Camptothecin enhances random integration of transfected DNA into the genome of mammalian cells

In order to study the involvement of DNA topoisomerase I (top1) in recombin ation, we examined the effect of the antineoplastic drug camptothecin, whic h selectively poisons top1 by trapping top1-cleavable complexes on integrat ion of exogenic vector into the genome of mammalian cells. We transfected m ouse F9 teratocarcinoma cells as well as Chinese hamster V79 cells with a p lasmid carrying a selectable neo gene treated with camptothecin, and determ ined the frequency of neo+ (G418(R)) colonies. We found that treatment with camptothecin for as short a time as 4 h after electroporation resulted in a 4- to 33-fold stimulation of plasmid integration into the recipient genom e via non-homologous recombination. These results imply that top1-cleavable complexes trapped by camptothecin could be potentially recombinogenic stru ctures and could stimulate non-homologous recombination in vivo, promoting the integration of transfected plasmids into mammalian genome. (C) 2000 Els evier Science B.V. All rights reserved.