Irinotecan HCl Trihydrate (CPT-11) is a semisynthetic derivative of camptothecin with IC50 value of 3.4μM in P388 leukemia [1].

CPT-11 is synthesized to avoid toxicity and to improve therapeutic efficacy of camptothecin. It has been approved by FDA for the treatment of patients with metastatic carcinoma of the colon or rectum whose disease has recurred or progressed following 5-fluorouracil-based therapy. CPT-11 is a soluble prodrug of SN-38, it is converted into SN-38 by carboxylesterase enzymes in vivo. SN-38 is a potent inhibitor of topoisomerase I [2].

CPT-11 is found to have efficacy against drug-resistant as well as drug-sensitive tumor cells. It inhibits the growth of the tumors which are VCR- resistant or ADM-resistant. The inhibition can also occur in VCR- and ADM-resistant tumor bearing mice [1].

References:
[1] Tsuruo T, Matsuzaki T, Matsushita M, Saito H, Yokokura T. Antitumor effect of CPT-11, a new derivative of camptothecin, against pleiotropic drug-resistant tumors in vitro and in vivo. Cancer Chemother Pharmacol. 1988;21(1):71-4.
[2] Slatter JG, Schaaf LJ, Sams JP, Feenstra KL, Johnson MG, Bombardt PA, Cathcart KS, Verburg MT, Pearson LK, Compton LD, Miller LL, Baker DS, Pesheck CV, Lord RS 3rd. Pharmacokinetics, metabolism, and excretion of irinotecan (CPT-11) following I.V. infusion of [(14)C]CPT-11 in cancer patients. Drug Metab Dispos. 2000 Apr;28(4):423-33.