Part I. Telomerase levels in human metastatic brain tumors show four-fold logarithmic variability but no correlation with tumor type or interval to patient demise

Prognostic implications of telomerase expression in pituitary adenomas

OBJECTIVES

To analyse the prognostic value of telomerase expression in patients with pituitary adenomas (PAs) followed-up for at least 8 years.

PATIENTS AND METHODS

A retrospective study was conducted of samples from 51 PAs (40 typical and 11 atypical) from patients who underwent transsphenoidal surgery between 2006 and 2008 and from 10 normal pituitary glands obtained by autopsy. Telomerase expression was assessed by immunohistochemistry, correlating the expression with that of Ki-67 and p53.

RESULTS

We observed telomerase expression in 43 PAs (84.3%, 32 of the 40 typical PAs and in the 11 atypical PAs), which was higher in the clinically nonfunctioning cases (P=.0034) and very rare in the patients with acromegaly (P=.0001). There was a significant association between the percentage of tumour cells (>10%) and the recurrence of the adenoma (P=.039). There was no correlation with the expression of Ki-67 and p53 (P=.4986), and there were no differences according to age, sex, tumour size and invasiveness.

CONCLUSIONS

A telomerase expression rate greater than 10% in the pituitary tumour tissue was associated with recurrence or progression of the PA, especially in the nonfunctioning cases.

Adenoviral vectors for prodrug activation-based gene therapy for cancer

Cancer cell heterogeneity is a common feature - both between patients diagnosed with the same cancer and within an individual patient's tumor - and leads to widely different response rates to cancer therapies and the potential for the emergence of drug resistance. Diverse therapeutic approaches have been developed to combat the complexity of cancer, including individual treatment modalities designed to target tumor heterogeneity. This review discusses adenoviral vectors and how they can be modified to replicate in a cancer-specific manner and deliver therapeutic genes under multi-tiered regulation to target tumor heterogeneity, including heterogeneity associated with cancer stem cell-like subpopulations. Strategies that allow for combination of prodrug-activation gene therapy with a novel replication-conditional, heterogeneous tumor-targeting adenovirus are discussed, as are the benefits of using adenoviral vectors as tumor-targeting oncolytic vectors. While the anticancer activity of many adenoviral vectors has been well established in preclinical studies, only limited successes have been achieved in the clinic, indicating a need for further improvements in activity, specificity, tumor cell delivery and avoidance of immunogenicity.

Telomerase reverse transcriptase (TERT) expression and proliferation in canine brain tumours

Telomerase is a ribonucleoprotein enzyme complex that synthesizes telomere DNA. It is detected in 85-90% of malignant tumours in humans, but not in most somatic cells. Because telomerase plays a critical role in cell immortality, it represents an important target for anticancer therapies. We have previously shown that the dog is a potentially useful model for evaluating telomerase-based therapeutics. In this present study we analysed 93 canine brain tumours for telomerase reverse transcriptase (TERT) expression by immunohistochemistry. TERT immunoreactivity was detected in 16 of 50 grade 1 (32%) and 29 of 43 grade 2 tumours (67.4%), demonstrating a statistically significant association with histological grade (P = 0.00012). A subset of 51 tumours was also assessed for MIB-1 expression. The MIB-1 labelling index (LI) was found to correlate significantly with tumour grade, with a mean MIB-1 LI of 1.5% for grade 1 tumours, as compared with a mean MIB-1 LI of 21.7% for grade 2 tumours (P << 0.001). The MIB-1 LI was also significantly associated with TERT expression in all brain tumours (P << 0.001). These data further support the dog as a model for the preclinical development of telomerase-based therapeutics in brain tumours.

Brain metastases from hepatocellular carcinoma in US patients

Hepatocellular carcinoma (HCC) is a disease on the rise in the United States, due to the epidemic of hepatitis C-induced liver disease. Better chemotherapy options, aggressive surgery, and liver transplantation have led to improved patient survival and an increase in late-appearing, distant metastases from HCC. Brain metastases, although formerly thought of as rare manifestations of HCC, may be more likely to come to clinical and pathological attention than extrahepatic metastases in other sites since they often produce clinical symptoms that necessitate neurosurgical intervention and metastasis removal. In addition, brain metastases from HCC are frequently associated with mass-producing hemorrhage, further requiring evacuation. Hence, pathologists are relatively more likely to encounter brain metastases from HCC as surgical specimens than metastases from HCC to some other common sites of spread, such as bone, lymph nodes, or adrenal. Brain metastases from HCC are being increasingly documented in areas of the world with high endemic rates such as Asia, but thus far have only very rarely been reported in patients native to the United States. We describe our institution's experience with three Caucasian US males, two with hepatitis C as risk factors, who developed metastatic HCC to the brain. We expect clinicians and pathologists will encounter more patients with HCC and extrahepatic metastases, particularly those to brain, in the near future.

Prognostic implication of telomerase activity in patients with brain tumors

Telomerase adds telomeric repeats to the ends of telomeres to compensate for their progressive loss. A favorable prognosis is associated with low or no telomerase in some tumors. The authors investigated whether telomerase activity is associated with survival of patients with brain tumors. Sixty-two consecutive patients with brain tumors underwent surgery, and their surgical specimens were investigated. The patients were pathologically categorized as group I (aggressive group) and group II (non-aggressive group). Telomerase activity was examined by the telomeric repeat amplification protocol (TRAP) assay. The median time was calculated in association with overall survival and progression-free survival in each group. The significant difference was noted in telomerase activity between high-grade gliomas and lowgrade gliomas (p=0.022). Telomerase activity was significantly associated with the median overall survival and progression-free survival in all tumors of the aggressive group. On the other hand, the median overall survival in the non-aggressive group was not dependent on telomerase activity, while the median progression-free survival was. Our data suggests that telomerase is an important prognostic indicator of survival in patients with brain tumors.

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

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

Part II. Telomerase expression in cerebrospinal fluid specimens as an adjunct to cytologic diagnosis

The diagnosis of meningeal carcinomatosis hinges on the cytologic examination of cerebrospinal fluid (CSF), which has a known low sensitivity for the identification of malignant cells. Often only 'suspicious' or 'atypical' diagnoses can be rendered, and specimens are commonly unsatisfactory for evaluation due to poor morphologic preservation. Telomerase is widely expressed in most brain metastases, medulloblastomas, lymphomas, oligodendrogliomas, and is expressed focally in glioblastomas. Little is known about the level of telomerase expression in these tumors, except for brain metastases, where a four-fold variation in telomerase levels exists. In our laboratory, as few as ten carcinoma cells can be detected by a sensitive polymerase chain reaction-based assay, the telomeric repeat amplification protocol (TRAP), for telomerase, but it was unclear whether varying levels of telomerase expressed by different types of metastases would influence detection. Using the TRAP protocol, we studied 281 CSF samples from a wide variety of patients with neurologic and non-neurologic conditions for telomerase expression. An adjusted specificity of 90% and a sensitivity of 64% were achieved for detection of malignant cells in CSF by telomerase expression. The TRAP assay for telomerase detection may serve as an adjunct to the traditional examination of CSF. Neither previously documented four-fold variation in the levels of telomerase expression in brain metastases, high CSF protein levels nor high white blood cell counts precluded detection of malignant cells in CSF.