Meningiomas, dicentric chromosomes, gliomas, and telomerase activity

High incidence of activating TERT promoter mutations in meningiomas undergoing malignant progression

Meningiomas are common central nervous system tumors. The World Health Organization (WHO) defines three grades, predictive of the risk of recurrence. These tumors can relapse frequently and sometimes undergo malignant transformation. Maintenance of telomere length is a key process in malignant progression, and mutations in TERT promoter have recently been identified in various types of cancer. We sequenced the TERT promoter in 85 meningiomas from 73 patients. We found a high incidence of TERT promoter mutations in patients with meningiomas undergoing malignant histological progression (28%, n = 5/18 patients). In this subset of patients with histological progression, TERT promoter mutations were found in both the lowest and the highest grade tumors, and in both NF2-mutated and nonmutated samples. In contrast, one mutation was identified in 35 meningiomas without recurrence or progression, belonging to various histological grades. This sample was an aggressive meningioma in a patient who died shortly after surgery. Interestingly, tumors showing relapse without histological progression were not mutated for TERT promoter (n = 20). Finally, TERT promoter mutations were associated with a marked increase in TERT expression. Thus, TERT promoter mutations are pivotal genetic alterations involved in malignant progression of meningiomas and could be used as a biomarker to identify meningiomas at risk of malignant transformation.

Pathology and genetics of meningiomas

This article constitutes a mini-review of the pathology and genetics of meningiomas. Meningiomas are the most common primary intracranial tumors. They are usually durally based and are often found adjacent to venous sinuses and dural infoldings. The majority of these tumors are WHO grade I, although a minority is WHO grade II, atypical, or WHO grade III, anaplastic. Grade II and III meningiomas show a greater tendency than Grade I tumors to recur and metastasize. The current WHO scheme recognizes 15 histologic subtypes of meningiomas. Nine of these are WHO grade I, three are grade II, and three are grade III. In addition to these histologic subtypes, meningiomas can also be graded on the basis of mitotic activity, evidence of brain invasion, growth pattern cellular density, nuclear atypia, and necrosis. Loss of the long arm of chromosome 22, which is usually associated with inactivation of the NF2 gene, is the most common genetic abnormality found in meningiomas. Other chromosomal abnormalities associated with tumorogenesis and increased gradeof meningiomas include loss of heterozygosity for chromosome 1p, loss of 14q, deletion of 9p21, abnormalities of chromosome 10 and 17q. Telomerase activity increases with meningiomas grade as well. The only proven environmental risk factor for meningiomas is ionizing radiation. Radiation-induced meningiomas are more often multiple and have higher recurrence rates than standard meningiomas.

Cytogenetic characterizations of central nervous system tumors: the first comprehensive report from a single institution in Korea

The World Health Organization (WHO) classification of central nervous system (CNS) tumors incorporates morphology, cytogenetics, molecular genetics, and immunologic markers. Despite the relatively large number of CNS tumors with clonal chromosome abnormalities, only few studies have investigated cytogenetic abnormalities for CNS tumors in Korea. Thus, we investigated 119 CNS tumors by conventional G-banded karyotypes to characterize patterns of chromosomal abnormalities involving various CNS tumors, and 92.4% of them were cultured and karyotyped successfully. Totally, 51.8% of karyotypable CNS tumors showed abnormal cytogenetic results, including neuroepithelial tumors (75.0%), meningeal tumors (71.1%), pituitary adenomas (4.2%), schwannomas (44.4%), and metastatic tumors (100.0%). Glioblastomas had hyperdiploid, complex karyotypes, mainly involving chromosomes Y, 1, 2, 6, 7, 10, 12, 13, and 14. Monosomy 22 was observed in 56.4% of meningiomas. There was a significant increase in the frequencies of karyotypic complexity according to the increase of WHO grade between grades I and II (P=0.0422) or IV (P=0.0101). Abnormal karyotypes were more complex at high-grade tumors, suggesting that the karyotype reflects the biologic nature of the tumor. More detailed cytogenetic and molecular characterizations of CNS tumors contribute to better diagnostic criteria and deeper insights of tumorigenesis, eventually resulting in development of novel therapeutic strategies.

Progression of astrocytomas and meningiomas: an evaluation in vitro

OBJECTIVES/BACKGROUND

In biological terms, progression means that malignancy increases as genetic mutations accumulate leading to increased proliferation and invasion capacity. By verifying the proliferation capacity, human telomerase reverse transcriptase (hTERT) expression and in vitro invasion, in a group of highly malignant glioblastomas, benign meningiomas and astrocytomas, at the initial stage of progression, we have analysed putative progression in vitro for proliferation and telomerase expression.

MATERIALS AND METHODS

The relative proliferation status (visualized with Ki-67 antibodies) and presence of hTERT protein was analysed in 27 intracranial tumours (6 astrocytomas, 8 glioblastomas and 13 meningiomas) by immunohistochemistry on paraffin-embedded biopsy tissue, as well as on primary tumour-derived cell cultures. A confrontation model was used to analyse invasiveness in vitro.

RESULTS

The mean proliferation indices were 22.3 (SD = 18.1) for glioblastomas and 2.1 (SD = 1.9) for low-grade (LG) astrocytomas. The group of benign meningiomas had a labelling index of 2.2 (SD = 2.7). Mean percentages of staining for hTERT varied between 36.5 (SD = 28.4) for glioblastomas and 10.2 (SD = 8.6) for LG astrocytomas. The group of benign meningiomas had a labelling index of 12.4 (SD = 19.2) for hTERT. A significant difference was seen for Ki-67 (P < 0.05) and hTERT (P < 0.001) in vivo versus in vitro. No difference was seen between the group of invasive and non-invasive tumour-derived cell cultures for the histopathological markers Ki-67 and hTERT (P > 0.05) in vitro.

CONCLUSIONS

The elevated expression of hTERT and Ki-67 in vitro provides a potential prognostic tool for early detection of the progression of brain tumours. As tumour cells require telomerase for continued proliferation, the expression of hTERT may mark immortality, leading to indefinite life span. On the other hand, hTERT expression and cell proliferation are not linked directly to invasion in vitro.

Molecular cytogenetic analysis in the study of brain tumors: findings and applications

Classic cytogenetics has evolved from black and white to technicolor images of chromosomes as a result of advances in fluorescence in situ hybridization (FISH) techniques, and is now called molecular cytogenetics. Improvements in the quality and diversity of probes suitable for FISH, coupled with advances in computerized image analysis, now permit the genome or tissue of interest to be analyzed in detail on a glass slide. It is evident that the growing list of options for cytogenetic analysis has improved the understanding of chromosomal changes in disease initiation, progression, and response to treatment. The contributions of classic and molecular cytogenetics to the study of brain tumors have provided scientists and clinicians alike with new avenues for investigation. In this review the authors summarize the contributions of molecular cytogenetics to the study of brain tumors, encompassing the findings of classic cytogenetics, interphase- and metaphase-based FISH studies, spectral karyotyping, and metaphase- and array-based comparative genomic hybridization. In addition, this review also details the role of molecular cytogenetic techniques in other aspects of understanding the pathogenesis of brain tumors, including xenograft, cancer stem cell, and telomere length studies.

mRNA quantification and clinical evaluation of telomerase reverse transcriptase subunit (hTERT) in intracranial tumours of patients in the island of Crete

Telomerase is a reverse transcriptase that maintains telomeres by adding telomeric TTAGGG repeats to the ends of human chromosomes. The aim of this study was to evaluate quantitatively the mRNA expression of telomerase catalytic subunit (hTERT) in different types of intracranial tumours in relation to their histologic pattern and grade and correlate it with progression-free (PFS) and overall survival (OS) of patients. Human telomerase reverse transcriptase mRNA levels were estimated by the use of real time RT–PCR in 68 samples of intracranial tumours. It revealed statistical correlation between hTERT mRNA expression levels and the grade of the tumours (P<0.001). Patients having negative expression of hTERT mRNA had statistically longer PFS (P=0.031) and OS (P=0.047). Cox univariate regression analysis revealed that hTERT mRNA-positive patients had a high and statistically significant risk of relapse (hazard ratio (HR) of 2.24 and P=0.038). In the Cox multivariate regression model, the levels of hTERT mRNA were adjusted for tumour grade and patients age, and since there was statistically significant relationship between the levels of hTERT mRNA and the grade of the tumours (P=0.003 or P=0.006, respectively), hTERT mRNA levels could not be considered as an independent prognostic factor for PFS or OS.

The hTERT-protein and Ki-67 labelling index in recurrent and non-recurrent meningiomas

Meningiomas are considered as benign neoplasms affecting the coverings of the central nervous system and compromise approximately 20% of all intracranial tumours. However, a number of these tumours recur even after total resection. The aim of this study is to evaluate the prognostic significance for recurrence of the human telomerase catalytic subunit (hTERT) in the cells of meningiomas. The expression of hTERT-protein can be evaluated by immunohistochemical staining using a monoclonal antibody against hTERT (clone 44F42, NCL-L-hTERT). The interdependence between tumour recurrence and cell proliferation in this study is analysed by Ki-67 immunoreactivity (clone MIB-1). Archival material from 29 non-recurrent and 32 recurrent tumours has been evaluated, including specimens from World Health Organization (WHO) stages I (n = 73), II (n = 2) and III (n = 12). Although the tumours were categorized as benign meningiomas following the WHO classification, recurrence in 22 of 50 cases did not correlate with the tumour stage. For hTERT staining, the following results were found for nucleolar and total nuclear staining, respectively: non-recurrent meningiomas, 2.9% (+/- 7.7) and 3.0% (+/- 8.0); recurrent meningiomas at first resection, 16.8% (+/- 19.7) and 31.6% (+/- 30.2). Concerning the Ki-67 labelling index (LI): for the group of non-recurrent meningiomas, results were 2.1% (+/- 1.7) and for the recurrent group at first resection, 1.7% (+/- 2.0). A significant difference was seen for the hTERT staining (P < 0.001) between the non-recurrent and recurrent meningiomas, whereas no statistical significance was found for Ki-67. In conclusion hTERT-positive meningiomas had a high incidence for recurrence. Ki-67 was a good marker of cell proliferation status of the tumours, but did not correlate with recurrence; thus, hTERT alone seemed to be a potential predictor for recurrence.

Meningiomas: Updating Basic Science, Management, and Outcome

BACKGROUND

Meningiomas are biologically complex and clinically and surgically challenging. These features, combined with the rewarding potential for cure, make them of great interest to neurologists, neurosurgeons, and neuroscientists alike.

REVIEW SUMMARY

Initially, we review the clinical context of meningiomas, particularly recent changes in histopathological classification, diagnosis, and neuroimaging. Secondly, the underlying basic science as it has evolved over the last decades is summarized. The status of areas recently of intense interest, such as steroid hormone receptors and oncogenic viruses is described. Additionally, emerging areas of great promise, such as cytogenetics and molecular biology are presented. Lastly, we describe recent advances in management. In particular, skull-base surgery, image-guided surgery, and advances in radiotherapy are emphasized. The possible impact of basic research on management and outcome is also outlined.

CONCLUSIONS

Although usually benign and amenable to cure, meningiomas still present significant diagnostic and treatment challenges. Advances in basic science, surgery, and adjuvant therapy are widening the potential for safe, effective, evidence-based management leading to even better outcomes

Alternative lengthening of telomeres and survival in patients with glioblastoma multiforme

Despite advances in the molecular pathogenesis of glioblastoma multiforme, no reliable prognostic markers have been identified. We analysed telomerase activity and telomere lengths in glioblastoma multiformes from 77 patients. 19 patients (25%) had tumours with the alternative-lengthening-of-telomere (ALT) phenotype. Median survival for patients with this phenotype was 542 days (95% CI 114-970) compared with 247 days (224-270) for glioblastoma multiformes with normal telomeres (p=0.0003). Cox's regression analysis showed that this association is independent of age. In patients with non-ALT tumours, telomerase activity did not affect survival (median 287 [199-375] vs 236 [230-242] days, p=0.275). We conclude that ALT is a prognostic indicator for patients with glioblastoma multiforme.

Telomerase as a therapeutic target for malignant gliomas

Telomerase, a ribonucleoprotein enzyme, is considered as a potential target of cancer therapy because of its preferential expression in tumors. In particular, malignant gliomas are one of the best candidates for telomerase-targeted therapy. It is because malignant gliomas are predominantly telomerase-positive, while normal brain tissues do not express telomerase. In theory, there are two telomerase-associated therapeutic approaches for telomerase-positive tumors. One approach is the anti-telomerase cancer therapy to directly inhibit telomerase activity, resulting in apoptotic cell death or growth arrest. Two major components of the telomerase holoenzyme complex, the RNA template (hTER) and catalytic subunit (reverse transcriptase, hTERT) are well considered as therapeutic targets. The other approach is the telomerase-specific cancer therapy by targeting telomerase-expressing tumor cells as a means to directly kill the cells. Strategies using the transfer of therapeutic gene under the hTERT promoter system as well as immunotherapy directed against telomerase-positive cells are generally included. These telomerase-associated therapies are very promising for the treatment of malignant gliomas.

Regulation of the human telomerase reverse transcriptase gene

Most somatic human cells lack telomerase activity because they do not express the telomerase reverse transcriptase (hTERT) gene. Conversely, most cancer cells express hTERT and are telomerase positive. For most tumors it is not clear whether hTERT expression is due to their origin from telomerase positive stem cells or to reactivation of the gene during tumorigenesis. Telomerase negative cells lack detectable cytoplasmic and nuclear hTERT transcripts; in telomerase positive cells 0.2 to 6 mRNA molecules/cell can be detected. This suggests that expression is regulated by changes in the rate of hTERT gene transcription. In tumor cell lines hTERT expression behaves like a recessive trait, indicating that lack of expression in normal cells is due to one or several repressors. Studies with monochromosomal hybrids indicate that several chromosomes may code for such repressors. A number of transcription factors, tumor suppressors, cell cycle inhibitors, cell fate determining molecules, hormone receptors and viral proteins have been implicated in the control of hTERT expression; but these studies have not yet provided a clear explanation for the tumor specific expression of the hTERT gene, and the cis-acting elements which are the targets of repression in normal cells still have to be identified.

Clinical implications of telomerase detection

In 1994 a sensitive method for the detection of telomerase was described. This assay, which was based on the polymerase chain reaction, suggested that telomerase activity was associated with immortal and cancer cells. Since then more than a thousand studies have documented the expression and activity of the enzyme in diseased tissues, primarily tumours. This review gives an overview of the biological significance of telomerase expression and methods for detecting its activity. This is followed by an organ system-based discussion of expression in normal tissues and disease states. We finish with speculation as to the future role of telomerase detection in diagnostic histopathology.

Induction of telomerase activity by irradiation in human lymphoblasts

Neuhof, D., Ruess, A., Wenz, F. and Weber, K. J. Induction of Telomerase Activity by Irradiation in Human Lymphoblasts. Radiat. Res. 155, 693-697 (2001). Telomerase activity is a radiation-inducible function, which suggests a role of this enzyme in DNA damage processing. Since the tumor suppressor TP53 plays a central role in the regulation of the cellular response to DNA damage, our study explored the ability of ionizing radiation to change telomerase activity and telomere length in two closely related human lymphoblast cell lines with different TP53 status. TK6 cells (wild-type TP53) and WTK1 cells (mutated TP53) were exposed to different doses of X rays, and telomerase activity was measured by PCR ELISA at different times after irradiation. A dose-dependent increase in telomerase activity was observed. One hour after irradiation with 4 Gy, TK6 and WTK1 cells showed an approximately 2.5-fold increase; for lower doses (0.1 to 1 Gy), telomerase induction was seen only in TK6 cells. Telomerase induction was observed by 0.5 h after irradiation, with a further increase up to 24 h. Irradiated TK6 and WTK1 cells had longer telomeres (+1.3 kb) than unirradiated cells 14 days after exposure. Our data demonstrate a dose-dependent induction of telomerase activity and lengthening of telomeres by ionizing radiation in human lymphoblasts. Induction of telomerase activity by radiation does not generally appear to be controlled by the TP53-dependent DNA damage response pathway. However, for low doses, induction of telomerase requires wild-type TP53.