The presence of telomerase activity in human cells is strongly correlated to the expression of hTERT which is repressed in normal adult human cells. We are undertaking a screen for compounds that activate telomerase expression using a transient expression system similar to the one previously described by Won et al. The telomerase minimal promoter sequence was inserted into a promoter-reporter plasmid to drive expression of the luciferase coding sequence. The plasmid was then transfected into normal MRC5 cells (human fetal lung fibroblasts) which represses the promoter and gives background levels of luciferase activity. These transfected cells were used in a high throughput screening system to identify small molecules that derepress the telomerase minimal promoter turning on luciferase expression.
During the screening process the MRC5 cells were transfected in bulk, seeded into 96-well plates and then the compounds are added to a final concentration of 33 uM for 48 hr treatment. Potential active compounds are identified by increased luciferase activity. We have presently screened 123,840 compounds and indentified 929 compounds that stimulate luciferase activity 3 to 20 fold over the DMSO negative controls. These 929 compounds represent several distinct chemical families. At least 7 of these active compounds have been shown to induce hTERT mRNA expression (RT-PCR) and telomerase activity (TRAP) in normal cells. Studies of these compounds with regards to specificity, selectivity, and an ability to extend cellular lifespan are ongoing.