Relationship between the intracellular effects of camptothecin and the inhibition of DNA topoisomerase I in cultured L1210 cells.
Results of filter elution assays of lesions produced in the DNA of cultured L1210 cells by the antineoplastic alkaloid camptothecin support the notion that topoisomerase I is an intracellular target of this drug. One to 10 microM camptothecin induced DNA single-strand, but not double-strand, breaks when incubated with intact cells or with their isolated nuclei. Approximately one half of the strand breakage was protein concealed, as judged by filter elution. Camptothecin-induced, protein-concealed DNA strand breaks disappeared rapidly after drug removal. DNA-protein cross-links were generated by camptothecin with frequencies approximately equal to those of protein-concealed DNA strand breaks. It is likely that camptothecin can inhibit topoisomerase I in intact cells in a manner similar to that in which other antineoplastic agents such as amsacrine or teniposide inhibit topoisomerase II. DNA-breaking lesions other than those resulting from trapped topoisomerase I-DNA complexes may also be generated by camptothecin. The yields of DNA strand breaks induced by camptothecin, amsacrine, or teniposide were approximately doubled when cells were incubated for 16 h with 3-aminobenzamide, an inhibitor of poly(ADP ribosylation) of proteins, prior to 1-h exposure to the antineoplastic compounds. 3-Aminobenzamide also enhanced the cytotoxic action of camptothecin, amsacrine, and teniposide. These results suggest that protein-concealed strand breaks can be lethal lesions and that intracellular topoisomerase I and II activity may be regulated coordinately through poly(ADP ribosylation).
D000818:Animals; D002166:Camptothecin / Q000633:toxicity*; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000302:isolation & purification / Q000528:radiation effects; D007939:Leukemia L1210 / Q000201:enzymology / Q000473:pathology*; D051379:Mice; D009363:Neoplasm Proteins / Q000528:radiation effects; D059004:Topoisomerase I Inhibitors
D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D059004:Topoisomerase I Inhibitors; D002166:Camptothecin