Telomeres and telomerase in cancer of esophagus

English: 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 in nearby normal tissue. Biopsies from 98 patients 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. Telomerase has attracted intense interest as a possible target for cancer therapeutics. Previous attempts at inhibiting telomerase activity utilized antisense oligonucleotides targeted at the template region of the RNA subunit of the enzyme. Although it worked well in cell extracts, getting the oligonucleotides into intact cells are difficult. We attempted a peptide-based approach to overcome the transport problem. A phage-display selection strategy was designed to isolate peptides (7 and 12 amino acids) capable of binding to the RNA template with high affinity and in so doing preventing the enzyme from elongating existing telomeres. Both libraries showed no high affinity binding to the RNA. The most probable explanation is that such short peptides are incapable of binding sequence-specifically to nucleic acids. Many studies have indicated the importance of telomerase activity as an independent prognostic indicator in a variety of cancers, but recent results have shown that telomere length is actually a better indicator, as it shows the final result oftelomerase activity. We thus decided to develop a flow cytrometric method that would allow us to analyze telomere length in small tissue samples. After the initial technique had been established on lymphocytes, it was tested on the SNO cell line before we switched to solid tissue. The background of cellular debris and cell clusters was much worse than for lymphocytes, but differences in signal strength could be seen. From the results obtained it is clear that this method is not optimized yet. The results also indicate that at this stage of development, flow-FISH is inferior to telomerase activity as prognostic indicator. The best way to validate the current method is to analyze the same samples by Southern hybridization and flow-FISH, preferably well defined tumor and normal tissue.