title: Telomerase inhibition using azidothymidine in the HT-29 colon cancer cell line.
abstract: BACKGROUND
  We investigated the effects of telomerase inhibition by using the reverse transcriptase inhibitor azidothymidine (AZT) in the human colorectal cancer cell line HT-29 in the presence and absence of 5-fluorouracil (5-FU).
  
  
  METHODS
  HT-29 cells were cultured in the presence of AZT. Telomerase activity was measured by using the telomerase repeat amplification protocol. Telomere length was determined by Southern analysis. The colorimetric microtiter assay was performed to determine the cytotoxic effects of AZT, alone and in combination with 5-FU.
  
  
  RESULTS
  The presence of 3'-azido-3'-deoxythymidine triphosphate (AZT-TP) effectively inhibited telomerase extracted from HT-29 cells. HT-29 cells cultured with 125 microM of AZT underwent fewer total population doublings over 91 days. Southern analysis revealed that telomere attrition occurred within this period. Exposure to 125 microM of AZT resulted in slightly reduced viability (10%) of HT-29 cells. However, the presence of AZT increased 5-FU cytotoxicity, suggesting that the effects of these two drugs are synergistic.
  
  
  CONCLUSIONS
  The data are consistent with telomerase inhibition having growth-inhibitory effects in addition to those predicted to accompany loss of telomere function. Further studies using specific small-molecule inhibitors will confirm whether the growth-inhibitory and 5-FU-sensitivity effects seen here are a direct result of telomerase inhibition.
authors.affiliation: Department of Surgical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA. t_brown@fccc.edu
authors.forename: Tommy
authors.initials: T
authors.lastname: Brown
authors.forename: Elin
authors.initials: E
authors.lastname: Sigurdson
authors.forename: Andre
authors.initials: A
authors.lastname: Rogatko
authors.forename: Dominique
authors.initials: D
authors.lastname: Broccoli
mesh_terms: D000704:Analysis of Variance; D015139:Blotting, Southern; D003110:Colonic Neoplasms / Q000201:enzymology; D005472:Fluorouracil / Q000494:pharmacology; D019073:HT29 Cells / Q000201:enzymology*; D006801:Humans; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*; D019098:Telomerase / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured; D015215:Zidovudine / Q000494:pharmacology*
chemical_list: D018894:Reverse Transcriptase Inhibitors; D015215:Zidovudine; D019098:Telomerase; D005472:Fluorouracil