Irinotecan hydrochloride is a semi-synthetic derivative of camptothecin, an alkaloid of Camptotheca acuminata. It is a prodrug that is converted into a potent metabolite (SN-38). Irinotecan inhibits DNA topoisomerase I, which is often overactive in tumors. Non-growing cells are therefore not affected. It is used to treat metastatic colon carcinomas (in combination with 5-FU and folinic acid) and experimentally it is used against other tumors.