Increased levels of human telomerase activity have been demonstrated in a wide variety of human tumours

We have used a 19mer, antisense oligonucleotide directed against the human telomerase RNA component (hTR) to inactivate this enzyme. These oligos are linked to a 2',5'-oligoadenylate moiety which activates RNAase L, resulting in degradation of the target RNA. Targeting hTR in variety of human tumour cells from different origins in vitro results in drastically reduced cell viability. In vivo tumours grown subcutaneously in nude mice reduce in size following treatment with the anti-hTR oligos. Normal fibroblast and epithelial cells do not show any reduction in viability following treatment. TUNEL assays demonstrate that the cytotoxic effects are mediated through apoptotic pathways where the maximum effect is seen after only 4 days of treatment. This response is p53 independent since the majority of the tumour cells used are deficient in p53 function. It also seems that telomere shortening is not the cause of cell death since the cells do not go through sufficient rounds of division for this to happen. In order to gain more insight into the pathways which are affected by the 2-5A anti-hTR treatment we investigated the changes in gene expression which are produced in the human glioma cell line U373 following 2-5A anti-hTR treatment using Affymetrix GeneChip microarray technology. We compared gene expression levels at 4 different time points after treatment using the Affymetrix HU6800 chips. The data demonstrates dysregulation of a significant number of genes implicating the possible involvement of a number of different pathways. The role of these genes in the response to inactivation of telomerase is currently under investigation.