Irinotecan (CPT-11) and characteristic mucosal changes in the mouse ileum and cecum

Irinotecan--or CPT-11; 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptotheci n--is an inhibitor of DNA topoisomerase I and is clinically effective against several cancers. A major toxic effect of CPT-11 is severe diarrhea; however, the exact mechanism by which the drug induces diarrhea has not been established. Cisplatin (CDDP; cis-diamminedichloroplatinum) and CPT-11 exhibit synergistic antitumor activity and have been used in combination-chemotherapy regimens. Single-agent chemotherapy with conventional doses of CDDP does not cause clinically relevant diarrhea.

To elucidate the mechanisms of induction of diarrhea by high-dose CPT-11 and to compare them with those of diarrhea induced by high-dose CDDP, we used histopathologic and immunohistochemical methods to examine the intestines of mice treated with either CPT-11, CDDP, or saline (control).

Male ICR mice were administered intraperitoneally either 100 mg/kg CPT-11 daily for 4 days, 10 mg/kg CDDP daily for 3 days, or phosphate-buffered saline (control) daily for 4 days (10 mice per group). Preliminary experiments indicated that diarrhea was induced in mice approximately 6 days after administration of CPT-11 or CDDP; therefore, in the experiments described, animals were killed 6 days after the first dose. Serial paraffin-embedded sections of the intestine were stained with hematoxylin-eosin, Grimelius (to identify endocrine cells), or high-iron diamine-alcian blue (stains sialomucin blue and sulfomucin brown-black). Immunohistochemical analyses were performed with the use of anti-proliferating cell nuclear antigen (anti-PCNA; to assay proliferation), anti-Le(y) (BM-1; indirect measure of apoptosis), and anti-synaptophysin antibodies (to identify the enteric nervous system and enterochromaffin cells). A terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) method was used to detect DNA fragmentation in situ (i.e., apoptosis). The concentrations of two intestinally active secretogogues, plasma serotonin and vasoactive intestinal polypeptide, were also measured.

The levels of plasma intestinal hormones were similar in control, CPT-11, and CDDP groups. No active necrotic changes were observed in the intestines of CPT-11- and CDDP-treated mice, even though marked thinning of the intestinal walls was observed in both cases. The intestines of CPT-11-treated mice, but not those of control or CDDP-treated mice, were characterized by epithelial vacuolation of the ileum (associated with increased apoptosis as measured by BM-1 and TUNEL) and goblet-cell hyperplasia with excessive amount of sulfomucin in the cecum (suggesting induction of differentiation). By contrast, CDDP treatment of mice reduced the number of villi in the jejunum and destroyed crypt cells containing large Paneth (secretory) granules in the ileum.

CPT-11 may produce characteristic mucosal changes in the intestine by inducing apoptosis and cell differentiation. The observed changes are likely to cause malabsorption of water and electrolytes and hypersecretion of mucin. These structural and functional effects are probably the main causes of CPT-11-induced diarrhea. CDDP appears to cause diarrhea in mice by causing diffuse mucosal damage in the intestines.