Topoisomerases (type I: , type II: ) are enzymes that regulate the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double helical structure.

DNA gyrase, topoisomerase IV, and the 4-quinolones.
Topoisomerase II levels during granulocytic maturation in vitro and in vivo
Re: Topoisomerase II alpha and responsiveness of breast cancer to adjuvant chemotherapy.
Camptothecin induces protein-linked DNA breaks via DNA topoisomerase
Camptothecin induces protein-linked DNA breaks via mammalian DNA topoisomerase I.
Alteration of Topoisomerase II–Alpha Gene in Human Breast Cancer: Association With Responsiveness to Anthracycline-Based Chemotherapy
Effect of adding the topoisomerase I poison 7-ethyl-10-hydroxycamptothecin (SN-38) to 5-fluorouracil and folinic acid in HCT-8 cells...
Intercalative antitumor drugs interfere with the breakage-reunion reaction of mammalian DNA topoisomerase II.
Resistance of human leukemic and normal lymphocytes to drug-induced DNA cleavage and low levels of DNA topoisomerase II
Chromosomal loop anchorage of the kappa immunoglobulin gene occurs next to the enhancer in a region containing topoisomerase II sites