On Jun. 14, 1996, topotecan (Hycamptin), the first of a class of drugs that interferes with the enzyme topoisomerase I, was approved by the FDA for the treatment of metastatic ovarian cancer. Topoisomerases uncoil DNA during DNA replication, and altering the work of this enzyme leads to tumor cell death. Topotecan is derived from the bark of a Chinese tree known as Camptotheca acuminata.