Azoxymethane (AOM)-induced colorectal tumorigenesis model

AOM was used to induce a sporadic colorectal tumorigenesis model, as previously described (22). Briefly, 8 week-old male mice [n=18; A/J strain; divided into 3 groups; weight, >18 g; maintenance conditions: temperature, 18-29°C; relative humidity, 50-60%; free access to clean food and water; lighting for 10-14 h (lights turned on at 8:00 every day and turned off at 18:00)] were intraperitoneally injected with 10 mg/kg body weight AOM (Sigma-Aldrich) six times. The mice were injected with AOM every week from the first to the sixth week. The mice were then provided with regular water and did not undergo any further treatment. Mice were sacrificed at various time-points, after which the colorectum was excised, opened longitudinally, flushed with ice-cold PBS and fixed in 10% formalin/PBS for 24 h at room temperature. Subsequently, macroscopic tumors were counted and morphological evaluation of normal, adenoma and tumor tissues were performed under a light microscope. All mice were divided into 3 groups; the blank control group was treated with normal saline, the adenoma and tumor groups were treated with AOM. The normal tissues were obtained from the blank control group, and the adenoma tissues were obtain from mice treated with AOM at the end of the 12th week. All animals received humane care according to the Institutional Animal Care and Treatment Committee of Central South University, and the proof number of ethics was 201603426.