any one of a class of *cytotoxic drugs that work by blocking the action of topoisomerase enzymes, which promote the uncoiling of the DNA double helix, a necessary preliminary to replication. Topoisomerase I inhibitors include irinotecan, used for treating advanced colorectal cancer (especially in combination with *fluorouracil); and topotecan, given for treating advanced ovarian cancer, relapsed small-cell lung cancer, and recurrent cervical cancer. Side-effects include delayed but severe diarrhoea and reduction in blood-cell production by the bone marrow. Topoisomerase II inhibitors include *etoposide and *doxorubicin.... topoisomerase inhibitor
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