Different modes of cell-killing action between DNA topoisomerase I and II inhibitors revealed by kinetic analysis.
We compared the modes of cell-killing by DNA topoisomerase I and II inhibitors. The effects of camptothecin (CPT), KT-6528 and UCE6 upon colony formation by inhibiting DNA topoisomerase I, and of etoposide (VP-16), teniposide, amsacrine and UCT4-A as inhibitors of DNA topoisomerase II were analyzed based upon a kinetic method that distinguishes between cell cycle phase-specific and -nonspecific agents. Human colorectal cancer WiDr cells were exposed to several concentrations of each agent for various periods and 90%-inhibitory concentrations (IC90) at each time were determined by means of a clonogenic assay. When exposure times and corresponding IC90s were plotted on a log-log scale, all inhibitors of DNA topoisomerase II gave curves including a linear portion with a slope of -1, which is characteristic of cell cycle phase-nonspecific agents. In contrast, the curves for all inhibitors of DNA topoisomerase I had a much steeper slope than -1, which is typical of cell cycle phase-specific agents. In agreement with this finding, the cells were remarkably accumulated in the G2-M phase when exposed to VP-16, but in late S-phase when exposed to CPT as determined by a flow cytometric assay. These results indicated that the two classes of agents kill cells in a quite different manner although they are inhibitors of similar enzymes.
Inaba
M
M
Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo.
Mitsuhashi
J
J
Kawada
S
S
Nakano
H
H
D000677:Amsacrine / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000201:enzymology; D004261:DNA Replication / Q000187:drug effects; D004224:Diterpenes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects; D011809:Quinones / Q000494:pharmacology; D016196:S Phase / Q000187:drug effects; D013713:Teniposide / Q000494:pharmacology; D013997:Time Factors; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology; D014410:Tumor Stem Cell Assay
D000970:Antineoplastic Agents; D002227:Carbazoles; D004224:Diterpenes; D007211:Indoles; D011809:Quinones; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D000677:Amsacrine; C047785:terpentecin; C078597:KT 6528; C082796:UCE6; D005047:Etoposide; D013713:Teniposide; D002166:Camptothecin