Azidothymidine inhibition of thymidine kinase and synergistic cytotoxicity with methotrexate and 5-fluorouracil in rat hepatoma and human colon cancer cells

Cancer Commun. 1990;2(4):129-33. doi: 10.3727/095535490820874498.


Azidothymidine (AZT, 3'-azido-3'-deoxythymidine, zidovudine) competitively inhibited the activity of thymidine kinase (EC in extracts of rat hepatoma and sarcoma cells; Dixon plots yielded a Ki = 1-2 microM. Azidothymidine (100 microM) exerted synergistic cytotoxicity with methotrexate (0.05 microM) in hepatoma cells in culture in clonogenic assay. Thymidine (50 microM) counteracted the effect of azidothymidine and prevented synergistic action. Azidothymidine (10 microM) was synergistically cytotoxic with 5-fluorouracil (0.3 and 0.5 microM) in HT-29 human colon carcinoma cells. Thymidine (10 microM) abolished synergism. These studies suggest a new role for azidothymidine which, as an inhibitor of thymidine salvage, should enhance synergistically the clinical anticancer impact of blockers of de novo biosynthesis of thymidylates (methotrexate, 5-fluorouracil).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cell Line
  • Cell Survival / drug effects
  • Colonic Neoplasms
  • Drug Synergism
  • Fluorouracil / pharmacology*
  • Humans
  • Kinetics
  • Liver Neoplasms, Experimental
  • Methotrexate / pharmacology*
  • Rats
  • Thymidine / pharmacology
  • Thymidine Kinase / antagonists & inhibitors*
  • Tumor Cells, Cultured / cytology
  • Tumor Cells, Cultured / drug effects*
  • Tumor Cells, Cultured / enzymology
  • Zidovudine / pharmacology*


  • Zidovudine
  • Thymidine Kinase
  • Fluorouracil
  • Thymidine
  • Methotrexate