Telomerase activity in human brain tumours

Génétique des gliomes, vers une classification moléculaire

Gliomas result from specific genetic alterations--such as activation of specific oncogenes and/or inactivation of specific tumor suppressor genes. These alterations affect specific pathways involved in either signal transduction or cell cycle control, leading to phenotypic changes such as uncontrolled proliferation, inhibition of apoptosis, genetic instability, invasive properties. Tumoral progression includes multiple molecular pathways of clinical relevance: early alterations (p53 mutations for astrocytomas, 1p and 19q loss for oligodendrogliomas) and late alterations (EGF-R amplification, PTEN and P16/CDKN2A inactivation). Genetic profile is not only of diagnostic--but also prognostic relevance, as shown by 1p associated to 19q loss in oligodendrogliomas which is predictive of better prognosis and higher response rate.

Antitumor effects of specific telomerase inhibitor GRN163 in human glioblastoma xenografts

Telomerase is a ribonucleoprotein complex that elongates telomeric DNA and appears to play an important role in cellular immortalization of cancers. Because telomerase is expressed in the vast majority of malignant gliomas but not in normal brain tissues, it is a logical target for gliomaspecific therapy. The telomerase inhibitor GRN163, a 13-mer oligonucleotide N3'-->P5' thio-phosphoramidate (Geron Corporation, Menlo Park, Calif.), is complementary to the template region of the human telomerase RNA subunit hTR. When athymic mice bearing U-251 MG human brain tumor xenografts in their flanks were treated intratumorally with GRN163, a significant growth delay in tumor size was observed (P < 0.01 in all groups) as compared to the tumor size in mice receiving a mismatched oligonucleotide or the carrier alone. We also investigated biodistribution of the drug in vivo in an intracerebral rat brain-tumor model. Fluorescein-labeled GRN163 was loaded into an osmotic minipump and infused directly into U-251 MG brain tumors over 7 days. Examination of the brains revealed that GRN163 was present in tumor cells at all time points studied. When GRN163 was infused into intracerebral U-251 MG tumors shortly after their implantation, it prevented their establishment and growth. Lastly, when rats with larger intracerebral tumors were treated with the inhibitor, GRN163 increased animal survival times. Our results demonstrate that the antitelomerase agent GRN163 inhibits growth of glioblastoma in vivo, exhibits favorable intracerebral tumor uptake properties, and prevents the growth of intracerebral tumors. These findings support further development of this compound as a potential anticancer agent.

hTERT Is highly expressed in Ewing's sarcoma and activated by EWS-ETS oncoproteins

Although the fusion proteins EWS-ETS are uniquely associated with Ewing's sarcoma and have been shown to have transformational properties, they are not the only determinants of oncogenesis. Therefore, before molecular-based therapy can be initiated, a better understanding of the molecular network specific to Ewing's sarcoma is mandatory. Specimens from 31 patients with Ewing's sarcoma were analyzed immunohistochemically. We found that human telomerase reverse transcriptase was expressed highly (78%) in Ewing's sarcoma. The mean followup was 7 years (range, 1-21 years), and human telomerase reverse transcriptase expression was correlated with outcome. Because we did not find an association between expression pattern and survival, human telomerase reverse transcriptase may not serve as a tumor marker in Ewing's sarcoma. However, the human telomerase reverse transcriptase promoter is shown to be activated by the fusion proteins. Therefore, transcriptional regulation via EWS-ETS may account for the high human telomerase reverse transcriptase expression in Ewing's sarcoma.

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

Differential expression of telomerase reverse transcriptase (hTERT) in lung tumours

Human telomerase reverse transcriptase is a ribonucleoprotein that synthesises telomeric sequences, which decrease at each cell division. In cancer cells, its activity is linked to telomere maintenance leading to unlimited cellular proliferation and immortality. To evaluate the prognostic value of the catalytic subunit telomerase reverse transcriptase (hTERT), we analysed its expression by immunohistochemistry in 122 formalin-fixed lung tumours including 42 squamous cell carcinoma (SCC), 43 adenocarcinoma (ADC), 19 basaloid carcinoma (BC) and 18 small-cell lung carcinoma (SCLC) in comparison with detection of hTERT mRNA by in situ hybridisation and relative telomerase activity by TRAP assay in a subset of tumours. We observed a high concordance between hTERT protein expression and detection of hTERT mRNA and telomerase activity. Telomerase expression varied according to histology (P=0.0002) being significantly lower in ADC than in SCC, BC and SCLC (P<0.0001). Adenocarcinoma and SCC exhibited either a nuclear or a nucleolar staining in contrast with a diffuse nuclear staining observed in most BC and all SCLC (P=0.01). In stage I NSCLC telomerase expression was lower than in other stages (P=0.04), and a nucleolar staining was correlated with a short survival (P=0.03). We concluded that telomerase expression and pattern are distinctive among histopathological classes of lung cancer and convey prognostic influence.

Telomere maintenance in childhood primitive neuroectodermal brain tumors

Primitive neuroectodermal tumors (PNETs), including medulloblastoma (PNET/MB) and supratentorial PNET (sPNET), are the most common malignant brain tumors of childhood. The stabilization of telomere lengths by telomerase activation is an important step in carcinogenesis and cell immortalization. Epigallocatechin gallate (EGCG), the major polyphenol in green tea, is a telomerase inhibitor with antiproliferative and anticarcinogenic effects against different types of cancer. In this study, we used real-time reverse transcriptase-polymerase chain reaction to measure the mRNA expression of the human telomerase reverse transcriptase (hTERT) in 50 primary PNET samples (43 PNET/MB, 7 sPNET), 14 normal human brain samples, and 6 human PNET cell lines. Compared to normal human cerebellum, 38/50 (76%) primary PNET samples had >or= 5-fold upregulated hTERT mRNA expression. We then examined PNET cell lines for telomerase activity using a quantitative telomeric repeat amplification protocol (TRAP), and for telomere length using terminal restriction fragment analysis. While a positive correlation between hTERT mRNA expression and telomerase activity was detected in PNET cell lines, no correlation was found between telomerase activity and telomere length. Treatment of PNET cell lines with EGCG resulted in a dose-dependent inhibition of telomerase activity at micromolar levels. Although EGCG displayed strong proliferation inhibitory effects against TRAP-positive PNET cell lines, it had no significant effect against TRAP-negative D425 cells. These results provide evidence for a possible role of telomerase in the pathogenesis of most PNETs and indicate that subsets of PNETs maintain telomere length by alternative mechanisms. Inhibition of telomerase function represents a novel experimental therapeutic strategy in childhood PNETs that warrants further investigation.

Telomerase activity in pituitary adenomas: significance of telomerase expression in predicting pituitary adenoma recurrence

Clinical and histopathological evaluations are inadequate for assessing biological aggressiveness and regrowth potential in benign pituitary adenomas. To develop reliable and prognostically informative means of predicting behavior remains an intractable problem. Telomerase, a reverse transcriptase that extends telomere length, may facilitate tumorigenesis and tumor immortality. In the present study, we investigated the telomerase activity of pituitary adenomas, and attempted to assess the value of telomerase expression for predicting their clinical course. In total, 31 (30 patients) benign pituitary adenoma samples including 8 recurrent adenomas were studied. Telomerase expression was evaluated by polymerase chain reaction (PCR)-based telomeric repeat amplification protocol (TRAP) assay and telomerase activity levels were quantitated by improved PCR enzyme-linked immunosorbent assay (ELISA). The data were analyzed in relation to clinical course which was reviewed at 4-5.5 years (median follow-up time, 52.5 months) after surgery. The relative values of the telomerase expression for predicting the clinical course were compared with the MIB-1 antigen-based proliferative cell index (PCI) and p53 immunoreactivity which have recently been suggested to correlate with aggressive behavior in pituitary adenomas. Overall, telomerase expression was detected in 13% of the adenomas (4 tumor tissues, 3 patients). These adenomas comprised large, invasive, and functioning adenomas. The number of telomerase-positive adenomas was small; however, the PCI was higher in cases with telomerase expression (4 tumor tissues; mean, 4.2 +/- 2.4%) than in those without it (27 tumor tissues; 1.4 +/- 1.3%) (p = 0.01). One tumor with detectable telomerase expression, which did not undergo additional pharmacological or radiotherapeutic intervention after first surgery, recurred rapidly despite gross total surgical resection, although the PCI of both the primary and recurrent adenomas was not high. Detection of telomerase expression may represent an additional useful means of identifying aggressive behavior, complementing the histopathological evaluation of benign-appearing pituitary adenomas.

Current and Future Gene Therapy for Malignant Gliomas

Malignant gliomas are the most common neoplasm in the central nervous system. When treated with conventional treatments including surgery, irradiation, and chemotherapy, the average life expectancy of the most malignant type, glioblastoma multiforme is usually less than 1 year. Therefore, gene therapy is expected to be an effective and possibly curative treatment. Many gene therapeutic approaches have demonstrated efficacy in experimental animal models. However, the current clinical trials are disappointing. This review focuses on current therapeutic genes/vectors/delivery systems/targeting strategies in order to introduce updated trends and hopefully indicate prospective gene therapy for malignant gliomas.

Clinical implications of quantitative real-time RT-PCR analysis of hTERT gene expression in human gliomas

The presence of telomerase activity in a glioma may be a predictor of its malignant potential. Activation of telomerase is regulated at the transcriptional level of the human telomerase reverse transcriptase (hTERT). Here, we evaluated whether the amount of hTERT mRNA provides a molecular marker of glioma malignancy that would have clinical utility. We used a real-time RT-PCR to assess the number of hTERT transcripts in primary tumour samples derived from 70 glioma patients. Results were standardised by quantifying the number of ABL transcripts as internal control and expressed as hTERT/ABL ratio. The percentage of patients with detectable hTERT mRNA markedly increased with enhanced malignancy: low-grade gliomas expressed hTERT in one out of 14 cases (7.1%), anaplastic gliomas in four out of 13 cases (30.8%) and glioblastoma multiforme (GBM) tumours in 30 out of 43 cases (69.8%). The mean hTERT/ABL ratio was significantly higher in GBMs than in non-GBMs. Subdividing hTERT/ABL ratios as low (< pr = 25%) and high (>25%), we found that the overall survival among hTERT-positive GBMs was significantly worse in high hTERT expressors than in low hTERT expressors (P=0.0082). We conclude that the amount of hTERT mRNA may represent a diagnostic and prognostic indicator for GBM patients.

Prediction of clinical course of diffusely infiltrating astrocytomas from telomerase expression and quantitated activity level

Telomerase, one of the reverse transcriptases that extend telomere length, has been suggested to facilitate tumorigenesis and tumor immortality. Little is yet known, however, concerning the clinical significance of telomerase expression in brain tumors. We found in the present study that telomerase expression may contribute to malignant progression and can be an important indicator of high grade diffusely infiltrating astrocytomas, and its quantitated activity level reflects their growth potential. Telomerase expression and its quantitated activity level are also a good predictor of clinical course as compared with other biological markers and clinical factors.

Protective effect of HO-1 against oxidative stress in human hepatoma cell line (HepG2) is independent of telomerase enzyme activity

Heme oxygenase-1 (HO-1) is a stress response protein and its induction is associated with protection against oxidative stress. Cell survival during exposure to environmental stresses is associated with elevation of HO-1. Telomerase plays an important role in cell proliferation and immortalization. Our objective was to determine whether the adaptive cellular response to survive exposure to environmental stresses is dependent on expression of HO-1 and telomerase activity in hepatoma cell line (HepG2). Exposure of HepG2 to oxidants, H(2)O(2) (100 microM), as well as HO-1 inducers, heme (10 microM) and stannic chloride (SnCl(2)) (10 microM), resulted in an increased HO-1 mRNA, protein and total HO activity. On the other hand, HO activity was inhibited by addition of stannic mesoporphyrin (SnMP) (10 microM). These effects were brought about without altering endogenous HO-2 protein levels. Telomerase activity was not affected by oxidants, inducers of HO-1 or inhibitors of HO activity. Similarly, the catalytic subunit of telomerase enzyme human telomerase reverse transcriptase (hTERT), which is considered as the major regulator of telomerase activity, was not affected by oxidants, heme and H(2)O(2), or downregulation of HO gene activity by SnMP. This study demonstrates, for the first time, that induction of HO-1 gene mediates protection against oxidants and increases cell survival by a mechanism independent of telomerase enzyme activity. Suppression of HO activity by SnMP decreased cell resistance to oxidant stressors without altering telomerase activity.

Immunohistochemical detection of telomerase reverse transcriptase in colorectal adenocarcinoma and benign colonic mucosa

Telomerase activity (TA) is increased in human cancers and cell lines and is thought to contribute to their immortality. High TA has been found to correlate with aggressive tumor behavior. The aim of this study was to determine whether increased TA in colorectal carcinoma (CRC) correlates with survival. Formalin-fixed and paraffin-embedded tissue sections from 82 CRC and 6 cases of benign colon with diverticulosis were immunohistochemically stained for telomerase reverse transcriptase (TRT) using the immunoperoxidase method. The percentage of positive nuclei was determined for each case. Survival analysis was performed using the Kaplan-Meier method. TRT immunoreactivity was always nuclear. In normal colonic mucosa, TRT immunoreactivity was detected in the bottom of crypts. However, in normal colon adjacent to CRC, telomerase immunoreactivity was detected throughout the length of the crypts, including the upper third, and frequently in the surface epithelium. Telomerase immunoreactivity in more than 25% of the cancer cell nuclei was associated with significantly poorer patient survival (P = 0.0081). We conclude that increased TA in CRC, as demonstrated by TRT immunostaining, is associated with poorer survival, and that TA is present in normal colonic mucosa and is increased in colonic mucosa near CRC. Additional studies with larger patient samples and multivariate analysis are needed to determine whether TRT expression is an independent prognostic factor in CRC.

Caspase-8 gene therapy using the human telomerase reverse transcriptase promoter for malignant glioma cells

Telomerase is a distinctive candidate for targeted gene therapy of malignant gliomas, because the vast majority of malignant gliomas express telomerase activity while normal brain tissues do not. Recently, we developed a telomerase-specific expression system of caspase-8 gene using the promoter of the human telomerase reverse transcriptase (hTERT) gene. However, the transcriptional activity of hTERT-181 promoter (a 181-base pair [bp] region upstream of the transcription start site) was relatively lower in malignant glioma cells than in other tumors such as prostate cancer cells. To establish the hTERT/caspase-8 construct as a novel therapy for malignant gliomas, we need to increase the transcriptional activity of the hTERT promoter in malignant glioma cells. In the present study, we demonstrate that the transcriptional activity of hTERT-378 promoter (a 378-bp region) was 2- to 40-fold higher in hTERT-positive malignant glioma cells (A172, GB-1, T98G, U87-MG, U251-MG, and U373-MG) than that of hTERT-181. We further demonstrate that by using the hTERT-378/caspase-8 construct, apoptosis was restricted to malignant glioma cells, and was not seen in astrocytes or fibroblasts lacking hTERT. Moreover, the growth of subcutaneously established U373-MG tumors in mice was significantly inhibited by seven daily intratumoral injections of hTERT-378/caspase-8 construct and its inhibitory effect persisted during 3 additional weeks without additional treatment. These results suggest that the telomerase-specific expression of caspase-8 under hTERT-378 promoter is a novel targeting approach for the treatment of telomerase-positive malignant gliomas.

Telomerase as a diagnostic and therapeutic target for cancer

Telomerase is a ribonucleoprotein enzyme responsible for the elongation of telomeres at the ends of chromosomes. It is widely expressed in most cancers, while absent from most normal somatic cells. Telomerase is partially responsible for the cellular immortalization that allows human cancers to progress indefinitely. Due to its widespread occurrence in cancer and its crucial role in the maintenance of the tumor, telomerase is an attractive target for cancer diagnosis and treatment.

Expression of telomerase reverse transcriptase (TERT) in malignant mesotheliomas

To evaluate the usefulness of determinations of telomerase activity for distinguishing malignant from benign mesothelial lesions, immunohistochemical (using a rabbit polyclonal antibody and the peroxidase method; n = 68) and in situ hybridization (using sense and antisense oligonucleotide probes; n = 46) studies were made on malignant mesotheliomas (epithelioid, 39; sarcomatoid, 18, including 2 of the desmoplastic type; and biphasic, 11) and 19 benign mesothelial lesions (benign mesothelial hyperplasia, 3; and reactive pleuritis, 16). In addition, biochemical studies of telomerase activity were made in 9 of the malignant mesotheliomas. Telomerase activity was detected histochemically in all but one of the malignant mesotheliomas, but only in one (pleuritis) of the benign lesions, in which it was present only in activated lymphocytes. Antisense hybridization signals indicated the presence of telomerase mRNA mainly in the cytoplasm of the malignant cells. Sense probes gave negative results. Biochemical determinations revealed a strong telomerase activity in the 9 malignant mesotheliomas examined. This study demonstrates the usefulness of immunohistochemical staining for the evaluation of mesotheliomas. The required immunostaining can be performed using paraffin sections of formalin-fixed tissues.

Telomere and telomerase in oncology

Shortening of the telomeric DNA at the chromosome ends is presumed to limit the lifespan of human cells and elicit a signal for the onset of cellular senescence. To continually proliferate across the senescent checkpoint, cells must restore and preserve telomere length. This can be achieved by telomerase, which has the reverse transcriptase activity. Telomerase activity is negative in human normal somatic cells but can be detected in most tumor cells. The enzyme is proposed to be an essential factor in cell immortalization and cancer progression. In this review we discuss the structure and function of telomere and telomerase and their roles in cell immortalization and oncogenesis. Simultaneously the experimental studies of telomerase assays for cancer detection and diagnosis are reviewed. Finally, we discuss the potential use of inhibitors of telomerase in anti-cancer therapy.

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.

A review of the cytogenetics of 58 pediatric brain tumors

We describe the cytogenetic results of 58 pediatric central nervous system (CNS) tumors of variable histology, investigated between 1992 and 2000. Successful cytogenetics were obtained for 53 patients, with clonal chromosome abnormalities demonstrated in 25. Notable findings included (1) 2p abnormality in four primitive neuroectodermal tumors (PNET); (2) 1p loss in four low-grade gliomas and two PNET; (3) telomeric associations in one pilocytic astrocytoma; (4) chromosome 7 gain in four astrocytomas and two PNET; (5) 17p loss in four PNET; (6) double minutes in one PNET and three glioblastomas; and (7) chromosome 10 loss in four PNET. Higher grade tumors demonstrated greater karyotype complexity. Low-grade tumors showed either minimal simple chromosome changes or a normal karyotype. Chromosome abnormalities were more frequent in supratentorial tumors than their infratentorial counterparts. Our results add weight to the limited existing body of cytogenetic documentation for pediatric CNS tumors and provide further evidence that 2p loss is a consistent region of chromosome involvement in PNET. We advocate further studies of CNS tumors, in particular, to evaluate the importance of 2p changes and to compare cytogenetic results for supratentorial tumors and their infratentorial counterparts.

Musashi1, an evolutionarily conserved neural RNA-binding protein, is a versatile marker of human glioma cells in determining their cellular origin, malignancy, and proliferative activity

Tumor cells often express phenotypic markers that are specific to the cells from which they originated. A neural RNA-binding protein, Musashil, is an evolutionarily well-conserved marker for neural stem cells/ progenitor cells. To examine the origin of gliomas, we examined the expression of the human Musashil homolog, MSI1, in human glioma tissues and in normal human adult and fetal brains. As we had seen previously in rodents, in the normal human brain, MSI1 was expressed in cells located in the ventricular and subventricular zones, in GFAP-negative glial cells, and in GFAP-positive astrocytes. In glioblastomas, MSI1 was expressed in GFAP-negative tumor cells forming foci that were clearly demarcated and surrounded by GFAP-positive cells. Tumor cells arranged in pseudopalisades were also strongly immunoreactive with MSI1 antibodies. The percentage of MSI1-labeled tumor cells increased in higher-grade astrocytomas and correlated with proliferative activity, as estimated by an MIB-1 staining index. Our results indicate that MSI1 is an excellent marker for neural progenitor cells including neural stem cells in normal human brains. Furthermore, the expression of MSI1 correlates well with the immature nature as well as the malignancy of tumor cells in human gliomas. Thus, we expect the analysis of MSI1 expression to contribute to the understanding of the cellular origin and biology of human gliomas.

Down-regulation of telomerase activity in malignant lymphomas by radiation and chemotherapeutic agents

The effects of radiation and cytotoxic agents on telomerase activity in lymphoma cells were analyzed by a polymerase chain reaction-based telomeric repeat amplification protocol coupled with an enzyme-linked immunosorbent assay, reverse transcriptase-polymerase chain reaction for the expression of the catalytic subunit of telomerase (hTERT), and by Western blot analysis in three lymphoma cell lines (Jurkat, Raji, CEM-6). Telomeric repeat amplification protocol-enzyme-linked immunosorbent assay demonstrated high basal levels of telomerase activity in all cell lines compared to normal and activated peripheral blood lymphocytes. A significant decrease in telomerase activity was observed in all cell lines after exposure to vincristine for 24 hours. The decrease in telomerase activity paralleled the decrease in cell viability in Jurkat and CEM-6 cells but not in Raji cells. Radiation exposure inhibited the telomerase activity of Jurkat and CEM-6 cells whereas Raji cells were unaffected. Cell cycle analysis demonstrated a significant G(2)/M arrest by cisplatin, VP-16, and vincristine. In contrast to the decline in telomerase activity, the level of hTERT RNA and protein increased. Furthermore, the induction of hTERT was preceded by increased expression of the cyclin-dependent kinase inhibitor, p27/Kip1 protein, and p53. These results indicate that telomerase activity is down-regulated by anti-neoplastic agents in lymphoma cells, however expression of hTERT may not be correlated with telomerase activity. We also show that p27/Kip1 may be involved in the G(2)/M growth arrest induced by anti-neoplastic agents.

Evidence for telomerase involvement in the angiogenesis of astrocytic tumors: expression of human telomerase reverse transcriptase messenger RNA by vascular endothelial cells

OBJECT

Evidence from recent in vitro studies indicates that reactivation of telomerase, the enzyme that synthesizes the telomere ends of chromosomes, is a crucial event in the unlimited clonal expansion of endothelial cells that precedes the neoplastic conversion of these cells. It is known that high-grade gliomas express telomerase and that, in these neoplasms, proliferating endothelial cells may undergo transformational changes with development of sarcomatous components within the primitive tumor. To assess whether telomerase is involved in the endothelial cell proliferation that characterizes brain tumor angiogenesis, the authors investigated at the single-cell level the expression of messenger (m)RNA for the human telomerase catalytic subunit human telomerase reverse transcriptase (hTERT) by vascular cells of astrocytic tumors.

METHODS

The in situ hybridization (ISH) method was performed by processing histological sections with specific riboprobes for hTERT and for c-myc, an oncogene that is known to upregulate hTERT. Results of the ISH studies were compared with proliferative activity, as estimated by Ki-67 immunostaining. The expression of hTERT mRNA by vascular endothelial cells was related to the histological grade of the tumor because it was detected in five (29%) of 17 low-grade astrocytomas, nine (56%) of 16 anaplastic astrocytomas, and 19 (100%) of 19 glioblastomas multiforme (GBMs). Expression of c-myc mRNA was strictly correlated with that of hTERT mRNA. In low-grade astrocytomas and anaplastic astrocytomas, a dissociation was noted between hTERT mRNA expression and the proliferation rate of endothelial cells. Conversely, GBMs displayed a significant correlation between the level of hTERT mRNA expression and endothelial cell proliferation. Data from an in vitro assay in which human umbilical vein endothelial cells were stimulated to proliferate by adding vascular endothelial growth factor and an ISH study of newly formed vessels surrounding brain infarcts confirmed that expression of hTERT mRNA does not merely reflect the proliferative status of endothelial cells but represents a specific feature of brain tumor neovascularization.

CONCLUSIONS

The results of this study are consistent with a role of telomerase in the angiogenesis of astrocytic tumors. Expression of hTERT mRNA by tumor vascular cells is an early event during the progression of astrocytic tumors, which precedes endothelial cell proliferation and may represent a first sign of dedifferentiation. Other than elucidating the mechanisms of tumor angiogenesis, these results encourage research on antitelomerase drugs for the treatment of malignant gliomas.

Telomerase, immortality and cancer

Replication of eukaryotic linear chromosomes is incomplete and leaves terminal gaps. The evolutionary widely distributed solution to this "end replication" is twofold: chromosome ends are capped with telomeres, bearing multiple copies of redundant telomeric sequences, and the telomerase enzyme can add (lost) telomeric repeats. Telomerase in humans, as in all mammals, is ubiquitous in all embryonic tissues. In adults, telomerase remains active in germs cells, and, although down-regulated in most somatic tissues, telomerase is active in regenerative tissues and notably, in tumor cells. Telomerase activity is linked to cellular proliferation, and its activation seems to be a mandatory step in carcinogenesis. In contrast to mammals, indeterminately growing multicellular organisms, like fish and crustaceae, maintain unlimited growth potential or 'immortality' in all somatic tissues throughout their entire life. Also this cell immortalization is brought about by maintaining telomerase expression. Disease prognosis for human tumors includes evaluation of cell proliferation, based on the detection of proliferation markers with monoclonal antibodies. The significance of the classical marker Ki-67, and of a novel marker repp-86 are compared with semiquantitative telomerase assays. For tumor therapy, telomerase inhibitors are attractive tools. Results with telomerase knock-out mice have revealed promise, but also risk of this approach. On the other side, telomerase stimulation is attractive for expanding the potential of cellular proliferation in vitro, with possible applications for transplantation of in vitro expanded human cells, for immortalizing primary human cells as improved tissue models, and for the isolation of otherwise intractable products, like genuine human monoclonal antibodies.

Telomere length and telomerase catalytic subunit expression in non-astrocytic gliomas

Telomerase activation has been implicated as a major factor in the development of cancer. In our previous study we reported on the telomerase activity of a variety of gliomas. To further investigate the role of telomere and telomerase regulation in the pathogenesis of non-astrocytic gliomas, we examined the telomere length and the mRNA expression of telomerase reverse transcriptase gene (hTERT) and telomerase-associated protein (hTEP) in a series of 27 oligodendroglial and 18 ependymal tumors in this study. No statistical difference was found between the mean telomere length in telomerase-positive and telomerase-negative tumors (11.5 kb vs 13.1 kb; p = 0.424), although a slightly shorter length was observed in telomerase-positive oligodendroglial tumors. mRNA expression of hTERT was highly correlated with the telomerase activity status. hTERT was expressed in 8/8 (100%) and 2/2 (100%) telomerase-positive oligodendroglial and ependymal tumors, respectively, whereas 3/6 (50%) telomerase-negative oligodendroglial tumors and no telomerase-negative ependymal tumors showed expression. In contrast, hTEP1 mRNA was widely expressed in both telomerase-positive and telomerase-negative oligodendroglial and ependymal tumors. Our data support the notion that hTERT plays a critical role in determining the enzymatic activity of human telomerase. It has recently been proposed that both p16(INK4)/Rb pathway inactivation and telomerase activity were required for immortalization of epithelial cells. Although lack of p(16INK4a) expression was detected in a substantial proportion of tumors, no correlation between the p16(INK4a) or pRb protein expression and telomerase activity was observed in our series of non-astrocytic tumors.

Chondrosarcoma is not characterized by detectable telomerase activity

Reactivation of telomerase, an enzyme which elongates human telomeres, is associated with cell immortilization. In approximately 90% of malignant tumours telomerase activity can be demonstrated, whereas in benign tumours it is mostly absent. Chondrosarcomas are relatively rare malignant cartilaginous neoplasms. A small number of chondrosarcomas located centrally in bone arise secondarily to an enchondroma, while the majority of chondrosarcomas developing from the surface arise within the cartilage cap of an osteochondroma. The histological distinction between a benign lesion and low-grade chondrosarcoma is generally considered difficult. To investigate whether the progression towards chondrosarcoma is characterized by reactivation of telomerase activity, this study determined telomerase activity in ten enchondromas, five osteochondromas, and 37 chondrosarcomas using the TRAP assay. In all tumour samples except one, telomerase activity was absent. By adding tumour lysates to the positive control, an increasing inhibition of telomerase activity was found with an increasing chondroid matrix, suggesting that it may contain inhibitory factors. Inhibition due to endogenous RNAse or Taq-polymerase inhibitors was excluded. The lack of detectable telomerase activity in the high-grade component of a dedifferentiated chondrosarcoma without matrix favours the possibility that telomerase is truly absent. Either its true absence or inhibitory effects disabling telomerase detection exclude the telomerase TRAP assay as a diagnostic tool in the differential diagnosis of benign and low-grade malignant cartilaginous tumours.

In situ detection of telomerase catalytic subunit mRNA in glioblastoma multiforme

Activation of telomerase may allow unlimited cell proliferation and immortalization. One of the telomerase protein subunits has a reverse transcriptase (hTERT) activity that is essential for telomerase function and regulation. In human gliomas, telomerase is frequently associated with malignant tumor progression. In our study, we investigated the expression of hTERT at the cellular level in 34 primary de novo glioblastoma multiforme (GBM) by in situ hybridization (ISH). The expression of hTERT in tumor tissue was also assessed by RT-PCR. In addition, telomerase activity measured by telomeric repeat amplification protocol (TRAP) and telomere length polymorphism assayed by telomere restriction fragment (TRF) Southern blot were investigated. We found that all GBM, including those with negative TRAP reaction, contained abundant amounts of cytoplasmic hTERT mRNA. Interestingly, the ISH analysis revealed that the hTERT mRNA was homogeneously expressed by the whole tumor cell population in about 60% of the GBM. In the remaining cases, hTERT was absent in subsets of tumor cells. TRF analysis, which shows that both TRAP-positive and TRAP-negative de novo GBM have elongated telomeres, further supports that telomerase activity is present in all de novo GBM. Correlations with tumor size and extent of necrosis suggest that hTERT reactivation is an early event in GBM development and that telomerase activity may be lost in subpopulations of neoplastic cells during tumor progression. Finally, ISH analysis of hTERT mRNA seems to provide a prognostic parameter for primary de novo GBM.

Combination therapy of malignant glioma cells with 2-5A-antisense telomerase RNA and recombinant adenovirus p53

Malignant gliomas of astrocytic origin have commonly expressed several features such as alterations in the tumor-suppressor gene p53 or p16 or the acquisition of telomerase activity, which are distinctive from astrocytes. Therefore, restoration of the tumor-suppressor gene or telomerase inhibition is expected to provide a cure for malignant gliomas. We have recently demonstrated that the treatment with a 19-mer antisense oligonucleotide against human telomerase RNA linked to a 2',5'-oligoadenylate (2-5A-anti-hTR) inhibited the growth of malignant glioma cells. From a therapeutic point of view, it is very important to investigate the antitumor efficacy of 2-5A-anti-hTR combined with the restoration of p53 or p16 gene. In this study, we evaluated the antitumor effect of 2-5A-anti-hTR in combination with recombinant adenoviruses bearing p53, its associated p21WAF1/CIP1, or p16CDKN2 gene (Ad5CMV-p53, Ad5CMV-p21, or Ad5CMV-p16) against malignant glioma cells in vitro and in vivo. Five malignant glioma cell lines expressing the mutant p53 gene (A172, GB-1, T98G, U251-MG and U373-MG) were more sensitive to the combination of 2-5A-anti-hTR and Ad5CMV-p53 than to other combinations. The additive effect of the combination therapy was due to induction of caspase-dependent apoptosis and cell growth arrest. Furthermore, the 2-5A-anti-hTR treatment when combined with Ad5CMV-p53 showed greater efficacy against subcutaneous U251-MG tumors in nude mice. In contrast, U87-MG cells expressing the wild-type p53 gene were insensitive to Ad5CMV-p53, although the treatment with 2-5A-anti-hTR was significantly effective. These results indicate that combining 2-5A-anti-hTR with Ad5CMV-p53 has the most therapeutic potential for malignant gliomas with mutant p53. For tumors exhibiting wild-type p53, it may be useful to treat with 2-5A-anti-hTR. Gene Therapy (2000) 7, 2071-2079.

Implication of telomerase activity and alternations of telomere length in the histologic characteristics of intracranial meningiomas

BACKGROUND

Telomerase activity and telomere length have been shown to be involved in the control of cell proliferation and regulation of cell senescence. The expression of telomerase activity may endow cells with the capacity of unlimited proliferation and immortality. The authors examined the telomerase activity and telomere length of intracranial meningiomas to determine the relation between the results and the clinicopathologic behavior of these tumors.

METHODS

Sixty-two specimens of meningiomas including 13 atypical and malignant tumors were used in this study. Telomerase activity was measured with polymerase chain reaction and enzyme-linked immunosolvent assay. Telomere length was measured by detecting the terminal restriction fragments using Southern blots.

RESULTS

Detectable telomerase activity was found in 4 of 13 (30.8%) malignant or atypical meningiomas and only 1 in 49 benign meningiomas (P = 0.006). Elongated telomere length was measured in 6 of 13 (46.1%) patients with malignant or atypical meningiomas and only 1 of 48 (2.1%) in those with benign tumors (P = 0.0002). Three of 4 (75%) of malignant or atypical meningiomas with detectable telomerase activity revealed shortened telomere length, and all tumors with elongated telomere length displayed undetectable telomerase activity. The percentage of malignant or atypical meningiomas with detectable telomerase activity or elongated telomere were significantly higher (76.9%) than that of benign tumors (4.0%). The proliferative index was calculated as the percentage of tumor cell nuclei immunoreactive for Ki-67 to total tumor nuclei. The mean values of proliferative index in benign, atypical, and malignant meningiomas were 1.2, 11.0, and 30.0, respectively.

CONCLUSIONS

The results indicate that telomerase activation may be a critical step in the pathogenesis of malignant or atypical meningioma. Elongation of the telomere length also implicates the high potential for malignant behavior in these tumors.

On the significance of telomerase activity in human malignant glioma cells

Telomerase is critical for tumor cell immortalization and is a novel target for cancer chemotherapy. Here, we examined whether telomerase is expressed in glioma cell lines, whether telomerase activity is regulated by bcl-2 or p53, and whether telomerase activity predicts response to chemotherapy. Further, we characterized the effects of a candidate telomerase inhibitor, penclomedine, in glioma cells. All 12 human malignant glioma cell lines examined were telomerase positive. Telomerase activity was not modulated during cell cycle progression, did not correlate with p53 status or bcl-2 family protein expression, and did not predict drug sensitivity, except for an association with resistance to carmustine. Ectopic bcl-2 expression did not enhance telomerase activity. Wild-type p53 reduced telomerase activity in cell lines retaining p53 activity but not in p53-mutant cell lines. Penclomedine killed glioma cells via an apoptotic, but death receptor-, bcl-2- and caspase-independent pathway, but did not inhibit telomerase and did not act synergistically with cytotoxic drugs. We conclude that telomerase activity does not account for the differential chemosensitivity of human glioma cells and that penclomedine kills glioma cells via a telomerase-independent pathway.

Telomerase activity in primary and secondary glioblastomas multiforme as a novel molecular tumor marker

OBJECT

Telomerase activity is responsible for cell immortality. To examine the role of telomerase in the carcinogenesis of human glioblastomas multiforme (GBMs), the authors studied telomerase activity, telomerase component expression, and telomere lengths in 42 GBM samples.

METHODS

In all samples, EGFR and MDM2 amplifications and overexpressions were examined using Southern and Northern blot analyses. The p53 mutation was analyzed using polymerase chain reaction-single strand conformational polymorphism and by direct sequence analysis. Specimens of tissues were immunostained with p53, EGFR, and MDM2 antibodies. Allelic loss on chromosomes 17p and 10 was assessed by loss of heterozygosity (LOH) assays. Telomerase activity, expression of its components (human telomerase reverse transcriptase [hTERT], human telomerase RNA component [hTERC], and telomerase-associated protein [TEP1]), and telomere lengths were analyzed using the telomeric repeat amplification protocol (TRAP)-hybridization protection assay, reverse transcription-polymerase chain reaction, and Southern blot analysis. According to the results of assessments of EGFR and MDM2 amplifications, p53 mutation, LOHs in chromosomes 17p and 10, and the clinical course of the disease, the 42 samples were classified into 22 primary and 20 secondary glioblastomas. Twenty-six (61.9%) of all 42 samples demonstrated detectable telomerase activity during the TRAP assay. Secondary GBMs displayed significantly higher levels of telomerase activity and hTERT expression than primary GBMs. Tumors with a p53 gene mutation demonstrated significantly higher telomerase activity than those without a p53 mutation. Four samples with a codon 175 mutation demonstrated an exceptionally high amount of telomerase activity. In secondary GBMs, the increase in telomerase activity and the hTERT expression level correlated with the increased frequency of p53 mutations. There was no significant difference in telomere length between primary and secondary GBMs.

CONCLUSIONS

These results suggest that telomerase activity and p53 mutations both play important roles in the multistep carcinogenesis of GBMs. Telomerase activity and hTERT expression may be considered as novel distinctive factors in human GBMs.

Detection of telomerase activity in peritoneal lavage fluid from patients with gastric cancer using immunomagnetic beads

Cytologic examination of peritoneal lavage fluid is a useful predictor of peritoneal recurrence in gastric cancer. However, this technique is not overly sensitive and requires special abilities in the cytologist. In this study, telomerase activity was used to detect free cancer cells in peritoneal lavage fluid from patients with gastric cancer. In the first part, 12 lavage-fluid samples obtained from 12 patients with gastric cancer were analysed using the conventional telomeric repeat amplification protocol (TRAP) assay. Three of five patients with early gastric cancer had positive telomerase activity. These false-positive results may have been due to lymphocyte contamination. Furthermore, polymerase chain reaction inhibitors were also detected in the lavage-fluid samples. Therefore, we developed a novel method for elimination of haematopoietic cell and Taq polymerase inhibitors to increase the accuracy of the TRAP assay using immunomagnetic beads, which bind to most normal and neoplastic human epithelial cells. Telomerase activity was found in 10 of 20 (50%) lavage-fluid samples from patients with serosal or subserosal invasion. Cytologic examination was positive in nine of 20 (45%) samples. Both the telomerase activity and cytology were negative in all 14 patients without serosal or subserosal invasion. These results suggest that the TRAP assay combined with immunomagnetic beads might be useful for detection of free cancer cells in the peritoneal space in gastric cancer without the aid of an experienced cytologist.

The clinical implications of telomerase activity in upper tract urothelial cancer and washings

OBJECTIVE

To measure telomerase activity in upper tract urothelial carcinomas (as renal pelvic tumours comprise nearly half of all kidney tumours in Taiwan, a much higher percentage than in other countries) and to determine whether telomerase activity could be used as an additional diagnostic marker in exfoliated cancer cells present in upper tract urothelial washing fluids, thus providing earlier diagnosis and treatment. Materials and methods Telomerase activity was assessed using the telomeric repeat amplification protocol assay in tissue samples from 31 upper tract urothelial carcinomas (from 29 patients). The feasibility of identifying cancer using telomerase activity in exfoliated cancer cells in 17 upper tract urothelial washing samples was also investigated.

RESULTS

Telomerase activity was found in 30 (97%) of the 31 upper tract urothelial cancer tissue samples; telomerase activity was detectable in 95% of superficial cancers and in all 11 invasive tumours. The sensitivity of measuring telomerase activity was 100% for grade 1, 93% for grade 2 and 100% for grade 3 tumours. In contrast, telomerase activity was detected in only two (8%) of 26 normal adjacent tissue samples. When the telomerase activity of urothelial washing fluid was compared with that in the corresponding tumours, there was compatible telomerase activity in 15 of the 17 samples. Telomerase activity was more sensitive than voided urine cytology (15%) and washing fluid cytology (53%). In addition, the telomerase activity was high in metastatic lesions.

CONCLUSION

Telomerase activity is present in most upper tract urothelial cancer tissues and may be present at an early stage of carcinogenesis. Telomerase activity can be detected in exfoliated cells in urothelial washing fluids in a high proportion of patients with upper tract urothelial cancer. These results suggest that measuring telomerase activity in the exfoliated cancer cells obtained from urothelial washing could be a potentially useful addition to the conventional diagnostic tools used to identify patients with upper tract urothelial carcinoma.

Prognostic value of proliferation index and expression of the RNA component of human telomerase (hTR) in papillary meningiomas

Papillary meningioma is a rare subtype of meningioma that often behaves aggressively. In order to characterize factors that may influence this behavior, we chose to compare MIB-1 labeling index (LI) and telomerase RNA localization (hTR) in papillary meningiomas, meningiomas, and atypical meningiomas. LI is now often used to supplement histologic grade in the evaluation of these lesions. More recent studies indicate that increased expression of hTR is detected in many neoplastic cells, and may play an essential role in cell immortalization. The study group consisted of five papillary meningiomas (and a recurrence in one case), 11 conventional meningiomas, and eight atypical meningiomas. Conventional meningiomas showed either negative or 1 + hTR. Atypical meningiomas showed 1 + hTR. Papillary meningiomas showed the highest hTR (five of six, including recurrence, 2-3+ and one 1+). Generally, the LI was very low for conventional meningiomas (< 2%). The LI of atypical meningiomas ranged from 3-19%, mean 12%, and from 5.5-17.5%, mean 11.75% for papillary meningiomas. LI differentiated between meningiomas, and papillary or atypical meningiomas. hTR further delineated papillary (moderate to high) from atypical meningiomas (low). The combined variable of LI and hTR expression could be a useful independent prognostic indicator in patients with papillary meningioma.

Telomerase activity significantly correlates with chromosome alterations, cell differentiation, and proliferation in lung adenocarcinomas

Telomerase activity was examined by the telomeric repeat amplification protocol assay in 25 cases of lung adenocarcinoma, in relation to cancer cell differentiation, proliferation, and chromosome alterations. Telomerase activity, chromosome alterations, and cell proliferation assessed by Ki-67 labeling were significantly lower (P < .001 to .05) in well-differentiated (10 cases) than in moderately differentiated (8 cases) or poorly differentiated (7 cases) lesions. Telomerase activity by semiquantitative analysis with scoring of 0 to 3 was significantly correlated with similarly graded chromosome alterations (P < .05) and Ki-67 labeling indices (P < .002). Telomerase activity and chromosome alteration (T-C) indices generated by multiplication of telomerase activity and chromosome alteration scores also showed a significant correlation with cell differentiation. The Clara cell subtype, confirmed by electron microscopic analysis, significantly predominated in the well-differentiated group, showing a low grade of telomerase activity and chromosome alterations and low Ki-67 labeling indices, suggesting clinical relevance. No significant association of telomerase activity was found with p53 protein accumulation or Bcl-2 protein expression. The good correlation of telomerase activity with chromosome alterations, cell differentiation, and Ki-67 labeling indices suggests that this parameter might have potential application in estimation of prognosis.

Telomerase activity and apoptosis as indicators of ageing in placenta with and without intrauterine growth retardation

Telomerase activity (TA) and apoptosis were analysed in placenta with and without intrauterine growth retardation (IUGR). Thirty-one specimens were taken from chorionic villi in the first trimester (Group A), 32 placenta specimens were obtained from cases without IUGR in second and third trimester (Group B) and 12 specimens of placenta tissue were obtained from cases of asymmetric IUGR between 26 and 39 weeks of gestation (Group C). TA was analysed by the Telomeric Repeat Amplification Protocol (TRAP) and in situ TRAP assay. Apoptotic changes were assessed by immunohistochemical staining using Bcl-2 monoclonal antibody and by terminal transferase-mediated in situ end-labelling (TUNEL). TA was detected in 29 of the 31 (93.5 per cent) chorionic villi (Group A) and in 20 of the 32 (62.5 per cent) placenta without IUGR (Group B), whereas weak TA was observed in the placenta of all 12 asymmetric IUGR cases (Group C). Significantly higher Bcl-2 immunoreactivity was observed in trophoblastic cells of Group A (85.9+/-4.2 per cent) and Group B (72.8+/-7.2 per cent) than Group C (54.84+/-4.83 per cent), while TUNEL positive cells were identified at a significantly higher frequency in the trophoblastic cells of Group C (9.7+/-7.4 per cent) than Group A (1.1+/-1.9 per cent) or Group B (2.9+/-3.7 per cent).

Role of telomerase in cell senescence and oncogenesis

The ends of linear chromosomes are capped by specialized nucleoprotein structures termed telomeres. Telomeres comprise tracts of noncoding hexanucleotide repeat sequences that, in combination with specific proteins, protect against degradation, rearrangement, and chromosomal fusion events. Due to the polarity of conventional DNA synthesis, a net loss of telomeric sequences occurs at each cell division. It has been proposed that this cumulative telomeric erosion is a limiting factor in replicative capacity and elicits a signal for the onset of cellular senescence. To proliferate beyond the senescent checkpoint, cells must restore telomere length. This can be achieved by telomerase, an enzyme with reverse-transcriptase activity. This enzyme is absent in differentiated somatic tissues, but telomerase reactivation has been detected in most tumors. Much investigative effort is focusing on telomere dynamics with a view to possible manipulation of cellular proliferative potential. In this article, we review the role of telomeres and telomerase in senescence and tumor progression, and we discuss the potential use of telomerase in diagnosis and treatment.

Telomerase activity in colorectal cancer and its relationship to bcl-2 expression

BACKGROUND AND OBJECTIVES

Telomerase is thought to be responsible for cell immortality, and bcl-2 has been demonstrated to regulate apoptosis. Recent studies have shown a wide occurrence of telomerase activation and bcl-2 deregulation in human carcinoma cells.

METHODS

We examined telomerase activity in tissues from 50 patients with colorectal carcinoma with a telomeric repeat amplification protocol assay. We also investigated the relationship between telomerase activity and expression of bcl-2 in 37 colorectal carcinoma specimens.

RESULTS

We detected telomerase activity in 33 (66%) of 50 colorectal carcinomas, whereas no activity was detected in the adjacent noncancerous mucosa of 13 tumor specimens. There was no correlation between pathological stage and telomerase activity. Telomerase activity in the bcl-2-expressing cases was higher than that in the bcl-2-non-expressing cases.

CONCLUSIONS

Expression of bcl-2 may be related to telomerase activity in colorectal carcinomas.

Telomerase activity as an indicator of malignant potential in iodine-nonreactive lesions of the esophagus

BACKGROUND

Iodine-nonreactive lesions of esophageal epithelium often are associated with dysplasia and carcinoma. The authors examined the usefulness of telomerase activity as an indicator for esophageal carcinogenesis in such lesions.

METHODS

Telomerase activity was measured using the telomeric repeat amplification protocol assay in 18 samples of iodine-nonreactive lesions apart from the primary tumor in surgically resected specimens obtained from patients with esophageal squamous cell carcinoma (ESCC) and 55 endoscopic punch biopsies of iodine-nonreactive lesions obtained from 25 patients with ESCC and 30 patients who had undergone endoscopic examination for other reasons.

RESULTS

Ten of 18 iodine-nonreactive samples (56%) obtained from surgically resected specimens showed telomerase activity. In all ten telomerase positive samples, carcinoma in situ (CIS) was observed in iodine-nonreactive mucosa by light microscopy. In eight telomerase negative samples, no tumor tissue was observed in iodine-nonreactive lesions. In a parallel study, telomerase activity was detected in 28 of 55 endoscopic punch biopsy specimens (51%). CIS was observed in 25 of 28 iodine-nonreactive lesions with positive telomerase activity (89%), and tumor tissue was not observed in the other 3 samples (11%), which included 2 cases of severe dysplasia and 1 case of moderate dysplasia. No tumor tissue was observed in any of the 27 telomerase negative samples.

CONCLUSIONS

Positive and negative telomerase activity was found to be correlated with the presence and absence, respectively, of immortalized tumor cells in iodine-nonreactive lesions. The measurement of telomerase activity in iodine-nonreactive lesions independently contributes to the selection of an appropriate therapeutic strategy.

Telomerase activity and the expression of telomerase components in pituitary adenoma with malignant transformation

BACKGROUND

Telomerase activity responsible for cellular immortality may participate the development of human cancers. Telomerase is a multisubunit ribonucleoprotein composed of at least three components: hTERT, hTERC, and TEP1. This is the first report showing telomerase activity and telomerase component expression in pituitary adenoma with histological malignant transformation.

DESCRIPTION

A 16-year-old male with a prolactin-producing pituitary adenoma with metastasis is presented. The patient underwent three partial resections of an intra- and suprasellar lesion over a 2-year period and received focal irradiation. Eight years after the first admission, a metastatic lesion to the subarachnoid space around the medulla oblongata was detected and the lesion was resected as the fourth operation. Furthermore, the suprasellar lesion showed regrowth and partial resection was performed as the fifth operation. The last two specimens were diagnosed as pituitary carcinoma. Radiotherapy with gamma knife was performed for the residual suprasellar lesion and a new lesion in the left temporal lobe after the fifth operation. Telomerase activity was examined by TRAP/TRAP-HPA methods, qualitatively and quantitatively. Telomere length was examined by Southern blot analysis, and the expression of telomerase components (hTERT, hTERC, and TEP1) was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). The MIB1 index, telomerase activity, and hTERT expression increased according to histologic malignancy chronologically in this patient. None of the specimens showed immunoreactivity for p53, EGFR, or bc12. No telomerase activity was detected in pituitary adenomas without malignant transformation, other benign brain tumors, or normal brain tissues.

CONCLUSION

We report a patient with pituitary adenoma transforming to carcinoma. The tumor cells acquired immortality and revealed malignant transformation during the course of the disease, that was proved by an increase of telomerase activity and hTERT expression.

Expression of telomerase activity and telomerase RNA in human soft tissue sarcomas

OBJECTIVE

To investigate whether telomerase is reactivated in soft tissue tumor and whether telomerase activity is regulated at the transcriptional level.

DESIGN

Fresh tissue samples of 24 soft tissue sarcomas were analyzed for telomerase activity by a radioactive polymerase chain reaction-based telomeric repeat amplification protocol assay and for human telomerase RNA (hTR) by an in situ hybridization assay.

SETTING

Tertiary care teaching hospital.

PATIENTS

Twenty-four patients with soft tissue tumor were surgically treated. Twelve patients had malignant fibrous histiocytoma, 5 had liposarcoma, 6 had leiomyosarcoma, and 1 had rhabdomyosarcoma.

RESULTS

Telomerase activity was detected in 4 sarcoma samples (17%), all of which were positive for hTR. Expression of hTR was demonstrated in 13 sarcomas (54%), 4 of which were positive for telomerase and 9 of which were negative for telomerase. One (50%) of 2 grade 1 tumors, 9 (50%) of 18 grade 2 tumors, and 3 (75%) of 4 grade 3 tumors showed hTR expression.

CONCLUSIONS

The relatively low frequency of telomerase activity in soft tissue sarcomas suggests that telomerase may not play an important role in tumorigenesis in these tumors. Telomerase ladders were demonstrated only in association with tumors expressing hTR. It is noteworthy that half of the patients with grade 1 and 2 tumors expressed hTR, suggesting that telomerase RNA may be useful as a marker for identifying tumor aggressiveness earlier than the conventional histopathologic grading scale.

Telomerase expression in uveal melanoma

BACKGROUND/AIMS

Accumulating evidence indicates that telomerase activity is repressed in normal human somatic cells but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity has a role in carcinogenesis and immortalisation. To date, telomerase in uveal melanoma and, whether, it may have a role in the development or progression of these tumours has not been described. The expression patterns and the activity of telomerase were investigated in 14 uveal melanoma and these results were correlated with histological and immunohistological features of these tumours.

METHODS

A modified PCR based telomeric repeat amplification protocol (TRAP) assay was used to demonstrate telomerase activity in 14 uveal melanomas. In addition, in situ hybridisation was used to demonstrate the expression pattern of the telomerase RNA component (hTR) at the single cell level in eight of these globes.

RESULTS

The TRAP assay revealed moderate telomerase activity in all uveal melanomas examined. In situ hybridisation visualised a moderate to high upregulation of hTR in the melanoma cells but not in the admixed reactive cells. There was no correlation among tumour location, cell type, or growth fraction and the amount of telomerase activity. In addition, the cells of the germinative zone of the lens demonstrated a strong hTR expression.

CONCLUSION

Telomerase activity is upregulated in uveal melanomas. The expression of hTR was located to the tumour cells and not the reactive tumour infiltrating cells. Strong telomerase expression was also demonstrated in cells of the germinative zone of the lens.

In situ nucleic acid detection of human telomerase in intrahepatic cholangiocarcinoma and its preneoplastic lesion

Human telomerase, an enzyme associated with cellular immortality and tumorigenesis, is expressed by most malignant tumor cells. Human telomerase consists of human telomerase RNA (hTR) and telomerase protein components. One of the latter has been cloned and was termed telomerase-associated protein 1 (TP1). Using an in situ hybridization method, expression of hTR and TP1 mRNA was surveyed in 20 cases of intrahepatic cholangiocarcinoma (ICC) (5 of them were associated with hepatolithiasis), 5 cases of hepatolithiasis alone and 6 normal livers. Biliary dysplasia, which is suspected as a preneoplastic lesion of ICC, was found in the biliary tree in all 5 ICC cases with hepatolithiasis and in 1 of 5 cases of hepatolithiasis alone. Normal colonic mucosa was used as positive control. In 17 (85%) of 20 ICC cases, hTR and TP1 mRNA were detected in carcinoma cells. There was no correlation between histological subtype of ICC and expression of hTR and TP1 mRNA. Biliary dysplasia was also positive for both RNA. These signals were mainly located in the cytoplasm of carcinoma and dysplastic cells, especially around their nuclei. The signals were homogeneously detected in the carcinoma, while their distribution was more or less heterogeneous in the dysplastic foci. These signals were not detected in nondysplastic biliary epithelia in hepatolithiasis and normal livers. It seems likely that almost all ICC acquired telomerase activities irrespective of histological subtype and more importantly that cellular immortalization has already occurred in biliary dysplasia and this lesion is already involved in the malignant progression of ICC.

Meningiomas, dicentric chromosomes, gliomas, and telomerase activity

Lack of telomere maintenance during cell replication leads to telomere erosion and loss of function. This can result in telomere associations which probably cause the dicentric chromosomes seen in some tumour cells. One mechanism of telomere maintenance in dividing cells is the action of telomerase, a ribonucleoprotein enzyme that adds TTAGGG repeats onto telomeres and compensates for their shortening during cell division. Over 90 per cent of extracranial malignant neoplasms have been found to have telomerase activity. This study sought to determine if there was a relationship between absence of telomerase activity and presence of dicentric chromosomes in meningiomas and to what extent the other main group of central nervous system tumours, the gliomas, expressed telomerase activity. Telomerase activity was measured on 25 meningiomas and 29 gliomas. Four of the meningiomas were atypical variants and 11 were positive for dicentric chromosomes. Twenty-five of 29 gliomas were glioblastoma multiforme tumours. Measures were taken to ensure absence of false positives due to primer-dimer interaction and false negatives due to protein degradation or the presence of Taq polymerase inhibitors. All 25 meningiomas and the four low-grade gliomas (WHO grade II) were telomerase activity-negative. Seven (28 per cent) of the 25 glioblastoma multiforme tumours showed telomerase activity. The absence of telomerase activity in meningiomas and the high frequency of telomere associations support the hypothesis that these tumours are benign, transformed but pre-crisis. The relatively low frequency of telomerase activity in the malignant glioblastoma multiforme suggests that most of these tumours may have other mechanisms of telomere maintenance and that the potentially therapeutic telomerase inhibitors will not be of great value in the future management of the majority of patients suffering from these tumours.

Telomerase activity in gestational trophoblastic disease

AIMS

To investigate the pattern of telomerase activity in hydatidiform mole as compared with normal placenta and choriocarcinoma, and to determine the prognostic significance of telomerase activity in hydatidiform mole.

METHODS

Telomerase activity in 35 cases of hydatidiform mole, 35 normal placentas, one choriocarcinoma sample, and two choriocarcinoma cell lines (JAR, JEG3) was determined using the sensitive polymerase chain reaction based telomeric repeat amplification protocol (TRAP) assay. Two cases of breast carcinoma and two cases of ovarian carcinoma were also included as positive controls in the telomerase assay.

RESULTS

Telomerase activity was detected in 11 of 30 early placentas (36.7%), one of five term placentas (20%), five of 27 hydatidiform moles which regressed spontaneously (18.5%), and six of eight hydatidiform moles which developed persistent trophoblastic disease (75%) (including three which developed metastases). Hydatidiform moles which subsequently developed persistent disease, especially those which metastasised, were more likely to express telomerase activity (p < 0.01). However, there was no significant difference in the frequency of telomerase activity between early placentas and hydatidiform mole. Strong telomerase activity was observed in choriocarcinoma tissue, choriocarcinoma cell lines, and ovarian and breast carcinomas.

CONCLUSIONS

Telomerase activation occurs in hydatidiform mole with a similar incidence to early normal placentas. This supports the concept that hydatidiform mole is essentially an abnormal conceptus. There is an association between telomerase activation and the development of persistent trophoblastic disease. Further study is warrant to confirm the prognostic significance of telomerase activity in hydatidiform mole.

Immortalization of human prostate epithelial cells by HPV 16 E6/E7 open reading frames

BACKGROUND

The exact pathogenesis for prostate cancer is not known. Progress made in prostate cancer research has been slow, largely due to the lack of suitable in vitro models. Here, we report our work on the immortalization of a human prostate epithelial cell line and show that it can be used as a model to study prostate tumorigenesis.

METHODS

Replication-defective retrovirus harboring the human papillomavirus (HPV) type 16 E6 and E7 open reading frames was used to infect primary human prostate epithelial cells. Polymerase chain reaction, followed by Southern hybridization for the HPV 16 E6/E7, Western blot for prostatic acid phosphatase, telomeric repeat amplification protocol assay for telomerase activity, two-dimensional gels for cytokeratins, and cytogenetic analysis were undertaken to characterized the infected cells.

RESULTS

The retrovirus-infected cell line, HPr-1, continued to grow in culture for more than 80 successive passages. Normal primary cells failed to proliferate after passage 6. HPr-1 cells bore close resemblance to normal primary prostate epithelial cells, both morphologically and biochemically. However, they possessed telomerase activity and proliferated indefinitely. Cytogenetic analysis of HPr-1 cells revealed a human male karyotype with clonal abnormalities and the appearance of multiple double minutes.

CONCLUSIONS

The HPr-1 cells expressed prostatic acid phosphatase and cytokeratins K8 and K18, proving that they were prostate epithelial cells. They were benign in nude mice tumor formation and soft agar colony formation assay. The HPr-1 cell line is an in vitro representation of early prostate neoplastic progression.

Controlling gene expression with 2-5A antisense

Recent work has demonstrated that the activity of a ubiquitous cellular enzyme, ribonuclease L (RNase L), can be harnessed to cleave targeted RNA species. Activation of RNase L is dependent on the presence of 2',5'-linked oligoadenylates (2-5A), usually produced by cells infected with viruses. By conjugating synthetic 2-5A to specific antisense compounds, it is now possible to selectively degrade RNAs in an RNase L-dependent manner, thereby providing an alternative to RNase H-dependent approaches. In this summary, we provide an updated description of the synthesis procedure for constructing these chimeric 2-5A antisense molecules. Examples of successful applications of the 2-5A antisense strategy are described, along with some of the procedures involved in those studies. Several methods are also provided for optimizing compound uptake and analyzing their effects on cells. Finally, we discuss the current body of evidence that supports the contention that RNase L is indeed the primary mediator of 2-5A antisense effects and the possible implications that this has on the future of this therapeutic approach.

Correlation of clinical features and telomerase activity in human gliomas

Telomerase is a ribonucleoprotein containing an RNA template that synthesizes telomeric DNA. The expression of telomerase activity is concomitant with the attainment of immortality in tumor tissues and cells. In this report, we analyzed telomerase activity in 39 human gliomas with different histological, and in 10 meningiomas, 3 neurinomas, and 2 normal brain tissues by using a polymerase chain reaction (PCR)-based telomeric repeat amplification protocol (TRAP) assay. Telomerase activity was detectable in almost all of the gliomas (36 of 39), but not in any of the meningiomas, neurinomas, or normal brain tissues. In addition, we also analyzed the level of telomerase activity in the 36 gliomas with positive telomerase activity. The relative telomerase activity of the glioma showed a clear association with the pathological grade of glioma; i.e., most of the tumors with high telomerase activity were pathologically of high grade. And also the relative level of telomerase activity could be correlated with the survival time of the patients. These results suggest that the level of telomerase activity in brain tumors is a diagnostic marker indicating the prognosis of the patient as well as the malignant potential of the tumor.