The molecular action of irinotecan occurs by trapping a subset of topoisomerase-1-DNA cleavage complexes, those with a guanine +1 in the DNA sequence. One irinotecan molecule stacks against the base pairs flanking the topoisomerase-induced cleavage site and poisons (inactivates) the topoisomerase 1 enzyme
The addition of Irinotecan to 5-FU did not show any improvement in survival in colon cancer - PETACC-03 trial - CALGB 8903 trail
