Irinotecan hydrochloride trihydrate, Irinotecan (CPT 11), a compound within the camptothecin family, is an inhibitor of Topo I (topoisomerase I) involved in cellular DNA replication and transcription. As a Topo I inhibitor, Irinotecan inhibits the religation step of the enzyme's normal action, inducing single stranded DNA breaks. These single stranded breaks are then converted to double-stranded breaks within the course of DNA replication which is reported to induce apoptosis or repair mechanisms as a result. Irinotecan is activated by esterases to produce the activated metabolite, SN 38 (sc-203697) and has been reported to be associated with cleavage of poly (ADP-ribose) polymerase (PARP) in colon carcinoma cells. Irinotecan's active metabolite SN 38 is additionally noted to activate p53 in the Huh7 cell line.