Etoposide

Etoposide (VP 16) is a semisynthetic antitumor alkaloid which is synthesized form podophyllotoxin [P1771] , a toxin found in the American Mayapple. Etoposide interferes with DNA synthesis by inhibiting the enzyme topoisomerase-II. In order to prevent and correct of topological problems caused by the DNA double helix, topoisomerase-II catalyzes the relaxation of negatively supercoiled DNA, the knotting and unknotting DNA and the linking complementary rings of single-stranded DNA into double-stranded rings. Then the inhibition action leads to cell cycle arrest at G₂/M, apoptosis or cell death. Bacterial type II topoisomerases (DNA gyrase and Topoisomerase-IV) are the targets of quinolone antibiotics.