Ribozyme cleavage of telomerase mRNA sensitizes breast epithelial cells toinhibitors of topoisomerase

Telomerase activity is necessary and sufficient for immortality in many cel ls and hence represents a prime target for antitumor strategies. Here, we s how that a hammerhead ribozyme cleaves human telomerase (hTERT) mRNA in vit ro, Stable transfection in clones of the human breast tumor line MCF-7 and the immortal breast cell line HBL-100 results in expression of the ribozyme , diminishes the abundance of hTERT mRNA, and inhibits telomerase activity. This led to shortened telomeres, inhibition of net growth, and induction o f apoptosis. In HBL-100 mass cultures infected with a ribozyme-expressing a denovirus diminution of hTERT mRNA, attenuation of telomerase activity, inh ibition of net growth, and induction of apoptosis was found as well. Attenu ation of telomerase activity increased the sensitivity of HBL-100 and MCF-7 clones specifically to inhibitors of topoisomerase, Likewise, expression o f exogenous telomerase in originally telomerase-negative human fibroblasts decreased their sensitivity to topoisomerase poisons but not to a number of other cytotoxic drugs. The data validate a ribozyme approach for telomeras e inhibition therapy in canter and suggest that it might be combined advant ageously with topoisomerase-directed chemotherapy.