We observed that 66% of gliomas showed mutated p53, while only 17% overexpressed Mdm2, the p53-regulatory molecule. Besides, almost 50% of gliomas lost p16 immunopositivity. Only p53 labeling showed a positive correlation with the grade of malignancy, according with the WHO classification. The association between mutated p53 and histological grade remained when prognostic variables were considered in a multivariate analysis. No association between p53 status and overall survival was found. On the other hand, Mdm2 overexpression and, unexpectedly, p16 immunopositivity were associated with a shorter survival in an univariate analysis. However, Cox-regression analysis showed that only Mdm2 in female patients was an independent prognostic factor, associated with shorter survival. In conclusion, our results suggest that Mdm2 could be a relevant marker in determining the evolution of glioma patients and could provide a more objective way to classify astrocytomas.

Malignant progression in meningioma: documentation of a series and analysis of cytogenetic findings

Object. The malignant progression of benign tumors is well documented in gliomas and other systemic lesions. It is also well known that some meningiomas become progressively aggressive despite their original benign status. The theory of clonal evolution is widely believed to explain malignant progression in meningioma; however, the data used to explain stepwise progression have typically been derived from the cytogenetic analysis of different types of tumors of different grades and in different patients. In this study, the authors examined the data obtained in a group of patients with meningiomas that showed clear histopathological progression toward a higher grade of malignancy and then analyzed the underlying cytogenetic findings.

Methods. Among 175 patients with recurrent meningiomas, 11 tumors showed a histopathological progression toward a higher grade that was associated with an aggressive clinical course. Six tumors progressed to malignancy and five to the atypical category over a period averaging 112 months. Tests for MIB-1 and p53 and cytogenetic studies with the fluorescence in situ hybridization (FISH) method were performed in successive specimens obtained in four patients.

The MIB-1 value increased in subsequent samples of tumors. Cytogenetic analysis with FISH showed deletions of 22, 1p, and 14q. In all but one case, these aberrations were also present in the previous specimen despite its lower hispathological grade.

Conclusions. The authors documented the progression of meningiomas from benign to a higher histological grade. These tumors were associated with a complex karyotype that was present ab initio in a histologically lower-grade tumor, contradicting the stepwise clonal evolution model. Although it was limited to the tested probes, the FISH method appears to be more accurate than the standard cytogenetic one in detecting these alterations. Tumors that present with complex genetic alterations, even those with a benign histological grade, are potentially aggressive and require closer follow up.

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.

MTH-68/H oncolytic viral treatment in human high-grade gliomas

Application of virus therapy to treat human neoplasms has over a three decade history. MTH-68/H, a live attenuated oncolytic viral strain of the Newcastle disease virus, is one of the viruses used in the treatment of different malignancies. Here we report on the administration of MTH-68/H to patients with glioblastoma multiforme, the most common and most aggressive neuroectodermal neoplasm with a poor prognosis, averaging six months to a year. Four cases of advanced high-grade glioma were treated with MTH-68/H after the conventional modalities of anti-neoplastic therapies had failed. This treatment resulted in survival rates of 5-9 years, with each patient still living today. Against all odds, each patient resumed a lifestyle that resembles their previous daily routines and enjoys a good quality of life, Each of these patients has regularly received MTH-68/H as their sole form of onco-therapy for a number of years now without interruption.

Molecular-genetic characterisation of gliomas that recur as same grade or higher grade tumours

BACKGROUND

Due to their invasive growth, gliomas usually cannot be removed completely and almost always recur as same grade or higher grade malignancies.

OBJECTIVE

To determine whether there were differences in the accumulation of genetic changes between the two types of glioma recurrence.

METHODS

We genetically characterised 14 cases of lower grade glioma with a same grade recurrence, 12 cases of glioblastoma recurrence, and 14 cases of lower grade glioma with a higher grade recurrence. We investigated LOH (loss of heterozygosity) at 1p36, 10p15, the PTEN region in 10q23, the DMBT1 region in 10q25, 19q13, 22q13, LOH and mutation of TP53, and EGFR amplification.

RESULTS

Genetic heterogeneity in the primary tumour was inferred in 3 cases of lower grade glioma with a higher grade recurrence. The cases of lower grade glioma with a higher grade recurrence displayed increased genetic instability in the recurrence (mean of 2.0 additional genetic changes per case) compared to cases with a same lower grade recurrence or those with a glioblastoma recurrence (mean of 0.6 and 0.8 additional changes per case, respectively). Compared to unselected primary glioblastomas, the glioblastomas that recurred as an operable tumour had infrequent EGFR amplification (8% v 30-40% of cases).

CONCLUSIONS

Gliomas recurring as higher grade lesions might be genetically heterogeneous and accumulate more genetic changes than gliomas recurring as same grade lesions (whether originally low or high grade). Primary glioblastomas from patients for which the recurrence is operated because of prognostically more favourable clinical indices have infrequent EGFR amplification.

Independent molecular development of metachronous glioblastomas with extended intervening recurrence-free interval

Two metachronous glioblastomas with different cerebral locations in a 53-year-old long-term survival patient were analyzed by multiple genetic approaches. Using comparative genomic hybridization a different pattern of chromosomal aberrations was observed, with 19 imbalances in the first tumor and only 2 imbalances in the second. Sequence analysis revealed a distinct mutation profile in each tumor, with amino acid substitutions in the p53 and PTEN genes only in the first tumor, ie, p53 in codon 273 (CGT-->TGT, Arg-->Cys) and PTEN in codon 336 (TAC-->TTC, Tyr-->Phe). A splicing acceptor site PTEN mutation (IVS8-2A>G) was observed only in the second GBM. EGFR amplification, mutations of p16INK4a/CDKN2A or p14ARF were not observed. According to the results of p53 mutational analysis and EGFR amplification studies, the first tumor is classified as a type 1 GBM, whereas the alterations in the second one are different from those typically encountered in type 1 or type 2 tumors. In conclusion, our data strongly suggest that the metachronous tumors in this patient are exceptional in that they developed independently from each other. Whether the molecular features of the first glioblastoma are associated with the notably extended recurrence-free period of 5 years remains to be elucidated.

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.

Long-term survivors of glioblastoma: statistical aberration or important unrecognized molecular subtype?

Unlike most patients with glioblastoma multiforme who survive less than a year, approximately 2% have an unusually long survival after diagnosis and contemporary treatment (> or = 3 or more years); rarely, the disease appears to be "cured." Understanding these rare patients may tell us something important about the biology of glioblastoma multiforme. Patients who are young, have good performance status, and receive multimodalitytherapy (i.e., surgical resection, radiotherapy, and adjuvant chemotherapy) are more likely to have a long survival than older patients with poor performance status who are treated identically. However, the aforementioned clinical characteristics of long-term survivors do not explain why most patients with glioblastoma multiforme who have this same constellation of favorable features succumb to the disease relatively quickly. "Glioblastoma multiforme" is a group of diseases, one subtype of which behaves in a more indolent fashion, or responds well to current therapies, or both. In this review, we summarize the molecular characteristics of glioblastoma multiforme and pay special attention to molecular predictors of survival outcome, an area of research that is still in its infancy. We conclude by suggesting a translational research strategy that is aimed at uncovering the molecular signatures of long survivorship.

Melanoma differentiation associated gene-7, mda-7/IL-24, selectively induces growth suppression, apoptosis and radiosensitization in malignant gliomas in a p53-independent manner

Malignant gliomas are extremely aggressive cancers currently lacking effective treatment modalities. Gene therapy represents a promising approach for this disease. A requisite component for improving gene-based therapies of brain cancer includes tumor suppressor genes that exhibit cancer constrained inhibitory activity. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7) as a gene associated with melanoma cell growth, differentiation and progression. Ectopic expression of mda-7 by means of a replication-incompetent adenovirus (Ad), Ad.mda-7, induces growth suppression and apoptosis selectively in diverse human cancers, without producing any apparent harmful effect in normal cells. We presently demonstrate that Ad.mda-7 induces growth inhibition and apoptosis in malignant human gliomas expressing both mutant and wild-type p53, and these effects correlate with an elevation in expression of members of the growth arrest and DNA damage (GADD) gene family. In contrast, infection with a recombinant Ad expressing wild-type p53, Ad.wtp53, specifically affects mutant p53 expressing gliomas. When tested in early passage normal and immortal human fetal astrocytes, growth inhibition resulting from infection with Ad.mda-7 or Ad.wtp53 is significantly less than in malignant gliomas and no toxicity is evident in these normal cells. Moreover, infection of gliomas with Ad.mda-7 or treatment with purified GST-MDA-7 protein sensitizes both wild-type and mutant p53 expressing tumor cells to the growth inhibitory and antisurvival effects of ionizing radiation, and this response correlates with increased expression of specific members of the GADD gene family. Since heterogeneity in p53 expression is common in evolving gliomas, the present findings suggest that Ad.mda-7 may, in many instances, prove more beneficial for the gene-based therapy of malignant gliomas than administration of wild-type p53.

Deregulation of the p14ARF/Mdm2/p53 pathway and G1/S transition in two glioblastoma sets

Sixty-one glioblastomas have been studied, subdivided into the categories of classic glioblastomas (GBM) and glioblastomas with astrocytic (GBA) and oligodendroglial (GBO) differentiated areas. On surgical samples, TP53, Mdm2, CDKN2A/p16-p14 alterations were studied by molecular biology techniques and by immunohistochemistry. It has been found that Mdm2 amplification was more frequent in GBM than in GBA and GBO, that p14ARF was inactivated in a high percentage of cases in the three tumor categories. Both these and other alterations did not reach a statistical significance, with the exception of CDKN2A/p16 homozygous deletion which showed the highest frequency in GBO. The latter finding could be in line with the observation that CDKN2A/p16 inactivation is a step in the molecular pathway to tumor progression in oligodendrogliomas. TP53 mutations and Mdm2 amplifications were mutually exclusive, whereas TP53 mutations and CDKN2A/p14 inactivation coexisted in 5 cases. The alterations of the p53/Mdm2/p14ARF pathway occurred in 73% of cases and in 80% of cases if CDKN2A homozygous deletions were associated. All glioblastomas with gemistocytic areas showed p14ARF inactivation. Immunohistochemistry showed higher percentages of positivity in comparison with molecular genetics, but with similar variations.

Cellular mechanisms targeted during astrocytoma progression

Astrocytomas are the commonest type of primary brain tumour. Four malignancy grades are recognized with very different prognosis. The most malignant and commonest form in adults is called glioblastoma and has a median survival with modern treatment of less than one year. Over the last 20 years, molecular genetic and cell biological data have helped identify some of the genes affected during oncogenesis and progression. This will be briefly reviewed. Many significant observations have been made but we are still far from understanding the neoplastic astrocyte at the molecular level. This is reflected in inconclusive attempts to date to use current molecular knowledge in providing additional prognostic information and in the design of molecular based treatments. However, it seems reasonable to assume that further understanding of oncogenesis and progression at the molecular level will provide a basis for improved clinical assessment and individually tailored treatment.

Glioblastoma multiforme in an Asian population: evidence for a distinct genetic pathway

In Singapore astrocytic tumours occur in only 25% of patients with primary brain tumours compared to 40-60% in other series. Glioblastoma multiforme arises either de novo as a primary glioblastomas associated with epidermal growth factor receptor (EGFR) and mdm2 over-expression or as a secondary glioblastomas, through malignant progression from low-grade astrocytomas, associated with p53 mutations and PDGFR-alpha over-expression. Using immunohistochemical methods and DNA sequencing, we studied our population of glioblastomas for overexpression of EGFR, mdm2, p53, and PDGFR-alpha as well directly for mutations of the p53 gene. While levels of over-expression of EGFR and mdm2 were consistent with levels expected for primary glioblastomas, levels of p53 and PDGFR-alpha were consistent with levels documented for secondary glioblastomas. Notably 96% of the samples over-expressed p53 as detected with monoclonal antibody pAb 240. Of the 39 samples available for DNA sequencing 18% (7/39) had p53 mutations, including three mutations previously undocumented in glioblastomas. These results provide strong evidence that glioblastomas in Asian patients do not conform to currently accepted models of glioblastoma development, and that clinically defined glioblastomas in these patients show genetic changes consistent with both 'primary' and 'secondary' glioblastomas.

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.