Camptothecin effect on nucleoid DNA in X-irradiated and benzamide-treated L-5178Y-R and L5178Y-S cells

摘要

L5178Y (LY) murine lymphoma sublines, LY-R and LY-S, are inversely cross resistant to X-rays and camptothecin (CPT). We studied the response to combined (X+CPT) treatment, with or without pre-treatment of cells for 20 h with 2 mM benzamide (BZ). The end-point was DNA damage measured in nucleoids by the comet assay or fluorescent halo assay. An increase in DNA damage was seen in LY-S cells after BZ+X+CPT treatment; in LY-R cells the level of damage was unaltered by the treatment, as compared to X+BZ. The increase in DNA damage seen between time zero and 5 and 10 min repair, may be taken as a direct indication of nicking of DNA at sites opposite to single strands breaks by topoisomerase I, as predicted by the hypothesis of Boothman et al. (9). (author). 26 refs, 3 figs. (Atomindex citation 28:049175)