p53 gene mutations in pontine gliomas of juvenile onset

Diffuse intrinsic pontine gliomas: Diagnostic approach and treatment strategies

Diffuse intrinsic pontine gliomas (DIPG) are high grade gliomas of the brainstem with fatal outcomes. Radiation is known to be partially effective to control the immediate flare but relapse is frequent. There has been ongoing research to study the role of molecular subgroups and identification of specific targets but this is not possible with histopathological diagnosis alone. The authors' objective is to highlight the need for and discuss ongoing molecular research. There is an inherent need for the availability of tumor tissue to be able to conduct research studies. The authors advocate the use of neuronavigation assisted stereotactic technique for tumor biopsy. The technique is feasible with a predefined surgical trajectory. After obtaining tissue diagnosis further work can be performed to isolate and identify histone protein genetic mutations and methylation changes responsible for DIPG molecular subgrouping. Moreover, convection enhanced delivery of therapeutic agents is being developed for better instillation of future drug agents. Despite identification of genetic/epigenetic mutations, growth factors, receptors, and tissue biomarkers, the oncogenesis of DIPG remains elusive. The authors' effort to provide a comprehensive review on DIPG to better understand the disease, need for tissue diagnosis, described surgical technique, and need for pre-clinical and clinical future research is novel.

H3K27M, IDH1, and ATRX expression in pediatric GBM and their clinical and prognostic significance

PURPOSE

Pediatric glioblastoma (pGBM) tumors have been identified as an entity distinct and different from the adult variety of GBM not only with respect to pathogenesis, genetics, and molecular alterations but also in clinical outcomes and overall survival. This study aims to evaluate the immunohistochemical profile of molecular markers in pediatric GBM and correlate them with clinical features and prognosis.

MATERIALS AND METHODS

We retrospectively analyzed 29 pGBMs (age range 3 to 18 years), operated at our institute between 2009 and 2014, and evaluated their clinical and histopathological features along with the immunohistochemical expression of clinically relevant molecular markers: H3K27M, p53, ATRX, and IDH1 (R132H), and correlated their expression with clinical features. We further assessed the prognostic value of these markers in our cohort of patients.

RESULTS

The median overall survival (OS) of the cohort was 6.00 ± 0.882 months. The mean overall survival was 7.571 ± 1.118 months which was lower than in most studies. Preoperative Karnofsky Performance Score (KPS), extent of surgical resection, and adjuvant radiotherapy were found to be the clinical factors strongly influencing median survival (p < 0.05). Loss of ATRX expression was predominantly noted in hemispheric tumors (84%), while p53 staining was maximum in thalamic tumors (8 out of 9 cases). H3K27M mutant protein expression was noted in 8/9 thalamic tumors and 5/7 tumors in the brain stem-cerebellar-peduncular region. Patients with tumors showing H3K27M immunopositivity had the worst prognosis with a mean OS of 5 months ± 0.832 months, as against patients with H3K27M-immunonegative tumors, which was 10.143 ± 1.866 months(p = 0.006). Other markers like p53, ATRX, and IDH1 did not influence the prognosis in this patient cohort. ATRX loss of expression was associated with a better OS, with a trend to significance, and such an association has not been reported earlier.

CONCLUSIONS

Ours is one among the few studies from India describing the clinical parameters and evaluating the key immunohistochemical markers in pGBM and deriving their prognostic significance. The study reiterates the poor prognostic significance of H3K27M immunopositivity.

Identification of novel long non-coding RNA in diffuse intrinsic pontine gliomas by expression profile analysis

Diffuse intrinsic pontine glioma (DIPG) is one of the most devastating types of pediatric cancer. Accumulating evidence suggests that the dysregulated expression of long non-coding (lnc)-RNAs is associated with various pathologies of the CNS. However, the expression patterns and prognostic roles of lncRNAs in DIPG have not yet been systematically determined. In the present study, lncRNA expression profiles were obtained from the Gene Expression Omnibus (GEO) database using the lncRNA-mining approach and a differential expression analysis for lncRNAs was performed between DIPG and low-grade brainstem glioma and DIPG and normal pediatric brainstem tissue. Using a two-tailed t-test, 58 and 197 lncRNAs were found to be significantly deferentially expressed (Fold change >2 or <0.5, FDR adjusted P<0.05). To identify the prognostic value of these 255 differentially expressed lncRNAs, univariate and multivariate Cox proportional hazards regression analysis were performed and a 9-lncRNA signature as a potential biomarker for predicting the prognosis of DIPG was constructed. Kaplan-Meier curve analysis showed that patients in the high-risk group exhibited a reduced survival time compared with patients in the low-risk group (median survival of 230 vs. 460 days, log-rank test P<0.001). Moreover, this lncRNA-signature could be used as an independent prognostic marker for DIPG patient survival. The present study provided novel candidates for the investigation of potential diagnostic or prognostic biomarkers and/or therapeutic targets of DIPG, as well as a novel insight into the underlying mechanisms of DIPG.

Convection-Enhanced Delivery for Diffuse Intrinsic Pontine Glioma Treatment

Convection-enhanced delivery (CED) is a technique designed to deliver drugs directly into the brain or tumors. Its ability to bypass the blood-brain barrier (BBB), one of the major hurdles in delivering drugs to the brain, has made it a promising drug delivery method for the treatment of primary brain tumors. A number of clinical trials utilizing CED of various therapeutic agents have been conducted to treat patients with supratentorial high-grade gliomas. Significant responses have been observed in certain patients in all of these trials. However, the insufficient ability to monitor drug distribution and pharmacokinetics hampers CED from achieving its potentials on a larger scale. Brainstem CED for diffuse intrinsic pontine glioma (DIPG) treatment is appealing because this tumor is compact and has no definitive treatment. The safety of brainstem CED has been established in small and large animals, and recently in early stage clinical trials. There are a few current clinical trials of brainstem CED in treating DIPG patients using targeted macromolecules such as antibodies and immunotoxins. Future advances for CED in DIPG treatment will come from several directions including: choosing the right agents for infusion; developing better agents and regimen for DIPG infusion; improving instruments and technique for easier and accurate surgical targeting and for allowing multisession or prolonged infusion to implement optimal time sequence; and better understanding and control of drug distribution, clearance and time sequence. CED-based therapies for DIPG will continue to evolve with new understanding of the technique and the disease.

Identification of novel biologic targets in the treatment of newly diagnosed diffuse intrinsic pontine glioma

Diffuse intrinsic pontine gliomas (DIPGs) carry an extremely poor prognosis. Standard practice has been to base the diagnosis on classic imaging and clinical characteristics and to treat with focal radiation therapy, usually accompanied with experimental therapy. As a result of the desire to avoid upfront biopsy, little has been learned regarding the molecular features of this disease. Findings from several autopsy series have included loss of p53 and PTEN, and amplification of PDGFR. Based on these and other findings, murine models have been generated and provide a new tool for preclinical testing. DIPG biopsy at diagnosis has increasingly become incorporated into national protocols at several centers, bringing the prospect of a better understanding of DIPG biology in the future. Initial analyses of pretreatment tumors cast valuable new light and establish the importance of p53 inactivation and the RTK-PI3K pathway in this disease.

WEE1 kinase inhibition enhances the radiation response of diffuse intrinsic pontine gliomas

Diffuse intrinsic pontine glioma (DIPG) is a fatal pediatric disease. Thus far, no therapeutic agent has proven beneficial in the treatment of this malignancy. Therefore, conventional DNA-damaging radiotherapy remains the standard treatment, providing transient neurologic improvement without improving the probability of overall survival. During radiotherapy, WEE1 kinase controls the G(2) cell-cycle checkpoint, allowing for repair of irradiation (IR)-induced DNA damage. Here, we show that WEE1 kinase is one of the highest overexpressed kinases in primary DIPG tissues compared with matching non-neoplastic brain tissues. Inhibition of WEE1 by MK-1775 treatment of DIPG cells inhibited the IR-induced WEE1-mediated phosphorylation of CDC2, resulting in reduced G(2)-M arrest and decreased cell viability. Finally, we show that MK-1775 enhances the radiation response of E98-Fluc-mCherry DIPG mouse xenografts. Altogether, these results show that inhibition of WEE1 kinase in conjunction with radiotherapy holds potential as a therapeutic approach for the treatment of DIPG.

B7-H3, a potential therapeutic target, is expressed in diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is a brain cancer with a median survival of only 1 year. Lack of molecular characterization of this tumor impedes the development of novel therapies. Membrane protein B7-H3, aka CD276, involved in interactions with host defenses in certain cancers, has been shown to be over-expressed in the majority of malignant neuroectodermal tumors including adult high-grade glioma. Targeting B7-H3 with a monoclonal antibody has demonstrated safety and efficacy in the salvage treatment of stage IV childhood neuroblastoma, another neuroectodermal tumor. It thus stands to reason that B7-H3 might serve as a therapeutic target in DIPG. B7-H3 immunoreactivity was determined in DIPG and non-diffuse brainstem glioma specimens with immunohistochemistry. In addition, B7-H3 mRNA expression was evaluated with microarrays in another set of specimens. All of the nine (100 %) DIPG specimens were shown to be B7-H3 immunoreactive. In the non-diffuse brainstem glioma group, none of the eight WHO grade I specimens showed B7-H3 immunoreactivity and nine of the 24 WHO grade II specimens (37.5 %) showed B7-H3 immunoreactivity. The association between histological grade and B7-H3 immunoreactivity was statistically highly significant. B7-H3 mRNA expression was also significantly higher in DIPG samples than in normal brain and juvenile pilocytic astrocytoma (WHO grade I) specimens. In summary, B7-H3 is over-expressed in DIPG. Given the need for novel treatment in this disease, antibody-based immunotherapy against B7-H3 in DIPG warrants further investigation.

Clinicopathological features of human brainstem gliomas

We describe the clinicopathological features of 25 brainstem gliomas (BSGs). Twenty BSGs located in the pons and were all in children. Four BSGs located in the medulla oblongata were in 2 children and 2 adults. One (in a child) was located in the midbrain. Radiological findings on MR images were low-intensity on T1 weighted images and high-intensity on T2 weighted images. Mean survival when pontine glioma was treated by radiotherapy and/or use of temozolomide was 14 months, although 4 patients (3 cervicomedullary types and one focal type arising from midbrain) are alive. Follow up was from 5 months to 6 years. Histopathological features of 10 cases of the diffuse type were: 4 grade II astrocytomas, 4 grade III astrocytomas, and 2 glioblastomas. MIB-1 index was from 0.8 to 38 %. P53 was positive for 80 % of 15 tumors and there were no negative results. MGMT was positive in 60 % of 15 tumors and negative in 12.4 %. IDH1 was negative in 61.6 %. There was no positive result for IDH1 in this study. Thus, our histopathological results were indicative of high p53 immunoreactivity and no IDH1 immunoreactivity related to secondary malignant change.

Genome-wide analyses identify recurrent amplifications of receptor tyrosine kinases and cell-cycle regulatory genes in diffuse intrinsic pontine glioma

PURPOSE

Long-term survival for children with diffuse intrinsic pontine glioma (DIPG) is less than 10%, and new therapeutic targets are urgently required. We evaluated a large cohort of DIPGs to identify recurrent genomic abnormalities and gene expression signatures underlying DIPG.

PATIENTS AND METHODS

Single-nucleotide polymorphism arrays were used to compare the frequencies of genomic copy number abnormalities in 43 DIPGs and eight low-grade brainstem gliomas with data from adult and pediatric (non-DIPG) glioblastomas, and expression profiles were evaluated using gene expression arrays for 27 DIPGs, six low-grade brainstem gliomas, and 66 nonbrainstem low-grade gliomas.

RESULTS

Frequencies of specific large-scale and focal imbalances varied significantly between DIPGs and nonbrainstem pediatric glioblastomas. Focal amplifications of genes within the receptor tyrosine kinase-Ras-phosphoinositide 3-kinase signaling pathway were found in 47% of DIPGs, the most common of which involved PDGFRA and MET. Thirty percent of DIPGs contained focal amplifications of cell-cycle regulatory genes controlling retinoblastoma protein (RB) phosphorylation, and 21% had concurrent amplification of genes from both pathways. Some tumors showed heterogeneity in amplification patterns. DIPGs showed distinct gene expression signatures related to developmental processes compared with nonbrainstem pediatric high-grade gliomas, whereas expression signatures of low-grade brainstem and nonbrainstem gliomas were similar.

CONCLUSION

DIPGs comprise a molecularly related but distinct subgroup of pediatric gliomas. Genomic studies suggest that targeted inhibition of receptor tyrosine kinases and RB regulatory proteins may be useful therapies for DIPG.

Preclinical evaluation of radiation and perifosine in a genetically and histologically accurate model of brainstem glioma

Brainstem gliomas (BSG) are a rare group of central nervous system tumors that arise mostly in children and usually portend a particularly poor prognosis. We report the development of a genetically engineered mouse model of BSG using the RCAS/tv-a system and its implementation in preclinical trials. Using immunohistochemistry, we found that platelet-derived growth factor (PDGF) receptor alpha is overexpressed in 67% of pediatric BSGs. Based on this observation, we induced low-grade BSGs by overexpressing PDGF-B in the posterior fossa of neonatal nestin tv-a mice. To generate high-grade BSGs, we overexpressed PDGF-B in combination with Ink4a-ARF loss, given that this locus is commonly lost in high-grade pediatric BSGs. We show that the likely cells of origin for these mouse BSGs exist on the floor of the fourth ventricle and cerebral aqueduct. Irradiation of these high-grade BSGs shows that although single doses of 2, 6, and 10 Gy significantly increased the percent of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive nuclei, only 6 and 10 Gy significantly induce cell cycle arrest. Perifosine, an inhibitor of AKT signaling, significantly induced TUNEL-positive nuclei in this high-grade BSG model, but in combination with 10 Gy, it did not significantly increase the percent of TUNEL-positive nuclei relative to 10 Gy alone at 6, 24, and 72 hours. Survival analysis showed that a single dose of 10 Gy significantly prolonged survival by 27% (P = 0.0002) but perifosine did not (P = 0.92). Perifosine + 10 Gy did not result in a significantly increased survival relative to 10 Gy alone (P = 0.23). This PDGF-induced BSG model can serve as a preclinical tool for the testing of novel agents.

Differential regulation of p53 and p21 by MKRN1 E3 ligase controls cell cycle arrest and apoptosis

Makorin Ring Finger Protein 1 (MKRN1) is a transcriptional co-regulator and an E3 ligase. Here, we show that MKRN1 simultaneously functions as a differentially negative regulator of p53 and p21. In normal conditions, MKRN1 could destabilize both p53 and p21 through ubiquitination and proteasome-dependent degradation. As a result, depletion of MKRN1 induced growth arrest through activation of p53 and p21. Interestingly, MKRN1 used earlier unknown sites, K291 and K292, for p53 ubiquitination and subsequent degradation. Under severe stress conditions, however, MKRN1 primarily induced the efficient degradation of p21. This regulatory process contributed to the acceleration of DNA damage-induced apoptosis by eliminating p21. MKRN1 depletion diminished adriamycin or ultraviolet-induced cell death, whereas ectopic expression of MKRN1 facilitated apoptosis. Furthermore, MKRN1 stable cell lines that constantly produced low levels of p53 and p21 exhibited stabilization of p53, but not p21, with increased cell death on DNA damage. Our results indicate that MKRN1 exhibits dual functions of keeping cells alive by suppressing p53 under normal conditions and stimulating cell death by repressing p21 under stress conditions.

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.

Expression of p53, EGFR, pRb and bcl-2 proteins in pediatric glioblastoma multiforme: a study of 54 patients

Pediatric glioblastoma multiforme (GBM) tumors, which have been established as 'de novo' neoplasms, are known to differ from their adult counterparts in terms of biology, genetics and ultimately survival of patients. In order to evaluate the utility of markers of tumor biology for refining prognostic assessment, we retrospectively analyzed 54 pediatric GBMs (age range 9 months to 15 years) occurring at different anatomical sites in the brain, operated at our institute between 1995 and 2001. The expression of p53, epidermal growth factor receptor (EGFR), bcl-2 and retinoblastoma proteins (pRb) was analyzed by immunohistochemistry and the results were compared with the clinical profile, MIB-1 labeling index (LI) and patient survival. p53 immunoreactivity was noted in 53.7% of cases, predominantly in thalamic (75%) and cerebral lobar (62.2%), followed by brainstem tumors (30%). It was absent in cerebellar tumors. p53-positive tumors had a higher MIB-1 LI, compared to p53-negative tumors (p=0.003). EGFR and bcl-2 overexpression was observed in 25.9% and 33.3% of cases, respectively, and loss of pRb expression was evident in only 7.4% of cases, indicating that loss of this gene function is not significantly involved in pediatric GBMs. p53 and bcl-2 expression were maximally noted in patients with poorer outcome. Our results indicate that p53 expression status is noted in a significant number of pediatric supratentorial neoplasms. p53 with bcl-2 overexpression is more often associated with ominous prognosis. Further molecular characterization would provide newer insights into the biology of these neoplasms and form a basis for future therapeutic decision making.

Role of temozolomide after radiotherapy for newly diagnosed diffuse brainstem glioma in children: results of a multiinstitutional study (SJHG-98)

BACKGROUND

The role of chemotherapy in the treatment of children with newly diagnosed diffuse brainstem glioma is uncertain. In the current study, the authors tested the efficacy of temozolomide treatment after radiotherapy (RT) in this setting.

METHODS

Patients ages 3-21 years were eligible for the current multiinstitutional study. An optional window therapy regimen consisting of 2 cycles of intravenous irinotecan (10 doses of 20 mg/m2 per day separated by 2 days of rest per cycle) was delivered over 6 weeks and was followed by conventionally fractionated RT. The 5-day schedule of temozolomide (200 mg/m2 per day) was initiated 4 weeks after RT and was continued for a total of 6 cycles. The pharmacokinetics of temozolomide and its active metabolite, 5-(3-methyltriazen-1-yl)imidazole-4-carboxamide (MTIC), were analyzed during Cycles 1 and 3.

RESULTS

Thirty-three patients (median age at diagnosis, 6.4 years) were enrolled. Of the 16 patients who received window therapy, 6 had irinotecan treatment discontinued due to clinical progression (n=5) or toxicity (n=1); the remaining 10 experienced disease stabilization after 2 cycles. All patients completed RT (median dose, 55.8 gray). Twenty-nine patients received a combined total of 125 cycles of temozolomide. Grade 3/4 neutropenia and thrombocytopenia occurred in 33% and 29% of all temozolomide cycles, respectively. In approximately one-third of the cycles, dose reduction was required due to myelosuppression. No correlation was demonstrated between temozolomide/MTIC exposure and myelosuppression at the conclusion of Cycle 1. All patients died of disease progression (median survival, 12 months). The estimated 1-year survival rate was 48% (standard error, 8%).

CONCLUSIONS

The administration of temozolomide after RT did not alter the poor prognosis associated with newly diagnosed diffuse brainstem glioma in children.

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.

Supratentorial high-grade astrocytoma and diffuse brainstem glioma: two challenges for the pediatric oncologist

Pediatric high-grade gliomas represent a heterogeneous group of tumors that accounts for 15%-20% of all pediatric central nervous system tumors. These neoplasms predominantly involve the supratentorial hemispheres or the pons, in which case the tumors are usually called diffuse brainstem gliomas. The diagnosis of supratentorial neoplasms is dependent on their histologic appearance. The maximum possible surgical resection is always attempted since the degree of surgical resection is the main prognostic factor for these patients. Older children (>3 years) with supratentorial neoplasms undergo a multimodality treatment comprised of surgical resection, radiation therapy, and chemotherapy. The addition of chemotherapy seems to improve the survival of a subset of these children, particularly those with glioblastoma multiforme. However, 2-year survival rates remain poor for children with supratentorial neoplasms, ranging from 10%-30%. The diagnosis of a diffuse brainstem glioma is based upon typical imaging, dispensing with the need for surgery in the majority of cases. Radiation therapy is the mainstay of treatment for children with diffuse brainstem gliomas. The role of chemotherapy for these children is not clear, and it is, in general, employed in the context of an investigational study. Less than 10% of children with diffuse brainstem gliomas survive 2 years. Because the outcome for patients with either type of tumor is poor when standard multimodality therapy is used, these children are ideal candidates for innovative treatment approaches.

Primitive neuroectodermal tumors of the brainstem: investigation of seven cases

OBJECTIVE

We discuss the clinical aspects, pathology, and molecular genetics of 7 patients with primitive neuroectodermal tumors (PNETs) arising in the brainstem that were treated at our institution from 1986 through 1995. Most neuro-oncologists avoid performing biopsies in children with pontine tumors. This article raises the question as to whether biopsies should be performed, because treatment recommendations might differ if a PNET was diagnosed rather than a pontine glioma.

PATIENTS AND METHODS

We reviewed the clinical neuro-oncology database and the files of the Division of Neuropathology at New York University Medical Center from 1986 through 1995 and identified 7 histologically confirmed PNETs arising in the brainstem among 146 pediatric brainstem tumors. The clinical, neuroradiological, and neuropathological data were reviewed. Postmortem examinations were performed in 2 cases. Formalin-fixed, paraffin-embedded tumor tissues were also available in 6 of 7 patients that were tested for p53 gene mutations using single-strand conformation polymorphism analysis. We also tested 9 cerebellar PNETs, 9 brainstem gliomas, and 3 normal brains for p53 gene mutations as controls.

RESULTS

All 7 patients presented with focal cranial nerve deficits, and 2 were also hemiparetic. The median age at diagnosis was 2.7 (1-8 years). Magnetic resonance imaging (MRI) characteristics included a focal intrinsic exophytic nonenhancing brainstem lesion that had low T1-weighted and high T2-weighted signals. Hydrocephalus was present in 5 patients at diagnosis, 3 of whom had leptomeningeal dissemination. Meningeal dissemination occurred later in the course of the disease in 3 other patients. Five children required shunts at diagnosis and another 2 at recurrence. Despite therapy, all 7 PNET patients died within 17 months of diagnosis with a mean survival of 8 (4-17) months. No mutation in the p53 gene was detected.

CONCLUSIONS

Brainstem PNETs tend to arise at a younger age than brainstem gliomas and medulloblastomas. The MRI pattern suggests a localized rather than a diffuse intrinsic nonenhancing brainstem tumor. Like other PNETs, brainstem PNETs have a high predilection to disseminate within the central nervous system. The absence of p53 mutations is similar to other PNETs. Despite their origin close to the cerebellum, brainstem PNETs exhibit a more aggressive behavior and result in worse clinical outcomes than do cerebellar PNETs.

Genetic alterations in pediatric high-grade astrocytomas

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

Establishment of two glioma cell lines from two surgical specimens obtained at different times from the same individual

We established two glioma cell lines from two surgical specimens obtained at different times from the same patient. One (No. 9R), which was derived from the recurrent tumor (glioblastoma, grade IV), proliferated more rapidly in vitro than the other (No. 9) from the primary tumor (slightly anaplastic astrocytoma, grade II-III). No. 9R showed heterotransplantability in nude mice, whereas No. 9 did not. These findings indicate that No. 9R has a more aggressive or malignant nature than No. 9. Both cell lines showed homozygous deletion of the representative tumor suppressor p16 and p15 genes, but no p53 gene alteration. However, examination of the overall mRNA expression profile using a commercially available cDNA-spotted membrane revealed much higher expression levels of several mRNAs, at least, in No. 9R than in No. 9, although the relationship between these mRNAs and the growth potentials remained unknown. These two cell lines, derived from the same individual, with different proliferating potentials may be useful for studies on the molecular bases of glioma malignancy and progression.

Parental occupation and childhood brain tumors: astroglial and primitive neuroectodermal tumors

Data from a population-based case-control study in 19 counties in California and Washington State were used to investigate the association between parental employment and childhood brain tumors. Parents of 540 cases (including 308 astroglial and 109 primitive neuroectodermal tumors) and 801 controls diagnosed from 1984 to 1991 were interviewed. Analysis was completed for parents' self-reported industry of employment and job tasks during the five years preceding the birth of the child. Parents who worked in the chemical industry were at increased risk of having had children with astroglial tumors (fathers' odds ratio [OR] = 2.1; 95% confidence interval [CI], 1.1-3.9); mothers' OR = 3.3; 95% CI, 1.4-7.7), but no trend by duration of employment was seen for mothers. Children of fathers employed as electrical workers were at increased risk of developing brain tumors of any histologic type (OR = 2.3; 95% CI, 1.3-4.0).

A comparative study of glioma cell lines for p16, p15, p53 and p21 gene alterations

A total of 10 glioma cell lines were examined for alterations of the p16, p15, p53 and p21 genes, which are tumor suppressor genes or candidates with direct or indirect CDK-inhibitory functions. Genetic alterations (deletions or mutations) were frequently seen in the p16, p15 and p53 genes in these cell lines, but not in the p21 gene. When the states of the p16, p15 and p53 genes were compared among cell lines, all the cell lines showed abnormalities in at least 1 gene, often in 2 or 3 genes coincidentally, suggesting that dysfunction of these genes is closely related to glioma cell growth. Although alteration of all 3 genes was most frequent, there were cell lines having either p16/p15 or p53 or pl6 and p53 gene alterations, suggesting that the time order of these genetic alterations was variable depending on the cell line. Among cell lines examined, one with homozygous p53 gene deletion seemed of particular practical value, since such a cell line might be useful in various studies, including investigation of the functions of various mutant p53 genes in the absence of heteromeric protein formation. On examination of the primary tumor tissues, the same alterations of the p16/p15 and p53 genes as detected in the cell lines were demonstrated in all 6 cases examined: p16/p15 gene deletion in 1, p16 gene mutation in 1 and p53 gene mutations in 5 cases. This suggested that the p16/p15 and the p53 gene alterations and their combinations in at least some glioma cell lines reflected those in the primary glioma tissues.

The p53 gene and its role in human brain tumors

Mutation of the p53 gene is among the most common lesions in a variety of human tumors, including those of the central nervous system. In most instances, mutation of one p53 allele is followed by loss of the remaining wild-type allele, resulting in cells with a complete absence of functional wild-type p53 protein. However, in some situations, such as at initiation of spontaneously arising gliomas or as the germline configuration of patients with the Li-Fraumeni syndrome, cells clearly carry both wild-type and mutant p53 alleles. These observations lead to the hypothesis that p53 mutations can give rise to loss of tumor suppressor functions as well as to gain of oncogenic transformation capabilities. In this review, we define the types of mutations that occur in the p53 gene in various glial tumors, contrast that with the spectra described in other human tumor types, and discuss the biochemistry and physiology of the p53 protein and its ability to regulate and be regulated by other gene products. We use this information to propose roles for p53 in the initiation and progression of human gliomas.

Mutations and immunohistochemistry of p53 and proliferation markers in astrocytic tumors of childhood

Thirty cases of hemispheric astrocytic tumors of childhood, consisting of 11 pilocytic astrocytomas, 2 fibrillary astrocytomas, 9 anaplastic astrocytomas, and 8 glioblastomas, were studied for the presence of p53 mutations and for immunohistochemical demonstrations of p53 and proliferation markers PCNA and Ki-67 MIB-1. The study was performed using polymerase chain reaction (PCR)-assisted single-strand conformation polymorphism analysis of exons 5-8 and direct sequence analysis of PCR products. For immunohistochemistry, DO1 and PAb 1801 were used. No mutation and no positivity for p53 protein were found in pilocytic astrocytomas. Mutations (at codons 144, 202, and 245) were found in 2 out of 8 glioblastomas and in 1 out of 9 anaplastic astrocytomas, whereas positive staining was found in 11 out of 17 malignant gliomas. Cases with mutations showed the highest p53 labeling index and also PCNA and MIB-1 labeling indices. The negative results in pilocytic astrocytomas are in line with the benign course of these tumors, whereas for malignant gliomas no difference seems to exist in comparison with adult cases.

Intracranial germ cell tumors: detection of p53 gene mutations by single-strand conformation polymorphism analysis

Using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) analysis, p53 gene mutation was examined in 12 intracranial germ cell tumors (5 yolk sac carcinomas and 7 germinomas), many of which were derived from young patients in the first to the second decade. A total of 10 mutations were detected in 4 of the 12 cases and, in 3 of them, the mutations were multiple or tandem. Among the 10 mutations, 7 were missense, 1 was splicing and 2 were silent. The 7 missense mutations were located at previously proposed hot spot codons or in their vicinity or, when outside the hot spots, at a codon encoding an amino acid conserved in most vertebrates. These findings suggested that all 7 missense mutations may actually give rise to functional alteration of the p53 protein. The splicing mutation was considered to be a germ-line mutation, though its biological effect was equivocal, since the neoplastic tissue contained an additional mutation. The pattern of the mutations was predominancy of G:C-A:T transition with frequent involvement of the CpG site. These mutations were more frequently detected in yolk sac carcinomas (60%; 3/5 cases) than in germinomas (14%; 1/7 cases), suggesting that the contribution of the p53 mutation to carcinogenesis differed with the histological type of the intracranial germ cell tumor.

Familial brain tumour syndrome associated with a p53 germline deletion of codon 236

This report describes clinical, neuropathological and molecular genetic findings in a Swiss family with four brain tumours in only two generations. The neoplasms observed covered a wide range of biologic behaviour, from a slowly growing lesion already apparent at birth, to anaplastic astrocytoma in a young adult and glioblastomas at the age of less than 10 years. The only non-neural neoplasms in this family were a case of leukemia and an adrenocortical carcinoma. A germline deletion of codon 236 of the p53 tumour suppressor gene was identified as an underlying cause and detected in all affected family members. This mutation has not previously been reported as germline transmission or in sporadic tumours. The unusual accumulation of CNS tumours may be due to a certain organ-specific effect of this particular p53 mutation or it may reflect the specific genetic back-ground of this family.