SN-38 is the active metabolite of irinotecan (an analog of camptothecin - a topoisomerase I inhibitor); it is 200 times more active than irinotecan itself.
SN38 is metabolized via glucoronidation by UGT1A1

Inhibits DNA and RNA synthesis (IC₅₀ values are 0.077 and 1.3 μM respectively) but does not affect protein synthesis. Displays potent antitumor activity against a range of human tumor cell lines (IC₅₀ values are 3.3, 13, 19 and 22 nM for HCT-116, BEL-7402, HL60 and HELA cells respectively). Active metabolite of CPT-11 that inhibits DNA topoisomerase I (IC₅₀ values are 0.74 and 1.9 μM in P388 and Ehrlich cells respectively).