Effect of topoisomerase poisoning by antitumor drugs VM 26, fostriecin and camptothecin on DNA repair replication by mammalian cell extracts.

A recently developed in vitro excision-repair system was used to investigate the effect of the topoisomerase poisons VM 26, fostriecin and camptothecin on DNA repair replication carried out by Chinese hamster ovary cell extracts. VM 26 and camptothecin partially inhibit topoisomerases II and I respectively, which are present in the repair-competent extracts, but have only slight effects on the repair efficiency. On the contrary, the antitumor drug fostriecin markedly affects repair replication but, in contrast to a previous report, does not seem to have, under the experimental conditions used, any inhibitory effect on topoisomerase II. This lack of correlation between the ability to inhibit DNA topoisomerases and the effect on DNA repair replication suggests that topoisomerases should not play a primary role in mammalian excision repair. The use of cleavable-complex stabilizing poisons to investigate the role of eukaryotic topoisomerases in DNA excision repair is discussed.