AZT: a biochemical response modifier of methotrexate and 5-fluorouracil cytotoxicity in human ovarian and pancreatic carcinoma cells.
In ovarian and pancreatic carcinoma cell lines, the activity of the salvage enzyme, thymidine kinase (EC 2.7.1.21), was 2- to 13-fold higher than that of the key enzyme of thymidylate de novo biosynthesis, thymidylate synthase (dTMP synthase, EC 2.1.1.45). AZT (3'-azido-3'-deoxythymidine, zidovudine) competitively inhibited thymidine kinase activity in extracts of human ovarian and pancreatic carcinoma cells, with Dixon plots yielding Ki = 1.1 microM in both cell lines. AZT (20 microM) yielded synergistic cytotoxicity with methotrexate (0.4 microM) in human pancreatic carcinoma cells in clonogenic assay and also with methotrexate (0.02 microM) in human ovarian carcinoma cells, as measured by cell counts. Thymidine (10 microM) and hypoxanthine (100 microM) reversed these inhibitions. AZT (20 or 40 microM) also provided synergistic cytotoxicity with 5-fluorouracil (0.5 and 1.0 microM) in human pancreatic carcinoma cells in clonogenic assay. These studies suggest a new role for AZT, which, as an inhibitor of thymidine salvage, should be useful as a biochemical response modifier to provide a synergistic clinical anticancer impact on de novo biosynthesis of thymidylates in conjunction with methotrexate or 5-fluorouracil.
Weber
G
G
Laboratory for Experimental Oncology, Indiana University School of Medicine, Indianapolis 46202-5200.
Nagai
M
M
Prajda
N
N
Nakamura
H
H
Szekeres
T
T
Olah
E
E
D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D019271:Hypoxanthine; D007042:Hypoxanthines / Q000494:pharmacology; D066298:In Vitro Techniques; D008727:Methotrexate / Q000494:pharmacology*; D010051:Ovarian Neoplasms / Q000188:drug therapy*; D010190:Pancreatic Neoplasms / Q000188:drug therapy*; D051381:Rats; D013936:Thymidine / Q000494:pharmacology; D013937:Thymidine Kinase / Q000096:biosynthesis / Q000187:drug effects; D014407:Tumor Cells, Cultured; D015215:Zidovudine / Q000494:pharmacology*
D007042:Hypoxanthines; D019271:Hypoxanthine; D015215:Zidovudine; D013937:Thymidine Kinase; D005472:Fluorouracil; D013936:Thymidine; D008727:Methotrexate