Telomerase expression of malignant epithelial cells correlates with Dukes' stage in colorectal cancer

Abstract

Background: The ribonucleoprotein telomerase has been proposed as a potential prognostic marker for malignancy. Whether telomerase activity of clinical specimens correlates with other clinico-pathological variables, however, remains controversial. This is at least in part due to the varying contribution that nonmalignant cells will make to the net activity when extracts are assayed for telomerase activity. We therefore designed experiments to assay telomerase activity of isolated malignant cells of primary colorectal cancers.

Methods: Thirty colorectal cancer and 20 corresponding specimen taken from macroscopically normal regions of the colon were mechanically disaggregated and digested with collagenase, DNase and hyaluronidase. The epithelial cell population was separated using Ber-EP4 pan-epithelial antibody and Magnetic Activated Cell Sorting technique. Haematoxylin and eosin staining was used to assess the proportion of recovered epithelial cells which were malignant. Telomerase activity was assayed by the Telomeric Repeat Amplification Protocol, which was quantified by PhosphorImager with Image Quant software.

Results: Epithelial cells of three of 20 normal mucosa specimens were telomerase positive with weak activity (mean 3.7 TPGs, Total Product Generated, range 1.4-5.1TPGs). In the cancer group the vast majority (>95%) of the epithelial cells recovered were malignant by cytological criteria. Epithelial cells were telomerase positive in all the cancers, with a wide range of telomerase activity values (mean 22.7 TPGs, range 0.19-308 TPGs). Telomerase activity correlated with Dukes' stage (r = 0.52, P=0.004, Spearman's rank).

Conclusions: Pathological stage correlates with telomerase activity of the malignant cell population of the primary tumour in colorectal cancer. This suggests that telomerase activity increases during the progression of a cancer and may have implications for the design of anticancer (antitelomerase) agents.