Clinical significance of telomerase activity in the non-cancerous epithelial region of oesophageal squamous cell carcinoma

Telomerase activity and survival of late-stage South African esophageal carcinoma patients

Squamous cell carcinoma of the esophagus is a cancer with a high incidence in South Africa. We have investigated the prognostic value of telomerase activity in tumors as well as nearby normal tissue. Biopsies from 98 patients (71 men and 27 women) were analyzed using an adaptation of the TRAP assay. We found all tumor biopsies to have moderate to high telomerase activity, while one third of biopsies from normal mucosa were negative. The telomerase activity level of the tumors had no prognostic value (P = 0.95) as determined by the log rank test. A P-value of 0.02 was found when the telomerase-negative and moderately positive normal biopsies were grouped together and compared to those with high activity. Our results show that telomerase activity of normal mucosa in the vicinity of the tumor can identify a population of patients with significantly worse prognosis, even in late stage patients.

Flow cytometric analysis of DNA, telomerase content and multi-gene expression in esophageal epithelial dysplasia

AIM: To investigate the alteration of molecular events and the early carcinogenesis mechanism of esophageal epithelial cells in the high incidence area of esophageal cancer.

METHODS: Esophageal epithelial cells of esophageal cancer patients were collected from the high incidence area in China. Content of DNA and telomerase as well as multi-gene expressions such as p53, p21 and cyclin D₁ in esophageal precancer cells were quantitatively analysed by flow cytometry (FCM) with indirect immunofluorescence technique and DNA propidium iodide fluorescence staining.

RESULTS: FCM analysis results showed the DNA content increased significantly and the heteroploid rate was 87.9% in occurred carcinogenesis. P53 protein accumulation and ras p21 increase were seen in the early carcinogenesis of the esophagus. The positive rate of p53 and ras p21 was 100% (5/5, 4/4 respectively) in the cancer group. Telomerase and oncogene cyclin D₁ were over- expressed in all of the cancer patients.

CONCLUSION: Increased DNA content and heteroploid rate, accumulation of p53 protein, and over-expression of p21, telomerase and cyclin D₁ proteins were early molecular events during the development of esophageal cancer.

Progressive transformation of immortalized esophageal epithelial cells

AIM: To investigate the progressive transformation of immortal cells of human fetal esophageal epithelium induced by human papillomavirus, and to examine biological criteria of sequential passage of cells, including cellular phenotype, proliferative rate, telomerase, chromosome and tumorigenicity.

METHODS: The SHEE cell series consisted of immortalized embryonic esophageal epithelium which was in malignant transformation when cultivated over sixty passages without co-carcinogens. Cells of the 10th, 31st, 60th and 85th passages were present in progressive development after being transfected with HPV. Cells were cultivated in a culture flask and 24-hole cultural plates. Progressive changes of morphology, cell growth, contact-inhibition, and anchorage-dependent growth characteristics were examined by phase contrast microscopy. The cell proliferation rate was assayed by flow cytometry. The modal number of chromosomes was analyzed. HPV18E₆E₇ was detected by Western blot methods and activities of telomerase were analyzed by TRAP. Tumorigenicity of cells was detected with soft agar plates cultivated and with tumor formation in SCID mice.

RESULTS: In morphological examination the 10th passage cells were in good differentiation, the 60th and 85th passages cells were in relatively poor differentiation, and the 31st passage cells had two distinct differentiations. The characteristics of the 85th and 60th passage cells were weakened at contact-inhibition and anchorage-dependent growth. Karyotypes of four stages of cells belonged to hyperdiploid or hypotriploid, and bimodal distribution of chromosomes appeared in the 31st and 60th passage cells. All of these characteristics combined with a increasing trend. The activities of telomerase were expressed in the latter three passages. Four fourths of SCID mice in the 85th passage cells and one fourth of SCID mice in the 60th passage cells developed tumors, but the cells in the 10th and 31st passage displayed no tumor formation.

CONCLUSION: In continual cultivation of fetal esophageal epithelial cells with transduction of HPV18E₆E₇, cells from the 10th to the 85th passage were changed gradually from preimmortal, immortal, precancerous to malignantly transformed stages. All of these changes were in a dynamic progressive process. The establishment of a continuous line of esophageal epithelium may provide a in vitro model of carcinogenesis induced by HPV.

Telomere and telomerase in the initial stage of immortalization of esophageal epithelial cell

AIM: To search for the biomarker of cellular immortalization, the telomere length, telomerase activity and its subunits in cultured epithelial cells of human fetal esophagus in the process of immortalization.

METHODS: The transgenic cell line of human fetal esophageal epithelium (SHEE) was established with E₆E₇ genes of human papillomavirus (HPV) type 18 in our laboratory. Morphological phenotype of cultured SHEE cells from the 6th to 30th passages, was examined by phase contrast microscopy, the telomere length was assayed by Southern blot method, and the activity of telomerase was analyzed by telomeric repeat amplification protocol (TRAP). Expressions of subunits of telomerase, hTR and hTERT, were assessed by RT-PCR. DNA content in cell cycle was detected by flow cytometry. The cell apoptosis was examined by electron microscopy (EM) and TUNEL label.

RESULTS: SHEE cells from the 6th to 10th passages showed cellular proliferation with a good differentiation. From the 12th to the 16th passages, many senescent and apoptotic cells appeared, and the telomere length sharply shortened from 23 kb to 17 kb without expression of hTERT and telomerase activity. At the 20th passage, SHEE cells overcame the senescence and apoptosis and restored their proliferative activity with expression of telomerase and hTERT at low levels, but the telomere length shortened continuously to the lowest of 3 kb. After the 30th passage cells proliferation was restored by increment of cells at S and G₂M phase in the cell cycle and telomerase activity expressed at high levels and with maintenance of telomere length.

CONCLUSION: At the early stage of SHEE cells, telomeres are shortened without expression of telomerase and hTERT causing cellular senescence and cell death. From the 20th to the 30th passages, the activation of telomerase and maintenance of telomere length show a progressive process for immortalization of esophageal epithelial cells. The expression of telomerase may constitute a biomarker for detection of immortalization of cells.

Telomerase activity in small cell esophageal carcinoma

Small cell carcinoma of the esophagus is a rare and aggressive malignant tumor. Telomerase activation is common in human cancers. There is a lack of data on telomerase activity in esophageal small cell cancers. The present report studied the role of telomerase activity in esophageal small cell carcinoma. The clinicopathologic data of five patients with small cell carcinoma of the esophagus who underwent primary surgical treatment between 1991 and 2000 were studied. Telomeric repeat amplification protocol assays were used to investigate telomerase activity in these tumors. The proliferative activity (MIB-1) and p53 expression of these tumors were also studied using immunohistochemistry and correlated with the telomerase activity. All five small cell carcinomas showed detectable telomerase activity in the primary tumor. Two out of the five morphologically normal esophageal mucosae adjacent to the primary tumor had detectable telomerase activity. There was no correlation between the p53 expression, tumor stage, survival of patients, and the presence of telomerase activity. High MIB-1 expression in esophageal small cell carcinomas was associated with high telomerase activity. Telomerase activation is common in small cell carcinoma of the esophagus. This fact may find application in anti-telomerase treatment for this aggressive tumor.

Telomerase activity of the Lugol-stained and -unstained squamous epithelia in the process of oesophageal carcinogenesis

Up-regulation of telomerase has been reported in many cancers. Our aim was to characterize telomerase activity in various states of the oesophagus to facilitate better understanding of carcinogenesis of oesophageal squamous cell carcinoma. During endoscopic examinations, we obtained 45 Lugol-stained normal epithelia, 31 Lugol-unstained epithelia (14 oesophagitis, 7 mild dysplasia, 5 severe dysplasia and 5 intramucosal cancer) and 9 advanced cancer. Telomerase activity was semi-quantified by a telomeric repeat amplification protocol using enzyme-linked immunosorbent assay, and expression of human telomerase reverse transcriptase mRNA was examined by in situ hybridization. In the Lugol-stained normal epithelia, telomerase activity increased in proportion to the increase of severity of the accompanying lesions, with a rank order of advanced cancer, intramucosal cancer, mild dysplasia and oesophagitis. In the Lugol-unstained lesions and advanced cancer, telomerase activity was highest in advanced cancer. Up-regulation of telomerase in normal squamous epithelium may be a marker of progression of oesophageal squamous cell carcinoma.

Clinical applications of telomerase in cancer treatment

Telomerase activity has been found in most cancer cells, but not in the majority of normal differentiated tissues. Therefore, telomerase has been considered a relatively selective and widely expressed tumor marker to be used as a diagnostic tool, and in some cases, as a potential prognostic indicator. Telomerase activity can also be used to evaluate chemosensitivity of neoplastic cells obtained from cancer patients, by measuring residual telomerase activity after drug treatment. Finally, telomerase has been considered to represent a suitable target for designing new anticancer strategies. This review focuses on present and future clinical applications of telomerase studies in cancer management. Copyright 2000 Harcourt Publishers Ltd.

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 reverse transcriptase expression is increased early in the Barrett's metaplasia, dysplasia, adenocarcinoma sequence

Barrett's esophagus is a multistage polyclonal disease that is associated with the development of adenocarcinoma of the esophagus and esophagogastric junction. Telomerase activation is associated with cellular immortality and carcinogenesis, and increased expression of the telomerase reverse transcriptase catalytic subunit (hTERT) has been used for the early detection of malignant diseases. To identify biomarkers associated with each stage of the Barrett's process, relative mRNA expression levels of hTERT were measured using a quantitative reverse transcription-polymerase chain reaction method (ABI 7700 Sequence Detector (TaqMan system) in Barrett's intestinal metaplasia (n = 14), Barrett's dysplasia (n = 10), Barrett's adenocarcinoma (n = 14), and matching normal squamous esophagus tissues (n = 32). hTERT expression was significantly increased at all stages of Barrett's esophagus, including the intestinal metaplasia stage, compared to normal tissues from patients without cancer (intestinal metaplasia vs. normal esophagus, P <0.0001; dysplasia, P = 0.001; adenocarcinoma, P = 0.007; all Mann-Whitney U test ). hTERT expression levels were significantly higher in adenocarcinoma tissues than in intestinal metaplasia tissues (P = 0.003), and were higher in dysplasia compared with intestinal metaplasia tissues (P = 0.056). hTERT levels were also significantly higher in histologically normal squamous esophagus tissues from cancer patients than in normal esophagus tissues from patients with no cancer (P = 0.013). Very high expression levels ([hTERT x 100: beta-actin] >20) were found only in patients with cancer. These findings suggest that telomerase activation is an important early event in the development of Barrett's esophagus and esophageal adenocarcinoma, that very high telomerase levels may be a clinically useful biomarker for the detection of occult adenocarcinoma, and that a widespread cancer "field" effect is present in the esophagus of patients with Barrett's cancer.