Topotecan Hydrochloride is the water-soluble hydrochloride salt preparation of Topotecan, a potent inhibitor of topoisomerase 1, and an apoptosis inducer, producing proapoptotic and antiproliferative effects. Topotecan is a semisynthetic derivative of the natural product alkaloid camptothecin. It is described to stabilize topoisomerase I/DNA cleavable complexes and promote rapid apoptotic cell death in radiation-resistant human B-lineage acute lymphoblastic leukemia cells.