Comparison of the effects of DNA topoisomerase inhibitors on lymphoblasts from normal and Fanconi anemia donors.

DNA topoisomerases modify supercoiled DNA through concerted breaking and rejoining of the DNA strands and consequently play a key role in DNA biosynthesis and processing. It has been suggested that topoisomerases may facilitate access to damaged sites of excision repair enzymes due to their property to relax supercoiled DNA. We show here that treatment with nalidixic acid and novobiocin, which affects topoisomerase II activity among other targets, impairs the incision of 8-methoxypsoralen photoinduced DNA interstrand cross-links in normal human fibroblasts. Since cells derived from Fanconi anemia (FA) demonstrate hypersensitivity to DNA cross-linking agents associated with a reduced repair efficiency of cross-links, we compared the effects of different topoisomerase I and II inhibitors on FA and normal lymphoblasts. No differences were found in growth inhibition or induction of chromosome aberrations between FA and normal cells. The specificity of inhibitors is questionable and even if topoisomerases are indeed inhibited alternative pathways may be involved. However, our observations provisionally suggested that topoisomerases activities are normal in FA cells.