Specific interaction of camptothecin, a topoisomerase I inhibitor, with guanine residues of DNA detected by photoactivation at 365 nm

UVA irradiation at 365 nanometers is employed to study the camptothecin-induced DNA photolesions. Supercoiled and relaxed SV40 DNA show an addition of DNA single-strand breaks. Guanines exhibit camptothecin-induced cleavage, and are improved by treatment with hot piperidine when human c-mye DNA is distinctly end-labeled. Extrabreaks are not observed when piperidine treatment is not conducted. Duplex oligonucleotides are less reactive than synthetic single-stranded oligonucleotides.