Azoxymethane protects intestinal stem cells and reduces crypt epithelial mitosis through a COX-1-dependent mechanism

Azoxymethane (AOM) is a potent DNA-damaging agent and carcinogen that induces intestinal and colonic tumors in rodents. Evaluation of the stem cell population by colony formation assay reveals that, within 8 h after treatment, AOM (10 mg/kg) elicited a prosurvival response. In wild-type (WT) mice, AOM treatment induced a 2.5-fold increase in intestinal crypt stem cell survival. AOM treatment increased stem cell survival in cyclooxygenase (COX)-2 ^-/- but not COX-1^-/- mice, confirming a role of COX-1 in the AOM-induced increase in stem cell survival. COX-1 mRNA and protein expression as well as COX-1-derived PGE₂ synthesis were increased 8 h after AOM treatment. Immunohistochemical staining of COX-1 demonstrated expression of the enzyme in the crypt epithelial cells, especially in the columnar epithelial cells between the Paneth cells adjacent to the stem cell zone. WT mice receiving AOM exhibited increased intestinal apoptosis and a simultaneous reduction in crypt mitotic figures within 8 h of injection. There were no significant differences in baseline or AOM-induced intestinal epithelial apoptosis between WT and COX-1^-/- mice, but there was a complete reversal of the AOM-mediated reduction in mitosis in COX-1^-/- mice. This suggests that COX-1-derived PGE₂ may play a key role in the early phase of intestinal tumorigenesis in response to DNA damage and suggests that COX-1 may be a potential therapeutic target in this model of colon cancer.