Telomerase activity in benign and malignant epithelial ovarian tumors

The status of telomerase enzyme activity in benign and malignant gynaecologic pathologies

BACKGROUND

Telomeres are essential for the function and stability of eukaryotic chromosomes. Telomerase consists of three subunits: human telomerase reverse transcriptase (hTERT), human telomerase RNA (hTR), and telomerase protein 1 (TP1). The hTERT subunit determines the activity of telomerase as an enzyme and is detected in most human tumors and regenerative cells. Telomerase activity is a useful cancer-cell detecting marker in some types of cancers.

AIMS

The aim of this study was to assess of telomerase hTERT mRNA in gynaecological tumors for diagnosis of malignancy.

STUDY DESIGN

Cross-sectional study.

METHODS

A total of 55 gynaecologic tumor samples (35 ovarian, 13 endometrial, 6 cervical and 1 placental site trophoblastic tumor tissue) were obtained at the time of surgery. Quantification of hTERT mRNA was performed in a real-time reverse transcriptase polymerase chain reaction (RT-PCR) using the LightCycler TeloTAGGG hTERT Quantification Kit.

RESULTS

It was histopathologically detected that 18 of the tissue samples were malignant and 37 of the samples were benign. 16 of the malignant tissue samples (88.9%) and 3 (8.1%) (endometrial tissue in proliferative phase, mucinous cyst adenoma and endometriosis) of the benign tissue samples were found to be hTERT positive. With the presence of these data, sensitivity and specificity of hTERT for the diagnosis of malignancy were calculated to be 88.9% and 91.9%, respectively.

CONCLUSION

It was suggested that the measurement of telomerase activity in gynaecologic tumors, except for endometrial tissue in the reproductive phase, is a valuable method for pathological investigation.

Prevalence of telomerase activity in human cancer

Telomerase activity has been measured in a wide variety of cancerous and non-cancerous tissue types, and the vast majority of clinical studies have shown a direct correlation between it and the presence of cancerous cells. Telomerase plays a key role in cellular immortality and tumorigenesis. Telomerase is activated in 80-90% of human carcinomas, but not in normal somatic cells, therefore, its detection holds promise as a diagnostic marker for cancer. Measurable levels of telomerase have been detected in malignant cells from various samples: tissue from gestational trophoblastic neoplasms; squamous carcinoma cells from oral rinses; lung carcinoma cells from bronchial washings; colorectal carcinoma cells from colonic luminal washings; bladder carcinoma cells from urine or bladder washings; and breast carcinoma or thyroid cancer cells from fine needle aspirations. Such clinical tests for telomerase can be useful as non-invasive and cost-effective methods for early detection and monitoring of cancer. In addition, telomerase activity has been shown to correlate with poor clinical outcome in late-stage diseases such as non-small cell lung cancer, colorectal cancer, and soft tissue sarcomas. In such cases, testing for telomerase activity can be used to identify patients with a poor prognosis and to select those who might benefit from adjuvant treatment. Our review of the latest medical advances in this field reveals that telomerase holds great promise as a biomarker for early cancer detection and monitoring, and has considerable potential as the basis for developing new anticancer therapies.

p21 WAF1 is involved in interferon-β-induced attenuation of telomerase activity and human telomerase reverse transcriptase (hTERT) expression in ovarian cancer

Telomerase activation is a key step in the development of human cancers. Interferon-β (IFN-β) signaling induces growth arrest in many tumors but the anticancer mechanism of IFN-β is poorly understood. In the present study, we show that IFN-β signaling represses telomerase activity and human telomerase reverse transcriptase (hTERT) transcription in ovarian cancer and suggest that this signaling is mediated by p21(WAF1). IFN-β triggered down-regulation of telomerase activity and hTERT mRNA expression and also induced p21 expression, independently of p53 induction. Ectopic expression of p21 attenuated hTERT promoter activity. Murine embryonic fibroblasts (MEFs) genetically deficient in p21 (p21-/-) showed elevated (> 15 times) hTERT promoter activity compared to wild-type MEFs. Overexpression of p21 reduced the hTERT promoter activity of p21-/- MEFs and hTERT mRNA expression in HCT119 p21(WAF1) null cell. These findings provide evidence that p21 is a potential mediator of IFN-β-induced attenuation of telomerase activity and tumor suppression.

Oncogenic transformation of human ovarian surface epithelial cells with defined cellular oncogenes

Ovarian surface epithelium (OSE) is considered to give rise to epithelial ovarian carcinomas (EOCs). To elucidate early processes contributing to the development of EOCs from the OSE, two batches of primary human OSE cells were transduced with non-viral human genes (mutant Cdk4, cyclinD1 and hTERT) so as to efficiently establish normal diploid OSE cells without chromosomal instability. Then defined genetic alterations frequently observed in EOCs were transduced into the OSE cells. A combination of p53 inactivation and oncogenic Kras transduction did not confer tumor-forming ability in immunodeficient mice, though additional transduction of Akt or combined transduction of c-myc with bcl-2 did result in tumor formation. In the latter case, tumors demonstrated phenotypes reminiscent of human EOCs, including cytokeratin expression, a highly aggressive phenotype, metastatic behavior and formation of ascites. These results indicate that inactivation of p53 and activation of the Ras pathway play critical roles in ovarian carcinogenesis in co-operation with the Akt or c-myc pathways. This first in vitro model system faithfully recapitulating the development of EOCs using normal human OSE cells should greatly facilitate further studies of EOCs.

Serous borderline ovarian tumors in long-term culture: phenotypic and genotypic distinction from invasive ovarian carcinomas

Serous borderline ovarian tumors (SBOTs) are differentiated, slow growing, noninvasive, and have a better prognosis than their invasive counterparts, but recurrence and progression to invasive carcinomas are common, and unlike high-grade serous carcinomas, they tend to be nonresponsive to chemotherapy. However, due to a lack of culture systems and animal models, information about the properties of SBOT and their changes with neoplastic progression is extremely limited. Our objective was to establish a cell culture model for SBOTs and to characterize their phenotype and genotype. We compared cultures derived from two SBOTs, one of which was a short-term culture containing a BRAF mutation but few other cytogenetic changes while the other culture developed into a spontaneously immortalized permanent cell line and had numerical and structural chromosomal abnormalities but lacked RAS/BRAF mutations. Both cultures formed whorl-like epithelial colonies and resembled low-grade invasive carcinomas by their secretion of CA125 and oviduct-specific glycoprotein, production of matrix metalloproteinases, E-cadherin expression, and telomerase activity. Other characteristics associated with neoplastic transformation, including invasiveness, anchorage-independent growth, and tumorigenicity, were not observed. Importantly, cell motility was reduced in both lines, likely contributing to the lack of invasiveness. The results reveal a striking phenotypic similarity between the two cell lines, regardless of their cytogenetic diversity, which suggests that their characteristic phenotype is regulated to a large degree by epigenetic and environmental factors. In conclusion, we have established the first permanent SBOT cell line, which provides a new model to elucidate the undefined relationship of SBOTs to invasive ovarian carcinomas.

Increased chromosomal stability in cultures of ovarian tumours of low malignant potential compared to cystadenomas

Cell cultures of ovarian cystadenomas transfected with SV40 large T antigen are not immortal because they invariably reach a phenomenon called crisis, which is triggered in part by telomere attrition. Recovery from crisis may be an integral component of the malignant transformation process. We reported earlier that such ovarian cystadenoma cell cultures undergo severe changes in DNA ploidy as they approach crisis and that such changes are an important determinant of crisis independent of telomere attrition. Here, we show that in sharp contrast to these benign ovarian tumours, the DNA content of ovarian tumours of low malignant potential (LMP) was remarkably stable as they approached crisis, suggesting that telomere attrition was the main determinant of this mortality checkpoint. Lack of a ploidy-based crisis was not due to loss of expression of a functional SV40 large T antigen protein. We conclude that ovarian LMP tumours are characterised by increased numerical chromosomal stability compared to cystadenomas. This might account for the fact that most LMP tumours are diploid or near diploid in vivo. This fundamental difference in chromosomal stability between ovarian cystadenomas and LMP tumours also suggests potential differences in predisposition to progression to malignancy between these two ovarian tumour subtypes.

Diagnostic value of telomerase expression in breast fine-needle aspiration biopsies

Fine-needle aspiration biopsy (FNAB) of breast is a minimally invasive sampling procedure with a proven value in the initial evaluation of patients with palpable breast lesions. FNAB is a simple, cost-effective, and relatively nontraumatic procedure that has replaced open surgical biopsy in majority of academic institutions across the world. There are, however, inherent limitations in the ability of FNAB to reliably diagnose small percentage of cases that are difficult to diagnose by cytomorphology alone and require excisional biopsy. This shortcoming may be minimized if the morphology can be complemented by a reliable diagnostic adjunct. This retrospective study was designed to assess the added value of telomerase immunostain in interpretation of breast FNABs. Telomerase is a ribonucleoprotein enzyme that has been shown to be activated in different malignant tumors, including breast cancer. Immunocytochemical detection of this molecular marker on cytologic smears and cellblocks may be helpful for interpretation of FNAB specimens. In our retrospective study, we found that 56% of the malignant breast cases (28/50) showed positive telomerase immunostaining while only 4% of the negative cases (2/50) stained with telomerase (positive predictive value: 93%, negative predictive value: 69%). Expression of telomerase on highly suspicious breast fine-needle aspirations may upgrade the diagnosis to malignancy. However, a negative telomerase cannot exclude the possibility of carcinoma.

Correlation of the expression of telomerase RNA with risk factors for recurrence of sebaceous gland carcinoma

AIMS

To investigate the expression of human telomerase gene RNA (hTR) and human telomerase reverse transcriptase (hTRT) in eyelid sebaceous gland carcinoma and to evaluate risk factors for sebaceous carcinoma recurrence.

METHODS

The expression patterns of hTR and hTRT were detected by in situ hybridization (ISH) in paraffin-embedded samples of 55 eyelid sebaceous gland carcinoma, 12 chalazia, and four sebaceous adenoma. The proliferation index (PI) of sebaceous gland carcinoma was determined by Ki-67 immunolabeling and the results were compared with the expression of hTR and hTRT. Several factors for recurrence of sebaceous gland carcinoma were evaluated by statistical analysis.

RESULTS

Expression of hTR and hTRT was present mainly in the sebaceous gland carcinoma tissues and not in adjacent tissues of carcinoma, chalazia, and sebaceous adenoma. The prevalence of hTR, hTRT, and Ki-67 expression in 55 sebaceous carcinoma samples were 84.45%, 58.1%, and 78.18%, respectively. hTR expression was highly associated with the degree of carcinoma differentiation (P<0.001) and hTRT expression was correlated with the proliferation index as determined by Ki-67 staining (P<0.005). There was a correlation between the recurrence of sebaceous gland carcinoma and the patient's onset age (OR=0.914, P<0.05), as well as the time to first treatment (OR=1.163, P<0.01).

CONCLUSIONS

Telomerase may play an important role in the carcinogenesis of sebaceous gland carcinoma, and expression of hTR and hTRT combined with other features of sebaceous gland carcinoma may be helpful for the diagnosis and evaluation of clinical prognosis. Risk factors for recurrence of sebaceous gland carcinoma are patients' onset age and the time to first treatment.

Telomerase in breast cancer: a critical evaluation

Human chromosomes have highly specialized structures at their ends termed telomeres, repetitive, non-coding DNA sequences (5'-TTAGGG-3'), ranging in size from 5 to 20 kb in human cells. These highly specialized structures prevent chromosome ends from being recognized as double-strand DNA breaks, and they also provide protection from destabilizing agents. The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences lost during replication by using an intrinsic RNA component as a template for polymerization. Telomerase has two core functional components required for its activity: the catalytic subunit of human telomerase reverse transcriptase (hTERT) and a telomerase RNA template (hTR). Telomerase is activated in the majority of immortal cell lines in culture and in most malignant tumors. This review outlines our current understanding of telomerase in breast cancer development and critically evaluates potential utilities in diagnosis, prognosis, and therapy.

Activation of antioxidant pathways in ras-mediated oncogenic transformation of human surface ovarian epithelial cells revealed by functional proteomics and mass spectrometry

Cellular transformation is a complex process involving genetic alterations associated with multiple signaling pathways. Development of a transformation model using defined genetic elements has provided an opportunity to elucidate the role of oncogenes and tumor suppressor genes in the initiation and development of ovarian cancer. To study the cellular and molecular mechanisms of Ras-mediated oncogenic transformation of ovarian epithelial cells, we used a proteomic approach involving two-dimensional electrophoresis and mass spectrometry to profile two ovarian epithelial cell lines, one immortalized with SV40 T/t antigens and the human catalytic subunit of telomerase and the other transformed with an additional oncogenic ras(V12) allele. Of approximately 2200 observed protein spots, we have identified >30 protein targets that showed significant changes between the immortalized and transformed cell lines using peptide mass fingerprinting. Among these identified targets, one most notable group of proteins altered significantly consists of enzymes involved in cellular redox balance. Detailed analysis of these protein targets suggests that activation of Ras-signaling pathways increases the threshold of reactive oxidative species (ROS) tolerance by up-regulating the overall antioxidant capacity of cells, especially in mitochondria. This enhanced antioxidant capacity protects the transformed cells from high levels of ROS associated with the uncontrolled growth potential of tumor cells. It is conceivable that an enhanced antioxidation capability may constitute a common mechanism for tumor cells to evade apoptosis induced by oxidative stresses at high ROS levels.

Detection of Residual Subclinical Ovarian Carcinoma after Completion of Adjuvant Chemotherapy

PURPOSE

We sought to test the hypothesis that the presence of telomerase activity in peritoneal washings of patients treated for ovarian carcinoma is a sensitive and specific indicator of the presence of residual disease. We hypothesized that this test, if added to second-look procedure protocols, could help determine whether residual disease is present or not in patients who have completed their adjuvant chemotherapy for ovarian carcinoma.

EXPERIMENTAL DESIGN

Peritoneal washings were obtained from 100 consecutive patients undergoing a second-look procedure after treatment for ovarian carcinoma (cases) and from 100 patients undergoing surgery for benign gynecological conditions (controls). The washings were assayed for telomerase activity using the telomerase repeat amplification protocol. The results were compared to the histological and cytological findings.

RESULTS

Among our 100 cases, 82 (82%) had either positive second-look procedures or expressed telomerase in their peritoneal washings. Fifty-three (53%) had positive second-look procedures, whereas 66 (66%) tested positive for telomerase. Twenty-nine of the 47 patients (62%) with negative second-look procedures tested positive for telomerase. Of the 53 patients with positive second-look procedures, 37 (70%) tested positive for telomerase. None of the 100 controls (0%) expressed telomerase in their peritoneal washings.

CONCLUSIONS

Telomerase activity in peritoneal washings of patients treated for ovarian carcinoma and undergoing a second-look procedure may provide a means of increasing the sensitivity of such procedures for the detection of residual disease while maintaining a high level of specificity.

A genetically defined model for human ovarian cancer

Disruptions of the p53, retinoblastoma (Rb), and RAS signaling pathways and activation of human telomerase reverse transcriptase (hTERT) are common in human ovarian cancer; however, their precise role in ovarian cancer development is not clear. We thus introduced the catalytic subunit of hTERT, the SV40 early genomic region, and the oncogenic alleles of human HRAS or KRAS into human ovarian surface epithelial cells and examined the phenotype and gene expression profile of those cells. Disruption of p53 and Rb pathway by SV40 early genomic region and hTERT immortalized but did not transform the cells. Introduction of HRAS(V12) or KRAS(V12) into the immortalized cells, however, allowed them to form s.c. tumors after injection into immunocompromised mice. Peritoneal injection of the transformed cells produced undifferentiated carcinoma or malignant mixed Mullerian tumor and developed ascites; the tumor cells are focally positive for CA125 and mesothelin. Gene expression profile analysis of transformed cells revealed elevated expression of several cytokines, including interleukin (IL)-1beta, IL-6, and IL-8, that are up-regulated by the nuclear factor-kappaB pathway, which is known to contribute to the tumor growth of naturally ovarian cancer cells. Incubation with antibodies to IL-1beta or IL-8 led to apoptosis in the ras-transformed cells and ovarian cancer cells but not in immortalized cells that had not been transformed. Thus, the transformed human ovarian surface epithelial cells recapitulated many features of natural ovarian cancer including a subtype of ovarian cancer histology, formation of ascites, CA125 expression, and nuclear factor-kappaB-mediated cytokine activation. These cells provide a novel model system to study human ovarian cancer.

Early events in ovarian oncogenesis

Ovarian cancer represents the most lethal of the gynecological neoplasms. The molecular and genetic events associated with early ovarian oncogenesis are still largely unknown, thus contributing to the lack of reliable biomarkers for disease detection. Since the majority of ovarian tumors are diagnosed at an advanced stage, the availability of early ovarian cancer tissue samples for molecular analyses is very limited. In this review, problems encountered in the study of early ovarian cancer are presented, along with the controversies concerning precursor lesions and stepwise progression towards ovarian malignancy. Experimental modeling in the development of ovarian cancer is also described, as well as genetic and epigenetic alterations associated with early ovarian cancer. Lastly, examples of technological advances in the study of early ovarian cancer are discussed. Hopefully, the increasing knowledge about molecular and genetic events involved in the early stages of ovarian tumorigenesis will provide the basis for management of ovarian cancer in the future.

Relationship between telomerase activity and its subunit expression and inhibitory effect of antisense hTR on pancreatic carcinoma

AIM: To directly investigate the relationship between telomerase activity and its subunit expression and the inhibitory effect of antisense hTR on pancreatic carcinogenesis.

METHODS: We examined the telomerase activity and its subunit expression by cell culture, polymerase chain reaction (PCR), PCR-silver staining, PCR-ELISA, DNA sequencing, MTT and flow cytometry methods.

RESULTS: PCR-silver staining and PCR-ELISA methods had the same specificity and sensitivity as the TRAP method. Telomerase activity was detected in the extract of the 10^th, 20^thand 30^th passages of P3 cells,while it was absent in fibroblasts. Furthermore, after the 30th generation, the proliferation period of fibroblast cells was significantly prolonged. Telomerase activity and hTERTmRNA were detected in two pancreatic carcinoma cell lines, but were found to be negative in human fibroblast cells. Telomerase activity and hTERTmRNA were tested in pancreatic carcinoma specimens of 24 cases. The telomerase activity was positive in 21 of the 24 cases (87.5%), and the hTERTmRNA in 20 cases (83.3%). In adjacent normal tissues positive rates were both 12.5%. There was a significant difference between the two groups. This indicated a significant correlation between the expression level of telomerase activity and histologic differentiation, metastasis and advanced clinical stage of pancreatic carcinoma. Our findings showed that the expressions of hTR and TP1mRNA were not correlated with the activity of telomerase but the expression of hTERTmRNA was. After treatment with PS-ODNs, telomerase activity in P₃ cells weakened and the inhibiting effect became stronger with an increase in PS-ODNs concentration. There was a significant difference between different PS-ODN groups (P < 0.05). Inhibition of telomerase activity occurred most significant with PS-ODN1.The results of the FCM test of pancreatic cancer P₃ cells showed an increase in the apoptotic rate with increasing PS-ODN1 and PS-ODN2 concentrations.

CONCLUSION: The expression of telomerase activity has a significant relationship to carcinogenesis. A strong correlation exists between telomerase activity and hTERTmRNA expression. The up-regulation of hTERTmRNA expression may play a critical role in human carcinogenesis. The expression of telomerase activity and its subunit level in pancreatic carcinoma significantly correlate with the clinical stage of pancreatic carcinoma and hence, may be helpful in its diagnosis and prognosis. The anti-hTR complementary to the template region of hTR is sufficient to inhibit P3 cell telomerase activity and cell proliferation in vitro, and can lead to a profound induction of programmed cell death.

Molecular aspects of ovarian cancer

Ovarian cancer is caused by genetic alterations that disrupt proliferation, apoptosis, senescence and DNA repair. Approximately 10% of ovarian cancers arise in women who have inherited mutations in cancer susceptibility genes (BRCA1 or BRCA2). The ability to perform genetic testing allows identification of women at increased risk who can be offered prophylactic oophorectomy or other interventions aimed at preventing ovarian cancer. The vast majority of ovarian cancers are sporadic, resulting from the accumulation of genetic damage over a lifetime. Several specific genes involved in ovarian carcinogenesis have been identified, including the p53 tumour suppressor gene and HER2/ neu andPIC3KA oncogenes. The recent availability of expression microarrays has facilitated the simultaneous examination of thousands of genes, and this promises to extend further our understanding of the molecular events involved in the development of ovarian cancers. Hopefully, this knowledge can be translated into effective screening, treatment, surveillance, and prevention strategies in the future.

Transcriptional targeting for ovarian cancer gene therapy

Ovarian carcinoma is a leading cause of cancer death in women. Though advances in conventional therapies have been achieved, long-term survival rates for most patients diagnosed with ovarian cancer are still low. Therefore, novel molecular therapeutic strategies such as gene therapy are being intensively pursued. Such approaches are based on the enormous progress that has been achieved in the elucidation of the molecular foundations of ovarian cancer. In this regard transcriptional control elements (promoters) of genes frequently upregulated or specifically expressed in tumors can be applied in a heterologous context to drive expression of therapeutic genes in targeted gene therapy strategies. This review discusses transcriptional targeting strategies in ovarian cancer gene therapy and gives an overview of tumor-specific promoters (TSPs) that have been applied for this purpose.

Applications of the telomerase assay in peritoneal washing fluids

OBJECTIVE

The aim of this study was to detect telomerase activity in peritoneal ascites and to assess whether it can be used as an assistant tool for the early detection of ovarian cancer.

METHODS

Telomerase activity was measured by TRAP assay in 47 patients with ovarian malignancies and 50 patients with benign uterine leiomyomas (control group).

RESULTS

All 26 peritoneal washing cytology positive cases were telomerase positive. Of the 21 peritoneal washing cytology negative cases, 3 were telomerase positive. When these 3 were reevaluated for peritoneal cytology, malignant ascitis was identified in 1. All telomerase negative cases were negative for peritoneal washing cytology. The sensitivity and specificity of peritoneal cytology and telomerase testing in correlation with true malignant cells were 96 (26/27) and 100% (20/20) versus 100 (27/27) and 90% (18/20), respectively. The false negative rate of peritoneal cytology was 4.7% (1/21). The false positive rate of the telomerase test in relation to malignant ascites was 6.9% (2/29).

CONCLUSION

Our preliminary results reveal a high sensitivity and specificity of both telomerase testing and conventional cytology in peritoneal fluids. Our data suggest that the telomerase test in peritoneal fluids can be used as an adjuvant to cytopathological methods in the diagnosis of malignant peritoneal ascites, particularly in cases of negative cytology. In these cases, a review of peritoneal histocytology is advised.

2-5A antisense directed against telomerase RNA produces apoptosis in ovarian cancer cells

OBJECTIVE

RNase L is converted to an active form upon binding short 2',5'-oligoadenylates (2-5A). To direct RNase L to an RNA target, 2-5A is attached to an antisense oligonucleotide (2-5A antisense). This chimera can be directed against telomerase-an RNA-protein complex that elongates telomeric DNA and is involved in cellular immortalization. Our objective is to investigate the effect of 2-5A antisense by targeting telomerase RNA (hTR) in the ovarian cancer cell line, HEY-1B.

METHODS

Baseline RNase L levels and telomerase activities were measured in both HEY-1B and normal ovarian epithelial cells (NOE). Cells were treated daily with chimeric oligonuclotides (ODN) directed against four different hTR sites, or control ODNs including nonchimeric antisense, 2-5A fused to a mismatched sequence, or inactive 2-5A fused to antisense. At 48 h, apoptosis was evaluated using the TUNEL assay. After six daily ODN administrations, telomerase activity was redetermined, and at 7 days viability counts were obtained.

RESULTS

Both cell lines expressed similar levels of RNase L. Hey-1B displayed telomerase activity while NOE did not. After 7 days of transfection, 2-5A antisense ODNs caused profound cell death in the HEY-1B cells, but not in the NOE cells. This effect was seen regardless of hTR target site, and ODN controls showed no significant decrease in cell viability in either cell line. HEY1B cells treated with 2-5A antisense against hTR showed a decrease in telomerase activity and a profound induction of programmed cell death.

CONCLUSIONS

The results suggest that 2-5A antisense directed against telomerase RNA results in apoptotic cell death in ovarian cancer cells, but not normal ovarian epithelial cells. The 2-5A antisense strategy may hold a considerable advantage over the conventional antisense approach in targeting cancer-causing genes.

Analysis of telomerase activity in ovarian cystadenomas, low-malignant-potential tumors, and invasive carcinomas

OBJECTIVE

Inappropriate telomerase expression has been reported to be associated with the development and/or progression of malignancies. Therefore, the purpose of the study was to determine and evaluate the levels of telomerase activity in normal ovary, cystadenomas, low-malignant-potential tumors, and carcinomas of the ovary.

METHODS

In the present study, telomerase activity was examined in frozen tissue specimens of normal ovary (n = 6), ovarian cystadenomas (n = 13), ovarian low-malignant-potential (LMP) tumors (n = 12), and ovarian invasive carcinomas (n = 81). Clinicopathological information including age at diagnosis, histological grade, FIGO stage, presence of distant metastasis at diagnosis, and residual disease was available for all patients with ovarian carcinomas (n = 81). Telomerase activity was assessed by the telomeric repeat amplification protocol (TRAP). Arbitrary values were assigned to processivity of telomerase activities based on the molecular weights of the telomeric repeat DNA ladders, and were graded as "negative," "moderate" (< or =99 bp), or "high" (>100 bp) activities. The specificity of telomerase activity was determined by the pretreatment of telomerase-positive control or tumor samples with RNase that led to the abolition of the activity. In addition, to determine the possibility of false negativity due to the presence of telomerase inhibitors, TRAP assay was performed on each of the telomerase-negative specimens by mixing them individually with the telomerase-positive control.

RESULTS

Telomerase activity in the progression of ovarian carcinogenesis was evaluated. In comparison with normal ovary/cystadenoma (32%), a much higher frequency of the moderate activity was observed in LMP tumors (67%) or invasive carcinomas (57%), suggesting a close association between the latter two categories. The results reflect a subpopulation of telomerase-positive LMP tumor cells with the potential to develop invasive carcinomas. None of the specimens of the benign or LMP tumors exhibited high activity. In contrast, 18% of ovarian invasive carcinomas showed high telomerase activity (P = 0.013, Fisher exact test) and further 57%, moderate activity (75% in all). A statistically significant difference was observed in the expression of telomerase activity between normal ovary/benign cystadenomas and ovarian invasive carcinomas (P = 0.001, chi(2) test).

CONCLUSIONS

The study showed a high prevalence of telomerase activity in LMP tumors or invasive carcinomas, the high levels of telomerase activity being associated exclusively with the invasive ovarian carcinomas. Therefore, the levels of processivity of telomerase activity and evidence of its statistically significant association with ovarian carcinoma suggest its role in the progression of ovarian carcinogenesis.

Differential telomerase activity, expression of the telomerase catalytic sub-unit and telomerase-RNA in ovarian tumors

Telomerase activity has been found in a variety of malignant tumors but only rarely in benign tumors or normal tissues. In this study, we investigated telomerase activation in 37 ovarian tumors, including benign, borderline and malignant neoplasms. Telomerase activity was detected using the telomeric repeat amplification protocol (TRAP) in 13/16 ovarian carcinomas, 9/10 borderline tumors and 3/11 cystadenomas/fibromas. mRNA expression of the putative human telomerase catalytic sub-unit gene (hTERT) was detected by RT-PCR in 14/15 ovarian carcinomas, 8/10 borderline tumors and 4/11 cystadenomas/fibromas. In situ hybridization was performed to evaluate telomerase-RNA (hTR) expression in the corresponding paraffin-embedded tumors. Variable expression levels of hTR were found over neoplastic tumor cells. The highest levels of hTR expression were found predominantly in ovarian carcinomas. Although the amount of telomerase activity varied, significantly high levels of telomerase activity were found predominantly in ovarian carcinomas. hTERT mRNA expression was closely associated with telomerase activity. These findings suggest that up-regulation of hTERT and hTR is important for telomerase activation during malignant-tumor progression. Telomerase activation might therefore be a valuable diagnostic parameter that could help to identify potentially progressive lesions. However, the diagnostic and therapeutic implications of telomerase activation need to be clarified in clinical trials. Int. J. Cancer (Pred. Oncol.) 84:426-431, 1999.

Telomerase activity in malignant ovarian tumors with deregulation of cell cycle regulatory proteins

Using a semiquantitative telomeric repeat amplification protocol assay, telomerase-positive frequencies and enzyme levels were measured. Out of 95% of 49 human ovarian tumors, the highest level of telomerase activity was observed in malignant tumors. Furthermore, by immunohistochemical staining of cell cycle regulatory proteins (pRB, p16, cyclin D1, cyclin E and p53) at the G1 checkpoint, we evaluated the relation between each protein alterations and the levels of telomerase activity. We could not demonstrate a clear relation with each molecule except for cyclin E, but suggesting that aberrant accumulation of these proteins was considered as a reason for telomerase deregulation, which may play an essential role in the pathway of telomerase regulation.

Telomeric instability and reduced proliferative potential in ovarian surface epithelial cells from women with a family history of ovarian cancer

OBJECTIVE

Increased telomeric instability in normal ovarian surface epithelium may contribute to ovarian carcinogenesis in women from families with a high frequency of breast/ovarian cancer. To test this hypothesis, we compared proliferative potential, mean telomeric length, and telomerase activity in SV-40 large T-antigen transfected cell lines derived from normal ovarian surface epithelium of women with and without a familial history of breast/ovarian cancer.

METHODS

Telomeric instability was examined in SV-40 large T-antigen transfected cell lines of normal ovarian surface epithelium from patients with (FHIOSE, N = 5) and without (NFHIOSE, N = 11) a history of familial breast/ovarian cancer. The duration and total attainable number of population doublings, mean telomeric length, rate of telomeric loss, and telomerase activity were determined by cell counts, Southern blot analysis, and PCR ELISA.

RESULTS

FHIOSE cells attained fewer population doublings than NFHIOSE cells and doubled at approximately half the rate of NFHIOSE cells, indicating a reduced proliferative capacity in FHIOSE cells. While telomerase activity was not detected in FHIOSE or NFHIOSE cell lines, mean telomeric lengths in FHIOSE were generally 1 kb shorter than in NFHIOSE cells and the rate of telomeric loss as a function of population doublings was up to threefold greater in FHIOSE cells.

CONCLUSIONS

Increased telomeric instability and reduced growth potential suggest greater proximity to replicative senescence in ovarian surface epithelium from women with a familial history of breast/ovarian cancer. Consequently, an accumulation of genetic aberrations due to accelerated cellular aging may contribute to the enhanced susceptibility for malignant transformation and earlier onset in heritable ovarian cancer.

Molecular aspects of ovarian cancer. Is gene therapy the solution?

Genetic abnormalities of cancer cells are complex and usually nonspecific. Genetic anomalies specific to ovarian cancer have not been reported. This article focuses on what molecular anomalies are known in ovarian cancer and describes the first trials that have used transfer of genes to reestablish a normal cellular function in this disease. Suicide gene therapy has been the prototype of this new therapeutic approach.

Telomeres and telomerase in endocrine pathology

Telomeres representing repetitive DNA sequences of chromosome ends are necessary for maintaining chromosomal integrity. The enzyme telomerase synthesizes de novo telomeric repeats and incorporates them onto the DNA 3'-ends of chromosomes. Stability of chromosome ends and activation of telomerase are elementary requirements for cell immortalization and tumor progression. The telomeric length and telomerase activity have been recently studied in several human neoplasms, including those of endocrine tissues. Assessment of telomerase activity may help to distinguish normal or hyperplastic from neoplastic tissues. Inhibition or inactivation of telomerase activity may provide novel strategies for cancer therapy.

Detection of ovarian cancer cells: comparison of a telomerase assay and cytologic examination

BACKGROUND

Telomerase is an enzyme essential for the normal replication of chromosomes. Telomerase activity is absent in most somatic cells in adults, but it is usually expressed in cancer cells, including ovarian carcinoma cells. Our principal goal was to compare the sensitivity of a telomerase assay, i.e., the telomeric repeat amplification protocol (TRAP) assay, with that of cytologic examination in detecting cancer cells in the peritoneal cavity of patients with ovarian carcinoma.

METHODS

TRAP assays and cytologic examinations were performed on peritoneal washings and ascitic fluids from 42 patients with active ovarian carcinoma. Control specimens included washings from 29 patients with benign ovarian diseases and ascitic fluids from 14 patients with liver failure. We also evaluated the stability of telomerase in ascitic fluids left unprocessed at room temperature as well as the ability of the TRAP assay to detect cancer cells in mixtures containing large numbers of normal cells.

RESULTS

Specimens from 37 (88%) of the 42 patients with ovarian carcinoma tested positive for telomerase. Cytologic examination detected cancer cells in only 27 of the telomerase-positive specimens (i.e., in specimens from 64% of the 42 patients). This difference of 24% (95% confidence interval = 17%-30%) in sensitivity between the two tests was statistically significant (two-sided P = .002). Specimens from five of the patients with ovarian carcinoma were cytologically negative and telomerase negative. All 43 control specimens were cytologically negative, but the TRAP assay detected telomerase in two of them. Telomerase activity was detected in unprocessed samples left at room temperature for 5 days and in mixtures containing a small number of cancer cells and a 2000- to 10000-fold excess of normal cells.

CONCLUSIONS

Assaying for telomerase is more sensitive than cytologic examination in detecting cancer cells in the peritoneal cavity of patients with ovarian carcinoma.

Establishment of long-term in vitro cultures of human ovarian cystadenomas and LMP tumors and examination of their spectrum of expression of matrix-degrading proteinases

OBJECTIVES

To obtain long-term cultures of ovarian cystadenomas and ovarian tumors of low malignant potential (LMP) displaying gene expression patterns similar to those found in vivo and test the hypothesis that such cultures would express different levels of matrix-degrading proteinases than cultured ovarian carcinomas.

METHODS

Transfection with an adenoviral expression vector for simian virus 40 (SV40) large T antigen was used to establish long-term cultures of the above tumors. Levels of expression of various genes were evaluated using molecular biological and immunohistochemical approaches. Zymography and reverse zymography were used to examine the activity of various metalloproteinases and plasminogen activators (PA). Two-sided P values for differences in plasminogen activator expression between different cell types were evaluated by Fisher's exact test.

RESULTS

Long-term cultures derived from cystadenomas and LMP tumors were obtained which formed colonies on semisolid supports, but were not tumorigenic in nude mice. The cultured cells expressed keratin, estrogen receptor, gonadotropin receptors, BRCA1, and originated from monoclonal populations. There was no apparent association between the malignant phenotype and the expression of either matrix metalloproteinases or tissue inhibitors of metalloproteinases. However, a correlation was seen between this phenotype and expression of urokinase (uPA) and tissue type (tPA) plasminogen activators (P = 0.08 and 0.02 respectively).

CONCLUSIONS

The above cell strains provide a useful model for investigating various aspects of the biology of benign ovarian tumors, including their response to steroid and gonadotropin hormones, and the role of specific proteinases in the acquisition of invasive and metastatic abilities.