Genetic pathways to primary and secondary glioblastoma

Astrocytic tumors

Astrocytic gliomas are the most common primary brain tumors and account for up to two thirds of all tumors of glial origin. In this review we outline the basic histological and epidemiological aspects of the different astrocytoma subtypes in adults. In addition, we summarize the key genetic alterations that have been attributed to astrocytoma patho-genesis and progression. Recent progress has been made by interpreting genetic alterations in a pathway-related context so that they can be directly targeted by the application of specific inhibitors. Also, the first steps have been taken in refining classical histopathological diagnosis by use of molecular predictive markers, for example, MGMT promoter hypermethylation in glioblastomas. Progress in this direction will be additionally accelerated by the employment of high-throughput profiling techniques, such as array-CGH and gene expression profiling. Finally, the tumor stem cell hypothesis has challenged our way of understanding astrocytoma biology by emphasizing intratumoral heterogeneity. Novel animal models will provide us with the opportunity to comprehensively study this multilayered disease and explore novel therapeutic approaches in vivo.

Simulating Brain Tumor Heterogeneity with a Multiscale Agent-Based Model: Linking Molecular Signatures, Phenotypes and Expansion Rate

We have extended our previously developed 3D multi-scale agent-based brain tumor model to simulate cancer heterogeneity and to analyze its impact across the scales of interest. While our algorithm continues to employ an epidermal growth factor receptor (EGFR) gene-protein interaction network to determine the cells' phenotype, it now adds an implicit treatment of tumor cell adhesion related to the model's biochemical microenvironment. We simulate a simplified tumor progression pathway that leads to the emergence of five distinct glioma cell clones with different EGFR density and cell 'search precisions'. The in silico results show that microscopic tumor heterogeneity can impact the tumor system's multicellular growth patterns. Our findings further confirm that EGFR density results in the more aggressive clonal populations switching earlier from proliferation-dominated to a more migratory phenotype. Moreover, analyzing the dynamic molecular profile that triggers the phenotypic switch between proliferation and migration, our in silico oncogenomics data display spatial and temporal diversity in documenting the regional impact of tumorigenesis, and thus support the added value of multi-site and repeated assessments in vitro and in vivo. Potential implications from this in silico work for experimental and computational studies are discussed.

Involvement of PTEN promoter methylation in cerebral cavernous malformations

BACKGROUND AND PURPOSE

Cerebral cavernous malformations (CCMs) are prevalent cerebral vascular lesions involving aberrant angiogenesis. However, the underlying mechanism is poorly understood. Phosphatase and tension homolog deleted on chromosome 10 (PTEN), a tumor suppressor, is frequently deficient in various pathologies due to mutation or epigenetic alterations. PTEN promoter hypermethylation is a major epigenetic silencing mechanism leading to activation of angiogenesis in tumors. The present study aimed to investigate whether PTEN promoter methylation was involved in CCMs.

METHODS

PTEN promoter methylation was detected in surgical specimens of CCMs (n=69) by methylation-specific polymerase chain reaction. The methylation status was correlated to the clinical manifestations and to PTEN expression, which was analyzed by both Western blot and immunohistochemistry. To investigate the endothelial proliferation and the potential signaling pathways affected by PTEN methylation, proliferating cell nuclear antigen as well as phosphor-Akt and phosphor-Erk1,2 were detected by immunofluorescence and Western blot, respectively, in CCM specimens.

RESULTS

Methylation-specific polymerase chain reaction revealed PTEN promoter methylation in 15.9% CCMs. Strikingly, 5 of 6 familial CCMs showed PTEN promoter methylation (83.3%), which was significantly higher than in sporadic cases (9.4%; P<0.001). In addition, PTEN promoter methylation appeared more frequently in multiple CCMs, including familial cases (46.7%), than that in single-lesioned CCMs (11.8%; P<0.05). Immunostaining and Western blot revealed a more significant PTEN downregulation in PTEN-methylated CCMs in comparison to PTEN-unmethylated CCMs. Reduced PTEN expression was inversely correlated to the expression of proliferating cell nuclear antigen and to the activation of Erk1,2, but not of Akt.

CONCLUSIONS

We reported here for the first time the involvement of PTEN promoter methylation in CCMs, particularly in familial CCMs, suggesting this epigenetic alteration as a potential pathomechanism of CCMs. The identification of Erk1,2 as triggered signaling in the lesions may be valuable for the development of effective therapy for this disease.

Applications of emerging molecular technologies in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. Median survival from the time of diagnosis is less than a year, with less than 5% of patients surviving 5 years. These tumors are thought to arise through two different pathways. Primary GBMs represent de novo tumors, while secondary GBMs represent the malignant progression of lower-grade astrocytomas. Moreover, despite improvements in deciphering the complex biology of these tumors, the overall prognosis has not changed in the past three decades. The hope for improving the outlook for these glial-based malignancies is centered on the successful clinical application of current high-throughput technologies. For example, the complete sequencing of the human genome has brought both genomics and proteomics to the forefront of cancer research as a powerful approach to systematically identify large volumes of data that can be utilized to study the molecular and cellular basis of oncology. The organization of these data into a comprehensive view of tumor growth and progression translates into a unique opportunity to diagnose and treat cancer patients. In this review, we summarize current genomic and proteomic alterations associated with GBM and how these modalities may ultimately impact treatment and survival.

Epigenetic markers in human gliomas: prospects for therapeutic intervention

Gliomas represent the most common CNS cancers in adults. Prognosis for patients harboring malignant gliomas is particularly dismal and, despite current treatment strategies comprising surgery, radiotherapy and chemotherapy, the median survival time after diagnosis is still in the range of just 12 months. In recent years, there has been an increased effort to identify tumor biomarkers that can be used as diagnostic tools, or markers for predicting therapeutic response and prognosis. Investigation of genetic changes has identified several such markers that have shown some success in predicting the most effective therapy. In recent years, however, it has become apparent that the biology of many cancers of the CNS is determined not only by their genetic profile but also their epigenetic profile. Epigenetic biomarkers show great potential in effectively predicting patient prognosis and response to therapy. The eventual application of epigenetic profiling of tumors may help to indicate the most effective tailored therapy for individual patients.

Utility of chromogenic in situ hybridization (CISH) for detection of EGFR amplification in glioblastoma: comparison with fluorescence in situ hybridization (FISH)

In this study, we test the reliability of chromogenic in situ hybridization (CISH) for the detection of epidermal growth factor receptor (EGFR) gene amplification in glioblastoma. Earlier reports have described EGFR CISH in glioblastoma multiforme, but a comparison of CISH with a "gold standard" testing method, such as fluorescence in situ hybridization (FISH), has not been described. Therapies targeting the EGFR-signaling pathway might increase the importance of assessment of EGFR-amplification status. CISH is a potential alternative to FISH as a testing method. To test its reliability, EGFR-amplification status by CISH was assessed in 89 cases of glioblastoma and compared with FISH results, and correlated with the protein expression using immunohistochemistry (IHC) for EGFR. FISH was scored as being EGFR-amplified in 47/89 tumors, CISH as being amplified in 43/89 tumors. The CISH and FISH results were in agreement in 83/89 cases (93%). Four glioblastomas were scored as being amplified by FISH, but not by CISH; whereas amplification was detected in 2 tumors by CISH that were not amplified using FISH. Forty-eight of the 89 cases were positive for EGFR expression by IHC. EGFR amplification was highly correlated with protein expression by IHC, as 40/48 (83%) EGFR IHC-positive cases were found to be EGFR-amplified. The high concordance of CISH and FISH for the assessment of EGFR gene-amplification status indicates that CISH is a viable alternative to FISH for the detection of EGFR gene amplification in glioblastoma. Detectable EGFR expression by IHC can occur in the absence of gene amplification, but is uncommon.

Epithelial and pseudoepithelial differentiation in glioblastoma and gliosarcoma: a comparative morphologic and molecular genetic study

BACKGROUND

Glioblastomas exhibit a remarkable tendency toward morphologic diversity. Although rare, pseudoepithelial components (adenoid or epithelioid) or true epithelial differentiation may occur, posing a significant diagnostic challenge.

METHODS

Hematoxylin and eosin-stained slides were reviewed, and immunohistochemistry and fluorescence in situ hybridization were performed.

RESULTS

The patients included 38 men and 20 women. The median age at diagnosis was 57 years (interquartile range [IQR], 50 years-67 years), and the median overall survival was 7 months (IQR, 4 months-11 months). "Adenoid" glioblastomas (A-GBM) predominated (48%). True epithelial glioblastomas (TE-GBM) were next most frequent based on morphology and immunohistochemistry (35%), followed by epithelioid glioblastomas (E-GBM) (17%). Overall, 25 (43%) tumors featured a sarcomatous component. Molecular cytogenetic abnormalities identified by fluorescent in situ hybridization in A-GBM, E-GBM, and TE-GBM, respectively, included p16 deletion/-9 (60%, 71%, 64%); chromosome 10 loss (40%, 63%, 57%), chromosome 7 gain without EGFR amplification (70%, 38%, 40%), EGFR amplification (10%, 50%, 27%), PTEN deletion (10%, 25%, 29%), PDGFRA amplification (10%, 25%, 0%), and RB1 deletion/-13q (50%, 0%, 14%). Abnormalities identified by immunohistochemistry included p21 immunonegativity (60%, 25%, 93%), which was most frequent in TE-GBM (P = .008), strong nuclear p53 staining (29%, 29%, 41%), strong membranous staining for epidermal growth factor receptor (EGFR) (21%, 63%, 19%), which was most frequent in E-GBM (P = .03), and an increased frequency of p27 immunonegativity in gliosarcomas (15% negative, 85% focal) compared with tumors without sarcoma (38% strongly positive) (P = .009).

CONCLUSIONS

Pseudoepithelial and true epithelial morphology are rare phenomena in GBM and may be associated with a similar poor prognosis. These tumors demonstrate proportions of molecular genetic abnormalities varying somewhat from conventional GBM.

Gemcitabine combined with gefitinib in patients with inoperable or metastatic pancreatic cancer: a phase II Study of the Hellenic Cooperative Oncology Group with biomarker evaluation

The combination of gemcitabine and gefitinib was evaluated in advanced pancreatic cancer. Totally, 53 patients were treated with a 7 week cycle of gemcitabine (1,000 mg/m(2) given weekly) followed by six 4 week cycles of gemcitabine given on days 1, 8 and 15. Gefitinib 250 mg was administered daily. Responses were seen in 6, and stabilization of the disease in 12 patients. The main toxicity was myelotoxicity (92%). The 6-month progression-free survival (PFS) was 30%. Median PFS was 4.1 months and median survival 7.3 months with a 1 year survival rate of 27%. The above combination demonstrated promising activity in advanced pancreatic cancer.

17-AAG sensitized malignant glioma cells to death-receptor mediated apoptosis

17-AAG is a selective HSP90-inhibitor that exhibited therapeutic activity in cancer. In this study three glioblastoma cell lines (U87, LN229 and U251) were treated with 17-AAG, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or the combination of both. Treatment with subtoxic doses of 17-AAG in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces rapid apoptosis in TRAIL-resistant glioma cells, suggesting that this combined treatment may offer an attractive strategy for treating gliomas. 17-AAG treatment down-regulated survivin through proteasomal degradation. In addition, over-expression of survivin attenuated cytotoxicity induced by the combination of 17-AAG and TRAIL. In summary, survivin is a key regulator of TRAIL-17-AAG mediated cell death in malignant glioma.

Pediatric glioblastomas: a histopathological and molecular genetic study

Glioblastoma multiforme (GBM) occurs rarely in children. Relatively few studies have been performed on molecular properties of pediatric GBMs. Our objective in this study was to evaluate the genetic alterations in pediatric GBM (age < or = 18 years) with special reference to p53, p16, and p27 protein expression, alterations of the epidermal growth factor receptor (EGFR), and deletion of the phosphate and tensin homolog gene (PTEN). Thirty cases of childhood GBMs reported between January 2002 and June 2007 were selected, and slides stained with hematoxylin and eosin were reviewed. Immunohistochemical staining was performed for EGFR, p53, p16, and p27, and tumor proliferation was assessed by calculating the MIB-1 labeling index (LI). Fluorescence in situ hybridization analysis was performed to evaluate for EGFR amplification and PTEN deletion. Histopathological features and MIB-1 LI were similar to adult GBMs. p53 protein expression was observed in 63%. Although EGFR protein overexpression was noted in 23% of cases, corresponding amplification of the EGFR gene was rare (5.5%). Deletion of the PTEN gene was also equally rare (5.5%). One case showed polysomy (chromosomal gains) of chromosomes 7 and 10. Loss of p16 and p27 immunoexpression was observed in 68% and 54% of cases, respectively. In pediatric de novo/primary GBMs, deletion of PTEN and EGFR amplification are rare, while p53 alterations are more frequent compared to primary adult GBMs. Frequency of loss of p16 and p27 immunoexpression is similar to their adult counterparts. This suggests that pediatric malignant gliomas are distinctly different from adult GBMs, highlighting the need for identification of molecular targets that may be adopted for future novel therapeutic strategies.

The interface between glial progenitors and gliomas

The mammalian brain and spinal cord contain heterogeneous populations of cycling, immature cells. These include cells with stem cell-like properties as well as progenitors in various stages of early glial differentiation. This latter population is distributed widely throughout gray and white matter and numerically represents an extremely large cell pool. In this review, we discuss the possibility that the glial progenitors that populate the adult CNS are one source of gliomas. Indeed, the marker phenotypes, morphologies, and migratory properties of cells in gliomas strongly resemble glial progenitors in many ways. We review briefly some salient features of normal glial development and then examine the similarities and differences between normal progenitors and cells in gliomas, focusing on the phenotypic plasticity of glial progenitors and the responses to growth factors in promoting proliferation and migration of normal and glioma cells, and discussing known mutational changes in gliomas in the context of how these might affect the proliferative and migratory behaviors of progenitors. Finally, we will discuss the "cancer stem cell" hypothesis in light of the possibility that glial progenitors can generate gliomas.

PTEN: a default gate-keeping tumor suppressor with a versatile tail

The tumor suppressor PTEN controls a variety of biological processes including cell proliferation, growth, migration, and death. As a master cellular regulator, PTEN itself is also subjected to deliberated regulation to ensure its proper function. Defects in PTEN regulation have a profound impact on carcinogenesis. In this review, we briefly discuss recent advances concerning PTEN regulation and how such knowledge facilitates our understanding and further exploration of PTEN biology. The carboxyl-tail of PTEN, which appears to be associated with multiple types of posttranslational regulation, will be under detailed scrutiny. Further, a comparative analysis of PTEN and p53 suggests while p53 needs to be activated to suppress tumorigenesis (a dormant gatekeeper), PTEN is probably a constitutive surveillant against cancer development, thus a default gatekeeper.

Suppression of putative tumour suppressor gene GLTSCR2 expression in human glioblastomas

Glioma tumour-suppressor candidate region gene 2 (GLTSCR2/PICT-1) is localized within the well-known 1.4 Mb tumour-suppressive region of chromosome 19q, which is frequently altered in various human tumours, including diffuse gliomas. Aside from its chromosomal localization, several lines of evidence, including PTEN-phosphorylating and cell-killing activities, suggests that GLTSCR2 participates in the suppression of tumour growth and development. However, little is known about the biological functions and molecular mechanisms of GLTSCR2 as a tumour suppressor gene. We investigated the pathological significance of GLTSCR2 expression in association with the development and progression of glioblastomas, the most common malignant brain tumour. We used real-time PCR and western blot analysis to examine the expression levels of GLTSCR2 mRNA and protein in glioblastomas, normal brain tissue and in non-glial tumour tissue of different origin, and found that GLTSCR2 expression is down-regulated in glioblastomas. In addition, direct sequencing analysis and fluorescence in situ hybridization clearly demonstrates the presence of genetic alterations, such as a nonsense mutation and deletion, in the GLTSCR2 gene in glioblastomas. Finally, our immunohistochemical study demonstrates that GLTSCR2 is sequentially down-regulated according to the histological malignant progression of the astrocytic glial tumour. Taken together, our results suggest that GLTSCR2 is involved in astrocytic glioma progression.

Oncolytic adenovirus retargeted to Delta-EGFR induces selective antiglioma activity

The fact that glioblastomas, which are one of the most devastating cancers, frequently express the Delta-EGFR (epithelial growth factor receptor) also called mutant variant III of EGFR (EGFRvIII) suggests that this cancer cell-specific receptor might serve as an ideal target for cancer therapy. To assess its potential as such a target, we constructed an oncolytic adenovirus with Retargeted Infectivity Via EGFR (Delta-24-RIVER) on the backbone of Delta-24. This new oncolytic adenovirus targets, as Delta-24 does, the disrupted Rb pathway in cancer cells; in addition, this adenovirus has also been retargeted through the abrogation of CAR binding (Y477A mutation in adenoviral fiber protein) and insertion of an EGFRvIII-specific binding peptide in the HI loop of the fiber protein. As compared with Delta-24, Delta-24-RIVER induced EGFRvIII-selective cytotoxicity in U-87 MG isogenic cell lines and in tetracycline-inducible EGFRVIII expressing U-251 MG cells. Accordingly, by tittering the viral progeny and examining fiber protein expression in the above cells, we showed that the replication of this new construct also correlated with EGFRvIII expression. Consistently, immunohistochemistry staining of the adenoviral capsid protein hexon in the virus-treated tumors revealed that the virus replicated more efficiently in EGFRvIII-expressing U-87 MG.DeltaEGFR xenografts than in the tumors grown from U-87 MG cells. Importantly, treatment with Delta-24-RIVER prolonged the survival of animals with intracranial xenografts derived from U-87 MG.DeltaEGFR cells. Therefore, our results constitute the first proof of the direct targeting of a cancer-specific receptor using an oncolytic adenovirus.

In silico cancer modeling: is it ready for prime time?

At the dawn of the era of personalized, systems-driven medicine, computational or in silico modeling and the simulation of disease processes is becoming increasingly important for hypothesis generation and data integration in both experiments and clinics alike. Arguably, the use of these techniques is nowhere more visible than in oncology. To illustrate the field's vast potential, as well as its current limitations, we briefly review selected studies on modeling malignant brain tumors. Implications for clinical practice, and for clinical trial design and outcome prediction, are also discussed.

Brain tumor epidemiology: consensus from the Brain Tumor Epidemiology Consortium

Epidemiologists in the Brain Tumor Epidemiology Consortium (BTEC) have prioritized areas for further research. Although many risk factors have been examined over the past several decades, there are few consistent findings, possibly because of small sample sizes in individual studies and differences between studies in patients, tumor types, and methods of classification. Individual studies generally have lacked samples of sufficient size to examine interactions. A major priority based on available evidence and technologies includes expanding research in genetics and molecular epidemiology of brain tumors. BTEC has taken an active role in promoting understudied groups, such as pediatric brain tumors; the etiology of rare glioma subtypes, such as oligodendroglioma; and meningioma, which, although it is not uncommon, has only recently been registered systematically in the United States. There also is a pressing need for more researchers, especially junior investigators, to study brain tumor epidemiology. However, relatively poor funding for brain tumor research has made it difficult to encourage careers in this area. In this report, BTEC epidemiologists reviewed the group's consensus on the current state of scientific findings, and they present a consensus on research priorities to identify which important areas the science should move to address.

An integrated genomic analysis of human glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and lethal type of brain cancer. To identify the genetic alterations in GBMs, we sequenced 20,661 protein coding genes, determined the presence of amplifications and deletions using high-density oligonucleotide arrays, and performed gene expression analyses using next-generation sequencing technologies in 22 human tumor samples. This comprehensive analysis led to the discovery of a variety of genes that were not known to be altered in GBMs. Most notably, we found recurrent mutations in the active site of isocitrate dehydrogenase 1 (IDH1) in 12% of GBM patients. Mutations in IDH1 occurred in a large fraction of young patients and in most patients with secondary GBMs and were associated with an increase in overall survival. These studies demonstrate the value of unbiased genomic analyses in the characterization of human brain cancer and identify a potentially useful genetic alteration for the classification and targeted therapy of GBMs.

Frequent promoter hypermethylation and transcriptional downregulation of the NDRG2 gene at 14q11.2 in primary glioblastoma

The N-myc downstream-regulated gene 2 (NDRG2) at 14q11.2 has been reported to be downregulated in glioblastoma, and NDRG2 overexpression represses glioblastoma cell proliferation in vitro (Deng et al., Int J Cancer 2003;106;342-7). To further address the role of NDRG2 as a candidate tumor suppressor in human gliomas, we analyzed 67 astrocytic tumors (10 diffuse astrocytomas, 11 anaplastic astrocytomas, 34 primary glioblastomas and 12 secondary glioblastomas) for NDRG2 gene mutation, promoter methylation and expression at the mRNA and protein levels. Using real-time reverse transcription PCR analysis, we found decreased NDRG2 mRNA levels in primary glioblastomas as compared to diffuse and anaplastic astrocytomas. Similarly, immunohistochemistry revealed low or absent NDRG2 protein expression in primary glioblastomas. Mutational analysis of the entire NDRG2 coding sequence did not reveal any tumor-associated DNA sequence alterations. However, sequencing of sodium bisulfite-modified DNA identified hypermethylation of the NDRG2 promoter region in 21 of 34 primary glioblastomas (62%). Moreover, NDRG2 promoter hypermethylation was associated with decreased NDRG2 mRNA expression. In contrast to primary glioblastomas, NDRG2 promoter hypermethylation was detected in only 1 of 11 anaplastic astrocytomas (9%) and was absent in 10 diffuse astrocytomas and 12 secondary glioblastomas. Taken together, our data support NDRG2 as a candidate tumor suppressor gene that is epigenetically silenced in the majority of primary glioblastomas, but not in lower grade astrocytomas and secondary glioblastomas.

Progress on potential strategies to target brain tumor stem cells

The identification of brain tumor stem cells (BTSCs) leads to promising progress on brain tumor treatment. For some brain tumors, BTSCs are the driving force of tumor growth and the culprits that make tumor revive and resistant to radiotherapy and chemotherapy. Therefore, it is specifically significant to eliminate BTSCs for treatment of brain tumors. There are considerable similarities between BTSCs and normal neural stem cells (NSCs), and diverse aspects of BTSCs have been studied to find potential targets that can be manipulated to specifically eradicate BTSCs without damaging normal NSCs, including their surface makers, surrounding niche, and aberrant signaling pathways. Many strategies have been designed to kill BTSCs, and some of them have reached, or are approaching, effective therapeutic results. Here, we will focus on advantages in the issue of BTSCs and emphasize on potential therapeutic strategies targeting BTSCs.

Differential sensitivity of human glioblastoma LN18 (PTEN-positive) and A172 (PTEN-negative) cells to Taxol for apoptosis

Glioblastoma is the most malignant brain tumor in humans and an average survival of glioblastoma patients hardly exceeds 12 months. Taxol is a plant-derived anti-cancer agent, which has been used in the treatments of many solid tumors. Deletion or mutation of phosphatase and tension homolog located on chromosome ten (PTEN) occurs in more than 80% of glioblastomas. We examined the sensitivity of human glioblastoma LN18 (PTEN-positive) and A172 (PTEN-negative) cells to Taxol for induction of apoptosis. Wright staining showed morphological features of apoptosis after treatment with different doses of Taxol for 24 h. Significant amount of apoptosis occurred in LN18 cells after treatment with 25 nM Taxol, while in A172 cells only after treatment with 50 nM Taxol. Western blotting with an antibody that could specifically detect activation or phosphorylation of Akt (p-Akt) did not show any p-Akt in LN18 cells but an increase in p-Akt in A172 cells. Activation of Akt in A172 cells could be reversed by pre-treatment of the cells with the phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002, indicating involvement of PI3K activity in this process. Apoptosis occurred with an increase in Bax:Bcl-2 and mitochondrial release of cytochrome c into the cytosol leading to activation of mitochondria-dependent caspase cascade. Taxol did not cause upregulation of vascular endothelial growth factor (VEGF), a key mediator of angiogenesis, in LN18 cells but substantial upregulation of VEGF in A172 cells. After treatment with Taxol, increases in p-Akt and VEGF could maintain survival and angiogenesis, respectively, in PTEN-negative glioblastoma. As a single chemotherapy, Taxol might be more efficacious in PTEN-positive glioblastoma than in PTEN-negative glioblastoma. Thus, our study showed differential sensitivity of PTEN-positive and PTEN-negative glioblastoma cells to Taxol.

Wild-type p53 in cancer cells: when a guardian turns into a blackguard

The tumor suppressor p53 controls a broad range of cellular responses. Induction of a transient (cell cycle arrest) or a permanent (senescence) block of cell proliferation, or the activation of cell death pathways in response to genotoxic stress comprise the major arms of the survival-death axis governed by p53. Due to these biological properties, inactivation of p53 is a crucial step in tumor development and progression, reflected by the high incidence of TP53 mutations in different types of human cancers. The remarkable potency of p53 in suppressing tumorigenic outgrowth has promoted the expectation that tumor cells expressing wild-type p53 (wtp53) should be more prone to elimination by cytotoxic treatments than tumor cells expressing mutant p53 (mutp53) with defunct wtp53 activities. However, recent findings yielded somewhat unexpected insights concerning the preponderance of the survival-promoting effects of wtp53 in cancer cells, a rather undesired property from the therapeutic point of view. In this commentary we will discuss the possibility that the developmentally established distinct patterns of wtp53 mediated responses in different tissues are an important factor in determining the ultimate outcome of cellular responses mediated by wtp53 in different types of tumor cells, with a particular focus on the divergent impact of wtp53 in malignant tumors of the central nervous system. We infer that a selective gain of pro-survival functions of wtp53 in cancer cells will confer a survival advantage that counteracts tumor therapy.

Cause and consequences of genetic and epigenetic alterations in human cancer

Both genetic and epigenetic changes contribute to development of human cancer. Oncogenomics has primarily focused on understanding the genetic basis of neoplasia, with less emphasis being placed on the role of epigenetics in tumourigenesis. Genomic alterations in cancer vary between the different types and stages, tissues and individuals. Moreover, genomic change ranges from single nucleotide mutations to gross chromosomal aneuploidy; which may or may not be associated with underlying genomic instability. Collectively, genomic alterations result in widespread deregulation of gene expression profiles and the disruption of signalling networks that control proliferation and cellular functions. In addition to changes in DNA and chromosomes, it has become evident that oncogenomic processes can be profoundly influenced by epigenetic mechanisms. DNA methylation is one of the key epigenetic factors involved in regulation of gene expression and genomic stability, and is biologically necessary for the maintenance of many cellular functions. While there has been considerable progress in understanding the impact of genetic and epigenetic mechanisms in tumourigenesis, there has been little consideration of the importance of the interplay between these two processes. In this review we summarize current understanding of the role of genetic and epigenetic alterations in human cancer. In addition we consider the associated interactions of genetic and epigenetic processes in tumour onset and progression. Furthermore, we provide a model of tumourigenesis that addresses the combined impact of both epigenetic and genetic alterations in cancer cells.

The antitumorigenic response of neural precursors depends on subventricular proliferation and age

Glioblastomas, the most aggressive primary brain tumors, occur almost exclusively in adult patients. Neural precursor cells (NPCs) are antitumorigenic in mice, as they can migrate to glioblastomas and induce tumor cell death. Here, we show that the antitumor effect of NPCs is age-dependently controlled by cell proliferation in the subventricular zone (SVZ) and that NPCs accumulating at a glioblastoma are diverted from their normal migratory path to the olfactory bulb. Experimentally induced cortical glioblastomas resulted in decreased subventricular proliferation in adult (postnatal day 90) but not in young (postnatal day 30) mice. Adult mice supplied fewer NPCs to glioblastomas and had larger tumors than young mice. Apart from the difference in proliferation, there was neither a change in cell number and death rate in the SVZ nor a change in angiogenesis and immune cell density in the tumors. The ability to kill glioblastomas was similar in NPCs isolated from young and adult mice. The proliferative response of NPCs to glioblastomas depended on the expression of D-type cyclins. In young mice, NPCs express the cyclins D1 and D2, but the expression of cyclin D1 is lost during aging, and in adult NPCs only cyclin D2 remains. In young and adult cyclin D2-deficient mice we observed a reduced supply of NPCs to glioblastomas and the generation of larger tumors compared with wild-type mice. We conclude that cyclin D1 and D2 are nonredundant for the antitumor response of subventricular NPCs. Loss of a single D-type cyclin results in a smaller pool of proliferating NPCs, lower number of NPCs migrating to the tumor, and reduced antitumor activity. Disclosure of potential conflicts of interest is found at the end of this article.

Bevacizumab: A Treatment Option for Recurrent Glioblastoma Multiforme

Objective:

To review the available literature evaluating the effect of bevacizumab on progression-free survival when used in combination with irinotecan for recurrent glioblastoma multiforme (GBM).

Data Sources:

Searches of MEDLINE (1966-June 2008), the Cochrane Library. and International Pharmaceutical Abstracts (1970-June 2008) were conducted using the terms bevacizumab. irinotecan, and glioblastoma multiforme.

Study Selection And Data Extraction:

The search was limited to studies conducted in humans. All articles identified trom the data sources were evaluated. All clinical trials evaluating the efficacy and safety of bevacizumab in the treatment of recurrent GBM were included in the review.

Data Synthesis:

Hypoxia, mutagenesis, and the secretion of various growth (actors can all lead to production of vascular endothelial growth factor (VEGF), a proangiogenic growth factor, and angiogenesis in GBM. Neoplastic progression is dependent on angiogenesis, and anti-VEGF therapy has been successful in multiple disease states. However, there are currently no available anti-VEGF therapies approved tor treatment of GBM. Bevacizumab is a humanized monoclonal antibody that binds to and inhibits the activity of VEGF. When compared with data from clinical trials that use single chemotherapeutic agents in recurrent GBM, the addition of bevacizumab to cytotoxic chemotherapy, such as irinotecan, appears to improve progression-Iree survival in patients progressing on the standard of care, with a 6-month progression-free survival rate of 46%. Bevacizumab is well tolerated by most patients, with modest risk (11% tn Phase 2 trials) of venous thromboembolism.

Conclusions:

Although the combination of bevacizumab and irinotecan is producing positive results in patients with recurrent GBM, larger, randomized clinical trials need to be performed to determine the magnitude of the benefit from bevacizumab. Bevacizumab administered biweekly at a dose of 10 mg/kg in combination with irinotecan may improve progression-free survival.

Analysis of 11C-methionine uptake in low-grade gliomas and correlation with proliferative activity

BACKGROUND AND PURPOSE

The relationship of (11)C-methionine (MET) uptake and tumor activity in low-grade gliomas (those meeting the criteria for World Health Organization [WHO] grade II gliomas) remains uncertain. The aim of this study was to compare MET uptake in low-grade gliomas and to analyze whether MET positron-emission tomography (PET) can estimate tumor viability and provide evidence of malignant transformation.

MATERIALS AND METHODS

We studied glioma metabolic activity in 49 consecutive patients with newly diagnosed grade II gliomas by using MET PET before surgical resection. On MET PET, we measured tumor/normal brain uptake ratio (T/N ratio) in 21 diffuse astrocytomas (DAs), 12 oligodendrogliomas (ODs), and 16 oligoastrocytomas (OAs). We compared MET T/N ratio among these 3 tumors and investigated possible correlation with proliferative activity, as measured by Mib-1 labeling index (LI).

RESULTS

MET T/N ratios of DA, OD, and OA were 2.11 +/- 0.87, 3.75 +/- 1.43, and 2.76 +/- 1.27, respectively. The MET T/N ratio of OD was significantly higher than that of DA (P < .005). In comparison of MET T/N ratios with the Mib-1 LI, a significant correlation was shown in DA (r = 0.63; P < .005) but not in OD and OA.

CONCLUSION

MET uptake in DAs may be closely associated with tumor viability, which depends on increased amino acid transport by an activated carrier-mediated system. DAs with lower MET uptake were considered more quiescent lesions, whereas DA with higher MET uptake may act more aggressively.

Clinical and biological implications of CD133-positive and CD133-negative cells in glioblastomas

A number of recent reports have demonstrated that only CD133-positive cancer cells of glioblastoma multiforme (GBM) have tumor-initiating potential. These findings raise an attractive hypothesis that GBMs can be cured by eradicating CD133-positive cancer stem cells (CSCs), which are a small portion of GBM cells. However, as GBMs are known to possess various genetic alterations, GBMs might harbor heterogeneous CSCs with different genetic alterations. Here, we compared the clinical characteristics of two GBM patient groups divided according to CD133-positive cell ratios. The CD133-low GBMs showed more invasive growth and gene expression profiles characteristic of mesenchymal or proliferative subtypes, whereas the CD133-high GBMs showed features of cortical and well-demarcated tumors and gene expressions typical of proneuronal subtype. Both CD133-positive and CD133-negative cells purified from four out of six GBM patients produced typical GBM tumor masses in NOD-SCID brains, whereas brain mass from CD133-negative cells showed more proliferative and angiogenic features compared to that from CD133-positive cells. Our results suggest, in contrast to previous reports that only CD133-positive cells of GBMs can initiate tumor formation in vivo CD133-negative cells also possess tumor-initiating potential, which is indicative of complexity in the identification of cancer cells for therapeutic targeting.

Issues of diagnostic review in brain tumor studies: from the Brain Tumor Epidemiology Consortium

Epidemiologists routinely conduct centralized single pathology reviews to minimize interobserver diagnostic variability, but this practice does not facilitate the combination of studies across geographic regions and institutions where diagnostic practices differ. A meeting of neuropathologists and epidemiologists focused on brain tumor classification issues in the context of protocol needs for consortial studies (http://epi.grants.cancer.gov/btec/). It resulted in recommendations relevant to brain tumors and possibly other rare disease studies. Two categories of brain tumors have enough general agreement over time, across regions, and between individual pathologists that one can consider using existing diagnostic data without further review: glioblastomas and meningiomas (as long as uniform guidelines such as those provided by the WHO are used). Prospective studies of these tumors benefit from collection of pathology reports, at a minimum recording the pathology department and classification system used in the diagnosis. Other brain tumors, such as oligodendroglioma, are less distinct and require careful histopathologic review for consistent classification across study centers. Epidemiologic study protocols must consider the study specific aims, diagnostic changes that have taken place over time, and other issues unique to the type(s) of tumor being studied. As diagnostic changes are being made rapidly, there are no readily available answers on disease classification issues. It is essential that epidemiologists and neuropathologists collaborate to develop appropriate study designs and protocols for specific hypothesis and populations.

MicroRNA involvement in brain tumors: from bench to bedside

MicroRNAs (miRNAs), a novel class of small non-coding RNAs, are effective post-transcriptional regulators of gene expression, exhibiting, when altered in human tumors, both oncogenic and tumor suppressive potential. Recently, miRNA involvement in the pathophysiology of brain cancer has been assessed. Aberrant gene expression is the main mechanism of miRNAs dysfunction in cancer, with abnormal expression levels of mature and/or precursor miRNA expression in tumor samples versus normal. MiRNA germline and somatic mutations or polymorphisms in the protein coding messenger RNA targeted by miRNAs may also occur, contributing to cancer predisposition, initiation and/or progression. If present in somatic cells, miRNA alterations may play a role in tumor initiation, while if present in germ line cells they could constitute a cancer predisposing event. MiRNA expression profiling of human tumors has led to the identification of signatures correlated with the tumor diagnosis, staging, progression, prognosis and response to treatment. MiRNA fingerprinting can therefore be added to the diagnostic and prognostic tools used by medical oncologists. Furthermore, new therapeutic strategies involving miRNA silencing or miRNA mimics could be proposed based on the roles of these small non-coding RNAs as oncogenes and tumor suppressors in brain tumors.

Common polymorphisms in the MDM2 and TP53 genes and the relationship between TP53 mutations and patient outcomes in glioblastomas

MDM2 SNP309 is associated with younger age of tumor onset in patients with Li-Fraumeni syndrome, and TP53 codon 72 polymorphism decreases its apoptotic potential. Glioblastomas frequently show genetic alterations in the TP53 pathway. In the present study, we assessed MDM2 SNP309 in 360 glioblastomas, and correlated these with patient age and survival, as well as other alterations in the TP53 pathway. Frequencies of the MDM2 SNP309 T/T, T/G and G/G genotypes in glioblastomas were 40%, 46% and 14%, respectively. Multivariate analysis showed that MDM2 SNP309 G/G allele was significantly associated with favorable outcome in female glioblastoma patients (hazard ratio 0.54; 95% CI = 0.32-0.92). There was a significant association between MDM2 SNP309 G alleles and TP53 codon 72 Pro/Pro in glioblastomas. Glioblastoma patients with TP53 codon 72 Pro/Pro genotype were significantly younger than Arg/Arg carriers (mean 50.2 vs. 56.1 years; P = 0.018). Multivariate analysis showed that those with TP53 codon 72 Arg/Pro allele had significantly shorter survival than those with Arg/Arg allele (hazard ratio 1.35; 95% CI = 1.07-1.71). Detailed analyses revealed that TP53 codon 72 Pro allele was significantly associated with shorter survival among patients with glioblastomas carrying a TP53 mutation, and among those treated with surgery plus radiotherapy.

Epithelial Growth Factor Receptor Inhibitors for treatment of recurrent or progressive high grade glioma: an exploratory study

INTRODUCTION

Erlotinib and Gefitinib (EGFRi) are small molecules specifically inhibiting epidermal growth factor receptor (EGFR). We present here data of an exploratory study evaluating EGFRi monotherapy in patients with recurrent or progressive malignant glioma.

PATIENTS

21 patients with recurrent or progressive malignant glioma were included in this study. EGFRi treatment was started at a median of 1.8 years (range 0.54 to 10.95) after initial surgery. 20/21 patients had undergone radiotherapy and all patients had received at least one (range 1 to 5, median 2) line of systemic antineoplastic therapy. Patients received 100 or 150 mg Erlotinib or 250 mg Gefitinib orally per day.

RESULTS

Median age at primary diagnosis was 47.9 years (range 31.9 to 76 years). 18 patients received a total of 92.8 months (median 3.03) of Erlotinib treatment and 3 patients received a total of 16.1 months (median 6.06) of Gefitinib treatment. The best responses were partial remission in one patient receiving Erlotinib and in two patients receiving Gefitinib, respectively. Median time to progression was 3.05 months. Six months after start of EGFRi treatment, 4/21 (19%) patients were progression-free and 6/21(29%) patients were alive. Expression of EGFRwt, EGFRvIII, PTEN, phospho-Akt or EGFRvIII/PTEN co-expression in tumor cells did not significantly associate with time to progression or survival time. In one patient EGFRi administration had to be discontinued due to toxicity (grade 3 rash).

CONCLUSION

EGFRi monotherapy is associated with therapeutic efficacy in only a small fraction of patients with malignant gliomas. Biomarkers reliably predicting tumor response to EGFRi need to be identified.

Emerging drugs for malignant glioma

BACKGROUND

Malignant gliomas are amongst the most devastating and intractable of all cancers. The most common malignant glioma, glioblastoma multiforme (GBM), is associated with a median survival in the range of 12-15 months. Survival for patients with GBM has improved with the addition of temozolomide chemotherapy to post-operative radiotherapy. Further advances in the treatment of malignant glioma will hinge on the discovery of novel and likely targeted therapies with activity against these diseases.

OBJECTIVE

Review recent published experience using targeted therapeutics for malignant glioma.

METHODS

Key studies from a Medline review of targeted therapies for malignant glioma performed between 2000 and the present are summarised in this review.

CONCLUSIONS

Experience with targeted therapeutics for malignant glioma has been to date disappointing. These agents are generally well tolerated, but activity is limited. Novel therapeutics with activity against malignant gliomas must be identified to improve prognosis for patients with these diseases.

Cancer: a profit-driven biosystem?

The argument is made that solid malignant tumors behave as profit-driven biological systems in that they expand their nutrient-uptaking surface to increase energetic revenue, at a comparably low metabolic cost. Within this conceptual framework, cancer cell migration is a critical mechanism as it maximizes systemic surface expansion while minimizing diffusion distance. Treating these tumor systems with adjuvant anti-proliferative regimen only should increase the energetic net gain of the viable cancer cells left behind, hence would facilitate tumor recurrence. Therapeutic attempts to better control tumor (re)growth should therefore aim primarily at containing its surface expansion, thus reducing its energetic revenue, or increasing its metabolic costs or better yet, both.

Surgical impact on brain tumor invasion: a physical perspective

It is conventional strategy to treat highly malignant brain tumors initially with cytoreductive surgery followed by adjuvant radio- and chemotherapy. However, in spite of all such efforts, the patients' prognosis remains dismal since residual glioma cells continue to infiltrate adjacent parenchyma and the tumors almost always recur. On the basis of a simple biomechanical conjecture that we have introduced previously, we argue here that by affecting the 'volume-pressure' relationship and minimizing surface tension of the remaining tumor cells, gross total resection may have an inductive effect on the invasiveness of the tumor cells left behind. Potential implications for treatment strategies are discussed.

Oncolytic herpes virus with defective ICP6 specifically replicates in quiescent cells with homozygous genetic mutations in p16

Oncolytic herpes simplex viruses (HSVs), in clinical trials for the treatment of malignant gliomas, are assumed to be selective for tumor cells because their replication is strongly attenuated in quiescent cells, but not in cycling cells. Oncolytic selectivity is thought to occur because mutations in viral ICP6 (encoding a viral ribonucleotide reductase function) and/or γ34.5 function are respectively complemented by mammalian ribonucleotide reductase and GADD34, whose genes are expressed in cycling cells. However, it is estimated that only 5–15% of malignant glioma cells are in mitosis at any one time. Therefore, effective replication of HSV oncolytic viruses might be limited to a subpopulation of tumor cells, since at any one time the majority of tumor cells would not be cycling. However, we report that an HSV with defective ICP6 function replicates in quiescent cultured murine embryonic fibroblasts obtained from mice with homozygous p16 deletions. Furthermore, intracranial inoculation of this virus into the brains of p16−/− mice provides evidence of viral replication that does not occur when the virus is injected into the brains of wild-type mice. These approaches provide in vitro and in vivo evidence that ICP6-negative HSVs are ‘molecularly targeted,’ because they replicate in quiescent tumor cells carrying specific oncogene deletions, independent of cell cycle status.

BAC array CGH distinguishes mutually exclusive alterations that define clinicogenetic subtypes of gliomas

The pathological classification of gliomas constitutes a critical step of the clinical management of patients, yet it is frequently challenging. To assess the relationship between genetic abnormalities and clinicopathological characteristics, we have performed a genetic and clinical analysis of a series of gliomas. A total of 112 gliomas were analyzed by comparative genomic hybridization on a BAC array with a 1 megabase resolution. Altered regions were identified and correlation analysis enabled to retrieve significant associations and exclusions. Whole chromosomes (chrs) 1p and 19q losses with centromeric breakpoints and EGFR high level amplification were found to be mutually exclusive, permitting identification of 3 distinct, nonoverlapping groups of tumors with striking clinicopathological differences. Type A tumors with chrs 1p and 19q co-deletion exhibited an oligodendroglial phenotype and a longer patient survival. Type B tumors were characterized by EGFR amplification. They harbored a WHO high grade of malignancy and a short patient survival. Finally, type C tumors displayed none of the previous patterns but the presence of chr 7 gain, chr 9p deletion and/or chr 10 loss. It included astrocytic tumors in patients younger than in type B and whose prognosis was highly dependent upon the number of alterations. A multivariate analysis based on a Cox model shows that age, WHO grade and genomic type provide complementary prognostic informations. Finally, our results highlight the potential of a whole-genome analysis as an additional diagnostic in cases of unclear conventional genetic findings.

Molecular and cell biology of brain tumor stem cells: lessons from neural progenitor/stem cells

✓ The results of studies conducted in the past several years have suggested that malignant brain tumors may harbor a small fraction of tumor-initiating cells that are likely to cause tumor recurrence. These cells are known as brain tumor stem cells (BTSCs) because of their multilineage potential and their ability to self-renew in vitro and to recapitulate original tumors in vivo. The understanding of BTSCs has been greatly advanced by knowledge of neural progenitor/stem cells (NPSCs), which are multipotent and self-renewing precursor cells for neurons and glia. In this article, the authors summarize evidence that genetic mutations that deregulate asymmetric cell division by affecting cell polarity, spindle orientation, or cell fate determinants may result in the conversion of NPSCs to BTSCs. In addition, they review evidence that BTSCs and normal NPSCs may reside in similar vascularized microenvironments, where similar evolutionarily conserved signaling pathways control their proliferation. Finally, they discuss preliminary evidence that mechanisms of BTSC-associated infiltrativeness may be similar to those underlying the migration of NPSCs and neurons.

TP53 codon 72 polymorphism in susceptibility, overall survival, and adjuvant therapy response of gliomas

TP53 is a key tumor suppressor gene that encodes a transcriptional factor involved in several cellular mechanisms, including growth arrest, DNA repair, and induction of apoptosis. In addition to TP53 gene mutations, a common polymorphism, Arg72Pro, has been involved in the carcinogenesis process. The Pro72 variant has been associated with a slower induction of apoptosis and may influence the risk of cancer development. The role of Arg72Pro polymorphism in glioma susceptibility is poorly characterized. With the objective of analyzing the role of the TP53 Arg72Pro polymorphism in glioma risk, overall survival, and patient therapy response in a Portuguese population, we conducted a retrospective case-control study, including 171 patients with gliomas and 526 cancer-free individuals. The Arg72Pro genotype was assessed by the polymerase chain reaction-restriction fragment length polymorphism technique. No statistically significant differences were observed in the genotypic and allelic frequencies between glioma and control groups, and no statistically significant differences were observed with stratification of gliomas into distinct histological subtypes: astrocytic (n = 115), glioblastoma (n = 75), and oligodendroglial (n = 54) tumors. No significant association was observed between TP53 Arg72Pro and patient overall survival, but Kaplan-Meier analysis of glioma patients harboring the Pro72 allele showed a significantly longer survival with adjuvant therapy. In this first assessment of the role of TP53 Arg72Pro polymorphism in a large series of Portuguese glioma tumors, no association was observed with glioma susceptibility or overall survival, except for patients submitted to adjuvant therapy.

Pitfalls in the assessment of MGMT expression and in its correlation with survival in diffuse astrocytomas: proposal of a feasible immunohistochemical approach

Immunohistochemical studies showed that O(6)-methylguanine-DNA methyltransferase (MGMT) protein expression is negatively associated with survival in glioblastomas treated with alkylating agents in accordance with previous results of methylation-specific PCR. Implementation of this data in routine clinical diagnostics is limited due to often inappropriate study designs, e.g. pooling of tumor entities, WHO grades or primary and secondary glioblastomas, disregard concerning the infiltration zone or various epidemiological factors. The aim of our study was to evaluate MGMT expression and its prognostic value taking into consideration the aforementioned deficiencies. For this, 162 astrocytic tumors WHO II-IV (36 diffuse astrocytomas WHO II, 51 anaplastic astrocytomas, 75 primary glioblastomas) as well as 25 glioblastoma infiltration zones and 19 glioblastoma relapses were analyzed for immunohistochemical MGMT protein expression using tissue microarray technique. Expression of MGMT significantly decreased from WHO grade II (25.6%) to glioblastoma (16.8%, p = 0.01) with lowest levels in grade III tumors (10.2%, II/III p < 0.0001). Significant negative associations of MGMT and survival were detected for WHO grade II and IV (p = 0.003 and 0.013). The optimal cut-off value of MGMT positive nuclei in primary glioblastomas discriminating patients with significantly different survival rates was at 15% (Log-Rank p = 0.0002). Individual relapse tumors showed changes of MGMT expression to a varying degree. The infiltration zone demonstrated a significant increase of MGMT (p < 0.0001). We conclude that immunohistochemical MGMT assessment has potential as a powerful diagnostic tool but analysis should only be performed in a grade dependent manner, before radio-/chemotherapy and with special attention to the infiltration zone of diffuse astrocytomas.

Regulation of glioblastoma cell invasion by PKC iota and RhoB

Glioblastoma multiforme is the most aggressive form of primary brain tumor and remains largely incurable, in large part, due to its highly invasive nature. The phosphoinositide (PI) 3-kinase pathway is often constitutively active in these tumors due to activating mutations in the epidermal growth factor receptor, or deletion/loss of function of the tumor suppressor PTEN. Protein kinase C type iota (PKC iota), a member of the atypical protein kinase C family, is activated by the PI 3-kinase pathway and is an important downstream mediator. Here, we have assessed the role of PKC iota in glioblastoma cell invasion. Depletion of PKC iota with RNA interference caused an increase in actin stress fibers and a decrease in cell motility and invasion. Gene expression microarray analysis of U87MG cells showed that PKC iota repressed expression of mRNA for RhoB, which has previously been shown to have a role in actin stress fiber formation. Western blot analysis showed that both PKC iota depletion and pharmacological inhibition of PKC iota caused an increase in the protein levels of RhoB, as did inhibition of PI 3-kinase. Expression of RhoB from a constitutive promoter caused changes in actin stress fibers and cell invasion that were similar to those seen with PKC iota depletion. These data show that PKC iota, activated as a consequence of aberrant upstream PI 3-kinase signaling, mediates glioblastoma cell motility and invasion, and that repression of RhoB is key downstream event in PKC iota signaling leading to enhanced cell motility. In addition, constitutive expression of RhoB repressed PKC iota activity, as assessed by its phosphorylation status on Thr555. PKC iota and RhoB are, therefore, mutually antagonistic, potentially creating a sensitive switch between invasive and non-invasive phenotypes.

Glioblastoma multiforme: the role of DSB repair between genotype and phenotype

Glioblastoma is the most frequent primary brain tumor in adults. The average survival time of less than 1 year did not improve notably over the last three decades. The dismal prognosis of glioblastoma patients is largely due to the striking radioresistance of this tumor. Here, we attempt a combined view on the genetics, the repair mechanisms and the radioresistance of glioblastoma. Specifically, we address the role of DNA-PKcs and the novel potential end-joining factor KUB3 in maintaining the radioresistant phenotype, the interrelationship between genetic lesions and repair mechanisms, and new perspectives that emerge from the identification of glioblastoma stem cells.

Glioblastoma-derived stem cell-enriched cultures form distinct subgroups according to molecular and phenotypic criteria

Tumor cells with stem cell-like properties can be cultured from human glioblastomas by using conditions that select for the expansion of neural stem cells. We generated cell lines from glioblastoma specimens with the goal to obtain model systems for glioma stem cell biology. Unsupervised analysis of the expression profiles of nine cell lines established under neural stem cell conditions yielded two distinct clusters. Four cell lines were characterized by the expression of neurodevelopmental genes. They showed a multipotent differentiation profile along neuronal, astroglial and oligodendroglial lineages, grew spherically in vitro, expressed CD133 and formed highly invasive tumors in vivo. The other five cell lines shared expression signatures enriched for extracellular matrix-related genes, had a more restricted differentiation capacity, contained no or fewer CD133+ cells, grew semiadherent or adherent in vitro and displayed reduced tumorigenicity and invasion in vivo. Our findings show that stable, multipotent glioblastoma cell lines with a full stem-like phenotype express neurodevelopmental genes as a distinctive feature, which may offer therapeutic targeting opportunities. The generation of another distinct cluster of cell lines showing similarly homogeneous profiling but restricted stem cell properties suggests that different phenotypes exist, each of which may lead to the typical appearance of glioblastoma.