Changes of telomerase and telomere lengths in paired normal and cancer tissues of breast

To attain the immortal phenotype, cancer cells must overcome the mitotic cl ock. Telomerase activity has been identified to be activated in malignant t umors including breast cancer. Telomerase activity was evaluated in 71 brea st cancer tissues and paired normal tissues with the TRAP (telomerase repea t amplification protocol) assay. Telomerase activity was calculated and tra nslated into arbitrary units by computer-assisted densitometry with the con trol of telomerase activity in the 293 control cell line. In 59 paired brea st tissues with telomerase activity, terminal restriction fragment (TRF) le ngths were measured using Southern blotting. Relative inhibition (RI), the ratio of inhibited telomerase activity in each tumor tissue compared to tha t of the 293 control cell line after pre-treatment with 150 mu g/ml of RNAs e A, was measured. Sixty-three of 71 cancer tissues showed telomerase activ ity (88.7%) with 75.3+/-17.9 units in densitometry, while no telomerase act ivity was detected in their paired normal tissues. Telomerase activity was correlated to node metastasis (p=0.02) and stage (p=0.005), but not to tumo r size or the hormonal receptor status. TRF lengths were 11.0+/-4.7 kb in 5 9 tumor tissues and 11.7+/-2.2 kb in paired normal tissues. TRF lengths did not correlate to any of the clinical parameters. However changes of TRF le ngths in tumor tissues compared to those of normal tissues correlated to te lomerase activity. RI in the tumor tissues was proportional to telomerase a ctivity without RNAse A pretreatment. In breast cancer, telomerase activity was specific to tumor tissues and increased with tumor progression. Telome rase activity and changes in TRF lengths can be used as guidelines in detec ting candidates for the telomerase inhibitor.