Telomeres and telomerase in cancer of esophagus

[摘要] English: Squamous cell carcinoma of the esophagus is a cancer with a high incidence in SouthAfrica. We have investigated the prognostic value of telomerase activity in tumors aswell as in nearby normal tissue. Biopsies from 98 patients were analyzed using anadaptation of the TRAP assay. We found all tumor biopsies to have moderate to hightelomerase activity, while one third of biopsies from normal mucosa were negative. Thetelomerase activity level of the tumors had no prognostic value (P=0.95) as determinedby the log rank test. A P-value of 0.02 was found when the telomerase-negative andmoderately positive normal biopsies were grouped together and compared to those withhigh activity. Our results show that telomerase activity of normal mucosa in the vicinityof 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 oligonucleotidestargeted at the template region of the RNA subunit of the enzyme. Although it workedwell in cell extracts, getting the oligonucleotides into intact cells are difficult. Weattempted a peptide-based approach to overcome the transport problem. A phage-displayselection strategy was designed to isolate peptides (7 and 12 amino acids) capable ofbinding to the RNA template with high affinity and in so doing preventing the enzymefrom elongating existing telomeres. Both libraries showed no high affinity binding to theRNA. The most probable explanation is that such short peptides are incapable of bindingsequence-specifically to nucleic acids. Many studies have indicated the importance of telomerase activity as an independentprognostic indicator in a variety of cancers, but recent results have shown that telomerelength is actually a better indicator, as it shows the final result oftelomerase activity. Wethus decided to develop a flow cytrometric method that would allow us to analyzetelomere length in small tissue samples. After the initial technique had been establishedon 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 forlymphocytes, but differences in signal strength could be seen. From the results obtainedit is clear that this method is not optimized yet. The results also indicate that at this stageof development, flow-FISH is inferior to telomerase activity as prognostic indicator. Thebest way to validate the current method is to analyze the same samples by Southernhybridization and flow-FISH, preferably well defined tumor and normal tissue.

[发布机构] University of the Free State