Camptothecin

Camptothecin is a DNA topoisomerase I inhibitor. Camptothecin inhibits topo I by blocking the rejoining step of the cleavage/religation reaction of topo-I, resulting in accumulation of a covalent reaction intermediate, the cleavable complex. Camptothecin induces extensive single strand DNA breaks in reactions containing purified mammalian DNA topoisomerase I. DNA breakage in vitro is immediate and reversible. Camptothecin showed remarkable anticancer activity in preliminary clinical trials.