Correlation between the formation of cleavable complex with topoisomerase I and growth-inhibitory activity for saintopin-type antibiotics.
New saintopin-type antibiotics (e.g., saintopin, saintopin E, UCE1022, UCE6) with a naphthacene-dione structure have been discovered through our mechanistically oriented screening using purified mammalian DNA topoisomerases. Saintopin is a dual inducer of topoisomerase I- and topoisomerase II-mediated DNA cleavages in a cell-free system using purified enzymes, whereas others induced topoisomerase I- but not topoisomerase II-mediated DNA cleavage. The order of topoisomerase I-mediated DNA cleavage activity at lower concentrations (<1 microM) was UCE6 > saintopin > saintopin E > UCE1022. The DNA cleavage-intensity patterns induced by these antibiotics with topoisomerase I were identical, indicating that saintopin-type antibiotics have a similar DNA sequence selectivity in stabilization of the cleavable complex with topoisomerase I. Increases in protein/DNA complexes were observed in saintopin-type antibiotic-treated HeLa S3 cells using the potassium/sodium dodecyl sulfate precipitation method. Brief heating of these drugs-treated cells at 65 degrees for 10 min resulted in a rapid reduction in the number of protein/DNA complexes. Immunoblot analysis using antibody against human topoisomerase I or II revealed that the protein linked to DNA in saintopin-type antibiotic-treated cells is most likely topoisomerase I. These results suggest that saintopin-type antibiotics interfere with topoisomerase I in cells by trapping reversible topoisomerase I/DNA cleavable complexes. The formation of topoisomerase I/DNA complexes by saintopin-type antibiotics correlates well with their growth-inhibitory activities, suggesting that topoisomerase I can be the principal target of these antibiotics.
Fujii
N
N
Tokyo Research Laboratories, Kyowa Hakko Kogyo Co., Ltd., Machida, Japan.
Yamashita
Y
Y
Mizukami
T
T
Nakano
H
H
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001551:Benz(a)Anthracenes / Q000494:pharmacology; D002417:Cattle; D004264:DNA Topoisomerases, Type I / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006801:Humans
D000903:Antibiotics, Antineoplastic; D001551:Benz(a)Anthracenes; C066552:saintopin; D004264:DNA Topoisomerases, Type I